Bio-inspired construction of ion conductive pathway in covalent organic framework membranes for efficient lithium extraction

As the most sophisticated separation system, biological membranes have served as natural prototypes for the design of artificial membranes because they provide high permeability and solute selectivity, owing to the presence of specialized ion channels. However, developing stable and selective artificial ion channels remains a formidable challenge. Herein, we demonstrate the construction of lithium nanochannels in two-dimensional covalent organic frameworks (COFs) to create biomimetic membranes. Implanted lithiophilic oligoethers conferred specificity and facilitated Li⁺ diffusion along the pore pathway of the COF. The ion channel characteristics were indicated by reversal potential measurements, showing that the relative permeability decreased in the order Li⁺ > K⁺ > Na⁺ > Ca²⁺ > Mg²⁺. The Li⁺ transfer was enhanced, while other ions were obstructed, allowing for high selectivity and permeability. A Li⁺/Mg²⁺ separation factor of 64 was achieved, confirming high lithium affinity. This study may serve as a design principle to develop selective artificial membranes for effective ion separation.