Research Article pubs.acs.org/journal/ascecg
Photoreactivity and Mechanism of g‑C3N4 and Ag Co-Modified Bi2WO6 Microsphere under Visible Light Irradiation Xiaoping Xiao, Jianhong Wei,* Yang Yang, Rui Xiong, Chunxu Pan, and Jing Shi Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, P. R. China S Supporting Information *
ABSTRACT: In this study, C3N4@Ag-Bi2WO6 with flowerlike architecture was successfully prepared through a facile process. The C3N4@Ag-Bi2WO6 particles with 2−4 μm diameters present remarkable enhanced visible light absorption and electron−hole separation efficiency. Compared with Bi2WO6, Ag-Bi2WO6, and C3N4@Bi2WO6 systems, the C3N4@Ag-Bi2WO6 system exhibits optimal photocatalytic activities in both the degradation of RhB and hydrogen production out of water under visible light irradiation. We propose that these results are attributed to the synergy effects of Ag, g-C3N4, and Bi2WO6 nanophase structures in the C3N4@Ag-Bi2WO6 composites, which results in a fast electron−hole separation and slow charge recombination by a Z-scheme mechanism and ultimately in a higher photocatalytic activity. KEYWORDS: C3N4-based nanocomposite, silver, Bi2WO6, Z-scheme mechanism, photocatalysis
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INTRODUCTION With the growing severity of environment problems and an energy crisis, semiconductor photocatalysts have attracted intense attention, and offer a “green” route for completely degradating pollutants, producing hydrogen out of water and converting carbon dioxide into hydrocarbons, etc.1−3 TiO2 has been considered as one of the most promising photocatalysts, based upon its advantages such as nontoxicity, stability, low cost, and high photocatalytic activity. However, the deficiency of requiring UV light for effectively photocatalysis seriously limited its overall application. Recently, Wang et al.4 reported that a novel metal-free polymeric semiconductor, graphitic carbon nitride (g-C3N4), could be an effective visible-lightinduced photocatalyst, which showed a high chemical and thermal stability, a medium bandgap of ∼2.7 eV, and make it respond to the visible light directly. Nevertheless, pure g-C3N4 suffers from a high recombination rate of photogenerated charge carriers and low specific surface area, and correspondingly results in low visible-light-driven photocatalytic performance.5 In order to overcome the above problems, many efforts have been proposed including metal or nonmetal deposition, textural property design, semiconductor couples, etc.6−8 For instance, deposition of silver nanoparticles was demonstrated as an effective method to inhibit photoinduced charge carrier recombination by a surface plasmon resonance effect.9 In our previous work, the silver-containing composites exhibited significant visible-light-driven photocatalytic activity.10,11 In addition, it has been approved that the coupling g-C3N4 with © XXXX American Chemical Society
semiconductors also exhibits an efficient promotion on the separation of photoexcited carriers by the mutual transfer of photogenerated electrons or holes in the nanocomposites through a heterojunction-transfer mechanism or Z-scheme mechanism.12−15 Therefore, the heart of the matter for constructing this heterojunction system is to find a semiconductor with well-matched band structure with g-C3N4. It has been reported that the energy levels of Bi2WO6 and g-C3N4 are well-matched.16,17 Also, the bismuth tungstate (Bi2WO6) with a bandgap of ∼2.8 eV exhibits obviously photocatalytic performance under both UV and visible light irradiations. Many research studies also revealed that photocatalysts with flowerlike structure show a much higher interfacial charge-transfer and lower recombination process than that with normal nanoparticles.18−22 The main reason is that the flower-like superstructures are the coupling of independently controllable mesopores or macropores, which are taken as transport paths, contributing the reactant molecules to reach the reactive place, and correspondingly resulting in an enhanced photocatalytic performance.23,24 Obviously, an ideal route is to prepare an artificial system consisting of Bi2WO6, g-C3N4, and Ag with flower-like superstructures for further expanding the light absorption region, improving the quantum yield and the photocatalytic activity. In this paper, we propose a novel ternary composite of Received: December 15, 2015 Revised: April 5, 2016
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DOI: 10.1021/acssuschemeng.5b01701 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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ACS Sustainable Chemistry & Engineering heterostructured C3N4@Ag-Bi2WO6 microspheres having flower-like superstructures for the photodegradation of Rhodamine B (RhB) and producing hydrogen out of water under visible light irradiation. The chemical compositions, morphologies, structures, photoelectrical properties, and photocatalytic activity were fully characterized, and the synergistic interaction and possible photocatalytic mechanism are also discussed.
