Study On Preparation And Photocatalytic Activity Of CeO₂ And Its Mixed Oxides

The current dissertation concerns study on the controlled synthesis and properties of CeO₂ and its mixed oxides with ordered mesostructures. The nano-scale CeO₂ particles with high crystallinity and mesoporous CeO₂-ZrO₂ mixed oxides are prepared by the hydrothermal method, then a series of mesoporous CeO₂-TiO₂ mixed oxides are also synthesized using one-step synthesis strategy. The photocatalytic activity of our obtained nanoparticles CeO₂ and mesoporous CeO₂-ZrO₂N CeO₂-TiO₂ mixed oxides were investigated in this thesis. The formation method and characterization of nanoparticles CeO₂ and mesoporous CeO₂-ZrO₂,CeO₂-TiO₂ mixed oxides were also presented in this dissertation.The nano-scale CeO₂ particles were prepared by the hydrothermal method. The physiochemical properties of the samples were characterized by means of XRD, TEM and FT-IR. The results indicate that the as-prepared CeO₂ particles are fluorite structure with some distant congregation. The influence of thermal treated temperature on particle size was also analyzed as well. The photocatalytic activity is investigated by the degradation of Rhodamine B irradiated by ultraviolet radiation. The results suggest that nano-sacle CeO₂ particles prepared by hydrothermal method exhibit strong absorption to UV light and show relatively high photocatalytic activity.The mesoporous CeO₂-ZrO₂ mixed oxides of different amount were prepared by the hydrothermal method. The results show that the photo-generated electron (e^-) and hole (h⁺) pairs recombination was inhibited through introduction zirconia source. The obtained mesoporous composites not only maintain the properties the original metal oxides, but also possess high specific surface area and high textual and thermal stability. Moreover oxygen vacancies are formed as Zr⁴⁺ and Ce⁴⁺ have different radius, which are benefit to the activate of RhB, then can improve the photocatalysis. The mesoporous CeO₂-ZrO₂ mixed oxides have higher photocatalytic activity than pure CeO₂, especially the Ce:Zr malor ratio is 2:1 and hydrothermal temperature is 160℃.The mesoporous CeO₂-TiO₂ mixed oxides which had been synthesized through evaporate-induced self-assembly method were characterized in detail by XRD, FT-IR, Raman, XPS, TEM and N₂ adsorption-desorption. As for the obtained samples, the template can be removed completely then ordered mesoporous structure which has high surface and small crystallize area was formed after being calcinated at 350℃. The effects of Ti/Ce molar ratio and calcining temperature on the photocatalytic activity are investigated. The results demonstrate that the highest photoactivity of the mesoporous CeO₂-TiO₂ mixed oxides are calcined at 500℃when Ti:Ce molar ratio is 1:0.1.