Room temperature L1₀ phase transformation in binary CoPt nanostructures prepared by focused-electron-beam-induced deposition

CoPt-C binary alloys have been fabricated by focused-electron-beam-induced deposition by the simultaneous use of Co?(CO)? and (CH?)?CH?C?H?Pt as precursor gases. The alloys are made of CoPt nanoparticles embedded in a carbonaceous matrix. TEM investigations show that as-grown samples are in an amorphous phase. By means of a room temperature low-energy electron irradiation treatment the CoPt nanoparticles transform into face-centered tetragonal L1? nanocrystallites. In parallel, the system undergoes a transition from a superparamagnetic to a ferromagnetic state at room temperature. By variation of the post-growth irradiation dose the electrical and magneto-transport properties of the alloy can be continuously tuned.     

水溶液中低代TEG—PAMAM树形分子存在下金纳米颗粒的制备

在水溶液中低代TEG—PAMAM树形分子存在时，用NaBH4还原HAuCI4制备出金纳米颗粒。用紫外可见吸收光谱（UV—Vis），红外光谱（FT-IR）和透射电子显微镜（TEM）对所制备的金纳米颗及其制备过程进行了表征，实验结果表明，以低代树形分子为模板，当HAuCI4与TEG—PAMAM物质量的比分别为2：1，1：1和1：2时，所制的金纳米颗粒的粒径分别为3．5±0．4nm，2．6±1．6nm和2．88±1．33nm，并且可在室温下储存数月。     

Low temperature fabrication of ZnO-whey protein isolate nanocomposite

Nanocrystalline zinc oxide (ZnO) particles coated with whey protein isolate (WPI) were fabricated in the weak basic aqueous solution condition at near room temperature. The X-ray diffraction and transmission electron microscopy measurements confirmed the nanoscaled composite structure of ZnO-WPI. The average composite granules size was about 300 nm and the embedded ZnO nanoparticles were uniform and monodisperse with an average diameter of 65 nm.     

Synthesis of CoPt nanoparticles by a modified polyol method: characterization and magnetic properties

CoPt nanoparticles with an average size of 3?nm and narrow distribution were synthesized by chemical reduction of Co(CH(3)COO)(2) and Pt(acac)(2) by polyethyleneglycol-200. The as-prepared nanoparticles have a disordered fcc structure which transformed after thermal treatment to an ordered fct structure, which results in coercivity up to 6?kOe at room temperature and 9?kOe at 5?K because of the high magnetocrystalline anisotropy of the tetragonal structure [Formula: see text].     

Evolution of High Coercivity in CoPt Nanoparticles Through Nitrogen Assisted Annealing

The presence of H ₂ along with an inert gas during annealing was considered as a prerequisite in achieving high coercivity in alloys such as FePt and CoPt nanoparticles synthesized through chemical methods. CoPt nanoparticles were synthesized using a one-step polyol process without using any surfactant and annealed at various temperatures in N ₂ atmosphere. The magnetic properties of Co ₄₀Pt ₆₀ sample annealed at 700 ^oC in N ₂ atmosphere showed a room temperature coercivity of 8.4 kOe. The magnetic interactions present in the samples were studied using δM measurements. The evolution of high coercivity in the samples annealed at 700 ^oC showed that N ₂ is a cheaper alternative to the existing reducing gas mixture.     

Novel phase-transfer preparation of monodisperse silver and gold nanoparticles at room temperature

In a novel water-cyclohexane two-phase system, the aqueous formaldehyde is transferred to cyclohexane phase via reaction with dodecylamine to form reductive intermediates in cyclohexane; the intermediates are capable of reducing silver or gold ions in aqueous solution to form dodecylamine protected silver and gold nanoparticles in cyclohexane solution at room temperature. The prepared silver and gold nanoparticles are examined by transmission electron microscopy (TEM), UV-Visible spectroscopy (UV-vis), X-photon electron spectroscopy (XPS) and Fourier transfer infrared spectroscopy (FT-IR). It is found that these nanoparticles are monodisperse in size of less than 10 nm and have good stability in cyclohexane due to the adsorbed dodecylamine on nanoparticle surface. Moreover, the synthesis mechanism is revealed via gas chromatography (GC), gas chromatography-mass spectroscopy (GC-MS), nuclear magnetic resonance (NMR) analyses of the solutions during the preparation process.     

Synthesis of monodisperse iron oxide and iron/iron oxide core/shell nanoparticles via iron-oleylamine complex

Monodisperse magnetic nanoparticles are of great scientific and technical interests. This paper reports a single-step synthesis of monodisperse magnetite nanoparticles with particle size of 8 nm. Iron/maghaemite core/shell nanoparticles with particle size of 11 nm were obtained by reducing the concentration of oleylamine. TEM and in-situ FTIR results suggested that iron-oleylamine intermediate was generated in-situ and decomposed at higher temperature. Oleylamine was also found on the surface of nanoparticles, indicating its role as capping agent which provided steric protection of as-synthesized nanoparticles from agglomeration. Both magnetite and iron/maghaemite core/shell nanoparticles were superparamagnetic at room temperature with a blocking temperature at 80 K and 67 K, respectively.     

