Fine‐Tuning of the Carbon Dioxide Capture Capability of Diamine‐Grafted Metal–Organic Framework Adsorbents Through Amine Functionalization

Abstract

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.

Diamine-Functionalization of a Metal-Organic Framework Adsorbent for Superb Carbon Dioxide Adsorption and Desorption Properties

“…The adsorption rates (7.83 wt % min −1 for 1 ‐een and 5.6 wt % min −1 for 1 ‐ipen) in the humid streams were faster than that (6.34 wt % min −1 for 1 ‐een and 2.9 wt % min −1 for 1 ‐ipen) under dry conditions. The CO 2 adsorption rate (7.83 wt % min −1 ) of 1 ‐een with the ethyl side group under wet conditions is greater than that of 1 ‐ipen with the bulkier isopropyl group and comparable to that of primary–primary diamine‐functionalized Mg 2 (dobpdc) systems . It appears that the water vapor in the mixed gas stream facilitated the CO 2 adsorption rate and amount, which was also found in the functionalized materials .…”

“…These results are consistent with amine‐containing mesoporous silica, the CO 2 capacities of which in the humid stream were higher than those in the dry stream . Notably, the adsorption capacity of 1 ‐een is significant and comparable to that of the best‐performing MOF materials …”

“…In addition, Mg 2 (dobpdc) functionalized with a primary–tertiary diamine showed a high working capacity and a low adsorption at low CO 2 loadings . The presence of the side group on the ethylene link of a diamine increased the adsorption capacity at low CO 2 pressures, and a high working capacity was maintained . In addition, a family of Mg 2 (dobpdc) appended with a comprehensive diamine library was reported recently, which reveals the extensive understanding of the thermodynamics upon CO 2 adsorption onto MOF adsorbents .…”

“…Indeed, under the TSA protocol (adsorption at 40 °C and 15 % CO 2 , desorption at 130 °C and 100 % CO 2 ), the grafting of a diamine (primary–primary or secondary–secondary) afforded a low working capacity and a high adsorption at low CO 2 concentrations, although the CO 2 adsorption behaviors relied on the adsorption and desorption temperatures . In addition, Mg 2 (dobpdc) functionalized with a primary–tertiary diamine showed a high working capacity and a low adsorption at low CO 2 loadings . The presence of the side group on the ethylene link of a diamine increased the adsorption capacity at low CO 2 pressures, and a high working capacity was maintained .…”

Kinetics of cooperative CO2 adsorption in diamine-appended variants of the metal–organic framework Mg2(dobpdc)

“…[16][17][18][19][20]22 Additionally, the high internal surface areas accessible with metal-organic frameworks can allow for rapid diffusion of CO 2 through the pores. 23 Diamine-appended variants of the metal-organic framework Mg 2 (dobpdc) [24][25][26][27][28][29][30][31] (dobpdc 4À ¼ 4,4 0 -dioxidobiphenyl-3,3 0 -dicarboxylate) represent a particularly promising class of aminefunctionalized frameworks, as they readily adsorb CO 2 through a chemically-specic, cooperative mechanism ( Fig. 1).…”