Bi2MoO6 heterostructure for simultaneous photocatalytic decontamination of sulfadiazine and Ni(II)

Journal of Hazardous Materials 381 (2020) 120953

Contents lists available at ScienceDirect

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

Bi spheres SPR-coupled Cu2O/Bi2MoO6 with hollow spheres forming Zscheme Cu2O/Bi/Bi2MoO6 heterostructure for simultaneous photocatalytic decontamination of sulfadiazine and Ni(II)

T

⁎

Xiaoming Xua, Lingjun Mengb, Yuxuan Daia, Mian Zhangc, Cheng Suna, , Shaogui Yangd, Huan Hed, Shaomang Wange, Hui Lif a

State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, Jiangsu 210023, PR China Department of Civil and Environmental Engineering, University of Alberta, Edmonton T6G 1H9, Alberta, Canada College of Engineering and Applied Science, Nanjing University, Nanjing, Jiangsu 210023, PR China d School of the Environment, Nanjing Normal University, Nanjing, Jiangsu 210046, PR China e School of Environment and Safety Engineering, Changzhou University, Changzhou, Jiangsu 213164, PR China f Department of Crop and Soil Sciences, Michigan State University, East Lansing, Michigan 48824, United States b c

G R A P H I C A L A B S T R A C T

A R T I C LE I N FO

A B S T R A C T

Editor: Danmeng Shuai

Environmental problem on the coexistence of organic pollutants and heavy metals in surface waters has become increasingly serious. Few relative researches have focused on their simultaneous decontamination. Herein, a ternary plasmonic Z-scheme Cu2O/Bi/Bi2MoO6 heterojunction was synthesized via two-step route followed by a wet-impregnation, where Bi spheres coupled with Cu2O particles were anchored on the surface of Bi2MoO6 with hollow microflower spheres. The composites were characterized via various measurements. The excellent photocatalytic activity of Cu2O/Bi/Bi2MoO6 displayed in single sulfadiazine (SDZ) oxidation or Ni(II) reduction, and their simultaneous removal. The degradation pathway for SDZ was investigated via LC–MS and Gaussian theory. DFT and FDTD calculations confirmed the electronic structural characteristics in the Cu2O/Bi/Bi2MoO6 heterostructure and the induced electric field enhancement around nearly touching Bi spheres. A possible photodegradation mechanism of the as-prepared photocatalyst was elucidated via combining scavenger experiments with EPR technique. The results suggested h+, •O2− and •OH all participated in SDZ oxidation, which verified that Z-Scheme electron transfer was major manner in Cu2O/Bi/Bi2MoO6, while •O2− and e−acted on Ni

Keywords: Cu2O/Bi/Bi2MoO6 Z-scheme SPR effect Simultaneous photocatalytic activity Photocatalytic mechanism

⁎

Corresponding author. E-mail address: [email protected] (C. Sun).

https://doi.org/10.1016/j.jhazmat.2019.120953 Received 6 May 2019; Received in revised form 30 July 2019; Accepted 31 July 2019 Available online 06 August 2019 0304-3894/ © 2019 Elsevier B.V. All rights reserved.

Journal of Hazardous Materials 381 (2020) 120953

X. Xu, et al.

(II) reduction. The improved photocatalytic activity of Cu2O/Bi/Bi2MoO6 could be ascribed to the unique Zscheme electron transfer among Cu2O, Bi and Bi2MoO6, particularly SPR and local electric field near Bi spheres.

1. Introduction

electrical resistances of different phases (Zhou et al., 2014). The noble metal (Au, Ag) with surface plasmon resonance (SPR) effect has often been used as an electron mediator in several Z-scheme systems in previous studies. Such as CdS/Au/BiVO4 (Bao et al., 2017) Ag3PO4/Ag/ BiVO4 (040) (Chen et al., 2017) have shown high photocatalytic activity for organic contaminant decomposition. However, these noble metals are scarce and expensive, which severely limits their large-scale application. The metallic bismuth (Bi) as an electron mediator promotes the formation of Z-scheme system between two semiconductors, which has recently gained extensive concern because its similar SPR effect of noble metal and low-cost properties (Wang et al., 2017). To our knowledge, no article has reported about the fabrication of the highly efficient Cu2O/Bi/Bi2MoO6 Z-scheme system and the investigation of its simultaneous redox activity. Herein, Bi spheres were anchored on Bi2MoO6 with hollow microflower sphere via a simple two-step route followed by the deposition of Cu2O nanoparticles onto Bi/Bi2MoO6 via a wet-impregnation method, forming Cu2O/Bi/Bi2MoO6 Z-scheme system. The single as well as simultaneous SDZ oxidation and Ni(II) reduction were adopted to test photocatalytic activity of as-prepared composites, demonstrating Cu2O/ Bi/Bi2MoO6 displayed much more favorable photocatalytic activity. A degradation pathway of SDZ was proposed through LC–MS and Gaussian calculation. The DFT calculations were used to analyze the electronic properties of Cu2O/Bi/Bi2MoO6 heterojunction and the local electric field near Bi spheres was simulated using FDTD simulation. Finally, the photocatalytic mechanism of as-fabricated photocatalyst was discussed via combing scavenger experiments with EPR technique.

