Electrochemical Oxidation of Methylene Blue by Cyclic Voltammetry on a Boron-Doped Diamond Electrode in Various Supporting Electrolytes

In this study, the electrochemical behavior of methylene blue (MB) dye was investigated at a boron-doped diamond (BDD) electrode in various supporting electrolyte solutions. The physical characterization of the BDD surface by scanning electron microscopy (SEM) reveals a polycrystalline structure with grain sizes ranging between 0.3 and 0.6 μm. With Raman spectroscopy, the BDD surface is composed of diamond-type carbon (Csp3) and graphitic-type carbon (Csp2). Electrochemical characterization of the BDD electrode in 0.1 M H2SO4 and Na2SO4 solutions showed the presence of an anodic wave close to the onset potential of oxygen evolution. In the presence of MB, four anodic peaks and one cathodic peak were recorded in both media. Analysis of the first anodic and cathodic peaks suggests a quasi-reversible electrochemical process. In 0.1 M NaOH, the electrochemical response revealed a distinct anodic peak associated with oxygen evolution. The oxidation of MB in this basic medium was characterized by a broad anodic wave beginning within the potential window for water stability on the BDD electrode. The results obtained across the different electrolytes indicate that methylene blue can be oxidized either through direct electron transfer at the electrode surface or indirectly via reactive oxidative species generated in solution. The electrochemical process is diffusion-controlled, and in all three media, the formation of a polymeric film on the electrode surface was observed. These findings confirm the suitability of BDD electrodes for the electrochemical investigation and quantification of methylene blue.