Effects of particle morphology and surface hydrogenation on the phase stability ofTiO2

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Abstract
Titanium dioxide nanoparticles are currently receiving a lot of attention due to their inherent suitability for advanced photochemical applications. Size, phase, and morphology of the nanoparticles are the critical parameters determining their performance in particular applications. A thermodynamic model devised to describe the shape of nanoparticles as a function of size has been used to predict the phase stability of titanium dioxide nanoparticles, with particular attention given to the crossover of stability between the anatase and rutile phases. Density functional calculations were used to accurately determine surface energies and surface tensions. The effects of nanocrystal morphology on the phase transition are addressed and comparisons drawn with previously reported studies. Further, the model has been applied to titanium dioxide nanoparticles with hydrogenated surfaces, to investigate the effects of surface passivation on the equilibrium shape and the phase transition, and show that surface passivation has an important impact on nanocrystal morphology and phase stability. The results show that surface hydrogenation induces significant changes in the shape of rutile nanocrystals, but not in anatase, and that the size at which the phase transition may be expected increases dramatically when the under-coordinated surface titanium atoms are H-terminated.