Unveiling the role of post-treatment in thin-film composite nanofiltration membranes: Performance and mechanism

The deep role and mechanism of post-treatment in the morphology and performance of thin-film composite (TFC) nanofiltration (NF) membranes have rarely been revealed. In this work, four solutions of pure water, hexane, Na₂CO₃, and glycerol were selected for the post-treatment of TFC-NF membranes, and the performances of the resultant NF membranes were systematically investigated. The results showed that the hexane could effectively remove the residual acyl chloride groups and prevent the subsequent second growth of polyamide (PA) layers, thus leading to the formation of smoother and thinner PA membranes with higher water permeance and excellent salt rejections. Hydrolysis and swelling of unstable PA fragments in solutions (water, Na₂CO₃, and glycerin) contributed to greater negative charge, higher hydrophilicity, and enlarged pore size. The resultant NF membranes exhibited significantly enhanced water permeance and comparable separation behaviors to the control NF membrane. In addition, the well-constructed NF membranes possessed superior monovalent/multivalent ion selectivity, excellent antifouling, and stability. The mechanisms of the post-treatment on the performance enhancement of NF membranes were proposed from the perspective of interfacial interactions. The facile post-treatment strategy provides new insights into tailoring high-performance NF membranes for water treatment applications.