Effect of oxygen gas on the decomposition of dye by pulsed discharge in water droplet spray

Abstract

AbstractThe effect of O2 on the decolorization of indigo carmine and on the production of dissolved species such as \documentclass{article}\usepackage{amsmath}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{amsfonts}\pagestyle{empty}\begin{document}$\mathrm{NO}_{2}^{-} , \mathrm{NO}_{3}^{-} $ \end{document}, O3, and H2O2 in the treatment water by pulsed discharges in a water droplet spray was investigated by controlling the O2/N2 ratios as carrier gases in the reactor. The decolorization rate gradually increased with a rise in the O2 ratio, which reached a constant value in the range of 50 to 90% for the O2 ratio and decreased in pure O2. The maximum value was about two times that of 20% for the O2 ratio. The decolorization efficiency was not affected by the gas flow rate in the range of 4 to 50 L/min. \documentclass{article}\usepackage{amsmath}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{amsfonts}\pagestyle{empty}\begin{document}$\mathrm{NO}_{2}^{-} $ \end{document} in the treatment water was detected only in pure N2, but \documentclass{article}\usepackage{amsmath}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{amsfonts}\pagestyle{empty}\begin{document}$\mathrm{NO}_{3}^{-} $ \end{document} was produced in O2/N2. \documentclass{article}\usepackage{amsmath}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{amsfonts}\pagestyle{empty}\begin{document}$\mathrm{NO}_{2}^{-} $ \end{document} added to the treatment water was not oxidized in pure N2, but was perfectly converted to \documentclass{article}\usepackage{amsmath}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{amsfonts}\pagestyle{empty}\begin{document}$\mathrm{NO}_{3}^{-} $ \end{document} in O2/N2. These results implied that the hydroxyl radicals produced in the gas phase do not directly contribute to the oxidation of substances in water. The O3 concentration gradually increased with a rise in the O2 ratio, whereas the H2O2 concentration decreased. In the range of 50 to 80% for the O2 ratio, the O3 and H2O2 concentrations stayed at approximately constant values, similar to the trend of the decolorization rate. The rate constants for various gas mixing ratios for O2/N2 were determined from a kinetic study. These results suggest that hydroxyl radicals produced in the treatment water by the chain reactions of O3 and hydroperoxy radical (HO2·) play an important role in the decomposition of molecules in water. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(4): 10–23, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22284