Ultrathin b-Oriented Co-Gallate MOF Membranes for Lithium Recovery: Precise Ion Sieving via Geometry-Confined Dehydration.

Selective K+ over Li+ separation is indispensable for lithium recovery from salt-lake brines, whereas simultaneous high-efficiency separation of K+ from interfering Na+ and Mg2+ cations remains challenging for pristine MOF membranes. Herein, an ultrathin b-oriented Co-gallate MOF membrane is fabricated using a gas-liquid interfacial soft-template approach. The membrane possesses 3D interconnected zigzag subnanochannels (≈3.7 Å) that impose geometry-confined ion dehydration, hindering the transport of Li+, Na+, and Mg2+ far more significantly than K+, as corroborated by molecular dynamics simulations. Under a concentration gradient driving force, the ub-CoG membrane achieves a prominent K+/Li+ selectivity of 13.5, as well as excellent K+/Na+ and K+/Mg2+ sieving capability. The recorded K+/Li+ selectivity stands as the highest value among MOF ion-sieving membranes. This interfacial orientation strategy provides a promising pathway to advanced ion-sieving membranes for multicomponent industrial brine lithium extraction.