Polyelectrolyte-multilayer-supported Au@Ag core-shell nanoparticles with high catalytic activity

One-step synthesis of noble metal/oxide nanocomposites with tunable size of noble metal particles and their size-dependent catalytic activity

A general one-step synthesis of noble metal/oxide nanocomposites with tunable size of noble metal particles and size-dependent catalytic activity.

Controllable synthesis of Ni/SiO2 hollow spheres and their excellent catalytic performance in 4-nitrophenol reduction

Hierarchical Ni nanoparticle supported silica hollow microspheres were synthesized by a unique and simple two-step method. Excellent catalytic activity in the reduction of 4-nitrophenol can be achieved on the catalysts.

Coarsening of silver nanoparticles in polyelectrolyte multilayers

In polyelectrolyte multilayer (PEM) films assembled from poly(diallyldimethylammonium chloride) and poly(styrene sulfonate) via the layer-by-layer deposition technique, the counterions were exchanged with silver ions, which were subsequently reduced in situ to produce silver (Ag) nanoparticles. The Ag nanoparticles embedded in the PEMs were found to undergo an interesting coarsening process over time, through which smaller Ag nanoparticles coalesce into larger ones until reaching an equilibrium. The process was investigated by monitoring the localized surface plasmon resonance of the Ag nanoparticles using UV-vis extinction spectroscopy, and the spectral evolution revealed an increase in nanoparticle size with time, a trend in qualitative agreement with theoretical calculation and further confirmed by transmission electron microscopy. The kinetics of the coarsening process and the size of Ag nanoparticles at equilibrium were found to be affected by the PEM structure as well as the temperature and relative humidity the PEM was exposed to, and coalescence was identified to be the mechanism.

One-pot environmentally friendly approach toward highly catalytically active bimetal-nanoparticle-graphene hybrids

A one-pot universal approach with simple metal sputtering onto room temperature ionic liquids has been developed to prepare bimetal-nanoparticle (NP)-graphene hybrids, and the process is environmentally friendly and completely free of additives and byproducts. The graphene-supported bimetallic NPs have an Ag-based core and an Au/Pd-rich shell, demonstrated by the scanning transmission electron microscopy. The X-ray absorption near-edge spectroscopy using synchrotron radiation reveals the occurrence of charge redistribution at both the Ag@Au and Ag@Pd core-shell interfaces. The as-prepared Ag@Au and Ag@Pd bimetal-NP-graphene hybrids are highly catalytically active for reduction of 4-nitrophenol, whose catalytic activity is superior to the corresponding monometallic hybrids. The catalytic superiority is ascribed to the electronic structure modification and morphological irregularity of the graphene-supported bimetallic NPs.

In situ loading of gold nanoparticles on Fe3O4@SiO2 magnetic nanocomposites and their high catalytic activity

In this work, a facile approach was successfully developed for in situ catalyzing Au nanoparticles loaded on Fe3O4@SiO2 magnetic nanospheres via Sn(2+) linkage and reduction. After the Fe3O4@SiO2 MNPs were first prepared via a sol-gel process, only one step was needed to synthesize the Fe3O4@SiO2-Au magnetic nanocomposites (Fe3O4@SiO2-Au MNCs), so that both the synthesis step and the reaction cost were remarkably decreased. Significantly, the as-synthesized Fe3O4@SiO2-Au MNCs showed high performance in the catalytic reduction of 4-nitrophenol to 4-aminophenol and could be reused for several cycles with convenient magnetic separability. This approach provided a useful platform based on Fe3O4@SiO2 MNPs for the fabrication of Au or other noble metal magnetic nanocatalysts, which would be very useful in various catalytic reductions.

