Kinetic and thermodynamic studies of methylene blue adsorption on sorghum stems

Abstract

The Raw Sorghum stems have been studied as to adsorb Methylene Blue from aqueous solution by batch technique. The effects of different parameters such as adsorbent dose, initial pH, ionic strength, contacttime and dye initial concentration have been studied. To describe the adsorption kinetics, five models were applied. Kinetic parameters for each adsorption kinetic equation were calculated and discussed. The experimental isotherm data were analyzed using three models. The recovery of methylene blue adsorption has been exceeded 80%.The pseudo-second order kinetic model adequately describes the kinetic data with high determination coefficient (R2=0.99). Langmuir isotherm model fits better than Freundlich and Temkin models for all temperatures studied, and the maximum methylene blue uptake was observed as 27.67 mg/g at 313 K. The estimated values for ΔG°were -2.56, -3.31and -3.78 kJ/mole at 295, 303 and 313 K respectively. The enthalpy changes ΔH°and entropy ΔS°of adsorption were 17.19 kJ/mole and 67.24 J/mole.K, respectively.