Molecular Simulation and Experimental Study on Low-Viscosity Ionic Liquids for High-Efficient Capturing of CO₂

In recent decades, ionic liquids (ILs) have been developed as an ideal and reversible decarbonization solvent. However, some pitfalls, such as the low CO₂ capacity and high viscosity of ILs, limit their further scale up and industrial application. Therefore, in this work, three novel functional ILs [N₈₈₈₁]­[NIA], [N₈₈₈₁]­[For], and [N₈₈₈₁]­[Ac] were synthesized after using a molecular design method to capture CO₂ at 303.15–333.15 K and pressures up to 1000 kPa. The experimental results illustrate that [N₈₈₈₁]­[NIA] presents the smallest viscosity and the highest CO₂ solubility. The capacity order is [N₈₈₈₁]­[NIA] > [N₈₈₈₁]­[For] > [N₈₈₈₁]­[Ac] under the same experimental conditions. The CO₂ recyclability experiments using [N₈₈₈₁]­[NIA] show the stability of CO₂ solubility after 5 cycles. The quantum chemistry simulations at the level of DFT/B3LYP with 6-311++G­(d,p) basis sets were used to study the CO₂ absorption mechanism in the studied ILs from the molecular viewpoint. Simulation results illustrated that the higher interaction energy between CO₂ and ILs means more CO₂ absorbed in these ILs, which agreed well with the experimental results. The atoms in molecules theory and the function of the reduced density gradient were also used to calculate the interactions in these IL–CO₂ systems. Results show that the majority of these interactions present an electrostatic character.