X-ray absorption reveals surface structure of titanium dioxide nanoparticles

The structures of TiO2 nanoparticles with a 19 Angstrom diameter have been probed using Ti K-edge XANES, revealing severe distortions in Ti site environments compared to those octahedral Ti sites in bulk anatase. The distorted Ti sites are likely to adopt a pentacoordinate square pyramid geometry due to the truncation of the lattice. Upon binding ascorbic acid on the surfaces of the 19 Angstrom particles, the octahedral Ti site observed in the bulk TiO2 is largely restored. This discovery shows that the distortions in TiO2 lattice are mainly located on the surface of the particles. The distorted Ti surface sites are responsible for the binding with other small molecules, which is often a prerequisite in surface chemistry.