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

TLDR

Singlet oxygen is a valuable reactive oxygen species with selective oxidation, yet its formation from superoxide radicals remains controversial and is often hindered by hydroxyl radicals. The study develops a molybdenum cocatalytic Fenton system designed to convert superoxide radicals into singlet oxygen while minimizing hydroxyl radical production. Molybdenum zero on the powder surface enhances Fe³⁺/Fe²⁺ cycling and suppresses hydroxyl radical generation, producing superoxide, while exposed Mo⁶⁺ facilitates the conversion of superoxide to singlet oxygen. The resulting system exhibits high oxidation activity for organic pollutant remediation, inactivates Staphylococcus aureus, adsorbs and reduces heavy metals, and improves Fe redox cycling, demonstrating a promising REDOX Fenton-like approach for water treatment.

Abstract

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.