Studies On The Modification Of SrTiO₃ Catalyst And Its Photocatalytic Activity Of Visble Light

SrTiO₃ perovskite-type oxides are widely regarded as the most developed potential photocatalytic material, however, its band gap is about 3.2 eV and it can not effectively absorb visible light so that its applications are limited. In order to use it effectively under visible light, the SrTiO₃ perovskite-type catalysts has been modified, and their activities under visible light were investigated in photocatalytical degradation of methylene blue in dyeing wastewater.Based on the preparation of SrTiO₃ perovskite-type oxides by fractional-precipitation method, a series of Sr@TiO2 composite oxide catalysts with different Sr/Ti molar ratios were prepared. These photocatalysts were characterized by X-ray diffraction（XRD）, Scanning Electron Microscope（SEM）, Transmission Electron Microscope（TEM）, ultraviolet visible diffuse reflectance absorption spectra（UV-VIS）. The results showed that the low Sr coated samples were spherical, while the high Sr coated samples presented plate-like or needle-like structure. What’s more, when percentage of Sr coated≤60%, the photocatalytic activity improved with increment of Sr coated. The catalysts had extensively improved their photocatalytic activity when percentage of Sr coated between 60% and 80%. Particularly the sample showed the highest photocatalytic activity when Sr@TiO2-80%, and its first-order reaction rate constant was 14.05 times more than that when Sr@TiO2-50%. Finally the photocatalytic activity was decreased as Sr coating amount continued to increase.A series of Sr-Zr-Ti mixed oxide catalysts were also prepared by fractional-precipitation method. The results showed that when Zr/Ti molar ratio<1, the SZT mixed oxide catalysts had a increase on photocatalytic activity because some lattice defects and photocatalytic active sites caused by Zr4+ doping. Particularly when Zr/Ti molar ratio≥1, the catalysts had extensively improved their photocatalytic activity due to new crystalline phases of SrZrO₃ and TinO2n-1 （n=4,9）, which were favorable for separation of photo-generated electron-hole conduction. Especially the SZT-5/5 sample showed the highest photocatalytic activity. The first-order reaction rate constant was determined to be 0.2133 min-1, which was 13.5 times more than that of the SrTiO₃ sample （0.0158 min-1）.