The influence of chloride ions on contaminant oxidation efficiency in a copper Fenton-like system at circumneutral pH is investigated in this study. Results demonstrate that increasing chloride concentrations in the Cu(II)/H2O2 system enhance Cu(III) production through dual mechanisms: (i) an increased rate of reaction between Cu(II) and H2O2 due to the formation of kinetically active Cu(II) complexes toward hydrogen peroxide (specifically CuCl(OH)); and (ii) greater Cu(I) stability resulting from a decreased rate of reaction between Cu(I) and O2 due to a lower abundance of Cu(I) complexes reactive toward molecular oxygen (Cu+, CuCl(OH)-, and CuCO3-). A kinetic model, developed for different chloride concentrations (0.01, 0.1, and 0.7 M) under environmentally relevant conditions of pH 7.5 and a bicarbonate concentration of 2 mM, successfully described the behavior of key system components (Cu(I), H2O2) as well as formate oxidation over a range of concentrations. Spectroscopic analysis confirmed Cu(III) as the primary oxidant, an efficient oxidant under circumneutral conditions, with its production rate increasing with increasing chloride concentration. Reactive chlorine species (RCS) were ruled out as major contributors to formate oxidation under the experimental conditions used.
Ferrer et al. (2025) studied this question.