  Efficient sterilization of pathogens with cleaner methods 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 sterilization ability and not
inducing any acute toxicity, and only water and air are consumed during
production. For more efficient water activation, plasma sources are commonly
placed near or fully in contact with water as possible, but the risks of
electrode corrosion and metal contamination of water threaten the safety and
stability of PAW production. Herein, plasma-activated gas rich in high-valence
NOx is generated by a hybrid plasma configuration and introduced into water for
off-site PAW production. Plasma-generated O3 is found to dominate the gas-phase
reactions for the formation of high-valence NOx. With the time-evolution of O3
concentration, gaseous NO3 radicals are produced behind N2O5 formation, but
will be decomposed before N2O5 quenching. By decoupling the roles of gaseous
NO3, N2O5, and O3 in the water activation, results show that short-lived
aqueous species induced by gaseous NO3 radicals play the most crucial role in
PAW sterilization, and the acidic environment induced by N2O5 is also
essential. Moreover, SEM photographs and biomacromolecule leakage assays
demonstrate that PAW disrupts the cell membranes of bacteria to achieve
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 50mL produced in 3 minutes using this device is more
effective in disinfection than 0.5% NaClO and 3% H2O2 with the same bacterial
contact time. This work provides new avenues for efficient PAW production and
deepens insights into the fundamental processes that govern the reactive
chemistry in PAW sterilization.
