Preparation,characterization And Photocatalytic Nitrogen Fixation Of BiOBr Based Composites

With the continuous progress of modern society,solar energy as a clean energy has been widely used in the treatment of environmental pollution,and industrial nitrogen fixation due to high temperature and high pressure,large energy consumption and many other factors are greatly restricted.Therefore,it is particularly important to find a clean and environmentally friendly nitrogen fixation method with low energy consumption.In this paper,based on the Bi OBr,the"junction"type composite material is constructed on the surface to improve the separation of photogenerated electrons and holes.Firstly,it is combined with semiconductor material g-C₃N₄ to form heterojunction to improve the separation of photogenerated carriers.Secondly,the surface loading of precious metals broadens the visible light absorption range and improves the photocatalytic activity.Through the combination of the above two methods,nitrogen fixation materials with multiple adsorption activation sites,high carrier separation efficiency and wide visible light response range were constructed.The main research contents are as follows:1.The Bi OBr compounds were prepared by adding surfactants,acid-base treatment and hydrogenation treatment.The ammonia yield of the Bi OBr compound prepared by different methods was compared.Without the use of scavengers,the flower-like microsphere Bi OBr?labeled as H-Bi OBr?synthesized by the low-temperature hydrogenation method showed the best photocatalytic nitrogen fixation performance under visible light.Compared with the other two methods,the nitrogen fixation yield of Bi OBr is significantly improved.In addition,it is found that the oxygen vacancy is the main factor for obtaining high yield of NH₃,H-Bi OBr has a higher concentration of oxygen vacancy,which promotes the strong absorption of visible light and improves the photocatalytic nitrogen fixation yield.2.G-C₃N₄ with lamellar structure was prepared by thermal polycondensation,and then g-C₃N₄/Bi OBr composites with different proportions were prepared by solvothermal method.The concentration of oxygen vacancy was increased by low-temperature hydrogen treatment,and the morphology and structure of the prepared materials were characterized and analyzed.The photocatalytic nitrogen fixation performance of binary composites with different proportions was explored,and the stability of the materials was evaluated by repeated experiments.G-C₃N₄/Bi OBr composite can increase the concentration of oxygen vacancy,promote the absorption of visible light,accelerate the electron transfer rate,and effectively improve the yield of photocatalytic nitrogen fixation.3.The thermal condensation method was used to prepare g-C₃N₄.Bi was deposited on the Bi OBr/g-C₃N₄ binary compound by solvothermal method by adding thiourea as reducing agent.The ternary compound Bi/Bi OBr/g-C₃N₄ with different mass ratio was prepared by controlling the mass ratio of Bi OBr to g-C₃N₄ and the addition amount of thiourea.Compared with monomer Bi OBr and Bi OBr/g-C₃N₄binary materials,the hydrogenated ternary composite Bi/Bi OBr/g-C₃N₄ exhibited better photocatalytic nitrogen fixation performance.The stability was tested by repeatability experiment.The results show that a certain amount of Bi metal can effectively improve the photocatalytic nitrogen fixation performance of the material,the heterojunction structure and oxygen vacancy defects after combination can effectively improve the reduction performance of photocatalyst.