ROS/RNS Production in Water Using Various Discharge Plasma

A pulsed discharge, a DC corona discharge and an atmospheric pressure plasma jet are generated above water, the off-gas of a packed-bed dielectric barrier discharge (PB-DBD) is sparged into water, and then reactive oxygen species and reactive nitrogen species in the water are investigated. H$_{2}$O$_{2}$, NO$_{3}^{-}$ and a trace of NO$_{2}^{-}$ are produced in the water after the plasma exposure. H$_{2}$O$_{2}$ concentration decreases when NO$_{3}^{-}$ concentration increases, so that this is likely that OH radical to produce H$_{2}$O$_{2}$ by OH $+$ OH $\to $ H$_{2}$O$_{2}$ is consumed in the NO$_{3}^{-}$ production by NO$_{2} \quad +$ OH $\to $ HNO$_{3} \to $ NO$_{3}^{-} \quad +$ H$^{+}$ (in water). Since no species is detected in water by the sparging of the PB-DBD off-gas containing more than 1000 ppm of O$_{3}$, O$_{3}$ does not contribute to produce H$_{2}$O$_{2}$ in water. Further, only NO$_{3}^{-}$ is produced by the sparging of the off-gas containing N$_{2}$O$_{5}$ and HNO$_{3}$. This leads that H$_{2}$O$_{2}$ and NO$_{2}^{-}$ can be produced by short-lifetime species in plasma. In this work, the highest generation efficiency of H$_{2}$O$_{2}$ and NO$_{2}^{-}$ are respectively 3,820 $\mu $g/Wh and 830 $\mu $g/Wh by the pulsed-plasma exposure, and that of NO$_{3}^{-}$ is 2,530 $\mu $g/Wh by the off-gas sparging of the PB-DBD.