- Email: [email protected]
Molybdenum disulfide (MoS2) as a co-catalyst for photocatalytic degradation of organic contaminants: A review
Accepted Manuscript Title: Molybdenum disulfide (MoS2 ) as a co-catalyst for photocatalytic degradation of organic contaminants: A review Authors: Ming-hong Wu, Lin Li, Ning Liu, De-jin Wang, Yuan-cheng Xue, Liang Tang PII: DOI: Reference:
S0957-5820(18)30357-4 https://doi.org/10.1016/j.psep.2018.06.025 PSEP 1427
To appear in:
Process Safety and Environment Protection
Received date: Revised date: Accepted date:
16-3-2018 15-6-2018 18-6-2018
Please cite this article as: Wu, Ming-hong, Li, Lin, Liu, Ning, Wang, De-jin, Xue, Yuancheng, Tang, Liang, Molybdenum disulfide (MoS2) as a co-catalyst for photocatalytic degradation of organic contaminants: A review.Process Safety and Environment Protection https://doi.org/10.1016/j.psep.2018.06.025 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Molybdenum disulfide (MoS2) as a co-catalyst for photocatalytic degradation of organic contaminants: A review Ming-hong Wua, Lin Lia, Ning Liub, De-jin Wangc,*, Yuan-cheng Xuea, Liang Tanga,* a
School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444, PR
b
IP T
China
School of Environment and Architecture, University of Shanghai for Science and Technology,
c
SC R
Shanghai 200093, PR China
School of Resources and Environment, Anqing Normal University, Anqing 246052, PR China
* Corresponding authors. E-mail addresses: [email protected] (L. Tang);
A
N
U
[email protected] (D. J. Wang)
A
CC E
PT
ED
M
Graphical abstract
1
Abstract Photocatalytic degradation is an emerging, efficient and energy-save technology for the removal of organic contaminants from the water environment. With the development of two-dimensional functional materials, molybdenum disulfide (MoS2) has become one of the most popular emerging co-catalysts due to its high photocatalytic activity, strong adsorptivity, low cost and non-toxicity, especially applied to the photocatalytic degradation of organic contaminants. In
IP T
this paper, we review the recent research progresses of graphene, carbon-nitrogen compounds, TiO2 and bismuth compounds supported on MoS2 co-catalyst, which were applied to
SC R
photocatalytic degradation of various organic contaminants such as methylene blue (MB), methyl orange (MO) and rhodamine B (RhB), etc. Meanwhile, the basic processes of photocatalytic degradation of organic pollutants have also been briefly analyzed and compared. More
U
importantly, MoS2 co-catalyst plays an integral role in nanocomposites, especially in accelerating
N
photo-induced electron transport and reducing electron recombination rates. It is indicated that
A
MoS2-based composites are promising photocatalysts for photocatalytic degradation of
M
environmental pollutants. Keywords
ED
Molybdenum disulfide; Two-dimensional (2D) materials; Photodegradation; Organic pollutants;
CC E
1. Introduction
PT
Heterojunctions
As global environmental problems become more and more serious, the demand for
sustainable and green materials has become a urgent concern (Guo et al., 2017). Especially,
A
excessive discharge of wastewater containing organic chemicals into the environment has become a major issue around the world, which poses a significant risk to living organisms and environment due to their persistence and toxicity (Cheng et al., 2014). Methylene blue (MB), methyl orange (MO) and rhodamine B (RhB) are widely present in textile wastewater. Insufficient treatment of textile effluents is directly or indirectly related to environmental pollution and various human diseases (Khan and Malik, 2018; Vane et al., 2009). For example, the presence of 2
dyes in water not only interferes with the operation of ecosystems, but toxic substances can seriously affect human health (Liu et al., 2017c; Tang et al., 2017b). In addition, some organic pollutants may affect fetal neurodevelopment and birth weight, such as polychlorinated biphenyls and organophosphorus pesticides (Vrijheid et al., 2016). It is hoped that certain approaches will be able to effectively and economically eliminate the harmful substances in the aqueous environment. By now, photocatalysis is commonly considered as one of the most economical and
IP T
environmentally-friendly methods (Liu et al., 2012). Under the premise that the photocatalyst property does not change, the principle of photocatalysis is to convert light energy into chemical
SC R
energy under the irradiation of light, and generate a corresponding free radical group to have the redox ability (Fujishima and Honda, 1972). Photocatalytic degradation makes full use of semiconductor photocatalysis properties for water treatment due to its efficient light response
U
capability (Kudo and Miseki, 2009; Shi, 2012). However, traditional photocatalysts containing
N
noble metals, such as Pt,Rh and Ag , may clearly limit their practical applications because of high
A
price and low reserve (Chen and Mao, 2007; Lei et al., 2016; Xiang et al., 2012). In order to efficiently harvest the light, researchers tried hard to exploit novel semiconductor photocatalysts
M
with high photo-response and practicability.
ED
Molybdenum disulfide (MoS2), a kind of two-dimensional (2D) layered transitionmetal dichalcogenide, has achieved significant development in the past few years (Cabán-Acevedo et al., 2015). It has been attached much attention because of its unique physical, chemical and electrical
PT
properties (Chhowalla et al., 2013; Li et al., 2014a). Moreover, MoS2 has superior adsorption capacity and tunable band structure. Base on the above merits, MoS2 has been widely used as
CC E
co-photocalyst in the preparation of composites, especially in the field of photocatalysis on removal of organic contaminants. Herein, we summarize the recent experience in the photocatalytic degradation of organic compounds with MoS2 co-catalyst, in order to better explore
A
the application of MoS2 in the field of photocatalytic degradation of organic matter, and promote the treatment approach for organic wastewater. 2. Structures and synthesis of MoS2 As the main component of molybdenite (Li et al., 1995), MoS2 belongs to the hexagonal system, is a kind of anti-magnetic compound and exhibits semiconductor properties. Starting from 3
the pioneering research done by Frindt and his collaborators, MoS2 has been studied for several decades (Frindt, 1966; Yang et al., 1991). So far, the crystal structures of MoS2 including 1T, 3R and 2H have been widely recognized (Fig. 1). Chemical stability, anisotropy and antiphotocorrosion of MoS2 are attributed to unique lamellar structure. 2.1 Structures of MoS2
IP T
As shown in Fig. 1, the single layer of MoS2 has S-Mo-S structure, which is similar to sandwich. The atoms are connected with each other by covalent bonds (Chang and Chen, 2011;
SC R
Chen et al., 2017; Wang, 2016; Zhang et al., 2016b). The stack between layers is combined by a weak van der Waals forces (Verble and Wieting, 1970). The Mo-S length, the crystal lattice constant, and the distance between the upper and lower sulfur atoms are 2.4, 3.2, 3.1 Å,
U
respectively (Han and Hu, 2016). It turns out that monolayer MoS2 has two phrases: metallic 1T and semiconducting 2H. MoS2 can be used as a semiconductor material with a direct (indirect)
N
band-gap of 1.96eV (1.2eV) (King et al., 2013; Lee et al., 2010; Li et al., 2013; Mak et al., 2010),
A
suggesting that such material can perform strong absorption in the visible region of the solar
M
spectrum, and it is suitable for the role of co-catalyst. Quantum effect can explain the band phenomenon (Wang et al., 2012b). The composite materials formed through hybridizing MoS2
ED
with other semiconductor materials, such as WS2@MoS2 (Li et al., 2015b), (Fe0) doped
A
CC E
performance.
PT
g-C3N4/MoS2 (Wang et al., 2016b), can significantly enhance the photocatalytic degradation
4
IP T SC R U N
2.2 Preparation of MoS2
ED
M
A
Fig. 1. Crystal structures of MoS2: (a) Top view of MoS2 monolayer hexagonal crystal structure. (b) Trigonal prismatic (2H) and octahedral (1T) unit cell structures. Reproduced with permission (Eda et al., 2011; Zeng et al., 2012).
Single layer of MoS2 can be obtained by mechanical and chemical methods. The preparation
PT
of MoS2 is usually classified as two strategies, that is to say, “top-down” exfoliation method and “bottom-up” synthesis method (Zhang et al., 2016c). Until current time, MoS2 with thin layers
CC E
were prepared with various synthesis methods. 2.2.1 Mechanical exfoliation
A
Exfoliating single-layer MoS2 from SiO2/Si with Scotch-tape method is similar to the
technique of preparing graphene sheets (Li et al., 2014a; Lopez-Sanchez et al., 2013; Zeng et al., 2012). The MoS2 flakes were mechanically stripped on a 300 nm thick SiO2 covered silicon substrate using a low track cleanroom tapes. Single-layer and multilayer MoS2 blocks were positioned with a bright field optical microscope (Eclipse LV100D, Nikon). At last, the layer assignment was confirmed by atomic force microscope (AFM) measuring film thickness in
5
tapping mode in air. Mechanically exfoliated MoS2 monolayers show significantly improved optical performance (Li et al., 2012). 2.2.2 Exfoliation method The exfoliation method includes chemical exfoliation (Guardia et al., 2014), liquid-phase exfoliation (Gupta et al., 2016) and electrochemical exfoliation (Fig. 2a) (Liu et al., 2014). The
IP T
studies have demonstrated that monolayer and few-layer MoS2 nanosheets can be obtained with exfoliation method. In addition, 1T metallic MoS2 can be received through ion intercalation (Bai et al., 2014; Maitra et al., 2013). Alkali metal ion intercalation is the most common way (Shuai et
SC R
al., 2016), especially the lithium ion intercalation (Chang et al., 2016). Under argon atmosphere (Guardia et al., 2014), a suitable amount of n-butyllithium in hexane is poured into a defined amount of MoS2 powder, and the dispersion is heated to 65°C overnight. The resulting lithium
U
intercalation product (LixMoS2) was rinsed with a sufficient amount of hexane to remove
N
unreacted n-butyllithium and its organic residue. Immediately afterwards, the embedded MoS2
A
was dispersed in deionized water and centrifuged at high speed to obtain a stable aqueous
M
suspension of MoS2 nanosheets. Ultrasonic method is classified as liquid-phase exfoliation (Coleman et al., 2011). MoS2 can effectively disperse in the solution by using sonication.
ED
Compared with lithium ion intercalation, this method can maintain the preparation of the MoS 2 nanosheets semiconductor properties. The electrochemical exfoliation process is performed by
PT
applying a positive bias to the working electrode (Liu et al., 2014). The exfoliation method is simple, fast and scalable, and other transition metal dichalcogenides are able to be exfoliated with
CC E
the same method.
2.2.3 Hydrothermal method Hydrothermal method is the most economical and universal method to synthesize MoS2.
A
Thiourea and thioacetamide are the most common source of sulfur (Zhou et al., 2013). Molybdenum salts, such as Na2MoO4 (Chung et al., 2014), (NH4)6Mo7O24 (Shi et al., 2015), can be used as the main source of molybdenum. For example, 60 mg of thioacetamide and 30 mg of sodium molybdate were added to 20 mL of deionized water to form a transparent solution. The mixed solution was transferred to a Teflon-lined stainless steel autoclave, which was heated in an electric oven at 200°C for 24 h. Afterward, a black product was collected after centrifugation and 6
dried at 60°C for 12 h. However, hydrothermal method cannot accurately control the number of MoS2 layers. It is prone to agglomeration, affecting the morphology and size of the products. 2.2.4 Solvothermal method Solvothermal method is developed on the basis of hydrothermal method, and the main difference of solvothermal method from the latter is that the preparation condition is organic
IP T
solvent rather than water. Different ratios of sulfur source and molybdenum source precursor were added to organic solvents such as N, N-dimethylformamide (DMF), 1-methyl-2-pyrrolidinone (NMP) and polyethylene glycol-600 to form a homogeneous solution, and then transferred to an
SC R
autoclave at 180°C (or 200°C) for 24 h. The black product was centrifuged and dried to obtain MoS2 powder. Solvothermal method (Fig. 2b) has the advantages of low energy consumption, less agglomeration, controllable particle shape and so on. Importantly, it was described that the
U
nanostructures MoS2 obtained by one-step low temperature solvent conditions had high surface
N
area (Berntsen et al., 2003). Thus, the shapes and properties of MoS2 can be effectively controlled
M
2.2.5 Chemical vapor deposition
A
by such method (Berntsen et al., 2003; Najmaei et al., 2013; Peng et al., 2002).
Chemical vapor deposition (CVD) has a long history that dates back to several centuries ago.
ED
CVD has been widely used to prepare high-quality atomic thin MoS2. MoS2 is synthesized by sulfurization of MoO3 with the CVD method (Fig. 2c) (Lee et al., 2012; Najmaei et al., 2013).
PT
Large-area MoS2 flakes could be grown on the substrates via CVD methods, including SiO2/Si
A
CC E
(Yang et al., 2016), sapphire (Dumcenco et al., 2015), polyimide (Ahn et al., 2015) and so on.
7
IP T SC R U N A M ED PT CC E
A
Fig. 2. Representative synthesis routes of MoS2: (a) Illustration of electrochemical exfoliation lithiation process. (b) Synthesis of MoS2 nanoparticles by solvothermal method. (c) Schematic diagram for the preparation of MoS2 thin layers with MoO3 sulfurization. Reproduced with permission (Li et al., 2011; Lin et al., 2012; Zeng et al., 2011).
3. Photocatalytic degradation mechanisms Photocatalytic degradation is the process of taking advantage of these highly active free radicals and then degrading all contaminants into small molecules or inorganic substances through
8
the processes of addition reaction, substitution reaction and electron transfer between free radicals and organic pollutants. According to previous studies, holes (h+), superoxide radicals (·O2-) and hydroxyl radicals (·OH) are considered as the main active species in the photocatalytic reaction (Chen et al., 2014a; Huang et al., 2017). In order to better understand the photocatalytic mechanisms of composite photocatalysts and find the most important active substances, several
IP T
scavengers can be used to explore the variation of reactivity during the photocatalytic processes. For example, ammonium oxalate (AO), benzoquinone (BQ) and isopropanol (IPA) can be usually
SC R
employed to scavenge h+, ·O2- and ·OH, respectively. To further investigate the photocatalytic pathways of the degradation process, it is necessary to study the conduction path of photoelectrons at the interface of the composites, since target organic contaminants mainly react
U
with reactive species at the interface. Because the redox reaction path is determined by the
N
oxidation-reduction potential of the material, thus the location of the holes and valence bands is
A
important. The location of the band and the migration path of the photogenerated carriers at the material interface are to be displayed with the scheme map. In Fig. 3d, the valence band (VB) and
M
conduction band (CB) potentials of semiconductors can be obtained from empirical formulas (Li
ED
et al., 2015d; Weng et al., 2015). The optical bandgap energy (Eg) of MoS2 can be estimated by the following formula (Fig. 3e): αhν = A(hν-Eg)n /2 (1)
PT
Where α, h, ν, A and Eg represent the absorption coefficient, Planck constant, light frequency, a constant and bandgap and constant, respectively. Simultaneously, n is a direct transition, whereas
CC E
the indirect transition is n = 4 (Radisavljevic et al., 2011; Wu et al., 2018). In general, the reduction in the number of layers in the pristine MoS2 structure results in a change from the
A
indirect bandgap semiconductor to direct gap semiconductor. 4. MoS2-based composites as photo-degradation catalysts MoS2 nanostructures are superior semiconductors, whose wonderful morphologies can be effectively controlled by a variety of methods (Hu, 2014). Various photocatalysts took advantage of semiconductor properties of MoS2 constructing composite catalysts, and showed favorable photocatalytic performance over organic compounds (as summarized in Table 1). Among them, in 9
this review, the photodegradation efficiency (E%) was calculated using the following equation (Lv et al., 2015; Zhao et al., 2016): E% = (C0-Ct)/C0 × 100% (2) Where C0 is the whole amount of organic pollutants in the solution before illumination; Ct is the concentration of organic pollutants in solution at time t. There are two methods for measuring the residual concentration after degradation of pollutants. One method is to measure the linear
IP T
relationship between the precise concentration of contaminants and the absorbance by a UV-vis spectrophotometer. Another method is to quantify the concentration of contaminants in aqueous
SC R
solutions by high performance liquid chromatography (HPLC). In this review, Ct is measured with the first simple method.
Light source
Contaminants
A
MoS2/GO
A Xe lamp (λ> 420 nm)
M
A mercury lamp 10 mg MoS2/GO
Initial concentration
N
Catalyst
U
Table 1. Summary of photo-catalytic degradation of MoS2-based composites
MB
Reaction time
Degradation efficiency
Reference
50 min
100%
Yuan et al.,
75 min
100%
2017
60 min
99%
50 mL 15 mg/L
80 mg MoS2-RGO
ED
5 W white LED light lamp
(450nm＜λ＜
Li et al.,
MB
80 mL 60 mg/L
2014b
MB
natural sunlight
MB
SOL2/500 S lamp
CC E
6.5 mg MoS2/rGO
PT
558nm)
8.5 mL 12.5 mg/L
96% al., 2016 98%
20 mg ZnO–MoS2–
50 mL 15.9
(intensity
RGO
Cravanzola et 5h
Kumar et 60 min
Carbendazim
mg/L
MO
50 mL 20 mg/L
97%
al., 2016
A
9.0×104 lux)
MoS2/Carbon nitride Peng and 50 mg MoS2/g-C3N4
500 W Xe lamp
5h
About 60% Li, 2014
40 mg MoS2/g-C3N4
300 W Xe lamp
RhB
(λ> 420 nm)
MO
20 min
96%
Li et al.,
180 min
95%
2016b
50 mL 10 mg/L
10
250 W metal 10 mg MoS2/g-C3N4
halide lamp (λ> 420 nm)
MO
2h
92.4%
4h
81.9%
4h
96%
150 min
78%
Lu et al., CIP
10 mL 10 mg/L
2016 TC
MoS2/TiO2
60 mL 10 mg/L
al., 2016a
1.
Catalyst
0.01 g MoS2/TiO2
Light source
Contaminants
50 W
RhB 100 mL 10 mg/L
MO
(λ=313nm) (λ≤420nm)
lamp 250 W infrared
N-TiO2-x@MoS2
(λ≥ 420 nm)
MoS2 with Bi-based materials
PT
300 W Xe lamp (λ＞ 400 nm)
300 W Xe lamp
CC E
0.02 g MoS2/BiOBr
30 mg MoS2/BiOI
(λ＞ 400 nm)
500 W Mercury
MoS2/Bi2O2CO3
lamp
A
50 mg
5 mg Bi2S3-MoS2
MO
ED
300 W Xe lamp
mg/L
M
lamp 50 mg
N
CDs/MoS2@H-TiO2
100mL 10
TC
A
350 W mercury
35 W Xe lamp
Degradation efficiency
97.0%
100 mL 10 mg/L
RhB
50 mL 10 mg/L
50 mL 100
PR
3h
2h
81.60% more than
Liu et al.,
80%
2017a
5h
about 33%
120 min
91.80%
ppm
Di et al., 50 min
about 94% 2014 Li et al.,
100 min
95.20% 2016d
150 min
more than
Wang et
99%
al., 2014 Vattikuti et
60 min
83.4% al., 2016
500 W Xe arc 30 mg 3D MoS2/Bi2S3
lamp (λ＞420
al., 2016d
2017c
mg/L
RhB
Zhang et
Liu et al., 50 mL 10 mg/L
100 mL 10
RhB
Reference
120 min
U
250 W Xe lamp
50 mg
Reaction time
98.2%
high-pressure mercury lamp
Initial concentration
SC R
Table (Continued)
(λ≥ 420 nm)
Wang et phenol
IP T
300 W Xe lamp
0.01 g TiO2/MoS2
Long et al., atrazine
60 mL 5 mg/L
240 min
89% 2016
nm) MoS2 with Ag-based 11
materials RhB A 300 W Xe arc
0.025 g Ag3PO4/MoS2
100 mL 10
MO
lamp (λ≥420 nm)
mg/L
4-CP
30 min
about 100%
30 min
100%
175 min
100%
Degradation efficiency
Wang et al., 2015
Contaminants
Initial concentration
Reaction time
MB
30 mL 20 mg/L
60 min
RhB
30 mL 20 mg/L
MO
30 mL 10 mg/L
phenol
30 mL 5 mg/L
RhB
50 mL 10 mg/L
A 35 W Xe arc lamp (λ≥420 nm)
50 mg Ag3PO4/MoS2
lamp (250 mW/cm2,
lamp
20 mg MoS2/ZnO
M
MoS2 with transition metal oxides mercury vapor
PR
ED
PT
lamp
UV-vis light
CC E
MoS2@CuO
A 18 W daylight
A
50 mg ZrO2/MoS2
MoS2/MoOx
0.2mg/mL Fe3O4@MoS2/Ag3PO4
A 25 W UV lam
A 300W Xe lamp (λ≥420 nm) A 500 W Xe
100 mL 10
MB
mg/L
Zhu et al.,
120 min
about 100%
2016
200 min
95%
16 min
Wan et al., 100% 2017
50 min
93%
Awasthi et al.,
80 min
90%
2016
100 min
92.7%
Tan et al., 2014 Li et al.,
MB
100 min 2015a 100 mL 10
MO
ppm
Prabhakar et 12 min
95.2%
8 mL 0.4 × 10-5
RhB
al.,2016 Zhou et al.,
120 min
97% 2014
mol/L RhB
lamp (λ＞420 nm)
about 100%
30 mL 10 ppm
natural sun light
0.02g MoS2@ZnO
80 min
A
λ≥420 nm)
N
A 300 W Xenon
Reference
98.2
%
SC R
30 mg Ag3PO4/MoS2
Light source
U
Catalyst
IP T
Table 1. (Continued)
98.90%
Guo et al.,
90.74%
2016
10 min CR
All reactions are performed under neutral conditions Methylene blue (MB); methyl orange (MO); rhodamine B (RhB); ciprofloxacin (CIP); tetracycline (TC); phenol red (PR); p-chlorophenol (4-CP); congo red (CR) 12
4.1 MoS2 /graphene oxide Graphene is a well-known 2D material, whose sp2 hybridized carbon atoms are tightly packed into a honeycomb single layer (Shi et al., 2012; Tang et al., 2017a; Wang et al., 2013). Remarkably, graphene has high theoretical surface area (~2600 m2), excellent carrier mobility (2 ×
IP T
105 cm2/V·sec), excellent thermal conductivity (5000 W/m·K), optical transmittance (～97.7%), and high elastic modulus (～1TPa) (Chabot et al., 2014; Xu et al., 2013). Moreover, it has been proved that graphene exhibits absorption enhancement in the visible region because of excellent
SC R
optical and electronic properties (Xiang et al., 2015; Xiong et al., 2015). These unique properties make graphene act as excellent electron acceptor and transporter, and significantly enhance pollutant adsorption. Reduced graphene oxide (rGO) displays the similar properties comparing to On the other hand, MoS2 itself has a low insufficient electronic separation capability
U
graphene.
N
(Li, 2015); however, the incorporation of MoS2 and graphene exhibits a good photocatalytic
A
degradation performance as a catalyst, since MoS2 can be better dispersed on the surface of
M
graphene and make the most of the properties of graphene. Yuan et al. used N, N- dimeth ylformamide (DMF) as solvent to synthesize MoS2/GO composites (Yuan et al., 2017). The
ED
prepared samples were then annealed in order to improve the crystallinity. MoS2 nanoflakes were rich in edges, and the grown MoS2 nanoflakes with three layers occupied the highest proportion
PT
(Fig. 3a-c). MB solution (15 mg/L) was used as the target contaminants to evaluate the photocatalytic performance of as-prepared composite catalysts. Among them, 10 mg sample was
CC E
dispersed in 50 mL of MB solution. The results suggested MB could be completely degraded by MoS2/rGO composites via both UV and visible light illumination, and the catalytic processes took 50 min and 75 min, respectively. In virtue of superior electron transported substrate of graphene
A
and strong solar absorption of MoS2, the synergistic effect between these two materials can efficiently inhibit the recombination of photoelectrons and holes, leading to enhancement of the photodegradation performance. The methods of synthesizing MoS2-rGO hybrids are not only solvothermal one mentioned above, but also other approaches. MoS2-rGO composites could be well prepared by microwave-assisted method (Li et al., 2014b; Pan et al., 2013). Through the microwave-assisted
13
approach, MoS2 scaled sheets were observed stacked on the curled and corrugated GO sheets. It is clear that the curled rGO surface is stably connected to MoS2 and contributes to the separation of photo-generated carriers. MoS2-rGO hybrids prepared by microwave-assisted method achieved the highest MB (the concentration of 60 mg/L) degradation rate of 99 % in 60 min under the visible light. In addition, the sonication method can also be used to prepare rGO/MoS2 hybrids (Cravanzola et al., 2016), which are regarded as complex and heterogeneous morphology. In the
IP T
presence of the catalyst, MB solution (the initial concentration of 12.5 mg/L) residue remained about 4% after 5 h under solar-light irradiation. Comparing to pure rGO and MoS2, the
SC R
photodegradation performance is greatly improved, which is attributed to promoting electron transfer and separation, as well as increasing the light absorption intensity and the adsorption
A
CC E
PT
ED
M
A
N
U
capability of organic pollutants.
14
IP T SC R U N A M ED PT CC E A
Fig. 3. Structure and morphology of MoS2/rGO composite prepared by solvothermal method. (a) TEM image of MoS2/rGO hybrids. (b) The HRTEM image of MoS2/rGO composites. (c) Schematic illustration of the number of layers of MoS2 nanosheets grown on graphene. (d) The scheme map the photocatalytic reduction mechanism of Cr(VI) in the aqueous phase of MoS2-Bi2S3 composites under visible light (λ> 400 nm). (e) The calculated band gaps of Bi2S3 and MoS2. (a-c reproduced with permission(Yuan et al., 2017) d-e reproduced with permission Weng et al., 2015).
