A green sorbent for CO₂ capture: α-cyclodextrin-based carbonate in DMSO solution

Cyclodextrin (α-CD)/KOH pellet dissolved in DMSO was utilized to capture CO₂. KOH has a dual function of enhancing the nucleophilicity of the hydroxyl groups on the α-CD rims and acting as a desiccant. ¹³C NMR spectroscopy provided evidence for the chemisorption of CO₂ through the formation of organic carbonate (RO-CO₂ ^-·K⁺). This was supported by the spectral changes obtained using ex situ ATR-FTIR spectroscopy upon bubbling CO₂. Activation of α-CD with NaH or bubbling with ¹³CO₂ verified that chemisorption occurred solely via RO-CO₂ ^-·K⁺ rather than inorganic bicarbonate. Volumetric gas uptake demonstrated a sorption capacity of 21.3 wt% (4.84 mmol g^-1). To the best of our knowledge, this is the highest chemisorption value reported to date for CD-based sorbents. DFT calculations of the Gibbs free energies indicated that the formation of RO-CO₂ ^-·K⁺ was more favoured at the primary carbinol rather than its secondary counterpart.