Study On Preparation And CO₂ Reduction Performance Of Photocatalysts Based On Covalent Organic Framework

Photocatalytic carbon dioxide reduction（CO₂RR）is regarded as an effective strategy to solve the energy crisis and environmental pollution problems.Due to the large bond energy of CO₂,photocatalytic CO₂RR needs to overcome the high energy barrier,resulting in low CO₂ reduction catalytic efficiency.Building efficient artificial photocatalysts to achieve efficient conversion of CO₂ under visible light is an effective way to solve energy and environmental problems.Covalent organic frameworks（COFs）are emerging crystalline porous materials with strong absorption capacity under visible light,high stability and adjustable bands,so as to show excellent photocatalytic performance.However,COFs photocatalysts still have problems such as poor separation efficiency of photogenerated carriers and slow proton transport in gas-solid reaction,resulting in low CO₂ reduction activity of COFs without sacrifices.In view of the above scientific problems,this paper constructs COFs photocatalysts with proton transport performance and artificial photocatalysts of non-noble metal plasma COFs,and for the first time deeply studies the role of COFs proton transportation performance and non-noble metal plasma resonance in photocatalytic CO₂RR.The specific research content is as follows:THFB-COF-1-Zn was synthesized of（1R,2R）-（-）-1,2-diaminocyclohexane with1,3,5-triazine-2,4,6-tri（4’-hydroxy-5’-formylphenyl）benzene（THFB）by in-situ introduction of Zn（Cl O₄）₂·6H₂O.Then Nafion/THFB-COF-1-Zn composites were prepared by introducing Nafion,a polymer ionomer with proton transport by impregnation method.The structure and morphology of the composites were characterized by X-ray powder diffraction（PXRD）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）,and the successful synthesis of crystalline Nafion/THFB-COF-1-Zn composites was confirmed.The results of photocatalytic CO₂ reduction performance test of a series of materials showed that Nafion/THFB-COF-1-Zn composites showed excellent photocatalytic CO₂activity,and the Nafion/THFB-COF-1-Zn composites with a load of50μL（0.4 wt%）Nafion/THFB-COF-1-Zn composites showed the best photocatalytic performance,and the HCOOH production and CO activities of photocatalytic CO₂RR were 255.50μmol·g^-1·h^-1 and 110.50μmol·g^-1·h^-1,which are 15.2 and 5.1 times higher than THFB-COF-1-Zn,respectively.The results of photocatalytic CO₂RR performance of Nafion/THFB-COF-1-Zn materials under different temperature gradients show that the photocatalytic performance of variable temperature is consistent with the trend of proton conductivity,and the normal distribution changes.The photocatalytic performance was the highest at 70°C,and the yields of HOOH and CO were 616.55μmol·g^-1·h^-1 and 23.49μmol·g^-1·h^-1,respectively.By comparing the photocatalytic performance of polytetrafluoroethylene（PTFE）and polyvinylidene fluoride（PVDF）with THFB-COF-1-Zn,the effect of polymer proton conductivity on the photocatalytic performance of THFB-COF-1-Zn was further confirmed.The photocatalytic CO₂ reduction mechanism of Bi NPs/Tp Bpy with non-noble metal plasma resonance was studied in depth,and the plasma resonance of Bi NPs in the Bi NPs/Tp Bpy composite structure was confirmed to promote photocatalytic CO₂reduction.PXRD and TEM were used to determine the structure and morphology of the complex.The results of photo/electrochemical characterization showed that Bi NPs enhanced the absorption and utilization of visible light of COFs,as well as the effective separation and full utilization of photogenerated charges,which significantly improved the performance of photocatalytic CO₂ reduction.The yield of CO₂ catalyzed CO₂reduction of Bi NPs/Tp Bpy-NS composites can reach 217μmol·g^-1·h^-1,which is about12.2 times that of Tp Bpy alone.The transfer path of photogenerated electrons was determined by XPS and in situ infrared tests,and the photocatalytic CO₂ reduction mechanism of Bi NPs/Tp Bpy-NS composites was proposed.