15
MoS2-rGO can also be incorporated with other semiconductor materials forming ternary photocatalysts. Kumar et al. synthesized ZnO-MoS2-rGO heterostructures through hydrothermal method (Kumar et al., 2016). The composite of doping 1 wt% ZnO nanoparticles on MoS2-rGO achieved the highest photodegradation performance, and ZnO were observed well dispersed on MoS2-rGO nanosheets. 50 mL of a 15.9 mg/L MB aqueous solution was degraded by 98% within 60 min under the natural sunlight. Besides, the same concentration of carbendazim was also
IP T
degraded by 97% in the same conditions. The reason for its high photocatalytic degradation efficiency is that the synergetic effect is conducive to rapidly transfer electrons across the
SC R
interface, which produces highly reactive ·OH for contaminant degradation.
From the previous literatures, it can be concluded that incorporation of MoS2 with graphene oxide mainly takes advantage of the good conductivity of graphene sheets, and efficiently inhibits
U
the recombination of photo-generated carriers. MoS2/rGO is a promising material in
N
photocatalytic degradation.
A
4.2 MoS2 /graphitic carbon nitride
M
Polymeric graphitic carbon nitride (g-C3N4) is an emerging celebrity photocatalyst recent
ED
years, which has many advantages, such as abundance of source, low cost, non-toxicity and chemical stability (Jo et al., 2016; Liang et al., 2016; Liu et al., 2010; Zhang et al., 2015; Zhang et al., 2016a). The g-C3N4 has unique stable 2D heptazine ring structure with a band gap of ~ 2.7 eV
PT
as well as proper valence band (VB) and conduction band (CB) positions (Liu et al., 2017b; Yang et al., 2011; Zhang et al., 2011; Zhao et al., 2015a), implying it is a promising material for
CC E
harvesting waves of solar light. However, pure g-C3N4 suffers from poor light-absorbance and low separation efficiency of electron-hole pairs (Chen et al., 2014b; Liao et al., 2012). To solve this problem, coupling g-C3N4 nanosheets with a co-photocatalyst is probably one of the most ideal
A
choices. Peng et al. employed few-layer MoS2 as the co-photocatalyst hybridizing novel MoS2/g-C3N4 composite (Peng and Li, 2014). When controlling the proportion of MoS2 as 3.0 wt%, the composite showed the greatest photodegradation performance on MO. 50 mg samples were dispersed 50 mL of 20 mg/L of MO in aqueous solution. The degradation efficiency of MO was about 60% under the simulated solar ligh for 5 h. In the photocatalytic process, MoS2 nanoparticles obviously promoted charge collector and transfer, thus preventing the recombination 16
of photoelectron-hole pairs. Currently, the 2D heteroconjuction of MoS2/g-C3N4 is mainly synthesized by impregnation and calcination method (Tisseraud et al., 2016). The 2D heterostructures with interfacial contact are formed between the MoS2 nanosheets and the g-C3N4 nanosheets. For the MoS2/g-C3N4 composites with 3 wt% of MoS2, whose specific surface area reaches about 85.4m2/g; therefore, it canprovide abundant surface active sites for contaminants photodegradation. Taking RhB and MO as the targets, whose concentration was both 10 mg/L. 40
IP T
mg photocatalyst was added to 50 mL of RhB or MO solution, and RhB could be degraded by 96% after 20 min irradiation with visible light. Furthermore, the concentration of MO could be reduced
SC R
by about 95% within 3 h. The 2D heterostructures promote the charge transfer and improve the separation efficiency of photoelectron-hole pairs, resulting in lifting of the photodegradation efficiency.
U
However, different preparation methods make the same materials exhibit different effects. Lu
N
et al. synthesized the MoS2/g-C3N4 nanostructured materials of type II hetero-structure by
A
ultrasonic and bathing method (Lu et al., 2016). Fig. 4 (a)-(c) show that ultrathin MoS2 nanosheets and g-C3N4 nanosheets are packed together to form heterostructures. To evaluate the
M
photocatalytic activities of MoS2/g-C3N4 hybrids, three different pollutants were degraded. MO
ED
solution was used as simulated organic wastewater, while two pharmaceutical compounds, ciprofloxacin (CIP) and tetracycline hydrochloride (TC) were also used. The 0.05-MoS2/g-C3N4 hybrids (WMoS2: WMoS2/g-C3N4= 0.05) obtained the highest degradation rates. After being irradiated
PT
in the visible light for 2 h, the photodegradation rate reached 92.4% for MO and the kinetic constant was 0.0189 min-1. As shown in Fig. 4 (d), removal of 81.9% CIP and 96% TC was
CC E
achieved after being irradiated for 4 h. Compared with pure g-C3N4, MoS2/g-C3N4 hybrids performed remarkable photodegradation efficiency due to the heterostructures formed between ultrathin MoS2 and g-C3N4 nanosheets. In addition, large transverse sizes and atomic thicknesses
A
imparted the ultrathin MoS2 with a high specific surface area (Mak et al., 2010), which made them construct functional hybrid heterostructures with g-C3N4 and formed more photocatalytic active sites. Thus, the separation rate and the mobility of photogenerated charge are enhanced by the ultrathin MoS2 nanosheets. However, with the gradual increase of MoS2 content, the degradation rate decreased accordingly, which may be attributed to the increase of MoS2 overlapping layer resulting in the reduction of the interfacial formation between g-C3N4 and MoS2. Eventually, the 17
visible light absorption of MoS2/g-C3N4 hybrids and the propagation of photogenerated electron
ED
M
A
N
U
SC R
IP T
holes were reduced.
PT
Fig. 4. (a) SEM images of 0.05-MoS2/g-C3N4 composites. (b)-(c)HRTEM images of 0.05-MoS2/g-C3N4 hybrids. (d) Degradation rates of MoS2/g-C3N4 hybrids in 120 min. Reproduced with permission (Lu et al., 2016).
To sum up, introducing MoS2 to g-C3N4 can form heterostructures on the interface, which
CC E
promotes the separation and transfer of photogenerated electron–hole pairs. The easy-to-prepared, stable and inexpensive photocatalyst has a broad prospect in photodegradation of pollutants. 4.3 MoS2 /TiO2
A
Owing to the abundant reserves, low cost, non-toxic, chemical stability and other advantages
of titanium dioxide (TiO2), it is one of the most well-known semiconductor photocatalytic functional materials (Dong et al., 2015; Hao et al., 2016; Yuan et al., 2016; Zhao et al., 2015b). Nevertheless, TiO2 has a wide band and can only absorb UV light (Zhong and Li, 2012). In order to increase the range of TiO2 absorption spectra, coupling TiO2 with narrow band gap co-photocatalysts is one of the best methods. Layered MoS2 can be deposited on different shapes 18
of TiO2, thereby increasing the spectral absorption range of TiO2 and the ability of photocatalytic degradation of environmental pollutants. Very recently, one dimensional (1D) semiconductor nanostructures TiO2 nanofibers (NFs) were prepared by the electro-spinning technique (Zhang et al., 2013), and then the NFs were intertwined to form a 3D network structure. With MoS2 wrapped on the surface of TiO2 NFs through a simple hydrothermal method (Fig. 5a), 3D MoS2 nanosheet/TiO2 nanofiber (MoS2/TiO2) heterostructures were synthetized (Zhang et al., 2016d).
IP T
The photocatalytic performance of the prepared samples was evaluated at room temperature by photocatalysis of organic dyes RhB and MO solution (10 mg/L). The photocatalytic degradation
SC R
ratio of RhB for MoS2/TiO2-2 (Mo/Ti molar ratio with 0.412) is 98.2%, while that of MO is 97.0% in the UV light irradiation (Fig. 5b). Significantly, 3D MoS2/TiO2 heterostructures exhibited fine stability and recyclability. One reason is that MoS2 not only improves the separation of
U
photo-generated electron-hole pairs, but also provides a greater number of photo-degradation sites.
N
The other reason is the synergistic effect of heterogeneous structures formed between the two
A
substances. Based on the results of UV-Vis absorption spectroscopy, the photocatalytic degradation activities of pure MoS2 and MoS2/TiO2-2 were both studied with the visible light.
M
Surprisingly, MO was not significantly degraded under visible light irradiation. This result
ED
precluded the possibility of photoactivating TiO2 with MoS2. In this experiment, the main role of MoS2 nanosheets was to collect electrons and suppress the recombination of photo-generated electron-hole pairs. In other similar literature, this phenomenon has also been mentioned (Jia et al.,
PT
2014).It is reported that hollow TiO2 spheres have excellent photocatalytic activity because the surface area is relatively larger compared to nanofibers (Qi et al., 2014). Wang et al. used
CC E
hydrothermal method to make MoS2 nanosheets tightly coating on TiO2 hollow spheres (Fig. 5c) (Wang et al., 2016a). The hollow structure possesses a high porosity, which can increase the reaction sites under the simulation from photo-irradiation. Compared to pure TiO2 or MoS2,
A
TiO2/MoS2 heterostructures can significantly enhance the photometric responsiveness to phenol (10 mg/L), which could be decomposed 78% with the heterojunctions after 150 min of visible light irradiation comparing with no photocatalytic effect for TiO2 and 20% removal for MoS2 (see Fig. 5d). The best sample exhibits higher photocurrent densities than pure MoS2 and TiO2, indicating that the heterostructures are more favorable for charge migration and collection.
19
IP T SC R U
M
A
N
Fig. 5. (a) MoS2 nanosheets/TiO2 NFs in low and high (illustrations) magnification. (b) SEM image of multi layers MoS2 coated TiO2 hollow. (c) Degradation curves of RhB and MO by different weight ratios of MoS2 nanosheets/TiO2 NFs. (d) Photodegradation of phenol with MoS2 coated TiO2 heterostructures. (a and b reproduced with permission from Ref.(Zhang et al., 2016d); c and d reproduced with permission from Ref.(Wang et al., 2016a)).
ED
In order to further enhance the photocatalytic reaction of TiO2, a variety of TiO2 modification techniques have been used to constructed photocatalysts (Low et al., 2017; Nasirian
PT
and Mehrvar, 2016). It is a very sensible strategy to dopant impurity elements into the TiO2, which can expand the absorption range of TiO2 to visible light (Akple et al., 2016; Qian et al., 2014). The
CC E
modified TiO2 coupled with the co-catalyst will significantly enhance the photocatalytic degradation performance. For instance, the TiO2 nanobelts were heated to 600℃ under a hydrogen atmosphere for 5 h to obtain the H-TiO2, and then carbon dots (CDs)/MoS2@H-TiO2
A
heterostructures were prepared by a simple hydrothermal process (Liu et al., 2017a). MoS2 nanosheets carrying CDs grew evenly on 3D network-like TiO2 nanobelts (Fig. 6a-b). The photodegradation experiments were evaluated in the process of tetracycline (TC) solution (10 mg/L) under UV, visible light and near-infrared (NIR) light irradiation. The sample with 5.0 wt% (WMoS2: WCDs= 4:1) content of CDs/MoS2 composite displayed the highest photocatalytic degradation activity. The TC solution was degraded by 81.6% for 3 h under visible light, and more 20
than 80% within 2 h UV irradiation (Fig. 6c). Compared to visible and UV light, the degradation rate of TC could also reach about 33% in the NIR light irradiation for 5 h. This composite displayed extremely high photocatalytic activities mainly due to the following three aspects. Firstly, the synergistic effect delays recombination of target electron-hole pairs; then, CDs/MoS2 thin sheets provide more active reaction sites; Finally, MoS2 play an indispensable role in the interface of electronic conduction. Similarly, nitrogen doping TiO2 (N-TiO2) nanospheres was
IP T
prepared by hydrothermal method using urea as nitrogen source, and N-TiO2-x@MoS2 were synthetized through the same way by Liu et al. (Liu et al., 2017d) N-TiO2-x nanospheres could be
SC R
seen being completely coated by the MoS2 nanoflowers (Fig. 6d-e). Such hybrid structures can effectively enhance the visible light response. The photocatalytic performance for MO solutions was carried out under visible light irradiation. Compared with pure TiO2, the N-TiO2-x@MoS2
U
executed the best photocatalytic effect, which could remove 91.8% of 10 mg/L MO solution
N
within 2 h under visible light irradiation (Fig. 6f). In this case, the hybrids were introduced Ti3+
A
and oxygen vacancy, resulting in lifting utilization of light energy. The electrons could be more efficiently separated due to the introduction of MoS2. Consequently, the possible photocatalytic
M
mechanisms of N-TiO2-x@MoS2 were proposed as illustrated in Fig. 6g.
ED
All in all, MoS2 incorporating with TiO2 can narrow the band gap of the latter, which can enhance the absorption capacity of the catalysts and promote the separation and transfer
A
CC E
PT
photogenerated electrons.
21
IP T SC R U N A M ED PT CC E
A
Fig. 6. (a) SEM image of CDs/MoS2@H-TiO2 nanocomposite (5 wt% of CDs/MoS2). (b) HRTEM image of the CDs/MoS2@H-TiO2 (5 wt% of CDs/MoS2). (c) Photo-degradation rate of TC of the photocatalysts with different weights of CDs/MoS2. (d) SEM image of N- TiO2−x @MoS2 hybrids. (e) TEM image of N-TiO2−x@MoS2 composites. (f) Photodegradation of MO with different photocatalysts. (g) Schematic of the MO photodegradation and the possible charge transfer mechanism for the N-TiO2−x@MoS2 samples. (a - c reproduced with permission from Ref.(Liu et al., 2017a); d - g reproduced with permission from Ref.(Liu et al., 2017d) ).
4.4 MoS2 with Bi-based materials Bismuth-based photocatalysts have received great attention because of its excellent optical properties (Chen et al., 2016; Cuellar et al., 2015; Li et al., 2016a; Zou et al., 2017). For example, 22
bismuth oxybromide (BiOBr) has been attracted interests because of its superior photocatalytic performance (Xiong et al., 2016; Yi-Zhu et al., 2016). In order to further enhance the photocatalytic performance of BiOBr, Di et al. synthesized sphere-like MoS2/BiOBr composites by solvothermal method (Di et al., 2014). MoS2 nanosheets were in close contact with BiOBr, which formed nanostructured heterojunctions (Fig. 7a-b), and then the prepared composite (0.02 g) was used to treat with RhB (10 mg/L) under the visible light irradiation. Surprisingly,
IP T
incorporation of MoS2 could significantly increase the degradation effect of BiOBr on RhB, and the 3 wt% MoS2/BiOBr (weight ratio with MoS2 of 3%) composite showed the highest
SC R
photocatalytic activity. In Fig. 7c, approximately 94% of the RhB was removed under 50 min of light irradiation. As can be seen from Fig. 7d, the rate constant of 3 wt% MoS2/BiOBr is greater than others. The porous structures on the surface of MoS2/BiOBr composites provided more
U
active sites for RhB degradation. BiOBr microspheres coated with several layers of MoS2
N
nanosheets act as an irreplaceable role in photocatalysis. The rapid separation and transport of
A
photo-induced charges was attributed to the synergistic effect of the heterogeneous structure between the thin layers of MoS2 nanosheets and BiOBr semiconductors.
M
Compared with BiOBr, BiOI has a narrower band gap (1.7～1.9eV), which has a higher
ED
visible light response (Jiang et al., 2017; Mousavi and Habibi-Yangjeh, 2016; Xiang et al., 2016). Nevertheless, BiOI suffers from the problem of slow separation of photoelectrons. For the sake of solving this flaw, modifying BiOI and coupling it with other excellent semiconductors are
PT
common methods. In consideration of superiority of thin layer MoS2, Li et al. coupled BiOI with thin layer MoS2 nanosheets to increase the visible light response of the photocatalysts (Li et al.,
CC E
2016c). After being illuminated 100 min, MoS2/BiOI material contaning 0.5 wt% MoS2 showed excellent photodegradation efficiency, resulting in the concentration of RhB being reduced about 95.2%. RhB (100 mL, 10 mg/L) can be degraded under visible light mainly due to the main active
A
material holes. Besides, the heterogeneous structures accelerated the separation of electron-hole pairs, which also enhanced the photocatalytic activity.
23
IP T SC R U N A
ED
M
Fig. 7. (a) SEM image of the 3 wt% MoS2/BiOBr spherical structure. (b) TEM image of 3 wt% MoS2/BiOBr. (c) Photodegradation of RhB with pure BiOBr and different weight ratios of MoS2/BiOBr. (d) The kinetic plots of photocatalytic degradation of RhB under visible light irradiation. Reproduced with permission(Di et al., 2014).
Except Bi-based materials mentioned above, bismuth subcarbonate (Bi2O2CO3) is also one of
PT
the important member in Bi-based nanostructured material family (Ni et al., 2016). It has a unique photocatalytic performance in the UV light owing to its matched band gap (3.1eV～3.5eV)
CC E
(Huang et al., 2016; Li et al., 2016b; Shan et al., 2016; Wang et al., 2016d). However, UV light only occupies about 4% photon energy from the solar spectrum. In order to make better utilization of solar energy, it is feasible to modify Bi2O2CO3 to prepare novel composite photocatalysts.
A
Wang et al. used ordinary hydrothermal synthesis to prepare MoS2/Bi2O2CO3 composites (Wang et al., 2014). When 0.5 wt% by weight of MoS2 was deposited on Bi2O2CO3, the composite exhibited the best photocatalytic performance, more than 99% of RhB (50mL, 10 mg/L) could be removed within 150 min under the UV light. The synergistic effect between MoS2 and Bi2O2CO3 promoted charge transfer process, and allowed more active charges involved in the oxidation reaction, which enhanced the photocatalytic performance.
24
In addition, Bi2S3 nanorods were embedded in MoS2 nanosheets to carry out a synergistic effect in photodegradation (Li et al., 2017; Weng et al., 2015). The Bi2S3-MoS2 nanocomposites were prepared through hydrothermal method, and whose photocatalytic activities were estimated by treating with phenol red (PR) in solutions (Vattikuti and Byon, 2016). When the weight ratio of Bi2S3 to MoS2 was set as 4:1, the composite showed excellent photocatalytic degradation efficiency under visible light irradiation. After being illuminated for 60 min, the PR could be
IP T
eliminated by 83.4%. The effective electron-hole pair separation and rapid interfacial charge transfer process promote photodegradation. The reason was that the addition of MoS2 enhanced
SC R
the surface area and active sites of composites, which provided more sites for photo-induced electrons and holes to participate in the redox reaction, resulting in higher photocatalytic activity. In order to further enlarge the specific surface area of MoS2/Bi2S3 to obtain much better catalytic
U
properties, Long et al. used one-pot hydrothermal method to prepare 3D MoS2/Bi2S3 (Long et al.,
N
2016). As illustrated in Fig. 8a-b, MoS2 was grown on a 3D Bi2S3 micro-nanometer flowers. In
A
Fig. 8c, the RhB solution (20 mL, 5 mg/L) could be effectively adsorbed and degraded by the composite photocatalysts under visible light irradiation. Besides, 3D MoS2/Bi2S3 was able to deal
M
with actual contaminants named atrazine. 30 mg of the composite photocatalyst was added to 60
ED
mL of a 5 mg/L atrazine solution. In the presence of visible light, the 3D MoS2/Bi2S3 hybrids showed the highest catalytic activity comparing to other reference materials, and 89% of atrazine could be removed within 240 min (Fig. 8d). 3D flower-like MoS2/Bi2S3 heterostructure
PT
accelerated photo-generated electrons separation and transfer, and adequate electrons could react with oxygen molecules at the interface of the composites to produce •O2-, which could strengthen
A
CC E
the degradation of RhB and atrazine.
25
IP T SC R U N A M
ED
Fig. 8. SEM images (a, b) of 3D MoS2/Bi2S3; Photocatalytic degradation efficiency of different photocatalysts for RhB and atrazine (c, d). Reproduced with permission (Long et al., 2016).
In conclusion, introduction of MoS2 into Bi-based material to form heterogeneous structure
PT
could enhance the surface area and active sites of the original Bi-based catalysts. More importantly, the incorporation of MoS2 can effectively inhibit the rapid recombination of
CC E
photoelectrons and holes pairs, as well as prolong the lifetime of carriers. The hybridization of MoS2 with Bi-based materials may be a hopeful candidate to be applied for photo-degradation of
A
harmful organic pollutants. 4.5 MoS2 with Ag-based materials Various semiconductors consist of silver (Ag) have been proved one of the most promising photocatalysts due to their superior utilization efficiencies of visible light and photocatalytic activities (Long and Cai, 2014; Martin et al., 2015). Among the Ag-based materials, silver orthophosphate (Ag3PO4) has been of great concern owing to its excellent photocatalytic 26
performance (Chen et al., 2015; Ma et al., 2016; Yang et al., 2015). However, Ag3PO4 suffers from photo-corrosion in a long time under light irradiation (Wang et al., 2012a). Therefore, it is very essential to couple Ag3PO4 with other co-photocatalysts or conductive materials. Researchers take consideration of MoS2 as a perfect co-catalyst due to its unique stability. Wang et al. prepared hierarchical Ag3PO4/MoS2 composites by a simple template free in situ precipitation method (Wang et al., 2015). Ag3PO4 nanoparticles were uniformly dispersed on the MoS2 nanosheets
IP T
surface (Fig. 9a), and the two components were in close contact with each other at the interface (Fig. 9b). The optimal photocatalytic performance over Ag3PO4/MoS2 composites on
SC R
p-chlorophenol (4-CP), MO and RhB were illustrated in Fig. 9c-e, respectively. The initial concentrations of the three target contaminants were 10 mg/L. The Ag3PO4/MoS2-15 wt% (containing 15 wt% by weight of MoS2) heterojunction composite showed the highest
U
photocatalytic activity under visible-light irradiation, about 100% of the RhB was degraded in 30
N
min, whose rate constant was about 4.8 times comparing with that of pure Ag3PO4. Besides, MO
A
in solution was completely degraded over the Ag3PO4/MoS2-15 wt% composite within 30 min, and 75% of the 4-CP in solution could be degraded in 175 min. The preferable results revealed
ED
under visible light irradiation.
M
that the synergistic effect between MoS2 and Ag3PO4 improved the photodegradation activity
Meanwhile, construction of Z-scheme Ag3PO4/MoS2 heterojunction could exhibit superior photodegradation activity and stability (Zhu et al., 2016). The Ag3PO4/MoS2 with 0.648 wt%
PT
MoS2 exhibited the best photocatalytic performance. It has excellent photocatalytic degradation properties for MB (20 mg/L), RhB (20 mg/L), MO (10mg/L) and phenol (5 mg/L), all of which
CC E
are nearly completely degraded. This composite material was more easily excited by visible light to produce photoelectrons, and the photoinduced electrons could be easily from VB transferred to the CB. The lifetime of the photogenerated electron-hole pairs was improved, thereby improving
A
the photocatalytic capacity. Therefore, the degradation of organic dyes can proceed smoothly. Selecting photocatalytic degradation of MB as a representative, the process can be described as follows: Ag3PO4 + hv → Ag3PO4 (h+ + e-) (3) Ag+ + e- → Ag0 (4) MoS2 + hv → MoS2 (h+ + e-) (5) 27
0 Ag3PO4 (h+ + e-) + MoS2 (h+ + e-) Ag Ag3PO4 (h+) + MoS2 (e-) (6) →
MoS2 (e-) + O2 → MoS2 + •O2- (7) •O2- + MB → Oxideproducts (8) Ag3PO4 (h+) + MB → Ag3PO4 + Oxideproducts (9) Therefore, the intermediate product is an oxidized small molecule organic. Besides,
IP T
Small-molecule organics will continue to be oxidized and eventually become CO2 and H2O. According to the Z-scheme charge carrier transfer process, the photo-carriers oxidation/reduction capacity should be enhanced and the lifetime of photo-generated holes from Ag3PO4 and
SC R
photo-generated electrons from MoS2 could be increased, thereby enhancing the catalytic ability
A
CC E
PT
ED
M
A
N
U
(Li et al., 2015c).
28
IP T SC R U N A M ED PT CC E A
Fig. 9. TEM image (a) and HRTEM image (b) of hierarchical Ag3PO4/MoS2 nanocomposites. Photocatalytic degradation of (c) 4-CP, (d) MO and (e) RhB by different samples. Reproduced with permission(Wang et al., 2015).
To further enhance the photocatalytic performance and stability of Ag3PO4 nanomaterials, Wan et al. used various of methods, including hydrothermal method, ultrasonic exfoliation method,
29
in-situ growth method, to synthesis the Ag3PO4 nanoparticle@MoS2 quantum dots/ few-layered MoS2 nanosheets (ANP@MQD/FL-MNS) heterostructure (Wan et al., 2017). A proper amount of bulk MoS2 was dispersed in N-methyl-2-pyrrolidone (NMP), followed by ultrasonic exfoliation for 10 h to obtain a suspension. After that, the Ag3PO4 nanoparticles were mixed with the prepared MoS2 solution to obtain ANP@MQD/FL-MNS photocatalyst (Fig. 10a). As shown in Fig. 10d, Ag3PO4 nanoparticles were tightly coated with several irregular layers of MoS2 nanosheets to
IP T
construct core@shell heterostructures. The degradation of the RhB solution (10mg/L) was evaluated as the photocatalytic activity of the composite photocatalyst. After 16 min of visible
RhB
solution
(Fig.
10e).
It
was
found
the
RhB
SC R
light exposure, the ANP@MQD/FL-MNS nanocomposites showed high photodegradability to was
completely degraded
by
ANP@MQD/FL-MNS-6 composite (6 mL volume of MoS2 suspension) within 16 min. Compared
U
with other samples, the ANP@MQD/FL-MNS-6 showed the highest photocatalytic performance
N
due to the introduction of few-layer MoS2 nanosheets improving band match. Additionally, MoS2
A
quantum dots were used as electron host to improve the transfer of photogenerated electrons from Ag3PO4 nanoparticles because of the excellent electron transport capacity of MoS2 quantum dots.
A
CC E
PT
ED
photocatalytic degradation activity.
M
In light of this, photogenerated electrons could be effectively separated at the interface to promote
30
IP T SC R U N A M ED PT
CC E
Fig. 10. (a) Schematic of the synthesis of ANP@MQD/FL-MNS nano-heterogeneous structural composites. TEM images of (b) MQD/FL-MNS; (c) Ag3PO4 nanoparticles; (d) ANP@MQD/FL-MNS nanocomposites. (e) Photocatalytic degradation efficiency of different photocatalysts for RhB. Reproduced with permission (Wan et al., 2017).
