A review on g-C3N4-based photocatalysts

Applied Surface Science 391 (2017) 72–123

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A review on g-C3 N4 -based photocatalysts Jiuqing Wen a , Jun Xie a , Xiaobo Chen b,∗ , Xin Li a,∗ a College of Materials and Energy, Key Laboratory of Energy Plants Resource and Utilization, Ministry of Agriculture, Key Laboratory of Biomass Energy of Guangdong Regular Higher Education Institutions, South China Agricultural University, Guangzhou, 510642, PR China b Department of Chemistry, University of Missouri – Kansas City, Kansas City, MO, 64110, USA

a r t i c l e

i n f o

Article history: Received 23 May 2016 Received in revised form 2 July 2016 Accepted 3 July 2016 Available online 9 July 2016 Keywords: Carbon nitride (g-C3 N4 ) Composite photocatalysts Co-catalysts Artificial photosynthesis Z-scheme heterojunction Nanocarbons

a b s t r a c t As one of the most appealing and attractive technologies, heterogeneous photocatalysis has been utilized to directly harvest, convert and store renewable solar energy for producing sustainable and green solar fuels and a broad range of environmental applications. Due to their unique physicochemical, optical and electrical properties, a wide variety of g-C3 N4 -based photocatalysts have been designed to drive various reduction and oxidation reactions under light irradiation with suitable wavelengths. In this review, we have systematically summarized the photocatalytic fundamentals of g-C3 N4 -based photocatalysts, including fundamental mechanism of heterogeneous photocatalysis, advantages, challenges and the design considerations of g-C3 N4 -based photocatalysts. The versatile properties of g-C3 N4 -based photocatalysts are highlighted, including their crystal structural, surface phisicochemical, stability, optical, adsorption, electrochemical, photoelectrochemical and electronic properties. Various design strategies are also thoroughly reviewed, including band-gap engineering, defect control, dimensionality tuning, pore texture tailoring, surface sensitization, heterojunction construction, co-catalyst and nanocarbon loading. Many important applications are also addressed, such as photocatalytic water splitting (H2 evolution and overall water splitting), degradation of pollutants, carbon dioxide reduction, selective organic transformations and disinfection. Through reviewing the important state-of-the-art advances on this topic, it may provide new opportunities for designing and constructing highly effective g-C3 N4 based photocatalysts for various applications in photocatalysis and other related fields, such as solar cell, photoelectrocatalysis, electrocatalysis, lithium battery, supercapacitor, fuel cell and separation and purification. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Nowadays, among the various possibilities for exploring attractive sustainable energy sources and technologies, photocatalytic technology is considered as one of the most appealing and promising technologies to directly harvest, convert and store renewable solar energy for generating sustainable and green energy and a broad range of environmental applications. In 1972, the pioneering work of photoelectrochemical (PEC) H2 production from water splitting using a Pt-attached n-TiO2 cell was firstly reported by Fujishima and Honda [1]. Subsequently, Bard extended the basic principle of PEC water splitting system to the heterogeneous photocatalytic systems with illuminated semiconductor particles suspended in water as photocatalysts [2–5]. Since then,

∗ Corresponding authors. E-mail addresses: [email protected] (X. Chen), [email protected] (X. Li). http://dx.doi.org/10.1016/j.apsusc.2016.07.030 0169-4332/© 2016 Elsevier B.V. All rights reserved.

the heterogeneous photocatalysis occurring on powdered semiconductors has been widely used in the different fields, such as water splitting [6–10], environmental remediation [9,11–15], CO2 reduction [16–20], disinfection [21] and selective organic transformations[22–24]. It is noteworthy that there has been a growing interest in the use of semiconductors as photocatalysts for various applications (the red columns in Fig. 1a). In 2015, more than 5500 papers about the photocatalytic applications have been published, further indicating the high importance and tremendous research interests in heterogeneous photocatalysis. Clearly, the presence of efficient photocatalysts plays an essential role in determining the overall quantum efficiency of all these photocatalytic reaction systems. During the past 40 years, various available semiconductor materials such as TiO2 , SrTiO3 , CdS, BiVO4 , Ta3 N5 , TaON, g-C3 N4 , Ag3 PO4 , and their nanostructured assemblies have been extensively employed as photocatalysts to directly harness solar energy for different redox reactions [7,25–30]. As the most widely employed “golden” photocatalyst, TiO2 has dominated the published work on heterogeneous photocatalysis owing to its

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Fig. 1. (a) The annual number of publications containing the word “graphene* (TiO2 *, g-C3 N4 * or carbon nitride*)” in the title and “photocataly*” in the topic since 2009. (b) The annual number of citations for Wang’s pioneering paper published on Nature Materials in 2009. (Using Web of Science, date of search: Jul 2, 2016).

chemical stability, high chemical inertness, nontoxicity, and low cost [31–36], which accounts for three-fifths of all photocatalytic research (the green columns in Fig. 1a). However, the large bandgap of anatase TiO2 (3.2 eV) restricts the utilization of broad spectrum of solar light (only utilization of the ultraviolet (UV) light in the sunlight, accounting for only 4% of the incoming solar spectrum), thus leading to much lower quantum efficiencies in using the solar spectra. To enhance the photocatalytic efficiency of titania under visible light (about 43% of the sunlight), a variety of modification strategies, including doping, surface sensitization, nanostructuring, introducing defects or amorphous disorder layers, loading co-catalysts, coupling with carbon and other semiconductors, have been utilized to overcome the TiO2 materials-related issues and limitations, such as the control of the band gap, band structure, optical properties and available surface area for photo-induced reactions [7,25,34–40]. Up to now, no one robust and commercially available material could meet all requirements, such as high visible-light quantum efficiency, stability, safety and cheapness [7,41]. Thus, to tackle these challenges, it is highly desirable to search for novel visiblelight-driven semiconductor materials and further fabricate highly efficient systems/architectures for energy supply and environmental remediation. The graphite-like carbon nitride (g-C3 N4 ), as a metal-free polymer n-type semiconductor, possess many promising properties, such as unique electric, optical, structural and physiochemical properties, which make g-C3 N4 -based materials a new class of multifunctional nanoplatforms for electronic, catalytic and energy applications [42,43]. Especially, g-C3 N4 -based photocatalysts have attracted increasing interest worldwide, since Wang and his coworkers first discovered the photocatalytic H2 and O2 evolution over C3 N4 in 2009 [44]. Clearly, the annual number of citations for Wang’s pioneering paper published on Nature Materials in 2009 significantly increases every year (as shown in Fig. 1b). Thus, the g-C3 N4 -based nanostructures are emerging as ideal candidates for a variety of energy and environmental photocatalytic applications, such as photocatalytic water reduction and oxidation, degradation of pollutants and carbon dioxide reduction [27,45–57]. More interestingly, as observed from Fig. 1b, although the annual number of publications about g-C3 N4 -based photocatalysts is much smaller than that about TiO2 photocatalysts, the publications of g-C3 N4 photocatalysis present an obvious approach to those of graphenebased photocatalysis [26,58]. More interestingly, the g-C3 N4 -based photocatalysts together with the graphene-based ones are significantly reducing the proportion of TiO2 photocatalysts (as shown in Fig. 1a). Absolutely, the g-C3 N4 , as the very exciting sustainable material, has become a shining star in the photocatalytic field. Interestingly, as a novel metal-free polymeric semiconductor, gC3 N4 was quite different from most other semiconductors, which could also be readily utilized to form various highly tailorable hybrid photocatalysts with controllable compositions, sizes, thick-

ness, pore structures, size distributions, and morphologies. Hence, it is of great interest to develop g-C3 N4 -based photocatalysts for various applications through suitable modification, which is still considered as a research topic of scientific and technological significance in the fields of energy and environmental chemistry. Importantly, many significant and major breakthroughs have been achieved in the synthesis and application of g-C3 N4 -based photocatalysts. In particular, many novel nanostructured g-C3 N4 -based photocatalysts, including 1D nanorods, 2D nanosheets and 3D hierarchical structures, have been extensively developed in the past several years due to their favorable absorption of solar radiation, efficient separation of charge carriers, high surface areas and exposed reactive sites. In fact, several excellent reviews are already available that focus on the synthesis and modification of g-C3 N4 -based photocatalysts and their applications in solving the energy and environmental issues [27,45–57,59]. However, only a handful of reviews have focused on the versatile properties and rational design of g-C3 N4 based photocatalysts. Thus, it seems timely to offer a relatively comprehensive and fully updated review on the state-of-the-art advances of g-C3 N4 -based photocatalysts for heterogeneous photocatalysis. In the present Review, we devote our attention to fundamentals, versatile properties, rational design and potential applications of g-C3 N4 photocatalysts. We believe that this review will not only promote the further developments of new g-C3 N4 based materials and architectures with improved utilization of solar energy and photocatalytic efficiency, but also could therefore help to address the challenges for the widespread use of g-C3 N4 based photocatalysts in the renewable and sustainable energy production and storage. It is also hoped that this review can provide some new ideas to develop new materials and architectures for the other sustainable energy-related fields such as solar cells [42,43,60,61], light emitting devices [62,63], fuel cells [64–69], batteries [70–75] and sensing devices [76–82].

2. Fundamentals of g-C3 N4 -based photocatalysts 2.1. Mechanism of heterogeneous photocatalysis So far, the fundamental mechanism of heterogeneous photocatalysis has been well proposed, as shown in Fig. 2. Basically speaking, the heterogeneous photocatalysis involves seven key stages, which could be usually classified into four major processes: light harvesting (stage 1); charge excitation (stage 2); charge separation and transfer (stages 3, 4 and 5) and surface electrocatalytic reactions (stages 6 and 7). Firstly, it is known that the light harvesting process (stage 1) is strongly dependent on the surface morphology and structure of photocatalysts, which can usually be significantly improved through constructing the hierarchical macroporous or mesoporous architectures, due to more efficient

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Table 1 Band gap structures of several typical photocatalysts. Semiconductor

TiO2 Cu2 O CdS g-C3 N4 g-C3 N4 Ta3 N5 TaON BiVO4 WO3 Ag3 PO4 a

Crystal structure

Anatase

cubic

Band Gap Structure (PH = 7,vs NHE)

Ref.

CB

VB

Eg /eV

−0.5 −1.16 −0.9 −1.3 −1.53 −0.75 −0.75 −0.3 −0.1 0.04

2.7 0.85 1. 5 1.4 1.16 1.35 1.75 2.1 2.7 2.49

3.2 2.0 2.4 2.7 2.7 2.1 2.5 2.4 2.8 2.45

[90] [91] [92] [44,84] [93]a [94] [94] [95] [96] [97]

Measurement by the valence band X-ray photoelectron spectroscopy (VB XPS) spectrum. Table 2 Standard redox potentials for some typical species [83,98].

Fig. 2. The fundamental mechanism of heterogeneous photocatalysis. The typical stages: (1) light harvesting; (2) charge excitation; (3) charge separation and transfer; (4) bulk charge recombination; (5) surface charge recombination; (6) surface reduction reactions; and (7) surface oxidation reactions.

utilization of light through its multiple reflections and scattering effects [83]. At this regard, the flat and smooth surface of 2D gC3 N4 is unfavorable for improving the light harvesting. Secondly, the charge excitation of a semiconductor is strongly associated with its unique electronic structures. Generally, an electron in the VB of the semiconductor could be thus excited to its CB under the light irradiation with energy higher than or equal to its band gap energy (Eg ), leaving a positive hole in the VB. The band gap structures of several typical photocatalysts were summarized in Table 1. As observed in Table 1, as compared to TiO2 , BiVO4 and WO3 , g-C3 N4 has the most negative CB level (−1.3 V vs NHE at pH 7) and a medium band gap (2.7 eV) [44,84], facilitating its wide application in visible-light photocatalysis. Thus, to achieve more utilization of visible light, the band gap of g-C3 N4 should be further narrowed by facile doping, defect and other possible sensitization strategies [7]. Thirdly, the unfavorable charge recombination in the bulk (stage 4) and on the surface (stage 5) of a semiconductor is detrimental to the charge separation and transfer (stage 3) to surface/interface active sites, which has been regarded as the decisive factor for determining the photocatalytic quantum efficiency. Usually, shortening the diffusion length of photo-generated charge carriers or constructing interfacial electric fields could efficiently reduce the recombination rates, thus substantially enhancing the photocatalytic activity [7,85,86]. Finally, it is clear that only energetic enough electrons and holes that migrate to the surface of the semiconductor without recombination can be trapped by the

Reaction

E0 (V) vs NHE at pH 0

2H+ + 2e− →H2 (g) O2 (g) + e− →O2 − (aq) O2 (g) + H+ + e− → HO2 • (aq) O2 (g) + 2H+ + 2e− → H2 O2 (aq) 2H2 O (aq) + 4 h+ → O2 (g) + 4H + OH− + h+ → • OH O3 (g) + 2 H+ + 2 e− → O2 (g) + H2 O CO2 + e− →CO2 − 2 CO2 (g) + 2 H+ + 2 e− → HOOCCOOH(aq) CO2 (g) + 2H+ + 2e− → HCOOH(aq) CO2 (g) + 2 H+ + 2e− → CO(g) + H2 O CO2 (g) + 4H+ + 4e− → C(s) + 2H2 O CO2 (g) + 4H+ + 4e− → HCHO(aq) + H2 O CO2 (g) + 6H+ + 6e− → CH3 OH(aq) + H2 O CO2 (g) + 8H+ + 8e− → CH4 (g) + 2H2 O 2CO2 (g) + 8H2 O + 12e− → C2 H4 (g) + 12OH− 2CO2 (g) + 9H2 O + 12e− → C2 H5 OH(aq) + 12OH− 3CO2 (g) + 13H2 O + 18e− → C3 H7 OH(aq) + 18OH− H2 O2 (aq) + H+ + e− → H2 O + OH− HO2 • + H+ + e− → H2 O2 (aq) H2 O2 (aq) + 2H+ + 2e− → 2H2 O

0 −0.33 −0.046 0.695 1.229 2.69 2.075 −1.9 −0.481 −0.199 −0.11 0.206 −0.07 0.03 0.169 0.07 0.08 0.09 1.14 1.44 1.763

surface active sites or co-catalysts, and further stimulate the elctrocatalytic reduction (stage 6) and oxidation (stage 7) reactions of the reactants adsorbed on the semiconductor, respectively. It should be noted that the surface reactions possibly occur only when the reduction and oxidation potentials are more positive and negative than CB and VB levels, respectively. Some typical standard redox potentials have been listed in Table 2. Notably, almost all reactions in Table 2 exhibit the same linear pH dependence with a slope of −0.059 V, apart from E0 (O2 /O2 − ) which is pH-independent [83,87]. Furthermore, for the surface electrocatalytic reactions (surface charge utilization), the large onset overpotential and sluggish kinetics are two key factors limiting the surface photocatalytic efficiency of reduction and oxidation reactions. Principally, these two restrictive factors can be overcome by loading suitable cocatalysts (electrocatalysts) simultaneously [88]. More importantly, the co-catalysts (electro-catalysts) can play the additional roles in improving the photostability and charge separation of semiconductors [89]. The complicated co-catalyst effects will be thoroughly discussed in the section 4.7. However, it should be noteworthy that the photocatalytic quantum efficiency (c ) is strongly determined by the cumulative effect of the efficiency in all four-step processes, including light harvesting efficiency (abs ), charge separation efficiency (cs ), charge migration and transport efficiency (cmt ), and charge utilization efficiency (cu ) for H2 generation. The relationship between them could be expressed according to Eq. (1) [7]: c = abs × cs × cmt × cu

(1)

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Fig. 3. The redox potentials of the relevant reactions with respect to the estimated position of the g-C3 N4 band edges at pH 7.

Therefore, to design highly efficient photocatalysts for various photocatalytic applications, all these typical four-step processes must be comprehensively considered and optimized. Despite the significant advances in heterogeneous photocatalysis, there are still many challenges related to the further enhancements of light harvesting (especially for the visible light region), charge carrier excitation, separation and utilization. In order to solve these key scientific problems, a variety of engineering modification strategies have been proposed and applied in improving the visible-light photocatalytic performances of heterogeneous semiconductor materials, such as band structure engineering, micro/nano engineering, bionic engineering, co-catalyst engineering, surface/interface engineering and their synergistic effects [7]. The detailed modification strategies and rational design on g-C3 N4 based photocatalysts will be thoroughly discussed in section 4. 2.2. Advantages and challenges of g-C3 N4 -based photocatalysts Based on the above mechanism analysis, it is clear that the band-gap and nano structures are crucial for their photocatalytic applications. The band gap structures of g-C3 N4 , as well as some standard potentials of typical redox reactions at pH 7 are illustrated in Fig. 3. Clearly, as shown in Fig. 3, g-C3 N4 has a moderate band gap of 2.7 eV, corresponding to an optical wavelength of 460 nm, which makes it active under visible light. Considering thermodynamic losses and overpotentials in the photocatalytic process, the band gap of 2.7 eV accidentally lies in between 2 eV and 3.1 eV, thus achieving both the water-splitting with enough endothermic driving forces (much larger than 1.23 eV) and light absorption in the visible range (smaller than 3.1 eV) [7]. More importantly, g-C3 N4 also has a suitable CB position for various reduction reactions. It is noted form Fig. 3 that the favorable level of top CB of g-C3 N4 is much more negative than those of conventional inorganic semiconductor counterparts in Table 1 and the potentials of H2 -evolution, CO2 -reduction and O2 -reduction reactions, suggesting that the photo-generated electrons in g-C3 N4 possess a large thermodynamic driving force to reduce various kinds of small molecules, like H2 O, CO2 and O2 . As a consequence, the appropriate electronic band structures of g-C3 N4 are favorable for its extensive applications in wide areas, such as photocatalytic water splitting, CO2 reduction, pollutant degradation, organic synthesis and disinfection. Apart from the simplest and straightforward advantage of suitable optical band gap and position, it is widely accepted to date that this metal-free g-C3 N4 material also possesses a stacked 2D layered structure, in which the single-layer nitrogen heteroatomsubstituted graphite nanosheets, formed through sp2 hybridization of C and N atoms, are bound by van der Waals forces, only (as shown in Fig. 4a) [99]. Ideally, condensed g-C3 N4 consists of only two earth-abundant elements: C and N, with a C/N molar ratio

Fig. 4. Fabrication strategies of g-C3 N4 and N-rich precursors.

of 0.75, suggesting that g-C3 N4 could be readily fabricated at low cost. It also turned out that the g-C3 N4 has the advantages of biocompatibility and nontoxicity. Surprisingly, the viability activity of HeLa cells could be maintained in the aqueous solution of gC3 N4 nanosheets with a concentration of up to 600 mg mL−1 [100]. Furthermore, g-C3 N4 could be readily fabricated through the traditional thermal condensation of several low-cost N-rich organic solid precursors such as urea, thiourea, melamine, dicyandiamide, cyanamide, and guanidine hydrochlorid, at 500–600 ◦ C in air or inert atmosphere (Fig. 4) [27,101]. However, the disordered and defective g-C3 N4 structures could be fabricated due to the incomplete removal of intermediates. Thus, the crystalline and condensed g-C3 N4 can be readily prepared by other various fabrication strategies, including the ionothermal synthesis (molten salt strategy) [102–106], molecular self-assembly [107–111], microwave irradiation [112,113] and ionic liquid strategy [114–117] (Fig. 4). In addition, the above three obvious advantages, as well as several other advantages of g-C3 N4 , including the rich surface properties, non-toxicity, abundance, and good stabilities, are summarized in Fig. 3, all of which give access to a wide variety of applications [48]. All these features principally already allow its direct use in sustainable chemistry as a multifunctional heterogeneous metal-free photocatalyst. Unfortunately, the bulk g-C3 N4 generally exhibits the low photocatalytic efficiency, due to some serious drawbacks of g-C3 N4 material itself. Specifically, we will highlight several prominent challenges of g-C3 N4 itself here: the high electron–hole recombination rate, insufficient visible absorption (below 460 nm), low surface area of g-C3 N4 (∼10 m2 /g, the high degree of conden-

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Table 3 Structural parameters and total energies for different C3 N4 phases [131]. C3 N4 phases

Space group

Lattice parameter (Å)

Z

GW approximation band gap (eV)

local density approximation band gap (eV)

Alpha Beta Cubic Pseudocubic g-h-triazine g-h-heptazine g-o-triazine

P31 c (159) P3 (143) I-43d (220) P–42 m (111) P-6m2 (187) Cmc21 (36) P2 mm (25)

a = 6.465, c = 4.709 a = 6.406, c = 2.406 a = 5.411 a = 3.426 a = 4.746, c = 6.586 a = 7.083, b = 12.269, c = 6.871 a = 4.147, b = 4.754, c = 6.474

4 2 2 1 2 4 2

5.49 4.85 4.30 4.13 2.97 2.88 0.93

3.76 3.12 2.87 2.53 1.16 0.89 –

composition, structures and properties. More definitely speaking, hetero-junction construction [120,121], dimensionality tuning (nano-templating [122,123]) and nanocarbon loading have been widely applied in promoting the charge transfer, mobility and separation respectively. Furthermore, suitable co-catalyst loading [44,124–127] and defect control have been available in accelerating the surface reaction kinetics (charge utilization). In addition, pore texture tailoring, surface sensitization, and band-gap engineering (non-metal doping [128] and co-polymerization [84,129,130] strategies) were utilized to create highly mesoporous g-C3 N4 with high surface area and to increase the light harvesting and visible absorption through the red-shift of its optical absorption edge, respectively. In future, it is expected more and more engineering modification strategies will be developed to improve the photocatalytic performances of g-C3 N4 -based photocatalysts. More importantly, all different photocatalytic stages such as light harvesting, charge excitation, charge transfer, mobility and separation, and surface charge utilization should be simultaneously considered and optimized [7]. In other words, the synergy and integration effect of these different strategies should be paid more attention. In the following sections, the versatile properties, design strategies and potential applications will be thoroughly summarized. Fig. 5. Design considerations of g-C3 N4 -based photocatalysts based on the different photocatalytic stages.

sation of the monomers) and small active sites for interfacial (photo)reactions, slow surface reaction kinetics, moderate oxidation ability, grain boundary effects and low charge mobility which disrupt the delocalization of electrons [51,118]. Additionally, it should be noted from Fig. 3 that the photo-generated holes of C3 N4 with moderate oxidation ability can only achieve oxygen evolution from water oxidation, instead of the formation of the nonselective hydroxyl radicals, • OH. At this point, the g-C3 N4 -based photocatalysts seem to be a suitable candidate for selective photooxidation and related transformations of organic compounds in aqueous media, avoiding the direct mineralization to CO2 by the strong • OH [119]. Thus, it is therefore highly desirable to lower the top level of VB of C3 N4 to enhance its water oxidation power, as 4-electron water oxidation reaction oxidation to O2 is a more challenge half-reaction for water splitting. Although these prominent challenges of g-C3 N4 itself greatly limit its photocatalytic performance enhancements, they also afford more opportunities to construct more efficient g-C3 N4 -based photocatalysts in the future studies. 2.3. Design considerations of g-C3 N4 -based photocatalysts For these above reasons, careful consideration must be given to the rational design of g-C3 N4 for achieving the optimum photocatalytic performances. To avoid some of these drawbacks and maximize the photocatalytic efficiency, several modification strategies have been pursued to design highly efficient g-C3 N4 -based photocatalysts. Fig. 5 summarizes the design considerations of g-C3 N4 -based photocatalysts based on their detailed

3. Versatile properties of g-C3 N4 -based photocatalysts As is known, the photocatalytic efficiency of g-C3 N4 -based photocatalysts is mainly governed by all parameters/properties of g-C3 N4 itself, including crystal structural, surface physicochemical, stability, optical, adsorption, electrochemical, photoelectrochemical and electronic properties. Thus, a fundamental understanding and deterministic control of these chemical and structural factors will enable the scalable production of g-C3 N4 -based composite photocatalysts with the best photocatalytic behavior, which will be favorable for creating some robust g-C3 N4 -based material systems for practical photocatalytic applications and fundamental insights into photocatalytic enhancement mechanisms at the single-atom level. 3.1. Crystal structural properties It is known that C3 N4 possesses seven different phases, e.g., ␣-C3 N4 , ␤-C3 N4 , cubic C3 N4 , pseudocubic C3 N4 , g-h-triazine, g-hheptazine and g-o-triazine, which exhibit the band gaps of 5.49, 4.85, 4.30, 4.13, 2.97, 2.88 and 0.93 eV, respectively, in terms of GW method (as shown in Table 3) [131]. Among them, the famous super hard ␤-C3 N4 crystalline phase has been demonstrated to possess the similar hardness/low compressibility to that of diamond [132]. Except the pseudocubic and g-h-triazine phases, other five phases have indirect band gaps in their bulk structures [127,131,133]. As observed from Table 3, it is clear that g-h-triazine and g-hheptazine phases exhibit the suitable band gaps of 2.97 and 2.88 eV for visible-light absorption, favoring their applications in different photocatalytic fields. More interestingly, g-C3 N4 also shows the stacked 2D layered structure, as displayed in Fig. 6a. Furthermore, two different condensation states have been demonstrated

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Fig. 6. The stacked 2D layered structure of g-C3 N4 (a); structures of s-triazine (b) and tri-s-triazine (c) as the primary building blocks of g-C3 N4 .

Fig. 7. XRD patterns of (a) the tubular carbon nitride and (b) the bulky g-C3 N4 synthesized by directly heating melamine at 520 ◦ C for 2 h [138].

as the primary building block in a single layer of g-C3 N4 networks: s-triazine units (ring of C3 N3 ; Fig. 6b) with a periodic array of single carbon vacancies; and tri-s-triazine/heptazine subunits (triring of C6 N7 ; Fig. 6c) connected through planar tertiary amino groups with larger periodic vacancies in the lattice [134]. More importantly, it has been experimentally and theoretically demonstrated that the energetically favored tri-s-triazine-based g-C3 N4 was 30 kJ mol−1 more stable than the triazine-based g-C3 N4 , adequately suggesting that tri-s-triazine is the most widely accepted basic unit for the g-C3 N4 networks [131,134–136]. It is known that XRD has been extensively employed to precisely measure the lattice constant and crystal structures. The typical experimental XRD pattern of bulky g-C3 N4 powders have two distinct diffraction peaks located at 27.40◦ and 13.0◦ (as shown in Fig. 7b), which can be indexed as (002) and (100) diffraction planes for graphitic materials (JCPDS 87-1526) [44]. Clearly, the XRD results indicate that the g-C3 N4 exhibits the flake-like structure with interplanar stacking distance of 0.325 nm revealed by (002) diffraction, which is similar to that of graphite with stacking distance of 0.34 nm [102,137]. The distance of 0.681 nm for in-plane structural packing motif is slightly smaller than that of the tris-striazine units (ca. 0.73 nm), presumably due to the bending of 2D layered structures [44]. However, the g-C3 N4 nanotubes exhibit one distinct XRD diffraction peak at 17.4◦ (corresponding to an interplanar separation of d = 0.49 nm, Fig. 7a), indicating the formation of the s-triazine units (with the theoretical value of d = 0.47 nm [127]) in g-C3 N4 [138]. Consequently, the exact periodic units in each layer

Fig. 8. Multiple functional surface properties of polymeric g-C3 N4 material with defects [101].

of g-C3 N4 could be readily identified by the XRD peak associated with an in-plane structural packing motif. 3.2. Surface physicochemical properties It is known that a variety of surface defects on the surface of polymeric g-C3 N4 material lead to the formation of multiple functionalities. Commonly, the basic primary and/or secondary amine groups (e.g., CNH2 and C2 NH) on the terminating edges in the single layer of g-C3 N4 (as shown in Fig. 8) could be created by a small quantity of hydrogen impurity, owing to the incomplete polycondensation [49,101]. Therefore, it is not surprising that the g-C3 N4 materials with surface defects and electron-rich properties also exhibit the unique nucleophilic character from basic surface functionalities (for the activation of CO2 ) or H-bonding motifs (as shown in Fig. 8), thus facilitating their more valuable applications in catalysis, as compared to the ideal and defect-free g-C3 N4 [101]. Furthermore, it is easily understood that the abundant basic groups ( NH , N , NH2 and N C ) on the surface of g-C3 N4 are beneficial for the removal of acidic toxic molecules through chemical adsorption based on electrostatic interactions [139]. Similar to the hydrophobic nature of the nanocarbon surface, hydrophobicity of g-C3 N4 could lead to the formation of weakly interacted interfacial layer, thus significantly restricting the electron transport and separation and surface electrocatalytic reactions [61]. At this point, the hydrophilicity of g-C3 N4 materials (with decreasing contact angle of water on their surface) could be improved through introducing oxygen-containing functional groups (hydroxyl and carboxyl) by

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Fig. 10. Comparison between the Raman spectra of coplanar bulk and 1-layer gC3 N4 samples (780 nm laser) [154].

Fig. 9. FTIR spectra of g-C3 N4 powders obtained by heating melamine (MCN), thiourea (TCN), and urea (UCN) [146].

means of chemical oxidation, thus greatly favoring their good dispersion in the aqueous solutions and further enhanced interfacial coupling and photocatalytic activities [140–145]. Commonly, these functional groups and networks (C N ) could be further identified by the Fourier transform infrared (FT-IR) spectra, X-ray photoelectron spectroscopy (XPS) measurements, Raman spectra, and Boehm titration analysis. Generally, the chemical composition and bonding information of g-C3 N4 could be partially identified by FT-IR measurement. Fig. 9 depicts typical FTIR spectra of g-C3 N4 powders obtained by heating melamine (MCN), thiourea (TCN), and urea (UCN) [146]. As shown, the main characteristic

peaks observed in the region from 900 to 1700 cm−1 were usually assigned to stretching vibration signals of aromatic heptazinederived repeating units, including the typical sp2 C N stretching modes and out-of-plane bending vibrations of the sp3 C N bonds [130,147–150], while the sharp absorption peak centered at approximately 810 cm−1 was attributed to the characteristic breathing mode of tri-s-triazine cycles [150–152]. Meanwhile, the absorption band at 883 cm−1 were indexed as the deformation mode of N H in amino groups [153], whereas the broadened peaks between 3000 and 3500 cm−1 were related to the stretching vibration [146,149,150,153] of residual free N H in the bridging C NH C units and O H originated from physically adsorbed water species on g-C3 N4 surface, respectively. In the recorded Raman spectra, several characteristic peaks of g-C3 N4 can be observed at 1616, 1555, 1481, 1234, 751, 705, 543, and 479 cm−1 , further confirming the vibration modes of CN heterocycles [151,154]. It should be noted that the peak at 1234 cm−1 , corresponding to the N C (sp2 ) bending vibration, exhibits significant blue shift (1250 cm−1 for 1-layer g-C3 N4 ), due to the phonon confinement and strong quantum confinement effect [154]. Moreover, it has also been experimentally and theoretically demonstrated that the ratios of peak heights of 751–705 cm−1 (I751 /I705 ) and 543–479 cm−1 (I543 /I479 ), corresponding to layer–layer deformation vibrations or the correlation vibrations, obviously increased with decreasing the layer number of g-C3 N4 [154]. Additionally, the nitrogen containing species can be further quantitatively analyzed by the element analysis and Boehm titration. For the element analysis, X-ray photoelectron spectroscopy (XPS) can not only reveal the atom ratio of carbon to nitrogen, but also identify the carbon and nitrogen species in g-C3 N4 . For example, the main peak at 288.2 eV in the high-resolution C 1s XPS spectra of the 1.0 wt% RGO/g-C3 N4 sample, indicates the existence of the N C N2 coordination [151]. The N 1 s binding energies at about 398.6, 399.8, and 401.5 eV in the high-resolutionN1 s XPS spectra of the 1.0 wt% RGO/g-C3 N4 sample can be assigned to sp2 -hybridized nitrogen (C N C), tertiary nitrogen (N (C)3 ) and amino functional groups having a hydrogen atom (C N H), respectively [146,151,155,156]. For Boehm titration analysis, it was found that the content of basic group per unit area of g-C3 N4 generally decreased with increasing the calcination temperature [157]. In a word, the combination of Raman vibration properties, FTIR, XPS spectra and Boehm titration analysis can fully reveal the surface functional groups of g-C3 N4 nanomaterials (Figs. 9,10 and 11). Interestingly, the basic surface functionalities can be further evidenced by the isoelectric point (IEP) and the zeta potentials of g-C3 N4 dispersions [146]. It is known that the IEP is an important physicochemical parameter of many compounds, such as oxides, sulfides, hydroxides, and nitrides, which has been widely used to estimate the surface charges of compound particles at various pH conditions. In general, the solid particles are positively

Fig. 11. High-resolution XPS spectra of C 1s (A) for the 1.0 wt% RGO/g-C3 N4 sample (a) and GO (b) and N 1s (B) for the 1.0 wt% RGO/g-C3 N4 sample [151].

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Fig. 12. Zeta potentials of MCN, TCN, and UCN powders as functions of the pH value of the suspensions (as shown in Fig. 12) [146].

charged and negatively charged at pH values below and above the IEP point, respectively. For example, Wang et al. found that the zeta-potential of bulk g-C3 N4 dispersions in water was −47.4 mV, showing a negative surface charge, whereas, g-C3 N4 exhibited a positive surface charge with a zeta-potential of +30 mV after the successful protonation in HCl solution [158]. Similarly, Yu and his coworkers experimentally demonstrated that the IEPs of TCN, MCN, and UCN samples are 4.4, 5.0 and 5.1, respectively, further confirming their basic and negatively charged surface. Thus, in the initial pH, the MCN, UCN and TCN samples exhibited the negative Zeta potentials of −17.0, −30.7 and −19.9 mV, respectively (as shown in Fig. 12) [146]. Thus, the surface protonation of g-C3 N4 treated by the acid solution with pH below its IEPs has become a popular strategy to reverse the surface properties of g-C3 N4 from negative to positive charge, facilitating the construction of composite materials through electrostatic interactions with negatively charged materials and the enormous enhancement in photocatalytic performance [138,158–162]. It was believed that surface protonation modification could simultaneously achieve better dispersion, adjusted electronic band gaps, and increased surface area and ionic conductivity [158]. In the contrary, the surface modification of g-C3 N4 via alkaline hydrothermal treatment (e.g. NaOH and ammonium hydroxide) can create more surface hydroxylation and rich surface H-bond network of g-C3 N4 with the negatively charged surface, thus greatly enhancing the interfacial charge transfer, and increasing the specific surface area and pore volume [163–165]. Particularly, the H-bonding network can offer multiple channels and inmate interfaces for the proton transfer from water to the photo-excited electrons on g-C3 N4 surface, stabilize the negatively charged intermediate and transition states, thus obviously promoting charge separation and photocatalytic H2 evolution [166]. 3.3. Stability properties The defect-rich and N-bridged tri-s-triazine-based g-C3 N4 was found to be energetically favored relative to the other phases, which exhibits extraordinary thermal stability up to 600 ◦ C [149,167–169]. In air, over a period of months, the stable g-C3 N4 only exhibited a slightly lighter color change, because of its strong water adsorption effects [167]. Fig. 13 gives the thermogravimetricdifferential scanning calorimetry (TG-DSC) analysis for melamine and g-C3 N4 prepared by heat polymerization of melamine at 520 ◦ C in air [149], which clearly indicated that the formation and decomposition of g-C3 N4 (stable up to 600 ◦ C) involve a series of processes, e.g., the sublimation and thermal condensation of melamine (297–390 ◦ C), de-ammonation process (545 ◦ C) and fur-

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ther oxidation decomposition (630–750 ◦ C) of g-C3 N4 material [44,149]. It has been observed that melem transforms into a g-C3 N4 material by temperature-dependent X-ray powder diffractometry investigations above 560 ◦ C [134]. The complete decomposition temperature of g-C3 N4 ranging from 700 to 750 ◦ C, is in good agreement with the Gillan’s report [167,170]. These typical processes were also observed during the formation of g-C3 N4 by using cyanamide as precursors (as shown in Fig. 14), except for the first formation of melamine through condensing the cyanamide precursors [101]. Notably, the thermal stability of g-C3 N4 has been regarded to be the highest in organic materials, which can be obviously affected by the different polymerization degrees of gC3 N4 in different preparation methods [149,167,170–173]. The high thermal stability of g-C3 N4 polymeric semiconductor not only features its various applications, as a heterogeneous organic catalyst, at operating temperature below 500 ◦ C, but also allows its easy removal by simply increasing the calcination temperature beyond 600 ◦ C, thus favoring its utilization as confinement templates, structuring agents or nitrogen sources for synthesizing a refined carbon nanostructure or metal nitride nanostructures with continuously adjustable composition, such as TaON, Ta3 N5 , ternary aluminum gallium nitride and titanium vanadium nitride [55,174–177]. Furthermore, the g-C3 N4 also exhibits superior chemical stability [167]. Similar to that of graphite, it has been demonstrated that the g-C3 N4 with optimized van der Waals interactions between the single layers is insoluble in water, acid, base, and various kinds of organic solvents, including ethanol, toluene, diethyl ether and THF [55,127,133,167]. However, notably, the molten alkali metal hydroxides and KMnO4 could lead to the hydroxolysis and the strong oxidation decomposition of intrinsic structures of the g-C3 N4 materials, respectively [178]. In particular, the excellent acid stability and interesting protonation effects have been also further confirmed [178]. Commonly, the concentrated-acid treatment at room temperature could result in the formation of a non-transparent solution containing highly dispersed nanosheets without destroying the graphite-like structure of g-C3 N4 [158], because the protonation effects could break both sheets and stacks from its defects, as well as fabricate a highly porous texture between the adjoining layers. Zhang et al. demonstrated that the relatively good-quality g-C3 N4 thin films could be fabricated by conventional dip/disperse-coating techniques using a stable protonated g-C3 N4 colloidal suspension [179]. More recently, the first liquid state NMR spectra and a lyotropic liquid crystal phase of g-C3 N4 have been successfully observed through the highly protonated g-C3 N4 thermodynamic solutions with concentration up to 300 mg mL−1 , highlighting the promising applications of g-C3 N4 solubilization technique in concentrated H2 SO4 [180]. 3.4. Electronic properties It is well known that the suitable electronic properties play important roles in better photocatalysis. To look insight into its electronic structure, the density-functional-theory (DFT) calculations were applied in obtaining the detailed oxidation and reduction levels of valance and conduction bands. The results shown in Fig. 15 demonstrated that the highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO-LUMO) gaps of melem molecule, polymeric melon and an infinite sheet of a hypothetically, fully condensed g-C3 N4 were 3.5, 2.6 and 2.1 eV, respectively [44]. Clearly, the calculated band gap of polymeric melon is very close to the experimentally measured medium-band gap of 2.7 eV. The wavefunction investigations of the valence band (Fig. 15b) and conduction band (Fig. 15c) are mainly derived from nitrogen pz orbitals and carbon pz orbitals, which serve as oxidation and reduction sites for O2 and H2 evolution reactions, respectively [44]. Recently, it was found that, compared to the underestimated

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Fig. 13. The TG-DSC analysis for heating the melamine (a) and the g-C3 N4 (b) obtained by heat polymerization of melamine at 520 ◦ C [149].

Fig. 14. Reaction path for the formation of g-C3 N4 starting from cyanamide.

Fig. 15. Electronic structure of g-C3 N4 . (a) DFT band structure for g-C3 N4 calculated along the –X and Y– directions. The potentials for H+ to H2 and H2 O to O2 are displayed by the blue and red dashed lines, respectively; the Kohn–Sham orbitals for the valence band (b) and conduction band (c) of g-C3 N4 . The C, N and H atoms are gray, blue and white, respectively. The isodensity surfaces are drawn for a charge density of 0.01qe ◦ A−3 [44]. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

band gaps of semiconductors and insulators calculated by density functional theory (DFT) with local density approximation (LDA), the band structures obtained by the GW approximation (larger than the LDA band gap by 1.73 eV) are much more close to the experimentally reported values [131]. Besides the DFT calculations, the band edge positions of g-C3 N4 materials can be determined by electrochemicalimpedance spectra (EIS), based on the Mott–Schottky (M–S) plot, and the valence band X-ray photoelectron spectra (VB-XPS), respectively [7]. Wang and his coworkers measured the flat band potentials of bulk gC3 N4 through the M–S method, indicating that its conduction band and valance band edges are located at −1.3 and 1.4 V vs NHE at pH 7, respectively [54,84,187]. Meanwhile, Yan et al. obtained the accurate conduction band and valance band edges of bulk g-C3 N4 located at −1.53 and 1.16 V vs NHE at pH 7 by the VB-XPS mehod, respectively [93]. However, it is worthy of noting that these two results seem to be slightly contradictory. The main reason is probably that many researchers directly equate the flat-band potential with the conduction band potential. In fact, for an n-type semiconductor, the conduction band potential is more negative by about −0.1 or −0.2 V than the flat-band potential [7]. Considering the slight difference (−0.2 V) between the flat-band potential and the conduction band potential, there was complete agreement between these two experimental results. The band structures of different types of g-C3 N4 samples obtained by these two methods have been summarized and listed in Fig. 16. As shown in Fig. 16, the doping of P and C can make the conduction and valance band edges of g-C3 N4 more negative and positive, respectively, thereby facilitating the reduction and oxidation reactions. In future, it is expected that more accurate band positions of g-C3 N4 could be available and applied in the design and development of highly efficient g-C3 N4 based photocatalysts.

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Fig. 16. Schematic illustration of the band structures of different types of g-C3 N4 samples: g-C3 N4 [84], Fe–g-C3 N4 [54,181], S–g-C3 N4 [182], P–g-C3 N4 [183], O–g-C3 N4 [184], C–g-C3 N4 [185], I–g-C3 N4 [186] and B–g-C3 N4 [84]. VB-XPS: valence band X-ray photoelectron spectroscopy; MS: electrochemical analysis by Mott–Schottky plots.

