Research On Photocatalytic Activity And Doping Mechanism Of Metal Ion-doped Nanometer TiO₂ Film

In this thesis, the doping mechanism of six kinds of metallic ions-doped TiO₂ film was systematically researched. The relationships between the ion species, the ion concentration, the ion radius, the ion valence, the electron charge, the electron affinity potential under stable oxidation state, the formation enthalpy of oxide and the photocatalytic activity of nanometer TiO₂ film were respectively studied in terms of the X-ray diffraction and the pattern analysis with scanning electron microscope.Acted as raw materials for the tetrabutylester titanic and the absolute ethyl alcohol, metal irons were introduced by nitrate solution. TiO₂ film was daubed on the surface of glass by sol-gel method and dipping-hang method with a coating speed 2³mm/min. Transparent and homogeneous TiO₂ film was obtained after heat-treating and the phase structure of this film was anatase and rutile. The mean particle size of nano particles prepared was 30⁵0nm every time. It was indicated from the results of photocatalytic degradation tests upon the methyl orange that the photocatalytic activity of TiO₂ was increased obviously by doped La³⁺, Ce³⁺, Fe³⁺, Ni²⁺ and Cu²⁺, especially the photocatalytic activity coefficient of that doped with Fe³⁺ was 90.01% which was the highest one, however, the activity was decreased by doped Zn²⁺. The photocatalytic activity under the given experiment condition was: Fe³⁺ > La³⁺ > Ni²⁺ > Cu²⁺ > Ce³⁺ > Zn²⁺. It was indicated from the results of tests on the relationship between the content of doped ions and the photocatalytic activity that the photocatalytic activity increased with the increasing of content of doped Fe³⁺ and decreased with the increasing of content of doped La³⁺; the optimum content of Cu²⁺ and Ce³⁺ was 5%, and that of Ni²⁺ was 3%; the photocatalytic activity was increased by all doped ions with the increasing of light time. It was proved from results of many tests that the content of anatase phase and the photocatalytic activity increased with the decreasing of particle size caused by the doped ions except for Ce³⁺. The minimum particle size of TiO₂ was 38.23nm and the photocatalytic activity was preferable when the content of doped Fe³⁺ was 5%, however, when doped with Zn²⁺, the particle size was 41.86nm and the photocatalytic activity was minor. Besides, the varying regularity of the ion charge-radius ratio q/r was similar to that of photocatalytic activity, the more the ratio q/r, the more the ability of capturing electron. The ratio of eletron affinity potential under stable oxidation state for the doped ions and ion radius (Ea/r) was in good consistence with the photocatalytic activity, the more the electron affinity potential under stable oxidation state for the doped ions, the higher the photocatalytic activity; there was little relationship between the initial ionization potential and the photocatalytic activity, but better correlation between the formation enthalpy of the corresponding metallic oxide and the photocatalytic activity of MO_X /TiO₂, the less the formation enthalpy of oxide, the higher the photocatalytic activity, and vice versa except for Fe³⁺.