Strong and Reversible Binding of Carbon Dioxide in a Green Metal–Organic Framework

Abstract

The efficient capture and storage of gaseous CO(2) is a pressing environmental problem. Although porous metal-organic frameworks (MOFs) have been shown to be very effective at adsorbing CO(2) selectively by dint of dipole-quadruple interactions and/or ligation to open metal sites, the gas is not usually trapped covalently. Furthermore, the vast majority of these MOFs are fabricated from nonrenewable materials, often in the presence of harmful solvents, most of which are derived from petrochemical sources. Herein we report the highly selective adsorption of CO(2) by CD-MOF-2, a recently described green MOF consisting of the renewable cyclic oligosaccharide γ-cyclodextrin and RbOH, by what is believed to be reversible carbon fixation involving carbonate formation and decomposition at room temperature. The process was monitored by solid-state (13)C NMR spectroscopy as well as colorimetrically after a pH indicator was incorporated into CD-MOF-2 to signal the formation of carbonic acid functions within the nanoporous extended framework.

Designed amyloid fibers as materials for selective carbon dioxide capture

“…2A). The steep initial increase at very low carbon dioxide pressure (<5 Torr) indicates a strong interaction between carbon dioxide and the material (9). After the steep slope region (>10 Torr), the carbon dioxide uptake increases gradually with an increase of pressure, which is similar to typical carbon dioxide physisorption process, and the uptake at 800 Torr reaches 40 cm 3 ·g −1 .…”

“…More importantly, because of the high heat capacity of aqueous MEA solutions, the energy required for MEA regeneration consumes roughly 30% of the energy output of the power plant (4,5). To overcome the high energy consumption for MEA regeneration, solid adsorbents such as zeolites, activated carbons, and metal-organic frameworks have been extensively exploited (4,(6)(7)(8)(9)(10). These classes of porous materials generally have high capacity and low energy cost for regeneration, but lose their efficiency when exposed to water vapor, as is the case in combustion gases (11,12).…”

Biologically derived metal organic frameworks

“…Inspired by weak nucleophilic functional groups, Stoddart et al found that CDMOF-2 had an atypically strong affinity between CO2 and the MOF indicative of a chemisorption process (see section 3.4 for structural details). [203] At low pressures, the selectivity for CO2 over CH4 was nearly 3000-fold. [203] The steep slopes in the isotherms suggest covalent bonding, which was confirmed by the abrupt transition in high pressure regimes (>1 Torr) which becomes more dependent on temperature (30% greater uptake at 273K vs 298K).…”

“…[203] At low pressures, the selectivity for CO2 over CH4 was nearly 3000-fold. [203] The steep slopes in the isotherms suggest covalent bonding, which was confirmed by the abrupt transition in high pressure regimes (>1 Torr) which becomes more dependent on temperature (30% greater uptake at 273K vs 298K). Therefore, at low pressures covalent bonding is preferential, giving way to physisorption at high pressures, with the change in mechanism occurring when the CO2 adsorbed by the MOF is approximately 23 cm 3 /g.…”

“…[168] Reversible CO2 capture in MOFs can occur in two ways: 1) CO2 binding to open metal sites, leading to materials with high selectivity for CO2, and 2) using weakly polar functional groups that bind CO2 by means of dipole interaction. [203] While both of these methods have their advantages and disadvantages, recycling CO2 has to be practical and not require more energy than necessary to regenerate the starting material. Inspired by weak nucleophilic functional groups, Stoddart et al found that CDMOF-2 had an atypically strong affinity between CO2 and the MOF indicative of a chemisorption process (see section 3.4 for structural details).…”