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electrode as a counter electrode.25 The photoluminescence (PL) spectra were measured at room temperature on a Hitachi F- 4600 fluorescence spectrophotometer with an excitation wavelength of 425 nm. Total organic carbon (TOC) of the samples was measured by a Analytik Jena multi-N/C 2100 analysis instrument. Photocatalytic Testing. Photocatalytic activity was quantified by monitoring the degradation of RhB, a model polluant. At first, a 100 mL of RhB solution with an initial concentration of 10 mg/L was mixed with 50 mg of solid catalyst. Then, the mixed solution was stirred in the dark for 30 min to obtain a good dispersion and establish the adsorption−desorption equilibrium. After that, the above solution was illuminated by a 350 W xenon arc lamp (10 cm away) through a UV cutoff filter (λ > 420 nm) at room temperature. The decreases of RhB concentrations were analyzed by a Shimadzu 2450/2550 UV−vis spectrophotometer at 660 nm with regular intervals (15 min). 1,4Benzoquinone (BQ), tert-butyl alcohol (TBA), and disodium ethylenediamine tetraacetate (EDTA) were added to investigate the main active species, such as superoxide radical (•O2−), hydroxyl radicals (•OH), and holes (h+) produced during the photoreaction process. The content of •OH was also detected by the PL technique, using terephthalic acid as probe molecule. H2 production experiments were performed at ambient temperature in a Labsolar-III (AG) photocatalytic reactor which was connected to a closed gas-circulation system. The C3N4@Ag-Bi2WO6 photocatalyst (15 mg) was suspended in an aqueous solutions (10 mL) containing 10 vol % triethanolamine (TEOA). The reactant solution was maintained at room temperature by a flow of cooling water during the reaction. The evolved gases were analyzed by gas chromatography. For stability test, the H2 production experiments of C3N4@Ag-Bi2WO6 were examined every 8 h and repeated 5 times.
EXPERIMENTAL SECTION
Synthesis of g-C3N4 Nanosheets. All chemical reagents used in this work were analytical grade and used as received without further purification. Pure g-C3N4 sheets were obtained by heating treated melamine at 550 °C in an alumina crucible for 4 h and then cooled naturally to ambient temperature. The g-C3N4 nanosheets were obtained in powder form. Synthesis of Flower-like Bi2WO6 Microspheres. The flowerlike Bi2WO6 microspheres were carried out as follows: At first, 0.5 mmol of Na2WO4·2H2O was dissolved in a 40 mL portion of a mixture solvent (8 mL acetic acid and 32 mL distilled water) to obtain a clear solution. Then, 1 mmol of Bi(NO3)3·5H2O solid was added, and a white precipitate immediately appeared. After the reaction mixture was stirred for 1 h, the resulting slurry was transferred into a 100 mL Teflon-lined stainless steel autoclave and maintained at 160 °C for 12 h in an oven, and then cooled naturally to ambient temperature. The resulting products were collected, washed, and dried at 60 °C for 12 h. Synthesis of Flower-like Ag-Bi2WO6 Microspheres. The AgBi2WO6 nanocomposites were prepared by a photodeposition method as follows: At first, a specified amount of AgNO3 solution (1 mg/mL) was added into 50 mL of Bi2WO6 dispersion (1 mmol) and then stirred vigorously until all reagents were completely dissolved in the dark. Subsequently, the above suspension was transferred into a 200 mL water-cooled reactor and irradiated for 1 h with a 500 W Xe lamp under magnetic stirring while Ag+ species were induced to form Ag