Au clusters have interesting size-dependent optical, electronic, chemical, and magnetic properties. These clusters are commonly used for several important applications, such as catalysis, biological imaging, plasmonics, and sensing. The size of the cluster is crucial for these applications, especially in catalysis. Using voltammetry, we recently showed a dramatic negative shift in the oxidation potential of Au nanoparticles (NPs) with sizes below 4 nm. The oxidation potential of Au NPs shifted by about 850 mV negative of the bulk oxidation potential for populations of Au nanoparticles in the range of 2 nm based on transmission electron microscopy imaging. In this size range, we could not correlate the oxidation potential with a particular Au cluster size, however. In this presentation, we describe the oxidation of well-defined Au25 (0.9 nm) and Au144 (1.6 nm). An indium-tin-oxide coated glass-electrode was functionalized with mercaptopropyltrimethoxy silane, and soaked in a solution of the Au25 and Au144 for 1-10 min in order to adsorb them to the electrode. Next, the thiol ligands coating the clusters were removed. Finally, the presumably bare metallic core of the Au cluster was oxidized in an electrolytic solution of KBr and HClO4 by linear sweep stripping voltammetry to determine the oxidation potential. The decrease in the size of the metallic core Au clusters leads to a dramatic negative shift in oxidation potential compared to bulk Au. For Au25 (0.9 nm) clusters, we observed a negative shift of 650 mV and for Au144 (1.6 nm) cluster, we observed a negative shift of about 300 mV. We correlated our voltammetry results mass spectrometry data on these highly pure, well-defined samples. This correlation will be used to understand the size-dependent oxidation of Au nanoparticles. This is important in understanding nanoparticle stability and it will allow us to use voltammetry to characterize the size of nanoparticles.

Voltammetric observation of the oxidation potential of Au<sub>25</sub> and Au<sub>144</sub> clusters

246th National Meeting (2013)

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Voltammetric observation of the oxidation potential of Au25 and Au144 clusters

Voltammetric observation of the oxidation potential of Au₂₅ and Au₁₄₄ clusters