Decolorization of tar dye aqueous solution by atmospheric-pressure plasma jet

The decolorization of tar dye aqueous solution by the irradiation of an atmospheric-pressure plasma jet was examined by absorbance spectrum measurement and nuclear magnetic resonance (NMR) and mass spectrometry (MS) analyses. An atmospheric-pressure argon (Ar) plasma jet was generated at a frequency of 10 kHz with an applied voltage of 10 kV and an Ar gas flow rate of 10 L/min. When 10 mL of 100 mg/L tartrazine aqueous solution was irradiated with this plasma jet, the yellow solution gradually became lighter with increasing irradiation time and was almost completely decolorized after 50 min of irradiation. In addition, the results of MS analysis revealed that tartrazine molecules with a mass-to-charge ratio ( m / z ) of 579 were decomposed mainly into unidentified substances with m / z = 271. This result indicated that the decolorization was caused by the destruction of the azo bond in the tartrazine molecules.