Generation of reactive oxygen species by promoting the Cu(II)/Cu(I) redox cycle with reducing agents in aerobic aqueous solution

This study investigated the generation of reactive oxygen species (ROS) (O 2 − •, H 2 O 2 , and HO•) by promoting the Cu(II)/Cu(I) redox cycle with certain reducing agents (RAs) in aerobic aqueous solution, and benzoic acid (BA) was employed as indicator for the hydroxyl radical (HO•). Hydroxylamine (HA) can reduce Cu(II) to Cu(I) to induce chain reactions of copper species resulting in the generation of the superoxide radical (O 2 − •) and hydrogen peroxide (H 2 O 2 ), and the intermediate Cu(I) can further activate H 2 O 2 via a Fenton-like reaction to produce HO•, creating the remarkable BA degradation. O 2 is indispensable, and unprotonated HA is the motive power in the O 2 /Cu/HA system. Moreover, pH is a crucial factor of the O 2 /Cu/HA system due to the protonated HA not being able to reduce Cu(II) into Cu(I). The oxidation of HA can be effectively induced by trace amounts of Cu(II), and both a higher HA dosage and a higher Cu(II) dosage can enhance H 2 O 2 generation and BA degradation. In addition, some other RAs that can reduce Cu(II) into Cu(I) could replace HA in the O 2 /Cu/HA system to induce the generation of these ROS in aerobic aqueous solution.