Synthesis And Characterization Of Covalent Organic Frameworks And Their Potential Applications

Generally,covalent organic frameworks are arranged in a long-range ordered periodic array structure.They are constructed by organic building blocks which are connected by the covalently bonded linkages.These materials are composed of lightweight elements,so they should be low in density.Due to the design and unique structure,COFs materials have uniform pores,large specific surface,good crystallinity,high thermal and chemical stability.In recent years,COFs attract much interest and exhibit potential applications in many fields with their unique structures and functions.In this work,I have been made some COFs which are having certain specific surface area and they can be modified based on their design and functionalization.Detailed information of the work has been explained chapter wise as follows:Constructing of three-dimensional covalent organic frameworks(3D COFs)with photoelectric functionality is a challenging synthetic task.In Chapter 3,we report the targeted synthesis and characterization of a highly porous 3D COF containing porphyrin photoelectric units.The obtained 3D COF-TATB exhibits a high surface area and is proposed to adopt a 2-fold interpenetrated pts topology with Pmc21 space group.Furthermore,we demonstrate that this porphyrinic 3D COF can be used as a photoelectrocatalyst for water splitting.An obvious photocurrent was observed under visible light irradiation,and the photocurrent increases remarkably under more negative potentials,revealing a representative behavior of photocathode and its p-type property.This work offers valuable guidance for the designing of 3D organic semiconductors for light-driven water splitting.In Chapter 4:A series of ionic COFs have been synthesized by optimization of the mixture of fluoro and functional monomers.The introduction of fluoro monomers into the frameworks will increase the stability and their crystallinity of desired COF.Initially,the equal proportion of ionic and non-ionic COFs was prepared,Py-TFIm I_25%COF and Py-TFIm_25%COF,respectively.Then,the continuous repeating ion exchange processes were applied to get other ionic COFs such as Py-TFIm Cl_25%and Py-TFIm Tf₂N_25%COF from Py-TFIm I_25%COF.The order of size of anion as follows:Py-TFIm Cl_25%COF<Py-TFIm I_25%COF<Py-TFIm Tf₂N_25%COF.Therefore,the comparative studies were done to get more information about the effect of ionic modification,influence of anionic size in properties of different COFs.It was observed from the results,there is no significant differences occured between ionic and nonionic COFs in terms of pore size,BET and gas adsorption.This work provides the basis for the design and synthesis of 2D ionic COFs for homogeneous catalysis.In Chapter 5:Generally,the solvothermal method is one of the best method to synthesis COFs,but that required harsh reaction conditions,such as high temperature,high pressure and long reaction time.In this chapter,I synthesized COF using green solvent,low temperature with less reaction time.Particularly,the ionic liquid used as a reaction medium and the reaction conditions maintain at 65?for 24 hrs under atmospheric pressure.Therefore,the whole reaction process follows green and sustainability.In this case,the 5-fold interpenetrated structure of COF 300 was synthesized successfully.The7-fold interpenetrated structure COF 300 was obtained when used 3 M acetic acid as a catalyst at the same reaction time.The morphology of COF 300 crystals with different penetrations was observed by a scanning electron microscope.The resulting BET confirms that the higher penetrated structural COF material gives high surface area and also they explored good gas adsorption properties.Hence,the overall studies explain the significance of the interspersed structure of the COF on the adsorption of CO₂.