Synthesis and Catalytic Activities of Metal Shells (Monolayer, Bilayer, and Alloy Layer)-Coated Gold Octahedra toward Catalytic Reduction of Nitroaromatics

Abstract

Different types of metal shells such as monolayer, bilayer, and alloy layer of gold (Au) and/or silver (Ag) on gold octahedra (AuOh) nanoparticles were synthesized using N-[3-(trimethoxysilyl)­propyl]­diethylenetriamine (TPDT) without employing any external reducing agents. TPDT, an alternative to sodium borohydride, was used to prepare 15 different core–shell metal nanostructures. The direct colloidal synthesis and stabilization of silver octahedra nanoparticles is still a challenging task. The proposed methodology is an alternative synthetic route for Ag or Au nanoshell coated onto the AuOh core. UV–vis absorption spectroscopy, high-resolution electron transmission microscopy analyses with selected area electron diffraction, energy-dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, and X-ray diffraction techniques were used to characterize the prepared core–shell octahedra nanostructures. High-angle annular dark field scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy (EDS) mapping images and scanning electron microscopy coupled with lines scan EDS were recorded to understand the alloy layer shell and bilayer shell in the core–shell Oh nanostructures. Catalytic reduction of toxic nitroaromatic compounds was chosen to investigate the catalytic activity of the core–shell octahedra nanostructures. The results reveal that the bimetal (AgAu) alloy shell layer coated over AuOh showed best catalytic activity, among the core–shell catalysts investigated for the reduction of nitroaromatics.

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