Showing papers on "Nanoparticle published in 1998"
TL;DR: Scanning and transmission electron microscopy images demonstrate that the wall thickness of the hollow spheres can be readily controlled by varying the number of nanoparticle-polymer deposition cycles, and the size and shape are determined by the morphology of the templating colloid.
Abstract: Hollow silica and silica-polymer spheres with diameters between 720 and 1000 nanometers were fabricated by consecutively assembling silica nanoparticles and polymer onto colloids and subsequently removing the templated colloid either by calcination or decomposition upon exposure to solvents. Scanning and transmission electron microscopy images demonstrate that the wall thickness of the hollow spheres can be readily controlled by varying the number of nanoparticle-polymer deposition cycles, and the size and shape are determined by the morphology of the templating colloid. The hollow spheres produced are envisioned to have applications in areas ranging from medicine to pharmaceutics to materials science.
3,924 citations
TL;DR: Large panels of aligned carbon nanotubes can be made under conditions that are suitable for device fabrication under plasma-enhanced hot filament chemical vapor deposition.
Abstract: Free-standing aligned carbon nanotubes have previously been grown above 700°C on mesoporous silica embedded with iron nanoparticles. Here, carbon nanotubes aligned over areas up to several square centimeters were grown on nickel-coated glass below 666°C by plasma-enhanced hot filament chemical vapor deposition. Acetylene gas was used as the carbon source and ammonia gas was used as a catalyst and dilution gas. Nanotubes with controllable diameters from 20 to 400 nanometers and lengths from 0.1 to 50 micrometers were obtained. Using this method, large panels of aligned carbon nanotubes can be made under conditions that are suitable for device fabrication.
2,530 citations
TL;DR: In this paper, a general approach to the making of metal nanoshell composite nanoparticles based on molecular self-assembly and colloid reduction chemistry is described, which can be used to construct a new, composite nanoparticle whose optical resonance can be designed in a controlled manner.
2,240 citations
TL;DR: A transition from metal-like double-layer capacitive charging to redox-like charging was observed in electrochemical ensemble Coulomb staircase experiments on solutions of gold nanoparticles of varied core size, consistent with new near-infrared spectroscopic data showing an emerging gap between the highest occupied and lowest unoccupied orbitals.
Abstract: A transition from metal-like double-layer capacitive charging to redox-like charging was observed in electrochemical ensemble Coulomb staircase experiments on solutions of gold nanoparticles of varied core size. The monodisperse gold nanoparticles are stabilized by short-chain alkanethiolate monolayers and have 8 to 38 kilodaltons core mass (1.1 to 1.9 nanometers in diameter). Larger cores display Coulomb staircase responses consistent with double-layer charging of metal-electrolyte interfaces, whereas smaller core nanoparticles exhibit redox chemical character, including a large central gap. The change in behavior is consistent with new near-infrared spectroscopic data showing an emerging gap between the highest occupied and lowest unoccupied orbitals of 0.4 to 0.9 electron volt.
963 citations
TL;DR: In this article, the main applications of current interest including some discussions of the underlying phenomena are dealt with, including some experiments for synthesizing nanoparticles in the gas phase aiming at any of the above mentioned functional applications.
713 citations
TL;DR: In this article, self-assembled multilayer thin films consisting of alternating layers of ∼6-nm Au nanoparticles and α,ω-dithiols have been prepared on glass substrates.
Abstract: Self-assembled multilayer thin films consisting of alternating layers of ∼6-nm Au nanoparticles and α,ω-dithiols have been prepared on glass substrates. They have been studied by UV/Vis spectroscopy, ellipsometry, scanning tunneling microscopy, and temperature-dependent conductivity measurements. The electronic and optical properties of the thin film material are nonmetallic, and the Au particles maintain their individual character without fusion to larger units. Electronic conduction within the films occurs via activated electron hopping.
595 citations
TL;DR: In this article, two methods, namely thermal reduction and sonochemical reduction of copper(II) hydrazine carboxylate Cu(N2H3COO)2·2H2O complex in an aqueous medium, are presented.