Fig. 17. (a), time-resolved PL spectrum monitored at 525 nm under 420 nm excitation at 298 K for bulk g-C3 N4 (black) and mpg-C3 N4 (red) [123];(b), time-resolved PL spectra monitored at 480 nm under 420 nm excitation at 77 K for CN and CNS–CN [121]. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

In addition, the underlying electronic properties and charge carrier dynamics, including the microscopic dynamic process of the charge generation, recombination, separation, and transfer, play crucial roles in determining the photocatalytic performance [7,58]. Thus, the in-depth understanding of the electrical properties and charge carrier dynamics is, therefore, fundamentally important to help us to design and construct the more efficient and stable g-C3 N4 -based composite photocatalysts. To date, many different advanced techniques, such as femtosecond transient absorption (TA) spectroscopy [188,189], time-resolved fluorescence spectroscopy, transient photocurrent decay, Nyquist impedance plots and the transient photovoltage (TPV) technique [190–195] have been available in studying the charge carrier dynamics of g-C3 N4 based composite photocatalysts. For instance, Wang et. al measured the time-resolved PL spectrum of bulk g-C3 N4 and revealed that the photoinduced charge carriers in bulk g-C3 N4 showed a lifetime of ∼5 ns even at 298 K, indicating the fast recombination rate (Fig. 17a) [123]. The greatly suppressed PL signal of mpg-C3 N4 further indicated that the surface terminal sites of mpg-C3 N4 can promote the electron relocalization, thus accelerating the catalytic functions of mpg-C3 N4 for surface redox reactions. Similarly, the isotype heterojunctions between g-C3 N4 and S-doped g-C3 N4 have been found to exhibit a matched band alignment, which can significantly promote the charge separation between them, thus resulting in prolonging the lifetime of photo-excited charge carriers by about 2.15 ns [121]. It is believed that the prolonged lifetime of photo-generated charge carriers could further increase their utilization efficiency in driving surface photoredox reactions. Recently, the TA spectra of g-C3 N4 also revealed that the existence of silica templates can prolong the lifetime of excited charge carriers by about hundreds of picoseconds, thereby achieving the high photocatalytic activities (Fig. 17b) [188]. More recently, it was demonstrated that the charge separate efficiency in g-C3 N4 -based photocatalysts could be also revealed by the SPV measurement, as an advanced and facile technology. As shown in Fig. 18, the obviously increased SPV signal in the range

Fig. 18. SPV of g-C3 N4 (Ni0) and Ni@g-C3 N4 (Ni10). The inset shows the schematic setup of SPV measurements [192].

of 300–450 nm could be achieved through loading Ni nanoparticles on g-C3 N4 as co-catalysts, suggesting the greatly accelerated charge separation efficiency [192,193]. 3.5. Optical properties For various kinds of photochemistry-related applications of gC3 N4 , the decisive optical properties, including Ultraviolet–visible (UV/Vis) absorption, photoluminescence (PL) and electrochemiluminescence (ECL), have been readily further revealed by means of the theoretical calculations or experimental characterizations [47,55,187]. The typical UV/Vis absorption spectrum of g-C3 N4 prepared at different temperature were displayed in Fig. 19a [44]. Indeed, the absorption edge of conventional g-C3 N4 shows an

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Fig. 19. (a) UV/Vis absorption spectra of g-C3 N4 prepared at different temperature. Inset: photograph of the photocatalyst [44]; (b) the room-temperature PL spectrum of g-C3 N4 solid powder (␭ = 365 nm, top figure) and the ECL spectrum of g-C3 N4 -modified electrode in 0.10 M K2 SO4 and 3.0 mM K2 S2 O8 solution by cycling the potential between 0.00 and −1.30 V (vs. Ag/AgCl) with a scan rate of 100 mV/s and step potential of 1 mV (bottom figure) [78].

obvious red shift towards longer wavelengths with increasing condensation temperatures, indicating that the increasing polymerization degrees can achieve a decreasing bandgap [44,196]. The results are also consistent with those obtained by the theoretical calculations. Furthermore, it can be seen that these two samples fabricated at 550 and 600 ◦ C exhibit very similar strong bandgap absorption, with edges at approximately 450 nm. The band gap energy (Eg ) can be further obtained according to the intercept of the tangents to the plots of (␣h␯)1/2 vs. photon energy [146,148]. The bandgap of the condensed g-C3 N4 prepared at 550 ◦ C is estimated to be 2.7 eV from its UV–vis spectrum, in good agreement with previous studies [148]. In fact, the greyish yellow color of gC3 N4 can further confirmed the favorable medium band gap for visible light absorption, as observed in the inset of Fig. 19a. More interestingly, other modification strategies, such as doping by Fe, S, P, C, I, O and B atomics (as shown in [16]) and barbituric acid moleculares [84] can also lead to a redshift of the adsorption edges. Apart from UV/Vis absorption spectrum of g-C3 N4 , intensive investigation also focus on its PL and ECL spectrum, due to its semiconductor properties. Both PL and ECL spectrum of g-C3 N4 were also displayed in Fig. 19b [78]. As observed in Fig. 19b (top figure), the room-temperature PL spectrum of g-C3 N4 solid powder at ␭ = 365 nm, exhibited a strong blue emission band ranging from 400 to 650 nm, with a maximum peak of ca. 470 nm in the blue region. It is generally believed that the intensity of roomtemperature PL signal is employed to directly and qualitatively elucidate the recombination rate of photo-generated electrons and holes in irradiated g-C3 N4 [155,156,197,198]. Commonly, lower peak intensities imply the improved charge trapping and efficiently transferring, thus further prolonging the lifetimes of charge carriers and facilitating the enhancements in photocatalytic activity [199–201]. It should be noted that the room-temperature PL spectrum of g-C3 N4 nanosheets are sensitively and markedly determined by their condensation degree (or optical band gap), thickness and sizes [47,100,202,203]. It was also observed in the bottom of Fig. 19b that the g-C3 N4 -modified electrode in 0.10 M K2 SO4 and 3.0 mM K2 S2 O8 showed the slightly broader ECL spectrum, with a maximum peak at ca. 470 nm (2.6 eV), which matches closely with the room-temperature PL spectrum of g-C3 N4 solid powder. The blue ECL emission from g-C3 N4 is strong enough to be observed with naked eyes as shown in the inset of bottom Fig. 19b [78]. Although there are obvious differences between the excited state of g-C3 N4 in ECL and the room-temperature PL spectrum, the similar maximum emission peak of both types of luminescence suggested that identical ECL emission is also attributed to the band gap luminescence [78]. The results clearly demonstrated that the g-C3 N4 semiconductor could be also a new kind of efficient and promising

luminophore for ECL sensing to achieve the sensitive and selective detection of trace metal ions, such as Cu2+ . Therefore, it is naturally expected that the metal-free and non-toxic g-C3 N4 could be extensively utilized as a multifunctional optical material for light emitting devices [62,63], bioimaging, [100,142,204,205] ECL sensing probe [76,78,206,207] and fluorescent probes [208–210]. 3.6. Adsorption properties Generally speaking, adsorption property of a given adsorbent is strongly dependent by both its porous microtexture and surface chemical property [211–215]. Similar to the 2D graphene or graphene oxide materials, a wide variety of targeted adsorbates can be adsorpted on the multiple different functional groups (e.g., amino groups) and defect sites on g-C3 N4 through different types of interactions such as physical adsorption (␲-␲ stacking interaction), electrostatic attraction, or chemical interaction (surface complexation or acid-base interactions) [216]. Due to the weaker ␲-␲ stacking interaction in the physical adsorption, the stronger electrostatic attraction and chemical interaction have been proposed to the improved adsorption properties of g-C3 N4 , which will be thoroughly discussed in this section. Based on the electrostatic attraction, it has been demonstrated that the selective photodecomposition of anionic methyl orange (MO) or cationic methyl violet (MV) and methylene blue (MB) could be achieved over positively or negatively charged TiO2 -based semiconductors, respectively [217–219]. Similarly, the electrostatic attraction between the negatively charged g-C3 N4 and positively charged adsorbate molecules, such as cationic MV and MB have been proposed to achieve the selective adsorption and photocatalysis in many studies. For example, Yu and his coworkers demonstrated that the negatively charged g-C3 N4 particles exhibited extraordinaryly higher adsorption capacity towards a cationic MB dye than anionic MO dye in aqueous suspension [146]. Further results showed that the adsorption kinetics of MB on three different kinds of g-C3 N4 (Fig. 20a) could be well depicted by a pseudo-second-order kinetic equation as follows [220]: dqt /dt = k2 (qe − qt )2 2

t/qt = 1/(k2 qe ) + t/qe

(2) (3)

where qt (mg g−1 ) is the adsorption amount at time t, and k2 (g mg−1 min−1 ) is the pseudo-second-order rate constant, and qe (mg g−1 ) is the maximum adsorption amount. Notably, it was also revealed that the adsorption kinetics of heavy metal cationic ions and perfluorooctane sulfonate over g-C3 N4 also followed the pseudo-second-order kinetic model [157,221]. Meanwhile, it can be also found that the Langmuir model, as compared to Freundlich

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Fig. 20. Adsorption kinetics (a) and adsorption isotherms (b) of methylene blue on MCN, TCN, and UCN [146].

model, could be used to better fit the adsorption isotherms of MB on three g-C3 N4 samples (Fig. 20b), indicating the homogeneity of the adsorbent surface [146]. Differences in the adsorption activity of three samples towards MB can be attributed to the synergistic effect of surface area and zeta potential. Apart from the electrostatic attraction, the chemical interaction (surface complexation or acid-base interactions) between g-C3 N4 and targeted adsorbates has been widely applied in manipulating the adsorption properties of g-C3 N4 . Fifty years ago, Pearson firstly proposed the well-known hard and soft acids and bases (HSAB) principle [222,223], stating that hard and soft acids will interact preferentially with hard and soft bases, respectively. So far, this principle has been widely employed to clarify the chemiadsorption interactions between various kinds of adsorbents and adsorbates with different acidic and basic properties [224,225]. According to the HSAB principle, it is clear that the acidic molecules such as CO2 , H2 S and NOx should be readily chemically bond to the basic nitrogen-containing groups of g-C3 N4 . Recently, Oh et al. demonstrated that the g-C3 N4 functionalized porous reduced graphene oxide aerogel could achieve a large CO2 adsorption capacity (0.43 mmol g−1 ) and high CO2 selectivity against N2 under ambient conditions, and an easy regeneration of 98% adsorpted CO2 by simple pressure swing [226]. Importantly, the DFT calculations further revealed that the strong dipole interaction induced by electron-rich nitrogen at the microporous edges of g-C3 N4 is the critical factor for achieving the high-capacity, regenerative and selective CO2 capture. It is highly desired that the chemoselectivity of g-C3 N4 interactions for other gases could be also further tailored through effectively developing the porous structure and increasing the content of nitrogen-containing groups on the surface of g-C3 N4 [227]. For example, Jia et al. demonstrated that a simple oxygen-atmosphere UV irradiation could create the sufficient acidic sites on hierarchically ordered macro-/mesostructured g-C3 N4 films, such as COOH and N-oxide groups through replacing its surface basic nitrogen-containing groups, [228] thereby achieving the highly selective chemi-adsorption of basic molecules. In the contrary, Yu and his coworkers demonstrated that the loading of amine groups on g-C3 N4 through monoethanolamine solution treatment can successfully achieved a 3.76-times enhancements in the adsorbed CO2 amount, as compared that of pristine g-C3 N4 under ambient pressure and temperature (Fig. 21), owing to the combination effects of both physical and chemical adsorption of CO2 [227]. Importantly, it was also observed that the enhanced adsorption and activation (favoring the formation of nonlinear HCO3 − ) of CO2 molecules over amine-functionalized g-C3 N4 were beneficial for the improvement of CO2 photoreduction efficiency and selective formation of CH4 [227]. More surprisingly, the CO2 adsorption capacity of g-C3 N4 microspheres with 3D hierarchical pores and a much higher BET surface area (550 m2 /g) could reach 2.90 and 0.97 mmol/g at 25 and 75 ◦ C, respectively [229]. However, even so, the CO2 adsorption capacity is still obviously lower

than those of famous “molecular basket” adsorbents (133 mg/g) [230–232], activated carbon (3.75 mmol/g) [233] and metal organic framework (3–5 mmol/g) [234–236], implying there are still ample room to enhance the CO2 adsorption capacity of g-C3 N4 semiconductor photocatalysts. In this end, the g-C3 N4 semiconductors with rich basic nitrogen-containing groups, high surface areas, porous structures and suitable band gaps seem to be very promising for the applications in the field of photocatalytic CO2 reduction, H2 evolution and the oxidation of NOx and H2 S, because porous g-C3 N4 could simultaneously serve as light-harvesting, charge-excitation, charge-transportation, adsorption (for acid CO2 , H+ , NOx and H2 S molecules) and catalytic centers [237]. 3.7. Electrochemical properties As shown in Fig. 2, the photocatalytic reduction and oxidation reactions on the surface of semiconductors are fundamentally electrocatalytic ones driven by the photo-generated electrons and positive holes, respectively. More interestingly, g-C3 N4 semiconductor itself can also serve as the multifunctional electrocatalysts with higher activity than pure carbon [238,239], which play significant roles in achieving the improved overall photocatalytic efficiency. Commonly, pyridinic N atoms of g-C3 N4 with strong electron-accepting ability can serve as active sites for the electrochemical reactions, making it a potential metal-free electrocatalyst [55]. Unfortunately, the moderate conductivity and poor electron transfer ability of g-C3 N4 greatly limit its electrochemical performances and applications in various electrocatalysis fields, such as O2 reduction reaction (ORR) for fuel cells [240] and H2 evolution reaction (HER) for water splitting [241]. Consequently, in the past several years, extensive research efforts have been devoted to the exploration of hybrid g-C3 N4 -based electrocatalysts with higher electroconductivity and more active sites, through several strategies, such as manipulating size, thickness and structure, coupling with various semimetal carbon materials and doping with heteroatoms [242]. It has been well accepted that surface electrocatalytic ORR over various heterogeneous semiconductors has been found to play key roles in determining the photocatalytic activity of pollutant degradation [20,25,243] and organic synthesis [244,245]. However, so far, most of ORR co-catalysts loaded on the surface of semiconductors for photodegradation and photosynthesis are mainly constituted of noble metal elements, such as Pt [246–248], Au [249,250] and Ag [251,252] nanoparticles/clusters. Fortunately, it has been recently revealed that the N-doped nanpcarbon materials, such as N/S or B/N co-doped graphene [253,254], N-doped graphene/porous carbon [255], Mn3 O4 /N-doped graphene [256] and N-doped graphene (carbon spheres, nanoyubes or nanocages) [257–261], exhibited excellent electrocatalytic ORR activities for direct methanol fuel cells (DMFC). More interestingly, it has been demonstrated that the electrocatalytic 4e− ORR activities of g-C3 N4

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Fig. 21. (a) CO2 -capture capacities of g-C3 N4 (CN) and amine-functionalized g-C3 N4 (3CN) [227]; (b) CO2 adsorption isotherms of the mesoporous g-C3 N4 microspheres at 25 and 75 ◦ C [229].

Fig. 22. (A), (a) Free energy plots of ORR on g-C3 N4 with 0e− , 2e− , and 4e− paths (corresponding to paths I, II, and III). (b–d), Schemes of ORR’s pathway on pristine g-C3 N4 with 0e− , 2e− or 4e− participation, respectively (red areas represent the active sites facilitating ORR). (B) ORR polarization curves for various electrocatalysts on rotating electrode at 1500 rpm in O2 -saturated 0.1 M KOH solution [69]. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

could be significantly enhanced via the coupling with different kinds of conductive carbon support, owing to the improved electron accumulation and transfer on the surface of g-C3 N4 . Accordingly, the new-generation metal-free g-C3 N4 -carbon hybrid cathode electrocatalysts in DMFC, could achieve both the superior electrochemical ORR efficiency and the high CO/methanol tolerances [48]. So far, various kinds of nanostructured g-C3 N4 -carbon hybrids, such as g-C3 N4 @carbon [64,69], 2D g-C3 N4 nanosheet/1D carbon nanotube [65], 2D g-C3 N4 nanosheets/graphene [66,262–264], hollow mesoporous g-C3 N4 nanosphere/3D graphene [265], graphene supported Co-g-C3 N4 [266] and g-C3 N4 @cobalt oxide[267] have been extensively fabricated and demonstrated to be high-efficiency ORR electrocatalysts. For example, Qiao and coworkers theoretically revealed that the limited electron transfer ability of g-C3 N4 leads to the low ORR catalytic activity of pure g-C3 N4 through an unfavorable 2e− pathway (as shown in Fig. 22A) [69], whereas, the accelerated electron transfer and increased active sites in the nanoporous g-C3 N4 @carbon composite could achieve a nearly 100% of selectivity for 4e− ORR pathway in alkaline aqueous solution. The further experimental results confirmed that the g-C3 N4 @ordered mesoporous carbon (CMK-3) exhibited a considerably lower onset potential and comparatively higher ORR current density, as compared to those of g-C3 N4 (m) and the g-C3 N4 /CMK-3 mixture electrodes (as shown in Fig. 22B). By the same way, the hybrid of g-C3 N4 and conductive metal has also been found to significantly improve its the sluggish cathodic ORR in fuel cells [241,268,269]. At this point, it is highly desired that more and more metalfree g-C3 N4 /carbon and earth-abundant metal/g-C3 N4 hybrid ORR electrocatalysts could be exploited and utilized as co-catalysts to greatly facilitate the photocatalytic activity of pollutant degradation and organic transformation.

Similar to the ORR, the thermodynamically uphill HER, as a central reaction in the electrochemical water splitting, always requires suitable catalysts with high electrocatalytic activity and durability to accelerate the sluggish kinetics. In contrast to most of Pt-free electrocatalysts, the best-known heterogeneous Pt/C composite has proven to be the most effective HER electrocatalyst, due to their high exchange current density at low overpotentials, chemical inertness, versatility, high conductivity, and resistance to oxidation [270]. However, high cost and low abundance of the noble metal Pt dramatically restricted its practical widespread applications. Although the cheap and earth-abundant transition metals, such as Fe, Co, Ni, W, Mo and their molecular derivatives, as Pt’s alternatives, have been found to display outstanding electrocatalytic HER activity, their low stability in acidic and basic media are unfavorable for the long-term operation [88,124,242,271–275]. In this regard, metal-free g-C3 N4 /conductive carbon hybrids beyond metals have also shown great promise as attractive HER electrocatalysts for water splitting reactions due to their earth abundance, tunable molecular structures, the unique advantages to easily fabricated a variety of nanostructures and strongly tolerance acid/alkaline environments [239]. The theoretical calculations revealed that the strong electronic coupling between g-C3 N4 and graphene could significantly improve electron conductivity and optical absorption of g-C3 N4 , thus leading to the greatly promoted charge separation and transfer at the graphene/g-C3 N4 interface [276]. Subsequently, Qiao and co-workers further experimentally verified that the asconstructed multilayered g-C3 N4 nanodomains on nitrogen doped ultrathin graphene sheets (C3 N4 @NG) exhibited superior HER activity, achieving a 10-mA cm−2 HER current density at an overpotential of ∼240 mV (as shown in Fig. 23a) [239]. From the viewpoint of thermodynamics, compared to too strong and weak chemical adsorption of H* on g-C3 N4 and N-graphene with the Gibbs free-

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Fig. 23. (a) The HER polarization curves of g-C3 N4 , NG, g-C3 N4 /NG mixture, 33 wt% of g-C3 N4 @NG and referenced 20% Pt/C smaples (electrolyte: 0.5 M H2 SO4 , scan rate: 5 mV s−1 ). (b) The calculated Gibbs free-energy for chemical adsorption of H* on three metal-free catalysts and Pt reference at the equilibrium potential. (c) Volcano plots of i0 as a function of the GH∗ for the C3 N4 @NG (red triangle), various metals (open symbols) and a nanostructured MoS2 electrocatalyst (closed symbol) [239]. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

energy of −0.54 and 0.57 eV (Fig. 23b), respectively, the C3 N4 @NG hybrid with the Gibbs free-energy of about 0.19 eV, exhibits a mediated adsorption–desorption behavior, facilitating the overall HER kinetics. In additional, as displayed in the volcano plot (Fig. 23c), the HER activity of metal-free C3 N4 @NG is very close to those of famous MoS2 electrocatalysts. It was also demonstrated that the broken N–3C bonds at the edge of g-C3 N4 lead to the formation of defect sites, pyridinic nitrogens, which could act as the stable H* adsorption sites and electrocatalytic HER active sites [239]. Inspired by this interesting work, Qu and co-workers developed a more active 3D porous HER elctrocatalyst based on the hybrid of 1D g-C3 N4 nanoribbons and 2D graphene sheets, exhibiting a current density of 10 mA cm−2 at an overpotential of ∼207 mV, in 0.5 M H2 SO4 solution [277]. It is believed that the high activity was attributed to the increased proton binding sites on 1D g-C3 N4 nanoribbons, close contact between g-C3 N4 and graphene, and unique 3D porous networks for improved mass transfer and diffusion. More recently, the supramolecular Cu-doped g-C3 N4 , as a biomimetic HER electrocatalyst, has been also demonstrated to show a high current density of 10 mA cm−2 at a low overpotential of 0.39 V in acidic media [278]. Thus, developing the novel non-noble-metal g-C3 N4 based HER electrocatalysts with high stability and activity is still a promising direction in the near future.

3.8. Photoelectrochemical properties Besides direct utilization as electrocatalysts, g-C3 N4 has proven to be a promising photoelectrode candidate for solar energy conversion in the PEC cells, due to its superior chemical and thermal stability and suitable electronic band structure. Initially, Zhang and Antonietti firstly observed the maximum cathodic photocurrent response (up to ca. 50 mA cm−2 at −0.3 V, IPCE ∼ 3% at 420 nm) of bulk mpg-C3 N4 film in KCl aqueous solution containing Fe(II) ions, under visible light (␭ > 420 nm, 150 W Xe lamp) [181]. The flat band potential (Efb ) of different g-C3 N4 semiconductors can also be further estimated from the onset photocurrent potential. More importantly, a tripled maximum photocurrent was also observed for the binary composite film of mpg-C3 N4 and standard Degussa P25 TiO2 (as the electron-transport channel) under the same conditions. However, the unfavorable factors of bulk g-C3 N4 film in this study, such as larger domain sizes, grain boundary defects and textural effects, implying there is still ample room to further optimize the g-C3 N4 photoelectrodes. Similarly, the weak transient photocurrent response of different bulk or modified g-C3 N4 solids was extensively confirmed in other works [84,114,123], which is generally used to identify the enhanced photocatalytic activity and charge separation as an auxiliary tool. To further improved the PEC properties of g-C3 N4 films

and extend their applications, various fabrication methods and modification strategies of g-C3 N4 films have been widely developed [43]. For example, Zhang et al. achievedan almost 3-fold higher cathodic PEC activity for hydrogen evolution from water than that of the pure g-C3 N4 through simultaneously fabricating a sponge-like structure and incorporating active carbon-dopant sites, under simulated solar-irradiation [279]. They attributed the enhanced activity to the increased charge mobility, surface area, mass transfer, active sites and ␲-conjugated structure. Furthermore, the g-C3 N4 -based composite photoelectrode films such as g-C3 N4 /CuInS2 [280], TiO2 /g-C3 N4 [281–283], CdS/g-C3 N4 [284], g-C3 N4 /WO3 [285–287], g-C3 N4 /N-doped graphene/NiFe-layered double hydroxide [288], Fe2 O3 /g-C3 N4 [289], and g-C3 N4 /MoS2 [290], also exhibited significantly enhanced PEC activity for hydrogen evolution or water oxidation, due to the promoted charge separation, enhanced visible-light absorption, accelerated surface reaction kinetics and suppressed photocorrosion. For example, Feng and coworkers demonstrated that the as-fabricated WO3 nanosheet Array/g-C3 N4 /CoOx layered heterojunction photoanode exhibited a photocurrent density of 3.61 mA cm−2 at 1.6 V vs. NHE (as shown in Fig. 24a) [285]. It is suggested that the increased light-harvesting ability, unique 3D nanostructures with 2D layered nano-junctions, accelerated water oxidation kinetics, and excellent charge transfer and separation are the possible reasons for the enhanced PEC water-oxidation activity (as shown in Fig. 24b). Additionally, the g-C3 N4 -based films have also been widely applied in the PEC degradation of organic pollutants [291–296]. Typically, Zhu and coworkers demonstrated that the g-C3 N4 film could achieve the removal of 89.3% of the total organic carbon (TOC) under a 2.5 V bias, which was 2.4 times higher than that of photocatalytic degradation [293]. It is believed that the dramatic enhancement in activity can be attributed to the promoted activity of electrocatalytic (EC) oxidation, improved charge separation, and increased reactive radical species, such as OH and O2 − , due to the combination effects of photocatalysis and electrocatalysis. Thus, in the near future, it is naturally expected that the g-C3 N4 -based films can be widely used in more and more PEC fields, and their activity should be further improved through better balancing electronic structures (e.g. bandgap and redox ability), stability, change-carrier mobility and active sites, surface area.

4. Design strategies of g-C3 N4 -based photocatalysts Although the multi-function properties endow g-C3 N4 a bright future in the various kinds of photocatalytic applications, low quantum efficiency limits its practical utilization in a large scale. To date, tremendous efforts have been made to improve the photocatalytic efficiency of g-C3 N4 through different design strategies,

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Fig. 24. (a) Variation of photocurrent density versus applied voltage. Number lables (3), (2), and (1) data represent the hybrid 3D WO3 /C3 N4 //CoOx , WO3 /C3 N4 , and WO3 , respectively. (b) Energy diagram and expected charge flow of WO3 /C3 N4 [285].

Fig. 25. Summary of band-gap engineering for g-C3 N4 .

including band-gap engineering, defect control, pore texture tailoring, dimensionality tuning, surface sensitization, heterojunction construction, co-catalyst and nanocarbon loading, which will be systematically discussed in this section. 4.1. Band-gap engineering In general, it is known that the ideal bandgap of a semiconductor should be ∼2.0 eV, which could harvest a variety of visible light to generate sufficient electrons and holes with strong driving forces for photocatalytic redox reactions [7,10]. However, the 2.7 eV bandgap of g-C3 N4 make it only utilize the solar light with wavelength below 460 nm. Thus, in order to further enhance the light harvesting ability of g-C3 N4 , various band-gap engineering strategies, including atom-level (foreign metal and non-metal elements) and molecular-level (copolymerization) doping, have been widely exploited and demonstrated to achieve the enhanced photocatalytic performance [27,54], which will be summarized in Fig. 25 and discussed in this section. As shown in Fig. 25, two possible kinds of cation doping, namely, cave doping and interlayer doping have been observed. Their detailed doping mechanism was shown in Fig. 26. On the one hand, the metal ions (Mn+ ) can be incorporated into the large caves (the triangular pores) between the connected triazine structures in the plane of g-C3 N4 (as shown in Fig. 26a), through the strong coordination interactions between them and negatively charged nitrogen atoms, thus achieving the so-called cave doping [297]. The previous studies revealed that the transition metal ions, such as Fe3+ , Zn2+ , Mn3+ , Co3+ , Ni3+ and Cu2+ can be doped into the large caves of g-C3 N4 [245,298–303]. The DFT calculations demonstrated that the cave doping of Pt and Pd atoms could effectively improve the carrier mobility, narrow the bandgap or optical gap, and enhance the light absorption, which are favorable for photocatalytic reactions [304]. More interestingly, it was revealed that the cave doping of alkali-metal ions such as Li+ , Na+ , and K+ will induce the un-uniform spatial charge distribution in different intercalated regions, increase the free carrier concentration, improve charge

transport and separation rate [106]. Recently, Zhu and coworkers demonstrated that the K+ doping could decrease the VB level of g-C3 N4 , thus resulting in enhanced separation and immigration of photo-generated carriers under visible light [305]. More recently, Dong and coworkers revealed that K atoms could achieve an interlayer doping (as shown in Fig. 26b), instead of the cave doping of Na atoms in g-C3 N4 [306]. It is believed that K atoms can bridge the two adjacent g-C3 N4 layers, which lead to the narrowed band gap, extended ␲ conjugated systems, and positive-shifted valence band position, thus achieving the increased visible-light harvesting, efficient charge separation, and strong oxidation capability, respectively. In contrary, despite of the increased in-planar electron density and visible-light absorption, the cave doping of Na atoms still exhibits high recombination rate of carriers in the g-C3 N4 planes, thus resulting in the reduced photocatalytic performance [306]. This work might provide new insights into the deep understanding on the metal doping of g-C3 N4 and the design of electronically optimized layered photocatalysts for enhanced solar energy conversion. Apart from metal doping, the non-metal doping of g-C3 N4 has been majorly realized through the chemically substituted doping. As displayed in Fig. 16, almost all the non-metal doping, such as S [118,182,307–311], P [183,312–316], B [114,317–320], O [184], C [185], and I [128,186], could narrow the bandgap of g-C3 N4 and enhance its light harvesting capability. In general, the C self-doping can substitute the bridging N atoms [185], whereas the O [184,321], S [307,309,322] and I [128,186] doping could achieve the replacement of N atoms in the aromatic triazine rings (as shown in Fig. 27). Interestingly, the doping of these different elements can promote the delocalization of the ␲-conjugated electrons, which is fundamentally important for improving the conductivity, mobility and separation of photo-generated electrons, thus greatly enhancing the photocatalytic performances of doped g-C3 N4 . In the contrary, the substituted doping of P [183,315,316,323–326] and B [327,328] atoms preferentially occur on the C atoms, thus leading to the formation of strong Lewis acid sites (P+ ) on the basic surface (from amine or imine groups) of g-C3 N4 , due to the intrinsic polarization of P–N bond and delocalization of one extra lone electron in electron-rich P atom [324]. Most recently, Qiao’s group demonstrated that the P-doping of porous g-C3 N4 nanosheets can drastically narrow the intrinsic band gap from 2.98 to 2.66 eV and promote the photo-excitation of electrons from the VB of P-doped g-C3 N4 , due to the formation of vacant midgap states below the CB minimum of g-C3 N4 through the hybridization of C 2s2p, N 2s2p and P 3s3p, thus enhancing visible light absorption [326]. Meanwhile, it was also demonstrated that the (NH4 )2 HPO4 as phosphorus precursor could achieve the cave doping (in the interstitial sites, as shown in Fig. 27). Furthermore, it is well known that S atoms have been found to preferentially substitute N atoms with a

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Fig. 26. Two kinds of metal ion doping of g-C3 N4 framework: (a) cave doping, the incorporation of metal ions (Mn + ) through the coordination interactions, Color scheme: C, red; N, yellow [27]; (b) interlayer doping (the interlayer bridging pattern for K) [306]. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 27. Possible substituted sites of non-metal doping in the single layer of g-C3 N4 .

larger electronegativity (3.04), thus leading to the decreased VB/CB levels and band gap [118,182,199,307,310,329]. Nevertheless, as special cases, in situ sulfur and boron doping of g-C3 N4 has also been found to replace the C and N atoms in the rings, respectively [182,330]. In addition, the F doping (NH4 F as a cheap fluorine source) can achieve the formation of the C F bonding in g-C3 N4 (as shown in Fig. 27), thus lowering the electronic band gaps [331]. However, it should be point out that excessive doping of nonmetal and metal is found to be detrimental to enhance the photocatalysis, because the more defects can also act as the recombination centers of electron–hole pairs. In future, the co-doping of different metals and/or nonmetals, such as Fe/P [332] S/Co/O [333], S/P [334], P/O [335], K/Na [336] and C/Fe [337] deserves more attention, due to their positive synergetic effects on the visible-light absorption and photocatalytic properties. In addition, copolymerization at molecular level was also widely employed to strongly enhance the photocatalytic activity of g-C3 N4 , via simultaneously modulating its band gap, electronic structures and physical and chemical properties. Commonly, it is believed that the copolymerization modification with structure-matching aromatic compounds or organic additives could increase the desired delocalization of ␲-conjugated electrons and improve the intrinsic drawbacks in g-C3 N4 , thus maximizing the photochemical activities [54,338–341]. For example, Wang and co-workers demonstrated that the tunable bandgaps of tri-striazine-based g-C3 N4 ranging from 2.67 to 1.58 eV could be obtained (as shown in Fig. 28a) through the copolymerization of dicyandiamide (monomer) and different amounts of barbituric acid (BA,

comonomer) [84]. More interestingly, 2D g-C3 N4 nanosheets fabricated by the one-pot condensation of urea and electron-rich thiophene co-monomers could achieve the highest quantum efficiency of 8.8% at 420 nm for H2 generation, (Fig. 28b) owing to the narrowed band gap, improved electron migration and through the formation of surface dyadic structures [129,342]. In contrary, the molecular doping by an electron-deficient pyromellitic dianhydride could thereby enhance the strong photooxidation capability of g-C3 N4 , due to greatly decreased both the CB and VB positions [343]. To sum up, as a unique bottom-up way for tailoring the bandgap of g-C3 N4 , the copolymerization approach provides more opportunities for designing highly effective polymeric photocatalysts with desired electrical properties and band gap through incorporating structure-matching organic moleculars, which also provides insights into the mechanism of heterogeneous photocatalysis of organic semiconductors at molecular levels. 4.2. Defect control It is widely accepted that a high degree of crystallinity is advantageous for enhancing the photocatalytic redox reactions, as compared to the negative roles of defects as chargerecombination sites [7]. For example, ionothermal synthesis [102,103,105,108,344,345] thermal polymerization in ammonia [346] and microwave-assisted heating synthesis [112,113] have been broadly employed to achieve the highly crystalline g-C3 N4 for efficient photocatalytic hydrogen evolution. It is believed that the enhanced crystallinity of g-C3 N4 could improve the charge-carrier

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Fig. 28. (a) UV–vis absoprtion spectra of g-C3 N4 and CNBx (arrow direction, x = 0.05, 0.1, 0.2, 0.5, 1, 2), where x refers to the weight ration of barbituric acid [84]. (b) H2 evolution over different g-C3 N4 copolymerized by urea and various monomers (3wt%Pt as co-catalyst) [129].

Fig. 29. (a) UV–vis absorption spectra g-C3 N4 (GCN) and amorphous g-C3 N4 (ACN). Inset: Schematic of monolayer crystalline GCN and ACN; (b) The detailed band structures of GCN and CAN, as well as the redox potentials of water splitting [348].

Fig. 30. (a) Lateral view and (b) vertical view for the interactions between water and a layer of defect g-C3 N4 sheet. Red, white, gray and white spheres represent O, H, C and N atoms, respectively. (c) Spatial distribution functions of O and H atoms projected onto the defect g-C3 N4 sheet within the first layer [353]. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

mobility and separation, thus leading to significantly improved photoactivity. However, more recently, as an effective strategy, the creation of nitrogen vacancies [347] or amorphous structures [348] in g-C3 N4 , has been extensively demonstrated to improve the visible-light activity, owing to the efficiently extended absorption edge and promoted lifetime of charge carriers. For example, Liu and co-workers demonstrated the high-temperature Ar-atmosphere treatment of bulk g-C3 N4 at 620 ◦ C could disrupt the weak interactions of hydrogen bonds and van der Waals forces, and destroy the long-range order in crystalline g-C3 N4 structures, thus fabricating the amorphous g-C3 N4 with the short-range order (as shown in the inset of Fig. 29a) [348]. Such structure disorder changes in

amorphous g-C3 N4 could effectively narrow its bandgap from 2.7 to 1.9 eV, corresponding to an obvious red-shift of absorption edge from 460 to 682 nm (as shown in Fig. 29a). The further valence band XPS analysis reveals that the levels of VB and CB could be reduced by 0.31 and 0.61 eV, respectively, without affecting the thermodynamic requirements for O2 evolution and water reduction (as shown in Fig. 29b). These results could open up new ways to develop visible light-driven amorphous or defective g-C3 N4 photocatalysts. Apart from Ar-atmosphere heat treatment, the hightemperature treatment of pristine g-C3 N4 in a H2 , NH3 or vacuum atmosphere could also create nitrogen or carbon vacan-

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cies in carbon nitrides, thus achieving the narrowed band gap and improved photocatalytic performances [347,349–351]. For example, a novel g-C3 N4 photocatalyst with N-vacancy structures and a bandgap of 2.03 eV could be fabricated by heating the melon in a H2 atmosphere [347], which exhibits promising photocatalytic activities towards generating • OH radicals and decomposing the organic pollutant Rhodamine B. It is believed that the nitrogen-vacancy defects could greatly widen visible light absorption range and suppress the unexpected fast recombination of photo-excited carriers, thus achieving the improved photoactivity. Similarly, it was also demonstrated that the introduction of hydrogenated defects in g-C3 N4 nanosheets could greatly enhance the photocatalytic hydrogen evolution [349,352]. Furthermore, a simple thermal treatment under an NH3 atmosphere can not only develop highly porous g-C3 N4 nanosheets with plenary carbon vacancies through etching their lattice carbon sites by the reactive radicals from the NH3 decomposition [350,351], but also can enhance the surface area, porosity and crystallinity of condensed g-C3 N4 , due to the greatly reduced N defects in the ␲-conjugated network [346]. More interestingly, through employing both DFT and molecular dynamics calculations, Wu et al. indicated that the defect within g-C3 N4 played a key role in the adsorption and dissociation of water, whereas, water does not dissociate on the perfect g-C3 N4 sheet (as shown in Fig. 30) [353]. However, it should be noted that the excessive nitrogen vacancies as the recombination centers could be also harmful for the photocatalysis [354]. To demonstrate this point, Osterloh and co-workers found that surface structure defects in g-C3 N4 , with energy levels at +0.97 V and −0.38 V (vs.NHE), limit visible light driven hydrogen evolution and photovoltage [191]. More interestingly, it was also demonstrated that the vacuum heat-treatment at 500 ◦ C could obtain the highest photoactivity for H2 evolution due to the increased content of the tri-s-triazine phase and suitable N defects in the tri-s-triazine ring building blocks [355], which are similar to the previous report about the vacuum-treated titanium dioxide [356]. Consequently, the controlled defect concentration in g-C3 N4 is crucial for achieving the ideal photoactivity. 4.3. Pore texture tailoring Another attractive design strategy is to tailor the porous structures/texture of g-C3 N4 materials, which can significantly increase their exposed surface area and accessible channels(porosity) and active sites in g-C3 N4 , thus facilitating the molecular mass transfer/transport, charge migration and separation, surface reactions and light harvesting [83]. All these advantageous features can benefit the enhancement of photocatalytic efficiency. So far, a variety of highly porous g-C3 N4 with diverse nanoarchitectures and morphology have been widely fabricated through several typical pathways, such as hard templating (nanocasting), soft templating (self-assembly along the structure directing agents), self-templating (supramolecular self-assembly) and template-free methods [27,48,54,357], which have been thoroughly summarized in Table 4. The detailed comparison and discussion between them will be highlighted in this section. As observed in Table 4, it is clear that the hard templating (nanocasting) strategy is deemed to be one of the most simple and effective methods to construct mesoporous g-C3 N4 photocatalysts with superior high surface area (up to 517–623 m2 /g) [69,229,360]. In theory, various kinds of macro/mesoporous materials with super high surface area can be employed as hard templates to construct porous g-C3 N4 . To date, various kinds of hard templates such as porous anodic Al2 O3 [358,359], CaCO3 [370], graphene oxide nanosheets, [151] CMK-3 mesoporous carbon [69], mesoporous silica (nanospheres, [123,361,363] foams, [229] SBA-15, [122,170,362] chiral silica, [365,366] silica KIT-6, [368] and KCC-

89

1 [369]) have been available in developing highly porous g-C3 N4 . Absolutely, the mesoporous silica materials have been demonstrated to be the most widely used hard templates. Unfortunately, the trapped air and the weak-acid walls of mesopores in the silica templates greatly prevent the infiltration and fast mass diffusion of basic organic precursor molecules into them, thus leading to the incomplete utilization of their porous structures and the limited enhancement in the surface area of porous g-C3 N4 [59]. Thus, to maximize the roles of porous silica templates, Zhang et al. demonstrated that the combined strategy of dilute HCl pretreatment of SBA-15 and sonication-vacuum insertion could increase the surface area of mesoporous g-C3 N4 up to 517 m2 g−1 , due to the improved surface reactivity of the silica and removed trapped air [360]. However, the hazardous agents for removing the silica templates, such as NH4 F or HF, are harmful for environment, g-C3 N4 itself or other materials in a g-C3 N4 -based composite photocatalysts, restricting the practical applications of hard-templating strategy in a large scale. Thus, it is expected that more and more easy-removal or nonremovable hard templates, such as CaCO3 , Al2 O3 , Fe2 O3 and various nanocarbons, should be further developed and applied in the fabricating the highly porous g-C3 N4 with different nanostructures [69]. The “greener” soft-template route is also an interesting strategy to avoid various kinds of unfavorable factors aforementioned for the hard-templating methods, which has also witnessed great advances in developing porous g-C3 N4 micro-and nanostructures. In general, the amphiphilic organic molecules are easy to form selfassembly micelles with different structures in solution, which can function as soft templates (structure directing agents) to induce the growth of precursors around them and further form expected composite structures [54,357]. Clearly, so far, various soft templates, such as ionic liquids [114,373], Pluronic P123, [374,375] Triton X-100 [374,376,377], bubble [378–381,383] and biomolecules [279,382,384] have been widely utilized in the fabrication of porous g-C3 N4 photocatalysts. For example, Zhang et al. demonstrated that the mixture of 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF4 , as a soft template) and dicyandiamide could achieve the B/F-co-doped mesoporous g-C3 N4 with a surface area of 444 m2 g−1 and a large total pore volume (0.32 m2 g−1 ) [114]. Similarly, the nanoporous g-C3 N4 fabricated by using Pluronic P123 block polymers as a soft template, could exhibit a high surface area of 299 m2 g−1 [374]. However, the obvious disadvantages of ionic liquids and polymers, such as the high cost, unexpected carbon residue and insolubility in water, greatly limit their extensive practical applications in a large scale. At this regard, the use of bubbles of water vapor as soft templates seems more promising in synthesis of porous g-C3 N4 , due to the absence of impurities and post treatments [380,383]. Also, the interesting biomolecules as soft templates are highly desirable in the future studies [279,382,384]. In addition, much attention has also been paid to the supramolecular self-assembly and template-free methods. For the supramolecular self-assembly strategies, it has been demonstrated that the formation of hydrogen-bonded supramolecular assemblies (or complex) between melamine precursores and triazine derivatives plays key roles in determining the different nanostructured morphologies of porous g-C3 N4 materials [385–388]. For the template-free route, the (hydro) solvothermal [328,394,397,398] and freezing assistant assembly [395,396] methods have been successfully exploited to fabricat porous g-C3 N4 materials. However, compared to the hard-templating methods, the surface area of porous g-C3 N4 prepared by these two strategies is still much smaller. More importantly, there are only limited precursors which could form ordered and stable supramolecular aggregates in a solvent, based on noncovalent interactions (e.g. hydrogen bonding). Accordingly, it is expected that these two appealing approaches could be finely controlled and combined with other strategies, such

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Table 4 Summarization of different fabrication methods for mesoporous g-C3 N4 . Morphology

Templates

Precursor

Hard templating methods Nanotubes Nanorods Ordered mesoporous Mesoporous

Porous anodic Al2 O3 (AAO) membranes Ordered Mesoporous SBA-15 12-nm SiO2 particles

EDA, CTC CA CA CA

SBA-15 pre-treated with 1 M HCl Mesostructured cellular silica foams Uniform-sized silica nanospheres SBA-15 nanorods

CA EDA, CTC CA

SBA-15 12-nm SiO2 particles Monodisperse silica@ mesoporous silica Chiral mesoporous silica Chiral silica nanorods 7 nm colloidal silica particles

ATC ATC CA

2.78

CA CA

2.75 2.7

Graphene oxide sheets CMK-3 mesoporous carbon Ordered mesoporous silica KIT-6 KCC-1 silica spheres CaCO3 ZnCl2 MA sponge

MA CA CA CA DCDA DCDA Urea

Ionic liquids(BmimBF4 ) BmimBF4 BMIM-PF6 BmimDCN Pluronic P123

DCDA Urea DCDA DCDA MA

Pluronic P123 Triton X-100 Triton X-100 Triton X-100 Bubble (urea) Bubble (thiourea) Bubble (water vapor) Ammonium alginate or gelatin Bubble (sublimed sulfur) Bubble (sucrose) Bubble (water) Diatomite

DCDA DCDA MA, GA MA sulfate DCDA DCDA Urea DCDA MA MA urea CA

Ordered mesoporous Hierarchical mesostructures Inverse opal structures Mesoporous nanorods Ordered mesoporous Mesoporous Hollow nanospheres Helical rodlike Porous nanorod Mesoporous sphere Porous composite g-C3 N4 @CMK-3 composite Cubic mesoporous Nanosheet-based nanospheres Porous Porous Macroscopic 3D Porous monolith Soft templating methods Sponge-like mesopore Porous nanosheets Nanoporous Worm-like porous Nanoporous Nanoporous Bimodal mesoporous Nanoporous Nanoporous Porous Sponge-like Mesopore Mesopore Honeycomb-like Diatom-structure

Template-free methods Nanobelts Porous Porous Hierarchical structure Nanoporous Nanosheets Seaweed-like architecture Monolayer mesoporous Porous microspheres Nanosheets Nanorod-network superstructures

MA MA hydrochloride DCDA MA MA urea DCDA DCDA CAC/MA Urea, Ph4 BNa CAC/MA

Solvothermal in acetonitrile (180 ◦ C)

BJH pore size (nm)

Pore volume (cm3 g−1 )

5.3

0.34

8.3 3.4 4/43 20 70 3.9

0.41 0.49 0.9 0.79 1.7

5.3

0.34 0.77

2.7

2.86

[365] (2014) [366] (2014)

7

224

[367] (2012)

0.08 0.76

26.6 623 208 160 38.6 46 78

[151] (2011) [69] (2011) [368] (2010) [369] (2014) [370] (2015) [371] (2015) [372] (2015)

25.0 23.4

0.32 0.40 0.51

444 73

5.6

0.179

81 90

0.128 0.284

299 116

17.6 3.0 3.6 3.8

0.09 0.49 0.4 0.4

2.47–2.57 3.7 18.2

0.321

2.49 50 13.2 2.65

0.355 0.68

30–40

0.4 0.3

12.84

0.31

2.79

2.7

2.75 2.42 2.83 1.92

[360] (2013) [229] (2010) [361] (2011) [362] (2012)

56 52

3.8 3.8/10–40

2.83 2.72 2.74 2.75 2.78

[358] (2009) [359] (2011) [122] (2009) [123] (2009)

3.8/10.7

1.55

2.73 2.25

25 239 373 126 517 550 230 140 110–200

Ref. (year)

[170] (2011) [363] (2012) [364] (2012)

2.89

2.72

BET surface area [m2 g−1 ]

239 176 79

2.9

Urea

CAA/MA MA/CAA MA/CAA CAA/MA MA, urea, CAA CA, MA, DPT CAA, MA, BA MA, TAP CAA/MA

Freezing assistant assembly Freezing assistant assembly/exfoliation Solvothermal in acetonitrile (200 ◦ C)

2.9 2.74 2.7

CA

Self-templating (Supramolecular self-assembly) methods Self-assembly Hollow box Self-assembly Hollow spheres Self-assembly Spherical particles Self-assembly Hollow tube-like Hollow to wormlike Self-assembly Self-assembly Fiber-type/sheet-like Self-assembly Roll-like Self-assembly Crystalline Self-assembly Porous

Ball milling/hydrothermal method

Band gap [eV]

15.8

0.50 0.15 1.41

<20 <20 16.2

0.62

90

[114] (2010) [373] (2014) [312] (2010) [374] (2010) [375] (2012)

50–135 60 46.4 69.6 63 46 121 106 5

[374] (2010) [374] (2010) [376] (2011) [377] (2014) [378] (2014) [379] (2013) [380] (2012) [279] (2013) [381] (2015) [382] (2015) [383] (2015) [384] (2013)

45 77 66 41 97.4 75 ± 5 60–70 119 77

[110] (2013) [107] (2013) [385] (2013) [386] (2015) [387] (2014) [111] (2014) [388] (2014) [108] (2014) [389] (2014)

69 201 35.6 30.9 288 130 331 8.5 144 30

[390] (2011) [391] (2012) [392] (2013) [393] (2014) [394] (2015) [153] (2013) [395] (2015) [396] (2016) [397] (2015) [328] (2013) [398] (2012)

BmimBF4 : 1-butyl-3methylimidazolium tetrafluoroborate; BMIM-PF6: 1-butyl3-methylimidazolium hexafluorophosphate; BmimDCN Ph4 BNa: sodium tetraphenylboron; CA: cyanamide; MA: melamine; DCDA: Dicyandiamide; CAA: cyanuric acid; CAC: Cyanuric chloride; DPT: 2,4-diamino-6-phenyl-1,3,5-triazine; BA: barbituric acid; ATC: ammonium thiocyanate; EDA: ethylenediamine; CTC: carbon tetrachloride; GA: glutaraldehyde, TAP: 2,4,6-triaminopyrimidine.

