Crown ethers decorated metal–organic framework for selective lithium ion sieving

Selective adsorption of lithium ion from aqueous media is one of important routes to solve the scarcity and high cost problems of this valuable resource. Crown ethers (CE) as classical Li-oriented molecules are commonly loaded in solid matrixes to construct adsorbents. However, unreasonable selection of matrixes easily leads to low loading efficiency and inadequate exposure of CE sites, resulting in unsatisfactory performances. Herein, we designed a novel crown ether-decorated metal–organic framework (MOF-808-12C4E), via grafting carboxybenzo 12-crown-4-ether (CB-12C4E) molecules in a highly porous MOF-808 platform. Based on the rich exchangeable sites, dense 12C4E units (1.47 mmol g −1 ) were successfully introduced in the Zr nodes of MOF-808. Thanks to the large ion diffusion channel and dense active sites, MOF-808-12C4E shows a high adsorption capacity (30.4 mg g −1 ) and very short adsorption equilibrium time (15 min). Selective adsorption of Li + ion over Na + , K + , Ca 2+ , and Mg 2+ ions was achieved, due to the higher suitability of Li + ion diameter with the size of 12C4E hole. Based on experimental characterizations and theoretical calculations, we confirm the crucial contribution of 12C4E units for the selective adsorption behavior of Li + ion. Thus, our work provides an efficient adsorbent for selectively capturing Li + ion, and meanwhile proves the promising potentials of porous MOFs for grafting active crown ethers.