Engineering BiVO4@Bi2S3 heterojunction by cosharing bismuth atoms toward boosted photocatalytic Cr(VI) reduction

Journal of Hazardous Materials 406 (2021) 124705

Contents lists available at ScienceDirect

Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat

Research paper

Engineering BiVO4@Bi2S3 heterojunction by cosharing bismuth atoms toward boosted photocatalytic Cr(VI) reduction Xinyi Lian a, Jiguang Zhang a, Yue Zhan a, Yanping Zhang a, Shuangli Yang a, Zhou Chen a, *, Yunyun Dong b, Weiping Fang a, Xiaodong Yi a, * a

National Engineering Laboratory for Green Chemical Productions of Alcohols, Ethers and Esters, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, PR China College of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng 252059, PR China

b

A R T I C L E I N F O

A B S T R A C T

Editor: Prof. G. Lyberatos

The photocatalytic efficiency is limited by poor charge separation efficiency and high carrier transport activation energy (CTAE) of photogenerated electron/hole pairs than traditional semiconductor. Hybridizing nanostructure with two staggered alignment band structure is proved as an effective strategy to mitigate these two challenges but still suffers a strong coulomb electrostatic repulsive force between two heterogeneous semiconductors. Here, we steer a friendly sulfurization process to construct BiVO4@Bi2S3 heterojunction with a scenario of cosharing Bi atoms. The intimate atomic-level contact between BiVO4 and Bi2S3 not only enhances the visible-light absorption and lowers CTAE, but also accelerate carrier’s separation efficiency, which enables it to deliver the best pho­ tocatalytic performance toward reduction of Cr(VI). BiVO4@Bi2S3 only needs less than 40 min to completely reduce 50 ppm Cr(VI) solution. The type II heterojunction photocatalytic mechanism is systematically studied to decipher the carriers’ transfer track between BiVO4 and Bi2S3. Our new finding of engineering inorganic het­ erojunction by cosharing atoms opens a new avenue to other similar materials for potential applications.

Keywords: Photocatalysis Heterojunction Atomic-level Cr(VI) removal Carrier transport activation energy

1. Introduction The visible-light-driven photocatalysis technology is an efficient pathway to solve industrial-environmental issues, including wastewater treatment and organism degradation (Li et al., 2020; Wu et al., 2020; Tang et al., 2019). The efficiency for both light absorption and carrier transfer of innovatively artificial semiconductors is highly associated with the photocatalytic performance. A typical photocatalytic process begins with photon absorption in which case the electrons are excited from the valance band (VB) to the conduction band (CB) on a femto­ second time scale (Linsebigler et al., 1995; Ma et al., 2016; Chen et al., 2017). Photogenerated charge carriers must be extracted for further reduction or oxidation reactions while carrier recombination should be suppressed (Kudo and Miseki, 2009; Lin et al., 2015). Therefore, the essential point to maximize the photocatalytic conversion efficiency of artificial materials relied on high-efficient photocatalyst with enhanced light absorption and faster carrier delivery. Prolonging the lifetime of carriers and lowering the intrinsic carrier transport activation energy (CTAE) in photocatalyst become the key but

still two big challenges to improve the photocatalytic conversion effi­ ciency (Roy et al., 1978). Despite of doping, morphology-tuning ap­ proaches, loading metals (Yu et al., 2019), engineering heterojunction has attracted great attentions in prolonging the lifetime of excited-state electron-hole pairs and lowering the CTAE and has consequently given rise to a new opportunity in realizing effectively photocatalytic perfor­ mance (Xiong et al., 2016; Chen et al., 2016a). Combination of two semiconductors with matched band structure have been pursued to form an ideal system in facilitating separation and transfer of photoinduced carriers and decreasing recombination chance of electron-hole pairs by synergetic effect (Zou et al., 2020; Jia et al., 2020; Zhan et al., 2020). The enhanced photocatalytic performance is ascribed to the higher charge carrier transfer efficiency between those two semiconductors. Hybridizing semiconductor nanostructures with a staggered align­ ment of band edges at the heterointerface can greatly improve spatial charge separation of photogenerated electrons and holes in different parts of the heterostructure (Huo et al., 2021; Chen et al., 2020; Wen et al., 2020; Zhu et al., 2018). However, the interactions on conventional heterostructure counterparts are usually noncovalent such as van der

* Corresponding authors. E-mail addresses: [email protected] (Z. Chen), [email protected] (X. Yi). https://doi.org/10.1016/j.jhazmat.2020.124705 Received 26 September 2020; Received in revised form 25 November 2020; Accepted 26 November 2020 Available online 8 December 2020 0304-3894/© 2020 Elsevier B.V. All rights reserved.

X. Lian et al.

Journal of Hazardous Materials 406 (2021) 124705

Waals forces and hydrogen bonding interactions (Wang et al., 2020), which leads to the existence of strong coulomb electrostatic repulsive force (CERF) between two different types of semiconductors and inevi­ table reduces the carriers transfer rate on those heterojunction bridge (Low et al., 2017; Xu et al., 2018). In addition, the coulombic attraction force (CAF) between the electrons (in conduction band) and holes (in valance band) also hinders this electron transfer (Fu et al., 2019). Therefore, linking two types of semiconductor at the atomic level with intimate contact to lower the CERF is effective strategy but lack of focuses. Bismuth vanadate (m-BiVO4) semiconductor with exceptional fea­ tures, including a suitable band gap (2.4 eV), good dispersibility, nontoxicity, resistance to corrosion, has been wildly utilized in the field of photo-catalysis. Its practical applications are still hindered by the poor quantum yield due to the rapid recombination rate of photogenerated electrons and holes (Zhou et al., 2017; Wang et al., 2017a; Kim and Choi, 2014; Ashokkumar and Arunachalam, 2018). To enhance the photo­ activity of pure BiVO4, constructing heterogeneous photocatalysts with other matched semiconductors, such as WO3/BiVO4 (Su et al., 2011), AgI/BiVO4 (Chen et al., 2016b), BiVO4/BiOI (Huang et al., 2015), have been proposed by previous studies. It is worthy of mentioning that the contact between two semiconductors in those elaborate designs is al­ ways in molecular level but not at the atomic level, in which charge transfer channel is obstructed because of the heterogeneous nature of those semiconductors. Moreover, the reported synthesis methods are complex and usually time- or energy-consumption, which hinder the practicability of those promising strategies. The synthesis processes of photocatalyst are also important parts for the whole cost of photo­ catalysis from the perspective of economic feasibility. Furthermore, the structure and morphology of a photocatalytic material are crucial fac­ tors in determining its performance by affecting the heterostructure formation, light-absorbing efficiency, and charge transfer pathway (Su et al., 2014; Gao et al., 2014; Ma et al., 2012). In particular, the core/shell structure could maximize the interfacial contact area thereby furnish a broader platform for efficient charge transfer (Wei et al., 2011; Zhao et al., 2017). Therefore, developing an economic and practical strategy to construct a heterojunction with atomic level contact and unique core/shell morphology is very necessary. Water pollution caused by heavy metal ions has drawn extensive attention; Cr(VI) is particularly hazardous owing to its acute toxicity, high mobility and less availability for biological uptake in water among the heavy metals. Various techniques have been used to treat Cr(VI) contamination, including ion exchange, electrocoagulation, membrane separation, adsorption, and photocatalytic reduction, which suffer from high operating costs, complicated procedures and harsh conditions (Zhang et al., 2016). Semiconductor-mediated photocatalysts, such as Fe3O4@Fe2O3/Al2O3, TiO2/Fe3O4, Cu–ZnO, WO3, have been widely employed as economical and efficient materials for the removal of Cr (VI) (Nagarjuna et al., 2017; Challagulla et al., 2016; Shraavan et al., 2017; Nagarjuna et al., 2017). However, most of the catalysts reported before have their limitations like insufficient photocatalytic efficiency. Therefore, Cr(VI) is selected as a representative substance in evaluating photocatalytic activity. In this work, we innovate a new and benign in situ solvothermal sulfurization pathway to engineer a heterojunction with atomic level contact between Bi2S3 and BiVO4. Cosharing the Bi atoms on the whole surface of BiVO4 core enables close contact in the BiVO4@Bi2S3 hybrid, resulting in faster carrier transfer between Bi2S3 and BiVO4 and lowering the CTAE of photocatalysis. The BiVO4@Bi2S3 hybrid not only enhances visible photon absorption ability but also accelerates carriers charge transport efficiency. Additionally, a lower CTAE (0.261 eV) between this type II band alignment structure has been investigated by in situ impedance spectra measurements, which efficiently reduce the activa­ tion barrier of excited-state electron-hole pairs separation in BiVO4. Accordingly, improved photocatalytic Cr(VI) reduction performance is achieved on the BiVO4 @Bi2S3 hybrid compared with the unadorned

