Academic literature on the topic 'Bimetallic nanocrystals'

In recent years, bimetallic nanocrystals have attracted great interest from many researchers. Bimetallic nanocrystals are expected to exhibit improved physical and chemical properties due to the synergistic effect between the two metals, not just a combination of two monometallic properties. More importantly, the properties of bimetallic nanocrystals are significantly affected by their morphology, structure, and atomic arrangement. Reasonable regulation of these parameters of nanocrystals can effectively control their properties and enhance their practicality in a given application. This review summarizes some recent research progress in the controlled synthesis of shape, composition and structure, as well as some important applications of bimetallic nanocrystals. We first give a brief introduction to the development of bimetals, followed by the architectural diversity of bimetallic nanocrystals. The most commonly used and typical synthesis methods are also summarized, and the possible morphologies under different conditions are also discussed. Finally, we discuss the composition-dependent and shape-dependent properties of bimetals in terms of highlighting applications such as catalysis, energy conversion, gas sensing and bio-detection applications.

Highly porous Au–Pt urchin-like bimetallic nanocrystals have been prepared by a one-pot wet-chemical synthesis method. The porosity of urchin-like bimetallic nanocrystals was controlled by amounts of hydrazine used as reductant. The prepared highly porous Au-Pt urchin-like nanocrystals were superior catalysts of electrochemical methanol oxidation due to high porosity and surface active sites by their unique morphology. This approach will pave the way for the design of bimetallic porous materials with unprecedented functions.

A method for the preparation of bimetallic Pd/Co nanoparticles with a core–shell structure is presented. The process involves synthesis of a pure Pd seed colloid using thermal decomposition of palladium acetylacetonate, Pd(acac)2. Reduction of cobalt acetate using a polyalcohol in the presence of the Pd seeds allows the formation of Pd-core/Co-shell nanocrystals. Transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX), and superconducting quantum interference (SQUID) magnetometry were used to characterize the bimetallic system.

AbstractBimetallic nanostructures with well-defined shapes have shown distinct and advantageous catalytic properties compared to their monometallic counterparts. The use of bimetallic electrocatalysts may improve activity and durability, in addition to the possibility of reducing the loading of precious metals. A variety of bimetallic nanocrystals with different shapes has been reported in recent years. Their activities toward electrochemical catalytic reactions such as oxygen reduction and alcohol oxidations have been intensively studied. In this review, we discuss some latest developments in the morphology-controlled synthesis of Pt- and Pd-based bimetallic nanocrystals with shapes such as nanodendrites, polyhedra, porous hollow structures, and core shells, as well as their applications as electrochemical catalysts.

A new nonhydrolytic route for the preparation of well-crystallized size-tunable barium titanate (BaTiO3) nanocrystals capped with surface ligands is reported. Our approach involves: (i) synthesizing a “pseudo” bimetallic precursor, and (ii) combining the as-synthesized bimetallic precursor with a mixture of oleylamine with different surface coordinating ligands at 320 °C for crystallization and crystal growth. Different alcohols in the precursor synthesis and different carboxylic acids were used to study the effect of size and morphological control over the nanocrystals. Nanocrystals of barium titanate with diameters of 6–10 nm (capped with decanoic acid), 3–5 nm (capped with oleic acid), 10–20 nm (a nanoparticle and nanorod mixture capped with oleyl alcohol), and 2–3 nm (capped with oleyl alcohol) were synthesized, and can be easily dispersed into nonpolar solvents such as hexane or toluene. Techniques including x-ray diffraction, transmission electron microscopy, selected area electron diffraction, and high-resolution electron microscopy confirm the crystallinity and morphology of these as-synthesized nanocrystals.

