Non-thermal atmospheric-pressure positive pulsating corona discharge in degradation of textile dye Reactive Blue 19 enhanced by Bi₂O₃ catalyst

In this work, monoclinic Bi₂O₃ was applied for the first time, to the best of our knowledge, as a catalyst in the process of dye degradation by a non-thermal atmospheric-pressure positive pulsating corona discharge. The research focused on the interaction of the plasma-generated species and the catalyst, as well as the role of the catalyst in the degradation process. Plasma decomposition of the anthraquinone reactive dye Reactive Blue 19 (RB 19) was performed in a self-made reactor system. Bi₂O₃ was prepared by electrodeposition followed by thermal treatment, and characterized by x-ray diffraction, scanning electron microscopy and energy-dispersive x-ray techniques. It was observed that the catalyst promoted decomposition of plasma-generated H₂O₂ into •OH radicals, the principal dye-degrading reagent, which further attacked the dye molecules. The catalyst improved the decolorization rate by 2.5 times, the energy yield by 93.4% and total organic carbon removal by 7.1%. Excitation of the catalyst mostly occurred through strikes by plasma-generated reactive ions and radical species from the air, accelerated by the electric field, as well as by fast electrons with an energy of up to 15 eV generated by the streamers reaching the liquid surface. These strikes transferred the energy to the catalyst and created the electrons and holes, which further reacted with H₂O₂ and water, producing •OH radicals. This was indentified as the primary role of the catalyst in this process. Decolorization reactions followed pseudo first-order kinetics. Production of H₂O₂ and the dye degradation rate increased with increase in the input voltage. The optimal catalyst dose was 500 mg∙dm⁻³. The decolorization rate was a little lower in river water compared with that in deionized water due to the side reactions of •OH radicals with organic matter and inorganic ions dissolved in the river water.