Capture of Carbon Dioxide from Air and Flue Gas in the Alkylamine-Appended Metal–Organic Framework mmen-Mg2(dobpdc)

Two new metal–organic frameworks, M2(dobpdc) (M = Zn (1), Mg (2); dobpdc4– = 4,4′-dioxido-3,3′-biphenyldicarboxylate), adopting an expanded MOF-74 structure type, were synthesized via solvothermal and microwave methods. Coordinatively unsaturated Mg2+ cations lining the 18.4-A-diameter channels of 2 were functionalized with N,N′-dimethylethylenediamine (mmen) to afford Mg2(dobpdc)(mmen)1.6(H2O)0.4 (mmen-Mg2(dobpdc)). This compound displays an exceptional capacity for CO2 adsorption at low pressures, taking up 2.0 mmol/g (8.1 wt %) at 0.39 mbar and 25 °C, conditions relevant to removal of CO2 from air, and 3.14 mmol/g (12.1 wt %) at 0.15 bar and 40 °C, conditions relevant to CO2 capture from flue gas. Dynamic gas adsorption/desorption cycling experiments demonstrate that mmen-Mg2(dobpdc) can be regenerated upon repeated exposures to simulated air and flue gas mixtures, with cycling capacities of 1.05 mmol/g (4.4 wt %) after 1 h of exposure to flowing 390 ppm CO2 in simulated air at 25 °C and 2.52 mmol/g (9...