nanoparticles loaded on the surface of Bi2WO6. After that, the powders were collected and dried under vacuum at 80 °C for 10 h, and the resulting Ag-Bi2WO6 photocatalyst was obtained. According to our initial experiments (Figure S1), the Ag-Bi2WO6 sample with molar ratio of Ag to Bi2WO6 of 0.05 shows optimal photocatalytic performance. Briefly, the molar ratio of Ag to Bi2WO6 was fixed to be 0.05 reported in this work unless otherwise stated. Synthesis of C3N4@Bi2WO6 and C3N4@Ag-Bi2WO6 Microspheres. A specified amount of as-prepared g-C3N4 and 0.5 g of Bi2WO6 (or 0.5 g Ag-Bi2WO6) were added to 100 mL of methanol solution and then ultrasonicated for 40 min; the above suspension was then stirred in a fume hood for 12 h. After that, the resulting suspension was filtered, washed, and dried under vacuum at 80 °C for 24 h. According to our initial experiments (Figure S2), both of the C3N4@Bi2WO6 and C3N4@Ag-Bi2WO6 samples with mass ratio of C3N4 to Bi2WO6 (or Ag-Bi2WO6) of 0.02 show optimal photocatalytic performance. Briefly, the mass ratio of C3N4 to Bi2WO6 (or AgBi2WO6) was fixed to be 0.02 reported in this work. Characterization. The crystal structures of the as-prepared samples were characterized by a Bruker D8 Advance X-ray diffraction (XRD) with Cu Kα radiation (λ = 1.541 78 Å). The morphologies and microsturctures of the samples were studied by a SHIMADZU SSX550 field emission scanning electron microscopy (SEM), and a high resolution JEOL JEM-2010 transmission electron microscopy (TEM). Energy dispersive X-ray spectroscopy (EDS) of C3N4@Ag-Bi2WO6 microspheres was also investigated during the FE-SEM measurement. Element mapping was used to determine the composition of C3N4@ Ag-Bi2WO6 composites. The diffuse reflectance spectra (DRS) were measured on a VARIAN Cary-5000 UV−vis−NIR spectrophotometer, using BaSO4 as the reference sample. The photocurrents and electrochemical impedance spectroscopy (EIS) were collected at room temperature by an electrochemical analyzer (CHI660A, CH Instruments Co.) in a standard three-electrode system using asprepared samples as the working electrode, a saturated calomel electrode as reference, and a platinum wire parallel to the working
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RESULTS AND DISCUSSION Figure 1 shows the XRD patterns of the different samples. The structure of the as-synthesized Bi2WO6 particles was found to
Figure 1. XRD patterns of the different samples.
be in orthorhombic form (JCPDS Card No. 73-1126), as shown in Figure 1a. As shown in curve b, the pure g-C3N4 has two significant peaks at 27.3° and 13.1°, indexed as the (002) and (100) reflections, respectively.26 Comparing curves c, d, and e, with b, it can be found that C3N4@Bi2WO6, Ag-Bi2WO6, and C3N4@Ag-Bi2WO6 had similar patterns. That is to say, the introduction of C3N4 or Ag nanoparticles had no obvious influence on their crystalline structure. The main reason can be ascribed to the low doping concentration of Ag nanoparticles in the composite, or ascribed to the overlap of the primary (100) B
DOI: 10.1021/acssuschemeng.5b01701 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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Figure 2. SEM images of (a) Bi2WO6; TEM images of (b) Ag-Bi2WO6 (inset, electron diffraction pattern), (c) g-C3N4 (inset, electron diffraction pattern), and (d) C3N4@Ag−Bi2WO6 (inset, electron diffraction pattern).
Figure 3. TEM images of (a) Bi2WO6 and (b) Ag-Bi2WO6. High resolution TEM images of (c, d) C3N4@Ag-Bi2WO6 microspheres.