A
4.6 MoS2 with transition metal oxides After the photocatalytic property of first-generation metal oxide photocatayst, TiO2 has been
proved, distinct transition metal oxide semiconductors with fine catalytic performance have been continuously exploited in the photocatalytic degradation on pollutants (Lee et al., 2016; Samu et al., 2017; Wang et al., 2016c; Wu et al., 2015). It is well known that zinc oxide (ZnO) is the most successful n-type semiconductor material 31
(Awasthi et al., 2016; Muruganandham et al., 2015; Sudha and Sivakumar, 2015), with a wide band gap of 3.37eV (Kołodziejczak-Radzimska and Jesionowski, 2014; Zalfani et al., 2016), leading to its very narrow absorption in the visible region of the solar spectrum. The photocatalytic performance of ZnO can be enhanced by combining with other narrow band gap semiconductors or plasma (Zheng et al., 2017). Based on such consideration, MoS2@ZnO nano-heterojunctions were synthesized via low-temperature hydrothermal method by Tan et al.
IP T
(Tan et al., 2014) The prepared photocatalysts were dispersed in 100 ml of MB aqueous solution (20 mg/L). An 18W daylight lamp was used as a solar analog light source. After irradiation
SC R
duration for 100 min, the C/C0 of MB was quickly dropped to 7.3% over the MoS2@ZnO heterojunctions. Besides, ZnO with different morphological structures could be also co-existed with MoS2, and ZnO nano-flowers were closely attached to the surface of MoS2 sheets (Awasthi et
U
al., 2016). The research of Awasthi et al. demostrated MoS2/ZnO composites showed a high
N
photocatalytic activity on phenol red solution. Under UV irradiation, approximately 93% of the
A
phenol red was degraded within 50 min. Meanwhile, 90% of phenol red could be removed within 80 min under the illumination of natural sun-light.
M
Cupric oxide (CuO) is also a good choice as a photocatalyst because of its excellent
ED
photochemical properties (Arai et al., 2008; Liu et al., 2013). Such indirect band gap p-type semiconductor has been widely applied in the field of photocatalysis (Jiang et al., 2009; Yu et al., 2015). When hybridizing to n-type MoS2, p-n heterojunction would form a role in promoting the
PT
use of optical energy. MoS2@CuO hetero-nanoflowers were obtained by hydrothermal method (Li et al., 2015a). The photo-degradability of MoS2@CuO samples were evaluated by MB solution
CC E
under UV-vis light. After irradiation for 100 min, the residual MB in solution remained 4.3% over MoS2@CuO hetero-nanoflowers. The photoelectrons and holes could be effectively separated at the interface of the MoS2@CuO nano-composites, thus the photocatalytic activity was enhanced.
A
Zirconium dioxide (ZrO2) is an emerging photocatalyst with a relatively wide band gap
(3.6～5.5eV) and negative conduction band potential (Hao et al., 2017; Sreethawong et al., 2013). From the inherent characteristics of ZrO2, the biggest drawback is that it only response to 4% of the solar energy, which is regarded as the biggest obstacle to its practical application. In order to improve its optical response, several approaches such as composite formation, semiconductor doping and metal ion deposition have been reported (Renuka et al., 2017; Sun et al., 2017). Taking 32
into account MoS2 as a unique co-catalyst, ZrO2/MoS2 hybrids are prepared by Chan et al. (Prabhakar Vattikuti et al., 2016), whose photocatalytic properties were tested by degradation of MO in solutions (100 mL, 10 ppm). The as-prepared sample with 20 wt% content of MoS2 exhibited the highest photodegradation efficiency under UV light, and degradation of 95.2% MO could be achieved. The combination effect of heterostructure, high specific surface area, plenty of surface active sites and high porosity of MoS2 make it play an irreplaceable role in MoS2/ZrO2
IP T
hybrid photocatalyst, which is vital for the transfer and separation of photoelectrons at the interface.
SC R
Molybdenum oxides (MoOx) can be also combined with MoS2 for environmental and energy issues (Cummins et al., 2015; Hu et al., 2015; Truong et al., 2017). Zhou et al. prepared vertically aligned MoS2/MoOx heterostructures by vapor deposition (Zhou et al., 2014). The photocatalytic
U
performance test was carried out by degradating 8 mL of 0.4×10-5 mol/L RhB aqueous solution.
N
The highest degradation rate of RhB could reach 97% after 120 min of visible light irradiation. In
A
order to study the practical value of the best sample in wastewater treatment, at different pH values (from 2 to 7), the degradation efficiency of RhB over MoS2/MoOx remained above 70%.
M
The integration with few-layered MoS2 can significantly increase the photocatalytic activity of
ED
MoOx, and the composite nanostructures play a synergistic role in collecting photogenerated carriers, resulting in promotion of photodegradation efficiency. Otherwise, the photocatalysts of MoS2 coupling with transition metal oxides and other
PT
components forming ternary composites were also well studied. For example, ternary mixed nanomaterials Fe3O4@MoS2/Ag3PO4 enhanced photocatalytic performance for organic dyes under
CC E
visible light irradiation comparing to the individual material (Guo et al., 2016). It can be seen from Fig. 11a-b that Ag3PO4 nanoparticles were uniformly deposited on the core-shell structure of Fe3O4@MoS2. RhB (20 mg/L) and congo red (CR, the concentration of 30 mg/L) as typical
A
organic contaminants were degraded by Fe3O4@MoS2/Ag3PO4 under visible light irradiation, whose degradation rate was up to 98.90% and 90.74% respectively after 10 min irradiation (Fig. 11c-d).
Novel
hierarchical
Fe3O4@MoS2/Ag3PO4
composites
exhibited
a
superior
photodegradation activity due to the Z-scheme mechanism between MoS2 and Ag3PO4, which reduced the recombination rate of photogenerated electrons. Remarkably, Fe3+ and Fe2+ of Fe3O4 played the role of photoelectron traps; and moreover, MoS2 nanosheets provided a large specific 33
M
A
N
U
SC R
IP T
surface area for Ag3PO4 deposition, resulting in a greater number of photocatalytic reactive sites.
PT
ED
Fig. 11. (a) TEM image of Fe3O4@MoS2/Ag3PO4-6%. (b) High-magnification TEM image of Fe3O4@MoS2/Ag3PO4-6%. Photocatalytic efficiency of different photocatalysts for (c) CR and (d) RhB. Reproduced with permission (Guo et al., 2016).
In conclusion, the incorporation of transition metal oxide nanoparticles into MoS2 can
CC E
promote photodegradation, being attributed to the reduced recombination rate of photogenerated electrons and holes. In addition, the MoS2 nanosheets provide a high specific surface area, which allows more metals to be deposited on the lamellar structure and contributes to the formation of
A
special structures. 5. Outlooks
As a unique representative of layered materials, MoS2 has been widely explored as co-catalyst for photodegradation contaminants. It can be compounded with a variety of materials, such as graphene, carbon nitride and TiO2, which is aimed to enhance photocatalytic degradation
34
efficiency. However, there are still many problems with the degradation of actual pollutants in MoS2-based composites. For example, the degradation mechanism of MoS2-based composites is not very clear and the practical application of materials is limited. It is due to the fact that the photocatalytic degradation technology has the disadvantages of low utilization of light energy, limited practical application, and low recovery rate. It is extremely urgent to develop efficient and inexpensive MoS2 composite photocatalysts for the practical pollutants of photodegradation.
IP T
It is highly important to use a reasonable way to control the number of MoS2 layers in order to obtain a matching band for charge separation. Meanwhile, modification of MoS2 is another
SC R
practical method in order to obtain more excellent photodegradation catalyst. Overall, in this review, we have outlined the recent progress in the construction of co-catalyst MoS2 nanomaterials for the photocatalytic degradation of organic pollutants. It will speed up the
U
exploration of novel, non-toxic, light-stable, scalable and inexpensive co-catalyst MoS2
N
nanomaterials for photocatalytic degradation of organic pollutants. In the near future, MoS2
A
nanocomposites will be the most promising photocatalyst in the field of photodegradation of
M
organic pollutants. Acknowledgement
ED
The authors of this work gratefully appreciate the financial support provided by National Natural Science Foundation of China (No. 41573096), Program for Changjiang Scholars and
CC E
References
PT
Innovative Research Team in University (No. IRT13078).
A
Ahn, C., Lee, J., Kim, H.U., Bark, H., Jeon, M., Ryu, G.H., Lee, Z., Yeom, G.Y., Kim, K., Jung, J., Kim, Y., Lee, C., Kim, T., 2015. Low-Temperature Synthesis of Large-Scale Molybdenum Disulfide Thin Films Directly on a Plastic Substrate Using Plasma-Enhanced Chemical Vapor Deposition. Adv Mater 27, 5223-5229. Akple, M.S., Low, J., Liu, S., Cheng, B., Yu, J., Ho, W., 2016. Fabrication and enhanced CO2 reduction performance of N-self-doped TiO2 microsheet photocatalyst by bi-cocatalyst modification. Journal of CO2 Utilization 16, 442-449. Arai, T., Yanagida, M., Konishi, Y., Iwasaki, Y., Sugihara, H., Sayama, K., 2008. Promotion effect of CuO co-catalyst on WO3-catalyzed photodegradation of organic substances. Catalysis Communications 9, 1254-1258. Awasthi, G.P., Adhikari, S.P., Ko, S., Kim, H.J., Park, C.H., Kim, C.S., 2016. Facile synthesis of ZnO flowers modified graphene like MoS2 sheets for enhanced visible-light-driven photocatalytic activity and antibacterial properties. Journal of Alloys and Compounds 682, 208-215.
35
A
CC E
PT
ED
M
A
N
U
SC R
IP T
Bai, S., Wang, L., Chen, X., Du, J., Xiong, Y., 2014. Chemically exfoliated metallic MoS2 nanosheets: A promising supporting co-catalyst for enhancing the photocatalytic performance of TiO2 nanocrystals. Nano Research 8, 175-183. Berntsen, N., Gutjahr, T., Loeffler, L., Seshadri, R., 2003. A Solvothermal Route to High-Surface-Area Nanostructured MoS2. Chem. Mater 15, 4498-4502. Cabán-Acevedo, M., Stone, M.L., Schmidt, J.R., Thomas, J.G., Ding, Q., Chang, H.-C., Jin, S., 2015. Ecient hydrogen evolution catalysis usingternary pyrite-type cobalt phosphosulphide. nature materials 14, 1245-1251. Chabot, V., Higgins, D., Yu, A., Xiao, X., Chen, Z., Zhang, J., 2014. A review of graphene and graphene oxide sponge: material synthesis and applications to energy and the environment. Energy & Environmental Science 7, 1564. Chang, K., Chen, W., 2011. In situ synthesis of MoS2/graphene nanosheet composites with extraordinarily high electrochemical performance for lithium ion batteries. Chem Commun (Camb) 47, 4252-4254. Chang, K., Hai, X., Pang, H., Zhang, H., Shi, L., Liu, G., Liu, H., Zhao, G., Li, M., Ye, J., 2016. Targeted Synthesis of 2H- and 1T-Phase MoS2 Monolayers for Catalytic Hydrogen Evolution. Adv Mater 28, 10033-10041. Chen, L., He, J., Liu, Y., Chen, P., Au, C.-T., Yin, S.-F., 2016. Recent advances in bismuth-containing photocatalysts with heterojunctions. Chinese Journal of Catalysis 37, 780-791. Chen, L., Shi, G., Shen, J., Peng, B., Zhang, B., Wang, Y., Bian, F., Wang, J., Li, D., Qian, Z., Xu, G., Liu, G., Zeng, J., Zhang, L., Yang, Y., Zhou, G., Wu, M., Jin, W., Li, J., Fang, H., 2017. Ion sieving in graphene oxide membranes via cationic control of interlayer spacing. Nature 550, 380. Chen, S., Hu, Y., Meng, S., Fu, X., 2014a. Study on the separation mechanisms of photogenerated electrons and holes for composite photocatalysts g-C3N4-WO3. Applied Catalysis B: Environmental 150-151, 564-573. Chen, X., Dai, Y., Wang, X., 2015. Methods and mechanism for improvement of photocatalytic activity and stability of Ag3PO4: A review. Journal of Alloys and Compounds 649, 910-932. Chen, X., Mao, S.S., 2007. Titanium Dioxide Nanomaterials Synthesis, Properties, Modifications, and Applications. Chemical Reviews 107, 2891-2959. Chen, Z.H., Sun, P., Fan, B., Zhang, Z.G., Fang, X.M., 2014b. In Situ Template-Free Ion-Exchange Process to Prepare Visible-Light-Active g-C3N4/NiS Hybrid Photocatalysts with Enhanced Hydrogen Evolution Activity. J Phys Chem C 118, 7801-7807. Cheng, X.L., Jiang, J.S., Jin, C.Y., Lin, C.C., Zeng, Y., Zhang, Q.H., 2014. Cauliflower-like α-Fe 2 O 3 microstructures: Toluene–water interface-assisted synthesis, characterization, and applications in wastewater treatment and visible-light photocatalysis. Chemical Engineering Journal 236, 139-148. Chhowalla, M., Shin, H.S., Eda, G., Li, L.J., Loh, K.P., Zhang, H., 2013. The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets. Nat Chem 5, 263-275. Chung, D.Y., Park, S.K., Chung, Y.H., Yu, S.H., Lim, D.H., Jung, N., Ham, H.C., Park, H.Y., Piao, Y., Yoo, S.J., Sung, Y.E., 2014. Edge-exposed MoS2 nano-assembled structures as efficient electrocatalysts for hydrogen evolution reaction. Nanoscale 6, 2131-2136. Coleman, J.N., Lotya, M., O’Neill, A., Bergin, S.D., Nicolosi, V., 2011. Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials. Science 331, 568-571. Cravanzola, S., Cesano, F., Magnacca, G., Zecchina, A., Scarano, D., 2016. Designing rGO/MoS2 hybrid nanostructures for photocatalytic applications. RSC Adv. 6, 59001-59008. Cuellar, E.L., Martínez-de la Cruz, A., Torres, N.C., Cortez, J.O., 2015. Deposition of BiOBr thin films by thermal evaporation and evaluation of its photocatalytic activity. Catalysis Today 252, 2-6.
36
A
CC E
PT
ED
M
A
N
U
SC R
IP T
Cummins, D.R., Martinez, U., Kappera, R., Voiry, D., Martinez-Garcia, A., Jasinski, J., Kelly, D., Chhowalla, M., Mohite, A.D., Sunkara, M.K., Gupta, G., 2015. Catalytic Activity in Lithium-Treated Core–Shell MoOx/MoS2Nanowires. The Journal of Physical Chemistry C 119, 22908-22914. Di, J., Xia, J., Ge, Y., Xu, L., Xu, H., Chen, J., He, M., Li, H., 2014. Facile fabrication and enhanced visible light photocatalytic activity of few-layer MoS2 coupled BiOBr microspheres. Dalton Trans 43, 15429-15438. Dong, H., Zeng, G., Tang, L., Fan, C., Zhang, C., He, X., He, Y., 2015. An overview on limitations of TiO2-based particles for photocatalytic degradation of organic pollutants and the corresponding countermeasures. Water Res 79, 128-146. Dumcenco, D., Ovchinnikov, D., Marinov, K., Lazi, P., Gillet, P., Kis, A., 2015. Large-Area Epitaxial Mono layer MoS2. ACS NANO 9, 4611-4620. Eda, G., Yamaguchi, H., Voiry, D., Fujita, T., Chen, M., Chhowalla, M., 2011. Photoluminescence from chemically exfoliated MoS2. Nano letters 11, 5111-5116. Frindt, R.F., 1966. Single Crystals of MoS2 Several Molecular Layers Thick. Journal of Applied Physics 37, 1928-1929. Fujishima, A., Honda, K., 1972. Electrochemical photolysis of water at a semiconductor electrode. Nature 238, 37-38. Guardia, L., Paredes, J.I., Munuera, J.M., Villar-Rodil, S., Ayan-Varela, M., Martinez-Alonso, A., Tascon, J.M., 2014. Chemically exfoliated MoS2 nanosheets as an efficient catalyst for reduction reactions in the aqueous phase. ACS applied materials & interfaces 6, 21702-21710. Guo, N., Li, H., Xu, X., Yu, H., 2016. Hierarchical Fe3O4@MoS2/Ag3PO4 magnetic nanocomposites: Enhanced and stable photocatalytic performance for water purification under visible light irradiation. Applied Surface Science 389, 227-239. Guo, Y., Gan, L., Shang, C., Wang, E., Wang, J., 2017. A Cake-Style CoS2@MoS2/RGO Hybrid Catalyst for Efficient Hydrogen Evolution. Advanced Functional Materials 27, 1602699. Gupta, A., Arunachalam, V., Vasudevan, S., 2016. Liquid-Phase Exfoliation of MoS2 Nanosheets: The Critical Role of Trace Water. J Phys Chem Lett 7, 4884-4890. Han, B., Hu, Y.H., 2016. MoS2 as a co-catalyst for photocatalytic hydrogen production from water. Energy Science & Engineering 4, 285-304. Hao, R., Wang, G., Tang, H., Sun, L., Xu, C., Han, D., 2016. Template-free preparation of macro/mesoporous g-C3N4/TiO2 heterojunction photocatalysts with enhanced visible light photocatalytic activity. Applied Catalysis B: Environmental 187, 47-58. Hao, Y., Li, L., Zhang, J., Luo, H., Zhang, X., Chen, E., 2017. Multilayer and open structure of dendritic crosslinked CeO2-ZrO2 composite: Enhanced photocatalytic degradation and water splitting performance. International Journal of Hydrogen Energy 42, 5916-5929. Hu, L., 2014. Fabrication of 3D Hierarchical MoS2@Polyaniline and MoS2@C Architectures for Lithium-Ion Battery Applications. ACS Appl. Mater. Interfaces 6, 14644-14652. Hu, X., Zhang, W., Liu, X., Mei, Y., Huang, Y., 2015. Nanostructured Mo-based electrode materials for electrochemical energy storage. Chem Soc Rev 44, 2376-2404. Huang, W., Liu, N., Zhang, X., Wu, M., Tang, L., 2017. Metal organic framework g-C3N4/MIL-53(Fe) heterojunctions with enhanced photocatalytic activity for Cr(VI) reduction under visible light. Applied Surface Science 425, 107-116. Huang, Y., Fan, W., Long, B., Li, H., Zhao, F., Liu, Z., Tong, Y., Ji, H., 2016. Visible light Bi2S3/Bi2O3/Bi2O2CO3 photocatalyst for effective degradation of organic pollutions. Applied Catalysis B:
37
A
CC E
PT
ED
M
A
N
U
SC R
IP T
Environmental 185, 68-76. Jia, T., Kolpin, A., Ma, C., Chan, R.C., Kwok, W.M., Tsang, S.C., 2014. A graphene dispersed CdS-MoS2 nanocrystal ensemble for cooperative photocatalytic hydrogen production from water. Chem Commun (Camb) 50, 1185-1188. Jiang, H.-q., Endo, H., Natori, H., Nagai, M., Kobayashi, K., 2009. Fabrication and efficient photocatalytic degradation of methylene blue over CuO/BiVO4 composite under visible-light irradiation. Materials Research Bulletin 44, 700-706. Jiang, J., Wang, H., Chen, X., Li, S., Xie, T., Wang, D., Lin, Y., 2017. Enhanced photocatalytic degradation of phenol and photogenerated charges transfer property over BiOI-loaded ZnO composites. J Colloid Interface Sci 494, 130-138. Jo, W.-K., Lee, J.Y., Selvam, N.C.S., 2016. Synthesis of MoS2 nanosheets loaded ZnO–g-C3N4 nanocomposites for enhanced photocatalytic applications. Chemical Engineering Journal 289, 306-318. Khan, S., Malik, A., 2018. Toxicity evaluation of textile effluents and role of native soil bacterium in biodegradation of a textile dye. Environmental science and pollution research international 25, 4446-4458. King, L.A., Zhao, W., Chhowalla, M., Riley, D.J., Eda, G., 2013. Photoelectrochemical properties of chemically exfoliated MoS2. Journal of Materials Chemistry A 1, 8935. Kołodziejczak-Radzimska, A., Jesionowski, T., 2014. Zinc Oxide—From Synthesis to Application: A Review. Materials 7, 2833-2881. Kudo, A., Miseki, Y., 2009. Heterogeneous photocatalyst materials for water splitting. Chemical Society Reviews 38, 253-278. Kumar, S., Sharma, V., Bhattacharyya, K., Krishnan, V., 2016. Synergetic effect of MoS2–RGO doping to enhance the photocatalytic performance of ZnO nanoparticles. New J. Chem. 40, 5185-5197. Lee, C., Yan, H., Brus, L.E., Heinz, T.F., Ryu, S., 2010. Anomalous Lattice Vibrations of Single- and Few-Layer MoS2. ACS NANO 4, 2695-2700. Lee, K.M., Lai, C.W., Ngai, K.S., Juan, J.C., 2016. Recent developments of zinc oxide based photocatalyst in water treatment technology: a review. Water research 88, 428-448. Lee, Y.H., Zhang, X.Q., Zhang, W., Chang, M.T., Lin, C.T., Chang, K.D., Yu, Y.C., Wang, J.T., Chang, C.S., Li, L.J., Lin, T.W., 2012. Synthesis of large-area MoS2 atomic layers with chemical vapor deposition. Adv Mater 24, 2320-2325. Lei, Z.D., Wang, J.J., Wang, L., Yang, X.Y., Xu, G., Tang, L., 2016. Efficient photocatalytic degradation of ibuprofen in aqueous solution using novel visible-light responsive graphene quantum dot/AgVO3 nanoribbons. Journal of hazardous materials 312, 298-306. Li, D., Bancroft, G.M., Kasrai, M., Fleet, M.E., Feng, X.H., 1995. Polarized X-ray Absorption Spectra and Electronic Structureof Molybdenite (2H-MoS2). Phys Chem Minerals 22, 123-128. Li, F., 2015. Synthesis of Cu-MoS2/rGO hybrid as non-noble metal electrocatalystsfor the hydrogen evolution reaction.pdf>. Journal of Power Sources 292, 15-22. Li, H., Liu, J., Hu, T., Du, N., Song, S., Hou, W., 2016a. Synthesis of belt-like BiOBr hierarchical nanostructure with high photocatalytic performance. Materials Research Bulletin 77, 171-177. Li, H., Wu, J., Yin, Z., Zhang, H., 2014a. Preparation and applications of mechanically exfoliated single-layer and multilayer MoS2 and WSe2 nanosheets. Acc Chem Res 47, 1067-1075. Li, H., Yin, Z., He, Q., Li, H., Huang, X., Lu, G., Fam, D.W., Tok, A.I., Zhang, Q., Zhang, H., 2012. Fabrication of single- and multilayer MoS2 film-based field-effect transistors for sensing NO at room temperature. Small 8, 63-67. Li, H., Yu, K., Lei, X., Guo, B., Li, C., Fu, H., Zhu, Z., 2015a. Synthesis of the MoS2@CuO heterogeneous
38
A
CC E
PT
ED
M
A
N
U
SC R
IP T
structure with improved photocatalysis performance and H2O adsorption analysis. Dalton Trans 44, 10438-10447. Li, H., Yu, K., Li, C., Guo, B., Lei, X., Fu, H., Zhu, Z., 2015b. Novel dual-petal nanostructured WS2@MoS2 with enhanced photocatalytic performance and a comprehensive first-principles investigation. J. Mater. Chem. A 3, 20225-20235. Li, J., Liu, X., Pan, L., Qin, W., Chen, T., Sun, Z., 2014b. MoS2–reduced graphene oxide composites synthesized via a microwave-assisted method for visible-light photocatalytic degradation of methylene blue. RSC Advances 4, 9647. Li, M., Wang, J., Zhang, P., Deng, Q., Zhang, J., Jiang, K., Hu, Z., Chu, J., 2017. Superior adsorption and photoinduced carries transfer behaviors of dandelion-shaped Bi2S3@MoS2: experiments and theory. Sci Rep 7, 42484. Li, T., Hu, X., Liu, C., Tang, C., Wang, X., Luo, S., 2016b. Efficient photocatalytic degradation of organic dyes and reaction mechanism with Ag2CO3/Bi2O2CO3 photocatalyst under visible light irradiation. Journal of Molecular Catalysis A: Chemical 425, 124-135. Li, W., Feng, C., Dai, S., Yue, J., Hua, F., Hou, H., 2015c. Fabrication of sulfur-doped g-C3N4/Au/CdS Z-scheme photocatalyst to improve the photocatalytic performance under visible light. Applied Catalysis B: Environmental 168-169, 465-471. Li, X., Xia, J., Zhu, W., Di, J., Wang, B., Yin, S., Chen, Z., Li, H., 2016c. Facile synthesis of few-layered MoS2 modified BiOI with enhanced visible-light photocatalytic activity. Colloids and Surfaces A: Physicochemical and Engineering Aspects 511, 1-7. Li, Y., Li, Y.-L., Araujo, C.M., Luo, W., Ahuja, R., 2013. Single-layer MoS2 as an efficient photocatalyst. Catalysis Science & Technology 3, 2214. Li, Y., Wang, H., Xie, L., Liang, Y., Hong, G., Dai, H., 2011. MoS2 nanoparticles grown on graphene: an advanced catalyst for the hydrogen evolution reaction. J Am Chem Soc 133, 7296-7299. Li, Y., Wu, S., Huang, L., Xu, H., Zhang, R., Qu, M., Gao, Q., Li, H., 2015d. g-C3N4 modified Bi2O3 composites with enhanced visible-light photocatalytic activity. Journal of Physics and Chemistry of Solids 76, 112-119. Liang, D., Jing, T., Ma, Y., Hao, J., Sun, G., Deng, M., 2016. Photocatalytic Properties of g-C6N6/g-C3N4 Heterostructure: A Theoretical Study. The Journal of Physical Chemistry C 120, 24023-24029. Liao, G., Chen, S., Quan, X., Yu, H., Zhao, H., 2012. Graphene oxide modified g-C3N4hybrid with enhanced photocatalytic capability under visible light irradiation. J. Mater. Chem. 22, 2721-2726. Lin, Y.C., Zhang, W., Huang, J.K., Liu, K.K., Lee, Y.H., Liang, C.T., Chu, C.W., Li, L.J., 2012. Wafer-scale MoS2 thin layers prepared by MoO3 sulfurization. Nanoscale 4, 6637-6641. Liu, C., Chen, J., Che, H., Huang, K., Charpentier, P.A., Xu, W.Z., Shi, W., Dong, H., 2017a. Construction and enhanced photocatalytic activities of a hydrogenated TiO2 nanobelt coated with CDs/MoS2 nanosheets. RSC Adv. 7, 8429-8442. Liu, G., Niu, P., Sun, C., Cheng, H.-M., 2010. Unique Electronic Structure Induced High Photoreactivity of Sulfur-Doped Graphitic C3N4. J Am Chem Soc 132, 11642-11648. Liu, H., Chen, D., Wang, Z., Jing, H., Zhang, R., 2017b. Microwave-assisted molten-salt rapid synthesis of isotype triazine-/heptazine based g-C3N4 heterojunctions with highly enhanced photocatalytic hydrogen evolution performance. Applied Catalysis B: Environmental 203, 300-313. Liu, N., Kim, P., Kim, J.H., Ye, J.H., Kim, S., Lee, C.J., 2014. Large-Area Atomically Thin MoS2 Nanosheets Prepared Using Electrochemical Exfoliation. ACS NANO 8, 6902-6910. Liu, W., Wang, M., Xu, C., Chen, S., 2012. Facile synthesis of g-C3N4/ZnO composite with enhanced visible
39
A
CC E
PT
ED
M
A
N
U
SC R
IP T
lightphotooxidation and photoreduction properties. Chemical Engineering Journal 209, 386-393. Liu, X., Steele, J.C., Meng, X.Z., 2017c. Usage, residue, and human health risk of antibiotics in Chinese aquaculture: A review. Environmental pollution 223, 161-169. Liu, X., Xing, Z., Zhang, Y., Li, Z., Wu, X., Tan, S., Yu, X., Zhu, Q., Zhou, W., 2017d. Fabrication of 3D flower-like black N-TiO2-x @MoS2 for unprecedented-high visible-light-driven photocatalytic performance. Applied Catalysis B: Environmental 201, 119-127. Liu, Y., Shi, J., Peng, Q., Li, Y., 2013. CuO quantum-dot-sensitized mesoporous ZnO for visible-light photocatalysis. Chemistry 19, 4319-4326. Long, L.-L., Chen, J.-J., Zhang, X., Zhang, A.-Y., Huang, Y.-X., Rong, Q., Yu, H.-Q., 2016. Layer-controlled growth of MoS2 on self-assembled flower-like Bi2S3 for enhanced photocatalysis under visible light irradiation. NPG Asia Materials 8, 1-9. Long, M., Cai, W., 2014. Advanced nanoarchitectures of silver/silver compound composites for photochemical reactions. Nanoscale 6, 7730-7742. Lopez-Sanchez, O., Lembke, D., Kayci, M., Radenovic, A., Kis, A., 2013. Ultrasensitive photodetectors based on monolayer MoS2. Nat Nanotechnol 8, 497-501. Low, J., Cheng, B., Yu, J., 2017. Surface modification and enhanced photocatalytic CO2 reduction performance of TiO2 : a review. Applied Surface Science 392, 658-686. Lu, X., Jin, Y., Zhang, X., Xu, G., Wang, D., Lv, J., Zheng, Z., Wu, Y., 2016. Controllable synthesis of graphitic C3N4/ultrathin MoS2 nanosheet hybrid nanostructures with enhanced photocatalytic performance. Dalton Trans 45, 15406-15414. Lv, J., Dai, K., Zhang, J., Geng, L., Liang, C., Liu, Q., Zhu, G., Chen, C., 2015. Facile synthesis of Z-scheme graphitic-C3N4/Bi2MoO6 nanocomposite for enhanced visible photocatalytic properties. Applied Surface Science 358, 377-384. Ma, J., Liu, Q., Zhu, L., Zou, J., Wang, K., Yang, M., Komarneni, S., 2016. Visible light photocatalytic activity enhancement of Ag3PO4 dispersed on exfoliated bentonite for degradation of rhodamine B. Applied Catalysis B: Environmental 182, 26-32. Maitra, U., Gupta, U., De, M., Datta, R., Govindaraj, A., Rao, C.N., 2013. Highly effective visible-light-induced H2 generation by single-layer 1T-MoS2 and a nanocomposite of few-layer 2H-MoS2 with heavily nitrogenated graphene. Angew Chem Int Ed Engl 52, 13057-13061. Mak, K.F., Lee, C., Hone, J., Shan, J., Heinz, T.F., 2010. Atomically thin MoS2: a new direct-gap semiconductor. Phys Rev Lett 105, 136805. Martin, D.J., Liu, G., Moniz, S.J., Bi, Y., Beale, A.M., Ye, J., Tang, J., 2015. Efficient visible driven photocatalyst, silver phosphate: performance, understanding and perspective. Chemical Society Reviews 44, 7808-7828. Mousavi, M., Habibi-Yangjeh, A., 2016. Magnetically separable ternary g-C3N4/Fe3O4/BiOI nanocomposites: Novel visible-light-driven photocatalysts based on graphitic carbon nitride. J Colloid Interface Sci 465, 83-92. Muruganandham, M., Zhang, Y.F., Suri, R., Lee, G.J., Chen, P.K., Hsieh, S.H., Sillanpaa, M., Wu, J.J., 2015. Environmental Applications of ZnO Materials. J. Nanosci. Nanotechnol. 15, 6900-6913. Najmaei, S., Liu, Z., Zhou, W., Zou, X., Shi, G., Lei, S., Yakobson, B.I., Idrobo, J.C., Ajayan, P.M., Lou, J., 2013. Vapour phase growth and grain boundary structure of molybdenum disulphide atomic layers. Nat Mater 12, 754-759. Nasirian, M., Mehrvar, M., 2016. Modification of TiO2 to enhance photocatalytic degradation of organics in aqueous solutions. Journal of Environmental Chemical Engineering 4, 4072-4082.
