Detection of free radicals produced by a pulsed electrohydraulic discharge using electron spin resonance

•Free radicals in an electrohydraulic discharge are detected using ESR.•We succeed to decolorize a difficult-to-treat reactive dye solution using the discharge.•We clarify hydroxyl radical generation from hydrogen peroxide induced by the discharge.•Hydroxyl and hydrogen radicals are main ones induced by the discharge.

The detection of free radicals such as hydroxyl radical and hydrogen radical for plasma in solution induced by a pulsed electrohydraulic discharge are successfully performed using electron spin resonance measurement. The plasma reactor is a barrier-type and consists of a stainless needle high-voltage (+35 to 65 kV) electrode partially immersed in the solution and a Pyrex glass solution container around which an aluminum film grounded electrode is wrapped. Streamers are induced in the solution. After adding iron (II) sulfate or radical trapping agent before the plasma application, the spectrum for radicals is clearly detected. A reactive dye solution is dramatically decolorized.