Cyan titania nanowires: Spectroscopic study of the origin of the self-doping enhanced photocatalytic activity

We report a detailed spectroscopic study of Ti3+ self-doped TiO2 nanowires prepared by high temperature annealing of the protonated titanate nanowires (TiONW) in hydrogen atmosphere. Hydrogenation causes a color change from white to cyan and a major increase of photocatalytic activity. Combination of synchrotron X-ray diffraction and Rutherford backscattering spectrometry revealed that the bulk of the protonated titanate and Ti3+ self-doped titania is identical. Raman spectroscopy combined with local laser heating indicated the presence of optically active states in the hydrogenated TiO2 nanowires. Using multi-frequency electron paramagnetic resonance spectroscopy (EPR), the presence of Ti3+ surface states on the cyan titania nanowires is confirmed. We argue that these surface point defects are responsible for enhanced visible light absorption and improved their photocatalytic performance. (C) 2016 Elsevier B.V. All rights reserved.