A Z-scheme visible-light-driven Ag/Ag₃PO₄/Bi₂MoO₆ photocatalyst: synthesis and enhanced photocatalytic activity

Abstract

A Ag/Ag₃PO₄/Bi₂MoO₆ hybrid was successfully prepared for the first time via an in situ precipitation method. The as-prepared Ag/Ag₃PO₄/Bi₂MoO₆ hybrid included Ag₃PO₄ nanoparticles (NPs) as well as Ag NPs assembling on the surface of Bi₂MoO₆ nanosheets. Under visible light irradiation (λ > 420 nm), the Ag/Ag₃PO₄/Bi₂MoO₆ hybrid photocatalyst degraded rhodamine B (Rh B) efficiently and showed much higher photocatalytic activity than pure Ag₃PO₄, Bi₂MoO₆, Ag/Ag₃PO₄, Ag/Bi₂MoO₆, or Ag₃PO₄/Bi₂MoO₆. It was elucidated that the excellent photocatalytic performance of Ag/Ag₃PO₄/Bi₂MoO₆ for the degradation of Rh B under visible light could be ascribed to the efficient separation of photogenerated electrons and holes through the Z-scheme system composed of Ag₃PO₄, Ag and Bi₂MoO₆, in which Ag NPs acted as the charge transmission-bridge. The quenching effects of different scavengers illustrated that O₂˙⁻ and h⁺ played the major role in Rh B degradation.

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1. Introduction

Semiconductor-based photocatalysis is a promising environmentally friendly technology to solve the environmental contamination issues.^1–4 Exploring high-efficiency semiconductor photocatalysts is of great importance to transform this technology into practical applications. Unfortunately, most widely applied semiconductor photocatalysts, such as TiO₂, ZnO, SiO₂, and CuO^5–9 are just active under UV-light irradiation, which greatly hinders their further applications under solar light. Therefore, great efforts have been made to synthesize efficient visible-light-driven photocatalysts such as BiVO₄, Bi₂WO₆, Bi₂MoO₆, and BiOX (X = Cl, Br, or I).^10–15 Among these visible-light catalysts, Bi₂MoO₆ has been found to reveal excellent visible-light-driven photocatalytic activity for water splitting and/or for the degradation of organic contaminants.^16,17 However, further research on the improvement of the photocatalytic efficiency of Bi₂MoO₆ is still indispensable due to its poor quantum yield. Among a variety of methods, the constructions of hybrid photocatalysts and heterostructures have been shown to be effective approaches for enhancing photocatalytic performance for the degradation of organic contaminants. So far, a variety of Bi₂MoO₆-based photocatalysts such as TiO₂/Bi₂MoO₆,¹⁸ C/Bi₂MoO₆,¹⁹ graphene/Bi₂MoO₆,²⁰ Bi_3.64Mo_0.36O_6.55/Bi₂MoO₆,²¹ ZnTiO₃/Bi₂MoO₆,²² Ag/AgBr/Bi₂MoO₆,²³ and g-C₃N₄/Bi₂MoO₆ (ref. 24) have been fabricated for improving the photocatalytic property of Bi₂MoO₆.

Ag₃PO₄ is well known as a photosensitive material and regarded as an appropriate candidate for the construction of hybrid photocatalysts with other semiconductors.^25,26 Zhang and co-workers reported Ag₃PO₄/Bi₂MoO₆ photocatalyst, which was fabricated by covering the surface of spherical Bi₂MoO₆ with Ag₃PO₄ nanoparticles through deposition–precipitation process.²⁷ This hybrid showed remarkably high photocatalytic efficiency for the degradation of rhodamine B (Rh B) and methyl blue (MB) under visible light irradiation. However, Ag₃PO₄ is subject to stability issues because it is prone to photoreduction and decomposition if no sacrificial reagent is supplied, which greatly hinders its practical application in the environmental management. It has been reported that elemental silver Ag⁰ on the surface of Ag₃PO₄ may act as an electron acceptor to enhance the charge separation and prevent the reductive decomposition of Ag₃PO₄.²⁸ In addition, metallic silver species can significantly improve the visible light absorption efficiency due to the effect of surface plasmon resonance. In addition, with more and more attention has been paid to the mechanism of Ag/Ag₃PO₄-based photocatalysts, the by-product Ag has been found to be a charge transmission bridge in the Ag/Ag₃PO₄-based Z-scheme systems. It has been reported that these Z-scheme systems can not only facilitate the charge separation but also retain the high reducibility and oxidability of the remaining electrons and holes for the corresponding photocatalysts.^28–30 Recently, there are a few reports on the photocatalytic activity evaluation of Ag/Ag₃PO₄-based Z-scheme systems, for instance Ag/Ag₃PO₄/SiC,²⁸ Ag/Ag₃PO₄/g-C₃N₄,²⁹ and Ag/Ag₃PO₄/WO_3−x.³⁰ Thus, by combining Bi₂MoO₆ and Ag/Ag₃PO₄ particles to constitute a Z-scheme photocatalyst, both the utilization of visible light and the surface-interface charge transfer efficiency of photo-generated carriers could be enhanced. However, until now, there is few report focusing on the assembly of Bi₂MoO₆ nanosheet with Ag/Ag₃PO₄ NPs. Furthermore, no attention has been paid to the mechanism of Ag/Ag₃PO₄/Bi₂MoO₆ photodegradation process under visible light irradiation, which has remained unclear to date.

