Single-Atom Copper Promotes Efficient Generation of Hydroxyl Radicals under Alkaline Circumstances in a Photoelectrochemical Oxygen Reduction Process

A traditional Fenton reaction suffers the limitation of acidic conditions, impeding its practical application for environmental remediation. Selective reduction of oxygen with sustainable photoelectrochemical (PEC) technology was first proposed to enlarge the practicable pH range of 7–11. A novel photoelectrode with single-atom copper anchored on oxygen vacancy anatase (Cu-SA/TiO2–x) was designed for the efficient production of hydroxyl radicals (HO•) in an alkaline solution. The in situ-formed O–Cu on the electrode surface promoted the decomposition of electrogenerated H2O2 into HO•. The optimal accumulated concentration of HO• was 276.23 μmol·L–1 during PEC reduction of O2 at pH = 9. The removal of sulfamethoxazole was up to 96.3% in 10 min with the Cu-SA/TiO2–x electrode with an apparent kinetic constant (kobs) of 0.311 min–1. The energy consumption, recycling capacity, and electrolyte effect were evaluated in detail from the perspective of actual application. Furthermore, the high removal of chemical oxygen demand (69.1–93.9%) and the efficient removal of total nitrogen (25.1–87.7%) in five real water samples were almost uninfluenced by water quality. This work not only proposed a strategy of HO• production in the alkaline environment but also provided guidance for developing sustainable and efficient technologies, especially for decentralized water treatment.