Study On The Photocatalytic Properties Of Visible Light Responsible Nano-tio₂ Film And Its Preparation

With the rapid development of economic, people pay more attention to the environment.Semiconductor photocatalysis is the most active areas of chemical research into pollution control, forming a new research field. So far, semiconductor photocatalysts including TiO2, CdS, WO3, Fe2O3, ZnO, ZnS, SnO2, etc. have been researched. Among a variety of semiconductor , CdS,TiO2 show better catalytic activity. However, CdS is not a good choice for its chemical instability under illumination. TiO2 have becomes the most commonly used catalyst for its more advantages such as good chemical stability,low-cost,non-toxic and high catalytic activity . TiO2 may show Photocataly activity only under irradiation of ultraviolet(UV) light for its wide band-gag (Eg-3.2eV),most of the sunlight is less utilized. Furthermore,the high recombination of photo-generated electrons and holes makes quantum productivity low. These shortcomings have greatly limited the wide application in practice. Modified TiO2 to improve solar energy conversion rate and improve the photocatalytic efficiency is a hot topic creating more and more interest of researchers.Considering the problems above,we advanced the vision that using precious metals (Pt), metal ions (Fe3+) and compound semiconductor to modify TiO2. In this paper, modified-TiO2 thin films were prepared by sol-gel method. The effects were reviewed by changing the doping element, doping consent and calcination temperature. Characterizations of micro-structure and UV-vis absorption of modified-TiO2 photocatalyst were analysed using XRD, SEM, UV-vis. In addition, the photocatalytic activities of modified- TiO2 were discussed by decomposing methylene blue under simulated sunlight.Crystal form of Pt-doped TiO2 does not change. Fe3+ doping can promote the TiO2 from anatase to rutile transformation. The calcination temperature and doping concentration of TiO2 catalysts were main factors affecting the crystal structure and grain size. As the calcination temperature increment, anatase was reduced and rutile was increased. Grain size was decreased with increasing doping concentration.The surfaces of modified-TiO2 were homogeneous and crack-free. Particles tightly arranged, evenly distributed and well crystallized forming dense films.UV-Vis measurements have shown that the intrinsic absorption edges of three kinds of modified TiO2 shifted towards longer wavelengths. Furthermore, the absorption of visible light has also been enhanced between 400-600nm.Three kinds of modified TiO2 photocatalyst thin films under visible light irradiation decomposing methylene blue (10 mg / L) experiments show that, Pt-TiO2 thin film with 0.2% (molar ratio) Pt calcined at 450℃has the best visible light photocatalytic activity, methylene blue degradation rate was 23% radiated 2.5 h; when the Fe3+ doped ratio of 5%, calcinated 2 h at 450℃, the TiO2 obtained the highest catalytic activity of visible light photocatalyst, radiated 2.5 h methylene blue degradation rate is 25%; Calcinated at 650℃, catalytic activity of homojunction TiO2 / Fe3+-TiO2 photocatalyst is clearly stronger than that of Fe3+-TiO2 thin film, degradation rate of methylene blue is 21% in the light 2.5 h.