Understanding the interaction mechanism of CO2 and position isomeric organic absorbents by density functional theory

The effect of position isomerism on absorbent-CO2 interaction for CO2-philic absorbents, ethers, ketones, and esters, were investigated at the molecular level by density functional theory simulation. It is found that C1OC7 and C1COC6 show superior CO2 absorption potential as their three-armed structure of the methyl group weakens the spatial resistance of the main absorbent molecule and enhances the Lewis acid-base interaction. The addition of carbonyl or ether group to form the corresponding ester usually results in decreased interaction energy. Notably, the stable configuration like the C4COOC3-CO2 system in claw-like structure as well as the C1COOC6CO2 system containing hydrogen atoms with hyperconjugation shows enhanced Lewis acid-base interaction and weak hydrogen bonding. Unlike ethers and ketones, esters with high symmetric structure, such as C3COOC4 and C4COOC3, exhibit superior CO2 absorption intensity. The findings are beneficial to the design of specific physical absorbents, especially position isomers for CO2 capture.