Inorganic-Salt-Assisted Morphological Evolution and Visible-Light

Sep 10, 2013 - Recently, the controlled synthesis of semiconductor photocatalysts has attracted intense attention. In this report, we first report the...
0 downloads 0 Views 4MB Size
Download PDF
Article pubs.acs.org/JPCC

Inorganic-Salt-Assisted Morphological Evolution and Visible-LightDriven Photocatalytic Performance of Bi2WO6 Nanostructures Yan Yan,† Yafan Wu,‡ Yuting Yan,† Weisheng Guan,‡ and Weidong Shi*,† †

School of Chemistry and Chemical Engineering, Jiangsu University, Xuefu Road 301, Zhenjiang 212013, P.R. China School of Environmental Science and Engineering, Chang’an University, Yanta Road 126, Xi’an 710054, P.R. China

‡

ABSTRACT: Recently, the controlled synthesis of semiconductor photocatalysts has attracted intense attention. In this report, we first report the controlled synthesis of Bi2WO6 nanostructures via the soluble inorganic salt Na2SO4-assisted hydrothermal method by simply adjusting the reaction time and pH value. Four typical Bi2WO6 nanostructures were obtained, namely nestlike nanostructures assembled by nanoplates (NNS-ANPs), rodlike nanostructures assembled by nanoplates (RNS-ANPs), quantum dots-modified nanoplates (QDs-NPs), and smooth-surfaced nanoplates (SSNPs). Tentative formation mechanisms of the different morphologies based on our observations are discussed. Photocatalytic degradation results show that the degradation ratios (DRs) of three-dimensional structures are higher than those of two-dimensional structures, and surface QDs play key roles in enhancing the DR of QDs-NPs. Morphology-dependent photocatalytic activities of different Bi2WO6 nanostructures are possibly due to different charge-separation abilities, which has been demonstrated by photoluminescence analyses.

1. INTRODUCTION The correlation between physical and chemical properties and morphology, including shape, size, porosity, surface nature, dimensionality, and structure, of inorganic materials has made the design and preparation of novel nano- and microstructured inorganic materials worldwide hot topics for their various applications in fields such as biological labeling and imaging,1,2 catalysis,3 drug delivery,4 sensing,5,6 environmental remediation,7 and surface-enhanced Raman scattering.8,9 Particularly, numerous works have demonstrated that the structure and morphology of inorganic semiconductors dramatically influence their photocatalytic activities.10,11 For example, TiO2 spheres with solid, hollow, or semihollow structures exhibit different photocatalytic activities.12 Another specific example is from visible-light-driven photocatalyst Ag3PO4 submicrocrystals with spherical, cubic, and rhombic dodecahedral morphologies that show differences in light absorption ability as well as in photocatalytic activity.13 Thus, in order to determine the factors of structure and morphology that influence photocatalytic activity, the controlled synthesis of semiconductor photocatalysts has attracted intense attention. To date, it is still a great challenge to develop versatile synthetic methods for the controlled synthesis of various semiconductor photocatalysts with tailored morphology and structure. As one of the simplest members of the Aurivillius oxide family, bismuth tungstate (Bi2WO6) has attracted significant attention since Kudo’s group demonstrated its photocatalytic O2 evolution abilities from aqueous AgNO3 solutions14 and Zou’s group reported its ability to mineralize organic contaminants under visible light irradiation.15 The morphology and structure of Bi2WO6 photocatalysts have also been found to be strongly related to their photocatalytic activities. Zhu et al. © 2013 American Chemical Society

