This research explores the ion-specific effects governing the charge and performance of a loose polyamide nanofiltration (NF) membrane. The study systematically evaluated the membrane's zeta potential under varying pH, salinity, and ionic composition, correlating this data with membrane performance. Results identify the pKa of carboxyl and amine groups, showing chloride anion adsorption increases negative charge. Monovalent cation effects on membrane charge are shown to vary due to differing sorption tendencies. The correlation between zeta potential and permeability highlights the significant contribution of solution ions to Donnan exclusion in NF membranes.

Rebecca S. Roth, Liat Birnhack, Mor Avidar, Elizabeth A. Hjelvik, Anthony P. Straub, Razi Epsztein