Study On The Performance Of Bismuth-based Composite Materials For Photocatalytic Nitrogen Fixation

As one of the most important processes in nature,biological nitrogen fixation converts solar energy into chemical energy an d the ammonia（NH₃）is the main product,which is essential for plants,animals and other life forms.Humans urgently need to develop an artificial nitrogen fixation method to balance the global nitrogen cycle.In this field,photocatalysis provides a sust ainable approach.Photocatalytic nitrogen fixation is one of the potential research directions in the fields of chemistry and heterogeneous catalysis.Bismuth-based photocatalysts have the characteristics of high chemical stability,low toxicity and low co st.In addition,their high electrical conductivity and suitable intrinsic band gap make them ha d good optical activity,and they have attracted much attention in recent years.However,in order to expand the response range of bismuth-based photocatalysts to light,improve the separation efficiency of photogenerated carriers and photogenerated holes,and improve their redox capacity,we designed and prepared heterojunction composite photocataly sts based on bismuth oxybromide,and applied to photocatalytic nitrogen fixation experiments,the content is as follows:（1）We adopted the in-situ reduction strategy,successfully prepared bismuth oxybromide supported on bismuth nanoparticles by a two-step solvothermal method,using Biwith low HER activity to constru ct a Schottky photocatalyst and applying it to reduction of nitrogen under visible light conditions.The results show that the in-situ reduction of Bi³⁺by solvent ethylene glycol can successfully prepare bismuth metal nanoparticles on BiOBr nanosheets.Th e bismuth nanoparticles act as metal promoters to generate the built-in Schottky junction effect on the Bi/semiconductor interface,which promotes it stimulates the interface electron transfer of the photocatalyst,and also promotes the on-site N₂ adsorption and the activation of photocatalytic nitrogen fixation.The unidirectional charge transfer to the active site of Bi,the photocatalytic nitrogen-ammonia conversion efficiency of BiOBr is greatly improved by 65 times.It has better photocatalytic nitroge n fixation performance than single-phase BiOBr.The introduction of bismuth nanoparticles as a metal promoter greatly enhances the photocatalytic performance,which indicates that bismuth nanoparticles act as active sites for nitrogen adsorption during the reaction.Moreover it is beneficial to capture charge carriers,catalyze surface reactions and inhibit photogeneration the recombination of electrons and photogenerated holes that can effectively improve the performance of photocatalytic nitrogen fixation.Therefore,at atmospheric pressure and room temperature,the compounding of bismuth metal promoter significantly improved the photocatalytic nitrogen fixation performance of BiOBr.This work provides a new way to design non-noble metal Schottky photocatalysts by in-situ reduction to achieve highly improved photocatalytic performance.（2）Based on the bismuth oxybromide material,we constructed a ternary all-solid Z-scheme heterojunction photocatalyst.First,graphite nitrite was obtained by calcining thiourea at high temperature.The bismuth oxybromide,and finally the composite material supported by gold nanoparticles,is obtained by light reduction.The photo-generated electrons of BiOBr are likely to migrate to Au nanoparticles through the Schottky barrier and react with holes in the valence band of g-C₃N₄.The precious metal gold particles with larger diameters act as a bridge between charges in different semiconductors in the Z-scheme system.This process effectively promotes the separation of photogenerated electron hole pairs in heterojunction photocatalysts,which can overcome the shortcomings of single-component photocatalysts.At the same time,we also noticed a significant increase in the photoresponse range,g-C₃N₄/Au/BiOBr has excellent photocatalytic nitrogen fixation performance showed an ammonia production efficiency of 1.8μmol/h/mg_cat in the experiment.