The interaction nature between hollow silica-based porous ionic liquids and CO2: A DFT study

Abstract

Carbon dioxide (CO2) is one of the main factors leading to the greenhouse effect, so the capture of CO2 gas is currently a hot spot of research. Hollow silica-based porous ionic liquids (HS-liquids) are porous liquids containing cavities that are not only fluid but also have a high specific surface area and were used for the capture of CO2. However, the mechanism of CO2 absorption by HS-liquids has not been studied. In this work, the mechanism of CO2 absorption by HS-liquids was systematic studied by density functional theory (DFT). First, five possible models for absorbing CO2 in HS-liquids were constructed and optimized. The interaction energies between HS-liquids and CO2 at different sites were obtained. Moreover, the effects of HS-liquids with different degrees of polymerization of polyethylene glycol and different alkyl chain lengths on CO2 absorption were also investigated. Results show that the strongest absorption site locates near the polyethylene glycol unit. Then, the electrostatic potential (ESP) and reduced density gradient (RDG) methods were employed to further understand the interaction nature between them. The results show that hydrogen bonding dominates the weak interaction between the HS-liquid and CO2.