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

The efficient capture and storage of flue gases is of current interest due to environmental problems. We report the adsorption of flue gases (CO2, N-2 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 N-2 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 N-2 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 (DHDE) 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.