A prebiotic chemistry inspired one-step functionalization of zwitterionic nanofiltration membranes for efficient molecular separation

Loose nanofiltration (LNF) membranes have shown promises in achieving efficient separation on molecular level at relatively low pressure. In this study, a zwitterionic PES/AMN/PSBAE LNF membrane was designed by co-depositing the AMN and an in-house made zwitterionic copolymer of poly(sulfobetaine methacrylate-co-2-aminoethyl methacrylate hydrochloride) (PSBAE), in which a bio-inspired molecule aminomalononitrile (AMN) with prebiotic chemistry was used to replace the commonly applied polydopamine for rapid membrane coating, significantly reducing the surface modification time from more than 20 h to less than 1 h. The AMN-based LNF, namely PES/AMN/PSBAE membrane, was demonstrated in the separation of dye/salt from synthetic textile wastewater, exhibiting superior performance with a high water permeance of 62.9 LMH bar⁻¹ and nearly complete dye/salt fractionation, i.e., simultaneously a high rejection of all dyes tested up to 99.9% and almost complete transport of salts. Combining with material and membrane characterization, the separation performance of the membrane was evaluated, demonstrating the advantages of the prebiotic chemistry coating and zwitterionic functionality. This study provides a new and facile strategy based on the AMN chemistry for LNF membrane surface functionalization to achieve efficient molecular separation.