Lithium complexing strategy based on host-guest recognition for efficient Mg2+/Li+ separation

Ion selective membranes with precise Mg 2+ /Li + separation have attracted extensive interest in lithium extraction to circumvent the lithium supply shortage. However, realizing this target remains a significant challenge mainly due to a high concentration ratio of Mg 2+ /Li + as well as the relatively close ionic hydration radius and chemical. Herein, inspired by the host-guest recognition between alkali-metal ions and crown ether (CE), a novel approach was proposed to regulate the membrane internal structure by introducing CE to strengthen the complexation between Li + and CE. The CE modified membranes achieved the unique outcome of “Li + rejection-Mg 2+ permeation” deriving from enhanced solubility ( K S ) and retarded diffusivity ( D S ) of Li + compared to that of Mg 2+ . The Mg 2+ /Li + separation factors for MgSO 4 /Li 2 SO 4 and MgCl 2 /LiCl of modified membranes ( i.e., 20.1 and 17.7) are about 21.9 and 19.9 time higher than that of pristine membranes, respectively. The results from density function theory (DFT) indicated that the stronger host-guest interaction between CE and Li + combined them closely, thereby increasing solubility and reducing diffusivity of Li + . Our findings develop a new efficient membrane-based strategy enabling the production of high-purity lithium salts from simulated brine.