Plasma-activated water: Effects of gas–liquid interface interaction and discharge intensity on activation properties

In this study, the additional force generated at the gas–liquid interface by a nanosecond-pulsed needle-ring electrode atmospheric pressure plasma jet (APPJ) and its impact on the activation performance of plasma-activated water (PAW) are investigated. The mechanism of APPJ interaction at the gas–liquid interface is thoroughly examined, and the effect of discharge intensity on PAW activation is explored by measuring the gas temperature and the reactive species in the gas phase. The gas-phase characteristics of APPJ are characterized using both electrical and optical properties, while reactive substances in PAW, such as H2O2, NO2−, and NO3−, are detected using the colorimetric method. The results reveal that the interaction of APPJ with the liquid surface can be linked to rapid plasma “bullets” impacting the surface, creating an additional force that facilitates the formation of a gas–liquid plasma channel. Empirical formulas derived from the study indicate that this force is closely related to the energy of the plasma bullets and is significantly influenced by the discharge intensity. Enhanced discharge intensity markedly increases the gas temperature and the reactive species in the gas phase. Variations in these factors, induced by changing discharge intensity, are responsible for the changes in the concentration of long-lived reactive substances in the liquid phase. Among the factors studied, discharge voltage exerts a more pronounced effect than discharge frequency.