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

as an infrared heating process [399] or a simple reflux method [400], to design and fabricate highly efficient porous g-C3 N4 -based semiconductors with high surface area and unique nanostructures in a low-temperature solution in future research [54]. In addition, it is also expected that the two strategies of in situ template-sacrificial dissolution [401] and chemically induced selftransformation [217,402–408] could be applied in developing highly porous g-C3 N4 -based semiconductors. 4.4. Dimensionality tuning Generally, compared with the bulk counterparts, nanostructured g-C3 N4 semiconductors with unique dimensions and configurations could exhibit several obvious advantages for solar photocatalysis, such as the higher surface area, shorter charge migration length, higher solubility and tunable electronic structure [37]. Detailedly speaking, the charge carriers generated in the ultrathin g-C3 N4 nanosheets can readily reach their surface for redox reactions through the very short paths, as compared to traditional 3D bulk g-C3 N4 semiconductors, thus achieving the rapid charge separation. More importantly, through controlling the layer number without changing the atomic structure, the energy band structure of g-C3 N4 could be effectively tailored due to the quantum confinement effects, thus leading to improved activity and selectivity for various reactions, such as CO2 reduction [409] and O2 reduction [410]. In addition, the nanostructured g-C3 N4 with different dimensions also exhibited significantly enhanced opened-up surface areas and highly exposed active sites, thereby greatly facilitating the photocatalytic enhancements. All these advanced features endow the nanostructured g-C3 N4 with attractive structure-dependent, morphology-dependent and thickness-dependent applications ranging from photocatalysis to other emerging fields. Thus, as a simple way, tuning physical dimensions of g-C3 N4 has become a popular strategy to manipulate the optical, electrical, and redox properties, thus achieving the desired catalytic activity, selectivity, and long-term stability. So far, nanostructured g-C3 N4 with various different dimensionality, such as 0D quantum dots [411–414], 1D nanowires/nanorods/nanotubes [138,277,359,395,400], 2D nanosheets [100,415,416], 3D hierarchical structures [393,417–419] have been widely exploited and applied in the photocatalysis [55]. Among them, the 2D ultrathin g-C3 N4 nanosheets have proven to be more promising for various photocatalytic applications [27,52,56], whose fabrication strategies will be highlighted in this section. Generally, the free-standing ultrathin g-C3 N4 nanosheets could be obtained via two distinct synthetic strategies, including the top-down exfoliation of layered bulk g-C3 N4 materials and bottomup assembly of precursors (molecular building blocks) in a 2D manner [52,56]. Typically, these two fabrication strategies can be further classified into five detailed categories: ultrasonicationassisted liquid exfoliation, chemical exfoliation, thermal oxidation etching, combined and other approaches. In order to facilitate further comparison, various different fabrication methods for gC3 N4 nanosheets have been thoroughly summarized in Table 5. As observed in Table 5, it is clear that the 2D single-layer and few-layer g-C3 N4 nanosheets could exhibit much higher surface areas in the range from 50 to 384 m2 g−1 , which are several times larger than that of bulk layered g-C3 N4 (10 m2 g−1 ), thus significantly favoring the photocatalytic enhancement. Inspired by the formation of graphene/metal dichalcogenide/double hydroxide nanosheets by liquid exfoliation of layered bulk counterparts [463–469], it is highly expected that the mono- or few-layer C3 N4 nanosheets could be obtained through a simple liquid exfoliation of bulk layered g-C3 N4 by sonication. Clearly, the well matched surface energy between a liquid solvent and g-C3 N4 (115 mJ m−2 ) could effectively reduce their enthalpy of

91

mixing, thus leading to the enhanced exfoliation efficiency of bulk g-C3 N4 into 2D nanosheets [426,465]. Thus, the ultrasonication treatments in various solvents with proper surface energy, such as water (102 mJ m−2 ), methanol, ethanol, N-methyl-pyrrolidone (NMP), 1-isopropanol(IPA), dimethyl formamide(DMF), acetone, acetonitrile, 1,4-dioxane and their mixtures, have been applied in overcoming the weak van der Waals forces between the two adjacent g-C3 N4 layers and successfully exfoliating the bulk layered g-C3 N4 into 2D ultrathin nanosheets [100,103,178,416,425,426]. For example, Xie and coworkers successfully prepared the ultrathin g-C3 N4 nanosheets (0.15 mg/mL) with a size distribution ranging from 70 to 160 nm and a height of ∼2.5 nm (about 7 layers) by a “green” liquid exfoliation route from bulk g-C3 N4 in water for the first time (as shown in Fig. 31a and b) [100]. To further enhance the dispersion concentration of exfoliated mono-layer or few-layer g-C3 N4 nanosheets, the better solvent effects of organic and mixed solvents have been utilized to exfoliate the bulk C3 N4 materials [424,429]. For example, the exfoliation of commercial g-C3 N4 in the mixed solution (ethanolamine, 1,3-butanediol and 3-pyridinemethanol) could obtain the 7-layer g-C3 N4 nanosheets with a concentration of 1 mg/mL [429]. In another example, the single layer of g-C3 N4 nanosheets with a concentration of 3 mg/mL have been achieved through the effective exfoliation in the mixed water/organic solvents [424]. However, some typical problems, including the use of organic solvents and additives, long ultrasonication exfoliation time and low yield, still need to be further overcome. Thus, the liquid ammonia-assisted lithiation and the intercalation of LiCl ions have been exploited to achieve the largescale exfoliation of bulk g-C3 N4 materials [430,431]. Especailly, the 8-layer-thick O-doped g-C3 N4 nanosheets could be fabricated by this liquid ammonia-assisted lithiation method in a large scale (10 g) and high yield (85%), under mild conditions [430]. More fortunately, it was demonstrated that the chemical exfoliation in acid or alkaline solution could not only obtain amphoteric singlelayer g-C3 N4 nanosheets with the negatively charged carboxyl and positively charged −NH2 /NH3 + groups, but also efficiently reduce the ultrasonication-treatment time from more than 10 h to 2 h [82,178,432,470]. For example, Xu et al. successfully obtained single layer of g-C3 N4 nanosheets with a thickness of 0.4 nm by means of the rapid exothermic effect of the intercalated concentrated H2 SO4 (98%) dissolving in deionized water [178]. Following this report, Tong et al. developed an interesting high-throughput method to rapidly fabricate g-C3 N4 nanosheets through combining the oxidation, protonation and heating effects of concentrated H2 SO4 [432]. The g-C3 N4 nanosheets with a thickness of 2.5 nm and different degree of exfoliation could be easily achieved though directly adding controlled amount of H2 O into a bulk g-C3 N4 suspension using the concentrated H2 SO4 as solvent. This facile acid-exfoliation method with low cost and controlled exfoliation degree would open up new opportunities for the large-scale fabrication and extensive application of g-C3 N4 nanosheets. Although bulk g-C3 N4 could be also easily thermally exfoliated into 2 nm-thickness nanosheets (around 6–7 layers) through the direct oxidation “etching” [415], the poor yield (<6%) and significant interface defects, thus leading to the significantly reduced photoability and photoactivity. Motivated by the successful thermal exfoliation of the NH4 Cl-intercalation g-C3 N4 materials [449], Wu and coworkers recently developed a facile one-step dicyandiamideblowing method with NH4 Cl as the gas template to achieve the scalable fabrication of high quality 2D g-C3 N4 nanosheets [443]. As shown in Fig. 32, it is believed that the gases (NH3 and HCl) released from NH4 Cl during heating directly achieved the fast exfoliation of bulk g-C3 N4 into the crinkly 8-layer g-C3 N4 nanosheets (with a thickness of 3.1 nm and a high band gap of 2.83 eV). Other methods such as thermal exfoliation of C3 N4 -based intercalation compound [449], microwave heating [462] and ball

92

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

Table 5 Summarization of different fabrication methods for g-C3 N4 nanosheets. Bulk g-C3 N4

Solvents, bulk powder/solvent (mg/ml), time (h)

Ultrasonication-assisted liquid exfoliation Water, 100/100, 16 h MA (P, 600 ◦ C) Poly(triazine imide) (I) Water, 2/1, 15 h Water, 200/200, 24 h CA (P, 530 ◦ C) Water, 50/50, 10 h MA (P, 600 ◦ C) Water, 50/50, 10 h MA (P, 600 ◦ C) ◦ Water, 100/200, 16 h MA (P, 600 C) ◦ MA (P, 550 C) Water, 50/50, 2 h Water/organic solvents, 500/150, 10 h MA (P, 550 ◦ C) Isopropanol, 30/10, 10 h Commercial g-C3 N4 (Carbodeon Ltd) CA (P, 550 ◦ C) Ethanol, 50/50, 2 h 1,3-butanediol, 60/25, 24 h DCDA (P, 600 ◦ C) ◦ MA (P, 550 C) 30 wt% isopropanol + water, 4/1, 10 h ◦ Water, 100/200, 16 h MA (P, 600 C) DMF, 50/200, 2h(80 ◦ C)+ melamine DCDA (P, 520 ◦ C) Ethanolamine/1,3-butanediol/3Commercial g-C3 N4 (Carbodeon Ltd) pyridinemethanol,30/10,4h Chemical exfoliation MA (P, 550 ◦ C) MA + LiCl(P, 380 + 550 ◦ C) DCDA (P, 550 ◦ C) MA (P, 550 ◦ C) DCDA (P, 550 ◦ C) DCDA (P, 550 ◦ C) MA (P, 550 ◦ C) MA (P, 550 ◦ C) MA (P, 520 ◦ C) MA (P, 600 ◦ C) Thermal oxidation etching DCDA (P, 550 ◦ C) DCDA(P, 550 ◦ C) Urea (P, 550 ◦ C) MA (P, 550 ◦ C) MA (P, 550 ◦ C) MA (P, 520 + 540 ◦ C) MA (P, 500 + 520 ◦ C) MA (P, 500 + 550 ◦ C) MA (P, 600 ◦ C) DCDA (P, 520 ◦ C) Commercial g-C3 N4 (Carbodeon Ltd) DCDA(P, 550 ◦ C) Mixed DCDA/NH4 Cl Mixed DCDA/NH4 Cl Mixed MA/KCl Mixed MA/KBH4 Guanidinium cyanurate Guanidinium chloride DCDA (P, 600 ◦ C) Combined approaches MA (P, 520 ◦ C) MA (P, 500 + 530 ◦ C) MA (P, 500 + 530 ◦ C) MA (P, 520 ◦ C) MA (P, 550 ◦ C) MA (P, 520 ◦ C) DCDA (P, 550 ◦ C) DCDA/2-aminobenzonitrile (P, 550 ◦ C) Urea (P, 600 ◦ C)

0.15/ 0.2/

2.70/

/14.5 /14.5 /8.6

2.5/7 1–2/3–6 ∼1.8/5–6 1.2/4 1.0/3

2.6/

3/

1.2/<5 0.38/1 2/ < 9

2.79/59.4 2.65/384

0.35/

2–3/5–8 0.9–2.1/3–6 2/6

2.73/112.5 2.79/32.54 2.70/

2–3/6–9 7

2.75/116.76

/8.6 1/

[100] (2013) [103] (2014) [410] (2013) [299,420](2013) [421] (2013) [422] (2013) [423] (2014) [424] (2015) [416] (2013) [425] (2014) [426] (2014) [427] (2014) [422] (2013) [428] (2015) [429] (2015)

/85%

2.5/8 2–3/6–9

2.78/22.5 2.82/186

[430] (2014) [431] (2016)

/30%

0.4/1

2.92/205.8

[178] (2013)

/70% 300/ /25–30%

2.5 /1 2–4/6–10

2.93/86.29 3.28/ 2.75/305 /109.3 /65

[432] (2015) [180] (2015) [82] (2014) [433] (2014) [164] (2013)

/25–30%

9.0/30

3.42/ 2.7/179.5

[82] (2014) [434] (2015)

Air, 500 ◦ C, 2 h Air, 500 ◦ C, 2 h Air, 550 ◦ C, 2 h Air, 500 ◦ C, 2 h Air, 500 ◦ C, 2 h Air, 540 ◦ C, 2 h Air, 520 ◦ C, 4 h Air, 500 ◦ C, 2 h Air, 500 ◦ C, 4 h Air, 400 ◦ C, 4 h H2 , 400 ◦ C, 4 h

/<6% /<6% /8.0

1.62–2.62/4–7 1.62–2.62/4–7 16/

2.97/306 2.97306 2.86/151 3.06/165.66 2.91/122.6 2.93/210 2.82/153.32 2.97/150.1

[415] (2012) [409] (2014) [435] (2015) [436] (2014) [326] (2015) [437] (2015) [438] (2016) [439] (2014) [440] (2015) [441] (2013) [442] (2015)

5–8/10–20 /0.35% 2.7/8 1.9/6 0.9/3 2/6

NH3 , 510 ◦ C, 1 h Air, 550 ◦ C, 2 h Air, 550 ◦ C, 4 h Air, 550 ◦ C, 4 h Air, 550 ◦ C, 4 h Air, 550 ◦ C, 4 h Air, 600 ◦ C, 4 h Air, 350 ◦ C, 2 h (NH4 Cl intercalation, N2 )

20/50 3.1/8 1.0/3 1.5–6.3 1.5/4 0.6–1.5/1–3

(Air, 550 ◦ C, 3 h)+ (isopropanol, 10/100, 8 h) (Air, 550 ◦ C, 3 h)+ (methanol, 100/100, 4 h) (Air, 550 ◦ C, 200 min)+ (methanol, 100/100, 4 h) (Air, 550 ◦ C, 3 h)+ (isopropanol, 8 h) (Air, 550 ◦ C)+ (H2 SO4 + HNO3 , 100/40, 5 h) (Air, 550 ◦ C, 3 h)+ (0.5 M HCl, 20/200, 8 h) (H2 SO4 (98 wt%), 2000/50, 2 h) + (water, 1 h) (5 M HNO3 , 400/80, 20 h/under reflux)+ (water, 4 h)

0.5/1 0.4–0.5/1 0.8–1.2/2–3 0.5/1

MA (P, 550 ◦ C) Other approaches MA (P, 550 ◦ C) MA and carbon fibre

Ball milling method Microwave heating approach

MA (P, 550 C)

Band gap (eV) /surface Ref. (year) area (m2 g−1 )

Liquid ammonia-assisted lithiation The intercalation of LiCl ions and the liquid exfoliation in water H2 SO4 (98 wt%) treatment for 8 h, then rapid exfoliation H2 SO4 (98 wt%), 1000/15, 15 min H2 SO4 (98 wt%) HCl treatment for 1 h, then exfoliation for 2 h 6 M HCl, 320/80, hydrothermal at 110 ◦ C for 5 h 0.1 M NaOH, 1000/90, hydrothermal at 150 ◦ C for 18 h HCl treatment for 1 h, then exfoliation for 2 h HNO3 (63 wt%) treatment for 8 h, then sonicated exfoliation

(H2 SO4 + HNO3 , 1000/200, 4 h)+ (water, 30/30, 2 h) (75 wt% H2 SO4 , 300/30, 2 h 130 ◦ C) + (water + 300/200,2 h) (H2 SO4 (98 wt%), 1000/10, 8 h) + (N2 , 550 ◦ C, 2 h)

◦

Thickess (nm) /Layer Concentration (mg/mL)/Yield (%) numbers

P, pyrolysis (or thermal polycondensation); DMF, dimethylformamide.

2–3/6–9

0.6/1 5–10/15–20 0.6–4/2–10

2.89/ /260 2.95/196 2.83/52.9 2.77/77.7 2.71/ 2.87/133.8 2.44/109.9 2.85/30.1

3.03/ 3.0/380 2.95/109.30 3.0/140 2.89/

/10.5

[350] (2015) [443] (2014) [444] (2015) [445] (2014) [446] (2014) [447] (2015) [448] (2014) [449] (2014) [450] (2014) [451] (2014) [452] (2015) [453] (2014) [454] (2014) [455] (2015) [456] (2015) [457] (2016) [458] (2016)

2.5/7

2.88/80

[459] (2015)

0.8–1.4/3–4

2.79/54.3

[460] (2016)

/1–2 1.6/5

2.98/ 2.88/239

[461] (2015) [462] (2016)

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

93

Fig. 31. (a) Schematic illustration for the synthesis process of ultrathin g-C3 N4 nanosheets via liquid exfoliation. (b) AFM image of the synthetic g-C3 N4 nanosheets. (d) The corresponding height image of two random nanosheets [100].

employed to further achieve the 600 nm or near-infrared (NIR) photocatalysis of g-C3 N4 nanosheets in aqueous solution [52,476–478]. 4.5. Surface sensitization

Fig. 32. Schematic illustration for fabricting the ultrathin nanosheets of g-C3 N4 through a dicyandiamide-blowing method [443].

milling [461] have also been successfully applied in obtaining 2D ultrathin C3 N4 nanosheets. More interestingly, the perfect combination of liquid, chemical exfoliation and thermal oxidation etching could fully explore their potentials and achieve the lowcost, simple, fast and scalable synthesis of 2D g-C3 N4 nanosheets [450,451,453,455,457,460], which deserves more attention in the near future. In addition to developing new fabrication methods of g-C3 N4 nanosheets, more efforts should be also devote to narrowing their larger band gaps (0.1–0.2 eV higher than that of bulk g-C3 N4 ) and promoting the fast utilization of photo-generated charge carriers migrated to the surface of g-C3 N4 nanosheets. As effective strategies, doping [84,118,128,328,471], introducing nitrogen vacancies [347,472], sensitization [473], copolymerization [130,474,475] and hybridization with other semiconductors or co-catalysts could be

In general, there are five typical strategies to increase the visiblelight absorbance of wide band gap semiconductors: band-gap engineering (impurity doping and solid solution), defect control, surface plasmon resonance (SPR) effect, sensitization by dye and quantum dot [16]. Although the aforementioned two strategies of band-gap engineering and defect control can partially extend their visible-light absorption, the moderate band gaps (∼2.7 eV) of g-C3 N4 -based semiconductors are still the main bottlenecks affecting the highly effective generation of photo-generated charge carriers, which thereby play the crucial roles in determining the visible-light photocatalytic performances of g-C3 N4 -based semiconductors. Thus, other three strategies, including loading plasmonic metals, sensitization by quantum dots (QDs) and organic dyes (the corresponding mechanisms shown in Fig. 33), have been also widely applied in enhancing the visible-light absorbance of gC3 N4 -based semiconductors, which will be thoroughly discussed in this section. Firstly, the famous SPR effects of noble metals, such as Au [77,200,479–482] and Ag [433,455,479,483–492], have been widely employed to improve the visible-light absorbance and charge separation of g-C3 N4 . In general, it is well accepted that the deposited plasmonic metals could function as electron sink, reduction co-catalyst and photosensitizers to enhance the visiblelight absorption of a given semiconductor [493]. For example, Bai et al. fabricated the core–shell nanostructured Ag@C3 N4 photocatalysts through the simple methanol-reflux treatment of g-C3 N4 nanosheets deposited by Ag nanoparticles (as shown in Fig. 34) [488]. The combination of LSPR effect of Ag nanoparticles and their hybrid effect with C3 N4 could achieve 1.8- and 30-time enhancements in the photocatalytic MB degradation and H2 evolution,

94

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

Fig. 33. Mechanisms for g-C3 N4 photocatalysts sensitized by (a) plasmonic metals, (b) quantum dots (QDs), (c) organic dyes.

Fig. 34. Synthetic route and charge-separation mechanism for C3 N4 and core–shell nanostructured Ag@C3 N4 photocatalysts under light irradiation [488].

respectively. In another example, Wei et al. constructed the type-II 2D-1D C3 N4 /TiO2 hybrid nanofibers and further decorated plasmonic noble metal nanoparticles (Au, Ag, or Pt) with sizes from 5 to 10 nm on them [479]. The resulting SPR sensitized heterostructures could achieve highly efficient photocatalytic H2 evolution due to the simultaneous implementation of improved light absorption, charge separation and utilization. In future, it is expected that the plasmonic alloys [494,495], Cu [496–498] and Bi [499–501] nanoparticles could be deposited onto g-C3 N4 to boost their visiblelight photocatalytic activity. Secondly, the quantum dots modified g-C3 N4 photocatalytic systems are still very interesting and promising [502–505]. For example, Ge et al. first demonstrated that the deposition of 30 wt% CdS QDs onto the bulk g-C3 N4 could achieve a 9-fold enhancement in the visible-light photocatalytic H2 -evolution activity, due to the increased the absorbance of visible light and promoted charge separation [502]. Since then, CdS QDs have been widely used to improve the visible-light activity of bulk g-C3 N4 for various kinds of applications [284,405,502,503,506–508]. In future, it is expected that more efficient CdS/g-C3 N4 composite photocatalysts with earthabundant co-catalysts should be further exploited. Thirdly, various kinds of low-cost organic dyes, such as magnesium phthalocyanine (MgPc) [509], zinc phthalocyanine [510–515], Xanthene [516], Erythrosin B (ErB) [473,517] and Eosin Y (EY) [518], have been readily coupled with different nanostructured g-C3 N4 to fabricate the highly efficient organic semiconductor heterojunctions. For example, Domen and his coworkers deposited an organic MgPc dye (with a band gap of 1.8 eV) on the Pt/mpg-C3 N4 composite semiconductors and achieve the enhanced photocatalytic

H2 evolution under long-wavelength irradiation (>600 nm) [509]. The results indicated that the monolayer dye could achieve the highest photocatalytic H2 -evolution performance due to promoted charge generation, transfer and utilization, whereas excess thickness of the dye layer will cover the co-catalyst sites, thus reducing the photocatalytic activity [509]. Similarly, Lu and coworkers successfully demonstrated that the sensitization of mesoporous g-C3 N4 with a EY dye could achieve an H2 -evolution AQE of 19.4% under 550 nm irradiation [519]. It is suggested that the high surface area and nanoporous structure of mpg-C3 N4 are greatly favorable for deposition of EY molecules on its surface, thus promoting the significantly increased and extended light harvesting in the visible-light response region and further improving H2 -evolution activity. More surprisingly, Xu and coworkers demonstrated that the deposition of ErB dye onto Pt/g-C3 N4 sample exhibited a remarkably enhanced H2 evolution rate (652.5 or 162.5 ␮mol h−1 ) from an aqueous solution of TEOA under visible light irradiation (␭ > 420 nm or > 550 nm), with an AQY of 33.4% at 460 nm [473]. The resulting ternary Pt/g-C3 N4 /ErB photocatalyst also showed the stability and good recyclability, remaining 90% of the activity after 5 runs [473]. Most recently, it has been demonstrated that the promising earth-abundant Co(OH)2 and MoS2 could be utilized as co-catalysts to boost the photocatlytic H2 evolution activity over these dye-sensitized g-C3 N4 photocatalysts [517,520,521]. More interestingly, the g-C3 N4 -based photocatalytic systems co-sensitized by two organic dyes or inorganic photosensitizers (plasmonic metals and QDs) are also highly desirable in future studies [510,512,521,522]. However, the apparent quantum effciency and stabilities of these systems are still needed to be further enhanced.

4.6. Heterojunction construction Enhancing photocatalytic activity of g-C3 N4 -based semiconductors could be also achieved through constructing semiconductor heterojunctions, which could induce the band bending and the formation of internal electrical field, thus significantly boosting the efficient spatial charge separation [7]. In general, according to the semiconductors’ energy bands and Femi levels of metal co-catalysts, semiconductor heterojunctions can be divided into four types: Schottky junction (Fig. 35A), Type I (Fig. 35B), Type II (Fig. 35C) and Type III (Fig. 35D) heterojunctions. Clearly, only Schottky junction and Type II heterojunctions can significantly promote the fast spatial separation of electrons and holes, thus retarding their recombination and prolonging their lifetime. Thus, for photocatalysis, the construction of Schottky junction and Type II alignment should be highly desired. The Schottky junction will be discussed in the next section. Here, we will focus on the Type II g-C3 N4 -based heterojunctions. As observed the CB and VB levels of different semiconductors in Table 1 and Fig. 16, it is easily found that several commonly used semiconductors, such as TiO2 [523], Cu2 O [524–526], ZnO [291,527–537], WO3 [286,538–544], BiVO4 [545–551], (BiO)2 CO3 [552], Ag3 PO4 [553–560], CdS

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Fig. 35. Spatial charge-separation mechanisms for four different types of semiconductor heterojunctions: (A) Schottky junction, (B) Type I, (C) Type II, and (D) Type III heterojunctions.

[197,284,405,502,503,506,508,561–566], BiOX [567–575], Bi2 WO6 [552,576–583], Fe2 O3 [115,289,584–587] and different types of gC3 N4 [121,588] can be combined with g-C3 N4 to construct the Type II heterojunctions and achieve the efficient charge separation. Here, the CdS/g-C3 N4 and the g-C3 N4 isotype heterojunctions will be discussed. Besides the above mentioned systems of CdS quantum dots/g-C3 N4 [502,503,561], various kinds of other nanostructured combinations, such as core/shell CdS@g-C3 N4 Nanowires [284,562], g-C3 N4 /Au/CdS Z-scheme [589,590], CdS nanoparticles/2D g-C3 N4 nanosheets [563] and CdS nanorods/g-C3 N4 nanosheets [197,562,591,592] have been also successfully constructed to obtain the highly efficient and stable composite photocatalysts. Among them, the core/shell heterojunctions seem to be more promising, due to the suppressed CdS photocorrosion and the optimized intimate interface contact. For example, Zhang et al. demonstrated that the as-constructed novel CdS/2 wt% gC3 N4 core/shell nanowires could achieve an optimal photocatalytic activity of up to 4152 ␮mol h−1 g−1 [562]. It is believed that the well-matched Type II g-C3 N4 /CdS heterojunctions could achieve the positive synergic effect of accelerating the separation of charge carriers and inhibiting the CdS corrosion (as shown in Fig. 36a), thus greatly enhancing the photocatalytic activity and photostability [562]. Interestingly, based on the slight difference in their electronic band structures (Fig. 36b), Wang and coworkers et al. firstly demonstrated that the as-prepared Type II isotype heterojunctions of g-C3 N4 /S-mediated g-C3 N4 (S-g-C3 N4 ) exhibited the matched band gaps and efficiently promoted charge separation of the band offsets (Fig. 36b), thus significantly enhancing photocatalytic activity for H2 evolution [121]. The isotype heterostructure is similar to that of phase junction in the formation mechanism, which provides new opportunities to construct buried layered junctions in the various copolymerized g-C3 N4 -based composites with improved charge photon-excitation and charge separation [54]. Similarly, Dong and coworkers in situ constructed a novel Type II layered g-C3 N4 /g-C3 N4 metal-free isotype heterojunction with enhanced photocatalytic activity for the removal of NO in air [588]. The results further confirmed the key roles of the Type II isotype heterojunction in achieving the efficient charge separation and transfer across the heterojunction interface as well as prolonged lifetime of charge carriers. As observed in Figs. 35 b and 36, for the favorable Type II heterojunction systems, the photocatalytic redox reactions mainly occur on the surface of semiconductor with lower CB and VB edges, implying the weaker reduction and oxidation ability (driving forces) in this kind of heterojunction-type photocatalytic system. In contrary, as observed in Fig. 37, for the all-solid-state Z-scheme photocatalytic system with the Ohmic-contact interfaces, their photocatalytic activities are majorly dependent on the surface properties of semiconductor with higher CB and VB edges, thus

leading to the strong redox ability and enhanced photocatalysis [593]. In nature, photosynthesis of plants generally proceeds according to the so-called Z-scheme photocatalytic process, in which two isolated reactions of water oxidation and CO2 reduction are linked together through the redox mediators [593]. Mimicking the natural photosynthesis process, the artificial Z-scheme semiconductor heterojunctions have been successfully proposed and constructed by combining two different semiconductors through liquid-state or all-solid-state mediators. Each semiconductor in the Z-scheme is only responsible for one (oxidation or reduction) reaction, thus achieving the extremely extended visible-light absorption, strengthened redox ability, improved photostability, charge-separation and photocatalytic efficiency [594,595]. In this regard, the all-solid-state g-C3 N4 -based Z-scheme photocatalytic systems seem to exhibit many advantages and great potential in practical applications in photocatalytic fields. Commonly, the artificial heterogeneous all-solid-state g-C3 N4 -based Z-scheme photocatalytic systems could overcome the weak oxidation ability and decrease the reduction capacity of single-g-C3 N4 and g-C3 N4 based heterojunctions, respectively, and simultaneously fulfill a wide absorption range, long-term stability, high charge-separation efficiency and strong redox ability [523,596,597]. Typically, two kinds of all-solid-state g-C3 N4 -based Z-scheme photocatalytic systems with and without mediators are displayed in Fig. 37a and b, respectively. For the rational design of these two kinds of all-solid-state g-C3 N4 -based Z-scheme photocatalytic systems, the achievement of the intimate Ohmic contact should be the most important point, which could be obtained through introducing the conductors, such as conductive carbon and metals, or fabricating the perfect interfacial contact. For example, Yu and coworkers, for the first time, constructed a direct g-C3 N4 –TiO2 Z-scheme photocatalyst without an electron mediator by a facile calcination route, which could achieve the intimate interfacial contact [523]. The results showed that the as-prepared Z-scheme photocatalysts was highly dependent on the g-C3 N4 content. Ideally, the surface of the TiO2 nanoparticles should be partially covered by the g-C3 N4 nanoparticles, which are favorable for the formation of a g-C3 N4 -TiO2 Z-scheme photocatalytic system (see Fig. 38a and b). In contrary, the excessively high contents of gC3 N4 can not only lead to the complete cover of TiO2 surface, which could decrease the charge carrier excitation of TiO2 , but also increase the recombination rate of photo-generated electrons and holes on g-C3 N4 (see Fig. 38c). Similar Z-scheme systems between g-C3 N4 and TiO2 have also been observed in other reports [598,599]. Some other direct g-C3 N4 -based Z-scheme photocatalysts, such as Bi2 O3 /g-C3 N4 [600], ZnO/g-C3 N4 [601,602], BiVO4 /g-C3 N4 [603], g-C3 N4 /Bi2 MoO6 [604], WO3 /g-C3 N4 [605,606], g-C3 N4 /Ag3 PO4 [607–609], BiOCl-g-C3 N4 [610], Bi2 WO6 /g-C3 N4 [505] have also been available. Additionally, some typical electron mediators, such as nanocarbon [611], Au [590,612], RGO [613] and Bi [614]

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Fig. 36. Schematic illustration of spatial charge separation in CdS/g-C3 N4 (a) and g-C3 N4 /S-g-C3 N4 (b).

Fig. 37. Schematic illustration of spatial charge separation in the all-solid-state g-C3 N4 -based Z-scheme photocatalytic systems with (a) and without (b) mediators.

Fig. 38. Schematic illustration for the charge transfer and separation in g-C3 N4 -TiO2 Z-scheme photocatalysts under UV light irradiation [523].

could be used to construct the indirect g-C3 N4 -based Z-scheme photocatalysts. In future, improvements in the morphology of semiconductors and interfacial coupling should be deeply and continually investigated to search for highly effective g-C3 N4 -based Z-scheme photocatalysts for practical applications [598,615–618].

More importantly, the direct or indirect experimental evidence for supporting the proposed Z-scheme charge-transfer mechanism should be provided as far as possible. In fact, the technologies such as radicals (• O2 − and • OH) trapping experiments, metal deposition and double-beam photoacoustic (DB-PA) spectroscopy have been

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be further enhanced through improving the tightness of interfaces and introducing the interfacial mediator [476,638].

4.7. Co-catalyst loading

Fig. 39. Schematic illustration of 2D layered composites in comparison with other kinds of composites [476].

employed to reveal the real Z-scheme charge-transfer mechanism [523,534,601,608,619,620]. In addition, it should be also noted that the interfacial contact/coupling performances could be further improved by several strategies, such as, increasing the contact areas, improving the tightness of interfaces [621–624] and introducing the highlyconductive interfacial mediator [625–627]. Clearly, larger contact area can provide sufficient charge transfer and trapping channels for achieving their fast separation. As compared with other types of composite pohotocatalysts with 1D (i.e. 0D/1D and 1D/1D) or 2D (i.e. 0D/2D and 1D/2D) contact interfaces, the unique 2D–2D layered nano-junctions possess the much larger contact surface between the two adjacent sheets (as shown in Fig. 39), thus favoring more efficient interfacial charge separation and photo-activity enhancement [476]. More fortunately, g-C3 N4 itself possesses a unique 2D layered structure, which holds great promise for potential applications in constructing 2D layered composite photocatalysts. In 2011, Xiang et al. first constructed graphene/g-C3 N4 composite photocatalysts with the larger 2D-2D coupling interfaces (as shown in Fig. 40a) [151], demonstrating a more than 3.07-time enhancement of photocatalytic H2 -evolution activity (using Pt and methanol as cocatalyst and sacrificial agent, respectively). Subsequently, a series of 2D g-C3 N4 -based layered heterojunctions (e.g. MoS2 [120,290,292,628–633], SnS2 [634–636], WS2 [637,638], graphene [482,639], SnNb2 O6 [640], WO3 [287], BiOBr [641], layered double hydroxide [288,642,643], Bi4 O5 I2 [644] and Bi2 O2 CO3 [645]) have been widely fabricated for different photocatalytic applications. Among them, g-C3 N4 /MoS2 2D-2D coupling systems have attracted much attention since the first report about concept of layered nanojunctions by Hou et al. in 2003 (as shown in Fig. 40b) [120]. It is believed that 2D layered MoS2 can function as co-catalysts [646], stable semiconductor sensitizers [647] or electron trapper [648,649] in these systems. More interestingly, the layered triple-nanojunctions in the ternary g-C3 N4 nanosheets/N-doped graphene/MoS2 have also been successfully fabricated, which has been shown to significantly improve the photocatalytic activity of MB oxidation and Cr(VI) reduction through the synergistic effects of multiple 2D-2D coupling interfaces [650]. These results highlighted that the unique 2D–2D layered nanojunctions with larger contact area are more promising for the fast separation of photo-excited charge carriers across the interfaces with respect to the 0D–2D and 1D–2D coupling systems. More interestingly, the coupling of g-C3 N4 nanosheets and semiconductor nanosheets with exposed facets seems to be more promising in various kinds of photocatalytic applications, due to the diversified synergy effects [418,427,559,572,641,651–656]. In future, it is expected that the 2D–2D interface coupling performances could

The level of the conduction bands of g-C3 N4 is −1.3 V (vs. NHE), which is more negative than the reduction potentials • of CO2 /CO(−0.51 V), H + /H2 (0.41 V), and O2 /O2 − (0.33 V), respectively (As shown in Fig. 41). Thermodynamically, the photogenerated electrons on the CB of g-C3 N4 have much stronger driving force (or over-potentials) for these three typical kinds of reduction reactions, as compared to those in TiO2 [28,657,658]. However, the obvious structure defects in bulk g-C3 N4 generally lead to their fast recombination with the photo-excited holes. More importantly, the photocatalytic H2 evolution and CO2 reduction are typical up-hill reactions, thus resulting in the sluggish kinetics on the surface of bulk g-C3 N4 . Fortunately, these disadvantageous factors could be simultaneously overcome by loading suitable reduction co-catalysts onto the surface of g-C3 N4 , which could lower the reaction activation energy (or electrochemical overpotentials), improve the charge separation and transport, increase stability of photocatalyts, and accelerate the sluggish reaction kinetics of various surface reduction reactions, thus greatly enhancing the photocatlytic activity [88,124]. Essentially speaking, the single-electron or multi-electron O2 -reduction reactions (as shown in Table 2) are of significant importance for photocatalytic degradation [83,410,657], selective organic transformations [119,244] and disinfection [659,660]. More interestingly, the cocatalysts can also achieve the selective photoreduction products of CO2 [16,661]. In addition, it is also necessary to deposit suitable hole co-catalysts to accelerate the difficult water oxidation reactions, due to the lower overpotential of g-C3 N4 for water oxidation (0.59 V), as well as the inherent challenges of four-electron water oxidation [7,662]. Thus, it is obvious that all these reduction and oxidation co-catalysts play decisive roles in achieving highly efficient and selective photocatalytic reactions. These four types of co-catalysts over g-C3 N4 (as shown in Fig. 41), namely, H2 -evolution, CO2 -reduction, O2 -reduction and H2 O-oxidation cocatalysts, are summarized in Table 6, which will be compared and discussed in this section in detail. Similar to those co-catalysts on TiO2 [25], these different cocatalysts over g-C3 N4 -based photocatalysts can be divided into three categories (as shown in Table 6): noble-metal co-catalysts, earth-abundant metal co-catalysts, metal-free and hybrid cocatalysts (nano carbons). The nano carbons as co-catalysts will be highlighted in the next section. Here, we will focus on the noble-metal and earth-abundant metal co-catalysts, especially for the latter. As observed from Table 5, it is clear that the more efforts have been devoted to the developments of H2 -evolution and O2 -reduction co-catalysts. On the one hand, the noble-metal co-catalysts (e.g., single-atom [664], bimetallic [193,194,481] and co-loading [200,668]) seem to be more promising for both photocatalytic H2 -evolution and O2 -reduction reactions, which deserve more attention in the future studies. On the other hand, for earthabundant metal co-catalysts, the 2D layered co-catalysts, such as MoS2 [292,328,517,599,628–630,632,735], Ni(OH)2 [126,669], WS2 [637,638], Cu(OH)2 [521], and NiSx [125,197,670–673], have become the shinning stars in the fields of photocatalytic H2 generation and degradation of pollutants (for O2 reduction), which will be still the prescriptive research topics in these fields. In addition, the fabrication of nanostructured hybrid cocatalysts [155,156,198,651,678] and development of molecular clusters (such as Fe(III)/Co(III) [245,736,758]) and amorphous cocatalysts[759] might become an attractive direction in the near future.

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Table 6 Summary of various kinds of co-catalysts over g-C3 N4 -based photocatalysts. Roles/functions of co-catalysts

Noble-metal co-catalysts

Earth-abundant metal co-catalysts

Metal-free and Hybrid co-catalysts (nano carbons)

H2 evolution

Metal: Pt [663], single-atom Pt [664] Sulfides: Ag2 S [665] Plasmonic: Au [666,667], Ag [479,488] Bimetallic: PtCo [193], AuPd [194] Co-loading: Au/Pt [668], Au/PtO [200] RuO2 , [44,133]

Ni(OH)2 [126,669], WS2 [637,638], Cu(OH)2 [521], MoS2 [328,517,628,632], NiSx [125,197,670–673], NiOx , Cu [674], Ni [675,676], Ni(dmgH) 2 [677], hollow Zn0.30 Co2.70 S4 [678], [Ni (TEOA)2 ]Cl2 [679], Co0.04 Mo0.96 S2 [651] CoOx [285,684], Co(OH)2 [685], layered double hydroxide (LDH) [288,686] Co(II) ions [687], Co3 O4 [688,689], Co-Pi [690] Layered double hydroxide [642]

Graphene [151], carbon black/NiS [156], carbon QDs [680], CNTs [681], CNTs/NiS [198], C60, carbon fiber [682], ZIF-8 derived carbon [683], acetylene black/Ni(OH)2 [155]

Hole co-catalysts

CO2 reduction

Pt [691–693], single-atom (Pd/Pt) [694], ruthenium complex [695–700]

O2 reduction (degradation)

Pt, Au [590], Ag [433,483,485,488,506,710–723], Ag2 O [724–728], Pd [729–732], bimetallic Au/Pt [481], Ag Quantum Cluster[733]

Relatively speaking, there are only limited reports about the photocatalytic water oxidation over g-C3 N4 -based photocatalysts modified by Co-based molecules or compounds, [285,684,685,687–689] RuO2 [44,133] or LDH [288,686]. In this regard, other water-oxidation co-catalysts such as cubic Co com-

NiO [734], MoS2 [292,599,629,630,735], Fe(III) [736], H3 BO3 [737], Phosphate [738,739], Fe (III)/Co(III) [245]

Graphene/LDH [288]

Phosphate [701], graphene [160,702–704], carbon [705], CNTs [706], S-doped porous carbon [707], UiO-66 (zirconium-based MOFs) [708], Co-ZIF-9 (cobalt-based MOFs)[709] Graphene [220,244,739–744], carbon QDs [745,746], CNTs [747], biochar [748], PANI [749–751], C60 [752,753] graphene/Ag [710,754], CNTs/Au [755], ordered mesoporous carbon [756,757]

plex [760,761], Nocera cobalt phosphate (CoPi) [762,763], IrO2 [764], NiOx [765–767], or g-C3 N4 /graphene [262], should be paid more attention in future studies. Similarly, so far, only few cocatalysts on g-C3 N4 , e.g., Pt-based, [691–694] ruthenium complex [695–700], LDH [642], Phosphate [701], MOFs [708,709] and car-

Fig. 40. Schematic illustration of 2D-2D coupling of g-C3 N4 /graphene (a) and g-C3 N4 /MoS2 (b).

Fig. 41. Four kinds of co-catalysts over g-C3 N4 .

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Fig. 42. Roles of carbon materials in enhancing the performance of g-C3 N4 -based composite photocatalysts [781].

bon [160,702–707], have been available for selective photocatalytic CO2 reduction. Thus, in future, it is expected that more and more earth-abundant CO2 -reduction co-catalysts with high activity and selectivity could be developed and utilized in the production of solar fuels from the CO2 photoreduction. 4.8. Nanocarbon loading So far, various kinds of carbon materials, CNTs [147,198,747,755,768], graphene including [151,160,288,650,702,703,769–773], C60 [752,753], carbon quantum dots [745,774–777], carbon fibers [682], activated carbon, carbon black [156,778,779], acetylene black [155], etc. have been widely coupled with g-C3 N4 to fabricated the g-C3 N4 /carbon hybrid materials [780]. The essential reasons can be attributed to the promoted charge separation by the as-formed carbon-based Schottky-junction between g-C3 N4 and the highly conductive nano carbon materials and the enhanced adsorption performances from narrowing band gap due to the carbon doping [25]. More specifically, coupling with various carbon rich materials with g-C3 N4 not only compensate the disadvantages of individual semiconductor materials, but also induce the interesting synergetic effects, like supporting material, increasing adsorption and active sites, electron acceptor and transport channel, cocatalyst, photosensitization, photocatalyst, and band gap narrowing effect (as shown in Fig. 42) [781]. Here, we will highlight the hybrids of g-C3 N4 /graphene, which have been the most widely investigated g-C3 N4 /carbon composite photocatalysts. Compared to the 0D and 1D carbon materials, graphene, a sp2 -hybridized 2D carbon nanosheet, exhibits a much higher optical transmittance, conductivity (∼5000 W m−1 K−1 ), electron mobility (200,000 cm2 V−1 s−1 ), theoretical specific surface area (∼2600 m2 g−1 ) and more suitable work function (4.42 eV) for H2 evolution [17,658,782–787]. Thus, the combination of g-C3 N4 and graphene has been widely shown to be one of promising strategies to favor the charge transfer and inhibit the charge recombination process, thereby leading to an enhanced photocatalytic activity for H2 production. As displayed in Fig. 40a, the 2D-2D coupling interface in the g-C3 N4 /graphene hybrids could achieve much larger interfacial coupling areas and more efficient charge separation, as compared to the 0D-2D and 1D-2D hybrids. For example, the doping of g-C3 N4 by graphene could be achieved through formation of C O C covalent bonding or ␲-␲ stacking interactions, both of which can effectively narrow the band gap of g-C3 N4 , thus leading to the enhanced visible-light photocatalytic activity [702,788–790]. Recently, based on the state-of-the-art hybrid DFT, Xu et al. systematically investigated the interaction between the g-C3 N4 and RGO sheets [773]. It was demonstrated that the appropriate O concentration plays a crucial role in altering the direct gap to indirect one.

Fig. 43. The proposed mechanism for photocatalytic water splitting over the gC3 N4 (electron sink and H2 -evolution site)/RGO-3 composite [773].

