Vertically Aligned Sub-Nanometer Channel Arrays Endow Chemically Robust PBI Membranes with High Ion Sieving Selectivity

Precise ion separation under chemically aggressive conditions remains a major challenge in membrane science. Here, we directly construct vertically aligned and structurally uniform sub-nanometer channels within chemically robust polybenzimidazole (PBI) membranes using a scalable track-UV method. These straight-through channels are embedded throughout the PBI matrix, providing well-defined pathways for ion transport while preserving the intrinsic durability of the polymer. These straight, through-pore channels reduce transport resistance and facilitate rapid monovalent ion transport. By precisely tuning the UV exposure time, highly uniform channel diameters in the narrow range of 6.2–7.2 Å are achieved, enabling effective size-based exclusion of multivalent ions. Simultaneously, negatively charged channel walls electrostatically attract monovalent cations, enhancing selectivity. This synergistic effect of spatial confinement and surface charge regulation enables high-performance ion sieving. Under binary-salt conditions, the membranes achieve K+/Mg2+ and Li+/Mg2+ selectivities of 1126 and 1402, with K+ and Li+ fluxes of 1.11 × 10–1 and 5.07 × 10–2 mol h–1 m–2, respectively. Even under strongly acidic conditions (pH = 1), the membranes maintain effective ion sieving, achieving a Li+/Mg2+ selectivity of 293. Notably, their ion transport performance remains substantially unchanged after extended exposure to strong acidic and alkaline environments, underscoring their outstanding chemical stability. This work presents a structurally and chemically tunable membrane platform for efficient ion separation, offering strong potential for lithium recovery and water treatment in harsh environments.