The role of Au loading for visible-light photocatalytic activity of Au-TiO2 (anatase)

Abstract

Plasmonic photocatalysis has recently accelerated the rapid progress in enhancing photocatalytic efficiency upon visible light illumination, increasing the prospect of utilizing sunlight for environmental and energy applications. It has been reported that Au-TiO2 photocatalysts exhibit photocatalytic activity for H2 evolution under visible light illumination above 420 nm. This visible-light photocatalytic activity was attributed to the surface plasmon resonance (SPR) effect of the Au nanoparticles and the underlying mechanism has been discussed between the direct electron transfer (DET) process and resonance energy transfer (RET) process. However, most of the experiments have been reported to employ a 420 nm cutoff filter which indeed covers the absorbance tail of TiO2. In this contribution, it was confirmed that photocatalytic H2 gas formation over Au-TiO2 (anatase) can be obtained upon visible light illumination near the absorption edge of TiO2 (using a 420 nm filter). By means of EPR spectroscopy and Laser Flash Photolysis spectroscopy, we obtained direct experimental evidence that bare anatase TiO2 can be excited by visible light illumination at 420 nm and excited-state electrons migrate to the surface-loaded Au nanoparticles. In the presence of a 500 nm cutoff filter, however, no SPR-induced H2 formation was detected, although the plasmon band maximum of Au was completely illuminated. The obtained results revealed the catalytic role of Au on Au-TiO2 for H2 evolution upon visible light illumination (≥420 nm), employing pure anatase as TiO2 source.