Efeito da temperatura na cinética de espécies reativas nitrogenadas por plasma frio de ar atmosférico na pós-descarga

Abstract

In this work, a kinetic study was developed during the post-discharge phase of nitrogen reactive species (NRS) produced in a cold plasma discharge reactor. The ultrapure water activation time in the plasma reactor was 60 minutes. After interrupting the plasma discharge (t0), the post-discharge time was measured up to 180 minutes. The experimental temperatures were 5.00, 15.00, 25.00, and 35.00 °C. These experimental temperatures remained constant during both discharge and post-discharge periods. Data on the rate constants (kobs) for HNO2 consumption, pH, and conductivity were collected. The presence of nitric and nitrous acids in plasma-activated water was identified. The kinetics of nitrous acid (HNO2) consumption were monitored spectrophotometrically at 372 nm, showing a second-order reaction concerning HNO2. It was demonstrated that the reaction proceeded fastest at 35.00 °C, where kobs = 4.96 x 10–3 ± 5.20 x 10–4 min–¹ and the half-life (t½) = 140.73 minutes. The activation parameters obtained were: activation energy, Eₐ = +20.73 kJ mol–¹, activation enthalpy, ΔH⧧ = +18.29 kJ mol–¹, activation entropy, ΔS⧧ = –230.29 J K–¹ mol–¹, and Gibbs free energy of activation, ΔG⧧ = +85.80 kJ mol–¹. A decrease in HNO3 concentration was observed at the beginning of the post-discharge, as evidenced by the reduction in absorbance at 302 nm, the decrease in conductivity, and the increase in pH. After this initial post-discharge period, the pH values tended to decrease, while conductivity and absorbance at 302 nm increased throughout the post-discharge.