Incorporation of acetate-based ionic liquids into a zeolitic imidazolate framework (ZIF-8) as efficient sorbents for carbon dioxide capture

Tuning the interior pores of solid sorbents to improve their adsorption characteristics is considered an effective approach to enhance gas separation performance. Herein, we examine the improvement of carbon dioxide (CO2) capture performance of a ZIF-8 impregnated with ionic liquid 1-Butyl-3-methylimidazolium Acetate [Bmim][Ac] and 1-Ethyl-3-methylimidazolium Acetate [Emim][Ac]. The synthesis and detailed characterizations of the developed composite materials are reported, and the impact of ionic liquid (IL) loading is studied. Fourier transform infrared (FTIR) spectroscopy was used to confirm the impregnation of the ILs into the pores of ZIF-8 and thermogravimetric analysis (TGA) was carried out to study the thermal stability of the composite materials. The powder X-ray diffraction (XRD) pattern of the ILs@ZIF-8 samples revealed that the crystal structure of ZIF-8 remained intact after the impregnation process. The Brunatuer-Emmett-Teller (BET) surface area and pore volumes have significantly decreased up to 80% for [Bmim][Ac]@ZIF-8 with 30 wt% IL loading confirming the presence of ILs inside the internal pores of ZIF-8. CO2 and N-2 adsorption isotherms of the ILs@ZIF-8 composites were evaluated gravimetrically at (303, 313, and 323) K. The impregnated samples exhibited substantially higher CO2 uptake and CO2/N-2 selectivity at all studied temperatures of up to 7 times higher the CO2 capacity at 0.2 bar and 303 K for [Bmim][Ac]@ZIF-30 as compared to the pristine ZIF-8. Findings from this work provide insights into the synthesis, structure, and sorption capacity of these novel composite materials, which could be utilized for the design of sorbents with outstanding properties to meet the environmental challenges.