Distribution Of Metal Nanoparticles Research Articles

Electrochromic properties of conducting polymer metal nanoparticles composites

Electrochromic devices were made using a nanocomposite blend of conducting polymer poly(3,4 ethylenedioxythiophene):poly styrene sulfonate (PEDOT:PSS) and metal nanoparticles of silver or gold. Microscopic analysis showed a random distribution of metal nanoparticles with little aggregation in the matrix. The two terminal devices exhibited an increase in absorption that is dependant on the loading of nanoparticles in the polymer. Further, the active electrochromic spectral window showed a bias dependant tuning and a broadened spectral response. All devices exhibited slow relaxivities which we interpret as resulting from the high capacitance of the metal nanoparticles embedded in the polymer matrix.

Highly selective Pd/titanate nanotube catalysts for the double-bond migration reaction

Pd(II) and Pd(0) catalysts supported onto titanate nanotubes (H 2Ti 3O 7) were prepared by an ion-exchange technique. The catalysts are characterised by narrow size distribution of metal nanoparticles on the external surface of the nanotubes. Pd(II) catalysts show high selectivity toward double-bond migration reaction versus hydrogenation in linear olefins. The catalytic activity exhibits a volcano-type dependence on the metal loading, with the maximum activity observed at ca. 8 wt%. The Pd(II) was shown to be rapidly reduced to Pd(0) by appropriate choice of solvent. Prereduced Pd(0) catalysts were found to be less active toward double-bond migration and more selective toward hydrogenation. The DBM reaction was faster in protic solvents, such as methanol or ethanol.

Studies of LaNiO 3 used as a precursor for catalytic carbon nanotubes growth

The growth of the carbon nanotubes is carried out on nickel containing catalysts. A fine distribution of metal nanoparticles is obtained by the reduction in situ of a perovskite phase. The LaNiO 3 perovskite is synthesized by three different methods in order to compare the nature of the tubes obtained after CH 4–CVD. These structures are analyzed by DRX, H 2-TPR and SEM before catalytic test. After CVD, the internal diameter of the tubes is constant no matter the method of preparation of the perovskite and the external diameter depends on the distribution of the metallic particles. The homogeneous distribution of the CNT is related to the homogeneous distribution of the metallic particles obtained after reduction under methane.

Deposition of Metal Nanoparticles on Carbon Nanotubes via Hexane Modified Water-in-CO<SUB>2</SUB> Microemulsion at Room Temperature

Carbon nanotube-supported metallic nanoparticles (Pd, Rh, and bimetallic Pd-Rh) with diameters in the range 2-10 nm can be synthesized by hydrogen reduction of metal ions dissolved in the water core of a CO2 microemulsion in liquid CO2 at room temperature. The microemulsion is stabilized by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and dissolved in liquid CO2 with the aid of hexane as a modifier. The metal nanoparticles synthesized in the microemulsion can be deposited on surfaces of multi-walled carbon nanotubes (MWCNTs) by stirring in the liquid CO2 phase. This simple method produces uniformly distributed metal nanoparticles on surfaces of the MWCNTs with high yields. The carbon nanotube-supported Pd/Rh bimetallic nanoparticles exhibit high catalytic activities for hydrogenation of aromatic compounds and can be reused without losing catalytic activity.

Microwave-Assisted One-Step Synthesis of Polyacrylamide−Metal (M = Ag, Pt, Cu) Nanocomposites in Ethylene Glycol

Polyacrylamide-metal (M = Pt, Ag, Cu) nanocomposites with metal nanoparticles homogeneously dispersed in the polymer matrix have been successfully prepared with the corresponding metal salt and acrylamide monomer in ethylene glycol by microwave heating. This method is based on the single-step simultaneous formation of metal nanoparticles and polymerization of the acrylamide monomer, leading to a homogeneous distribution of metal nanoparticles in the polyacrylamide matrix. Ethylene glycol acts as both a reducing reagent and a solvent, thus no additional reductant is needed. Another advantage is that no initiator for AM polymerization and no surfactant for stabilization of metal nanoparticles are necessary. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), ultraviolet visible (UV-vis) absorption spectra, and thermogravimetric (TG) and differential scanning calorimetric analysis (DSC).

