Surface modification of thin-film composite polyamide reverse osmosis membranes with thermo-responsive polymer (TRP) for improved fouling resistance and cleaning efficiency

Abstract

Interfacially synthesized thin-film composite (TFC) aromatic polyamide reverse osmosis membranes were modified by depositing a thermo-responsive polymer poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAM-co-Am)) with low critical solution temperature (LCST) on membrane surface, and the modified membranes showed significantly improved antifouling properties and cleaning efficiency. In the experiments, membrane modifications were conducted in situ with dilute P(NIPAM-co-Am) solutions under different modifying conditions (e.g., P(NIPAM-co-Am) concentration and deposition time), after which fouling properties of the virgin and modified membranes were studied through cross-flow fouling experiments using bovine serum albumin (BSA) aqueous solution under different feed concentrations and pHs, and membrane cleaning tests were also carried out with the fouled membranes using de-ionized water under different feed temperatures. The membrane properties were also characterized by ATR-FT-IR, contact angle and streaming potential measurements as well as permeation tests. It was found that membrane modification improved the water permeability and fouling resistance to BSA due to the increased membrane surface hydrophilicity, and that the phase transition of the thermo-responsive polymer surface coating layer above LCST facilitated the removal of foulant located on membrane surface. Furthermore, the in situ membrane surface modification approach would be of particular interest for treating existing commercial membranes in their original module assembly.