Herein, we report a successful attempt at the fabrication of Ag/Ag₃PO₄/Bi₂MoO₆ hierarchical nanostructures via a facile in situ precipitation method, and the photocatalytic activity of these nanostructures was investigated by measuring the degradation of rhodamine B (Rh B) under visible light (λ > 420 nm). Furthermore, the photocatalytic mechanism of the Ag/Ag₃PO₄/Bi₂MoO₆ hybrid was investigated through reactive species trapping experiments. Finally, the stability of the Ag/Ag₃PO₄/Bi₂MoO₆ hybrid photocatalyst was also examined.

2. Experimental

2.1 Preparation of photocatalysts

2.1.1 Preparation of Bi₂MoO₆ nanosheets. All reagents for synthesis and analysis were commercially available and used without further treatments. The Bi₂MoO₆ nanosheets were synthesized through a facile hydrothermal method. Briefly, a solution of Bi(NO₃)₃ (0.40 mol L⁻¹, 5 mL H₂O) was stirred for 30 min. Then, (NH₄)₆Mo₇O₂₄ (0.20 mol L⁻¹, 5 mL H₂O) was added to the suspension, which was stirred magnetically for another 30 min. After carefully adjusting the pH value of 3 using 25 wt% NH₃·H₂O solution, the mixed solution was transferred into a 20 mL Teflon-lined steel autoclave, which was heated in an oven at 160 °C for 24 h. Then the system was allowed to cool to room temperature naturally. At last, the obtained samples were collected and washed with ethanol and distilled water several times, and dried at 70 °C for 2 h.

2.1.2 Preparation of Ag/Ag₃PO₄/Bi₂MoO₆ photocatalyst. The Ag/Ag₃PO₄/Bi₂MoO₆ hybrid photocatalyst was synthesized through an in situ precipitation method at room temperature. In a typical process, Bi₂MoO₆ nanosheets (500 mg) were dispersed in 100 mL deionized water by ultrasound for 30 min, and then 50 mL 0.0075 M AgNO₃ aqueous solution was dropped into the Bi₂MoO₆ dispersed solution. After stirring for 15 min, a 50 mL of 0.0025 M Na₃PO₄ aqueous solution was added to the above solution drop by drop under magnetic stirring. The pH value was adjusted to 3 by adding 1.0 M NaOH. The resulting suspension was stirred in the dark for another 30 min. Then, the suspension was irradiated by a 300 W Xe lamp equipped with an optical cut-off filter (λ > 420 nm) for 30 min. Finally, the precipitate was washed with deionized water for 3 times and collected by centrifugation, and then dried at 60 °C in the vacuum drying oven. The theoretical value of Ag₃PO₄ loading amount was 10 wt%. For comparison, pure Ag₃PO₄, Ag/Bi₂MoO₆, Ag/Ag₃PO₄, and Ag₃PO₄/Bi₂MoO₆ samples were prepared under the same conditions.

