Imidazolium based ionic liquids confined into mesoporous silica MCM-41 and SBA-15 for carbon dioxide capture

Abstract

Abstract Ordered mesoporous silica MCM-41 and SBA-15 were impregnated by two imidazolium-based ionic liquids 1-Butyl-3-methylimidazolium Acetate [bmim][Ac] and 1-propyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide [pmim][Tf2N] using a facile impregnation-evaporation approach. The immobilization of ILs into the mesoporous silica supports was found to reduce the derivative decomposition temperatures (Tonset) by about 30 °C compared to the bulk ILs, however the decomposition process was found to occur over a wider temperature range for the IL-immobilized samples. These observations are indicative of interionic interactions between the ILs and the surface of the mesoporous silica supports, which was further corroborated by the shifts in the FTIR bands. The X-ray diffraction patterns (XRD) of the pristine MCM-41, SBA-15 and the IL-modified samples have shown that no textural or morphological changes were observed for the IL-impregnated samples and that the crystal structure of the mesoporous silica supports remained intact. The BET surface area and pore volumes of the composite sorbents have remarkably decreased after the incorporation of the ILs due to the occupation of the pore surface. All the composite sorbents modified with [bmim][Ac] ILs have shown a substantial increase in CO2 sorption capacity especially in the low pressure region up to 6 times higher CO2 uptake at 0.2 bar and 30 °C. On the other hand, the immobilization of [pmim][Tf2N] did not show any improvements in the sorption capacity for all impregnation amounts used. Furthermore, unlike the slow adsorption kinetics in the bulk ILs, the supported ILs exhibited significantly rapid sorption rates, with a stable cyclic adsorption-regeneration performance.