In-situ Raman spectroscopy measurements of non-thermal plasma driven aniline oxidation in aqueous solution

The interface between non-thermal plasma, or plasma at or near room temperature, and liquid solutions is a complex system containing electric fields, solvated charged species, energetic chemical reactants, vacuum ultraviolet photons, and charged droplets which can all drive interesting chemical reactions. Due to the number of processes at the plasma-liquid interface, there is much to be learned about the interaction between the two states and what variables control chemical reactions. To begin to understand how plasmas interact with solutions, we studied the oxidation of aniline via non-thermal plasma irradiation of aqueous solutions using in-situ Raman spectroscopy to probe the reaction. We were able to show that the plasma irradiation of aniline selectively forms five-membered aniline oligomers via aniline oxidation. We also showed that the oxidation is predominantly driven by the formation of superoxide. We intend to use this information to further determine the impact of superoxide at the interface and identify methods for optimizing the transport of superoxide to drive chemical oxidation reactions. This work illustrates the use of spectroscopic measurements to better understand plasma-liquid interactions and how we can begin to understand plasma-liquid interfacial interactions.