40
A
CC E
PT
ED
M
A
N
U
SC R
IP T
Ni, Z., Sun, Y., Zhang, Y., Dong, F., 2016. Fabrication, modification and application of (BiO)2CO3-based photocatalysts: A review. Applied Surface Science 365, 314-335. Pan, L., Liu, X., Sun, Z., Sun, C.Q., 2013. Nanophotocatalysts via microwave-assisted solution-phase synthesis for efficient photocatalysis. Journal of Materials Chemistry A 1, 8299. Peng, W.-c., Li, X.-y., 2014. Synthesis of MoS2/g-C3N4 as a solar light-responsive photocatalyst for organic degradation. Catalysis Communications 49, 63-67. Peng, Y., Meng, Z., Zhong, C., Lu, J., Yang, Z., Qian, Y., 2002. Tube- and ball-like amorphous MoS2 prepared by a solvothermal method. Materials Chemistry and Physics 73, 327-329. Prabhakar Vattikuti, S.V., Byon, C., Reddy, C.V., 2016. ZrO2/MoS2 heterojunction photocatalysts for efficient photocatalytic degradation of methyl orange. Electronic Materials Letters 12, 812-823. Qi, Y., Luan, Y., Yang, M., Wang, G., Tan, L., Li, J., 2014. Alkali concentration-dependent tailoring of highly controllable titanate nanostructures: From yolk-shell, hollow 3D nanospheres to 1D nanowires. Applied Surface Science 293, 359-365. Qian, W., Greaney, P.A., Fowler, S., Chiu, S.-K., Goforth, A.M., Jiao, J., 2014. Low-Temperature Nitrogen Doping in Ammonia Solution for Production of N-Doped TiO2-Hybridized Graphene as a Highly Efficient Photocatalyst for Water Treatment. ACS Sustainable Chemistry & Engineering 2, 1802-1810. Radisavljevic, B., Whitwick, M.B., Kis, A., 2011. Integrated circuits and logic operations based on single-layer MoS2. ACS NANO 5, 9934-9938. Renuka, L., Anantharaju, K.S., Vidya, Y.S., Nagaswarupa, H.P., Prashantha, S.C., Sharma, S.C., Nagabhushana, H., Darshan, G.P., 2017. A simple combustion method for the synthesis of multi-functional ZrO 2 /CuO nanocomposites: Excellent performance as Sunlight photocatalysts and enhanced latent fingerprint detection. Applied Catalysis B: Environmental 210, 97-115. Samu, G.F., Veres, Á., Tallósy, S.P., Janovák, L., Dékány, I., Yepez, A., Luque, R., Janáky, C., 2017. Photocatalytic, photoelectrochemical, and antibacterial activity of benign-by-design mechanochemically synthesized metal oxide nanomaterials. Catalysis Today 284, 3-10. Shan, W., Hu, Y., Bai, Z., Zheng, M., Wei, C., 2016. In situ preparation of g-C3N4/bismuth-based oxide nanocomposites with enhanced photocatalytic activity. Applied Catalysis B: Environmental 188, 1-12. Shi, J., 2012. On the Synergetic Catalytic Effect in Heterogeneous Nanocomposite Catalysts. Chemical Reviews 113, 2139-2181. Shi, L., Wang, T., Zhang, H., Chang, K., Meng, X., Liu, H., Ye, J., 2015. An Amine-Functionalized Iron(III) Metal-Organic Framework as Efficient Visible-Light Photocatalyst for Cr(VI) Reduction. Advanced science 2, 1500006. Shi, Y., Zhou, W., Lu, A.Y., Fang, W., Lee, Y.H., Hsu, A.L., Kim, S.M., Kim, K.K., Yang, H.Y., Li, L.J., Idrobo, J.C., Kong, J., 2012. van der Waals epitaxy of MoS2 layers using graphene as growth templates. Nano Lett 12, 2784-2791. Shuai, J., Yoo, H.D., Liang, Y., Li, Y., Yao, Y., Grabow, L.C., 2016. Density functional theory study of Li, Na, and Mg intercalation and diffusion in MoS2 with controlled interlayer spacing. Materials Research Express 3, 064001. Sreethawong, T., Ngamsinlapasathian, S., Yoshikawa, S., 2013. Synthesis of crystalline mesoporous-assembled ZrO2 nanoparticles via a facile surfactant-aided sol–gel process and their photocatalytic dye degradation activity. Chemical Engineering Journal 228, 256-262. Sudha, D., Sivakumar, P., 2015. Review on the photocatalytic activity of various composite catalysts. Chemical Engineering and Processing: Process Intensification 97, 112-133. Sun, T., Zhao, Z., Liang, Z., Liu, J., Shi, W., Cui, F., 2017. Efficient removal of arsenite through photocatalytic
41
A
CC E
PT
ED
M
A
N
U
SC R
IP T
oxidation and adsorption by ZrO 2 -Fe 3 O 4 magnetic nanoparticles. Applied Surface Science 416, 656-665. Tan, Y.-H., Yu, K., Li, J.-Z., Fu, H., Zhu, Z.-Q., 2014. MoS2@ZnO nano-heterojunctions with enhanced photocatalysis and field emission properties. Journal of Applied Physics 116, 064305. Tang, L., Jia, C.-t., Xue, Y.-c., Li, L., Wang, A.-q., Xu, G., Liu, N., Wu, M.-h., 2017a. Fabrication of compressible and recyclable macroscopic g-C3N4/GO aerogel hybrids for visible-light harvesting: A promising strategy for water remediation. Applied Catalysis B: Environmental 219, 241-248. Tang, L., Wang, J.-j., Jia, C.-t., Lv, G.-x., Xu, G., Li, W.-t., Wang, L., Zhang, J.-y., Wu, M.-h., 2017b. Simulated solar driven catalytic degradation of psychiatric drug carbamazepine with binary BiVO4 heterostructures sensitized by graphene quantum dots. Applied Catalysis B: Environmental 205, 587-596. Tisseraud, C., Comminges, C., Pronier, S., Pouilloux, Y., Le Valant, A., 2016. The Cu–ZnO synergy in methanol synthesis Part 3: Impact of the composition of a selective Cu@ZnO x core–shell catalyst on methanol rate explained by experimental studies and a concentric spheres model. Journal of Catalysis 343, 106-114. Truong, T.G., Meriadec, C., Fabre, B., Bergamini, J.F., de Sagazan, O., Ababou-Girard, S., Loget, G., 2017. Spontaneous decoration of silicon surfaces with MoOx nanoparticles for the sunlight-assisted hydrogen evolution reaction. Nanoscale 9, 1799-1804. Vane, C.H., Harrison, I., Kim, A.W., Moss-Hayes, V., Vickers, B.P., Hong, K., 2009. Organic and metal contamination in surface mangrove sediments of South China. Marine pollution bulletin 58, 134-144. Vattikuti, S.V.P., Byon, C., 2016. Bi2S3 nanorods embedded with MoS2 nanosheets composite for photodegradation of phenol red under visible light irradiation. Superlattices and Microstructures 100, 514-525. Verble, J.L., Wieting, T.J., 1970. Lattice Mode Degeneracy in MoS2 and Other Layer Compounds. Phys.rev.lett 25, 362-365. Vrijheid, M., Casas, M., Gascon, M., Valvi, D., Nieuwenhuijsen, M., 2016. Environmental pollutants and child health-A review of recent concerns. International journal of hygiene and environmental health 219, 331-342. Wan, J., Du, X., Liu, E., Hu, Y., Fan, J., Hu, X., 2017. Z-scheme visible-light-driven Ag3PO4 nanoparticle@MoS2 quantum dot/few-layered MoS2 nanosheet heterostructures with high efficiency and stability for photocatalytic selective oxidation. Journal of Catalysis 345, 281-294. Wang, H., Bai, Y., Yang, J., Lang, X., Li, J., Guo, L., 2012a. A facile way to rejuvenate Ag3PO4 as a recyclable highly efficient photocatalyst. Chemistry 18, 5524-5529. Wang, J., 2016. A molybdenum disulfide reduced oxide-graphenenanoflakelet-on-sheet structure for lithium ion batteries. Applied Surface Science 399, 237-244. Wang, J., Wei, B., Xu, L., Gao, H., Sun, W., Che, J., 2016a. Multilayered MoS2 coated TiO2 hollow spheres for efficient photodegradation of phenol under visible light irradiation. Materials Letters 179, 42-46. Wang, L., Chai, Y., Ren, J., Ding, J., Liu, Q., Dai, W.L., 2015. Ag3PO4 nanoparticles loaded on 3D flower-like spherical MoS2: a highly efficient hierarchical heterojunction photocatalyst. Dalton transactions 44, 14625-14634. Wang, Q., Yun, G., Bai, Y., An, N., Lian, J., Huang, H., Su, B., 2014. Photodegradation of rhodamine B with MoS2/Bi2O2CO3 composites under UV light irradiation. Applied Surface Science 313, 537-544. Wang, Q.H., Kalantar-Zadeh, K., Kis, A., Coleman, J.N., Strano, M.S., 2012b. Electronics and optoelectronics of two-dimensional transition metal dichalcogenides. Nature Nanotechnology 7, 699-712. Wang, X., Hong, M., Zhang, F., Zhuang, Z., Yu, Y., 2016b. Recyclable Nanoscale Zero Valent Iron Doped g-C3N4/MoS2 for Efficient Photocatalysis of RhB and Cr(VI) Driven by Visible Light. ACS Sustainable
42
A
CC E
PT
ED
M
A
N
U
SC R
IP T
Chemistry & Engineering 4, 4055-4063. Wang, Y., Yang, Y., Xi, L., Zhang, X., Jia, M., Xu, H., Wu, H., 2016c. A simple hydrothermal synthesis of flower-like ZnO microspheres and their improved photocatalytic activity. Materials Letters 180, 55-58. Wang, Z., Chen, T., Chen, W., Chang, K., Ma, L., Huang, G., Chen, D., Lee, J.Y., 2013. CTAB-assisted synthesis of single-layer MoS2–graphene composites as anode materials of Li-ion batteries. J. Mater. Chem. A 1, 2202-2210. Wang, Z., Huang, Y., Ho, W., Cao, J., Shen, Z., Lee, S.C., 2016d. Fabrication of Bi2O2CO3/g-C3N4 heterojunctions for efficiently photocatalytic NO in air removal: In-situ self-sacrificial synthesis, characterizations and mechanistic study. Applied Catalysis B: Environmental 199, 123-133. Weng, B., Zhang, X., Zhang, N., Tang, Z.R., Xu, Y.J., 2015. Two-dimensional MoS2 nanosheet-coated Bi2S3 discoids: synthesis, formation mechanism, and photocatalytic application. Langmuir 31, 4314-4322. Wu, M.-h., Li, L., Xue, Y.-c., Xu, G., Tang, L., Liu, N., Huang, W.-y., 2018. Fabrication of ternary GO/g-C3N4/MoS2 flower-like heterojunctions with enhanced photocatalytic activity for water remediation. Applied Catalysis B: Environmental 228, 103-112. Wu, W., Jiang, C., Roy, V.A., 2015. Recent progress in magnetic iron oxide–semiconductor composite nanomaterials as promising photocatalysts. Nanoscale 7, 38-58. Xiang, Q., Cheng, B., Yu, J., 2015. Graphene-Based Photocatalysts for Solar-Fuel Generation. Angew Chem Int Ed Engl 54, 11350-11366. Xiang, Q., Yu, J., Jaroniec, M., 2012. Synergetic effect of MoS2 and graphene as cocatalysts forenhanced photocatalytic H2 production activity of TiO2 nanoparticles. Journal of the American Chemical Society 134, 6575-6578. Xiang, Z., Wang, Y., Zhang, D., Ju, P., 2016. BiOI/BiVO4 p-n heterojunction with enhanced photocatalytic activity under visible-light irradiation. Journal of Industrial and Engineering Chemistry 40, 83-92. Xiong, F., Zhang, J., Zhu, Z., Yuan, X., Qin, S., 2015. Ultrabroadband, More than One Order Absorption Enhancement in Graphene with Plasmonic Light Trapping. Sci Rep 5, 16998. Xiong, X., Ding, L., Wang, Q., Li, Y., Jiang, Q., Hu, J., 2016. Synthesis and photocatalytic activity of BiOBr nanosheets with tunable exposed {010} facets. Applied Catalysis B: Environmental 188, 283-291. Xu, C., Xu, B., Gu, Y., Xiong, Z., Sun, J., Zhao, X.S., 2013. Graphene-based electrodes for electrochemical energy storage. Energy & Environmental Science 6, 1388. Yang, D., Sandoval, S.J., Divigalpitiya, W.M., Irwin, J.C., Frindt, R.F., 1991. Structure of single-molecular-layer MoS2. Phys Rev B Condens Matter 43, 12053-12056. Yang, J., Wu, X., Li, X., Liu, Y., Gao, M., Liu, X., Kong, L., Yang, S., 2011. Synthesis and characterization of nitrogen-rich carbon nitride nanobelts by pyrolysis of melamine. Applied Physics A 105, 161-166. Yang, S.Y., Shim, G.W., Seo, S.-B., Choi, S.-Y., 2016. Effective shape-controlled growth of monolayer MoS2 flakes by powder-based chemical vapor deposition. Nano Research 10, 255-262. Yang, X., Qin, J., Jiang, Y., Chen, K., Yan, X., Zhang, D., Li, R., Tang, H., 2015. Fabrication of P25/Ag3PO4/graphene oxide heterostructures for enhanced solar photocatalytic degradation of organic pollutants and bacteria. Applied Catalysis B: Environmental 166-167, 231-240. Yi-Zhu, P., Wan-Hong, M., Man-Ke, J., Xiao-Rong, Z., Johnson, D.M., Ying-Ping, H., 2016. Comparing the degradation of acetochlor to RhB using BiOBr under visible light: A significantly different rate-catalyst dose relationship. Applied Catalysis B: Environmental 181, 517-523. Yu, J., Zhuang, S., Xu, X., Zhu, W., Feng, B., Hu, J., 2015. Photogenerated electron reservoir in hetero-p–n CuO–ZnO nanocomposite device for visible-light-driven photocatalytic reduction of aqueous Cr(vi). J. Mater. Chem. A 3, 1199-1207.
43
A
CC E
PT
ED
M
A
N
U
SC R
IP T
Yuan, Y.-J., Ye, Z.-J., Lu, H.-W., Hu, B., Li, Y.-H., Chen, D.-Q., Zhong, J.-S., Yu, Z.-T., Zou, Z.-G., 2016. Constructing Anatase TiO2 Nanosheets with Exposed (001) Facets/Layered MoS2 Two-Dimensional Nanojunctions for Enhanced Solar Hydrogen Generation. ACS Catalysis 6, 532-541. Yuan, Y., Liu, B., Li, Q., Shen, P., Chen, G., 2017. Excellent photocatalytic performance of few-layer MoS2/graphene hybrids. Journal of Alloys and Compounds. Zalfani, M., van der Schueren, B., Mahdouani, M., Bourguiga, R., Yu, W.-B., Wu, M., Deparis, O., Li, Y., Su, B.-L., 2016. ZnO quantum dots decorated 3DOM TiO2 nanocomposites: Symbiose of quantum size effects and photonic structure for highly enhanced photocatalytic degradation of organic pollutants. Applied Catalysis B: Environmental 199, 187-198. Zeng, H., Dai, J., Yao, W., Xiao, D., Cui, X., 2012. Valley polarization in MoS2 monolayers by optical pumping. Nat Nanotechnol 7, 490-493. Zeng, Z., Yin, Z., Huang, X., Li, H., He, Q., Lu, G., Boey, F., Zhang, H., 2011. Single-layer semiconducting nanosheets: high-yield preparation and device fabrication. Angew Chem Int Ed Engl 50, 11093-11097. Zhang, G., Huang, C., Wang, X., 2015. Dispersing molecular cobalt in graphitic carbon nitride frameworks for photocatalytic water oxidation. Small 11, 1215-1221. Zhang, G., Lan, Z.-A., Lin, L., Lin, S., Wang, X., 2016a. Overall water splitting by Pt/g-C3N4 photocatalysts without using sacrificial agents. Chem. Sci. 7, 3062-3066. Zhang, J.-J., Gao, B., Dong, S., 2016b. Strain-enhanced superconductivity ofMoX2(X=S or Se)bilayers with Na intercalation. Physical Review B 93. Zhang, J., Sun, J., Maeda, K., Domen, K., Liu, P., Antonietti, M., Fu, X., Wang, X., 2011. Sulfur-mediated synthesis of carbon nitride: Band-gap engineering and improved functions for photocatalysis. Energy Environ. Sci. 4, 675-678. Zhang, X., Lai, Z., Tan, C., Zhang, H., 2016c. Solution-Processed Two-Dimensional MoS2 Nanosheets: Preparation, Hybridization, and Applications. Angewandte Chemie International Edition 55, 8816-8838. Zhang, X., Li, X., Shao, C., Li, J., Zhang, M., Zhang, P., Wang, K., Lu, N., Liu, Y., 2013. One-dimensional hierarchical heterostructures of In2S3 nanosheets on electrospun TiO2 nanofibers with enhanced visible photocatalytic activity. J Hazard Mater 260, 892-900. Zhang, X., Shao, C., Li, X., Miao, F., Wang, K., Lu, N., Liu, Y., 2016d. 3D MoS2 nanosheet/TiO2 nanofiber heterostructures with enhanced photocatalytic activity under UV irradiation. Journal of Alloys and Compounds 686, 137-144. Zhao, W., Liu, Y., Wei, Z., Yang, S., He, H., Sun, C., 2016. Fabrication of a novel p–n heterojunction photocatalyst n-BiVO4@p-MoS2 with core–shell structure and its excellent visible-light photocatalytic reduction and oxidation activities. Applied Catalysis B: Environmental 185, 242-252. Zhao, Z., Sun, Y., Dong, F., 2015a. Graphitic carbon nitride based nanocomposites: a review. Nanoscale 7, 15-37. Zhao, Z., Tian, J., Sang, Y., Cabot, A., Liu, H., 2015b. Structure, synthesis, and applications of TiO2 nanobelts. Adv Mater 27, 2557-2582. Zheng, Y., Zhang, W., Li, Y., Chen, J., Yu, B., Wang, J., Zhang, L., Zhang, J., 2017. Energy related CO 2 conversion and utilization: Advanced materials/nanomaterials, reaction mechanisms and technologies. Nano Energy 40, 512-539. Zhong, X.-L., Li, Z.-Y., 2012. Giant Enhancement of Near-Ultraviolet Light Absorption by TiO2 via a Three-Dimensional Aluminum Plasmonic Nano Funnel-Antenna. The Journal of Physical Chemistry C 116, 21547-21555. Zhou, G., Xu, X., Yu, J., Feng, B., Zhang, Y., Hu, J., Zhou, Y., 2014. Vertically aligned
44
A
CC E
PT
ED
M
A
N
U
SC R
IP T
MoS2/MoOxheterojunction nanosheets for enhanced visible-light photocatalytic activity and photostability. CrystEngComm 16, 9025-9032. Zhou, W., Yin, Z., Du, Y., Huang, X., Zeng, Z., Fan, Z., Liu, H., Wang, J., Zhang, H., 2013. Synthesis of few-layer MoS2 nanosheet-coated TiO2 nanobelt heterostructures for enhanced photocatalytic activities. Small 9, 140-147. Zhu, C., Zhang, L., Jiang, B., Zheng, J., Hu, P., Li, S., Wu, M., Wu, W., 2016. Fabrication of Z-scheme Ag3PO4/MoS2 composites with enhanced photocatalytic activity and stability for organic pollutant degradation. Applied Surface Science 377, 99-108. Zou, X., Dong, Y., Zhang, X., Cui, Y., Ou, X., Qi, X., 2017. The highly enhanced visible light photocatalytic degradation of gaseous o-dichlorobenzene through fabricating like-flowers BiPO 4/BiOBr pn heterojunction composites. Applied Surface Science 391, 525-534.
