Electrosynthesis and characterization of nanostructured manganese dioxide thin film on stainless steel electrode for electrochemical degradation of phenol

An adherent nanostructured thin film of manganese dioxide γ-MnO₂ with a particle size of 16.287 nm and a specific surface area of 368.390 m² g⁻¹ was successfully prepared on a stainless steel (SS) substrate by chronoamperometry method in acidic solution of manganese (II) sulphate monohydrate at pH = 1.8 adjusted with H₂SO₄. The resulting electrode SS/MnO₂ was used for the electrochemical oxidation of phenol in aqueous solution. The effects of experimental conditions such as applied potential, pH and initial phenol concentration on removal efficiency of phenol were investigated. The results of this study suggest that the particle size and specific surface area of MnO₂ favor better adsorption and that electrochemical oxidation of phenol can be successfully carried out on this material. The almost total elimination of phenol was obtained under optimal experimental conditions of applied potential E = 0.8 V vs. SSE, pH = 5 and initial phenol concentration of 5 mg L⁻¹, and, with pseudo-first-order kinetics. In addition, the main intermediates include hydroquinone, 1,4-benzoquinone, formic and acetic acids generated during phenol degradation were identified by high-pressure liquid chromatography (HPLC) and a mechanism for the electrochemical degradation of phenol on the SS/MnO₂ electrode was proposed.