A novel route for surface zwitterionic functionalization of polyamide nanofiltration membranes with improved performance

Zwitterionic polymers are attracting significant interest for nanofiltration (NF) membranes featuring exceptional permeability and antifouling performance. Here we introduce a facile strategy incorporating a controlled amount of zwitterionic component (N-aminoethyl piperazine propane sulfonate, AEPPS) onto polyamide thin film composite NF membranes that are prepared via interfacial polymerization between trimesoyl chloride (TMC) and piperazine (PIP). By immersing pristine polyamide NF membranes in AEPPS aqueous solution, reactive AEPPS molecules were effectively anchored to the membrane surfaces via chemical reactions between amine groups on AEPPS and acyl chloride groups on the membrane surfaces. The chemical reactions were characterized, and the incorporated AEPPS is shown to improve the membrane permeability without compromising salt rejection. When the concentration of AEPPS is 1 wt%, the water flux increases from 28.0 L m−2 h−1 to 57.6 L m−2 h−1 while Na2SO4 rejection is maintained above 99.5%. Last but not the least, the membrane׳s antifouling property is simultaneously improved, with the flux recovery ratio being as high as 91.6% (pH 3.7) and 95.5% (pH 6.0).