Synthesis And Modification Of Mesoporous TiO₂ Photocatalyst Nanomaterials

Mesoporous TiO2 has better physical and chemical properties than usual TiO2 because of its high specific surface area, mean pore-size distribution and easily recyclable. However, it is very difficult to enhance the crystallintity of TiO2 framework and protect the mesostructure at the same time. Usually, the mesostructure is destroyed seriously when the surfactant template is removed at high calcination temperature, and the specific surface area decreases significantly, the photocatalytic activity become lower. Moreover, the band gap of TiO2 catalyst is some kind of broad, andTiO2 catalyst is active only in UV light which limits its commercial applications. Therefore, it is a great significance to synthesize mesoporous TiO2 with high crystallinity and large specific surface area, and broaden the response to the visible light range, increase the photocatalytic activity of mesoporous TiO2 under visible light.In the third chapter, mesoporous TiO2 with good crystallinity and high photocatalytic activity was prepared by sol-gel method combined with hydrothermal method using dodecylamine as template. The results of XRD, BET and TEM indicate that the sample has mesostructure with anatase and brookite. In the process of sample preparation, the higher sol temperature, the higher hydrothermal temperature and the longer hydrothermal time, the more serious TiO2 pariticles aggregate, which are harmful to the formation and the ordering of mesostruture. The sample exhibits high UV light photocatalytic activity because the organic species in the sample is removed under calcinaion and the sample possesses small crystalline size and high surface area.In the fourth chapter, highly ordered mesostructure TiO2 were synthesized by an evaporation-induced self-assembly (EISA) method, and the effects of different titanium sources, solvent and calcination temperature on the formation of mesostructure were investigated. The results of XRD and TEM suggest that the sample prepared by n-butyl titanate or mixture of n-butyl titanate and TiCl4 has ordered hexagonal mesostructure, and the sample prepared by isopropyl titanate has ordered cubic mesostructure. Moreover, the mesostructure ordering of the sample using ethanol or butanol as solvent is higher than that of the sample using isopropanol, n-propanol or tetrahydrofuran. The sample without thermal treatment has loose framework and poor ordered mesostructure. The framework structure is enhanced when the sample is calcined at 250℃. However, the mesostructure of the sample is destroyed because of the growth of TiO2 crystalline and the mesostructure ordering becomes poor when the sample is calcined above 350℃.In the fifth chapter, highly ordered bicontinuous cubic mesoporous titania-silica composites with crystalline framework were synthesized by EISA method. In the process of experiment, the solution acidity and sol water content show important effects on the formation of ordered mesostructures. The mesoporous titania-silica composite with the material ratio HCl/(Ti+Si)=1.5 and H2O/(Ti+Si)=10 has high thermal stability, large specific surface area, uniform pore diameter, open-pore structures and small nanocrystal size, which is favorable for the photodegradation of RhB solution under the irradiation of UV light.In the sixth chapter, mesoprous TiO2 with high crystallinity, large specific surface area and high thermally stable anatase wall were synthesized by doping Si, Zr or Al. The results of XRD and BET imply that the samples doping with Si, Zr or Al all have high thermally stable anatase, and posses large surface area, high pore volume and mean pore-size distribution under high temperature calcination. The effects of Si, Al and Zr on the anatase stability, mesostructure stability and surface area preservation are sorted as Si> Al> Zr. The method that doping with Si or Zr can improve the photocatalytic activity of mesoporous TiO2, and it shows a better photocatalytic activity compared with P25 at a large extent of doping concentration and calcination temperatures. However, the sample doping with Al shows a poor photocatalytic activity.In the seventh chapter, N,B,Si-tridoped and N,P-codoped mesoporous TiO2 catalysts were synthesized. The nonmetal codoped samples have small crystalline size, very large specific surface area, high pore volume and mean pore-size distribution. Si, B or P dopant can inhibit the growth of TiO2 crytalline and the phase transformation of antase. Si or P dopant can suppress the formation of brookite but B dopant can not. The sample tridoped with N, B and Si exhibits excellent photocatalytic activity on the degradation of 2,4-diclorophenol solution under visible light irradiation, and the sample codoped N and P showes high photocatalytic activity on the degradation of RhB under visible light illumination.