Imine-based Covalent Organic Framework Materials For On-line Solid-phase(micro)extraction Of Organic Pollutants

At present,analytical tasks are often faced with the problem of large matrix interference and low analyte content,which makes it difficult to obtain accurate and sensitive results by only using existing analytical instruments to detect samples.Efficient sample pretreatment technology can availably eliminate the interference of complex sample matrix and enrich trace analytes,which has been widely used in the field of analysis and detection.Traditional sample pretreatment technologies include liquid-liquid extraction,Cable extraction,etc.,which generally have the disadvantages of large amounts of organic solvent,complex operation,low recovery rate,and so on.While solid-phase extraction and solid-phase microextraction have the advantages of simple equipment,convenient operation,low cost,high enrichment efficiency,and less amount of organic solvent.Therefore,they are widely used in environmental analysis,food safety,biomedicine and other fields.Among them,the key to the solid-phase（micro）extraction efficiency is the adsorbent/extraction coating.Therefore,the development of efficient and stable adsorbent/coating materials is a hot spot in the research of sample pretreatment field.Covalent organic framework（COFs）is a kind of organic polymer material composed of light elements（C,H,O,N,B）with crystalline structure.Its appearance breaks people’s understanding of the crystal structure formed by the connection of organic molecules.It is divided into three main types based on covalent bond formation,namely boron,imine,and triazine-based COFs.Boron-based COFs are unstable in humid environment;the available monomers of triazine-based COFs are limited and their crystallinity is not ideal,while imine-based COFs are stable in common organic solvents and even in water,and more monomers are synthesized,which is obviously better than above.In addition,due to the large number of phenyl,amino and other groups in their structure,they can provideπ-πstacking,hydrogen bonding interactions,and so on.Therefore,their introduction into the field of sample pretreatment can greatly improve the extraction efficiency of adsorbent.Specific research contents are as follows:1.Using TiO₂ nanorod arrays modified carbon fiber as a matrix and aminated it,then an imine COF nanosphere（COF-V）were in-situ generated on it and the preparation conditions were optimized.The synthetic extraction fibers were characterized to confirm their successful preparation and then they were loaded into the polyether ether ketone tube to obtain the extraction tube,as well as combined with high-performance liquid chromatography（HPLC）to construct an online analysis system.Firstly,the relationship between performance and structures of materials was investigated and the extraction mechanism was revealed with this system.After that,the optimal extraction efficiency of bisphenols were selected as the targets,the extraction and desorption conditions were optimized,and the on-line analysis method was established.The linear ranges were 0.017-15.0μg L^-1,the limits of detection were 0.005-0.010μg L^-1,and the enrichment factors were 2884-3745.Finally,the method was applied to the detection of real samples（spiked recoveries:77.4%-131.7%）.2.1,3,5-tri（4-aminophenyl）benzene and 2,5-divinyl-1,4-benzenedicarboxaldehyde were selected as monomers,COF nanocoatings（COF-V）were prepared on the surface of porous silica,and two ionic liquids were grafted to the coating by clicking reaction.The material before and after ionic liquid modification was loaded into solid-phase extraction（SPE）columns and combined with HPLC to establish an online analysis system.By investigating the extraction mechanisms of 5 polycyclic aromatic hydrocarbons,2 bisphenols and the corresponding chemical structure of no hydroxyl diphenyl alkane,as well as 4 benzoic acids,it was confirmed thatπ-πstacking,hydrogen bonding,and electrostatic interactions existed in the extraction process,and the best adsorbent material was selected.The extraction selectivity of the optimal material was investigated and estrogens were selected as the targets.Then the analytical method was established and applied to the real samples detection(limits of detection were as low as0.005μg L^-1,linear ranges were as wide as 0.017-10.0μg L^-1,enrichment factors were as high as 3635,and spiked recoveries were 67.1%-123.2%).Therefore,satisfactory experimental results were obtained.3.Similarly,using 1,3,5-tri（4-aminophenyl）benzene and 2,5-dihydroxy-1,4-benzenedicarboxaldehyde as reaction monomers,micron-scale COF spheres（COF-H）were prepared at room temperature.It was doped with spherical all-porous silica and loaded into an SPE column to construct an online SPE-HPLC system.4 neonicotinoid insecticides were used as analytes and the conditions which affect the analytical efficiency were optimized.The analytical method for the detection of neonicotinoid insecticides was established(the linear ranges were 0.033 to 15.0μg L^-1,the limits of detection were 0.01-0.15μg L^-1,and the enrichment factors were 3019-3255).Finally,the method was applied to the detection of neonicotinoid insecticides in real water samples（the recoveries were between 65.7%and129.6%）.