Abstract: Nanoscale particles of metallic copper clusters have been prepared by two methods, namely the thermal reduction and sonochemical reduction of copper(II) hydrazine carboxylate Cu(N2H3COO)2·2H2O complex in an aqueous medium. Both reduction processes take place under an argon atmosphere over a period of 2−3 h. The FT-IR, powder X-ray diffraction, and UV−visible studies support the reduction products of Cu2+ ions as metallic copper nanocrystallites. The powder X-ray analysis of the thermally derived products show the formation of pure metallic copper, while the sonochemical method yields a mixture of metallic copper and copper oxide (Cu2O). The formation of Cu2O along with the copper nanoparticles in the sonochemical process can be attributed to the partial oxidation of copper by in situ generated H2O2 under the sonochemical conditions. However, the presence of a mixture of an argon/hydrogen (95:5) atmosphere yields pure copper metallic nanoparticles, which could be due to the scavenging action of the hydroge...
575 citations
TL;DR: In this paper, the optical absorption of colloidal nanoparticles is investigated, formed by the UV illumination of aqueous solutions containing AgClO4 ((1−4) × 10-4 M), acetone (2 × 10 −2 M), 2-propanol (1 M), and various polymer stabilizers.
Abstract: The optical absorption of the colloidal nanoparticles is investigated, formed by the UV illumination of aqueous solutions containing AgClO4 ((1−4) × 10-4 M), acetone (2 × 10-2 M), 2-propanol (1 M), and various polymer stabilizers. The 7 nm particles, which are produced in the presence of polyethyleneimine, possess an unusally narrow plasmon absorption band. The wavelength and shape of this band are affected by various adsorbed solutes; adsorption phenomena can therefore be studied spectrophotometrically. The changes in band shape that occur in the presence of oxygen and of carbon tetrachloride are attributed to a partial oxidation of the silver particles by these solutes. During the oxidation, the Fermi level in the nanoparticles shifts to a more positive potential, until the oxidation comes to a halt. Chemisorbed metal cations (Cd2+, Ni2+, Ag+, Hg2+) affect the plasmon absorption band of the silver nanoparticles more strongly the more electropositive is the metal. The effect is interpreted in terms of th...
565 citations
TL;DR: In this paper, a new route to the synthesis of colloidal Au nanoparticles with diameters between 30 and 100 nm is described, on the basis of surface-catalyzed reduction of Au3+ by NH2OH.
Abstract: A new route to the synthesis of colloidal Au nanoparticles with diameters between 30 and 100 nm is described. On the basis of surface-catalyzed reduction of Au3+ by NH2OH, the approach grows existing nanoparticles into larger particles of a size determined solely by the initial particle diameter and the amount of Au3+ added. The resulting particles exhibit improved monodispersity relative to those prepared in one step by the reduction of Au3+ by citrate. Importantly, surface-confined colloidal Au nanoparticles can also be enlarged by this method, providing an attractive route to colloidal Au monolayers with variable interparticle spacing (at fixed particle coverage).
520 citations
TL;DR: In this article, the effect of metal oxide support on the catalytic activity of gold for CO oxidation was investigated and it was shown that the perimeter interface around gold particles in contact with the metal oxide supports appears to be essential for the genesis of high catalytic activities at low temperatures.
Abstract: In order to clarify the effect of metal oxide support on the catalytic activity of gold for CO oxidation, gold has been deposited on SiO2 with high dispersion by chemical vapor deposition (CVD) of an organo-gold complex. Comparison of Au/SiO2 with Au/Al2O3 and Au/TiO2, which were prepared by both CVD and liquid phase methods, showed that there were no appreciable differences in their catalytic activities as far as gold is deposited as nanoparticles with strong interaction. The perimeter interface around gold particles in contact with the metal oxide supports appears to be essential for the genesis of high catalytic activities at low temperatures.
471 citations
TL;DR: In this paper, the luminescence spectrum of nanocrystalline, lanthanide-doped Europium-oxide nanoparticles was analyzed and it was shown that the dopant ions entered the same lattice site as in bulk material despite the nanocrystaline nature of the sample and the low-temperature synthesis.
Abstract: Colloidal solutions and redispersible powders of nanocrystalline, lanthanide-doped YVO4 have been prepared via a hydrothermal method at 200 °C. High-resolution transmission electron micrographs of size-selected samples show highly crystalline particles ranging in size from about 10 to 30 nm. The particles exhibit the tetragonal zircon structure known for bulk material. Upon UV excitation of the vanadate host, the energy is transferred to the lanthanide ion and strong luminescence (f−f transitions) is observed. By analyzing line splitting and intensity pattern in the luminescence spectrum of the europium-doped sample, we are able to verify that the dopant ions enter the same lattice site as in bulk material despite the nanocrystalline nature of the sample and the low-temperature synthesis. For YVO4:Eu nanoparticles a luminescence quantum yield of 15% at room-temperature was observed.
