Degradation mechanism of Methyl Orange by electrochemical process on RuO_x–PdO/Ti electrode

The electrochemical degradation of Methyl Orange in 0.1 M NaCl solution over RuO_x–PdO/Ti anode was investigated. Chemical oxygen demand (COD), ion chromatography (IC), Fourier Transform Infrared Spectroscopy (FTIR) and Gas chromatography-mass spectrometry (GC-MS) were employed to detect the intermediates formed during the electrochemical degradation. In the present reaction system, Methyl Orange could be effectively degraded. After 1 h treatment, the discoloration could reach 97.9% with COD removal of 57.6%. The results indicated that in the presence of chloride, the electrolysis was able to oxidise the dye with partial mineralisation of carbon, nitrogen and sulfur into CO₂, NO₃⁻ and SO₄²⁻, respectively. After 8 h electrolysis, 62% of sulfur contained in Methyl Orange was transformed to SO₄²⁻, and 17.6% of nitrogen changed to NO₃⁻. The intermediates during electroprocess were detected to be low molecular weight compounds, chlorinated compounds, derivatives of benzene and long chain alkanes. Based on these data, a possible degradation mechanism of Methyl Orange was proposed.