Studies of Nanosized Iron-Doped TiO₂ Photocatalysts by Spectroscopic Methods

Iron-doped TiO₂ nanoparticles with iron content in the range of 0.005 <Fe/Ti <0.3 were prepared using the flame spray pyrolysis method and investigated with CW X-band electron paramagnetic resonance (EPR), X-ray diffraction, and Fourier transform infrared spectroscopy. This allowed for the clarification of the internal organization of Fe–TiO₂ nanoparticles. Different types of Fe(III) centers were distinguished in the samples: isolated high-spin paramagnetic Fe(III) ions (S = 5/2) in rhombic ligand fields state at 0.005 <Fe/Ti <0.05, and Fe(III) ferromagnetic clusters at Fe/Ti <0.1. All Fe-doped samples had rather high activity for the photocatalytic mineralization of oxalic acid under visible light illumination (λ > 400 nm) at 25 °C. Correlations were made between EPR and photocatalytic activity results. The specific surface area [S] data allowed us to deduce that the isolated Fe(III) centers were responsible for the photomineralisation of oxalic acid, while the Fe(III) ferromagnetic aggregates decreased the total efficiency of the system.