In this study, we loaded a reactive ionic liquid (IL), 1-ethyl-3-methylimidazolium 2-cyanopyrolide ([EMIM][2-CNpyr]), into a metal organic framework (MOF) ZIF-8 (zeolitic imidazolate framework) to prepare a powder composite, showing an exceptional CO₂ capture performance particularly in the low-pressure region. IL/MOF composite samples were prepared with IL loading of 5, 20, and 35 wt% via the wet impregnation method, followed by a detailed characterization. BET analyses confirmed the successful incorporation of IL into ZIF-8, while XRD and SEM results showed that the MOF retains its structural integrity. The presence of interactions between IL and ZIF-8 in the IL/MOF composite were confirmed by TGA and FTIR results. The CO₂ isotherm and absorption (30 °C) - desorption (60 °C) cycling were assessed as shown in Figure 1. The isotherm measured by BET (Figure 1a-b) demonstrated a significant increase in CO₂ uptake with IL loading; up to 200 times higher uptake in IL/MOF composite with 35wt% IL, compared to the naked MOF. The CO₂ capacities at 1 bar of CO₂ determined by TGA (Figure 1c) for bare ZIF-8 and IL₃₅/ZIF-8 were 0.24 and 1.19 mmol/g, respectively. CO₂ breakthrough measurements (Figure 1d) were performed to further examine the potential of IL/MOF composite for direct air capture (DAC) using a gas feed of 500 ppm of CO₂ balanced with N₂. The CO₂ capacity of IL₃₅/ZIF-8 was determined as 0.17 mmol/g at 500 ppm CO₂feed, while ZIF-8 showed no quantifiable CO₂ capacity. This study demonstrates the functionalization of a porous substrate with a reactive IL can achieve CO₂ sorption capacities that are suitted for DAC applications.

<b>Figure </b><b>1</b><b>. </b>(a) CO<sub>2</sub> adsorption/absorption isotherm of ZIF-8 and IL/ZIF-8 composites at 30 °C; (b) Isotherm at low partial pressure region; (c) Cycling measured by thermal gravimetric analyzer curves for CO<sub>2</sub> adsorption at 1 bar, and (d) TGA curves for CO<sub>2</sub> adsorption under 500 ppm CO<sub>2</sub> concentrations. Results were reproducible within an error range of ±5%.

Figure 1. (a) CO₂ adsorption/absorption isotherm of ZIF-8 and IL/ZIF-8 composites at 30 °C; (b) Isotherm at low partial pressure region; (c) Cycling measured by thermal gravimetric analyzer curves for CO₂ adsorption at 1 bar, and (d) TGA curves for CO₂ adsorption under 500 ppm CO₂ concentrations. Results were reproducible within an error range of ±5%.

Muhammad Zeeshan

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