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Article Cite This: ACS Omega 2019, 4, 3871−3880
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Facile Formation of Bi2O2CO3/Bi2MoO6 Nanosheets for Visible LightDriven Photocatalysis Junlei Zhang,† Zhendong Liu,† and Zhen Ma*,†,‡ †
Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention (LAP3), Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, P.R. China ‡ Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, P.R. China
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S Supporting Information *
ABSTRACT: Bi2O2CO3/Bi2MoO6 heterojunction catalysts were prepared by treating Bi2MoO6 sheets with aqueous NaHCO3 solutions at room temperature. All the Bi2O2CO3/ Bi2MoO6 heterojunctions exhibited higher activities than pristine Bi2MoO6 in the photocatalytic degradation of rhodamine B (RhB), methyl orange, and ciprofloxacin under visible-light irradiation, and the most active photocatalyst was found to be the one with a C/Bi molar ratio of ∼1/2.3. Relevant samples were characterized by X-ray diffraction, Xray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, N2 adsorption− desorption, Fourier transform infrared spectroscopy, and UV−vis spectroscopy. The higher activity of Bi2O2CO3/Bi2MoO6 than pristine Bi2MoO6 is explained by the enhanced separation and transfer of photogenerated electron/hole pairs, as verified by transient photocurrent densities, photoluminescence spectroscopy, and electrochemical impedance spectroscopy. Photogenerated holes (h+) and superoxide radical anions (•O2−) were found to be the main active species. The good reusability of Bi2O2CO3/Bi2MoO6 was testified by cycling degradation of RhB and tetracycline hydrochloride.
1. INTRODUCTION TiO2, a benchmark photocatalyst, works efficiently under UV light that merely accounts for a very small fraction of sunlight. Seeking new catalysts that can make full use of sunlight, especially the visible light portion, is a meaningful topic. Bi2MoO6, a nontoxic and visible light-responsive semiconductor, is promising for making photocatalysts.1−4 Bi2MoO6 photocatalysts with different morphologies or structures (e.g., nanoparticles,5 nanotubes,6 nanosheets,7 flowerlike structures,8,9 and hollow microspheres10,11) have been developed. However, the recombination of photogenerated carriers is still a serious problem when using pristine Bi2MoO6 as a photocatalyst.12 It is of great interest to develop Bi2MoO6-based modified photocatalysts with enhanced photocatalytic performance. Bi2MoO6-based modified photocatalysts can be prepared by depositing metals (e.g., Pt,13 Pd,14 and Ag15) onto Bi2MoO6, doping Bi2MoO6 with metal ions (e.g., Er3+,16 Gd3+,17 Ho3+,17 and Yb3+17), and integrating Bi2MoO6 with other substances such as TiO2,18 RGO,19 g-C3N4,20 MoS2,21 Ag/AgCl,22 Ag 2 MoO 4 , 23,24 Ag 3 VO 4 , 25 Ag 2 O, 26−28 Ag−Ag 2 CO 3 , 29 Ag2CO3,30 MxOy (M = Cu, Co, Ni),31 Fe2O3,32 ZnFe2O4,33 Bi2S3,34 BiOX (X = Cl, Br, I),35−37 Bi2O2CO3,38−40 BiVO4,41 Ta 3N5,42 Bi4MoO9,43 Bi2Mo2O9,44 Bi3.64Mo0.36O6.55,45,46 Bi4V2O11,47 and Bi2Mo3O12.48 The numerous references cited above indicate that research along this direction is popular. © 2019 American Chemical Society
However, Bi2O2CO3/Bi2MoO6 photocatalysts have been seldom reported,38−40 although Bi2O2CO3 has been combined with other substances (e.g., Cu2O,49 Co3O4,50 ZnFe2O4,51 Bi,52 Au−Bi2O3,53 Bi2O4,54,55 Bi4O7,56 Bi2S3,57 BiOCl,58,59 BiOBr,60 BiOI,61 BiVO4,62 Bi2WO6,63 Ag2O,64 Ag2CO3,65 AgI,66 carbon quantum dots,67 and porphyrins68) to form heterojunction photocatalysts.69 In general, the formation of heterojunction systems is an efficient way to design visible light-responsive photocatalysts.70−72 As for the Bi2O2CO3/Bi2MoO6 heterojunction system, Xu et al. prepared Bi2O2CO3/Bi2MoO6 by subjecting a mixture containing BiOCl, MoO42−, and g-C3N4 to hydrothermal treatment at 180 °C.38 The formed sesame-biscuit-like Bi2O2CO3/Bi2MoO6 heterostructures showed enhanced performance in photocatalytic degradation of rhodamine B (RhB). Zhang and co-workers prepared microsphere-like Bi2O2CO3/ Bi2MoO6 heterojunctions composed of nanoplatelets of Bi2O2CO3 and Bi2MoO6 via a template-free solvothermal process.39 The obtained samples showed high photocatalytic activity in the degradation of RhB. Wang and co-workers prepared a meshlike Bi2O2CO3/Bi2MoO6 composite composed of many nanoparticles via a hydrothermal method using Received: December 31, 2018 Accepted: February 7, 2019 Published: February 22, 2019 3871
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urea to tune the morphology.40 They again demonstrated the superior photocatalytic activity of Bi2O2CO3/Bi2MoO6 than Bi2MoO6 in the degradation of RhB. A quaternary heterostructured Ag−Bi2O2CO3/Bi3.64Mo0.36O6.55/Bi2MoO6 composite was also synthesized and tested in visible light-driven photocatalysis.73 In these relevant papers,38−40 the morphologies of the Bi2O2CO3/Bi2MoO6 materials are very interesting, but there is still room for developing Bi2O2CO3/Bi2MoO6 materials with different morphologies via facile preparation methods, demonstrating the advantages of the materials in different reactions and elucidating the reaction mechanisms. Herein, Bi2O2CO3/Bi2MoO6 nanosheets were prepared via a facile route, that is, by reacting Bi2MoO6 with aqueous NaHCO3 at room temperature. These materials were characterized and tested in the photocatalytic degradation of industrial dyes [RhB and methyl orange (MO)], ciprofloxacin (CIP), and tetracycline hydrochloride (TC) under visible-light irradiation. Reasons for the enhanced photocatalytic activity were investigated. A possible photodegradation mechanism based on Bi2O2CO3/Bi2MoO6 was proposed. Even though Bi2O2CO3/Bi2MoO6 has been reported by other groups,38−40 the current work differs from these previous studies, in terms of the preparation method, morphology of the heterojunctions, and scope of photocatalytic reactions. At the end of the paper, we will provide more discussions on what is learned from this work and what can be done in the future.