BiVO4 under visible light illumination, which can be attributed to the enhanced light absorption, boosted charge separation efficiency and lower CTAE after connecting the Bi2S3 with atomic interface. 2. Experimental details 2.1. Materials Bismuth nitrate pentahydrate (Bi(NO3)3.5H2O), sodium meta­ vanadate (Na3VO4), thioacetamide (TAA), ethanol, ethylene glycol, isopropanol, acetone and sodium sulfate (Na2SO4), potassium dichro­ mate (K2Cr2O7), diphenylcarbazide (DPC), nafion PFSA polymer (dis­ persions D520, 5%), 2-mercaptoethanol, rhodamine B (RhB), Bi catalyst (bismuth). All the above chemicals were purchased from Aldrich and Sigma and used without any further purification. 2.2. Preparation of the precursor BiVO4 The BiVO4 sample was synthesized by a facile solvothermal process. First of all, Bi(NO3)3.5H2O (1 mmol) and NH4VO3 (1 mmol) were mixed in 20 mL glycol solution and 10 mL deionized water a and subjected to ultrasonication for 30 min. Then they were transferred into a 50 mL Teflon lined stainless steel autoclave and treated at 160 ℃ for 6 h. The system was allowed to cool down to room temperature, after which the collected yellow powders were centrifuged, washed with deionized water/ethanol to remove unreacted ions, and dried in air at 60 ℃ overnight. 2.3. Preparation of BiVO4@Bi2S3 heterojunction 0.1 g BiVO4 was mixed with 0.2 g TAA in 30 mL ethanol and then the mixture was stirring for 30 min. Then they were transferred into a 50 mL Teflon lined stainless steel autoclave and treated at 120 ℃ for 8 h. The products were centrifuged and washed with ethanol 3 times, then dried in air at 60 ℃ overnight. The process is shown in Scheme 1. 2.4. Preparation of Bi2S3 and physically mixed BiVO4 and Bi2S3 Bi2S3 nanowires were synthesized via a solvothermal approach (Whittaker-Brooks et al., 2015). 0.5 g of Bi(NO3)3.5H2O was dissolved in 20 mL ethylene glycol. This solution was heated at 60 ℃ and stirred for 30 min until homogeneous and clear. Subsequently, 2 mL of 2-mercap­ toethanol was added to the clear solution. The solution was then transferred to a 50 mL Teflon-lined stainless-steel autoclave. The auto­ clave was sealed and kept at 150 ℃ for 24 h. After the reaction, the resulting black product was cooled to room temperature and washed repeatedly with copious amounts of isopropanol. Finally, the product was vacuum-dried at 60 ℃ for 6 h.

Scheme 1. The fabrication process of BiVO4@Bi2S3.

2

X. Lian et al.

Journal of Hazardous Materials 406 (2021) 124705

The V/S atomic ratio determined by EDX analysis is around 1.38 corresponding to a BiVO4@Bi2S3 molar ratio of 4:1 in the BiVO4@Bi2S3. For comparison, we physically mixed Bi2S3 and BiVO4 at the mole ratio of 12:1 accordingly, the amount of BiVO4 and Bi2S3 is 30.87 mg and 4.13 mg, respectively.

Brunauer-Emmett-Teller (BET) surface area test was performed at 77 K on a TRISTAR-3020 surface area analyzer.

2.5. Photocatalytic activity evaluation

The transient photocurrent response was carried out on an electro­ chemical analyzer (CHI 760e Instruments) in a standard three-electrode system using platinum wire as the counter electrode, and Ag/AgCl (saturated in KCl solution) as the reference electrode. Fluorine-doped tin oxide (FTO) glass plate deposited with the photocatalysts was used as the work electrode. The working electrodes were prepared as follows: 10 mg of the as-prepared BiVO4 or BiVO4@Bi2S3 was dispersed in 1 mL isopropanol and 200 μL nafion solution (5 wt%) to produce a slurry, then 35 μL suspension was coated on a 1 cm × 1 cm Fluorine-doped tin oxide (FTO) glass plate at room temperature and then drying in a vac­ uum oven at 40 ℃ for 12 h. 0.1 M Na2SO4 solution is used as electrolyte. The photocurrent measurement was measured with an interval of 50 s under visible light illumination. The in situ impedance spectrum of the samples was carried out by an electrochemical analyzer (Ivium Stat, Netherlands).

2.7. Photoelectric characterization

Photocatalytic reduction of Cr(VI) under visible light illumination was chosen as a model reaction to evaluate BiVO4@Bi2S3 hetero­ junction, and further confirmed our hypothesis that realizing lower CTAE and faster carrier transfer of photocatalysis by cosharing atoms between two semiconductors. The visible light was provided with a 350 W Xe lamp using an ultraviolet cutoff filter (λ > 420 nm). In a typical process, 35 mg of as-prepared photocatalyst was added into 100 mL Pyrex glass bottle which contained 50 mL of Cr(VI) solution (50 mg⋅L− 1 based on Cr in a dilute K2Cr2O7 solution). Before irradiation, the suspensions were treated under ultrasound for 10 min and magnetically stirred in the dark for 1.0 h to ensure the establishment of adsorption-desorption equilibrium. During photoreaction, 4 mL of the suspension was removed from the reactor at given time intervals. The supernatant liquid was obtained for further analysis. The diphenylcarbazide (DPC) method was used to determine the concentration of Cr(VI) ions in the supernatant solution obtained after photocatalytic experiment. 1 mL Cr(VI) solution obtained after photo­ catalytic reduction was mixed with 9 mL 0.2 M H2SO4 aqueous solution in a 25 mL volumetric flask. Then, 0.2 mL of newly prepared 0.25% (w/ v) DPC in acetone was added to the volumetric flask. After vortexing the mixture about 15–30 s, it was allowed to stand for 10–15 min to ensure full color development (Zhang et al., 2016; Wan et al., 2017; Zhang et al., 2018; Xie et al., 2017). The red-violet to purple color mixed so­ lution was then measured at 540 nm by the UV–vis spectroscopy using deionized water as reference. The photocatalytic reduction of 10 mg/L RhB degradation over BiVO4 and BiVO4@Bi2S3 is carried out. The visible light was provided with a 350 W Xe lamp using an ultraviolet cutoff filter (λ > 420 nm). In a typical process, 10 mg of as-prepared photocatalyst was added into 50 mL Pyrex glass bottle which contained 30 mL of RhB solution. Before irradiation, the suspensions were treated under ultrasound for 10 min and magnetically stirred in the dark for 0.5 h to ensure the establishment of adsorption-desorption equilibrium.

3. Results and discussions 3.1. Synthesis and characterization of the BiVO4@Bi2S3 hybrid The BiVO4@Bi2S3 heterostructure was fabricated by the sol­ vothermal sulfurization of synthesized BiVO4 nanorod in TAA solution, as shown in Scheme 1. Here, the sulfurization period was 8 h for BiVO4@Bi2S3 heterostructure. The morphology of BiVO4 and BiVO4@­ Bi2S3 was studied by scanning electron microscope (SEM), transmission electron microscopy (TEM) and corresponding energy dispersive X-ray (EDX) analyses. The as-prepared BiVO4 with uniform nanorod morphology (average width of 6–8 µm) can be clearly seen in Fig. 1a. The surface of BiVO4@Bi2S3 consists of small petals while the core re­ mains as the nanorod BiVO4 (Fig. 1b and c). The mapping results show uniform distribution of Bi, V, O and S elements in the whole BiVO4@­ Bi2S3 (Fig. 1d-g) particle. The crystallographic structure and phase purity of the BiVO4 and BiVO4@Bi2S3 were examined by powder X-ray diffraction (XRD) anal­ ysis, as shown in Fig. 2a. All the diffraction peaks can be indexed as the body-centered monoclinic phase of BiVO4 with lattice constants of a = 5.195, b = 11.700 and c = 5.092 (JCPDS card No. 00–14–0688). Noticeably, a series of new peaks at 15.67◦ , 22.38◦ , 23.71◦ , 25.21◦ , 32.95◦ , 33.92◦ can be well indexed to the Bi2S3 (JCPDS NO.00–006–0333) in BiVO4@Bi2S3, indicating that the heterostructure is successfully constructed (Gao et al., 2014). It is worthwhile to note that the VO34 species on the outmost surface is easier to be replaced by S atoms during sulfurization process (Eqs. 1–2) (Yang et al., 2018), resulting in a new structure and morphology on the surface. As a result, the surface of BiVO4@Bi2S3 is reconstructed and the whole sample turns out to be a core-shell structure connected by cosharing the Bi atoms.

