Utilization of activated carbon for the adsorption of methylene blue from waste coffee husk

Abstract

This study investigated the pyrolysis of coffee husks to produce activated carbon (AC) and its effectiveness in adsorbing methylene blue (MB) from wastewater. Various techniques, including physical adsorption, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy, were employed to analyze the sorbent. Several experiments were conducted to evaluate the effects of initial pH, adsorption duration, and MB concentration on the process. The results indicated that the optimal equilibrium time for AC adsorption was 60 minutes. The activated carbon exhibited a substantial surface area of 184.535  m²/g and was composed of heterogeneous, fibrous, and mineralized particles, primarily silica. The pH of the medium influenced the removal efficiency of MB. Kinetic data analysis showed that the second-order kinetic model described the adsorption process more accurately than other models, suggesting that MB diffusion occurred within the pores of the AC. However, this was not the only mechanism at play, as indicated by the applicability of the Elovich, Bangham, and intraparticle diffusion models. In terms of isotherm models, the Redlich-Peterson model provided the best fit when compared to the Freundlich, Temkin, and Sips models, reflecting the adsorption behavior at equilibrium. These findings highlight the significant potential of coffee husks as a low-cost alternative to commercial activated carbon for treating dye-laden wastewater.