According to scanning electron microscopy (SEM) characterization, pure Bi2MoO6 manly consists of irregular nanosheets (Figure 2A). Bi2O2CO3/Bi2MoO6 (S1−S5) samples
2. RESULTS AND DISCUSSION 2.1. Basic Characterization of Samples. X-ray diffraction (XRD) was used to characterize Bi2MoO6 and Bi2O2CO3/ Bi2MoO6 (S1−S5). As seen in Figure 1, the obtained pristine
Figure 2. SEM images of (A) Bi2MoO6 and (B) S3 (Bi2O2CO3/ Bi2MoO6).
contain Bi2MoO6 nanosheets with slightly smaller sizes (Figures 2B and S1) probably because of the vigorous stirring (1200 rpm) of the system for 4 h, after mixing Bi2MoO6 nanosheets with NaHCO3 solution. Transmission electron microscopy (TEM) and highresolution TEM (HRTEM) were used to characterize Bi2MoO6 and typical Bi2O2CO3/Bi2MoO6 samples (S3 and S5). These samples show a 2D nanosheet structure with irregular sizes (Figure 3), consistent with the SEM results (Figures 2 and S1). Figure 3B shows an HRTEM image of Bi2MoO6. The lattice spacing is determined to be 0.313 nm, corresponding to the (131) plane of orthorhombic Bi2MoO6 (JCPDS no. 21-0102). The HRTEM image of S3 (Figure 3D) also shows the lattice stripe belonging to the (131) plane of orthorhombic Bi2MoO6. The surface is covered by a thin layer, most likely Bi2O2CO3 because the corresponding XRD pattern shows a peak corresponding to Bi2O2CO3 (Figure 1). Figure S2 enables us to take a closer look at the interface. For S5, the HRTEM image shows the presence of tetragonal Bi2O2CO3 nanoparticles on the Bi2MoO6 surface (Figure 3F). The elemental distribution and composition in S3 were analyzed by scanning TEM (STEM) mapping and TEM− energy-dispersive X-ray (EDX). The STEM image confirms the nanosheet structure of S3 (Figure 4A). Bi, Mo, O, and C elements distribute homogeneously (Figure 4B−E). The measured molar ratio of C/Bi is 1/2.4 (Figure 4F), consistent with the theoretical value (1/2.3). Additionally, EDX element mapping and EDX data from S5 confirmed the existence of the related elements in Bi2O2CO3/Bi2MoO6 (Figure S3). The measured molar ratio of C/Bi is 1/1.99 (Figure S3F), whereas
Figure 1. XRD patterns of Bi2MoO6 and Bi2O2CO3/Bi2MoO6 (S1− S5), and standard XRD patterns of orthorhombic Bi2MoO6 (JCPDS no. 21-0102) and tetragonal Bi2O2CO3 (JCPDS no. 41-1488).
Bi2MoO6 is orthorhombic Bi2MoO6 (JCPDS no. 21-0102). Bi2O2CO3/Bi2MoO6 (S1−S5) samples mainly exhibit orthorhombic Bi2MoO6 peaks. The strongest (013) peak (2θ = 30.3°) of tetragonal Bi2O2CO3 (JCPDS no. 41-1488) appears for S3, S4, and S5 with theoretical C/Bi molar ratio of 1/2.3, 1/1.8, and 1/1.5, respectively (Figure 1). This peak enhances when going from S3 to S5 because of the addition of more NaHCO3 during the synthesis. No other impurity peaks can be observed. The presence of residual NaHCO3 can be excluded because the Bi2O2CO3/Bi2MoO6 samples were thoroughly washed by water and our later X-ray photoelectron spectroscopy (XPS) characterization excludes the presence of residual Na. 3872
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Figure 5. FTIR spectra of Bi2MoO6 and S3 (Bi2O2CO3/Bi2MoO6).
and bending vibrations of octahedral BiO6.76 Two bands at 1628.6 and 1384.7 cm−1 are ascribed to the stretching and bending vibrations of adsorbed water, respectively. These absorption bands exist in both samples. Besides, S3 also shows a peak at 1478.4 cm−1 because of the internal vibration of CO32− for Bi2O2CO3.77 In addition, compared to S3, pristine Bi2MoO6 shows a clear peak located at 934.0 cm−1, which can be ascribed to C−H bonds; this is because Bi2MoO6 was prepared in the presence of organic solvent (i.e., ethanol and ethylene glycol).34 The surface composition and chemical status of Bi2MoO6 and S3 were probed by XPS. In the survey spectra for Bi2MoO6 and S3 (Figure S4), characteristic C, O, Bi, and Mo peaks are detected; no impurities (such as Na) are detected. The data indicate that no NaHCO3 is left behind after thorough washing during the synthesis stage. Next, selected elements were picked for precise XPS scanning. For the C 1s orbit scan of S3 (Figure 6A), three peaks at 284.6, 286.1, and 288.5 eV (attributed to the C−C, C−O, and O−CO groups, respectively) are found, indicating the existence of adventitious carbon and CO32− in S3.78 S3 has apparently more carbonate species than Bi2MoO6. The O 1s peaks are deconvoluted (Figure 6B). Bi2MoO6 shows two deconvoluted O 1s peaks assigned to Bi−O (529.7 eV) and Mo−O (531.8 eV). However, for S3, the carbonate
Figure 3. TEM and HRTEM images of Bi2MoO6 (A,B), S3 (C,D), and S5 (E,F).
the theoretical value is 1/1.5. Note that Bi2O2CO3/Bi2MoO6 samples denoted as S1−S5 were prepared by adding a certain amount (3, 5, 7, 9, or 11 mL) of NaHCO3 solution (0.1 mol/ L) to a suspension containing 0.5 g of Bi2MoO6 (0.82 mmol) and 50 mL of water under vigorous stirring (1200 rpm), followed by continuous stirring for 4 h. Thus, the EDX data indicate that NaHCO3 in the solution can not be completely consumed via reacting it with Bi2MoO6 when it is overdosed. Figure 5 presents Fourier transform infrared (FTIR) spectra of Bi2MoO6 (red line) and S3 (blue line). Bi2MoO6 shows absorption bands at 400−900 cm−1.7 The bands at 843.0 and 796.3 cm−1 can be assigned to the asymmetric and symmetric stretching modes of MoO6, respectively, involving vibrations of the apical oxygen atoms.74 The band at 731.2 cm−1 is attributed to the asymmetric stretching mode of MoO6 involving vibrations of the equatorial oxygen atoms, and the band at 573.4 cm−1 corresponds to the bending vibration of MoO6.75 The band at 442.0 cm−1 is attributed to the stretching
Figure 4. (A) STEM, (B−E) EDX elemental mapping, and (F) EDX data images of S3. 3873
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Figure 6. High-resolution XPS spectra of (A) C 1s, (B) O 1s, (C) Bi 4f, and (D) Mo 3d from Bi2MoO6 and S3 (Bi2O2CO3/Bi2MoO6).