S3). The SEM images of Ag-Bi2WO6, C3N4@Bi2WO6, and C3N4@Ag-Bi2WO6 (see Figure S4) demonstrate that they inherit the similar hierarchical structure of Bi2WO6; this similarity maybe due to the use of the same Bi2WO6 template but only with some modification. The typical TEM image of Ag-Bi2WO6 in Figure 2b shows that the microsphere is constructed by nanosheets with thickness about 20 nm, which
peak of g-C3N4 (at 27.4°) with the main (113) diffraction of Bi2WO6 at 2θ of 28°. The existence of C3N4 and/or Ag nanoparticles in these composites was further identified through TEM measurement. The morphologies of as-prepared samples were shown in Figure 2. Pure Bi2WO6 sample (Figure 2a) exhibits 3D flowerlike microstructure with diameter about 2−4 μm (see Figure C
DOI: 10.1021/acssuschemeng.5b01701 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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Bi2WO6 and C3N4@Ag-Bi2WO6 samples, the introduction of C3N4 results in a broad absorption in the UV−vis region even up to the near-infrared region. Meanwhile, the adsorption strength of C3N4@Ag-Bi2WO6 was significantly higher than that of C3N4@Bi2WO6 due to the introduction of Ag nanoparticles. The photoinduced charge separation efficiency of different samples was investigated by transient photocurrent experiments and electrochemical impedance spectroscopy (EIS) measurements (Figure 5). The transient photocurrent response curves
are originally assembled from tiny nanoplates. The TEM image of pure g-C3N4 shown in Figure 2c appears to be a lamellar structure, which was formed by the accumulation of the graphitic-like planes. With the loading of Ag nanoparticles and g-C3N4 on the surface of Bi2WO6 microspheres, the TEM image of the C3N4@Ag-Bi2WO6 composite (Figure 2d) shows poor transparence. The TEM image of Bi2WO6 shown in Figure 3a indicates an agglomerated structure assembled from tiny nanoplates; this result is consistent with Figure 2b. With Ag loading, some small dark spots (Ag nanoparticles) were found to adhere to the nanosheet surface, indicating the formation of Ag-Bi2WO6. Distinct lattice fringes can be observed in the high resolution TEM images of C3N4@Ag-Bi2WO6 as shown in Figure 3c,d. Here, fringe spaced by ∼0.315 nm corresponded to the (113) plane of Bi2WO6, and ∼0.323 nm corresponded to the (002) plane of g-C3N4; ∼0.23 nm corresponded to the (111) plane of Ag nanoparticles, indicating that g-C3N4, Ag, and Bi2WO6 coexist in the microspheres. The EDX pattern further confirms their existence in the ternary composite (see Figure S5). Figure S6 shows the SEM images of C3N4@Ag-Bi2WO6 microspheres with corresponding elemental mapping images. It can be seen that the elemental mapping images of Bi, W, C, N, O, and Ag were well-defined with distinct contrast, and the maps of W, O, Bi, and Ag have the same shape and location in Figure S6. Besides, the maps of C and N show the homogeneous distribution of g-C3N4 sheets on the AgBi2WO6 microsphere. The above result demonstrates the definite existence of g-C3N4, Ag, and Bi2WO6 in the C3N4@ Ag-Bi2WO6 microspheres. The optical absorption properties of the as-synthesized photocatalysts were investigated by the UV−vis diffuse reflectance spectra (DRS). As shown in Figure 4, the pure
Figure 5. (a) Photocurrent transient responses at a constant potential of 0.5 V for as-prepared samples, and (b) EIS Nyquist plots of different samples under an applied voltage of −0.5 (vs Ag/AgCl) in aqueous Na2SO4 (0.5 M) solution. The solution was continuously N2 purged and was irradiated under λ > 420 nm. Figure 4. UV−vis absorption spectra of different samples.
for different samples were shown in Figure 5a. The photocurrent generated by the undoped Bi2WO6, Ag-Bi2WO6, gC3N4, C3N4@Bi2WO6, and C3N4@Ag-Bi2WO6 electrodes were 0.14, 0.28, 0.45, 0.76, and 1.31 μA, respectively. The photocurrent of the Ag-Bi2WO6 and C3N4@Bi2WO6 electrodes were about 2.0 and 5.4 times as high as those of the Bi2WO6 electrode, and C3N4@Ag-Bi2WO6 increased the photocurrent further to 9.4 times that of the Bi2WO6 electrode. The visible enhancement of C3N4@Ag-Bi2WO6 in photocurrent demonstrated more efficient separation and less recombination of photoinduced charge at its interface. Figure 5b shows the EIS changes of different samples. In general, the semicircle diameter
Bi2WO6 sample possessed photoabsorption from the UV to visible light until 450 nm.27 After the surface of Bi2WO6 nanoparticles is coated with Ag nanoparticles, the obtained Ag-Bi2WO6 sample not only exhibited a characteristic absorption of Bi2WO6 in the visible region but also showed a new absorption band from 400 to 600 nm which can be assigned to the surface plasmon resonance effect of spatially confined electrons in Ag nanoparticles. The absorption threshold of pure g-C3N4 was located at ca. 470 nm corresponding to the bandgap of 2.62 eV. For the C3N4@ D
