Hexane Treatment to Facilely Tailor Polyamide Nanofiltration Membrane Performance: The Critical Role of Treatment Duration

Facile methods for simultaneously tailoring various properties of nanofiltration (NF) membranes are of great significance for fit-for-purpose membrane design and thus achieving more efficient NF applications. This study revealed that, when preparing polyamide (PA) thin-film composite (TFC) NF membranes, a simple hexane treatment right after the interfacial polymerization reaction could substantially alter membrane properties and enhance separation performance for drinking water treatment, with the degree particularly dependent on the treatment time even in the magnitude of tens of seconds. Hexane rinsing for 5 s could lead to a thinner active layer and achieve more improvement (>60%) of water permeance, while a more effective reduction (∼70%) of membrane surface negative charge density could be realized by hexane soaking for a prolonged time. These property variations rendered the hexane-treated membranes more competitive than representative commercial and lab-made conventional PA membranes for hardness removal. Moreover, the membrane rejection performance for organic micropollutants could be maintained after hexane treatments of varying durations due to the barely unaltered membrane pore sizes. The involved mechanisms include removal of loosely polymerized PA segments and unreacted monomers from the membrane surface and the provision of a solvent environment for the further cross-linking of residual monomers. This study provides a facile strategy and mechanistic insights for the development of TFC membranes with tailored properties for efficient drinking water treatment.