Structural and Chemical Engineering of Sub‐Nanochannel Membranes Toward Ion Selectivity

ABSTRACT Sub‐nanochannel membranes offer unique opportunities for achieving selective ion transport by integrating confined pore architectures with precisely engineered chemical functionalities. However, efficiently discriminating between mono‐ and divalent ions, and achieving single‐ion recognition, remains a challenge. This review summarizes recent advances in structural and chemical engineering of sub‐nanochannels for ion selectivity. We first introduce fundamental ion transport mechanisms within sub‐nanochannels. As the major part, the strategies to tune pore size, geometry, and surface functionalities, categorized into charge‐based groups, specific ion recognition groups, and hydrophilic bonding groups with raised the ion‐selective performance, have been summarized in detail. Beyond fundamental understanding and strategies, we highlight emerging neuromorphic applications that exploit ionic signal modulation. Finally, we discuss current challenges and future perspectives on rational design of ion‐selective membranes with precise mono‐/divalent and single‐ion selectivity.