The Preparation Of Covalent Organic Framework-Based Composite Photocatalysts And The Application In Photocatalysis

The massive consumption of fossil fuels releases excessive greenhouse gases such as carbon dioxide（CO₂）,which brings about serious energy and environmental problems,such as the greenhouse effect and sea level rise.Therefore,the conversion of atmospheric CO₂ into energy chemicals,carbon monoxide（CO）,methanol（CH₃OH）,methane（CH₄）and formic acid（HCOOH）,is considered to be one of the most direct and effective ways to alleviate the energy crisis and address the greenhouse effect.The photocatalysis technology is a green technology with important application prospects in the energy and environmental fields,and the use of photochemical conversion of greenhouse gases has greater advantages.The solar energy,as an inexhaustible energy driver,can catalyze the conversion of CO₂for CO₂ recycling in the presence of suitable photocatalysts and under relatively mild and controllable catalytic conditions.In this paper,a series of COF/MOF composite photocatalytic materials with excellent photocatalytic activity were prepared using different synthetic methods,and the composites were characterized by powder X-ray diffraction tests,Fourier transform infrared spectroscopy and scanning electron microscopy,while the photocatalytic performance of the materials was tested by simulating artificial photosynthesis in different concentrations of CO₂ environment,and the possible electron transport mechanism was explored and analyzed,and the main works carried out are as follows:1.The 2D-COF TpPa-1 material with good light capture ability was selected as the carrier,and then the MOF material ZIF-8 was introduced into the system,based on which a series of composite photocatalytic materials TpPa/ZIF-8 were constructed with the help of physical milling method,and the structural morphology of the materials were characterized by tests,etc.The results of artificial photosynthesis tests showed that the photocatalytic products of the composites all exhibited high CO selectivity（>90%）,and TpPa/ZIF-8-6G showed the best photocatalytic CO₂ reduction performance in a pure CO₂environment with a CO yield of 43.94μmol·g^-1·h^-1.Notably,the TpPa/ZIF-8-3G exhibited superior catalytic activity at low CO₂ concentration（10%CO₂+90%N₂,hereafter）with a CO yield of 84.87μmol·g^-1·h^-1.Therefore,the conjecture that materials containing-OH can enrich CO₂ in low concentration CO₂ environment was proposed and verified.2.The Ti-based MOF IEF-11 and TpPa-1 with more abundant active sites and smaller particle size were used to obtain a series of composite photocatalysts with core-shell structure TpPa@IEF with the help of solvothermal method.The composites are core-shell structures with TpPa-1 as the core and IEF-11 as the shell,and exhibit great chemical stability.The CO₂ photocatalytic reduction performance of these composite photocatalysts TpPa@IEF was evaluated by visible light driving in pure CO₂ and low CO₂ concentration environments,and the CO yields were able to reach 78.87μmol·g^-1·h^-1 and 116.47μmol·g^-1·h^-1,respectively.The characterization test results demonstrate that the excellent photocatalytic results result from the high charge transport separation efficiency and CO₂capture ability in the core-shell structure,as well as the abundant catalytic active sites and the strong visible light capture ability.3.The composite MOP-NH₂@TpPa-CH₃ was designed and synthesized by covalent bridging.The composite was synthesized by a facile room temperature evaporation method using MOP-NH₂,which contains a linking group,and TpPa-CH₃,which has a stronger light trapping ability.Subsequently,the characterization analysis of the synthesized materials demonstrated that the two were connected by covalent bonds.The photocatalytic CO₂ reduction performance was also tested under visible light drive.These heterostructured photocatalysts MOP-NH₂@TpPa-CH₃ showed a CO yield of 54.74μmol·g^-1·h^-1 in a pure CO₂ environment and were able to reach a CO yield of 119.25μmol·g^-1·h^-1 in a low CO₂ concentration environment.The covalent bridging composites synthesized at room temperature promote the efficient transport of photogenerated electrons and achieve excellent photocatalytic performance.This work provides a new strategy for the synthesis of artificial photocatalysts at room temperature.