Mesoporous-rich calcium and potassium-activated carbons prepared from degreased spent coffee grounds for efficient removal of MnO42− in aqueous media

Commercial ACs typically possess high surface areas and high microporosity. However, ACs with appreciable mesoporosity are growing in consideration and demand because they are beneficial for the adsorption of large species, such as heavy metal ions. Thus, in this study, degreased coffee grounds (DCG) were used as precursors for the production of ACs by means of chemical activation at 600 °C for the efficient removal of manganese in the form of MnO42−. One of the most common activating agents, ZnCl2, is replaced by benign and sustainable CaCl2 and K2CO3. Three ratios 1 : 1, 1 : 0.5 and 1 : 0.1 of precursor-to-activating agent (g g−1) were investigated. Porosimetry indicates 1 : 1 CaCl2 DCGAC is highly mesoporous (mesopore volume 0.469 cm3 g−1). CaCl2 DCGAC and K2CO3 DCGAC shows high adsorption capacities of 0.494 g g−1 and 0.423 g g−1, respectively for the uptake of MnO42− in aqueous media. The adsorption process follows pseudo-second order kinetics inline with the Freundlich isotherm (R2 > 0.9). Thermodynamic data revealed negative values of ΔG (approx −0.1751 kJ mol−1) demonstrating that the adsorption process on 1 : 1 CaCl2DCGAC was spontaneous.