Combination of NO _<i>x</i> mode and O ₃ mode air discharges for water activation to produce a potent disinfectant

Abstract

Abstract Air plasma is commonly used to treat water for activation or purification, and plasma-activated water (PAW) is a promising green disinfectant that has attracted much attention in recent years. However, either the O 3 discharge mode or the NO x discharge mode of air plasma lacks efficiency for water activation, mainly due to the low solubility of O 3 , NO and NO 2 . The transition process between those two modes could produce high-valence NO x such as N 2 O 5 which should be more efficient for water activation, but this process is not easily controlled and water activation by N 2 O 5 has rarely been reported before. In this letter, N 2 O 5 is found to be produced effectively and stably by mixing the effluent gases of a NO x mode air plasma, produced by gliding arc discharge, and an O 3 mode air plasma, produced by dielectric barrier discharge. The mixed gas rich in N 2 O 5 is found to be very efficient for water activation. A colony-forming unit reduction of nearly 6 logs was achieved for a methicillin-resistant Staphylococcus aureus suspension by using PAW treated by the mixed gas, and the high bactericidal effect of the PAW could persist for more than 1 h after the plasma activation. The main reactive species for the bactericidal effect in the PAW are discussed, and the chemical pathways for N 2 O 5 production and its usage for water activation are illustrated.