The Role of Interfacial Reactions in Determining Plasma–Liquid Chemistry

In this work, we investigate the production of highly oxidative species in solutions exposed to a self-pulsed corona discharge in air. We examine how the properties of the target solution (pH, conductivity) and the discharge power affect the discharge stability and the production of H₂O₂. Indigo carmine, a common organic dye, is used as an indicator of oxidative strength and in particular, hydroxyl radical (OH^·) production. The observed rate of indigo oxidation in contact with the discharge far exceeds that predicted from reactions based on concentrations of species measured in the bulk solution. The generation of H₂O₂ and the oxidation of indigo carmine indicate a high concentration of highly oxidizing species such as OH^· at the plasma–liquid interface. These results indicate that reactions at the air plasma–liquid interface play a dominant role in species oxidation during direct non-equilibrium atmospheric pressure plasma treatment.