Parmi les différents nanocatalyseurs, ceux constitués de nanoparticules de métaux nobles méritent une attention particulière en raison de leurs propriétés électroniques, chimiques et même optiques (dans le cas de transformations renforcées par les plasmons). Le platine ou le palladium sont bien connus pour leurs remarquables propriétés catalytiques, mais ils sont chers et leurs ressources sont limitées. En outre, les nanocatalyseurs monométallique ne peuvent conduire qu'à une gamme limitée de réactions chimiques. Ainsi, notre stratégie a été de développer des nanocatalyseurs bimétalliques composés de deux éléments métalliques qui peuvent présenter des effets synergiques entre leurs propriétés physicochimiques et une activité catalytique accrue. Nous avons ainsi conçu des nanocatalyseurs bimétalliques de type cœur-coquille composés d'un cœur en argent et d'une coquille en platine. L'intérêt est de combiner les activités catalytiques élevées et efficaces de la coquille de platine avec le cœur d'argent hautement énergétique, capable de renforcer les activités de la coquille grâce à ses propriétés plasmoniques. En outre, ces nanoparticules bimétalliques présentent souvent une activité catalytique supérieure en raison de la modification de la distance inter-atomique Pt-Pt (c'est-à-dire l'effet de contrainte). Dans ce travail de thèse, les nanoparticules Ag@Pt ont été synthétisées via un processus en deux étapes utilisant d'une part des nanoparticules d'Ag synthétisées chimiquement comme germes et d'autre part des complexes platine-oleylamine qui sont ensuite réduits à la surface des germes à une température contrôlée. Différentes tailles de germes d'Ag de 8 à 14 nm avec une très faible distribution de taille (<10%) ont été obtenues en ajustant le temps de réaction, la rampe de température, la concentration en précurseur d'Ag et la température finale pendant la synthèse. Différentes épaisseurs de coquille (de 1 à 6 couches atomiques) ont été obtenues en ajustant le rapport entre les concentrations de précurseur de platine et de germe d'argent. L'activité catalytique des nanoparticules Ag@Pt a été testée en considérant une réaction modèle de réduction du 4-nitrophénol en 4-aminophénol par NaBH4 en phase aqueuse. Nous avons observé que l'épaisseur de la coquille de Pt et la taille du noyau d'Ag influençaient les propriétés catalytiques et conduisaient à une activité catalytique accrue par rapport à l'argent ou au platine pur. Ceci a été attribué à des effets synergiques. De plus, nous avons observé une augmentation de l'activité catalytique des nanoparticules Ag et Ag@Pt sous irradiation lumineuse. Ce phénomène a été corrélé à la génération d'électrons chauds dans les noyaux d'Ag. Afin de développer une plateforme de nanocatalyse supportée, nous avons fabriqué des auto-assemblages 3D appelés aussi supercristaux composés de nanoparticules d'Ag@Pt obtenus spontanément après dépôt sur un substrat solide en raison de leur distribution de taille étroite et de leur forme homogène. L'activité catalytique de ces supercristaux pour la réaction d'évolution de l’hydrogène (HER) a été étudiée en suivant in situ par microscopie optique la production de nanobulles de gaz H2. Trois comportements distincts dans l'activité photo-catalytique (activité, activité intermittente et non-activité) ont été observés sur les supercristaux dans la même région d'intérêt. En outre, 50 % des assemblages ont été déterminés comme étant actifs pour l'HER qui a été démontrée comme étant accompagnée par une corrosion oxydative de l’argent
Among several nanocatalysts, those based on noble metal NPs deserve particular attention because of their electronic, chemical and even optical properties (in the case of plasmonic-enhanced transformations). Platinum or palladium are well known for their remarkable catalytic properties, but they are expensive and their resources are limited. In addition, single component nanocatalysts can only lead to a limited range of chemical reactions. Thus, our strategy was to develop bimetallic nanocatalysts composed of two metal elements that can exhibit synergistic effects between their physicochemical properties and enhanced catalytic activity. We have thus designed bimetallic nanocatalysts of the core-shell type composed of a silver core and a platinum shell. The interest is to combine the high and efficient catalytic activities of the platinum shell surface with the highly energetic silver core capable of enhancing the activities of the shell through its plasmonic properties. In addition, these bimetallic NPs often exhibit superior catalytic activity due to the modification of the Pt-Pt atomic bonding distance (i.e. the strain effect). In this thesis work, Ag@Pt NPs have been synthesized via a two-step process using chemically synthesized spherical Ag NPs as seeds on the one hand and platinum complexes with oleylamine on the other hand which are then reduced on the surface of the seeds at a controlled temperature. Different Ag seed sizes from 8 to 14 nm with a very low size distribution (<10%) have been obtained by adjusting the reaction time, temperature ramp, Ag precursor concentration and final temperature during the synthesis. The control of the shell thicknesses (from 1 to 6 atomic layers) has been possible by adjusting the ratio of platinum precursor to silver seed concentrations. The catalytic activity of the core-shell Ag@Pt NPs was tested by a model reaction of reduction of 4-nitrophenol to 4-aminophenol by NaBH4 in aqueous phase. We have observed that the thickness of the Pt shell and the size of the Ag core influence the catalytic properties and led increased catalytic activity compared to pure silver or platinum. This was attributed to synergistic effects. Furthermore, we have observed an enhancement of the catalytic activity of Ag and Ag@Pt NPs under light irradiation. This is correlated to the generation of hot electrons in the Ag core. Finally, in order to develop a supported nanocatalysis platform, 3D self-assemblies also called supercrystals composed of Ag@Pt nanoparticles have been spontaneously obtained after deposition on a solid substrate due to their narrow size distribution and homogeneous shape. The catalytic activity of these supercrystals for the hydrogen evolution reaction (HER) has been studied by following in situ by optical microscopy the production of H2 gas nanobubbles. Three distinct behaviors in photo-catalytic activity (activity, intermittent activity and non-activity) have been observed on the supercrystals in the same region of interest. In addition, 50% of the assemblies were determined to be active for HER which was shown to be accompanied by oxidative corrosion of silver