Environmental pollution becomes severe and prominent problem at present, as is seriously threatening human health and social sustainable development. Pharmaceutical substances are deemed to environmental micro-contaminants (Yang et al., 2019; Wang et al., 2016a). The sulfadiazine (SDZ) as one of sulfonamide antibiotics is applied in animal husbandry for preventing bacterial infections in livestock, and it has been widely found in the aqueous environment due to its overuse (Dong et al., 2019). Furthermore, the presence of heavy metals in the aquatic environment has caused a serious concern owing to their toxicity (Wang et al., 2019a). Nickel as the protective coating material of iron and steel is widely used in electroplating industry (Li et al., 2018). It is an effective way that highly toxic Ni(II) is reduced into Ni(0) to diminish its toxicity and mobility in aqueous environment (Boujelben et al., 2009). It is worth noting that organic pollutants and heavy metals are often coexisted in surface waters or industrial wastewaters. However, the effective approach to remove these environmental contaminants remains a most essential challenge. The semiconductor photocatalytic technology has a great potential for diminishing environmental pollution by harnessing sunlight (Najafian et al., 2019; Ma et al., 2019; Lee et al., 2018a). Bismuth-based photocatalysts have recently attracted considerable attention owing to their unique band structures and high stability (Lee et al., 2018b; Xu et al., 2019a; Zhao et al., 2019a). Among them, the Bi2MoO6 as a n-type semiconductor featuring a layered structure is recognized as a promising photocatalyst for pollutant removal and energy production in visible light catalysis on account of its appropriate bandgap, nontoxicity, and tunable morphology (Xu et al., 2019b; Guo et al., 2018; Shang et al., 2011). The morphological structure of the Bi2MoO6 has significant influence on its physical/chemical properties (Di et al., 2019). In particular, the hierarchical hollow structures can reduce migration distance of photo-induced carriers and allow multiple light reflections (Girish Kumar and Koteswara Rao, 2015). However, the quantum yield and photocatalytic activity are restricted owing to the intrinsic limitation of the single photocatalyst, generating rapid recombination of photo-induced carriers (Guo et al., 2018). The design of the heterojunction photocatalyst with the formation of Schottky junction or p–n junction is regarded as an effective way to solve these shortcomings via an efficient charge transport process (Wu et al., 2018; Chen et al., 2019). The cuprous oxide (Cu2O) representing a p-type semiconductor with a narrow band gap serves as a cocatalyst to construct p-n junction. (Wang et al. (2018)) reported that the p − n junction Cu2O/CdS nanorod arrays could effectively improve the separation efficiency of electron − hole pairs. However, the redox ability of the transferred electrons/holes on the traditional heterojunction was unavoidably reduced during the carrier transfer process. In recent decades, all-solid-state Z-scheme system has gradually become a focus of research due to its unique charge transfer pathway different from traditional charge transfer (Zhang et al., 2019; Wang et al., 2019b). The aggregated method of photo-generated electrons and holes which not only effectively improve photo-generated carriers’ separation but also preserve their strong redox ability (Wang et al., 2016b). It has been reported that benzothiadiazole/Bi2MoO6 (Yang et al., 2017), Bi2O3/g-C3N4 (Zhang et al., 2014a), CdS/WO3 (Jin et al., 2015), etc. were applied to photocatalysis in many researches. However, traditional charge transfer pathway competes with Z-scheme carrier transfer process in Z-scheme heterojunction of two phases, thus an electron mediator is employed to promote and accelerate Z-scheme carrier transfer pathway because of the remarkable difference in

2. Experimental 2.1. Preparation of catalysts The preparation methods of Bi2MoO6 and Bi/Bi2MoO6 were adapted via two-step hydrothermal route, then Cu2O/Bi/Bi2MoO6 was prepared via a wet-impregnation. The detailed methods were referred to Supporting Information (SI).

2.2. Characterizations The as-prepared samples were characterized via X-ray powder diffractometer (XRD), Raman spectra, Fourier-transform infrared spectra (FT-IR), X-ray photo-electron spectroscopy (XPS), Scanning electron microscopy (SEM)–X-ray spectroscopy (EDS), Transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), UV–vis diffuse reflectance spectra (DRS), Photoluminescence spectra (PL), Time-resolved fluorescence decay (T-RFD), Electrochemical impedance spectroscopy (EIS) and Electron paramagnetic resonance (EPR). The detailed information about experimental instruments and setting parameters were referred to SI.

2.3. Photocatalytic activity measurements The SDZ and metal salts (NiCl2) as Ni(II) source were used to prepare the synthetic wastewater. The photocatalytic activity was measured in SDZ (10 mg/L) or Ni(II) (10 mg/L) wastewater and their mixed wastewater under visible light (λ > 420 nm). The detailed information of experimental and analytical methods (HPLC, LC–MS, FAAS, TOC and ICS) and Gaussian calculation were described in SI. 2

Journal of Hazardous Materials 381 (2020) 120953

X. Xu, et al.

1–2 μm from the SEM images (Fig. 3a and b) of a broken microsphere with several nanosheets. Fig. 3c displays the homogeneous Bi microspheres with the size of approximate 100–200 nm and smooth surfaces, and many tiny Cu2O nanoparticles were tightly anchored on the surface of Bi2MoO6. As shown by the SEM-EDS mapping spectrum in Fig. S3. Cu2O/Bi/Bi2MoO6 consisted of Bi, Mo, O, C and Cu elements. TEM images reflected the similar results of SEM images. In Fig. 4a, the erect fragment and the contrast graph between the pale center and the dark edges could be observed, the inserted SAED image expressed polycrystalline nature. This confirmed Bi2MoO6 presented structure of hollow flower-like spheres. From the TEM image of Cu2O/Bi/Bi2MoO6 (Fig. 4b-d), some Bi spheres and tiny Cu2O nanoparticles were formed on the surface of Bi2MoO6. The HRTEM image of the Cu2O/Bi/Bi2MoO6 was further provided in Fig. 4e. Two sets of lattice fringes with the lattice spacings of 0.260 and 0.189 nm were attributed to the (220) and (222) lattice planes of Bi2MoO6, besides, (111) and (200) crystalline phases of Cu2O, and the (012) lattice plane of Bi were presented. The SAED image (Fig. 4f) demonstrates the polycrystalline subunits of Bi2MoO6 and Cu2O could be observed. In addition, the SAED image (Fig. 4g) displays the characteristics of two components: one weak set of spots was ascribed to single crystalline corresponding to the (104), (214) and (110) lattice planes of Bi sphere, and another weak set of rings was indexed to polycrystalline of Cu2O coming from the coating of Cu2O nanoparticles. The {104} plane was oriented at 58.60° from the {110} plane in simulated SAED pattern (Fig. 4h), which was consistent with the experimental SAED pattern (Fig. 4g). It inferred that Cu2O/Bi/ Bi2MoO6 photocatalysts had been successfully synthesized and the intimate interface among Cu2O, Bi and Bi2MoO6 was formed.

