Synthesis Of Trifluoromethyl And Ionic Covalent Organic Framework For The Extraction Of Per- And Polyfluorinated Alkyl Substances

Sample pretreatment technology is the key step of trace detection in analytical chemistry.The development of sample pretreatment technology depends on the continuous innovation of the adsorbents.Covalent organic frameworks(COFs)have shown immense potential in analytical chemistry because of their excellent properties.Aiming at the synthesis of functionalized COFs for extraction of per-and polyfluorinated alkyl substances(PFASs),the trifluoromethyl COFs(CF₃-COF)and ionic COFs(TPB-BFBIm-i COF)were synthesized by the dehydration condensation reaction of aldehydes and amines.Based on the functionalized COFs,solid-phase microextraction(SPME)and online solid-phase extraction(SPE)was established to adsorb PFASs from milk products and seafoods,respectively.The relationship between the adsorption efficiency and functional groups was also investigated.These results can provide the experimental method and theoretical basis for assembling functional COFs with specific application.The research contents of this thesis include three parts.1.The synthesis of COFs,their application in sample pretreatment,the pollution status of PFASs,their sample pretreatment methods and the application of COFs in PFASs are summarized and discussed.2.Aiming at the poor selectivity of COFs as adsorbents for sample pretreatment,a trifluoromethyl imine-linked COF(CF₃-COF)was facilely synthesized at room temperature using 3,3'-bis(trifluoromethyl)benzidine and 1,3,5-triformylbenzene as condensation reaction monomers.The structure and morphologies of CF₃-COF were assessed by Fourier transform infrared(FT-IR)spectra,elemental analysis,scanning electron microscope(SEM),N₂ adsorption-desorption,contact angle(CA),powder X-ray diffraction(XRD),and solid-state ¹³C NMR spectra.To further clarify the selectivity of CF₃-COF to the PFASs,competitive experiment in complex samples was designed by employing four different kinds of chemicals(imidacloprid,anthracene,ciprofloxacin and chlorobenzene).The extraction performance of PFASs were higher than those of the four different kinds of chemicals,indicating the excellent selectivity of CF₃-COF to PFASs.The CF₃-COF coating displayed the preferable extraction performance for PFASs comparing to amorphous polymer coating,non-contained fluorine covalent organic framework coating and the commercial polydimethylsiloxane(PDMS),PDMS/divinylbenzene(PDMS/DVB)coating.After optimizing the extraction and desorption conditions,the CF₃-COF-SPME coupled with ultrahigh performance liquid chromatography tandem mass spectrometry(UHPLC-MS/MS)method was established to detect PFASs in milk and milk products.Under the optimized conditions,the linear ranges for milk and milk powder are 0.5?20000.0 pg g^-1 with R²?0.990.The limits of detection(LOD)and quantification(LOQ)were below 0.8 pg g^-1and 2.5 pg g^-1,respectively.The intra-day and inter-day precisions were below 9.9%.The relative recovery of the method is from 89.8 to 111%with the relative standard deviation(RSD)?10%.The above results evidence that the CF₃-COF-SPME-UHPLC-MS/MS method shows satisfactory feasibility and applicability for trace PFASs analysis in milk and milk products.3.Aiming at the irregular morphology and sub-micrometer particle size of COFs,the spherical ionic COFs(TPB-BFBIm-i COF),were fabricated from 1,3,5-tris(4-aminophenyl)benzene and 5,6-bis(4-formylbenzyl)-1,3-dimethyl-benzimidazolinium bromide via condensation reaction.The structure and morphologies of TPB-BFBIm-i COF were assessed by FT-IR,SEM,N₂ adsorption-desorption,CA,XRD,and solid-state ¹³C NMR spectra.The adsorption characteristics of TPB-BFBIm-i COF towards PFASs were investigated,indicating that TPB-BFBIm-i COF showed fast adsorption equilibrium(5 min)and high adsorption capacity(87.7?140.8 mg g^-1)for PFASs.After optimizing the loading and eluting conditions,the TPB-BFBIm-i COF-online SPE-UHPLC-MS/MS method was established to detect PFASs in five complicated seafood medias.Under the optimized conditions,the linear ranges for seafoods are 0.001?5 ng g^-1 with R²?0.990.The LOD and LOQ were below0.0040 ng g^-1and 0.0120 ng g^-1,respectively.The intra-day and inter-day precisions were below 9.7%.The matrix effect values for PFASs are 91.1?107%in various seafoods matrices,which are within the acceptable limits.Outstanding relative recoveries of PFASs are from 85.3%to 109%with RSD?9.9%.The above results evidence that the TPB-BFBIm-i COF-online SPE-UHPLC-MS/MS method shows satisfactory feasibility and applicability for trace PFASs analysis in five complicated seafood medias.