Preparation of acid-resistant nanofiltration membrane with dually charged separation layer for enhanced salts removal

Acid-resistant nanofiltration (NF) membrane with precise ionic separation performance and high permeability is imperative for acidic wastewater reuse. However, the trade-off between ions rejection and water permeability is especially serious for acid resistant NF membrane because of the uneven separation layer structure. Herein, we dissect the two-layer reverse interfacial polymerization (r-IP) process for the preparation of high-performance acid-resistant membrane by investigating monomer reactions and phase interface properties. Mixed organic monomers of 1,4-phenylene diisocyanate and trimesoyl chloride are used to react with the negatively charged aqueous monomer 3-aminobenzenesulfonamide to fabricate interlayer with high negative charge density, and then performs a secondary r-IP reaction with another positively charged aqueous monomer polyethyleneimine to construct a positively charged top layer. By changing the monomer compositions and concentrations, the relationship between monomer reaction and membrane performance is elucidated. Importantly, when aqueous additives of ethanol and glycerol are used to regulate the monomer diffusion coefficient, the membrane surface properties and permselectivity can be improved. Compared to the blank, the prepared membrane shows a 200% water permeability enhancement (2.6 Lm-2h-1bar−1) and desirable rejections of both Na2SO4 (97.7%) and MgCl2 (93.0%). Moreover, the smooth and hydrophilic surface endows the membrane with excellent anti-fouling performance at acidic pH. Benefiting from the robust structure of poly(amide-sulfonamide) and polyurea in the backbone, the membrane shows impressive acid resistance in 10 wt% H2SO4 and long-term stability in heavy metal removal. This work opens new pathways to prepare acid stable NF membrane with desirable permselectivity.