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

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.