Design, Synthesis And Catalytic Performance Of 2D Functionalized Covalent Organic Frameworks Based On Imine Bonds

Covalent Organic Frameworks(COFs)are networked polymer materials with porous structure and crystallinity linked by covalent bonds.COFs are mainly composed of C,O,H,B,N and other light elements connected by covalent bonds to form organic porous crystalline materials.Due to its good crystallinity and high stability,high specific surface area and porosity,tunable pores and modifiable framework structure,this material is widely used in gas adsorption and separation,sensing,small molecule absorption,catalysis,etc.The field has broad application prospects.Since the Yaghi group first reported COFs in 2005,in the past ten years,most of the research on COFs has focused on the design and synthesis of COFs and the exploration of new topologies.However,as a new type of functional materials,COFs still have a lot of room for their functionalization,especially in catalysis.COFs are considered to be promising heterogeneous chemical catalysis platforms due to their highly designable organic frameworks,abundant open active sites,and good chemical stability.Therefore,rational design of functionalized covalent organic framework materials is of great significance to enrich the structure of functionalized COFs and expand their functional applications.Based on the diversity of COFs that can be pre-designed and functionalized,we successfully designed two types of two-dimensional functionalized COFs materials and studied their exploration in catalytic applications.The research content of this paper is mainly divided into the following two parts:(1)We selected TPA and DPBT as linear ligands,and designed and synthesized two metal-free and heteroatom-containing porphyrin-based framework COFs(JUC-605 and J-606)through a up-down strategy with the planar structural unit TAPP,as an electrochemical catalyst for efficient ORR.Due to the thiadiazole(N and S)structure contained in the JUC-606 framework,the metal-free COFs containing nitrogen and sulfur atoms exhibit more efficient oxygen reduction reaction activity than COFs containing nitrogen single atoms,resulting in changes in the electronic properties of the frameworks.Based on the structural tunability of metalloporphyrin-free COFs,this work will open a new avenue for future development of high-performance heteroatom-containing COFs electrocatalysts for energy conversion.(2)Our pre-designed TEMPO-based linear monomers were connected to two four-node organic building blocks,respectively,and we successfully synthesized two two-dimensional radical-based COFs(TAPPs-TEMPO-COF and Py TA-TEMPO-COF)through a bottom-up strategy.Both of these COFs have high stability,large specific surface area,suitable pores,and abundant TEMPO radicals on the walls of the framework.Therefore,these radical COFs exhibit excellent selective catalytic performance in the oxidation of aromatic primary and secondary alcohols with different groups attached to the para position to the corresponding aldehydes or ketones under an oxygen atmosphere and milder reaction conditions.Cyclic test results show that the catalytic performance of these radical-COFs decreased slightly after four cycles of reuse,but still maintained good crystallinity and chemical stability.Therefore,rational design of immobilized TEMPO-COFs materials provides a new way to construct heterogeneous catalysts for the selective oxidation of alcohols.In summary,we have successfully designed two types of two-dimensional functionalized COFs materials and applied them to electrocatalysis and organocatalysis,respectively,according to their specific functionalized structures,and both exhibit their unique and excellent properties.The results show that rational design of functionalized covalent organic framework materials is helpful to explore the potential applications of COFs in different fields,which is of great significance for the development of COFs materials in the future.