Preparation And Photocatalytic Activity Of WO₃/TiO₂ Photoacitivity Nanocomposites

Photocatalytic technology is a promising way for its significance in energy-saving and environmental protection, which under relatively mild reaction condition can decomposes organic substances only by using solar energy without secondary pollution. Among various oxide semiconductor photocatalysts, TiO₂ is a very important photocatalyst due to its biological and chemical inertness, strong oxidizing power, nontoxicity, and long-term stability against photo and chemical corrosion. Despite its great potential, the low photocatalytic efficiency of TiO₂ hinders the commercialization due to the high recombination ratio of photo-induced electrons (e-) and holes (h+) and lower solar energy utilization efficiency (5% energy of the solar spectrum). Thus development of solar light active TiO₂ photocatalyst with high catalytic efficiency is always of great interest and demand in both academic and commercial sectors. In this paper we modified TiO₂ by both increasing its specific surface area and coupling with other metal oxides, to prepare a high photoacitivity nanocomposites material.To achieve these high photoactivity nanocomposites material, titanate nanotubes with high dispersivity and high specific surface area were first prepared by a hydrothermal reaction using TiO₂ (P25) as precursor. The effects of calcination temperature on the microstructures, morphology and photocatalytic activity of the titanate nanotubes were investigated and discussed systematically. The calcined sample that was proved with highest photoactivity, was chosen as the support to deposit WO₃ nanoparticles by a sol-gel method and the new nanocomposites photocatalysts (WO₃/TiO₂-NRs) were prepared.Experiments results show that open-ended structural nanotubes with inner diameters of 3⁴ nm, outer diameters of 7¹2 nm and lengths of several hundreds nanometers are obtained. It was found that the crystalline phase, morphology, specific surface area and photocatalytic activity of the titanate nanotubes strongly depended on the calcination temperature. When the calcination temperature was below 300°C, the calcined samples showed lower photocatalytic activity due to the absence or weak crystallization of anatase phase. While the calcination temperature was higher than 300°C, the morphology of calcined samples were damaged to different extents, and broken to nanorods with different length diameter ratio and different specific surface area. It is obvious that post-treatment is believed to improve the photoactivity of TiO₂ nanotubes, but, on the downside, adversely affect its physical characterizations. In order to maintain the advantage of high specific surface area of titanate nanotubes and obtain crystallization of anatase phase simultaneously. It was found by controlling the calcination temperature at 400°C, TiO₂ nanorods showed a largest specific surface area, and photoactivity is 2.5 times higher than that of P25.Nanocomposites WO₃/TiO₂ nanorods (WO₃/TiO₂-NDs) were prepared by a sol-gel method using 400°C calcined TiO₂ nanorods as support material. It was found that charge separation was well improved by the coupling of WO₃ and TiO₂. The nanocomposites with loadings of 2% wt WO₃ were demonstrated to have the best photocatalytic activity, which was 2 times higher than that of TiO₂ nanorods, and 5 times higher than that of P25.In order to obtain best photocatalytic nanocomposites without damage the morphology of titanate nanotubes,"chemical morphology freezing method"was attempted by filling titanate nanotubes with carbon and WO₃, and then covered the nanotubes with silica layer. After calcination, nanocomposites photocatalysts SiO₂@@WO₃/TiO₂-NTs with both prefect nanotube morphology and anatase phase were obtained successfully. The nanocomposites were demonstrated to have the best photocatalytic activity, which was 12 times higher than that of TiO₂.Finally, we proposed to construct a ternary nanocomposites material system based on the investigation of nanocomposites photocatalysts SiO₂@@WO₃/TiO₂-NTs, and showed some preliminary feasibility study. The study presents an attractive avenue and seems an ideal candidate in extensive applications.