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.