Structure and Phase Transition Behavior of Sn⁴⁺-Doped TiO₂ Nanoparticles

Abstract

Sn4+-doped TiO2 nanoparticles have been prepared by sol−gel method and annealed at different temperatures. Doping mode and existing states of Sn4+ dopants as well as the constituents and phase transition of the resultant nanoparticles have been investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and high resolution transmission electron microscopy techniques. Under a low-temperature annealing (300 °C), the majority of Sn4+ dopants are connected with Cl− ions, forming −Sn−Clx at the sample surface, while the others are doped into TiO2 lattice in substitutional mode. The amount of substitutional Sn4+ dopants decreases with the increasing annealing temperature. No −Sn−Clx is observed at 450 °C. When the annealing temperature is high enough, Sn4+ ions can replace lattice Ti4+ ions no matter whether the crystal structure of TiO2 is anatase or rutile. Furthermore, rutile SnO2 crystal evolves with the increasing annealing temperature, which can act as seeds for the growth of rutile TiO2. Accordingly, the phase transition temperature from anatase to rutile of TiO2 decreases obviously. This may help prepare Sn-doped TiO2 materials with high photoelectric properties that can be used in many fields, such as photocatalysis and solar cell.