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

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.