Location and catalytic role of iron species in TiO2:Fe photocatalysts: An EPR study

A usual approach to improve the photocatalytic activity of wide band gap oxide semiconductors is through doping with transition metals. Dopants are primarily selected according to their capacity to introduce energy levels in the oxide band gap, promoting light absorbance. In the present work, we carefully characterize iron-doped titania powders obtained by a sol–gel route. Iron cations are introduced in the initial solution, before gelification, what promotes their lattice localization. X-ray diffraction and electron spin resonance spectroscopy are used to determine the temperature evolution of the crystalline structure and the dopant local environment. These results allow us to correlate the structural, electronic and chemical properties of the iron-doped titania powders with their activity towards the photocatalytic degradation of methylene blue (MB). The obtained results showed that Fe3+ cations far from improve the photocatalytic properties of bare TiO2, decreased the activity towards methylene blue degradation. We associated such decrease with the role played by the iron cations depending on their position inside the lattice of TiO2. And second, iron cations located near or at the surface tend to form iron-based structures, such as iron titanate or pseudobrookite which are highly inactive as photocatalyst.