Preparation of a Highly Active Bicrystalline Tio2 Photocatalyst and the Characterization of the Synergetic Effect of Its Dural Crystalline Phases

摘要

[[abstract]]The primary goal of this three-year proposal is to investigate whether there is a synergetic effect between two metal oxide semiconductors with different band structure (which is the positions of conduction and valence band and band gap energy) within a bicrystalline photocatalyst. A photoelectrochemical method using methyl viologen will be established to measure the flat band potential of all the metal oxide semiconductors. A diffuse-reflectance UV-Vis spectrometer will be used to measure the band gap energy. By combining both measurements, we will be able to determine exactly the band structures of metal oxide semiconductors. In the first year of the project, a hydrothermal method will be utilized to synthesize titania particles with well-defined crystalline phase (including anatase, rutile and brookite) and particle size. We will investigate how the variation in titania particle size modifies their band structures. Furthermore, TiO2 (B) nanotube/titania nanoparticle bicrystalline mixtures will be prepared using dry physical mixing and wet mixing to investigate synergetic effect between the two components. In the second year, a precipitation method using aqueous ammonia and metal salts will be used to prepare SiO2, Fe2O3, SnO2 and ZrO2 powder, which will be mixed with TiO2(B) nanotubes to prepare bicrystalline mixture. Nanoparticles contained in a sol solution will be impregnated on the TiO2(B) nanotubes for preparing a better dispersed bicrystalline mixture. The mixtures from both preparation methods will be used to investigate the synergetic effect between TiO2 (B) and four different metal oxides. In the third year, we will attempt to prepare sulfated TiO2(B) nanotubes. They will be prepared by impregnating TiO2 (B) nanotubes with sulfate solution. The effect of volume/mass ratio of SO4 2- solution/TiO2(B), SO4 2- concentration, sulfate source (such as H2SO4 or (NH4)2SO4) and the calcination temperature on the physical and acidic properties as well as the band structure of the sulfated TiO2(B) nanotubes will all be investigated. Metal oxide nanoparticles will also be dispersed onto sulfated TiO2 (B) nanotubes to prepare a sulfated TiO2 (B) nanotube/metal oxide bicrystalline mixture for synergetic effect investigation. All the above photocatalysts will be characterized by various spectroscopic methods such as XRD, SEM, TEM, BET, TPD/NH3, DRIFTS/pyridine, diffuse-reflectance UV-Vis spectroscopy, XPS and photoelectrochemical measurements for their physical (particle size, surface area, morphology, fine structure, band structure and phase composition) and chemical properties (acidity, sulfate structure, oxidation state and content of sulfur). The activities of the above single or bicrystalline photocatalysts will be measured by photocatalytic degradation of salicylic acid in aqueous solution to see whether there is a synergetic effect. The kinetic data of the photocatalytic degradation will be analyzed using Langmuir-Hinshelwood model to obtain the degradation rate constant, and the adsorption of salicylic acid on these titania photocatalyst will also be performed to obtain the adsorption equilibrium constant. Combining both set of data, we can obtain the scientific reasons underneath the synergetic effect. Furthermore, Pt metal will be deposited on TiO2(B) nanotube/anatse particle and TiO2(B)/metal oxide by photodeposition method, respectively. Subsequently, XPS and TEM will be used to analyze the location of the deposited Pt, from which we can verify the validity of the synergetic effect predicted by the measured band structure.