reported that the photocatalytic activity of square Bi2WO6 nanoplates is 3 times greater than that of Bi2WO6 bulk materials synthesized by the solid state reaction (SSR) method.16 As a result, much effort has been made to develop new synthetic techniques to control Bi2WO6 nanostructures, including template-assisted or template-free hydro/solvothermal synthesis,17,18 biomimetic synthesis,19 electrospinning synthesis,20 ultrasonic spray pyrolysis synthesis,21 sol−gel method,22 and microwave-assisted synthesis.23,24 Among them, the hydrothermal method is a very effective and promising soft chemical route in terms of low reaction temperature, environmentally friendly treatment, and largescale production. Outstanding works based on hydrothermal methods with the introducing of organic additives (such as PVP, CTAB, EDTA, etc.) have been done to control the structure and morphology of Bi2WO6 nanostructures.25−27 Introducing these organic additives usually leads to a complicated experimental process, increased production costs, and unavoidable impurities in the products. Moreover, calcinations as well as chemical corrosions are supposed to destroy the already prepared nano- or microstructures while the surface adhesion of these organic additives blocks full contact between the photocatalysts and water or target reactants.28 Recently, several convenient and effective soluble inorganic-salt-assisted hydrothermal methods for Bi2WO6 two-dimensional (2D) nanoplates and threedimensional (3D) hierarchical microspheres have been developed.28,29 Although these soluble inorganic-salt-assisted Received: July 3, 2013 Revised: September 9, 2013 Published: September 10, 2013 20017

dx.doi.org/10.1021/jp406574y | J. Phys. Chem. C 2013, 117, 20017−20028

The Journal of Physical Chemistry C

Article

electron microscopy (SEM) images were collected on an S4800 field emission SEM (FESEM, Hitachi, Japan). Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were collected on an F20 S-TWIN electron microscope (Tecnai G2, FEI Co.), using a 200 kV accelerating voltage. UV−vis absorption spectra of the samples were obtained from a UV2550 (Shimadzu, Japan) UV−vis spectrophotometer. BaSO4 was used as a reflectance standard. The photoluminescence spectra were obtained on a F4500 (Hitachi, Japan) photoluminescence detector. Total organic carbon (TOC) analyses were conducted on a multi N/C 2100 (Analytik Jena AG, Germany) TOC analyzer. 2.4. Photocatalytic Degradation of Tetracycline. The photodegradation of tetracycline (TC) was carried out at 308 K in a photochemical reactor under visible light. The photochemical reactor contained 100 mg samples and 100 mL of 10 mg/L TC solution. To exclude the influence of physical adsorption, the reactor was kept in the dark for 30 min to reach the adsorption equilibrium. The photochemical reactor was irradiated with a 300 W xenon lamp which was located 8 cm to one side of the containing solution. UV light with a wavelength 420 nm). Morphology and structure are essential to the photocatalytic activity of Bi2WO6 nanostructures. From Figure 12a, the DR of sample NNS-ANPs, RNSANPs, QDs-NPs, and SSNPs are 88.2%, 83.4%, 73.4% ,and 56.5%, respectively. The DR of NNS-ANPs is higher than that of RNS-ANPs, which may result from the smaller particle size and advantages of layer-by-layer surface structures over the crisscross surface patterns. Another important discovery is that in our experimental conditions 3D samples (NNS-ANPs, RNSANPs) possess DRs that are higher than those of 2D samples (QDs-NPs, SSNPs). The outperformance of 3D nanostructures

may stem from the general advantages of 3D hierarchical structures, such as high surface area, plenty of reactive sites, superior light absorption ability, and superior contact with water and target pollutants.17,41,49 The DR of Bi2WO6 QDsNPs (73.4%) is about 20% higher than that of SSNPs (56.5%), indicating surface QDs can greatly enhance the photocatalytic activity of 2D Bi2WO6 nanoplates. Surface QDs can produce plenty of reactive sites as well as increase the surface area, benefitting the photocatalytic reaction. Moreover, the Zeng group proposed an interface charge-transfer model on QDsmodified Bi2WO6 microspheres caused by the “quantum size effect” of QDs.38,39 According to their model, the enlarged band gap of QDs would lead to an up-shifted conduction band (CB) position and a down-shifted valence band (VB) position, which may facilitate the mobility of charge-carriers from Bi2WO6 QDs to nanoplates. In this model, the QDs-NPs could be regarded as the homojunction between Bi2WO6 QDs and NPs. To demonstrate that the measured DR is from photocatalytic degradation rather than from physical adsorption or other effects, TOC analyses were conducted. As shown in Figure 12b, TOC contents of different samples decreased in the same order as that of the photocatalytic degradation curves (Figure 12a). However, the removal rate of TOC is lower than that of the DR. This is reasonable because the degradation curve data were measured after the photocatalyst separation step by centrifugation. Similar trends of TOC removal and the degradation curves indicate our experiments of photodegradation successfully removed the effect of physical adsorption and correctly 20025