2.4. Theoretical calculation method Density Functional Theory (DFT) and three dimensional finite difference time domain (FDTD) simulations were employed to investigate the electronic structural characteristics of as-prepared samples and SPR effect of metallic Bi to visible light harvesting, respectively. The computational details of calculation modes were referred to SI. 3. Results and discussion 3.1. Phase structure analyses The crystallographic structure and the characteristic bands of the asprepared samples were measured by XRD and Raman spectra, respectively. The XRD patterns (Fig. 1) show that the characteristic peaks could be mainly indexed to the standard spectrum of Bi2MoO6 (JCPDS card no. 76-2388). No obvious peaks of copper oxide were detected in the XRD patterns of the Cu2O/Bi2MoO6 and Cu2O/Bi/Bi2MoO6 because of its low loading and high dispersion. The apparent diffraction peaks of metallic Bi (JCPDS card no. 85-1329) could be observed in Bi/Bi2MoO6 and Cu2O/Bi/Bi2MoO6 composites in addition to Bi2MoO6, which was consistent with the Raman spectra. The detailed analysis of Raman spectra could be referred to SI (Fig. S1), which demonstrated Bi2MoO6 had been coupled with Cu2O and Bi with strong interaction. 3.2. Chemical composition analyses The surface chemical states of as-prepared Bi2MoO6 and Cu2O/Bi/ Bi2MoO6 were measured by XPS and FT-IR spectra. The XPS survey spectra are shown in Fig. 2. The as-prepared samples were mainly composed of Bi, Mo, O, and C elements (Fig. 2a), Moreover, Cu element could be observed in the Cu2O/Bi/Bi2MoO6 spectrum. A doublet Bi 4f7/ 2 and Bi 4f5/2 in XPS corresponding to Bi element is displayed in Fig. 2b. The Bi 4f7/2 and Bi 4f5/2 of Cu2O/Bi/Bi2MoO6 were composed of four components, where the binding energies at 156.9 and 162.8 eV were ascribed to Bi0 4f7/2 and 4f5/2, respectively (Lv et al., 2018; Zhang et al., 2017; Zhao et al., 2016), while the peaks at 158.8 and 164.2 eV could be attributed to Bi3+ 4f7/2 and 4f5/2, respectively (Zhao et al., 2016). Fig. 2c reveals that the binding energies of Mo 4d5/2 and 4d3/2 centered at 232.0 and 235.1 eV, respectively (Zhao et al., 2016). The O 1s spectrum at 529.4 eV for Cu2O/Bi/Bi2MoO6 (Fig. 2d) could be further deconvoluted into four peaks of 529.1, 530.4, 531.8 and 533.0 eV corresponding to lattice oxygen (Bi − O, Cu − O (Deng et al., 2017), Mo-O) and hydroxyl groups (OeH), respectively. The main characteristic peak of Cu 2p3/2 and Cu 2p1/2 located at 928.2–929.7 (Xin et al., 2008), 933.3 (Li et al., 2017) and 952.3 eV (Lin et al., 2017) corresponding to Cu 2p bands of Cu2O crystallites, respectively (Fig. 2e). As Cu2O nanoparticles could be partially oxidized during synthetic process via the wet impregnation method, the peaks at 936.7 (Zhang et al., 2014b), 941.4 (Cao et al., 2015) with obvious satellite peaks at 942.7 and 944.2 eV (Mali et al., 2014), 948.2 and 949.4 eV (Zhao et al., 2019b) could assign to Cu2+. The Bi, Mo and O binding energies of Cu2O/Bi/Bi2MoO6 slightly shifted to the higher binding energies compared with that of Bi2MoO6, indicating the interaction among Cu2O, Bi and Bi2MoO6 with chemical bonds in the composites rather than a simple physical mixing (Yang et al., 2013). Moreover, FT-IR spectra was obtained to further investigate the composition and structures of the asprepared samples, which was discussed in SI (Fig. S2). The results showed the formation and interface interaction of Cu2O/Bi/Bi2MoO6 heterojunction.

3.4. Optical characteristic, carrier separation and BET analyses UV-vis absorption spectra of as-prepared samples were recorded in Fig. 5a. The absorption edges of Bi2MoO6 were measured to be ∼500 nm due to the intrinsic band gap transition. A strong absorption of metallic Bi in the visible spectral region could be observed due to its SPR effect. When Cu2O and Bi were loaded on the surface of Bi2MoO6, the optical absorption of the corresponding composites could be significantly enhanced. The separation, capture and migration of the photo-generated carriers on the surface of catalysts were investigated by PC, EIS, PL and T-RFD. Fig. 5b displays a comparison of the PC responses of as-prepared catalysts. For the pure Bi2MoO6, there were

3.3. Morphology structure analyses The morphology and detailed microstructures of as-prepared samples were characterized by SEM-EDS and TEM. Bi2MoO6 exhibited a hierarchical hollow microflower sphere with uniformly-sized of about

Fig. 1. XRD patterns of the as-prepared Bi2MoO6, Cu2O/Bi2MoO6, Bi/Bi2MoO6 and Cu2O/Bi/Bi2MoO6. 3

Journal of Hazardous Materials 381 (2020) 120953

X. Xu, et al.

Fig. 2. XPS spectra of Bi2MoO6 and Cu2O/Bi/Bi2MoO6: (a) Survey scan; (b) Bi 4f; (c) Mo 3d; (d) O 1s; (e) Cu 2p.

EIS analysis of different samples was carried out to further obtain the electron-transport-recombination properties, as shown in Fig. 5c. The EIS response demonstrated the Cu2O/Bi/Bi2MoO6 possessed a smaller impedance radius compared with other composites. This was further confirmed by the results of PL (Fig. 5d)) and T-RFD (Fig. 5e). The emission spectrum of Cu2O/Bi/Bi2MoO6 presented the lowest fluorescence emission intensity. The PL lifetime was quantitatively analyzed

less photocurrent response due to its the intrinsic limitation of the quantum yield. The loads of Bi and Cu2O could further enhance the photocurrent response of Bi2MoO6, while Bi/Bi2MoO6 presented higher response compared with Cu2O/Bi2MoO6. Importantly, Cu2O/Bi/ Bi2MoO6 exhibited highest photocurrent, suggesting a more efficient separation and longer lifetimes of charge carriers, which was in good agreement with the orders of their photocatalytic measurements. The 4

Journal of Hazardous Materials 381 (2020) 120953

X. Xu, et al.

Fig. 3. SEM images of (a, b) Bi2MoO6 and (c) Cu2O/Bi/Bi2MoO6.

