Electrochemical and theoretical studies for a better insight of the features of doped TiO2 nanoparticles

Doping titania by both metals and non-metals has attracted considerable attention due to a red-shift of the light absorption edge. A lively debate on the causes that provoke the shift of the absorption onset has arisen and grown. The main point of discussion concerns the eventual narrowing of the semiconductor band gap as a consequence of the doping or the creation of intra gap states. Also, the chemical nature and the location in the solid of the guest species responsible for visible light activity is still controversial. In this work, we report on TiO2 samples obtained by a sol-gel synthesis using different dopant species. From the electrochemical point of view the shift of the flat-band potentials (Efb) of semiconductors plays an important role deciding photocatalytic as well as photoelectrochemical properties of thin oxide films and powders in general. In particular, impedance spectroscopy has been applied to determine the value of the flat-band potential of TiO2 thin film electrodes prepared on conducting glass substrates and photovoltage measurements in slurry to assess the Quasi Fermi level. Theoretical ab initio Density Functional Theory (DFT) calculations were performed to evaluate the Fermi Energy location at the band-gap and the presence of intra-gap states for doped samples. By the conjunction of the theoretical DOS calculations and the electrochemical measurements a deeper insight of the properties of doped titania semiconductors was achieved.