DOI: 10.1021/acssuschemeng.5b01701 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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C3N4@Ag-Bi2WO6 can be attributed to the fact that it possesses a stronger visible light absorption, a higher photocurrent density and efficiency in separation, and transmission of photogenerated charge carrier than all the other samples. Figure S7 presented the mineralization ability of C3N4@AgBi2WO6 composite for the RhB in terms of TOC removal. It can be seen that the TOC removal was slightly slower than the photodegradation of RhB, but the TOC removal can reach about 94% with the irradiation time extending to 2 h, suggesting that there are no more byproducts generated during the degradation process. To reveal the photodegradation mechanism, the trapping experiments to determine the main active species during the photodegradation process were performed by using three different sacrificial agents (Figure 6b). The photodegradation efficiency of C3N4@Ag-Bi2WO6 was significantly suppressed by the addition of 1 mM BQ, suggesting that the superoxide radicals are the main active species in RhB photodegradation process. Besides, when 1 mM of t-BuOH was added, the degradation rate of RhB was decreased from 100% to 43%, indicating that the hydroxyl radical plays a relatively important role in the photocatalytic oxidation process. This result agrees well with the terephthalic acid photoluminescence probing analysis (Figure S8). In contrast, the photocatalytic activity of C3N4@Ag-Bi2WO6 shows slight changes by the addition of 1 mM EDTA, indicating that the holes were not the main oxidation species to the degradation process. To further reveal the photoreactivity mechanism, photoinduced H2 production experiments were carried out using the as-prepared photocatalysts under visible light illumination by using triethanolamine (TEOA) as the sacrificial electron donor (Figure 7). Compared with pure g-C3N4, the C3N4@Bi2WO6 and C3N4@Ag-Bi2WO6 catalysts exhibit markedly enhanced photoactivity. Typically, C 3 N 4 @Ag-Bi 2 WO 6 gives a H 2 production activity of 105.8 μmol/h, which is about 4.2 times that of the pure g-C3N4 samples (25.2 μmol/h) and 1.9 times that of C3N4@Bi2WO6 samples (50.3 μmol/h). This result infers a Z-scheme photocatalytic mechanism for C3N4@Ag-
of EIS in the Nyquist diagrams is equal to surface chargetransfer resistance (Rct).28,29 From Figure 5b, we can see that the semicircle radius increases in the order of C3N4@AgBi2WO6 < C3N4@Bi2WO6 < C3N4 < Ag-Bi2WO6 < Bi2WO6. The smaller the radius is, the smaller transfer resistance is. So, this result means that the C3N4@Ag-Bi2WO6 composites possess the optimal efficiency in separation and transfer of photogenerated charge carrier. The result agrees well with that of transient photocurrent measurement result. The photoreactivity and mechanism of the as-synthesized samples were shown in Figure 6. The photocatalytic perform-
Figure 6. (a) Visible-light-driven photocatalytic degradation of RhB using as-prepared samples. (b) Comparison of photocatalytic activities of C3N4@Ag-Bi2WO6 for the degradation of RhB with the addition of (a) BQ, (b) t-BuOH, (c) EDTA, or (d) without scavengers.
ance of as-synthesized samples was estimated toward RhB under visible light irradiation (Figure 6a). It was demonstrated that the photolysis of RhB without a photocatalyst could be ignored according to the blank experiments, which means that the degradation of RhB by as-prepared photocatalysts was mainly due to photocatalysis. Obviously, of all the as-prepared samples reported in this study, C3N4@Ag-Bi2WO6 exhibited much higher photocatalytic activity. It completely degraded RhB within 90 min under visible light irradiation, while under the same conditions, the degradation percent of Bi2WO6, AgBi2WO6, g-C3N4, and C3N4@Bi2WO6 was 25%, 34%, 51%, and 70%, respectively. The higher photodegradation efficiency of
Figure 7. Stable hydrogen evolution from water under visible light irradiation (λ > 420 nm) (a typical time courses of H2 production from water containing 10 vol % triethanolamine as an electron donor) using (a) Bi2WO6, (b) g-C3N4, (c) C3N4@Bi2WO6, and (d) C3N4@AgBi2WO6. E
DOI: 10.1021/acssuschemeng.5b01701 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
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ACS Sustainable Chemistry & Engineering Bi2WO6 composites. Besides, it can be seen that C3N4@AgBi2WO6 exhibits good H2 production stability. The hydrogen evolution rate shows no noticeable deterioration after the fifth run, which means that the C3N4@Ag-Bi2WO6 catalyst possesses excellent recycling stability. On the basis of the above results, the photocatalytic mechanism for the C3N4@Ag-Bi2WO6 is proposed and illustrated in Scheme 1. According to the recently reported
electrons in the CB of Bi2WO6 would shift to metallic Ag and recombine with the photogenerated hole from g-C3N4. This process also efficiently promotes the separation of electron−hole pairs and retains the electrons still on the CB of g-C3N4, while holes are on the VB of Bi2WO6. Because of the negative ECB of g-C3N4, these electrons exhibit strong reducibility and can easily reduce H+ to H2, which agrees well with the H2 evolution experiments.