Most importantly, a higher O concentration could achieve a type-II, staggered band alignment at the g-C3 N4 -RGO interface, leading to the high hydrogen-evolution activity over O atoms (as active sites) in the RGO (Fig. 43) [773]. The findings pave the way for developing RGO-based composites for photocatalytic applications. At this point, the semiconductor properties of RGO are more promising in constructing composite photocatalysts [740], which deserves more attention in future studies. In addition, doping or co-doping of RGO materials with heteroatoms has also been demonstrated to exhibit the significantly enhanced electrocatalytic performances [791], which are also highly expected to be utilized in constructing g-C3 N4 /doped RGO composite photocatalysts. 5. Potential applications of g-C3 N4 -based composite photocatalysts 5.1. Photocatalytic water splitting Since the pioneering works by Honda and Fujishima in 1972 [1], various heterogeneous photocatalysts have been widely applied in the attracted photocatalytic hydrogen production from water reduction [7]. Normally, photocatalytic water splitting systems can be divided into half-reaction water splitting (for H2 and O2 ) and overall water splitting systems [7]. Interestingly, g-C3 N4 has been extensively applied in these two systems to boost their photocatalytic activity for water splitting. Table 7 summarizes the photocatalytic activities of g-C3 N4 based photocatalysts for H2 generation on various conditions, including the amount of photocatalysts, the sacrificial reagents, H2 generation rate, and the corresponding quantum efficiency in this review. As shown in Table 7, co-catalysts and sacrificial reagents are crucial for achieving the highly efficient photocatalytic H2 evolution, which will be discussed in detail. As observed in Table 7, it is clear that the high H2 -evolution activity over nanostructured g-C3 N4 -based semiconductors is generally obtained via loading the shape-dependent noble-metal Pt nanoparticles as co-catalysts [315,321,348,445,562,809,819,823]. In the pioneering work, Wang and co-workers found that the loading 3 wt% Pt as co-catalysts on g-C3 N4 could achieve the H2 evolvtion amount of 770 ␮mol after 72 h in the TEOA aqueous

100

Table 7 Summary of the photocatalytic H2 evolution on g-C3 N4 -based photocatalysts. QY (%)

photocatalyst

structure

synthetic method

co-catal./mass ratio

mass (g)

light source

incident light

aqueous reaction

cocatal./activity (␮mol h−1 )

Ni@/g-C3 N4 NiS/g-C3 N4

particles/lamellar nanoparticles/lamellar

solvothermal method hydrothermal method

Ni/10 wt.% NiS/1.25 wt.%

0.05 0.1

quartz reactor Pyrex reactor

10 vol.% TEOA 15 vol.% TEOA

Ni/8.41 NiS/46

NiS/g-C3 N4

nanoparticles/lamellar

in stiu ion-exchange method

NiS/1.5 mol%

0.1

10 vol.% TEOA

NiS/44.77

[670] (2014)

NiS/e-C3 N4

ultrathin nanosheets/nanoparticles

NiS/1.0 wt.%

0.05

quartz reactor

10 vol.% TEOA

NiS/4.2

[671] (2015)

Ni(OH)2 /gC3 N4 Ni/NiO/g-C3 N4

nanoparticles/lamellar

liquid exfoliation-hydrothermal method precipitation method

500 W Xe lamp 300 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ > 420 nm 150 W Xe lamp, ␭ > 400 nm

Ni(OH)2 /0.5 wt.%

0.05

Pyrex reactor

10 vol.% TEOA

Ni(OH)2 /7.6

core-shell/lamellar

in situ immersion method

Ni/NiO/2 wt.%

0.05

Pyrex reactor

10 vol.% TEOA

Ni/NiO/10

[792] (2015)

NiS/CNT/mpgC3 N4 NiS/CB/g-C3 N4

nanoparticles/nanotubes/lamellar sol-gel-precipitation method

NiS/1 wt.%

0.05

quartz reactor

10 vol.% TEOA

NiS/26.05

[198] (2015)

nanoparticles/lamellar

quartz reactor

15 vol.% TEOA

CB, NiS/49.6

[156] (2015)

sub-mircowires/lamellar

CB/0.5 wt.%, NiS/1.0 wt.% Ni(dmgH)2 /3.5 wt.%

0.05

Ni(dmgH)2 /gC3 N4 g-C3 N4

physical mixing-chemical deposition chemical deposition

quartz reactor

15 vol.% TEOA

Ni(dmgH)2 /1.18

[677] (2014)

Pt/3 wt.%

0.05

Pyrex reactor

10 vol.% TEOA

Pt/28.55

[793] (2016)

pm-g-C3 N4

porous

co-polymerization-surface activation-exfoliation sintering

Pt/3 wt.%

0.1

10 vol.% TEOA

Pt/41.7

[159] (2017)

g-C3 N4

microsphere

solvothermal method

Pt/3 wt.%

15 vol.% TEOA

Pt/1.80

g-C3 N4

lamellar

Pt/1 wt.%

0.1

Pyrex reactor

10 vol.% TEOA

Pt/34

g-C3 N4

flower-like nanorods

heating acetic acid treat melamine recrystallization method

Pt/3 wt.%

0.05

quartz reactor

10 vol.% TEOA

Pt/261.8

Pt/0.6 wt.%

0.1

10 vol.% TEOA

Pt/89.28

[794] (2015) [795] (2015) [428] (2015)

Pt/3 wt.%

0.05

Pyrex reactor

10 vol.% TEOA

Pt/272

[796] (2015)

0.1

350 W Xe arc lamp, ␭ > 400 nm 350 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ ≥ 420 nm 300 W Xe lamp, ␭ ≥ 420 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe arc lamp, ␭ > 420 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ > 420 nm 300 W xenon lamp, ␭ > 400 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe arc lamp, ␭ > 420 nm 300 W Xe arc lamp, ␭ > 400 nm 350 W Xe arc lamp, ␭ > 420 nm visible light, ␭ > 420 nm

Pyrex reactor

10 vol.% TEOA

Pt/502

10 vol.% TEOA

Pt/39.4

mg-C3 N4

mesoporous

melamine-assisted exfoliation method calcinating-dissolving method

CNIC

nanotubes

molten salt

Pt/3 wt.%

CNT/g-C3 N4

nanotubes/lamellar

calcinating method

CNT/2 wt.%, Pt/1.2 wt.% 0.1

MVNTs/g-C3 N4 nanotubes/particles

calcinating method

MVNTs/2.0 wt.%

0.1

C/g-C3 N4

fiber/lamellar

Pt/1.0 wt.%

0.05

C/g-C3 N4

mixing-calcinating method

carbon black/0.5 wt.%, Pt/3 wt.% C-dots/0.25 wt.%

0.1

C-dots/g-C3 N4

nanoparticles/rectangular nanotube dots/lamellar

electrospinning and calcinations method molten salt method

0.05

CQDs/g-C3 N4

quantum dots/lamellar

hydrothermal method

CQDs, Pt/3 wt.%

0.05

C-dots/g-C3 N4

hydrothermal method thermal condensation

C-dots/0.2 wt.%, Pt/0.2 wt.% C-ZIF/1 wt.%

0.05

C-ZIF/g-C3 N4

nanodots/ultrathin nanosheets nanoparticles/lamellar

0.1

N/g-C3 N4

nanosheet

calcinating method

N-doped,Pt/3 wt.%

0.05

C3 N4+x

lamellar

co-thermal condensation

N-doped,Pt/3 wt.%

0.08

quasi-2D-C3 N4 lamellar

4 × UV-LEDs (3 W, ␭ = 420 nm) 400 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ > 400 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ > 400 nm

1.1 (420 nm)

1.62 (420 nm)

21.2 (420 nm)

[192] (2015) [125] (2013)

[126] (2013)

[397] (2015)

[106] (2013) [147] (2014)

quartz reactor

25 vol.% CH3 OH MVNTs/1.15

[681] (2012)

Pyrex reactor

10 vol.% TEOA

[682] (2015)

quartz reactor

25 vol.% CH3 OH C, Pt/69.8

[779] (2014)

Pyrex reactor

25 vol.% CH3 OH 8.6

[797] (2015)

Pyrex reactor

10 vol.% TEOA

Pt/5.805

[680] (2016)

5 vol.% CH3 OH

Pt/88.1

0 vol.% TEOA

C-ZIF/32.58

[777] (2016) [683] (2016)

10 vol.% TEOA

Pt/64

[798] (2016)

10 vol.% TEOA

Pt/44.28

[799] (2015)

Pyrex reactor

Pt/54

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

ultrathin nanosheets

0.005

1.9 (440 nm)

reference (year)

Table 7 (Continued) QY (%)

photocatalyst

structure

synthetic method

co-catal./mass ratio

mass (g)

light source

incident light

aqueous reaction

cocatal./activity (␮mol h−1 )

P/g-C3 N4

calcinating method

P-doped, Pt/3 wt.%

0.05

10 vol.% TEOA

Pt/104.1

[315] (2015)

copolymerization

P-doped

0.1

Pyrex reactor

10 vol.% TEOA

Pt/50.6

Br/g-C3 N4

lamellar

calcinating method

Br-doped, Pt/3 wt.%

10 vol.% TEOA

Pt/48

[324] (2015) [800] (2016)

g-C3 N4

calcinating method

O-doped, Pt/3 wt.%

0.05

Pyrex reactor

10 vol.% TEOA

Pt/60.2

S/g-C3 N4

nanosheets have a porous network lamellar

calcinating method

S-doped, Pt/1 wt.%

0.1

quartz reactor

25 vol.% CH3 OH Pt/12.16

[307] (2013)

K-g-C3 N4

lamellar

KCl-template method

K, Pt/0.5 wt.%

0.01

Pyrex reactor

10 vol.% TEOA

[445] (2014)

Zn/g-C3 N4

lamellar

calcinating method

Zn-doped, Pt/0.5 wt.%

0.2

Pyrex reactor

Co-Pi/g-C3 N4

in situ photodepositions

Co–Pi, Pt/1 wt.%

0.1

Au/g-C3 N4

nanoparticles/aggregated sheets nanoparticles/lamellar

Pt/59.5 18.5 vol.% CH3 OH 25 vol.% CH3 OH Pt/19.48 0.05 M AgNO3 10 vol.% TEOA Au/177.4

AuPd/g-C3 N4

nanoparticles/lamellar

0.05

300 W Xe arc lamp, ␭ > 400 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ ≥ 420 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe arc lamp, ␭ > 400 nm 300 W Xe lamp, ␭ > 420 nm 200 W Xe arc lamp, ␭ ≥ 420 nm 300 W Xe arc lamp, ␭ > 400 nm 125 W Hg lamp, ␭ > 400 nm 300 W Xe arc lamp, ␭ ≥ 400 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe arc lamp, ␭ > 400 nm 300 W Xe lamp,

Pyrex reactor

P/g-C3 N4

flowers of in-plane mespores lamellar

0.1

Au/PtO/g-C3 N4 nanoparticles/lamellar

photodeposition method

0.05

CsTaWO6 /Au/g- gathered impregnaton method C3 N4 block/nanoparticles/lamellar nanoparticles/lamellar hydrothermal method Cd0.5 Zn0.5 S/gC3 N4

Au/0.33 wt.%, Pt/0.40 wt.% Au/0.5 wt.%

0.05 0.08

Pt/102.8

[300] (2011) [690] (2013) [666] (2014)

quartz reactor

10 vol.% TEOA

AuPd/16.3

[194] (2015)

Pyrex reactor

6.2 vol.% TEOA

Pt-Au/17

[350] (2015)

Pyrex reactor

25 vol.% CH3 OH Au/PtO/16.9

[200] (2016)

quartz reactor

20 vol.% CH3 OH Au/0.458

[667] (2015)

Xe lamp, ␭ > 420 nm

Pyrex reactor

20.8 mL/h

300 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ > 400 nm 300 W Xe lamp, ␭ > 420 nm 350 W Xe arc lamp, ␭≥420 nm

Pyrex reactor

0.35 M Na2 S and 0.25 M Na2 SO3 0.1 M Na2 S and 0.1 M Na2 SO3 0.1 M Na2 S and 0.5 M Na2 SO3 0.1 M L-ascorbic acid 25% vol.% CH3 OH 10 vol.% TEOA 0.35 M Na2 S and 0.25 M Na2 SO3 0.35 M Na2 S and 0.25 M Na2 SO3 10 vol.% TEOA

Pt/265.15

3.16 (420 nm)

[348] (2015)

Pt/207.6

4.3 (420 nm)

[562] (2013)

NiS/128.2

[197] (2015)

Ni(OH)2 /115.18 16.7 (450 nm)

[669] (2016)

MoS2 /2.52

[632] (2015)

37 (425 nm)

[801] (2015)

299.24

7.1 (420 nm)

Pt/22.47

8 (420 nm)

[802] (2015) [803] (2016) [503] (2013)

nanoparticles/lamellar

hydrothermal method

0.05

particles/lamellar

hydrothermal method

0.05

QDs/lamellar

in situ hydrothermal method

Pt/0.5 wt.%

0.005

QDs/lamellar

chemical impregnation method

Pt/1.0 wt.%

0.1

Pt/3 wt.%

0.02

particles/particles

in situ self-transformation method

Pt/1.0 wt.%

0.05

CdS/g-C3 N4

core/cell nanowires

solvothermal-chemisorption method

Pt/0.6 wt.%

0.05

350 W Xe arc lamp, ␭≥420 nm

Pyrex reactor

nanoparticles/nanorodes/lamellar in situ hydrothermal method NiS/CdS/gC3 N4 Ni(OH)2 /CdS/g- core/shell nanorodes hydrothermal method C3 N4

NiS/9 wt.%

0.05

quartz reactor

Ni(OH)2 /4.76

0.001

300 W Xe lamp, ␭≥420 nm 300 W Xe lamp, ␭ > 420 nm

MoS2 /g-C3 N4

flower-like/lamellar

in situ light-assisted method

MoS2 /2.89 wt.%

0.01

Pyrex reactor

MoS2 /g-C3 N4

nanoparticles/lamellar

mixing-calcinating method

MoS2 /0.5 wt.%, Pt/1.0 wt.%

0.1

300 W Xe lamp, ␭ > 400 nm 300 W Xe arc lamp, ␭ > 400 nm

0.25 M Na2 S and 0.35 M Na2 SO3 10 vol.% TEOA

quartz reactor

25 vol.% CH3 OH MoS2 , Pt/23.1

quartz reactor quartz reactor quartz reactor Pyrex reactor Pyrex reactor

quartz reactor

208.8

Pt/17.27

[502] (2012)

Pt/601

[804] (2015)

[628] (2013) 101

Cd0.2 Zn0.8 S/gC3 N4 CdLa2 S4 /mpgC3 N4 CdS QDs/g-C3 N4 CdS QDs/g-C3 N4 CdS QDs/g-C3 N4 g-C3 N4 /CdS

QDs/hollow

3.2 (420 nm)

[321] (2015)

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

0.02

Pt-Au@ g-C3 N4 lamellar

deposition-precipitation Au/1 wt.% method chemical reduction-calcinating AuPd/0.5 wt.% method photodeposition method Pt, Au

quartz reactor

7.8 (420 nm)

reference (year)

102

Table 7 (Continued) photocatalyst

structure

synthetic method

MoS2 /CN-Py

flower-like/lamellar

ZnS/g-C3 N4 WS2 /g-C3 N4

QY (%)

mass (g)

light source

incident light

aqueous reaction

cocatal./activity (␮mol h−1 )

in suit solvothermal method

0.05

Pyrex reactor

10 vol.% TEOA

25

[805] (2016)

microsphere/lamellar

precipitation method

0.05

Pyrex reactor

25 vol.% CH3 OH 9.7

[806] (2014)

slabs/porous sheet-like

gas-solid reaction

WS2 /0.01 wt.%

0.05

Pyrex reactor

25 vol.% CH3 OH WS2 /5.05

[638] (2015)

WS2 /0.3 wt.%

0.05

Pyrex reactor

10 vol.% TEOA

WS2 /6.12

[637] (2014)

CaIn2 S4 /g-C3 N4 nanoplate-lamellar

impregnation-sulfidation method hydrothermal method

Pt/1.0 wt.%

0.05

Pyrex reactor

nanoparticles/lamellar

H2 reduction

Cu

0.05

0.5 M Na2 S and Pt/5.1 0.5 M Na2 SO3 25 vol.% CH3 OH Cu/1.025

[807] (2015)

Cu/g-C3 N4

300 W Xe lamp, ␭ > 420 nm 4 × UV-LEDs (3 W, ␭ = 420 nm) 300 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ > 420 nm 4 × UV-LEDs (3 W, ␭ = 420 nm) Xe lamp, ␭ > 400 nm

CuO/g-C3 N4

mono-dispersed wet impregnation-calcination method sphere/lamellar clusters/spherical particles precipitation method

Pt/1.0 wt.%

0.1

Cu(OH)2 /0.34mol%

0.1

WS2 /mpg-C3 N4 mesoporous nanosheets

nanoparticles/lamellar

in situ reduction method

Pt/3 wt.%

0.1

CuO2 @g-C3 N4

core@shell octahedra

Pt/3 wt.%

0.3

g-C3 N4 /InVO4

lamellar/nanoparticles

solvothermal and chemisorption method hydrothermal method

Pt/0.6 wt.%

0.05

ZnFe2 O4 /gC3 N4 CuFe2 O4 /gC3 N4 FeOX /g-C3 N4

flakes/lamellar

calcinating method

Pt/1 wt.%

0.1

nanoparticles/lamellar

calcinating method

Pt/3 wt.%

0.1

granular-like

calcinating method

Pt/3 wt.%, FeOX (20 g 0.1 urea/100 mg ferrocene) Pt/1 wt.% 0.05

N-CeOx /g-C3 N4 nanoparticles/lamellar

one-pot annealing method

Ag2 O/g-C3 N4

nanaosheets

hydrothermal method

0.01

Ag2 S/g-C3 N4

particle/mesopores sheets

precipitation method

0.05

TiO2 /g-C3 N4

yolk-shell spheres/lamellar solvothermal method

0.05

g-C3 N4 /B-TiO2

0.1

CoTiO3 /g-C3 N4

two removed the top of the solvothermal method pyramids rods/lamellar a facial in situ growth method

C, N–TiO2 /g-C3 N4 N,S–TiO2 /gC3 N4

nanoparticles/ultrathin nanosheets semi-spherical nanoparticles/lamellar

Pt/3 wt.%

0.02

one-pot solvothermal method

0.1

in situ thermal induced polymerization method

0.05

chemical g-C3 N4 /Pt–TiO2 nanoparticles/nanoparticles/lamellar 1% wt.%Pt/TiO2 adsorption-calcinating method lamellar/nanosheets/nanorodes hydrothermal method gC3 N4 /MoS2 /TiO2 hydrothermal method Pt/1 wt.% C3 N4 /rGO/WO3 nanosheets/nanosheets/nanoparticles

0.1

W18 O49 /g-C3 N4 nanowires/lamellar

0.005

solvothermal method

Pt/3 wt.%

0.1 0.02

300 W Xe lamp, ␭ > 420 nm 300 W Xe arc lamp, ␭ > 400 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe arc lamp, ␭ > 420 nm 300 W Xe arc lamp, ␭ > 430 nm 300 W Xe lamp, 680 nm >␭ > 420 nm 300 W Xe lamp, 780 nm > ␭ > 420 nm 300 W Xe lamp, ␭ > 420 nm 300 W Xe lamp, ␭ > 420 nm 4 × UV-LEDs (3 W, ␭ = 420 nm) 4 × UV-LEDs (3 W, ␭ = 420 nm) 300 W Xe arc lamp, ␭ > 400 nm 300 W Xe lamp 300 W Xe lamp, ␭ > 400 nm 125 W medium pressure Hg lamp, ␭ ≥ 400 nm 300 W Xe lamp, ␭ ≥ 420 nm 300 W Xe arc lamp, ␭ > 400 nm 250 W iron doped metal halid UV–vis lamp (␭ > 420 nm) 300 W Xe arc lamp, ␭ > 420 nm

10 vol.% TEOA

0.35 (420 nm)

Pt/93.7

reference (year)

[674] (2016) [808] (2016)

Pyrex reactor

25 vol.% CH3 OH Cu(OH)2 /4.87

[809] (2014)

Pyrex reactor

10 vol.% TEOA

Pt/24.13

[525] (2014)

Pyrex reactor

10 vol.% TEOA

Pt/79.5

[802] (2015)

20 vol.% CH3 OH Pt/10.6

4.9 (420 nm)

[351] (2015)

Pyrex reactor

10 vol.% TEOA

Pt/20

[439] (2014)

quartz reactor

10 vol.% TEOA

Pt/76

[810] (2016)

quartz reactor

10 vol.% TEOA

FeOX , Pt/108

[811] (2016)

Pyrex reactor

10 vol.% TEOA

Pt/14.62

[812] (2015)

Pyrex reactor

10 vol.% TEOA

33.04

[813] (2015)

Pyrex reactor

20 vol.% CH3 OH 10

[665] (2014)

Pyrex reactor

25 vol.% CH3 OH 5.6

[814] (2016)

Pyrex reactor

25 vol.% CH3 OH 47.3

[815] (2016)

quartz reactor

10 vol.% C2 H5 OH 10 vol.% TEOA

Pt/11.7 3.92

[817] (2015)

10 vol.% TEOA

317

[818] (2015)

Pyrex reactor

10 vol.% TEOA

Pt/178

[819] (2012)

Pyrex reactor

25 vol.% CH3 OH 125

Pyrex reactor

deionized water

Pt/2.84

0.9 (420 nm)

[820] (2016) [821] (2015)

quartz reactor

10 vol.% TEOA

Pt/3.69

1.79 (400 nm)

[822] (2016)

Co-Pi: cobalt-phosphate; MVNTS: multi-walled carbon nanotubes; py:pyridine; CNIC: carbon nitride intercalation compound; C-ZIF: ZIF-8 derived.

38.4 (365 nm)

[816] (2016)

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

Cu(OH)2 /gC3 N4 CuO2 /g-C3 N4

co-catal./mass ratio

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

Fig. 44. The photocatalytic H2 -evolution rate over g-C3 N4 modified by Pt cocatalysts with different shapes [823].

solution, whereas the bare g-C3 N4 exhibits the negligible H2 production activity. This is due to the rapid recombination of CB electrons and VB holes, and the large H2 -evolution overpotential over pure g-C3 N4 . Subsquently, various engineering strategies, highlighted in the section 4, have been employed to enhance the H2 evolution activity over the g-C3 N4 /Pt systems [369,395,396]. For example, Wang and coworkers demonstrated that nanospherical g-C3 N4 frameworks, with interconnecting nanosheets and highly open-up spherical surfaces with sharp edges, achieved an AQY of 9.6% at 420 nm for H2 evolution [369]. More recently, Cao et al. also demonstrated that the spherical Pt nanoparticles on g-C3 N4 exhibiter much better H2 -evolution activity than those of octahedral and cubic Pt nanoparticles on g-C3 N4 , due to its favorable exposed facets, disparity and adsorption energies induced by the spherical shape (as shown in Fig. 44) [823]. More interestingly, it was also demonstrated that the single-atom Pt co-catalyst on g-C3 N4 exhibited a 8.6-fold enhancement in photocatalytic H2 -evolution activity, as compared to that of Pt nanoparticles-loaded g-C3 N4 , due to the maximized atom efficiency and improved surface trap states [664]. Unfortunately, their high cost and low stability significantly limit their practical application in a large scale. Therefore, design and preparation of advanced alternative co-catalysts with excellent performance and low cost are of great importance for the development of these photocatalytic systems. Accordingly, the earth-abundant first-row transition metal electrocatalysts, including Fe-, Co-, Ni- and Cu-based co-catalysts have been of increasing interest in both electrocatalysis and photocatalysis in the recent years [124,272–274,824]. Importantly, loading suitable earth-abundant co-catalysts onto the g-C3 N4 provides a facile and strategy to construct real robust g-C3 N4 -based H2 -evolution photocatalytic systems. Here, we will highlight the unique Ni-based co-catalysts for enhancing the activity of the g-C3 N4 semiconductor. To date, various kinds of Ni-based co-catalysts, including Ni [192,675,676,825], Ni(OH)x [126,155,669], NiSx [125,156,197,198,670,672,673], [Ni(TEOA)2 ] Cl2 [679], NiOx [734,792], and Ni(dmgH)2 [677,826] have been widely employed as co-catalysts to accelerated the photocatalytic activity of the g-C3 N4 for different applications [272]. For example, Yu et al. demonstrated that the as-fabricated 0.5 mol% Ni(OH)2 -modified g-C3 N4 composite photocatalysts exhibited the highest H2 production rate of 7.6 ␮mol h−1 (with an AQE of 1.1% at 420 nm, as shown in Fig. 45a), approaching that of optimal 1.0 wt% Pt/g-C3 N4 (8.2 ␮mol h−1 ), due to the promoted charge separation and surface reaction rate induced by the loading of Ni(OH)2 (as shown in Fig. 45b) [126]. This work perfectly highlighted the promising uti-

103

lization of low cost Ni(OH)2 as a substitute for noble metals (such as Pt) in the photocatalytic H2 production for g-C3 N4 . Following this work, Li and co-workers recently demonstrated that the dual electron co-catalysts of robust acetylene black and Ni(OH)2 could significantly enhance the photocatalytic H2 -evolution activity over g-C3 N4 /Ni (OH)2 hybrid systems. When inserting 0.5% acetylene black into the interface regions between Ni(OH)2 and g-C3 N4 , a 3.31 time enhancement in H2 -evolution activity can be thus achieved. It is suggested that the enhanced activity can be attributed to the effectively promoted separation of photo-generated electron-hole pairs and enhanced the following H2 -evolution kinetics [155]. Especially, various cheap nanoconbons should be fully integrated with robust co-catalysts and g-C3 N4 to maximize the functions of co-catalyst and g-C3 N4 semiconductor. In addition, several other highly efficient ternary g-C3 N4 -based photocatalysts have also been developed recently, For instance, Li and co-workers confirmed that the CdS photosensitizer and NiS co-catalysts in ternary g-C3 N4 -CdS-NiS composites play key roles in boosting the H2 -generation acticity of g-C3 N4 under visiblelight illumination [197]. The highest H2 -production activity of 2563 ␮molg−1 h−1 is about 1528 times as high as that of the pure g-C3 N4 (Fig. 46). In another work, when inserting carbon black into the interfaces between g-C3 N4 and NiS, the average H2 -evolution rate of g-C3 N4 /0.5%CB/1.5%NiS can reach 992 ␮mol g−1 h−1 , which is about 2.51-fold higher than that of g-C3 N4 /1.5%NiS with a photocatalytic H2 production rate of 395 ␮mol g−1 h−1 (Fig. 47) [156]. In another paper by Li and co-workers, mpg-C3 N4 /CNT/NiS was synthesized via the sol-gel method and the direct precipitation process [198]. The results show that the mpg-C3 N4 /CNT/NiS composite exhibits the highest H2 -evolution rate of 521 ␮mol g−1 h−1 , which is about 148 times as high as that of mpg-C3 N4 /CNT. These results highlighted that the ternary hybrid should be a promising direction for constructing highly efficient earth-abundant g-C3 N4 -based composite H2 -evolution photocatalysts. However, there are few attempt reported to reveal the nature and structural features of the Ni co-catalyst as well as the possible structural and bonding situation occurring at the co-catalyst active sites under light irradiation [676]. To achieve this aim, in situ EPR measurements (Fig. 48a) confirmed that a continuous increase of the Ni0 signal was detected (though, not all Ni2+ species were reduced to Ni0 at the same time), indicating the Ni0 acts as the HER active sites during the photocatalysis (Fig. 48b) [676]. For other Ni species, although the electrochemical performances, including polarization curves, time dependence of the current density, and electrochemical impedance spectroscopy of g-C3 N4 have been widely determined [197], the accurate catalytic mechanism still needs to be uncovered in future. Therefore, both the deep mechanism studies and continuous efforts in developing new co-catalysts are highly expected, to achieve the rational design of highly efficient Ni-based co-catalysts modified g-C3 N4 photocatalysts for practical applications. Finally, it should be pointed out that the oxidation half reaction of g-C3 N4 should be paid more attention, which is crucial for improving the photocatalytic H2 -evolution activity and deeply understand the underlying mechanism for water splitting [444,685–687]. Clearly, constructing the practical g-C3 N4 -based overall water splitting systems is still very challenging. Recently, Kang and coworkers demonstrated that the metal-free carbon nanodots–carbon nitride nanocomposite exhibited the impressive performance for photocatalytic solar water splitting [774]. The measured quantum efficiencies of 16% (420), 6.29% (580 nm), and 4.42% (600 nm), correspond to an overall solar energy conversion efficiency of 2.0%. It was verified that carbon dots-C3 N4 catalyzes water splitting to hydrogen and oxygen via the stepwise two-electron/two-electron two-step pathway under visible light irradiation. The composite nature of the catalyst provides suffi-

104

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

Fig. 45. (a) Comparison of the photocatalytic H2 -production activity of the Nix (x, Ni(OH)2 to (g-C3 N4 + Ni(OH)2 ) was 0, 0.1, 0.5, 1.0, 1.6, and 10 (mol%))and Pt-deposited g-C3 N4 samples in triethanolamine aqueous solution. (b) Charge separation mechanisms in the Ni(OH)2 /g-C3 N4 system under visible light [126].

Fig. 46. (A) Time courses and (B) the average rate of photocatalytic H2 evolution over the photocatalysts: (a) g-C3 N4 ; (b) g-C3 N4 -CdS; (c) g-C3 N4 -9%NiS; (d) CdS-9%NiS; (e) g-C3 N4 -CdS-3%NiS; (f) g-C3 N4 -CdS-6%NiS; (g) g-C3 N4 -CdS-9%NiS; (h) g-C3 N4 -CdS-12%NiS; (i) g-C3 N4 -CdS-15%NiS [197].

Fig. 47. (A) The average rate of H2 evolution and (B) proposed charge transfer mechanisms in the g-C3 N4 /CB/NiS composite under visible light irradiation: A g-C3 N4 , B g-C3 N4 -0.5% CB, C g-C3 N4 -1.5% NiS, D g-C3 N4 -0.5%CB-1.5%NiS, E g-C3 N4 -1.0% CB-1.5% NiS, F g-C3 N4 -1.5% CB-1.5% NiS, G g-C3 N4 -1.5% NiS-0.5% CB [156].

Fig. 48. (a) In situ EPR studies of a suspension of Cat-1 in TEOA solution under continuous visible-light irradiation with increasing the time. (b) Charge separation in sg-CN and the formation of Ni0 nanoparticles during photocatalysis [676].

cient proximity between the H2 O2 generation sites on the C3 N4 surface and the carbon dots so that H2 O2 decomposition and O2 generation in the second stage become efficient [774]. This work demonstrated that the control of oxidation half reaction played key roles in achieving the overall water splitting. More recently, Wang and coworkers discovered the irradiated g-C3 N4 loaded by Pt, PtOx ,

and CoOx as redox cocatalysts, can split pure water without the use of sacrificial reagents, while pure g-C3 N4 is virtually inactive for overall water splitting by photocatalysis [827]. In addition, the liquid state Z-scheme systems, including the g-C3 N4 (3 wt% Pt)/WO3 (0.5 wt% Pt)/NaI (5 mM) and g-C3 N4 (3 wt% Pt)/BiVO4 /FeCl2 (2 mM), have proven to achieve the overall water splitting [828]. However,

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

in these systems, the Pt and PtOx are still the noble metal. Thus, it is clear that developments of low-cost kinetic promoters for both H2 and O2 evolution are still the major bottleneck for achieving the practical H2 evolution or overall water splitting on g-C3 N4 . 5.2. Photocatalytic degradation of pollutants With rapid growth of population and accelerating industrialization, the environmental contamination has become a major threat to public health all over the world. Since the first report on heterogeneous photocatalytic remediation of environmental pollutants (CN− in water) on titania by Frank and Bard in 1977 [829], the heterogeneous photocatalysis has been widely used in widespread environmental purification such as air and water purification [309,830–839]. Furthermore, a variety of ways for increasing the photodecomposition efficiency of pollutants over g-C3 N4 -based semiconductors have been exploited [9,11,20,840], which have been summarized in Table 8. As observed in Table 8, constructing the g-C3 N4 -based semiconductor heterojunction and loading suitable O2 -reduction co-catalysts are the general two strategies to achieve the improved photocatalytic degradation activity, which will be discussed in this section. It is clear that the • OH radicals in g-C3 N4 -based photocatalysts mainly originated from multi-electron O2 reduction reactions driven by photo-generated electrons on the CB of g-C3 N4 , because the photo-generated holes exhibited much negative potentials (1.4 V) than that of • OH/OH− (+2.29 V, vs NHE, pH = 7), leading to the failure in driving the oxidation reaction of adsorbed OH− groups to • OH radicals [83,410]. Thus, for improving the photocatalytic activity of g-C3 N4 , more efforts have been devoted to strengthening the decisive O2 -reduction reactions. On the one hand, the photocatalytic degradation of gas-phase pollutants over g-C3 N4 -based photocatalysts has been extensively investigated, such as NOx [144,883,884], formaldehyde [523], acetaldehyde [539,885] and so forth. For example, Dong and coworkers deposited the monodispersed plasmonic Ag nanoparticles onto g-C3 N4 nanosheets to extend visible-light absorption, increase the generation of • O2− and enhance the charge separation, thus achieving the enhanced the photocatalytic activity of g-C3 N4 nanosheets towards oxidation of NO to final products [884]. Katsumata et al. demonstrated that WO3 /g-C3 N4 heterojunction photocatalysts showed a 1.4 times enhancement in photodegradation of acetaldehyde gas, as compared to pristine g-C3 N4 [539]. In another paper by Yu et al., a direct TiO2 /g-C3 N4 Z-scheme photocatalyst without an electron mediator (as shown in Fig. 38) exhibited a high photocatalytic performance in the oxidation decomposition of formaldehyde in air [523]. In these studies, the enhancement in photoactivity was primarily accredited to the improved transfer and separation of photogenerated charge carriers and promoted O2 reduction. A mechanically mixed g-C3 N4 and TiO2 sample with similar content did not remarkably improve the conversion of NOx , thus confirming that the interaction between g-C3 N4 and P25 is vital for the enhanced activity. EPR measurements once again indicated that • O2− was the main active species involved in the oxidation of NO under both visible and UV light irradiation [886]. In addition, it should be noted that the adsorption of gas-phase pollutants on the g-C3 N4 should be carefully optimized to achieve the ideal photocatalytic degradation efficiency. On the other hand, the g-C3 N4 -based photocatalysts have been widely used in the photocatalytic degradation of liquidphase pollutants, such as MB [319,506,734,843,887–893], MO [314,330,576,580,617,688,894–898], RhB [324,330,742,857,858,872,899–906] and so forth. As observed in Table 8, in pure g-C3 N4 -based visible-light systems, the two main reactive species, • O2− and h+ species, are generally involved in the degradation of pollutants. Interestingly, besides the afore-

105

mentioned two species, the presence of • OH radicals in Ag/g-C3 N4 systems further provides the direct evidence for its increased catalytic performance [489]. The further enhanced photocatalytic activity was observed over the Z-scheme Ag@AgBr/g-C3 N4 plasmonic photocatalyst. It is believed that the Z-scheme system retained the photoinduced electrons and hole with strong reduction and oxidation power in the CB of g-C3 N4 and VB of AgBr, respectively, thus achieving the high efficient photodegradation of MB. During the photocatalysis, the generated Br0 atoms and superoxide radicals with high oxidizing capabilities are favorable for the further enhancement in the degradation reaction [486]. Furthermore, it is also noted that the g-C3 N4 -based heterojunctions are widely used in the photocatalytic degradation, whereas, few systems were further loaded by co-catalysts. For those systems loaded by co-catalysts, the expensive Ag- and Pt-based co-catalysts are widely chosen. At this point, the atomically dispersed noblemetal co-catalysts with much stronger metal-g-C3 N4 interactions are considerably promising for the applications of photodegradation [664,694,907]. Therefore, it is expected that more and more earth-abundant co-catalysts and other modification strategies can be applied in the photocatalyctic degradation of liquid-phase pollutants. The homogeneous molecular systems [908] and metal-ion clusters (such as Fe(III) and Cu (II)) [909–916] with the maximum atom utilization efficiency are highly appealing as co-catalysts for applications in the photodegradation of pollutants over g-C3 N4 based photocatalysts. What’s more, the deep investigation on the degradation mechanism is also extremely expected. Similar to TiO2 -based semiconductors, particular attention should be focused on the investigations on the tunable photocatalytic selectivity of g-C3 N4 -based photocatalysts towards decomposition of pollutants with positive/negative charge carriers through precisely controlling the surface charge properties of g-C3 N4 [217–219]. In addition, the interesting photocatalytic degradation of antibiotics over gC3 N4 -based multi-junctions and deep mechanisms also deserve more attention in the near future [481,744,917–919]. 5.3. Photocatalytic carbon dioxide reduction From the viewpoint of development of sustainable energy, conversion of the rapidly increasing greenhouse gases to valuable energy-bearing compounds (such as CO, methane, and methanol) using solar energy would be one of the best solutions to overcome both serious problems of the global warming and shortages of fossil fuels. Therefore, since the first demonstration of photocatalytic CO2 reduction by Inoue and co-workers in 1979 [920], significant advancements have been made in exploiting efficient and feasible semiconductors for reduction of carbon dioxide with water during last two decades [16,18,921–925]. Among these semiconductor materials, the g-C3 N4 -based photocatalysts have attracted an increasing interesting in selective photocatalytic conversion of CO2 to hydrocarbons or chemicls, due to its excellent stability, sufficiently negative CB levels, innocuity and low price [17,19,658]. Significant progresses were summarized in Table 9, which will thoroughly discussed in this section. On the one hand, various strategies such as loading co-catalysts and nanocarbons, doping, constructing Z-scheme and heterojunction, have been widely used to enhance the photocatalytic activity for CO2 reduction [704,940,941]. For example, Yu et al. demonstrated that the Pt content showed a significant influence on both the activity and selectivity of g-C3 N4 for photocatalytic reduction of CO2 into CH4 , CH3 OH and HCHO (Fig. 49a) [691]. It is believed that the Pt cocatalyst not only facilitates the interfacial electron transfer from g-C3 N4 to Pt NPs (as shown in Fig. 49b), but also lower the overpotential for the CO2 reduction. More recently, Maeda and his coworkers fabricated the Ru complex decorated g-C3 N4 photocatalysts through the continuous stirring of a methanol solution

106

Table 8 Summary of the photocatalytic degradation of pollutants over g-C3 N4 -based photocatalysts. Mass (g) Light source

Targe pollutant/ concentration/volume

Degradation time/ efficiency

calcinating method

0.1

RhB/1 × 10−5 M/100 mL

40 min/99%

TiO2 –In2 O3 @g- nanoparticles/ C3 N4 nanoparticles- lamellar CaIn2 S4 /g-C3 N4 nanoplate/lamellar

solvothermal method

0.08

RhB/0.01 g L−1 /80 mL

60 min/100%

hydrothermal method

0.05

MO/0.01 g L−1 /100 mL

SiO2 /g-C3 N4

calcinating method

0.07

RhB/0.01 g L−1 /70 mL

Photocatalyst

Structure

Synthetic method

In2 O3 /g-C3 N4

particles/lamellar

core-shell nanosphere

Co-catal./optimized mass ratio

lamellar/particles

sol-gel method

0.1

TiO2 /g-C3 N4

core-cell

self-assembly method

0.05

TiO2 /g-C3 N4 TiO2 /g-C3 N4

melt-infiltrating-calcinating mesoporous method spheres/lamellar yolk-shell spheres/lamellar solvothermal method

g-C3 N4 /TiO2

lamellar/nanoparticles

g-C3 N4 /TiO2

lamellar/roundish particles sol-gel method

g-C3 N4 /TiO2

0.05 0.01

calcinating method

0.1 0.04

g-C3 N4 /F-TiO2 lamellar

hydrothermal-calcination method hydrothermal method

0.03

gC3 N4 /Ag/TiO2 K-Na/g-C3 N4

lamellarparticles/microspheres lamellar

photodeposition-Physical mixing method calcinating method

mg-C3 N4

mesopores

calcinating-dissolving method

0.05

g-C3 N4

lamellar

thermal condensation

0.02

mg-C3 N4

mesoporous

calcinating dissolving method

0.05

0.1 Ag/2 wt.%

0.03

K-Na co-doped

0.05

C60 /mg-C3 N4

particles/lamellar

calcinating method

C60 /0.03 wt.%

0.025

CDs/g-C3 N4

dots/lamellar

mixing-calcinating method

carbon dots/0.5 wt.%

0.05

C-dots/g-C3 N4 dots/lamellar

mixing-calcinating method

C-dots/0.25 wt.%

0.1

Pd/mpg-C3 N4

chemical reduction

Pd-doped/1.5 wt.%

particles/mesoporous

Pt/C3 N4

nanoparticles/nanotubes

hydrothermal method

Pt/2 wt.%

0.1

Au/Pt/g-C3 N4

particles/lamellar

photodeposition method

Au/2 wt.%, Pt/0.5 wt.%

0.1

Au/g-C3 N4 /␣Fe2 O3

particles/lamellar/ rhombohedral-like

hydrothermal and ultrasonication method

Au

0.05

−1

MB/0.01 g L

/100 mL

O2 − , • OH

[841] (2014)

•

OH

[797] (2015)

120 min/90%

•

O2 − , h+

[807] (2015)

150 min/94.3%

•

OH, h+

[842] (2015)

+

[843] (2016)

RhB/0.01 g L−1 /50 mL

140 min/100%

/80 mL

4.6

360 min/92% 80 min/82%

RhB/0.01 g L

Ref. (year)

•

RhB/10 ppm/200 mL

−1

Main active species

h 4.4

[844] (2015) [845] (2016) −

150 min/99.3% 33.5

•

O2 , h

[814] (2016)

OH, h+ , e−

[846] (2015)

+

ciprofloxacin//0.01 g L−1 / 100 mL RhB/0.01 g L−1 /40 mL

60 min/95%

•

150 min/100%

h+

[436] (2014)

acyclovir/10 ppm/100 mL

90 min/100%

1.57

h+

60 min/89%

3.74

[847] (2016) [655] (2014)

−1

MB/0.01 g L

/100 mL

MO/0.0135 g L−1 /30 mL 240 min/94% phenol/0.0166 g L−1 /30 mL 240 min/96% RhB/1 × 10−5 M/200 mL 120 min/90%

[848] (2014) 0.86

RhB/0.005 g L−1 /100 mL

20 min/95%

2,4,6-TCP/10−4 M/20 mL

180 min/100% 1.17

MO/0.01 g L−1 /100 mL

120 min/90%

−5

•

O2 − , • OH

[336] (2015)

[849] (2015) •

O2 − , • OOH

15.13

[850] (2013) [796] (2015)

MB/1 × 10 M/50 mL phenol/5 × 10−6 M/50 mL phenol/0.01 g L−1 /50 mL

300 min/100% 1.73 300 min/46% 0.15 200 min/100%

•

RhB/1 × 10−5 M/100 mL

60 min/84%

•

O2 −

[745] (2016)

BPA/0.02 g L−1 /50 mL

360 min/100% 1

•

O2 −

[729] (2013)

−1

PCP/0.02 g L

/100 mL

TC-HCl/0.02 g L−1 /100 mL RhB/0.004 g L−1 /250 mL

1.3

420 min/98% 180 min/93%

+

OH, h

[753] (2014) [851] (2016)

[852] (2015) 42.86

[481] (2015)

3.16

[853] (2015)

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

g-C3 N4 /TiO2

300 W halogen tungsten lamp, ␭ > ≥ 400 nm 350 W xenon arc lamp, ␭ > 420 nm 500 W tungsten lamp, ␭ > 400 nm 300 W xenon lamp, ␭ ≥ 400 nm 500 W xenon lamp, ␭ > 420 nm 500 W xenon lamp, UV–vis light 500 W xenon lamp, ␭ > 400 nm 350 W xenon arc lamp, ␭ > 420 nm 2 × 150 W tungsten lamp, ␭ > 420 nm 400 W halide lamp, ␭ > 400 nm 300 W xenon lamp, ␭ > 420 nm 50 W LED light, ␭ = 410 nm 300 W xenon lamp, ␭ > 420 nm 250 W high-pressure sodium lamp, 420 < ␭ < 800 nm 300 W xenon lamp, ␭ > 420 nm 300 W xenon lamp, ␭ > 420 nm 300 W xenon lamp, ␭ > 400 nm 500 W xenon lamp, ␭ > 420 nm 300 W xenon lamp, ␭ > 420 nm 3 W LED lamp, ␭ = 365 ± 5 nm 350 W xenon lamp, ␭ > 420 nm 300 W xenon lamp, ␭ > 420 nm 500 W xenon lamp, ␭ > 400 nm halogen lamp

Kapp [10−2 min−1 ]

Table 8 (Continued) Mass (g) Light source

Targe pollutant/ concentration/volume

Degradation time/ efficiency

physically mixing method

0.025 0.05

MB/1 × 10−5 M/50 mL MB/1 × 10−5 M/100 mL

150 min/100% 2.05 – 13.5

0.02 0.1

MB/1 × 10−6 M/30 mL RhB/2.5 × 10−5 M/250 mL

90 min/98.3% 270 min/99%

1.54

•

OH

particles/lamellar

hydrothermal method precipitation and refluxing method mixing-calcinating method

RhB/0.01 g L−1 /100 mL

120 min/97%

3.8

•

O2 − , h+

[854] (2015) [535] (2015) [855] (2015)

particles/lamellar

mixing-calcinating method

0.05

RhB/0.01 g L−1 /100 mL

60 min/95.5%

4.91

·O2 − , h+

[616] (2016)

lamellar/nanoparticles

one-pot method

0.05

RhB/0.01 g L−1 /50 mL

80 min/100% −

[856] (2015) [857] (2013)

Photocatalyst

Structure

Synthetic method

ZnO@mpgC3 N4

core-shell

ZnO/g-C3 N4 gC3 N4 /ZnO/AgCl Zn2 SnO4 /gC3 N4 V2 O5 /g-C3 N4

flowerlike/lamellar lamellar/particles

g-C3 N4 /V2 O5

Co-catal./optimized mass ratio

0.2

0.3

g-C3 N4 /SmVO4 lamellar/aggregated particles lamellar/nanoparticles g-C3 N4 /SnO2

mixing-calcinating method

0.3

mixing-calcinating method

0.1

SnNb2 O6 /gC3 N4 Ag/g-C3 N4 AgI@ g-C3 N4

nanosheets/lamellar

mixing-calcinating method

particles/lamellar

photodeposition method

core-shell

AgCl@pg-C3 N4 nanoparticles/lamellar Ag3 VO4 /g-C3 N4 particles/lamellar

modified precipitation method

0.2

particles/lamellar

Ag2 O/g-C3 N4

nanoparticles/lamellar

coprecipitation method refluxing method

nanoparticles/lamellar in situ ion exchange method Ag@AgCl/gC3 N4 AgVO3 /g-C3 N4 nanoribbons/ultrathin in situ hydrothermal method nanosheets Ag3 PO4 /g-C3 N4 spherical particles/lamellar chemisorptions method Ag/Fe3 O4 /gC3 N4 g-C3 N4 /CdS

0.1 0.1

g-C3 N4 /Ag2 O

core-shell

Ag/2 wt.%

precipitation method

deposition-precipitation method precipitation method

Ag@g-C3 N4

0.02

0.05

Ag/0.5 wt.%

0.02 0.1 0.025 0.025 0.05 0.02

particles/nanoclusters/lamellar hydrothermal-photodeposition Ag/3 wt.%, Fe3 O4 /9 wt.% 0.05 method lamellar/nanotube precipitation method 0.08