2.6. Characterizations Powder X-ray diffraction (XRD) was performed on an X′ Pert Pro automatic powder diffractometer operated at 35 kV and 15 mA using CuKa (k = 0.15406 nm) monochromatized radiation in all cases. Scan­ ning electron microscopy (SEM) images were obtained on Hitachi 4800. The transmission electron microscopy (TEM) experiments were per­ formed using a FEI Tecnai 30 high-resolution transmission electron microscope (Philips Analytical). X-ray photoelectron spectroscopy (XPS) measurements were made with a Qtac100 spectrometer using the inci­ dent radiation Al Ka of 1486.6 eV at 250 W, 20 mA, and 50 eV pass energy. The C 1s peak at 284.6 eV was used as the internal standard to compensate for sample charging. Diffuse-reflectance UV–vis spectra were recorded on a Varian-Cary 5000 spectrometer equipped with a diffuse-reflectance accessory. The spectra were collected with BaSO4 as a reference. The steady-state photoluminescence (PL) spectroscopy measurements were performed using a Hitachi F-7000 fluorescence spectrophotometer with the maximum excitation wavelength of 530 nm. Time-resolved PL decay curves were recorded on a FLS980 fluorescence lifetime spectrophotometer (Edinburgh Instruments, UK) under the excitation of 377 nm and probed at 445 nm. The Raman measurement was performed on the Nanophoton Raman-11 system equipped with an upright microscope (Nikon Eclipse 90i) and a 600 grooves/mm grating. 532 nm laser was used for all measurements.

CH3 CS(NH2 ) + H2 O = CH3 CO(NH2 ) + 2H+ + S2−

(1)

2BiVO4 + 3S2− →Bi2 S3 + 2VO4 3−

(2)

To reveal the evolution process of the morphology and structural of BiVO4 @Bi2S3 heterostructure, different sulfurization period of 4 h, 6 h, 8 h and 10 h were also investigated, and the corresponding products were denoted as S-BiVO4-4, S-BiVO4-6, S-BiVO4-8 (BiVO4@Bi2S3) and SBiVO4-10, respectively. As shown in Fig. 2a, the S-BiVO4-4 mainly keeps the characteristic peaks belonging to BiVO4. The surface of the BiVO4 turns to rough and the small petals start covering on the surface in the initial 4 h (Fig. 3), indicating the surface reconstruction begins. As the sulfurization duration ascends to 6 h and 8 h, much more VO34 were reacted with sulfur species (Eq. (2)). The petals are gradually spread 3

X. Lian et al.

Journal of Hazardous Materials 406 (2021) 124705

Fig. 1. SEM images of (a) BiVO4 and (b, c) BiVO4@Bi2S3, and the elemental mappings of (d) Bi, (e) S, (f) O, (g) V elements of BiVO4@Bi2S3.

over the surface of the products and become denser while the product keeps the rod shape and finally forms a core-shell structure with petals outside on the rod. The characteristic peaks belonging to Bi2S3 appear at this time, as confirmed by XRD results. Finally, as the sulfurization going on, the sulfur continues substituting VO34 sites, and the product mostly turn into nanowires after 10 h sulfurization. At that time, the crystalline texture is almost converted to Bi2S3. To disclose how the substitution process happens, we performed the EDX and Raman tests of the sulfuration samples. The detailed EDX re­ sults are shown in Figs. S1-S5, and the detailed concentration of the content have been concluded in the Figs. S6 and S7. It can be clearly seen from Figs. S6 and S7 that the amount of V and O decreases as the sul­ furation goes on, while the concentration of sulfur increases. The V/S atomic ratio determined by EDX analysis is around 1.38 (Fig. S4), cor­ responding to a BiVO4@Bi2S3 molar ratio of 4:1 in the BiVO4@Bi2S3 heterostructure. In addition, the average concentration of sulfur is up to 10.25% according to the EDX results. Moreover, we notice that the percentage of S and Bi on the out surface is higher than interior while the O and V is nearly undetected on the out surface, confirmed by the line scanning EDX of BiVO4@Bi2S3 (Fig. S8). The Raman spectra of the 200–1200 cm− 1 region for the sulfuration samples are shown in Fig. 2b. Two typical vibrational peaks at 815 and 133 cm− 1, which can be assigned to the symmetric stretching and translation modes of VO3− 4 units, respectively (Jiang et al., 2016). Bands identified in the 328–370 cm− 1 regions and in the 404–498 cm− 1 re­ gions are assigned to the ʋ2 and ʋ4 bending modes of VO34 (Frost et al., 2006). And it can be clearly seen that the bands intensities at 815 cm− 1 and 344 cm− 1 weaken greatly as the sulfuration goes on, which means the VO34 is partially successfully replaced during this process. In addi­ tion, the red shift of the 815 cm− 1 vibrational peak may due to drastic changes in the electronic band structure caused by strong charge transferred preferential doping which in turn renormalizes the phonon dispersion (Bhalerao et al., 2012) which is the result of S substitution. Here, we can make a conclusion that the S2- is reacted with VO34 from the out most surface to interior of BiVO4 as time goes by. With a suitable reaction period, an optimized BiVO4@Bi2S3 heterojunction structure could form by cosharing the Bi atoms, which will show an enhanced photocatalytic activity. We suggest that the slow substitution is essential to form a coreshell BiVO4@Bi2S3 structure that it is linked by cosharing Bi atoms between BiVO4 and Bi2S3. A typical low resolution transmission electron microscopy (LRTEM) (Fig. 4a and b) and high resolution transmission electron microscopy (HRTEM) (Fig. 4c) images of BiVO4@Bi2S3 show that the BiVO4 core are surrounding by the Bi2S3 petals. The lattice spacing distances of 0.35 nm and 0.56 nm correspond to the (310) plane and (020) plane of Bi2S3 in

Fig. 2. (a) XRD patterns of BiVO4 and the samples during the different sulfu­ rization period. (* stands for the characteristic peaks of BiVO4, ♥ stands for SBiVO4, S-BiVO4-8 is also known as BiVO4@Bi2S3), (b) Raman spectra of sulfu­ ration samples. 4

X. Lian et al.

Journal of Hazardous Materials 406 (2021) 124705

Fig. 3. SEM images of (a) BiVO4, (b) S-BiVO4-4, (c) S-BiVO4-6, (d) S-BiVO4-8, (e) S-BiVO4-10.

Fig. 4. (a, b) Low resolution transmission electron microscopy (LRTEM) and (c, d, e,f) high resolution transmission electron microscopy (HRTEM) of BiVO4@Bi2S3.

the BiVO4@Bi2S3, respectively (Fig. 4d and e) (Paul et al., 2017; Guo et al., 2019; Shi et al., 2018), suggesting that the Bi2S3 is formed on the surface of the BiVO4@Bi2S3. In Fig. 4f, the HRTEM image of BiVO4@­ Bi2S3 exhibits two interplanar spacing of 0.56 nm and 0.36 nm, corre­ sponding to the (020) and (211) planes of hexagonal Bi2S3, respectively. Meanwhile, another interplanar spacing of 0.31 nm is corresponding to the (211) plane of BiVO4, which infers the existence of Bi2S3 phase connected with the atomic BiVO4 layers. To further verify the cosharing of the Bi atoms, we calculated the mismatching factor. As shown in Fig. 5, in the direction perpendicular to the (020) plane, the distance between the two adjacent planes in Bi2S3 is 5.635 Å, which is similar to that of BiVO4 (d = 5.849 Å). Mismatch factor (f = 3.66%) is calculated according to the following formula (Wang et al., 2019):

f = [1–d(Bi2 S3 )/d(BiVO4 )] ∗ 100% .

