Activation of oxygen via accelerating the copper-redox cycle by UV irradiation

This study proposes a new method showing that the addition of UV strongly enhanced the oxidation capacity of the Cu(II)/O₂ process, which subsequently produced reactive oxidants using copper as a catalyst via the Fenton-like reactions of in situ generated hydrogen peroxide (H₂O₂). Acid orange 7 (AO7) was degraded more than 70% after 70 min at an initial pH of 3.5 in the Cu(II)/O₂/UV process. The mechanism investigation showed that a remarkable amount of Cu(I) and H₂O₂ was produced in the Cu(II)/O₂/UV process, which was due to UV irradiation and activation of oxygen (O₂). The addition of a radical scavenger, tert-butyl alcohol, inhibited AO7 degradation, which verified that hydroxyl radical (·OH) was the primary radical for the degradation of AO7. Superoxide radical (O₂·⁻) was also generated in the Cu(II)/O₂/UV process, indicating that (O₂·⁻) was considered as the intermediate of the production of ·OH. The results showed that the acidic condition was favorable for AO7 degradation, and the degradation of AO7 followed the pseudo-first-order kinetics. The high dosage of Cu(II) enhanced AO7 degradation, but exceeding the optimal dosage of Cu(II) would inhibit AO7 degradation.