Adsorption Of Fluorinated Acid Substances Based On Pyridine-functionalized And Molecularly Imprinted Covalent Organic Frameworks

Perfluorinated compounds（PFASs）are a group of persistent,bioaccumulative,and toxic contaminants that can case a serious risk to food safety and human health.Due to the trace levels of PFASs in complex matrices,instrumental detection results in low sensitivity and serious matrix effects.Given that,sample pretreatment is essential.As new adsorbents,covalent organic frameworks（COFs）are widely used for sample pretreatment of PFASs due to the advantages of pore channels,pre-defined structure,and functionalization.Thus,based on the structural characteristics of target analyte,the functionalized COFs have great potential to detect PFASs in food samples and great importance to develop in food analytical chemistry and functionalized organic porous materials fields.In this work,according to the structural characteristics of PFASs,we designed and synthesized two types of functionalized COFs.They were been used solid-phase microextraction（SPME）and in vivo SPME sample pretreatment to achieve efficient adsorption of PFASs in different types of foods and aloe,respectively.We explored the relationship between the special functional groups of functionalized COFs and PFASs.This work provides experimental and theoretical support for functionalized COFs with high adsorption selectivity and expands their applications in adsorption and separation fields.This work is divided into three sections:1.The classification of COFs,the synthesis strategy of functionalized COFs,the adsorption applications of functionalized COFs,the pollution status of PFASs,the research progress of PFASs sample pretreatment,and the research application of functionalized COFs for PFASs were reviewed.2.For the carboxyl group of PFASs,we synthesized the easily post-modified Br-COF by aldehyde/amine condensation reaction.Then,we introduced the pyridine group into Br-COF by Heck cross-coupling reaction to obtain pyridine-functionalized COF（Py-COF）with good crystallinity,large specific surface area,and abundant adsorption sites.The structures and properties were characterized by PXRD,FT-IR,¹³C NMR,N₂adsorption and desorption experiments,TEM,SEM,TGA,and WCA.Based on the successful synthesis of Py-COF,we used it for SPME coating and optimized adsorption time,sample p H,ionic strength,desorption solvent,and desorption time.Under optimal SPME conditions,Py-COF was 2-5 times more effective than commercial materials such as polydimethylsiloxane（PDMS）.Then,we developed Py-COF-SPME-HPLC-MS/MS method using six new PFASs in nine different foods（fruits,vegetables,and meat）,which displayed good linearity of 0.005-7.5 ng g^-1,the detection limits of 0.001-0.004 ng g^-1,the recoveries of 82.5%-112%and the relative standard deviations were less than 9.5%,indicating the method with wide linear range,low detection limit,and high accuracy.Compared with literature,this method was better sensitivity by at least 50-fold.Additionally,the bioconcentration kinetics of ether PFASs in goldfish was explored,indicating the increase of ether bond and carbon chain length leads to stronger bioaccumulation.It is important to the toxicological study of new PFASs.3.For the single interaction of functionalized COFs,we combined molecular imprinting techniques with COFs and prepared imidazole-linked imprinted COF（CMIP）by Debus-Radziszewski multicomponent reaction using Gen X as a template molecule.The characterized of structures and properties by FT-IR,¹³C NMR,N₂ adsorption and desorption experiments,SEM,and WCA.Isothermal adsorption,kinetic adsorption,and selectivity experiments showed that CMIP had higher adsorption capacity and better selectivity than non-imprinted COF.Based on the advantages of CMIP,we used it for in vivo SPME coating,optimizing the extraction time,desorption solvent,and desorption time.Under the optimal conditions,we developed a sensitive and rapid in vivo SPME-CMIP-UHPLC-MS/MS used for the monitoring of trace PFASs in aloe.A comparative experiment with the liquid phase extraction method demonstrated the method with good accuracy and feasibility.And it was 1.2-2 times more than commercial materials（PDMS/DVB,PDMS）.The environmental behavior of PFASs including uptake,migration,and elimination in aloe was explored by uptake and elimination experiments.The results indicated the concentration of PFASs peaked on the fourth day.PFASs transferred toward the vertical direction and showed a linear relationship with Log K_o/w.In addition,the increase of ether bonds and carbon-fluorine chains in PFASs was difficult to be eliminated in aloe.Finally,a risk assessment was performed for the eventual residues of PFASs in aloe.The research provided a preliminary explanation for the dynamic changes of PFASs from environmental to edible plants,which provides a valuable theoretical basis for food safety and human health risk assessment.