Singlet oxygen dominance for phenolic degradation mediated by mixed-valence FeO_x nanospheres

In this investigation, we successfully synthesized magnetic FeO_x nanosphere catalysts with mixed-valence and high operational stability through the pyrolysis of a hybrid material containing polyferrocenlyphosphazene with coordinating heteroatoms (N, P, O). We evaluated the degradation performance of these catalysts using the peroxymonosulfate (PMS) activation process against four different phenolic compounds, namely phenol, 4-nitrophenol, 2,4-dinitrophenol, and 2,4,5-trinitrophenol. Our results demonstrate the significant role of FeO_x in the degradation process. The presence of mixed iron species, such as ferric iron, zero-valent iron, and iron oxides, activated PMS to generate radicals. Additionally, the heteroatoms facilitated the anchoring and dispersion of FeO_x nanospheres while also breaking the inertness of the carbon structure. Notably, the FeO_x-800 catalyst exhibited a maximum degradation activity of 98% for phenol, surpassing its counterparts. Electron paramagnetic resonance and free radical scavenging experiments confirmed that singlet oxygen (¹O₂) is the principal reactive oxygen species (ROS) that leads to the oxidative breakdown of phenolic compounds. This study introduces new concepts for designing Fenton-like catalysts incorporating heteroatoms into the carbon matrix. Due to their low cost and non-toxicity, these catalysts have recently received a great deal of attention for peroxymonosulfate (PMS) activation and environmental remediation.