On the mechanism of OH radical formation by nanosecond pulsed corona discharge in water

Abstract

Electrical discharge plasmas in liquids have been studied for a number of years for applications in different environmental, biological or medical applications. However, the physics underlying the complex phenomena of electric discharge formation in liquid media as well as the chemistry of plasma/liquid interactions induced by these discharges is not fully understood. OH radical is one of the most strongly oxidative species produced by plasma in water and is also building block of H2O2 which is an important agent in the chemical activity of plasma-liquid systems. So far, pulse durations applied for generation of discharge plasmas in liquids were typically in the range of microseconds. The average energy of electrons formed by streamer-like discharges in water was estimated to be 0.5–2 eV This would be sufficient to cause only vibration and rotational excitation rather than electron dissociative reactions of water. Therefore, metastable induced or thermal dissociation of water molecules and electron dissociative recombination of water ions are proposed as more likely pathways of plasmachemical production of OH radicals in water. Recently, a fundamentally different type of discharge generated in water by application of high-voltage pulses with nanosecond duration was reported by several authors. The observed discharge was reported to have a completely different nature from the discharges with microsecond pulse duration. This suggests, that it might be possible to vary electron energy distribution in the discharge and plasmachemical processes in water by pulse duration of pulsed power used for discharge in water.