Off-site Production of Plasma-activated Water for Efficient Disinfection: The Crucial Role of High Valence NO and New Chemical Pathways

Efficient disinfection of pathogens is a critical concern for environmental disinfection and clinical anti-infective treatment. Plasma-activated water (PAW) is a promising alternative to chemical disinfectants and antibiotics for its strong disinfection ability and not inducing any acute toxicity. Previous plasma sources are commonly placed near or fully in contact with water as possible for more efficient activation, but the risk of electrode corrosion and metal particle contamination of water threatens the safety and stability of PAW. In this work, plasma-activated gas (PAG) rich in high-valence NO is generated by a hybrid plasma configuration and introduced into water for off-site PAW production. It is found that plasma-generated O dominates the gas-phase reactions for the formation of high-valence NO. With the time-evolution of O concentration, the gaseous NO radicals are produced behind NO formation, but will be decomposed before NO quenching. By decoupling the roles of gaseous NO, NO, and O in the water activation, results show that short-lived aqueous species induced by gaseous NO radicals play the most crucial role in PAW disinfection, and the acidic environment induced by NO is also beneficial for microbial inactivation. Moreover, SEM photographs and biomacromolecule leakage assays demonstrate that PAW disrupts the cell membranes of bacteria and thus achieves inactivation. In real-life applications, an integrated device for off-site PAW production with a yield of 2 L/h and a bactericidal efficiency of >99.9 % is developed. The PAW of 50 mL produced in 3 min using this device is more effective in disinfection than 0.5 % NaClO and 3 % HO with the same bacterial contact time. Overall, this work provides new avenues for efficient PAW production and deepens insights into the fundamental chemical processes that govern the reactive chemistry in PAW for environmental and biomedical applications.