Preparation And Properties Of BiOBr-based Composites Photocatalysts

BiOBr（Bismuth oxybromide）,a novel visible light response semiconductor photocatalyst,has attracted much attention due to its moderate band gap,open layered structure,high oxidation capacity and indirect transition mode.At the present stage,improving the photodegradation activity is one of the important problems.Compounding BiOBr with the other semiconductor photocatalysts would reduce the recombination rates of photoinduced electron-hole pairs and enhance the photocatalystic property.In this study,BiOCl（bismuth oxychloride）,ZnO（zinc oxide）,BiVO₄（bismuth vanadate）and RGO（reduced graphene）were selected to modify BiOBr,respectively.The results of photocatalytic degradation experiments showed that the photocatalytic activities of the composite photocatalysts were higher than that of pure BiOBr.The main contents are as following:1.Preparation and photocatalystic properties of BiOCl/BiOBr composites: flower-like BiOCl/BiOBr composites were synthesized by a hydrothermal process using citric acid as chelating agent.The as-prepared samples were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,UV-vis diffuse reflectance spectroscopy（DRS）and photoluminescence（PL）spectroscopy,respectively.The photocatalytic activity of BiOCl/BiOBr photocatalyst was investigated via degradation of methyl blue dye（MB）under simulated sunlight irradiation.Flower-like BiOCl/BiOBr composites exhibited higher photocatalytic activity than pure BiOX.BiOCl0.1Br0.9 exhibited a superior photocatalytic activity.2.Preparation and photocatalystic properties of BiOBr/ZnO composites: BiOBr/ZnO composite photocatalysts were prepared by a simple hydrothermal method.The as-prepared samples were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,high-resolution transmission electron microscopy（HRTEM）,UV-Vis diffusion reflectance spectroscopy（DRS）and photoluminescence（PL）spectroscopy,respectively.The photocatalytic activities were evaluated by the degradation of methyl blue（MB）under the simulated sunlight irradiation.Among all the samples,the BiOBr/ZnO composite with a mole ratio of 3: 1（Bi: Zn）exhibited the best photocatalytic activity.The improvement of photocatalytic activity was mainly attributed to the low recombination ratio of photo-induced electron-hole pairs.The possible photocatalytic mechanism was discussed on the basis of the band structures of BiOBr and ZnO.The results of free radical trapping experiments showed that various active particles such as ·OH、h+ and ·O2-were involved in the reaction and promoted the photocatalytic reaction.3.Preparation and photocatalystic properties of BiOBr/BiVO₄ composites: A facile hydrothermal method was applied to fabricate BiOBr/BiVO₄ catalysts.The results of XRD,SEM and EDS showed that BiOBr and BiVO₄ doped together successfully.The photocatalytic performance of BiOBr/BiVO₄ was evaluated by the degradation of methylene blue（MB）.The 0.5BiOBr:0.5BiVO₄ composites displayed higher adsorption capacity and photocatalytic activity than the pure BiVO₄ and BiOBr.Based on the relative band position of the semiconductors,a possible photocatalytic mechanism was proposed.The p-n heterojunction promotes the separation of photoinduced electron-hole pairs,and the built-in electric field also promotes the transfer of photoinduced carriers.4.Preparation and photocatalystic properties of BiOBr/RGO composites: BiOBr/RGO was successfully prepared by CTAB-modified hydrothermal method.The structure,morphology,element composition and optical properties of the catalysts were characterized by XRD,SEM,FT-IR,DRS and PL,respectively.The mechanism of the reaction was discussed: The deposition of graphene significantly changed the absorptive capacity of the material,and the photoelectrons of BiOBr were easily captured by graphene,and then the separation of electron-hole pairs improved the efficiency of photocatalytic reaction.