High-flux dual-charged composite nanofiltration membranes with electrical double layer architectures for efficient low-pressure water purification

Traditional thin-film composite (TFC) nanofiltration (NF) membranes are constrained by a permeability–selectivity trade-off arising from limited surface charge density and high hydraulic resistance contributed by non-woven fabric backing layers. Here we report high-flux composite Nanofiltration membranes engineered with a dual electrical double layer (EDL) architecture that integrates charged functional groups into both the porous support and the ultrathin selective layer. Strongly negatively charged membranes based on sulfonated polyvinylidene fluoride or sulfonated polyethersulfone achieved multivalent salt rejections of 95.6%–99.3% while delivering pure-water permeances up to approximately 37 L m -2 h -1 bar -1 . Non-woven-free variants maintained stable, high-efficiency removal of multivalent salts, heavy-metal ions (Pb 2+ ), viruses, and bacteria under ultra-low operating pressures (≤0.1 MPa). Zeta-potential measurements confirmed that the dual-charged EDL structures sustain high-magnitude, pH-invariant surface potentials across the range pH 1–13. These membranes enable pump-free household filtration, municipal water treatment, wastewater reclamation, and decentralized rural water supply, directly addressing the need for energy-efficient, high-selectivity water purification technologies.