Plasma Water Activation with an Inductive Plasma Torch at Atmospheric Pressure

The production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), collectively referred to as RONS, has been of increasing interest in recent years. This is based on the wide range of applications for the components mentioned. Examples include the food industry and agriculture or biological applications [1 – 3]. The generation of RONS by plasma-liquid interaction in plasma-activated water is a widely used method. Due to the plasma properties, such as high electron temperatures at low gas temperatures, mainly cold or non-equilibrium plasmas are used [4 – 5]. Plasmas in thermal equilibrium at atmospheric pressure have so far played a subordinate role in PAW generation due to their moderate electron temperatures and high thermal losses. This leads to a lack of publications in this field.
In our work, we have developed an inductively driven plasma (ICP) torch, which was used for plasma water activation. An atmospheric pressure inductive Argon plasma was generated with a power of 1.2 kW at a frequency of 3 MHz. The used setup is shown in Figure 1. The plasma was pointed to distilled water in a distance of 1 cm. During a one-hour treatment, the concentration of hydrogen peroxide (H2 O2), nitrite (NO2 −), nitrate (NO−3) and the pH value was measured every 10 minutes by using Quantofix test strips (Peroxide 100, Nitrite, Nitrate 100, pH-Fix 0-14, Machery-Nagel, Düren, Germany).
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Furthermore, a simulation model of the lab setup used was created. The FEM software COMSOL multiphysics was used to simulate the plasma behaviour and to determine the electron temperature at the atmosphere and the water impact region [6]. With the results, the formation rate of the components mentioned were approximated and compared with other methods for PAW generation.
1. Bradu, C.; Kutasi, K.; Magureanu, M.; Puaˇ c, N.; Živkovi´ c, S. Reactive nitrogen species in plasma-activated water: generation chemistry and application in agriculture. Journal of Physics D: Applied Physics 2020 , 53, 223001. https://doi.org/10.1088/1361-6463/ab795a.
2. Xiang, Q.; Fan, L.; Li, Y.; Dong, S.; Li, K.; Bai, Y. A review on recent advances in plasma-activated water for food safety: current applications and future trends. Critical reviews in food science and nutrition 2022 , 62, 2250–2268. https://doi.org/10.1080/10408398 .2020.1852173.
3. Zhou, R.; Zhou, R.; Wang, P.; Xian, Y.; Mai-Prochnow, A.; Lu, X.; Cullen, P.J.; Ostrikov, K.; Bazaka, K. Plasma-activated water: generation, origin of reactive species and biological applications. Journal of Physics D: Applied Physics 2020 , 53, 303001. https://doi.org/10.1088/1361-6463/ab81cf.
4. Oh.; Szili.; Hatta.; Ito.; Shirafuji. Tailoring the Chemistry of Plasma-Activated Water Using a DC-Pulse-Driven Non-Thermal Atmospheric-Pressure Helium Plasma Jet. Plasma 2019, 2, 127–137. https://doi.org/10.3390/plasma2020010.
5. van Gils, C.A.J.; Hofmann, S.; Boekema, B.K.H.L.; Brandenburg, R.; Bruggeman, P.J. Mechanisms of bacterial inactivation in the liquid phase induced by a remote RF cold atmospheric pressure plasma jet. Journal of Physics D: Applied Physics 2013, 46, 175203. https://doi.org/10.1088/0022-3727/46/17/175203.
6. COMSOL Multiphysicsv. 6. www.comsol.com. COMSOL AB, Stockholm, Sweden.