To understand and improve the applications of titanium-oxide nanoparticles, it is extremely important to perform a detailed investigation of the surface and the interior structural properties of nanocrystalline materials, such as rutile and anatase with diameter of few nanometers. Here, x-ray absorption spectroscopy has been used to identify the local Ti environment and characterize the related electronic structure. We combine experimental results at the Ti K edge in both bulk and nanocrystal samples to determine the lattice distortion via the characteristic pre-edge features and the variation in the multiple-scattering region of the x-ray absorption near-edge structure spectra. The correlation between peak intensities and surface-to-volume ratio of nanoparticles is also discussed.

The preedge features in a system with "even" symmetry, apart from quadrupolar transition contribution, are mainly dipolar in character, associated with the existence of unoccupied states made up of mixed cation-4p with higher-neighboring cation-3d orbitals, and reflect the density of states due to the medium-range order of the system. In "odd" symmetry materials these preedge features are the result of a transition from the 1s to a final density of states of p symmetry due to an unsymmetrical mixing of the ligand wave functions with the central cation 3d orbitals, similar to atetrahedral configuration. These results are validated for Fe as a photoabsorber by comparing XAS spectra of Fe2SiO4 (fayalite) to ab initio full multiple scattering calculations at the Fe K edge, but pertain to all systems containing sixfold-coordinated cations.