Synthesis, characterization and growth mechanism of ZnO/TiO 2 nanohybrid arrays
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1035-L02-11
Synthesis, characterization and growth mechanism of ZnO/TiO2 nanohybrid arrays Cheng Chun, and Wang Ning Department of Physics, Tower B, 005c, HKUST, Hong Kong, China, People's Republic of ABSTRACT In this paper, we demonstrate a simple method to synthesize ZnO/TiO2 nanohybrid structure arrays based on the site-specific deposition of titanium oxide on ZnO nanorods under the hydrothermal condition. We have found that the polarity of the ZnO (0001) surface plays an important role in the formation of the nanohybrid structures. Each ZnO nanorod is assembled with one TiO2 particle only at the (0001) end surface. High-resolution transmission electron microscopy study shows that the TiO2 particles that are connected to ZnO nanorods are amorphous. By annealing at different temperatures, these particles can be transformed to nanocrystals of the anatase and rutile phases, which have a particular relationship with the orientation of ZnO NRs and good interface structures. This work provides a rational approach to the assembly of complex nanohybrids using the intrinsic properties of ZnO nanocrystals. INTRODUCTION To realize many potential applications of one-dimensional nanostructures, fabrication of heterostructured and functional nanowires has drawn extensive attention in recent years. Considerable effort has been devoted to combining semiconductor nanoparticles with suitable materials to synergize the properties of both components, which has led to many promising applications such as the enhancement of photocatalytic performance through the deposition of metal or metal islands on ZnO and TiO2 nanoparticles.[1-2] In this case, the photocatalytic efficiency is limited by the fast recombination of photogenerated charge carriers. In semiconductor/metal nanocomposites, the photo-induced charge carriers are trapped by the metal component, which may largely promote interfacial charge-transfer processes. [3] Coupled ZnO/TiO2 crystals have been found to show a greater photocatalytic activity, such as in the degradation of phenol, 2-chlorophenol, and pentachlorophenol [4] and in the decomposition of salicylic acid. [5-6] Most coupled ZnO/TiO2 structures produced previously are simply core-shell (surface coating) or sandwich (particles randomly adhere to each other) geometries and have poor interface structures, which limit the interfacial charge-transfer processes and thus the photocatalytic activity of the nanocomposite material.[7-11] The interface structures in the coupled nanowires formed by chemical reaction are important issues for low dimensional devices. The fabrication of individual nanoscale building blocks and their assembly into nanohybrid structures and functional devices are still major challenges to nanotechnologists. In this paper, we demonstrate a simple method of synthesizing ZnO/TiO2 nanohybrid structures and their arrays by the site-specific deposition of titanium oxide on ZnO nanorods (NRs). We have observed that the polarity of the ZnO (0001) surface plays an important role in the formation of ZnO/TiO
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