mg/L). In this case, the reaction takes less time, and a similar activity trend can be observed (Figure S6). S1−S5 samples are still more active than Bi2MoO6 in the photocatalytic degradation of MO (50 mL, 10 mg/L) and CIP (50 mL, 10 mg/L), as shown in Figure 7B,C. The activities of S1−S5 still show the sequence S1< S2 < S3 > S4 > S5. We additionally found that S3 is effective for the degradation of TC (50 mL, 5 mg/L, Figure S7). The recyclability of S3 was tested. To minimize the testing time, low-concentration solutions of RhB (50 mL, 2.5 mg/L) and TC (50 mL, 5 mg/L) were used. In each run, 30 min dark adsorption and 60 min reaction were involved. As shown in Figure S8, S3 can be reused without any loss of activity. By comparing the XRD patterns (Figure S9) and SEM images (Figure S10) of S3 before and after five runs, we can clearly see that S3 remains the stable phase composition and morphology/structure. 2.3. Reasons for the Enhanced Activity. The question now arises why S3 is more active than Bi2MoO6 in visible lightdriven photocatalysis. One reason may be traced to its visiblelight absorption. However, our UV−vis−diffuse reflectance measurement (Figure S11) data indicate that the addition of Bi2O2CO3 to Bi2MoO6 (S1−S5) does not lead to enhanced visible-light absorption (λ > 400 nm). Thus, that effect is excluded as a reason. The difference in BET surface areas (Bi2MoO6: 7.1 m2/g; S3: 7.8 m2/g) is also small (Figure S5), whereas the difference in photocatalytic activity is obvious (Figure 7). The separation and migration of photogenerated carriers usually play an important role in determining the activity of a photocatalyst.79 The photocurrent response tests of Bi2MoO6 and S3 were conducted in the dark and under visible light in 0.1 M Na2SO4 (Figure 8). Both Bi2MoO6 and S3 generated transient photocurrent when the light was on, and the photocurrent decreased sharply when the light was off. After
peak (530.4 eV) increases greatly at the expense of the Mo−O peak (531.8 eV), whereas the Bi−O (529.5 eV) peak is still obvious. The data are consistent with the TEM observation for S3, that is, the surface of Bi2MoO6 is covered by a Bi2O2CO3 layer (Figure 3D). Figure 6C shows Bi 4f5/2 and Bi 4f7/2 peaks at 164.1 and 158.8 eV, respectively, confirming the presence of Bi3+ in S3.11 From Figure 6D, two peaks at 232.0 and 235.1 eV can be attributed to Mo 3d5/2 and Mo 3d3/2, respectively, confirming the presence of Mo6+ in S3.11 The positions of Bi 4f, Mo 3d, O 1s, and C 1s peaks of S3 are identical to the corresponding positions of Bi2MoO6. From the N2 sorption isotherms of Bi2MoO6 and S3 (Figure S5A), Brunauer−Emmett−Teller (BET) surface areas of Bi2MoO6 and S3 are determined to be 7.1 and 7.8 m2/g, respectively. The pore volumes of Bi2MoO6 and S3 are 0.0089 and 0.0097 m2/g, respectively (Figure S5B). The low surface areas and small pore volumes of these materials are consistent with the bulk morphology of the materials (Figures 2 and 3). 2.2. Photocatalytic Performance. Photocatalytic degradation of RhB (50 mL, 10 mg/L) was studied. As shown in Figure 7A, after 30 min in the dark and 150 min under visiblelight irradiation, RhB does not degrade when no catalyst exists. The photodegradation efficiencies clearly show the sequence S1 < S2 < S3 > S4 > S5. All the S1−S5 samples are more active than Bi2MoO6. It is noted that the rigorous stirring during the treatment of Bi2MoO6 by an aqueous NaHCO3 solution may make the Bi2MoO6 sheets smaller (Figures 2 and S1). Thus, a control experiment was carried out, in which Bi2MoO6 was rigorously stirred in water for 4 h, dried, and subjected to photocatalytic testing. The sample (Bi2MoO6-S) adsorbs less RhB than Bi2MoO6 during the dark adsorption stage, and the adsorption amount is the same of those of S1−S5 samples. Thus, the activity trend mentioned above can be confirmed. We also repeated the catalytic experiments by using RhB (50 mL, 2.5 mg/L) with a concentration lower than before (10 3874
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To gain insight into the electron-transport and recombination properties of the samples, EIS analyses were performed. The smaller radius of the EIS Nyquist plot demonstrates the lower impedance and a higher efficiency of charge transfer.80 As shown in Figure 9A, S3 shows a much smaller arc radius than Bi2MoO6, implying that the separation efficiency of photogenerated charge carriers is enhanced for Bi2O2CO3/ Bi2MoO6, thus extending the lifetime of photoexcited electron−hole pairs. PL spectra were employed to confirm the enhanced separation efficiency of photogenerated charge carriers. A lower PL emission intensity usually means that a semiconductor has a stronger ability to facilitate the separation and migration of photogenerated carriers.81 From Figure 9B, both Bi2MoO6 and S3 show a strong emission peak centered at around 580 nm. S3 shows a lower peak intensity than Bi2MoO6, meaning that S3 (Bi2O2CO3/Bi2MoO6) can facilitate the separation and migration of photoexcited electron/hole pairs more efficiently. Radical-capture experiments involving corresponding scavengers were performed to monitor the active radicals involved in the photoreaction (Figure 10). For the reaction system involving Bi2MoO6 (Figure 10A) or S3 (Figure 10B), the addition of ammonium oxalate (1 mmol, scavenger of h+) could inhibit RhB degradation obviously. Adding benzoquinone (0.02 mmol, scavenger of •O2− species) also led to the decrease of RhB degradation obviously. The existence of isopropyl alcohol (1 mmol, scavenger of •OH species) almost has no effect on RhB degradation. The data imply that the main active species in photocatalytic degradation of RhB are h+ and •O2−, whereas •OH is not relevant. An ESR spin-trap with the DMPO technique was employed to confirm the results of radical-capture experiments. Bi2MoO6 does not generate DMPO ESR spin-trapping signals of •O2− and •OH in the dark (Figure 11A,B). With light irradiation, Bi2MoO6 leads to the formation of •O2− but no •OH. Similar results are obtained when testing S3 (Figure 11C−D). However, S3 can lead to the generation of more •O2−, as seen from stronger DMPO ESR spin-trapping signals. This can be a reason for the enhanced activity of Bi2O2CO3/Bi2MoO6. In reference to the energy band positions of Bi2MoO6 (ECB = −0.37 V, EVB = 2.27 V)29 and Bi2O2CO3 (ECB = 0.16 V, EVB = 3.56 V),49 we propose a possible photocatalytic mechanism for Bi2O2CO3/Bi2MoO6 (Figure 12). Although Bi2O2CO3 cannot be excited by visible light because of its wide band gap (Eg = ∼3.4 eV),49,82 Bi2MoO6 can be excited by visible light,83 thus producing photogenerated electrons (e−) and holes (h+). Moreover, because the ECB of Bi2O2CO3 (0.16 V) is more positive than that of Bi2MoO6 (−0.37 V), the photogenerated electrons will be able to flow to the conduction band of Bi2O2CO3. Thus, the photogenerated e−/h+ pairs in the heterojunction system can be efficiently separated, which prolongs the lifetime of active species existing in the reaction system. This explanation is consistent with our mechanistic experiments (Figures 8−11). It should be mentioned that Bi2O2CO3 cannot be excited by visible light because of its wide band gap (Eg = ∼3.4 eV),49,82 and it has poor photocatalytic activity under visible light.50,56,84,85 Thus, the presence of more Bi2O2CO3 (exceeding the optimal content in S3) in the Bi2O2CO3/Bi2MoO6 heterojunction catalyst (for the cases of S4 and S5) may lead to decreased photocatalytic activity compared with that associated with S3.
Figure 7. Degradation curves of (A) RhB (50 mL, 10 mg/L), (B) MO (50 mL, 10 mg/L), and (C) CIP (50 mL, 10 mg/L) with using Bi2MoO6 or Bi2O2CO3/Bi2MoO6 (S1−S5) as a catalyst (30 mg).
Figure 8. Transient photocurrent densities of Bi2MoO6 and S3.
four intermittent on−off irradiation cycles, the photocurrent intensity kept steady. S3 showed a remarkably enhanced photocurrent density compared to Bi2MoO6, demonstrating the effective separation of photoinduced electron/hole pairs in Bi2O2CO3/Bi2MoO6 upon exposure to visible light. 3875
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Figure 9. (A) Electrochemical impedance spectroscopy (EIS) Nyquist plots and (B) photoluminescence (PL) spectra of Bi2MoO6 and S3.
