Constructing reverse osmosis membranes with an excellent anti-fouling performance via a highly effective photoinitiated radical polymerization strategy

Abstract

Reverse osmosis (RO) membranes are inevitably subject to membrane fouling during the treatment process, severely deteriorating the separation performance and increasing the cost and energy consumption. Zwitterionic grafting can effectively resist foulant adhesion by forming a stable hydration layer on the membrane surface, which shows great potential for industrial applications. The current reported grafting methods are complicated and time-consuming, which are unfavorable for industrial scale-up. In this paper, a simple and time-saving (∼3 min) photoinitiated radical polymerization (PRP) technique is employed to introduce zwitterionic polymer onto the RO membrane surface. The photoinitiator is firstly anchored onto the membrane surface via the reaction between the phenolic hydroxyl group and acyl chloride and then initiates the radical polymerization to graft poly-zwitterionic brushes onto the membrane surface. The precise-grafted zwitterionic polymer brushes effectively facilitate the membrane with increased surface hydrophilicity (80.3° to 57.4°), reduced electronegativity (−46.9 mV to −41.2 mV) and enhanced surface steric hindrance. The PRP-modified membranes demonstrate superior flux recovery performance, achieving flux recovery ratios (FRR) of 97.8 % for bovine serum albumin, 98.4 % for humic acid, 98.1 % for sodium alginate, 97.5 % for sodium dodecyl sulfate, and 90.6 % for cetyltrimethylammonium bromide (CTAB), respectively, outperforming the commercial BW30 and control RO membranes. More importantly, the anti-scaling test and practical secondary effluent wastewater treatment further demonstrate superior anti-fouling performance (the FRR of 97.8 % and 97.7 %). The Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and molecular dynamics simulation elucidate the corresponding anti-fouling mechanism. In addition, the PRP strategy is suitable for the nanofiltration membrane and commercial RO membrane, demonstrating its outstanding versatility. This work demonstrates a creative approach to achieving desired anti-fouling properties relying on grafting zwitterionic polymer brushes by photoinitiation technique and provides an effective, extensible and energy-efficient pathway to develop anti-fouling RO membranes.