Insights into the mechanisms of plasma physicochemical characteristics on ultralong-lasting plasma-activated water: the influence of DC power polarity on RONS generation

Abstract

In our recent work, we successfully developed an innovative method based on pin-water discharge for preparing ultralong-lasting plasma-activated water (PAW) with a lifetime of up to 720 hours at room temperature. However, the impact of power polarity on the preparation method for ultralong-lasting PAW remains unclear. In this study, we discovered that ultralong-lasting PAW could only be achieved with positive polarity. Further analysis of the liquid reactive oxygen and nitrogen species (RONS) revealed that the absence of H₂O₂ in the discharge chamber was crucial for the failure of ultralong-lasting PAW preparation at negative polarity. To elucidate the mechanism underlying the generation of RONS at different polarities, we conducted plasma feature diagnosis, compared discharge morphologies, and performed theoretical analyses based on chemical reactions. Our results indicated that the introduction of water vapor molecules through intense spraying at positive polarity led to an increase in the generation of H₂O₂-related source particles, while also interfering with N₂-related electron collision reactions and chemical reaction coefficients, ultimately affecting the production of NO₂⁻. Consequently, there was relatively less liquid NO₂⁻ and more abundant H₂O₂ in the discharge chamber at positive polarity, whereas the opposite trend was observed for these two key RONS at negative polarity. Furthermore, the minimal amount of NO₂⁻ at positive polarity and the tiny amount of H₂O₂ at negative polarity in the discharge chamber would be respectively consumed by the relatively abundant H₂O₂ at positive polarity and NO₂⁻ at negative polarity.