Synthesis of hollow Ag-Au bimetallic nanoparticles in polyelectrolyte multilayers

Ag nanoparticles of ~20 nm size and rather uniform size distribution were synthesized in polyelectrolyte multilayers (PEMs) via an ion-exchange/reduction process in two stages (seeding and growth), which were used as sacrificial templates to fabricate Ag-Au bimetallic hollow nanoparticles via galvanic replacement reaction. The reaction process was monitored by UV-vis spectroscopy. The morphology and structure of the nanoparticles were characterized by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy, which confirmed the formation of hollow Ag-Au bimetallic nanoparticles. UV-vis absorbance spectroscopy and TEM results indicated that both size and optical properties of the Ag nanoparticles in the PEM can be controlled by manipulating ion content in the PEM and the number of the ion-exchange/reduction cycle, whereas that of Ag-Au bimetallic nanoparticles were dependent on size of the Ag templates and the replacement reaction kinetics. The hollow Ag-Au bimetallic nanoparticles exhibited a significant red shift in the surface plasmon resonance to the near-infrared region. The strategy enables facile preparation of hollow bimetallic nanoparticles in situ in polymer matrixes.

Heterogeneous silver-polyaniline nanocomposites with tunable morphology and controllable catalytic properties

This paper introduces not only a simple hydrothermal route to silver-polyaniline (Ag-PANI) nanocomposites with controllable morphology, but also a type of catalyst possessing tunable and switchable catalytic capability. Ag-PANI Janus nanoparticles (NPs) and Ag@PANI core-shell NPs have been constructed successfully at different hydrothermal temperatures. The diameter of both Ag and PANI hemispheres of Janus NPs, as well as the PANI shell thickness of core-shell NPs, was finely tuned via adjustment of the feed ratio. We also gained a deeper insight into the functionalities of PANI components in the catalytic capability of the heterogeneous catalysts, choosing catalytic reductions of nitrobenzene (NB) and 4-nitrophenol (4-NP) as model reactions. Our results showed that the catalytic capability of the nanocomposites was dependent on the PANI morphology and hydrophobicity. The PANI shell coating on Ag NPs can concentrate the lipophilic NB, thus leading to an enhanced catalytic capability of Ag@PANI core-shell NPs. However, this enhanced catalytic capability was not observed for Ag-PANI Janus NPs when catalytically reducing NB. More importantly, the catalytic capability of the core-shell NPs in the reduction of hydrophilic 4-NP is switchable by varying the PANI shell from an undoped to a doped state.

Graphene oxide supported Au-Ag alloy nanoparticles with different shapes and their high catalytic activities

A simple method was developed to fabricate Au-Ag nanoparticle/graphene oxide nanocomposites (Au-Ag/GO) by using simultaneous redox reactions between AgNO3, HAuCl4 and GO. The Au-Ag/GO was characterized by x-ray photoelectron spectroscopy, transmission electron microscopy and energy dispersive x-ray spectroscopy. The GO nanosheets acted as the reducing agent and the support for the Au-Ag alloy nanoparticles. In addition, Au-Ag alloy nanoparticles with different shapes including core-shell-like, dendrimer-like and flower-like were obtained by simply modifying the concentration of the reactants and the reaction temperature. With no reducing or stabilizing agents added, the Au-Ag/GO nanocomposites show superior catalytic performance for the reduction of 4-nitrophenol and for the aerobic homocoupling of phenylboronic acid.

Retracted Article: Aqueous synthesis of human serum albumin-stabilized fluorescent Au/Ag core/shell nanocrystals for highly sensitive and selective sensing of copper(ii)

Using human serum albumin as a reductive plus stabilizing agent, fluorescent Au/Ag core/shell nanocrystals were prepared at pH 9.0 and 37 °C, and further developed as a highly sensitive and selective sensor of Cu²⁺.

Fabrication of Au@Ag core-shell nanoparticles using polyelectrolyte multilayers as nanoreactors

A new synthetic strategy has been developed for the fabrication of Au-Ag bimetallic core-shell nanoparticles (NPs) using polyelectrolyte multilayers (PEMs) as unique nanoreactors. Bimetallic NPs composed of Au core and Ag shell were successively incorporated into PEMs by repeating anion/cation exchange/reduction cycle multiple times in a stepwise manner. The strategy described here allows for the facile preparation of Au@Ag core-shell NPs with well-controlled core and shell dimensions and geometrically tunable optical properties by simply varying the number of ion-exchange/reduction cycles in the PEM matrix. The strategy can be extended to synthesize in situ other core-shell NPs in polymer matrix.