by T-RFD. The exponential function fitted the experimental curves according to the equation: f(t) = B + A1×exp (-t/τ1) + A2×exp (-t/τ2). Average lifetime (τavg), the lifetimes (τ1 and τ2) and pre-exponential factors (A1 and A2) were summarized in Table S1. The τavg (3.1238 ns) of photo-induced carriers in Cu2O/Bi/Bi2MoO6 was 4.95, 2.40 and 1.92 times slower than that of Bi2WO6 (0.6312 ns), Cu2O/Bi2MoO6 (1.3036 ns) and Bi/Bi2MoO6 (1.6255 ns), respectively. It could be concluded that the Cu2O/Bi/Bi2MoO6 Z-scheme system could efficiently slow down the recombination rate of the electron-hole pairs and noticeably promote the photocatalytic activity. BET surface area and BJH pore structure were investigated and discussed in SI (Fig. S4a and Table S2). The results demonstrated that Cu2O/Bi/Bi2MoO6 catalysts presented smaller specific surface area and slightly reductive pore volume among all samples, indicating that specific surface area and pore volume were not main factor for boosting photocatalytic efficiency.

influenced the rate constants (k) of the Bi2MoO6. According to the summarized parameters, the reaction rate constants followed the order as: Cu2O/Bi/Bi2MoO6 > Bi/Bi2MoO6 > Cu2O/Bi2MoO6 > Bi2MoO6, which was consistent with the photocatalytic efficiency. The reusability of the Cu2O/Bi/Bi2MoO6 catalyst was also investigated during SDZ degradation and Ni(II) reduction process to examine the stability of catalysts (Fig. 6g). The Cu2O/Bi/Bi2MoO6still maintained good photocatalytic activities for SDZ and Ni(II) removal, and the photocatalytic efficiency was no significant decrease after five cycling runs, which demonstrated SDZ oxidation and Ni(II) reduction could be realized over the Cu2O/Bi/Bi2MoO6 with good stability. The TOC, SO42− and NH4+ measurements were conducted to deeply investigate photocatalytic properties (Fig. S5a-c). The mineralization rate (73.1%) of TOC was lower than that of photocatalytic degradation rate (98.6%) of SDZ, while the concentration of SO42− and NH4+ were 2.91 and 2.17 mg/L, respectively, indicating the structure of SDZ could be completely decomposed and some small intermediate products were generated during the photocatalytic process.

3.5. Evaluation of photocatalytic activity The photocatalytic activity of as-prepared samples was mainly evaluated in terms of SDZ oxidation and Ni(II) reduction under visiblelight irradiation. The dark adsorption of the SDZ and Ni(II) before illumination was measured and discussed in Fig. S4b-c. The results demonstrated their adsorption efficiencies onto Cu2O/Bi/Bi2MoO6 were slower than that of other samples. Fig. 6a and c show the degradation and reduction curve of SDZ and Ni(II) as a function of reaction time, respectively. The direct photolysis/reduction of SDZ and Ni(II) could be negligible under visible light irradiation. The Cu2O/Bi/Bi2MoO6 heterojunctions could effectively improve photocatalytic activity compared with Bi2MoO6, Cu2O/Bi2MoO6 and Bi/Bi2MoO6 catalysts. A highest degradation and reduction rate of SDZ and Ni(II) could be attained 98.6% and 93.2% within 100 and 60 min, respectively. Fig. 6e shows the Ni(II) could be nearly converted into Ni(0) over 100 min for Cu2O/Bi/Bi2MoO6, and the degradation efficiency of SDZ also reached to 92.1% simultaneously. It was because the SDZ acted as the hole scavengers, which suppressed the recombination of carries leaving more electrons to participate in Ni(II) reduction in the mixed system. Nevertheless, there were only 35.3% oxidation of SDZ and 54.6% reduction of Ni(II) for Bi2MoO6 under the identical conditions. As for the reaction kinetics of single SDZ oxidation and Ni(II) reduction as well as their simultaneous removal, a similar trend could be also observed during photocatalytic reaction process (Fig. 6b, d and f). The SDZ degradation and Ni(II) reduction process over all of samples followed pseudo-first-order kinetics. The coating of Bi and Cu2O significantly

3.6. Reaction intermediates and transformation pathways The degradation products of SDZ were detected by LC–MS. The total ion current (TIC) chromatograms of SDZ before and after oxidation are displayed in Fig. S6. The transformation pathways of SDZ were deduced in Fig. 7a according to measured degradation products (Table S3). In addition, the theoretical calculation of FEDs was applied to predict the positions attacked by reactive species. The positions with high values of FED2HOMO + FED2LUMO were suffered from attack by •OH, the sites with high 2FED2HOMO were susceptible to electron extraction, and the atoms with a negative point charge were easily oxidized according to FEDs theory (Meng et al., 2017). The Mulliken atomic charges and the HOMO isosurface are shown in Fig. 7b-d, and the 2FED2HOMO and FED2HOMO+FED2 LUMO values are summarized in Table S4 (higher values are highlighted in bold). Three pathways were proposed for the degradation of SDZ. The first pathway illustrated the SDZ could occur hydroxylation obtaining product S(1). The product S(2) was generated through the cleavage of C–N bonds in heterocyclic ring. The C–N bond joining the benzene was further cleaved yielding product S(3). These radical reactions could occur owing to 12C, 14C with high FED2HOMO+FED2LUMO values (boldface in Table S4) and 9 N with low negative Mulliken atomic charges. The second pathway was that the product (S4) was obtained by the loss of SO2 in SDZ, followed by C–N bond cleavage generating 5

Journal of Hazardous Materials 381 (2020) 120953

X. Xu, et al.

Fig. 4. TEM images of (a) Bi2MoO6 and (b, c, d) Cu2O/Bi/Bi2MoO6; (e) HRTEM images of Cu2O/Bi/Bi2MoO6 interface area; (f, g) SAED patterns of Cu2O/Bi/Bi2MoO6 in the region I, II for Fig. 4b and 4d, and (h) corresponding simulated SAED pattern for Fig. 4g.

product S(5), which attributed to the high 2FED2HOMO values of the 4C (boldface in Table S4). The third pathway was that the amino groups of SDZ were oxidized into product (S6), then the CSe bond was cleaved by the attack of •OH resulting in product S(7). These compounds were further decomposed ring-opening products S(8) and S(9) in advanced oxidation, which could be explained by the radical attack at 7 N with the relatively high 2FED2HOMO values. The results of 2FED2HOMO at 4C and 7 N agreed with the main orbital distribution of the HOMO isosurfaces (0.05 and 0.08) over 4C and 7 N atoms.