Figure 10. Effects of scavengers on RhB degradation in presence of (A) Bi2MoO6 or (B) S3.
Figure 11. 5,5-Dimethyl-pyrroline N-oxide (DMPO) electron spin resonance (ESR) spin-trapping signals of (A,B) Bi2MoO6 and (C,D) S3 (Bi2O2CO3/Bi2MoO6) for •O2− and •OH.
2.4. Discussion. It should be mentioned that the objective of this work was not to develop the most active photocatalyst in the world. Numerous new catalysts with different levels of activities have been reported. It is interesting to develop catalysts with new compositions, structures/morphologies, functions, or preparation methods and to understand the correlations among preparation methods/details, structures/ morphologies, and catalytic performance.86,87
To put the current work in perspective, we compare the activity of the most active S3 catalyst in this work with those of Ag2O/Bi2MoO6,26 Ag2MoO4/Bi2MoO6,23 and Ag−Ag2CO3/ Bi2MoO629 studied under identical reaction conditions. As seen in Figure S12, the activity of the samples follows the sequence Ag2MoO4/Bi2MoO6 ∼ Ag−Ag2CO3/Bi2MoO6 ∼ Ag2O/Bi2MoO6 > Bi2O2CO3/Bi2MoO6. 3876
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ratio was determined to be ∼1/2.3. The optimal Bi2O2CO3/ Bi2MoO6 catalyst (S3) was also found to be more active than Bi2MoO6 in degrading MO, CIP, or TC by visible-light photocatalysis. The cycling degradation of RhB and TC together with relevant XRD and SEM characterization proved the stability of Bi2MoO6/Bi2MoO6 in catalytic reactions. Transient photocurrent densities, PL, and EIS data demonstrated that S3 can separate and transfer photogenerated electrons and holes more efficiently than Bi2MoO6. Photogenerated holes (h+) and superoxide radical anions (•O2−) were confirmed as the main active species by radical-capture experiments, whereas •OH is not relevant in the reaction. ESR data indicated that S3 can generate more •O2− species than Bi2MoO6 upon visible-light irradiation, whereas •OH is not generated for both S3 and Bi2MoO6. This work provides a simple and effective way for developing Bi2MoO6-based photocatalysts that can work under visible light.
Figure 12. Possible photocatalytic degradation mechanism based on Bi2O2CO3/Bi2MoO6.
No attempt was made to compare the activity of our Bi2O2CO3/Bi2MoO6 catalyst with those of Bi2O2CO3/ Bi2MoO6 catalysts reported in the literature because the reaction conditions are all different.38−40 Nevertheless, the trend seen in our study is in line with the trend seen in others’ work,38−40 in the sense that the optimal Bi2O2CO3/Bi2MoO6 catalyst is more active than Bi2MoO6. Further research may be conducted to study the influence of the morphologies and sizes of Bi2MoO6 and the preparation details (e.g., synthesis and calcination temperatures) on the catalytic performance of Bi2O2CO3/Bi2MoO6 catalysts. In fact, the Bi2MoO6 supports used for the preparation of Ag2O/Bi2MoO6 and Ag2MoO4/ Bi2MoO6 mentioned above are flowerlike microspheres,23,26 whereas the Bi2MoO6 supports used for the preparation of Ag−Ag2CO3/Bi2MoO629 and Bi2O2CO3/Bi2MoO6 in this study are sheets. A recent study by others shows that Bi2MoO6 microspheres (instead of sheets) can also be used to make efficient Ag2CO3/Bi2MoO6 photocatalysts.30 Thus, the morphology effect may be a subtle effect that needs more carful studies in the future. This work also has important implications to the synthesis of Bi2MoO6-based heterojunction catalysts. In some cases, NaHCO3 was used as a precipitation agent for the formation of Ag2CO3/Bi2MoO6 catalysts.29 Our current work indicates that the reaction between Bi2MoO6 and aqueous NaHCO3 to form surface Bi2O2CO3 can happen even at room temperature. Thus, this side reaction should be considered when synthesizing Ag2CO3/Bi2MoO6 catalysts. Care should be taken to control the synthesis procedure and the amount of NaHCO3 to avoid the formation of Bi2O2CO3/Bi2MoO6 unless the formation of Ag2CO3−Bi2O2CO3/Bi2MoO6 is needed. In our previous work,29 AgNO3 solution was first mixed with Bi2MoO6 powders to allow for the adsorption of Ag+ onto Bi2MoO6 powders. A stoichiometric amount of NaHCO3 solution was then added into the system to allow for complete reaction between Ag+ and NaHCO3 to form Ag2CO3 on Bi2MoO6. The reaction between Ag+ and aqueous NaHCO3 is supposed to be much faster than the conversion of solid-phase Bi2MoO6 to Bi2O2CO3/Bi2MoO6. Thus, under the right synthesis conditions, the unintentional formation of Bi2O2CO3 can be avoided.
4. EXPERIMENTAL SECTION 4.1. Materials. Bi(NO3)3·5H2O, Na2MoO4·2H2O, HNO3, NaHCO3, RhB, MO, and CIP of analytical grade were purchased from Sinopharm Chemical Reagent. TC was purchased from Aladdin. All reagents were used as received. 4.2. Synthesis of Bi2O2CO3/Bi2MoO6. Typically, 0.5 g of Bi2MoO6 (0.82 mmol) prepared according to our previous report29 was dispersed in 50 mL deionized water with the aid of ultrasonic treatment for 15 min. A certain amount (3, 5, 7, 9, or 11 mL) of NaHCO3 solution (0.1 mol/L) was dropped therein under vigorous stirring (1200 rpm). The mixture was further stirred continuously for 4 h. Bi2O2CO3/Bi2MoO6 samples (denoted as S1−S5) were collected by removing the supernatant, washed with deionized water three times, and dried at 60 °C for 24 h. The theoretical C/Bi molar ratios of S1−S5 samples, by simply assuming that NaHCO3 reacts with Bi2MoO6 completely, are 1/5.5, 1/3.3, 1/2.3, 1/1.8, and 1/1.5, respectively. 4.3. Characterization. XRD data were obtained on an MSAL XD2 X-ray diffractometer with Cu Kα radiation at 40 kV and 30 mA at a scanning speed of 8° min−1. SEM experiments were conducted on a Shimadzu SUPERSCAN SSX-550 field emission scanning electron microscope. TEM experiments were performed using a JEOL JEM-2100F highresolution transmission electron microscope. FTIR spectra were recorded with a Thermo Fisher Nexus 670 FTIR spectrometer using a standard KBr disk method. XPS data were obtained on a multifunctional photoelectron spectroscopy instrument (Axis Ultra DLD, Kratos). Optical diffuse reflectance spectra were recorded on a UV−vis−near-infrared spectroscopy scanning spectrophotometer (LAMBDA 35, PerkinElmer) with an integrating sphere accessory. PL experiments were conducted using a LabRAM HR Evolution instrument (HORIBA JY Company, France) with an excitation wavelength of 355 nm. EIS data were obtained by an electrochemical analyzer (CHI 660B Chenhua Instrument Company). Electron paramagnetic resonance signals of paramagnetic species spin-trapped with DMPO were recorded on a Bruker ESR 300E spectrometer. 4.4. Evaluation of Photocatalytic Activity. Photocatalytic degradation of RhB (10 mg/L), MO (10 mg/L), CIP (10 mg/L), and TC (5 mg/L) was conducted using a Xe lamp (300 W, HSX-F300, Beijing NeT Technology Co., Ltd.) coupled with a UV-cutoff filter (420 nm) as the light source.23,26,29,88−96 The distance between the lamp and the
