Chemically Activating Agrichar Made from Peanut Shells: Fe3+and Ca2+Functionalization for Methylene Blue Removal

In this study, peanut shell-derived activated carbon, produced by orthophosphoric acid activation, was used as a material to adsorb methylene blue (MB). An optimization process was conducted to determine the optimal values for the adsorption parameters, including adsorbent dosage, temperature, pH, and contact duration. The outcomes of experiments were analyzed using four adsorption isotherms, while the pseudo-first and second-order models were deployed for assessing the kinetics. The adsorption of MB achieved equilibrium after 120 min, following the pseudo-second-order kinetic model. The Langmuir model accurately represented the sorption process and achieved a maximum amount adsorbed of 219.7 mg/g at 25 °C. The thermodynamic variables (ΔH0, ΔG0, and ΔS0) were calculated by investigating the impact of temperature, revealing that the adsorption was both exothermic and spontaneous. Carbon functionalization with Fe3+or Ca2+ions enhances the adsorption capacity and expedites the adsorption process, with equilibrium being achieved in 70 min and 50 min, respectively.