Citation

Jincheng Ding, Huiqing Wu*, and Peiyi Wu*. Zwitterionic conjoined-network enables loose nanofiltration membrane with ultrahigh dye/salt selectivity. Sep. Purif. Technol. 2026, 380, 135341.

Abstract

Loose nanofiltration (LNF) membranes with high permeability and precise dye/salt selectivity are critically needed for textile wastewater treatment, yet achieving low salt rejection especially for divalent ions remains challenging. We developed an innovative zwitterionic conjoined-network membrane through synergistic ionic complexation and metal-chelation among sulfonated polyethylenimine (SPEI), phytic acid (PA), and FeCl3, forming a tunable permselective layer. The zwitterionic groups of SPEI enabled rapid water/ion transport while minimizing electrostatic interactions in the loosely structured membrane. Meanwhile, PA’s multidentate phosphate groups and Fe3+-mediated chelation created a robust crosslinked network, enhancing structural stability and sieving performance. The optimized membrane achieved exceptional pure water permeance (53.5 L·m−2·h−1·bar−1) and near-complete dye rejection (>99 % for Victoria blue B and Congo red), while maintaining ultralow salt rejection (Na2SO4: 2.1 %; NaCl: 1.6 %). Its Congo red/Na2SO4 selectivity reached 47.2, surpassing most reported LNF membranes. The membrane also demonstrated superior permeability and dye/salt separation in mixed feeds, along with long-term stability and antifouling performance. This work provides a strategic approach to designing high-performance LNF membranes.