Carbonization of corn (Zea mays) cob agricultural residue by one-step activation with sulfuric acid for methylene blue adsorption

Corn (Zea mays) cob, an agricultural biomass residue, was carbonized by chemical activation with H2SO4 and examined for its suitability as a low-cost adsorbent for methylene blue (MB) adsorption from aqueous solution. Carbonized corn cob (CCC) was characterized by a CHNS-O analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction (XRD), Brunauer-Emmett-Teller, and point-of-zero charge (pH(pzc)) analysis. Batch mode adsorption studies were conducted by varying operational parameters such as adsorbent dosage (0.02-0.20 g), solution pH (3-10), initial MB concentrations (50-300 mg/L), and contact time (0-360 min). The equilibrium data were well correlated by the Freundlich isotherm compared with Langmuir and Temkin models. The maximum adsorption capacity (q(max)) of CCC for MB adsorption at equilibrium was 216.6 mg/g at 303 K. The kinetic uptake profiles were well-described by the nonlinear pseudo-first-order model. The thermodynamic adsorption parameters such as standard enthalpy (Delta H degrees), standard entropy (Delta S degrees), and standard free energy (Delta G degrees) showed that the adsorption of MB onto CCC surface is endo-thermic in nature and spontaneous under the experimental conditions. The above-mentioned results indicate that the CCC can be feasibly employed for the removal of MB from aqueous solution.