Pulsed dielectric barrier discharge generated at the gas-liquid interface for the degradation of the organic dye methyl red in aqueous solution

The decomposition of the azo dye methyl red in aqueous solution was performed using a pulsed dielectric barrier discharge reactor (DBD) in coaxial configuration. The solution was made to flow as a thin layer on the surface of the inner electrode of the DBD reactor and the discharge was generated at the gas-liquid interface. In this way the oxidizing species formed in the discharge can easily penetrate the solution and react with the dye molecules in order to decompose them. After 10 minutes plasma treatment 93% removal of the dye was reached for 50 mg/L initial concentration of methyl red in solution. The corresponding removal yield was 52.5 g/kWh. Lower concentrations of the dye are removed faster, however the efficiency is lower in this case. It was found that the degradation of methyl red depended on the initial dye concentration, being faster for lower concentration, but the energy yield was higher for the higher initial concentration. Methyl red was degraded faster when decreasing the solution pH. Several degradation products, investigated by gas chromatography-mass spectrometry (GC-MS), were identified and discussed.