Reconfiguring hydration shells by rigidly confined interaction within graphene oxide membranes for ultra-efficient anion separation

The understanding of anion transporting behaviors under sub-nanoconfined regimes can guide the design of high-performance anion selective membranes (ASMs), yet it is little known. Here, we build membrane channels that combine physical rigidity with chemical affinity to anions simply through bridging graphene oxide nanosheets with charged linkers. We observe that the rigidly confined interaction imposed by channels to anions can reconfigure hydration shells in varying degrees for different anions via compensating for hydration-induced energy barriers and differentiating their rearrangement behaviors. During the configuration evolution, water molecules within hydration shells would rotate and simultaneously change their distance from the ion center. Based on the big discrepancy in configuration evolution, these membranes can realize ultrahigh selectivity of, for example, 125 for Cl−/SO42− and surpass the performance upper bound concerning Cl−/SO42− separation by other membranes. The knowledge of the configuration change of hydration shells during the dehydration process will be key to designing next-generation ASMs.