(3)

The lower mismatch indicates that two planes have lower matched energy, which provide rational condition for the substitution of S for V-O in the lattice, or the epitaxial growth of Bi2S3 on BiVO4 crystal lattice. The XPS survey spectra of the BiVO4 and BiVO4@Bi2S3 are compared in Fig. 6a. The BiVO4 contains only Bi, V and O with sharp photoelectron peaks appearing at binding energies of 158.6 eV (Bi 4f), 516.9 eV (V 2p), 531.2 eV (O 1s). All of those peaks are consistent with the previously reported BiVO4 crystal (Zhou and Yin, 2017; Wang et al., 2017b). The atomic ratios of each elements are plotted in Fig. 5b, we can see that the content of O species is reduced, further confirming the successfully partial substitution of S2- to VO34 . From the high resolution XPS 5

X. Lian et al.

Journal of Hazardous Materials 406 (2021) 124705

nanowire was synthesized by the solvothermal approach, the SEM image and XRD pattern of which is shown in Fig. S12. The physically mixed BiVO4 and Bi2S3 was synthesized in molar ratio of 4:1 according to the EDX result of BiVO4@Bi2S3. However, the physically mixed BiVO4 and Bi2S3 (PM-BiVO4 + Bi2S3) exhibits lower reduction rate, the Cr(VI) so­ lution was reduced in 2 h with 80% Cr(VI) removal rate, which indicates that BiVO4@Bi2S3 heterojunction with atomic level contact exhibits excellent photocatalytic activity and stability as compared to conven­ tional heterojunction counterparts with physical attachment. However, the Bi2S3 nanowire exhibits strong absorbance towards Cr(VI) which has been shown in the Fig. S13. Therefore, we neglect the discussion of the Bi2S3 photocatalyst. Samples with different sulfuration period were also tested in the same reduction process (Figs. S14-S15). Absolutely, S-BiVO4-4 and SBiVO4-6 samples show poor photocatalytic performance than that of SBiVO4-8 (BiVO4@Bi2S3). 40% and 100% reduction rate are obtained on S-BiVO4-4 and S-BiVO4-6 samples with 120 min visible light irradiation (Fig. S14). We should note it that the S-BiVO4-10 also exhibits strong absorption ability of Cr(VI) (Fig. S15), this may due to most of samples turn into Bi2S3 while the sulfuration period lasts for 10 h, and Bi2S3 shows strong absorbance towards Cr(VI) solution (Fig. S13). The influ­ ence of pH values on the reaction was investigated from 1.0 to 6 at in­ terval of 1.0 on 35 mg coreshell BiVO4@Bi2S3 heterojunction, and conducted in the same procedure (Fig. S16). It can be clearly seen that the removal efficiency of Cr(VI) is the highest at pH = 2.0. The detail statements are shown in Supporting information. Brunauer-Emmett-Teller (BET) surface area test was performed, as shown in Table S1. Compared to pure BiVO4 (surface area = 4.51 m2 g− 1), sulfuration samples displayed a higher surface area with sulfu­ ration progress goes on, suggesting that the sulfuration process facili­ tated the enhanced reaction area, which is in highly accordance with the adsorption results in darkness. When the sulfuration duration goes up to 10 h, the BET surface goes up to 68.9 m2 g− 1, and the S-BiVO4-10 ex­ hibits the strongest adsorption ability. In conclusion, sulfuration process has impact on the BiVO4 precursor, and the sulfuration process enhanced the available reaction area. To study the photocatalytic reduction kinetics, the photo-catalytic Cr (VI) reduction rate on BiVO4 and BiVO4@Bi2S3 catalysts are investigated by the pseudo first-order kinetic (Fig. 7b and c). The rate constants are calculated by the following equation (Kang et al., 2017):

Fig. 5. Matching planes of the BiVO4 and Bi2S3.

spectrum (Fig. 6c and d), it can be seen that the signal of O 1s and V 2p spectrum of BiVO4 is centered at 531.2 eV and 516.9 eV, respectively (Wang et al., 2017c). For the BiVO4@Bi2S3, both peaks of O 1s and V 2p become weaker and occur a slight shift, which further confirms the partial substitution of the VO34 following the Eq. (2). The characteristic peaks of the Bi 4f 7/2 and Bi 4f 5/2 of the BiVO4 are observed at approximately 159.3 eV and 164.5 eV (Fig. 6e) (Zhou and Yin, 2017; Wang et al., 2017b; Liu et al., 2017). The Bi 4f 7/2 and Bi 4f 5/2 of Bi2S3 appear at 158.3 eV and 163.6 eV (Chai et al., 2019). However, the binding energies of Bi 4f of BiVO4@Bi2S3 shift to 158.6 eV and 164.0 eV, which lay between the value of pure BiVO4 and Bi2S3. Moreover, there are two weak and broad peaks appeared at 161.4 eV, 163.0 eV in the BiVO4@Bi2S3, which are assigned to the binding energy of S 2p (Fig. 6f). Together, these results strongly demonstrate the formation of S‒Bi‒V bond (Wang et al., 2017c). Based on the analyses above, we can conclude that sulfur is suc­ cessful partially replaced some VO34 and form a BiVO4@Bi2S3 hetero­ junction with atomic-level contact by cosharing the Bi atoms. The BiVO4@Bi2S3 heterojunction constructed here by cosharing Bi atoms, which will further alter the photoelectrochemical properties and pho­ tocatalytic performance of BiVO4@Bi2S3 heterojunction.

ln(Ct/C0) = − kappt

(4)

where Ct is the concentration of pollutants at the time of t (mg/L), C0 is the initial concentration of the pollutants (mg/L) and kapp is the apparent pseudo first-order rate constant. As result, the photocatalytic reduction rate of BiVO4@Bi2S3 (kapp = 0.071 min-1) heterojunction is 35.5 times higher than that of BiVO4 (kapp = 0.002 min-1). It should be emphasized that the BiVO4@Bi2S3 (S-BiVO4-8) hetero­ junction demonstrates the best photocatalytic performance toward reduction of Cr(VI) in our system. Importantly, the photocatalytic per­ formance of Cr(VI) reduction without noticeable deactivation can be observed after 5 cycles (Fig. 7d), which confirms that BiVO4@Bi2S3 photocatalyst is configurable stable during the photo-catalytic process. The photocatalytic reduction rate of BiVO4@Bi2S3 is kapp = 0.070 min− 1 after one cycle (Fig. S17), which is nearly the same as the first cycle value and further confirms that BiVO4@Bi2S3 is quite stable and efficient during photocatalytic reaction. The photocatalytic activity achieved here is not only beyond to currently reported BiVO4-based photocatalysts but also other types of porous photocatalysts reported before (Table S2). It is well known that pure BiVO4 photocatalyst shows very poor photoactivity because of its limited light harvesting ability, higher activation of carrier transport and quick recombination rate of photo-generated electrons and holes pairs. The promoted photocatalytic performance on BiVO4@Bi2S3 hetero­ junction should be discussed on these three aspects.

3.2. Photocatalytic performance Aiming to confirm the advantages of the BiVO4@Bi2S3 hetero­ junction with atomic level contact, photocatalytic reduction of Cr(VI) was used as a probe reaction to investigate the photocatalytic perfor­ mance. The XRD and SEM results of Bi are shown in Fig. S9 and Fig. S10, respectively. BiVO4, Bi, and physically mixed BiVO4 and Bi2S3 are conducted as the parallel experiments and the results were shown in Fig. 7a. All samples with different sulfurization period were also tested to explore the optimism one. The concentration of Cr(VI) was measured by DPC method. In the case wherein the absorbance of different con­ centration Cr(VI) were measured (Fig. S11). All of the reactions have a good linearity, indicating that visible-light-driven photo-reduction of Cr (VI) solutions in the presence of the photo-catalysts followed the firstorder kinetics. The Cr(VI) concentration remain almost unchanged after photo­ catalytic reduction process under BiVO4 and Bi photocatalysts (Fig. 7a). On the contrary, it can be clearly seen that even at such high concen­ tration of Cr(VI) solution, the BiVO4@Bi2S3 only needs less than 40 min to completely reduce Cr(VI). To further compare the heterojunction with atomic level with the traditional one with physical attachment, Bi2S3 6

X. Lian et al.

Journal of Hazardous Materials 406 (2021) 124705

Fig. 6. XPS of (a) full spectra, (b) atomic ratio, high resolution spectra of (c) O 1s, (d) V 2p and (e) Bi 4f, (f) S 2p of BiVO4 and BiVO4@Bi2S3.

7

X. Lian et al.

Journal of Hazardous Materials 406 (2021) 124705

Fig. 7. (a) Photocatalytic reduction of 50 ppm Cr(VI) solution over BiVO4, BiVO4@Bi2S3, Bi and physically mixed BiVO4 and Bi2S3 (PM-BiVO4 + Bi2S3), (b) linear fit of the degradation rate constants based on pseudo-first order kinetics over (b) BiVO4@Bi2S3 and (c) BiVO4, (d) Cycling of photocatalytic Cr(VI) reduction of BiVO4@Bi2S3.

