Activity of Pt/MnO2 electrode in the electrochemical degradation of methylene blue in aqueous solution

Abstract

The electrochemical oxidation of methylene blue (MB) in aqueous solution was studied by galvanostatic electrolysis using MnO2 electrode as anode. The MnO2 electrode was prepared by electroplating method, and was characterized by X-ray diffraction (XRD), the cyclic voltammetry (CV) and amperometry j = f(t). This study has been done in synthetic media using sulfate sodium as electrolyte and thus only the contribution of the direct effect of electrolysis has been put into evidence. The electrochemical oxidation performance of the prepared electrode was investigated using MB as a model pollutant. UV spectroscopy and chemical oxygen demand (COD) measurements were conducted to study the kinetics of MB electrochemical degradation and the mineralization under different operating conditions. An experimental design methodology (Box–Behnken design) has been applied to determine the optimal experimental condition in term of effectiveness. The best conditions have been found after 120 min of electrolysis with Pt/MnO2 operated at pH ≈ 8 with a current density of 7 mA cm−2 in presence of <0.1 mol L−1 of sodium sulfate. In these conditions, higher than 90% of MB removal can be obtained with an abatement of slightly over 70% of COD. These results indicate that the suggested modified electrode was highly efficient in the treatment of effluents containing methylene blue dye with very slight effect of matrix.