Crown Ether Confined in a 2D MXene Membrane for Mono-/Divalent Ion Separation

Mono-/divalent ion separation is a key and challenging industrial process. Two-dimensional (2D) material membranes are promising for molecular separation, while it remains a grand challenge to achieve high ion separation performance owing to the undesirable nanochannel microenvironment and small size difference of ions. Herein, we reported on the construction of the crown ether confined 2D MXene membrane for mono-/divalent ion separation. The introduction of crown ether finely tuned the interlayer spacing that facilitates ion dehydration and significantly enhanced the affinity toward monovalent ions. The resulting membrane exhibits a high monovalent ion permeation rate (0.85 mol·m^–2·h^–1 for K⁺ and 0.81 mol·m^–2·h^–1 for Li⁺) and mono-/divalent ion selectivity (39 for Li⁺/Mg²⁺ and 40.2 for K⁺/Mg²⁺). This performance is superior to the limits for the state-of-the-art membranes, showing great potential for ion separation.