3.3. Photochemical properties

The photoluminescence (PL) emission spectrum is commonly used technique to evaluate the extent of transfer and separation, as well as the trapping of charge carriers, within an activated semiconductor photo­ catalyst. The transfer behavior of the photoinduced electron and hole pairs was investigated because the recombination of the free charges contributes significantly to emission signals of the PL spectra. As depicted in (Fig. 8c), the pure BiVO4 exhibits higher peak intensities at a wavelength of around 691 nm, which can be attributed to the band gap recombination of electron-hole pairs. However, the peak intensities of BiVO4@Bi2S3 are weaker, suggesting that the recombination rate of photo-generated electrons and holes are suppressed owing to the faster separation rate on BiVO4@Bi2S3 semiconductors. The fluorescence lifetime of BiVO4 and BiVO4@Bi2S3 is also exam­ ined by recording time-resolved PL (TRPL) decay spectra. Generally, a longer fluorescence lifetime means that the photo-generated carriers is stabilized for a longer time until a redox reaction happens. The decay exponentially spectra are shown in Fig. 8d. To quantitatively calculate the TRPL lifetimes of two samples, the TRPL decay curves are fitted by the following equation (Zhang et al., 2015; Niu et al., 2012): { t} { t} Fit = A + B1exp − + B2exp − (6) τ1 τ2

The optical absorption properties of BiVO4 and BiVO4@Bi2S3 sam­ ples were determined by UV–vis diffuse reflectance spectra (DRS). As illustrated in Fig. 8a, the BiVO4 only presents absorption edge about 530 nm. It can be clearly seen that BiVO4@Bi2S3 has a notable enhanced optical absorption in visible light regions (beyond 1007 nm), which can be verified by the changed color from yellow to black (Fig. S18). The transformed Kubelka-Munk function is used to determine the bandgaps of BiVO4 and BiVO4@Bi2S3, as shown in Fig. 8b. According to the Tauc equation (Pan et al., 2011), values of n equal to 1/2 and 2 are indicative of indirect and direct transitions, respectively. It has been proved that m-BiVO4 is an indirect bandgap semiconductor as identified by resonant inelastic X-ray scattering method (Zhao et al., 2011; Cooper et al., 2014). Therefore, the value of n was 1/2 in the case of BiVO4. ) ( (5) (αhv)n = A hv − Eg The Eg values of BiVO4 and BiVO4@Bi2S3 are 2.30 eV and 1.25 eV, respectively. The BiVO4@Bi2S3 shows narrow band gap, which indicates that constructing heterojunction between BiVO4 and Bi2S3 changes the absorption ability and modifies the electronic structures of BiVO4@Bi2S3. 8

X. Lian et al.

Journal of Hazardous Materials 406 (2021) 124705

Fig. 8. (a) UV–vis DRS spectra, (b) corresponding Kubelka-Munk transformed reflectance spectra, (c) PL spectra, (d) TRPL decay lifetime spectra, (e) the photo­ current density and (f) EIS of BiVO4 and BiVO4@Bi2S3.

9

X. Lian et al.

Journal of Hazardous Materials 406 (2021) 124705

represents a better ability to transfer the charge carriers (Bai et al., 2012; He et al., 2019) to the targeted reactive sites compared to that of pristine BiVO4 (Fig. 8f). Together, these results demonstrate well that both the light-harvesting capability and charge separation efficiency are enhanced because of the introduction of atomic-level contact in the BiVO4@Bi2S3 photocatalyst. Thus, the separation and transfer rate of photo-induced electron-hole pairs are more efficient in the case of BiVO4@Bi2S3, which contributes to the best photocatalytic reduction activity. To further determine the intrinsic carrier transport activation energy (CTAE), the in situ impedance spectra of BiVO4 and BiVO4@Bi2S3 were carried out at temperatures ranging from 50 to 150 ℃ in air condition. Fig. 9 shows the typical imaginary versus real impedance. The linear plots in Fig. 10 indicate that the charge carrier transport followed the Arrhenius equation (He et al., 2019), namely ) ( A − Ea σ = exp T (8) T kB

where A, B1, and B2 are constants and obtained after fitting corre­ sponding decay curve. Radiative lifetimes (τ1, τ2) are given by decon­ volution of the fluorescence decay spectra. According to the above fitting data, the intensity-average fluorescence lifetimes (τ) are calcu­ lated by the following equation:

τ=

B1 τ21 + B2 τ22 B1 τ1 + B2 τ2

(7)

The intensity-average PL lifetimes results (shown in Table S3) sug­ gest that BiVO4@Bi2S3 exhibits longer lifetimes (5.059 ns with 6.14%) than that of BiVO4 (4.712 ns with 5.45%). Thus, this also suggests that BiVO4@Bi2S3 heterojunction can effectively restrain the recombination of photo-generated charge carriers, which delivers a longer lifetime of carriers. These results indicate that photo-excited electrons and holes are easily separated during the transfer process, thereby improving quan­ tum efficiency greatly and thus enhancing the photo-catalytic activity (Bai et al., 2013), which can be confirmed by the enhanced photocurrent density of BiVO4@Bi2S3. A comparison of the photo-current density versus time curves of the photo-catalysts under visible light irradiation (> 420 nm) are displayed in Fig. 8e. The photocurrent density for BiVO4@Bi2S3 (0.89 μA/cm2) is 11 times higher than that of BiVO4 (0.08 μA/cm2). Additionally, the smaller arc radius of the BiVO4@Bi2S3

Detailed calculation processes of the CTAE are discussed below. Firstly, the conductivity (σ) is calculated by σ = L/RS, where R can be obtained by AC impedance. The “L” and “S” represent the thickness and section area of the disc, respectively. The KB = 1.381 × 10− 23 J⋅K− 1. 1 eV = 1.602 × 10− 19 J. Take the ln(σT) as Y-axis, 1000/T as X-axis,

Fig. 9. Arrhenius conductivity of (a) S-BiVO4-2, (b) S-BiVO4-4, (c) S-BiVO4-6, (d) S-BiVO4-8. 10

X. Lian et al.

Journal of Hazardous Materials 406 (2021) 124705

Fig. 10. The impedance plots of (a) S-BiVO4-2, (b) S-BiVO4-4, (c) S-BiVO4-6, (d) S-BiVO4-8.

Kslope is the slope of the plot line according to the Eq. (7), then we can obtain: ln(σT) = ln(A) + ( − Ea /kB T)

contact results in the formation of a synergistic heterojunction be­ tween the two semiconductor interphases which facilitates migration of charge carriers and reduces the probability of charge recombination.

(9)

Therefore, the Ea (eV) = − 0.0862 Kslope is obtained. Secondly, ac­ cording to the conductive mechanism of “small polaron”, the relation­ ship between conductivity (σ) and temperature (T) can be expressed as Arrhenius equation. We first compare the real impedance plots of SBiVO4-8 (which is also denoted as BiVO4@Bi2S3) and BiVO4 at different temperatures. However, it is clearly shown that the arc radius of BiVO4 is too large to measure under our experimental conditions, and ac­ cording to the Eqs. (5) and (6), it can be observed that the CTAE of BiVO4 (Fig. S19) is much larger than BiVO4@Bi2S3 (S-BiVO4-8, Fig. 9d). In order to verify that engineering heterojunction by cosharing Bi atoms could indeed decrease the CTAE and gain insights of this process, we further compared the CTAE of the S-BiVO4-2 (Fig. 9a), S-BiVO4-4 (Fig. 9b), S-BiVO4-6 (Fig. 9c), S-BiVO4-8 (BiVO4@Bi2S3) (Fig. 9d). Ac­ cording to the slope value of the fitting results (Fig. 10), the CTAE values of S-BiVO4-8 (BiVO4@Bi2S3), S-BiVO4-6, S-BiVO4-4 and S-BiVO4-2 are 0.261, 0.371, 0.384 and 0.696 eV, respectively, which indicates that the charge carrier on BiVO4@Bi2S3 could easily separate. Thus, on the basis of the above results, we can conclude that the successful hybridization of the BiVO4 and Bi2S3 with atomic-level

3.4. Mechanism studies The photocatalyst’s band alignment structure is very important to photocatalytic process. To explore the potential photocatalytic mecha­ nism on BiVO4@Bi2S3, it is very necessary to calculate the band energy structure of BiVO4, BiVO4@Bi2S3, and Bi2S3 semiconductors respec­ tively. The valence band maximum (VBM) of BiVO4 (2.75 eV) and BiVO4@Bi2S3 (1.75 eV) are calculated obtained from the intercept of the extrapolated linear part of the curve with the energy axis in the XPS VB spectra (Fig. S20). The conduction band edge (ECB) and valence band edge (EVB) of a semiconductor could be acquired by the following formulas (Huang et al., 2014, 2015): ECB = X − Ee − 0.5Eg

(10)

EVB = ECB + Eg

(11)

The X for BiVO4 and Bi2S3 can be figured out to be 6.11 eV (Zou et al., 2017) and 5.28 eV (Weng et al., 2015), respectively. The bandgap for 11

