Synthesis of Monodisperse Ag?Au Alloy Nanoparticles with Independently Tunable Morphology,Composition, Size,and Surface Chemistry and Their 3‐D Superlattices

Here, a strategy for synthesizing monodisperse Ag? Au alloy nanoparticles whereby particle attributes such as morphology, composition, size, and surface chemistry may be independently controlled, varied, and customized is presented. The synthesis uses a multi‐step procedure to deliver control of morphology, size, and composition in discrete and independent steps. Specifically Ag nanoparticles with the same morphology but different sizes are first prepared by the chemical reduction of Ag ions. A digestive ripening post‐treatment followed by seed‐mediated growth is then applied to narrow the size distribution and to vary the particle size. Monodisperse Ag? Au alloy nanoparticles are then formed by a replacement reaction with HAuCl₄. Both single‐crystalline truncated octahedral (TO) Ag? Au alloy nanoparticles and icosahedral multiply twinned particles can be easily prepared by this procedure. By using truncated octahedrons as the model morphology, the syntheses of nanoparticles with the same size but different compositions, of nanoparticles with the same composition but variable sizes, and of nanoparticles with different surface chemistry are demonstrated and discussed in detail. Because of the shape and size monodispersity, all of the as‐synthesized Ag? Au alloy nanoparticles easily form superlattices on a solid substrate upon slow evaporation of the solvent. The packing pattern of the nanoparticles is strongly dependent on the native morphology of the nanoparticles.     

Structural characterization of SiC nanoparticles

The structure and size of SiC nanoparticles were studied by different characterization methods including small angle X-ray scattering (SAXS), transmission electron microscope (TEM), and X-ray diffraction (XRD). The results showed that particle size distributions determined respectively from SAXS and TEM are comparable and follow the log-normal function. The size distribution of the particles is between 10 to 100 nm with most of them being in the range of 20–50 nm. The average particle size is around 42 nm. XRD identifies the phase of the SiC nanoparticles and suggests the average size of the single crystalline domain to be around 21 nm. The combined results from XRD and SAXS suggest the existence of many polycrystals, which is confirmed by the HRTEM observation of particles with twins and stacking faults. The material synthesis methods leading to various particle sizes are also discussed.     

White‐Emitting Protein Nanoparticles for Cell‐Entry and pH Sensing

Facile synthesis of white‐emitting, protein‐based, metal‐free, stable, nontoxic, and pH sensitive, advanced functional nanoparticles (GlowDots), as alternatives to quantum dots, is reported here. Controlled cross‐linking of bovine serum albumin resulted in facile formation of spherical nanoparticles of 35 nm in diameter with a sharp size distribution (±10 nm), which were then conjugated with specific dyes to produce white‐emitting particles with tunable excitation wavelengths. Chemical novelty is that the particle size, size distribution, stability, surface chemistry, and emission properties are under full chemical control where the size and absorption/emission properties are independently tuned. Up to 100 dye molecules were attached to each particle, on an average, and hence, particles acquired strong absorption cross‐sections as well as high brightness. White fluorescence of GlowDots is strongly sensitive to pH over a range of pH 2–11, and pH‐induced emission changes are fully reversible. The particles readily entered HeLa cells and emission color depended on particle location in the live cells, which is most likely due to the local environment surrounding the particles. These are the very first reports of white‐emitting advanced functional nanoparticles that are biodegradable, sensitive to pH, and amenable for live cell imaging to probe the subcellular compartments.     

Structural,morphological and optical behaviour of PVP capped binary (ZnO)0.4 (CdO)0.6 nanoparticles synthesised by a facile thermal route

The synthesis of binary (ZnO)_0.4 (CdO)_0.6 nanoparticles was achieved using a novel thermal treatment method. The structural, morphological, elemental composition and optical behaviour of these nanoparticles were determined using various techniques. X-ray diffraction of the sample at a calcination temperature above 500 °C showed the presence of both hexagonal and face-centred cubic crystalline structures. With increasing calcination temperature, the dispersion of the nanoparticles was improved, and the mean particle size determined by TEM micrographs suggested a corresponding increasing trend. Increased particle size led to a rise in the photoluminescent intensity as demonstrated by photoluminescence spectra, and multiple energy band gaps which lessen with increasing calcination temperature. The resulting (ZnO)_0.4 (CdO)_0.6 nanoparticles are likely to have widespread uses within numerous semiconductor applications.     

