Spatial Size Manipulation of 1D/2D Channels in Covalent Organic Framework Membranes Through Dopamine Chemistry for Ion Separations

Abstract Covalent organic framework (COF) membranes feature with well‐developed 1D in‐plane pores and parallelly arranged 2D interlayer gallery, presenting promising platform for precise separations. However, it remains a formidable challenge to construct and regulate membrane channels at angstrom scale. Herein, pH‐sensitive dopamine is taken advantage to elaborately engineer the spatial size of 1D/2D channels in COF membranes for the separations of alkali metal ions. Acid treatment allows monomolecular dopamine to segment 1D in‐plane pores of COF membrane, achieving ultramicroporous regulation from 1.25 nm to 0.71 nm, which enables high selectivity of 18.7 for K + /Li + separation. Molecular dynamics simulations reveal the higher dehydration degree, weaker channel‐cation interaction and faster diffusion coefficient of K + than Li + . For alkaline treatment, dopamine self‐polymerizes to form nanoparticles between COF layers, which enlarges the 2D interlayer channels from 0.33 nm to 0.45 nm in COF membrane, enabling high‐permeance ion/molecule separations. The water permeance increases 86.7% to 404 L m −2 h −1 bar −1 , without the sacrifice of membrane sieving ability. Both cation separation and ion/molecule separation performances outperform the current state‐of‐the‐art membranes. This dopamine‐mediated channel engineering strategy may provide the new insights for the design of membrane channels in precise separations.