X. Lian et al.

Journal of Hazardous Materials 406 (2021) 124705

BiVO4 according to UV–vis (Fig. 8b) is 2.30 eV. And the bandgap is 1.30 eV for Bi2S3 (Wang et al., 2017b). We can calculate that the ECB of BiVO4 and Bi2S3 are 0.44 and 0.13 eV, respectively. Pure Bi2S3 and BiVO4 have the nested band structure before contact, which cannot effectively facilitate separation of photogenerated e--h+ pairs. With the construction of heterojunction by cosharing Bi atoms, the Bi2S3 are assembled on BiVO4 surface to construct the n–n heterojunction. The energy levels of BiVO4 shift upward, whereas the energy band of Bi2S3 shifts downward until the EF of Bi2S3 and BiVO4 reaches an equilibrium. Consequently, the VB and CB energy level of the BiVO4@Bi2S3 are be­ tween the value of the BiVO4 and Bi2S3, which is consistence with the XPS-VB results. As shown in Scheme 2, the excited e− in the CB of Bi2S3 can easily migrate to that of BiVO4. The internal electric field also improves the migration of photo-generated electrons and holes. Considering that the oxidation potential of H2O to⋅OH radicals is 2.27 eV, it is obvious that the energy levels of the holes on the valance band of BiVO4 (EVB = 2.75 eV) is positive enough to oxidize the H2O to form⋅OH radical. But this oxidation process cannot happen in the VB of Bi2S3 (EVB = 1.42 eV). However, the BiVO4@Bi2S3 shows no photocatalytic activity for RhB degradation compared to BiVO4 (Fig. S21), while BiVO4 degraded 40% 10 mg/L RhB within 60 min, which means that the holes on BiVO4 is transferred to Bi2S3 in BiVO4@Bi2S3. Coupling Bi2S3 with BiVO4 at atomic levels offers an interesting approach to achieving better charge separation and thus improving the overall performance of the photocatalytic system. Type II band align­ ment in these two semiconductor systems spontaneously allows photoexcited electrons from the CB of Bi2S3 to be transferred into CB of BiVO4, whereas the photogenerated holes transfer from BiVO4 to Bi2S3, restraining the recombination of photoinduced electron-hole pairs. That is to say, the enhanced photoactivity of BiVO4 after coupling Bi2S3 with atomic level is based on the enhanced electron mobility of the hetero­ junction. In situ impedance spectrum experiments confirm that the CTAE of BiVO4@Bi2S3 is reduced, which implies that the charge carrier of BiVO4@Bi2S3 transfer more easily. Thus, the decreased CTAE on BiVO4@Bi2S3 could further promote the photogenerated electrons transportation. As a result, the n-n junction in the BiVO4@Bi2S3 core/ shell heterostructure promotes the separation of photo-generated elec­ tron/hole pairs and reduces recombination of electron/hole pairs thus improves the photocatalytic activity.

exhibits superior photocurrent response and photocatalytic reduction of Cr(VI) under visible light illumination which beyond currently reported photocatalysts. Cosharing similar atoms between two inorganic semi­ conductors is identified as an effective strategy to construct hetero­ junction that can boost the photocatalytic performance. This work will shed light on further exploration for traditional inorganic heteronanostructures with high potential for photocatalytic applications. Supporting information Additional information includes SEM images, EDS data and the line scanning EDX of BiVO@Bi2S3, EDX of all sulfuration samples, the atomic ratio of the samples according to the EDX results, the percentage of Bi2S3 of the samples according to the EDX results, the absorbance over different concentration of Cr(VI) using DPC method and corresponding linear fitting of the concentration versus absorbance, SEM image and XRD pattern of Bi2S3 nanowire, photocatalytic Cr(VI) reduction over SBiVO4-4 and S-BiVO4-6, Cr(VI) absorption over S-BiVO4-10, the photo­ graph of the samples, the photocatalytic reduction of RhB degradation over BiVO4 and BiVO4@Bi2S3, the XPS-VB spectra, the TRPL decay, and the detailed table in comparison with other photocatalysts in Cr(VI) reduction. Author contributions X. Y. Lian, Z. Chen, W. P. Fang and X. D. Yi conceived the research grants and discussed the study. X. Y. Lian fabricated the samples, per­ formed XRD, SEM, TEM, EDS, PL, UV–VIS, CTAE, EIS experiments and measured the catalytic performance. J. G. Zhang carried out the photocurrent, XRD and calculated the mismatching factor. Y. Zhang and Y. P. Zhang fabricated the precursor and carried out the BET experiment. S. L. Yang carried out the XPS experiment. X. Y. Lian, Z. Chen and X. D. Yi wrote the manuscript. Y. Y. Dong, W. P. Fang and X.D. Yi discussed the manuscript. All authors discussed the results and commented on the manuscript. CRediT authorship contribution statement Xinyi Lian: Conceptualization; Data curation; Formal analysis; Investigation; Methodology; Validation; Roles/Writing – original draft. Jiguang Zhang: Methodology/Validation. Yue Zhan: Methodology. Yanping Zhang: Methodology. Shuangli Yang: Methodology. Zhou Chen: Conceptualization; Project administration; Writing - review & editing. Yunyun Dong: Conceptualization. Weiping Fang: Conceptu­ alization; Project administration; Supervision. Xiaodong Yi: Concep­ tualization; Project administration; Supervision, Writing - review & editing.

4. Conclusion In summary, a benign sulfurization strategy is proposed here to en­ gineer heterojunction with an atomic-level contact between two semi­ conductors to enhance the photocatalyst’s efficiency. This new concept solves the intrinsic obstacles on constructing heterojunction by tradi­ tional method. Cosharing the same atoms could lower the coulomb electrostatic repulsive force, which enables the acceleration of separa­ tion rate of photoinduced electrons and holes and lower carrier transport activation energy during photocatalytic process. The sulfurization period is found to play a pivotal role for constructing BiVO4@Bi2S3 heterojunction. Interestingly, the obtained BiVO4@Bi2S3 heterojunction

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgment This work is supported by the National Natural Science Foundation of China (No. 21773194) and the Natural Science Foundation of Shan­ dong Province (ZR2019PB007). Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at doi:10.1016/j.jhazmat.2020.124705.