Large‐Scale Synthesis of Uniform and Crystalline Magnetite Nanoparticles Using Reverse Micelles as Nanoreactors under Reflux Conditions

We have synthesized uniform and highly crystalline magnetite nanoparticles from the reaction of iron salts in microemulsion nanoreactors. The particle size can be controlled from 2 nm to 10 nm by varying the relative concentrations of the iron salts, surfactant, and solvent. Transmission electron microscope images of the nanoparticles reveal that they are very uniform in size distribution. Structural characterization using X‐ray diffraction and X‐ray magnetic circular dichroism shows that the nanoparticles are magnetite. The magnetic characterization of the nanoparticles showed that they are superparamagnetic at room temperature. Using a similar synthetic procedure, we have been able to synthesize nanoparticles of several mixed metal ferrites including cobalt ferrite, manganese ferrite, nickel ferrite, and zinc ferrite.     

BaCO_3和TiO_2的物化特性对PTC热敏电阻器性能的影响

探讨了ＢａＣＯ３与ＴｉＯ２的物化特性，诸如纯度、杂质含量、晶型、热特性、颗粒形状、粒度分布及平均粒径等对ＰＴＣ热敏电阻器性能的影响。并据此提出了ＢａＣＯ３与ＴｉＯ２的技术标准。     

Highly Asymmetric,Interfaced Dimers Made of Au Nanoparticles and Bimetallic Nanoshells: Synthesis and Photo‐Enhanced Catalysis

Synthesis of a class of exotic interfaced dimers with high asymmetries in terms of composition, morphology, structure (solid versus hollow), and dimension of the individual nanoscale components in the dimers is successfully accomplished. Typical examples include the interfaced dimers made of solid Au nanoparticles and hollow bimetallic nanoshells with different compositions, such as Au/Ag, Pt/Ag, and Pd/Ag. The success of the synthesis relies on the combination of asymmetric overgrowth of Ag nanodomains on the partially passivated Au nanoparticles and a following galvanic replacement reaction between the Ag nanodomains and appropriate noble metal precursors. The entire synthesis is processed on the unique superparamagnetic colloidal substrates that offer many advantages, such as time‐efficiency, scalability, and high yield. The Au nanoparticle and the bimetallic nanoshell in each interfaced dimer are in direct contact, resulting in the possible strong coupling between them as well as novel properties that cannot be observed in either the nanoparticle or the nanoshell. For example, dimers made of Au nanoparticles and Pd/Ag nanoshells exhibit enhanced catalytic performance toward Suzuki coupling reactions under illumination of visible light because the strong surface plasmon resonances in the Au nanoparticles can influence the catalytic activity of the Pd/Ag nanoshells through coupling between the nanoparticles and the nanoshells.     

Au@Hg Nanoalloy Formation Through Direct Amalgamation: Structural,Spectroscopic, and Computational Evidence for Slow Nanoscale Diffusion

Dynamic core–shell nanoparticles have received increasing attention in recent years. This paper presents a detailed study of Au–Hg nanoalloys, whose composing elements show a large difference in cohesive energy. A simple method to prepare Au@Hg particles with precise control over the composition up to 15 atom% mercury is introduced, based on reacting a citrate stabilized gold sol with elemental mercury. Transmission electron microscopy shows an increase of particle size with increasing mercury content and, together with X‐ray powder diffraction, points towards the presence of a core–shell structure with a gold core surrounded by an Au–Hg solid solution layer. The amalgamation process is described by pseudo‐zero‐order reaction kinetics, which indicates slow dissolution of mercury in water as the rate determining step, followed by fast scavenging by nanoparticles in solution. Once adsorbed at the surface, slow diffusion of Hg into the particle lattice occurs, to a depth of ca. 3 nm, independent of Hg concentration. Discrete dipole approximation calculations relate the UV–vis spectra to the microscopic details of the nanoalloy structure. Segregation energies and metal distribution in the nanoalloys were modeled by density functional theory calculations. The results indicate slow metal interdiffusion at the nanoscale, which has important implications for synthetic methods aimed at core–shell particles.     

