Constructing Angstrom-Level Ion Pocket Array in 1D Channel Wall for Efficient Lithium Ion Sieving

The rapid development of new energy industry is leading to the scarcity of lithium (Li) metal. Rational design of adsorbents for efficient separation of Li⁺ ion from aqueous media is pivotal to solve the recovery of this valuable resource. Current adsorbents generally suffer from the drawbacks in adsorption capacity, kinetics, and selectivity. Herein, a novel and ultra-stable metal–organic framework is designed for Li⁺ separation. The dense oxygen atoms on the cambered wall of its 1D channel encircle to form angstrom-level tetrahedral ion pockets array, acting as the dominant adsorption sites. This rational distribution of the array avoids the pore blockage caused by the pre-adsorbed ions, thereby accelerating the diffusion of subsequent ions into the interior pore. Meanwhile, this tetrahedral pocket shows distinct electronegativity and strong chelation effect for Li⁺. Benefiting from these specifics, this adsorbent exhibits a record-breaking adsorption capacity for Li⁺ (76.1 mg g⁻¹) and short equilibrium time (30 min). Moreover, the selective adsorption of Li⁺ over Na⁺, K⁺, Ca²⁺, and Mg²⁺ is achieved due to the matched Li⁺ ion diameter with the pocket/channel sizes and lower energy barrier for dehydration. Thus, this work proposes a feasible strategy for the construction of novel MOFs for ions adsorption.