Fine-Tuning of the Carbon Dioxide Capture Capability of Diamine-Grafted Metal–Organic Framework Adsorbents Through Amine Functionalization

A combined sonication and microwave irradiation procedure provides the most effective functionalization of ethylenediamine (en) and branched primary diamines of 1-methylethylenediamine (men) and 1,1-dimethylethylenediamine (den) onto the open metal sites of Mg₂(dobpdc) (1). The CO₂capacities of the advanced adsorbents 1-en and 1-men under simulated flue gas conditions are 19 wt % and 17.4 wt %, respectively, which are the highest values reported among amine-functionalized metal-organic frameworks (MOFs) to date. Moreover, 1-den exhibits both a significant working capacity (12.2 wt %) and superb CO₂uptake (11 wt %) at 3 % CO₂. Additionally, this framework showcases the superior recyclability; ultrahigh stability after exposure to O₂, moisture, and SO₂; and exceptional CO₂adsorption capacity under humid conditions, which are unprecedented among MOFs. We also elucidate that the performance of CO₂adsorption can be controlled by the structure of the diamine ligands grafted such as the number of amine end groups or the presence of side groups, which provides the first systematic and comprehensive demonstration of fine-tuning of CO₂uptake capability using different amines.