Competitive reactions in Cl− solutions treated by plasma-supplied O atoms

Reactions accompanying the hypochlorite formation in Cl− solutions oxidized by plasma-supplied O atoms were studied. The concentration of oxychlorine compounds from reaction of O atoms with solutions of NaCl, NaOCl and NaClO2 was measured. The concentration dependence of O + Cl− reaction rate was evaluated using the simplified kinetic model leading to estimation of the 2nd order rate constant, k = 1.64 ± 0.01 × 105 M−1s−1. The limiting reaction rate at highly concentrated NaCl corresponds well with the delivery rate of O atoms to the gas-liquid interface calculated from the previously measured O concentration at the plasma jet outlet. Virtually all plasma-supplied O atoms can be captured by Cl− ions in highly concentrated solutions. The measurements confirmed the reactions O + OCl−, and O + ClO2− as loss channels decreasing the hypochlorite production in O-treated Cl− solutions. These loss channels are less effective at more acidic pH, where the formation of ClO2− is minimized and as a consequence, also the solution post-discharge reactivity. The validity of described reaction system was confirmed by chemical kinetics modelling. The fitted rate coefficients for the O reactions with ionic Cl forms were 3–4 orders of magnitude lower than those predicted in the literature.