Mechanism and Kinetic Modeling of Chloride-Enhanced Copper Fenton-Like Systems: The Role of Copper Speciation and Cu(III) Formation in Contaminant Degradation

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.