One-dimensional Structure Of Zno Nano-tio <sub> 2 </ Sub> Heterostructures Built And Photoelectric Properties

Zinc oxide (ZnO) and Titanium oxide (TiO₂) are two kinds of very popular functional materials, which have been widely investigated as the key semiconducting materials for applications in photovoltaic cells, batteries, sensing, optical emissions, photonic crystals, catalysis, and photocatalysis. Thereinto, they are mainly used as semiconductor nanoparticles and nanoparticle films so as to the comparatively simple material structure, which limits the performance enhancement of materials in some extent. Our strategy is to design and construct novel nanostructured composite semiconductor films. The composite films not only reserve the characteristics of the primary nanoparticle film, but also have the properties of the one dimensional arrays. Therefore, it can be expected that the construction of new nanostructured semiconductor composite film materials would provide great possibility for further enhancing the performance. In this paper, the one-dimensional orderd ZnO nanorod arrays are directly deposited vertically onto the nanostructured anatase TiO₂ films via low temperature hydrothermal processes, and the effects of depositing conditions on the growth and orientation of one-dimensional ZnO nanocrystals are investigated in detail. Moreover, the superhydrophilic and PL characteristics of the as-prepared novel nanostructured composite films were also explored.The controllable deposition of the one-dimensional structured ZnO onto the nanostructured nanosized TiO₂ films are realized via low temperature hydrothermal processes, achieving the construction of the heterojunction composite material. Firstly, TiO₂ nanoparticle films are prepared utilizing pasty TiO₂ system which is obtained through a sol-hydrothermal process, then the as-prepared TiO₂ film substrates are vertically suspended in a sealed aqueous system, in which zinc nitrate solution and HMT solution have been added. The effects of the reactive time, temperature, and reactant concentration on the growth of the as-prepared one-dimensional ZnO crystals are investigated in detail, and the possible mechanism of ZnO nanorod growth is also suggested. The results show that the low reactant concentration is in favor of the increase in the aspect ratio of ZnO nanorods with weak orientation, while the long reactive time and high reactant concentration are useful to prepare well-aligned ZnO nanorod arrays.Secondly, Mesoporous TiO₂ film (with P123) and non-mesoporous TiO₂ film (without P123) are produced via a dip-coating method, and ZnO nanorods are synthesized on the nanostructured TiO₂ films in the above aqueous system. The effects of the film surface microstructure and composition on the orientation of ZnO nanorod arrays are also investigated. The obtained ZnO nanorod arrays onto the mesoporous TiO₂ films exhibit rather good orientation, compared with that on the glass or the nanoparticle TiO₂ film. The possible formation mechanisms of well-oriented nanorod arrays are also suggested.The tests of water contact angle and photoluminescence performance show that the TiO₂ film itself does not have superhydrophilic characteristic, but the typically constructed semiconductor composite films, based on the oriented ZnO nanorod arrays vertically onto the TiO₂ nanoparticle films, exhibit superhydrophilic characteristic without UV irradiation, mainly attributed to the cooperation between the top layer of the oriented ZnO nanorod arrays and the bottom layer of the TiO₂ nanoparticles. The composite films can appear a strong near-ultraviolet PL band and a comparable weak green PL band, which are related to the crystallinity and surface defects of one-dimensional ZnO nanorods, respectively.