Visible-light photoresponse of gold nanoparticles supported on TiO2 : a combined photocatalytic, photoelectrochemical, and transient spectroscopy study.

In the context of gaining understanding on the origin of the visible-light photoresponse of TiO2 containing gold nanoparticles, the photocurrent spectra and photocatalytic H-2 evolution of titania (P25) and Au-P25 were compared. Whereas no photocurrent was detected upon visible-light irradiation for either of the two photocatalysts, Au-P25 exhibited photocatalytic H-2 evolution for wavelengths between 400 and 575 nm. This contradictory behavior under visible-light irradiation of Au-P25 was rationalized by transient absorption spectroscopy. It was suggested that photocatalytic H-2 generation results from methanol quenching of the charge-separation state in each semiconductor nanoparticle, but the lack of photocurrent is due to the short lifetime of the charge separation, which makes interparticle charge migration for micrometric distances unlikely.