The Preparation And Application Of Photocatalyst With Visible Light Photoresponse

With the rapid development of industry, energy crisis and environment pollution become more and more serious. The treatment of organic wastewater by conventional methods has drawback due to expensive and difficulties. From the viewpoint of protecting environment and saving energy, many researches focused on the photocatalytic process of water treatment using titanium dioxide (TiO₂) have been developed, but the energy gap of pure anatase TiO₂ is about 3.2eV, only ultraviolet light (λ< 387 nm, about 4% of the solar light) can be absorbed by pure anatase TiO₂. It is of interest to find TiO₂-based photocatalysts which are sensitive to visible light. In this paper, on the foundation of the summarizing the development of the modification of TiO₂ photocatalyst, the following aspects were mainly studied.1. In order to extend the range of photo-response spectrum of TiO₂ and increase its photocatalytic activity, TiO₂ photocatalysts doped with La, La·N and La·N·Fe were prepared by Sol-Gel method, respectively. Compared with pure TiO₂, the band gap of the La-doped sample was decreased with the dopant concentration, the paper explained the reason from the atom orbit view of TiO₂. It also can be found that all of the doped samples had the phenomena of"red move", which means the doped samples'band gap was decreased, and the La·N·Fe-doped sample has the longest photoresponse wavelength. The photocatalytic activity of the samples was investigated to be high by degrading nitrobenzene and the results showed the degradation rate of the sample doped with La·N·Fe was more than 70%, but that of TiO₂ was only 17.5%, so the doped sample had the most excellent photocatalytic properity.2. The TiO₂ photocatalyst doped with upconversion luminescence agent (Er³⁺ respective doped NaYF₄, Y₃Al₅O₁₂ and Ca_0.9Y_0.1F_2.1) which can emit upconversion fluorescent peaks belong to ultraviolet light under the excitation of visible light were synthesized. The doped samples were characterized by X-ray diffraction, transmission electron microscope and ultraviolet–visible absorption spectra. The photocatalytic activity of the doped samples was investigated by decomposing methylene blue. The results indicated that the COD degradation ratio of methylene blue in the presence of doped sample was better than the un-doped one under visible light irradiation, especially the Er³⁺/Ca_0.9Y_0.1F_2.1 doped sample, which can degrade 70% of the methylene blue in 5 hours under visible light irradiation, this degradation rate was about two times as that of TiO₂. The photocatalytic mechanism on degradation was investigated by degradation of methylene blue. The results showed two reaction mechanisms (photoproduction hole and·OH oxidization mechanism) in degradation. It was a mixture reaction mechanism in the presence of doped sample under visible light irradiation, butphotoproduction hole oxidization mechanism occupied majority.3. The N-doped TiO₂ photocatalyst was prepared by immersion method. The prepared sample was investigated to degrade ammonia nitrogen waster water of aquiculture under solar light irradiation. The results showed that after 5 hours irradiation the degradation rate of doped sample reached 86.7%, which proved the N-doped TiO₂ photocatalyst has better application prospect in disposal the ammonia nitrogen waster water of aquiculture. The material CaA12O4 with high adsorbency was prepared by Sol-Gel combustion method, and the N-doped TiO₂ photocatalyst loaded with CaA12O4 was prepared by Sol-Gel method. The results of degrading the waster water of paper mill under solar light irradiation in the presence of the loaded sample, N-doped TiO₂ and TiO₂ showed the loaded sample has the best photocatalytic properity, the reason can be ascribed to the high adsorbency of CaA12O4.In a word, TiO₂ photocatalysts were modified by different methods, many significance results were obtained including ion doping mechanics, photocatalysis mechanics and so on. To a certain extent all the results had some innovation, and at the same time laid the foundation for the further study and practical application on visible light photoresponse photocatalyst.