Nanoparticle ordering by dewetting of Co on SiO2

Most metals on SiO₂ have a finite contact angle and are therefore subject to dewetting during thermal processing. The resulting dewetting morphology is determined primarily by nucleation and growth or instabilities. The dewetting mechanism implies a disordered spatial arrangement for homogeneous nucleation, but an ordered one for instabilities such as spinodal decomposition. Here, we show that the morphology of laser-melted ultrathin Co film (4-nm thick) can be attributed to dewetting via an instability. Dewetting leads to breakup of the continuous Co film into nanoparticles with a monomodal size distribution with an average particle diameter of 75 nm±23 nm. These nanoparticles have short-range order (SRO) of 130 nm in their separation. This result has important implications for nanomanufacturing with a robust spacing or size selection of nanoparticles in addition to spatial ordering.     

Recrystallization and intermetallic formation in Au/Al and Au/Zn bimetallic films

Bimetallic thin films are of interest for use in microelectromechanical systems (MEMS) for the fabrication of sensors and actuators. The coefficient of thermal expansion (CTE) mismatch between the two metal films of the bimetallic structure can be used to attain the desired level of deflection or actuation in the MEMS device. Gold/aluminum and gold/zinc films have desirable properties for use in bimetallic films because of their differences in CTE. The stress-temperature behavior of these bimetal configurations has been studied. The effect of deposition technique and recrystallization of the metal films on the total stress and strain of the bimetallic films has been investigated. It has been shown that the formation of intermetallic compounds between the metal layers changes the mechanical properties of composite films. The intermetallic compounds are often undesirable because of their uncontrolled composition and poor mechanical properties. The degree of formation of the intermetallic compounds in the gold/aluminum bimetallic films can be reduced by use of a diffusion barrier between the two metals. It is shown that aluminum oxide is an effective diffusion barrier, and it can be easily fabricated. Stress-strain measurements and chemical depth profiling of the bimetallic films with the diffusion barrier have been used to quantify the reduction in the formation of the intermetallic compounds.     

One‐Pot Synthesis of Dealloyed AuNi Nanodendrite as a Bifunctional Electrocatalyst for Oxygen Reduction and Borohydride Oxidation Reaction

A novel one‐pot approach for synthesizing the dealloyed nanomaterials at room temperature is introduced for the first time. In such a synthetic strategy, applying modulated potentials effectively simplifies the traditional dealloying route, which usually requires additional corrosion process to dissolve nonprecious metals. The dealloyed AuNi nanodendrites (AuNi NDs) with tunable composition and uniformly elemental distribution are well developed by the one‐pot strategy. Impressively, the as‐synthesized AuNi NDs exhibit a higher electrochemically active area and definite improvements in electrocatalytic activity for oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) compared to the commercial Pt/C. In particular, the AuNi NDs are 81 mV more positive in half‐wave potential and about 3.1 times higher in specific activity (at 0.85 V) for the ORR than Pt/C, together with excellent stability and methanol tolerance. The superior BOR activity is highly promising compared to the previously reported catalysts. The unique nanodendritic structure with Au‐rich surface and bimetallic electronic effect is the main factor to greatly enhance the bifunctional catalytic performance for the AuNi NDs. Furthermore, such a newly developed facile method is of great significance because it is one of the first examples to effectively engineer dealloyed bimetallic nanostructures via the practical and low‐cost route for electrocatalytic applications.     

