Synthesis Of Covalent Organic Frameworks And Its Application In Open Tubular Capillary Electrochromatography

Covalent organic frameworks(COFs)is a kind of porous crystalline material connected by light elements such as C,H,O,N,S,B through covalent bonds.Due to their low density,high porosity,large surface area,good thermal stability and chemical stability,COFs are widely applied in energy storage,catalysis,gas adsorption and separation,electrochemical sensing,sample pretreatment,chromatographic separation and so on.Since the first work on COFs was reported by Omar M.Yaghi group in 2005,researchers have successively synthesized two-dimensional(2D)and threedimensional(3D)COFs.At present,the synthesis methods of COFs mainly include solvothermal,ionothermal,microwave assisted,mechanochemical method and room temperature synthesis.Open-tubular capillary electrochromatography(OT-CEC)is a kind of electrochromatographic separation technology based on the difference of mobility and distribution behavior between analytes.Recently,in order to increase the phase ratio and column capacity,a variety of nanomaterials have been used as stationary phases of OT-CEC.COFs also attracted researchers' attention in the field of chromatography because of their ordered channels and high surface area.The preparation methods of COFs coated capillary are mostly based on covalent bonding at present,which can be divided into two methods: post-modification and in-situ growth.In-situ growth method is favored by most chromatographic scientists because of its simple preparation process and uniform material coating.Now,most of the modified coating materials are 2D COFs,3D COFs coating as stationary phase is still in its early stage.Based on this,we have carried out the following innovative studies:(1)Hydrazone COF has the characteristic of easy monomer modification and syhthesis,and abundant N,O and other sites can interact with analytes,which is conducive to the separation of analytes in capillary eectrochromatography.Therefore,in order to obtain hydrazone COF with better crystallinity for application in OT-CEC,Tf-DHz OH with better crystallinity and good chemical stability was successfully synthesized by solvothermal synthesis after optimizing the synthesis conditions.Then,the Tf-DHz OH coated capillaries with compact coating were firstly prepared by postmodification method.It was found that Tf-DHz OH coated capillaries with different coating thickness could be obtained by contronling the concentration of COF solution in capillary.The coated capillary has good separation ability not only for charged compounds such as amino acids,tetracycline and sulfonamides,but also for neutral analytes such as substituted benzene.In addition,the OT-CEC method was established and applied for the determination of three kinds of target analytes in real sample.(2)In order to develop the in-situ growth method with mild condition for the preparation of COF open-tubular capillary,a novel synthesis method was developed for the first time to synthesize hydrazine-linked COF-LZU8 with high crystallinity at room temperature,and the method was introduced into the preparation the COF-LZU8 coated capillary by in-situ growth at room temperature.Then,the COF-LZU8 coated capillaries with different coating thickness and good stability were prepared in-situ growth by contronling the concentration of monomers filled in capillary.Four phthalic acid esters(PAEs)and three groups of isomers were selected as the target analytes to investigate the separation performance of the in-situ growth COF-LZU8 coated capillary,which was compared with that of capillary prepared by post-modification method.Because the excessive penetration of PAEs into environments will cause great harm to human body,the proposed OT-CEC method was used to the detection of PAEs in several plastic products commonly used in daily life.(3)Based on the application advantages of 3D COFs in chromatographic separation,spherical 3D COFs were successfully synthesized by a new method after optimizing the synthesis conditions.3D COFs was modified on the inner surface of capillary by in-situ growth.Eight groups of analytes,including acidic,basic,neutral analytes and isomers,were selected to evaluate the wide spectrum separation performance and stability of 3D-IL-COF-1 coated capillary.The results shown that the separation performance of the 3D-IL-COF-1 coated capillary was better than that of the reported 3D COFs open-tubular capillaries.