Markedly improved CO2 uptake using imidazolium-based ionic liquids confined into HKUST-1 frameworks

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.