Enhanced restoration and durability of deteriorated polyamide reverse osmosis membranes through sequential polyethyleneimine grafting and zwitterion construction

This research addresses the critical issue of deteriorated polyamide (PA) reverse osmosis (RO) membranes, whose efficiency and lifespan are significantly reduced by fouling and chlorine exposure. To combat these challenges, an innovative solution was developed, combining polyethyleneimine (PEI) grafting and zwitterion construction under mild aqueous conditions at room temperature, tailored for large-scale industrial applications. The restoration process starts with the covalent bonding of branched PEI, rich in amine groups, to the damaged membrane surfaces through amidation targeting the primary amine groups of PEI and the carboxyl groups on the membranes. The process continues with tertiary amination using dimethylaminopropyl methacrylamide (DMA), which introduces additional tertiary amine moieties, and concludes with quaternization and sulfonation using sodium 3-chloro-2-hydroxypropanesulfonate (SCHPS) to form a robust zwitterionic structure. This dual modification significantly enhances NaCl rejection from 94.1 % to 98.2 % and improves the membrane's resistance to both fouling and chlorine, thus extending its operational lifespan. Evaluations confirm the enhancements in hydrophilicity and charge neutrality effectively prevent pollutant adhesion and mitigate environmental degradation, presenting a potential practical and efficient solution for prolonging the usability of RO membranes in industrial and environmental settings.