• • Mg2+ permeation rate drops from 3.16 × 10−3 to 3.2 × 10−5 mol m−2 h−1 (two orders of magnitude) upon adding 0.2 M KCl, demonstrating reversible ion-pairing-based gating with industrial relevance for selective ion recovery.
• • The MLM–γ-PGA membrane maintains structural integrity after prolonged salt exposure, indicating robust stability for continuous operation in harsh feed streams.
• • The membrane achieves K+/Mg2+ selectivity rivalling leading ion-separation membranes, as benchmarked in Fig. 1k, offering a competitive alternative for lithium/magnesium separation in brine processing.
• • Dynamic manipulation of ion-ion interactions via external ionic stimuli enables reversible modulation of Mg2+ permeation over multiple cycles, providing a tunable separation mechanism without membrane modification.