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 (O-1(2)) has wide application prospects in biology and the environment. However, the mechanism of O-1(2) formation, especially the conversion of superoxide radicals (center dot O-2(-)) to O-1(2), has been a great controversy. This process is often disturbed by hydroxyl radicals (center dot OH). Here, we develop a molybdenum cocatalytic Fenton system, which can realize the transformation from center dot O-2 to O-1(2) on the premise of minimizing OH. The Mo-0 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 center dot O-2(-). Meanwhile, the exposed Mo6+ can realize the transformation of center dot O-2(-) to O-1(2). 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 center dot O-2(-) to O-1(2) during the Fenton-like reaction and provide a promising REDOX Fenton-like system for water treatment.