Bi2MoO6, and Bi 6p of metallic Bi, while the conduction band maximum (CBM) was predominantly composed of Bi 6p, O 2p and Mo 4d of Bi2MoO6, and Cu 3d of Cu2O in Cu2O/Bi/Bi2MoO6 Z-scheme heterostructure. The electronic migration mainly occurred from hybridized orbitals of Cu2O and metallic Bi to the orbitals of Bi2MoO6. Its enhanced DOS contributed to energy transformation that the CB of Bi2MoO6 with high energy level (Eg = 2.663 eV) shifted to low energy levels (Eg = 2.358 eV) of Cu2O/Bi/Bi2MoO6 with the aid of low energy levels (Eg = 2.012 eV) of Cu2O (Fig S7d-f). The charge difference distribution among Cu2O, Bi and Bi2MoO6 surfaces in Cu2O/Bi/Bi2MoO6 heterostructure (Fig. 8e) revealed that the underlying Bi atoms on metallic Bi surface took the light-induced electrons from Mo and O atoms on Bi2MoO6 surfaces, and then its upper Bi atoms delivered these electrons along with the electrons donated by SPR to the Cu atoms on Cu2O surface. The metallic Bi surface acted as an electron mediator corresponding to the carrier transfer pattern of Z-scheme heterojunction. Combined with the electronic location function of Cu2O/Bi/Bi2MoO6 (Fig. 8f), there existed a strong covalent interaction among Bi, Mo and O atoms on Bi2MoO6 surface, Bi atoms on Bi surface and Cu and O

3.7. Theoretical calculation To check the interactions among Cu2O, Bi and Bi2MoO6, their electron properties were investigated by density functional theory (DFT) (Fig. 8a and Fig. S7a-c: crystal structures). The energy band structures and density of states (DOS) for Bi2MoO6, Cu2O and Cu2O/Bi/ Bi2MoO6 are plotted in Fig. S7d-f and Fig. 8b-d, respectively. Compared with the DOS (Fig. 8b-d) among the three semiconductors, the valence band maximum (VBM) was mainly consist of Cu 3d of Cu2O, O 2p of 6

Journal of Hazardous Materials 381 (2020) 120953

X. Xu, et al.

Fig. 5. (a) UV–vis diffuses reflectance spectra, (b) transient photocurrent responses and (c) EIS response, (d) photoluminescence spectra and (e) the ns-level timeresolved fluorescence spectra monitored at 467 nm under 300 nm of the as-prepared Bi2MoO6, Cu2O/Bi2MoO6, Bi/Bi2MoO6 and Cu2O/Bi/Bi2MoO6.

7

Journal of Hazardous Materials 381 (2020) 120953

X. Xu, et al.

Fig. 6. (a) Photocatalytic degradation curves and (b) The reaction kinetics curves of SDZ over different photocatalysts under visible light irradiation; (c) Photocatalytic reduction curves and (d) The reaction kinetics curves of Ni(Ⅱ) over different photocatalysts under visible light irradiation; (e) The variation curves and (f) The reaction kinetics curves of simultaneous SDZ oxidation and Ni(Ⅱ) reduction by Bi2MoO6 and Cu2O/Bi/Bi2MoO6 under visible light irradiation; (g) Cycling runs for photodegradation of SDZ and photoreduciton of Ni(Ⅱ) over the Cu2O/Bi/Bi2MoO6.

8

Journal of Hazardous Materials 381 (2020) 120953

X. Xu, et al.

Fig. 7. (a) Proposed photocatalytic degradation pathways of SDZ over the Cu2O/Bi/Bi2MoO6 under visible-light irradiation (The arrow lines indicate theoretical analysis); Mulliken atomic charges, highest occupied molecular orbital (HOMO) shown as isosurfaces of SDZ calculated by Gaussian 09 program at the B3LYP/6311G** level: (b) Mulliken atomic charges of SDZ, (c) Isodensity surfaces of HOMO with an isovalue of 0.05, (d) Isodensity surfaces of HOMO with an isovalue of 0.08. (The yellow and cyan arrows imply the positions for oxidization and electron extraction, respectively.).

the reaction system, respectively, suggesting •OH and •O2− were produced and participated in photocatalytic degradation. The effect of •OH is less obvious than that of h+ and •O2−. The N2 was poured into individual photocatalytic system of Ni(II) to remove oxygen, showing 36.3% reduction efficiency of Ni(II) was hindered (Fig. 10b). Thus, it could be seen that the contribution rates for Ni(II) reduction were 36.3% and 63.7% by •O2− and electrons, respectively. The reduction reaction among Ni(II), •O2− and electrons was discussed and the formation of Ni(0) during photocatalytic reduction was verified through TEM and XPS, whch were referred to SI (Fig. S8a-c and Fig. S9a-b). In summary, •OH, •O2− and h+ all took part in the degradation of SDZ, and the •O2− radicals also made effect on the removal of Ni(II). The DMPO-EPR spin trapping further verified the results of the scavenger experiments (Fig. 10c-d). The detected signals of •OH and •O2− were observed for Bi2MoO6 and Cu2O/Bi/Bi2MoO6, while both signals were strengthened in Cu2O/Bi/Bi2MoO6 compared with pure Bi2MoO6. The increased •OH and •O2− were in favor of the removal of SDZ and Ni(II). There were two possible mechanisms for sulfadiazine (SDZ) oxidation and Ni(II) reduction by Cu2O/Bi/Bi2MoO6, which were presented in Scheme 1 based on the above analytical results. One possible mechanism (Scheme 1a) was a typical p–n heterojunction. According to previous reports, CB and VB energy levels of Bi2MoO6 (Zhao et al., 2016) and Cu2O (Fu et al., 2015) were located at ca. -0.32 and 2.34 eV, and -1.4 and 0.6 eV (vs NHE), respectively. The both p-type Cu2O and ntype Bi2MoO6 could generated the photo-excited carriers under

atoms on Cu2O surface, further indicating the charge carriers mainly generated on Cu2O, Bi and Bi2MoO6 surfaces forming charge transfer channel from Bi2MoO6 to Cu2O. The FDTD solution simulated the electromagnetic response of the plasmonic catalysts to express the increase to visible light absorption. As shown in Fig. 9a–c, the local “hot spots” could be seen in regions around nearly touching Bi spheres. The electric field intensity on the surface the Bi2MoO6 with hollow structure reached 1.6, intensive 2.5 and 2.5 times as much as the incident electric field under wavelength illuminations of 420, 550 and 620 nm, respectively. Therefore, the photo-absorption rate, i.e. photon-induced carrier generation was 2.5 times higher than that of the incident light when visible illumination wavelength was above 550 nm, explaining the Bi spheres could promote SPR and the catalytic activity. 3.8. Enhanced photocatalytic mechanism The trapping experiments were conducted to investigate the main active species during the degradation process of the SDZ. Trapping of radicals and holes in experiments were conducted using EDTA, BQ, and IPA as h+, •O2− and •OH scavengers, respectively, as shown in Fig. 10a. Notably, the photocatalytic performance was significantly inhibited (73.2%) after adding the EDTA scavenger, indicating h+ served as the main active species. The degradation rate of 52.6% and 28.5% for SDZ was also hampered to some extent when BQ and IPA were added into 9

