We describe the photochemical and antimicrobial synergy between ambient-condition air plasma and ultraviolet photons at near-UV (UVA) wavelengths. Plasma treatments generate reactive oxygen and nitrogen species in aqueous solution. When UVA treatment followed plasma treatment of Escherichia coli, the antimicrobial effect exceeded the effect predicted from the two treatments alone. Exposing individual plasma-associated species to UVA photons indicated that the synergy is associated with nitrite and hydrogen peroxide in combination. An antioxidant present during UVA treatment prevented the synergistic effect, suggesting oxidant-mediated bacterial inactivation. Addition of nitrite to aqueous solution, followed by photolysis of nitrite by UVA photons, is hypothesized as the primary mechanism of synergy. UVA photons near 360 nm synergize with chemical species created by air plasma to produce a strong antimicrobial effect in solution. Treatment of a solution with air plasma adds oxygen and nitrogen compounds including nitrite to the solution, and UVA photons can photolyze nitrite to produce hydroxyl radical, a strong oxidizer. Combining photon treatment with plasma treatment boosts disinfection speed and efficacy.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Polymers and Plastics
- bacterial inactivation
- dielectric barrier discharges (DBD)
- non-thermal plasma