Adsorption of methylene blue onto activated carbon prepared under N2/microwave radiation supported cobalt: kinetics, isotherms, and thermodynamics studies

This study aims to investigate the kinetics, isotherms, and thermodynamics of methylene blue (MB) dye adsorption from aqueous solution onto activated carbon prepared from orange peel waste (PO). This material was chemically treated with sulfuric acid, pyrolyzed, and activated in microwave apparatus under nitrogen flow. The resulting activated carbon was supported using cobalt transition metal by a wet impregnation process at different cobalt (Co) contents; the optimum condition was achieved at cobalt impregnations of 20 wt.%. The supported carbon Co20 wt.%-POAC catalyst was characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, and Brunauer-Emmett-Teller surface area analysis. The results show that the equilibrium was reached at 270 min with an adsorption capacity of 27 mg center dot g(-1); the Langmuir isotherm was the best model that describes the experimental data. Besides, the pseudo-first-order adsorption model best depicts the adsorption kinetics of the MB by Co20 wt.%-POAC. Thermodynamic analysis shows that the standard Gibb's free energy change (Delta G degrees) has negative values, confirming, therefore, the feasibility and spontaneity of the process. The changes in enthalpy (Delta H degrees) and entropy (Delta S degrees) were found to be -2,011 J center dot mol(-1) and18.9 J center dot K-1 center dot mol(-1), respectively. Finally, our results revealed that grafting cobalt onto the surface of the orange peel-activated carbon improves its adsorption capacity, and hence its efficiency in removing MB from wastewater.