X-ray absorption reveals surface structure of titanium dioxide nanoparticles

The structures of TiO₂ nanoparticles with a 19 Å 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 Å 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.