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

Comprehensive Summary The post‐synthetic modification of two‐dimensional sub‐stoichiometric covalent organic frameworks (COFs) for gas separation, particularly for the efficient removal of CO 2 from CO 2 /N 2 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 CO 2 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 CO 2 adsorption capacity (55.7 cm 3 ·g –1 at 298 K and 1 bar) and CO 2 /N 2 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.