Physicochemical process of non-thermal plasma at gas-liquid interface and synergistic effect of plasma with catalyst

An atmospheric-pressure plasma jet (APPJ) was directly irradiated at a gas-liquid interface under ambient conditions. The reactive oxygen species (ROS) like hydroxyl radicals (•OH), hydrogen peroxide (H₂O₂) and ozone (O₃) and also reactive nitrogen species (RNS) such as nitrogen oxides (NO_x) and nitric acid (HNO₃) formed during the plasma discharge were quantified under various experimental parameters. In a chemical dosimetry method, terephthalic acid (TA) was employed for the quantification of •OH and titanium sulfate was used to quantify the H₂O₂. Quantitative determination of NO₃⁻ was carried out by using Ion chromatography (IC). The changes in the solution pH were studied during the plasma treatment. Strong acidification along with the production of dominant reactive nitrogen species and ozone formation were observed with air. The effect of various gases, gas flow rate, various applied voltage and catalyst were studied to optimize the experimental conditions for the best performance. The influence of catalyst Fe²⁺ salt, TiO₂ on the formation of reactive species were studied. The efficiency of the plasma device for the degradation of crystal violet (CV) was also investigated with TiO₂ and Fe²⁺ salt.