Design, Synthesis And Properties Of Three Dimensional Bifunctional Covalent Organic Frameworks (COFs)

Covalent organic frameworks(COFs),as a new class of crystalline polymers,have attracted considerable attention over the past decade with promising performance in gas adsorption and separation,catalysis,optoelectronics,proton conduction,chemical sensing,and drug delivery.Since the pioneering work of Yaghi in 2005,a variety of COFs have been prepared through several condensation reactions.However,while the design and synthesis of 2D COFs is already well established,the construction of 3D COFs is limited,and the successful synthetic methods for 3D COFs have been confined to only one type of covalent bond formation.Thus,the exploration of a new synthetic strategy is of paramount importance for the development of 3D COFs materials and diversifying their properties.Herein we discussesed a new general way to construct 3D COFs with the formation of two types of covalent bonds and the application of 3D COFs as acid-base bifunctional catalysts in the catalytic reaction.This thesis mainly includes the following aspects:Part ?,the development,design strategy,synthesis method,properties and applications of COFs are mainly described.The development of acid-base dual function catalyst and its influencing factors were introduced.A brief understanding of significance of this study has been stated.Part ?,two new 3D COFs(DL-COF-1 and DL-COF-2)with the formation of two types of covalent bonds have been successfully synthesized by the solvent thermal synthesis.After that,we characterized these materials by powder X-ray diffraction(PXRD),solid-state nuclear magnetic resonance(NMR),scanning electron microscopy(SEM)and so on.The results show that the structure of the both materials have long-range order,large surface areas,high thermal stability and chemical stability,which are the ideal materials for storing gas.Part ?,we explored the catalytic activity of new COFs materials,in acid-base catalyzed one-pot cascade reactions.In this work,the employed reaction involveshydrolysis of the acetal catalyzed by the acidic sites of boroxine group followed by Knoevenagel condensation catalyzed by the basic sites of imine bonds.After the reactions,the results of PXRD and N2 adsorption confirmed the structural integrity of DL-COFs,thus revealing the high stability of new COFs materials in the acid-base catalytic reaction.The COFs crystals can be easily isolated from the reaction mixture by a simple filtration and reused at least three times with almost no loss of activity,which illustrates that the materials have good potential application in catalysis.