Interfacial charge transfer in Pt-loaded TiO2 P25 photocatalysts studied by in-situ diffuse reflectance FTIR spectroscopy of adsorbed CO.

Graphical abstract Highlights • In-situ DRIFTS on adsorbed CO was employed to study UV induced charge transfer in Pt-TiO 2 P25. • Largest UV-induced shift is +0.5 cm−1 for CO adsorbed on atomic Pt species. • CO adsorbed on large Pt clusters or particles does not experience large shifts upon illumination. • Contrary to solid–liquid interfaces, shifts of ν(CO) at the solid–gas interface are small. Abstract The efficiency of photocatalytic systems is strongly depending on the charge carrier transfer from the excited semiconductor to co-catalyst particles attached on its surface. In this study, we investigated the influence of photo-induced charge transfer in photoplatinized TiO 2 P25 photocatalysts by diffuse reflectance FTIR spectroscopy of CO molecules adsorbed on the Pt co-catalyst under well-defined gas phase conditions. In contrast to aqueous conditions, where shifts of the CO stretching vibration of up to 50 cm−1 have been reported, the observed shifts under gas phase conditions are very small (<1 cm−1). This demonstrates that the difference in dielectric properties between aqueous electrolytes and vacuum are critical for the development of prominent shifts of adsorbed CO bands upon trapping of photogenerated charge carriers on co-catalyst particles. The experimental findings are discussed in terms of an electrostatic Stark effect, charge screening, co-adsorption, coverage-dependent shifts of the vibrational bands of adsorbed CO and photocatalytic surface reactions. [ABSTRACT FROM AUTHOR]