Decomposition of Methylene Blue in an Aqueous Solution Using a Pulsed-Discharge Plasma at Atmospheric Pressure

The decomposition characteristics of methylene blue in an aqueous solution on exposure to a pulsed‐discharge plasma generated above a water surface are investigated for different background‐gas compositions (N2‐O2 mixture and Ar‐O2 mixture) and electrode configurations (1 needle and 55 needles). It is likely that OH radicals produced by reaction between H2O vapor and high‐energy electrons in the pulsed plasma expanding on the water surface contribute to the decomposition of methylene blue. Further, O3 is found to contribute to methylene blue decomposition at high oxygen concentrations, and a slight contribution of OH radicals, produced by the reaction between N2 molecules excited in a metastable state [N2(A3\documentclass{article}\usepackage{amsmath}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{amsfonts}\pagestyle{empty}\begin{document}$\Sigma_{u}^{+}$\end{document})] and H2O vapor, is observed in pure N2. In a N2‐O2 mixture, the O3 concentration decreases significantly and simultaneously NOx is produced by the pulsed plasma. Therefore, NOx probably destroys O3 and inhibits O3 generation. In an Ar‐O2 mixture, a high decomposition rate of methylene blue is obtained regardless of the O3 concentration. It is likely that Ar atoms in metastable states, such as 3P2 and 3P0, contribute to the decomposition of methylene blue. A higher decomposition rate of methylene blue and a higher O3 concentration are observed when a streamer‐like discharge is generated with 55 needle electrodes, than with a single needle electrode. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(3): 1–9, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21217