Characterization of the structures of size-selected TiO2 nanoparticles using x-ray absorption spectroscopy

To investigate the relationship between the size and structure of TiO2 nanoparticles, three size-selected samples of TiO2 nanoparticles were prepared via a hydrolysis method that uses Ti[OCH(CH3)(2)](4) as the starting material. The structures of the nanoparticles were characterized using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS). Analysis of the XRD patterns and of the TEM images showed that the samples were dispersed, with an average particle size of similar to30 nm (sample A), similar to12 nm (sample B), and similar to7 nm (sample C). Their X-ray absorption spectra indicate that samples A and B have an anatase structure, whereas sample C has a structure very similar to that of the TiO2 II phase, which generally arises only under high-pressure conditions. This difference can be attributed to size-induced radial pressure within the smaller nanoparticles, which plays an important role in the phase of TiO2 nanoparticles in sample C.