Scheme 2. The mechanism of the electron migrations of the BiVO4@Bi2S3. 12

X. Lian et al.

Journal of Hazardous Materials 406 (2021) 124705

References

Linsebigler, A.L., Lu, G., Yates, J.T., 1995. Photocatalysis on TiO2 surfaces: principles, mechanisms, and selected results. Chem. Rev. 95, 735–758. Liu, T., Tan, G., Zhao, C., Xu, C., Su, Y., Wang, Y., Ren, H., Xia, A., Shao, D., Yan, S., 2017. Enhanced photocatalytic mechanism of the Nd-Er co-doped tetragonal BiVO4 photocatalysts. Appl. Catal. B Environ. 213, 87–96. Low, J., Yu, J., Jaroniec, M., Wageh, S., Al-Ghamdi, A.A., 2017. Heterojunction photocatalysts. Adv. Mater. 29, 1601694. Ma, D.-K., Guan, M.-L., Liu, S.-S., Zhang, Y.-Q., Zhang, C.-W., He, Y.-X., Huang, S.-M., 2012. Controlled synthesis of olive-shaped Bi2S3/BiVO4 microspheres through a limited chemical conversion route and enhanced visible-light-responding photocatalytic activity. Dalton Trans. 41, 5581–5586. Ma, X.-C., Dai, Y., Yu, L., Huang, B.-B., 2016. Energy transfer in plasmonic photocatalytic composites. Light Sci. Appl. 5, e16017, 16017-16017. Nagarjuna, R., Challagulla, S., Sahu, P., Roy, S., Ganesan, R., 2017. Polymerizable sol–gel synthesis of nano-crystalline WO 3 and its photocatalytic Cr(VI) reduction under visible light. Adv. Powder Technol. 28, 3265–3273. Nagarjuna, R., Challagulla, S., Ganesan, R., Roy, S., 2017. High rates of Cr(VI) photoreduction with magnetically recoverable nano-Fe 3 O 4 @Fe 2 O 3 /Al 2 O 3 catalyst under visible light. Chem. Eng. J. 308, 59–66. Niu, P., Liu, G., Cheng, H.-M., 2012. Nitrogen vacancy-promoted photocatalytic activity of graphitic carbon nitride. J. Phys. Chem. C. 116, 11013–11018. Pan, C., Li, D., Ma, X., Chen, Y., Zhu, Y., 2011. Effects of distortion of PO4 tetrahedron on the photocatalytic performances of BiPO4. Catal. Sci. Technol. 1, 1399–1405. Paul, S., Ghosh, S., Barman, D., De, S.K., 2017. Maximization of photocatalytic activity of Bi2S3/TiO2/Au ternary heterostructures by proper epitaxy formation and plasmonic sensitization. Appl. Catal. B Environ. 219, 287–300. Roy, B., Chakraborty, B.R., Bhattacharya, R., Dutta, A.K., 1978. Electrical and magnetic properties of antimony sulphide (Sb2S3) crystals and the mechanism of carrier transport in it. Solid State Commun. 25, 937–940. Shi, Y., Xiong, X., Ding, S., Liu, X., Jiang, Q., Hu, J., 2018. In-situ topotactic synthesis and photocatalytic activity of plate-like BiOCl/2D networks Bi2S3 heterostructures. Appl. Catal. B Environ. 220, 570–580. Shraavan, S., Challagulla, S., Banerjee, S., Roy, S., 2017. Unusual photoluminescence of Cu–ZnO and its correlation with photocatalytic reduction of Cr(VI. Bull. Mater. Sci. 40, 1415–1420. Su, J., Guo, L., Bao, N., Grimes, C.A., 2011. Nanostructured WO3/BiVO4 heterojunction films for efficient photoelectrochemical water splitting. Nano Lett. 11, 1928–1933. Su, R., Tiruvalam, R., Logsdail, A.J., He, Q., Downing, C.A., Jensen, M.T., Dimitratos, N., Kesavan, L., Wells, P.P., Bechstein, R., Jensen, H.H., Wendt, S., Catlow, C.R.A., Kiely, C.J., Hutchings, G.J., Besenbacher, F., 2014. Designer titania-supported Au–Pd nanoparticles for efficient photocatalytic hydrogen production. ACS Nano 8, 3490–3497. Tang, L., Lv, Z.-Q., Xue, Y.-C., Xu, L., Qiu, W.-H., Zheng, C.-M., Chen, W.-Q., Wu, M.-h, 2019. MIL-53(Fe) incorporated in the lamellar BiOBr: promoting the visible-light catalytic capability on the degradation of rhodamine B and carbamazepine. Chem. Eng. J. 374, 975–982. Wan, Z., Zhang, G., Wu, X., Yin, S., 2017. Novel visible-light-driven Z-scheme Bi12GeO20/g-C3N4 photocatalyst: oxygen-induced pathway of organic pollutants degradation and proton assisted electron transfer mechanism of Cr(VI) reduction. Appl. Catal. B Environ. 207, 17–26. Wang, H., Qian, C., Liu, J., Zeng, Y., Wang, D., Zhou, W., Gu, L., Wu, H., Liu, G., Zhao, Y., 2020. Integrating suitable linkage of covalent organic frameworks into covalently bridged inorganic/organic hybrids toward efficient photocatalysis. J. Am. Chem. Soc. 142, 4862–4871. Wang, J., Jin, J., Wang, X., Yang, S., Zhao, Y., Wu, Y., Dong, S., Sun, J., Sun, J., 2017b. Facile fabrication of novel BiVO4/Bi2S3/MoS2 n-p heterojunction with enhanced photocatalytic activities towards pollutant degradation under natural sunlight. J. Colloid Interface Sci. 505, 805–815. Wang, L., Yang, G., Peng, S., Wang, J., Ji, D., Yan, W., Ramakrishna, S., 2017c. Fabrication of MgTiO3 nanofibers by electrospinning and their photocatalytic water splitting activity. Int. J. Hydrog. Energy 42, 25882–25890. Wang, S., Chen, P., Yun, J.-H., Hu, Y., Wang, L., 2017a. An Electrochemically treated BiVO4 photoanode for efficient photoelectrochemical water splitting. Angew. Chem. Int. Ed. 56, 8500–8504. Wang, X.-D., Huang, Y.-H., Liao, J.-F., Jiang, Y., Zhou, L., Zhang, X.-Y., Chen, H.-Y., Kuang, D.-B., 2019. In Situ construction of a Cs2SnI6 perovskite nanocrystal/SnS2 nanosheet heterojunction with boosted interfacial charge transfer. J. Am. Chem. Soc. 141, 13434–13441. Wei, S., Wang, Q., Zhu, J., Sun, L., Lin, H., Guo, Z., 2011. Multifunctional composite core–shell nanoparticles. Nanoscale 3, 4474–4502. Wen, X.-J., Shen, C.-H., Fei, Z.-H., Fang, D., Liu, Z.-T., Dai, J.-T., Niu, C.-G., 2020. Recent developments on AgI based heterojunction photocatalytic systems in photocatalytic application. Chem. Eng. J. 383, 123083. 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. Whittaker-Brooks, L., Gao, J., Hailey, A.K., Thomas, C.R., Yao, N., Loo, Y.-L., 2015. Bi2S3 nanowire networks as electron acceptor layers in solution-processed hybrid solar cells. J. Mater. Chem. C. 3, 2686–2692. Wu, Z., Liang, Y., Yuan, X., Zou, D., Fang, J., Jiang, L., zhang, J., Yang, H., Xiao, Z., 2020. MXene Ti3C2 derived Z–scheme photocatalyst of graphene layers anchored TiO2/ g–C3N4 for visible light photocatalytic degradation of refractory organic pollutants. Chem. Eng. J. 394, 124921. Xie, Q., Zhou, H., Lv, Z., Liu, H., Guo, H., 2017. Sn4+ self-doped hollow cubic SnS as an efficient visible-light photocatalyst for Cr(vi) reduction and detoxification of cyanide. J. Mater. Chem. A 5, 6299–6309.