2.2. Characterization of photocatalysts

The crystal structures of the samples were characterized by X-ray diffraction (XRD) on a Rigaku (Japan) D/max 2500 X-ray diffractometer (Cu K_α radiation, λ = 0.15418 nm). The morphologies and structure details of the as-synthesized samples were detected using field emission scanning microscopy (SEM, JSM-6510) and transmission electron microscopy (TEM, JEM-2100F). X-ray photoelectron spectroscopy (XPS) analysis was performed with an ESCALa-b220i-XL electron spectrometer (VGScientific, England) using 300 W Al K_α radiation. The optical properties were obtained by the photoluminescence (PL) measurement using HR800 LabRam Infinity Spectro photometer excited by a continuous He–Cd laser with a wavelength of 325 nm at a power of 50 mW. The UV-vis diffuse reflectance spectra (DRS) were recorded using a scan UV-vis spectrophotometer (UV-2550).

2.3. Photocatalytic activities studies

The photocatalytic properties of the as-prepared samples were evaluated using Rh B as a model compound. The Rh B is a very stable compound, which has been used widely as a representative reaction for examining the performance of numerous visible light active photocatalysts. In experiments, the Rh B solution (0.01 mmol L⁻¹, 100 mL) containing 0.02 g of photocatalyst were mixed in a pyrex reaction glass. A 300 W Xe lamp (λ > 420 nm) was employed to provide visible light irradiation. A 420 nm cut-off filter was inserted between the lamp and the sample to filter out UV light (λ < 420 nm). Prior to visible light illumination, the suspension was strongly stirred in the dark for 40 min. Then the solution was exposed to visible light irradiation under magnetic stirring. At given time intervals, 4 mL of the suspension was periodically collected and analyzed after centrifugation. The Rh B concentration was analyzed by a UV-2550 spectrometer to record intensity of the maximum band at 552 nm in the UV-vis absorption spectra.

2.4 Active species trapping experiments

For detecting the active species during photocatalytic reactivity, some sacrificial agents, such as 2-propanol (IPA), disodium ethylenediamine tetraacetic acid (EDTA-2Na), and 1,4-benzoquinone (BQ) were used as the hydroxyl radical (˙OH) scavenger, hole (h⁺) scavenger and superoxide radical (O₂˙⁻) scavenger, respectively. The method was similar to the former photocatalytic activity test with the addition of 1 mmol of quencher in the presence of Rh B.

3. Results and discussion

Fig. 1 displays the XRD pattern of the Ag/Ag₃PO₄/Bi₂MoO₆ hybrid photocatalyst, together with those of pure Ag₃PO₄, Bi₂MoO₆, Ag/Bi₂MoO₆, Ag/Ag₃PO₄, and Ag₃PO₄/Bi₂MoO₆ samples. As can be seen in Fig. 1, Ag₃PO₄ is a cubic phase (JCPDS no. 06-0505), while Bi₂MoO₆ is an orthorhombic crystal (JCPDS no. 21-0102). It is observed that no peaks assigned to Ag⁰ were found in the as-prepared Ag/Ag₃PO₄/Bi₂MoO₆, Ag/Ag₃PO₄, and Ag/Bi₂MoO₆ samples, owing to its low amount. Moreover, the changes of all diffractions and lattice parameters were not detectable, which indicates that Ag related species resided in the lattice sites and have no separate phase. No obvious peaks of the Ag₃PO₄ phases were detected in the patterns of Ag/Ag₃PO₄/Bi₂MoO₆ and Ag₃PO₄/Bi₂MoO₆, suggesting that all the as-synthesized composites possess the same crystal structure. This may be resulted from the low concentration or small crystal size of Ag₃PO₄.

Fig. 1 XRD patterns of Ag₃PO₄, Bi₂MoO₆, Ag/Bi₂MoO₆, Ag/Ag₃PO₄, Ag₃PO₄/Bi₂MoO₆, and Ag/Ag₃PO₄/Bi₂MoO₆ hybrids.

In order to confirm the existence of metallic Ag and Ag₃PO₄, XPS technology has been employed to analyze the surface element composition and chemical state of Ag/Ag₃PO₄/Bi₂MoO₆, and the obtained results are shown in Fig. 2. From Fig. 2a, the Ag 3d peaks of Ag/Ag₃PO₄/Bi₂MoO₆ have separated as Ag⁺ peaks and Ag⁰ peaks. The peaks at 367.1 and 373.1 eV are attributed to Ag⁰,²⁸ indicating existence of metallic Ag on the surface of Ag/Ag₃PO₄/Bi₂MoO₆ sample. The peaks at 366.4 and 372.3 eV are assigned to Ag⁺ of Ag₃PO₄.²⁸ A broad peak in the range of 129 to 134 eV of the P 2p spectrum (Fig. 2b) is observed for the Ag/Ag₃PO₄/Bi₂MoO₆ sample which is corresponding to the phosphorus of Ag₃PO₄.²⁹ The results give solid evidence of the formation of metallic Ag and Ag₃PO₄. The Bi 4f fine XPS spectrum of the sample is shown in Fig. 2c. XPS signals of Bi 4f are observed at binding energies at about 162.9 eV (Bi 4f_7/2) and 157.5 eV (Bi 4f_5/2), ascribed to Bi³⁺.²⁷ The characteristic spin–orbital splitting photoelectrons for Mo 3d (234.8 and 231.6 eV) indicate a six-valent oxidation state for Mo⁶⁺ (ref. 27) (Fig. 2d).