45
S0957-5820(18)30357-4 https://doi.org/10.1016/j.psep.2018.06.025 PSEP 1427
To appear in:
Process Safety and Environment Protection
Received date: Revised date: Accepted date:
16-3-2018 15-6-2018 18-6-2018
Please cite this article as: Wu, Ming-hong, Li, Lin, Liu, Ning, Wang, De-jin, Xue, Yuancheng, Tang, Liang, Molybdenum disulfide (MoS2) as a co-catalyst for photocatalytic degradation of organic contaminants: A review.Process Safety and Environment Protection https://doi.org/10.1016/j.psep.2018.06.025 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Molybdenum disulfide (MoS2) as a co-catalyst for photocatalytic degradation of organic contaminants: A review Ming-hong Wua, Lin Lia, Ning Liub, De-jin Wangc,*, Yuan-cheng Xuea, Liang Tanga,* a
School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444, PR
b
IP T
China
School of Environment and Architecture, University of Shanghai for Science and Technology,
c
SC R
Shanghai 200093, PR China
School of Resources and Environment, Anqing Normal University, Anqing 246052, PR China
* Corresponding authors. E-mail addresses: [email protected] (L. Tang);
A
N
U
[email protected] (D. J. Wang)
A
CC E
PT
ED
M
Graphical abstract
1
Abstract Photocatalytic degradation is an emerging, efficient and energy-save technology for the removal of organic contaminants from the water environment. With the development of two-dimensional functional materials, molybdenum disulfide (MoS2) has become one of the most popular emerging co-catalysts due to its high photocatalytic activity, strong adsorptivity, low cost and non-toxicity, especially applied to the photocatalytic degradation of organic contaminants. In
IP T
this paper, we review the recent research progresses of graphene, carbon-nitrogen compounds, TiO2 and bismuth compounds supported on MoS2 co-catalyst, which were applied to
SC R
photocatalytic degradation of various organic contaminants such as methylene blue (MB), methyl orange (MO) and rhodamine B (RhB), etc. Meanwhile, the basic processes of photocatalytic degradation of organic pollutants have also been briefly analyzed and compared. More
U
importantly, MoS2 co-catalyst plays an integral role in nanocomposites, especially in accelerating
N
photo-induced electron transport and reducing electron recombination rates. It is indicated that
A
MoS2-based composites are promising photocatalysts for photocatalytic degradation of
M
environmental pollutants. Keywords
ED
Molybdenum disulfide; Two-dimensional (2D) materials; Photodegradation; Organic pollutants;
CC E
1. Introduction
PT
Heterojunctions
As global environmental problems become more and more serious, the demand for
sustainable and green materials has become a urgent concern (Guo et al., 2017). Especially,
A
excessive discharge of wastewater containing organic chemicals into the environment has become a major issue around the world, which poses a significant risk to living organisms and environment due to their persistence and toxicity (Cheng et al., 2014). Methylene blue (MB), methyl orange (MO) and rhodamine B (RhB) are widely present in textile wastewater. Insufficient treatment of textile effluents is directly or indirectly related to environmental pollution and various human diseases (Khan and Malik, 2018; Vane et al., 2009). For example, the presence of 2
dyes in water not only interferes with the operation of ecosystems, but toxic substances can seriously affect human health (Liu et al., 2017c; Tang et al., 2017b). In addition, some organic pollutants may affect fetal neurodevelopment and birth weight, such as polychlorinated biphenyls and organophosphorus pesticides (Vrijheid et al., 2016). It is hoped that certain approaches will be able to effectively and economically eliminate the harmful substances in the aqueous environment. By now, photocatalysis is commonly considered as one of the most economical and
IP T
environmentally-friendly methods (Liu et al., 2012). Under the premise that the photocatalyst property does not change, the principle of photocatalysis is to convert light energy into chemical
SC R
energy under the irradiation of light, and generate a corresponding free radical group to have the redox ability (Fujishima and Honda, 1972). Photocatalytic degradation makes full use of semiconductor photocatalysis properties for water treatment due to its efficient light response
U
capability (Kudo and Miseki, 2009; Shi, 2012). However, traditional photocatalysts containing
N
noble metals, such as Pt,Rh and Ag , may clearly limit their practical applications because of high
A
price and low reserve (Chen and Mao, 2007; Lei et al., 2016; Xiang et al., 2012). In order to efficiently harvest the light, researchers tried hard to exploit novel semiconductor photocatalysts
M
with high photo-response and practicability.
ED
Molybdenum disulfide (MoS2), a kind of two-dimensional (2D) layered transitionmetal dichalcogenide, has achieved significant development in the past few years (Cabán-Acevedo et al., 2015). It has been attached much attention because of its unique physical, chemical and electrical
PT
properties (Chhowalla et al., 2013; Li et al., 2014a). Moreover, MoS2 has superior adsorption capacity and tunable band structure. Base on the above merits, MoS2 has been widely used as
CC E
co-photocalyst in the preparation of composites, especially in the field of photocatalysis on removal of organic contaminants. Herein, we summarize the recent experience in the photocatalytic degradation of organic compounds with MoS2 co-catalyst, in order to better explore
A
the application of MoS2 in the field of photocatalytic degradation of organic matter, and promote the treatment approach for organic wastewater. 2. Structures and synthesis of MoS2 As the main component of molybdenite (Li et al., 1995), MoS2 belongs to the hexagonal system, is a kind of anti-magnetic compound and exhibits semiconductor properties. Starting from 3
the pioneering research done by Frindt and his collaborators, MoS2 has been studied for several decades (Frindt, 1966; Yang et al., 1991). So far, the crystal structures of MoS2 including 1T, 3R and 2H have been widely recognized (Fig. 1). Chemical stability, anisotropy and antiphotocorrosion of MoS2 are attributed to unique lamellar structure. 2.1 Structures of MoS2
IP T
As shown in Fig. 1, the single layer of MoS2 has S-Mo-S structure, which is similar to sandwich. The atoms are connected with each other by covalent bonds (Chang and Chen, 2011;
SC R
Chen et al., 2017; Wang, 2016; Zhang et al., 2016b). The stack between layers is combined by a weak van der Waals forces (Verble and Wieting, 1970). The Mo-S length, the crystal lattice constant, and the distance between the upper and lower sulfur atoms are 2.4, 3.2, 3.1 Å,
U
respectively (Han and Hu, 2016). It turns out that monolayer MoS2 has two phrases: metallic 1T and semiconducting 2H. MoS2 can be used as a semiconductor material with a direct (indirect)
N
band-gap of 1.96eV (1.2eV) (King et al., 2013; Lee et al., 2010; Li et al., 2013; Mak et al., 2010),
A
suggesting that such material can perform strong absorption in the visible region of the solar
M
spectrum, and it is suitable for the role of co-catalyst. Quantum effect can explain the band phenomenon (Wang et al., 2012b). The composite materials formed through hybridizing MoS2
ED
with other semiconductor materials, such as WS2@MoS2 (Li et al., 2015b), (Fe0) doped
A
CC E
performance.
PT
g-C3N4/MoS2 (Wang et al., 2016b), can significantly enhance the photocatalytic degradation
4
IP T SC R U N
2.2 Preparation of MoS2
ED
M
A
Fig. 1. Crystal structures of MoS2: (a) Top view of MoS2 monolayer hexagonal crystal structure. (b) Trigonal prismatic (2H) and octahedral (1T) unit cell structures. Reproduced with permission (Eda et al., 2011; Zeng et al., 2012).
Single layer of MoS2 can be obtained by mechanical and chemical methods. The preparation
PT
of MoS2 is usually classified as two strategies, that is to say, “top-down” exfoliation method and “bottom-up” synthesis method (Zhang et al., 2016c). Until current time, MoS2 with thin layers
CC E
were prepared with various synthesis methods. 2.2.1 Mechanical exfoliation
A
Exfoliating single-layer MoS2 from SiO2/Si with Scotch-tape method is similar to the
technique of preparing graphene sheets (Li et al., 2014a; Lopez-Sanchez et al., 2013; Zeng et al., 2012). The MoS2 flakes were mechanically stripped on a 300 nm thick SiO2 covered silicon substrate using a low track cleanroom tapes. Single-layer and multilayer MoS2 blocks were positioned with a bright field optical microscope (Eclipse LV100D, Nikon). At last, the layer assignment was confirmed by atomic force microscope (AFM) measuring film thickness in
5
tapping mode in air. Mechanically exfoliated MoS2 monolayers show significantly improved optical performance (Li et al., 2012). 2.2.2 Exfoliation method The exfoliation method includes chemical exfoliation (Guardia et al., 2014), liquid-phase exfoliation (Gupta et al., 2016) and electrochemical exfoliation (Fig. 2a) (Liu et al., 2014). The
IP T
studies have demonstrated that monolayer and few-layer MoS2 nanosheets can be obtained with exfoliation method. In addition, 1T metallic MoS2 can be received through ion intercalation (Bai et al., 2014; Maitra et al., 2013). Alkali metal ion intercalation is the most common way (Shuai et
SC R
al., 2016), especially the lithium ion intercalation (Chang et al., 2016). Under argon atmosphere (Guardia et al., 2014), a suitable amount of n-butyllithium in hexane is poured into a defined amount of MoS2 powder, and the dispersion is heated to 65°C overnight. The resulting lithium
U
intercalation product (LixMoS2) was rinsed with a sufficient amount of hexane to remove
N
unreacted n-butyllithium and its organic residue. Immediately afterwards, the embedded MoS2
A
was dispersed in deionized water and centrifuged at high speed to obtain a stable aqueous
M
suspension of MoS2 nanosheets. Ultrasonic method is classified as liquid-phase exfoliation (Coleman et al., 2011). MoS2 can effectively disperse in the solution by using sonication.
ED
Compared with lithium ion intercalation, this method can maintain the preparation of the MoS 2 nanosheets semiconductor properties. The electrochemical exfoliation process is performed by
PT
applying a positive bias to the working electrode (Liu et al., 2014). The exfoliation method is simple, fast and scalable, and other transition metal dichalcogenides are able to be exfoliated with
CC E
the same method.
2.2.3 Hydrothermal method Hydrothermal method is the most economical and universal method to synthesize MoS2.
A
Thiourea and thioacetamide are the most common source of sulfur (Zhou et al., 2013). Molybdenum salts, such as Na2MoO4 (Chung et al., 2014), (NH4)6Mo7O24 (Shi et al., 2015), can be used as the main source of molybdenum. For example, 60 mg of thioacetamide and 30 mg of sodium molybdate were added to 20 mL of deionized water to form a transparent solution. The mixed solution was transferred to a Teflon-lined stainless steel autoclave, which was heated in an electric oven at 200°C for 24 h. Afterward, a black product was collected after centrifugation and 6
dried at 60°C for 12 h. However, hydrothermal method cannot accurately control the number of MoS2 layers. It is prone to agglomeration, affecting the morphology and size of the products. 2.2.4 Solvothermal method Solvothermal method is developed on the basis of hydrothermal method, and the main difference of solvothermal method from the latter is that the preparation condition is organic
IP T
solvent rather than water. Different ratios of sulfur source and molybdenum source precursor were added to organic solvents such as N, N-dimethylformamide (DMF), 1-methyl-2-pyrrolidinone (NMP) and polyethylene glycol-600 to form a homogeneous solution, and then transferred to an
SC R
autoclave at 180°C (or 200°C) for 24 h. The black product was centrifuged and dried to obtain MoS2 powder. Solvothermal method (Fig. 2b) has the advantages of low energy consumption, less agglomeration, controllable particle shape and so on. Importantly, it was described that the
U
nanostructures MoS2 obtained by one-step low temperature solvent conditions had high surface
N
area (Berntsen et al., 2003). Thus, the shapes and properties of MoS2 can be effectively controlled
M
2.2.5 Chemical vapor deposition
A
by such method (Berntsen et al., 2003; Najmaei et al., 2013; Peng et al., 2002).
Chemical vapor deposition (CVD) has a long history that dates back to several centuries ago.
ED
CVD has been widely used to prepare high-quality atomic thin MoS2. MoS2 is synthesized by sulfurization of MoO3 with the CVD method (Fig. 2c) (Lee et al., 2012; Najmaei et al., 2013).
PT
Large-area MoS2 flakes could be grown on the substrates via CVD methods, including SiO2/Si
A
CC E
(Yang et al., 2016), sapphire (Dumcenco et al., 2015), polyimide (Ahn et al., 2015) and so on.
7
IP T SC R U N A M ED PT CC E
A
Fig. 2. Representative synthesis routes of MoS2: (a) Illustration of electrochemical exfoliation lithiation process. (b) Synthesis of MoS2 nanoparticles by solvothermal method. (c) Schematic diagram for the preparation of MoS2 thin layers with MoO3 sulfurization. Reproduced with permission (Li et al., 2011; Lin et al., 2012; Zeng et al., 2011).
3. Photocatalytic degradation mechanisms Photocatalytic degradation is the process of taking advantage of these highly active free radicals and then degrading all contaminants into small molecules or inorganic substances through
8
the processes of addition reaction, substitution reaction and electron transfer between free radicals and organic pollutants. According to previous studies, holes (h+), superoxide radicals (·O2-) and hydroxyl radicals (·OH) are considered as the main active species in the photocatalytic reaction (Chen et al., 2014a; Huang et al., 2017). In order to better understand the photocatalytic mechanisms of composite photocatalysts and find the most important active substances, several
IP T
scavengers can be used to explore the variation of reactivity during the photocatalytic processes. For example, ammonium oxalate (AO), benzoquinone (BQ) and isopropanol (IPA) can be usually
SC R
employed to scavenge h+, ·O2- and ·OH, respectively. To further investigate the photocatalytic pathways of the degradation process, it is necessary to study the conduction path of photoelectrons at the interface of the composites, since target organic contaminants mainly react
U
with reactive species at the interface. Because the redox reaction path is determined by the
N
oxidation-reduction potential of the material, thus the location of the holes and valence bands is
A
important. The location of the band and the migration path of the photogenerated carriers at the material interface are to be displayed with the scheme map. In Fig. 3d, the valence band (VB) and
M
conduction band (CB) potentials of semiconductors can be obtained from empirical formulas (Li
ED
et al., 2015d; Weng et al., 2015). The optical bandgap energy (Eg) of MoS2 can be estimated by the following formula (Fig. 3e): αhν = A(hν-Eg)n /2 (1)
PT
Where α, h, ν, A and Eg represent the absorption coefficient, Planck constant, light frequency, a constant and bandgap and constant, respectively. Simultaneously, n is a direct transition, whereas
CC E
the indirect transition is n = 4 (Radisavljevic et al., 2011; Wu et al., 2018). In general, the reduction in the number of layers in the pristine MoS2 structure results in a change from the
A
indirect bandgap semiconductor to direct gap semiconductor. 4. MoS2-based composites as photo-degradation catalysts MoS2 nanostructures are superior semiconductors, whose wonderful morphologies can be effectively controlled by a variety of methods (Hu, 2014). Various photocatalysts took advantage of semiconductor properties of MoS2 constructing composite catalysts, and showed favorable photocatalytic performance over organic compounds (as summarized in Table 1). Among them, in 9
this review, the photodegradation efficiency (E%) was calculated using the following equation (Lv et al., 2015; Zhao et al., 2016): E% = (C0-Ct)/C0 × 100% (2) Where C0 is the whole amount of organic pollutants in the solution before illumination; Ct is the concentration of organic pollutants in solution at time t. There are two methods for measuring the residual concentration after degradation of pollutants. One method is to measure the linear
IP T
relationship between the precise concentration of contaminants and the absorbance by a UV-vis spectrophotometer. Another method is to quantify the concentration of contaminants in aqueous
SC R
solutions by high performance liquid chromatography (HPLC). In this review, Ct is measured with the first simple method.
Light source
Contaminants
A
MoS2/GO
A Xe lamp (λ> 420 nm)
M
A mercury lamp 10 mg MoS2/GO
Initial concentration
N
Catalyst
U
Table 1. Summary of photo-catalytic degradation of MoS2-based composites
MB
Reaction time
Degradation efficiency
Reference
50 min
100%
Yuan et al.,
75 min
100%
2017
60 min
99%
50 mL 15 mg/L
80 mg MoS2-RGO
ED
5 W white LED light lamp
(450nm＜λ＜
Li et al.,
MB
80 mL 60 mg/L
2014b
MB
natural sunlight
MB
SOL2/500 S lamp
CC E
6.5 mg MoS2/rGO
PT
558nm)
8.5 mL 12.5 mg/L
96% al., 2016 98%
20 mg ZnO–MoS2–
50 mL 15.9
(intensity
RGO
Cravanzola et 5h
Kumar et 60 min
Carbendazim
mg/L
MO
50 mL 20 mg/L
97%
al., 2016
A
9.0×104 lux)
MoS2/Carbon nitride Peng and 50 mg MoS2/g-C3N4
500 W Xe lamp
5h
About 60% Li, 2014
40 mg MoS2/g-C3N4
300 W Xe lamp
RhB
(λ> 420 nm)
MO
20 min
96%
Li et al.,
180 min
95%
2016b
50 mL 10 mg/L
10
250 W metal 10 mg MoS2/g-C3N4
halide lamp (λ> 420 nm)
MO
2h
92.4%
4h
81.9%
4h
96%
150 min
78%
Lu et al., CIP
10 mL 10 mg/L
2016 TC
MoS2/TiO2
60 mL 10 mg/L
al., 2016a
1.
Catalyst
0.01 g MoS2/TiO2
Light source
Contaminants
50 W
RhB 100 mL 10 mg/L
MO
(λ=313nm) (λ≤420nm)
lamp 250 W infrared
N-TiO2-x@MoS2
(λ≥ 420 nm)
MoS2 with Bi-based materials
PT
300 W Xe lamp (λ＞ 400 nm)
300 W Xe lamp
CC E
0.02 g MoS2/BiOBr
30 mg MoS2/BiOI
(λ＞ 400 nm)
500 W Mercury
MoS2/Bi2O2CO3
lamp
A
50 mg
5 mg Bi2S3-MoS2
MO
ED
300 W Xe lamp
mg/L
M
lamp 50 mg
N
CDs/MoS2@H-TiO2
100mL 10
TC
A
350 W mercury
35 W Xe lamp
Degradation efficiency
97.0%
100 mL 10 mg/L
RhB
50 mL 10 mg/L
50 mL 100
PR
3h
2h
81.60% more than
Liu et al.,
80%
2017a
5h
about 33%
120 min
91.80%
ppm
Di et al., 50 min
about 94% 2014 Li et al.,
100 min
95.20% 2016d
150 min
more than
Wang et
99%
al., 2014 Vattikuti et
60 min
83.4% al., 2016
500 W Xe arc 30 mg 3D MoS2/Bi2S3
lamp (λ＞420
al., 2016d
2017c
mg/L
RhB
Zhang et
Liu et al., 50 mL 10 mg/L
100 mL 10
RhB
Reference
120 min
U
250 W Xe lamp
50 mg
Reaction time
98.2%
high-pressure mercury lamp
Initial concentration
SC R
Table (Continued)
(λ≥ 420 nm)
Wang et phenol
IP T
300 W Xe lamp
0.01 g TiO2/MoS2
Long et al., atrazine
60 mL 5 mg/L
240 min
89% 2016
nm) MoS2 with Ag-based 11
materials RhB A 300 W Xe arc
0.025 g Ag3PO4/MoS2
100 mL 10
MO
lamp (λ≥420 nm)
mg/L
4-CP
30 min
about 100%
30 min
100%
175 min
100%
Degradation efficiency
Wang et al., 2015
Contaminants
Initial concentration
Reaction time
MB
30 mL 20 mg/L
60 min
RhB
30 mL 20 mg/L
MO
30 mL 10 mg/L
phenol
30 mL 5 mg/L
RhB
50 mL 10 mg/L
A 35 W Xe arc lamp (λ≥420 nm)
50 mg Ag3PO4/MoS2
lamp (250 mW/cm2,
lamp
20 mg MoS2/ZnO
M
MoS2 with transition metal oxides mercury vapor
PR
ED
PT
lamp
UV-vis light
CC E
MoS2@CuO
A 18 W daylight
A
50 mg ZrO2/MoS2
MoS2/MoOx
0.2mg/mL Fe3O4@MoS2/Ag3PO4
A 25 W UV lam
A 300W Xe lamp (λ≥420 nm) A 500 W Xe
100 mL 10
MB
mg/L
Zhu et al.,
120 min
about 100%
2016
200 min
95%
16 min
Wan et al., 100% 2017
50 min
93%
Awasthi et al.,
80 min
90%
2016
100 min
92.7%
Tan et al., 2014 Li et al.,
MB
100 min 2015a 100 mL 10
MO
ppm
Prabhakar et 12 min
95.2%
8 mL 0.4 × 10-5
RhB
al.,2016 Zhou et al.,
120 min
97% 2014
mol/L RhB
lamp (λ＞420 nm)
about 100%
30 mL 10 ppm
natural sun light
0.02g MoS2@ZnO
80 min
A
λ≥420 nm)
N
A 300 W Xenon
Reference
98.2
%
SC R
30 mg Ag3PO4/MoS2
Light source
U
Catalyst
IP T
Table 1. (Continued)
98.90%
Guo et al.,
90.74%
2016
10 min CR
All reactions are performed under neutral conditions Methylene blue (MB); methyl orange (MO); rhodamine B (RhB); ciprofloxacin (CIP); tetracycline (TC); phenol red (PR); p-chlorophenol (4-CP); congo red (CR) 12
4.1 MoS2 /graphene oxide Graphene is a well-known 2D material, whose sp2 hybridized carbon atoms are tightly packed into a honeycomb single layer (Shi et al., 2012; Tang et al., 2017a; Wang et al., 2013). Remarkably, graphene has high theoretical surface area (~2600 m2), excellent carrier mobility (2 ×
IP T
105 cm2/V·sec), excellent thermal conductivity (5000 W/m·K), optical transmittance (～97.7%), and high elastic modulus (～1TPa) (Chabot et al., 2014; Xu et al., 2013). Moreover, it has been proved that graphene exhibits absorption enhancement in the visible region because of excellent
SC R
optical and electronic properties (Xiang et al., 2015; Xiong et al., 2015). These unique properties make graphene act as excellent electron acceptor and transporter, and significantly enhance pollutant adsorption. Reduced graphene oxide (rGO) displays the similar properties comparing to On the other hand, MoS2 itself has a low insufficient electronic separation capability
U
graphene.
N
(Li, 2015); however, the incorporation of MoS2 and graphene exhibits a good photocatalytic
A
degradation performance as a catalyst, since MoS2 can be better dispersed on the surface of
M
graphene and make the most of the properties of graphene. Yuan et al. used N, N- dimeth ylformamide (DMF) as solvent to synthesize MoS2/GO composites (Yuan et al., 2017). The
ED
prepared samples were then annealed in order to improve the crystallinity. MoS2 nanoflakes were rich in edges, and the grown MoS2 nanoflakes with three layers occupied the highest proportion
PT
(Fig. 3a-c). MB solution (15 mg/L) was used as the target contaminants to evaluate the photocatalytic performance of as-prepared composite catalysts. Among them, 10 mg sample was
CC E
dispersed in 50 mL of MB solution. The results suggested MB could be completely degraded by MoS2/rGO composites via both UV and visible light illumination, and the catalytic processes took 50 min and 75 min, respectively. In virtue of superior electron transported substrate of graphene
A
and strong solar absorption of MoS2, the synergistic effect between these two materials can efficiently inhibit the recombination of photoelectrons and holes, leading to enhancement of the photodegradation performance. The methods of synthesizing MoS2-rGO hybrids are not only solvothermal one mentioned above, but also other approaches. MoS2-rGO composites could be well prepared by microwave-assisted method (Li et al., 2014b; Pan et al., 2013). Through the microwave-assisted
13
approach, MoS2 scaled sheets were observed stacked on the curled and corrugated GO sheets. It is clear that the curled rGO surface is stably connected to MoS2 and contributes to the separation of photo-generated carriers. MoS2-rGO hybrids prepared by microwave-assisted method achieved the highest MB (the concentration of 60 mg/L) degradation rate of 99 % in 60 min under the visible light. In addition, the sonication method can also be used to prepare rGO/MoS2 hybrids (Cravanzola et al., 2016), which are regarded as complex and heterogeneous morphology. In the
IP T
presence of the catalyst, MB solution (the initial concentration of 12.5 mg/L) residue remained about 4% after 5 h under solar-light irradiation. Comparing to pure rGO and MoS2, the
SC R
photodegradation performance is greatly improved, which is attributed to promoting electron transfer and separation, as well as increasing the light absorption intensity and the adsorption
A
CC E
PT
ED
M
A
N
U
capability of organic pollutants.
14
IP T SC R U N A M ED PT CC E A
Fig. 3. Structure and morphology of MoS2/rGO composite prepared by solvothermal method. (a) TEM image of MoS2/rGO hybrids. (b) The HRTEM image of MoS2/rGO composites. (c) Schematic illustration of the number of layers of MoS2 nanosheets grown on graphene. (d) The scheme map the photocatalytic reduction mechanism of Cr(VI) in the aqueous phase of MoS2-Bi2S3 composites under visible light (λ> 400 nm). (e) The calculated band gaps of Bi2S3 and MoS2. (a-c reproduced with permission(Yuan et al., 2017) d-e reproduced with permission Weng et al., 2015).
15
MoS2-rGO can also be incorporated with other semiconductor materials forming ternary photocatalysts. Kumar et al. synthesized ZnO-MoS2-rGO heterostructures through hydrothermal method (Kumar et al., 2016). The composite of doping 1 wt% ZnO nanoparticles on MoS2-rGO achieved the highest photodegradation performance, and ZnO were observed well dispersed on MoS2-rGO nanosheets. 50 mL of a 15.9 mg/L MB aqueous solution was degraded by 98% within 60 min under the natural sunlight. Besides, the same concentration of carbendazim was also
IP T
degraded by 97% in the same conditions. The reason for its high photocatalytic degradation efficiency is that the synergetic effect is conducive to rapidly transfer electrons across the
SC R
interface, which produces highly reactive ·OH for contaminant degradation.
