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 envir onments compared to those octahedral Ti sites in bulk anatase. The distorte d Ti sites are likely to adopt a pentacoordinate square pyramid geometry du e to the truncation of the lattice. Upon binding ascorbic acid on the surfa ces of the 19 Angstrom particles, the octahedral Ti site observed in the bu lk TiO2 is largely restored. This discovery shows that the distortions in T iO2 lattice are mainly located on the surface of the particles. The distort ed Ti surface sites are responsible for the binding with other small molecu les, which is often a prerequisite in surface chemistry.