3. CONCLUSIONS Bi2MoO6 nanosheets modified with Bi2O2CO3 were prepared by chemical deposition. The enhanced photocatalytic activities of Bi2O2CO3/Bi2MoO6 were identified in degrading RhB under visible light, and the optimal C/Bi theoretical molar 3877
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(9) Dai, W.; Yu, J.; Xu, H.; Hu, X.; Luo, X.; Yang, L.; Tu, X. Synthesis of hierarchical flower-like Bi2MoO6 microspheres as efficient photocatalyst for photoreduction of CO2 into solar fuels under visible light. CrystEngComm 2016, 18, 3472−3480. (10) Yin, W.; Wang, W.; Sun, S. Photocatalytic degradation of phenol over cage-like Bi2MoO6 hollow spheres under visible-light irradiation. Catal. Commun. 2010, 11, 647−650. (11) Kashfi-Sadabad, R.; Yazdani, S.; Alemi, A.; Huan, T. D.; Ramprasad, R.; Pettes, M. T. Block copolymer-assisted solvothermal synthesis of hollow Bi2MoO6 spheres substituted with samarium. Langmuir 2016, 32, 10967−10976. (12) Peng, Y.; Zhang, Y.; Tian, F.; Zhang, J.; Yu, J. Structure tuning of Bi2MoO6 and their enhanced visible light photocatalytic performances. Crit. Rev. Solid State Mater. Sci. 2017, 42, 347−372. (13) Zhang, J. L.; Zhang, L. S.; Ju, X. T.; Liu, J. S. Study on the fabrication and photocatalytic properties of Bi2MoO6-Pt heterojunction. Acta Sci. Circumstantiae 2016, 36, 2050−2058. (14) Meng, X.; Zhang, Z. Pd-doped Bi2MoO6 plasmonic photocatalysts with enhanced visible light photocatalytic performance. Appl. Surf. Sci. 2017, 392, 169−180. (15) Mohamed, R. M.; Ibrahim, F. M. Visible light photocatalytic reduction of nitrobenzene using Ag/Bi2MoO6 nanocomposite. J. Ind. Eng. Chem. 2015, 22, 28−33. (16) Zhou, T.; Hu, J.; Li, J. Er3+ doped bismuth molybdate nanosheets with exposed {010} facets and enhanced photocatalytic performance. Appl. Catal., B 2011, 110, 221−230. (17) Alemi, A. A.; Kashfi, R.; Shabani, B. Preparation and characterization of novel Ln (Gd3+, Ho3+ and Yb3+)-doped Bi2MoO6 with Aurivillius layered structures and photocatalytic activities under visible light irradiation. J. Mol. Catal. Chem. 2014, 392, 290−298. (18) Tian, G.; Chen, Y.; Zhai, R.; Zhou, J.; Zhou, W.; Wang, R.; Pan, K.; Tian, C.; Fu, H. Hierarchical flake-like Bi2MoO6/TiO2 bilayer films for visible-light-induced self-cleaning applications. J. Mater. Chem. A 2013, 1, 6961−6968. (19) Zhang, Y.; Zhu, Y.; Yu, J.; Yang, D.; Ng, T. W.; Wong, P. K.; Yu, J. C. Enhanced photocatalytic water disinfection properties of Bi2MoO6-RGO nanocomposites under visible light irradiation. Nanoscale 2013, 5, 6307−6310. (20) Li, H.; Liu, J.; Hou, W.; Du, N.; Zhang, R.; Tao, X. Synthesis and characterization of g-C3N4/Bi2MoO6 heterojunctions with enhanced visible light photocatalytic activity. Appl. Catal., B 2014, 160−161, 89−97. (21) Chen, Y.; Tian, G.; Shi, Y.; Xiao, Y.; Fu, H. Hierarchical MoS2/ Bi2MoO6 composites with synergistic effect for enhanced visible photocatalytic activity. Appl. Catal., B 2015, 164, 40−47. (22) Li, X.; Fang, S.; Ge, L.; Han, C.; Qiu, P.; Liu, W. Synthesis of flower-like Ag/AgCl-Bi2MoO6 plasmonic photocatalysts with enhanced visible-light photocatalytic performance. Appl. Catal., B 2015, 176−177, 62−69. (23) Zhang, J.; Ma, Z. Flower-like Ag2MoO4/Bi2MoO6 heterojunctions with enhanced photocatalytic activity under visible light irradiation. J. Taiwan Inst. Chem. Eng. 2017, 71, 156−164. (24) Wang, Z.; Huo, Y.; Zhang, J.; Lu, C.; Dai, K.; Liang, C.; Zhu, G. Facile preparation of two-dimensional Bi2MoO6@Ag2MoO4 coreshell composite with enhanced visible light photocatalytic activity. J. Alloys Compd. 2017, 729, 100−108. (25) Jonjana, S.; Phuruangrat, A.; Thongtem, S.; Wiranwetchayan, O.; Thongtem, T. Preparation and characterization of Ag3VO4/ Bi2MoO6 nanocomposites with highly visible-light-induced photocatalytic properties. Mater. Lett. 2016, 180, 93−96. (26) Zhang, J.; Liu, H.; Ma, Z. Flower-like Ag2O/Bi2MoO6 p-n heterojunction with enhanced photocatalytic activity under visible light irradiation. J. Mol. Catal. A: Chem. 2016, 424, 37−44. (27) Meng, X.; Zhang, Z. Plasmonic Z-scheme Ag2O-Bi2MoO6 p-n heterojunction photocatalysts with greatly enhanced visible-light responsive activities. Mater. Lett. 2017, 189, 267−270.
top of the beaker mouth was ca. 15 cm. The temperature of the reaction system was controlled at around 25 °C. Before visible-light illumination, 30 mg of the catalyst was suspended in 50 mL of solution in a 100 mL beaker, and the suspension was stirred (800 rpm) for 30 min. Subsequently, visible-light irradiation was conducted for 60 min for each experiment. 4 mL of the suspension was sampled every 15 min and separated by centrifugation at a speed of 8000 rpm for 15 min. The supernatant was then analyzed by using a UV5200PC spectrometer. Cycling degradation experiments involving RhB and TC were conducted according to the procedure reported before.29
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.8b03699.
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Additional characterization data and reaction testing data of relevant samples (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Zhen Ma: 0000-0002-2391-4943 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We acknowledge the financial support by the National Natural Science Foundation of China (grant no. 21477022) and the Shanghai Tongji Gao Tingyao Environmental Science & Technology Development Foundation.