dx.doi.org/10.1021/jp406574y | J. Phys. Chem. C 2013, 117, 20017−20028

The Journal of Physical Chemistry C

Article

catalytic activities for the photodegradaton of TC. The DR values of 3D nanostructures are higher than those of 2D nanostructures. QDs also play key roles in enhancing the DR of QDs-NPs. The evidence from PL spectra indicates that the morphology-dependent photocatalytic activities of different Bi2WO6 nanostructures are mainly from the different chargeseparation ability.

evaluated the photocatalytic activity of different photocatalysts. Moreover, the reduced TOC contents suggest that Bi2WO6 nanostructures have huge potential in environmental applications such as the mineralization of TC. For the explanation of morphology-dependent photocatalytic activities, most researchers tend to suggest that specific morphologies facilitate the mobility of photoinduced chargecarriers and support the fast separation of electron−hole pairs rather than contribute an enhanced visible light absorption ability.50,51 In our case, we also attribute the different chargeseparation ability as the main cause of the morphologydependent photocatalytic activities of different Bi 2 WO 6 structures. To demonstrate our assumption, photoluminescence (PL) analyses were conducted on different samples. Before the measurement, samples (10 mg) were well-dispersed into 5 mL of ethanol. The measurement was conducted at the excitation wavelength of 220 nm with a photomultiplier tube voltage of 500 V. From Figure 13, the PL intensity of different

■

AUTHOR INFORMATION

Corresponding Author

*Phone: +86 511 8879 0187. Fax: +86 511 8879 1108. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We gratefully acknowledge the financial support of the National Natural Science Foundation of China (21001086, 21276116), the Postgraduate Research Foundation of Jiangsu Province (1102123C), National Postgraduate Research Foundation of China (2011M500853), Science Department of Jiangsu Province (BK2010340), and Jiangsu University (10JDG070).

