A novel salt-responsive TFC RO membrane having superior antifouling and easy-cleaning properties

• A salt-responsive polymer PSVBP was grafted onto the RO membrane.
• PSVBP grafting led to negatively charged and hydrophilic membrane surface.
• Salt rejection increased from 98.0% to 99.7% while the flux lost 20%.
• The membrane has superior antifouling and easy-cleaning properties.

A novel salt-responsive thin-film composite (TFC) reverse osmosis (RO) membrane was prepared by tethering a zwitterionic polymer poly (4-(2-sulfoethyl)-1-(4-vinylbenzyl) pyridinium betaine) (PSVBP) onto a commercial RO membrane. The graft polymerization was conducted by surface-initiated free radical polymerization of SVBP initiated by a K2S2O8–NaHSO3 redox system. The membrane surface before and after graft polymerization was investigated in detail using ATR-FTIR, XPS, zeta potential, water contact angle and SEM. The change on surface chemical composition demonstrated successful grafting of PSVBP onto the RO membrane surface. The PSVBP grafting added negative charge onto the membrane surface and significantly improved membrane surface hydrophilicity. The RO test indicates that PSVBP grafting can increase the rejection from 98.0% to 99.7% with the trade-off 20% of the permeation flux. A cross-flow protein fouling test as long as 100 h indicates that the resulted PA-g-PSVBP membrane had superior antifouling property in the short term but lost the advantage for long-term operation. In spite of the long-term fouling, the PA-g-PSVBP membrane can restore 90% of the initial flux by rinsing with brine. The salt-responsive property of the PSVBP brush is believed to provide a driving force for the release of protein foulants.