CdS QDs/lamellar QDs/npg-C3 N4 CdWO4 /g-C3 N4 nanorods/lamellar

mixing-calcinating method mixing-calcinating method

0.05

Cd0.2 Zn0.8 S/g- nanoparticles/lamellar C3 N4 BiPO4 /mg-C3 N4 nanorods/mesoporous

hydrothermal method

0.05

in situ method

0.1

0.1

300 W xenon lamp, 420 < ␭ < 800 nm 250 W xenon lamp, ␭ > 420 nm 200 W xenon lamp 350 W xenon lamp, ␭ > 420 nm 350 W xenon lamp, ␭ > 420 nm 300 W xenon lamp, ␭ > 420 nm 500 W tungsten light lamp, ␭ > 420 nm 300 W xenon lamp, 400 < ␭ < 680 nm 250 W halide lamp, ␭ > 420 nm 300 W xenon lamp, ␭ > 420 nm 400 W metal halide lamp, ␭ > 420 nm 300 W xenon lamp, ␭ ≥ 400 nm 300 W xenon lamp, ␭ ≥ 400 nm 500 W xenon arc lamp, ␭ > 420 nm 300 W xenon lamp, 400 < ␭ < 700 nm 500 W xenon lamp, ␭ > 420 nm 500 W xenon lamp, ␭ > 400 nm 300 W xenon lamp, ␭ > 420 nm 500 W xenon lamp, ␭ > 420 nm 500 W tungsten light lamp, ␭ > 400 nm 500 W xenon lamp, ␭ ≥ 400 nm 500 W xenon lamp, ␭ > 420 nm 300 W xenon arc lamp, ␭ > 420 nm

−1

RhB/0.01 g L

/300 mL

120 min/96.7% 4.34

RhB/0.01 g L−1 /300 mL

120 min/100% 3.45

MO/10 ppm/100 mL

180 min/73%

−1

Main active species

Ref. (year)

–

[533] (2014)

•

0.78

[859] (2014)

1.73

MO/0.01 g L−1 /100 mL PNP/0.01 g L−1 /100 mL RhB/0.01 g L−1 /100 mL

120 min/100% 120 min/100% 120 min/96% 2.52

•

atrazine/100 ppm/500 mL

60 min/99%

/80 mL

−1

RhB/0.005 g L

240 min/99%

/100 mL

MO/0.02 g L−1 /50 mL phenol/0.02 g L−1 /50 mL RhB/0.005 g L−1 /100 mL −5

MB/1 × 10

M/50 mL

RhB/0.01 g L−1 /100 mL

30 min/100%

BF/0.02 g L−1 /50 mL 90 min/100% Bisphenol/0.02 g L−1 /50 mL 90 min/85% MO/0.02 g L−1 /40 mL 60 min/100% −1

tetracycline/0.02 g L

/100 mL 90 min/88%

−

+

O2 , h

[640] (2016)

– [489] (2013) O2 − , h+ • O2 − , h+ , • OH [860] (2015) [861] (2015)

100 min/99.5% 5.56 30 min/90% 180 min/82% 40 min/100%

O2 , h

[858] (2013)

•

MB/0.01 g L

+

•

−

+ •

O2 , h , OH [862] (2015) [728] (2013)

10.53

•

O2 − , h+

[726] (2014)

+

[488] (2014)

O2 − , h+

[433] (2014)

1.4

h

19.54

•

5.52 2.08 4

•

2.18

•

•

OH, h+ OH, h+ h+

[863] (2015)

−

O2 , h

[865] (2016)

+

[864] (2014)

MB/0.025 g L−1 /200 mL

180 min/90.45%

•

OH, h+

[506] (2014)

RhB/0.01 g L−1 /100 mL

90 min/88.2%

•

O2 − , h+

[866] (2016)

240 min/46%

•

−5

RhB/1 × 10

M/50 mL

RhB/0.01 g L−1 /50 mL phenol/0.01 g L−1 /50 mL MO/0.02 g L−1 /100 mL

0.27

80 min/95.8% 180 min/76.1% 120 min/100% 0.77

+

OH, h

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

GdVO4 /g-C3 N4 small particles/big particles mixing-calcinating method

500 W xenon lamp, ␭ > 420 nm 500 W xenon lamp, ␭ = 254 nm mild UV light 50 W LED lamp

Kapp [10−2 min−1 ]

[867] (2015) [802] (2015) [868] (2014) 107

108

Table 8 (Continued) Photocatalyst

Structure

Synthetic method

BiOCl/C3 N4

flowerlike/amorphous

solvothermal method

g-C3 N4 /BiOBr BiOx Iy /g-C3 N4

lamellar/nanosheets

deposition-precipitation method square thin-plates/lamellar controlled hydrothermal

Mass (g) Light source

Targe pollutant/ concentration/volume

Degradation time/ efficiency

0.2

MO/0.01 g L−1 /500 mL

80 min/95%

0.02 0.04 0.01

lamellar/plates

mixing-calcinating method

0.05

lamellar/nanosheets

hydrothermal method

0.4

QDS-lamellar

in situ method

0.05

agglomeration

mixing-calcinating method

0.15

lamellar-hollow sphere

hydrothermal method

0.02

lamellar-flakelike

hydrothermal method

0.1

lamellar/particles

ball milling

2 g L−1

small particles/big particles mixing-calcinating method

0.3

CuTCPP/g-C3 N4 rodlike/lamellar

ethanol dispersion method

0.025

g-C3 N4 /CuOx lamellar/nanoparticles nanoparticles ␤-Fe2 O3 /gC3 N4 lamellar [WO4 ]2− /gC3 N4 nanorods/lamellar WO3 /g-C3 N4 H3 PW12 O40 /C3 Nparticles/tubular 4 NTs g-C3 N4 /MoO3 lamellar/broader particles

mixed solvent-thermal method in situ growth strategy method

0.01 0.2

lamellar/nanoparticles gC3 N4 /Bi2 MoO6 MoS2 /g-C3 N4 nanosheets/lamellar

calcinating method

0.05 0.2

mixing-calcinating method

0.1

solvothermal method

0.03

Ce/g-C3 N4

lamellar

CoO4 /g-C3 N4

lamellar

mixing and heating method

nanoparticles/lamellar

0.1

mixing-calcinating method hydrothermal method

impregnation and calcinating method calcinating method

NiO/g-C3 N4

[WO4 ]2— doped

calcinating method

0.04 Ce-doped

0.05

CoO4 -doped/0.2 wt.%

0.1 0.05

300 W xenon arc lamp, ␭ > 400 nm 400 W halogen lamp, ␭ > 400 nm 100 W xenon arc lamp 1000 W xenon lamp, ␭ > 420 nm 300 W xenon lamp, ␭ > 400 nm 300 W xenon lamp, ␭ ≥ 400 nm 500 W xenon lamp, ␭ > 420 nm 400 W metal halide lamp, ␭ ≥ 420 nm 400 W xenon lamp, ␭ > 400 nm 500 W xenon lamp, ␭ > 420 nm 400 W halogen-tungsten lamp, ␭ > 420 nm 500 W xenon lamp, ␭ > 420 nm 350 W xenon lamp 300 W xenon arc lamp, ␭ > 420 nm 300 W xenon lamp, ␭ > 420 nm 500 W tungsten lamp 300 W xenon lamp, ␭ > 420 nm 300 W xenon lamp, ␭ > 400 nm 50 W LED light, ␭ = 410 nm 300 W xenon lamp, ␭ > 400 nm 250 W high-pressure sodium lamp, 400 < ␭ < 800 nm 250 W xenon lamp, ␭ > 420 nm 500 W xenon lamp, ␭ > 420 nm

−1

Kapp [10−2 min−1 ]

Main active species

Ref. (year)

h+

[869] (2013)

+

[870] (2013)

RhB/0.06 g L /40 mL 2,4-DCP/0.01 g L−1 /40 mL CV/10 ppm/100 mL

100 min/98% 180 min/80% 36 h/99%

4.01 3.91 0.283

h • OH • O2 −

RhB/1 × 10−5 M/50 mL

240 min/56%

17

•

MO/0.01 g L−1 /200 mL

180 min/94.82%1.66

RhB/0.01 g L−1 /50 mL

30 min/100%

MO/0.01 g L−1 /50 mL

180 min/99.9% 3.66

RhB/0.01 g L−1 /50 mL

70 min/98%

16.8

O2 − , h+

[871] (2016) [872] (2014) [580] (2014)

•

O2 − , h+ , • OH [505] (2015) [576] (2011)

5.15

•

O2 −

[873] (2014)

MO/0.005 g L /100 mL 120 min/93% 2,4-DCP/0.02 g L−1 /100 mL 300 min/92% acid orange II/0.05 g L−1

– 0.856 4.1

•

O2

−

[874] (2013)

•

O2 − , h+

RhB/0.015 g L−1 /100 mL

1.41

•

O2 −

[875] (2016) [876] (2015)

0.04

•

O2 − , h+

[877] (2015)

O2 − , h+ O2 − , • OH

[878] (2016) [587] (2016)

O2 − , • OH

[879] (2015)

−1

240 min/90%

phenol/5 ppm/50 mL MO/0.02 g L−1 /50 mL MO/0.01 g L−1 /160 mL

70 min/83.3% 240 min/86%

2.05 0.88

•

RhB/10 ppm/100 mL

90 min/87%

2.2

•

−1

RhB/0.005 g L /100 mL MO/0.01 g L−1 /100 mL DEP/0.01 g L−1 /100 mL MB/0.01 g L−1 /100 mL

90 min/91% 2.61 240 min/99% 1440 min/85% 180 min/93% 1.47

MB/0.01 g L−1 /30 mL

40 min/90%

−1

RhB/0.01 g L /50 mL MO/0.01 g L−1 /50 mL RhB/10 ppm/200 mL

20 min/96% 180 min/95% 120 min/90%

MO/0.01 g L−1 /100 mL

120 min/100%

−1

MB/0.005 g L

/100 mL

40 min/100%

•

[544] (2015) [880] (2014) [881] (2013)

6.88 15.2 1.61 1.55

+

h h+ • O2 −

•

5.1

O2 −

[604] (2015) [633] (2016) [882] (2015)

[688] (2014) [734] (2014)

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

gC3 N4 /Bi2 O2 CO3 gC3 N4 /Bi2 WO6 Bi2 WO6 QDS/g-C3 N4 gC3 N4 /Bi2 WO6 gC3 N4 /Bi2 MoO6 gC3 N4 /Bi2 WO6 gC3 N4 /Bi4 Ti3 O12 HSbO3 /g-C3 N4

Co-catal./optimized mass ratio

Table 9 Summary of the photocatalytic CO2 reduction over g-C3 N4 -based photocatalysts. Material

Morphologies and microstructures

Gas-solid systems for CO2 photoreduction nanoparticles/nanosheets Ag3 PO4 /g-C3 N4 g-C3 N4 /Bi2 WO6 m-CeO2 /g-C3 N4 g-C3 N4 /KNbO3 SnO2-x /g-C3 N4

g-C3 N4 /NaNbO3

Bi2 WO6 nanoflakes/thin layer g-C3 N4 nanosheets mesoporous g-C3 N4 nanosheets/layered structure KNbO3 SnO2-x nanoparticles/g-C3N4 sheets are

Synthesis method

Cocatalyst

direct thermolysis in-situ deposition in situ hydrothermal approach hard-template route ultrasonic dispersion followed by heat treatment method directly calcining simple calcination of g-C3 N4 and Sn6 O4 (OH) 4 calcination

Light source

Mass [g]/systems/Volume [mL]

Selective products (activity) [␮M h−1 g−1 ]

Ref. (year)

300 W Xe lamp, ␭ ≥ 420 nm 300 W Xe lamp, ␭ ≥ 420 nm 300 W of Xenon-arc lamp 300 W Xe lamp, ␭≥ 420 nm 500 W Xe lamp

/

CO(44) CH3 OH(8.5) CH4 (2) C2 H5 OH(1.1) CO(5.19)

[608] (2015)

CO(10.16) CH4 (13.88)

[927] (2016)

CH4 (2.5)

[693] (2015)

0.02/CO2 and H2 O vapor

CO(19.2) CH4(1.4) CH3 OH(3.1)

[928] (2015)

0.05/CO2 and H2 O vapor/230 mL 0.1/CO2 and H2 O vapor/780 mL 0.1/CO2 and H2 O vapor/2700 mL / 0.006/CO2 and H2 O vapor/100 mL

CH4 (6.4)

[929] (2014)

CO(12.25)

[930] (2014)

CO(111) CH4 (15.4)

[931] (2016)

CH3 CHO(8) CH4 (0.85)

[932] (2015) [933] (2016)

CO2 and H2 O vapor

CH4 (1.302)

[692] (2015)

0.1 g/CO2 and H2 O vapor/200 mL 0.01/CO2 and H2 O vapor/132 mL 0.1/CO2 and H2 O vapor/200 mL CO2 and H2 O vapor

CH3 CHO(0.37)

[199] (2015)

CO(39) CH3OH(10) CH4(4) C2H5OH(1.5) CH3 OH(0.6)

[536] (2015)

CH4 (1.393)

[934] (2015)

CO(3.44) CH4 (0.2)

[614] (2016)

CH4(0.3) HCHO(0.075) CH3OH(0.24)

[691] (2014)

in situ synthesized by thermal treatment simple pyrolysis method

/

300 W xenon arc lamp ␭ > 420 nm 300 W xenon arc lamp

/

300 W Hg lamp

C3 N4 –MCF B4 C/C3 N4

sponge-like structure B4 C particles/g-C3 N4 nanosheets

hard-template synthesis solvent evaporation method

/ 0.8%wt Pt

Pt/g-C3 N4

nanoparticles/lamellar

2 wt% Pt

S-doped g-C3 N4

layered structures contain many irregular pore sizes highly mesoporous

chemical reduction process in ethylene glycol simply calcinating thiourea

/ 300 W Xenon short arc lamp 405 nm < ␭ < 723 nm 15 W energy-saving daylight bulb 300-W simulated solar Xe arc lamp 500 W Xe lamp

g-C3 N4 -N-TiO2 Mo-doped g-C3 N4

ZnO/g-C3 N4 g-C3 N4 /ZnO RGO/g-C3 N4 BiOI/g-C3 N4 g-C3 N4 –Pt

AgX/g-C3 N4 (X = Cl and Br)

ZnO microcrystals/g-C3 N4 nanosheets sandwich-Like Hybrid Nanosheets BiOI particles/g-C3N4 nanosheets two-dimensional lamellar structure and numerous randomly organized nanosheets irregular spheres of AgX/g-C3N4 nanosheets

AgCl/C3 N4

AgCl nanoparticles/C3 N4 nanosheet

GO-g-C3 N4

sandwich-like

RGO/p-C3 N4

sandwich-like

g-C3 N4 /ZnO

a direct Z-scheme mechanism

1 wt% Pt

a simple impregnation method a one-step facile calcination method electrostatic self-assembly construction of 2D/2D in situ syntheized directly heating and Pt was deposited on g-C3 N4

sonication-assisted deposition-precipitation approach in situ deposition–precipitation approach. a facile one-pot impregnation–thermal reduction strategy a novel combined ultrasonic dispersion and electrostatic self-assembly strategy a one-step facile calcination method

15 wt% RGO

1 wt% Pt

300 W simulated solar Xe arc lamp 15 W energy-saving Daylight bulb 300 W xenon arc lamp (␭ > 400 nm). 300 W simulated solar Xe arc lamp

0.1/CO2 and H2 O vapor/180 mL 0.1/CO2 and H2 O vapor/200 mL

[926] (2015)

[220] (2015)

500 W Xenon arc lamp, (␭ > 400 nm)

0.1/CO2 and H2 O vapor

30%AgBr/g-C3 N4 CH4 (1.092)

[935] (2016)

15 W energy-saving daylight lamp

CO2 and H2 O vapor

CH4 (0.95)

[936] (2016)

15 wt% GO

15 W energy-saving daylight bulb

CO2 and H2 O vapor

CH4 (5.87)

[702] (2015)

15 wt% rGO

15 W energy-saving daylight lamp

0.1 g/CO2 and H2 O vapor

CH4 (1.393)

[160] (2015)

300 W simulated solar Xe arc lamp

0.1 g/CO2 and H2 O vapor/200 mL

CH3 OH(0.6)

[601] (2015)

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

NaNbO3 nanowires/g-C3 N4 nanosheets TiO2 nanoparticles/g-C3 N4 nanosheets worm-like mesostructures

0.1/CO2 and H2 O vapor/500 mL 0.05/CO2 and H2 O vapor/500 mL 0.1/CO2 and H2 O vapor

109

[939] (2016) 250 W lamp, ␭ = 365 nm nanospheres/flaky morphology CdS/g-C3 N4

polycondensation and hydrothermal methods

/

/ a facile one-pot chemical condensation of urea dense and stacked particles and sheets CNU–BAX

300 W Xe lamp, ␭ > 420 nm

0.03/CO2 saturated solution of CoCl2 , 2,2-bipyridine, triethanolamine 0.02/CO2 saturated methanol solution/20 mL

HCOOH (1352.07)

[938] (2015)

[620] (2014)

Ag/g-C3 N4 + WO3 : CH3 OH(24.05) Au/g-C3 N4 + WO3 CH3 OH(34.02) CO(469) light-emitting diode (LED), ␭ = 435 nm 0.5%wt Au, 0.5%wt Ag WO3 / g-C3 N4 (P-CW)

planetary mill photodeposition method

300 W Xe arc lamp /

two-dimensional lamellar and porous structure with anomalous shape highly dispersed WO3 particles/g-C3 N4 particles amine-functionalized g-C3 N4

/ ten layers CNNS/the UiO-66 microspheres

2D hydroxyl-rich C3 N4 nanosheets UiO-66/10%CNNS

thin nanosheets

thermal condensation of melamine facile electrostatic self-assembly method

/

simple thermal condensation amine functionalization

0.003/CO2 and H2 O

[227] (2015) CH4 (0.34) CH3 OH(0.28)

[708] (2015) CO(9.9)

[937] (2015) CH4 (0.75)

80 mL CO2 saturated water solution 5 mL CO2 saturated of solution (MeCN/TEOA 4:1)/330 mL 0.1/CO2 saturated water solution/200 mL

HCOOH(7.8) 0.005/CO2 and MeCN/TEOA mixture (4:1, v/v) 4 mL

400 W high pressure Hg lamp with a NaNO2 solution filter 300 W Xe lamp, ␭ > 420 nm 300 W xenon arclamp, 400 nm< ␭ < 800 nm RuP adsorption Suspension systems for CO2 photoreduction RuP/g-C3 N4 mesoporous structure

Selective products (activity) [␮M h−1 g−1 ] Mass [g]/systems/Volume [mL] Light source Cocatalyst Synthesis method Morphologies and microstructures Material

Table 9 (Continued)

[697] (2016)

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

Ref. (year)

110

containing two materials at room temperature overnight [695]. The resulting heterogeneous photocatalyst systems could achieve the highest apparent quantum yield of 5.7% at 400 nm for the photocatalytic reduction of CO2 into formic acid under visible-light irradiation (as shown in Fig. 50) [695]. Surprisingly, the ternary hybrid of plasmonic Ag nanoparticles and g-C3 N4 /binuclear Ru(II) complex could achieve a very high turnover number of > 33,000 with a high selectivity of 87–99% for HCOOH production, due to the combination effects of plasmonic Ag and Z-Scheme charge transfer (as shown in Fig. 51) [700]. These are the best values that have been reported for heterogeneous photocatalysts for CO2 reduction under visible-light irradiation to date. The present study clearly highlighted the great potential of complex molecular co-catalyst on carbon nitride in photocatalytic CO2 reduction under visible light. Thus, it is expected that the multi coupling of complex molecular co-catalyst, g-C3 N4 and other photosensitizers may provide exciting opportunities for promising CO2 photoreduction over gC3 N4 -based photocatalysts. In addition, it is also noted from Table 9 that there are few earth-abundant co-catalysts reported to accelerate the CO2 photoreduction over g-C3 N4 -based photocatalysts, which should be urgently developed in the near future. At this point, the nano-carbons, such as RGO and CNTs, are highly expected to coupling with the g-C3 N4 to obtain highly efficient metal-free g-C3 N4 -based photocatalysts for CO2 photoreduction [934]. Besides co-catalysts, doping and nanostructured heterojunction were also extensively used to enhance the visible light absorption and photocatalytic CO2 reduction activity of g-C3 N4 -based photocatalysts. Wang et al. fabricated sulfur-doped g-C3 N4 photocatalysts by employing thiourea as the sulfur precursor for the reduction of CO2 to CH3 OH [199]. The DFT studies confirmed that the electrons can be easily excited from the VB to the impurity state, and then to the CB of sulfur-doped g-C3 N4 owing to the impurity sulfur doping (as shown in Fig. 52a), which induced additional electrons, resulting in the spin polarization. As the band gap was narrowed from 2.7 to 2.63 eV, the light absorption was broadened in the sulfur-doped g-C3 N4 , generating more electrons and holes under the light irradiation. Thus, the CH3 OH yield (1.12 ␮mol g−1 ) was 1.5 times higher than that the unmodified gC3 N4 (0.81 ␮mol g−1 ) (as shown in Fig. 52b). In another example, Yu et al. constructed a binary g-C3 N4 /ZnO photocatalyst with an intimate contact interface via a one-step facile calcination method [220]. The results showed that the as-prepared g-C3 N4 /ZnO photocatalytic system exhibited enhanced photocatalytic activity for CO 2 reduction by a factor of 2.3 compared with pure g-C3 N4 (as shown in Fig. 53a). The better performances of the g-C3 N4 /ZnO binary composite photocatalytic system could be well explained by the direct Z-scheme mechanism rather than the conventional heterojunction-type mechanism (as shown in Fig. 53b and c), which was achieved due to the highly efficient ZnO-to-g-C3 N4 electron transfer occurring at the intimate contact interface between the gC3 N4 phase and ZnO phase. This work highlighted that the rational construction of direct Z-scheme g-C3 N4 -based photocatalytic system without an electron mediator should be promising strategy for the applications in the photocatalytic CO2 reduction. On the other hand, the product selectivity of photocatalytic CO2 reduction should be also a major consideration in designing semiconductor photocatalysts [942]. For example, Liu and coworkers obtained the g-C3 N4 nanosheets by the thermal delamination of bulk g-C3 N4 in air. It was shown that g-C3 N4 nanosheets with a band gap of 2.97 eV yielded the major product of CH4 , whereas bulk gC3 N4 with a smaller band gap of 2.77 eV formed the main product of CH3 CHO (Fig. 54a) [409]. This elucidated that the nanosheets had a larger band gap by 0.2 eV, leading to a lower VB edge by 80 meV and a higher CB edge by 120 meV. Therefore, the nanosheets provided a larger thermodynamic diving force for the hole and electron transfer by means of a greater difference in energy level between redox

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

111

Fig. 49. (a) Photoconversion of CO2 into CH4 , CH3 OH and HCHO over PtX -loaded g-C3 N4 (x, the weight percentage ratios of Pt against g-C3 N4 were 0, 0.25, 0.5, 0.75, 1.0 and 2.0 wt%); (b) Charge separation mechanisms in the Pt/g-C3 N4 systems [691].

to confirm the obtained prodcuts stemmed from the photofixation of CO2 in order to exclude the possibility of photodissociation of the organic impurities or even carbon-containing catalysts. 5.4. Photocatalytic selective organic transformations

Fig. 50. Scheme illustration for CO2 reduction using a Ru complex/C3 N4 hybrid photocatalyst.

Fig. 51. Scheme illustration for Z-Scheme CO2 reduction using a ternary Hybrid of Ag/g-C3 N4 /Binuclear Ru(II) Complex [700].

potentials of the reactants and band edges (Fig. 54b). This indirectly led to a larger proportion of long-lived charge carriers for the nanosheets in contrast to the bulk. As a consequence, the formation of CH4 was more favorable due to rapid transfer of photoexcited electrons in the nanosheets to the intermediate species. However, it is worth mentioning that the current apparent quantum efficiency is still low for the commercial applications. Thus, there is still ample room to further improve the CO2 photoreduction in g-C3 N4 -based photocatalytic system. Furthermore, the exact reaction mechanism for the CO2 photoreduction should be paid more attention. In this regard, various strategies to enhance the CO2 adsorption of porous absorbents could be employed to improve the adsorption and activation of CO2 on g-C3 N4 -based photocatalysts [943–945]. Especially, the selectivity of CO2 photoreduction should be deeply investigated for each system. In fact, it is strongly suggested that all products from the CO2 conversion requires should be measured, in gas and liquid phase for suspension systems. To well understand the photocatalytic reaction steps, DFT can be used to identify the activation state of CO2 . In addition, the isotopic labeling analysis using 13CO2 as the reactant is nacessary

Recently, the robust metal-free g-C3 N4 -based photocatalysts have been shown to have great potential for selective organic transformation under mild conditions, including oxidation of aromatic compounds [395,507,946–956], photo catalytic esterification of benzaldehyde and alcohol [957], oxidative cleavage of the carbon–carbon bond of ␣-hydroxy ketones [958] and allylic oxidation [959]. For example, Wang and coworkers demonstrated that direct oxidation of benzene to phenol with H2 O2 catalyzed by porous Fe-g-C3 N4 could be achieved, in both the presence and absence of visible light irradiation [950]. By taking advantage of the photocatalytic functions of g-C3 N4 , the yield of the phenol synthesis can be markedly improved. Furthermore, the same research group demonstrated that the metal-free graphene sheet/g-C3 N4 nanocomposite could achieve the selective photocatalytic oxidation of cyclohexane to cyclohexanone through the superoxide radical anion (• O2 − ) induced from the activation of O2 (as shown in Fig. 55), highlighting the key roles of O2 -reduction reaction in the photocatalytic selective organic transformations [244]. In another report, Zhang et al. [956] revealed that a 38% conversion of benzene to phenol with 97% selectivity could be achieved using FeCl3 -modified mesoporous carbon nitride as a visible-light photocatalyst to activate H2 O2 . Li et al. [960] developed a Mott–Schottky photocatalyst consisting of mesoporous carbon nitride with Pd nanoparticles. The efficient electron transfer from the g-C3 N4 to the Pd resulted in a high photocatalytic activity and selectivity for the room-temperature C C bond formation by coupling aryl halides with different coupling partners. More recently, Yin and coworkers demonstrated that an acid-base bifunctional P-doped g-C3 N4 photocatalysts could achieve the cycloaddition reactions, due to the synergetic effect of acid (halide anions) and basic sites for ring opening of epoxide and adsorption/activation of CO2 [325]. In future, it is expected that various kinds of multifunctional g-C3 N4 composite photocatalysts could be widely used in the selective photocatalytic organic transformations, which are hardly proceed by traditionary thermal catalysis. Also, the deep mechanism investigation is highly desired. 5.5. Photocatalytic disinfection As a nontoxic, efficient, and stable method, photocatalytic disinfection has been shown to be superior in comparison with traditional water disinfection methods, including chlorination, ozone, and ultraviolet (UV), have some disadvantages [659]. Commonly, the toxic metals in the efficient metal-based photocatalysts for bacterial inactivation is unfavorable for “green” water disinfection

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J. Wen et al. / Applied Surface Science 391 (2017) 72–123

Fig. 52. (a) Schematic of band structure of pure g-C3 N4 (left) and S-doped g-C3 N4 (right); (b) Comparison of photocatalytic CH3 OH production over S-doped g-C3 N4 (TCN) and un-doped g-C3 N4 (MCN) at 3 h under UV–vis light irradiation [199].

Fig. 53. Comparison of photocatalytic CH3 OH production rates of cm-ZnO, pure ZnO, G10, and pure g-C3 N4 . Schematic illustration of two different mechanisms for charge carrier separation: (b) conventional heterojunction-type and (c) direct Z-scheme mechanisms [220].

Fig. 54. (a) Schematic illustration of the photoreduction CO2 to CH3 CHO and CH4 on bulk g-C3 N4 and g-C3 N4 nanosheets. (b) Band structures of g-C3 N4 nanosheets (left) and bulk g-C3 N4 (right) and the redox potentials of the reactions [409].

Fig. 55. Schematic illustration of the selective oxidation of secondary C H bonds of cyclohexane through the superoxide radical anion (• O2 − ) [244].

[660]. At this point, the robust and non-toxic metal-free g-C3 N4 seems to be more promising in water disinfection. However, limited studies have concentrated on the visible-light-induced photocat-

alytic inactivation of bacteria over g-C3 N4 [450,659,660,961]. For example, Huang et al. demonstrated that metal-free robust g-C3 N4 photocatalyst exhibit antibacterial activity for the inactivation of Escherichia coli K-12 (E. coli) under visible light irradiation [961]. Especially, a novel heterojunction related to g-C3 N4 was synthesized via cowrapping the RGO and g-C3 N4 (CN) sheets on ␣-sulfur (␣-S8 ) by Wang and his coworkers. The results indicated that the visible-light-driven photocatalytic activities of this system for bacterial inactivation was significantly improved, which will also change with the shells arrangement evolution of RGO and CN. The enhanced activities can be ascribed to the electrons or holes migration in the system as shown in Fig. 56 [660]. In addition, Zhao et al. indicated that the atomic single layer g-C3 N4 with the thickness of 0.5 nm exhibited performance of photocatalytic disinfection for inactivation of Escherichia coli, due to low charge transfer resistance and efficient charge separation [450]. More recently, An and coworkers demonstrated that the g-C3 N4 /TiO2 hybrid photocatalyst, comprised of micron-sized TiO2 spheres wrapped with lamellar g-C3 N4 , exhibited significantly enhanced photocatalytic

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

113

Fig. 56. Schematic illustration of the visible-light-driven photocatalytic bacterial inactivation mechanisms of (a) CNRGOS8 ; (b) RGOCNS8 in aerobic condition; (c) CNRGOS8 ; (d) RGOCNS8 in anaerobic condition [660].

activity for the inactivation of Escherichia coli K-12, due to improved light absorption and the effective charge separation [659]. 6. Conclusions and future prospects In summary, this review highlights the advantages, versatile properties, design strategies and potential application of robust g-C3 N4 -based composite photocatalysts. Obviously, g-C3 N4 has proven to be one of the most promising candidates suitable for designing and fabricating advanced composite photocatalysts for various applications. Therefore, there is little doubt that the explosive growth of g-C3 N4 -based composite photocatalysts will continue to accelerate in the near future. To date, although considerable progress has been achieved in the recent years, there are still many challenges to rationally fabricate the highly efficient g-C3 N4 -based photocatalysts towards various applications and deeply understand the underlying enhancement mechanism of composite photocatalysts by g-C3 N4 . There are still many open issues and opportunities for further research effort. Accordingly, more studies are also needed to make full use of the outstanding structural and electronic properties of g-C3 N4 in the composite photocatalysts. On the one hand, versatile properties of g-C3 N4 -based photocatalysts are still needed to be explored carefully. Since the highly effective and stable g-C3 N4 -based photocatalysts with narrowed band gaps are difficult to obtain, the design and development of conjugated narrow-band polymer might provide alternative ideas for boosting the advancements of photocatalysis based on the organic semiconductors [962–968]. Furthermore, the accurate control of surface defects and facile scale preparation methods of g-C3 N4 nanosheets are highly desired. The advanced electrocatalysts and photoelectrocatalysts based g-C3 N4 should be exploited as an important research community for extending the applications of g-C3 N4 -based photocatalysts. Among various design strategies, the dimensionality tuning, pore texture tailoring, heterojunction construction (especially for Z-scheme construction), co-catalyst

and nanocarbon loading seem to be more promising in developing practical g-C3 N4 -based photocatalysts. Typically, Z-scheme construction is more interesting and promising than the traditional heterojunction. At this point, more investigations should be paid to this strategy. Absolutely, the developments of earth-abundant co-catalysts are still a hard task in these photocatalytic fields. The magical nanocarbons will play the irreplaceable roles in constructing highly efficient g-C3 N4 -based photocatalysts for all the time. In addition, the applications of g-C3 N4 -based photocatalysts are mainly focused on the H2 evolution and degradation of pollutants. However, the photocatalytic CO2 reduction over g-C3 N4 -based photocatalysts become more and more attractive in the past three years. The basic nature of the g-C3 N4 surface determines its bright future in the fields of CO2 reduction. Furthermore, work on the O2 evolution from the other half-reaction of H2 O splitting should gain more attention in the near future, which involves in both the water splitting and CO2 reduction. Additionally, the exact reaction mechanism, particularly the CO2 reduction using g-C3 N4 based photocatalysts, still remains doubtful and unresolved to date. The deep studying of reaction pathways is crucial for revealing the photocatalytic enhancement fundamental and further rationally design the highly efficient g-C3 N4 -based photocatalysts in the future. Furthermore, some key issues that account for the high photocatalytic activity, i.e. optical absorption, electronic band structure, and charge transfer dynamics, should be exhaustively investigated to gain theoretical insights by means of both computational (first-principles DFT) and experimental simulations. In terms of experimental work, reactant adsorption sites, charge transfer dynamics, and molecular orbitals should also be deeply researched. The joint efforts by researchers from various fields and countries must bring one and one exciting time for g-C3 N4 -based photocatalysts.

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Acknowledgments Li would like to thank Industry and Research Collaborative Innovation Major Projects of Guangzhou (201508020098), NSFC (20906034) and the State Key Laboratory of Advanced Technology for Material Synthesis and Processing (Wuhan University of Technology) (2015-KF-7) for their support. X. Chen would like to thank the College of Arts and Sciences, University of Missouri—Kansas City and University of Missouri Research Board for their financial support.

References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

[14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53]

A. Fujishima, K. Honda, Nature 238 (1972) 37–38. B. Kraeutler, A.J. Bard, J. Am. Chem. Soc. 100 (1978) 4317–4318. A.J. Bard, J. Photochem. 10 (1979) 59–75. A.J. Bard, Science 207 (1980) 139–144. A.J. Bard, J. Phys. Chem. 86 (1982) 172–177. A. Bard, M. Fox, Acc. Chem. Res. 28 (1995) 141–145. X. Li, J. Yu, J. Low, Y. Fang, J. Xiao, X. Chen, J. Mater. Chem. A 3 (2015) 2485–2534. X. Chen, S. Shen, L. Guo, S.S. Mao, Chem. Rev. 110 (2010) 6503–6570. C. Chen, W. Ma, J. Zhao, Chem. Soc. Rev. 39 (2010) 4206–4219. A. Kudo, Y. Miseki, Chem. Soc. Rev. 38 (2009) 253–278. M. Hoffmann, S. Martin, W. Choi, D. Bahnemann, Chem. Rev. 95 (1995) 69–96. H. Zhang, G. Chen, D.W. Bahnemann, J. Mater. Chem. 19 (2009) 5089–5121. M. Pelaez, N.T. Nolan, S.C. Pillai, M.K. Seery, P. Falaras, A.G. Kontos, P.S.M. Dunlop, J.W.J. Hamilton, J.A. Byrne, K. O’Shea, M.H. Entezari, D.D. Dionysiou, Appl. Catal. B: Environ. 125 (2012) 331–349. C.C. Wang, J.R. Li, X.L. Lv, Y.Q. Zhang, G.S. Guo, Energy Environ. Sci. 7 (2014) 2831–2867. M.N. Chong, B. Jin, C.W.K. Chow, C. Saint, Water. Res. 44 (2010) 2997–3027. X. Li, J. Wen, J. Low, Y. Fang, J. Yu, Sci. China Mater. 57 (2014) 70–100. J. Low, J. Yu, W. Ho, J. Phys. Chem. Lett. 6 (2015) 4244–4251. W. Tu, Y. Zhou, Z. Zou, Adv. Mater. 26 (2014) 4607–4626. M. Marszewski, S. Cao, J. Yu, M. Jaroniec, Mater. Horiz. 2 (2015) 261–278. H. Park, Y. Park, W. Kim, W. Choi, J. Photochem. Photobiol. C 15 (2013) 1–20. S. Malato, P. Fernandez-Ibanez, M.I. Maldonado, J. Blanco, W. Gernjak, Catal. Today 147 (2009) 1–59. Y. Shiraishi, T. Hirai, J. Photochem. Photobiol. C 9 (2008) 157–170. H. Kisch, Angew. Chem. Int. Ed. 52 (2013) 812–847. X. Lang, X. Chen, J. Zhao, Chem. Soc. Rev. 43 (2014) 473–486. J. Wen, X. Li, W. Liu, Y. Fang, J. Xie, Y. Xu, Chin. J. Catal. 36 (2015) 2049–2070. Q. Li, X. Li, S. Wageh, A.A. Al-Ghamdi, J. Yu, Adv. Energy Mater. 5 (2015) 1500010. S. Cao, J. Low, J. Yu, M. Jaroniec, Adv. Mater. 27 (2015) 2150–2176. S. Cao, J. Yu, J. Phys. Chem. Lett. 5 (2014) 2101–2107. A. Linsebigler, G. Lu, J. Yates Jr., Chem. Rev. 95 (1995) 735–758. H. Tong, S.X. Ouyang, Y.P. Bi, N. Umezawa, M. Oshikiri, J.H. Ye, Adv. Mater. 24 (2012) 229–251. A. Fujishima, T. Rao, D. Tryk, J. Photochem. Photobiol. C 1 (2000) 1–21. K. Nakata, A. Fujishima, J. Photochem. Photobiol. C 13 (2012) 169–189. X. Chen, S.S. Mao, Chem. Rev. 107 (2007) 2891–2959. R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, Y. Taga, Science 293 (2001) 269–271. X.B. Chen, L. Liu, P.Y. Yu, S.S. Mao, Science 331 (2011) 746–750. S.U.M. Khan, M. Al-Shahry, W.B. Ingler, Science 297 (2002) 2243–2245. X. Chen, C. Li, M. Gratzel, R. Kostecki, S.S. Mao, Chem. Soc. Rev. 41 (2012) 7909–7937. L. Liu, X. Chen, Chem. Rev. 114 (2014) 9890–9918. Y. Ma, X. Wang, Y. Jia, X. Chen, H. Han, C. Li, Chem. Rev. 114 (2014) 9987–10043. X. Chen, L. Liu, F. Huang, Chem. Soc. Rev. 44 (2015) 1861–1885. A.J. Bard, J. Am. Chem. Soc. 132 (2010) 7559–7567. J. Xu, G. Wang, J. Fan, B. Liu, S. Cao, J. Yu, J. Power Sources 274 (2015) 77–84. J. Xu, T.J.K. Brenner, L. Chabanne, D. Neher, M. Antonietti, M. Shalom, J. Am. Chem. Soc. 136 (2014) 13486–13489. X. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J. Carlsson, K. Domen, M. Antonietti, Nat. Mater. 8 (2009) 76–80. G. Dong, Y. Zhang, Q. Pan, J. Qiu, J. Photochem. Photobiol. C 20 (2014) 33–50. X.-H. Li, M. Antonietti, Chem. Soc. Rev. 42 (2013) 6593–6604. Y. Wang, X. Wang, M. Antonietti, Angew. Chem. Int. Ed. 51 (2012) 68–89. Y. Zheng, J. Liu, J. Liang, M. Jaroniec, S.Z. Qiao, Energy Environ. Sci. 5 (2012) 6717–6731. J. Zhu, P. Xiao, H. Li, S.A.C. Carabineiro, ACS Appl. Mater. Interfaces 6 (2014) 16449–16465. S. Ye, R. Wang, M.-Z. Wu, Y.-P. Yuan, Appl. Surf. Sci. 358 (2015) 15–27. S. Yin, J. Han, T. Zhou, R. Xu, Catal. Sci. Technol. 5 (2015) 5048–5061. J. Zhang, Y. Chen, X. Wang, Energy Environ. Sci. 8 (2015) 3092–3108. Z. Zhao, Y. Sun, F. Dong, Nanoscale 7 (2015) 15–37.

[54] Y. Zheng, L. Lin, B. Wang, X. Wang, Angew. Chem. Int. Ed. 54 (2015) 12868–12884. [55] J. Liu, H. Wang, M. Antonietti, Chem. Soc. Rev. 45 (2016) 2308–2326. [56] X. Dong, F. Cheng, J. Mater. Chem. A 3 (2015) 23642–23652. [57] Y. Gong, M. Li, H. Li, Y. Wang, Green Chem. 17 (2015) 715–736. [58] N. Zhang, M.-Q. Yang, S. Liu, Y. Sun, Y.-J. Xu, Chem. Rev. 115 (2015) 10307–10377. [59] W.-J. Ong, L.-L. Tan, Y.H. Ng, S.-T. Yong, S.-P. Chai, Chem. Rev. 116 (2016) 7159–7329. [60] X. Chen, Q. Liu, Q. Wu, P. Du, J. Zhu, S. Dai, S. Yang, Adv. Funct. Mater. 26 (2016) 1719–1728. [61] L. Zhou, Y. Xu, W. Yu, X. Guo, S. Yu, J. Zhang, C. Li, J. Mater. Chem. A 4 (2016) 8000–8004. [62] I. Yuta, K. Toshiaki, T. Hidekazu, S. Masaya, K. Shinsuke, T. Kenichi, I. Kunio, Jpn. J. Appl. Phys. 47 (2008) 7842. [63] R. Reyes, C. Legnani, P.M. Ribeiro Pinto, M. Cremona, P.J.G. de Araújo, C.A. Achete, Appl. Phys. Lett. 82 (2003) 4017–4019. [64] J. Liang, Y. Zheng, J. Chen, J. Liu, D. Hulicova-Jurcakova, M. Jaroniec, S.Z. Qiao, Angew. Chem. Int. Ed. 51 (2012) 3892–3896. [65] T.Y. Ma, S. Dai, M. Jaroniec, S.Z. Qiao, Angew. Chem. Int. Ed. 53 (2014) 7281–7285. [66] S. Yang, X. Feng, X. Wang, K. Muellen, Angew. Chem. Int. Ed. 50 (2011) 5339–5343. [67] X. Fu, X. Hu, Z. Yan, K. Lei, F. Li, F. Cheng, J. Chen, Chem. Commun. 52 (2016) 1725–1728. [68] L. Zhao, L. Wang, P. Yu, D. Zhao, C. Tian, H. Feng, J. Ma, H. Fu, Chem. Commun. 51 (2015) 12399–12402. [69] Y. Zheng, Y. Jiao, J. Chen, J. Liu, J. Liang, A. Du, W. Zhang, Z. Zhu, S.C. Smith, M. Jaroniec, G.Q. Lu, S.Z. Qiao, J. Am. Chem. Soc. 133 (2011) 20116–20119. [70] J. Yi, K. Liao, C. Zhang, T. Zhang, F. Li, H. Zhou, ACS Appl. Mater. Interfaces 7 (2015) 10823–10827. [71] Y. Liu, N. Li, S. Wu, K. Liao, K. Zhu, J. Yi, H. Zhou, Energy Environ. Sci. 8 (2015) 2664–2667. [72] Y. Hou, J.Y. Li, Z.H. Wen, S.M. Cui, C. Yuan, J.H. Chen, Nano Energy 8 (2014) 157–164. [73] Y. Fu, J. Zhu, C. Hu, X. Wu, X. Wang, Nanoscale 6 (2014) 12555–12564. [74] Y. Wu, T. Wang, Y. Zhang, S. Xin, X. He, D. Zhang, J. Shui, Sci. Rep. U. K. 6 (2016) 24314. [75] W.-B. Luo, S.-L. Chou, J.-Z. Wang, Y.-C. Zhai, H.-K. Liu, Small 11 (2015) 2817–2824. [76] Q. Shang, Z. Zhou, Y. Shen, Y. Zhang, Y. Li, S. Liu, Y. Zhang, ACS Appl. Mater. Interfaces 7 (2015) 23672–23678. [77] J. Zhuang, W. Lai, M. Xu, Q. Zhou, D. Tang, ACS Appl. Mater. Interfaces 7 (2015) 8330–8338. [78] C. Cheng, Y. Huang, X. Tian, B. Zheng, Y. Li, H. Yuan, D. Xiao, S. Xie, M.M.F. Choi, Anal. Chem. 84 (2012) 4754–4759. [79] M. Rong, L. Lin, X. Song, Y. Wang, Y. Zhong, J. Yan, Y. Feng, X. Zeng, X. Chen, Biosens. Bioelectron. 68 (2015) 210–217. [80] H. Huang, R. Chen, J. Ma, L. Yan, Y. Zhao, Y. Wang, W. Zhang, J. Fan, X. Chen, Chem. Commun. 50 (2014) 15415–15418. [81] M.K. Kundu, M. Sadhukhan, S. Barman, J. Mater. Chem. B 3 (2015) 1289–1300. [82] T.Y. Ma, Y. Tang, S. Dai, S.Z. Qiao, Small 10 (2014) 2382–2389. [83] X. Li, J. Yu, M. Jaroniec, Chem. Soc. Rev. 45 (2016) 2603–2636. [84] J. Zhang, X. Chen, K. Takanabe, K. Maeda, K. Domen, J.D. Epping, X. Fu, M. Antonietti, X. Wang, Angew. Chem. Int. Ed. 49 (2010) 441–444. [85] X. Li, J. Yu, Heterogeneous Photocatalysis, in: J.C. Colmenares, Y.-J. Xu (Eds.), Springer, Berlin Heidelberg, 2016, pp. 175–210. [86] X. Li, J. Low, J. Yu, Photocatalysis: Applications, in: G.L.P.D. Dionysios Dionysiou, Jinhua Ye, Jenny Schneider, Detlef Bahnemann (Eds.), The Royal Society of Chemistry, 2016, pp. 255–302. [87] P.M. Wood, Biochem. J. 253 (1988) 287–289. [88] J. Yang, D. Wang, H. Han, C. Li, Accounts. Chem. Res. 46 (2013) 1900–1909. [89] S. Chen, S. Shen, G. Liu, Y. Qi, F. Zhang, C. Li, Angew. Chem. Int. Ed. 54 (2015) 3047–3051. [90] M.D. Ward, J.R. White, A.J. Bard, J. Am. Chem. Soc. 105 (1983) 27–31. [91] P.E. de Jongh, D. Vanmaekelbergh, J.J. Kelly, Chem. Commun. (1999) 1069–1070. [92] M.F. Finlayson, B.L. Wheeler, N. Kakuta, K.H. Park, A.J. Bard, A. Campion, M.A. Fox, S.E. Webber, J.M. White, J. Phys. Chem. 89 (1985) 5676–5681. [93] S.C. Yan, S.B. Lv, Z.S. Li, Z.G. Zou, Dalton Trans. 39 (2010) 1488–1491. [94] W.-J. Chun, A. Ishikawa, H. Fujisawa, T. Takata, J.N. Kondo, M. Hara, M. Kawai, Y. Matsumoto, K. Domen, J. Phys. Chem. B 107 (2003) 1798–1803. [95] Cai Long, H. Kisch, J. Phys. Chem. C 112 (2008) 548–554. [96] K.L. Hardee, A.J. Bard, J. Electrochem. Soc. 124 (1977) 215–224. [97] Z.G. Yi, J.H. Ye, N. Kikugawa, T. Kako, S.X. Ouyang, H. Stuart-Williams, H. Yang, J.Y. Cao, W.J. Luo, Z.S. Li, Y. Liu, R.L. Withers, Nat. Mater. 9 (2010) 559–564. [98] A.J. Bard, R. Parsons, J. Jordan, Standard Potentials in Aqueous Solution, CRC Press, 1985. [99] Y. Gong, M. Li, Y. Wang, ChemSusChem 8 (2015) 931–946. [100] X. Zhang, X. Xie, H. Wang, J. Zhang, B. Pan, Y. Xie, J. Am. Chem. Soc. 135 (2013) 18–21. [101] A. Thomas, A. Fischer, F. Goettmann, M. Antonietti, J.-O. Muller, R. Schlogl, J.M. Carlsson, J. Mater. Chem. 18 (2008) 4893–4908.

