Postdischarge Long Life Reactive Intermediates Involved in the Plasma Chemical Degradation of an Azoic Dye

The gliding electric discharge is a source of nonthermal plasma at atmospheric pressure efficient for pollutant abatement. It was used with a wet airflow to determine the kinetics of the postdischarge oxidation process of methyl orange dye in acidic solution (i.e., an oxidation reaction occurring after switching off the discharge). A strong postdischarge degradation of the dye giving N.N dimethyl-4-nitroaniline, as the major yellow intermediate product with a relevant overall first-order kinetics, was observed. Effects of both discharge exposure time and wet airflow were studied, showing linear correlations between these parameters and the overall rate constant. Such results combined with the studies of nitrous acid occurrence and oxidation of the dye by HNO₂ and H₂O₂ suggest that nitrous and peroxonitrous acids are the main oxidizing species involved in the phenomenon