Fig. 2 XPS spectra of the as-obtained Ag/Ag₃PO₄/Bi₂MoO₆ sample: (a) Ag 3d spectrum, (b) P 2p spectrum, (c) Bi 4f, (d) Mo 3d spectrum.

The SEM images of Bi₂MoO₆, Ag/Bi₂MoO₆, Ag₃PO₄/Bi₂MoO₆ and Ag/Ag₃PO₄/Bi₂MoO₆ samples are revealed in the Fig. S1.† The as-prepared Bi₂MoO₆ particles are composed of nanosheets with average sizes of about 100 nm and thickness of tens of nanometers (Fig. S1a†). The Ag/Bi₂MoO₆, Ag₃PO₄/Bi₂MoO₆, and Ag/Ag₃PO₄/Bi₂MoO₆ samples display a similar morphology to pure Bi₂MoO₆ (Fig. S1b–d†), indicating that low amount Ag₃PO₄ and Ag loading did not have any influence on the morphology of Bi₂MoO₆ crystals. Moreover, the component and connection of Ag/Ag₃PO₄/Bi₂MoO₆ were investigated by TEM, as shown in Fig. 3. Fig. 3a shows the sheet-like structure of the as-synthesized Bi₂MoO₆ sample. It can be seen that the sizes of Ag₃PO₄ crystals are of 10–20 nm (Fig. 3b). From Fig. 3c, it can be clearly found that the Ag NPs and Ag₃PO₄ NPs were loaded on the surface of Bi₂MoO₆. Fig. 3d shows the HRTEM image of the as-fabricated Ag/Ag₃PO₄/Bi₂MoO₆ sample. By measuring the lattice fringes, the resolved interplanar distances are about 0.236, 0.213, and 0.314 nm, which correspond to the (111) plane of Ag, the (210) plane of Ag₃PO₄, and the (131) plane of Bi₂MoO₆, respectively.

Fig. 3 TEM images of Bi₂MoO₆ (a), Ag₃PO₄ (b), Ag/Ag₃PO₄/Bi₂MoO₆ (c), and HRTEM image of Ag/Ag₃PO₄/Bi₂MoO₆ (d).

Fig. 4a displays the UV-vis diffuse reflectance spectra of Bi₂MoO₆, Ag₃PO₄, Ag/Bi₂MoO₆, Ag/Ag₃PO₄, Ag₃PO₄/Bi₂MoO₆, and Ag/Ag₃PO₄/Bi₂MoO₆. It can be seen that bare Bi₂MoO₆ exhibits strong absorbance in wavelengths shorter than 520 nm, and pure Ag₃PO₄ shows strong absorbance in wavelengths shorter than 510 nm. The Ag₃PO₄/Bi₂MoO₆ sample shows the similar absorption edge and a broader absorption in the visible region as comparison with pure Bi₂MoO₆. Ag/Bi₂MoO₆ and Ag/Ag₃PO₄ samples show obvious visible-light absorption, which can be attributed to the surface plasmon resonance (SPR) of the loading Ag, further confirming the formation of Ag. The absorption curve of the Ag/Ag₃PO₄/Bi₂MoO₆ shows distinctly enhanced visible-light absorption compared to the pure Bi₂MoO₆ and Ag₃PO₄/Bi₂MoO₆ samples. According to the plot of (αhν)² versus energy, as shown in Fig. 4b, the band gap energies (E_g) of Ag₃PO₄ and Bi₂MoO₆ have been calculated to be 2.42 and 2.36 eV, respectively. The band structure of Ag₃PO₄ and Bi₂MoO₆ can be estimated according to the empirical eqn (1) and (2) below;

E_VB = X − E^e + 0.5E_g (1)

