Kinetic and thermodynamic studies of fenton oxidative decolorization of methylene blue

The need for light intensity has made dye degradation very costly for industry. In this work, Fenton reagent was used for the efficient degradation of an aqueous solution of dye without the need for a light source. The influences of the pH of the media, the initial concentrations of Fe²⁺, H₂O₂, and methylene blue (MB) dye; in addition to temperature on the oxidation of MB dye were studied. The optimum amounts of the Fenton reagent were 4mM of Fe²⁺ and 70mM of H₂O₂ at 20 mg/L of dye. The optimum ratio of 0.05 of Fe²⁺/H₂O₂ was found to give the best result for the decolorization of dye. The Fenton process was effective at pH 3 with a maximum dye decolorization efficiency of 98.8% within 30 min of reaction, corresponding to a COD removal of 85%. The decolorization process was thermodynamically feasible, spontaneous, and endothermic. The activation energy (E_a) was 33.6 kJ/mol suggesting that the degradation reaction proceeded with a low energy barrier.