Singlet Oxygen Triggered by Superoxide Radicals in a Molybdenum Cocatalytic Fenton Reaction with Enhanced REDOX Activity in the Environment

As an important reactive oxygen species (ROS) with selective oxidation, singlet oxygen (¹O₂) has wide application prospects in biology and the environment. However, the mechanism of ¹O₂ formation, especially the conversion of superoxide radicals (·O₂^-) to ¹O₂, has been a great controversy. This process is often disturbed by hydroxyl radicals (·OH). Here, we develop a molybdenum cocatalytic Fenton system, which can realize the transformation from ·O₂^- to ¹O₂ on the premise of minimizing ·OH. The Mo⁰ exposed on the surface of molybdenum powder can significantly improve the Fe³⁺/Fe²⁺ cycling efficiency and weaken the production of ·OH, leading to the generation of ·O₂^-. Meanwhile, the exposed Mo⁶⁺ can realize the transformation of ·O₂^- to ¹O₂. The molybdenum cocatalytic effect makes the conventional Fenton reaction have high oxidation activity for the remediation of organic pollutants and prompts the inactivation of Staphylococcus aureus, as well as the adsorption and reduction of heavy metal ions (Cu²⁺, Ni²⁺, and Cr⁶⁺). Compared with iron powder, molybdenum powder is more likely to promote the conversion from Fe³⁺ to Fe²⁺ during the Fenton reaction, resulting in a higher Fe²⁺/Fe³⁺ ratio and better activity regarding the remediation of organics. Our findings clarify the transformation mechanism from ·O₂^- to ¹O₂ during the Fenton-like reaction and provide a promising REDOX Fenton-like system for water treatment.