Scheme 1. Postulate Schematic Diagram of the Separation and Transfer of Photogenerated Charges in the C3N4@AgBi2WO6 Nanocompsosites
CONCLUSIONS A ternary photocatalyst C3N4@Ag-Bi2WO6 was successfully synthesized by anchoring Ag nanoparticles on the g-C3N4 and Bi2WO6 nanosheets, which exhibited a superior photocatalytic performance to the corresponding single- and two-component systems such as Bi2WO6, g-C3N4, Ag-Bi2WO6, and C3N4@AgBi2WO6. The reactive species trapping experiments and the markedly enhanced photoactivity in H2 generation reveal that the C3N4@Ag-Bi2WO6 composites follow the Z-scheme transfer mechanism. In this way, it can efficiently improve the separation and restrain the possible recombination of photoexcited charge carriers, and make them possess higher oxidation or reduction capability. The novel photocatalyst may have potential applications in pollutant removal and overall water splitting in the future.
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ASSOCIATED CONTENT
* Supporting Information S
references,30,31 the CB and VB potentials of C3N4 are −1.12 and 1.58 eV, and the corresponding CB and VB potentials of Bi2WO6 are 0.46 and 3.26 eV, respectively. For C3N4@Bi2WO6, when the g-C3N4 shell harvested visible light, electrons on the CB of g-C3N4 would transfer into the CB of Bi2WO6 now that the CB of g-C3N4 was energetically higher than that of the CB of Bi2WO6. On the other hand, the holes in Bi2WO6 would transfer to the VB of C3N4. Thus, the photogenerated electrons and holes are distributed on different semiconductors, which means the separation and transfer process of charge carrier are significantly increased, and the carrier recombination processes are distinctly inhibited, corresponding to stronger photocatalytic performance. For C3N4@Ag-Bi2WO6, if it follows a similar transfer mechanism with C3N4@Bi2WO6, when it was illuminated under visible light, the electrons on the g-C3N4 would transfer into the CB of Bi2WO6 or maybe directly injected into the Fermi level of Ag, and the holes in Bi2WO6 would transfer to the VB of C3N4. Such heterojunction-transfer mechanism can effectively explain the photodegradation phenomenon of RhB, as the electrons in the CB of Bi2WO6 and holes in the VB of g-C3N4 or metallic Ag have enough reducibility or oxidability to degrade RhB dye molecules. However, with H2 generation taken into account, the heterojunction-transfer mechanism cannot interpret the result of C 3 N 4 @Ag-Bi 2 WO 6 composites in photocatalytic H 2 generation. The CB band edge of Bi2WO6 is ∼0.46 eV, demonstrating a poor ability to reduce H+ into H2, as proven in Figure 7. On the other hand, if the C3N4@Ag-Bi2WO6 composites follow the Z-scheme transfer mechanism, the markedly enhanced photoactivity in H2 generation can be explained perfectly. In this manner, Ag nanoparticles might serve as a charge transport center to form the C3N4@Ag-Bi2WO6 Z-scheme system. The CB potentials of Bi2WO6 are more negative than that of metallic Ag due to its high Schottky barriers at the metal−semiconductor interface. Thus, the photogenerated
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.5b01701. Figures showing photocatalytic degradation, SEM images, size distribution, EDX pattern, elemental mapping images, and fluorescence spectra (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Phone: +86-27-68754613. Fax: +86-27-68752569. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (No. 51272185) and the National Program on Key Basic Research Project (973 Grant 2012CB821404).
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REFERENCES
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DOI: 10.1021/acssuschemeng.5b01701 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
