Mechanochemical Strategies for the Preparation of SiO2-Supported AgAu Nanoalloy Catalysts

Silver-gold nanoalloys were prepared from their metal salts precursors through bottom-up mechanochemical synthesis, using one-pot or galvanic replacement reaction strategies. The nanostructures were prepared over amorphous SiO2 as an inert supporting material, facilitating their stabilization without the use of any stabilizing agent. The nanomaterials were extensively characterized, confirming the formation of the bimetallic nanostructures. The nanoalloys were tested as catalysts in the hydrogenation of 2-nitroaniline and exhibited up to 4-fold the rate constant and up to 37% increased conversion compared to the respective single metal nanoparticles. Our approach is advantageous to produce nanoparticles with clean surfaces with available catalytic sites, directly in the solid-state and in an environmentally friendly manner.

A Review on Metal- and Metal Oxide-Based Nanozymes: Properties, Mechanisms, and Applications

Since the ferromagnetic (Fe3O4) nanoparticles were firstly reported to exert enzyme-like activity in 2007, extensive research progress in nanozymes has been made with deep investigation of diverse nanozymes and rapid development of related nanotechnologies. As promising alternatives for natural enzymes, nanozymes have broadened the way toward clinical medicine, food safety, environmental monitoring, and chemical production. The past decade has witnessed the rapid development of metal- and metal oxide-based nanozymes owing to their remarkable physicochemical properties in parallel with low cost, high stability, and easy storage. It is widely known that the deep study of catalytic activities and mechanism sheds significant influence on the applications of nanozymes. This review digs into the characteristics and intrinsic properties of metal- and metal oxide-based nanozymes, especially emphasizing their catalytic mechanism and recent applications in biological analysis, relieving inflammation, antibacterial, and cancer therapy. We also conclude the present challenges and provide insights into the future research of nanozymes constituted of metal and metal oxide nanomaterials.

Synthesis of ultrafine AuPd bimetallic nanoparticles using a magnetite-cored poly(propyleneimine) dendrimer template and its sustainable catalysis of the Suzuki coupling reaction

A rational synthesis of magnetically recyclable PPI dendrimer encapsulated AuPd bimetallic nanoparticle and its catalytic examination in the Suzuki coupling reaction.

Synthesis, Properties, and Biological Applications of Metallic Alloy Nanoparticles

Metallic alloy nanoparticles are synthesized by combining two or more different metals. Bimetallic or trimetallic nanoparticles are considered more effective than monometallic nanoparticles because of their synergistic characteristics. In this review, we outline the structure, synthesis method, properties, and biological applications of metallic alloy nanoparticles based on their plasmonic, catalytic, and magnetic characteristics.

A unique pathway of PtNi nanoparticle formation observed with liquid cell transmission electron microscopy

An understanding of nanoparticle growth is significant for controlled synthesis of nanomaterials with desired physical and chemical properties. Here we report the in situ study of platinum-nickel alloy nanoparticle growth using in situ liquid cell transmission electron microscopy (TEM). The observation revealed that Ni dendrites can form at the beginning and subsequently PtNi nanoparticles nucleate and grow by consumption of the Ni dendrites. The resulting PtNi alloy nanoparticles have a narrow size distribution with an average diameter of 3.7 nm, which are smaller than those obtained via classical solution growth. This work shed light on using such a unique growth pathway for the synthesis of novel nanoparticles.

Localized surface plasmon enhanced electrocatalytic methanol oxidation of AgPt bimetallic nanoparticles with an ultra-thin shell

AgPt bimetallic hollow nanoparticles (AgPt-BHNPs) with an ultra-thin shell were synthesized.

Chemically Engineered Au-Ag Plasmonic Nanostructures to Realize Large Area and Flexible Metamaterials

We developed a simple and systematic method to fabricate optically tunable and thermally and chemically stable Au-Ag nanocrystal-based plasmonic metamaterials. An Ag nanocrystal-based metamaterial with desirable optical properties was fabricated via nanoimprinting and ligand-exchange process. Its optical properties were controlled by selectively substituting Ag atoms with Au atoms through a spontaneous galvanic replacement reaction. The developed Au-Ag-based metamaterials provide excellent tunable plasmonic properties required for various applications in the visible and near-infrared regions by controlling the Au-Ag composition according to the conditions of the galvanic displacement. Furthermore, their thermal and chemical stabilities significantly improved because of the protective Au thin layer on the surface. Using this developed process, chemically and thermally stable and flexible plasmonic metamaterials were successfully fabricated on a flexible polyester terephthalate substrate.

