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 Mg 2+ 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 Mg 2+ far more significantly than K + , as corroborated by molecular dynamics simulations. Under a concentration gradient driving force, the u b ‐CoG membrane achieves a prominent K + /Li + selectivity of 13.5, as well as excellent K + /Na + and K + /Mg 2+ 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.