The techniques of optoperforation, spectral characterization of alloy disorder, and metal-enhanced fluorescence were applied to previously unconsidered or disregarded systems in order to demonstrate that such applications are both feasible and consequential. These applications were the subject of three disparate works and, as such, are independently discussed. Despite being ostensibly restricted to mammalian cells, optoperforation was demonstrated in intact plant cells by means of successful femtosecond-laser-mediated infiltration of a membrane impermeable dextran-conjugated dye into cells of vital Arabidopsis seedling stems. By monitoring the rate of dye uptake, and the reaction of both CFP-expressing vacuoles and nanocellulose substrates, the intensity and exposure time of the perforating laser were adjusted to values that both preserved cell vitality and permitted the laser-assisted uptake of the fluorophore. By using these calibrated laser parameters, dye was injected and later observed in targeted cells after 72 hours, all without deleteriously affecting the vital functions of those cells. In the context of alloy disorder, photoluminescence of excitonic transitions in two InAsxP1-x alloys were studied through temperature and magnetic field strength dependencies, as well as compositionally-dependent time-resolved behavior. The spectral shape, behavior of the linewidths at high magnetic fields, and the divergence of the peak positions from band gap behavior at low temperatures indicated that alloy disorder exists in the x=0.40 composition while showing no considerable presence in the x=0.13 composition. The time-resolved photoluminescence spectrum for both compositions feature a fast and slow decay, with the slow decay lifetime in x=0.40 being longer than that of x=0.13, which may be due to carrier migration between localized exciton states in x=0.40. In order to achieve broadband metal-enhanced fluorescence in upconverting NaYF4:Yb,Er nanocrystals, two nanocomposite architectures were proposed that retrofit metallic nanoshells to these lanthanide-doped nanocrystals. The typical monometallic construction was rejected in favor of architectures featuring Au-Ag bimetallic concentric surfaces, a decision supported by the considerable overlap of the calculated plasmon modes of the metallic structures with the emission and absorption spectrum of the nanocrystals. Furthermore, precursors of these nanocomposites were synthesized and photoluminescence measurements were carried out, ultimately verifying that these precursors produce the requisite upconversion emissions.
Ph. D.

Philosophiae Doctor - PhD
Lithium ion cathode systems based on composites of lithium iron phosphate (LiFePO₄), iron-cobalt-derivatised carbon nanotubes (FeCo-CNT) and polyaniline (PA) nanomaterials were developed. The FeCo-functionalised CNTs were obtained through in-situ reductive precipitation of iron (II) sulfate heptahydrate (FeSO₄.7H₂O) and cobalt (II) chloride hexahydrate (CoCl₂.6H₂O) within a CNT suspension via sodium borohydrate (NaBH₄) reduction protocol. Results from high Resolution Transmission Electron Microscopy (HRTEM) and Scanning Electron Microscopy (SEM) showed the successful attachment FeCo nanoclusters at the ends and walls of the CNTs. The nanoclusters provided viable routes for the facile transfer of electrons during lithium ion deinsertion/insertion in the 3-D nanonetwork formed between the CNTs and adjacent LiFePO₄ particles.

Li, Qian = 單金屬與雙金屬納米晶體材料 : 合成及表面等離子體共振特性 / 李倩.
Thesis Ph.D. Chinese University of Hong Kong 2014.
Includes bibliographical references.
Abstracts also in Chinese.
Title from PDF title page (viewed on 20, September, 2016).
Li, Qian = Dan jin shu yu shuang jin shu na mi jing ti cai liao : he cheng ji biao mian deng li zi ti gong zhen te xing / Li Qian.

碩士
國立虎尾科技大學
機械與機電工程研究所
95
In this thesis, the reduced bimetallic oxide nanocrystal (BONs) embedded in the hafnium oxynitride (HfON) high-k film have been developed by means of the low-temperature chemical-vapor-deposition (CVD) method. The bimetallic acetate solutions were prepared by dissolving the X-metal acetate (CH3COOH)2X and Y-metal acetate (CH3COOH)2Y (X, Y= Co or Mo, or Fe) into ethanol. By modulated the various weight percentage of the bimetallic acetate, the different acetates mixed solutions, the various thicknesses of the HfON blocking oxide, the various dip-coating times, the drop-coating and the HfON surface treatment, the high-quality BON can be achieved for the nonvolatile flash memory (NFM) devices applications. Capacitance-voltage (C-V) measurements estimate that a charge trap states density of 1.1 x 1012 cm-2 and a flatband voltage shift of 700 mV were achieved during the C-V hysteresis sweep at �b5 V for memory devices with CoxMoyO BONs. Scanning electron microscopy image displays that the CoxMoyO BONs with a diameter of ~4-20 nm and a surface density of ~1 x 1011 cm-2 were obtained. The results also show that the electrical and surface characteristics of memory devices with CoxMoyO BONs are better than those of memory devices with FexCoyO or FexMoyO. The electrical and surface properties of nonvolatile memory devices with CoxMoyO BONs can be further improved by the drop techniques and the TiOx incorporated into HfON surface. The writing characteristics measurements illustrate that the memory effects of devices with CoxMoyO, FexCoyO, and FexMoyO as charge trapping layers are mainly due to the holes trapping.