From the previous literatures, it can be concluded that incorporation of MoS2 with graphene oxide mainly takes advantage of the good conductivity of graphene sheets, and efficiently inhibits
U
the recombination of photo-generated carriers. MoS2/rGO is a promising material in
N
photocatalytic degradation.
A
4.2 MoS2 /graphitic carbon nitride
M
Polymeric graphitic carbon nitride (g-C3N4) is an emerging celebrity photocatalyst recent
ED
years, which has many advantages, such as abundance of source, low cost, non-toxicity and chemical stability (Jo et al., 2016; Liang et al., 2016; Liu et al., 2010; Zhang et al., 2015; Zhang et al., 2016a). The g-C3N4 has unique stable 2D heptazine ring structure with a band gap of ~ 2.7 eV
PT
as well as proper valence band (VB) and conduction band (CB) positions (Liu et al., 2017b; Yang et al., 2011; Zhang et al., 2011; Zhao et al., 2015a), implying it is a promising material for
CC E
harvesting waves of solar light. However, pure g-C3N4 suffers from poor light-absorbance and low separation efficiency of electron-hole pairs (Chen et al., 2014b; Liao et al., 2012). To solve this problem, coupling g-C3N4 nanosheets with a co-photocatalyst is probably one of the most ideal
A
choices. Peng et al. employed few-layer MoS2 as the co-photocatalyst hybridizing novel MoS2/g-C3N4 composite (Peng and Li, 2014). When controlling the proportion of MoS2 as 3.0 wt%, the composite showed the greatest photodegradation performance on MO. 50 mg samples were dispersed 50 mL of 20 mg/L of MO in aqueous solution. The degradation efficiency of MO was about 60% under the simulated solar ligh for 5 h. In the photocatalytic process, MoS2 nanoparticles obviously promoted charge collector and transfer, thus preventing the recombination 16
of photoelectron-hole pairs. Currently, the 2D heteroconjuction of MoS2/g-C3N4 is mainly synthesized by impregnation and calcination method (Tisseraud et al., 2016). The 2D heterostructures with interfacial contact are formed between the MoS2 nanosheets and the g-C3N4 nanosheets. For the MoS2/g-C3N4 composites with 3 wt% of MoS2, whose specific surface area reaches about 85.4m2/g; therefore, it canprovide abundant surface active sites for contaminants photodegradation. Taking RhB and MO as the targets, whose concentration was both 10 mg/L. 40
IP T
mg photocatalyst was added to 50 mL of RhB or MO solution, and RhB could be degraded by 96% after 20 min irradiation with visible light. Furthermore, the concentration of MO could be reduced
SC R
by about 95% within 3 h. The 2D heterostructures promote the charge transfer and improve the separation efficiency of photoelectron-hole pairs, resulting in lifting of the photodegradation efficiency.
U
However, different preparation methods make the same materials exhibit different effects. Lu
N
et al. synthesized the MoS2/g-C3N4 nanostructured materials of type II hetero-structure by
A
ultrasonic and bathing method (Lu et al., 2016). Fig. 4 (a)-(c) show that ultrathin MoS2 nanosheets and g-C3N4 nanosheets are packed together to form heterostructures. To evaluate the
M
photocatalytic activities of MoS2/g-C3N4 hybrids, three different pollutants were degraded. MO
ED
solution was used as simulated organic wastewater, while two pharmaceutical compounds, ciprofloxacin (CIP) and tetracycline hydrochloride (TC) were also used. The 0.05-MoS2/g-C3N4 hybrids (WMoS2: WMoS2/g-C3N4= 0.05) obtained the highest degradation rates. After being irradiated
PT
in the visible light for 2 h, the photodegradation rate reached 92.4% for MO and the kinetic constant was 0.0189 min-1. As shown in Fig. 4 (d), removal of 81.9% CIP and 96% TC was
CC E
achieved after being irradiated for 4 h. Compared with pure g-C3N4, MoS2/g-C3N4 hybrids performed remarkable photodegradation efficiency due to the heterostructures formed between ultrathin MoS2 and g-C3N4 nanosheets. In addition, large transverse sizes and atomic thicknesses
A
imparted the ultrathin MoS2 with a high specific surface area (Mak et al., 2010), which made them construct functional hybrid heterostructures with g-C3N4 and formed more photocatalytic active sites. Thus, the separation rate and the mobility of photogenerated charge are enhanced by the ultrathin MoS2 nanosheets. However, with the gradual increase of MoS2 content, the degradation rate decreased accordingly, which may be attributed to the increase of MoS2 overlapping layer resulting in the reduction of the interfacial formation between g-C3N4 and MoS2. Eventually, the 17
visible light absorption of MoS2/g-C3N4 hybrids and the propagation of photogenerated electron
ED
M
A
N
U
SC R
IP T
holes were reduced.
PT
Fig. 4. (a) SEM images of 0.05-MoS2/g-C3N4 composites. (b)-(c)HRTEM images of 0.05-MoS2/g-C3N4 hybrids. (d) Degradation rates of MoS2/g-C3N4 hybrids in 120 min. Reproduced with permission (Lu et al., 2016).
To sum up, introducing MoS2 to g-C3N4 can form heterostructures on the interface, which
CC E
promotes the separation and transfer of photogenerated electron–hole pairs. The easy-to-prepared, stable and inexpensive photocatalyst has a broad prospect in photodegradation of pollutants. 4.3 MoS2 /TiO2
A
Owing to the abundant reserves, low cost, non-toxic, chemical stability and other advantages
of titanium dioxide (TiO2), it is one of the most well-known semiconductor photocatalytic functional materials (Dong et al., 2015; Hao et al., 2016; Yuan et al., 2016; Zhao et al., 2015b). Nevertheless, TiO2 has a wide band and can only absorb UV light (Zhong and Li, 2012). In order to increase the range of TiO2 absorption spectra, coupling TiO2 with narrow band gap co-photocatalysts is one of the best methods. Layered MoS2 can be deposited on different shapes 18
of TiO2, thereby increasing the spectral absorption range of TiO2 and the ability of photocatalytic degradation of environmental pollutants. Very recently, one dimensional (1D) semiconductor nanostructures TiO2 nanofibers (NFs) were prepared by the electro-spinning technique (Zhang et al., 2013), and then the NFs were intertwined to form a 3D network structure. With MoS2 wrapped on the surface of TiO2 NFs through a simple hydrothermal method (Fig. 5a), 3D MoS2 nanosheet/TiO2 nanofiber (MoS2/TiO2) heterostructures were synthetized (Zhang et al., 2016d).
IP T
The photocatalytic performance of the prepared samples was evaluated at room temperature by photocatalysis of organic dyes RhB and MO solution (10 mg/L). The photocatalytic degradation
SC R
ratio of RhB for MoS2/TiO2-2 (Mo/Ti molar ratio with 0.412) is 98.2%, while that of MO is 97.0% in the UV light irradiation (Fig. 5b). Significantly, 3D MoS2/TiO2 heterostructures exhibited fine stability and recyclability. One reason is that MoS2 not only improves the separation of
U
photo-generated electron-hole pairs, but also provides a greater number of photo-degradation sites.
N
The other reason is the synergistic effect of heterogeneous structures formed between the two
A
substances. Based on the results of UV-Vis absorption spectroscopy, the photocatalytic degradation activities of pure MoS2 and MoS2/TiO2-2 were both studied with the visible light.
M
Surprisingly, MO was not significantly degraded under visible light irradiation. This result
ED
precluded the possibility of photoactivating TiO2 with MoS2. In this experiment, the main role of MoS2 nanosheets was to collect electrons and suppress the recombination of photo-generated electron-hole pairs. In other similar literature, this phenomenon has also been mentioned (Jia et al.,
PT
2014).It is reported that hollow TiO2 spheres have excellent photocatalytic activity because the surface area is relatively larger compared to nanofibers (Qi et al., 2014). Wang et al. used
CC E
hydrothermal method to make MoS2 nanosheets tightly coating on TiO2 hollow spheres (Fig. 5c) (Wang et al., 2016a). The hollow structure possesses a high porosity, which can increase the reaction sites under the simulation from photo-irradiation. Compared to pure TiO2 or MoS2,
A
TiO2/MoS2 heterostructures can significantly enhance the photometric responsiveness to phenol (10 mg/L), which could be decomposed 78% with the heterojunctions after 150 min of visible light irradiation comparing with no photocatalytic effect for TiO2 and 20% removal for MoS2 (see Fig. 5d). The best sample exhibits higher photocurrent densities than pure MoS2 and TiO2, indicating that the heterostructures are more favorable for charge migration and collection.
19
IP T SC R U
M
A
N
Fig. 5. (a) MoS2 nanosheets/TiO2 NFs in low and high (illustrations) magnification. (b) SEM image of multi layers MoS2 coated TiO2 hollow. (c) Degradation curves of RhB and MO by different weight ratios of MoS2 nanosheets/TiO2 NFs. (d) Photodegradation of phenol with MoS2 coated TiO2 heterostructures. (a and b reproduced with permission from Ref.(Zhang et al., 2016d); c and d reproduced with permission from Ref.(Wang et al., 2016a)).
ED
In order to further enhance the photocatalytic reaction of TiO2, a variety of TiO2 modification techniques have been used to constructed photocatalysts (Low et al., 2017; Nasirian
PT
and Mehrvar, 2016). It is a very sensible strategy to dopant impurity elements into the TiO2, which can expand the absorption range of TiO2 to visible light (Akple et al., 2016; Qian et al., 2014). The
CC E
modified TiO2 coupled with the co-catalyst will significantly enhance the photocatalytic degradation performance. For instance, the TiO2 nanobelts were heated to 600℃ under a hydrogen atmosphere for 5 h to obtain the H-TiO2, and then carbon dots (CDs)/MoS2@H-TiO2
A
heterostructures were prepared by a simple hydrothermal process (Liu et al., 2017a). MoS2 nanosheets carrying CDs grew evenly on 3D network-like TiO2 nanobelts (Fig. 6a-b). The photodegradation experiments were evaluated in the process of tetracycline (TC) solution (10 mg/L) under UV, visible light and near-infrared (NIR) light irradiation. The sample with 5.0 wt% (WMoS2: WCDs= 4:1) content of CDs/MoS2 composite displayed the highest photocatalytic degradation activity. The TC solution was degraded by 81.6% for 3 h under visible light, and more 20
than 80% within 2 h UV irradiation (Fig. 6c). Compared to visible and UV light, the degradation rate of TC could also reach about 33% in the NIR light irradiation for 5 h. This composite displayed extremely high photocatalytic activities mainly due to the following three aspects. Firstly, the synergistic effect delays recombination of target electron-hole pairs; then, CDs/MoS2 thin sheets provide more active reaction sites; Finally, MoS2 play an indispensable role in the interface of electronic conduction. Similarly, nitrogen doping TiO2 (N-TiO2) nanospheres was
IP T
prepared by hydrothermal method using urea as nitrogen source, and N-TiO2-x@MoS2 were synthetized through the same way by Liu et al. (Liu et al., 2017d) N-TiO2-x nanospheres could be
SC R
seen being completely coated by the MoS2 nanoflowers (Fig. 6d-e). Such hybrid structures can effectively enhance the visible light response. The photocatalytic performance for MO solutions was carried out under visible light irradiation. Compared with pure TiO2, the N-TiO2-x@MoS2
U
executed the best photocatalytic effect, which could remove 91.8% of 10 mg/L MO solution
N
within 2 h under visible light irradiation (Fig. 6f). In this case, the hybrids were introduced Ti3+
A
and oxygen vacancy, resulting in lifting utilization of light energy. The electrons could be more efficiently separated due to the introduction of MoS2. Consequently, the possible photocatalytic
M
mechanisms of N-TiO2-x@MoS2 were proposed as illustrated in Fig. 6g.
ED
All in all, MoS2 incorporating with TiO2 can narrow the band gap of the latter, which can enhance the absorption capacity of the catalysts and promote the separation and transfer
A
CC E
PT
photogenerated electrons.
21
IP T SC R U N A M ED PT CC E
A
Fig. 6. (a) SEM image of CDs/MoS2@H-TiO2 nanocomposite (5 wt% of CDs/MoS2). (b) HRTEM image of the CDs/MoS2@H-TiO2 (5 wt% of CDs/MoS2). (c) Photo-degradation rate of TC of the photocatalysts with different weights of CDs/MoS2. (d) SEM image of N- TiO2−x @MoS2 hybrids. (e) TEM image of N-TiO2−x@MoS2 composites. (f) Photodegradation of MO with different photocatalysts. (g) Schematic of the MO photodegradation and the possible charge transfer mechanism for the N-TiO2−x@MoS2 samples. (a - c reproduced with permission from Ref.(Liu et al., 2017a); d - g reproduced with permission from Ref.(Liu et al., 2017d) ).
4.4 MoS2 with Bi-based materials Bismuth-based photocatalysts have received great attention because of its excellent optical properties (Chen et al., 2016; Cuellar et al., 2015; Li et al., 2016a; Zou et al., 2017). For example, 22
bismuth oxybromide (BiOBr) has been attracted interests because of its superior photocatalytic performance (Xiong et al., 2016; Yi-Zhu et al., 2016). In order to further enhance the photocatalytic performance of BiOBr, Di et al. synthesized sphere-like MoS2/BiOBr composites by solvothermal method (Di et al., 2014). MoS2 nanosheets were in close contact with BiOBr, which formed nanostructured heterojunctions (Fig. 7a-b), and then the prepared composite (0.02 g) was used to treat with RhB (10 mg/L) under the visible light irradiation. Surprisingly,
IP T
incorporation of MoS2 could significantly increase the degradation effect of BiOBr on RhB, and the 3 wt% MoS2/BiOBr (weight ratio with MoS2 of 3%) composite showed the highest
SC R
photocatalytic activity. In Fig. 7c, approximately 94% of the RhB was removed under 50 min of light irradiation. As can be seen from Fig. 7d, the rate constant of 3 wt% MoS2/BiOBr is greater than others. The porous structures on the surface of MoS2/BiOBr composites provided more
U
active sites for RhB degradation. BiOBr microspheres coated with several layers of MoS2
N
nanosheets act as an irreplaceable role in photocatalysis. The rapid separation and transport of
A
photo-induced charges was attributed to the synergistic effect of the heterogeneous structure between the thin layers of MoS2 nanosheets and BiOBr semiconductors.
M
Compared with BiOBr, BiOI has a narrower band gap (1.7～1.9eV), which has a higher
ED
visible light response (Jiang et al., 2017; Mousavi and Habibi-Yangjeh, 2016; Xiang et al., 2016). Nevertheless, BiOI suffers from the problem of slow separation of photoelectrons. For the sake of solving this flaw, modifying BiOI and coupling it with other excellent semiconductors are
PT
common methods. In consideration of superiority of thin layer MoS2, Li et al. coupled BiOI with thin layer MoS2 nanosheets to increase the visible light response of the photocatalysts (Li et al.,
CC E
2016c). After being illuminated 100 min, MoS2/BiOI material contaning 0.5 wt% MoS2 showed excellent photodegradation efficiency, resulting in the concentration of RhB being reduced about 95.2%. RhB (100 mL, 10 mg/L) can be degraded under visible light mainly due to the main active
A
material holes. Besides, the heterogeneous structures accelerated the separation of electron-hole pairs, which also enhanced the photocatalytic activity.
23
IP T SC R U N A
ED
M
Fig. 7. (a) SEM image of the 3 wt% MoS2/BiOBr spherical structure. (b) TEM image of 3 wt% MoS2/BiOBr. (c) Photodegradation of RhB with pure BiOBr and different weight ratios of MoS2/BiOBr. (d) The kinetic plots of photocatalytic degradation of RhB under visible light irradiation. Reproduced with permission(Di et al., 2014).
Except Bi-based materials mentioned above, bismuth subcarbonate (Bi2O2CO3) is also one of
PT
the important member in Bi-based nanostructured material family (Ni et al., 2016). It has a unique photocatalytic performance in the UV light owing to its matched band gap (3.1eV～3.5eV)
CC E
(Huang et al., 2016; Li et al., 2016b; Shan et al., 2016; Wang et al., 2016d). However, UV light only occupies about 4% photon energy from the solar spectrum. In order to make better utilization of solar energy, it is feasible to modify Bi2O2CO3 to prepare novel composite photocatalysts.
A
Wang et al. used ordinary hydrothermal synthesis to prepare MoS2/Bi2O2CO3 composites (Wang et al., 2014). When 0.5 wt% by weight of MoS2 was deposited on Bi2O2CO3, the composite exhibited the best photocatalytic performance, more than 99% of RhB (50mL, 10 mg/L) could be removed within 150 min under the UV light. The synergistic effect between MoS2 and Bi2O2CO3 promoted charge transfer process, and allowed more active charges involved in the oxidation reaction, which enhanced the photocatalytic performance.
24
In addition, Bi2S3 nanorods were embedded in MoS2 nanosheets to carry out a synergistic effect in photodegradation (Li et al., 2017; Weng et al., 2015). The Bi2S3-MoS2 nanocomposites were prepared through hydrothermal method, and whose photocatalytic activities were estimated by treating with phenol red (PR) in solutions (Vattikuti and Byon, 2016). When the weight ratio of Bi2S3 to MoS2 was set as 4:1, the composite showed excellent photocatalytic degradation efficiency under visible light irradiation. After being illuminated for 60 min, the PR could be
IP T
eliminated by 83.4%. The effective electron-hole pair separation and rapid interfacial charge transfer process promote photodegradation. The reason was that the addition of MoS2 enhanced
SC R
the surface area and active sites of composites, which provided more sites for photo-induced electrons and holes to participate in the redox reaction, resulting in higher photocatalytic activity. In order to further enlarge the specific surface area of MoS2/Bi2S3 to obtain much better catalytic
U
properties, Long et al. used one-pot hydrothermal method to prepare 3D MoS2/Bi2S3 (Long et al.,
N
2016). As illustrated in Fig. 8a-b, MoS2 was grown on a 3D Bi2S3 micro-nanometer flowers. In
A
Fig. 8c, the RhB solution (20 mL, 5 mg/L) could be effectively adsorbed and degraded by the composite photocatalysts under visible light irradiation. Besides, 3D MoS2/Bi2S3 was able to deal
M
with actual contaminants named atrazine. 30 mg of the composite photocatalyst was added to 60
ED
mL of a 5 mg/L atrazine solution. In the presence of visible light, the 3D MoS2/Bi2S3 hybrids showed the highest catalytic activity comparing to other reference materials, and 89% of atrazine could be removed within 240 min (Fig. 8d). 3D flower-like MoS2/Bi2S3 heterostructure
PT
accelerated photo-generated electrons separation and transfer, and adequate electrons could react with oxygen molecules at the interface of the composites to produce •O2-, which could strengthen
A
CC E
the degradation of RhB and atrazine.
25
IP T SC R U N A M
ED
Fig. 8. SEM images (a, b) of 3D MoS2/Bi2S3; Photocatalytic degradation efficiency of different photocatalysts for RhB and atrazine (c, d). Reproduced with permission (Long et al., 2016).
In conclusion, introduction of MoS2 into Bi-based material to form heterogeneous structure
PT
could enhance the surface area and active sites of the original Bi-based catalysts. More importantly, the incorporation of MoS2 can effectively inhibit the rapid recombination of
CC E
photoelectrons and holes pairs, as well as prolong the lifetime of carriers. The hybridization of MoS2 with Bi-based materials may be a hopeful candidate to be applied for photo-degradation of
A
harmful organic pollutants. 4.5 MoS2 with Ag-based materials Various semiconductors consist of silver (Ag) have been proved one of the most promising photocatalysts due to their superior utilization efficiencies of visible light and photocatalytic activities (Long and Cai, 2014; Martin et al., 2015). Among the Ag-based materials, silver orthophosphate (Ag3PO4) has been of great concern owing to its excellent photocatalytic 26
performance (Chen et al., 2015; Ma et al., 2016; Yang et al., 2015). However, Ag3PO4 suffers from photo-corrosion in a long time under light irradiation (Wang et al., 2012a). Therefore, it is very essential to couple Ag3PO4 with other co-photocatalysts or conductive materials. Researchers take consideration of MoS2 as a perfect co-catalyst due to its unique stability. Wang et al. prepared hierarchical Ag3PO4/MoS2 composites by a simple template free in situ precipitation method (Wang et al., 2015). Ag3PO4 nanoparticles were uniformly dispersed on the MoS2 nanosheets
IP T
surface (Fig. 9a), and the two components were in close contact with each other at the interface (Fig. 9b). The optimal photocatalytic performance over Ag3PO4/MoS2 composites on
SC R
p-chlorophenol (4-CP), MO and RhB were illustrated in Fig. 9c-e, respectively. The initial concentrations of the three target contaminants were 10 mg/L. The Ag3PO4/MoS2-15 wt% (containing 15 wt% by weight of MoS2) heterojunction composite showed the highest
U
photocatalytic activity under visible-light irradiation, about 100% of the RhB was degraded in 30
N
min, whose rate constant was about 4.8 times comparing with that of pure Ag3PO4. Besides, MO
A
in solution was completely degraded over the Ag3PO4/MoS2-15 wt% composite within 30 min, and 75% of the 4-CP in solution could be degraded in 175 min. The preferable results revealed
ED
under visible light irradiation.
M
that the synergistic effect between MoS2 and Ag3PO4 improved the photodegradation activity
Meanwhile, construction of Z-scheme Ag3PO4/MoS2 heterojunction could exhibit superior photodegradation activity and stability (Zhu et al., 2016). The Ag3PO4/MoS2 with 0.648 wt%
PT
MoS2 exhibited the best photocatalytic performance. It has excellent photocatalytic degradation properties for MB (20 mg/L), RhB (20 mg/L), MO (10mg/L) and phenol (5 mg/L), all of which
CC E
are nearly completely degraded. This composite material was more easily excited by visible light to produce photoelectrons, and the photoinduced electrons could be easily from VB transferred to the CB. The lifetime of the photogenerated electron-hole pairs was improved, thereby improving
A
the photocatalytic capacity. Therefore, the degradation of organic dyes can proceed smoothly. Selecting photocatalytic degradation of MB as a representative, the process can be described as follows: Ag3PO4 + hv → Ag3PO4 (h+ + e-) (3) Ag+ + e- → Ag0 (4) MoS2 + hv → MoS2 (h+ + e-) (5) 27
0 Ag3PO4 (h+ + e-) + MoS2 (h+ + e-) Ag Ag3PO4 (h+) + MoS2 (e-) (6) →
MoS2 (e-) + O2 → MoS2 + •O2- (7) •O2- + MB → Oxideproducts (8) Ag3PO4 (h+) + MB → Ag3PO4 + Oxideproducts (9) Therefore, the intermediate product is an oxidized small molecule organic. Besides,
IP T
Small-molecule organics will continue to be oxidized and eventually become CO2 and H2O. According to the Z-scheme charge carrier transfer process, the photo-carriers oxidation/reduction capacity should be enhanced and the lifetime of photo-generated holes from Ag3PO4 and
SC R
photo-generated electrons from MoS2 could be increased, thereby enhancing the catalytic ability
A
CC E
PT
ED
M
A
N
U
(Li et al., 2015c).
28
IP T SC R U N A M ED PT CC E A
Fig. 9. TEM image (a) and HRTEM image (b) of hierarchical Ag3PO4/MoS2 nanocomposites. Photocatalytic degradation of (c) 4-CP, (d) MO and (e) RhB by different samples. Reproduced with permission(Wang et al., 2015).
To further enhance the photocatalytic performance and stability of Ag3PO4 nanomaterials, Wan et al. used various of methods, including hydrothermal method, ultrasonic exfoliation method,
29
in-situ growth method, to synthesis the Ag3PO4 nanoparticle@MoS2 quantum dots/ few-layered MoS2 nanosheets (ANP@MQD/FL-MNS) heterostructure (Wan et al., 2017). A proper amount of bulk MoS2 was dispersed in N-methyl-2-pyrrolidone (NMP), followed by ultrasonic exfoliation for 10 h to obtain a suspension. After that, the Ag3PO4 nanoparticles were mixed with the prepared MoS2 solution to obtain ANP@MQD/FL-MNS photocatalyst (Fig. 10a). As shown in Fig. 10d, Ag3PO4 nanoparticles were tightly coated with several irregular layers of MoS2 nanosheets to
IP T
construct core@shell heterostructures. The degradation of the RhB solution (10mg/L) was evaluated as the photocatalytic activity of the composite photocatalyst. After 16 min of visible
RhB
solution
(Fig.
10e).
It
was
found
the
RhB
SC R
light exposure, the ANP@MQD/FL-MNS nanocomposites showed high photodegradability to was
completely degraded
by
ANP@MQD/FL-MNS-6 composite (6 mL volume of MoS2 suspension) within 16 min. Compared
U
with other samples, the ANP@MQD/FL-MNS-6 showed the highest photocatalytic performance
N
due to the introduction of few-layer MoS2 nanosheets improving band match. Additionally, MoS2
A
quantum dots were used as electron host to improve the transfer of photogenerated electrons from Ag3PO4 nanoparticles because of the excellent electron transport capacity of MoS2 quantum dots.
A
CC E
PT
ED
photocatalytic degradation activity.
M
In light of this, photogenerated electrons could be effectively separated at the interface to promote
30
IP T SC R U N A M ED PT
CC E
Fig. 10. (a) Schematic of the synthesis of ANP@MQD/FL-MNS nano-heterogeneous structural composites. TEM images of (b) MQD/FL-MNS; (c) Ag3PO4 nanoparticles; (d) ANP@MQD/FL-MNS nanocomposites. (e) Photocatalytic degradation efficiency of different photocatalysts for RhB. Reproduced with permission (Wan et al., 2017).
