Homodiamine-functionalized metal-organic frameworks with a MOF-74-type extended structure for superior selectivity of CO2 over N-2

Abstract

A porous Mg-2(dondc) framework (H(4)dondc = 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 N-2 were evident in 1-ppz. Such exceptional CO2 uptake and CO2/N-2 selectivity of diamine-unctionalized materials hold potential promise for post-combustion CO2 capture applications.