An isoporous ion exchange membrane for selective Na+ transport

Biological sodium channels have selectivity filters with extraordinary Na+ selectivity. Realizing this function in ion exchange membranes is highly desirable for technologies related to water, energy, and the environment, but it remains a challenge. Here we report a sodium selective isoporous membrane (NaSIM) derived from lyotropic liquid crystals. This membrane consists of uniform ion conductive channels lined with carboxylate groups. These negatively charged ion channels demonstrate charge-governed ion transport, pH responsiveness, and Na+ selectivity. The Na+ selectivity was 1.88 against K+ as revealed from single ion permeation experiment and approached 2.10 in binary salt solutions. The prominent Na+ selectivity may arise from specific interactions between Na+ ions and the carboxylate groups inside the channels, which regulate the energy barriers for monovalent cation transfer. The NaSIM we developed may promote high-precision separation and provides a cornerstone for designing a new generation of ion selective membranes.