Evidence of interfacial charge transfer upon UV-light irradiation in novel titanium oxide gel

We report on the combined magnetization and electron paramagnetic resonance characterization of a novel Ti-O organic-inorganic get hybrid and the related electron-hole generation process upon UV illumination. We find that electrons are injected into the conduction band of the Ti-O framework, photoreducing Ti-IV to Ti-III. Ti-III sites are mainly located on the surface, owing to the nanometric dimensions of the inorganic component. Surprisingly, the symmetry of the TiO6 octahedra depends on the level of illumination: in the lightly UV-exposed samples Ti-III is sited in the weakly distorted TiO6 octahedra to which methanoate groups are bonded, as suggested by electron spin echo envelope modulation (ESEEM) experiments. Extensive illumination causes structural rearrangements, leading to enhanced tetragonal TiO6 distortion and shifting the Ti-III interaction towards the hydroxide groups or water. The results provide clear evidence for an interfacial charge transfer between the quantum-size TiO lattice and coordinated species upon in situ and ex situ UV illumination at temperatures from room temperature to 5 K.