J. Wen et al. / Applied Surface Science 391 (2017) 72–123 [102] M.J. Bojdys, J.-O. Mueller, M. Antonietti, A. Thomas, Chem. Eur. J. 14 (2008) 8177–8182. [103] K. Schwinghammer, M.B. Mesch, V. Duppel, C. Ziegler, J. Senker, B.V. Lotsch, J. Am. Chem. Soc. 136 (2014) 1730–1733. [104] W.-r. Lee, Y.-S. Jun, J. Park, G.D. Stucky, J. Mater. Chem. A 3 (2015) 24232–24236. [105] G. Algara-Siller, N. Severin, S.Y. Chong, T. Bjorkman, R.G. Palgrave, A. Laybourn, M. Antonietti, Y.Z. Khimyak, A.V. Krasheninnikov, J.P. Rabe, U. Kaiser, A.I. Cooper, A. Thomas, M.J. Bojdys, Angew. Chem. Int. Ed. 53 (2014) 7450–7455. [106] H. Gao, S. Yan, J. Wang, Y.A. Huang, P. Wang, Z. Li, Z. Zou, Phys. Chem. Chem. Phys. 15 (2013) 18077–18084. [107] Y.-S. Jun, E.Z. Lee, X. Wang, W.H. Hong, G.D. Stucky, A. Thomas, Adv. Funct. Mater. 23 (2013) 3661–3667. [108] M.K. Bhunia, K. Yamauchi, K. Takanabe, Angew. Chem. Int. Ed. 53 (2014) 11001–11005. [109] M. Shalom, S. Gimenez, F. Schipper, I. Herraiz-Cardona, J. Bisquert, M. Antonietti, Angew. Chem. Int. Ed. 53 (2014) 3654–3658. [110] M. Shalom, S. Inal, C. Fettkenhauer, D. Neher, M. Antonietti, J. Am. Chem. Soc. 135 (2013) 7118–7121. [111] Y. Ishida, L. Chabanne, M. Antonietti, M. Shalom, Langmuir 30 (2014) 447–451. [112] Y.-P. Yuan, L.-S. Yin, S.-W. Cao, L.-N. Gu, G.-S. Xu, P. Du, H. Chai, Y.-S. Liao, C. Xue, Green Chem. 16 (2014) 4663–4668. [113] L. Lin, P. Ye, C. Cao, Q. Jin, G.-S. Xu, Y.-H. Shen, Y.-P. Yuan, J. Mater. Chem. A 3 (2015) 10205–10208. [114] Y. Wang, J. Zhang, X. Wang, M. Antonietti, H. Li, Angew. Chem. Int. Ed. 49 (2010) 3356–3359. [115] L. Xu, J. Xia, H. Xu, S. Yin, K. Wang, L. Huang, L. Wang, H. Li, J. Power Sources 245 (2014) 866–874. [116] J. Di, J. Xia, S. Yin, H. Xu, M. He, H. Li, L. Xu, Y. Jiang, RSC Adv. 3 (2013) 19624–19631. [117] J. Di, J. Xia, S. Yin, H. Xu, L. Xu, Y. Xu, M. He, H. Li, J. Mater. Chem. A 2 (2014) 5340–5351. [118] J. Zhang, J. Sun, K. Maeda, K. Domen, P. Liu, M. Antonietti, X. Fu, X. Wang, Energy Environ. Sci. 4 (2011) 675–678. [119] F. Su, S.C. Mathew, G. Lipner, X. Fu, M. Antonietti, S. Blechert, X. Wang, J. Am. Chem. Soc. 132 (2010) 16299–16301. [120] Y. Hou, A.B. Laursen, J. Zhang, G. Zhang, Y. Zhu, X. Wang, S. Dahl, I. Chorkendorff, Angew. Chem. Int. Ed. 52 (2013) 3621–3625. [121] J. Zhang, M. Zhang, R.-Q. Sun, X. Wang, Angew. Chem. Int. Ed. 51 (2012) 10145–10149. [122] X. Chen, Y.-S. Jun, K. Takanabe, K. Maeda, K. Domen, X. Fu, M. Antonietti, X. Wang, Chem. Mater. 21 (2009) 4093–4095. [123] X.C. Wang, K. Maeda, X.F. Chen, K. Takanabe, K. Domen, Y.D. Hou, X.Z. Fu, M. Antonietti, J. Am. Chem. Soc. 131 (2009) 1680–1681. [124] J. Ran, J. Zhang, J. Yu, M. Jaroniec, S.Z. Qiao, Chem. Soc. Rev. 43 (2014) 7787–7812. [125] J. Hong, Y. Wang, Y. Wang, W. Zhang, R. Xu, ChemSusChem 6 (2013) 2263–2268. [126] J. Yu, S. Wang, B. Cheng, Z. Lin, F. Huang, Catal. Sci. Technol. 3 (2013) 1782–1789. [127] D.M. Teter, R.J. Hemley, Science 271 (1996) 53–55. [128] G. Zhang, M. Zhang, X. Ye, X. Qiu, S. Lin, X. Wang, Adv. Mater. 26 (2014) 805–809. [129] M. Zhang, X. Wang, Energy Environ. Sci. 7 (2014) 1902–1906. [130] J. Zhang, G. Zhang, X. Chen, S. Lin, L. Moehlmann, G. Dolega, G. Lipner, M. Antonietti, S. Blechert, X. Wang, Angew. Chem. Int. Ed. 51 (2012) 3183–3187. [131] Y. Xu, S.-P. Gao, Int. J. Hydrogen Energy 37 (2012) 11072–11080. [132] A.Y. Liu, M.L. Cohen, Science 245 (1989) 841–842. [133] K. Maeda, X. Wang, Y. Nishihara, D. Lu, M. Antonietti, K. Domen, J. Phys. Chem. C 113 (2009) 4940–4947. [134] B. Jürgens, E. Irran, J. Senker, P. Kroll, H. Müller, W. Schnick, J. Am. Chem. Soc. 125 (2003) 10288–10300. [135] J. Sehnert, K. Baerwinkel, J. Senker, J. Phys. Chem. B 111 (2007) 10671–10680. [136] E. Kroke, M. Schwarz, E. Horath-Bordon, P. Kroll, B. Noll, A.D. Norman, New J. Chem. 26 (2002) 508–512. [137] M.J. McAllister, J.-L. Li, D.H. Adamson, H.C. Schniepp, A.A. Abdala, J. Liu, M. Herrera-Alonso, D.L. Milius, R. Car, R.K. Prud’homme, I.A. Aksay, Chem. Mater. 19 (2007) 4396–4404. [138] J. Gao, Y. Zhou, Z. Li, S. Yan, N. Wang, Z. Zou, Nanoscale 4 (2012) 3687–3692. [139] E. Haque, J.W. Jun, S.N. Talapaneni, A. Vinu, S.H. Jhung, J. Mater. Chem. 20 (2010) 10801–10803. [140] S.Y. Kim, J. Oh, S. Park, Y. Shim, S. Park, Chem. Eur. J. 22 (2016) 5142–5145. [141] J. Liu, W. Li, L. Duan, X. Li, L. Ji, Z. Geng, K. Huang, L. Lu, L. Zhou, Z. Liu, W. Chen, L. Liu, S. Feng, Y. Zhang, Nano Lett. 15 (2015) 5137–5142. [142] J. Oh, R.J. Yoo, S.Y. Kim, Y.J. Lee, D.W. Kim, S. Park, Chem. Eur. J. 21 (2015) 6241–6246. [143] L. Ming, H. Yue, L. Xu, F. Chen, J. Mater. Chem. A 2 (2014) 19145–19149. [144] G. Dong, Z. Ai, L. Zhang, RSC Adv. 4 (2014) 5553–5560. [145] H.-J. Li, B.-W. Sun, L. Sui, D.-J. Qian, M. Chen, Phys. Chem. Chem. Phys. 17 (2015) 3309–3315. [146] B. Zhu, P. Xia, W. Ho, J. Yu, Appl. Surf. Sci. 344 (2015) 188–195. [147] Y. Chen, J. Li, Z. Hong, B. Shen, B. Lin, B. Gao, Phys. Chem. Chem. Phys. 16 (2014) 8106–8113.

115

[148] F. Dong, L. Wu, Y. Sun, M. Fu, Z. Wu, S.C. Lee, J. Mater. Chem. 21 (2011) 15171–15174. [149] S.C. Yan, Z.S. Li, Z.G. Zou, Langmuir 25 (2009) 10397–10401. [150] J. Zhang, M. Zhang, G. Zhang, X. Wang, ACS Catal. 2 (2012) 940–948. [151] Q. Xiang, J. Yu, M. Jaroniec, J. Phys. Chem. C 115 (2011) 7355–7363. [152] P. Wang, Z. Wang, L. Jia, Z. Xiao, Phys. Chem. Chem. Phys. 11 (2009) 2730–2740. [153] F. Dong, Z. Wang, Y. Sun, W.-K. Ho, H. Zhang, J. Colloid Interface Sci. 401 (2013) 70–79. [154] J. Jiang, O.-y. Lei, L. Zhu, A. Zheng, J. Zou, X. Yi, H. Tang, Carbon 80 (2014) 213–221. [155] G. Bi, J. Wen, X. Li, W. Liu, J. Xie, Y. Fang, W. Zhang, RSC Adv. 6 (2016) 31497–31506. [156] J. Wen, X. Li, H. Li, S. Ma, K. He, Y. Xu, Y. Fang, W. Liu, Q. Gao, Appl. Surf. Sci. 358 (2015) 204–212. [157] T. Yan, H. Chen, X. Wang, F. Jiang, RSC Adv. 3 (2013) 22480–22489. [158] Y.J. Zhang, A. Thomas, M. Antonietti, X.C. Wang, J. Am. Chem. Soc. 131 (2009) 50. [159] Y. Zhong, Z. Wang, J. Feng, S. Yan, H. Zhang, Z. Li, Z. Zou, Appl. Surf. Sci. 295 (2014) 253–259. [160] W.-J. Ong, L.-L. Tan, S.-P. Chai, S.-T. Yong, A.R. Mohamed, Nano Energy 13 (2015) 757–770. [161] C. Ye, J.-X. Li, Z.-J. Li, X.-B. Li, X.-B. Fan, L.-P. Zhang, B. Chen, C.-H. Tung, L.-Z. Wu, ACS Catal. 5 (2015) 6973–6979. [162] Y. Xu, M. Xie, S. Huang, H. Xu, H. Ji, J. Xia, Y. Li, H. Li, RSC Adv. 5 (2015) 26281–26290. [163] X.-j. Wang, X. Tian, F.-t. Li, Y.-p. Li, J. Zhao, Y.-j. Hao, Y. Liu, Int. J. Hydrogen Energy 41 (2016) 3888–3895. [164] T. Sano, S. Tsutsui, K. Koike, T. Hirakawa, Y. Teramoto, N. Negishi, K. Takeuchi, J. Mater. Chem. A 1 (2013) 6489–6496. [165] H. Nie, M. Ou, Q. Zhong, S. Zhang, L. Yu, J. Hazard. Mater. 300 (2015) 598–606. [166] X.L. Wang, W.Q. Fang, H.F. Wang, H. Zhang, H. Zhao, Y. Yao, H.G. Yang, J. Mater. Chem. A 1 (2013) 14089–14096. [167] E.G. Gillan, Chem. Mater. 12 (2000) 3906–3912. [168] D.R. Miller, J. Wang, E.G. Gillan, J. Mater. Chem. 12 (2002) 2463–2469. [169] Y. Li, J. Zhang, Q. Wang, Y. Jin, D. Huang, Q. Cui, G. Zou, J. Phys. Chem. B 114 (2010) 9429–9434. [170] Y. Cui, J. Zhang, G. Zhang, J. Huang, P. Liu, M. Antonietti, X. Wang, J. Mater. Chem. 21 (2011) 13032–13039. [171] T. Komatsu, T. Nakamura, J. Mater. Chem. 11 (2001) 474–478. [172] Y. Yuan, L. Zhang, J. Xing, M.I.B. Utama, X. Lu, K. Du, Y. Li, X. Hu, S. Wang, A. Genc, R. Dunin-Borkowski, J. Arbiol, Q. Xiong, Nanoscale 7 (2015) 12343–12350. [173] L. Shi, L. Liang, F. Wang, J. Ma, J. Sun, Catal. Sci. Technol. 4 (2014) 3235–3243. [174] A. Fischer, M. Antonietti, A. Thomas, Adv. Mater. 19 (2007) 264–267. [175] Q. Gao, S. Wang, Y. Ma, Y. Tang, C. Giordano, M. Antonietti, Angew. Chem. Int. Ed. 51 (2012) 961–965. [176] X.-H. Li, M. Antonietti, Angew. Chem. Int. Ed. 52 (2013) 4572–4576. [177] A. Fischer, J.O. Mueller, M. Antonietti, A. Thomas, ACS Nano 2 (2008) 2489–2496. [178] J. Xu, L. Zhang, R. Shi, Y. Zhu, J. Mater. Chem. A 1 (2013) 14766–14772. [179] J. Zhang, M. Zhang, L. Lin, X. Wang, Angew. Chem. Int. Ed. 54 (2015) 6297–6301. [180] Z. Zhou, J. Wang, J. Yu, Y. Shen, Y. Li, A. Liu, S. Liu, Y. Zhang, J. Am. Chem. Soc. 137 (2015) 2179–2182. [181] Y. Zhang, M. Antonietti, Chem. Asian. J. 5 (2010) 1307–1311. [182] H. Jindui, X. Xiaoyang, W. Yongsheng, X. Rong, J. Mater. Chem. 22 (2012) 15006–15012. [183] S. Guo, Z. Deng, M. Li, B. Jiang, C. Tian, Q. Pan, H. Fu, Angew. Chem. Int. Ed. 55 (2016) 1830–1834. [184] J. Li, B. Shen, Z. Hong, B. Lin, B. Gao, Y. Chen, Chem. Commun. 48 (2012) 12017–12019. [185] G. Dong, K. Zhao, L. Zhang, Chem. Commun. 48 (2012) 6178–6180. [186] Q. Han, C. Hu, F. Zhao, Z. Zhang, N. Chen, L. Qu, J. Mater. Chem. A 3 (2015) 4612–4619. [187] X. Wang, S. Blechert, M. Antonietti, ACS Catal. 2 (2012) 1596–1606. [188] M.K. Bhunia, S. Melissen, M.R. Parida, P. Sarawade, J.-M. Basset, D.H. Anjum, O.F. Mohammed, P. Sautet, T. Le Bahers, K. Takanabe, Chem. Mater. 27 (2015) 8237–8247. [189] M. Lan, G. Fan, L. Yang, F. Li, RSC Adv. 5 (2015) 5725–5734. [190] T. Dittrich, S. Fiechter, A. Thomas, Appl. Phys. Lett. 99 (2011) 084105. [191] P. Wu, J. Wang, J. Zhao, L. Guo, F.E. Osterloh, J. Mater. Chem. A 2 (2014) 20338–20344. [192] L. Bi, D. Xu, L. Zhang, Y. Lin, D. Wang, T. Xie, Phys. Chem. Chem. Phys. 17 (2015) 29899–29905. [193] C. Han, Y. Lu, J. Zhang, L. Ge, Y. Li, C. Chen, Y. Xin, L. Wu, S. Fang, J. Mater. Chem. A 3 (2015) 23274–23282. [194] C. Han, L. Wu, L. Ge, Y. Li, Z. Zhao, Carbon 92 (2015) 31–40. [195] F. Dong, P. Li, J. Zhong, X. Liu, Y. Zhang, W. Cen, H. Huang, Appl. Catal. A-Gen. 510 (2016) 161–170. [196] T. Tyborski, C. Merschjann, S. Orthmann, F. Yang, M.C. Lux-Steiner, S.-N. Th, J. Phys.: Condens. Matter 24 (2012) 162201. [197] J. Yuan, J. Wen, Y. Zhong, X. Li, Y. Fang, S. Zhang, W. Liu, J. Mater. Chem. A 3 (2015) 18244–18255. [198] Y. Zhong, J. Yuan, J. Wen, X. Li, Y. Xu, W. Liu, S. Zhang, Y. Fang, Dalton Trans. 44 (2015) 18260–18269.

116

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

[199] K. Wang, Q. Li, B. Liu, B. Cheng, W. Ho, J. Yu, Appl. Catal. B: Environ. 176–177 (2015) 44–52. [200] J. Jiang, J. Yu, S. Cao, J. Colloid Interface Sci. 461 (2016) 56–63. [201] L. Yuan, C. Han, M. Pagliaro, Y.J. Xu, J. Phys. Chem. C 120 (2016) 265–273. [202] Y. Zhang, Q. Pan, G. Chai, M. Liang, G. Dong, Q. Zhang, J. Qiu, Sci. Rep. U. K. 3 (2013) 1943. [203] Z. Zhou, Y. Shen, Y. Li, A. Liu, S. Liu, Y. Zhang, ACS Nano 9 (2015) 12480–12487. [204] N.Y. Liu, J. Liu, W.Q. Kong, H. Li, H. Huang, Y. Liu, Z.H. Kang, J. Mater. Chem. B 2 (2014) 5768–5774. [205] Y.-C. Lu, J. Chen, A.-J. Wang, N. Bao, J.-J. Feng, W. Wang, L. Shao, J. Mater. Chem. C 3 (2015) 73–78. [206] L. Chen, D. Huang, S. Ren, T. Dong, Y. Chi, G. Chen, Nanoscale 5 (2013) 225–230. [207] Y. Feng, Q. Wang, J. Lei, H. Ju, Biosens. Bioelectron. 73 (2015) 7–12. [208] S. Zhang, J. Li, M. Zeng, J. Xu, X. Wang, W. Hu, Nanoscale 6 (2014) 4157–4162. [209] Z. Yang, M. Xu, Y. Liu, F. He, F. Gao, Y. Su, H. Wei, Y. Zhang, Nanoscale 6 (2014) 1890–1895. [210] X. Qin, W. Lu, A.M. Asiri, A.O. Al-Youbi, X. Sun, Catal. Sci. Technol. 3 (2013) 1027–1035. [211] X. Li, Z. Li, Q. Xia, H. Xi, Z. Zhao, Adsorpt. Sci. Technol. 24 (2006) 363–374. [212] X. Li, Z. Li, Q. Xia, H. Xi, Appl. Therm. Eng. 27 (2007) 869–876. [213] X. Li, Z. Li, J. Chem. Eng. Data 55 (2010) 5729–5732. [214] X. Li, H. Li, S. Huo, Z. Li, Kinet. Catal. 51 (2010) 754–761. [215] X. Li, X. Chen, Z. Li, J. Chem. Eng. Data 55 (2010) 3164–3169. [216] R.K. Upadhyay, N. Soin, S.S. Roy, RSC Adv. 4 (2014) 3823–3851. [217] S. Liu, J. Yu, M. Jaroniec, J. Am. Chem. Soc. 132 (2010) 11914–11916. [218] Q. Xiang, J. Yu, M. Jaroniec, Chem. Commun. 47 (2011) 4532–4534. [219] S. Liu, C. Liu, W. Wang, B. Cheng, J. Yu, Nanoscale 4 (2012) 3193–3200. [220] F. Wu, W. Liu, J. Qiu, J. Li, W. Zhou, Y. Fang, S. Zhang, X. Li, Appl. Surf. Sci. 358 (2015) 425–435. [221] C. Shen, C. Chen, T. Wen, Z. Zhao, X. Wang, A. Xu, J. Colloid Interface Sci. 456 (2015) 7–14. [222] R.G. Pearson, J. Am. Chem. Soc. 85 (1963) 3533–3539. [223] R.G. Parr, R.G. Pearson, J. Am. Chem. Soc. 105 (1983) 7512–7516. [224] M. Yu, Z. Li, Q. Xia, H. Xi, S. Wang, Chem. Eng. J. 132 (2007) 233–239. [225] A. Alfarra, E. Frackowiak, F. Béguin, Appl. Surf. Sci. 228 (2004) 84–92. [226] Y. Oh, V.-D. Le, U.N. Maiti, J.O. Hwang, W.J. Park, J. Lim, K.E. Lee, Y.-S. Bae, Y.-H. Kim, S.O. Kim, ACS Nano 9 (2015) 9148–9157. [227] Q. Huang, J. Yu, S. Cao, C. Cui, B. Cheng, Appl. Surf. Sci. 358 (2015) 350–355. [228] L. Jia, H. Wang, D. Dhawale, C. Anand, M.A. Wahab, Q. Ji, K. Ariga, A. Vinu, Chem. Commun. 50 (2014) 5976–5979. [229] Q. Li, J. Yang, D. Feng, Z. Wu, Q. Wu, S.S. Park, C.-S. Ha, D. Zhao, Nano Res. 3 (2010) 632–642. [230] X. Xu, C. Song, J.M. Andrésen, B.G. Miller, A.W. Scaroni, Microporous Mesoporous Mater. 62 (2003) 29–45. [231] X. Xu, C. Song, J.M. Andresen, B.G. Miller, A.W. Scaroni, Energy Fuel 16 (2002) 1463–1469. [232] X. Ma, X. Wang, C. Song, J. Am. Chem. Soc. 131 (2009) 5777–5783. [233] Z. Zhang, M. Xu, H. Wang, Z. Li, Chem. Eng. J. 160 (2010) 571–577. [234] Z. Zhang, Y. Zhao, Q. Gong, Z. Li, J. Li, Chem. Commun. 49 (2013) 653–661. [235] Z. Zhang, Z. Li, J. Li, Langmuir 28 (2012) 12122–12133. [236] Z. Zhang, S. Huang, S. Xian, H. Xi, Z. Li, Energy Fuel 25 (2011) 835–842. [237] S. Liu, J. Xia, J. Yu, ACS Appl. Mater. Interfaces 7 (2015) 8166–8175. [238] S.M. Lyth, Y. Nabae, S. Moriya, S. Kuroki, M.-a. Kakimoto, J.-i. Ozaki, S. Miyata, J. Phys. Chem. C 113 (2009) 20148–20151. [239] Y. Zheng, Y. Jiao, Y. Zhu, L.H. Li, Y. Han, Y. Chen, A. Du, M. Jaroniec, S.Z. Qiao, Nat. Commun. 5 (2014) 3783. [240] J.J. Li, Y.M. Zhang, X.H. Zhang, J.C. Han, Y. Wang, L. Gu, Z.H. Zhang, X.J. Wang, J.K. Jian, P. Xu, B. Song, ACS Appl. Mater. Interfaces 7 (2015) 19626–19634. [241] M.K. Kundu, T. Bhowmik, S. Barman, J. Mater. Chem. A 3 (2015) 23120–23135. [242] Y. Xu, M. Kraft, R. Xu, Chem. Soc. Rev. 45 (2016) 3039–3052. [243] H. Tada, Q. Jin, A. Iwaszuk, M. Nolan, J. Phys. Chem. C 118 (2014) 12077–12086. [244] X.-H. Li, J.-S. Chen, X. Wang, J. Sun, M. Antonietti, J. Am. Chem. Soc. 133 (2011) 8074–8077. [245] Z. Ding, X. Chen, M. Antonietti, X. Wang, ChemSusChem 4 (2011) 274–281. [246] L. Nie, P. Zhou, J. Yu, M. Jaroniec, J. Mol. Catal. A: Chem. 390 (2014) 7–13. [247] C. Yu, J. Chen, F. Cao, X. Li, Q. Fan, J.C. Yu, L. Wei, Chin. J. Catal. 34 (2013) 385–390. [248] L. Zhang, Y. Li, Q. Zhang, H. Wang, Appl. Surf. Sci. 319 (2014) 21–28. [249] J. Yu, L. Yue, S. Liu, B. Huang, X. Zhang, J. Colloid Interface Sci. 334 (2009) 58–64. [250] C. Yu, G. Li, S. Kumar, H. Kawasaki, R. Jin, J. Phys. Chem. Lett. 4 (2013) 2847–2852. [251] J. Yu, J. Xiong, B. Cheng, S. Liu, Appl. Catal. B: Environ. 60 (2005) 211–221. [252] B. Cheng, Y. Le, J. Yu, J. Hazard. Mater. 177 (2010) 971–977. [253] J. Liang, Y. Jiao, M. Jaroniec, S.Z. Qiao, Angew. Chem. Int. Ed. 51 (2012) 11496–11500. [254] Y. Zheng, Y. Jiao, L. Ge, M. Jaroniec, S.Z. Qiao, Angew. Chem. Int. Ed. 52 (2013) 3110–3116. [255] J. Liang, X. Du, C. Gibson, X.W. Du, S.Z. Qiao, Adv. Mater. 25 (2013) 6226–6231. [256] J. Duan, S. Chen, S. Dai, S.Z. Qiao, Adv. Funct. Mater. 24 (2014) 2072–2078.

[257] T. Yang, J. Liu, R. Zhou, Z.G. Chen, H. Xu, S. Qiao, M. Monteiro, J. Mater. Chem. A 2 (2014) 18139–18146. [258] S. Chen, J. Bi, Y. Zhao, L. Yang, C. Zhang, Y. Ma, Q. Wu, X. Wang, Z. Hu, Adv. Mater. 24 (2012) 5593–5597. [259] Q. Mi, D. Chen, J. Hu, Z. Huang, J. Li, Chin. J. Catal. 34 (2013) 2138–2145. [260] K. Gong, F. Du, Z. Xia, M. Durstock, L. Dai, Science 323 (2009) 760–764. [261] L. Qu, Y. Liu, J.-B. Baek, L. Dai, ACS Nano 4 (2010) 1321–1326. [262] J. Tian, Q. Liu, A.M. Asiri, K.A. Alamry, X. Sun, ChemSusChem 7 (2014) 2125–2130. [263] J. Tian, R. Ning, Q. Liu, A.M. Asiri, A.O. Al-Youbi, X. Sun, ACS Appl. Mater. Interfaces 6 (2014) 1011–1017. [264] S.S. Shinde, A. Sami, J.-H. Lee, ChemCatChem 7 (2015) 3873–3880. [265] Y. Qin, J. Li, J. Yuan, Y. Kong, Y. Tao, F. Lin, S. Li, J. Power Sources 272 (2014) 696–702. [266] Q. Liu, J. Zhang, Langmuir 29 (2013) 3821–3828. [267] J. Jin, X. Fu, Q. Liu, J. Zhang, J. Mater. Chem. A 1 (2013) 10538–10545. [268] E. Negro, S. Polizzi, K. Vezzu, L. Toniolo, G. Cavinato, V. Di Noto, Int. J. Hydrogen Energy 39 (2014) 2828–2841. [269] E. Negro, K. Vezzu, F. Bertasi, P. Schiavuta, L. Toniolo, S. Polizzi, V. Di Noto, ChemElectroChem 1 (2014) 1359–1369. [270] M.G. Walter, E.L. Warren, J.R. McKone, S.W. Boettcher, Q. Mi, E.A. Santori, N.S. Lewis, Chem. Rev. 110 (2010) 6446–6473. [271] F. Wen, C. Li, Acc. Chem. Res. 46 (2013) 2355–2364. [272] Y. Xu, R. Xu, Appl. Surf. Sci. 351 (2015) 779–793. [273] M.S. Faber, S. Jin, Energy Environ. Sci. 7 (2014) 3519–3542. [274] P. Du, R. Eisenberg, Energy Environ. Sci. 5 (2012) 6012–6021. [275] X. Zou, Y. Zhang, Chem. Soc. Rev. 44 (2015) 5148–5180. [276] A. Du, S. Sanvito, Z. Li, D. Wang, Y. Jiao, T. Liao, Q. Sun, Y.H. Ng, Z. Zhu, R. Amal, S.C. Smith, J. Am. Chem. Soc. 134 (2012) 4393–4397. [277] Y. Zhao, F. Zhao, X. Wang, C. Xu, Z. Zhang, G. Shi, L. Qu, Angew. Chem. Int. Ed. 53 (2014) 13934–13939. [278] X. Zou, R. Silva, A. Goswami, T. Asefa, Appl. Surf. Sci. 357 (2015) 221–228. [279] Y. Zhang, Z. Schnepp, J. Cao, S. Ouyang, Y. Li, J. Ye, S. Liu, Sci. Rep. U. K. 3 (2013) 2163. [280] F. Yang, V. Kuznietsov, M. Lublow, C. Merschjann, A. Steigert, J. Klaer, A. Thomas, T. Schedel-Niedrig, J. Mater. Chem. A 1 (2013) 6407–6415. [281] Y. Li, R. Wang, H. Li, X. Wei, J. Feng, K. Liu, Y. Dang, A. Zhou, J. Phys. Chem. C 119 (2015) 20283–20292. [282] M. Yang, J. Liu, X. Zhang, S. Qiao, H. Huang, Y. Liu, Z. Kang, Phys. Chem. Chem. Phys. 17 (2015) 17887–17893. [283] X. Zhou, F. Peng, H. Wang, H. Yu, Y. Fang, Chem. Commun. 47 (2011) 10323–10325. [284] Y. Li, X. Wei, H. Li, R. Wang, J. Feng, H. Yun, A. Zhou, RSC Adv. 5 (2015) 14074–14080. [285] Y. Hou, F. Zuo, A.P. Dagg, J. Liu, P. Feng, Adv. Mater. 26 (2014) 5043–5049. [286] F. Zhan, R. Xie, W. Li, J. Li, Y. Yang, Y. Li, Q. Chen, RSC Adv. 5 (2015) 69753–69760. [287] Y. Li, X. Wei, X. Yan, J. Cai, A. Zhou, M. Yang, K. Liu, Phys. Chem. Chem. Phys. 18 (2016) 10255–10261. [288] Y. Hou, Z. Wen, S. Cui, X. Feng, J. Chen, Nano Lett. 16 (2016) 2268–2277. [289] Y. Liu, Y.-X. Yu, W.-D. Zhang, Int. J. Hydrogen Energy 39 (2014) 9105–9113. [290] L. Ye, D. Wang, S. Chen, ACS Appl. Mater. Interfaces 8 (2016) 5280–5289. [291] P.-Y. Kuang, Y.-Z. Su, G.-F. Chen, Z. Luo, S.-Y. Xing, N. Li, Z.-Q. Liu, Appl. Surf. Sci. 358 (2015) 296–303. [292] J. Yan, Z. Chen, H. Ji, Z. Liu, X. Wang, Y. Xu, X. She, L. Huang, L. Xu, H. Xu, H. Li, Chem. Eur. J. 22 (2016) 4764–4773. [293] F. Liang, Y. Zhu, Appl. Catal. B: Environ. 180 (2016) 324–329. [294] J. Wang, W.-D. Zhang, Electrochim. Acta 71 (2012) 10–16. [295] L. Liu, G. Zhang, J.T.S. Irvine, Y. Wu, Energy Technol. 3 (2015) 982–988. [296] Z. Mo, X. She, Y. Li, L. Liu, L. Huang, Z. Chen, Q. Zhang, H. Xu, H. Li, RSC Adv. 5 (2015) 101552–101562. [297] H. Gao, S. Yan, J. Wang, Z. Zou, Dalton Trans. 43 (2014) 8178–8183. [298] X. Wang, X. Chen, A. Thomas, X. Fu, M. Antonietti, Adv. Mater. 21 (2009) 1609–1612. [299] J. Tian, Q. Liu, A.M. Asiri, A.H. Qusti, A.O. Al-Youbi, X. Sun, Nanoscale 5 (2013) 11604–11609. [300] B. Yue, Q. Li, H. Iwai, T. Kako, J. Ye, Sci. Technol. Adv. Mater. 12 (2011) 034401. [301] S. Hu, R. Jin, G. Lu, D. Liu, J. Gui, RSC Adv. 4 (2014) 24863–24869. [302] S. Tonda, S. Kumar, S. Kandula, V. Shanker, J. Mater. Chem. A 2 (2014) 6772–6780. [303] Z. Li, C. Kong, G. Lu, J. Phys. Chem. C 120 (2016) 56–63. [304] H. Pan, Y.-W. Zhang, V.B. Shenoy, H. Gao, ACS Catal. 1 (2011) 99–104. [305] M. Zhang, X. Bai, D. Liu, J. Wang, Y. Zhu, Appl. Catal. B: Environ. 164 (2015) 77–81. [306] T. Xiong, W.L. Cen, Y.X. Zhang, F. Dong, ACS Catal. 6 (2016) 2462–2472. [307] L. Ge, C. Han, X. Xiao, L. Guo, Y. Li, Mater. Res. Bull. 48 (2013) 3919–3925. [308] S. Stolbov, S. Zuluaga, J. Phys. Condens. Matter 25 (2013) 085507. [309] F. Liang-Liang, Z. Yongcun, L. Chunguang, G. Shuang, Z. Li-Jing, S. Qiushi, F. Meihong, W. Huijie, W. Dejun, L. Guo-Dong, Z. Xiaoxin, Int. J. Hydrogen Energy 39 (2014) 15373–15379. [310] C. Wang, Y. Guo, Y. Yang, S. Chu, C. Zhou, Y. Wang, Z. Zou, ACS Appl. Mater. Interfaces 6 (2014) 4321–4328. [311] L. Cao, R. Wang, D.X. Wang, Mater. Lett. 149 (2015) 50–53. [312] Y.J. Zhang, T. Mori, J.H. Ye, M. Antonietti, J. Am. Chem. Soc. 132 (2010) 6294–6295.

J. Wen et al. / Applied Surface Science 391 (2017) 72–123 [313] Z. Ligang, C. Xiufang, G. Jing, J. Yijun, H. Tonggang, M. Xindong, Mater. Res. Bull. 48 (2013) 3485–3491. [314] J. Luo, X. Zhou, L. Ma, X. Xu, RSC Adv. 5 (2015) 68728–68735. [315] Y.P. Zhu, T.Z. Ren, Z.Y. Yuana, ACS Appl. Mater. Interfaces 7 (2015) 16850–16856. [316] J.J. Liu, J. Alloy Compd. 672 (2016) 271–276. [317] C. Lu, R. Chen, X. Wu, M. Fan, Y. Liu, Z. Le, S. Jiang, S. Song, Appl. Surf. Sci. 360 (2016) 1016–1022. [318] T. Bharathidasan, A. Mandalam, M. Balasubramanian, P. Dhandapani, S. Sathiyanarayanan, S. Mayavan, ACS Appl. Mater. Interfaces 7 (2015) 18450–18459. [319] W. Tian, Q. Shen, N. Li, J. Zhou, RSC Adv. 6 (2016) 25568–25576. [320] F. Raziq, Y. Qu, X. Zhang, M. Humayun, J. Wu, A. Zada, H. Yu, X. Sun, L. Jingo, J. Phys. Chem. C 120 (2016) 98–107. [321] Z.-F. Huang, J. Song, L. Pan, Z. Wang, X. Zhang, J.-J. Zou, W. Mi, X. Zhang, L. Wang, Nano Energy 12 (2015) 646–656. [322] X. Ma, Y. Lv, J. Xu, Y. Liu, R. Zhang, Y. Zhu, J. Phys. Chem. C 116 (2012) 23485–23493. [323] S. Hu, L. Ma, J. You, F. Li, Z. Fan, F. Wang, D. Liu, J. Gui, RSC Adv. 4 (2014) 21657–21663. [324] Y. Zhou, L. Zhang, J. Liu, X. Fan, B. Wang, M. Wang, W. Ren, J. Wang, M. Li, J. Shi, J. Mater. Chem. A 3 (2015) 3862–3867. [325] D.-H. Lan, H.-T. Wang, L. Chen, C.-T. Au, S.-F. Yin, Carbon 100 (2016) 81–89. [326] J. Ran, T.Y. Ma, G. Gao, X.-W. Du, S.Z. Qiao, Energy Environ. Sci. 8 (2015) 3708–3717. [327] Y. Wang, H.R. Li, J. Yao, X.C. Wang, M. Antonietti, Chem. Sci. 2 (2011) 446–450. [328] L. Zhenzhen, W. Xinchen, Angew. Chem. Int. Ed. 52 (2013) 1735–1738. [329] C. Xu, Q. Han, Y. Zhao, L. Wang, Y. Li, L. Qu, J. Mater. Chem. A 3 (2015) 1841–1846. [330] S.C. Yan, Z.S. Li, Z.G. Zou, Langmuir 26 (2010) 3894–3901. [331] Y. Wang, Y. Di, M. Antonietti, H. Li, X. Chen, X. Wang, Chem. Mater. 22 (2010) 5119–5121. [332] S. Hu, L. Ma, J. You, F. Li, Z. Fan, G. Lu, D. Liu, J. Gui, Appl. Surf. Sci. 311 (2014) 164–171. [333] H. Ma, S. Zhao, S. Li, N. Liu, RSC Adv. 5 (2015) 79585–79592. [334] S. Hu, L. Ma, Y. Xie, F. Li, Z. Fan, F. Wang, Q. Wang, Y. Wang, X. Kang, G. Wu, Dalton Trans. 44 (2015) 20889–20897. [335] H. Ma, Y. Li, S. Li, N. Liu, Appl. Surf. Sci. 357 (2015) 131–138. [336] J. Zhao, L. Ma, H. Wang, Y. Zhao, J. Zhang, S. Hu, Appl. Surf. Sci. 332 (2015) 625–630. [337] S. Zhang, J. Li, M. Zeng, J. Li, J. Xu, X. Wang, Chem. Eur. J. 20 (2014) 9805–9812. [338] X. Fan, L. Zhang, R. Cheng, M. Wang, M. Li, Y. Zhou, J. Shi, ACS Catal. 5 (2015) 5008–5015. [339] W. Ho, Z. Zhang, W. Lin, S. Huang, X. Zhang, X. Wang, Y. Huang, ACS Appl. Mater. Interfaces 7 (2015) 5497–5505. [340] D. Zheng, C. Pang, Y. Liu, X. Wang, Chem. Commun. 51 (2015) 9706–9709. [341] X. Fan, L. Zhang, M. Wang, W. Huang, Y. Zhou, M. Li, R. Cheng, J. Shi, Appl. Catal. B: Environ. 182 (2016) 68–73. [342] J. Zhang, M. Zhang, S. Lin, X. Fu, X. Wang, J. Catal. 310 (2014) 24–30. [343] S. Chu, Y. Wang, Y. Guo, J. Feng, C. Wang, W. Luo, X. Fan, Z. Zou, ACS Catal. 3 (2013) 912–919. [344] M.J. Bojdys, N. Severin, J.P. Rabe, A.I. Cooper, A. Thomas, M. Antonietti, Macromol. Rapid Commun. 34 (2013) 850–854. [345] K. Schwinghammer, S. Hug, M.B. Mesch, J. Senker, B.V. Lotsch, Energy Environ. Sci. 8 (2015) 3345–3353. [346] Y. Cui, G. Zhang, Z. Lin, X. Wang, Appl. Catal. B: Environ. 181 (2016) 413–419. [347] P. Niu, L.-C. Yin, Y.-Q. Yang, G. Liu, H.-M. Cheng, Adv. Mater. 26 (2014) 8046–8052. [348] Y. Kang, Y. Yang, L.-C. Yin, X. Kang, G. Liu, H.-M. Cheng, Adv. Mater. 27 (2015) 4572–4577. [349] X. Li, G. Hartley, A.J. Ward, P.A. Young, A.F. Masters, T. Maschmeyer, J. Phys. Chem. C 119 (2015) 14938–14946. [350] Q. Liang, Z. Li, Z.-H. Huang, F. Kang, Q.-H. Yang, Adv. Funct. Mater. 25 (2015) 6885–6892. [351] P. Yang, J. Zhao, W. Qiao, L. Li, Z. Zhu, Nanoscale 7 (2015) 18887–18890. [352] Q. Tay, P. Kanhere, C.F. Ng, S. Chen, S. Chakraborty, A.C.H. Huan, T.C. Sum, R. Ahuja, Z. Chen, Chem. Mater. 27 (2015) 4930–4933. [353] H.-Z. Wu, L.-M. Liu, S.-J. Zhao, Appl. Surf. Sci. 358 (2015) 363–369. [354] Y. Shiraishi, Y. Kofuji, H. Sakamoto, S. Tanaka, S. Ichikawa, T. Hirai, ACS Catal. 5 (2015) 3058–3066. [355] Y. Cao, Z. Zhang, J. Long, J. Liang, H. Lin, H. Lin, X. Wang, J. Mater. Chem. A (2014). [356] T. Xia, Y. Zhang, J. Murowchick, X. Chen, Catal. Today 225 (2013) 2–9. [357] Z. Yang, Y. Zhang, Z. Schnepp, J. Mater. Chem. A 3 (2015) 14081–14092. [358] S.-W. Bian, Z. Ma, W.-G. Song, J. Phys. Chem. C 113 (2009) 8668–8672. [359] X.-H. Li, J. Zhang, X. Chen, A. Fischer, A. Thomas, M. Antonietti, X. Wang, Chem. Mater. 23 (2011) 4344–4348. [360] J. Zhang, F. Guo, X. Wang, Adv. Funct. Mater. 23 (2013) 3008–3014. [361] Y. Fukasawa, K. Takanabe, A. Shimojima, M. Antonietti, K. Domen, T. Okubo, Chem. Asian J. 6 (2011) 103–109. [362] X.-H. Li, X. Wang, M. Antonietti, Chem. Sci. 3 (2012) 2170–2174. [363] Y. Cui, J. Huang, X. Fu, X. Wang, Catal. Sci. Technol. 2 (2012) 1396–1402. [364] J. Sun, J. Zhang, M. Zhang, M. Antonietti, X. Fu, X. Wang, Nat. Commun. 3 (2012) 1139.

