Amine-Functionalized Quasi-MOF for Direct Air Capture of CO₂

Direct air capture of CO 2 from ambient air conditions remains a huge challenge due to the strongly competitive adsorption of water and low CO 2 pressure. Here, we successfully developed a class of amine-functionalized quasi-MOF (X-UIO-EDA) with high CO 2 capture capacity and found a water-assisted enhancement effect under 400 ppm of CO 2 in the presence of humidity. In the quasi X-UIO-EDA series, 2-UIO-EDA displays a CO 2 capture capacity of 0.44 mmol/g under humid air conditions, which is 10-fold that under dry air conditions, and exhibits lower CO 2 desorption energy under humid air conditions. The comparative experiments also demonstrated that quasi-UIO-66 provided more amine modification sites, leading to higher CO 2 capture capacity. The in situ FT-IR analysis demonstrated that water plays a crucial role in facilitating the transformation of −NHCOO – to – OCOOH species due to the steric hindrance and micropore confinement effects. Combining solid-state 13 C CP-MAS NMR and XPS measurements, we concluded that the observed enhancement of the CO 2 capture capacity under humid air conditions is due to the formation of bicarbonate and hydronium carbamate species, along with the formation of weak hydrogen bonds between these species.