Preparation And Properties Of BiOCl_1-xBr_x Solid Solution Photocatalysts With Dominant Crystal Facets Or Heterojunction Structures

In recent years,with the development of industrialization and urbanization,global energy shortages and environmental pollution problems have aroused extensive interest.The development of semiconductor photocatalysts for degrading organic pollutants under solar-light or visible light has become an effective way to solve the problem of energy shortages and environmental pollution.TiO₂ is widely used in photodegradation of organic pollutants due to its low price and high stability.However,due to its wide bandgap,it can only be excited by ultraviolet light,which limits its application under visible light irradiation.Therefore,in order to improve the utilization rate of solar energy,developing photocatalysts has become one of the major issues in photocatalytic research.In this paper,the preparation,photocatalytic performance and photocatalytic activity of solid solution photocatalysts with dominant crystal structure and heterojunction structure were studied.And the morphology,structure,phase composition,surface structure,specific surface area and optical properties of the synthesized catalyst were characterized by a variety of test techniques.The photocatalytic properties of the catalysts were investigated by using organic pollutants such as rhodamine B,methyl orange and phenol solution.The effects of the structure and composition of the photocatalyst on the photocatalytic activity were investigated.Specific work is as follows:A new type of BiOCl1-xBr,（0≤x≤1）solid solution photocatalysts was prepared by hydrothermal method and solvothermal method.The BiOCl_1-xBr_x solid solution synthesized under different solvent conditions was compared and found that those have exposed {001} crystal plane exhibited higher photocatalytic activity than the BiOC_1-xBr_x solid solution with the exposed {101} crystal plane.And the rose-like BiOCli1-xBrx solid solutions show the highest photocatalytic activity at x=0.5,while the spherical BiOCl_1-xBr_x solid solutions show the highest photocatalytic activity at x=0.75.The rose-like BiOCl_0.5Br_0.5 solid solution can completely degrade rhodamine B within 12min,and exhibits excellent stability in photocatalytic reaction.The improvement in photocatalytic performance can be attributed to the interaction between surfaces and the reactants RhB and the promoted separation of the electron-hole pairs at the interface.Radical trap experiments showed that h⁺ and ·O₂^-were the major active species in photodegradation experiments.In this study,WO₃-BiOCl_1-xBr_x heterojunction photocatalysts were successfully prepared by hydrothermal method.The photocatalytic properties of WO₃-BiOCl_1-xBr_x heterojunction were evaluated by the photocatalytic degradation of RhB under visible light irradiation.The results showed that 5%WO₃-BiOCl_1-xBr_x greatly enhanced the photocatalytic degradation efficiency of RhB compared to the pure BiOCl_1-xBr_x and WO₃.And 5%WO₃-BiOCl_0.25Bro_0.75 heterojunction was able to completely degrade rhodamine B in 6 min under visible light,which also could degrade methyl orange in 60 min under simulated sunlight.The improvement of the photocatalytic activity of heterojunctions can be attributed to the interaction between light absor:ption and the appropriate band structure.The results of free radical capture experiments showed that h⁺ and ·O₂^-free radicals were the main active species in the photodegradation process.In this study,the Au-BiOCl_1-xBr_x heterojunction and BiOCl_1-xBr_x solid solution were obtained by chemical precipitation method and ultrasonic assisted method.Among them,1.3%Au-BiOCl-（0.25）Br_0.75 heterojunction showed the best photocatalytic activity.Under the simulated solar light irradiation,the phenol solution could be completely degraded in 75 min.The increase of light absorption and the effective separation of photogenerated electron-hole pairs are the key to the improvement of photocatalytic activity of heteroiunction.In addition,radical trap experiments confirmed that the ·OH and hole（h⁺）were the primary reactive species during the photodecomposition phenol process.In this study,the Ag₃PO₄-BiOCl_1-xBr_x heterojunction photocatalysts were successfully prepared by continuous chemical precipitation method.And the band structure is regulated by adjusting the relative content of Cl and Br in compounds.The Ag₃PO₄-BiOCl_0.75Br_0.25 heterojunction with the mass ratio of 1:5 was found to have the best photocatalytic activity compared with the Ag₃PO₄ and BiOCl_0.75Br_0.25,and it can photodegrade phenol completely in 75 min under the simulated solar light irradiation.The improved photocatalytic activity of heterojunction can be attributed to the effective separation of photogenerated carriers.The results of free radical capture experiments showed that ·O₂^-,h⁺ and ·OH radicals were the main active species in photodegradation of phenol solution.