■

REFERENCES

(1) Cao, Y. C.; Jin, R. C.; Mirkin, C. A. Nanoparticles with Raman Spectroscopic Fingerprints for DNA and RNA Detection. Science 2002, 297, 1536−1540. (2) Rosi, N. L.; Mirkin, C. A. Nanostructures in Biodiagnostics. Chem. Rev. 2005, 105, 1547−1562. (3) Burda, C.; Chen, X. B.; Narayanan, R.; El-Sayed, M. A. Chemistry and Properties of Nanocrystals of Different Shapes. Chem. Rev. 2005, 105, 1025−1102. (4) Zhu, Y. F.; Shi, J. L.; Shen, W. H.; Dong, X. P.; Feng, J. W.; Ruan, M. L.; Li, Y. S. Stimuli-Responsive Controlled Drug Release from a Hollow Mesoporous Silica Sphere/Polyelectrolyte Multilayer Core− Shell Structure. Angew. Chem., Int. Ed. 2005, 117, 5213−5217. (5) Favier, F.; Walter, E. C.; Zach, M. P.; Benter, T.; Penner, R. M. Hydrogen Sensors and Switches from Electrodeposited Palladium Mesowire Arrays. Science 2001, 293, 2227−2231. (6) Tao, A.; Kim, F.; Hess, C.; Goldberger, J.; He, R. R.; Sun, Y. G.; Xia, Y. N.; Yang, P. D. Langmuir−Blodgett Silver Nanowire Monolayers for Molecular Sensing Using Surface-Enhanced Raman Spectroscopy. Nano Lett. 2003, 3, 1229−1233. (7) Wang, C. Y.; Zhang, H.; Li, F.; Zhu, L. Y. Degradation and Mineralization of Bisphenol A by Mesoporous Bi2WO6 under Simulated Solar Light Irradiation. Environ. Sci. Technol. 2010, 44, 6843−6848. (8) Dick, L. A.; McFarland, A. D.; Haynes, C. L.; Van Duyne, R. P. Metal Film over Nanosphere (MFON) Electrodes for SurfaceEnhanced Raman Spectroscopy (SERS): Improvements in Surface Nanostructure Stability and Suppression of Irreversible Loss. J. Phys. Chem. B 2002, 106, 853−860. (9) Kim, K.; Park, H. K.; Kim, N. H. Silver-Particle-Based SurfaceEnhanced Raman Scattering Spectroscopy for Biomolecular Sensing and Recognition. Langmuir 2006, 22, 3421−3427. (10) Hoffmann, M. R.; Martin, S. T.; Choi, W. Y.; Bahemann, D. W. Environmental Applications of Semiconductor Photocatalysis. Chem. Rev. 1995, 95, 69−96. (11) Wang, X. C.; Yu, J. C.; Ho, C. M.; Hou, Y. D.; Fu, X. Z. Photocatalytic Activity of a Hierarchically Macro/Mesoporous Titania. Langmuir 2005, 21, 2552−2559. (12) Li, H. X.; Bian, Z. F.; Zhu, J.; Zhang, D. Q.; Li, G. S.; Huo, Y. N.; Li, H.; Lu, Y. F. Mesoporous Titania Spheres with Tunable Chamber Stucture and Enhanced Photocatalytic Activity. J. Am. Chem. Soc. 2007, 129, 8406−8407.

Figure 13. PL emission spectra of Bi2WO6 nanostructures with excitation wavelength of 220 nm.

specific samples is in the order SSNPs, QDs-NPs, RNS-ANPs, and NSS-ANPs, which is the exact reverse order of DR. It is well-acknowledged that the PL emission intensity of a semiconductor is proportional to the opportunity for the recombination of photoinduced electron−hole pairs. In other words, the lower PL intensity suggests a stronger chargeseparation ability. The completely opposite PL and DR data sufficiently demonstrate the validity of our assumption. In addition, the DR of Bi2WO6 nanostructures decreased as the corresponding band gap energy increased, indicating the light absorption ability also affects the morphology-dependent photocatalytic activity.

4. CONCLUSION In this report, we have successfully realized the controlled synthesis of Bi2WO6 nanostructures via a facile and versatile inorganic-salt-assisted hydrothermal method. The pH value, amount of Na2SO4 added, and reaction time all play important roles in the formation of different nanostructures. Particularly, by varying the pH value and reaction time, four well-defined nanostructures can be obtained, namely nestlike nanostructures assembled by nanoplates (NNS-ANPs), rodlike nanostructures assembled by nanoplates (RNS-ANPs), quantum dots-modified nanoplates (QDs-NPs), and smooth-surfaced nanoplates (SSNPs). Possible formation mechanisms are also proposed based on the experimental results and our understanding. These typical samples exhibit morphology-dependent photo20026

