The geometric, electronic and chemical properties of Au nanoparticles supported by TiO2 have been the subject of much work since the discovery by Haruta that Au is a low temperature oxidation catalyst. Despite this earlier work there is no definitive evidence for the binding site or the direction of charge transfer associated with gold atoms and nanoparticles on the model substrate TiO2(110). In this work we have used STM to examine the nucleation properties of Au nanoparticles dispersed over a reduced rutile TiO2(110) surface. From comparisons of the surface before and after Au deposition, and using atomic manipulation, the nucleation site of single Au atoms was directly observed to be at oxygen vacancies on the substrate (Ob-vacs), with dimers similarly anchored. Associated DFT calculations suggest electron transfer from bridging O vacancies to Au. In another attempt to gauge the degree of Au/TiO2 charge transfer, synchrotron based X-ray photoelectron emission microscopy (XPEEM) was used in conjunction with STM and low energy electron microscopy (LEEM) to probe the electronic character of Au nanoparticles as a function of particle size and coverage. Core-level binding energy measurements reveal a two stage shift in Au 4f binding energy as the nanoparticle size increased in line with electron transfer from bridging oxygen vacancies to Au for small nanoparticles (&lt;4 nm) on TiO2(110). To reduce experimental error, a method was developed to precisely pattern the substrate with discrete regions of varying Au coverage on the nanometer scale. Turning to the Au naoparticle size dependent behavior of photocatalysis, we show that H2 evolution from ethanol varies as the separation between nanoparticles. This appears to originate from a competition betweeen the nanoparticles to trap photogenerated electrons.

Gold nanoparticle interactions with rutile TiO2(110)

2019 Spring National Meeting

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