Keggin ion-mediated synthesis of aqueous phase-pure Au@Pd and Au@Pt core–shell nanoparticles

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Abstract
Development of simple and reliable protocols for the synthesis of phase-pure core–shell metal nanoparticles is an important problem in nanomaterials synthesis; the synthesis of Au core–Pd/Pt shell nanoparticles is described in this paper. This is accomplished by utilizing Keggin ions bound to the surface of gold nanoparticles as UV-switchable reducing agents. Exposure of Keggin ion-capped gold nanoparticles to aqueous solutions of Pd2+ and Pt4+ ions after UV activation of the Keggin ions results in selective reduction of the metal ions only on the surface of the nanoparticles and thus, to phase-pure core–shell nanostructures. The synthesis of the Au@Pd and Au@Pt core–shell nanoparticles was followed by UV-vis spectroscopy, X-ray photoemission spectroscopy and high-resolution transmission electron microscopy measurements.