Ionic liquid-enabled migration of the interfacial polymerization region toward substrate pore interiors for dye/salt separation membranes

Efficient separation of dyes and inorganic salts from dyeing wastewater is critical for achieving resource recovery from industrial effluents. Tight ultrafiltration (TUF) membranes, featuring selective dye retention and salt permeation, have shown great potential for wastewater treatment. However, conventional IP often suffers from rapid monomer diffusion and uncontrolled reaction-zone migration, causing excessive PA growth on membrane surfaces and limiting the permeability-selectivity balance. Herein, a molecular-feature-guided IP regulation strategy is proposed by introducing 1-butyl-3-methylimidazolium chloride (BMIC) to regulate TUF membrane formation. DFT calculations and MD simulations reveal that BMIC undergoes spontaneous dissociation, with released Cl – ions accelerating IP kinetics by reducing the reaction barrier, while its amphiphilic structure promotes TMC migration and shifts the IP reaction zone toward pore interiors. Structural characterization demonstrates that BMIC suppresses surface PA accumulation, optimizes pore size distribution, and enhances surface hydrophilicity and negative charge. At an optimized BMIC concentration of 5 wt.%, the TUF membrane achieves excellent dye/salt separation performance, with a water flux of 235.62 L m –2 h –1 , 99.83% CR rejection, 5.44% Na 2 SO 4 rejection, and a dye/salt selectivity factor of 18.35. Furthermore, the BMIC-modified membrane exhibits enhanced antifouling performance with an FRR of 84.33%. This work elucidates the molecular-level role of ionic liquids in regulating IP and provides a new strategy for constructing high-performance dye/salt separation membranes through rational molecular design.