Paper PS+SE-ThA3
Understanding Charge Transfer Reactions at a Plasma-Liquid Interface

Thursday, November 13, 2014, 3:00 pm, Room 308

The interaction of atmospheric-pressure plasma jets with liquids is becoming increasingly important for medical and materials applications. Despite empirical evidence of reactions occurring both in the bulk plasma and liquid phases, a basic understanding of the chemistry, particularly at the interface of the plasma and liquid, remains poorly understood. Previous studies have shown that species produced in the plasma phase such as nitric oxide (NO) and hydroxyl radicals (OH) can solvate in the liquid, yielding products such as nitrous acid (HNO₂) and hydrogen peroxide (H₂O₂) in the bulk solution [1]. In addition, we have recently shown that charge can be transferred from a DC microplasma jet into an aqueous solution to promote electrolytic reduction reactions [2]. However, it remains unclear how these charge transfer reactions occur and, in particular, if plasma electrons solvate in the liquid before subsequently reducing solution species.

To clarify the role of electrons solvating at a plasma-liquid interface, we have designed and built an experiment to detect solvated electrons using optical absorption spectroscopy. Electrons solvated in aqueous solutions are well known to absorb strongly in the red. Initial models suggest that because of the short lifetime of solvated electrons in aqueous solutions (~1 μ s) and anticipated solvation depths on the order 10 – 100 nm, optical absorption will be on the order of one part in 10⁶, making this an inherently challenging measurement. In this presentation, we will give an overview of our experimental method and present preliminary findings on direct measurements of electron solvation.

[1] P. Rumbach, M. Witzke, R. M. Sankaran, and D. B. Go, J. Am. Chem. Soc. 135 16264-16267 (2013).

[2] M. Witzke,P. Rumbach, D. B. Go, and R. M. Sankaran, J. Phys. D: Appl. Phys. 45 442001 (2012).