Putting an ultrahigh concentration of amine groups into a metal-organic framework for CO2 capture at low pressures.

Tremendous efforts have been devoted to increasing the CO2 capture performance of porous materials, especially for low CO2 concentration environments. Here, we report that hydrazine can be used as a diamine short enough to functionalize the small-pore metal-organic framework [Mg2(dobdc)] (H4dobdc = 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 [Mg2(dobdc)(N2H4)1.8] achieves a series of new records for CO2 capture, such as single-component isotherm uptakes of 3.89 mmol g-1 or 4.58 mmol cm-3 at the atmospheric CO2 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 CO2 concentrations similar to those in flue gases and ambient air.