Kinetic pathways of sub-bandgap induced electron transfer in Ag/TiO2 and the effect on isopropanol dehydrogenation under gaseous conditions

Abstract

Electron transfer and its kinetics play a major role in the photocatalysis of metal/semiconductor systems. Using in situ photoconductances, in situ photoabsorption, and photoinduced spectroscopic techniques, the present research aimed to gain a deep insight into electron transfer pathways and their kinetics for Ag/TiO₂ systems under sub-bandgap light illumination and gaseous conditions. The results revealed that electrons generated in TiO₂ can transfer to Ag nanoparticles at fast rates, and plasmon-generated electrons in Ag nanoparticles can also transfer to TiO₂. However, it was found that plasmon-assisted hot electron transfer efficiency is much lower than the electron transition from the valence band to the conduction band of TiO₂. Rather than plasmonic active spots, the results showed that Ag nanoparticles acted as co-catalyst sites bridging electron transfer to recombination in a methanol-containing N₂ atmosphere. As a result, photocatalytic isopropanol dehydrogenation was decreased. Independent of Ag decorations, it was also indicated that isopropanol dehydrogenation mainly occurred over TiO₂ surfaces; therefore, Ag nanoparticles did not increase photocatalytic activities. Our results may provide a different viewpoint on sub-bandgap light-induced Ag/TiO₂ photocatalysis under gaseous conditions; this may also facilitate the understanding of the photocatalytic mechanism of metal/semiconductor systems.