117

[365] Y. Zheng, L. Lin, X. Ye, F. Guo, X. Wang, Angew. Chem. Int. Ed. 53 (2014) 11926–11930. [366] J. Liu, J. Huang, H. Zhou, M. Antonietti, ACS Appl. Mater. Interfaces 6 (2014) 8434–8440. [367] S.C. Lee, H.O. Lintang, L. Yuliati, Chem. Asian J. 7 (2012) 2139–2144. [368] E.Z. Lee, Y.-S. Jun, W.H. Hong, A. Thomas, M.M. Jin, Angew. Chem. Int. Ed. 49 (2010) 9706–9710. [369] Z. Jinshui, Z. Mingwen, Y. Can, W. Xinchen, Adv. Mater. 26 (2014) 4121–4126. [370] J. Wang, C. Zhang, Y. Shen, Z. Zhou, J. Yu, Y. Li, W. Wei, S. Liu, Y. Zhang, J. Mater. Chem. A 3 (2015) 5126–5131. [371] X.D. Sun, Y.Y. Li, J. Zhou, C.H. Ma, Y. Wang, J.H. Zhu, J. Colloid Interface Sci. 451 (2015) 108–116. [372] Q. Liang, Z. Li, X. Yu, Z.-H. Huang, F. Kang, Q.-H. Yang, Adv. Mater. 27 (2015) 4634–4639. [373] Z. Lin, X. Wang, ChemSusChem 7 (2014) 1547–1550. [374] Y. Wang, X. Wang, M. Antonietti, Y. Zhang, ChemSusChem 3 (2010) 435–439. [375] H. Yan, Chem. Commun. 48 (2012) 3430–3432. [376] W. Shen, L. Ren, H. Zhou, S. Zhang, W. Fan, J. Mater. Chem. 21 (2011) 3890–3894. [377] Q. Fan, J. Liu, Y. Yu, S. Zuo, RSC Adv. 4 (2014) 61877–61883. [378] M. Zhang, J. Xu, R. Zong, Y. Zhu, Appl. Catal. B: Environ. 147 (2014) 229–235. [379] J. Xu, Y. Wang, Y. Zhu, Langmuir 29 (2013) 10566–10572. [380] Y. Zhang, J. Liu, G. Wu, W. Chen, Nanoscale 4 (2012) 5300–5303. [381] F. He, G. Chen, Y. Yu, Y. Zhou, Y. Zheng, S. Hao, Chem. Commun. 51 (2015) 425–427. [382] F. He, G. Chen, Y. Zhou, Y. Yu, Y. Zheng, S. Hao, Chem. Commun. 51 (2015) 16244–16246. [383] Z. Wang, W. Guan, Y. Sun, F. Dong, Y. Zhou, W.-K. Ho, Nanoscale 7 (2015) 2471–2479. [384] J. Liu, M. Antonietti, Energy Environ. Sci. 6 (2013) 1486–1493. [385] Y.-S. Jun, J. Park, S.U. Lee, A. Thomas, W.H. Hong, G.D. Stucky, Angew. Chem. Int. Ed. 52 (2013) 11083–11087. [386] T. Jordan, N. Fechler, J. Xu, T.J.K. Brenner, M. Antonietti, M. Shalom, ChemCatChem 7 (2015) 2826–2830. [387] Y. Liao, S. Zhu, J. Ma, Z. Sun, C. Yin, C. Zhu, X. Lou, D. Zhang, ChemCatChem 6 (2014) 3419–3425. [388] M. Shalom, M. Guttentag, C. Fettkenhauer, S. Inal, D. Neher, A. Llobet, M. Antonietti, Chem. Mater. 26 (2014) 5812–5818. [389] J. Xu, T.J.K. Brenner, Z. Chen, D. Neher, M. Antonietti, M. Shalom, ACS Appl. Mater. Interfaces 6 (2014) 16481–16486. [390] J. Yang, X. Wu, X. Li, Y. Liu, M. Gao, X. Liu, L. Kong, S. Yang, Appl. Phys. A 105 (2011) 161–166. [391] G. Dong, L. Zhang, J. Mater. Chem. 22 (2012) 1160–1166. [392] K.K. Han, C.C. Wang, Y.Y. Li, M.M. Wan, Y. Wang, J.H. Zhu, RSC Adv. 3 (2013) 9465–9469. [393] B. Shen, Z. Hong, Y. Chen, B. Lin, B. Gao, Mater. Lett. 118 (2014) 208–211. [394] Q. Cai, J. Shen, Y. Feng, Q. Shen, H. Yang, J. Alloy Compd. 628 (2015) 372–378. [395] J. Ding, Q. Liu, Z. Zhang, X. Liu, J. Zhao, S. Cheng, B. Zong, W.-L. Dai, Appl. Catal. B: Environ. 165 (2015) 511–518. [396] Q. Han, B. Wang, J. Gao, Z. Cheng, Y. Zhao, Z. Zhang, L. Qu, ACS Nano 10 (2016) 2745–2751. [397] Q. Gu, Y. Liao, L. Yin, J. Long, X. Wang, C. Xue, Appl. Catal. B: Environ. 165 (2015) 503–510. [398] Y. Cui, Z. Ding, X. Fu, X. Wang, Angew. Chem. Int. Ed. 51 (2012) 11814–11818. [399] H.-J. Li, D.-J. Qian, M. Chen, ACS Appl. Mater. Interfaces 7 (2015) 25162–25170. [400] X. Bai, L. Wang, R. Zong, Y. Zhu, J. Phys. Chem. C 117 (2013) 9952–9961. [401] J. Yu, W. Liu, H. Yu, Cryst. Growth Des. 8 (2008) 930–934. [402] J. Yu, H. Guo, S.A. Davis, S. Mann, Adv. Funct. Mater. 16 (2006) 2035–2041. [403] J. Yu, S. Liu, H. Yu, J. Catal. 249 (2007) 59–66. [404] Y. Jiaguo, Y. Huogen, G. Hongtao, L. Mei, S. Mann, Small 4 (2008) 87–91. [405] H. Yu, F. Chen, F. Chen, X. Wang, Appl. Surf. Sci. 358 (2015) 385–392. [406] S. Liu, J. Yu, S. Mann, J. Phys. Chem. C 113 (2009) 10712–10717. [407] J. Yu, S. Liu, M. Zhou, J. Phys. Chem. C 112 (2008) 2050–2057. [408] L. Qi, B. Cheng, J. Yu, W. Ho, J. Hazard. Mater. 301 (2016) 522–530. [409] P. Niu, Y. Yang, J.C. Yu, G. Liu, H.-M. Cheng, Chem. Commun. 50 (2014) 10837–10840. [410] H. Zhang, L.-H. Guo, L. Zhao, B. Wan, Y. Yang, J. Phys. Chem. Lett. 6 (2015) 958–963. [411] S. Barman, M. Sadhukhan, J. Mater. Chem. 22 (2012) 21832–21837. [412] Y. Tang, Y. Su, N. Yang, L. Zhang, Y. Lv, Anal. Chem. 86 (2014) 4528–4535. [413] W. Wang, J.C. Yu, Z. Shen, D.K.L. Chan, T. Gu, Chem. Commun. 50 (2014) 10148–10150. [414] X. Wang, G. Sun, N. Li, P. Chen, Chem. Soc. Rev. 45 (2016) 2239–2262. [415] P. Niu, L. Zhang, G. Liu, H.-M. Cheng, Adv. Funct. Mater. 22 (2012) 4763–4770. [416] S. Yang, Y. Gong, J. Zhang, L. Zhan, L. Ma, Z. Fang, R. Vajtai, X. Wang, P.M. Ajayan, Adv. Mater. 25 (2013) 2452–2456. [417] F. Deng, X. Lu, L. Zhao, Y. Luo, X. Pei, X. Luo, S. Luo, J. Mater. Sci. 51 (2016) 6998–7007. [418] J. Ma, X. Tan, T. Yu, X. Li, Int. J. Hydrogen Energy 41 (2016) 3877–3887. [419] Z. Zhang, K. Liu, Z. Feng, Y. Bao, B. Dong, Sci. Rep. U. K. 6 (2016). [420] J. Tian, Q. Liu, C. Ge, Z. Xing, A.M. Asiri, A.O. Al-Youbi, X. Sun, Nanoscale 5 (2013) 8921–8924.

118

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

[421] J. Tian, Q. Liu, A.M. Asiri, A.O. Al-Youbi, X. Sun, Anal. Chem. 85 (2013) 5595–5599. [422] N. Cheng, J. Tian, Q. Liu, C. Ge, A.H. Qusti, A.M. Asiri, A.O. Al-Youbi, X. Sun, ACS Appl. Mater. Interfaces 5 (2013) 6815–6819. [423] W. Ma, D. Han, M. Zhou, H. Sun, L. Wang, X. Dong, L. Niu, Chem. Sci. 5 (2014) 3946–3951. [424] Q. Lin, L. Li, S. Liang, M. Liu, J. Bi, L. Wu, Appl. Catal. B: Environ. 163 (2015) 135–142. [425] J. Hong, S. Yin, Y. Pan, J. Han, T. Zhou, R. Xu, Nanoscale 6 (2014) 14984–14990. [426] X. She, H. Xu, Y. Xu, J. Yan, J. Xia, L. Xu, Y. Song, Y. Jiang, Q. Zhang, H. Li, J. Mater. Chem. A 2 (2014) 2563–2570. [427] S. Bai, X. Wang, C. Hu, M. Xie, J. Jiang, Y. Xiong, Chem. Commun. 50 (2014) 6094–6097. [428] L. Ma, H. Fan, M. Li, H. Tian, J. Fang, G. Dong, J. Mater. Chem. A 3 (2015) 22404–22412. [429] M. Ayan-Varela, S. Villar-Rodil, J.I. Paredes, J.M. Munuera, A. Pagan, A.A. Lozano-Perez, J.L. Cenis, A. Martinez-Aonso, J.M.D. Tascon, ACS Appl. Mater. Interfaces 7 (2015) 24032–24045. [430] Y. Yin, J. Han, X. Zhang, Y. Zhang, J. Zhou, D. Muir, R. Sutarto, Z. Zhang, S. Liu, B. Song, RSC Adv. 4 (2014) 32690–32697. [431] L. Ma, H. Fan, J. Wang, Y. Zhao, H. Tian, G. Dong, Appl. Catal. B: Environ. 190 (2016) 93–102. [432] J. Tong, L. Zhang, F. Li, K. Wang, L. Han, S. Cao, RSC Adv. 5 (2015) 88149–88153. [433] S. Zhang, J. Li, X. Wang, Y. Huang, M. Zeng, J. Xu, ACS Appl. Mater. Interfaces 6 (2014) 22116–22125. [434] Y. Ma, E. Liu, X. Hu, C. Tang, J. Wan, J. Li, J. Fan, Appl. Surf. Sci. 358 (2015) 246–251. [435] F. Dong, Y. Li, Z. Wang, W.-K. Ho, Appl. Surf. Sci. 358 (2015) 393–403. [436] F. Chang, J. Zhang, Y. Xie, J. Chen, C. Li, J. Wang, J. Luo, B. Deng, X. Hu, Appl. Surf. Sci. 311 (2014) 574–581. [437] Q. Gu, Z. Gao, H. Zhao, Z. Lou, Y. Liao, C. Xue, RSC Adv. 5 (2015) 49317–49325. [438] Y. Li, R. Jin, X. Fang, Y. Yang, M. Yang, X. Liu, Y. Xing, S. Song, J. Hazard. Mater. 313 (2016) 219–228. [439] F. Chang, Y. Xie, J. Zhang, J. Chen, C. Li, J. Wang, J. Luo, B. Deng, X. Hu, Rsc. Adv. 4 (2014) 28519–28528. [440] S. Deng, P. Yuan, X. Ji, D. Shan, X. Zhang, ACS Appl. Mater. Interfaces 7 (2015) 543–552. [441] L. Huang, Y. Li, H. Xu, Y. Xu, J. Xia, K. Wang, H. Li, X. Cheng, RSC Adv. 3 (2013) 22269–22279. [442] P. Qiu, H. Chen, C. Xu, N. Zhou, F. Jiang, X. Wang, Y. Fu, J. Mater. Chem. A 3 (2015) 24237–24244. [443] X. Lu, K. Xu, P. Chen, K. Jia, S. Liu, C. Wu, J. Mater. Chem. A 2 (2014) 18924–18928. [444] G. Liu, T. Wang, H. Zhang, X. Meng, D. Hao, K. Chang, P. Li, T. Kako, J. Ye, Angew. Chem. Int. Ed. 54 (2015) 13561–13565. [445] M. Wu, J.-M. Yan, X.-N. Tang, M. Zhao, Q. Jiang, ChemSusChem 7 (2014) 2654–2658. [446] N. Cheng, P. Jiang, Q. Liu, J. Tian, A.M. Asiri, X. Sun, Analyst 139 (2014) 5065–5068. [447] Z. Huang, F. Li, B. Chen, G. Yuan, RSC Adv. 5 (2015) 14027–14033. [448] Z. Huang, F. Li, B. Chen, G. Yuan, Catal. Sci. Technol. 4 (2014) 4258–4264. [449] H. Xu, J. Yan, X. She, L. Xu, J. Xia, Y. Xu, Y. Song, L. Huang, H. Li, Nanoscale 6 (2014) 1406–1415. [450] H. Zhao, H. Yu, X. Quan, S. Chen, Y. Zhang, H. Zhao, H. Wang, Appl. Catal. B: Environ. 152 (2014) 46–50. [451] H. Zhao, H. Yu, X. Quan, S. Chen, H. Zhao, H. Wang, RSC Adv. 4 (2014) 624–628. [452] X. Dang, X. Zhang, W. Zhang, X. Dong, G. Wang, C. Ma, X. Zhang, H. Ma, M. Xue, RSC Adv. 5 (2015) 15052–15058. [453] H. Wang, Y. Su, H. Zhao, H. Yu, S. Chen, Y. Zhang, X. Quan, Environ. Sci. Technol. 48 (2014) 11984–11990. [454] X. She, L. Liu, H. Ji, Z. Mo, Y. Li, L. Huang, D. Du, H. Xu, H. Li, Appl. Catal. B: Environ. 187 (2016) 144–153. [455] W. Zhao, Y. Guo, S. Wang, H. He, C. Sun, S. Yang, Appl. Catal. B: Environ. 165 (2015) 335–343. [456] J.H. Lee, M.J. Park, S.J. Yoo, J.H. Jang, H.-J. Kim, S.W. Nam, C.W. Yoon, J.Y. Kim, Nanoscale 7 (2015) 10334–10339. [457] X. Li, H. Ren, Z. Zou, J. Sun, J. Wang, Z. Liu, Chem. Commun. 52 (2016) 453–456. [458] X. Guo, Y. Wang, F. Wu, Y. Ni, S. Kokot, Microchim. Acta 183 (2016) 773–780. [459] J. Tong, L. Zhang, F. Li, M. Li, S. Cao, Phys. Chem. Chem. Phys. 17 (2015) 23532–23537. [460] X. Yuan, C. Zhou, Y. Jin, Q. Jing, Y. Yang, X. Shen, Q. Tang, Y. Mu, A.-K. Du, J. Colloid Interface Sci. 468 (2016) 211–219. [461] K. Zhu, W. Wang, A. Meng, M. Zhao, J. Wang, M. Zhao, D. Zhang, Y. Jia, C. Xu, Z. Li, RSC Adv. 5 (2015) 56239–56243. [462] Y. Yu, Q. Zhou, J. Wang, Chem. Commun. 52 (2016) 3396–3399. [463] V. Nicolosi, M. Chhowalla, M.G. Kanatzidis, M.S. Strano, J.N. Coleman, Science 340 (2013) 1226419. [464] Y. Hernandez, V. Nicolosi, M. Lotya, F.M. Blighe, Z.Y. Sun, S. De, I.T. McGovern, B. Holland, M. Byrne, Y.K. Gun’ko, J.J. Boland, P. Niraj, G. Duesberg, S. Krishnamurthy, R. Goodhue, J. Hutchison, V. Scardaci, A.C. Ferrari, J.N. Coleman, Nat. Nanotechnol. 3 (2008) 563–568.

[465] J.N. Coleman, M. Lotya, A. O’Neill, S.D. Bergin, P.J. King, U. Khan, K. Young, A. Gaucher, S. De, R.J. Smith, I.V. Shvets, S.K. Arora, G. Stanton, H.-Y. Kim, K. Lee, G.T. Kim, G.S. Duesberg, T. Hallam, J.J. Boland, J.J. Wang, J.F. Donegan, J.C. Grunlan, G. Moriarty, A. Shmeliov, R.J. Nicholls, J.M. Perkins, E.M. Grieveson, K. Theuwissen, D.W. McComb, P.D. Nellist, V. Nicolosi, Science 331 (2011) 568–571. [466] D. Voiry, H. Yamaguchi, J. Li, R. Silva, D.C.B. Alves, T. Fujita, M. Chen, T. Asefa, V.B. Shenoy, G. Eda, M. Chhowalla, Nat. Mater. 12 (2013) 850–855. [467] F. Song, X. Hu, Nat. Commun. 5 (2014) 4477. [468] T. Ndlovu, A.T. Kuvarega, O.A. Arotiba, S. Sampath, R.W. Krause, B.B. Mamba, Appl. Surf. Sci. 300 (2014) 159–164. [469] V.Z. Baldissarelli, T. de Souza, L. Andrade, H.J. Cappa de Oliveira, R.d.F. Peralta Muniz Moreira, Appl. Surf. Sci. 359 (2015) 868–874. [470] F. Cheng, H. Wang, X. Dong, Chem. Commun. 51 (2015) 7176–7179. [471] G. Liu, P. Niu, C. Sun, S.C. Smith, Z. Chen, G.Q. Lu, H.-M. Cheng, J. Am. Chem. Soc. 132 (2010) 11642–11648. [472] P. Niu, G. Liu, H.-M. Cheng, J. Phys. Chem. C 116 (2012) 11013–11018. [473] Y. Wang, J. Hong, W. Zhang, R. Xu, Catal. Sci. Technol. 3 (2013) 1703–1711. [474] D.J. Martin, K. Qiu, S.A. Shevlin, A.D. Handoko, X. Chen, Z. Guo, J. Tang, Angew. Chem. Int. Ed. 53 (2014) 9240–9245. [475] V.W.-h. Lau, M.B. Mesch, V. Duppel, V. Blum, J. Senker, B.V. Lotsch, J. Am. Chem. Soc. 137 (2014) 1064–1072. [476] J. Low, S. Cao, J. Yu, S. Wageh, Chem. Commun. 50 (2014) 10768–10777. [477] J. Zhang, X. Wang, Angew. Chem. Int. Ed. 54 (2015) 7230–7232. [478] E. Cheng, W. Yin, S. Bai, R. Qiao, Y. Zhong, Z. Li, Mater. Lett. 146 (2015) 87–90. [479] X. Wei, C. Shao, X. Li, N. Lu, K. Wang, Z. Zhang, Y. Liu, Nanoscale 8 (2016) 11034–11043. [480] S. Tonda, S. Kumar, V. Shanker, Mater. Res. Bull. 75 (2016) 51–58. [481] J. Xue, S. Ma, Y. Zhou, Z. Zhang, M. He, ACS Appl. Mater. Interfaces 7 (2015) 9630–9637. [482] J. Xue, S. Ma, Y. Zhou, Q. Wang, RSC Adv. 5 (2015) 88249–88257. [483] K. Dai, J. Lv, L. Lu, C. Liang, L. Geng, G. Zhu, Mater. Chem. Phys. 177 (2016) 529–537. [484] D. Chen, Z. Wang, Y. Du, G. Yang, T. Ren, H. Ding, Catal. Today 258 (2015) 41–48. [485] T. Zhou, Y. Xu, H. Xu, H. Wang, Z. Da, S. Huang, H. Ji, H. Li, Ceram. Int. 40 (2014) 9293–9301. [486] Y. Yang, W. Guo, Y. Guo, Y. Zhao, X. Yuan, Y. Guo, J. Hazard. Mater. 271 (2014) 150–159. [487] Y. Li, Y. Zhao, L. Fang, R. Jin, Y. Yang, Y. Xing, Mater. Lett. 126 (2014) 5–8. [488] X. Bai, R. Zong, C. Li, D. Liu, Y. Liu, Y. Zhu, Appl. Catal. B: Environ. 147 (2014) 82–91. [489] Y. Yang, Y. Guo, F. Liu, X. Yuan, Y. Guo, S. Zhang, W. Guo, M. Huo, Appl. Catal. B: Environ. 142 (2013) 828–837. [490] Y.-S. Xu, W.-D. Zhang, ChemCatChem 5 (2013) 2343–2351. [491] Y. Xu, H. Xu, J. Yan, H. Li, L. Huang, J. Xia, S. Yin, H. Shu, Colloid Surf. A 436 (2013) 474–483. [493] L.G. Devi, R. Kavitha, Appl. Surf. Sci. 360 (2016) 601–622. [494] N.E. Motl, E. Ewusi-Annan, I.T. Sines, L. Jensen, R.E. Schaak, J. Phys. Chem. C 114 (2010) 19263–19269. [495] K.K.M., B.K., N.G., S.B., V.A., Appl. Catal. B: Environ. 199 (2016) 282–291. [496] E. Liu, L. Qi, J. Bian, Y. Chen, X. Hu, J. Fan, H. Liu, C. Zhu, Q. Wang, Mater. Res. Bull. 68 (2015) 203–209. [497] J.A. Jiménez, J. Alloy Compd. 656 (2016) 685–688. [498] Y. Cheng, Y. Lin, J. Xu, J. He, T. Wang, G. Yu, D. Shao, W.-H. Wang, F. Lu, L. Li, X. Du, W. Wang, H. Liu, R. Zheng, Appl. Surf. Sci. 366 (2016) 120–128. [499] S. Yu, H. Huang, F. Dong, M. Li, N. Tian, T. Zhang, Y. Zhane, ACS Appl. Mater. Interfaces 7 (2015) 27925–27933. [500] Y. Sun, Z. Zhao, F. Dong, W. Zhang, Phys. Chem. Chem. Phys. 17 (2015) 10383–10390. [501] F. Dong, Q. Li, Y. Sun, W.-K. Ho, ACS Catal. 4 (2014) 4341–4350. [502] L. Ge, F. Zuo, J. Liu, Q. Ma, C. Wang, D. Sun, L. Bartels, P. Feng, J. Phys. Chem. C 116 (2012) 13708–13714. [503] S.-W. Cao, Y.-P. Yuan, J. Fang, M.M. Shahjamali, F.Y.C. Boey, J. Barber, S.C.J. Loo, C. Xue, Int. J. Hydrogen Energy 38 (2013) 1258–1266. [504] C.-z. Zheng, C.-y. Zhang, G.-h. Zhang, D.-j. Zhao, Y.-z. Wang, Mater. Res. Bull. 55 (2014) 212–215. [505] W. Chen, T.-Y. Liu, T. Huang, X.-H. Liu, J.-W. Zhu, G.-R. Duan, X.-J. Yang, Appl. Surf. Sci. 355 (2015) 379–387. [506] F. Jiang, T. Yan, H. Chen, A. Sun, C. Xu, X. Wang, Appl. Surf. Sci. 295 (2014) 164–172. [507] X. Dai, M. Xie, S. Meng, X. Fu, S. Chen, Appl. Catal. B: Environ. 158 (2014) 382–390. [508] Y. Cui, Chin. J. Catal. 36 (2015) 372–379. [509] K. Takanabe, K. Kamata, X. Wang, M. Antonietti, J. Kubota, K. Domen, Phys. Chem. Chem. Phys. 12 (2010) 13020–13025. [510] X. Zhang, T. Peng, L. Yu, R. Li, Q. Li, Z. Li, ACS Catal. 5 (2015) 504–510. [511] L. Yu, X. Zhang, C. Zhuang, L. Lin, R. Li, T. Peng, Phys. Chem. Chem. Phys. 16 (2014) 4106–4114. [512] X. Zhang, B. Peng, T. Peng, L. Yu, R. Li, J. Zhang, J. Power Sources 298 (2015) 30–37. [513] H. Dai, S. Zhang, G. Xu, Y. Peng, L. Gong, X. Li, Y. Li, Y. Lin, G. Chen, RSC Adv. 4 (2014) 58226–58230. [514] X. Zhang, L. Yu, C. Zhuang, T. Peng, R. Li, X. Li, ACS Catal. 4 (2014) 162–170. [515] X. Zhang, L. Yu, R. Li, T. Peng, X. Li, Catal. Sci. Technol. 4 (2014) 3251–3260.

J. Wen et al. / Applied Surface Science 391 (2017) 72–123 [516] H. Zhang, S. Li, R. Lu, A. Yu, ACS Appl. Mater. Interfaces 7 (2015) 21868–21874. [517] J. Xu, Y. Li, S. Peng, Int. J. Hydrogen Energy 40 (2015) 353–362. [518] J. Xu, Y. Li, S. Peng, G. Lu, S. Li, Phys. Chem. Chem. Phys. 15 (2013) 7657–7665. [519] S. Min, G. Lu, J. Phys. Chem. C 116 (2012) 19644–19652. [520] T. Jia, M.M.J. Li, L. Ye, S. Wiseman, G. Liu, J. Qu, K. Nakagawa, S.C.E. Tsang, Chem. Commun. 51 (2015) 13496–13499. [521] Z. Li, Y. Wu, G. Lu, Appl. Catal. B: Environ. 188 (2016) 56–64. [522] J. Qin, J. Huo, P. Zhang, J. Zeng, T. Wang, H. Zeng, Nanoscale 8 (2016) 2249–2259. [523] J. Yu, S. Wang, J. Low, W. Xiao, Phys. Chem. Chem. Phys. 15 (2013) 16883–16890. [524] L. Liu, Y. Qi, J. Hu, Y. Liang, W. Cui, Appl. Surf. Sci. 351 (2015) 1146–1154. [525] J. Chen, S. Shen, P. Guo, M. Wang, P. Wu, X. Wang, L. Guo, Appl. Catal. B: Environ. 152 (2014) 335–341. [526] L. Liu, Y. Qi, J. Hu, W. An, S. Lin, Y. Liang, W. Cui, Mater. Lett. 158 (2015) 278–281. [527] Y. Wang, R. Shi, J. Lin, Y. Zhu, Energy Environ. Sci. 4 (2011) 2922–2929. [528] W. Liu, M. Wang, C. Xu, S. Chen, Chem. Eng. J. 209 (2012) 386–393. [529] J.-X. Sun, Y.-P. Yuan, L.-G. Qiu, X. Jiang, A.-J. Xie, Y.-H. Shen, J.-F. Zhu, Dalton Trans. 41 (2012) 6756–6763. [530] W. Liu, M. Wang, C. Xu, S. Chen, X. Fu, J. Mol. Catal. A: Chem. 368 (2013) 9–15. [531] Y. Bu, Z. Chen, RSC Adv. 4 (2014) 45397–45406. [532] D. Chen, K. Wang, T. Ren, H. Ding, Y. Zhu, Dalton Trans. 43 (2014) 13105–13114. [533] D. Chen, K. Wang, D. Xiang, R. Zong, W. Yao, Y. Zhu, Appl. Catal. B: Environ. 147 (2014) 554–561. [534] S. Kumar, A. Baruah, S. Tonda, B. Kumar, V. Shanker, B. Sreedhar, Nanoscale 6 (2014) 4830–4842. [535] A. Akhundi, A. Habibi-Yangjeh, Appl. Surf. Sci. 358 (2015) 261–269. [536] Y. He, Y. Wang, L. Zhang, B. Teng, M. Fan, Appl. Catal. B: Environ. 168 (2015) 1–8. [537] W.-K. Jo, N.C.S. Selvam, J. Hazard. Mater. 299 (2015) 462–470. [538] L. Huang, H. Xu, Y. Li, H. Li, X. Cheng, J. Xia, Y. Xu, G. Cai, Dalton Trans. 42 (2013) 8606–8616. [539] K.-i. Katsumata, R. Motoyoshi, N. Matsushita, K. Okada, J. Hazard. Mater. 260 (2013) 475–482. [540] Y. Zang, L. Li, Y. Zuo, H. Lin, G. Li, X. Guan, RSC Adv. 3 (2013) 13646–13650. [541] D. An Tran, T. Xuan Dieu Nguyen, N. Phi Hung, T. Viet Nga Nguyen, S.J. Kim, V. Vien, B. Korean, Chem. Soc. 35 (2014) 1794–1798. [542] I. Aslam, C. Cao, M. Tanveer, W.S. Khan, M. Tahir, M. Abid, F. Idrees, F.K. Butt, Z. Ali, N. Mahmood, New J. Chem. 38 (2014) 5462–5469. [543] M. Yang, S. Hu, F. Li, Z. Fan, F. Wang, D. Liu, J. Gui, Ceram. Int. 40 (2014) 11963–11969. [544] J. Zhao, Z. Ji, X. Shen, H. Zhou, L. Ma, Ceram. Int. 41 (2015) 5600–5606. [545] C. Li, S. Wang, T. Wang, Y. Wei, P. Zhang, J. Gong, Small 10 (2014) 2783–2790. [546] M. Ou, Q. Zhong, S. Zhang, J. Sol-Gel. Sci. Technol. 72 (2014) 443–454. [547] Y. Huang, M. Fu, T. He, Acta Phys. Chim. Sin. 31 (2015) 1145–1152. [548] M. Ou, Q. Zhong, S. Zhang, L. Yu, J. Alloy Compd. 626 (2015) 401–409. [549] J. Zhang, F. Ren, M. Deng, Y. Wang, Phys. Chem. Chem. Phys. 17 (2015) 10218–10226. [550] H.J. Kong, D.H. Won, J. Kim, S.I. Woo, Chem. Mater. 28 (2016) 1318–1324. [551] G. Miao, D. Huang, X. Ren, X. Li, Z. Li, J. Xiao, Appl. Catal. B: Environ. 192 (2016) 72–79. [552] Z. Ni, Y. Sun, Y. Zhang, F. Dong, Appl. Surf. Sci. 365 (2016) 314–335. [553] S. Kumar, T. Surendar, A. Baruah, V. Shanker, J. Mater. Chem. A 1 (2013) 5333–5340. [554] F.-J. Zhang, F.-Z. Xie, S.-F. Zhu, J. Liu, J. Zhang, S.-F. Mei, W. Zhao, Chem. Eng. J. 228 (2013) 435–441. [555] P. He, L. Song, S. Zhang, X. Wu, Q. Wei, Mater. Res. Bull. 51 (2014) 432–437. [556] D. Jiang, J. Zhu, M. Chen, J. Xie, J. Colloid Interface Sci. 417 (2014) 115–120. [557] K. Shen, M.A. Gondal, R.G. Siddique, S. Shi, S. Wang, J. Sun, Q. Xu, Chin. J. Catal. 35 (2014) 78–84. [558] S. Meng, X. Ning, T. Zhang, S.-F. Chen, X. Fu, Phys. Chem. Chem. Phys. 17 (2015) 11577–11585. [559] C. Tang, E. Liu, J. Fan, X. Hu, Y. Ma, J. Wan, RSC Adv. 5 (2015) 91979–91987. [560] L. Liu, Y. Qi, J. Lu, S. Lin, W. An, Y. Liang, W. Cui, Appl. Catal. B: Environ. 183 (2016) 133–141. [561] J. Fu, B. Chang, Y. Tian, F. Xi, X. Dong, J. Mater. Chem. A 1 (2013) 3083–3090. [562] J. Zhang, Y. Wang, J. Jin, J. Zhang, Z. Lin, F. Huang, J. Yu, ACS Appl. Mater. Interfaces 5 (2013) 10317–10324. [563] M. Lu, Z. Pei, S. Weng, W. Feng, Z. Fang, Z. Zheng, M. Huang, P. Liu, Phys. Chem. Chem. Phys. 16 (2014) 21280–21288. [564] Z.L. Fang, H.F. Rong, Z.L. Ya, P. Qi, J. Mater. Sci. 50 (2015) 3057–3064. [565] J. Liu, J. Phys. Chem. C 119 (2015) 28417–28423. [566] Y. Xu, W.-D. Zhang, Eur. J. Inorg. Chem 2015 (2015) 1744–1751. [567] S. Shi, M.A. Gondal, A.A. Al-Saadi, R. Fajgar, J. Kupcik, X. Chang, K. Shen, Q. Xu, Z.S. Seddigi, J. Colloid Interface Sci. 416 (2014) 212–219. [568] S. Shi, M.A. Gondal, S.G. Rashid, Q. Qi, A.A. Al- Saadi, Z.H. Yamani, Y. Sui, Q. Xu, K. Shen, Colloid Surf. A 461 (2014) 202–211. [569] W. Zhang, Y. Sun, F. Dong, W. Zhang, S. Duan, Q. Zhang, Dalton Trans. 43 (2014) 12026–12036. [570] H. Gu, T. Zhou, G. Shi, Talanta 132 (2015) 871–876. [571] L. Lei, H. Jin, Q. Zhang, J. Xu, D. Gao, Z. Fu, Dalton Trans. 44 (2015) 795–803. [572] Q. Li, X. Zhao, J. Yang, C.-J. Jia, Z. Jin, W. Fan, Nanoscale 7 (2015) 18971–18983.

119

[573] W. Wang, H. Cheng, B. Huang, X. Liu, X. Qin, X. Zhang, Y. Dai, J. Colloid Interface Sci. 442 (2015) 97–102. [574] Y. Yang, F. Zhou, S. Zhan, Y. Liu, Y. Yin, J. Inorg. Organomet. Polym. Mater. 26 (2016) 91–99. [575] S. Yin, J. Di, M. Li, Y. Sun, J. Xia, H. Xu, W. Fan, H. Li, J. Mater. Sci. 51 (2016) 4769–4777. [576] L. Ge, C. Han, J. Liu, Appl. Catal. B: Environ. 108 (2011) 100–107. [577] L. Ge, C. Han, J. Liu, in: H.B. Ji, Y. Chen, S.Z. Chen (Eds.), Advanced Materials and Processes Ii, Pts 1–3, 2012, pp. 957–960. [578] Y. Wang, X. Bai, C. Pan, J. He, Y. Zhu, J. Mater. Chem. 22 (2012) 11568–11573. [579] M.-S. Gui, P.-F. Wang, D. Yuan, Y.-K. Yang, Chin. J. Inorg. Chem. 29 (2013) 2057–2064. [580] H. Wang, J. Lu, F. Wang, W. Wei, Y. Chang, S. Dong, Ceram. Int. 40 (2014) 9077–9086. [581] L. Liu, Y. Qi, J. Lu, S. Lin, W. An, J. Hu, Y. Liang, W. Cui, RSC Adv. 5 (2015) 99339–99346. [582] M. Wang, M.H. Fang, C. Tang, L.N. Zhang, Z.H. Huang, Y.G. Liu, X.W. Wu, J. Mater. Res. 31 (2016) 713–720. [583] S. Girish Kumar, K.S.R. Koteswara Rao, Appl. Surf. Sci. 355 (2015) 939–958. [584] J. Theerthagiri, R.A. Senthil, A. Priya, J. Madhavan, R.J.V. Michael, M. Ashokkumar, RSC Adv. 4 (2014) 38222–38229. [585] D. Xiao, K. Dai, Y. Qu, Y. Yin, H. Chen, Appl. Surf. Sci. 358 (2015) 181–187. [586] Y. Xu, S. Huang, M. Xie, Y. Li, H. Xu, L. Huang, Q. Zhang, H. Li, RSC Adv. 5 (2015) 95727–95735. [587] K.C. Christoforidis, T. Montini, E. Bontempi, S. Zafeiratos, J.J. Delgado Jaen, P. Fornasiero, Appl. Catal. B: Environ. 187 (2016) 171–180. [588] F. Dong, Z. Zhao, T. Xiong, Z. Ni, W. Zhang, Y. Sun, W.-K. Ho, ACS Appl. Mater. Interfaces 5 (2013) 11392–11401. [589] X. Ding, Y. Li, J. Zhao, Y. Zhu, Y. Li, W. Deng, C. Wang, APL Mater. 3 (2015) 104410. [590] W. Li, C. Feng, S. Dai, J. Yue, F. Hua, H. Hou, Appl. Catal. B: Environ. 168 (2015) 465–471. [591] D. Wang, Z. Xu, Q. Luo, X. Li, J. An, R. Yin, C. Bao, J. Mater. Sci. 51 (2016) 893–902. [592] L. Zhang, F. Huang, C. Liang, L. Zhou, X. Zhang, Q. Pang, J. Taiwan Inst. Chem. Eng. 60 (2016) 643–650. [593] P. Zhou, J. Yu, M. Jaroniec, Adv. Mater. 26 (2014) 4920–4935. [594] K. Maeda, ACS Catal. 3 (2013) 1486–1503. [595] Q. Wang, T. Hisatomi, Q. Jia, H. Tokudome, M. Zhong, C. Wang, Z. Pan, T. Takata, M. Nakabayashi, N. Shibata, Y. Li, I.D. Sharp, A. Kudo, T. Yamada, K. Domen, Nat. Mater. 15 (2016) 611. [596] L. Xiong, F. Yang, L. Yan, N. Yan, X. Yang, M. Qiu, Y. Yu, J. Phys. Chem. Solids 72 (2011) 1104–1109. [597] S. Hu, F. Zhou, L. Wang, J. Zhang, Catal. Commun. 12 (2011) 794–797. [598] W.-K. Jo, T.S. Natarajan, Chem. Eng. J. 281 (2015) 549–565. [599] W.-K. Jo, T. Adinaveen, J.J. Vijaya, N.C.S. Selvam, RSC Adv. 6 (2016) 10487–10497. [600] J. Zhang, Y. Hu, X. Jiang, S. Chen, S. Meng, X. Fu, J. Hazard. Mater. 280 (2014) 713–722. [601] W. Yu, D. Xu, T. Peng, J. Mater. Chem. A 3 (2015) 19936–19947. [602] Y. Liu, R. Wang, Z. Yang, H. Du, Y. Jiang, C. Shen, K. Liang, A. Xu, Chin. J. Catal. 36 (2015) 2135–2144. [603] N. Tian, H. Huang, Y. He, Y. Guo, T. Zhang, Y. Zhang, Dalton Trans. 44 (2015) 4297–4307. [604] J. Lv, K. Dai, J. Zhang, L. Geng, C. Liang, Q. Liu, G. Zhu, C. Chen, Appl. Surf. Sci. 358 (2015) 377–384. [605] H. Katsumata, Y. Tachi, T. Suzuki, S. Kaneco, RSC Adv. 4 (2014) 21405–21409. [606] S. Chen, Y. Hu, X. Jiang, S. Meng, X. Fu, Mater. Chem. Phys. 149 (2015) 512–521. [607] H. Katsumata, T. Sakai, T. Suzuki, S. Kaneco, Ind. Eng. Chem. Res. 53 (2014) 8018–8025. [608] Y. He, L. Zhang, B. Teng, M. Fan, Environ. Sci. Technol. 49 (2015) 649–656. [609] X. Chen, X. Huang, Z. Yi, Chem. Eur. J. 20 (2014) 17590–17596. [610] Y. Bai, P.-Q. Wang, J.-Y. Liu, X.-J. Liu, RSC Adv. 4 (2014) 19456–19461. [611] F. Shi, L. Chen, M. Chen, D. Jiang, Chem. Commun. 51 (2015) 17144–17147. [612] X. Ma, Q. Jiang, W. Guo, M. Zheng, W. Xu, F. Ma, B. Hou, RSC Adv. 6 (2016) 28263–28269. [613] D. Ma, J. Wu, M. Gao, Y. Xin, T. Ma, Y. Sun, Chem. Eng. J. 290 (2016) 136–146. [614] J.-C. Wang, H.-C. Yao, Z.-Y. Fan, L. Zhang, J.-S. Wang, S.-Q. Zang, Z.-J. Li, ACS Appl. Mater. Interfaces 8 (2016) 3765–3775. [615] X. Yang, Z. Chen, J. Xu, H. Tang, K. Chen, Y. Jiang, ACS Appl. Mater. Interfaces 7 (2015) 15285–15293. [616] Y. Hong, Y. Jiang, C. Li, W. Fan, X. Yan, M. Yan, W. Shi, Appl. Catal. B: Environ. 180 (2016) 663–673. [617] Y. He, L. Zhang, X. Wang, Y. Wu, H. Lin, L. Zhao, W. Weng, H. Wan, M. Fan, RSC Adv. 4 (2014) 13610–13619. [618] H. Cheng, J. Hou, O. Takeda, X.-M. Guo, H. Zhu, J. Mater. Chem. A 3 (2015) 11006–11013. [619] X. Yang, H. Tang, J. Xu, M. Antonietti, M. Shalom, ChemSusChem 8 (2015) 1350–1358. [620] T. Ohno, N. Murakami, T. Koyanagi, Y. Yang, J. CO2 Util. 6 (2014) 17–25. [621] A.S. Cherevan, P. Gebhardt, C.J. Shearer, M. Matsukawa, K. Domen, D. Eder, Energy Environ. Sci. 7 (2014) 791–796. [622] F.-X. Xiao, S.-F. Hung, H.B. Tao, J. Miao, H.B. Yang, B. Liu, Nanoscale 6 (2014) 14950–14961.

120

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

[623] B. Weng, M.-Q. Yang, N. Zhang, Y.-J. Xu, J. Mater. Chem. A 2 (2014) 9380–9389. [624] D. Jena, K. Banerjee, G.H. Xing, Nat. Mater. 13 (2014) 1076–1078. [625] N. Zhang, M.Q. Yang, Z.R. Tang, Y.J. Xu, ACS Nano 8 (2014) 623–633. [626] C. Han, M.-Q. Yang, N. Zhang, Y.-J. Xu, J. Mater. Chem. A 2 (2014) 19156–19166. [627] S. Bai, J. Ge, L. Wang, M. Gong, M. Deng, Q. Kong, L. Song, J. Jiang, Q. Zhang, Y. Luo, Y. Xie, Y. Xiong, Adv. Mater. 26 (2014) 5689. [628] L. Ge, C. Han, X. Xiao, L. Guo, Int. J. Hydrogen Energy 38 (2013) 6960–6969. [629] Q. Li, N. Zhang, Y. Yang, G. Wang, D.H.L. Ng, Langmuir 30 (2014) 8965–8972. [630] W.-c. Peng, X.-y. Li, Catal. Commun. 49 (2014) 63–67. [631] Y. Tian, L. Ge, K. Wang, Y. Chai, Mater. Charact. 87 (2014) 70–73. [632] H. Zhao, Y. Dong, P. Jiang, H. Miao, G. Wang, J. Zhang, J. Mater. Chem. A 3 (2015) 7375–7381. [633] J. Li, E. Liu, Y. Ma, X. Hu, J. Wan, L. Sun, J. Fan, Appl. Surf. Sci. 364 (2016) 694–702. [634] M. Sun, Q. Yan, T. Yan, M. Li, D. Wei, Z. Wang, Q. Wei, B. Du, RSC Adv. 4 (2014) 31019–31027. [635] Z. Zhang, J. Huang, M. Zhang, Q. Yuan, B. Dong, Appl. Catal. B: Environ. 163 (2015) 298–305. [636] Y. Liu, P. Chen, Y. Chen, H. Lu, J. Wang, Z. Yang, Z. Lu, M. Li, L. Fang, RSC Adv. 6 (2016) 10802–10809. [637] Y. Hou, Y. Zhu, Y. Xu, X. Wang, Appl. Catal. B: Environ. 156 (2014) 122–127. [638] M.S. Akple, J. Low, S. Wageh, A.A. Al-Ghamdi, J. Yu, J. Zhang, Appl. Surf. Sci. 358 (2015) 196–203. [639] S. Hu, W. Zhang, J. Bai, G. Lu, L. Zhang, G. Wu, RSC Adv. 6 (2016) 25695–25702. [640] Z. Zhang, D. Jiang, D. Li, M. He, M. Chen, Appl. Catal. B: Environ. 183 (2016) 113–123. [641] L. Ye, J. Liu, Z. Jiang, T. Peng, L. Zan, Appl. Catal. B: Environ. 142 (2013) 1–7. [642] J. Hong, W. Zhang, Y. Wang, T. Zhou, R. Xu, ChemCatChem 6 (2014) 2315–2321. [643] L. Zhang, M. Ou, H. Yao, Z. Li, D. Qu, F. Liu, J. Wang, J. Wang, Z. Li, Electrochim. Acta 186 (2015) 292–301. [644] N. Tian, Y. Zhang, C. Liu, S. Yu, M. Li, H. Huang, RSC Adv. 6 (2016) 10895–10903. [645] Q. Zhang, H. Wang, S. Hu, G. Lu, J. Bai, X. Kang, D. Liu, J. Gui, RSC Adv. 5 (2015) 42736–42743. [646] Q. Xiang, J. Yu, M. Jaroniec, J. Am. Chem. Soc. 134 (2012) 6575–6578. [647] W.K. Ho, J.C. Yu, J. Lin, J.G. Yu, P.S. Li, Langmuir 20 (2004) 5865–5869. [648] Y. Lu, D. Wang, P. Yang, Y. Du, C. Lu, Catal. Sci. Technol. 4 (2014) 2650–2657. [649] S. Bai, L. Wang, X. Chen, J. Du, Y. Xiong, Nano Res. 8 (2015) 175–183. [650] Y. Hou, Z. Wen, S. Cui, X. Guo, J. Chen, Adv. Mater. 25 (2013) 6291–6297. [651] X. Hao, Z. Jin, S. Min, G. Lu, RSC Adv. 6 (2016) 23709–23717. [652] D. Lu, G. Zhang, Z. Wan, Appl. Surf. Sci. 358 (2015) 223–230. [653] Z.a. Huang, Q. Sun, K. Lv, Z. Zhang, M. Li, B. Li, Appl. Catal. B: Environ. 164 (2015) 420–427. [654] L. Gu, J. Wang, Z. Zou, X. Han, J. Hazard. Mater. 268 (2014) 216–223. [655] K. Dai, L. Lu, C. Liang, Q. Liu, G. Zhu, Appl. Catal. B: Environ. 156 (2014) 331–340. [656] C.P. Sajan, S. Wageh, A.A. Al- Ghamdi, J. Yu, S. Cao, Nano Res. 9 (2016) 3–27. [657] C. Wang, X. Zhang, Y. Liu, Appl. Surf. Sci. 358 (2015) 28–45. [658] J. Low, B. Cheng, J. Yu, M. Jaroniec, Energy Storage Mater. 3 (2016) 24–35. [659] G. Li, X. Nie, J. Chen, Q. Jiang, T. An, P.K. Wong, H. Zhang, H. Zhao, H. Yamashita, Water. Res. 86 (2015) 17–24. [660] W. Wang, J.C. Yu, D. Xia, P.K. Wong, Y. Li, Environ. Sci. Technol. 47 (2013) 8724–8732. [661] S. Xie, Q. Zhang, G. Liu, Y. Wang, Chem. Commun. 52 (2016) 35–59. [662] L. Yang, H. Zhou, T. Fan, D. Zhang, Phys. Chem. Chem. Phys. 16 (2014) 6810–6826. [663] F. Fina, H. Menard, J.T.S. Irvine, Phys. Chem. Chem. Phys. 17 (2015) 13929–13936. [664] X. Li, W. Bi, L. Zhang, S. Tao, W. Chu, Q. Zhang, Y. Luo, C. Wu, Y. Xie, Adv. Mater. 28 (2016) 2427–2431. [665] D. Jiang, L. Chen, J. Xie, M. Chen, Dalton Trans. 43 (2014) 4878–4885. [666] S. Samanta, S. Martha, K. Parida, ChemCatChem 6 (2014) 1453–1462. [667] J. Lang, M. Liu, Y. Su, L. Yan, X. Wang, Appl. Surf. Sci. 358 (2015) 252–260. [668] S. Liang, Y. Xia, S. Zhu, S. Zheng, Y. He, J. Bi, M. Liu, L. Wu, Appl. Surf. Sci. 358 (2015) 304–312. [669] Z. Yan, Z. Sun, X. Liu, H. Jia, P. Du, Nanoscale 8 (2016) 4748–4756. [670] Z. Chen, P. Sun, B. Fan, Z. Zhang, X. Fang, J. Phys. Chem. C 118 (2014) 7801–7807. [671] Y. Lu, D. Chu, M. Zhu, Y. Du, P. Yang, Phys. Chem. Chem. Phys. 17 (2015) 17355–17361. [672] Y.-N. Zhang, X.-H. Li, Y.-Y. Cai, L.-H. Gong, K.-X. Wang, J.-S. Chen, RSC Adv. 4 (2014) 60873–60877. [673] L. Yin, Y.-P. Yuan, S.-W. Cao, Z. Zhang, C. Xue, RSC Adv. 4 (2014) 6127–6132. [674] M. Fan, C. Song, T. Chen, X. Yan, D. Xu, W. Gu, W. Shi, L. Xiao, RSC Adv. 6 (2016) 34633–34640. [675] K. Mori, T. Itoh, H. Kakudo, T. Iwamoto, Y. Masui, M. Onaka, H. Yamashita, Phys. Chem. Chem. Phys. 17 (2015) 24086–24091. [676] A. Indra, P.W. Menezes, K. Kailasam, D. Hollmann, M. Schroeder, A. Thomas, A. Brueckner, M. Driess, Chem. Commun. 52 (2016) 104–107. [677] S.-W. Cao, Y.-P. Yuan, J. Barber, S.C.J. Loo, C. Xue, Appl. Surf. Sci. 319 (2014) 344–349.