Sonochemically Prepared high Dispersed Ru/TiO2 Mesoporous Catalyst for Partial Oxidation of Methane to Syngas

Highly dispersed Ru nanoparticles on mesoporous TiO2 have been synthesized by a one-step ultrasound assisted polyol reduction procedure. The catalysts have been characterized by XRD, TEM and HR-TEM, EDX, BET and TPR methods. It has been demonstrated that the sonochemical method reduces the Ru+3 ions creating a narrow size distribution of metallic nanoparticles deposited on the mesoporous support without damaging its pore structure. The nanoparticles of Ru are highly dispersed and stable because of their incorporation into the mesopores, and the strong metal-support interaction. The catalytic properties of Ru/TiO2(MSP) have been tested in the partial oxidation of methane, and high activity and selectivity towards CO and H2 have been demonstrated.

Optical properties and applications of dendrimer–metal nanocomposites

The use of novel nanostructured materials for optical applications continues to be an important issue for the creation of new devices. New materials including metal nanoparticles have played an important role for applications in photonics, biology, as well as medicine. This review primarily concerns the use of one particular metal nanoparticle topology, dendrimer–metal nanocomposites. The focus of this review is to describe the optical properties of dendrimer–metal nanocomposites as well as functionalized dendrimer–metal nanocomposites. The description of various synthetic methodologies to produce transition metal (Au, Ag, Pd, Pt, and Cu) dendrimer nanocomposites as well as lanthanide ion-cored dendrimers are presented in this review, with further details regarding the basic characterization of these systems. The experimental procedures of the optical measurements used to probe the steady-state and time-resolved dynamics in these novel nanoparticle architectures are provided. Analysis of optical properties of dendrimer nanocomposites (DNCs) includes a description of the characterization of the metal nanoparticles as well as the size and distribution of metal nanoparticles formed by use of organic dendrimer template synthetic procedures (such as PAMAM). The non-linear transmission properties of certain dendrimer–metal nanocomposites show promising behaviour, which may be useful for applications involving eye and sensor protection. Reports of non-linear transmission properties of both Au and Ag dendrimer nanocomposites are discussed. Metal nanoparticles have also been suggested as useful materials for biological fluorescence imaging and sensing applications. However, it is well known that the efficiency of metal emission is very small. Recent measurements using ultra-fast spectroscopic techniques (fluorescence upconversion) have shed new light on this matter in metal nanoparticles and in dendrimer–metal nanocomposites. Dendrimer–metal nanocomposites have been used to investigate the dynamics of both metal particle emission and the interaction of metal particles with dipolar chromophores. The measurement and mechanism of ultra-fast transient absorption and emission dynamics in metal topologies including dendrimer nanocomposites are also discussed in the review. Future directions regarding the optical properties of dendrimer nanocomposites in the areas of photonics, biology, and medicine are also discussed in this review.

Microlens formation in microgel/gold colloid composite materials via photothermal patterning.

We report on the nature of photothermally patterned regions inside self-assembled hydrogel nanoparticle materials containing coassembled colloidal Au. These composite materials are prepared from approximately 226-nm diameter particles composed of the environmentally responsive polymer, poly(N-isopropylacrylamide) (pNIPAm). Upon centrifugation to achieve a proper volume fraction, these close-packed assemblies display a sharp Bragg diffraction peak in the midvisible region of the spectrum and can be reversibly converted into a nondiffracting glassy material as the temperature is raised above the characteristic phase transition temperature of the polymer. The addition of 16-nm colloidal Au prior to centrifugation allows the homogeneous distribution of metal nanoparticles throughout the close-packed material. Localized heating is then possible upon excitation of the Au plasmon absorption with a frequency doubled Nd:YAG laser (lambda = 532 nm). Such localized heating events lead to patterned regions of ordered crystalline phases inside of bulk glassy phases. We illustrate that the nature of the locally patterned area results in the formation of a microlens due to density/refractive index gradient in the patterned crystalline region. The Gaussian power distribution of the incident beam is thought to be a contributing factor in the microlens formation. Microlens formation is shown by observing interference patterns similar to Newton's rings, which change over time as the region is formed. A true hallmark of the lens is also demonstrated by focusing an image through the patterned structure.

