Bio-Inspired 2D Asymmetric Nanochannels for High-Resolution Li⁺/Mg²⁺ Separation

Extracting lithium from salt lake brines is crucial to achieve sustainable development of lithium resources. However, it remains a major challenge to design nanochannels with efficient selectivity and fast transport for target ions. Here, inspired by biological membranes, we reported a Janus graphene oxide membrane (JGOM) with an asymmetric structure that exhibits diode-like ion transport behavior and achieves high-efficiency Li⁺/Mg²⁺ separation for lithium extraction applications. During the forward transport of ions, the nGO nanochannels modified by sulfonate groups (SO₃ ^-) with precise size provide hopping recognition sites and additional electrostatic attraction for the fast transport of Li⁺, while imposed Mg²⁺ dehydration and exposure to a stronger positive charge. The continuous pGO nanochannels modified by amino groups (NH₃ ⁺) further prevent the passage of dehydrated Mg²⁺ by enhanced electrostatic repulsion while allowing Li⁺ to transfer. Under the synergy of the two nanochannels, the JGOM demonstrates robust Li⁺/Mg²⁺ separation performance, outperforming symmetrical structure GO membranes and other reported membranes, which was further confirmed by simulation results. This study provides a new insight into the rational design of ion sieving membranes.