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 m easured by femtosecond diffuse reflectance spectroscopy and the dynamics of photogenerated electrons in TiO2 were investigated. The Pt-loaded TiO2 sho wed a new decay component of a few ps under 390 nm excitation in addition o f normal charge recombination kinetics. This fast decay process can be inte rpreted as migration of electrons in TiO2 to Pt on the basis of detailed me asurements changing experimental conditions such as Pt-loading, excitation wavelength and excitation fluence. These results clearly indicate that char ge separation is responsible for the well-known enhancement of the catalyti c reactivity of Pt-loaded TiO2. (C) 2001 Published by Elsevier Science B.V.