In silico studies on the origin of selective uptake of carbon dioxide with cucurbit[7]uril amorphous material

Abstract

The efficient capture and storage of flue gases is of current interest due to environmental problems. We report the adsorption of flue gases (CO₂, N₂ and CH₄) on amorphous solid Cucurbit[7]uril (CB[7]) computationally. The DFT calculations revealed that CO₂ can be adsorbed more strongly inside the cavity of CB[7] compared to N₂ and CH₄ molecules. The glycoluril units of CB[7] are the preferential sites for the adsorption of CO₂ gas molecules. The cooperative binding of CO₂ molecules inside the cavity of CB[7] has been observed. The geometrical analysis reveals that the carbon atom of CO₂ is in close proximity to the nitrogen atom of the glycoluril of CB[7] and the CO₂ oxygen atom is in close contact to the carbonyl carbon of the glycoluril unit. The calculated results show that four CO₂ and four CH₄ molecules can reside inside the CB[7] cavity. However, five N₂ gas molecules can be accommodated inside the CB[7] cavity. The energy decomposition analysis (EDA) performed with the adsorbed CO₂ on the wall of CB[7] shows that the dispersive force is playing an important role for the uptake of CO₂ inside the cavity. The process of desorption was also examined with the desorption enthalpies (ΔH_DE) calculated per gas molecule, which suggests that both adsorption and desorption processes are kinetically feasible. The origin of the interactions between the amorphous solid CB[7] and the flue gases can help to design materials to maximize the capture and separation of such gases.