Design Of Covalent Organic Framework Polymers And Study Of Their Photocatalytic Propertie

To face severe global environmental and energy issues,seeking renewable and clean energy has become an urgent need.Solar-powered hydrogen production from water splitting is of great significance for directly converting widely existing solar energy into high-density,high-value energy.Developing efficient,stable,and costeffective photocatalysts is a key bottleneck in photocatalytic hydrogen production technology.The preliminary research mainly focused on the field of inorganic semiconductors.They have shown excellent performance in photocatalytic hydrogen production,but there are still a series of problems such as photo corrosion,environmental pollution,and poor cost-effectiveness.Covalent organic framework(COF)is a newly emerging porous crystalline material in recent years.As a new functional material that can replace inorganic semiconductors,it has become a research hotspot.Its highly crystalline-ordered framework ensures excellent charge transfer and significant carrier capture.The inherent structural porosity and large specific surface area of COFs increase the likelihood of contact between reactants and catalysts.Therefore,to meet the needs of hydrogen production,it is crucial to explore new technologies that endow COFs with new characteristics and capabilities.In this dissertation,a series of functionalized COFs photocatalysts have been constructed from the perspective of chemical synthesis and applied to the photocatalytic hydrogen production system.The main research content includes:(1)The modification of the edge sites of the covalent organic framework TP-COF using boron pyrrole hydrazine(BODIPY)enhances the light absorption ability,accelerates charge separation efficiency,and significantly improves photocatalytic performance;(2)Based on the COF framework,a novel sulfone containing covalent organic framework photocatalyst with high hydrophilicity and charge separation transfer efficiency was constructed by introducing sulfone groups into the COF framework.The specific research results are as follows:(1)TP-COF was synthesized by Schiff base reaction with tri aldehyde phloroglucinol and p-phenylenediamine as building units.Under the premise of guaranteeing the skeleton structure of TP-COF,TP-BDP-COF was obtained by the chemical reaction between the unreacted aldehyde group at the edge of TP-COF and the photosensitizer borapyrrolizide(BODIPY)with an amino group.The research results indicate that TPBDP-COF has stronger light absorption ability,fast photo-generated electron-hole separation speed,and accelerated charge transfer,and its photocatalytic performance has been improved by 3.2 times compared to the TP-COF system.(2)Using the highly crystalline and covalent organic framework BD-COF composed of benzidine and trialdehyde phloroglucinol as the model molecule,the sulfone modified highly crystalline photocatalyst SD-COF was constructed by inserting a highly active sulfone group into the framework while maintaining its original molecular framework.The research results indicate that the introduction of sulfone groups enables SD-COF to exhibit unique donor-receptor properties.The enhancement of the intramolecular charge transfer effect suppresses electron-hole coincidence.Meanwhile,SD-COF exhibits a significant improvement in hydrophilicity,increasing the possibility of exciton diffusion to the catalyst surface and water interface.The density functional theory calculation results indicate that the proton hydrogen adsorption energy barrier on the SD-COF surface is lower,which is more conducive to the desorption of H2.Compared with amorphous pure sulfone-containing polymers(BS-CMP),SD-COF exhibits wider light absorption capacity due to its stronger main chain conjugation effect.Under visible light irradiation(λ ≥ 420 nm),the hydrogen evolution rate of SD-COF reached 12.96 mmol·h-1·g-1,which is 6.45 times that of BSCMP and 1.75 times that of BD-COF.The research results indicate that introducing the photocatalytic dominant group S=O into the COF skeleton can effectively regulate the photoelectric properties of COF,significantly improve photocatalytic efficiency,and broaden the idea of constructing simple,efficient,and cost-effective COF photocatalysts.