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REFERENCES
(1) Shimodaira, Y.; Kato, H.; Kobayashi, H.; Kudo, A. Photophysical properties and photocatalytic activities of bismuth molybdates under visible light irradiation. J. Phys. Chem. B 2006, 110, 17790−17797. (2) Bi, J.; Wu, L.; Li, J.; Li, Z.; Wang, X.; Fu, X. Simple solvothermal routes to synthesize nanocrystalline Bi2MoO6 photocatalysts with different morphologies. Acta Mater. 2007, 55, 4699−4705. (3) Tian, G.; Chen, Y.; Zhou, W.; Pan, K.; Dong, Y.; Tian, C.; Fu, H. Facile solvothermal synthesis of hierarchical flower-like Bi2MoO6 hollow spheres as high performance visible-light driven photocatalysts. J. Mater. Chem. 2011, 21, 887−892. (4) Guo, C.; Xu, J.; Wang, S.; Li, L.; Zhang, Y.; Li, X. Facile synthesis and photocatalytic application of hierarchical mesoporous Bi2MoO6 nanosheet-based microspheres. CrystEngComm 2012, 14, 3602−3608. (5) la Cruz, A. M.; Alfaro, S. O.; Cuellar, E. L.; Mendez, U. O. Photocatalytic properties of Bi2MoO6 nanoparticles prepared by an amorphous complex precursor. Catal. Today 2007, 129, 194−199. (6) Zhao, J.; Lu, Q. F.; Wang, C. Q.; Liu, S. W. One-dimensional Bi2MoO6 nanotubes: controllable synthesis by electrospinning and enhanced simulated sunlight photocatalytic degradation performances. J. Nanopart. Res. 2015, 17, 189. (7) Zhang, L.; Xu, T.; Zhao, X.; Zhu, Y. Controllable synthesis of Bi2MoO6 and effect of morphology and variation in local structure on photocatalytic activities. Appl. Catal., B 2010, 98, 138−146. (8) Imani, M.; Farajnezhad, M.; Tadjarodi, A. 3D hierarchical flower-like nanostructure of Bi2MoO6: Mechanochemical synthesis, the effect of synthesis parameters and photocatalytic activity. Mater. Res. Bull. 2017, 87, 92−101. 3878
DOI: 10.1021/acsomega.8b03699 ACS Omega 2019, 4, 3871−3880
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Article
enhanced photocatalytic activity for organic pollutants degradation. J. Alloys Compd. 2018, 766, 1037−1045. (47) Ri, C.-N.; Kim, S.-G.; Ju, K.-S.; Ryo, H.-S.; Mun, C.-H.; Kim, U.-H. The synthesis of a Bi2MoO6/Bi4V2O11 heterojunction photocatalyst with enhanced visible-light-driven photocatalytic activity. RSC Adv. 2018, 8, 5433−5440. (48) Song, L.-N.; Chen, L.; He, J.; Chen, P.; Zeng, H.-K.; Au, C.-T.; Yin, S.-F. The first synthesis of Bi self-doped Bi2MoO6-Bi2Mo3O12 composites and their excellent photocatalytic performance for selective oxidation of aromatic alkanes under visible light irradiation. Chem. Commun. 2017, 53, 6480−6483. (49) Lin, S.; Cui, W.; Li, X.; Sui, H.; Zhang, Z. Cu2O NPs/ Bi2O2CO3 flower-like complex photocatalysts with enhanced visible light photocatalytic degradation of organic pollutants. Catal. Today 2017, 297, 237−245. (50) Guo, Y.; Dai, Y.; Zhao, W.; Li, H.; Xu, B.; Sun, C. Highly efficient photocatalytic degradation of naphthalene by Co3O4/ Bi2O2CO3 under visible light: A novel p−n heterojunction nanocomposite with nanocrystals/lotus-leaf-like nanosheets structure. Appl. Catal., B 2018, 237, 273−287. (51) Liu, Y.; Ren, H.; Lv, H.; Guang, J.; Cao, Y. Synthesis of magnetic Bi2O2CO3/ZnFe2O4 composite with improved photocatalytic activity and easy recyclability. Appl. Surf. Sci. 2018, 433, 610−616. (52) Zhou, H.; Zhong, S.; Shen, M.; Hou, J.; Chen, W. Formamideassisted one-pot synthesis of a Bi/Bi2O2CO3 heterojunction photocatalyst with enhanced photocatalytic activity. J. Alloys Compd. 2018, 769, 301−310. (53) Yu, C.; Zhou, W.; Zhu, L.; Li, G.; Yang, K.; Jin, R. Integrating plasmonic Au nanorods with dendritic like α-Bi2O3/Bi2O2CO3 heterostructures for superior visible-light-driven photocatalysis. Appl. Catal., B 2016, 184, 1−11. (54) Sun, M.; Li, S.; Yan, T.; Ji, P.; Zhao, X.; Yuan, K.; Wei, D.; Du, B. Fabrication of heterostructured Bi2O2CO3/Bi2O4 photocatalyst and efficient photodegradation of organic contaminants under visiblelight. J. Hazard. Mater. 2017, 333, 169−178. (55) Wang, J.; Chen, K.; Shen, Y.; Wang, X.; Guo, Y.; Zhou, X.; Bai, R. Enhanced photocatalytic degradation for organic pollutants by a novel m-Bi2O4/Bi2O2CO3 photocatalyst under visible light. Res. Chem. Intermed. 2018, 44, 3061−3079. (56) Sun, M.; Yan, T.; Zhang, Y.; He, Y.; Shao, Y.; Wei, Q.; Du, B. Rod-like Bi4O7 decorated Bi2O2CO3 plates: Facile synthesis, promoted charge separation, and highly efficient photocatalytic degradation of organic contaminants. J. Colloid Interface Sci. 2018, 514, 240−249. (57) Liang, N.; Zai, J.; Xu, M.; Zhu, Q.; Wei, X.; Qian, X. Novel Bi2S3/Bi2O2CO3 heterojunction photocatalysts with enhanced visible light responsive activity and wastewater treatment. J. Mater. Chem. A 2014, 2, 4208−4216. (58) Yu, L.; Zhang, X.; Li, G.; Cao, Y.; Shao, Y.; Li, D. Highly efficient Bi2O2CO3/BiOCl photocatalyst based on heterojunction with enhanced dye-sensitization under visible light. Appl. Catal., B 2016, 187, 301−309. (59) Wu, Y.; Han, Q.; Wang, L.; Jiang, X.; Wang, X.; Zhu, J. Roomtemperature synthesis of BiOCl and (BiO)2CO3 with predominant {001} facets induced by urea and their photocatalytic performance. J. Environ. Chem. Eng. 2017, 5, 987−994. (60) Qiu, F.; Li, W.; Wang, F.; Li, H.; Liu, X.; Ren, C. Preparation of novel p-n heterojunction Bi2O2CO3/BiOBr photocatalysts with enhanced visible light photocatalytic activity. Colloids Surf., A 2017, 517, 25−32. (61) Liu, C.; Chai, B. Facile ion-exchange synthesis of BiOI/ Bi2O2CO3 heterostructure for efficient photocatalytic activity under visible light irradiation. J. Mater. Sci.: Mater. Electron. 2015, 26, 2296− 2304. (62) Lopes, O. F.; Carvalho, K. T. G.; Avansi, W.; Milori, D. M. B.; Ribeiro, C. Insights into the photocatalytic performance of Bi2O2CO3/BiVO4 heterostructures prepared by one-step hydrothermal method. RSC Adv. 2018, 8, 10889−10897.
