Controlling Reactivity at the Plasma-Liquid Interface: Applications to Remediation of PFAS in Water

Abstract Atmospheric pressure plasmas (APPs) can efficiently activate liquids by simultaneous delivery of electrons, ions, photons, and excited neutral species to the liquid surface. With the goal of controlling APP-liquid interactions, the impact of operational parameters on the formation and development of surface ionization waves (SIWs) was investigated with a two-dimensional numerical model, including the effects of the: (i) applied voltage pulse; (ii) liquid thickness (capacitance); (iii) liquid conductivity; and (iv) Ar/He gas mixture ratio. These parameters can be used to control the type and flux of reactive species arriving at the liquid surface, providing a means to tune the plasma-initiated chemistry. Higher voltages, thinner liquids, higher liquid conductivities, and helium-rich mixtures shift the system towards charge-dominated interfacial reactivity, whereas lower voltages, thicker liquids, lower conductivities, and argon-rich mixtures enhance photon-driven pathways. The ability to control reactivity delivered to the surface was applied to an investigation of APP destruction of per- and polyfluoroalkyl substances (PFAS) in water. Since long-chain PFAS preferentially accumulate at the gas–liquid interface, APPs that generate SIWs provide a targeted means of delivering reactive fluxes directly to these contaminants.