Decolorization of indigo carmine solution was performed by excitation of argon dielectric barrier discharge (DBD) on a target solution and the effect of the gap distance on the water treatment characteristics was investigated for a gap distance between 1.0 and 2.5 mm. The argon DBD was excited by a 3 kHz sinusoidal voltage with a fixed discharge power between 1.72 and 1.76 W for each gap distance. Voltage and current waveforms and Lissajous figures were acquired to investigate the electrical characteristics of the DBD. Compared with fixing the discharge energy, a higher decolorization rate was obtained with shorter gap distance. Therefore, shortening the gap distance could lead to increased decolorization efficiency of the indigo carmine solution. The mechanism of higher efficiency with shorter gap distance is discussed on the basis of the electrical characteristics and possible plasma chemical reactions in the argon DBD on the solution surface.

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