Dendrimer templated synthesis of one nanometer Rh and Pt particles supported on mesoporous silica: catalytic activity for ethylene and pyrrole hydrogenation

Monodisperse rhodium (Rh) and platinum (Pt) nanoparticles as small as approximately 1 nm were synthesized within a fourth generation polyaminoamide (PAMAM) dendrimer, a hyperbranched polymer, in aqueous solution and immobilized by depositing onto a high-surface-area SBA-15 mesoporous support. X-ray photoelectron spectroscopy indicated that the as-synthesized Rh and Pt nanoparticles were mostly oxidized. Catalytic activity of the SBA-15 supported Rh and Pt nanoparticles was studied with ethylene hydrogenation at 273 and 293 K in 10 torr of ethylene and 100 torr of H 2 after reduction (76 torr of H 2 mixed with 690 torr of He) at different temperatures. Catalysts were active without removing the dendrimer capping but reached their highest activity after hydrogen reduction at a moderate temperature (423 K). When treated at a higher temperature (473, 573, and 673 K) in hydrogen, catalytic activity decreased. By using the same treatment that led to maximum ethylene hydrogenation activity, catalytic activity was also evaluated for pyrrole hydrogenation.     

无溶剂SiO2纳米流体的制备及其导电性能研究

本文中首先以SiO2纳米粒子为核,通过脱水反应在SiO2纳米粒子表面接枝3-硅羟基-1-丙基磺酸(SIT),再通过一元弱碱解离反应,以离子键接枝反离子聚氧乙烯十八烷基胺(Ethomeen18/25),所形成的有机/无机杂化纳米材料在室温下呈金黄色的透明液体状,称其为无溶剂纳米流体.单分散态无溶剂SiO2纳米流体中,Si...     

Tailoring silver nanoparticle construction using dendrimer templated silica networks

We have examined the role of the internal environment of dendrimer templated silica networks in tailoring the construction of silver nanoparticle assemblies. Silica networks from which 3,5-dihydroxybenzyl alcohol based dendrimer templates have been completely removed, slowly wet with an aqueous solution of silver acetate. The latter then reacts with internal silica silanol groups, leading to chemisorption of silver ions, followed by the growth of silver oxide nanoparticles. Silica network constructed using generation 4 dendrimer contains residual dendrimer template, and mixes with aqueous silver acetate solution easily. Upon chemisorption, silver ions get photolytically reduced to silver metal under a stabilizing dendrimer environment, leading to the formation of silver metal nanoparticles.     

Water-Soluble Anisotropic Iron Oxide Nanoparticles: Dextran-Coated Crystalline Nanoplates and Nanoflowers

We report a simple phase transfer based synthesis route for two novel anisotropic water soluble iron oxide nanoparticle shapes, namely, nanoplates and nanoflowers. The nanoplates and nanoflowers are initially prepared in an organic solvent via a modified “heat-up” method. Then, the crystalline nanoparticles are rendered hydrophilic via sonication in the presence of dextran and water. These nanoparticles are highly monodisperse and superparamagnetic at room temperature. High resolution transmission electron microscopy indicates that the iron oxides cores are not affected by the phase transfer. Dextran coating is confirmed by dynamic light scattering, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The obtained dextran coverage was 26 wt% for the nanoplates and 37 wt% for the nanoflowers. The nanoplates and nanoflowers were not only water soluble, but also remained stable at different pH (4–7) and in common aqueous buffer solutions. Thorough characterizations of the nonspherical iron oxide nanoparticles indicate that these particles could be useful for potential biomedical applications and magnetic resonance imaging.     

FePt and CoPt nanoparticles co-deposited on silicon dioxide-a comparative study

We compare CoPt and FePt nanoparticles grown under identical conditions on oxidized Si?substrates by electron beam co-evaporation. Growth was performed under high vacuum conditions at substrate temperatures of 1023?K and was immediately followed by an annealing step. This process forms CoPt and FePt nanoparticles with mean diameters between ～17 and ～22?nm. In particular, the annealing step results in grain size enlargement for all samples and in a progressive magnetic hardening of the nanoparticles which reach maximum perpendicular coercivities of ～6.6?kOe (for the CoPt) and ～10.2?kOe (for the FePt nanoparticles). We show that, during this annealing step, a progressive transition towards the hard magnetic L1(0) ordered phase takes place in both materials. In contrast to FePt, CoPt nanoparticles must be annealed in order to crystallize in this phase.     

Synthesis of triethanolamine (TEA) capped CdSe nanoparticles

We report the synthesis of water soluble triethanolamine capped CdSe nanoparticles by a simple, green room temperature route. The route involves the reaction of selenide ions to an aqueous solution containing cadmium chloride and triethanolamine (TEA) at room temperature.     

低温液相化学法在合成单分散纳米微粒中的应用

单分散纳米微粒的获得,为进一步研究某一特定尺寸的纳米微粒的各种性质提供了方便.单分散纳米微粒比多分散纳米微粒具有更显著的性能,更适合于应用.国内外在这方面开展了大量的研究工作,主要报道了低温液相化学法在合成单分散金属纳米颗粒、单分散半导体纳米颗粒、单分散复合氧化物纳米颗粒、单分散聚合物纳米微球、单分散核壳结构复合纳米微粒等方面的应用情况.     

