Cu(III) generation and air sparging extend catalytic effectiveness of Cu₂S/H₂O₂ from neutral to acidic condition: performance and mechanism in comparison with CuS/H₂O₂

Heterogeneous Fenton dominated by ·OH is limited in its application, as pre-acidification is required to maximize the generation amount and redox potential of ·OH. It is thus featured to consume resources and generate pollutants. In this study, both CuS/H₂O₂ and Cu₂S/H₂O₂ are found to show better performances under close-to-neutral condition (pH 5.0 to 9.0) than acidic condition (pH 3.0) when degrading a model contaminant, sulfamethazine (SMZ), because ·OH does not play a major role in both systems. The Cu valence-dependent catalytic mechanisms are responsible for the varied kinetics between CuS/H₂O₂ and Cu₂S/H₂O₂. In CuS/H₂O₂, Cu(III) and ¹O₂ contribute to the SMZ degradation, and their contributions are pH-dependent. In Cu₂S/H₂O₂, Cu(III) is responsible for the degradation regardless of the pH. Both systems with optimal performances under neutral condition are advantageous as pre-acidification can be avoided. In addition, air sparging induces additional 16% SMZ degradation in Cu₂S/H₂O₂ under acidic condition, because the sparged O₂ reacts with dissolved Cu(I). The more O₂ reacts with the dissolved Cu(I), the less generated Cu(III) is ineffectively depleted. Air sparging is readily applicable to different operations, thus its combination with Cu₂S/H₂O₂ potentially benefits the development of environmentally-friendly treatment process for industrial wastewater.