Mixed Counter-Ion Sorption in Ion-Exchange Membranes: Understanding the Role of Membrane Water Content

This research investigates the influence of membrane water content on counter-ion partitioning selectivity in ion-exchange membranes (IEMs) through synthesis and characterization of cation-exchange and anion-exchange membranes with varying water uptake while maintaining constant charge content. Differential scanning calorimetry distinguishes between freezable (free and weakly bound) and bound water states in membranes. Results demonstrate that water content significantly affects selectivity of anions through specific ion effects (kosmotropic versus chaotropic interactions), with applications in selective lithium extraction from brines, water softening for RO pretreatment, and removal of nitrate from groundwater. Membrane water content has minimal impact on CEM selectivity where electrostatic interactions dominate, providing design insights for tailored ion-separation membranes.