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

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.