Journal of Hazardous Materials 381 (2020) 120953

X. Xu, et al.

Fig. 8. (a) Crystal structures of Cu2O/Bi/Bi2MoO6; Density of states (DOS) of (b) Cu2O, (c) Bi2MoO6 and (d) Cu2O/Bi/Bi2MoO6; (e) Charge difference distribution with charge accumulation in yellow and depletion in green, and (f) Electronic location function (ELF) of Cu2O/Bi/Bi2MoO6.

into •OH owing to the less positive potential of the VB on Cu2O (0.6 eV vs NHE) compared with the standard reduction potential of •OH/H2O (2.27 eV vs NHE) or •OH/OH- (1.99 eV vs NHE) (Cui et al., 2012). The signal of •OH in EPR measurement should be decreased. On the contrary, the ESR measurement demonstrated the photo-generated holes

illumination, and then the electrons from CB of Cu2O would migrate to that of Bi2MoO6, meanwhile the holes from VB of Bi2MoO6 would move to VB of Cu2O owing to the driving force of the band potentials’ alignment between two semiconductors, effectively separating carriers. However, the aggregated h+ on Cu2O could not oxidize H2O or OH− 10

Journal of Hazardous Materials 381 (2020) 120953

X. Xu, et al.

Fig. 9. Electric field distributions at the cross-sections of Bi/Bi2MoO6 with hollow structure using the FDTD solution with visible light wavelengths of (a) 420 nm, (b) 550 nm and (c) 620 nm (The diameter of simulative Bi2MoO6 is 1 μm with hollow diameter of 300 nm and that of Bi is 200 nm.).

charge transfer pathway of the Z-scheme not only dramatically enhanced the separation of electron–hole pairs but also preserved stronger redox ability.

onto Cu2O/Bi/Bi2MoO6 accumulated in the VB of Bi2MoO6. Therefore, the traditional carries transferring modes did not fit this photocatalytic mechanism. The other possible mechanism was Z-scheme heterojunction, as shown in Scheme 1b. Since the CB of Bi2MoO6 (-0.32 eV) was more negative than the Fermi level of metallic Bi (−0.17 eV) (Zhao et al., 2016), the photo-induced electrons could easily transfer from Bi2MoO6 to Bi forming Mott − Schottky barrier. The enhanced electric field intensity around interface of the touching Bi spheres prompted the electrons to migrate to the VB of Cu2O for eventually recombining with holes via a direct electron migration because the VB (0.6 eV) of Cu2O was more positive than the Fermi level (−0.17 eV) of metallic Bi. Subsequently, the accumulated holes on Bi2MoO6 were capable of oxidizing H2O/OH− into •OH because the VB edge potential of Bi2MoO6 (2.34 eV) was enough positive or directly degraded SDZ molecules, meanwhile the accumulated photoelectrons on the CB of Cu2O (-1.4 vs NHE) could further picked up O2 to form •O2− (O2/•O2− =−0.28 eV vs NHE) (Wang et al., 2014). Therefore, these formed h+, •OH and O2− could take part in simultaneous photo-redox reaction. The photo-induced carrier transfer process corresponded with the result of EPR trapping experiments and fits Z-scheme charge-transfer system. The

4. Conclusion In summary, a ternary plasmonic Cu2O/Bi/Bi2MoO6 Z-scheme photocatalyst was successfully synthesized for the single as well as simultaneous SDZ oxidation and Ni(II) reduction and exhibited excellent photocatalytic activity. The LC–MS analysis was combined with Gaussian theory to elaborate the degradation path of SDZ. DFT and FDTD calculations expressed a charge transfer channel of Cu2O/Bi/ Bi2MoO6 and the enhanced absorption to visible light owing to SPR effect of Bi, respectively. The possible photocatalytic mechanism was proposed based on the scavenger experiments and EPR technique. The enhanced photocatalytic activity was attributed to SPR effect and the Zscheme charge transfer pathway in the composites, which not only brought about the fast separation of the carries but also maintained their excellent redox ability and improved visible light absorption. 11

Journal of Hazardous Materials 381 (2020) 120953

X. Xu, et al.

Fig. 10. (a) Trapping measurement with different scavengers (EDTA→h+, BQ→•O2−, IPA→•OH,) for photodegradation of SDZ; (b) Photoreduction rate constants of Ni(II) under different atmospheres; (c, d) DMPO-EPR spin-trapping spectra of Bi2MoO6 and Cu2O/Bi/Bi2MoO6 for detection of •OH and •O2− under visible light irradiation (λ > 420 nm).

Scheme 1. Schematic illustration of the proposed photocatalytic mechanism in the (a) Cu2O/Bi2MoO6 and (b) Cu2O/Bi/Bi2MoO6 for SDZ degradation and Ni(II) reduction under visible light irradiation. 12

