Preparation And Photocatalytic Activities Of Bismuth Oxyhalides Based Catalysts

Since1972, Fujishima and Honda first reported that water can be decomposed into H2and O2by TiO2under light irradiation, TiO2has become the most popular semiconductor photocatalyst because of its high photocatalytic activity, light stability, high efficiency、low cost and non-toxic. However, its wide application is limited because TiO2has a large band-gap and can only be excited by ultraviolet or near ultraviolet. In addition, its quantum efficiency is very low. Therefore, in order to improve the photoactivity under visible light two methods are usually applied. One is the modification of TiO2including precious metal deposition, nonmetal ions doped, the introduction of oxygen vacancy defects and compound semiconductor. Another approach is to develop novel photocatalyst with high efficient. BiOCl photocatalyst has a unique electronic structure, good optical properties and photocatalytic properties for rhodamine B degradation.Therefore, BiOCl might be a promising, efficient, visible-light-response catalyst. In this thesis, we mainly investigated the preparation, characterization and catalytic activity of three types of composite semiconductors: flowerlike BiOCl.g-C3N4/BiOCl and BiOBr/BiOCl.1、A series of flowerlike BiOCl composite photocatalysts with high visible light photocatalytic activity were prepared by the sol-gel method. We investigated the effects of reaction time and HCl concentration on the morphology of catalyst and catalytic performance of the composite catalyst. The results indicated that the BiOCl sample prepared with lmol/L HCl and60min of reaction time, showed the flower-like morphology and the highest photocatalytic activity in rhodamine B degradation. The structures of the flower-like BiOCl composites were characterized by X-ray powder diffraction. The optical properties of the composite photocatalysts were characterized by UV-vis diffuse reflectance spectra and photoluminescence spectra. Simultaneously, the photocurrents were characterized by photoelectrochemical method. From the investigation results, we believe that the high photocatalytic activity of the flower-like BiOCl can be attributed to its special morphology and band structure.2^A series of g-C3N4/iOCl composite was prepared using sol-gel method. The effect of photocatalyst amount, dyes and the light souce on the photocatalytic activity of the synthesized composites were investigated. X-ray powder diffraction, scanning electron microscopy, UV-vis diffuse reflectance spectra, and photoluminescence spectra, Fourier transform spectrophotometer, photoluminescence spectra and photoelectrochemical were applied to investigate the structure, morphology, and optical properties of the photocatalysts. The experimental results showed that the8wt.%g-C3N4/BiOCl composite exhibited excellent performance on the photocatalytic oxidation of RhB under visible-light irradiation. The5×10-5mg/L RhB was decolored completely after25min of visible-light illumination. Besides, the8wt.%g-C3N4/BiOCl composite shows high stability. After5cycles of repetition tests, the photocatalytic activity was not decreased. Finally, we believe that the enhancement in activity could be attributed to the coupling effect of g-C3N4and BiOCl, which can induce high electron-hole pair separation.3, Based on the same principle, BiOBr/BiOCl composite with high visible light photocatalytic activity were prepared by the sol-gel method. The1BiOBr:3BiOCl sample exhibits the highest photocatalytic activity. After visible-light irradiation for20min, the degradation efficiency of RhB reached99.8%. Based on the results of the XRD、SEM、UV-vis and PC experiments, the high photocatalytic activity of BiOBr/BiOCl composite was discussed.