Nanofiltration membranes form throughinterfacial polymerization and its property of dye separation
In general,m-phenylenediamine or piperazine could be used as an aqueous phase monomer for the preparation of nanofiltration and reverse osmosis membrane by the interfacial polymerization method.However,these monomers were toxic and irritants risking both human health and environments.Chitosan oligosaccharide(COS),as a green renewable and nontoxic marine polysaccharide with low molecular weight obtained from chitosan by special enzyme treatment.The water-soluble property of COS was better than chitosan.COS had similar chemical properties to chitosan,and their molecules contained amino and hydroxyl groups,which were suitable for preparing nanofiltration composite membranes through interfacial polymerization reaction as aqueous monomers.In this study,COS/PES membranes were successfully prepared on polyether sulfone ultrafiltration membrane(PES)by interfacial polymerization with COS as aqueous phase monomer and trimesoyl chloride(TMC)as oily phase monomer.The surface of membrane was characterized by Field Emission Scanning Electron Microscopy(SEM)and Atomic Force Microscopy(AFM).The membrane flux and dye separation performance were tested by cross-flow filtration.Re-sults show that the surface of COS/PES-2 membrane had a spot-like structure and a high membrane flux.According to Zisman's critical surface tension extrapolation method,the surface tension of liquid was mapped with cosθ,and it was found that COS/PES membrane had better anti-biological adhesion performance.The specific flux(J/Jw)of COS/PES membrane was always higher than that of commercial PES ultrafiltration membrane,indicating that the cross-linked chitosan oligosaccharide active layer has a certain performance of anti-microbial fouling.The results of dye separation experiment showed that the rejection rate of chitosan oligosaccharide composite nanofiltration mem-brane for methyl orange was between 0.45-0.53,and the rejection rate of primroselin was between 0.66-0.77.When the molecular weight of dye molecule was greater than 600 Da,three types of COS/PES membrane remained above 90％,which proved that the prepared COS/PES membranes belonged to the category of nanofiltration mem-brane.The COS/PES composite nanofiltration membrane is responsive to the development demands of environmen-tally friend new marine materials home and abroad,and it is a far reaching application potential in environmental protection fields and medicine industries.
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