| Covalent organic frameworks are a kind of crystalline porous organic polymer that use small organic monomers as building units and are connected by covalent bonds.These materials have the characteristics of abundant building units,low density,large specific surface area,long-range orderly pore structure,strong light absorption capacity,and adjustable structure and so on.These characteristics make covalent organic frameworks have great application potential in many fields,such as heterogeneous catalysis,proton conduction,gas adsorption and separation,iodine adsorption,photoelectricity,photocatalysis,etc.At present,most of the covalent organic frameworks are synthesized by reversible reactions controlled by thermodynamics,such as Schiff base reaction,borate condensation and so on.Therefore,the common covalent bonds in covalent organic frameworks include carbon-carbon double bond,imine bond,amide bond,borate ester and hydrazone bond,etc.A series of covalent organic frameworks connected by different covalent bonds were synthesized through different covalent bond formation reactions in this article.Subsequently,we characterize these materials in detail and explore their applications in the field of photocatalysis.The research content mainly includes the following two parts:1.As a kind of macromolecular heterocyclic compound with highly conjugated system,porphyrin has unique photoelectric properties and is widely used in the fields of optical materials,chemical catalysis and so on.Therefore,we used porphyrin monomer 5,10,15,20-tetraethylenyl porphyrins as the building unit,and successfully constructed fully conjugated,diyne-linked covalent organic frameworks through Pd-catalyzed Sonogashira coupling reaction.The crystal structure,composition,stability,photoelectric properties and morphology of COFs were characterized by means of infrared spectroscopy,solid-state NMR,powder X-ray diffraction,thermogravimetric analysis,UV-Vis diffuse reflection spectroscopy,Mott-Schottky electrochemical test,X-ray photoelectron spectroscopy,scanning electron microscopy and transmission electron microscopy.Subsequently,COF-JLU10 was used as a photocatalyst to catalyze borylation of aromatic amine under visible light irradiation.The experimental results show that COF-JLU10 has good photocatalytic performance,and the reaction has a wide range of substrate adaptability.After five cycles of use,COF-JLU10 still retains catalytic activity,crystallinity and complete skeleton structure,showing excellent stability.2.Using 1,3,5-tris（4-aminophenyl）benzene and benzotrithiophene trialdehyde as monomers,the imine-linked covalent organic framework material COF-JLU38 was synthesized by schiff base reaction.Subsequently,COF-JLU39 was obtained by oxidizing the imine bond of COF-JLU38 to amide bond using Na Cl O2 as oxidant through post-modification method.Through detailed characterization and analysis,we have a further understanding of the structure and properties of the materials.Both materials have the characteristics of high crystallinity,large specific surface area,wide light absorption range,good stability and excellent photoelectric properties.And,the energy level structure of the two COFs materials can meet the requirements of photocatalytic hydrogen generation of semiconductor materials.Therefore,we evaluate the photocatalytic performance of the two materials by using the experiment of photocatalytic hydrogen evolution.The experimental results show that both materials show good catalytic properties in photocatalytic hydrogen generation.Subsequently,we used COF-JLU38,which has better catalytic performance among the two COFS materials,to conduct a long-term hydrogen evolution experiment and five recycling experiments to evaluate the stability of the material.Finally,we also studied the apparent quantum efficiency（AQY）of COF-JLU38 under different wavelengths of light. |
