Synthesis Of Bismuth-Based Bimetallic MOF And Their Applications In Composite Photocatalyst Performance

At present,the bismuth-based semiconductor photocatalyst has attracted much attention due to its unique layered structure,electronic structure,strong visible light absorption capacity and suitable forbidden bandwidth.Among them,bismuth oxyhalide BiOX（X=Cl,Br,I）has an excellent visible light response.However,this type of catalyst has high photo-generated electron-hole recombination efficiency and a narrow light response range,which limits its application in real life.Metal-organic-frameworks（MOFs）are special pore framework structures with certain stability constructed by organic ligands and metals.The part of MOFs（eg.MIL-125（Ti）,CAU-17,UIO-66）can degrade pollutants under visible light,but they are limited by their stability and electronic efficiency,and further modifications are required for application.Therefore,this paper selects suitable photocatalytic materials to compound with MOF to synthesize a new type of photocatalyst,which can effectively inhibit the recombination of holes and photogenerated electrons and enhance the photocatalytic activity.The research content obtained in this paper is as follows:1)Trimellitic acid（H₃BTC）,metal Mg salt and BiOBr are used to synthesize BiOBr/MgBTC binary composite photocatalyst by solvothermal method.Under visible light induction（>420 nm）,RhB was used as a calibrated pollutant to measure its photocatalytic activity.The research results show that within 60 min,the RhB removal rate of BiOBr and BM-55 reached 85.5%and 98.3%,respectively.The enhanced photocatalytic activity can be attributed to the formation of a heterojunction between BiOBr and MgBTC,which effectively inhibits the recombination of photogenerated carriers.The results of free radical capture experiments show that the process of degrading pollutants by composite materials is mainly the oxidation of holes and superoxide free radicals.Cyclic experiments show that the addition of BiOBr is beneficial to stabilizing the frame structure of MgBTC so that BM-55 has good stability.2)Bi-Fe MOF（HBF）was synthesized by solvothermal method.Using this as a carrier,silver vanadate nanoparticles（AGV）were deposited on MOF to prepare AGV/HBF composite photocatalysts with different MOF content.Under 2 h irradiation,the RhB removal rate of HBF can reach 77%,which can be attributed to the addition of the second metal,which expands the light absorption range of the hybrid material,constructs unique crystal defects,and increases the metal The pore size of the skeleton.AGV/0.25HBF can completely degrade RhB under the same conditions.This is because the appropriate ratio of the two provides sufficient reactive sites,effectively inhibits the recombination of holes and electrons,and enhances the separation efficiency.3)Using trimesic acid（H₃BTC）as the first ligand,1,10-phen as the second ligand,bismuth nitrate and zinc acetate as raw materials,solvothermal synthesis of bimetallic double ligands metal-organic structure.The effects of ligand ratio,reaction temperature,pH,reaction time and Bi source on its synthesis were discussed.Based on the above conditions,a modified MOF（defined as HPBZ-120-24-2OH）is obtained,where m（H₃BTC）:m（1,10-phen）=1:3,m（Bi）:m（Zn）=1:0.3,the reaction temperature is 120°C,the reaction time is 24 h,and under the conditions of 2 mmol NaOH,the degradation efficiency of RhB reaches 87.2%.The influence of the Bi source on the catalyst was further discussed,and the above temperature was changed to 140°C,and the bismuth source was a catalyst for BiOBr synthesis,defined as HPBOBZ-140-24-2OH,and its catalytic efficiency could reach 99%in 50 min.