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

Facile methods for simultaneously tailoring various propertiesof nanofiltration (NF) membranes are of great significance for fit-for-purposemembrane design and thus achieving more efficient NF applications.This study revealed that, when preparing polyamide (PA) thin-filmcomposite (TFC) NF membranes, a simple hexane treatment right afterthe interfacial polymerization reaction could substantially altermembrane properties and enhance separation performance for drinkingwater treatment, with the degree particularly dependent on the treatmenttime even in the magnitude of tens of seconds. Hexane rinsing for5 s could lead to a thinner active layer and achieve more improvement(>60%) of water permeance, while a more effective reduction (& SIM;70%)of membrane surface negative charge density could be realized by hexanesoaking for a prolonged time. These property variations rendered thehexane-treated membranes more competitive than representative commercialand lab-made conventional PA membranes for hardness removal. Moreover,the membrane rejection performance for organic micropollutants couldbe maintained after hexane treatments of varying durations due tothe barely unaltered membrane pore sizes. The involved mechanismsinclude removal of loosely polymerized PA segments and unreacted monomersfrom the membrane surface and the provision of a solvent environmentfor the further cross-linking of residual monomers. This study providesa facile strategy and mechanistic insights for the development ofTFC membranes with tailored properties for efficient drinking watertreatment.