Design,synthesis And Photocatalytic Application Of Covalent Organic Frameworks Based On Donor-Acceptor System

As human civilization has gradually entered the modern society,more and more countries and regions around the world have begun to vigorously develop industrialization and urbanization,which has increased the intensity of human’s demand for energy.However,with the massive exploitation and consumption of non-renewable resources such as coal and oil,the energy crisis and environmental pollution are imminent.If we do not take reasonable measures to solve these issues as soon as possible,it will inevitably become a huge obstacle to the progress of human civilization.At the same time,solar energy,as the most abundant clean and renewable energy,has become the first choice to replace traditional energy,and will play a vital role in the future development of human society.Therefore,how to realize the efficient development and utilization of solar energy has always been the focus of the industry and academia,and its core is to find stable and efficient photocatalytic materials.Covalent organic frameworks（COFs）,as a kind of highly crystalline porous organic polymer materials,have shown great application potential in the field of photocatalysis due to their advantages of pre-designed structures,good physicochemical stability and excellent photoelectric properties.Owing to the diversity of COF structures,COF materials have a wide range of functions as a new type of photocatalyst,which allows them to adjust their structures according to different light absorption capacities or band gaps.Compared with traditional semiconductor materials,COF materials exhibit more excellent separation and transfer efficiency of electrons and holes.Meanwhile,high specific surface area and pore structure greatly enrich the photocatalytic sites.These unique advantages provide a solid guarantee for COF materials to achieve efficient photocatalytic energy conversion.In order to obtain more stable and efficient COFs photocatalysts,it is essential to introduce functional groups and innovate structural characteristics.In this study,a series of new imine-based COF materials were synthesized by pre-designing the monomer structure,and their photocatalytic properties,including photocatalytic hydrogen evolution and photocatalytic organic reactions,were studied in depth.The details are as follows:（1）A D-A type imine-linked COF material（DABT-Py-COF）was innovatively synthesized by self-assembly of building unit 4,4’,4’’,4’’’-（benzo[c][1,2,5]thiadiazole-4,7-diylbis（9,9-dimethyl-9,10-dihydroacridine-10,2,7-triyl））tetrabenzaldehyde（DABT-4CHO）with another unit 1,3,6,8-tetra（4-aminophenyl）pyrene（PyTA）via Schiff-base reaction under solvothermal conditions.A series of technical characterization methods such as powder X-ray diffraction,high power electron microscopy,solid-state infrared and ultraviolet spectroscopy have proved that the material has high crystallinity,good stability and photoelectric properties,and the possibility for efficient photolysis of water and hydrogen evolution.Subsequently,under visible light irradiation,DABT-Py-COF showed excellent hydrogen evolution performance,and its maximum hydrogen evolution rate reached 5458μmol g^-1h^-1,and it can maintain the stable hydrogen evolution rate for more than 20 hours,which is much higher than most reported COFs materials.（2）Porphyrins have good visible light absorption properties,and their optical properties can be controlled by the coordination modification of central metal ions.A series of new imine-bonded COFs materials（BDF-TPH-COF and BDF-TPH-Zn-COF）were synthesized by self-assembly of benzodifuranyl monomer（BDF-CHO）with porphyrin-based monomer（TPH-2H）and zinc metal ion-modified porphyrin-based monomer（TPH-Zn）under solvothermal conditions.The different physical and chemical functions and photosensitive properties of zinc metallized porphyrin-based COFs and metalloporphyrin-free COFs were studied by powder X-ray diffraction,BET test,high power electron microscopy,solid-state infrared and ultraviolet spectroscopy as well as thermogravimetric analysis.The activities and types of photocatalytic organic conversion reactions of porphyrin-based COF materials by the introduction of zinc metal ions were deeply discussed,and the photocatalytic sulfide oxidation reaction and the photocatalytic boric acid oxidation reaction were effectively realized,which further deepened the understanding of the mechanism of COFs materials in photocatalytic organic conversion.