Putting an ultrahigh concentration of amine groups into a metal-organic framework for CO capture at low pressures

Tremendous efforts have been devoted to increasing the CO 2 capture performance of porous materials, especially for low CO 2 concentration environments. Here, we report that hydrazine can be used as a diamine short enough to functionalize the small-pore metal-organic framework [Mg 2 (dobdc)] (H 4 dobdc = 2,5-dihydroxyl-1,4-benzenedicarboxylic acid). By virtue of the ultrahigh concentration of free amine groups (6.01 mmol g −1 or 7.08 mmol cm −3 ) capable of reversible carbamic acid formation, the new material [Mg 2 (dobdc)(N 2 H 4 ) 1.8 ] achieves a series of new records for CO 2 capture, such as single-component isotherm uptakes of 3.89 mmol g −1 or 4.58 mmol cm −3 at the atmospheric CO 2 concentration of 0.4 mbar at 298 K and 1.04 mmol g −1 or 1.22 mmol cm −3 at 328 K, as well as more than a 4.2 mmol g −1 or 4.9 mmol cm −3 adsorption/desorption working capacity under dynamic mixed-gas conditions with CO 2 concentrations similar to those in flue gases and ambient air. Hydrazine can be grafted in CPO-27-Mg/MOF-74-Mg to provide an ultrahigh concentration of amine groups on the pore surface, giving an exceptionally high CO 2 capture performance, especially at extremely low pressures.