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.

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