Valorization of Corn Cobs into Activated Carbon through Chemical Activation and Evaluation of Their Methylene Blue Adsorption Performance for Contaminated Water Treatment

Abstract

Surface water and groundwater are subject to significant degradation due to human activities. The aim of this study is to evaluate the capacity of methylene blue removal by adsorption on activated carbon derived from corn cobs, activated by H3PO4. The corn cobs were pyrolyzed at 400, 500, and 600 °C; the materials obtained were characterized by FTIR and SEM-EDS to link surface chemistry, elemental composition, and texture. Methylene blue adsorption was evaluated at pH 6.68, followed by UV-Vis spectrophotometry, with adjustment to Langmuir and Freundlich isotherms and thermodynamic analysis between 305.15 and 334.15 K. The results show specific functionalization (P–O–C, P=O groups, –OH, C=O, C=C functions) and hierarchical porosity favorable to kinetics and adsorption capacity. The sample activated at 500 °C exhibits exceptionally high adsorption capacity, with a Qmax of 1,250 mg.g-1, a surface area of 1,887.45 m2.g-1, and a dye removal efficiency of 98.62 %. Separation factors 0 < RL < 1 et \(\frac{1}{n_F}\) between 0.485 and 0.792 indicate favorable adsorption. The thermodynamic study shows ΔH° = +29.20 kJ.mol⁻¹ and ΔS° = +110.643 J.mol⁻¹.K⁻¹, leading to ΔG° < 0, denoting an endothermic, spontaneous process dominated by physisorption reinforced by electrostatic and π–π interactions. In terms of sustainability, this approach valorizes corn cobs as a high-performance adsorbent and provides a local, reliable, and economical solution for treating contaminated water.