Low-temperature synthesis of hexamethylenetetramine-stabilised ZnS nanoparticles and its photocatalytic properties

ZnS nanoparticles have been synthesised at low temperature by short reaction (80°C for 2?h) via wet chemical route. The nanoparticles were stabilised using hexamethylenetetramine (HMTA) as surfactant in aqueous solution. The average particle size calculated from X-ray diffraction studies was about 4?nm with cubic zincblende structure. The presence of HMTA in the synthesised ZnS nanoparticles was confirmed by FTIR studies. A significant blue shift was observed in the optical absorption band edge for the ZnS nanoparticles as compared to the bulk, indicating a strong quantum confinement. The room temperature photoluminescence (PL) spectrum showed a broad green emission peak at around 502?nm. The photocatalytic property of HMTA-stabilised ZnS nanoparticles were investigated on the decolourisation of methylene blue aqueous solution under UV light irradiation.     

Highly Active Metastable Ruthenium Nanoparticles for Hydrogen Production through the Catalytic Hydrolysis of Ammonia Borane

Late transition metal nanoparticles (NPs) with a favorably high surface area to volume ratio have garnered much interest for catalytic applications. Yet, these NPs are prone to aggregation in solution, which has been mitigated through attachment of surface ligands, additives or supports; unfortunately, protective ligands can severely reduce the effective surface area on the NPs available for catalyzing chemical transformations. The preparation of ‘metastable’ NPs can readily address these challenges. We report herein the first synthesis of monodisperse metastable ruthenium nanoparticles (RuNPs), having sub 5 nm size and an fcc structure, in aqueous media at room temperature, which can be stored for a period of at least 8 months. The RuNPs can subsequently be used for the catalytic, quantitative hydrolysis of ammonia‐borane (AB) yielding hydrogen gas with 21.8 turnovers per min at 25 °C. The high surface area available for hydrolysis of AB on the metastable RuNPs translated to an E_a of 27.5 kJ mol^‐1, which is notably lower than previously reported values for RuNP based catalysts.     

Amine-terminated TEG-derived PAMAM dendrimer as template for preparation of gold nanoparticles in water

Nano-sized monodisperse gold particles (AuNPs) have received significant attention in the past decade, due to their unique physical properties and good chemical stability, which can lead to a wide variety of potential applications. In this work, TEG-derived PAMAM dendrimers with amine-terminating groups were synthesized and characterized by ¹H NMR and FT-IR. These dendrimers were investigated as the templates for preparation of gold nanoparticles through the reduction of HAuCl₄ by NaBH₄ in water. Stable gold nanoparticles with diameters around 10 nm were obtained in the presence of G2.0 – G5.0 dendrimers and characterized by UV-Vis spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS). The particle size of the produced AuNPs decreased with increasing dendrimer generations. A dendrimer of higher generation has a rigid structure with many end groups on the surface and may play a powerful role in the growth of the AuNPs, as well as having a solid stabilization effect on the AuNPs.     

Self-assembled copt nanoparticles monolayer film and its IR optical properties

CoPt nanoparticles were prepared by galvanic displacement reaction, followed by a chemical reduction. The CoPt nanoparticles were spherical and the average diameter was about 33 nm obtained from the results of transmission electron microscopy (TEM), high resolution TEM and scanning electron microscopy (SEM). The results of powder X-ray diffration (XRD), energy dispersed X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) demonstrated that the surface of the product was mostly consist of Pt nanoparticles. An ordered monolayer film of CoPt nanoparticles on Si wafer was obtained by a Liquid/Liquid interface technique. In situ FTIR transmission spectral study indicates that the ordered self-assembled monolayer film of the CoPt nanoparticles shows Fano-like infrared effects, while the deposited CoPt nanoparticles exhibit normal enhanced IR adsorption. The results of the present paper demonstrated that the IR optical properties are closely related to the interactions and thickness of the nanomaterials and significant to understand the anomalous IR properties of nanometer materials.     

Size-controlled synthesis of dendrimer-protected gold nanoparticles by microwave radiation

Well-stable dendrimer-protected gold nanoparticles were synthesized by microwave radiation of a third-generation poly(propyleneimine) dendrimer (PPI G3)–HAuCl₄ aqueous solution without the additional step of introducing other reducing agents and protective agents. The size of these gold nanoparticles thus formed can be controlled by molar ratio of dendrimer to gold.     

Rapid,single-step preparation of dendrimer-protected silver nanoparticles through a microwave-based thermal process

The microwave-based thermal process was applied to the preparation of dendrimer-protected silver nanoparticles. The formation of silver nanoparticles occurs rapidly in a single step, carried out by directly heating a third-generation poly(propyleneimine) dendrimer–AgNO₃ aqueous solution in a microwave oven without the introduction of additional reducing reagents and protective reagents. The nanoparticles thus formed were characterized by UV–vis spectra and transmission electron microscopy (TEM). The influence of the molar ratio of dendrimer to silver on the formation of silver particles was also examined.