Simple, Low-Cost Fabrication of Highly Uniform and Reproducible SERS Substrates Composed of Ag⁻Pt Nanoparticles

Ag⁻Pt nanoparticles, grafted on Ge wafer, were synthesized by the galvanic replacement reaction based on their different potentials. Detailed characterization through scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS) and X-ray photo-elelctron spectroscopy (XPS) proved that Ag⁻Pt nanoparticles are composed of large Ag nanoparticles and many small Pt nanoparticles instead of an Ag⁻Pt alloy. When applied as surface-enhanced Raman scattering (SERS) substrates to detect Rhodamine 6G (1 × 10-8 M) or Crystal violet (1 × 10-7 M) aqueous solution in the line mapping mode, all of the obtained relative standard deviation (RSD) values of the major characteristic peak intensities, calculated from the SERS spectra of 100 serial spots, were less than 10%. The fabrication process of the SERS substrate has excellent uniformity and reproducibility and is simple, low-cost and time-saving, which will benefit studies on the platinum-catalyzed reaction mechanisms in situ and widen the practical application of SERS.

In-situ generation of gold nanoparticles on MnO2 nanosheets for the enhanced oxidative degradation of basic dye (Methylene Blue)

In this work, the gold nanoparticles (Au-NPs) were in-situ generated on the surface of MnO₂ nanosheets to form MnO₂/Au-NPs nanocomposite in a simple and cost-effective way. Multiple experiments were carried out to optimize the oxidation of basic dye (Methylene Blue (MB)), including the molar ratio of MnO₂ to chloroauric acid (HAuCl₄), the pH of the solution and the effect of initial material. Under the optimal condition, the highest degradation efficiency for MB achieved to 98.9% within 60 min, which was obviously better than commercial MnO₂ powders (4.3%) and MnO₂ nanosheets (74.2%). The enhanced oxidative degradation might attribute to the in-situ generation of ultra-small and highly-dispersed Au-NPs which enlarged the synergistic effect and/or interfacial effect between MnO₂ nanosheets and Au-NPs and facilitated the uptake of electrons by MnO₂ from MB during the oxidation, thus validating the application of MnO₂/Au-NPs nanocomposite for direct removal of organic dyes from wastewater in a simple and convenient fashion.

Asymmetrical etching of Ag nanoparticles into symmetry-reduced bi-metallic nanocups at the single-nanoparticle level

By employing the water/air interface-confinement effect, local nanomasking and thus selective etching were achieved on single interfacial nanoparticles, developing a series of symmetry-reduced cubic, spherical, trough-like nanocups.

l-Arginine-assisted one-pot synthesis of hierarchical Ag1Pt2 nanocorallines for surface-enhanced Raman spectroscopy

The hierarchical multi-branched Ag₁Pt₂ nanocorallines (NCs) were prepared in a large scale by a rapid aqueous method, using l-arginine as the eco-friendly shape-directing agent. The product was mainly characterized by microscopy measurements, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The architectures exhibited superior surface-enhanced Raman scattering (SERS) with 4-nitrothiophenol (4-NTP), the enhancement factor (EF) of 1.3×10⁵, a wide linear range of 10-100μM and a low detection limit of 0.01μM. Meanwhile, the SERS-active substrate was explored for the assay of 4-mercaptobenzoic acid (4-MBA) with significantly enhanced SERS performance. It means Ag₁Pt₂ NCs as a good Raman-active platform for sensing in food and environment analysis, owing to their rough surfaces and unique multi-branched structures.

Tailoring gold and silver colloidal bimetallic nanoalloys towards SERS detection of rhodamine 6G

Nanoparticles of gold, silver and their bimetallic alloys were tailored for SERS sensing towards trace amounts of rhodamine 6G.

Direct Cross-Linking of Au/Ag Alloy Nanoparticles into Monolithic Aerogels for Application in Surface-Enhanced Raman Scattering