Journal of Hazardous Materials 381 (2020) 120953

X. Xu, et al.

Mali, S.S., Patil, P.S., Bhosale, P.N., Hong, C.K., 2014. Novel hybrid solar cells based on αcopper phthalocyanine–cadmium sulfide planar heterojunction. J. Mater. Sci. 49, 5100–5111. Meng, L., Yang, S., Sun, C., He, H., Xian, Q., Li, S., Wang, G., Zhang, L., Jiang, D., 2017. A novel method for photo-oxidative degradation of diatrizoate in water via electromagnetic induction electrodeless lamp. J. Hazard. Mater. 337, 34–46. Najafian, H., Manteghi, F., Beshkar, F., Salavati-Niasari, M., 2019. Fabrication of nanocomposite photocatalyst CuBi2O4/Bi3ClO4 for removal of acid brown 14 as water pollutant under visible light irradiation. J. Hazard. Mater. 361, 210–220. Shang, M., Wang, W., Ren, J., Sun, S., Zhang, L., 2011. Nanoscale Kirkendall effect for the synthesis of Bi2MoO6 boxes via a facile solution-phase method. Nanoscale 3, 1474–1476. Wang, D., Guo, L., Zhen, Y., Yue, L., Xue, G., Fu, F., 2014. AgBr quantum dots decorated mesoporous Bi2WO6 architectures with enhanced photocatalytic activities for methylene blue. J. Mater. Chem. A Mater. Energy Sustain. 2, 11716–11727. Wang, Z., Lin, Y., Xu, B., Xia, S., Zhang, T., Gao, N., 2016a. Degradation of iohexol by UV/ chlorine process and formation of iodinated trihalomethanes during post-chlorination. Chem. Eng. J. 283, 1090–1096. Wang, D., Shen, H., Guo, L., Fu, F., Liang, Y., 2016b. Design and construction of the sandwich-like Z-scheme multicomponent CdS/Ag/Bi2MoO6 heterostructure with enhanced photocatalytic performance in RhB photodegradation. New J. Chem. 40, 8614–8624. Wang, J., Tang, L., Zeng, G., Liu, Y., Zhou, Y., Deng, Y., Wang, J., Peng, B., 2017. Plasmonic Bi metal deposition and g-C3N4 coating on Bi2WO6 microspheres for efficient visible-light photocatalysis. ACS Sustain. Chem. Eng. 5, 1062–1072. Wang, L., Wang, W., Chen, Y., Yao, L., Zhao, X., Shi, H., Cao, M., Liang, Y., 2018. Heterogeneous p–n Junction CdS/Cu2O nanorod arrays: synthesis and superior visible-light-driven photoelectrochemical performance for hydrogen evolution. ACS Appl. Mater. Interfaces 10, 11652–11662. Wang, Y., Wang, B., Wang, Q., Di, J., Miao, S., Yu, J., 2019a. Amino-functionalized porous nanofibrous membranes for simultaneous removal of oil and heavy-metal ions from wastewater. ACS Appl. Mater. Interfaces 11, 1672–1679. Wang, R., Tang, J., Zhang, X., Wang, D., Wang, X., Xue, S., Zhang, Z., Dionysiou, D.D., 2019b. Construction of novel Z-scheme Ag/ZnFe2O4/Ag/BiTa1-xVxO4 system with enhanced electron transfer capacity for visible light photocatalytic degradation of sulfanilamide. J. Hazard. Mater. 375, 161–173. Wu, Y., Wang, H., Tu, W., Liu, Y., Tan, Y.Z., Yuan, X., Chew, J.W., 2018. Quasi-polymeric construction of stable perovskite-type LaFeO3/g-C3N4 heterostructured photocatalyst for improved Z-scheme photocatalytic activity via solid p-n heterojunction interfacial effect. J. Hazard. Mater. 347, 412–422. Xin, B., Wang, P., Ding, D., Liu, J., Ren, Z., Fu, H., 2008. Effect of surface species on CuTiO2 photocatalytic activity. Appl. Surf. Sci. 254, 2569–2574. Xu, X., Meng, L., Li, Y., Sun, C., Yang, S., He, H., 2019a. Bi2S3 nanoribbons-hybridized {001} facets exposed Bi2WO6 ultrathin nanosheets with enhanced visible light photocatalytic activity. Appl. Surf. Sci. 479, 410–422. Xu, X., Ding, X., Yang, X., Wang, P., Li, S., Lu, Z., Chen, H., 2019b. Oxygen vacancy boosted photocatalytic decomposition of ciprofloxacin over Bi2MoO6: oxygen vacancy engineering, biotoxicity evaluation and mechanism study. J. Hazard. Mater. 364, 691–699. Yang, W., Ma, B., Wang, W., Wen, Y., Zeng, D., Shan, B., 2013. Enhanced photosensitized activity of a BiOCl–Bi2WO6 heterojunction by effective interfacial charge transfer. Phys. Chem. Chem. Phys. 15, 19387–19394. Yang, X., Xiang, Y., Qu, Y., Ding, X., Chen, H., 2017. Novel in situ fabrication of conjugated microporous poly(benzothiadiazole)–Bi2MoO6 Z-scheme heterojunction with enhanced visible light photocatalytic activity. J. Catal. 345, 319–328. Yang, L., Wen, Q., Zhao, Y., Chen, Z., Wang, Q., Bürgmann, H., 2019. New insight into effect of antibiotics concentration and process configuration on the removal of antibiotics and relevant antibiotic resistance genes. J. Hazard. Mater. 373, 60–66. Zhang, J., Hu, Y., Jiang, X., Chen, S., Meng, S., Fu, X., 2014a. Design of a direct Z-scheme photocatalyst: preparation and characterization of Bi2O3/g-C3N4 with high visible light activity. J. Hazard. Mater. 280, 713–722. Zhang, R., Li, Y., Zhen, T., 2014b. Ammonia selective catalytic reduction of NO over Fe/ Cu-SSZ-13. RSC Adv. 4, 52130–52139. Zhang, Q., Zhao, Z., Shen, Z., Wei, Q., 2017. One-step hydrothermal method to synthesize Bi/Bi2MoO6 composite for photoelectric catalyst. Funt. Mater. Lett. 10, 1–4. Zhang, J., Zhou, D., Dong, S., Ren, N., 2019. Respective construction of Type-II and direct Z-scheme heterostructure by selectively depositing CdS on {001} and {101} facets of TiO2 nanosheet with CDots modification: a comprehensive comparison. J. Hazard. Mater. 366, 311–320. Zhao, Z., Zhang, W., Sun, Y., Yu, J., Zhang, Y., Wang, H., Dong, F., Wu, Z., 2016. Bi cocatalyst/Bi2MoO6 microspheres nanohybrid with SPR-promoted visible-light photocatalysis. J. Phys. Chem. C 120, 11889–11898. Zhao, W., Feng, Y., Huang, H., Zhou, P., Li, J., Zhang, L., Dai, B., Xu, J., Zhu, F., Sheng, N., 2019a. A novel Z-scheme Ag3VO4/BiVO4 heterojunction photocatalyst: study on the excellent photocatalytic performance and photocatalytic mechanism. Appl. Catal. B: Environ. 245, 448–458. Zhao, F., Li, S., Wu, X., Yue, R., Li, W., Chen, Y., 2019b. Synergetic effect over flame-made manganese doped CuO–CeO2 nanocatalyst for enhanced CO oxidation performance. RSC Adv. 9, 2343–2352. Zhou, P., Yu, J., Jaroniec, M., 2014. All-solid-state Z-scheme photocatalytic systems. Adv. Mater. 26, 4920–4935.

