Hydration channel engineering in Tröger’s base-POP membranes for mono/multivalent cation and anion discrimination

Sustainable recovery of critical resources from complex aqueous streams is constrained by membranes that fail to combine rapid ion transport with precise mono/multivalent discrimination. Here, we report Tröger’s base-derived porous organic polymer (POP) membranes with rigid, covalently crosslinked microporous frameworks that stabilize angstrom-scale transport channels while suppressing hydration-induced swelling. These membranes render rapid monovalent-ion transport with near-complete exclusion of multivalent cations and anions, including Mg 2+ , Al 3+ , SO 4 2− , and PO 4 3− . Experiments and simulations show that steric confinement, dehydration penalties, and electrostatic interactions cooperatively raise migration barriers for multivalent ions in confined channels. The membranes achieve comprehensive mono/multivalent discrimination across both cationic and anionic systems. In multistage electrodialysis, they enable stage-amplified lithium enrichment from high-Mg brines with stable long-term operation and downstream recovery of crystalline Li 2 CO 3 . They also facilitate high-purity NaCl enrichment from simulated seawater. Overall, this platform offers a durable and energy-efficient route to selective resource recovery from complex aqueous streams.