Interface-enhanced CO2 capture via the synthetic effects of a nanomaterial-supported ionic liquid thin film

Ionic liquids (ILs) are effective CO2 capture media and recent experimental evidence has demonstrated that the addition of two-dimensional (2D) nanomaterials into ILs can effectively improve their CO2 capturing capability. However, an in-depth mechanism on how 2D nanomaterials enhance CO2 absorption is poorly documented. In this study, the adsorption of CO2 by a representative IL, namely 1-ethyl-3-methyl-imidazole-tetrafluoroborate ([EMIM][BF4]), coated on graphene (GRA, the prototype 2D nanomaterial) and nitrogenized graphene (C3N) was investigated by molecular dynamics simulations. The influence of the IL film thickness on the amount of CO2 adsorption was systematically analyzed. Our data clearly indicate that at the IL-gas interface the CO2 accumulation is significantly enhanced. In contrast, at the IL-GRA and IL-C3N interfaces, only slight enhancement was observed for CO2 accumulation. Quantitative calculations of the adsorption-free energy for CO2 inside the IL film further support the simulation results. Our present results also reveal that the sub-nanometer IL film possesses a considerably high CO2 capture efficiency because of the formation of the reduced bulk IL region. Moreover, the nanomaterial substrate surfaces can effectively accelerate the diffusion of CO2, which is beneficial for the CO2 mass transfer. In general, our theoretical study provides a deep microscopic understanding of the CO2 capture by nanomaterials and IL composites. These results could benefit the design and fabrication of a high-performance CO2 capture and storage medium through the synthetic effects of ILs and nanomaterials.