E_CB = E_VB − E_g (2)

where E_VB is the valence band edge potential, E_CB is the conduction band edge potential, X is the electronegativity of the semiconductor, which is the geometric mean of the electronegativity of the constituent atoms, E^e is the energy of free electrons on the hydrogen scale (about 4.5 eV), E_g is the band gap energy of the semiconductor. Thus, the E_VB of Ag₃PO₄ and Bi₂MoO₆ are calculated to be 2.67 and 2.33 eV, respectively, and their corresponding E_CB are determined to be 0.25 and −0.31 eV, respectively. The results are in agreement with the reported works.^22,28 The energy band structure diagram of Ag₃PO₄, Ag, and Bi₂MoO₆ is thus schematically illustrated, as shown in Scheme 1. Under visible light irradiation, both Ag₃PO₄ and Bi₂MoO₆ are excited, and the photogenerated holes and electrons are in their conduction and valence band, respectively. The electrons on the CB of Ag₃PO₄ can easily shift into metal Ag (electron transfer I: Ag₃PO₄ CB → Ag) through the Schottky barrier because the CB potential of Ag₃PO₄ is more negative than the Fermi level of the loaded metal Ag. Meanwhile, the holes on the VB of Bi₂MoO₆ can also migrate to metal Ag (hole transfer II: Bi₂MoO₆ VB → Ag) because the Fermi level of Ag is more negative than the VB of Bi₂MoO₆, and then combine with the electron here. Therefore, simultaneous electron (I) and hole (II) transfers enhance the charge separation of Ag₃PO₄ and Bi₂MoO₆.

Fig. 4 (a) UV-vis DRS of as-synthesized samples. (b) The plots of (αhν)² versus photon energy (hν) for the band gap energies of Ag₃PO₄ and Bi₂MoO₆.

Scheme 1 Schematic diagram of the separation and transfer of photogenerated charges in the hybrid under visible light irradiation.

The photocatalytic properties of the as-prepared samples under visible light irradiation were evaluated, as shown in Fig. 5. This result clearly demonstrates that the Ag/Ag₃PO₄/Bi₂MoO₆ hybrid exhibited higher photocatalytic activity than pure Ag₃PO₄, Bi₂MoO₆, Ag/Ag₃PO₄, Ag/Bi₂MoO₆, and Ag₃PO₄/Bi₂MoO₆, which suggests that combining Ag/Ag₃PO₄ and Bi₂MoO₆ is an efficient route to enhance their photocatalytic activities. In the presence of Ag/Ag₃PO₄/Bi₂MoO₆, almost 100% of the Rh B molecules were decomposed within 80 min visible light irradiation. The Ag₃PO₄ NPs and Ag NPs coating can improve the visible light absorption efficiency (Fig. 4a), which is beneficial for the hybrid to photolyze Rh B. In addition, efficient Z-scheme system can separate the photoinduced charges effectively, thus enhancing the photocatalytic performance of Ag/Ag₃PO₄/Bi₂MoO₆.

Fig. 5 Photodegradation efficiencies of Rh B as a function of irradiation time for different photocatalysts.

The photoluminescence (PL) emission spectra were studied to investigate the charge recombination and transfer behaviour of the Ag/Ag₃PO₄/Bi₂MoO₆ photocatalyst, as shown in Fig. 6. It is well-known that the recombination of electron–hole pairs can release energy in the form of PL emission. In general, a lower PL intensity indicates lower recombination of charge carriers, leading to higher photocatalytic activity. However, the Ag/Ag₃PO₄/Bi₂MoO₆ with the higher photocatalytic activity showed a higher PL intensity than that of Bi₂MoO₆ and Ag₃PO₄/Bi₂MoO₆. The higher PL intensity of Ag/Ag₃PO₄/Bi₂MoO₆ would be resulted from higher recombination of photogenerated electron–hole pairs in the metallic Ag. The photogenerated electrons in the CB of Ag₃PO₄ and holes in the VB of Bi₂MoO₆ will shift to the metallic Ag simultaneously and then combine here, which leads to higher PL intensity. The recombination in the metallic Ag is beneficial for accelerating the separation of the photogenerated electron–hole pairs in both Ag₃PO₄ and Bi₂MoO₆, so the photocatalytic performance of Ag/Ag₃PO₄/Bi₂MoO₆ improved. In addition, it can be clearly observed that the PL intensity of Ag₃PO₄/Bi₂MoO₆ was lower than that of pure Bi₂MoO₆ because of the formation of heterojunction between Ag₃PO₄ and Bi₂MoO₆ can efficiently suppress the recombination of the photogenerated electron–hole in the hybrid. On the basis of the above results, the Ag/Ag₃PO₄/Bi₂MoO₆ system is a typical Z-scheme photocatalyst rather than heterojunction photocatalyst. It is suggested that rich electrons in the CB of Bi₂MoO₆ and holes in the VB of Ag₃PO₄ participate in the reduction reaction of dissolved O₂ and the oxidation of Rh B, respectively. The stability and reusability of Ag/Ag₃PO₄/Bi₂MoO₆ photocatalyst were evaluated by the cycling degradation experiment, as shown in Fig. S2.† The results revealed that the Ag/Ag₃PO₄/Bi₂MoO₆ did not show obvious decrease of photocatalytic degradation activity under visible light, indicating that the Ag/Ag₃PO₄/Bi₂MoO₆ hybrid photocatalyst is sufficient stable for photocatalytic degradation of Rh B.

