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Published online by Cambridge University Press: 31 January 2011
Rutile nanocrystals were directly prepared under hydrothermal conditions using TiCl4 as the starting material. The formation reactions proceeded by suppressing the crystallization of the other TiO2 polymorphs using a fixed concentration of 0.62 M [Ti4+]. With increasing reaction temperatures from 140 to 220°C, rutile nanocrystals were found to grow from 5.4 to 26.4 nm in size, and by varying the reaction time from 2 to 120 h at 200°C the particle size increased from 17 to 40 nm. The grain-growth kinetics of rutile TiO2 nanocrystals under hydrothermal conditions was found to follow the equation, Dn = k0 × t × e(-Ea/RT) with a grain-growth exponent n = 5 and an activation energy of Ea = 170.8 kJ mol-1. The nanocrystals thus obtained consist of an interior rutile lattice and a surface hydration layer. With decreasing particle size, the hydration effects at the surface increase, while the rutile structure shows a lattice expansion and covalency enhancement in the Ti-O bonding.