The role of ion‐membrane interactions in fast and selective mono/multivalent ion separation with hierarchical nanochannels

Abstract Precise control over the nanofluid behavior of polyelectrolyte‐based membranes is a primary step toward understanding the structure‐morphology‐property relationships to ultimately determine the mass transfer characteristics. In this study, a high‐performance multistacked polyelectrolyte‐based cation exchange membrane (CEM) with a heterogeneous structure and versatile surface chemistry was developed to achieve selective ion conductance. The self‐assembled CEM can facilitate ion permeation with fluxes of 2.9 mol m −2 h −1 for K + and 0.22 mol m −2 h −1 for Mg 2+ , reaching a mono/multivalent ionic selectivity of up to 13, outperforming mono/divalent fractionation when compared with state‐of‐the‐art membranes. Molecular dynamic (MD) simulations illustrated the ionic transport trajectory in hierarchical channels with angstrom‐scale cavities using multilayered CEMs. Both the experimental measurements and theoretical simulations indicated that ionic fractionation was associated with a large disparity in the energy barrier between mono/multivalent cations, which was the primary origin of the differences in the ion dehydration‐rehydration processes in the angstrom‐confinement membrane ion channels.