The amine functionalized material 1-dmen shows a record high working capacity for CO2 capture at low regeneration temperatures compared with other MOFs. Furthermore, this performance is maintained upon exposure to humidity.

A combined sonication and microwave irradiation procedure provides the most effective functionalization of ethylenediamine (en) and branched primary diamines of 1-methylethylenediamine (men) and 1,1-dimethylethylenediamine (den) onto the open metal sites of Mg (dobpdc) (1). The CO capacities of the advanced adsorbents 1-en and 1-men under simulated flue gas conditions are 19 wt % and 17.4 wt %, respectively, which are the highest values reported among amine-functionalized metal-organic frameworks (MOFs) to date. Moreover, 1-den exhibits both a significant working capacity (12.2 wt %) and superb CO uptake (11 wt %) at 3 % CO . Additionally, this framework showcases the superior recyclability; ultrahigh stability after exposure to O , moisture, and SO ; and exceptional CO adsorption capacity under humid conditions, which are unprecedented among MOFs. We also elucidate that the performance of CO adsorption can be controlled by the structure of the diamine ligands grafted such as the number of amine end groups or the presence of side groups, which provides the first systematic and comprehensive demonstration of fine-tuning of CO uptake capability using different amines.

Eutectic mixtures of alkali nitrates are known to increase the sorption capacity and kinetics of MgO-based sorbents. Underlying principles and mechanisms for CO capture on such sorbents have already been established; however, real-time observation of the system was not yet accomplished. In this work, we present the direct-observation of the CO capture phenomenon on a KNO-LiNO eutectic mixture (EM)-promoted MgO sample, denoted as KLM, via in situ transmission electron microscopy (in situ TEM). Results revealed that the pseudoliquid EM undergoes structural rearrangement as MgCO evolves from the surface of MgO, resulting in surface roughening and evolution of cloudy structures that stay finely distributed after regeneration. From this, we propose a nucleation and structural rearrangement scheme for MgCO and EM, which involves the rearrangement of bulk EM to evenly distributed EM clusters due to MgCO saturation as adsorption proceeds. We also conducted studies on the interface between EM over solid MgO and MgCO formed during sorption, which further clarifies the interaction between MgO and EM. This study provides better insight into the sorption and regeneration mechanism, as well as the structural rearrangements involved in EM-promoted sorbents by basing not only on intrinsic evolutions but also on real-time observation of the system as a whole.

A porous Mg 2 (dondc) framework (H 4 dondc ¼ 1,5-dioxido-2,6-naphthalenedicarboxylic acid) with open metal sites was prepared and functionalized with primary or secondary diamines (en ¼ ethylenediamine, mmen ¼ N,N 0 -dimethylethylenediamine, or ppz ¼ piperazine). The CO 2 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 CO 2 adsorption mechanism is based on the combination of physisorption and chemisorption. The CO 2 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 CO 2 over N 2 were evident in 1-ppz. Such exceptional CO 2 uptake and CO 2 /N 2 selectivity of diaminefunctionalized materials hold potential promise for post-combustion CO 2 capture applications.