Sustainable activated carbon from corn cob for efficient removal of methyl orange and methyl red from water

This study reports the synthesis of activated carbon from corncob biomass via hydrochloric-acid chemical activation (HCl). The resulting bio-based activated carbon was subsequently evaluated as an efficient adsorbent for the aqueous-phase removal of model synthetic azo dyes—methyl orange (MO) and methyl red (MR). The physicochemical and morphological characteristics of the activated carbon were examined using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The effects of key operational parameters, including adsorbent dosage, initial dye concentration, and temperature, were systematically investigated. The results indicated that the corn cob-based activated carbon exhibited a favorable surface morphology, relatively high surface area, and significant dye removal efficiency. MR showed better adsorption performance than MO, which can be attributed to differences in molecular structure, ionic properties, and specific interactions with surface functional groups on the activated carbon. Opposite-charge attraction and π–π stacking with the carbon surface boosted adsorption, most notably for MR. An increase in adsorbent dosage led to higher dye removal percentages due to more available binding sites; however, the adsorption capacity per unit mass (qe) decreased at higher doses, likely due to particle agglomeration and reduced effective surface area. These findings suggest that corn cob-derived activated carbon is a promising low-cost, environmentally friendly adsorbent for wastewater treatment applications.