Partitioning COF Membrane Channels into Ultramicroporous and π‐Electron‐Rich Compartments for Multicomponent Ion Separations

Abstract Covalent organic frameworks (COFs) build a versatile platform for constructing separation membranes, affording them disruptive candidates for nanoscale molecule/ion sieving. However, the reported aperture of COFs mainly concentrates on 0.8–10.0 nm, leaving a daunting challenge in fabrication of ultramicroporous (<0.7 nm) COF membranes. Herein, the channel partition of COF membranes is elaborately implemented by taking advantage of the copper‐catalyzed azide–alkyne cycloaddition (CuAAC) based on click chemistry. Two kinds of novel alkynyl COF membranes bearing symmetric alkynyl monomers are predesigned and synthesized. The alkynyl groups can react with dual‐azide molecules to form triazole ring bridge, which allows the partition of hexagonal or tetragonal channels. Moreover, the π‐electron‐rich structures of triazole ring offer cation‐philic or anion‐repulsive region, showing great potentials in precise ion separations. Consequently, the superior performance is obtained in separating ternary/binary ion mixtures: Li + /Mg 2+ /(K + ) and F − /SO 4 2− /(Cl − ). Example of dealing with a K + /Li + /Mg 2+ ternary mixture, the optimum p ‐TpPa‐C≡CH membrane exhibits an actual selectivity of 101.2 for K + /Mg 2+ and 30.9 for Li + /Mg 2+ . The strong adaptability and wide range of application scenarios of our COF membranes exceed the ever‐reported membranes. This work provides a fundamental to comprehending the channel manipulation mechanisms and advances the development of high‐performance ion separation membranes.