Polyamide nanofiltration membranes with carboxylated cellulose nanofiber interlayers for enhanced water permeance and selective removal of mineral ions and per- and polyfluoroalkyl substances

Per- and polyfluoroalkyl substances (PFASs) in drinking water pose major concerns for public health and water resource protection. Nanofiltration (NF) is a promising technology for PFAS removal; however, many NF membranes achieve high PFAS rejection at the expense of rejecting beneficial mineral ions. In this study, we utilized carboxylated cellulose nanofiber (C–CNF) interlayers to fabricate highly selective NF membranes, enabling efficient PFAS removal at uncompromised mineral ion passage. The optimized NF-60 membrane featured a higher negative surface charge, looser structure, enhanced hydrophilicity, and larger pore size, resulting in more than a 2.5-fold increase in pure water permeance (50.8 LMH/bar), lower rejection of mineral ions (<20.2%), and high PFAS rejection (>87.7%). The selectivity for Ca 2+ over perfluorooctane sulfonic acid (PFOS) selectivity was improved by more than fourfold owing to stronger electrostatic repulsion and reduced hydrophobic interactions, outperforming many reported NF membranes. Density function theory calculations further revealed a reduced adsorption tendency of PFOS on the NF-60 membrane. These results provide valuable guidance for the development of NF membranes with high selectivity between mineral ions and PFASs in advanced drinking water purification.