Gliding arc discharge used for water activation: the production mechanism of aqueous NO and its role in sterilization

Gliding arc is a promising plasma technology for water activation due to its high energy efficiency for producing reactive nitrogen species (RNS), which is believed as the key agent for the sustained bactericidal effect of plasma-activated water (PAW). Nitric oxide (NO) is the major product of gliding arc and also widely exists in PAW, but the production mechanism of aqueous NO and its role in sterilization have been little investigated before. In this paper, NO-rich plasma effluent gas is produced by gliding arc discharge and introduced into water to produce PAW. The concentrations of gaseous and aqueous reactive species are detected, which decrease with the increasing air flowrate of the gliding arc. To clarify the contribution of plasma-induced RNS on water activation, the NO + air mixed gas is used to simulate the plasma effluent gas, and the results show that the two gases have similar gaseous composition and aqueous NO yield. Compared with the NO + Ar mixed gas with the same NO proportion, the NO + air mixed gas produces much more aqueous NO, implying that the presence of O₂ significantly enhances the production of aqueous NO. The sterilization experiments demonstrate the key role of aqueous NO in sterilization, but an acidic environment is necessary for aqueous NO to achieve a potent bactericidal effect.