Fig. 6 Room temperature PL spectra of as-synthesized samples.

To investigate the photocatalytic mechanism of the Ag/Ag₃PO₄/Bi₂MoO₆ hybrid, the effect of scavengers on the degradation of Rh B was tested in the photocatalytic oxidation process and the results are shown in Fig. 7. As revealed in Fig. 7, under the visible-light irradiation of the Ag/Ag₃PO₄/Bi₂MoO₆ sample, the photodegradation rate of Rh B had slight decrease after the addition of hydroxyl radical scavenger IPA, indicating that ˙OH was not the main reactive specie in the photocatalytic process. In contrast, the photocatalytic degradation of Rh B was significantly repressed in presence of EDTA-2Na and BQ. According to these results, it can be concluded that h⁺ and O₂˙⁻ are the main oxygen active species for Ag/Ag₃PO₄/Bi₂MoO₆ photocatalyst in the Rh B solution under visible light illumination. It can be deduced that the electrons left on the E_CB of Bi₂MoO₆ reduce O₂ to O₂˙⁻ through one-electron reducing reaction because the E_CB potential of Bi₂MoO₆ is more negative than E₀(O₂/O₂˙⁻) (−0.046 eV vs. NHE). Both the holes in the E_VB of Ag₃PO₄ and the O₂˙⁻ radicals can completely oxidize Rh B molecules to water and carbon dioxide.

Fig. 7 Trapping experiments of active species during the photocatalytic degradation of Rh B over Ag/Ag₃PO₄/Bi₂MoO₆ sample under visible light irradiation.

4. Conclusions

A high-efficiency visible-light-driven Ag/Ag₃PO₄/Bi₂MoO₆ Z-scheme photocatalyst was successfully synthesized through an in situ precipitation process. The Ag/Ag₃PO₄/Bi₂MoO₆ hybrid photocatalyst displayed obviously superior photocatalytic performance than that of bare Ag₃PO₄, Bi₂MoO₆, Ag/Ag₃PO₄, Ag/Bi₂MoO₆, and Ag₃PO₄/Bi₂MoO₆ for the photo-degradation of Rh B under visible light irradiation. The superior photocatalytic activity of Ag/Ag₃PO₄/Bi₂MoO₆ may be resulted from the efficient separation of photogenerated electron–hole pairs through the Z-scheme system composed of Ag₃PO₄, Ag and Bi₂MoO₆. On the basis of the results of this study, the Ag/Ag₃PO₄/Bi₂MoO₆ hybrid photocatalyst is expected to be a useful visible-light photocatalyst for practical applications.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (21407059, 21576112), the Science Development Project of Jilin Province (20130522071JH, 20130521019JH), and the Science and Technology Research Project of the Department of Education of Jilin Province (2015220).