烟幕粒子粒度的分形特征及红外消光性能研究

以分形理论为基础,提出了一种表征烟幕粒子粒度特征的指标——粒度分形维数(D),研究了烟幕粒子粒度的分形特征。研究表明,烟幕粒子的粒度分布是分形的,烟幕中大颗粒占的比例越高,粒度分形维数越小,基于米氏理论的红外消光性能也越好。粒度分形维数(D)可用于表征烟幕粒子粒度分布的特征,为烟幕系统的研究提供了一种新思路。     

Ultrasound-assisted preparation of CdSe nanocrystals in the presence of Polyvinyl alcohol as a capping agent

Nanosized Polyvinyl alcohol-capped CdSe particles were prepared via a simple and fast ultrasound-assisted technique through the reaction between aqueous solutions of cadmium acetate and sodium selenosulfate. The nanoparticles are characterized using X-ray diffraction (XRD), UV–Visible spectrophotometer, Scanning electron microscope (SEM), Energy dispersive X-ray (EDAX) analysis and Fourier transform infrared (FTIR) spectrometer. XRD pattern reveals that the nanoparticles are in well-crystalline cubic phase. The broadening of diffraction peaks indicated the formation of particles in the nanometer size regime. A shift in absorption peak is observed in the spectra near 544 nm due to quantum confinement effect. Particle sizes calculated from the X-ray diffraction studies agree fairly well with those estimated from optical absorption studies. The homogeneity of the sample could be controlled by adjusting the concentration of Polyvinyl alcohol. SEM images of a specific concentration of Polyvinyl alcohol for as-prepared CdSe nanocrystals show uniform particles distribution. The particle size is found to be less than 100 nm based on the observed SEM images and the reason of this mismatch is discussed. The calculated result from XRD and optical characterizations shows that the particles size is smaller than those observed in SEM images. The elemental analysis from EDAX shows that the average atomic percentage of Cd:Se was 50:50 showing that the prepared samples are exactly stoichiometric.     

Bulk Synthesis and Surface Patterning of Nanoporous Metals and Alloys from Supraspherical Nanoparticle Aggregates

Supraspheres (SS) composed of hundreds to thousands of metal nanoparticles (NPs) and crosslinked by dithiol linkers are assembled into larger structures, which are subsequently converted into nanoporous metals (NMs). Conversion is achieved by heating which removes organic molecules stabilizing the NPs and allows for NP fusion. Heating of SS solutions leads to NMs of overall macroscopic dimensions; localized radiation using collimated electron beam is used to prepare metallized surface micropatterns. Depending on the composition of supraspherical precursors, nanoporous materials composed of up to three metals can be obtained. Strategies for controlling pore size and nanoscale surface roughness of these materials are discussed.     

Real‐Time Imaging of Nanoscale Redox Reactions over Bimetallic Nanoparticles

The catalytic performance of bimetallic nanoparticles (NPs) strongly depends on their structural and compositional changes under reaction conditions. At the fundamental level, these changes are driven by redox reactions that occur on the surface of the NPs. The degree of complexity in the redox reactions is further amplified in bimetallic NPs because both metals can have their own reactions with the reactant molecules, in addition to any synergistic effects between the metal nanocatalysts and their reducible oxides. Here, the gas phase oxidation and reduction reactions, and the oxidation of carbon monoxide (CO) over Pt–Ni rhombic dodecahedron NPs with segregated Pt frames and Pt–Ni alloy NPs are investigated using in situ gas cell transmission electron microscopy. The real‐time observations show that NiO shell formation and Pt segregation are two important features during the oxidation and reduction of Pt–Ni NPs, respectively. Moreover, the two types of NPs evolved in different ways. By combining high‐resolution imaging, mass spectroscopy, and modeling, it is shown that the evolution of NP morphology and composition during redox reactions plays an important role in controlling the catalytic activity of the NPs.     

Direct Growth of Uniform Bimetallic Core-Shell or Intermetallic Nanoparticles on Carbon via a Surface-Confinement Strategy for Electrochemical Hydrogen Evolution Reaction

Due to the surface inhomogeneity of the solid supports, direct growth of uniform bimetallic nanoparticles (NPs) with controllable structure and size thereon is particularly challenging. Herein, a surface-confinement strategy is reported to directly prepare ultrafine bimetallic Pt M NPs (MFe, Cu, and Co) with structure of core-shell or intermetallic compounds on an N functionalized carbon support (NC). It is found that the N species of NC support can atomically disperse metal cations of precursors, which largely renders uniform nucleation and growth of bimetallic NPs and fine structure modulation of them. In another regard, metal transfer is confined to a narrow region on NC via N-mediation, hence greatly favoring localized particle growth and formation of ultrafine bimetallic NPs. Remarkably, the ultrafine 3.1 ± 0.7 nm intermetallic Pt₃Fe NPs on NC displayed excellent catalytic activity and durability toward electrochemical hydrogen evolution reaction.     

