Ammonia Hydrothermal Preparation, Modification And Photocatalytic Activity Of Highly Active TiO₂

Titania has been frequently concerned in photocatalysis for environmental applications and solar energy conversion. Generally, the chemical reactivity and photocatalytic behavior of nano TiO2is strongly influenced by the crystalline phase, grain size, morphology, microstructure and the separation of photogenerated electron-hole pairs.In Chapter2of this thesis, the hydrothermal phase transition of ammonium titanate into TiO2in aqueous ammonia media was investigated in the presence of F-ions by adding various kinds of electrolytes. With the assistance of F-ions, pure brookite TiO2can be hydrothermally prepared with a wide range of Na+ion concentrations from0.25M to1.5M in just24h. Moreover, photocatalytic degradation of MO shows that both anatase and brookite prepared in the presence of F-ions show superior photocatalytic activities than those prepared in the absence of F-ions. F-ions are suggested to play two key roles during the hydrothermal process:catalyzing the condensation reaction of Ti-OH to produce Ti-O-Ti linkages by forming Ti-F and regulating the intercalation and the de-intercalation of Na+ions by counteracting the electrostatic interaction between the Na+ions and the titanate layers.In Chapter3, Ag0/Ag+/TiO2composites were prepared via alkalescent hydrothermal process in aqueous ammonia, and Ag+/TiO2was prepared by eluting the Ag0cluster from the Ag0/Ag+/TiO2composites with K3[Fe (CN)6]/aqueous ammonia. MO and RhB were used to test the photocatalytic activity of the photocatalysts. The photocatalytic activity of the composites was greatly improved after eluting Ag0clusters from the Ag0/Ag+/TiO2composites. Interfacial lattice Ag+cations but not Ag0clusters are responsible for improving the photocatalytic performance of the composites in this work. XPS measurement shows that the chemical state of the interfacial lattice Ag+cation is different with the surface chemical adsorbed Ag+cation. Surface chemical adsorbed Ag+cation is invalid to promote the photocatalytic activity of TiO2while Na+cation can cancel the promotional effect of the interfacial lattice Ag+cation by competitively occupying the interfacial lattice defects. The2h turn over numbers of the interfacial lattice Ag+cations to the degradation of MO and RhB reach8and10, respectively, which show that the interfacial lattice Ag+cations act as recyclable catalytic sites but not one-time consumptive species.