Energy-efficient production of plasma-activated water: insights into controllable peroxynitrite chemistry

Pathogenic bacteria pose a continuous threat to human health. Plasma-activated water (PAW), produced by the interaction between cold atmospheric plasma and water, shows great potential as a broad-spectrum disinfectant towards pathogenic bacteria, among others. Previous studies have indicated that low levels of peroxynitrite (ONOO⁻) present in PAW play an important role in effectively inactivating pathogenic microorganisms; however, producing ONOO⁻ in a controlled and energy-efficient manner remains a challenge. In this study, we propose a new, green PAW production strategy based on the H₂O₂ + NO₂⁻ → ONOO⁻ + H₂O pathway using a dual underwater double bubble reactor (DR) with Ar and/or N₂ as the feed gases. The results show that Ar plasma-water interactions can effectively generate H₂O₂, while N₂ plasma favors the generation of aqueous NO₂⁻. By adjusting the Ar/N₂ ratio, the system achieves an ONOO⁻ production rate of 51.3 μmol h⁻¹ and an energy efficiency of 2850 μmol (kW h)⁻¹. Additionally, the DR-produced PAW demonstrates effective inactivation of Staphylococcus aureus, reducing the bacterial population by more than five orders of magnitude within 10 min. Scavenger experiments confirm that ONOO⁻ can be classified as the primary bactericidal agent, underscoring the importance of energy-efficient synthesis of ONOO⁻ for sustainable disinfection methods. Overall, this work not only emphasizes the importance of ONOO⁻ in PAW-based sterilization and shows effective strategies for controllable and highly energy-ONOO⁻ efficient peroxynitrite synthesis, but also provides new insights into PAW-related chemistry and the development of environmentally friendly disinfection reagents.