N-Oxide Zwitterionic-Based Antifouling Loose Nanofiltration Membranes with Superior Water Permeance and Effective Dye/Salt Separation

Loose nanofiltration (LNF) membranes with high permeance and separation selectivity are highly desired for the effective separation of organic dyes and inorganic salts. Herein, a novel polyamide LNF membrane was fabricated using zwitterionic amine reactant trimethylamine N-oxide-based polyethylenimine (TPEI) and trimesoyl chloride (TMC) via interfacial polymerization (IP). A thin, loose, and smooth polyamide layer was formed due to the low diffusion rate and modified chemical structure of TPEI. The optimized membrane (NF-TPEI) exhibited an extremely high water permeance of 213.0 L m^–2 h^–1 bar^–1, accompanied by outstanding dye rejections of Congo Red (99.8%), Coomassie Brilliant Blue R250 (99.5%), and Evans Blue (99.9%). Meanwhile, the membrane possessed low rejections (<7.0%) of inorganic salts (Na₂SO₄, MgSO₄, MgCl_2, and NaCl). Additionally, the NF-TPEI membrane exhibited outstanding antifouling performance, achieving a superior recovery ratio of 96.0 and 98.1% after the filtration of humic acid and sodium alginate solution, respectively. Compared to the commercial NF270 membrane, the NF-TPEI membrane exhibited significantly improved separation performance in terms of permeance and fouling resistance, which provided more possibilities for high-performance LNF membranes toward the treatment of wastewater with organic contaminants.