The direct cross-linking of Au/Ag alloy nanoparticles (NPs) into high surface area, mesoporous Au/Ag aerogels via chemical oxidation of the surface ligands is reported. The precursor alloy NPs with composition-tunable morphologies were produced by galvanic replacement of the preformed Ag hollow NPs. The effect of Au:Ag molar ratio on the NP morphology and surface plasmon resonance has been thoroughly investigated and resulted in smaller Au/Ag alloy NPs (4-8 nm), larger Au/Ag alloy hollow NPs (40-45 nm), and Au/Ag alloy hollow particles decorated with smaller Au NPs (2-5 nm). The oxidative removal of surfactant ligands, followed by supercritical drying, is utilized to construct large (centimeter to millimeter) self-supported Au/Ag alloy aerogels. The resultant assemblies exhibit high surface areas (67-73 m(2)/g), extremely low densities (0.051-0.055 g/cm(3)), and interconnected mesoporous (2-50 nm) networks, making them of great interest for a number of new technologies. The influence of mesoporous gel morphology on surface-enhanced Raman scattering (SERS) has been studied using Rhodamine 101 (Rd 101) as the probe molecule. The alloy aerogels exhibit SERS signal intensities that are 10-42 times higher than those achieved from the precursor Au/Ag alloy NPs. The Au/Ag alloy aerogel III exhibits SERS sensing capability down to 1 nM level. The increased signal intensities attained for alloy aerogels are attributed to highly porous gel morphology and enhanced surface roughness that can potentially generate a large number of plasmonic hot spots, creating efficient SERS substrates for future applications.

Hollow AgPt/SiO2 nanomaterials with controlled surface morphologies: is the number of Pt surface atoms imperative to optimize catalytic performances?

This paper investigates how the number of Pt surface atoms and exposed facets affected the catalytic performances of AgPt nanomaterials.

Heterostructured Au/Pd-M (M = Au, Pd, Pt) nanoparticles with compartmentalized composition, morphology, and electrocatalytic activity

The synthesis, processing, and galvanic exchange of three heterostructured nanoparticle systems is described. The surface accessibility and redox potential of a Au/Pd-Ag dumbbell nanoparticle, where a Au/Pd core/shell region, and a silver region make up the domains, was used to prepare the new nanostructures with controlled composition, morphology, and microstructure. Results indicate that the silver domain was particularly susceptible to galvanic displacement, and was exchanged to Au/Pd-M (M = Au, Pd, Pt). Interestingly, the dumbbell morphology remained after exchange, and the silver region was transformed to hollow, parachute, or concentric domains respectively. The morphology and microstructure change was visualized via TEM and HRTEM, and the composition changes were probed via STEM-EDS imaging and XPS. The electrocatalytic activity of the Au/Pd-M towards methanol oxidation was studied, with results indicating that the Au/Pd-Pt nanoparticles had high activity attributed to the porous nature of the platinum domains.

Green synthesis of bimetallic Au@Pt nanostructures and their application for proliferation inhibition and apoptosis induction in human cervical cancer cell

Bimetallic Au@Pt nanostructures (Au@Pts) are potential candidates for optical, electrical, catalytic and biological applications. However, methods for the fabrication of Au@Pts using total tea polyphenols (TPPs), studies of the mechanism of action of Au@Pts on biological systems and studies on the application of Au@Pts in cancer diagnosis and therapy are sparse. In this study, we developed a simple, eco-friendly and low-cost method for the synthesis of Au@Pts to examine the cytotoxic effect of these Au@Pts on human cervical cancers in vitro. The gold and platinum ions were successfully reduced simultaneously using TPPs at room temperature. The prepared Au@Pts were characterized using UV-Vis spectrophotometery, X-ray diffractometery (XRD), energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). EDS and XRD confirmed the formation of the Au@Pt. Formation of Au@Pts with a size of 5-20 nm was confirmed using TEM. The cytotoxic properties of the Au@Pts were evaluated in human cervical cancer cells (SiHa). The cell viability results revealed that Au@Pts induce cell death in a dose- and time-dependent manner. The morphological features of the Au@Pt-exposed SiHa cells were observed and indicated cell death via cell shrinkage, intranucleosomal DNA fragmentation and chromatin condensation. During progression of the different phases of the cell cycle, the proportion of cells in the G2/M phase of the treated SiHa cells was significantly increased, which strongly confirmed that the Au@Pts induced apoptosis through the G2/M phase check points. Our findings demonstrate the activity of Au@Pts against cervical cancer cells and reveal strategies for the development of highly active bimetallic nanostructures for cancer therapeutics.

Cellulose assisted combustion synthesis of porous Cu–Ni nanopowders

Cu–Ni nanoparticles were synthesized using cellulose assisted combustion synthesis method. The BET area, pore volume and pore size of these nanoparticles were higher than nanoparticles synthesized by solution combustion synthesis (SCS) method.

Food safety control of zeranol through voltammetric immunosensing on Au–Pt bimetallic nanoparticle surfaces

This study reports an accurate and sensitive strategy for zeranol (ZER) determination in bovine urine samples.

Novel Ag/Au/Pt trimetallic nanocages used with surface-enhanced Raman scattering for trace fluorescent dye detection

Trimetallic nanocages possess inter-metallic synergies among elements and are able to generate significant SERS signal enhancement due to “hot spot” formation.