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CO2 capture performance of two imidazolium-based ionic liquids 1-Butyl-3-methylimidazolium Acetate [BMIM][Ac] and 1-propyl-3-methylimidazolium bis(trifluoro -methylsulfonyl)imide [PMIM][Tf2N] supported on a commercial Cu-BTC metal organic framework (HKUST-1) was investigated. The thermogravimetric analysis (TGA) was employed to analyse the impacts of ILs impregnation on the thermal stability of the composites. Furthermore, other characterization techniques such as powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) were used to confirm the successful incorporation of the ILs within the cages of HKUST-1. The as-synthesized ILs@HKUST-1 composites exhibited a stable crystal structure after the encapsulation of the ILs indicating that the structural features of the HKUST-1 support were retained and not impacted by the presence of ILs inside the pores. Moreover, the BET surface area and total pore volume of the ILs@HKUST-1 composites decreased considerably with the increase in IL loading in the composite which suggests the efficient incorporation of the ILs into the porous surface of the HKUST-1 support. Remarkably, the composite sorbent prepared with 5 wt% [bmim][Ac] exhibited the highest CO2 capacity in the low pressure region with almost double that of the pristine HKUST-1 at 303 K and 0.15 bar. On the other hand, the introduction of [pmim][Tf2N] into the pores of HKUST-1 did not show any enhancement in the CO2 uptake at all IL loadings. The samples also displayed a fast adsorption kinetics and a stable adsorption-regeneration performance up to ten cycles. The developed IL@HKUST-1 composites provide a great opportunity to design sorbent materials with excellent merits for potential industrial gas separation applications.

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.