Design And Regulation Of Multi-level Structure Of Imine-based Covalent Organic Framework

Covalent Organic Frameworks(COF)is a type of crystalline porous polymer composed of rigid organic units that are covalently bonded.They possess characteristics such as tunable ordered pore structures,facile functionalization of the skeleton structure,high surface area,and low density,making them promising materials for applications in gas storage and separation,heterogeneous catalysis,energy conversion and storage,and other fields.Since the first COF material was reported in 2005,a large number of COF,especially 2D COF,have been developed and reported.A significant amount of work has been carried out to design and prepare COF with specific topologies and functionalities through the use of different monomers and linking chemistry at the molecular level.However,most of these COF products are structurally disordered aggregates of particles,and precise control over their microstructure and morphology is difficult,which greatly limits their performance and application.Therefore,this study focuses on the preparation process of imine-based 2D COF.By studying the reaction kinetics of polymerization,the regulation strategies,and their effects on the assembly structure of the products,a customized technology for controlling the aggregation state structure and microstructure of COF materials was developed,achieving precise control over the preparation of COF materials and their multi-level structure.The study also explored the application of the products in catalytic loading,encapsulation,and controlled release.The main research achievements and innovations of this thesis are as follows:(1)Investigating the influence of water and monomer concentration on the formation rate of COF and the regulation of morphology:In the reversible reaction of imine formation via the condensation of amine and aldehyde,the effect of initial water concentration on COF formation rate and the mechanism for regulating COF morphology under different monomer concentrations were revealed.This enabled the controllable preparation of COF particles with ordered nanosheets.(2)Developing the reversible polymerization-termination method to precisely regulate the aggregated structure and morphology of COF:By simultaneously introducing mono-functional amines and aldehydes as competitive agents into the reaction system,the reversible reaction pathways are increased,and the COF formation rate is effectively controlled.As a result,the kinetic controlled system transforms into a thermodynamic-controlled system,producing highly ordered and nanoscale-regulated COF particles and hollow fibers.Furthermore,the strategy also enables the postconversion of low-crystalline products to high-crystalline products.(3)Controllable preparing SiO2@COF core-shell and yolk-shell particles:By controlling the COF generation rate and tuning the surface functional groups and amount of SiO2 particles,the controllable growth of COF shell layer on SiO2 particle surfaces was realized,resulting in the production of three SiO2@COF samples with shell thicknesses of 116-242 nm.Moreover,the preparation of complex yolk-shell COF particles was realized by using amorphous imine polymer as seeds in the reversible polymerization-termination system.Furthermore,the core-shell particles(SiO2@COF)were utilized as thee catalyst support in a tandem polymerization of ethylene,producing ethylene/hexene random copolymers of superior mechanical properties while significantly reducing the amount of COF used and providing insights for industrial applications.(4)Controllable preparing of COF microcapsules and COF particle-stabilized Pickering emulsions:Using regular and re-dispersible spherical COF particles as stabilizers,oil-in-water Pickering emulsions with droplet sizes ranging from 10 to 120μm were prepared.With the combination of Pickering emulsion droplets as templates and interfacial polymerization strategy,COF microcapsules with tunable shell thickness and particle size were achieved.These COF microcapsules can be used to encapsulate and selectively release water-soluble functional molecules such as salts,dyes,and protein molecules.