How gold affects TiO2 based photocatalysis
Promotion of photocatalytic events over semiconductors by Gold currently receives extensive attention in the literature. Two situations have been considered: activation of the semiconductor (usually by UV radiation), or excitation of the system with wavelengths corresponding to plasmon absorption energies. In the first situation the commonly accepted image of promotion is that Au provides an antenna for the photo-excited electrons and acts catalytically on chemical conversions . In this presentation Time Resolved Microwave Conductivity measurements will be presented to provide evidence for the antenna effect, as well as spectroscopic data providing evidence for promotion of catalysis by deposition of Au on the semiconductor (TiO2), if care has been taken not to affect the surface-OH population too extensively .
Plasmon Resonance absorption by metal particles, such as Au and Ag, has also recently been reported to induce dramatic increase in photocatalytic activity in e.g. solar water splitting . The mechanism behind the promotion is not so well understood, and has been explained by various physical phenomena (Figure 1) . The theories proposed will be briefly dealt with, and in particular the assumption that electrons of the plasmon excited state of the Au particle can transfer into the conduction band of the semiconductor will be discussed in detail. For the particular catalysts that we have investigated, neither electron transfer or catalytic effects could be demonstrated. Heat effects appear to be more relevant .
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