Active Species Generation in Gas–liquid Discharge Non-thermal Plasma: Operating Conditions, Influencing Factors, and Mechanisms

In this study, gas–liquid phase non-thermal plasma in a needle-plate reactor was used to evaluate the generation of active species (·OH, H 2 O 2 , and O 3 ). Specifically, the effects of different factors, including initial pH, conductivity, gas flow rate, and solution circulation flow rate, on the generation of these active species were investigated. Tert-butanol (TBA) was chosen as the scavenger of ·OH given that formaldehyde is a specific product of their reaction. The results showed that the generation of ·OH and H 2 O 2 occurs at a faster rate in acidic solutions than in alkaline and neutral solutions. High-conductivity solutions hindered the generation of these active species, which were also affected by the electrolyte type. Further, oxygen and liquid circulation flow rates had little effect on ·OH and H 2 O 2 generation in aqueous solutions. However, they exerted a greater impact on ozone mass transfer in gas and liquid phases. Furthermore, the simulation of the effects of UV irradiation, H 2 O 2 oxidation, and ozone oxidation on the generation of these active species during discharge showed that individually, UV radiation and ozone oxidation had no significant effect on the generation of ·OH and H 2 O 2 . However, various combinations of these processes, especially UV/O 3 /H 2 O 2 and UV/O 3 , significantly enhanced ·OH production.