Encircling Angstrom-Scale Channels with Three-Dimensional Network Charges for Enhancing Ion Separation

Membrane-based ion separation plays a critical role in applications ranging from lithium extraction and wastewater treatment to energy harvesting and bioseparation. The selectivity of ion separation, particularly through tailored charge interactions, is essential for optimizing efficiency and performance in these processes. Here, we discover that 3D network charges-encirclement endows angstrom-scale channels with remarkable ion separation selectivity. Such a unique concentric structure is created by bombarding commercial polyimide film with swift heavy ions, followed by UV treatment. The channel diameter is determined to be ∼7 Å, and the K⁺/Mg²⁺ selectivity reaches up to 1.2 × 10⁵ in single-salt solutions and 1.8 × 10³ in binary-salt solutions, outperforming most state-of-the-art channels. Characterizations and simulations reveal that the 3D configuration of network charges minimizes localized interactions and establishes a more homogeneous electric field, which promotes monovalent ion transport while preserving high barriers for multivalent ions. These findings provide new insights into membrane design for next-generation high-precision ion separation.