Preparation and Characterization of Graphite Substrate Manganese Dioxide Electrode for Indirect Electrochemical Removal of Phenol

Abstract

Manganese dioxide rotating cylinder electrode prepared by anodic deposition on a graphite substrate using MnSO₄ solution in the presence of 0.918 M of H₂SO₄. The influence of different operational parameters (MnSO₄ concentration, current density, time, and rotation speed) on the structure, and morphology of MnO₂ deposit film was examined widely. The structure and crystal size determined by X-ray diffraction (XRD), the morphology examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The γ-MnO₂ obtained as the main product of the deposition process. It found that the four parameters have a significant influence on the structure, morphology, and roughness of the prepared MnO₂ deposit. The crystal size increases with MnSO₄ concentration, current density, and rotation speed, and decreasing with time, while the roughness decreases with increasing all of four parameters. It found that the optimum conditions used in preparing MnO₂ rotating electrode that gave the smallest crystal size, low roughness and less cracking were 0.33 M of MnSO₄, 6 mA/cm², 2 h, and 200 rpm. Electrochemical oxidation of phenol in a batch reactor was carried out in the presence of NaCl to examine the performance of the prepared MnO₂ electrode for degrading phenol and any organic byproducts at different current densities. The results indicate that as the current density increased from 25 to 100 mA/cm², the chemical oxygen demand (COD) removal efficiency was increased from 59.26 to 99.90%. Kinetics and the effect of temperature on the COD disappearance have been studied. It was clear that COD decreases with time and as the temperature increases, and the value of reaction order equals to 1 as has been found.