Process optimization of deep eutectic solvent mediated interfacial polymerization for high performance nanofiltration membranes

Thin film composite (TFC) membranes fabricated via interfacial polymerization (IP) are widely used in nanofiltration (NF) and reverse osmosis (RO), but conventional fabrication commonly relies on volatile organic solvents such as hexane. In this study, a hydrophobic deep eutectic solvent (DES) composed of DL-menthol and lauric acid was used as the organic phase for DES-mediated IP, and the effects of IP reaction time, thermal curing, acetone rinsing, and DES reuse on polyamide (PA) layer formation and membrane performance were systematically investigated. The results show that PA selective layer formation can be achieved in the DES medium even at short reaction times, with the optimized condition of 60 s IP and 60 °C curing providing the best balance between water permeance and solute rejection. After a brief 15 s acetone rinse, the optimized membrane exhibited a pure water permeance of 45 L·m⁻ 2 ·h⁻ 1 ·bar⁻ 1 , with 96% methylene blue rejection, 84% NaCl rejection, and 97% MgSO 4 rejection. Acetone rinsing significantly improved surface hydrophilicity and antifouling behavior, likely by removing loosely bound surface residues and residual DES. However, prolonged rinsing reduced NaCl rejection, highlighting the importance of controlling post-treatment duration. Recycled DES retained membrane forming ability over multiple fabrication cycles, although modest changes in performance suggest the need for further optimization of solvent recovery and reuse. Overall, this work demonstrates that careful optimization of DES-mediated IP parameters can provide a promising route toward safer and more sustainable fabrication of high performance TFC nanofiltration membranes.