Systematic study of electronic properties of Fe-doped TiO 2 nanoparticles by X-ray photoemission spectroscopy

The importance of investigating the electronic structure of Fe doped TiO2 nanoparticles lies in understanding their various magnetic and optical applications. In this study Fe doped TiO2 nanoparticles were synthesized by sol–gel method in a wide range of Fe/Ti molar ratios (1, 3, 5, 8, and 10%) and post annealing at 400, 600 and 800 °C in air. The structure and size of nanoparticles were studied by X-ray diffraction and transmission electron microscopy, respectively. Systematic study of the existing states of Fe ions in Fe doped TiO2 and transformation of the existing states as a function of annealing temperature and Fe concentration were carried out utilizing high-resolution X-ray photoemission spectroscopy (XPS). The XPS results showed that Fe was present in all samples while Fe ions were detected in mixed valence (Fe2+ and Fe3+) states. The Fe3+ ions were dominant in the surface region of the nanoparticles. Moreover, the Ti in Fe:TiO2 nanoparticles was assigned to the Ti4+ while a small shift towards lower binding energies was observed upon increasing the annealing temperature and dopant level. This confirms the successful incorporation of Fe into TiO2, and the shifts in binding energies were attributed to the anatase to rutile transformation. The results verify that doping by Fe up to 10% do not exceed the limit of Fe substitutation into TiO2 lattice.