A
4.6 MoS2 with transition metal oxides After the photocatalytic property of first-generation metal oxide photocatayst, TiO2 has been
proved, distinct transition metal oxide semiconductors with fine catalytic performance have been continuously exploited in the photocatalytic degradation on pollutants (Lee et al., 2016; Samu et al., 2017; Wang et al., 2016c; Wu et al., 2015). It is well known that zinc oxide (ZnO) is the most successful n-type semiconductor material 31
(Awasthi et al., 2016; Muruganandham et al., 2015; Sudha and Sivakumar, 2015), with a wide band gap of 3.37eV (Kołodziejczak-Radzimska and Jesionowski, 2014; Zalfani et al., 2016), leading to its very narrow absorption in the visible region of the solar spectrum. The photocatalytic performance of ZnO can be enhanced by combining with other narrow band gap semiconductors or plasma (Zheng et al., 2017). Based on such consideration, MoS2@ZnO nano-heterojunctions were synthesized via low-temperature hydrothermal method by Tan et al.
IP T
(Tan et al., 2014) The prepared photocatalysts were dispersed in 100 ml of MB aqueous solution (20 mg/L). An 18W daylight lamp was used as a solar analog light source. After irradiation
SC R
duration for 100 min, the C/C0 of MB was quickly dropped to 7.3% over the MoS2@ZnO heterojunctions. Besides, ZnO with different morphological structures could be also co-existed with MoS2, and ZnO nano-flowers were closely attached to the surface of MoS2 sheets (Awasthi et
U
al., 2016). The research of Awasthi et al. demostrated MoS2/ZnO composites showed a high
N
photocatalytic activity on phenol red solution. Under UV irradiation, approximately 93% of the
A
phenol red was degraded within 50 min. Meanwhile, 90% of phenol red could be removed within 80 min under the illumination of natural sun-light.
M
Cupric oxide (CuO) is also a good choice as a photocatalyst because of its excellent
ED
photochemical properties (Arai et al., 2008; Liu et al., 2013). Such indirect band gap p-type semiconductor has been widely applied in the field of photocatalysis (Jiang et al., 2009; Yu et al., 2015). When hybridizing to n-type MoS2, p-n heterojunction would form a role in promoting the
PT
use of optical energy. MoS2@CuO hetero-nanoflowers were obtained by hydrothermal method (Li et al., 2015a). The photo-degradability of MoS2@CuO samples were evaluated by MB solution
CC E
under UV-vis light. After irradiation for 100 min, the residual MB in solution remained 4.3% over MoS2@CuO hetero-nanoflowers. The photoelectrons and holes could be effectively separated at the interface of the MoS2@CuO nano-composites, thus the photocatalytic activity was enhanced.
A
Zirconium dioxide (ZrO2) is an emerging photocatalyst with a relatively wide band gap
(3.6～5.5eV) and negative conduction band potential (Hao et al., 2017; Sreethawong et al., 2013). From the inherent characteristics of ZrO2, the biggest drawback is that it only response to 4% of the solar energy, which is regarded as the biggest obstacle to its practical application. In order to improve its optical response, several approaches such as composite formation, semiconductor doping and metal ion deposition have been reported (Renuka et al., 2017; Sun et al., 2017). Taking 32
into account MoS2 as a unique co-catalyst, ZrO2/MoS2 hybrids are prepared by Chan et al. (Prabhakar Vattikuti et al., 2016), whose photocatalytic properties were tested by degradation of MO in solutions (100 mL, 10 ppm). The as-prepared sample with 20 wt% content of MoS2 exhibited the highest photodegradation efficiency under UV light, and degradation of 95.2% MO could be achieved. The combination effect of heterostructure, high specific surface area, plenty of surface active sites and high porosity of MoS2 make it play an irreplaceable role in MoS2/ZrO2
IP T
hybrid photocatalyst, which is vital for the transfer and separation of photoelectrons at the interface.
SC R
Molybdenum oxides (MoOx) can be also combined with MoS2 for environmental and energy issues (Cummins et al., 2015; Hu et al., 2015; Truong et al., 2017). Zhou et al. prepared vertically aligned MoS2/MoOx heterostructures by vapor deposition (Zhou et al., 2014). The photocatalytic
U
performance test was carried out by degradating 8 mL of 0.4×10-5 mol/L RhB aqueous solution.
N
The highest degradation rate of RhB could reach 97% after 120 min of visible light irradiation. In
A
order to study the practical value of the best sample in wastewater treatment, at different pH values (from 2 to 7), the degradation efficiency of RhB over MoS2/MoOx remained above 70%.
M
The integration with few-layered MoS2 can significantly increase the photocatalytic activity of
ED
MoOx, and the composite nanostructures play a synergistic role in collecting photogenerated carriers, resulting in promotion of photodegradation efficiency. Otherwise, the photocatalysts of MoS2 coupling with transition metal oxides and other
PT
components forming ternary composites were also well studied. For example, ternary mixed nanomaterials Fe3O4@MoS2/Ag3PO4 enhanced photocatalytic performance for organic dyes under
CC E
visible light irradiation comparing to the individual material (Guo et al., 2016). It can be seen from Fig. 11a-b that Ag3PO4 nanoparticles were uniformly deposited on the core-shell structure of Fe3O4@MoS2. RhB (20 mg/L) and congo red (CR, the concentration of 30 mg/L) as typical
A
organic contaminants were degraded by Fe3O4@MoS2/Ag3PO4 under visible light irradiation, whose degradation rate was up to 98.90% and 90.74% respectively after 10 min irradiation (Fig. 11c-d).
Novel
hierarchical
Fe3O4@MoS2/Ag3PO4
composites
exhibited
a
superior
photodegradation activity due to the Z-scheme mechanism between MoS2 and Ag3PO4, which reduced the recombination rate of photogenerated electrons. Remarkably, Fe3+ and Fe2+ of Fe3O4 played the role of photoelectron traps; and moreover, MoS2 nanosheets provided a large specific 33
M
A
N
U
SC R
IP T
surface area for Ag3PO4 deposition, resulting in a greater number of photocatalytic reactive sites.
PT
ED
Fig. 11. (a) TEM image of Fe3O4@MoS2/Ag3PO4-6%. (b) High-magnification TEM image of Fe3O4@MoS2/Ag3PO4-6%. Photocatalytic efficiency of different photocatalysts for (c) CR and (d) RhB. Reproduced with permission (Guo et al., 2016).
In conclusion, the incorporation of transition metal oxide nanoparticles into MoS2 can
CC E
promote photodegradation, being attributed to the reduced recombination rate of photogenerated electrons and holes. In addition, the MoS2 nanosheets provide a high specific surface area, which allows more metals to be deposited on the lamellar structure and contributes to the formation of
A
special structures. 5. Outlooks
As a unique representative of layered materials, MoS2 has been widely explored as co-catalyst for photodegradation contaminants. It can be compounded with a variety of materials, such as graphene, carbon nitride and TiO2, which is aimed to enhance photocatalytic degradation
34
efficiency. However, there are still many problems with the degradation of actual pollutants in MoS2-based composites. For example, the degradation mechanism of MoS2-based composites is not very clear and the practical application of materials is limited. It is due to the fact that the photocatalytic degradation technology has the disadvantages of low utilization of light energy, limited practical application, and low recovery rate. It is extremely urgent to develop efficient and inexpensive MoS2 composite photocatalysts for the practical pollutants of photodegradation.
IP T
It is highly important to use a reasonable way to control the number of MoS2 layers in order to obtain a matching band for charge separation. Meanwhile, modification of MoS2 is another
SC R
practical method in order to obtain more excellent photodegradation catalyst. Overall, in this review, we have outlined the recent progress in the construction of co-catalyst MoS2 nanomaterials for the photocatalytic degradation of organic pollutants. It will speed up the
U
exploration of novel, non-toxic, light-stable, scalable and inexpensive co-catalyst MoS2
N
nanomaterials for photocatalytic degradation of organic pollutants. In the near future, MoS2
A
nanocomposites will be the most promising photocatalyst in the field of photodegradation of
M
organic pollutants. Acknowledgement
ED
The authors of this work gratefully appreciate the financial support provided by National Natural Science Foundation of China (No. 41573096), Program for Changjiang Scholars and
CC E
References
PT
Innovative Research Team in University (No. IRT13078).
A
Ahn, C., Lee, J., Kim, H.U., Bark, H., Jeon, M., Ryu, G.H., Lee, Z., Yeom, G.Y., Kim, K., Jung, J., Kim, Y., Lee, C., Kim, T., 2015. Low-Temperature Synthesis of Large-Scale Molybdenum Disulfide Thin Films Directly on a Plastic Substrate Using Plasma-Enhanced Chemical Vapor Deposition. Adv Mater 27, 5223-5229. Akple, M.S., Low, J., Liu, S., Cheng, B., Yu, J., Ho, W., 2016. Fabrication and enhanced CO2 reduction performance of N-self-doped TiO2 microsheet photocatalyst by bi-cocatalyst modification. Journal of CO2 Utilization 16, 442-449. Arai, T., Yanagida, M., Konishi, Y., Iwasaki, Y., Sugihara, H., Sayama, K., 2008. Promotion effect of CuO co-catalyst on WO3-catalyzed photodegradation of organic substances. Catalysis Communications 9, 1254-1258. Awasthi, G.P., Adhikari, S.P., Ko, S., Kim, H.J., Park, C.H., Kim, C.S., 2016. Facile synthesis of ZnO flowers modified graphene like MoS2 sheets for enhanced visible-light-driven photocatalytic activity and antibacterial properties. Journal of Alloys and Compounds 682, 208-215.
35
A
CC E
PT
ED
M
A
N
U
SC R
IP T
Bai, S., Wang, L., Chen, X., Du, J., Xiong, Y., 2014. Chemically exfoliated metallic MoS2 nanosheets: A promising supporting co-catalyst for enhancing the photocatalytic performance of TiO2 nanocrystals. Nano Research 8, 175-183. Berntsen, N., Gutjahr, T., Loeffler, L., Seshadri, R., 2003. A Solvothermal Route to High-Surface-Area Nanostructured MoS2. Chem. Mater 15, 4498-4502. Cabán-Acevedo, M., Stone, M.L., Schmidt, J.R., Thomas, J.G., Ding, Q., Chang, H.-C., Jin, S., 2015. Ecient hydrogen evolution catalysis usingternary pyrite-type cobalt phosphosulphide. nature materials 14, 1245-1251. Chabot, V., Higgins, D., Yu, A., Xiao, X., Chen, Z., Zhang, J., 2014. A review of graphene and graphene oxide sponge: material synthesis and applications to energy and the environment. Energy & Environmental Science 7, 1564. Chang, K., Chen, W., 2011. In situ synthesis of MoS2/graphene nanosheet composites with extraordinarily high electrochemical performance for lithium ion batteries. Chem Commun (Camb) 47, 4252-4254. Chang, K., Hai, X., Pang, H., Zhang, H., Shi, L., Liu, G., Liu, H., Zhao, G., Li, M., Ye, J., 2016. Targeted Synthesis of 2H- and 1T-Phase MoS2 Monolayers for Catalytic Hydrogen Evolution. Adv Mater 28, 10033-10041. Chen, L., He, J., Liu, Y., Chen, P., Au, C.-T., Yin, S.-F., 2016. Recent advances in bismuth-containing photocatalysts with heterojunctions. Chinese Journal of Catalysis 37, 780-791. Chen, L., Shi, G., Shen, J., Peng, B., Zhang, B., Wang, Y., Bian, F., Wang, J., Li, D., Qian, Z., Xu, G., Liu, G., Zeng, J., Zhang, L., Yang, Y., Zhou, G., Wu, M., Jin, W., Li, J., Fang, H., 2017. Ion sieving in graphene oxide membranes via cationic control of interlayer spacing. Nature 550, 380. Chen, S., Hu, Y., Meng, S., Fu, X., 2014a. Study on the separation mechanisms of photogenerated electrons and holes for composite photocatalysts g-C3N4-WO3. Applied Catalysis B: Environmental 150-151, 564-573. Chen, X., Dai, Y., Wang, X., 2015. Methods and mechanism for improvement of photocatalytic activity and stability of Ag3PO4: A review. Journal of Alloys and Compounds 649, 910-932. Chen, X., Mao, S.S., 2007. Titanium Dioxide Nanomaterials Synthesis, Properties, Modifications, and Applications. Chemical Reviews 107, 2891-2959. Chen, Z.H., Sun, P., Fan, B., Zhang, Z.G., Fang, X.M., 2014b. In Situ Template-Free Ion-Exchange Process to Prepare Visible-Light-Active g-C3N4/NiS Hybrid Photocatalysts with Enhanced Hydrogen Evolution Activity. J Phys Chem C 118, 7801-7807. Cheng, X.L., Jiang, J.S., Jin, C.Y., Lin, C.C., Zeng, Y., Zhang, Q.H., 2014. Cauliflower-like α-Fe 2 O 3 microstructures: Toluene–water interface-assisted synthesis, characterization, and applications in wastewater treatment and visible-light photocatalysis. Chemical Engineering Journal 236, 139-148. Chhowalla, M., Shin, H.S., Eda, G., Li, L.J., Loh, K.P., Zhang, H., 2013. The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets. Nat Chem 5, 263-275. Chung, D.Y., Park, S.K., Chung, Y.H., Yu, S.H., Lim, D.H., Jung, N., Ham, H.C., Park, H.Y., Piao, Y., Yoo, S.J., Sung, Y.E., 2014. Edge-exposed MoS2 nano-assembled structures as efficient electrocatalysts for hydrogen evolution reaction. Nanoscale 6, 2131-2136. Coleman, J.N., Lotya, M., O’Neill, A., Bergin, S.D., Nicolosi, V., 2011. Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials. Science 331, 568-571. Cravanzola, S., Cesano, F., Magnacca, G., Zecchina, A., Scarano, D., 2016. Designing rGO/MoS2 hybrid nanostructures for photocatalytic applications. RSC Adv. 6, 59001-59008. Cuellar, E.L., Martínez-de la Cruz, A., Torres, N.C., Cortez, J.O., 2015. Deposition of BiOBr thin films by thermal evaporation and evaluation of its photocatalytic activity. Catalysis Today 252, 2-6.
36
A
CC E
PT
ED
M
A
N
U
SC R
IP T
Cummins, D.R., Martinez, U., Kappera, R., Voiry, D., Martinez-Garcia, A., Jasinski, J., Kelly, D., Chhowalla, M., Mohite, A.D., Sunkara, M.K., Gupta, G., 2015. Catalytic Activity in Lithium-Treated Core–Shell MoOx/MoS2Nanowires. The Journal of Physical Chemistry C 119, 22908-22914. Di, J., Xia, J., Ge, Y., Xu, L., Xu, H., Chen, J., He, M., Li, H., 2014. Facile fabrication and enhanced visible light photocatalytic activity of few-layer MoS2 coupled BiOBr microspheres. Dalton Trans 43, 15429-15438. Dong, H., Zeng, G., Tang, L., Fan, C., Zhang, C., He, X., He, Y., 2015. An overview on limitations of TiO2-based particles for photocatalytic degradation of organic pollutants and the corresponding countermeasures. Water Res 79, 128-146. Dumcenco, D., Ovchinnikov, D., Marinov, K., Lazi, P., Gillet, P., Kis, A., 2015. Large-Area Epitaxial Mono layer MoS2. ACS NANO 9, 4611-4620. Eda, G., Yamaguchi, H., Voiry, D., Fujita, T., Chen, M., Chhowalla, M., 2011. Photoluminescence from chemically exfoliated MoS2. Nano letters 11, 5111-5116. Frindt, R.F., 1966. Single Crystals of MoS2 Several Molecular Layers Thick. Journal of Applied Physics 37, 1928-1929. Fujishima, A., Honda, K., 1972. Electrochemical photolysis of water at a semiconductor electrode. Nature 238, 37-38. Guardia, L., Paredes, J.I., Munuera, J.M., Villar-Rodil, S., Ayan-Varela, M., Martinez-Alonso, A., Tascon, J.M., 2014. Chemically exfoliated MoS2 nanosheets as an efficient catalyst for reduction reactions in the aqueous phase. ACS applied materials & interfaces 6, 21702-21710. Guo, N., Li, H., Xu, X., Yu, H., 2016. Hierarchical Fe3O4@MoS2/Ag3PO4 magnetic nanocomposites: Enhanced and stable photocatalytic performance for water purification under visible light irradiation. Applied Surface Science 389, 227-239. Guo, Y., Gan, L., Shang, C., Wang, E., Wang, J., 2017. A Cake-Style CoS2@MoS2/RGO Hybrid Catalyst for Efficient Hydrogen Evolution. Advanced Functional Materials 27, 1602699. Gupta, A., Arunachalam, V., Vasudevan, S., 2016. Liquid-Phase Exfoliation of MoS2 Nanosheets: The Critical Role of Trace Water. J Phys Chem Lett 7, 4884-4890. Han, B., Hu, Y.H., 2016. MoS2 as a co-catalyst for photocatalytic hydrogen production from water. Energy Science & Engineering 4, 285-304. Hao, R., Wang, G., Tang, H., Sun, L., Xu, C., Han, D., 2016. Template-free preparation of macro/mesoporous g-C3N4/TiO2 heterojunction photocatalysts with enhanced visible light photocatalytic activity. Applied Catalysis B: Environmental 187, 47-58. Hao, Y., Li, L., Zhang, J., Luo, H., Zhang, X., Chen, E., 2017. Multilayer and open structure of dendritic crosslinked CeO2-ZrO2 composite: Enhanced photocatalytic degradation and water splitting performance. International Journal of Hydrogen Energy 42, 5916-5929. Hu, L., 2014. Fabrication of 3D Hierarchical MoS2@Polyaniline and MoS2@C Architectures for Lithium-Ion Battery Applications. ACS Appl. Mater. Interfaces 6, 14644-14652. Hu, X., Zhang, W., Liu, X., Mei, Y., Huang, Y., 2015. Nanostructured Mo-based electrode materials for electrochemical energy storage. Chem Soc Rev 44, 2376-2404. Huang, W., Liu, N., Zhang, X., Wu, M., Tang, L., 2017. Metal organic framework g-C3N4/MIL-53(Fe) heterojunctions with enhanced photocatalytic activity for Cr(VI) reduction under visible light. Applied Surface Science 425, 107-116. Huang, Y., Fan, W., Long, B., Li, H., Zhao, F., Liu, Z., Tong, Y., Ji, H., 2016. Visible light Bi2S3/Bi2O3/Bi2O2CO3 photocatalyst for effective degradation of organic pollutions. Applied Catalysis B:
37
A
CC E
PT
ED
M
A
N
U
SC R
IP T
Environmental 185, 68-76. Jia, T., Kolpin, A., Ma, C., Chan, R.C., Kwok, W.M., Tsang, S.C., 2014. A graphene dispersed CdS-MoS2 nanocrystal ensemble for cooperative photocatalytic hydrogen production from water. Chem Commun (Camb) 50, 1185-1188. Jiang, H.-q., Endo, H., Natori, H., Nagai, M., Kobayashi, K., 2009. Fabrication and efficient photocatalytic degradation of methylene blue over CuO/BiVO4 composite under visible-light irradiation. Materials Research Bulletin 44, 700-706. Jiang, J., Wang, H., Chen, X., Li, S., Xie, T., Wang, D., Lin, Y., 2017. Enhanced photocatalytic degradation of phenol and photogenerated charges transfer property over BiOI-loaded ZnO composites. J Colloid Interface Sci 494, 130-138. Jo, W.-K., Lee, J.Y., Selvam, N.C.S., 2016. Synthesis of MoS2 nanosheets loaded ZnO–g-C3N4 nanocomposites for enhanced photocatalytic applications. Chemical Engineering Journal 289, 306-318. Khan, S., Malik, A., 2018. Toxicity evaluation of textile effluents and role of native soil bacterium in biodegradation of a textile dye. Environmental science and pollution research international 25, 4446-4458. King, L.A., Zhao, W., Chhowalla, M., Riley, D.J., Eda, G., 2013. Photoelectrochemical properties of chemically exfoliated MoS2. Journal of Materials Chemistry A 1, 8935. Kołodziejczak-Radzimska, A., Jesionowski, T., 2014. Zinc Oxide—From Synthesis to Application: A Review. Materials 7, 2833-2881. Kudo, A., Miseki, Y., 2009. Heterogeneous photocatalyst materials for water splitting. Chemical Society Reviews 38, 253-278. Kumar, S., Sharma, V., Bhattacharyya, K., Krishnan, V., 2016. Synergetic effect of MoS2–RGO doping to enhance the photocatalytic performance of ZnO nanoparticles. New J. Chem. 40, 5185-5197. Lee, C., Yan, H., Brus, L.E., Heinz, T.F., Ryu, S., 2010. Anomalous Lattice Vibrations of Single- and Few-Layer MoS2. ACS NANO 4, 2695-2700. Lee, K.M., Lai, C.W., Ngai, K.S., Juan, J.C., 2016. Recent developments of zinc oxide based photocatalyst in water treatment technology: a review. Water research 88, 428-448. Lee, Y.H., Zhang, X.Q., Zhang, W., Chang, M.T., Lin, C.T., Chang, K.D., Yu, Y.C., Wang, J.T., Chang, C.S., Li, L.J., Lin, T.W., 2012. Synthesis of large-area MoS2 atomic layers with chemical vapor deposition. Adv Mater 24, 2320-2325. Lei, Z.D., Wang, J.J., Wang, L., Yang, X.Y., Xu, G., Tang, L., 2016. Efficient photocatalytic degradation of ibuprofen in aqueous solution using novel visible-light responsive graphene quantum dot/AgVO3 nanoribbons. Journal of hazardous materials 312, 298-306. Li, D., Bancroft, G.M., Kasrai, M., Fleet, M.E., Feng, X.H., 1995. Polarized X-ray Absorption Spectra and Electronic Structureof Molybdenite (2H-MoS2). Phys Chem Minerals 22, 123-128. Li, F., 2015. Synthesis of Cu-MoS2/rGO hybrid as non-noble metal electrocatalystsfor the hydrogen evolution reaction.pdf>. Journal of Power Sources 292, 15-22. Li, H., Liu, J., Hu, T., Du, N., Song, S., Hou, W., 2016a. Synthesis of belt-like BiOBr hierarchical nanostructure with high photocatalytic performance. Materials Research Bulletin 77, 171-177. Li, H., Wu, J., Yin, Z., Zhang, H., 2014a. Preparation and applications of mechanically exfoliated single-layer and multilayer MoS2 and WSe2 nanosheets. Acc Chem Res 47, 1067-1075. Li, H., Yin, Z., He, Q., Li, H., Huang, X., Lu, G., Fam, D.W., Tok, A.I., Zhang, Q., Zhang, H., 2012. Fabrication of single- and multilayer MoS2 film-based field-effect transistors for sensing NO at room temperature. Small 8, 63-67. Li, H., Yu, K., Lei, X., Guo, B., Li, C., Fu, H., Zhu, Z., 2015a. Synthesis of the MoS2@CuO heterogeneous
38
A
CC E
PT
ED
M
A
N
U
SC R
IP T
structure with improved photocatalysis performance and H2O adsorption analysis. Dalton Trans 44, 10438-10447. Li, H., Yu, K., Li, C., Guo, B., Lei, X., Fu, H., Zhu, Z., 2015b. Novel dual-petal nanostructured WS2@MoS2 with enhanced photocatalytic performance and a comprehensive first-principles investigation. J. Mater. Chem. A 3, 20225-20235. Li, J., Liu, X., Pan, L., Qin, W., Chen, T., Sun, Z., 2014b. MoS2–reduced graphene oxide composites synthesized via a microwave-assisted method for visible-light photocatalytic degradation of methylene blue. RSC Advances 4, 9647. Li, M., Wang, J., Zhang, P., Deng, Q., Zhang, J., Jiang, K., Hu, Z., Chu, J., 2017. Superior adsorption and photoinduced carries transfer behaviors of dandelion-shaped Bi2S3@MoS2: experiments and theory. Sci Rep 7, 42484. Li, T., Hu, X., Liu, C., Tang, C., Wang, X., Luo, S., 2016b. Efficient photocatalytic degradation of organic dyes and reaction mechanism with Ag2CO3/Bi2O2CO3 photocatalyst under visible light irradiation. Journal of Molecular Catalysis A: Chemical 425, 124-135. Li, W., Feng, C., Dai, S., Yue, J., Hua, F., Hou, H., 2015c. Fabrication of sulfur-doped g-C3N4/Au/CdS Z-scheme photocatalyst to improve the photocatalytic performance under visible light. Applied Catalysis B: Environmental 168-169, 465-471. Li, X., Xia, J., Zhu, W., Di, J., Wang, B., Yin, S., Chen, Z., Li, H., 2016c. Facile synthesis of few-layered MoS2 modified BiOI with enhanced visible-light photocatalytic activity. Colloids and Surfaces A: Physicochemical and Engineering Aspects 511, 1-7. Li, Y., Li, Y.-L., Araujo, C.M., Luo, W., Ahuja, R., 2013. Single-layer MoS2 as an efficient photocatalyst. Catalysis Science & Technology 3, 2214. Li, Y., Wang, H., Xie, L., Liang, Y., Hong, G., Dai, H., 2011. MoS2 nanoparticles grown on graphene: an advanced catalyst for the hydrogen evolution reaction. J Am Chem Soc 133, 7296-7299. Li, Y., Wu, S., Huang, L., Xu, H., Zhang, R., Qu, M., Gao, Q., Li, H., 2015d. g-C3N4 modified Bi2O3 composites with enhanced visible-light photocatalytic activity. Journal of Physics and Chemistry of Solids 76, 112-119. Liang, D., Jing, T., Ma, Y., Hao, J., Sun, G., Deng, M., 2016. Photocatalytic Properties of g-C6N6/g-C3N4 Heterostructure: A Theoretical Study. The Journal of Physical Chemistry C 120, 24023-24029. Liao, G., Chen, S., Quan, X., Yu, H., Zhao, H., 2012. Graphene oxide modified g-C3N4hybrid with enhanced photocatalytic capability under visible light irradiation. J. Mater. Chem. 22, 2721-2726. Lin, Y.C., Zhang, W., Huang, J.K., Liu, K.K., Lee, Y.H., Liang, C.T., Chu, C.W., Li, L.J., 2012. Wafer-scale MoS2 thin layers prepared by MoO3 sulfurization. Nanoscale 4, 6637-6641. Liu, C., Chen, J., Che, H., Huang, K., Charpentier, P.A., Xu, W.Z., Shi, W., Dong, H., 2017a. Construction and enhanced photocatalytic activities of a hydrogenated TiO2 nanobelt coated with CDs/MoS2 nanosheets. RSC Adv. 7, 8429-8442. Liu, G., Niu, P., Sun, C., Cheng, H.-M., 2010. Unique Electronic Structure Induced High Photoreactivity of Sulfur-Doped Graphitic C3N4. J Am Chem Soc 132, 11642-11648. Liu, H., Chen, D., Wang, Z., Jing, H., Zhang, R., 2017b. Microwave-assisted molten-salt rapid synthesis of isotype triazine-/heptazine based g-C3N4 heterojunctions with highly enhanced photocatalytic hydrogen evolution performance. Applied Catalysis B: Environmental 203, 300-313. Liu, N., Kim, P., Kim, J.H., Ye, J.H., Kim, S., Lee, C.J., 2014. Large-Area Atomically Thin MoS2 Nanosheets Prepared Using Electrochemical Exfoliation. ACS NANO 8, 6902-6910. Liu, W., Wang, M., Xu, C., Chen, S., 2012. Facile synthesis of g-C3N4/ZnO composite with enhanced visible
39
A
CC E
PT
ED
M
A
N
U
SC R
IP T
lightphotooxidation and photoreduction properties. Chemical Engineering Journal 209, 386-393. Liu, X., Steele, J.C., Meng, X.Z., 2017c. Usage, residue, and human health risk of antibiotics in Chinese aquaculture: A review. Environmental pollution 223, 161-169. Liu, X., Xing, Z., Zhang, Y., Li, Z., Wu, X., Tan, S., Yu, X., Zhu, Q., Zhou, W., 2017d. Fabrication of 3D flower-like black N-TiO2-x @MoS2 for unprecedented-high visible-light-driven photocatalytic performance. Applied Catalysis B: Environmental 201, 119-127. Liu, Y., Shi, J., Peng, Q., Li, Y., 2013. CuO quantum-dot-sensitized mesoporous ZnO for visible-light photocatalysis. Chemistry 19, 4319-4326. Long, L.-L., Chen, J.-J., Zhang, X., Zhang, A.-Y., Huang, Y.-X., Rong, Q., Yu, H.-Q., 2016. Layer-controlled growth of MoS2 on self-assembled flower-like Bi2S3 for enhanced photocatalysis under visible light irradiation. NPG Asia Materials 8, 1-9. Long, M., Cai, W., 2014. Advanced nanoarchitectures of silver/silver compound composites for photochemical reactions. Nanoscale 6, 7730-7742. Lopez-Sanchez, O., Lembke, D., Kayci, M., Radenovic, A., Kis, A., 2013. Ultrasensitive photodetectors based on monolayer MoS2. Nat Nanotechnol 8, 497-501. Low, J., Cheng, B., Yu, J., 2017. Surface modification and enhanced photocatalytic CO2 reduction performance of TiO2 : a review. Applied Surface Science 392, 658-686. Lu, X., Jin, Y., Zhang, X., Xu, G., Wang, D., Lv, J., Zheng, Z., Wu, Y., 2016. Controllable synthesis of graphitic C3N4/ultrathin MoS2 nanosheet hybrid nanostructures with enhanced photocatalytic performance. Dalton Trans 45, 15406-15414. Lv, J., Dai, K., Zhang, J., Geng, L., Liang, C., Liu, Q., Zhu, G., Chen, C., 2015. Facile synthesis of Z-scheme graphitic-C3N4/Bi2MoO6 nanocomposite for enhanced visible photocatalytic properties. Applied Surface Science 358, 377-384. Ma, J., Liu, Q., Zhu, L., Zou, J., Wang, K., Yang, M., Komarneni, S., 2016. Visible light photocatalytic activity enhancement of Ag3PO4 dispersed on exfoliated bentonite for degradation of rhodamine B. Applied Catalysis B: Environmental 182, 26-32. Maitra, U., Gupta, U., De, M., Datta, R., Govindaraj, A., Rao, C.N., 2013. Highly effective visible-light-induced H2 generation by single-layer 1T-MoS2 and a nanocomposite of few-layer 2H-MoS2 with heavily nitrogenated graphene. Angew Chem Int Ed Engl 52, 13057-13061. Mak, K.F., Lee, C., Hone, J., Shan, J., Heinz, T.F., 2010. Atomically thin MoS2: a new direct-gap semiconductor. Phys Rev Lett 105, 136805. Martin, D.J., Liu, G., Moniz, S.J., Bi, Y., Beale, A.M., Ye, J., Tang, J., 2015. Efficient visible driven photocatalyst, silver phosphate: performance, understanding and perspective. Chemical Society Reviews 44, 7808-7828. Mousavi, M., Habibi-Yangjeh, A., 2016. Magnetically separable ternary g-C3N4/Fe3O4/BiOI nanocomposites: Novel visible-light-driven photocatalysts based on graphitic carbon nitride. J Colloid Interface Sci 465, 83-92. Muruganandham, M., Zhang, Y.F., Suri, R., Lee, G.J., Chen, P.K., Hsieh, S.H., Sillanpaa, M., Wu, J.J., 2015. Environmental Applications of ZnO Materials. J. Nanosci. Nanotechnol. 15, 6900-6913. Najmaei, S., Liu, Z., Zhou, W., Zou, X., Shi, G., Lei, S., Yakobson, B.I., Idrobo, J.C., Ajayan, P.M., Lou, J., 2013. Vapour phase growth and grain boundary structure of molybdenum disulphide atomic layers. Nat Mater 12, 754-759. Nasirian, M., Mehrvar, M., 2016. Modification of TiO2 to enhance photocatalytic degradation of organics in aqueous solutions. Journal of Environmental Chemical Engineering 4, 4072-4082.
