Enhanced uptake capacities and isosteric heats of CO$_{2}$ and CH$_{4}$ adsorption on spent coffee ground activated carbons loaded with metal ions

Abstract

Low-cost activated carbon (AC) samples obtained from waste coffee grounds were used for CO$_{2}$ and CH$_{4}$ adsorption. ACs were prepared by chemical activation and carbonized at three different temperatures. AC carbonized at 800 $^{\circ}$C showed a relatively high surface area (582.92 m$^{2}$ g$^{-1})$ and high adsorption capacities of 2.6 mmol g$^{-1}$ and 1.1 mmol g$^{-1}$ at 25 $^{\circ}$C for CO$_{2}$ and CH$_{4}$, respectively. Adsorbent samples were prepared by loading of Fe$^{3+}$ metal ions onto ACs and their adsorption capacities were compared with those of nonloaded ACs. As expected, the loading of Fe$^{3+}$ metal ions increased the adsorption capacities at all temperatures and the adsorption capacity of Fe$^{3+}$-loaded AC carbonized at 800 $^{\circ}$C was 3.1 mmol g$^{-1}$ for CO$_{2}$ and 1.2 mmol g$^{-1}$ for CH$_{4}$ at 25 $^{\circ}$C. The isosteric heats of adsorption were calculated at 0-35 $^{\circ}$C with the range of 20-35 kJ mol$^{-1}$ and 18-23 kJ mol$^{-1}$ for CO$_{2}$ and CH$_{4}$, respectively. According to our findings, bio-based ACs can be used as an effective and alternative adsorbent for capturing different gas molecules.