“…Indeed, previous studies have shown that the actual nitrogen content in TiO2 lattice is generally much lower than the nominal amount, since an appreciable loss of N containing species occurs during calcination. 11,14 Nitrogen bulk quantification is quite a challenging task, since conventionally used techniques, such as X-ray photoelectron spectroscopy (XPS), provide information about the surface and near-subsurface composition of the oxide, which is greatly influenced by the presence of atmospheric contaminants (C, N and O). 8 Previous studies on Nb-doped TiO2 have also underlined other relevant discrepancies between bulk and surface compositions in such systems, such as a higher Nb content at the surface due to the occurrence of surface segregation phenomena 58 .…”