Quinone Reduction in Ionic Liquids for Electrochemical CO₂ Separation

We report the redox activity of quinone materials, in the presence of ionic liquids, with the ability to bind reversibly to CO₂. The reduction potential at which 1,4-naphthoquinone transforms to the quinone dianion depends on the strength of the hydrogen-bonding characteristics of the ionic liquid solvent; under CO₂, this transformation occurs at much lower potentials than in a CO₂-inert environment. In the absence of CO₂, two consecutive reduction steps are required to form first the radical anion and then the dianion, but with the quinones considered here, a single two-electron wave reduction with simultaneous binding of CO₂ occurs. In particular, the 1,4-napthoquinone and 1-ethyl-3-methylimidazolium tricyanomethanide, [emim]­[tcm], system reported here shows a higher quinone solubility (0.6 and 1.9 mol·L^–1 at 22 and 60 °C, respectively) compared to other ionic liquids and most common solvents. The high polarity determined through the Kamlet–Taft parameters for [emim]­[tcm] explains the measured solubility of quinone. The achieved high quinone solubility enables effective CO₂ separation from the dilute gas mixture that is contact with the cathode by overcoming back-diffusive transport of CO₂ from the anodic side

Alkali Metal Nitrate-Promoted High-Capacity MgO Adsorbents for Regenerable CO₂ Capture at Moderate Temperatures

Regenerable high capacity CO₂ sorbents are desirable for the establishment of widespread carbon capture and storage (CCS) systems to reduce global CO₂ emissions. We report on the marked effects of molten alkali metal nitrates on CO₂ uptake by MgO particles and their impact on the development of highly regenerable CO₂ adsorbents with high capacity (>10.2 mmol g^–1) at moderate temperatures (∼300 °C) under ambient pressure. The molten alkali metal nitrates are shown to prevent the formation of a rigid, CO₂-impermeable, unidentate carbonate layer on the surfaces of MgO particles and promote the rapid generation of carbonate ions to allow the high rate of CO₂ uptake

Postsynthetic Functionalization of Mg-MOF-74 with Tetraethylenepentamine: Structural Characterization and Enhanced CO₂ Adsorption

Postsynthetic functionalization of magnesium 2,5-dihydroxyterephthalate (Mg-MOF-74) with tetraethylenepentamine (TEPA) resulted in improved CO₂ adsorption performance under dry and humid conditions. XPS, elemental analysis, and neutron powder diffraction studies indicated that TEPA was incorporated throughout the MOF particle, although it coordinated preferentially with the unsaturated metal sites located in the immediate proximity to the surface. Neutron and X-ray powder diffraction analyses showed that the MOF structure was preserved after amine incorporation, with slight changes in the lattice parameters. The adsorption capacity of the functionalized amino-Mg-MOF-74 (TEPA-MOF) for CO₂ was as high as 26.9 wt % versus 23.4 wt % for the original MOF due to the extra binding sites provided by the multiunit amines. The degree of functionalization with the amines was found to be important in enhancing CO₂ adsorption, as the optimal surface coverage improved performance and stability under both pure CO₂ and CO₂/H₂O coadsorption, and with partially saturated surface coverage, optimal CO₂ capacity could be achieved under both wet and dry conditions by a synergistic binding of CO₂ to the amines as well as metal centers