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Heterogeneous Lollipop-like V2O5/ZnO Array: A Promising Composite Nanostructure for Visible Light Photocatalysis C. W. Zou,*,† Y. F. Rao,‡ A. Alyamani,§ W. Chu,‡ M. J. Chen,‡ D. A. Patterson,† E. A. C. Emanuelsson,† and W. Gao*,† †
Department of Chemical and Materials Engineering, The University of Auckland, Private Bag 92019, Auckland, New Zealand, ‡Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, and §King Abdul-Aziz City of Science and Technology (KACST), Saudi Arabia Received April 4, 2010. Revised Manuscript Received June 16, 2010
ZnO/V2O5 core-shell nanostructures have been prepared by a two-step synthesis route through combined hydrothermal growth and magnetron sputtering. After annealing under oxygen ambience, a ZnO/V2O5 heterogeneous lollipop-like nanoarray formed. The microstructure and crystal orientation of those nanolollipops were investigated by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), which show single crystal structure. The optical properties were characterized by UV-vis spectroscopy and showed quite different absorption curves for the as-deposited and annealed samples. The ZnO/V2O5 nanolollipops demonstrated excellent photocatalytic activity in terms of decomposing 2,6-dichlorophenol (2,6-DCP) under visible light, indicating their promising potential as catalysts for industrial wastewater and soil pollution treatments.
Introduction Functional one-dimensional (1D) metallic oxides have attracted much attention because of their potential use in electronic, optoelectronic, and spintronic devices.1-5 Among them, ZnO and V2O5 nanowires have been extensively studied due to their special electronic, chemical, and optical properties.6-9 Incorporating these two materials into an integrated structure is of great interest because the resulting products may possess improved physical and chemical properties. The applications of these materials can be extended to biosensors, dye sensitized solar cells, and photocatalyts.1-7 Composite oxide nanorods such as TiO2/ZnO, ZnO/MgO, or ZnO/Er2O3 core-shell structures have been previously studied.9-12 Increasing light emission or enhanced efficiency of dye-sensitized solar cells based on those core-shell structures is observed. However, few studies have been performed to investigate the effect of composite ZnO/V2O5 nanorod arrays, which may have great *To whom correspondence should be addressed. E-mail: czou003@ aucklanduni.ac.nz (C.W.Z.);
[email protected] (W.G.).
(1) Zhang, W.; Cunningham, B. T. Appl. Phys. Lett. 2008, 93, 133115. (2) Zou, C.; Yan, X.; Han, J.; Chen, R.; Gao, W. J. Phys. D: Appl. Phys. 2009, 42, 145402. (3) Liao, L.; Zheng, Z.; Yan, B.; Zhang, J. X.; Gong, H.; Li, J. C.; Liu, C.; Shen, Z. X.; Yu, T. J. Phys. Chem. C 2008, 112, 10784. (4) Scott, J. F.; Fan, H. J.; Kawasaki, S.; Banys, J.; Ivanov, M.; Krotkus, A.; Macutkevic, J.; Blinc, R.; Laguta, V. V.; Cevc, P.; Liu, J. S.; Kholkin, A. L. Nano Lett. 2008, 8, 4404. (5) Zhang, W.; Ganesh, N.; Mathias, P. C.; Cunningham, B. T. Small 2008, 4, 2199. (6) Dı´ az-Guerra, C.; Piqueras, J. Cryst. Growth Des. 2008, 8, 1031. (7) Gopal, K. M.; Karthik, S.; Maggie, P.; Oomman, K. V.; Craig, A. Nano Lett. 2006, 6, 215. (8) Takahashi, K.; Wang, Y.; Cao, G. Appl. Phys. Lett. 2005, 86, 053102. (9) Zou, C. W.; Yan, X. D.; Han, J.; Chen, R. Q.; Gao, W. Chem. Phys. Lett. 2009, 476, 84. (10) Greene, E.; Law, M.; Yuhas, B. D.; Yang, P. J. Phys. Chem. C . 2007, 111, 18451. (11) Plank, N. O. V.; Snaith, H. J.; Ducati, C.; Bendall, J. S.; Schmidt-Mende, L.; Welland, M. E. Nanotechnology 2008, 19, 465603. (12) Li, S. Z.; Gan, C. L.; Cai, H.; Yuan, C. L.; Guo, J.; Lee, P. S.; Ma, J. Appl. Phys. Lett. 2007, 90, 263106.
Langmuir 2010, 26(14), 11615–11620
potential for photocatalysis or dye sensitized solar cell applications due to band gaps of 3.4 and 2.2 eV for ZnO and V2O5, respectively, which cover the UV and visible light bands. In this work, ZnO/V2O5 core-shell nanorods were prepared by a two-step synthesis route combined with hydrothermal growth and magnetron sputtering. After postannealing treatment under oxygen ambience, highly ordered ZnO/V2O5 heterogeneous nanolollipop arrays were formed. The microstructure and optical properties were investigated. A model chemical compound 2,6dichlorophenol (2,6-DCP) was selected to evaluate the photocatalytic activities of ZnO/V2O5 under the irradiation of visible light, since this compound is always found in industrial wastewaters and as a soil pollutant and is currently one of the 126 priority pollutants listed by the U.S. Environmental Protection Agency due to its toxic and recalcitrant properties.13
Experimental Section The two-step process to prepare ZnO/V2O5 core-shell nanostructures is as follows: First, ZnO nanorods arrays were synthesized on glass substrates (25 mm 10 mm) by the seed-assisted low temperature (95 °C) hydrothermal method. The details of the hydrothermal method are described elsewhere.14 The V2O5 shell layer was then deposited onto the surfaces of ZnO nanorods by using a magnetron sputter at room temperature. V2O5 with high purity (∼99.9%) was used as the target, and Ar as the working gas. The base vacuum of the sputtering chamber was
