Imine‐Linked 3D Covalent Organic Framework Membrane Featuring Highly Charged Sub‐1 nm Channels for Exceptional Lithium‐Ion Sieving

Abstract Coupling ion exclusion and interaction screening within sub‐nanoconfinement channels in novel porous material membranes hold great potential to realize highly efficient ion sieving, particularly for high‐performance lithium‐ion extraction. Diverse kinds of advanced membranes have been previously reported to realize this goal but with moderate performance and complex operations gained. Herein, these issues are circumvented by preparing the consecutive and intact imine‐linked three‐dimensional covalent organic framework (i.e., COF‐300) membranes via a simple solvothermal approach and employing the intrinsically interconnected sub‐1 nm one‐dimensional channels for exceptional lithium‐ion sieving. The synthesized membranes with highly charged angstrom scale channels of ≈0.78 nm achieve an excellent Li⁺ permeance (0.123 mol m⁻² h⁻¹) with an ultrahigh Li⁺/Mg²⁺ of 36 in the binary system. The experimental measurement and theoretical calculation reveal that a channel size right exactly between Li⁺ and Mg²⁺ enables restricted Mg²⁺ penetration. Meanwhile, the ion affinity interaction screening with imine groups further strengthens the fast Li⁺ permeability but severely suppresses the Mg²⁺ passage. In particular, the synthesized three‐dimensional covalent organic framwork membranes also have a remarkable separation performance during a long‐term operation test without sacrificing trade‐off, demonstrating chemistry stability and mechanical integrity under the high‐salinity aqueous environment.