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CO₂ Adsorption Enhanced by Tuning the Layer Charge in a Clay Mineral.

ABSTRACT: Due to the compact two-dimensional interlayer pore space and the high density of interlayer molecular adsorption sites, clay minerals are competitive adsorption materials for carbon dioxide capture. We demonstrate that with a decreasing interlayer surface charge in a clay mineral, the adsorption capacity for CO₂ increases, while the pressure threshold for adsorption and swelling in response to CO₂ decreases. Synthetic nickel-exchanged fluorohectorite was investigated with three different layer charges varying from 0.3 to 0.7 per formula unit of Si₄O₁₀F₂. We associate the mechanism for the higher CO₂ adsorption with more accessible space and adsorption sites for CO₂ within the interlayers. The low onset pressure for the lower-charge clay is attributed to weaker cohesion due to the attractive electrostatic forces between the layers. The excess adsorption capacity of the clay is measured to be 8.6, 6.5, and 4.5 wt % for the lowest, intermediate, and highest layer charges, respectively. Upon release of CO₂, the highest-layer charge clay retains significantly more CO₂. This pressure hysteresis is related to the same cohesion mechanism, where CO₂ is first released from the edges of the particles thereby closing exit paths and trapping the molecules in the center of the clay particles.

SUBMITTER: Bo Hunvik KW

PROVIDER: S-EPMC8675214 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Alkyldiamine-functionalized variants of the metal-organic framework Mg2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) are promising for CO2 capture applications owing to their unique step-shaped CO2 adsorption profiles resulting from the cooperative formation of ammonium carbamate chains. Primary,secondary (1°,2°) alkylethylenediamine-appended variants are of particular interest because of their low CO2 step pressures (≤1 mbar at 40 °C), minimal adsorption/desorption hysteresis, and high thermal stability. Herein, we demonstrate that further increasing the size of the alkyl group on the secondary amine affords enhanced stability against diamine volatilization, but also leads to surprising two-step CO2 adsorption/desorption profiles. This two-step behavior likely results from steric interactions between ammonium carbamate chains induced by the asymmetrical hexagonal pores of Mg2(dobpdc) and leads to decreased CO2 working capacities and increased water co-adsorption under humid conditions. To minimize these unfavorable steric interactions, we targeted diamine-appended variants of the isoreticularly expanded framework Mg2(dotpdc) (dotpdc4- = 4,4''-dioxido-[1,1':4',1''-terphenyl]-3,3''-dicarboxylate), reported here for the first time, and the previously reported isomeric framework Mg-IRMOF-74-II or Mg2(pc-dobpdc) (pc-dobpdc4- = 3,3'-dioxidobiphenyl-4,4'-dicarboxylate, pc = para-carboxylate), which, in contrast to Mg2(dobpdc), possesses uniformally hexagonal pores. By minimizing the steric interactions between ammonium carbamate chains, these frameworks enable a single CO2 adsorption/desorption step in all cases, as well as decreased water co-adsorption and increased stability to diamine loss. Functionalization of Mg2(pc-dobpdc) with large diamines such as N-(n-heptyl)ethylenediamine results in optimal adsorption behavior, highlighting the advantage of tuning both the pore shape and the diamine size for the development of new adsorbents for carbon capture applications.

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CO₂ Adsorption Enhanced by Tuning the Layer Charge in a Clay Mineral.

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CO2 Adsorption Enhanced by Tuning the Layer Charge in a Clay Mineral.

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OmicsDI is part of the ELIXIR infrastructure

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CO₂ Adsorption Enhanced by Tuning the Layer Charge in a Clay Mineral.