Among the various types of gold nanoparticle systems providing features that enable field localization, gold nanostars have been widely recognized for their ability to create strong Localized Surface Plasmon Resonances (LSPRs) that significantly enhance the local electric field, as a consequence of the presence of sharp protruding spikes. Multiple LSPR resonances can be observed in gold nanostars, that depend on the size, shape, and length of the spikes. Unfortunately, traditional protocols for the synthesis of gold nanostars have failed to provide sufficient sample monodispersity and reproducibility to enable fundamental studies on the plasmon modes. We will discuss here a new seed-mediated synthesis in which the morphology of gold nanostars, and thus their plasmon resonances, can be tuned by changing the concentration of three reagents, Triton-X, silver nitrate (AgNO3), and ascorbic acid (C6H8O6). Herein we will show how AgNO3 plays a significant role on the kinetics of the growth process and how the extremely high monodispersity of the samples enables us to compare the experimental results to the scattering and absorption spectra calculated with finite element modeling. We will also show our most recent results in which TiO2-coated gold nanostars have been employed as photocatalysts for methanol oxidation reactions. In these nanoparticles, the tunable LSPR absorption bands of the plasmonic core can be leveraged to study the formation of hot electrons at the nanostar tips, their dynamics as they transfer across the Schottky barrier, and their effect on reaction rates and selectivity. To do so, we have first synthesized amorphous TiO2-coated gold nanostars and then crystallized the TiO2 by heat treatments, that needed to be optimized to preserve the sharp morphology of the protruding spikes, extremely sensitive to atom migration. Compared to other nanoparticle-based catalyst systems, gold nanostars promise to become a much more versatile and tunable Vis-NIR photocatalyst.

Colloidal metal and semiconductor nanostructures: Theory, synthesis, and application

254th National Meeting (2017)

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