Monomer Quaternization Enables Antibiofouling and Superior Perm-selectivity of Nanofiltration Membranes for Sustainable Water Purification

Abstract Biofouling poses a substantial challenge to advanced wastewater treatment and reuse via nanofiltration (NF) membranes, while current strategies for enhancing antibiofouling performance often compromise membrane perm-selectivity. Herein, quaternized NF (QPIP-NF) membranes were fabricated via piperazine (PIP) quaternization to simultaneously enhance antibiofouling performance and perm-selectivity. Compared with PIP-NF membranes, QPIP-NF membranes exhibited 1.4-fold higher pure water permeance, slightly increased Na2SO4 rejection, and 1.4-fold higher water/Na2SO4 selectivity, owing to increased surface roughness, reduced polyamide thickness, and improved size-sieving. Furthermore, QPIP-NF membranes also exhibited a 91% improvement in antibacterial efficiency against Escherichia coli and a 48% enhancement in dynamic antibiofouling performance. Kit-based measurements of key bacterial enzyme activities and reactive-species levels, postfouling antibacterial evaluations, and confocal laser scanning microscopy analyses of live/dead cell distributions and biofilm thickness on the membrane surface collectively revealed the antibiofouling mechanism of the QPIP-NF membrane through inhibition of biofilm formation via surface bactericidal activity. Specifically, QPIP-NF membranes inhibited catalase, superoxide dismutase, DNA gyrase, and Na+/K+-ATPase activities while inducing excessive intracellular generation of H2O2 and superoxide anions, thereby ensuring lasting antibacterial activity in the near-membrane region and achieving excellent antibiofouling performance. Our study provides a new avenue for the design of antibiofouling NF membranes with improved perm-selectivity.