Direct observation of a picosecond charge separation process in photoexcited platinum-loaded TiO2 particles by femtosecond diffuse reflectance spectroscopy

Transient absorption spectra of Pt-loaded TiO2 powder photocatalysts were measured by femtosecond diffuse reflectance spectroscopy and the dynamics of photogenerated electrons in TiO2 were investigated. The Pt-loaded TiO2 showed a new decay component of a few ps under 390 nm excitation in addition of normal charge recombination kinetics. This fast decay process can be interpreted as migration of electrons in TiO2 to Pt on the basis of detailed measurements changing experimental conditions such as Pt-loading, excitation wavelength and excitation fluence. These results clearly indicate that charge separation is responsible for the well-known enhancement of the catalytic reactivity of Pt-loaded TiO2.