Promoting Fe3+/Fe2+ cycling under visible light by synergistic interactions between P25 and small amount of Fenton reagents

Merits of adding P25 to homogeneous photo-Fenton-like process (ph-F) were evaluated under visible light using Bisphenol A (BPA) as a model pollutant. Interactions between P25 and Fe3+/H2O2 were emphasized. Results show that adsorption of Fe(III) on P25 produced redshift of light absorption, and interactions between P25 and H2O2 promoted photoelectron generation, effectively introducing visible light into ph-F. The visible-light-driven ph-F demonstrated adequate performance at high Fe3+/H2O2 dosage, while P25 addition showed significant acceleration of BPA degradation with saving amount of Fe3+/H2O2. The mechanism was confirmed to be enhanced Fe3+/Fe2+ cycling by photo-electrons, particularly pronounced at low [Fe(III)]. Additionally, H2O2 was utilized more efficiently in P25-ph-F than that in ph-F by diminishing the radical scavenging role of H2O2 at lower [Fe(III)]. Kinetics and ESR analysis supported this mechanism. Compared to ph-F, the P25-ph-F process also demonstrated stronger potentials in degrading BPA at high concentrations and better mineralization capability with reduced Fe3+/H2O2 reagents. The sustainability of P25-ph-F was also examined in regard to its advantage under sunlight and the strong recyclable and reusable capability. BPA decomposition was dominated by •OH attack at both the aromatic ring and the connecting carbon, and P25-ph-F was more competent in transforming the primary intermediates than ph-F.