Facile synthesis of nanofiltration membrane with asymmetric selectivity towards enhanced water recovery for groundwater remediation

Groundwater remediation by nanofiltration (NF) membrane is still hindered by low water recovery due to membrane scaling. In this study, a simple NaOH-promoted interfacial polymerization strategy was proposed to tailor the membrane asymmetric selectivity of calcium over sulfate ions to reduce scaling potential towards high water recovery. A 0.5 wt% NaOH was introduced during the interfacial polymerization of piperazine (PIP) and trimesoyl chloride on a polysulfone support. The promoted interfacial polymerization reduced polyamide defects for better rejection and enabled the use of lower PIP concentrations. Enhanced hydrolysis of the polyamide layer created a more negatively charged surface with larger pore sizes to achieve asymmetrical selectivity together with enhanced permeance. The water permeance of fabricated TFC-0.1 membrane with the aid of NaOH was 2.1 times that of commercial NF270 membrane, while exhibiting comparable perfluorooctanesulfonic acid rejections (>95%). This membrane also achieved ∼50% more water recovery than that of NF270 membrane under simulated gypsum scaling condition, owing to the selective passage of calcium (low rejection of 11.4 ± 0.6%). The exemplified strategy of NaOH-promoted interfacial polymerization is facile and readily scalable, which demonstrated strong potential towards high water recovery in groundwater remediation contaminated by emerging pollutants.