The influence of gold on the optical properties of sol–gel derived titania

The absorption spectra of TiO2 and Au–TiO2 have been measured as a function of calcination temperature in order to study the effect of Au on the band gap energy of TiO2. Our results indicate that a signature of the presence of Au is a decrease in the band gap energy of TiO2 to a value less than the commonly quoted band gap energies of bulk anatase and rutile. In addition, a drastic decrease in the band gap energy of Au–TiO2 is observed with samples heated at 700 °C in an argon atmosphere, which is attributed to the influence of defects in the structure of TiO2. The reduction in the band gap energy of TiO2 in the presence of Au is correlated to enhanced photo chemical processes previously described and is associated with a strong interaction between Au and TiO2.