Unraveling the Unique Properties of Transient Discharges in Bubbles and Liquid Water

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This project is focused on the understanding of the production of reactive species when plasmas interact with liquids. Plasmas in and in contact with liquids are one of the most exciting and important intellectual frontiers in plasma science, with broad potential applications ranging from environmental remediation and green chemistry to biomedical applications. The complex interaction of plasmas with liquids offers a rich source of short-lived chemically reactive species, many of which are critical for chemical and biological applications. Plasmas are often considered to be an advanced oxidation technology for liquid waste treatment and also have great promise in the destruction of pharmaceuticals in drinking water. The presence of these pharmaceuticals in the water supply is an increasing public concern and for several cases no alternative technologies exist to remove them from drinking water. In addition, plasmas in liquids can be used for environmentally friendly chemical synthesis of hydrogen peroxide, hydrogen and even nanoparticles. Producing hydrogen and hydrogen peroxide from water with better energy efficiency than electrolysis or other chemical processes would be a major step forward. The nanoparticles in the context of advanced material science could also strongly affect energy research that increasingly uses complex nanostructured materials. Since energy efficiency is often a bottleneck for applications of plasmas in liquids, a better understanding of the reactive species production in these plasmas is the necessary step to lead to a breakthrough in technologies based on plasmas in liquids. To date, progress in the field of plasmas in liquids has been hindered by the lack of quantitative correlations between plasma properties and the plasma induced liquid phase chemistry. The key idea of this project is to generate a non-equilibrium plasma filament in liquid water by a nanosecond pulsed high voltage supply in a needle-needle electrode geometry. This offers an excellent control of the plasma dynamics and allows detailed investigation of a stabilized plasma filament. The short-lived reactive species production mechanisms will be investigated both temporally and spatially resolved by a combination of advanced laser diagnostics. In addition, plasma induced liquid reactivity will be measured and a direct link between plasma chemistry and liquid phase chemistry will be established. This is expected to lead to the necessary knowledge for optimizing and establishing many promising applications as stated above. This project enables education of students and a post-doctoral researcher in the cross-disciplinary field of plasma engineering. The outcomes of this work will be used to extend an existing graduate course on Plasma Technology to cover non-equilibrium liquid phase plasmas including laboratory demonstrations. Within the framework of the project, collaboration with the Science Museum of Minnesota will be initiated to establish an exhibit about plasmas.