Issue 46, 2022

CO2 capture from ambient air via crystallization with tetraalkylammonium hydroxides

Abstract

Aqueous solutions of a series of short carbon chain tetra(n-alkyl)ammonium hydroxides, [Nnnnn][OH] with n = 2: n-ethyl, 3: n-propyl, 4: n-butyl, have been serendipitously found to be potential candidates for direct air carbon capture (DAC) when being used as reagents in more complicated reactions. Aqueous solutions of [N3333][OH], [N2222][OH], or [N3333][OH] with UO2SO4·3H2O and 1,4-diamidoximylbenzene, and [N4444][OH] with cytosine (HCyt) directly absorb CO2 from the atmosphere upon mild heating in the open atmosphere crystallizing in complexes reaching up to 2 : 1 CO2/[Nnnnn]OH ratio. [N2222][HCO3]·3H2O (1), [N2222]2[H(HCO3)3]·5H2O (2), [N3333][HCO3]·0.5H2O (3), [N3333][H(HCO3)2] (4), [N3333]2[(tpa)(H2CO3)2] (5; tpa = terephthalate), [N4444][H(Cyt)(HCO3)]·H2O (6) and [N4444][H2(Cyt)2(HCO3)]·H2O (7) have been isolated in crystalline form and structurally characterized by single crystal X-ray diffraction. The compounds are characterized by complex polyanionic formations from bicarbonate dimers ([(HCO3)2·(H2O)]24−) or chains ([H(HCO3)2]nn or [H2(tpa)(HCO3)2]n2n) to water-bicarbonate associates ([(HCO3)2·6H2O]2− and [(H2CO3·(HCO3)2)2·6H2O·2H2O]2−) and three-component anionic layers ([H(Cyt)(HCO3)·H2O]nn and [H2(Cyt)2(HCO3)·H2O]nn) frequently showing proton sharing. While some hydroxides themselves can maintain a high CO2/[Nnnnn][OH] ratio, particularly 2 and 4, the presence of secondary hydrogen bond donors/acceptors may increase the sorption efficiency through decreased solubility and enhanced crystallization.

Graphical abstract: CO2 capture from ambient air via crystallization with tetraalkylammonium hydroxides

Supplementary files

Article information

Article type
Paper
Submitted
12 jul 2022
Accepted
07 okt 2022
First published
08 nov 2022
This article is Open Access
Creative Commons BY-NC license

Dalton Trans., 2022,51, 17724-17732

CO2 capture from ambient air via crystallization with tetraalkylammonium hydroxides

M. K. Mishra, V. Smetana, E. A. Hiti, H. B. Wineinger, F. Qu, A. Mudring and R. D. Rogers, Dalton Trans., 2022, 51, 17724 DOI: 10.1039/D2DT02262A

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