Optimization of Oxidative Decolorization of Acid Violet 7 by Peroxydisulfate using Response Surface Methodology, Kinetic, and Thermodynamic Evaluation

Response surface methodology based on central composite design was successfully applied to the optimization of the operating conditions in the Fe2+ catalyzed decolorization of acid violet 7 using peroxydisulfate. The impact of four process variables, initial dye concentration, concentrations of Fe2+, temperature, and pH on the decolorization of acid violet 7 was evaluated. Predicted values of decolorization efficiency were found to be in good agreement with experimental values (R2 = 98.18%), which indicated the suitability of the central composite design model employed. The interaction of the parameters is also studied based on its P-value with the help of analysis of variance. The experimental data were examined employing kinetics of both first and second order. The decolorization kinetics of acid violet 7 in the peroxydisulfate process adhered to the principles of second-order reaction kinetics. Initial dye concentration of 2.5 µM, pH of 2.0, temperature 313 K, and Fe2+ concentration of 0.6 mM were the best conditions. The predicted decolorization rate under the optimum conditions determined by response surface methodology was 100%. Confirmatory tests were carried out under the optimum conditions and the decolorization rate of 99.6% was observed, which closely agreed with the predicted value. Fe2+ activates $${{{\text{S}}}_{{\text{2}}}}{\text{O}}_{8}^{{2 - }}$$ to generate sulfate radical ion, amplifying acid violet 7 decolorization. Peroxydisulfate decolorized acid violet 7 with a low activation energy of 45.32 kJ mol–1 at 2.25 mM starting concentration. The positive ΔG value indicates the non-spontaneity of the decolorization process.