Preparation,Characterization And Photocatalytic Nitrogen Fixation Research Of BiOX Composite Modified Materials

Ammonia is an important industrial raw material.At present,the Haber-Bosch process is mainly used in industrial synthesis of ammonia,but it has serious energy consumption and environmental pollution problems.Therefore,it is urgent to find a environmentally friendly and low energy consumption nitrogen fixation process that can replace it.This thesis is based on BiOX（X=Cl,Br）photocatalytic materials,the photocatalytic nitrogen fixation activity of the catalyst was improved by semiconductor recombination,supported（precious）metals（Bi,Ag）and vacancy defects.The absorption range of visible light is broadened,the separation and transfer rates of photogenerated electrons and holes are improved,and the adsorption activation sites of nitrogen are increased.The main contents are as follows:1.The monomeric BiOCl catalyst was prepared by the solvothermal method,and then flake graphite phase g-C₃N₄ monomer was obtained by high temperature heat treatment with melamine after ultrasonic treatment.Then,the g-C₃N₄/BiOCl binary in different ratios was prepared by the dissolution thermal method and through hydrogenation treatment to form vacancy defects on the surface of the catalyst to obtain oxygen vacancies.Subsequently,metal Biwas introduced by adding thiourea reducing agent.The ternary compound Bi/BiOCl/g-C₃N₄ with different mass ratio was prepared by controlling the mass ratio of BiOCl to g-C₃N₄ and the addition amount of thiourea.Compared with monomer BiOCl and BiOCl/g-C₃N₄ binary materials,the hydrogenated ternary composite Bi/BiOCl/g-C₃N₄exhibited better photocatalytic nitrogen fixation performance,and has a certain degree of stability.It is found that the introduction of oxygen vacancies can accelerate the rate of electron transfer,broaden the absorption of visible light and effectively improve the photocatalytic activity of nitrogen fixation under the dual effects of heterojunction and SPR effect of Bi.2.The flower-like BiOBr catalyst was prepared with ethylene glycol as the solvent,and then the binary AgBr/BiOBr catalysts in different proportions were prepared by in-situ ion exchange method.The Ag/AgBr/BiOBr ternary catalysts with different ratios were prepared by photoreduction method.The photocatalytic activity of the Ag/AgBr/BiOBr catalyst with the best loading ratio was much higher than that of the binary best composite AgBr/BiOBr catalyst.This is due to the heterojunction structure constructed by the composite catalyst which promotes the separation efficiency of photogenerated electron-hole pairs.Moreover,the increase of oxygen vacancy concentration can increase the adsorption activation sites of N₂,accelerate the carrier transfer rate,and effectively improve the photocatalytic reduction performance of the catalyst.On the other hand,the introduction of Agnanoparticles can effectively broaden the optical absorption range,and form a synergistic effect with heterojunction,which can effectively promote the separation of photogenerated carriers and improve the photocatalytic nitrogen fixation activity.