Preparation And Immobilization Of BiOBr Photocatalyst

BiOBr as a novel semiconductor photocatalytic material, has drawn considerable attention and been considered to a competitive and promising photocatalytic material, due to its open-layered structure, indirect transition mode and moderate energy band structure. In order to thoroughly understand the effect of preparing conditions on crystal structure, morphology and photocatalytic activity of BiOBr powder, this paper proposed a facile hydrolysis (alcoholysis) method to synthesize BiOBr with different morphologies and crystallinity using BiBr3as precursor at a low temperature. At the same time, the photocatalytic activities of BiOBr have been evaluated by the degradation of methyl orange (MO) under simulated sunlight and the optimum conditions for the preparation of BiOBr have been determined. Furthermore, in order to overcome the solid-liquid separation defects of conventional nano-powder catalysts, we also prepared BiOBr thin film photocatalyst using an alcoholysis-coating method, which is simple, pollution free and low energy consumption. In addition, through controlling the reaction and calcining temperatures, the BiOBr thin films with different intensity ratios of (110) to (102) peaks were synthesized, and furthermore through the evaluation of MO degradation under UV light irradiation, we have obtained the optimum immobilization conditions of BiOBr thin films and mastered the basic regularity of the influences of the preparation conditions on the membrane catalytic activity. All the obtained results are listed as follows:1. The BiOBr photocatalysts with higher activity and different morphologies, crystallinity and crystalline facets orientation are synthesized using BiBr3as precursor at different solvent and reaction temperature. This method is lower temperature, environmentally friendly, economical and practical.2. According to the photocatalytic efficiency of BiOBr for decomposing MO under simulated sunlight, we find when distilled water is used as solvent, the degradation of MO can reaches90%in75min. and the as-prepared BiOBr also displays good stability, its photocatalytic activity still remains above90%after being used five times. When alcohol is used as solvent, the photocatalytic efficiency of BiOBr will change according to alcoholysis reaction temperature and species of alcohols. And the best photocatalytic degradation efficiency of MO for as-prepared BiOBr-60(IPA) is98%under75min simulated sunlight irradiation. But the photoactivity of the BiOBr decreased in the first recycling experiment, and no significant loss in the next three recycling reactions, the degradation efficiency of methyl orange (MO) also can reaches98.5%in120min.3. According to the SEM, XRD characterization, we find that when distilled water is used as solvent, the as-prepared BiOBr is composed of flake structure. The crystallinity and the crystalline facets orientation both have no significant changed with the temperature of the hydrolysis reaction increases. However when alcohols are used as solvent, the morphology and the crystallinity make noticeable changes along with the different solvents. In addition, the crystallinity was increased with the rising of alcoholysis reaction temperature. Furthermore, the crystalline facets orientation of BiOBr powders changes with solvents, and shows a big difference between distilled water and alcohols. So, the high photocatalytic efficiency of BiOBr, which is prepared in distilled water, should be attributed to the best crystallinity and unique crystalline facets orientation, while the high photocatalytic efficiency of BiOBr, which is prepared in isopropyl alcohol, should be ascribed to the specific structural characteristics and a better crystallinity. In addition, the photoactivity of BiOBr-60(IPA) decreased in the first recycling experiment due to the change of surface adsorption ability and crystallinity.4. The flower-like morphology BiOBr thin films have been prepared via a facile alcoholysis-coating method using BiBr3as the raw material and isopropyl alcohol as the solvent. And we can find that the sample was composed by Bi, O and Br three elements, and has a ratio close to the stoichiometric ratio of BiOBr.5. The intensity ratios of (110) to (102) peaks of BiOBr thin films can be controlled by the choice of solvents, the reaction and calcination temperatures, and further indicated the different photocatalytic activity. The degradation experimental results confirmed that the film prepared at60℃in isopropyl alcohol solvent posses the best photocatalytic activity and the degradation efficiency of MO can reach98.5%under2.5h UV irradiation. In addition, the BiOBr sample also displays good stability and its photocatalytic activity still remains above90%after being used five times.6. A possible formation mechanism of BiOBr thin film was also inferred and the results suggested that the isopropyl alcohol solvent can decrease the crystallite size and significantly inhibit the agglomeration of nanosheets, resulting in the nanosheets independently-rotating and reassemble, finally, the stable micro-nano-structure BiOBr thin film are formed and the nano-size effects of BiOBr thin film are remained.