Surface modification of a commercial thin-film composite polyamide reverse osmosis membrane through graft polymerization of N-isopropylacrylamide followed by acrylic acid

• PA membrane was modified through graft polymerization of NIPAm followed by AA.
• Modification increased the membrane surface hydrophilicity and negative charge.
• Modification enhanced the membrane water flux and salt rejection simultaneously.
• Modification improved the membrane fouling resistance and chlorine stability.

Surface modifications including physical and chemical treatments are effective approaches to improve the fouling and chlorine resistances of the commercial thin-film composite (TFC) aromatic polyamide reverse osmosis (RO) membranes. However, the major problem facing the modification is the influence on membrane performance. In this study, surface modification of a commercial TFC RO membrane was performed through redox initiated graft polymerization of N-isopropylacrylamide (NIPAm) followed by acrylic acid (AA) and the modified membrane showed improved membrane properties. Membrane characterization was conducted through ATR-FTIR analysis, zeta-potential analysis, contact angle measurement and cross-flow permeation test. Changes in surface characteristics confirmed the graft polymerizations of NIPAm and AA. The surface of the membrane became more hydrophilic and negatively charged after modification. The membrane modified under certain conditions showed both increased water flux and salt rejection. Fouling experiments with bovine serum albumin (BSA) aqueous solution demonstrated that the modification could mitigate the deposition of foulants on the membrane surface through enhancing electrostatic repulsion and lowering hydrophobic interaction between BSA molecules and membrane surface and thereby improving fouling resistance. Furthermore, chlorination tests also showed that surface modification through graft polymerization of NIPAm followed by AA could effectively enhance the chlorine stability of the polyamide membrane.