Research On Preparation And Application Of Photocatalytic Material Of La-doped Nano-TiO₂/Kaolinite

Nano-TiO₂ photocatalysts have been the focus of the investigations, for its high photocatalytic activity, no toxicity, low price and chemical stability. However, the band gap of TiO₂ is large(Eg=3.2eV), and it is only active in the ultraviolet region which is about 3% of the overall solar intensity. La-doped was adopted to extend the light responsible range and improve the photocatalytic activity of TiO₂.In this thesis, La-doped nano-TiO₂/Kaolinite was prepared with sol-gel method. These factors has been researched such as the dosages of La, calcination temperature and time, hydrolysis temperature and time which affecting crystal structure and photocatalytic activity. The acid red G, RhB, AZO-dye has been degradated to make use of the photocatalyst. The photocatalytic activity was also evaluated under the visible light and UV light irradiation. The influences of photocatalyst dosage, degradable time, solution pH, difference illumination condition, H₂O₂ quantity were investigated. XRD, Raman, FT-IR and TEM were adopted respectively to characterize the structure of the molecular and crystal, and morphology of TiO₂. As the same time the doping mechanism has been also discussed.The conclusions are as follows:1. The optimized process conditions of preparation are La doping dosage of 0.5%, calcined at 550℃for 2h and hydrolyzed at 50℃for 3h.2. The XRD, Raman and FT-IR were adopted to characterize and analyze the mechanisms of modification. TiO₂ crystal doped with La presented as phase of anatase only on the surface of kaolinite in XRD spectra of samples. The results obtained are in fair agreement with the results from the analysis of Raman. The results showed that the doping of La inhibited the phase transformation of TiO₂. Results of FTIR spectroscopy testing showed that La entered into TiO₂ crystal lattice or combined on TiO₂ surface at least. Transforming temperature of TiO₂ crystal structure was improved due to heat effect differences. It could be seen that TiO₂ had been loaded on the surface of kaolinite successfully and uniformly from photo-TEM which is still a positive factor to promote the photocatalytic rate. 3. Acid red G, RhB and AZO-dye wastewater were degraded in order to evaluate the photocatalytic activity of La-doped nano-TiO₂/Kaolinite. The results showed that under the UV-light, the rate of decolorization of wastewater were 97.03%, 98.18% and 99.57% respectively; compared with the un-doped nano-TiO₂/Kaolinite, the decolorization rate increased 14.36%, 17.45% and 12.34% respectively, and the rate of decolorization increased 13.87%, 6.73% and 5.96% respectively under the visible light. The photocatalytic effects enhanced obviously with doping of La in sunlight. Doping element La could develop effectively towards visible light area.4. The initial pH of wastewater had obviously influence on the decolorization rate. It was more than 90% in acidic solutions.5. Additive H₂O₂ will benefit to change of hydroxy·OH and enhence the photocatalytic rate and efficiency.