40
A
CC E
PT
ED
M
A
N
U
SC R
IP T
Ni, Z., Sun, Y., Zhang, Y., Dong, F., 2016. Fabrication, modification and application of (BiO)2CO3-based photocatalysts: A review. Applied Surface Science 365, 314-335. Pan, L., Liu, X., Sun, Z., Sun, C.Q., 2013. Nanophotocatalysts via microwave-assisted solution-phase synthesis for efficient photocatalysis. Journal of Materials Chemistry A 1, 8299. Peng, W.-c., Li, X.-y., 2014. Synthesis of MoS2/g-C3N4 as a solar light-responsive photocatalyst for organic degradation. Catalysis Communications 49, 63-67. Peng, Y., Meng, Z., Zhong, C., Lu, J., Yang, Z., Qian, Y., 2002. Tube- and ball-like amorphous MoS2 prepared by a solvothermal method. Materials Chemistry and Physics 73, 327-329. Prabhakar Vattikuti, S.V., Byon, C., Reddy, C.V., 2016. ZrO2/MoS2 heterojunction photocatalysts for efficient photocatalytic degradation of methyl orange. Electronic Materials Letters 12, 812-823. Qi, Y., Luan, Y., Yang, M., Wang, G., Tan, L., Li, J., 2014. Alkali concentration-dependent tailoring of highly controllable titanate nanostructures: From yolk-shell, hollow 3D nanospheres to 1D nanowires. Applied Surface Science 293, 359-365. Qian, W., Greaney, P.A., Fowler, S., Chiu, S.-K., Goforth, A.M., Jiao, J., 2014. Low-Temperature Nitrogen Doping in Ammonia Solution for Production of N-Doped TiO2-Hybridized Graphene as a Highly Efficient Photocatalyst for Water Treatment. ACS Sustainable Chemistry & Engineering 2, 1802-1810. Radisavljevic, B., Whitwick, M.B., Kis, A., 2011. Integrated circuits and logic operations based on single-layer MoS2. ACS NANO 5, 9934-9938. Renuka, L., Anantharaju, K.S., Vidya, Y.S., Nagaswarupa, H.P., Prashantha, S.C., Sharma, S.C., Nagabhushana, H., Darshan, G.P., 2017. A simple combustion method for the synthesis of multi-functional ZrO 2 /CuO nanocomposites: Excellent performance as Sunlight photocatalysts and enhanced latent fingerprint detection. Applied Catalysis B: Environmental 210, 97-115. Samu, G.F., Veres, Á., Tallósy, S.P., Janovák, L., Dékány, I., Yepez, A., Luque, R., Janáky, C., 2017. Photocatalytic, photoelectrochemical, and antibacterial activity of benign-by-design mechanochemically synthesized metal oxide nanomaterials. Catalysis Today 284, 3-10. Shan, W., Hu, Y., Bai, Z., Zheng, M., Wei, C., 2016. In situ preparation of g-C3N4/bismuth-based oxide nanocomposites with enhanced photocatalytic activity. Applied Catalysis B: Environmental 188, 1-12. Shi, J., 2012. On the Synergetic Catalytic Effect in Heterogeneous Nanocomposite Catalysts. Chemical Reviews 113, 2139-2181. Shi, L., Wang, T., Zhang, H., Chang, K., Meng, X., Liu, H., Ye, J., 2015. An Amine-Functionalized Iron(III) Metal-Organic Framework as Efficient Visible-Light Photocatalyst for Cr(VI) Reduction. Advanced science 2, 1500006. Shi, Y., Zhou, W., Lu, A.Y., Fang, W., Lee, Y.H., Hsu, A.L., Kim, S.M., Kim, K.K., Yang, H.Y., Li, L.J., Idrobo, J.C., Kong, J., 2012. van der Waals epitaxy of MoS2 layers using graphene as growth templates. Nano Lett 12, 2784-2791. Shuai, J., Yoo, H.D., Liang, Y., Li, Y., Yao, Y., Grabow, L.C., 2016. Density functional theory study of Li, Na, and Mg intercalation and diffusion in MoS2 with controlled interlayer spacing. Materials Research Express 3, 064001. Sreethawong, T., Ngamsinlapasathian, S., Yoshikawa, S., 2013. Synthesis of crystalline mesoporous-assembled ZrO2 nanoparticles via a facile surfactant-aided sol–gel process and their photocatalytic dye degradation activity. Chemical Engineering Journal 228, 256-262. Sudha, D., Sivakumar, P., 2015. Review on the photocatalytic activity of various composite catalysts. Chemical Engineering and Processing: Process Intensification 97, 112-133. Sun, T., Zhao, Z., Liang, Z., Liu, J., Shi, W., Cui, F., 2017. Efficient removal of arsenite through photocatalytic
41
A
CC E
PT
ED
M
A
N
U
SC R
IP T
oxidation and adsorption by ZrO 2 -Fe 3 O 4 magnetic nanoparticles. Applied Surface Science 416, 656-665. Tan, Y.-H., Yu, K., Li, J.-Z., Fu, H., Zhu, Z.-Q., 2014. MoS2@ZnO nano-heterojunctions with enhanced photocatalysis and field emission properties. Journal of Applied Physics 116, 064305. Tang, L., Jia, C.-t., Xue, Y.-c., Li, L., Wang, A.-q., Xu, G., Liu, N., Wu, M.-h., 2017a. Fabrication of compressible and recyclable macroscopic g-C3N4/GO aerogel hybrids for visible-light harvesting: A promising strategy for water remediation. Applied Catalysis B: Environmental 219, 241-248. Tang, L., Wang, J.-j., Jia, C.-t., Lv, G.-x., Xu, G., Li, W.-t., Wang, L., Zhang, J.-y., Wu, M.-h., 2017b. Simulated solar driven catalytic degradation of psychiatric drug carbamazepine with binary BiVO4 heterostructures sensitized by graphene quantum dots. Applied Catalysis B: Environmental 205, 587-596. Tisseraud, C., Comminges, C., Pronier, S., Pouilloux, Y., Le Valant, A., 2016. The Cu–ZnO synergy in methanol synthesis Part 3: Impact of the composition of a selective Cu@ZnO x core–shell catalyst on methanol rate explained by experimental studies and a concentric spheres model. Journal of Catalysis 343, 106-114. Truong, T.G., Meriadec, C., Fabre, B., Bergamini, J.F., de Sagazan, O., Ababou-Girard, S., Loget, G., 2017. Spontaneous decoration of silicon surfaces with MoOx nanoparticles for the sunlight-assisted hydrogen evolution reaction. Nanoscale 9, 1799-1804. Vane, C.H., Harrison, I., Kim, A.W., Moss-Hayes, V., Vickers, B.P., Hong, K., 2009. Organic and metal contamination in surface mangrove sediments of South China. Marine pollution bulletin 58, 134-144. Vattikuti, S.V.P., Byon, C., 2016. Bi2S3 nanorods embedded with MoS2 nanosheets composite for photodegradation of phenol red under visible light irradiation. Superlattices and Microstructures 100, 514-525. Verble, J.L., Wieting, T.J., 1970. Lattice Mode Degeneracy in MoS2 and Other Layer Compounds. Phys.rev.lett 25, 362-365. Vrijheid, M., Casas, M., Gascon, M., Valvi, D., Nieuwenhuijsen, M., 2016. Environmental pollutants and child health-A review of recent concerns. International journal of hygiene and environmental health 219, 331-342. Wan, J., Du, X., Liu, E., Hu, Y., Fan, J., Hu, X., 2017. Z-scheme visible-light-driven Ag3PO4 nanoparticle@MoS2 quantum dot/few-layered MoS2 nanosheet heterostructures with high efficiency and stability for photocatalytic selective oxidation. Journal of Catalysis 345, 281-294. Wang, H., Bai, Y., Yang, J., Lang, X., Li, J., Guo, L., 2012a. A facile way to rejuvenate Ag3PO4 as a recyclable highly efficient photocatalyst. Chemistry 18, 5524-5529. Wang, J., 2016. A molybdenum disulfide reduced oxide-graphenenanoflakelet-on-sheet structure for lithium ion batteries. Applied Surface Science 399, 237-244. Wang, J., Wei, B., Xu, L., Gao, H., Sun, W., Che, J., 2016a. Multilayered MoS2 coated TiO2 hollow spheres for efficient photodegradation of phenol under visible light irradiation. Materials Letters 179, 42-46. Wang, L., Chai, Y., Ren, J., Ding, J., Liu, Q., Dai, W.L., 2015. Ag3PO4 nanoparticles loaded on 3D flower-like spherical MoS2: a highly efficient hierarchical heterojunction photocatalyst. Dalton transactions 44, 14625-14634. Wang, Q., Yun, G., Bai, Y., An, N., Lian, J., Huang, H., Su, B., 2014. Photodegradation of rhodamine B with MoS2/Bi2O2CO3 composites under UV light irradiation. Applied Surface Science 313, 537-544. Wang, Q.H., Kalantar-Zadeh, K., Kis, A., Coleman, J.N., Strano, M.S., 2012b. Electronics and optoelectronics of two-dimensional transition metal dichalcogenides. Nature Nanotechnology 7, 699-712. Wang, X., Hong, M., Zhang, F., Zhuang, Z., Yu, Y., 2016b. Recyclable Nanoscale Zero Valent Iron Doped g-C3N4/MoS2 for Efficient Photocatalysis of RhB and Cr(VI) Driven by Visible Light. ACS Sustainable
42
A
CC E
PT
ED
M
A
N
U
SC R
IP T
Chemistry & Engineering 4, 4055-4063. Wang, Y., Yang, Y., Xi, L., Zhang, X., Jia, M., Xu, H., Wu, H., 2016c. A simple hydrothermal synthesis of flower-like ZnO microspheres and their improved photocatalytic activity. Materials Letters 180, 55-58. Wang, Z., Chen, T., Chen, W., Chang, K., Ma, L., Huang, G., Chen, D., Lee, J.Y., 2013. CTAB-assisted synthesis of single-layer MoS2–graphene composites as anode materials of Li-ion batteries. J. Mater. Chem. A 1, 2202-2210. Wang, Z., Huang, Y., Ho, W., Cao, J., Shen, Z., Lee, S.C., 2016d. Fabrication of Bi2O2CO3/g-C3N4 heterojunctions for efficiently photocatalytic NO in air removal: In-situ self-sacrificial synthesis, characterizations and mechanistic study. Applied Catalysis B: Environmental 199, 123-133. Weng, B., Zhang, X., Zhang, N., Tang, Z.R., Xu, Y.J., 2015. Two-dimensional MoS2 nanosheet-coated Bi2S3 discoids: synthesis, formation mechanism, and photocatalytic application. Langmuir 31, 4314-4322. Wu, M.-h., Li, L., Xue, Y.-c., Xu, G., Tang, L., Liu, N., Huang, W.-y., 2018. Fabrication of ternary GO/g-C3N4/MoS2 flower-like heterojunctions with enhanced photocatalytic activity for water remediation. Applied Catalysis B: Environmental 228, 103-112. Wu, W., Jiang, C., Roy, V.A., 2015. Recent progress in magnetic iron oxide–semiconductor composite nanomaterials as promising photocatalysts. Nanoscale 7, 38-58. Xiang, Q., Cheng, B., Yu, J., 2015. Graphene-Based Photocatalysts for Solar-Fuel Generation. Angew Chem Int Ed Engl 54, 11350-11366. Xiang, Q., Yu, J., Jaroniec, M., 2012. Synergetic effect of MoS2 and graphene as cocatalysts forenhanced photocatalytic H2 production activity of TiO2 nanoparticles. Journal of the American Chemical Society 134, 6575-6578. Xiang, Z., Wang, Y., Zhang, D., Ju, P., 2016. BiOI/BiVO4 p-n heterojunction with enhanced photocatalytic activity under visible-light irradiation. Journal of Industrial and Engineering Chemistry 40, 83-92. Xiong, F., Zhang, J., Zhu, Z., Yuan, X., Qin, S., 2015. Ultrabroadband, More than One Order Absorption Enhancement in Graphene with Plasmonic Light Trapping. Sci Rep 5, 16998. Xiong, X., Ding, L., Wang, Q., Li, Y., Jiang, Q., Hu, J., 2016. Synthesis and photocatalytic activity of BiOBr nanosheets with tunable exposed {010} facets. Applied Catalysis B: Environmental 188, 283-291. Xu, C., Xu, B., Gu, Y., Xiong, Z., Sun, J., Zhao, X.S., 2013. Graphene-based electrodes for electrochemical energy storage. Energy & Environmental Science 6, 1388. Yang, D., Sandoval, S.J., Divigalpitiya, W.M., Irwin, J.C., Frindt, R.F., 1991. Structure of single-molecular-layer MoS2. Phys Rev B Condens Matter 43, 12053-12056. Yang, J., Wu, X., Li, X., Liu, Y., Gao, M., Liu, X., Kong, L., Yang, S., 2011. Synthesis and characterization of nitrogen-rich carbon nitride nanobelts by pyrolysis of melamine. Applied Physics A 105, 161-166. Yang, S.Y., Shim, G.W., Seo, S.-B., Choi, S.-Y., 2016. Effective shape-controlled growth of monolayer MoS2 flakes by powder-based chemical vapor deposition. Nano Research 10, 255-262. Yang, X., Qin, J., Jiang, Y., Chen, K., Yan, X., Zhang, D., Li, R., Tang, H., 2015. Fabrication of P25/Ag3PO4/graphene oxide heterostructures for enhanced solar photocatalytic degradation of organic pollutants and bacteria. Applied Catalysis B: Environmental 166-167, 231-240. Yi-Zhu, P., Wan-Hong, M., Man-Ke, J., Xiao-Rong, Z., Johnson, D.M., Ying-Ping, H., 2016. Comparing the degradation of acetochlor to RhB using BiOBr under visible light: A significantly different rate-catalyst dose relationship. Applied Catalysis B: Environmental 181, 517-523. Yu, J., Zhuang, S., Xu, X., Zhu, W., Feng, B., Hu, J., 2015. Photogenerated electron reservoir in hetero-p–n CuO–ZnO nanocomposite device for visible-light-driven photocatalytic reduction of aqueous Cr(vi). J. Mater. Chem. A 3, 1199-1207.
43
A
CC E
PT
ED
M
A
N
U
SC R
IP T
Yuan, Y.-J., Ye, Z.-J., Lu, H.-W., Hu, B., Li, Y.-H., Chen, D.-Q., Zhong, J.-S., Yu, Z.-T., Zou, Z.-G., 2016. Constructing Anatase TiO2 Nanosheets with Exposed (001) Facets/Layered MoS2 Two-Dimensional Nanojunctions for Enhanced Solar Hydrogen Generation. ACS Catalysis 6, 532-541. Yuan, Y., Liu, B., Li, Q., Shen, P., Chen, G., 2017. Excellent photocatalytic performance of few-layer MoS2/graphene hybrids. Journal of Alloys and Compounds. Zalfani, M., van der Schueren, B., Mahdouani, M., Bourguiga, R., Yu, W.-B., Wu, M., Deparis, O., Li, Y., Su, B.-L., 2016. ZnO quantum dots decorated 3DOM TiO2 nanocomposites: Symbiose of quantum size effects and photonic structure for highly enhanced photocatalytic degradation of organic pollutants. Applied Catalysis B: Environmental 199, 187-198. Zeng, H., Dai, J., Yao, W., Xiao, D., Cui, X., 2012. Valley polarization in MoS2 monolayers by optical pumping. Nat Nanotechnol 7, 490-493. Zeng, Z., Yin, Z., Huang, X., Li, H., He, Q., Lu, G., Boey, F., Zhang, H., 2011. Single-layer semiconducting nanosheets: high-yield preparation and device fabrication. Angew Chem Int Ed Engl 50, 11093-11097. Zhang, G., Huang, C., Wang, X., 2015. Dispersing molecular cobalt in graphitic carbon nitride frameworks for photocatalytic water oxidation. Small 11, 1215-1221. Zhang, G., Lan, Z.-A., Lin, L., Lin, S., Wang, X., 2016a. Overall water splitting by Pt/g-C3N4 photocatalysts without using sacrificial agents. Chem. Sci. 7, 3062-3066. Zhang, J.-J., Gao, B., Dong, S., 2016b. Strain-enhanced superconductivity ofMoX2(X=S or Se)bilayers with Na intercalation. Physical Review B 93. Zhang, J., Sun, J., Maeda, K., Domen, K., Liu, P., Antonietti, M., Fu, X., Wang, X., 2011. Sulfur-mediated synthesis of carbon nitride: Band-gap engineering and improved functions for photocatalysis. Energy Environ. Sci. 4, 675-678. Zhang, X., Lai, Z., Tan, C., Zhang, H., 2016c. Solution-Processed Two-Dimensional MoS2 Nanosheets: Preparation, Hybridization, and Applications. Angewandte Chemie International Edition 55, 8816-8838. Zhang, X., Li, X., Shao, C., Li, J., Zhang, M., Zhang, P., Wang, K., Lu, N., Liu, Y., 2013. One-dimensional hierarchical heterostructures of In2S3 nanosheets on electrospun TiO2 nanofibers with enhanced visible photocatalytic activity. J Hazard Mater 260, 892-900. Zhang, X., Shao, C., Li, X., Miao, F., Wang, K., Lu, N., Liu, Y., 2016d. 3D MoS2 nanosheet/TiO2 nanofiber heterostructures with enhanced photocatalytic activity under UV irradiation. Journal of Alloys and Compounds 686, 137-144. Zhao, W., Liu, Y., Wei, Z., Yang, S., He, H., Sun, C., 2016. Fabrication of a novel p–n heterojunction photocatalyst n-BiVO4@p-MoS2 with core–shell structure and its excellent visible-light photocatalytic reduction and oxidation activities. Applied Catalysis B: Environmental 185, 242-252. Zhao, Z., Sun, Y., Dong, F., 2015a. Graphitic carbon nitride based nanocomposites: a review. Nanoscale 7, 15-37. Zhao, Z., Tian, J., Sang, Y., Cabot, A., Liu, H., 2015b. Structure, synthesis, and applications of TiO2 nanobelts. Adv Mater 27, 2557-2582. Zheng, Y., Zhang, W., Li, Y., Chen, J., Yu, B., Wang, J., Zhang, L., Zhang, J., 2017. Energy related CO 2 conversion and utilization: Advanced materials/nanomaterials, reaction mechanisms and technologies. Nano Energy 40, 512-539. Zhong, X.-L., Li, Z.-Y., 2012. Giant Enhancement of Near-Ultraviolet Light Absorption by TiO2 via a Three-Dimensional Aluminum Plasmonic Nano Funnel-Antenna. The Journal of Physical Chemistry C 116, 21547-21555. Zhou, G., Xu, X., Yu, J., Feng, B., Zhang, Y., Hu, J., Zhou, Y., 2014. Vertically aligned
44
A
CC E
PT
ED
M
A
N
U
SC R
IP T
MoS2/MoOxheterojunction nanosheets for enhanced visible-light photocatalytic activity and photostability. CrystEngComm 16, 9025-9032. Zhou, W., Yin, Z., Du, Y., Huang, X., Zeng, Z., Fan, Z., Liu, H., Wang, J., Zhang, H., 2013. Synthesis of few-layer MoS2 nanosheet-coated TiO2 nanobelt heterostructures for enhanced photocatalytic activities. Small 9, 140-147. Zhu, C., Zhang, L., Jiang, B., Zheng, J., Hu, P., Li, S., Wu, M., Wu, W., 2016. Fabrication of Z-scheme Ag3PO4/MoS2 composites with enhanced photocatalytic activity and stability for organic pollutant degradation. Applied Surface Science 377, 99-108. Zou, X., Dong, Y., Zhang, X., Cui, Y., Ou, X., Qi, X., 2017. The highly enhanced visible light photocatalytic degradation of gaseous o-dichlorobenzene through fabricating like-flowers BiPO 4/BiOBr pn heterojunction composites. Applied Surface Science 391, 525-534.
45