A combined radical and non-radical oxidation processes for efficient degradation of Acid Orange 7 in the homogeneous Cu(II)/PMS system: important role of chloride

Trace copper ion (Cu(II)) in water and wastewater can trigger peroxymonosulfate (PMS) activation to oxidize organic compounds, but it only works under alkaline conditions. In this work, we found that the presence of chloride could significantly accelerate the oxidation of Acid Orange 7 (AO7) by the Cu(II)/PMS process at a wide pH range (4.0-9.0). The observed pseudo-first-order rate constant k for AO7 oxidation was linearly correlated with the increased Cl- concentration (0-300 mM). An increase in mineralization rate was observed in the presence of Cl-, while the overall mineralization was quite low. Decomposition of PMS facilitated when Cl- concentration or pH value increased. Based on the scavenger experiments and electron paramagnetic resonance (EPR) measurement, the mechanism of Cu(II)-catalyzed PMS oxidation process in the presence of Cl- was proposed as both the radical and non-radical pathway, and O-1(2) was the reactive oxygen species in the Cu(II)/PMS system. Finally, a possible degradation pathway of AO7 was elucidated. The feasibility of in situ utilizing high salinity and trace cupric species to accelerate the degradation of organic pollutants by the Cu(II)/PMS process in water and wastewater was demonstrated. However, the identification of undesired chlorinated by-products reminds us of cautiousness in assessing the application of Cu(II)/PMS system under chloride-rich environment. The findings of this work provide a simple and efficient approach to apply PMS in the remediation of refractory organic contaminants in the presence of trace cupric species under a high salinity environment with a wide range of pH.

Automated summary

The presence of chloride significantly accelerates the oxidation of AO7 by the Cu(II)/PMS process over a wide pH range, with an increase in mineralization rate observed but with overall low mineralization. The increase in Cl- concentration leads to a higher rate of mineralization, and the decomposition of PMS is facilitated with higher Cl- concentration or pH values.