Identification of Nitrogen doping sites by Valence to Core X-ray Emission Spectroscopy of Niobium and Titanium in (Nb,N) co-doped TiO2 p

In the field of photocatalysis, balanced co-doping of TiO2 with transition metal cations and nitrogen emerged as a promising approach to modify the optoelectronic properties of TiO2 in order to reduce its bandgap while limiting the density of defects. Our work on (Nb,N) codoped materials confirmed the improved photocatalytic activity depending on the synthesis conditions. The presence of Nb5+ in substitution of Ti4+ in the anatase TiO2 lattice was confirmed by XPS and XRD. But for the N doping atoms, while they seem to play a key role in the structure/efficiency relationship, the nature of doping sites remains largely unknown. This is due to the lack of characterization methods allowing to distinguish N from O in this type of structure. Valence to Core (VTC) X-ray Emission Spectroscopy (XES) at Nb and Ti K edge could then be a useful method to probe the coordination sphere of these cations and identify the presence of nitrogen in their environment.