Ashokkumar, M., Madhavan, J., Malathi, M., Arunachalam, P., 2018. A review on BiVO4 photocatalyst: activity enhancement methods for solar photocatalytic applications. Appl. Catal. A Gen. 555, 47–74. Bai, X., Wang, L., Zhu, Y., 2012. Visible photocatalytic activity enhancement of ZnWO4 by graphene hybridization. ACS Catal. 2, 2769–2778. Bai, X., Wang, L., Zong, R., Lv, Y., Sun, Y., Zhu, Y., 2013. Performance enhancement of ZnO photocatalyst via synergic effect of surface oxygen defect and graphene hybridization. Langmuir 29, 3097–3105. Bhalerao, G.M., Singh, M.K., Sinha, A.K., Ghosh, H., 2012. Optical redshift in the Raman scattering spectra of Fe-doped multiwalled carbon nanotubes: experiment and theory. Phys. Rev. B 86, 125419. Chai, W., Yang, F., Yin, W., You, S., Wang, K., Ye, W., Rui, Y., Tang, B., 2019. Bi2S3/C nanorods as efficient anode materials for lithium-ion batteries. Dalton Trans. 48, 1906–1914. Challagulla, S., Nagarjuna, R., Ganesan, R., Roy, S., 2016. Acrylate-based polymerizable Sol–Gel synthesis of magnetically recoverable TiO2 supported Fe3O4 for Cr(VI) photoreduction in aerobic atmosphere. ACS Sustain. Chem. Eng. 4, 974–982. Chen, F., Yang, Q., Zhong, Y., An, H., Zhao, J., Xie, T., Xu, Q., Li, X., Wang, D., Zeng, G., 2016a. Photo-reduction of bromate in drinking water by metallic Ag and reduced graphene oxide (RGO) jointly modified BiVO4 under visible light irradiation. Water Res. 101, 555–563. Chen, F., Yang, Q., Sun, J., Yao, F., Wang, S., Wang, Y., Wang, X., Li, X., Niu, C., Wang, D., Zeng, G., 2016b. Enhanced photocatalytic degradation of tetracycline by AgI/BiVO4 heterojunction under visible-light irradiation: mineralization efficiency and mechanism. ACS Appl. Mater. Interfaces 8, 32887–32900. Chen, F., Yang, Q., Li, X., Zeng, G., Wang, D., Niu, C., Zhao, J., An, H., Xie, T., Deng, Y., 2017. Hierarchical assembly of graphene-bridged Ag3PO4/Ag/BiVO4 (040) Zscheme photocatalyst: an efficient, sustainable and heterogeneous catalyst with enhanced visible-light photoactivity towards tetracycline degradation under visible light irradiation. Appl. Catal. B Environ. 200, 330–342. Chen, L., Ren, J.-T., Yuan, Z.-Y., 2020. Atomic heterojunction-induced electron interaction in P-doped g-C3N4 nanosheets supported V-based nanocomposites for enhanced oxidative desulfurization. Chem. Eng. J. 387, 124164. Cooper, J.K., Gul, S., Toma, F.M., Chen, L., Glans, P.-A., Guo, J., Ager, J.W., Yano, J., Sharp, I.D., 2014. Electronic structure of monoclinic BiVO4. Chem. Mater. 26, 5365–5373. Frost, R.L., Henry, D.A., Weier, M.L., Martens, W., 2006. Raman spectroscopy of three polymorphs of BiVO4: clinobisvanite, dreyerite and pucherite, with comparisons to (VO4)3- bearing minerals: namibite, pottsite and schumacherite. J. Raman Spectrosc. 37, 722–732. Fu, J., Xu, Q., Low, J., Jiang, C., Yu, J., 2019. Ultrathin 2D/2D WO3/g-C3N4 step-scheme H2-production photocatalyst. Appl. Catal. B Environ. 243, 556–565. Gao, X., Wu, H.B., Zheng, L., Zhong, Y., Hu, Y., Lou, X.W., 2014. Formation of mesoporous heterostructured BiVO4/Bi2S3 hollow discoids with enhanced photoactivity. Angew. Chem. Int. Ed. 53, 5917–5921. Guo, Y., Ao, Y., Wang, P., Wang, C., 2019. Mediator-free direct dual-Z-scheme Bi2S3/ BiVO4/MgIn2S4 composite photocatalysts with enhanced visible-light-driven performance towards carbamazepine degradation. Appl. Catal. B Environ. 254, 479–490. He, Y., Rao, H., Song, K., Li, J., Yu, Y., Lou, Y., Li, C., Han, Y., Shi, Z., Feng, S., 2019. 3D hierarchical ZnIn2S4 nanosheets with Rich Zn vacancies boosting photocatalytic CO2 reduction. Adv. Funct. Mater. 29, 1905153. Huang, H., He, Y., He, R., Jiang, X., Lin, Z., Zhang, Y., Wang, S., 2014. Novel Bi-based iodate photocatalysts with high photocatalytic activity. Inorg. Chem. Commun. 40, 215–219. Huang, H., He, Y., Du, X., Chu, P.K., Zhang, Y., 2015. A general and facile approach to heterostructured core/shell BiVO4/BiOI p–n junction: room-temperature in situ assembly and highly boosted visible-light photocatalysis. ACS Sustain. Chem. Eng. 3, 3262–3273. Huo, X., Yang, Y., Niu, Q., Zhu, Y., Zeng, G., Lai, C., Yi, H., Li, M., An, Z., Huang, D., Fu, Y., Li, B., Li, L., Zhang, M., 2021. A direct Z-scheme oxygen vacant BWO/oxygenenriched graphitic carbon nitride polymer heterojunction with enhanced photocatalytic activity. Chem. Eng. J. 403, 126363. Jia, X., Han, Q., Liu, H., Li, S., Bi, H., 2020. A dual strategy to construct flowerlike Sscheme BiOBr/BiOAc1− Br heterojunction with enhanced visible-light photocatalytic activity. Chem. Eng. J. 399, 125701. Jiang, Z., Liu, Y., Jing, T., Huang, B., Zhang, X., Qin, X., Dai, Y., Whangbo, M.-H., 2016. Enhancing the photocatalytic activity of BiVO4 for oxygen evolution by ce doping: Ce3+ ions as hole traps. J. Phys. Chem. C. 120, 2058–2063. Kang, S., Zhang, L., Yin, C., Li, Y., Cui, L., Wang, Y., 2017. Fast flash frozen synthesis of holey few-layer g-C3N4 with high enhancement of photocatalytic reactive oxygen species evolution under visible light irradiation. Appl. Catal. B Environ. 211, 266–274. Kim, T.W., Choi, K.-S., 2014. Nanoporous BiVO4 photoanodes with dual-layer oxygen evolution catalysts for solar water splitting. Science 343, 990–994. Kudo, A., Miseki, Y., 2009. Heterogeneous photocatalyst materials for water splitting. Chem. Soc. Rev. 38, 253–278. Li, L., Yu, X., Xu, L., Zhao, Y., 2020. Fabrication of a novel type visible-light-driven heterojunction photocatalyst: Metal-porphyrinic metal organic framework coupled with PW12/TiO2. Chem. Eng. J. 386, 123955. Lin, X., Guo, X., Shi, W., Zhao, L., Yan, Y., Wang, Q., 2015. Ternary heterostructured Ag–BiVO4/InVO4 composites: synthesis and enhanced visible-light-driven photocatalytic activity. J. Alloy. Compd. 635, 256–264.

13

X. Lian et al.

Journal of Hazardous Materials 406 (2021) 124705

Xiong, T., Wen, M., Dong, F., Yu, J., Han, L., Lei, B., Zhang, Y., Tang, X., Zang, Z., 2016. Three dimensional Z-scheme (BiO)2CO3/MoS2 with enhanced visible light photocatalytic NO removal. Appl. Catal. B Environ. 199, 87–95. Xu, Q., Zhang, L., Yu, J., Wageh, S., Al-Ghamdi, A.A., Jaroniec, M., 2018. Direct Zscheme photocatalysts: principles, synthesis, and applications. Mater. Today 21, 1042–1063. Yang, L., Zhang, L., Xu, G., Ma, X., Wang, W., Song, H., Jia, D., 2018. Metal–organicframework-derived hollow CoSx@MoS2 microcubes as superior bifunctional electrocatalysts for hydrogen evolution and oxygen evolution reactions. ACS Sustain. Chem. Eng. 6, 12961–12968. Yu, H., Jiang, L., Wang, H., Huang, B., Yuan, X., Huang, J., Zhang, J., Zeng, G., 2019. Modulation of Bi2MoO6-based materials for photocatalytic water splitting and environmental application: a critical review. Small 15, 1901008. Zhan, W., Yuan, Y., Yang, B., Jia, F., Song, S., 2020. Construction of MoS2 nanoheterojunction via ZnS doping for enhancing in-situ photocatalytic reduction of gold thiosulfate complex. Chem. Eng. J. 394, 124866. Zhang, G., Chen, D., Li, N., Xu, Q., Li, H., He, J., Lu, J., 2018. Preparation of ZnIn2S4 nanosheet-coated CdS nanorod heterostructures for efficient photocatalytic reduction of Cr(VI). Appl. Catal. B Environ. 232, 164–174. Zhang, X., Peng, T., Yu, L., Li, R., Li, Q., Li, Z., 2015. Visible/near-infrared-light-induced H2 production over g-C3N4 Co-sensitized by organic dye and zinc phthalocyanine derivative. ACS Catal. 5, 504–510.

Zhang, X., Zhang, P., Wang, L., Gao, H., Zhao, J., Liang, C., Hu, J., Shao, G., 2016. Template-oriented synthesis of monodispersed SnS2@SnO2 hetero-nanoflowers for Cr(VI) photoreduction. Appl. Catal. B Environ. 192, 17–25. Zhao, H., Xia, Q., Xing, H., Chen, D., Wang, H., 2017. Construction of pillared-layer MOF as efficient visible-light photocatalysts for aqueous Cr(VI) reduction and dye degradation. ACS Sustain. Chem. Eng. 5, 4449–4456. Zhao, Z., Li, Z., Zou, Z., 2011. Electronic structure and optical properties of monoclinic clinobisvanite BiVO4. Phys. Chem. Chem. Phys. 13, 4746–4753. Zhou, F.Q., Fan, J.C., Xu, Q.J., Min, Y.L., 2017. BiVO4 nanowires decorated with CdS nanoparticles as Z-scheme photocatalyst with enhanced H2 generation. Appl. Catal. B Environ. 201, 77–83. Zhou, S., Yin, L., 2017. CdS quantum dots sensitized mesoporous BiVO4 heterostructures for solar cells with enhanced photo-electrical conversion efficiency. J. Alloy. Compd. 691, 1040–1048. Zhu, M., Sun, Z., Fujitsuka, M., Majima, T., 2018. Z-Scheme photocatalytic water splitting on a 2D heterostructure of black phosphorus/bismuth vanadate using visible light. Angew. Chem. Int. Ed. 57, 2160–2164. Zou, L., Wang, H., Wang, X., 2017. High efficient photodegradation and photocatalytic hydrogen production of CdS/BiVO4 heterostructure through Z-Scheme Process. ACS Sustain. Chem. Eng. 5, 303–309. Zou, X., Dong, Y., Ke, J., Ge, H., Chen, D., Sun, H., Cui, Y., 2020. Cobalt monoxide/ tungsten trioxide p-n heterojunction boosting charge separation for efficient visiblelight-driven gaseous toluene degradation. Chem. Eng. J. 400, 125919.

14