Construction of highly cross linked defect free acid resistant nanofiltration membrane via span 80 accelerated monomer diffusion

Acidic wastewater, primarily generated from mining, metallurgical, and chemical industries, poses significant risks to both the environment and human health. Nanofiltration (NF) has emerged as a promising approach for treating such wastewater, yet the performance of acid-resistant membranes remains limited. In this work, acid-stable poly(amide-sulfonamide) (PASA) thin-film composite (TFC) NF membranes were fabricated via interfacial polymerization (IP), with the nonionic surfactant sorbitan monooleate (Span 80) employed to modulate the IP process, markedly enhancing membrane performance. Specifically, Span 80 was found to orient at the water–organic interface, significantly reducing interfacial tension and accelerating the diffusion of 3-aminobenzenesulfonamide (ABSA) monomers, thereby forming a thicker, highly cross-linked, and defect-free PASA selective layer. The optimized NF-0.1 membrane exhibited the smallest average pore size (0.635 nm) and a defect-free selective layer, with Na₂SO₄ and MgSO₄ (the concentration of the salt solution is 1000 mg/L) rejection exceeding 99 % and 95 %, respectively, while maintaining a moderate permeance of 3.05 ± 0.15 L·m −2 ·h −1 ·bar −1 . Long-term stability tests, pressure-resistance evaluations, and 35-day static acid immersion experiments demonstrated excellent operational stability, pressure tolerance, and acid resistance. Compared with previously reported acid-resistant NF membranes and commercial high-acid-stability membranes, NF-0.1 had a higher retention effect on monovalent and divalent sulfates. This work provides a simple and scalable strategy for producing defect-free, highly selective PASA acid-resistant NF membranes and highlights the critical role of surfactant-assisted monomer diffusion in optimizing membrane structure and performance.