Chemical Effects of Air Plasma Species on Aqueous Solutes in Direct and Delayed Exposure Modes: Discharge, Post-discharge and Plasma Activated Water

Abstract

The chemical interaction between non-thermal plasma species and aqueous solutions is considered in the case of discharges in humid air burning over aqueous solutions with emphasis on the oxidizing and acidic effects resulting from formed peroxynitrite ONOO− and derived species, such as transient nitrite and stable HNO3. The oxidizing properties are mainly attributed to the systems ONOO−/ONOOH [E°(ONOOH/NO2) = 2.05 V/SHE], ·OH/H2O [E°(·OH/H2O) = 2.38 V/SHE] and to the matching dimer system H2O2/H2O [E°(H2O2/H2O) = 1.68 V/SHE]. ONOOH tentatively splits into reactive species, e.g., nitronium NO+ and nitrosonium NO 2 + cations. NO+ which also results from both ionization of ·NO and the presence of HNO2 in acidic medium, is involved in the amine diazotation/nitrosation degradation processes. NO 2 + requires a sensibly higher energy than NO+ to form and is considered with the nitration and the degradation of aromatic molecules. Such chemical properties are especially important for organic waste degradation and bacterial inactivation. The kinetic aspect is also considered as an immediate consequence of exposing an aqueous container to the discharge. The relevant chemical effects in the liquid result from direct and delayed exposure conditions. The so called delayed conditions involve both post-discharge (after switching off the discharge) and plasma activated water. An electrochemical model is proposed with special interest devoted to the chemical mechanism of bacterial inactivation under direct or delayed plasma conditions.