dx.doi.org/10.1021/jp406574y | J. Phys. Chem. C 2013, 117, 20017−20028

The Journal of Physical Chemistry C

Article

Enhanced Photocatalytic Properties. Mater. Sci. Eng., B 2011, 176, 1264−1270. (33) Mi, Y. W.; Zeng, S. Y.; Li, L.; Zhang, Q. F.; Wang, S. N.; Liu, C. H.; Sun, D. Z. Solvent Directed Fabrication of Bi2WO6 Nanostructures with Different Morphologies: Synthesis and Their Shape-Dependent Photocatalytic Properties. Mater. Res. Bull. 2012, 47, 2623−2630. (34) Zhang, G. Q.; Chang, N.; Han, D. Q.; Zhou, A. Q.; Xu, X. H. The Enhanced Visible Light Photocatalytic Activity of Nanosheet-Like Bi2WO6 Obtained by Acid Treatment for the Degradation of Rhodamine B. Mater. Lett. 2010, 64, 2135−2137. (35) Tang, P. S.; Chen, H. F.; Cao, F. One-Step Preparation of Bismuth Tungstate Nanodisks with Visible-Light Photocatalytic Activity. Mater. Lett. 2012, 68, 171−173. (36) Zhang, L. W.; Zhu, Y. F. A Review of Controllable Synthesis and Enhancement of Performances of Bismuth Tungstate Visible-LightDriven Photocatalysts. Catal. Sci. Technol. 2012, 2, 694−706. (37) Shi, W. D.; Yan, Y.; Yan, X. Microwave-Assisted Synthesis of Nano-Scale BiVO4 Photocatalysts and Their Excellent Visible-LightDriven Photocatalytic Activity for the Degradation of Ciprofloxacin. Chem. Eng. J. 2013, 215−216, 740−746. (38) Cui, Z. K.; Zeng, D. W.; Tang, T. T.; Liu, J.; Xie, C. S. Enhanced Visible Light Photocatalytic Activity of QDS Modified Bi2WO6 Nanostructures. Catal. Commun. 2010, 11, 1054−1057. (39) Cui, Z. K.; Zeng, D. W.; Tang, T. T.; Liu, J.; Xie, C. S. Processing−Structure−Property Relationships of Bi2WO6 Nanostructures as Visible-Light-Driven Photocatalyst. J. Hazard. Mater. 2010, 183, 211−217. (40) Yao, S. S.; Wei, J. Y.; Huang, B. B.; Feng, S. Y.; Zhang, X. Y.; Qin, X. Y.; Wang, P.; Wang, Z. Y.; Zhang, Q.; Jing, X. Y.; Zhan, J. Morphology Modulated Growth of Bismuth Tungsten Oxide Nanocrystals. J. Solid State Chem. 2009, 182, 236−239. (41) Zhang, G. Y.; Feng, Y.; Wu, Q. S.; Xu, Y. Y.; Gao, D. Z. Facile Fabrication of Flower-Shaped Bi2WO6 Superstructures and VisibleLight-Driven Photocatalytic Performance. Mater. Res. Bull. 2012, 47, 1919−1924. (42) Shi, W. D.; Yu, S.; Liu, P.; Fan, W. Q. Hydrothermal Synthesis and Thermoelectric Transport Properties of Sb2Te3−Te Heterogeneous Nanostructures. CrystEngComm 2013, 15, 2978−2985. (43) Liu, Y. B.; Gan, X. J.; Zhou, B. X.; Xiong, B. T.; Li, J. H.; Dong, C. P.; Bai, J.; Cai, W. M. Photoelectrocatalytic Degradation of Tetracycline by Highly Effective TiO2 Nanopore Arrays Electrode. J. Hazard. Mater. 2009, 171, 678−683. (44) Palominos, R. A.; Mondaca, M. A.; Giraldo, A.; Penuela, G.; Perez-Moya, M.; Mansilla, H. D. Photocatalytic Oxidation of the Antibiotic Tetracycline on TiO2 and ZnO Suspensions. Catal. Today 2009, 144, 100−105. (45) Reyes, C.; Fernandez, J.; Freer, J.; Mondaca, M. A.; Zaror, C.; Malato, S.; Mansilla, H. D. Degradation and Inactivation of Tetracycline by TiO2 Photocatalysis. J. Photochem. Photobiol., A 2006, 184, 141−146. (46) Wang, P. H.; Yap, P. S.; Lim, T. C−N−S Tridoped TiO2 for Photocatalytic Degradation of Tetracycline Under Visible-Light Irradiation. Appl. Catal., A 2011, 399, 252−261. (47) Huo, P. W.; Lu, Z. Y.; Liu, X. L.; Liu, X. L.; Gao, X.; Pan, J. M.; Wu, D.; Ying, J.; Li, H. M.; Yan, Y. S. Preparation Molecular/ions Imprinted Photocatalysts of La3+@POPD/TiO2/Fly-Ash Cenospheres: Preferential Photodegradation of TCs Antibiotics. Chem. Eng. J. 2012, 198−199, 73−80. (48) Chen, M. J.; Chu, W. Efficient Degradation of an Antibiotic Norfloxacin in Aqueous Solution via a Simulated Solar-Light-Mediated Bi2WO6 Process. Ind. Eng. Chem. Res. 2012, 51, 4887−4893. (49) Xu, C. X.; Wei, X.; Guo, Y. M.; Wu, H. Q.; Ren, Z. H.; Xu, G.; Shen, G.; Han, G. R. Surfactant-Free Synthesis of Bi2WO6 Multilayered Disks with Visible-Light-Induced Photocatalytic Activity. Mater. Res. Bull. 2009, 44, 1635−1641. (50) Zhang, L. S.; Wang, W. Z.; Zhou, L.; Xu, H. L. Bi2WO6 Nanoand Microstructures: Shape Control and Associated Visible-LightDriven Photocatalytic Activities. Small 2007, 3, 1618−1625.

