Elimination of a cationic dye in aqueous solution by adsorption on activated carbon: Optimization of analytical parameters, modeling and thermodynamic study

Abstract

Adsorption techniques are widely used to remove certain classes of pollutants from waters, especially those that are not easily biodegradable. The aim of this study was to evaluate the adsorption of Methylene Blue (MB) dye onto activated carbon from aqueous solutions was realized in a batch system. However, some examined factors such as contact time, pH solution, initial concentration of MB, adsorbent dosage and temperature were found to have significant impacts on the adsorption capacity of AC. The AC was characterized by BET surface area measurement, Point of Zero Charge (pHpzc), FTIR spectroscopy and X-ray diffraction analysis. Batch studies were conducted in order to determine the optimal parameters required to reach the adsorption equilibrium. The maximum adsorption capacity of the AC for MB at 298 K was determined to be 170.357 mg/g. The adsorption kinetic data were analyzed employing several kinetic models: pseudo-first order, pseudo-Second order, Elovich equation, and intraparticles diffusion model. It was established that the adsorption process obeyed the pseudo-second-order kinetic model with a determination coefficient (R2) equal to 0.999. The evaluation of thermodynamics parameters such as the Gibbs free energy ΔG° (−7.856 to −6.142 kJ/mol), positive enthalpy ΔH° (13.384 kJ/mol) and the change of entropy (63.46 J/mol K) indicated a spontaneous and endothermic nature of the reaction with a chemisorption process. Comparative tests by the heterogeneous photocatalysis of MB in the presence of a semiconductor will be the subject of the rest of this study.