A loose nanofiltration membrane from aqueous monomer 8-amino-1-naphthol-3,6-disulfonic acid for highly selective separation of natural organic matter from minerals in drinking water

Loose nanofiltration (LNF) offers a promising solution for producing high-quality drinking water by selectively removing natural organic matter (NOM) while permeating beneficial minerals. Herein, we presented a molecular design strategy to fabricate a novel polyamide-polyester LNF membrane via interfacial polymerization (IP) of trimesoyl chloride (TMC) and an aqueous monomer, 8-amino-1-naphthol-3,6-disulfonic acid (ANDSA). Mechanistically, the steric hindrance of the bulky naphthalene skeleton prevents tight polymer chain packing, inherently creating a loose separation structure. The optimized ANDSA-0.5 membrane achieved a high water permeability of 62.4 L·m −2 ·h −1 ·bar −1 and excellent rejection (>90%) for both humic acid (HA) and tannic acid (TA), while maintaining low salt rejection (<13.0%) for various inorganic salts (Na 2 SO 4 , MgSO 4 , MgCl 2 , CaCl 2 , and NaCl). Furthermore, the membrane exhibited superior antifouling performance, with a flux recovery ratio (FRR) of 84.1% after three filtration-cleaning cycles using HA/CaCl 2 foulants, significantly outperforming the piperazine (PIP) control membrane (73.5%). Moreover, the membrane exhibited a low irreversible fouling tendency, enabling sustained operational performance through simple hydraulic cleaning cycles. Compared to the commercial NF270 membrane, the ANDSA-0.5 membrane achieved an approximately 5-fold higher water permeability, along with enhanced antifouling properties and superior NOM/mineral ions selectivity, offering a novel strategy for fabricating high-performance LNF membranes.