Formation Mechanism of Epitaxial Palladium–Platinum Core–Shell Nanocatalysts in a One‐Step Supercritical Synthesis

The scarcity of platinum group metals provides a strong incentive to optimize the catalytic activity and stability, e.g., through nanoalloys or core–shell nanoparticles. Here, time‐resolved X‐ray total scattering and transmission electron microscopy characterization are used to study the formation of palladium–platinum core–shell nanoparticles under solvothermal conditions. It is shown that Pd rapidly forms small (5–10 nm), disordered primary particles, which agglomerate and crystallize when reaching 20–25 nm. The primary Pd particles provide nucleation sites for Pt, and, with extended reaction time, the Pd cores become fully covered with Pt shells. The observed core–shell material is surprising when considering the Pt–Pd phase diagram and relative surface energies, but it can be rationalized through the kinetics of precursor conversion. To bridge the gap between scientific studies and industrial demand for large‐scale production, the synthesis process is successfully transferred to a continuous flow supercritical reactor providing a simple scalable and green process for production of bimetallic nanocatalysts.     

Size,morphology and optical properties of SnO2 nanoparticles synthesized by facile surfactant-assisted solvothermal processing

Spherical and dumbbell-shaped SnO₂ nanoparticles were grown by a facile solvothermal using different amounts (0.5, 1 and 1.5 g) of three different surfactants (cetyltrimethylammonium bromide, polyethylene glycol and sodium dodecyl sulfate) in ethylenediamine, serving as both a coordinating and an alkaline reagent. The average particle size, measured by powder X-ray diffraction, was determined to be ∼3–6 nm and was confirmed by transmission electron microscopy. The chemical structure of products was studied by Fourier transform infrared spectroscopy. Morphologies and composition of products were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. Optical properties of products were investigated by ultraviolet–visible (UV–vis) absorption and photoluminescence spectroscopies. Finally, the formation mechanism of SnO₂ nanoparticles is discussed.     

脉冲激光烧蚀法制备Ag纳米粒子胶体

为了研究激光参数对Ag纳米粒子胶体的影响,采用不同重复率和能量密度的脉冲激光对蒸馏水中的Ag靶烧蚀10 min来制备Ag纳米粒子胶体.通过透射电镜(TEM)和紫外-可见(UV-Vis)分光光度计分析了Ag纳米粒子胶体的大小、形貌和吸收光谱,同时由Image-ProPlus软件分析计算了粒子的平均粒径及其分布.结果表明,由重复率为10 Hz,能量密度为4.2 J/cm2的脉冲激光烧蚀10 min后制备的Ag胶体纳米粒子平均粒径最小(D=17.54 nm),粒径分布最窄(δ=36.86 nm),且形貌较均匀.从而证实了通过调节激光参数来控制纳米粒子尺寸和形貌的可行性.另外,在实验基础上,应用熔化生长"与爆炸"模型讨论了激光烧蚀工艺参数对Ag纳米粒子胶体的影响规律.     

Template‐Confined Dewetting Process to Surface Nanopatterns: Fabrication,Structural Tunability,and Structure‐Related Properties

Metallic surface nanopatterns are prepared by a template‐confined dewetting process with multiple structural controllabilities. The morphology of the building blocks is homogeneous throughout the surface nanopatterns, as the dewetting process proceeds separately in each bowl. The features of the building units in the surface patterns are highly dependent on the annealing temperature. Importantly, the size and composition of the nanoparticles in the surface nanopatterns can be pre‐calculated and designed by manipulating the thickness of the evaporated metallic films. The heating temperature and composition of the building units influence the surface‐enhanced Raman scattering (SERS) and plasmonic properties, thus tuning the localized surface plasmon resonance peaks over a broad range (from visible to near infrared). The introduction of silver in the gold surface nanopatterns enhances the SERS performance dramatically. This work not only provides a powerful route to fabricate surface nanopatterns, but also supplies a platform to study the mechanism of the complicated dewetting processes of metals.