Hybrid alloys among gold, palladium and platinum become a new category of catalysts primarily due to their enhanced catalytic effects. Enhancement means not only their effectiveness, but also their uniqueness as catalysts for the reactions that individual metals may not catalyze. Here, preparation of hollow Au@Pd and Au@Pt core-shell nanoparticles (NPs) and their use as electrocatalysts are reported. Galvanic displacement with Ag NPs is used to obtain hollow NPs, and higher reduction potential of Au compared to Ag, Pd, and Pt helps to produce hollow Au cores first, followed by Pd or Pt shell growth. Continuous and highly crystalline shell growth was observed in Au@Pd core-shell NPs, but the sporadic and porous-like structure was observed in Au@Pt core-shell NPs. Along with hollow core-shell NPs, hollow porous Pt and hollow Au NPs are also prepared from Ag seed NPs. Twin boundaries which are typically observed in large size (>20 nm) Au NPs were not observed in hollow Au NPs. This absence is believed to be due to the role of the hollows, which significantly reduce the strain energy of edges where the two lattice planes meet. In ethanol oxidation reactions in alkaline medium, hollow Au@Pd core-shell NPs show highest current density in forward scan. Hollow Au@Pt core-shell NPs maintain better catalytic activities than metallic Pt, which is thought to be due to the better crystallinity of Pt shells as well as the alloy effect of Au cores.

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Synthesis of monodisperse polymer-inorganic nanoparticle composites and the study of their mechanical properties are described. Surface-modified MPt (M ) Fe, Ni) nanoparticles undergo hydrosilation reaction with siloxane backbones and make covalent networks by acting as crosslinkers. Monodispersity and the spatial resolution of nanoparticles were identified with atomic force microscopy and transmission electron microscopy. The properties of covalent bonding in the elastomeric network between nanoparticles, allyl-modified dopamine, and siloxane backbones were studied with X-ray photoelectron spectroscopy and IR. The added amount of dopamine-modified FePt nanoparticles affected the crosslinking density in the siloxane backbones. The intensity of Si-H bonding was decreased in IR spectra with increasing density of FePt nanoparticles. Mechanical properties were measured with nanoindentation. FePt nanoparticle polymer composites have more enhanced tensile strength (E r ) 1.56 GPa, H ) 0.126 GPa) than simple elastomers crosslinked with diallyl carbonate (E r ) 0.67 GPa, H ) 0.115 GPa). Further improvement of mechanical strength was achieved with increased amount of dopamine-modified nanoparticles due to the increase in the crosslinking density between siloxane backbones.

SERS provides great sensitivity at low concentrations of analytes. SERS combined with near infrared (NIR)-resonant gold nanomaterials are important candidates for theranostic agents due to their combined extinction properties and sensing abilities stemming from the deep penetration of laser light in the NIR region. Here, highly branched gold nanoflowers (GNFs) grown from Pd and Pt seeds are prepared and their SERS properties are studied. The growth was performed at 80 °C without stirring, and this high temperature growth method is assumed to provide great shape stability of sharp tips in GNFs. We found that seed size must be large enough (>30 nm in diameter) to induce the growth of those SERS-active and thermally stable GNFs. We also found that the addition of silver nitrate (AgNO3) is important to induce sharp tip growth and shape stability. Incubation with Hela cells indicates that GNFs are taken up and reside in the cytoplasm. SERS was observed in those cells incubated with 1,10-phenanthroline (Phen)-loaded GNFs.