[678] Z.-F. Huang, J. Song, K. Li, M. Tahir, Y.-T. Wang, L. Pan, L. Wang, X. Zhang, J.-J. Zou, J. Am. Chem. Soc. 138 (2016) 1359–1365. [679] J. Dong, M. Wang, X. Li, L. Chen, Y. He, L. Sun, ChemSusChem 5 (2012) 2133–2138. [680] K. Li, F.-Y. Su, W.-D. Zhang, Appl. Surf. Sci. 375 (2016) 110–117. [681] L. Ge, C. Han, Appl. Catal. B: Environ. 117 (2012) 268–274. [682] J. Zhang, F. Huang, Appl. Surf. Sci. 358 (2015) 287–295. [683] F. He, G. Chen, Y. Zhou, Y. Yu, L. Li, S. Hao, B. Liu, J. Mater. Chem. A 4 (2016) 3822–3827. [684] G. Zhang, S. Zang, L. Lin, Z.-A. Lan, G. Li, X. Wang, ACS Appl. Mater. Interfaces 8 (2016) 2287–2296. [685] G. Zhang, S. Zang, X. Wang, ACS Catal. 5 (2014) 941–947. [686] S. Nayak, L. Mohapatra, K. Parida, J. Mater. Chem. A 3 (2015) 18622–18635. [687] Z. Guigang, H. Caijin, W. Xinchen, Small 11 (2015) 1215–1221. [688] C. Han, L. Ge, C. Chen, Y. Li, X. Xiao, Y. Zhang, L. Guo, Appl. Catal. B: Environ. 147 (2014) 546–553. [689] J.S. Zhang, M. Grzelczak, Y.D. Hou, K. Maeda, K. Domen, X.Z. Fu, M. Antonietti, X.C. Wang, Chem. Sci. 3 (2012) 443–446. [690] L. Ge, C. Han, X. Xiao, L. Guo, Appl. Catal. B: Environ. 142 (2013) 414–422. [691] J. Yu, K. Wang, W. Xiao, B. Cheng, Phys. Chem. Chem. Phys. 16 (2014) 11492–11501. [692] W.-J. Ong, L.-L. Tan, S.-P. Chai, S.-T. Yong, Dalton Trans. 44 (2015) 1249–1257. [693] H. Shi, C. Zhang, C. Zhou, G. Chen, RSC Adv. 5 (2015) 93615–93622. [694] G. Gao, Y. Jiao, E.R. Waclawik, A. Du, J. Am. Chem. Soc. 138 (2016) 6292–6297. [695] R. Kuriki, K. Sekizawa, O. Ishitani, K. Maeda, Angew. Chem. Int. Ed. 54 (2015) 2406–2409. [696] R. Kuriki, O. Ishitani, K. Maeda, Acs Appl. Mater. Interfaces 8 (2016) 6011–6018. [697] K. Maeda, R. Kuriki, O. Ishitani, Chem. Lett. 45 (2016) 182–184. [698] G. Zhang, Z.-A. Lan, X. Wang, ChemCatChem 7 (2015) 1422–1423. [699] K. Maeda, K. Sekizawa, O. Ishitani, Chem. Commun. 49 (2013) 10127–10129. [700] R. Kuriki, H. Matsunaga, T. Nakashima, K. Wada, A. Yamakata, O. Ishitani, K. Maeda, J. Am. Chem. Soc. 138 (2016) 5159–5170. [701] L. Ye, D. Wu, K.H. Chu, B. Wang, H. Xie, H.Y. Yip, P.K. Wong, Chem. Eng. J. (2016). [702] W.-J. Ong, L.-L. Tan, S.-P. Chai, S.-T. Yong, Chem. Commun. 51 (2015) 858–861. [703] H. Li, S. Gan, H. Wang, D. Han, L. Niu, Adv. Mater. 27 (2015) 6906–6913. [704] J. Yu, J. Jin, B. Cheng, M. Jaroniec, J. Mater. Chem. A 2 (2014) 3407–3416. [705] Y. Wang, X. Bai, H. Qin, F. Wang, Y. Li, X. Li, S. Kang, Y. Zuo, L. Cui, ACS Appl. Mater. Interfaces 8 (2016) 17212–17219. [706] X. Lu, T.H. Tan, Y.H. Ng, R. Amal, Chem. Eur. J. (2016), http://dx.doi.org/10. 1002/chem.201601674. [707] M. Seredych, S. Los, D.A. Giannakoudakis, E. Rodriguez-Castellon, T.J. Bandosz, ChemSusChem 9 (2016) 795–799. [708] L. Shi, T. Wang, H. Zhang, K. Chang, J. Ye, Adv. Funct. Mater. 25 (2015) 5360–5367. [709] S. Wang, J. Lin, X. Wang, Phys. Chem. Chem. Phys. 16 (2014) 14656–14660. [710] X. Lu, J. Shen, J. Wang, Z. Cui, J. Xie, RSC Adv. 5 (2015) 15993–15999. [711] O. Fontelles-Carceller, M.J. Munoz-Batista, M. Fernandez-Garcia, A. Kubacka, ACS Appl. Mater. Interfaces 8 (2016) 2617–2627. [712] Y. Fu, T. Huang, L. Zhang, J. Zhu, X. Wang, Nanoscale 7 (2015) 13723–13733. [713] C. Min, C. Shen, R. Li, Y. Li, J. Qin, X. Yang, Ceram. Int. 42 (2016) 5575–5581. [714] M. Zang, L. Shi, L. Liang, D. Li, J. Sun, RSC Adv. 5 (2015) 56136–56144. [715] J. Xue, S. Ma, Y. Zhou, Z. Zhang, X. Liu, RSC Adv. 5 (2015) 58738–58745. [716] Z.W. Tong, D. Yang, Y.Y. Sun, Z.Y. Jiang, RSC Adv. 5 (2015) 56913–56921. [717] K. Tian, W.-J. Liu, H. Jiang, ACS Sustain. Chem. Eng. 3 (2015) 269–276. [718] Y. Su, Y. Zhao, Y. Zhao, J. Lang, X. Xin, X. Wang, Appl. Surf. Sci. 358 (2015) 213–222. [719] Z. Li, J. Wang, K. Zhu, F. Ma, A. Meng, Mater. Lett. 145 (2015) 167–170. [720] X. Yao, X. Liu, X. Hu, ChemCatChem 6 (2014) 3409–3418. [721] Y. Bu, Z. Chen, W. Li, Appl. Catal. B: Environ. 144 (2014) 622–630. [722] J. Cao, Y. Zhao, H. Lin, B. Xu, S. Chen, Mater. Res. Bull. 48 (2013) 3873–3880. [723] L. Ge, C. Han, J. Liu, Y. Li, Appl. Catal. A: Gen. 409 (2011) 215–222. [724] H.-T. Ren, S.-Y. Jia, S.-H. Wu, T.-H. Zhang, X. Han, Mater. Lett. 142 (2015) 15–18. [725] S. Ma, J. Xue, Y. Zhou, Z. Zhang, RSC Adv. 5 (2015) 40000–40006. [726] L. Shi, L. Liang, J. Ma, F. Wang, J. Sun, Catal. Sci. Technol. 4 (2014) 758–765. [727] H.-T. Ren, S.-Y. Jia, Y. Wu, S.-H. Wu, T.-H. Zhang, X. Han, Ind. Eng. Chem. Res. 53 (2014) 17645–17653. [728] M. Xu, L. Han, S. Dong, ACS Appl. Mater. Interfaces 5 (2013) 12533–12540. [729] C. Chang, Y. Fu, M. Hu, C. Wang, G. Shan, L. Zhu, Appl. Catal. B: Environ. 142 (2013) 553–560. [730] Y. Li, X. Xu, P. Zhang, Y. Gong, H. Li, Y. Wang, RSC Adv. 3 (2013) 10973–10982. [731] Z. Zhang, M. Xu, W. Ho, X. Zhang, Z. Yang, X. Wang, Appl. Catal. B: Environ. 184 (2016) 174–181. [732] S.K. Konda, M. Amiri, A. Chen, J. Phys. Chem. C 120 (2016) 14467–14473. [733] K. Sridharan, E. Jang, J.H. Park, J.-H. Kim, J.-H. Lee, T.J. Park, Chem. Eur. J. 21 (2015) 9126–9132. [734] H.-Y. Chen, L.-G. Qiu, J.-D. Xiao, S. Ye, X. Jiang, Y.-P. Yuan, RSC Adv. 4 (2014) 22491–22496. [735] W.-K. Jo, J.Y. Lee, N.C.S. Selvam, Chem. Eng. J. 289 (2016) 306–318. [736] J.-Y. Hu, K. Tian, H. Jiang, Chemosphere 148 (2016) 34–40. [737] C. Li, F. Raziq, C. Liu, Z. Li, L. Sun, L. Jing, Appl. Surf. Sci. 358 (2015) 240–245. [738] C. Liu, L. Jing, L. He, Y. Luan, C. Li, Chem. Commun. 50 (2014) 1999–2001.

J. Wen et al. / Applied Surface Science 391 (2017) 72–123 [739] [740] [741] [742] [743] [744] [745] [746] [747] [748] [749] [750] [751] [752] [753] [754] [755] [756] [757] [758] [759] [760] [761] [762] [763] [764] [765] [766] [767] [768] [769] [770] [771] [772] [773] [774] [775] [776] [777] [778] [779] [780] [781] [782] [783] [784] [785] [786] [787] [788] [789] [790] [791] [792]

Y. Min, X.F. Qi, Q. Xu, Y. Chen, CrystEngComm 16 (2014) 1287–1295. D. Xu, B. Cheng, S. Cao, J. Yu, Appl. Catal. B: Environ. 164 (2015) 380–388. R.C. Pawar, V. Khare, C.S. Lee, Dalton Trans. 43 (2014) 12514–12527. B. Yuan, J. Wei, T. Hu, H. Yao, Z. Jiang, Z. Fang, Z. Chu, Chin. J. Catal. 36 (2015) 1009–1016. L. Wang, J. Ding, Y. Chai, Q. Liu, J. Ren, X. Liu, W.-L. Dai, Dalton Trans. 44 (2015) 11223–11234. M. Yan, F. Zhu, W. Gu, L. Sun, W. Shi, Y. Hua, RSC Adv. 6 (2016) 61162–61174. S. Fang, Y. Xia, K. Lv, Q. Li, J. Sun, M. Li, Appl. Catal. B: Environ. 185 (2016) 225–232. X. Jian, X. Liu, H.-m. Yang, J.-g. Li, X.-l. Song, H.-y. Dai, Z.-h. Liang, Appl. Surf. Sci. 370 (2016) 514–521. Y. Xu, H. Xu, L. Wang, J. Yan, H. Li, Y. Song, L. Huang, G. Cai, Dalton Trans. 42 (2013) 7604–7613. L. Pi, R. Jiang, W. Zhou, H. Zhu, W. Xiao, D. Wang, X. Mao, Appl. Surf. Sci. 358 (2015) 231–239. Q. Yu, X. Li, L. Zhang, X. Wang, Y. Tao, X. Wang, J. Polym. Mater. 32 (2015) 411–422. X.-H. Li, L.-G. Zhang, X.-X. Wang, Q.-B. Yu, Acta Phys. Chim. Sin. 31 (2015) 764–770. X.-H. Li, L.-G. Zhang, X.-X. Wang, Q.-B. Yu, J. Inorg. Mater. 30 (2015) 1018–1024. B. Chai, X. Liao, F. Song, H. Zhou, Dalton Trans. 43 (2014) 982–989. X. Bai, L. Wang, Y. Wang, W. Yao, Y. Zhu, Appl. Catal. B: Environ. 152 (2014) 262–270. S. Zhang, J. Li, X. Wang, Y. Huang, M. Zeng, J. Xu, J. Mater. Chem. A 3 (2015) 10119–10126. R.C. Pawar, S. Kang, S.H. Ahn, C.S. Lee, RSC Adv. 5 (2015) 24281–24292. L. Chen, H. Tao, T. Pang, J. Dong, X. Song, Chem. Lett. 44 (2015) 348–350. L. Shi, L. Liang, J. Ma, F. Wang, J. Sun, Dalton Trans. 43 (2014) 7236–7244. X. Wang, K. Wang, K. Feng, F. Chen, H. Yu, J. Yu, J. Mol. Catal. A: Chem. 391 (2014) 92–98. H. Yu, P. Xiao, P. Wang, J. Yu, Appl. Catal. B: Environ. 193 (2016) 217–225. Y. Wang, F. Li, H. Li, L. Bai, L. Sun, Chem. Commun. 52 (2016) 3050–3053. S. Ye, R. Chen, Y. Xu, F. Fan, P. Du, F. Zhang, X. Zong, T. Chen, Y. Qi, P. Chen, Z. Chen, C. Li, J. Catal. 338 (2016) 168–173. D. Wang, R. Li, J. Zhu, J. Shi, J. Han, X. Zong, C. Li, J. Phys. Chem. C 116 (2012) 5082–5089. M.W. Kanan, D.G. Nocera, Science 321 (2008) 1072–1075. D. Wang, T. Hisatomi, T. Takata, C. Pan, M. Katayama, J. Kubota, K. Domen, Angew. Chem. Int. Ed. 52 (2013) 11252–11256. K.R. Yoon, J.W. Ko, D.-Y. Youn, C.B. Park, I.-D. Kim, Green Chem. 18 (2016) 944–950. S. Hu, M.R. Shaner, J.A. Beardslee, M. Lichterman, B.S. Brunschwig, N.S. Lewis, Science 344 (2014) 1005–1009. M.J. Kenney, M. Gong, Y. Li, J.Z. Wu, J. Feng, M. Lanza, H. Dai, Science 342 (2013) 836–840. Q. Yu, J. Xu, C. Wu, L. Guan, RSC Adv. 5 (2015) 65303–65307. G. Liao, S. Chen, X. Quan, H. Yu, H. Zhao, J. Mater. Chem. 22 (2012) 2721–2726. K. Dai, L. Lu, Q. Liu, G. Zhu, X. Wei, J. Bai, L. Xuan, H. Wang, Dalton Trans. 43 (2014) 6295–6299. X. Li, Y. Dai, Y. Ma, S. Han, B. Huang, Phys. Chem. Chem. Phys. 16 (2014) 4230–4235. Y. Li, Y. Sun, F. Dong, W.-K. Ho, J. Colloid Interface Sci. 436 (2014) 29–36. L. Xu, W.-Q. Huang, L.-L. Wang, Z.-A. Tian, W. Hu, Y. Ma, X. Wang, A. Pan, G.-F. Huang, Chem. Mater. 27 (2015) 1612–1621. J. Liu, Y. Liu, N. Liu, Y. Han, X. Zhang, H. Huang, Y. Lifshitz, S.-T. Lee, J. Zhong, Z. Kang, Science 347 (2015) 970–974. Z. Ma, R. Sa, Q. Li, K. Wu, Phys. Chem. Chem. Phys. 18 (2016) 1050–1058. G. Gao, Y. Jiao, F. Ma, Y. Jiao, E. Waclawik, A. Du, Phys. Chem. Chem. Phys. 17 (2015) 31140–31144. Q. Liu, T. Chen, Y. Guo, Z. Zhang, X. Fang, Appl. Catal. B: Environ. 193 (2016) 248–258. S. Hu, H. Wang, F. Wang, J. Bai, L. Zhang, X. Kang, G. Wu, B. Korean, Chem. Soc. 36 (2015) 2527–2533. Z. Wu, H. Gao, S. Yan, Z. Zou, Dalton Trans. 43 (2014) 12013–12017. S. Patnaik, S. Martha, S. Acharya, K.M. Parida, Inorg. Chem. Front. 3 (2016) 336–347. S. Cao, J. Yu, J. Photochem. Photobiol. C 27 (2016) 72–99. R. Czerw, B. Foley, D. Tekleab, A. Rubio, P. Ajayan, D. Carroll, Phys. Rev. B 66 (2002) 033408. Q.J. Xiang, J.G. Yu, M. Jaroniec, Chem. Soc. Rev. 41 (2012) 782–796. Q. Xiang, J. Yu, J. Phys. Chem. Lett. 4 (2013) 753–759. G. Xie, K. Zhang, B. Guo, Q. Liu, L. Fang, J.R. Gong, Adv. Mater. 25 (2013) 3820–3839. F. Bonaccorso, L. Colombo, G. Yu, M. Stoller, V. Tozzini, A.C. Ferrari, R.S. Ruoff, V. Pellegrini, Science 347 (2015) 1246501. Q. Xiang, B. Cheng, J. Yu, Angew. Chem. Int. Ed. 54 (2015) 11350–11366. Y. Zhang, T. Mori, L. Niu, J. Ye, Energy Environ. Sci. 4 (2011) 4517–4521. Y. Li, H. Zhang, P. Liu, D. Wang, Y. Li, H. Zhao, Small 9 (2013) 3336–3344. S.W. Hu, L.W. Yang, Y. Tian, X.L. Wei, J.W. Ding, J.X. Zhong, P.K. Chu, J. Colloid Interface Sci. 431 (2014) 42–49. L.K. Putri, W.-J. Ong, W.S. Chang, S.-P. Chai, Appl. Surf. Sci. 358 (2015) 2–14. G. Zhang, G. Li, X. Wang, ChemCatChem 7 (2015) 2864–2870.

121

[793] M.Z. Rahman, J. Ran, Y. Tang, M. Jaroniec, S.Z. Qiao, J. Mater. Chem. A 4 (2016) 2445–2452. [794] M. Wu, J.-M. Yan, X.-w. Zhang, M. Zhao, Appl. Surf. Sci. 354 (2015) 196–200. [795] Z. Huang, F. Li, B. Chen, G. Yuan, RSC Adv. 5 (2015) 102700–102706. [796] L. Shi, L. Liang, F. Wang, M. Liu, K. Chen, K. Sun, N. Zhang, J. Sun, ACS Sustain. Chem. Eng. 3 (2015) 3412–3419. [797] Z. Jiang, D. Jiang, Z. Yan, D. Liu, K. Qian, J. Xie, Appl. Catal. B: Environ. 170 (2015) 195–205. [798] Y. Zhou, L. Zhang, W. Huang, Q. Kong, X. Fan, M. Wang, J. Shi, Carbon 99 (2016) 111–117. [799] J. Fang, H. Fan, M. Li, C. Long, J. Mater. Chem. A 3 (2015) 13819–13826. [800] Z.-A. Lan, G. Zhang, X. Wang, Appl. Catal. B: Environ. 192 (2016) 116–125. [801] X. Wang, J. Chen, X. Guan, L. Guo, Int. J. Hydrogen Energy 40 (2015) 7546–7552. [802] H. Liu, Z. Jin, Z. Xu, Dalton Trans. 44 (2015) 14368–14375. [803] H. Liu, Z. Xu, Z. Zhang, D. Ao, Appl. Catal. B: Environ. 192 (2016) 234–241. [804] D. Zheng, G. Zhang, X. Wang, Appl. Catal. B: Environ. 179 (2015) 479–488. [805] M. Li, L. Zhang, X. Fan, M. Wu, Y. Du, M. Wang, Q. Kong, L. Zhang, J. Shi, Appl. Catal. B: Environ. 190 (2016) 36–43. [806] F. Shi, L. Chen, C. Xing, D. Jiang, D. Li, M. Chen, RSC Adv. 4 (2014) 62223–62229. [807] D. Jiang, J. Li, C. Xing, Z. Zhang, S. Meng, M. Chen, ACS Appl. Mater. Interfaces 7 (2015) 19234–19242. [808] B. Li, Y. Wang, Y. Zeng, R. Wang, Mater. Lett. 178 (2016) 308–311. [809] X. Zhou, Z. Luo, P. Tao, B. Jin, Z. Wu, Y. Huang, Mater. Chem. Phys. 143 (2014) 1462–1468. [810] R. Cheng, X. Fan, M. Wang, M. Li, J. Tian, L. Zhang, RSC Adv. 6 (2016) 18990–18995. [811] R. Cheng, L. Zhang, X. Fan, M. Wang, M. Li, J. Shi, Carbon 101 (2016) 62–70. [812] J. Chen, S. Shen, P. Wu, L. Guo, Green Chem. 17 (2015) 509–517. [813] M. Wu, J.-M. Yan, X.-W. Zhang, M. Zhao, Q. Jiang, J. Mater. Chem. A 3 (2015) 15710–15714. [814] Z. Jiang, C. Zhu, W. Wan, K. Qian, J. Xie, J. Mater. Chem. A 4 (2016) 1806–1818. [815] L. Chen, X. Zhou, B. Jin, J. Luo, X. Xu, L. Zhang, Y. Hong, Int. J. Hydrogen Energy 41 (2016) 7292–7300. [816] R. Ye, H. Fang, Y.-Z. Zheng, N. Li, Y. Wang, X. Tao, ACS Appl. Mater. Interfaces 8 (2016) 13879–13889. [817] W. Chen, T.-Y. Liu, T. Huang, X.-H. Liu, G.-R. Duan, X.-J. Yang, S.-M. Chen, RSC Adv. 5 (2015) 101214–101220. [818] S. Pany, K.M. Parida, Phys. Chem. Chem. Phys. 17 (2015) 8070–8077. [819] C. Bo, P. Tianyou, M. Jing, L. Kan, Z. Ling, Phys. Chem. Chem. Phys. 14 (2012) 16745–16752. [820] X. Yang, H. Huang, M. Kubota, Z. He, N. Kobayashi, X. Zhou, B. Jin, J. Luo, Mater. Res. Bull. 76 (2016) 79–84. [821] G. Zhao, X. Huang, F. Fina, G. Zhang, J.T.S. Irvine, Catal. Sci. Technol. 5 (2015) 3416–3422. [822] K. Song, F. Xiao, L. Zhang, F. Yue, X. Liang, J. Wang, X. Su, J. Mol. Catal. A: Chem. 418 (2016) 95–102. [823] S. Cao, J. Jiang, b. zhu, J. Yu, Phys. Chem. Chem. Phys. 18 (2016) 19457–19463. [824] D. Kong, J.J. Cha, H. Wang, H.R. Lee, Y. Cui, Energy Environ. Sci. 6 (2013) 3553–3558. [825] Z. Zhao, H. Yang, J. Mol. Catal. A: Chem. 398 (2015) 268–274. [826] D. Wang, Y. Zhang, W. Chen, Chem. Commun. 50 (2014) 1754–1756. [827] X. Wang, G. Zhang, Z.-a. Lan, L. Lin, S. Lin, Chem. Sci. 7 (2016) 3062–3066. [828] D.J. Martin, P.J.T. Reardon, S.J.A. Moniz, J. Tang, J. Am. Chem. Soc. 136 (2014) 12568–12571. [829] S.N. Frank, A.J. Bard, J. Am. Chem. Soc. 99 (1977) 303–304. [830] J. Yu, B. Wang, Appl. Catal. B: Environ. 94 (2010) 295–302. [831] J. Yu, G. Dai, B. Cheng, J. Phys. Chem. C 114 (2010) 19378–19385. [832] J. Yu, G. Wang, B. Cheng, M. Zhou, Appl. Catal. B: Environ. 69 (2007) 171–180. [833] J. Yu, Y. Wang, W. Xiao, J. Mater. Chem. A 1 (2013) 10727–10735. [834] J. Yu, G. Dai, B. Huang, J. Phys. Chem. C 113 (2009) 16394–16401. [835] J. Yu, G. Dai, Q. Xiang, M. Jaroniec, J. Mater. Chem. 21 (2011) 1049–1057. [836] P. Madhusudan, J. Zhang, B. Cheng, J. Yu, Phys. Chem. Chem. Phys. 17 (2015) 15339–15347. [837] J. Yu, X. Yu, Environ. Sci. Technol. 42 (2008) 4902–4907. [838] Q. Xiang, J. Yu, M. Jaroniec, Phys. Chem. Chem. Phys. 13 (2011) 4853–4861. [839] G. Dai, J. Yu, G. Liu, J. Phys. Chem. C 115 (2011) 7339–7346. [840] D. Chatterjee, S. Dasgupta, J. Photochem. Photobiol. C 6 (2005) 186–205. [841] L.-Y. Chen, W.-D. Zhang, Appl. Surf. Sci. 301 (2014) 428–435. [842] B. Lin, C. Xue, X. Yan, G. Yang, G. Yang, B. Yang, Appl. Surf. Sci. 357 (2015) 346–355. [843] C.Q. Li, Z.M. Sun, Y.L. Xue, G.Y. Yao, S.L. Zheng, Adv. Powder Technol. 27 (2016) 330–337. [844] B. Korean, Chem. Soc. 36 (2015) 333–339. [845] X. Chen, J. Wei, R. Hou, Y. Liang, Z. Xie, Y. Zhu, X. Zhang, H. Wang, Appl. Catal. B: Environ. 188 (2016) 342–350. [846] H. Wang, J. Li, C. Ma, Q. Guan, Z. Lu, P. Huo, Y. Yan, Appl. Surf. Sci. 329 (2015) 17–22. [847] G. Li, X. Nie, Y. Gao, T. An, Appl. Catal. B: Environ. 180 (2016) 726–732. [848] Y. Chen, W. Huang, D. He, S. Yue, H. Huang, ACS Appl. Mater. Interfaces 6 (2014) 14405–14414. [849] L. Shi, L. Liang, F. Wang, M. Liu, S. Zhong, J. Sun, Catal. Commun. 59 (2015) 131–135. [850] H. Ji, F. Chang, X. Hu, W. Qin, J. Shen, Chem. Eng. J. 218 (2013) 183–190.

122

J. Wen et al. / Applied Surface Science 391 (2017) 72–123

[851] H. Zhang, L. Zhao, F. Geng, L.-H. Guo, B. Wan, Y. Yang, Appl. Catal. B: Environ. 180 (2016) 656–662. [852] K. Li, Z. Zeng, L. Yana, S. Luo, X. Luo, M. Huo, Y. Guo, Appl. Catal. B: Environ. 165 (2015) 428–437. [853] R.C. Pawar, Y. Pyo, S.H. Ahn, C.S. Lee, Appl. Catal. B: Environ. 176 (2015) 654–666. [854] S.P. Adhikari, H.R. Pant, H.J. Kim, C.H. Park, C.S. Kim, Ceram. Int. 41 (2015) 12923–12929. [855] Y. Li, J. Wang, Y. Yang, Y. Zhang, D. He, Q. An, G. Cao, J. Hazard. Mater. 292 (2015) 79–89. [856] Q. Liu, C. Fan, H. Tang, X. Sun, J. Yang, X. Cheng, Appl. Surf. Sci. 358 (2015) 188–195. [857] Y. He, J. Cai, T. Li, Y. Wu, H. Lin, L. Zhao, M. Luo, Chem. Eng. J. 215 (2013) 721–730. [858] T. Li, L. Zhao, Y. He, J. Cai, M. Luo, J. Lin, Appl. Catal. B: Environ. 129 (2013) 255–263. [859] Y. Zang, L. Li, X. Li, R. Lin, G. Li, Chem. Eng. J. 246 (2014) 277–286. [860] L. Liu, Y. Qi, J. Yang, W. Cui, X. Li, Z. Zhang, Appl. Surf. Sci. 358 (2015) 319–327. [861] R.M. Mohamed, Ceram. Int. 41 (2015) 1197–1204. [862] S.-Z. Wu, K. Li, W.-D. Zhang, Appl. Surf. Sci. 324 (2015) 324–331. [863] W. Zhao, Z. Wei, H. He, J. Xu, J. Li, S. Yang, C. Sun, Appl. Catal. A: Gen. 501 (2015) 74–82. [864] Z. Xiu, H. Bo, Y. Wu, X. Hao, Appl. Surf. Sci. 289 (2014) 394–399. [865] Z. Zhu, Z. Lu, D. Wang, X. Tang, Y. Yan, W. Shi, Y. Wang, N. Gao, X. Yao, H. Dong, Appl. Catal. B: Environ. 182 (2016) 115–122. [866] Q. Fan, Y. Huang, C. Zhang, J. Liu, L. Piao, Y. Yu, S. Zuo, B. Li, Catal. Today 264 (2016) 250–256. [867] N. Tian, H. Huang, Y. Zhang, Appl. Surf. Sci. 358 (2015) 343–349. [868] Z. Li, S. Yang, J. Zhou, D. Li, X. Zhou, C. Ge, Y. Fang, Chem. Eng. J. 241 (2014) 344–351. [869] X.J. Wang, Q. Wang, F.T. Li, W.Y. Yang, Y. Zhao, Y.J. Hao, S.J. Liu, Chem. Eng. J. 234 (2013) 361–371. [870] F. Chang, C. Li, J. Chen, J. Wang, P. Luo, Y. Xie, B. Deng, X. Hu, Superlattice Microstruct. 76 (2014) 90–104. [871] S.-Y. Chou, C.-C. Chen, Y.-M. Dai, J.-H. Lin, W.W. Lee, RSC Adv. 6 (2016) 33478–33491. [872] N. Tian, H. Huang, Y. Guo, Y. He, Y. Zhang, Appl. Surf. Sci. 322 (2014) 249–254. [873] H. Li, J. Liu, W. Hou, N. Du, R. Zhang, X. Tao, Appl. Catal. B: Environ. 160 (2014) 89–97. [874] Y. Tian, B. Chang, J. Lu, J. Fu, F. Xi, X. Dong, ACS Appl. Mater. Interfaces 5 (2013) 7079–7085. [875] Y. Guo, J. Li, Z. Gao, X. Zhu, Y. Liu, Z. Wei, W. Zhao, C. Sun, Appl. Catal. B: Environ. 192 (2016) 57–71. [876] C. Wen, H. Zhang, Q. Bo, T. Huang, Z. Lu, J. Lv, Y. Wang, Chem. Eng. J. 270 (2015) 405–410. [877] D. Chen, K. Wang, W. Hong, R. Zong, W. Yao, Y. Zhu, Appl. Catal. B: Environ. 166 (2015) 366–373. [878] Y. Shi, Z. Yang, Y. Liu, J. Yu, F. Wang, J. Tong, B. Su, Q. Wang, RSC Adv. 6 (2016) 39774–39783. [879] J. Ding, L. Wang, Q. Liu, Y. Chai, X. Liu, W.-L. Dai, Appl. Catal. B: Environ. 176 (2015) 91–98. [880] K. Li, L. Yan, Z. Zeng, S. Luo, X. Luo, X. Liu, H. Guo, Y. Guo, Appl. Catal. B: Environ. 156 (2014) 141–152. [881] L. Huang, H. Xu, R. Zhang, X. Cheng, J. Xia, Y. Xu, H. Li, Appl. Surf. Sci. 283 (2013) 25–32. [882] B. Korean, Chem. Soc. 36 (2015) 17–23. [883] S. Hu, L. Ma, F. Li, Z. Fan, Q. Wang, J. Bai, X. Kang, G. Wu, RSC Adv. 5 (2015) 90750–90756. [884] Y. Sun, T. Xiong, Z. Ni, J. Liu, F. Dong, W. Zhang, W.-K. Ho, Appl. Surf. Sci. 358 (2015) 356–362. [885] Z. Jin, N. Murakami, T. Tsubota, T. Ohno, Appl. Catal. B: Environ. 150 (2014) 479–485. [886] J. Ma, C. Wang, H. He, Appl. Catal. B: Environ. 184 (2016) 28–34. [887] F. Chang, Y. Xie, C. Li, J. Chen, J. Luo, X. Hu, J. Shen, Appl. Surf. Sci. 280 (2013) 967–974. [888] W. Tian, N. Li, J. Zhou, Appl. Surf. Sci. 361 (2016) 251–258. [889] Q. Wang, L. Zheng, Y. Bai, J. Zhao, F. Wang, R. Zhang, H. Huang, B. Su, Appl. Surf. Sci. 347 (2015) 602–609. [890] G. Xin, Y. Meng, J. Chem. N. Y. 2013 (2013) 1–5. [891] Y. Ke, H. Guo, D. Wang, J. Chen, W. Weng, J. Mater. Res. 29 (2014) 2473–2482. [892] Y. Meng, G. Xin, D. Chen, Optoelectron. Adv. Mater. 5 (2011) 648–650. [893] Y. Meng, J. Shen, D. Chen, G. Xin, Rare Met. 30 (2011) 276–279. [894] Y. Liu, X. Yuan, H. Wang, X. Chen, S. Gu, Q. Jiang, Z. Wu, L. Jiang, Y. Wu, G. Zeng, Catal. Commun. 70 (2015) 17–20. [895] Q. Wang, Y. Shi, Z. Du, J. He, J. Zhong, L. Zhao, H. She, G. Liu, B. Su, Eur. J. Inorg. Chem. (2015) 4108–4115. [896] T. Xian, H. Yang, L.J. Di, J.F. Dai, J. Alloy Compd. 622 (2015) 1098–1104. [897] X. Gao, X. Jiao, L. Zhang, W. Zhu, X. Xu, H. Ma, T. Chen, RSC Adv. 5 (2015) 76963–76972. [898] Z. Li, B. Li, S. Peng, D. Li, S. Yang, Y. Fang, RSC Adv. 4 (2014) 35144–35148. [899] S. Fang, K. Lv, Q. Li, H. Ye, D. Du, M. Li, Appl. Surf. Sci. 358 (2015) 336–342. [900] H. Pan, X. Li, Z. Zhuang, C. Zhang, J. Mol. Catal. A: Chem. 345 (2011) 90–95. [901] W. Chen, G.-R. Duan, T.-Y. Liu, S.-M. Chen, X.-H. Liu, Mater. Sci. Semicond. Process. 35 (2015) 45–54.

[902] Y. Liu, J. Wang, P. Yang, RSC Adv. 6 (2016) 34334–34341. [903] X. Wang, L. Zhang, H. Lin, Q. Nong, Y. Wu, T. Wu, Y. He, RSC Adv. 4 (2014) 40029–40035. [904] H. Xiao, W. Wang, G. Liu, Z. Chen, K. Lv, J. Zhu, Appl. Surf. Sci. 358 (2015) 313–318. [905] J. Cai, Y. He, X. Wang, L. Zhang, L. Dong, H. Lin, L. Zhao, X. Yi, W. Weng, H. Wan, RSC Adv. 3 (2013) 20862–20868. [906] X. Rong, F. Qiu, J. Yan, H. Zhao, X. Zhu, D. Yang, RSC Adv. 5 (2015) 24944–24952. [907] P. Liu, Y. Zhao, R. Qin, S. Mo, G. Chen, L. Gu, D.M. Chevrier, P. Zhang, Q. Guo, D. Zang, B. Wu, G. Fu, N. Zheng, Science 352 (2016) 797–801. [908] W. Bi, X. Li, L. Zhang, T. Jin, L. Zhang, Q. Zhang, Y. Luo, C. Wu, Y. Xie, Nat. Commun. 6 (2015) 8647. [909] H. Yu, G. Cao, F. Chen, X. Wang, J. Yu, M. Lei, Appl. Catal. B: Environ. 160 (2014) 658–665. [910] H. Yu, W. Chen, X. Wang, Y. Xu, J. Yu, Appl. Catal. B: Environ. 187 (2016) 163–170. [911] H. Yu, L. Xu, P. Wang, X. Wang, J. Yu, Appl. Catal. B: Environ. 144 (2014) 75–82. [912] H. Yu, X. Huang, P. Wang, J. Yu, J. Phys. Chem. C 120 (2016) 3722–3730. [913] H. Yu, H. Irie, Y. Shimodaira, Y. Hosogi, Y. Kuroda, M. Miyauchi, K. Hashimoto, J. Phys. Chem. C 114 (2010) 16481–16487. [914] X. Wang, R. Yu, P. Wang, F. Chen, H. Yu, Appl. Surf. Sci. 351 (2015) 66–73. [915] P. Wang, Y. Xia, P. Wu, X. Wang, H. Yu, J. Yu, J. Phys. Chem. C 118 (2014) 8891–8898. [916] Q. Liu, Y. Guo, Z. Chen, Z. Zhang, X. Fang, Appl. Catal. B: Environ. 183 (2016) 231–241. [917] C. Zhao, M. Pelaez, X. Duan, H. Deng, K. O’Shea, D. Fatta-Kassinos, D.D. Dionysiou, Appl. Catal. B: Environ. 134 (2013) 83–92. [918] L. Rizzo, D. Sannino, V. Vaiano, O. Sacco, A. Scarpa, D. Pietrogiacomi, Appl. Catal. B: Environ. 144 (2014) 369–378. [919] H. Wang, Z. Ye, C. Liu, J. Li, M. Zhou, Q. Guan, P. Lv, P. Huo, Y. Yan, Appl. Surf. Sci. 353 (2015) 391–399. [920] T. Inoue, A. Fujishima, S. Konishi, K. Honda, Nature 277 (1979) 637–638. [921] S.N. Habisreutinger, L. Schmidt- Mende, J.K. Stolarczyk, Angew. Chem. Int. Ed. 52 (2013) 7372–7408. [922] Y. Izumi, Coord. Chem. Rev. 257 (2012) 171–186. [923] S.C. Roy, O.K. Varghese, M. Paulose, C.A. Grimes, ACS Nano 4 (2010) 1259–1278. [924] X. Chang, T. Wang, J. Gong, Energy Environ. Sci. 9 (2016) 2177–2196. [925] L. Yuan, Y.-J. Xu, Appl. Surf. Sci. 342 (2015) 154–167. [926] M. Li, L. Zhang, X. Fan, Y. Zhou, M. Wu, J. Shi, J. Mater. Chem. A 3 (2015) 5189–5196. [927] M. Li, L. Zhang, M. Wu, Y. Du, X. Fan, M. Wang, L. Zhang, Q. Kong, J. Shi, Nano Energy 19 (2016) 145–155. [928] Y. He, L. Zhang, M. Fan, X. Wang, M.L. Walbridge, Q. Nong, Y. Wu, L. Zhao, Sol. Energy Mater. Sol. Cells 137 (2015) 175–184. [929] H. Shi, G. Chen, C. Zhang, Z. Zou, ACS Catal. 4 (2014) 3637–3643. [930] S. Zhou, Y. Liu, J. Li, Y. Wang, G. Jiang, Z. Zhao, D. Wang, A. Duan, J. Liu, Y. Wei, Appl. Catal. B: Environ. 158–159 (2014) 20–29. [931] Y. Wang, Y. Xu, Y. Wang, H. Qin, X. Li, Y. Zuo, S. Kang, L. Cui, Catal. Commun. 74 (2016) 75–79. [932] M. Ovcharov, N. Shcherban, S. Filonenko, A. Mishura, M. Skoryk, V. Shvalagin, V. Granchak, Mat. Sci. Eng. B: Adv. 202 (2015) 1–7. [933] X. Zhang, L. Wang, Q. Du, Z. Wang, S. Ma, M. Yu, J. Colloid Interface Sci. 464 (2016) 89–95. [934] Z. Tong, D. Yang, J. Shi, Y. Nan, Y. Sun, Z. Jiang, ACS Appl. Mater. Interfaces 7 (2015) 25693–25701. [935] W.-J. Ong, L.K. Putri, L.-L. Tan, S.-P. Chai, S.-T. Yong, Appl. Catal. B: Environ. 180 (2016) 530–543. [936] L.K. Putri, W.-J. Ong, W.S. Chang, S.-P. Chai, Catal. Sci. Technol. 6 (2016) 744–754. [937] Y. Huang, Y. Wang, Y. Bi, J. Jin, M.F. Ehsan, M. Fu, T. He, RSC Adv. 5 (2015) 33254–33261. [938] J. Qin, S. Wang, H. Ren, Y. Hou, X. Wang, Appl. Catal. B: Environ. 179 (2015) 1–8. [939] X. Yang, W. Xin, X. Yin, X. Shao, Chem. Phys. Lett. 651 (2016) 127–132. [940] J. Fu, S. Cao, J. Yu, J. Low, Y. Lei, Dalton Trans. 43 (2014) 9158–9165. [941] J. Yu, J. Low, W. Xiao, P. Zhou, M. Jaroniec, J. Am. Chem. Soc. 136 (2014) 8839–8842. [942] Q. Xu, J. Yu, J. Zhang, J. Zhang, G. Liu, Chem. Commun. 51 (2015) 7950–7953. [943] J. Ge, K. Deng, W. Cai, J. Yu, X. Liu, J. Zhou, J. Colloid Interface Sci. 401 (2013) 34–39. [944] W.Q. Cai, Y.Z. Hu, J.G. Yu, W.G. Wang, J.B. Zhou, M. Jaroniec, RSC Adv. 5 (2015) 7066–7073. [945] J. Yu, Y. Le, B. Cheng, RSC Adv. 2 (2012) 6784–6791. [946] F. Su, S.C. Mathew, L. Moehlmann, M. Antonietti, X. Wang, S. Blechert, Angew. Chem. Int. Ed. 50 (2011) 657–660. [947] Z.J. Wang, K. Garth, S. Ghasimi, K. Landfester, K.A.I. Zhang, ChemSusChem 8 (2015) 3459–3464. [948] L. Song, S. Zhang, X. Wu, H. Tian, Q. Wei, Ind. Eng. Chem. Res. 51 (2012) 9510–9514. [949] X. Xiao, J. Jiang, L. Zhang, Appl. Catal. B: Environ. 142 (2013) 487–493. [950] X. Chen, J. Zhang, X. Fu, M. Antonietti, X. Wang, J. Am. Chem. Soc. 131 (2009) 11658–11659.

J. Wen et al. / Applied Surface Science 391 (2017) 72–123 [951] G.D. Ding, W.T. Wang, T. Jiang, B.X. Han, H.L. Fan, G.Y. Yang, ChemCatChem 5 (2013) 192–200. [952] T. Fu, P. Hu, T. Wang, Z. Dong, N. Xue, L. Peng, X. Guo, W. Ding, Chin. J. Catal. 36 (2015) 2030–2035. [953] G. Shiravand, A. Badiei, G.M. Ziarani, M. Jafarabadi, M. Hamzehloo, Chin. J. Catal. 33 (2012) 1347–1353. [954] X. Ye, Y. Cui, X. Qiu, X. Wang, Appl. Catal. B: Environ. 152 (2014) 383–389. [955] X. Ye, Y. Cui, X. Wang, ChemSusChem 7 (2014) 738–742. [956] P. Zhang, Y. Gong, H. Li, Z. Chen, Y. Wang, RSC Adv. 3 (2013) 5121–5126. [957] M. Potowski, J.O. Bauer, C. Strohmann, A.P. Antonchick, H. Waldmann, Angew. Chem. Int. Ed. 51 (2012) 9512–9516. [958] H. Zhan, W. Liu, M. Fu, J. Cen, J. Lin, H. Cao, Appl. Catal. A: Gen. 468 (2013) 184–189. [959] P. Zhang, Y. Wang, J. Yao, C. Wang, C. Yan, M. Antonietti, H. Li, Adv. Synth. Catal. 353 (2011) 1447–1451. [960] X.-H. Li, M. Baar, S. Blechert, M. Antonietti, Sci. Rep. U. K. 3 (2013). [961] J. Huang, W. Ho, X. Wang, Chem. Commun. 50 (2014) 4338–4340. [962] C. Su, R. Tandiana, B. Tian, A. Sengupta, W. Tang, J. Su, K.P. Loh, ACS Catal. 6 (2016) 3594–3599. [963] Q. Zhou, G. Shi, J. Am. Chem. Soc. 138 (2016) 2868–2876. [964] S. Ghosh, N.A. Kouame, L. Ramos, S. Remita, A. Dazzi, A. Deniset- Besseau, P. Beaunier, F. Goubard, P.-H. Aubert, H. Remita, Nat. Mater. 14 (2015) 505–511.

123

[965] R.S. Sprick, B. Bonillo, R. Clowes, P. Guiglion, N.J. Brownbill, B.J. Slater, F. Blanc, M.A. Zwijnenburg, D.J. Adams, A.I. Cooper, Angew. Chem. Int. Ed. 55 (2016) 1824–1828. [966] Z.J. Wang, S. Ghasimi, K. Landfester, K.A.I. Zhang, Chem. Commun. 50 (2014) 8177–8180. [967] B.C. Ma, S. Ghasimi, K. Landfester, F. Vilela, K.A.I. Zhang, J. Mater. Chem. A 3 (2015) 16064–16071. [968] P. Bornoz, M.S. Prevot, X. Yu, N. Guijarro, K. Sivula, J. Am. Chem. Soc. 137 (2015) 15338–15341.