(13) Bi, Y. P.; Ouyang, S. X.; Umezawa, N.; Cao, J. Y.; Ye, J. H. Facet Effect of Single-Crystalline Ag3PO4 Sub-microcrystals on Photocatalytic Properties. J. Am. Chem. Soc. 2011, 133, 6490−6492. (14) Kudo, A.; Hijii, S. H2 or O2 Evolution from Aqueous Solutions on Layered Oxide Photocatalysts Consisting of Bi 3+ with 6s2 Configuration and d0 Transition Metal Ions. Chem. Lett. 1999, 10, 1103−1104. (15) Tang, J. W.; Zou, Z. G.; Ye, J. H. Photocatalytic Decomposition of Organic Contaminants by Bi2WO6 Under Visible Light Irradiation. Catal. Lett. 2004, 92, 53−56. (16) Zhang, C.; Zhu, Y. F. Synthesis of Square Bi2WO6 Nanoplates as High-Activity Visible-Light-Driven Photocatalysts. Chem. Mater. 2005, 17, 3537−3545. (17) Liu, S. W.; Yu, J. G. Cooperative Self-Construction and Enhanced Optical Absorption of Nanoplates-Assembled Hierarchical Bi2WO6 Flowers. J. Solid State Chem. 2008, 181, 1048−1055. (18) Hu, S. P.; Xu, C. Y.; Zhen, L. Solvothermal Synthesis of Bi2WO6 Hollow Structures with Excellent Visible-Light Photocatalytic Properties. Mater. Lett. 2013, 95, 117−120. (19) Yao, F.; Yang, Q. Q.; Yin, C.; Zhu, S. M.; Zhang, D.; Moon, W. J.; Kim, Y. S. Biomimetic Bi2WO6 with Hierarchical Structures from Butterfly Wings for Visible Light Absorption. Mater. Lett. 2012, 77, 21−24. (20) Shang, M.; Wang, W. Z.; Ren, J.; Sun, S. M.; Wang, L.; Zhang, L. A Practical Visible-Light-Driven Bi2WO6 Nanofibrous Mat Prepared by Electrospinning. J. Mater. Chem. 2009, 19, 6213−6218. (21) Mann, A. K. P; Skrabalak, S. E. Synthesis of Single-Crystalline Nanoplates by Spray Pyrolysis: A Metathesis Route to Bi2WO6. Chem. Mater. 2011, 23, 1017−1022. (22) Zhang, G. K.; Lu, F.; Li, M.; Yang, J. L.; Zhang, X. Y.; Huang, B. B. Synthesis of Nanometer Bi2WO6 Synthesized by Sol−Gel Method and Its Visible-Light Photocatalytic Activity for Degradation of 4BS. J. Phys. Chem. Solids 2010, 71, 579−582. (23) Li, G. S.; Zhang, D. Q.; Yu, J. C.; Leung, M. K. H. An Efficient Bismuth Tungstate Visible-Light-Driven Photocatalyst for Breaking Down Nitric Oxide. Environ. Sci. Technol. 