Preparation Of Novel Covalent Organic Framework Liquid-chromatographic Monolithic Columns For Separation Of Organic Pollutants

Covalent Organic Framework(COFs)shows great application potential in the field of separation science,their unique advantages such as convenient modification,low density,large specific surface area,and good stability.However,the traditional COF particles usually are irregular sub-micron particles,which can easily block the column and subsequently lead to ultrahigh column pressure when used as the packing materials of liquid chromatography(LC),and therefore their applications in this field are limited greatly.Taking advantage of the good permeability of monolithic column,preparation of COF-based LC monolithic columns can effectively address this issue.At present,two-step strategies have been reported for preparing the COF-based LC monolithic columns.Namely,the common COF submicron particles are synthesized first,and then the mixture containing COF particles,solvent,porogen,cross-linker and initiator is loaded into an empty LC column,followed by the polymerization at 60~oC in a water bath.After that,a COF-based LC monolithic column is obtained.One shortcoming of this synthesis method is its time-consuming procedure.To address this problem,a one-step strategy was developed in this dissertation for the in-situ synthesis of COF-based LC monolithic columns,which is easily to carried out.In addition,to overcome the shortcoming that the existing COFs’particles are non-uniform,a new method was developed for synthesizing uniform COF single crystals herein,and subsequently a new COF-single-crystal-incorporated LC monolithic column was prepared.The research contents in more detail are listed as follows:In the first part,two COF monomers,1,3,5-tris(4-aminobiphenyl)(TABPB)and 2,5-divinyl-terephthalaldehyde(DVA),were synthesized using 1,3,5-tris(4-bromophenyl)benzene and 2,5-dibromo-p-xylene as reagents,respectively.Then,TABPB,DVA,ethylene-glycol-dimethacrylate(EDMA),polyethylene-glycol-6000(PEG6000),azobisisobutyronitrile(AIBN)and 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide([BMIm][NTf2])were mixed,and then the mixtures were loaded into an empty LC column.After kept at room temperature for a certain time for the formation of DVA-TABPB-COF,the column was put in a water bath at 60~oC for polymerization,and finally the COF-based LC monolithic column was obtained.The permeability,thermal stability and pore structure of the monolithic column were investigated.Results showed that the COF monolithic column had good permeability,good thermal stability and large specific surface area.The separation ability of the new column was also evaluated.Results indicated that the LC monolithic column showed good separation ability for three types of small-molecule organic pollutants(benzenes,amines,and polycyclic aromatic hydrocarbons).Especially,polycyclic aromatic hydrocarbons can be baseline separated.In the second part,1,3,6,8-tetra(p-aminophenyl)pyrene(TAPP)monomer was synthesized first using 1,3,6,8-tetrabromopyrene as reagent,and then TAPP,DVA,EDMA,PEG6000,AIBN and[BMIm][NTf2]were mixed and loaded into an empty LC column.After kept at room temperature for a certain time for the formation of DVA-TAPP-COF,the column was put in a water bath at 60~oC for polymerization,and finally the COF-based LC monolithic column was obtained in situ.The permeability,thermal stability and pore structure of the monolithic column were investigated.Results showed that the COF monolithic column had good permeability,good thermal stability and large specific surface area.The separation ability of the new column was also evaluated.Results indicated that the LC monolithic column showed good separation ability for four types of small-molecule organic pollutants(benzenes,amines,phenols and polycyclic aromatic hydrocarbons).The benzenes,amines and phenols can be separated within5 min,and polycyclic aromatic hydrocarbons can be baseline separated.In the third part,TAM monomer was synthesized using triphenylchloromethane as regent,and then COF-300 single crystals with uniform size was synthesized at room temperature via Schiff base reaction of TAM and BDA using dichloroacetic acid as catalyst.Then,the COF crystals were homogeneously dispersed in the mixture containing EDMA,PEG6000 and AIBN.After the mixture was loaded into an empty LC column,the LC column was put in a water bath at 60~oC for polymerization,and finally a COF-single-crystal-incorporated LC monolithic column was obtained for the first time.Results showed that the stirring and dichloroacetic acid(6 mol/L)catalyst were needed for the formation of COF crystals.The COF-300 crystals was converted gradually from the amorphous particles with the reaction time of 42 hours,which is much shorter than those in literatures.The crystals were characterized by FT-IR,XRD,and SEM.Results showed that the COF-300 crystals exhibited a uniform spindle shape(about 2～3μm)with a better size uniformity than those in literature.Moreover,five diffraction peaks in XRD curve are in accordance with those in literature.The COF-300-single-crystal-incoporated LC monolithic column can be applied to the chromatographic separation of small-molecule organic pollutants.