According to literatures , researchers have compared the reaction energy barriers of two mechanisms (Eq. (1) and Eq. ( )) for primary and secondary amines through the DFT methods. The results show that the reaction energy barriers of the zwitterion mechanism (Eq. (1)) are lower than those of the trimolecular reaction mechanism (Eq. (3)), indicating that the zwitterionic mechanism is more suitable to describe the CO2 chemical absorptions in primary and secondary amines. Besides, the literatures find that the rate of the second reaction step in the zwitterion mechanism is generally faster than that of the first step. Thus, the first reaction step in the zwitterionic mechanism is usually the rate-determining step. Therefore, this work employs the first step of the zwitterion mechanism (Eq. ( )) as the rate-determining reaction step to study the CO2 chemical absorptions in primary and secondary amines. As for tertiary amines, the rate-determining reaction step (Eq. (1)) in the base catalysis mechanism is considered.