Characterization of the Structures of Size-Selected TiO2 Nanoparticles Using X-Ray Absorption Spectroscopy

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Abstract
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 ∼30 nm (sample A), ∼12 nm (sample B), and ∼7 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.