In Situ Synthesis of Noble Metal Nanoparticles in Ultrathin TiO2−Gel Films by a Combination of Ion-Exchange and Reduction Processes

We have explored in situ synthesis of noble metal nanoparticles in ultrathin TiO2−gel films, in view of the increasing importance of such nanoparticle-containing thin films. The two-step procedure consists of ion exchange in the ultrathin matrix and subsequent reduction of metal ions to nanoparticles by low-temperature H2 plasma, by aqueous NaBH4, and by UV irradiation. Smooth and transparent ultrathin TiO2 films containing noble metal (Ag, Au, Pd, Pt) particles of 2−10 nm were readily obtained by this approach. The size and distribution of metal nanoparticles could be controlled by changing reaction conditions. The film thickness was precisely controlled by the cycle of film assembly. The low-temperature H2 plasma treatment, first used for preparation of noble metal nanoparticles, showed interesting advantages over chemical and photoinduced reductions in fabrication of nanoparticle-containing inorganic thin films.

Preparation and Characterization of Electrolessly Deposited Platimum and Palladium Nanoparticles on Pyrolyzed Photoresist Films on Silicon Substrates

The effects of metal depositions on pyrolyzed photoresist films (PPF) grown on silicon substrates were investigated. A silicon chip, spin-coated with a positive photoresist was pyrolyzed through heating to form a PPF, or a conductive carbon film. For increasing periods of time, nanometersized metal particles of platinum and palladium were spontaneously deposited on conductive carbon films by immersion in solutions of 0.049% HF containing 100 ppm, 200 ppm, and 500 ppm concentrations of metal ions Pt2+ or Pd2+. Following each hour of deposition, the electrochemical behavior of the metal-deposited carbon films were investigated by cyclic voltammetry, utilizing a 0.1 M H2SO4 electrolyte system. The electron-transfer rates and characteristics of hydrogen evolution exhibited positive catalytic effects when the platinum and palladium nanoparticles were deposited on the carbon films. Scanning electron microscopy and energy-dispersive x-ray analysis were employed to characterize the surface morphology and distribution of metal nanoparticles on the PPF surface based on metal ion concentration and deposition time. The depositions of metal nanoparticles accelerate the electron transfer process, which could improve the efficiency and performance of PPF electrodes in the production of hydrogen fuel.

In situ deposition of silver and palladium nanoparticles prepared by the polyol process, and their performance as catalytic converters of automobile exhaust gases

In situ deposition of silver particles onto alumina and palladium particles onto mixed CeZr oxides has been achieved upon chemical reduction of the corresponding metal species (AgNO3 and PdCl2) by ethylene glycol in the presence of polyvinylpyrrolidone. The support oxide powders were found to keep their crystalline structure and morphology after treatment with hot ethylene glycol while the BET surface area decreased after metal deposition. Microprobe maps obtained from energy dispersive X-ray analysis revealed a homogeneous distribution of metal nanoparticles on the surfaces of alumina and of the mixed CeZr oxides. Supported silver and palladium were tested as catalytic converters of simulated exhaust automobile gases. The catalytic activity of silver-loaded alumina powder catalyst for CO and hydrocarbon oxidation as well as NO and NOx reduction, was found to be higher than that of a reference silver catalyst. Palladium-loaded mixed CeZr oxides powder catalyst showed a similar performance to that of a reference palladium catalyst as a three-way catalyst converter.

Metallic Particles from Complexing Microcapsules Dispersed in a Silica Gel

A new process to control the distribution of metal nanoparticles is proposed. It involves the use of complexing microcapsules obtained by interfacial polycondensation. The latter are hollow spheres constituted of a polymer membrane, containing an insoluble active ingredient, such as a polyacrylic acid, which can complex Co2+ ions. These capsules are dispersed in a silica sol followed by thermal treatments and reduction under H2 which results in metallic Co nanoparticles confined in the capsules domains. The particles do not diffuse in the matrix.

