Tailoring charged nanochannels in covalent organic framework membranes for efficient lithium recovery

Efficient and selective extraction of Li⁺ from mixed-ion solutions is critical for sustainable lithium recovery but remains challenging owing to the similar physicochemical properties of coexisting metal cations. In this work, two-dimensional covalent organic framework (COF) membranes with tailor-made charged nanochannels were developed via a dual-activated interfacial polymerization strategy. The resulting membranes possess continuous, defect-free structures with ordered crystalline nanochannels within a stacked layered COF framework densely functionalized with -SO₃H groups. Benefiting from the difference in affinity of Li⁺, Co²⁺, Mn²⁺ and Ni²⁺ with the functional sulfonated groups, combined with the narrowly defined framework pore sizes, the obtained anionic COF membrane can achieve a high Li⁺/M²⁺ selectivity up to 29.5 in simulated spent battery leachates. Moreover, the COF membranes exhibit robust thermal stability and maintain performance over multiple cycles. This work demonstrates a rational design of charged nanochannel membranes for high-efficiency ion sieving, offering a promising route toward selective lithium recovery from complex mixed-salt solutions.