Recyclable ionic liquid-Regulated interfacial Polymerization: A strategy for fabricating loose nanofiltration membranes with efficient dye/salt separation

The precise separation of dyes and inorganic salts in industrial dyeing wastewater is crucial for achieving efficient dye removal while recovering salt resources. Conventional nanofiltration membranes suffer from limitations due to their limited pore size tunability range. In this study, a novel polyamide (PA)-based loose nanofiltration (LNF) membrane was fabricated via interfacial polymerization (IP), with cyclen as the aqueous monomer, isophthaloyl chloride (IPC) as the organic monomer, and ionic liquid (IL) as the aqueous cosolvent. Characterizations and MD simulations demonstrate that IL decouples bulk and interfacial diffusion, enabling membrane pore size tuning. The IL-95 v/v% membrane featured a loose PA selective layer characterized by thin thickness, low cross-linking degree, and large pore sizes. It exhibited a high permeance of 26.9 LMH·bar −1 and excellent AB172 dye rejection (99.8%), while maintaining low rejection (<10.0%) for various inorganic salts, outperforming most currently reported LNF membranes. Notably, the IL can be efficiently recovered via salt-induced phase separation (SIPS) from the post-IP waste aqueous solution, realizing the cyclic reuse of IL and reducing the environmental impact and cost of the process. This work offers new avenues for the application of high-performance LNF membranes to separate organics and salts in organic pollutant-laden wastewater.