Impressive demonstrations of this phenomenon were provided by Haruta and co-workers, 2 who found Au nanoparticles (supported on transition metal oxides) to have a high catalytic activity in CO and H 2 oxidation, even at low temperatures. 1 Radiolysis experiments have demonstrated that Au atoms have a redox potential similar to sodium borohydride, one of the most potent reductants in chemistry. Experiments have shown that isolated Au atoms are readily oxidized in air. However, gold's noble characteristics spectacularly vanish as the dimensions of the material are reduced to the nanometer scale. Corrosion and oxidation resistance are the hallmarks of Au, with these properties being exploited in many technological and everyday applications, such as dentistry, jewelry and electronics.
Introduction The noble character of bulk Au has been well known for centuries. Ex situ SEM images demonstrate that only the region of the sample that was exposed to O 3 shows the presence of ridges on the Au surface. In the Au 4f spectra, an additional component at low binding energy (83.3 eV), which appears during/after O 3 treatment, is assigned to the presence of low-coordinated atoms which appear on the Au surface as a result of surface restructuring under oxidation.
These morphological changes do not disappear even under vacuum.
The surface oxidation led to structural modifications of the gold surface. Assuming that an oxide overlayer completely covers the Au surface, the thickness of the oxide phase was estimated to be between 0.29 and 0.58 nm by energy-dependent XPS depth profiling. Our in situ observations show that a surface oxide phase is formed during the exposure to ozone however this phase decomposes under vacuum and even in the presence of ozone at temperatures higher than 300 ☌. The surface of a gold foil under ozone oxidation was examined by near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and scanning electron microscopy (SEM).
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