Preparation And Properties Of Bismuth Tungstate Composite Photocatalytic Materials

Photocatalysis is a new technology that develops rapidly in recent years.It can convert energy and clean the environment by using solar energy.Photocatalytic degradation technology has become the main means of wastewater treatment due to its characteristics of simple process,ecological friendliness,economy and high degradation rate.Bismuth tungstate（Bi₂WO₆）has been widely concerned for its good visible light response,high stability,strong oxidation capacity,non-toxicity,low preparation cost and unique layered structure.Bi₂WO₆ can efficiently separate photogenerated charge and increase the utilization rate of photogenerated carriers.However,its photocatalytic activity is limited by high carrier recombination rate and narrow visible light response frequency band.Based on the study of Bi₂WO₆,in order to improve the photocatalytic activity of Bi₂WO₆,a semiconductor heterojunction composite structure was constructed by hydrothermal and solvothermal methods.By comparing the crystal structure,microstructure,elemental composition and light absorption properties of heterojunction photocatalysts,various improvement mechanisms of heterojunction photocatalysts in the decomposition of organic pollutants（methyl orange MO）were studied.The main research contents are as follows:（1）Bi₂WO₆/BiOBr composite photocatalyst was prepared.Bi₂WO₆/BiOBr composite photocatalyst was synthesized by one-step hydrothermal method,which improved the photoreaction range and photocarrier separation efficiency,and further improved the photocatalytic activity.When the molar ratio of Bi₂WO₆ and BiOBr is 1:1,the degradation efficiency of pollutant MO reaches 90%in 60 minutes of light.The reason for the improvement of photocatalytic performance is that the combination of Bi₂WO₆ and BiOBr reduces the band gap energy of Bi₂WO₆ and improves the separation efficiency of photogenerated electrons and holes.（2）Bi₂WO₆/BiOCl composite photocatalyst was prepared.The Bi₂WO₆/BiOCl composite photocatalyst was synthesized by simple hydrothermal method,and the reaction range of the composite to light and the efficiency of photogenic carrier separation were improved,as well as the photocatalytic performance.When the molar ratio of Bi₂WO₆ to BiOCl was 1:2,the photocatalytic efficiency of the composite was the highest,and the MO degradation rate of pollutants reached 94.34%within 40min of illumination.The improvement of photocatalytic activity is due to the formation of a composite structure of Bi₂WO₆ and BiOCl,which promotes the separation of photogenerated carrier,and the synergistic effect between the materials promotes the catalytic reaction（3）Bi₂WO₆/BiOBr/CNT composite photocatalyst was constructed.Bi₂WO₆/BiOBr/CNT photocatalysts were prepared by hydrothermal and solvothermal methods.The photocatalytic activity of Bi₂WO₆/BiOBr/CNT composites with 0.3%CNT content was the highest,and the degradation rate of MO reached 81%within 5min.The combination of CNT not only increases the absorption range of visible light,but also can adsorb more pollutants on the surface of catalyst and efficiently separate photogeneration and photogeneration carriers,thus greatly improving the photocatalytic performance.（4）Bi/Bi₂WO₆/BiOBr composite photocatalyst was prepared.Heterogeneous Bi/Bi₂WO₆/BiOBr composites were prepared by one-pot solvothermal method with ethylene glycol as solvent and reducing agent.Bi/Bi₂WO₆/BiOBr triplet heterostructure composites showed the best photocatalytic performance,degrading 97.8%MO in 60min.The improvement of photocatalysis is due to the large specific surface area of nano-flower structure,higher light absorption capacity and lower carrier recombination efficiency.