Theoretical study of hydrogen-bond interactions of CO₂in organic absorbent 1,3-diphenylguanidine

Carbon capture and storage technology have been rapidly developed to reduce the carbon dioxide (CO2) emission into the environment. It has been found that the amine-based organic molecules could absorb CO2 efficiently and form the bicarbonate salts through hydrogen-bond (H-bond) interactions. Recently, the aqueous 1,3-diphenylguanidine (DPG) solution was developed to trap and convert CO2 to valuable chemicals under ambient conditions. However, how the DPG molecules interact with CO2 in an aqueous solution remains unclear. In this work, we perform molecular dynamics simulations to explore the atomistic details of CO2 in the aqueous DPG. The simulated results reveal that the protonated DPGH+ and the bicarbonate anions prefer to form complexes through different H-bond patterns. These double H-bonds are quite stable in thermodynamics, as indicated from the accurate density functional theory calculations. This study is helpful to understand the catalytic mechanism of CO2 conversion in the aqueous DPG.