(28) Geng, B.; Wei, B.; Gao, H.; Xu, L. Ag2O nanoparticles decorated hierarchical Bi2MoO6 microspheres for efficient visible light photocatalysts. J. Alloys Compd. 2017, 699, 783−787. (29) Zhang, J.; Ma, Z. Ag-Ag2CO3/Bi2MoO6 composites with enhanced visible-light-driven catalytic activity. J. Taiwan Inst. Chem. Eng. 2018, 88, 121−129. (30) Li, S.; Jiang, W.; Hu, S.; Liu, Y.; Liu, Y.; Xu, K.; Liu, J. Hierarchical heterostructures of Bi2MoO6 microflowers decorated with Ag2CO3 nanoparticles for efficient visible-light-driven photocatalytic removal of toxic pollutants. Beilstein J. Nanotechnol. 2018, 9, 2297−2305. (31) Li, H.; Hu, T.; Zhang, R.; Liu, J.; Hou, W. Preparation of solidstate Z-scheme Bi2MoO6/MO (M=Cu, Co3/4, or Ni) heterojunctions with internal electric field-improved performance in photocatalysis. Appl. Catal., B 2016, 188, 313−323. (32) Li, S.; Hu, S.; Zhang, J.; Jiang, W.; Liu, J. Facile synthesis of Fe2O3 nanoparticles anchored on Bi2MoO6 microflowers with improved visible light photocatalytic activity. J. Colloid Interface Sci. 2017, 497, 93−101. (33) Zhao, C.; Shao, C.; Li, X.; Li, X.; Tao, R.; zhou, X.; Liu, Y. Magnetically separable Bi2MoO6/ZnFe2O4 heterostructure nanofibers: Controllable synthesis and enhanced visible light photocatalytic activity. J. Alloys Compd. 2018, 747, 916−925. (34) Zhang, J.; Zhang, L.; Yu, N.; Xu, K.; Li, S.; Wang, H.; Liu, J. Flower-like Bi2S3/Bi2MoO6 heterojunction superstructures with enhanced visible-light-driven photocatalytic activity. RSC Adv. 2015, 5, 75081−75088. (35) Zuo, Y.; Wang, C.; Sun, Y.; Cheng, J. Preparation and photocatalytic properties of BiOCl/Bi2MoO6 composite photocatalyst. Mater. Lett. 2015, 139, 149−152. (36) Miao, Y.; Yin, H.; Peng, L.; Huo, Y.; Li, H. BiOBr/Bi2MoO6 composite in flower-like microspheres with enhanced photocatalytic activity under visible-light irradiation. RSC Adv. 2016, 6, 13498− 13504. (37) Chen, F.; Niu, C.; Yang, Q.; Li, X.; Zeng, G. Facile synthesis of visible-light-active BiOI modified Bi2MoO6 photocatalysts with highly enhanced photocatalytic activity. Ceram. Int. 2016, 42, 2515−2525. (38) Xu, Y.-S.; Zhang, W.-D. Anion exchange strategy for construction of sesame-biscuit-like Bi2O2CO3/Bi2MoO6 nanocomposites with enhanced photocatalytic activity. Appl. Catal., B 2013, 140− 141, 306−316. (39) Xu, Y.-S.; Yu, Y.-X.; Zhang, W.-D. Wide bandgap Bi2O2CO3coupled Bi2MoO6 heterostructured hollow microspheres: one-pot synthesis and enhanced visible-light photocatalytic activity. J. Nanosci. Nanotechnol. 2014, 14, 6800−6808. (40) Lin, X.; Guo, X.; Shi, W.; Guo, F.; Wang, Q.; Yan, Y. Hydrothermal synthesis of mesh-like Bi2O2CO3/Bi2MoO6 heterojunction with enhanced photocatalytic activity. Nanosci. Nanotechnol. Lett. 2015, 7, 691−696. (41) Ma, Y.; Jia, Y.; Wang, L.; Yang, M.; Bi, Y.; Qi, Y. Bi2MoO6/ BiVO4 heterojunction electrode with enhanced photoelectrochemical properties. Phys. Chem. Chem. Phys. 2016, 18, 5091−5094. (42) Li, S.; Shen, X.; Liu, J.; Zhang, L. Synthesis of Ta3N5/Bi2MoO6 core-shell fiber-shaped heterojunctions as efficient and easily recyclable photocatalysts. Environ. Sci.: Nano 2017, 4, 1155−1167. (43) Peng, Y.; Liu, Q.; Zhang, J.; Zhang, Y.; Geng, M.; Yu, J. Enhanced visible-light-driven photocatalytic activity by 0D/2D phase heterojunction of quantum dots/nanosheets on bismuth molybdates. J. Phys. Chem. C 2018, 122, 3738−3747. (44) Xiong, Y.; Yang, L.; He, H.; Wan, J.; Xiao, P.; Guo, W. Enhanced charge separation and transfer by Bi2MoO6@Bi2Mo2O9 compound using SILAR for photoelectrochemical water oxidation. Electrochim. Acta 2018, 264, 26−35. (45) Ren, J.; Wang, W.; Shang, M.; Sun, S.; Gao, E. Heterostructured bismuth molybdate composite: preparation and improved photocatalytic activity under visible-light irradiation. ACS Appl. Mater. Interfaces 2011, 3, 2529−2533. (46) Wang, M.; You, M.; Zhang, K.; Zhang, Y.; Han, J.; Fu, R.; Liu, S.; Zhu, T. Bi3.64Mo0.36O6.55/Bi2MoO6 heterostructure composite with 3879
DOI: 10.1021/acsomega.8b03699 ACS Omega 2019, 4, 3871−3880
ACS Omega
Article
interfacial charge transfer as photocatalysts and optical limiters. Phys. Chem. Chem. Phys. 2017, 19, 28696−28709. (82) Yu, S.; Zhang, Y.; Dong, F.; Li, M.; Zhang, T.; Huang, H. Readily achieving concentration-tunable oxygen vacancies in Bi2O2CO3: Triple-functional role for efficient visible-light photocatalytic redox performance. Appl. Catal., B 2018, 226, 441−450. (83) Sun, C.; Xu, Q.; Xie, Y.; Ling, Y.; Jiao, J.; Zhu, H.; Zhao, J.; Liu, X.; Hu, B.; Zhou, D. High-efficient one-pot synthesis of carbon quantum dots decorating Bi2MoO6 nanosheets heterostructure with enhanced visible-light photocatalytic properties. J. Alloys Compd. 2017, 723, 333−344. (84) Fan, H.; Zhou, H.; Li, H.; Liu, X.; Ren, C.; Wang, F.; Li, W. Novel Ag2CrO4/Bi2O2CO3 heterojunction: Simple preparation, wide visible-light absorption band and excellent photocatalytic activity. Chem. Phys. 2019, 517, 60−66. (85) Zerjav, G.; Djinovic, P.; Pintar, A. TiO2-Bi2O3/Bi2O2CO3reduced graphene oxide composite as an effective visible light photocatalyst for degradation of aqueous bisphenol A solutions. Catal. Today 2018, 315, 237−246. (86) Xue, X.; Zhang, J.; Saana, I. A.; Sun, J.; Xu, Q.; Mu, S. Rational inert-basal-plane activating design of ultrathin 1T′ phase MoS2 with MoO3 heterstructure for enhancing hydrogen evolution performances. Nanoscale 2018, 10, 16531−16538. (87) Xia, H. C.; Xu, Q.; Zhang, J. N. Recent progress on twodimensional nanoflake ensembles for energy storage applications. Nano-Micro Lett. 2018, 10, 66. (88) Zhang, J.; Ma, Z. Novel β-Ag2MoO4/g-C3N4 heterojunction catalysts with highly enhanced visible-light-driven photocatalytic activity. RSC Adv. 2017, 7, 2163−2171. (89) Zhang, J.; Ma, Z. Ag6Mo10O33/g-C3N4 1D-2D hybridized heterojunction as an efficient visible-light-driven photocatalyst. Mol. Catal. 2017, 432, 285−291. (90) Zhang, J.; Ma, Z. Flower-like Ag3VO4/BiOBr n-p heterojunction photocatalysts with enhanced visible-light-driven catalytic activity. Mol. Catal. 2017, 436, 190−198. (91) Zhang, J.; Ma, Z. AgI/β-Ag2MoO4 heterojunctions with enhanced visible-light-driven catalytic activity. J. Taiwan Inst. Chem. Eng. 2017, 81, 225−231. (92) Zhang, J.; Ma, Z. Enhanced visible-light photocatalytic performance of Ag3VO4/Bi2WO6 heterojunctions in removing aqueous dyes and tetracycline hydrochloride. J. Taiwan Inst. Chem. Eng. 2017, 78, 212−218. (93) Zhang, J.; Ma, Z. Ag3VO4/BiOIO3 heterojunction with enhanced visible-light-driven catalytic activity. J. Taiwan Inst. Chem. Eng. 2018, 88, 177−185. (94) Zhang, J.; Ma, Z. Ag3VO4/AgI composites for photocatalytic degradation of dyes and tetracycline hydrochloride under visible light. Mater. Lett. 2018, 216, 216−219. (95) Zhang, J.; Ma, Z. Ag-Ag3VO4/AgIO3 composites with enhanced visible-light-driven catalytic activity. J. Colloid Interface Sci. 2018, 524, 16−24. (96) Zhang, J.; Ma, Z. Porous g-C3N4 with enhanced adsorption and visible-light photocatalytic performance for removing aqueous dyes and tetracycline hydrochloride. Chin. J. Chem. Eng. 2018, 26, 753− 760.
