Hydroxyl radicals and hydrogen peroxide formation at nonthermal plasma-water interface

Zhao, Yi Yi and Wang, Tao and Wilson, Mark P. and MacGregor, Scott J. and Timoshkin, Igor V. and Ren, Qing Chun (2016) Hydroxyl radicals and hydrogen peroxide formation at nonthermal plasma-water interface. IEEE Transactions on Plasma Science, 44 (10). 2084 - 2091. ISSN 0093-3813

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    Abstract

    This paper investigated hydroxyl radicals and hydrogen peroxide formation under a needle-plate electrode con- figuration using positive-polarity dc discharges generated in air, nitrogen, and helium. The discharge mode in air and nitrogen was found to change above ultrapure water; initially, a nanosecond pulse discharge was observed, transitioning to a diffuse discharge due to the increasing conductivity of the water. The discharge in helium was a nanosecond pulse discharge and the repetition rate increased with increasing water conductivity. It was found that hydroxyl radicals contribute to 7%, 78%, and 70% of hydrogen peroxide formation when using the ultrapure water in air, nitrogen, and helium, respectively. It is suggested that hydroxyl radicals are formed by water reactions with energetic positive ions and the neutral particles, such as N + 2 ,He + ,O,H, and HO 2 . Part of hydrogen peroxide is directly formed from atoms and radical reactions with water in nitrogen and helium, while oxygen reactions are heavily involved for hydrogen peroxide formation in air. A fluorophotometry method, using terephthalic acid, was used to directly quantify the formation of hydroxyl radicals and compared with the tert-butanol method.