Grain-growth kinetics of rutile TiO_2 nanocrystals under hydrothermal conditions

摘要

Rutile nanocrystals were directly prepared under hydrothermal conditions using TiCl_4 as the starting material. The formation reactions proceeded by suppressing the crystallization of the other TiO_2 polymorphs using a fixed concentration of 0.62 M [Ti~(4+)]. With increasing reaction temperatures from 140 to 220℃, 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 ℃ the particle size increased from 17 to 40 nm. The grain-growth kinetics of rutile TiO_2 nanocrystals under hydrothermal conditions was found to follow the equation, D~n= k_o x t x e~(-E_a/RT) with a grain-growth exponent n = 5 and an activation energy of E_a = 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.