(63) Ma, J.; Tian, L.; Xu, C.; Zhang, Y.; Zhang, T.; Li, H.; Zhao, P.; Liang, Y.; Wang, J.; Fan, X. Hydrothermal synthesis and visible light photocatalytic properties of Bi2O2CO3/Bi2WO6 composite. Catal. Lett. 2018, 148, 41−50. (64) Liang, N.; Wang, M.; Jin, L.; Huang, S.; Chen, W.; Xu, M.; He, Q.; Zai, J.; Fang, N.; Qian, X. Highly efficient Ag2O/Bi2O2CO3 p-n heterojunction photocatalysts with improved visible-light responsive activity. ACS Appl. Mater. Interfaces 2014, 6, 11698−11705. (65) Li, T.; Hu, X.; Liu, C.; Tang, C.; Wang, X.; Luo, S. Efficient photocatalytic degradation of organic dyes and reaction mechanism with Ag2CO3/Bi2O2CO3 photocatalyst under visible light irradiation. J. Mol. Catal. A: Chem. 2016, 425, 124−135. (66) Chen, J.; Mei, W.; Huang, Q.; Chen, N.; Lu, C.; Zhu, H.; Chen, J.; Hou, W. Highly efficient three-dimensional flower-like AgI/ Bi2O2CO3 heterojunction with enhanced photocatalytic performance. J. Alloys Compd. 2016, 688, 225−234. (67) Zhang, Z.; Lin, S.; Li, X.; Li, H.; Zhang, T.; Cui, W. Enhanced photocatalytic activity toward organic pollutants degradation and mechanism insight of novel CQDs/Bi2O2CO3 composite. Nanomaterials 2018, 8, 330. (68) Wang, A.; Zhang, J.; Zhao, W.; Zhu, W.; Zhong, Q. Porphyrin decorated Bi2O2CO3 nanocomposites with efficient difunctional properties of photocatalysis and optical nonlinearity. J. Alloys Compd. 2018, 748, 929−937. (69) Ni, Z.; Sun, Y.; Zhang, Y.; Dong, F. Fabrication, modification and application of (BiO)2CO3-based photocatalysts: A review. Appl. Surf. Sci. 2016, 365, 314−335. (70) Wang, H.; Zhang, L.; Chen, Z.; Hu, J.; Li, S.; Wang, Z.; Liu, J.; Wang, X. Semiconductor heterojunction photocatalysts: design, construction, and photocatalytic performances. Chem. Soc. Rev. 2014, 43, 5234−5244. (71) Yu, C.; Zhou, W.; Yu, J. C.; Liu, H.; Wei, L. Design and fabrication of heterojunction photocatalysts for energy conversion and pollutant degradation. Chin. J. Catal. 2014, 35, 1609−1618. (72) An, X.; Wang, Y.; Lin, J.; Shen, J.; Zhang, Z.; Wang, X. Heterojunction: important strategy for constructing composite photocatalysts. Sci. Bull. 2017, 62, 599. (73) Lin, X.; Guo, X.; Shi, W.; Zhai, H.; Yan, Y.; Wang, Q. Quaternary heterostructured Ag−Bi 2 O2 CO 3 /Bi 3.64 Mo 0.36 O 6.55 / Bi2MoO6 composite: Synthesis and enhanced visible-light-driven photocatalytic activity. J. Solid State Chem. 2015, 229, 68−77. (74) Meng, X.; Zhang, Z. Plasmonic ternary Ag-rGO-Bi2MoO6 composites with enhanced visible light-driven photocatalytic activity. J. Catal. 2016, 344, 616−630. (75) Wan, S.; Ou, M.; Zhong, Q.; Zhang, S.; Song, F. Construction of Z-scheme photocatalytic systems using ZnIn2S4, CoOx-loaded Bi2MoO6 and reduced graphene oxide electron mediator and its efficient nonsacrificial water splitting under visible light. Chem. Eng. J. 2017, 325, 690−699. (76) Kandi, D.; Martha, S.; Thirumurugan, A.; Parida, K. M. CdS QDs-decorated self-doped γ-Bi2MoO6: A sustainable and versatile photocatalyst toward photoreduction of Cr(VI) and degradation of phenol. ACS Omega 2017, 2, 9040−9056. (77) Zhang, Q.; Xu, B.; Yuan, S.; Zhang, M.; Ohno, T. Improving gC3N4 photocatalytic performance by hybridizing with Bi2O2CO3 nanosheets. Catal. Today 2017, 284, 27−36. (78) Huang, H.; Li, X.; Wang, J.; Dong, F.; Chu, P. K.; Zhang, T.; Zhang, Y. Anionic group self-doping as a promising strategy: band-gap engineering and multi-functional applications of high-performance CO32‑-doped Bi2O2CO3. ACS Catal. 2015, 5, 4094−4103. (79) Guo, J.; Shi, L.; Zhao, J.; Wang, Y.; Tang, K.; Zhang, W.; Xie, C.; Yuan, X. Enhanced visible-light photocatalytic activity of Bi2MoO6 nanoplates with heterogeneous Bi2MoO6‑x@Bi2MoO6 core-shell structure. Appl. Catal., B 2018, 224, 692−704. (80) Song, J.-L.; Wang, X.; Wong, C. C. Simple preparation of fluorine-doped TiO2 photoanode for high performance dye sensitized solar cells. Electrochim. Acta 2015, 173, 834−838. (81) Zhao, W.; Li, C.; Wang, A.; Lv, C.; Zhu, W.; Dou, S.; Wang, Q.; Zhong, Q. Polyaniline decorated Bi2MoO6 nanosheets with effective 3880
DOI: 10.1021/acsomega.8b03699 ACS Omega 2019, 4, 3871−3880
