Mechanisms of multielectron reactions at the plasma/water interface: Interfacial catalysis, RONS, nitrogen fixation, and plasma activated water

There are three major multi-electron reactions in nature: nitrogen fixation by bacteria, water oxidation in photosynthesis, and oxygen reduction during respiration. Here we found that a cold atmospheric pressure He-plasma jet (CAPPJ) can oxidize N-2 to HNO3 and HNO2 at low temperature and atmospheric pressure at the plasma-air/water interface. Redox reactions induced by cold plasma occur not only at the plasma/air and plasma/water interfaces, but also in the volume of the aqueous phase. Analysis of the images which displayed the presence of pH indicators in the aqueous phase showed that redox reactions and acid formation occur at the plasma-air/water interface and the products of electrochemical reactions slowly diffuse into the bulk of the aqueous solution. Acidification of an aqueous solution during the CAPPJ treatment correlates with an increase in HNOx concentration in the aqueous phase. HNO2 is unstable and can be oxidized to HNO3 by plasma-generated H2O2 or ozone. The mechanisms of the interfacial multielectron reactions at the plasma-air/water interface are discussed and evaluated. Plasma activated water can be used in medicine, food industry, and agriculture for disinfection, sterilization, and decontamination. Plasma-induced production of HNOx at the plasma/water interface at room temperature and atmospheric pressure can be used in the industry for nitrogen fixation and production of nitrogen compounds, replacing the expensive old technology processes. (C) 2021 Elsevier Ltd. All rights reserved.