2010, 44, 4276−4281. (24) Wu, L.; Bi, J. H.; Li, Z. H.; Wang, X. X.; Fu, X. Z. Rapid Preparation of Bi2WO6 Photocatalyst with Nanosheet Morphology via Microwave-Assisted Solvothermal Synthesis. Catal. Today 2008, 131, 15−20. (25) Li, Y. Y.; Liu, J. P.; Huang, X. T.; Li, G. Y. Hydrothermal Synthesis of Bi2WO6 Uniform Hierarchical Microspheres. Cryst. Growth Des. 2007, 7, 1350−1355. (26) Tian, Y.; Fang, M.; Xu, W.; Li, N.; Chen, Y. Z.; Zhang, L. D. The Morphology-Dependent Photocatalysis for Rhodamine B Degradation Over Bi2WO6 Hierarchical Nanostructure. J. Nanosci. Nanotechnol. 2011, 11, 7802−7806. (27) Xu, L.; Yang, X. Y.; Zhai, Z.; Hou, W. H. EDTA-Mediated Shape-Selective Synthesis of Bi2WO6 Hierarchical Self-Assemblies with High Visible-Light-Driven Photocatalytic Activities. CrystEngComm 2011, 13, 7267−7275. (28) Chen, Z.; Qian, L. W.; Zhu, J.; Yuan, Y. P.; Qian, X. F. Controlled Synthesis of Hierarchical Bi2WO6 Microspheres with Improved Visible-Light-Driven Photocatalytic Activity. CrystEngComm 2010, 12, 2100−2106. (29) Zhou, Y.; Vuille, K.; Heel, A.; Patzke, G. R. Studies on Nanostructured Bi2WO6: Convenient Hydrothermal and TiO2-Coating Pathways. Z. Anorg. Allg. Chem. 2009, 635, 1848−1855. (30) Xia, J. X.; Li, H. M.; Luo, Z. J.; Xu, H.; Wang, K.; Yin, S.; Yan, Y. S. Self-Assembly and Enhanced Optical Absorption of Bi2WO6 Nests via Ionic Liquid-Assisted Hydrothermal Method. Mater. Chem. Phys. 2010, 121, 6−9. (31) Wu, J.; Duan, F.; Zheng, Y.; Xie, Y. Synthesis of Bi2WO6 Nanoplate-Built Hierarchical Nest-like Structures with Visible-LightInduced Photocatalytic Activity. J. Phys. Chem. C 2007, 111, 12866− 12871. (32) Liu, Y.; Wang, W. M.; Fu, Z. Y.; Wang, H.; Wang, Y. C.; Zhang, J. Y. Nest-like Structures of Sr Doped Bi2WO6: Synthesis and 20027

dx.doi.org/10.1021/jp406574y | J. Phys. Chem. C 2013, 117, 20017−20028

The Journal of Physical Chemistry C

Article

(51) He, D. Q.; Wang, L. Q.; Li, H. Y.; Yan, T. Y.; Wang, D. J.; Xie, T. F. Self-Assembled 3D Hierarchical Clew-Like Bi2WO6 Microspheres: Synthesis, Photo-Induced Charges Transfer Properties, and Photocatalytic Activities. CrystEngComm. 2011, 13, 4053−4059.

20028

dx.doi.org/10.1021/jp406574y | J. Phys. Chem. C 2013, 117, 20017−20028