Synthesis Of Schiff Base Covalent-Organic Frameworks And Photocatalytic Reduction Of CO₂

The overuse of fossil energy has caused the concentration of CO₂ in the atmosphere to far exceed the warning line.Photocatalytic CO ₂ reduction to convert it into usable energy is one of the ideal ways to recycle carbon resources and thus the research of developing effiecent photocatalytsts for CO₂ reduction is great significant.Covalent-organic framework materials are considered to be one of the most promising photocatalysts due to their excellent visible-light absorption capacity,porous characteristics,and the advantages of adjustable energy bands and structures.However,due to the lack of active sites for CO ₂adsorption and reduction,the performance of COFs for photocatalytic reduction of CO₂ is still not ideal.In response to the above scientific issues,this research first designed and synthesized TFBD-COF-ABH,which chelated metal ions and supported Au nanoparticles?Au NPs?to improve the photocatalytic CO₂performance of COF.Furthermore,TFBD-COFs were designed and synthesized,which were further used to immobilize molecular complex catalysts through chelation of metal ions and the coordination of Salicyl aniline?SA?to improve their photocatalytic activities of CO₂reduction.The main research contents are as follows:?1?TFBD-COF-ABH was prepared by solvothermal method by the reaction of3,3',5,5'-tetraformyl-4,4'-dihydroxybiphenyl?TFBD?and p-aminobenzoylhy-drazine?ABH?,and the structure was determined by X-ray powder diffraction and structural simulations.Au Nps@TFBD-ABH-COF-M compsiting with Au NPs.X-ray Powder Diffraction,Fourier Transform-Infrared spectroscopy,N₂ adsorption and thermogravimetry were used to determine the chelation of metal ions and the loading of Au NPs.The results of ultraviolet-visible absorption spectra,AC impedance,and photo-current response confirmed that the Au Nps can promot the visible light absorption and the separation of photogenerated charges of the resulting materias.Photocatalytic CO₂ reduction performance tests show that the photocatalytic performance of Au Nps@TFBD-COF-ABH-Co for CO₂ to CO production is 540?mol·g^-1 in 5 h,which is 10.1 times and 31.6 times highter than that of TFBD-COF-ABH-Co and TFBD-COF-ABH,respectively.?2?TFBD-COFs were prepared by solvothermal method by the reaction of3,3',5,5'-tetraformyl-4,4'-dihydroxybiphenyl and p-phenylenediamine?-1?and biphenyldiamine?-2?.TFBD-COF-M and TFBD-COF-M-SA were prepared by chelating metal ions M(M=Co²⁺?Ni²⁺?Zn²⁺)and the coordination of SA ligand.The structure was determined by X-ray Powder Diffraction and structural simulation.The morphology of these materials was confirmed by Scanning Electron Microscope and Transmission Electron Microscope.The results of X-ray Photoelectron Spectroscopy,In Situ Infrared,Electron Paramagnetic Resonance testing,and Mulliken charge calculations show that the coordination of SA ligands can enhance the electron density of the metal center and induce the increased activity of the metal center.Photocatalytic CO₂ reduction performance tests show that after chelating metal ions,the performance of TFBD-COF-1-Co and TFBD-COF-2-Co for CO₂ to CO production are 1.8 and 1.5 mmol·g^-1 in 5 h,which is 2.6 and 3.8 times of the parent TFBD-COFs,respectively.After the coordination of the SA ligand,the CO production rate of TFBD-COF-1-Co-SA in5 hours is 7.4 mmol·g^-1,which is 4.1 times that of TFBD-COF-1-Co.Besides,TFBD-COF-1-Co-SA shows an excellent selectivity of 90%to CO and stalbe performance.