Decomposition of Methylene Blue by using an Atmospheric Plasma Jet with Ar, N2, O2, or Air

We have performed experiments on the decomposition of methylene blue by using an atmospheric plasma jet with various working gases. The decomposition efficiencies of Ar, N-2, and O-2 plasmas are almost equivalent; on the other hand, the rate of methylene blue decomposition by air plasma is lower than those by the other plasmas. From the absorption spectra, it has been found that HONO (nitrous acid) is produced by air plasma-liquid reactions. It has been clarified by a series of experiments, where oxygen concentration in N-2 plasma is varied, that the concentration of HONO increases and the rate of methylene blue decomposition degrades with increasing oxygen gas flow rate. Furthermore, the presence of nitrate ions and nitrite ions was confirmed by ion chromatography and pH measurement. (C) 2013 The Japan Society of Applied Physics