Homodiamine-functionalized metal-organic frameworks with a MOF-74-type extended structure for superior selectivity of CO₂ over N₂

A porous Mg₂(dondc) framework (H₄dondc = 1,5-dioxido-2,6-naphthalenedicarboxylic acid) with open metal sites was prepared and functionalized with primary or secondary diamines (en = ethylenediamine, mmen = N,N′-dimethylethylenediamine, or ppz = piperazine). The CO₂ adsorption was substantial under post-combustion flue gas conditions as compared to other reported metal-organic frameworks. Interestingly, the IR spectroscopic measurements demonstrated that the CO₂ adsorption mechanism is based on the combination of physisorption and chemisorption. The CO₂ adsorption capacity of 1-mmen was greater than that of 1-en and 1-ppz, which can likely be attributed to the basicity of the free amine groups tethered to the open coordination sites. Ultrahigh selectivity and superior dynamic separation of CO₂ over N₂ were evident in 1-ppz. Such exceptional CO₂ uptake and CO₂/N₂ selectivity of diamine-functionalized materials hold potential promise for post-combustion CO₂ capture applications.