Covalently Grafting of Ethylenediamine onto a 2D Sub-stoichiometric COF for Enhanced CO2/N2 Separation†

Abstract

The post-synthetic modification of two-dimensional sub-stoichiometric covalent organic frameworks (COFs) for gas separation, particularly for the efficient removal of CO₂ from CO₂/N₂ mixtures, is an area of growing interest yet remains relatively unexplored. In this study, we report the precise tuning of functional groups in sub-stoichiometric COFs to enhance CO₂ capture performance. A sub-stoichiometric COF with free aldehyde groups (HPCOF) was designed and synthesized, followed by covalent modification via ethylenediamine (EDA) grafting, yielding HPCOF-EDA. This post-modification strategy significantly increased CO₂ adsorption capacity (55.7 cm³·g^–1 at 298 K and 1 bar) and CO₂/N₂ selectivity (58), primarily attributed to the formation of additional N—H···O interactions. These findings demonstrate the potential of functional engineering to broaden the application prospects of sub-stoichiometric COFs in gas adsorption and separation technologies.