Two new metal-organic frameworks, M 2(dobpdc) (M = Zn (1), Mg (2); dobpdc 4- = 4,4′-dioxido-3,3′-biphenyldicarboxylate), adopting an expanded MOF-74 structure type, were synthesized via solvothermal and microwave methods. Coordinatively unsaturated Mg 2+ cations lining the 18.4-Å-diameter channels of 2 were functionalized with N,N′-dimethylethylenediamine (mmen) to afford Mg 2(dobpdc)(mmen) 1.6(H 2O) 0.4 (mmen-Mg 2(dobpdc)). This compound displays an exceptional capacity for CO 2 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 CO 2 from air, and 3.14 mmol/g (12.1 wt %) at 0.15 bar and 40 °C, conditions relevant to CO 2 capture from flue gas. Dynamic gas adsorption/desorption cycling experiments demonstrate that mmen-Mg 2(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 CO 2 in simulated air at 25 °C and 2.52 mmol/g (9.9 wt %) after 15 min of exposure to flowing 15% CO 2 in N 2 at 40 °C. The purity of the CO 2 removed from dry air and flue gas in these processes was estimated to be 96% and 98%, respectively. As a flue gas adsorbent, the regeneration energy was estimated through differential scanning calorimetry experiments to be 2.34 MJ/kg CO 2 adsorbed. Overall, the performance characteristics of mmen-Mg 2(dobpdc) indicate it to be an exceptional new adsorbent for CO 2 capture, comparing favorably with both amine-grafted silicas and aqueous amine solutions.
ASJC Scopus subject areas
- Colloid and Surface Chemistry