Excellent CO2 adsorption performance of amine-impregnated highly porous ZIF-8 adsorbent: Experimental and isotherm modeling studies

Zeolitic imidazolate framework-8 (ZIF-8), a metal–organic framework (MOF) is well known for its large surface area, and superior thermal and chemical stability with respect to other adsorbents. The adsorbents are synthesized and analyzed using HR-XRD, FTIR, BET, TGA, FESEM, EDX, and CHNS techniques. Pure ZIF-8 demonstrates comparatively low CO2 capture capacity. The present study aims to improve the CO2 adsorption capacity of ZIF-8 by functionalization with 10 to 40 % triethylenetetramine (TETA) using the wet impregnation process. The iSorpHP2 pressure sorption apparatus is employed to evaluate the carbon dioxide uptake capacity in the range of varying pressure (0 to 30 bar) and temperature conditions (25 to 80 °C) of ZIF-8 and TETA-grafted ZIF-8 adsorbents. The impact of temperature, pressure, and amine loading as independent variables on the experimental CO2 adsorption capacity as the response function was assessed and optimized using the response surface methodology (RSM) based on the Box-Behnken design (BBD). An excellent match was found between the experimental data and the model prediction. The isoteric heat of adsorption of ZIF-8 and TETA-incorporated ZIF-8 adsorbents is measured in the temperature range of 25 to 60 °C through the utilization of the Van't Hoff depicted in the iSorbHP2-Win software for acquiring knowledge on the level of heterogeneity and the distribution of surface energy of materials. The Sips model has demonstrated superior performance in its ability to correlate experimental data as compared to the Toth, Langmuir, and Freundlich models. Among the amine-impregnated ZIF-8 adsorbents, ZIF-8–30 % TETA adsorbs 3.89 mmol CO2/g of solid adsorbent at 25 °C and 1 bar pressure which is 4.52 times greater than that of ZIF-8.