The Uitilization Of 2D Photoresponsive-COF-based Hybrids For Photocatalytic Reduction

In recent years,as excessive human demand for fossil fuels that has led to severe global energy shortages and excessive CO₂concentrations,the need to develop renewable and clean energy source(e.g.,water splitting for hydrogen generation),and reduce CO₂concentration in atmosphere(e.g.,carbon neutral for C1 compounds production).Recently,semiconductors have been extensively investigated for photocatalytic reduction of CO₂,hydrogen evolution from water splitting,and pollutant degradation.However,but the disadvantages of commonly used semiconductors with narrow response range to visible light and easy recombination of photogenerated charges lead to their low photocatalytic activity.Therefore,modifications of semiconductors are usually required to achieve an increase in their catalytic activity.Two-dimensional covalent organic framework(COFs)are large?-conjugated polymers with strong visible light capture capability,uniform hole distribution and tunable structure,thus showing great potential in the field of photocatalytic solar fuel production.In this paper,we review the background and elementary theory and induce preparation,type and the application of COFs-based photocatalysts.Subsequently,we study the structural characteristics of COFs and their modification of semiconductors,as well as their application to photocatalytic reduction of CO₂and hydrogen evolution.The main research contents and results of this thesis are as follows.(1)TiO₂-INA@CuP-Ph COF for photocatalytic CO₂reduction:A dynamic covalent chemical synthesis method was used to prepare two-dimensional CuP-Ph COF,which was grown into structurally ordered and thermodynamically stable crystalline porous materials.The TiO₂surface was first pyridine-functionalized using isonicotinic acid,and then the pyridine-functionalized TiO₂was connected with CuP-Ph COF by ligand bonding by refluxing method,and then a series of TiO₂-INA@CuP-Ph COF composite hybrids with different mass percentages were obtained,and all materials were tested for photocatalytic CO₂reduction.The results showed that the 1.5%TiO₂-INA@CuP-Ph COF composite hybrids exhibited optimal photocatalytic activity as well as good photocatalytic stability,in which the CO generation rate reached 50.5?mol.g^-1.h^-1,which was 24.5 and 9.9 times higher than that of TiO₂and CuP-Ph COF,respectively.In addition,the Z-scheme photocatalytic mechanism was explored and proposed by the mechanism of TiO₂-INA@CuP-Ph COF composite hybrids.This experiment mainly utilizes the photosensitization of CuP-Ph COF based on porphyrin monomer to chemically modify TiO₂,so that the response range of TiO₂in the composite hybrids can be extended to the visible region and the compounding efficiency of photogenerated charges can be reduced,thus effectively promoting the photocatalytic activity of the composite hybrids.(2)NH₂-MIL-68(In)@Triazine-COF,NH₂-Ui O-66(Zr)@Triazine-COF,and NH₂-MIL-101(Fe)@Triazine-COF photocatalytic CO₂reduction:firstly,a solvent thermal method was used to prepare rod-shaped NH₂-MIL-68(In),nanoparticle-shaped NH₂-Ui O-66(Zr)and prismatic NH₂-MIL-101(Fe).Then,a series of MOFs@COFs complexes were obtained by using in situ solvothermal method to grow Triazine-COF on the surface of MOFs.The results showed that NH₂-MIL-68(In)@Triazine-COF exhibited the optimal photocatalytic CO₂reduction activity under the same conditions,where the production rate of CO was:25?mol.g^-1.h^-1and that of CH₄was:11.67?mol.g^-1.h^-1.This experiment utilized the structure of Triazine-COF and amidated MOFs by covalent bonding,and the two were stably linked together.This MOF@COF structure connected by covalent bonding can improve the charge transfer rate and separation efficiency.Finally,the possible photocatalytic mechanism of the NH₂-MIL-68(In)@Triazine-COF composite was proposed through the analysis of the catalytic performance and energy band of the composite.(3)Photocatalytic cracking of hydrogen from water by ZnIn₂S₄@CuP-Ph COF:2D/2D type ZnIn₂S₄@CuP-Ph COF heterojunctions were prepared and used for photocatalytic decomposition of hydrogen from water by in situ solvothermal method.A possible reaction mechanism of photocatalytic hydrogen cracking by water was proposed through a series of characterizations.The results showed that the hydrogen production rate of ZnIn₂S₄@CuP-Ph COF heterojunction with a mass ratio of 10%reached the maximum rate of H₂precipitation of 408.36?mol.h^-1,and the hydrogen precipitation rate after the addition of 1.5%Pt co-catalyst reached:2667.94?mol.h^-1.The experiment utilized the ZnIn₂S₄and CuP-Ph COF 2D/2D heterojunctions were successfully constructed by in situ growth,which accelerated the photogenerated charge transfer and exhibited excellent catalytic activity with Pt as a co-catalyst.