Promotion of superoxide radical production by photo-Fenton over Fe^III/Fe₃O₄/TiO₂ catalysts for antibiotics degradation

The photo-Fenton method improves pollutant degradation by using hydrogen peroxide (H₂O₂) to produce more free radicals, which then break down the pollutant molecules. However, existing research on photo-Fenton reactions focuses predominantly on the generation of hydroxyl radicals (·OH) as the main reactive oxygen species, which limits the overall degradation efficiency. Therefore, controlling the types of free radicals generated is a challenge in optimizing pollutant degradation. In this study, we investigate the various types of free radicals produced by different catalysts and assess their effects in degrading pollutants·H₂O₂ reacts with both Fe^Ⅲ and Fe^Ⅱ at different rates, resulting in various reaction products. The types of radicals generated can be controlled by adjusting the ratio of Fe^Ⅲ and Fe₃O₄ within the catalyst system. In this study, by optimizing the ratio of Fe^Ⅲ and Fe₃O₄, high concentrations of tetracycline (TC) can be efficiently degraded by Fe^III(₃)/Fe₃O₄/TiO₂₍₅₎–H₂O₂ sample we prepared. The degradation reached 100 % within 15 min, with a degradation rate of 33.33 mg·g⁻¹·min⁻¹, surpassing results from previously reported TC degradation studies. Mechanistic studies revealed that the coexistence of Fe^Ⅲ and Fe^Ⅱ in the photocatalyst leads to the formation of superoxide radical (·O₂⁻) as the primary reactive oxygen species in the process of TC degradation, resulting in high degradation efficiency.