Adsorption of Methyl Orange onto Peanut Shell-Derived Activated Carbon: Characterization, Isotherms, and Kinetic Behavior

Driven by the need to develop innovative solutions for wastewater treatment and to reduce waste generation, this study proposes the valorization of agricultural residues, specifically peanut shells, as a precursor for the synthesis of surface-area activated carbon (AC) through chemical activation with KOH (ratio 1:3). AC derived from peanut shells showed a microporous structure with a surface area of 1171 m2/g and a highly heterogeneous surface. Physicochemical analysis confirmed that the presence of oxygen-containing functional groups may contribute to contaminant adsorption. Equilibrium data were best fitted by the Sips isotherm model (R2 = 0.997), indicating surface heterogeneity and yielding an estimated adsorption capacity (qs) of 67.83 mg/g for methyl orange (MO). Kinetic analysis indicated rapid adsorption during the initial stage, favored by the porous structure of the AC, followed by a slower stage associated with mass transfer within the material’s internal pores. The adsorption kinetics were best described by the pseudo-second-order model (R2 = 0.992, qe = 25.78 mg/g). Overall, the results establish a relationship between the porous structure of the adsorbent and its adsorption behavior, demonstrating the potential of peanut shell valorization for the development of sustainable and efficient adsorbent materials for wastewater treatment within a circular economy framework.