Computational Modelling of RONS Generation and its Enhancement by UV Photolysis in Plasma-Liquid System

Abstract

Active attempts have been ongoing to utilize abundant reactive oxygen and nitrogen species (RONS) produced by atmospheric pressure plasmas in various fields such as biomedicine, agriculture, and food cycle. One of the interesting ways of utilizing RONS is via the plasma-treated water (PTW) because PTW effectively maintains a large amount of RONS and relevant intermediates for a long post-discharge period. While applying PTW containing RONS for applications, identifying the key chemical species and their kinetics is a prerequisite because they strongly depend on application systems [1]. In this presentation, our numerical code developed to obtain spatiotemporal distribution of RONS in a plasma-water system will be discussed. The code calculates RONS concentration in the 1D gas and liquid model from the 0D plasma global model with Boltzmann equation solver (BOLSIG+), to calculate mean electron energy and mobility [2], [3]. In the model, the decomposition reaction of chemical species by photons, i.e. photolysis, was included to predict how chemical products change depending on the spectrum and intensity of UV light source. The result shows that the concentrations of O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , and NOx are higher than other species in the entire gas region, and O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , and NO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> concentrations are higher than other species in the liquid region. hydroxyl radical (OH) and nitric oxide (NO) and other radicals in the plasma region generated these species by reactions with the electron, ions, and radicals. However, OH and NO concentration is relatively low due to their high reactivity. By UV photolysis, O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , NO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , HNO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , and NO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−</sup> were decomposed, resulting in the additional production of OH NO in PTW. The developed model gives valuable insights into controlling the RONS generation in the UV-combined PTW system, and it will provide a better understanding of the change in chemical composition of PTW in the presence of a light source.