Impact of Au on the transition temperature and photocatalytic activity of TiO₂

The effect of gold (Au) addition on the anatase to rutile transition temperature (ART) of titanium dioxide (TiO₂) was investigated. Concentrations of 2, 4, 8 and 16 mol. % of Au have been synthesised via a sol–gel technique and calcined at various temperatures (500–900 °C). The inclusion of gold improves the ART at 700 °C, maintaining 44.5 % anatase content for 4 % Au. Density functional theory studies indicated that the addition of Au in the anatase phase results in considerable lattice distortions, while Au 4d states and occupied Ti 3d orbitals contribute to the valence-conduction band energy gap upon doping. However, no sign of lattice substitution was observed in the experimental analysis. Instead, we demonstrate that the actual structure is well described by gold nanoparticles deposited on anatase and present a detailed DFT description of gold-modified anatase (1 0 1). All Au-TiO₂ samples exhibit reduced photocatalytic degradation properties compared to the control TiO₂ at 500 °C. However, after calcining at 600 °C the addition of Au increases the photocatalytic activity of TiO₂ from 49 % to 61 %, at an optimal concentration of 2 % Au-TiO_2. The modification of titania with gold does push the transition temperature higher. However, this comes at the cost of reduced activity for 1,4-dioxane degradation, with the unmodified titania sample having better overall photocatalytic activity.