Theoretical investigation of CO2 adsorption pathway over N-[3-(trimethoxysilyl)propyl] ethylenediamine-modified mesoporous silica sorbents

Elucidation of the adsorption pathways of carbon dioxide (CO2) over mesoporous silica sorbents modified by amines is significant for the development of high-performance sorbents that would meet the future challenges regarding the emissions. This study aims to investigate the CO2 adsorption pathway over N-[3-(trimethoxysilyl)propyl] ethylenediamine (AEAPS)-modified mesoporous silica sorbents by using DFT modeling to reveal whether the intra-molecular CO2 capture is possible and which amine groups (primary or secondary) are more reactive in this process. Our calculations showed that CO2 was captured in the forms of carbamate and carbamic acid; and hydrogen bonding interactions (both amine-amine and amine-surface) were critical for the thermodynamic and kinetic feasibility of the adsorption pathways. Intra-molecular capture was possible, but the long chain length of the molecule seemed to restrict the amine-amine interactions within the molecule. Both primary and secondary amine groups contributed to the adsorption of the CO2, meaning that amine functionality was less deterministic on the process in comparison to the hydrogen bonding interactions.