MXene membrane with directionally functionalized channel entrances for enhanced ion selectivity and permeability

while preserving high permeability for monovalent ion, thereby surpassing the selectivity-permeability trade-off limit of reported ion-separation membranes. Combined experiments and simulations reveal that alterations in ion transport pathways caused by differences in ion hydration structures within sub-nanochannels are the primary mechanism for ion separation. This mechanism contrasts with conventional interpretation that primarily attributes ion separation to differences in ion-molecule binding energies. This work establishes channel-entrance engineering as a useful strategy for the design of ion-separation membranes for mono-/divalent cation separation in brine upgrading and resource-recovery.