Decolouration of organic dye in aqueous solution by pulsed-discharge plasmaover water surface

Decomposition characteristics of methylene blue in an aqueous solution by the exposure of pulsed-discharge plasma generated above a water surface are investigated for different background-gas composition. It is likely that OH radicals are produced by the reaction between high energy electrons and H₂O vapour, and that the OH radicals contribute to the decomposition of methylene blue. Further, O₃ is found to contribute to the decomposition of methylene blue at high oxygen concentration, and slight contribution of OH radicals, produced by the reaction between N₂, excited in metastable state (N₂(A³S_u ⁺)), and H₂O vapour, is observed in pure N₂. However, NO_x, produced in N₂-O₂ mixture, decompose O₃ and inhibits O₃ generation. In Ar-O₂ mixture, the high decomposition rate of methylene blue is obtained regardless of O₃ concentration. This is probably due to Ar atoms in metastable states, such as ³P₂ and ³P₀.