Boosting Photo-Fenton Activity of FeWO4 via Mn Doping for Pollutant Degradation: Band Structure Engineering and Enhanced Reactive Oxygen Species Generation

Photo-Fenton technology is considered an effective method for removing organic pollutants from water. In this work, a novel Mn-doped FeWO4 (Mn-FeWO4) photocatalyst was synthesized via a one-step hydrothermal method and applied for the photo-Fenton degradation of tetracycline (TC). The optimal Mn-FeWO4-0.05 achieved 100% removal of TC within 60 min under visible light irradiation with a degradation rate constant of 0.0793 min−1, which is 4.5 times higher than that of pristine FeWO4. Systematic characterization revealed that Mn2+ ions were successfully incorporated into the FeWO4 lattice, inducing lattice expansion and narrowing the bandgap from 2.37 eV to 2.25 eV, while also adjusting the conduction and valence band positions. This modulation significantly enhanced visible light absorption and promoted the separation and migration of photogenerated electron–hole pairs. In addition, the Mn2+/Mn3+ and Fe2+/Fe3+ dual redox cycles ensure the continuous generation of reactive oxygen species. Radical trapping experiments and electron paramagnetic resonance (EPR) spectroscopy demonstrated that superoxide radicals (•O2−) and photogenerated holes (h+) were the dominant reactive species, while singlet oxygen (1O2) and hydroxyl radicals (•OH) played auxiliary roles. Moreover, Mn-FeWO4-0.05 exhibited excellent stability, strong anti-interference ability against common anions, and high degradation efficiency toward various pollutants.