Epitaxial growth of Au@Pd core–shell nanocrystals prepared using a PVP-assisted polyol reduction method

Abstract

Au@Pd core-shell nanocrystals were prepared using a two-step polyol reduction method. First, decahedral Au core seeds with small amounts of octahedral, triangular-platelike, and icosahedral Au particles were prepared by reducing HAuCl 4 $4H 2 O in diethylene glycol (DEG) under oil-bath heating in the presence of polyvinylpyrrolidone (PVP) as a polymer surfactant. Then Pd shells were overgrown epitaxially on Au core seeds by reducing Na 2 PdCl 4 in EG with PVP, KBr, and H 2 O. The resultant crystal shapes were characterized using transmission electron microscopic (TEM), TEM-energy dispersed X-ray spectroscopic (EDS), and selected area electron diffraction (SAED) measurements. Effects of addition of KBr and H 2 O in the second step and reaction temperature for the yield of coreshell particles and their shape, size, and composition distributions were examined. Results show that both {111} and {100} facets of Pd shells were formed in the presence of KBr, depending on the shapes of Au core seeds, whereas only {111} facets were produced in the absence of KBr. New triangularplatelike, five-twin rod, decahedral, and icosahedral shapes of Au@Pd nanocrystals were prepared using triangular-platelike, decahedral, and icosahedral Au cores. When decahedral Au particles were used as seeds, monodispersed decahedral Au@Pd nanocrystals were prepared in high yield at low temperatures of 20-100 C in PVP/EG solution. Au acts as a catalyst for Pd 2+ reduction in the presence of PVP at low temperatures. This work demonstrates a simple two-step technique for the epitaxial growth of various shapes of Au@Pd nanocrystals.

Highly monodisperse multiple twinned AuCu–Pt trimetallic nanoparticles with high index surfaces

“…41 Besides the lattice mismatch, many other factors and the synergetic effects determine the growth mode. One could simply give the explanation in terms of the low surface free energy.…”

Facile Synthesis of Bimetallic Au@Pd Nanoparticles with Core-shell Structures on Graphene Nanosheets

“…As for the growth mechanism of the polygonal Au@PdeG (3) NPs, using 1.6 mL PdCl 2 and 550.6 mL HAuCl 4 in Fig. 2, with increasing the Au content, Au cores are easy to form triangular, cubic, octahedral, decahedral, icosahedral and tetrahexahedral structures, which are described in detail in literature [40] . The Pdshell component is overgrown on the (111) plane of the Au core, forming the aggregated polygonal Au@Pd NPs with core-shell structures on the graphene surface.…”

Multifaceted core–shell nanoparticles: superparamagnetism and biocompatibility

“…It is well known that materials in nano-scale domain exhibit very 20 unique electronic, 1 optical, 2 magnetic 3 properties which their bulk counterparts 4 cannot achieve. Among assorted nanomaterials, the magnetic metallic nanoparticles can provide high magnetic moment 5 which is useful in ferrofluids, magnetic carriers for targeted drug delivery, magnetic data storage and cell separation.…”

“…X-ray Photoelectron Spectroscopy: X-ray photoelectron spectra (XPS) of the catalysts were recorded with custom built ambient pressure photoelectron spectrometer (APPES) (Prevac, Poland), 20 equipped with VG Scienta's R3000HP analyzer and MX650 monochromator 29,30 Monochromatic Al Kα X-ray was generated at 450 W and used for measuring X-ray photoelectron spectrum (XPS) of the above samples. Base pressure in the analysis chamber was maintained in the range of 2 × 10 −10 Torr.…”

“…This was attributed to the presence of Ni within the photoelectron escape (or probing) depth of 5 nm, with Ag-layers on the top of Ni layers. The electrons released from Ni-core suffered more 20 collisions than the electrons from Ag-shell, and the high background observed in Ni 2p core level was rather very natural for the element which was enveloped by another. 33 XPS was also recorded from pristine Ni nanoparticles for comparison (Supporting Information SI-1).…”