High-recovery, antifouling polyamide membranes via Fe-facilitated assembly of betaine-like cationic layers

The intrinsic hydrophobicity and electronegative surface charge of polyamide (PA) membranes render them highly susceptible to organic and biological fouling, constraining their efficiency in water treatment. Here, we present a molecularly rational, coordination-driven strategy to construct electropositive PA membranes by grafting a family of betaine-derived quaternary ammonium materials (QAMs) (Bet-1N ⊕ , Bet-2N ⊕ , Bet-4N ⊕ ) via Fe 3+ -mediated interfacial coordination. The single-step-synthesized modifiers provide dense −OH, −COOH and −NMe 3 + functionalities that synergistically increase hydrophilicity, smooth surface morphology, and positive surface charge. Forward-osmosis evaluation shows significant flux enhancements of 142%, 150% and 167% for Bet-1N ⊕ , Bet-2N ⊕ , Bet-4N ⊕ membranes, respectively, relative to pristine PA membranes. Beyond permeability, the membranes, particularly the Bet-4N ⊕ variant, achieves >99% bactericidal efficacy against both E. coli and S. aureus , limits lysozyme-induced flux decline to 25% over 12 h, and recovers 88% of initial flux after hydraulic cleaning (vs. 54% decline and 61% recovery for pristine PA). Mechanistic analysis reveals that a sterically and electrostatically selective Fe-QAM interphase underpins these antifouling advantages. This work establishes a facile and eco-friendly approach for constructing high-performance antifouling membranes, offering broad potential for sustainable water treatment applications.