Optical transmission of dielectric layers with metallic nanoparticles inhomogeneously distributed over the sample thickness

Dielectric layers with silver nanoparticles in the bulk, synthesized by the vacuum evaporation of metal onto viscous-flow softened polymer substrates are analyzed. New materials with a nonuniform distribution of nanoparticles over the sample thickness are obtained. Optical characteristics of the composition layers are calculated from the transmission spectra. To calculate the optical spectra, a model of a multilayered plane-parallel film structure is considered. Functions of dielectric constants of separate composition layers are determined using the Bruggeman theory of effective medium. A qualitative agreement between the experimental and simulated optical spectra is achieved taking into account nonuniform distribution of metal nanoparticles over the composition material thickness.

High-Resolution Backscattered Electron Microscopy: Determining the 3-D Distribution of Metallic Nanoparticles in Supported Catalysts

Metallic nanoparticles play an important role in heterogeneous catalysis; these nanoparticles are usually finely dispersed onto high-surface-area supports and act as active centers during a catalytic reaction. The performance of a supported metal catalyst is often directly related to the size and spatial distribution of the nanoparticles. Traditionally, TEM/STEM techniques have to be used to visualize highly dispersed nanoparticles. A major limitation of TEM/STEM techniques is, however, the stringent requirements of samples that can be examined: Useful information can be extracted from only very thin areas of a sample. The preparation of samples suitable for TEM/STEM observation can also pose a challenging problem for examining certain types of catalyst samples such as catalyst beads, pellets, powders, cylinders, or other forms that are often used in industrial applications. These and other limitations preclude the application of TEM/STEM techniques to extracting useful information about the surface or subsurface properties of thick or bulk catalyst samples.

Optical reflection from dielectric layers containing metal particles formed by ion implantation

Dielectric layers with silver nanoparticles, which are synthesized in a soda-silicate glass by implantation of 60-keV ions with a dose of 7.0×1016 Ag+/cm2 at an ion current density of 10 μmA/cm2, are analyzed. The depth of silver distribution was measured by Rutherford backscattering. Data on optical characteristics of composite layers were obtained from the transmission spectra and from the reflection, which were measured both from the side of an implanted glass surface and from the unimplanted side. To calculate reflection spectra, a multilayer plane-parallel film structure was considered, which was modeled on the basis of the matrix method using complex Fresnel coefficients. Dielectric functions of separate layers were determined using the Maxwell-Garnet theory of an effective medium. A qualitative agreement between the experimental and the model optical spectra was obtained taking into account a nonuniform depth distribution of metal nanoparticles in a composite material.

X-ray studies of polymer/gold nanocomposites

We demonstrate that x-ray reflection standing wave fluorescence spectroscopy is a highly sensitive technique for the determination of the distribution of metal nanoparticles inside polymer thin films. We investigate both the depth profile and the in-plane spatial correlation of gold nanoparticles in an asymmetric polystyrene-b-poly(2-vinylpyridine) block copolymer film. These copolymer films self-assemble into alternating, nanometer-sized domains that are, upon annealing, selectively decorated by thermally evaporated metal nanoparticles to form metal/polymer composites.

High-Resolution Scanning Electron Microscopy and Microanalysis of Supported Metal Catalysts

AbstractThe use of a high-brightness field emission gun and novel secondary electron detection systems makes it possible to acquire nanometer-resolution surface images of bulk materials, even at low electron beam voltages. The advantages of low-voltage SEM include enhanced surface sensitivity, reduced sample charging on non-conducting materials, and significantly reduced electron range and interaction volume. High-resolution images formed by collecting the backscattered electron signal can give information about the size and spatial distribution of metal nanoparticles in supported catalysts. Low-voltage XEDS can provide compositional information of bulk samples with enhanced surface sensitivity and significantly improved spatial resolution. High-resolution SEM techniques enhance our ability to detect and, subsequently, analyze the composition of nanoparticles in supported metal catalysts. Applications of high-resolution SEM imaging and microanalysis techniques to the study of industrial supported catalysts are discussed.