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Grain-growth kinetics of rutile TiO2 nanocrystals under hydrothermal conditions
Published online by Cambridge University Press: 31 January 2011
Abstract
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.
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