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A new class of core−shell metallic nanostructures with tunable near-surface composition and surface morphology with excellent catalytic activity is reported. Very thin shells of metal nanoassemblies such as monolayer (Ag and Au), bilayer of Ag or Au, and AgAu alloy layer with controlled size and morphology were deposited onto a gold nanocube (AuNC) core. UV−vis absorption spectroscopy and high-resolution transmission electron microscopy analyses along with selected-area electron diffraction, energy dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometer, and X-ray diffraction techniques were used to characterize the prepared core−shell nanocubes. High-angle annular dark field scanning transmission electron microscopy−energy dispersive X-ray spectroscopy mapping images were recorded for the bilayer shell and alloy layer shell in the core−shell nanostructures. Reduction of 4-nitroaniline in the presence of sodium borohydride was chosen to validate the catalytic activity of the prepared core−shell metal nanocubes. Interestingly, the AgAu alloy shell layer over the AuNC (AuNC 1 @ Ag 0.25 Au 0.25 ) showed excellent catalytic activity compared with the pristine AuNC and monolayer and bilayer core−shell nanostructures.

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