Construction Of Heterostructures Based On MOFs And Transition Metal Sulfides And Their Performance Of Photo-splitting Water For Hydrogen Production

At present,the energy crisis and environmental pollution have become global problems,which have attracted widespread attention of scientists.Therefore,people are committed to developing green,environmentally friendly and renewable clean energy.Semiconductor photocatalytic water splitting technology is considered to be one of the most promising ways to obtain hydrogen energy from solar energy.The rational design of stable,efficient,and low-cost photocatalysts is of great significance.In recent years,metal-organic frameworks（MOFs）have been widely used due to their advantages of high specific surface area,large porosity,and modifiable structure/channel,and have been developed into a new type of photocatalyst.However,most MOFs have large band gaps and poor photoresponsivity,which limit their application in photocatalysis.Due to the narrow band gap and high conduction band position,transition metal sulfide has a wide range of optical response.However,its application in photocatalysis is also limited because of its poor stability and easy recombination of photogenerated carriers.Combining the advantages and disadvantages of MOFs and transition metal sulfides,this paper improves the photocatalytic performance of the materials by combining MOFs and transition metal sulfides to form a heterojunction.The details are as follows:（1）Preparation of NH₂-UiO-66/CdIn₂S₄ and study on its photocatalytic hydrogen production performance:Firstly,NH₂-UiO-66 with octahedral morphology was prepared by solvothermal method,and then the photocatalyst NH₂-UiO-66/CdIn₂S₄was prepared by compounding NH₂-UiO-66 with CdIn₂S₄ via hydrothermal method.The morphology,structure and properties of the prepared NH₂-UiO-66/CdIn₂S₄composite catalyst were characterized by XRD,SEM,TEM,UV-vis,PL,IR,LSV and other analysis and testing techniques.Using lactic acid with a concentration of 1.2 M as the sacrificial agent and Pt as the cocatalyst,the activity of the NH₂-UiO-66/CdIn₂S₄ composite catalyst for decomposing water to hydrogen under visible light（λ≥420 nm）irradiation was tested.The effects of different loadings of NH₂-UiO-66on the hydrogen production performance were investigated experimentally,and the results showed that the prepared NH₂-UiO-66/CdIn₂S₄ had higher stability and photocatalytic activity when the loading of NH₂-UiO-66 was 8%.The hydrogen production rate of 8%NH₂-UiO-66/CdIn₂S₄ was as high as 113.8μmol·g^-1·h^-1,which was about 7.8 times that of pure CdIn₂S₄.It can be seen that when CdIn₂S₄ was combined with NH₂-UiO-66 to form a heterojunction,the photocatalytic performance of the catalyst was greatly improved due to the accelerated migration rate of photogenerated carriers and the improved separation efficiency of electron-hole pairs.（2）Preparation and photocatalytic hydrogen production of Zr-MOF-S@CdS:Zr-MOF crystals were first prepared by a solvothermal method,and then thioglycolic acid was modified as molecular linker onto Zr-MOF to form Zr-MOF-S.Finally,CdS was grown on Zr-MOF-S by S^2-exchange process by reflux method,and a highly stable and highly active photocatalyst Zr-MOF-S@CdS was obtained.Using lactic acid as the sacrificial agent and Pt as the cocatalyst,the activity of the Zr-MOF-S@CdS composite catalyst for decomposing water to hydrogen under visible light irradiation was detected.The experiments compared the hydrogen production activity of Zr-MOF-S@CdS and the catalyst Zr-MOF/CdS without thioglycolic acid,and investigated the effect of different loadings of CdS on the hydrogen production performance of the catalyst.The results showed that the addition of thioglycolic acid greatly improved the photocatalytic activity of the catalyst,and when the content of CdS was 48%,Zr-MOF-S@CdS had the best photocatalytic performance with a hydrogen production rate of 1861.7μmol·g^‐1·h^-1,which was 4.5 times that of pure CdS and 2.3 times that of Zr-MOF/CdS.In this work,Zr-MOF-S@CdS heterostructures were constructed through a pore functionalization strategy,and the introduced thioglycolic acid can act as a molecular linker to enhance the interaction between MOFs and CdS,thereby improving their carrier separation performance and photocatalytic activity.