Singlet oxygen synergistic surface-adsorbed hydroxyl radicals for phenol degradation in CoP catalytic photo-Fenton

In recent years, there have been numerous studies on Fenton or Fenton-like reactions mediated by nonfree radicals such as singlet oxygen (1O2); however, there are few studies on the synergistic effect of 1O2 and free radicals on the degradation of organic molecules, such as phenol in Fenton reaction. In this study, a cocatalyst, CoP, commonly used in photocatalysis was synthesized using a simple two-step method, and a CoP/Fe2+/AM1.5 system was constructed by introducing Fe2+ and simulated sunlight (AM1.5) irradiation. The newly constructed CoP/Fe2+/AM1.5 system could effectively degrade various organic pollutants, including dyes, phenols, and antibiotics. Radical quenching experiments and electron paramagnetic resonance detection confirmed that there were three reactive oxygen species (ROS) in the CoP/Fe2+/AM1.5 system, including •OHads, •O2−, and 1O2. Further, combined with the liquid chromatogram of phenol, its intermediate products, and the fluorescence diagram of o-hydroxybenzoic acid, it can be concluded that a synergistic effect exists between 1O2 and the surface-adsorbed ·OHads in the CoP/Fe2+/AM1.5 system. The controllable formation of surface 1O2 and •OHads was achieved through the oxidation (Co3+) and reduction (Pδ−) centers exposed on the CoP surface, and the synergistic effect between them results in phenol's hydroxylation, ring-opening, and degradation. The study of this new mechanism provides a new perspective for revealing the surface interface reaction between ROS and organic pollutants.