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.

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.

A facile synthetic method for depositing copper­(I) oxide (Cu2O) shell on Au nanocube (AuNC) core with different core–shell ratios (1:1, 1:5, 1:10, and 1:20) is reported. An innovative approach of tuning the Cu2O nanoshell for utilizing the catalytic activity of the AuNC@Cu2O core–shell nanostructures is investigated. N-[3-(trimethoxysilyl)­propyl]­diethylenetriamine (TPDT) silane played a dual role in the formation and stabilization of the Cu2O shell on the AuNC core. The optimal concentration of TPDT silane required for forming a stable Cu2O shell is studied systematically and deployed for fabricating AuNC@Cu2O core–shell nanostructures with various core-to-shell ratios. UV–vis absorption spectroscopy, high-resolution electron transmission microscopy analyses, scanning electron microscopy coupled with line scan energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and inductively coupled plasma mass spectrometry techniques were used to characterize the prepared AuNC@Cu2O core–shell nanostructures. High-angle annular dark-field scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy mapping images–line scan image and scanning electron microscopy coupled with line scan energy-dispersive X-ray spectroscopy were recorded to understand the core–shell nature of AuNC@Cu2O nanostructures. The electrocatalytic activity of AuNC@Cu2O core–shell nanostructures with different Cu2O shell thicknesses toward nitrite detection was investigated using the cyclic voltammetry technique. The TPDT-stabilized AuNC@Cu2O nanostructure with the core–shell ratio of 1:10 showed the best electrocatalytic activity, and the estimated detection limit of nitrite concentration was found to be as low as 14.7 nM.

A facile synthetic methodology for the deposition of different concentrations of Ag nanoparticles (AgNPs) on α-Ni(OH) 2 sheets (α-Ni 1 (OH) 2 -Ag 0.5 , α-Ni 1 (OH) 2 -Ag 1 , α-Ni 1 (OH) 2 -Ag 2 , and α-Ni 1 (OH) 2 -Ag 3 ) is reported using N- [3-(trimethoxysilyl)propyl]diethylenetriamine (TPDT) silane. The TPDT aminosilane facilitates the formation of α-Ni(OH) 2 sheets and reduces the Ag + precursor to AgNPs, leading to the deposition of AgNPs on α-Ni(OH) 2 sheets. UV− vis absorption spectroscopy, transmission microscopy analyses, X-ray photoelectron spectroscopy, X-ray diffraction, and attenuated total reflectance−Fourier transform infrared spectroscopy techniques were used to characterize the prepared α-Ni 1 (OH) 2 -Ag 0.5−3 composite materials. High-angle annular dark-field scanning transmission electron microscopy−energy-dispersive X-ray spectroscopy mapping images and scanning electron microscopy−energy-dispersive X-ray spectroscopy mapping images were recorded to understand the α-Ni 1 (OH) 2 -Ag composite sheet materials. The optical sensing property of α-Ni 1 (OH) 2 -Ag 0.5−3 composite materials toward toxic Hg 2+ ions were investigated using a UV−vis absorption spectroscopy technique. The α-Ni 1 (OH) 2 -Ag 2 composite material showed selective sensing behavior.

Various types of metal layer shells such as mono‐, bi‐, and alloy layer using gold and silver on preformed gold spherical nanoparticles core were synthesizing using sodium borohydride as reducing agent. UV‐vis absorption spectroscopy, transmission electron microscopy images, and X‐ray diffraction techniques were used to characterize the prepared pristine gold spherical nanoparticles and various core‐shell metal nanoparticles. High‐angle annular dark field scanning transmission electron microscopy‐energy dispersive X‐ray spectroscopy mapping images were recorded for the alloy and bilayer shell coated core‐shell nanoparticles. Catalytic reduction of 4‐nitroaniline in the presence of sodium borohydride was taken to study the catalytic activity of the prepared core‐shell nanostructures. Interestingly, the alloy shell coated gold spherical nanoparticles (AuNP@AgAu) showed the best catalytic activity (higher rate constant; 21.61×10−3 s−1) than that of mono‐, and bilayer core‐shell and pristine gold spherical nanoparticles.