Acknowledgements This work was financially supported by National Natural Science Foundation of China (Nos. 51578279 and 21777067) and the Major Science and Technology Program for Water Pollution Control and Treatment of China (No. 2015ZX07204-007). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jhazmat.2019.120953. References Bao, S., Wu, Q., Chang, S., Tian, B., Zhang, J., 2017. Z-scheme CdS–Au–BiVO4 with enhanced photocatalytic activity for organic contaminant decomposition. Catal. Sci. Technol. 7, 124–132. Boujelben, N., Bouzid, J., Elouear, Z., 2009. Adsorption of nickel and copper onto natural iron oxide-coated sand from aqueous solutions: study in single and binary systems. J. Hazard. Mater. 163, 376–382. Cao, C., Xiao, L., Chen, C., Cao, Q., 2015. Synthesis of novel Cu2O/BiOCl heterojunction nanocomposites and their enhanced photocatalytic activity under visible light. Appl. Surf. Sci. 357, 1171–1179. 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) Z-scheme 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, M., Guo, C., Hou, S., Wu, L., Lv, J., Hu, C., Zhang, Y., Xu, J., 2019. In-situ fabrication of Ag/P-g-C3N4 composites with enhanced photocatalytic activity for sulfamethoxazole degradation. J. Hazard. Mater. 366, 219–228. Cui, Y., Huang, J., Fu, X., Wang, X., 2012. Metal-free photocatalytic degradation of 4chlorophenol in water by mesoporous carbon nitride semiconductors. Catal. Sci. Technol. 2, 1396–1402. Deng, Y., Tang, L., Zeng, G., Feng, C., Dong, H., Wang, J., Feng, H., Liu, Y., Zhou, Y., Pang, Y., 2017. Plasmonic resonance excited dual Z-scheme BiVO4/Ag/Cu2O nanocomposite: synthesis and mechanism for enhanced photocatalytic performance in recalcitrant antibiotic degradation. Environmen. Sci.: Nano 4, 1494–1511. Di, J., Zhao, X., Lian, C., Ji, M., Xia, J., Xiong, J., Zhou, W., Cao, X., She, Y., Liu, H., Loh, K.P., Pennycook, S.J., Li, H., Liu, Z., 2019. Atomically-thin Bi2MoO6 nanosheets with vacancy pairs for improved photocatalytic CO2 reduction. Nano Energy 61, 54–59. Dong, F., Li, C., Crittenden, J., Zhang, T., Lin, Q., He, G., Zhang, W., Luo, J., 2019. Sulfadiazine destruction by chlorination in a pilot-scale water distribution system: kinetics, pathway, and bacterial community structure. J. Hazard. Mater. 366, 88–97. Fu, J., Cao, S., Yu, J., 2015. Dual Z-scheme charge transfer in TiO2–Ag–Cu2O composite for enhanced photocatalytic hydrogen generation. J. Materiomics 1, 124–133. Girish Kumar, S., Koteswara Rao, K.S.R., 2015. Tungsten-based nanomaterials (WO3 & amp; Bi2WO6): modifications related to charge carrier transfer mechanisms and photocatalytic applications. Appl. Surf. Sci. 355, 939–958. Guo, J., Shi, L., Zhao, J., Wang, Y., Tang, K., Zhang, W., Xie, C., Yuan, X., 2018. Enhanced visible-light photocatalytic activity of Bi2MoO6 nanoplates with heterogeneous Bi2MoO6-x@Bi2MoO6 core-shell structure. Appl. Catal. B: Environ. 224, 692–704. Jin, J., Yu, J., Guo, D., Cui, C., Ho, W., 2015. A hierarchical Z-scheme CdS–WO3 photocatalyst with enhanced CO2 reduction activity. Small 11, 5262–5271. Lee, Y., Cui, M., Choi, J., Kim, J., Son, Y., Khim, J., 2018a. Degradation of polychlorinated dibenzo-p-dioxins and dibenzofurans in real-field soil by an integrated visible-light photocatalysis and solvent migration system with p-n heterojunction BiVO4/Bi2O3. J. Hazard. Mater. 344, 1116–1125. Lee, Y.W., Boonmongkolras, P., Son, E.J., Kim, J., Lee, S.H., Kuk, S.K., Ko, J.W., Shin, B., Park, C.B., 2018b. Unbiased biocatalytic solar-to-chemical conversion by FeOOH/ BiVO4/perovskite tandem structure. Nat. Commun. 9, 4208. Li, H., Su, Z., Hu, S., Yan, Y., 2017. Free-standing and flexible Cu/Cu2O/CuO heterojunction net: a novel material as cost-effective and easily recycled visible-light photocatalyst. Appl. Catal. B: Environ. 207, 134–142. Li, T., Zhang, W., Zhai, S., Gao, G., Ding, J., Zhang, W., Liu, Y., Zhao, X., Pan, B., Lv, L., 2018. Efficient removal of nickel(II) from high salinity wastewater by a novel PAA/ ZIF-8/PVDF hybrid ultrafiltration membrane. Water Res. 143, 87–98. Lin, S., Cui, W., Li, X., Sui, H., Zhang, Z., 2017. Cu2O NPs/Bi2O2CO3 flower-like complex photocatalysts with enhanced visible light photocatalytic degradation of organic pollutants. Catal. Today 297, 237–245. Lv, J., Zhang, J., Liu, J., Li, Z., Dai, K., Liang, C., 2018. Bi SPR-promoted Z-scheme Bi2MoO6/CdS-diethylenetriamine composite with effectively enhanced visible light photocatalytic hydrogen evolution activity and stability. ACS Sustain. Chem. Eng. 6, 696–706. Ma, H., Zhao, L., Guo, L., Zhang, H., Chen, F., Yu, W., 2019. Roles of reactive oxygen species (ROS) in the photocatalytic degradation of pentachlorophenol and its main toxic intermediates by TiO2/UV. J. Hazard. Mater. 369, 719–726.

13