References

1. M. R. Hoffmann, S. T. Martin, W. Choi and D. W. Bahnemannt, Chem. Rev., 1995, 95, 69.
2. Y. Mao and S. S. Wong, J. Am. Chem. Soc., 2006, 128, 8217.
3. R. Mohan, K. Krishnamoorthy and S. J. Kim, Solid State Commun., 2012, 152, 375.
4. L. Zhang, W. Z. Wang, S. M. Sun, Y. Y. Sun, E. P. Gao and Z. J. Zhang, Appl. Catal., B, 2014, 148–149, 164.
5. W. Yao, B. Zhang, C. Huang, C. Ma, X. Song and Q. Xu, J. Mater. Chem., 2012, 22, 4050.
6. X. Ma, H. Li, Y. Wang, H. Li, B. Liu, S. Yin and T. Sato, Appl. Catal., B, 2014, 158, 314.
7. W. Liu, M. Wang, C. Xu, S. Chen and X. Fu, Mater. Res. Bull., 2013, 48, 106.
8. L. Zhang, H. Zhang, H. Huang, Y. Liu and Z. Kang, New J. Chem., 2012, 36, 1541.
9. B. Cao, P. Dong, S. Cao and Y. Wang, J. Am. Ceram. Soc., 2013, 96, 544.
10. X. Li, R. Huang, Y. Hu, Y. Chen, W. Liu, R. Yuan and Z. Li, Inorg. Chem., 2012, 51, 6245.
11. H. F. Cheng, B. B. Huang, Y. Dai, X. Y. Qin and X. Y. Zhang, Langmuir, 2010, 26, 6618.
12. X. Xiao and W. D. Zhang, J. Mater. Chem., 2010, 20, 5866.
13. G. P. Dai, J. G. Yu and G. Liu, J. Phys. Chem. C, 2011, 115, 7339.
14. Y. F. Sun, B. Y. Qu, Q. Liu, S. Gao, Z. X. Yan, W. S. Yan, B. C. Pan, S. Q. Wei and Y. Xie, Nanoscale, 2012, 4, 3761.
15. W. Z. Yin, W. Z. Wang and S. M. Sun, Catal. Commun., 2010, 11, 647.
16. M. Y. Zhang, C. L. Shao, J. B. Mu, X. M. Huang, Z. Y. Zhang, Z. C. Guo, P. Zhang and Y. C. Liu, J. Mater. Chem., 2012, 22, 577.
17. M. Y. Zhang, C. L. Shao, J. B. Mu, Z. Y. Zhang, Z. C. Guo, P. Zhang and Y. C. Liu, CrystEngComm, 2012, 14, 605.
18. Y. L. Tian, B. B. Chang, J. L. Lu, J. Fu, F. N. Xi and X. P. Dong, ACS Appl. Mater. Interfaces, 2013, 5, 7079.
19. M. Y. Zhang, C. L. Shao, P. Zhang, C. Y. Su, X. Zhang, P. P. Liang, Y. Y. Sun and Y. C. Liu, J. Hazard. Mater., 2012, 225–226, 155.
20. P. F. Wang, Y. H. Ao, C. Wang, J. Hou and J. Qian, Carbon, 2012, 5, 5256.
21. J. Ren, W. Z. Wang, M. Shang, S. M. Sun and E. P. Gao, ACS Appl. Mater. Interfaces, 2011, 3, 2529.
22. P. Zhang, C. L. Shao, M. Y. Zhang, Z. C. Guo, J. B. Mu, Z. Y. Zhang, X. Zhang and Y. C. Liu, J. Hazard. Mater., 2012, 217–218, 422.
23. G. H. Tian, Y. J. Chen, X. Y. Meng, J. Zhou, W. Zhou, K. Pan, C. G. Tian, Z. Y. Ren and H. G. Fu, ChemPlusChem, 2013, 78, 117.
24. H. P. Li, J. Y. Liu, W. G. Hou, N. Du, R. J. Zhang and X. T. Tao, Appl. Catal., B, 2014, 160–161, 89.
25. Y. P. Bi, S. X. Ouyang, N. Umezawa, J. Y. Cao and J. H. Ye, J. Am. Chem. Soc., 2011, 133, 6490.
26. C. T. Dinh, T. D. Nguyen, F. Kleitz and T. O. Do, Chem. Commun., 2011, 47, 7797.
27. Y. S. Xu and W. D. Zhang, Dalton Trans., 2013, 42, 1094.
28. Z. H. Cheng, F. Bing, Q. Liu, Z. G. Zhang and X. M. Fang, J. Mater. Chem. A, 2014, 1.
29. H. Katsumata, T. Sakai, T. Suzuki and S. Kaneco, Ind. Eng. Chem. Res., 2014, 53, 8018.
30. Y. Y. Bu, Z. Y. Chen and C. J. Sun, Appl. Catal., B, 2015, 179, 363.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c5ra22110b

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