TL;DR: In this paper, the shape distribution of colloidal nanoparticles during the growth period and its dependence on the concentration of the capping polymer as well as the pH of the solution were investigated.
Abstract: Recently, we have been able to synthesize platinum colloidal nanoparticles of different shapes (Science, 1996, 272, 1924). In this report, we present transmission electron microscopic (TEM) results on the time-dependent shape distribution of platinum nanoparticles during the growth period and its dependence on the concentration of the capping polymer as well as the pH of the solution. The results suggest a shape-controlled growth mechanism in which the difference between the rate of the catalytic reduction process of Pt2+ on the {111} and {100} faces, the competition between the Pt2+ reduction and the capping process on the different nanoparticle surfaces, and the concentration-dependent buffer action of the polymer itself all control the final distribution of the different shapes observed.
TL;DR: In this paper, the optical properties of nanosized silver particles self-assembled in a 2D or 3D network were investigated. But the optical property of the self-assembly was not investigated.
Abstract: In this paper we compare the optical properties of nanosized silver particles dispersed in hexane solution and self-assembled in a 2D or 3D network. When the particles form monolayers organized in a hexagonal network, the plasmon peak of silver nanosized particles is shifted toward lower energy, with an increase in bandwidth compared to that observed with free coated particles dispersed in hexane solution. Such a shift is attributed to an increase in the dielectric constant of the matrix environment of the nanoparticles. When the particles form a 3D superlattice with a face-centered cubic (fcc) structure, the optical properties could be interpreted as an increase in the mean free path of the conduction electrons, which could indicate the presence of tunneling electrons across the double layers due to the coating of the particles.
15 Sep 1998
TL;DR: The particle mean size of magnetite precipitated in aqueous solution can be adjusted and stabilized against ripening over a large range at the nanometric scale (1.5-12.5 nm); the stabilization of nanoparticles seems to result from thermodynamics rather than kinetics.
Abstract: The particle mean size of magnetite precipitated in aqueous solution can be adjusted and stabilized against ripening over a large range at the nanometric scale (1.5-12.5 nm). Such a tailoring of particles is obtained by controlling the pH and the ionic strength imposed by a noncomplexing salt in the precipitation medium. The higher the pH and the ionic strength are, the smaller the particle size is. Above a critical pH value, which depends on the ionic strength and the temperature, the secondary particle growth by Ostwald ripening does not take place anymore. The stabilization of nanoparticles seems to result from thermodynamics rather than kinetics. Copyright 1998 Academic Press.
Patent•
22 Jan 1998
TL;DR: In this article, the dynamics of nanoparticle formation, transport, and deposition by pulsed laser ablation of c-Si into 1-10 Torr He and Ar gases are revealed by imaging laser-induced photoluminescence and Rayleigh-scattered light from gas-suspended 1−10 nm SiOx particles.
Abstract: The dynamics of nanoparticle formation, transport, and deposition by pulsed laser ablation of c-Si into 1–10 Torr He and Ar gases are revealed by imaging laser-induced photoluminescence and Rayleigh-scattered light from gas-suspended 1–10 nm SiOx particles. Two sets of dynamic phenomena are presented for times up to 15 s after KrF-laser ablation. Ablation of Si into heavier Ar results in a uniform, stationary plume of nanoparticles, while Si ablation into lighter He results in a turbulent ring of particles which propagates forward at 10 m/s. Nanoparticles unambiguously formed in the gas phase were collected on transmission electron microscope grids for Z-contrast imaging and electron energy loss spectroscopy analysis. The effects of gas flow on nanoparticle formation, photoluminescence, and collection are described.
TL;DR: In this article, a mechanism is proposed in which the radicals transfer electrons to the gold particles and Au(CN)2- is subsequently reduced by the stored electrons directly at the surface of the particles.
Abstract: Solutions containing KAu(CN)2 (∼5 × 10-4 M), methanol (0.3 M), and nitrous oxide (2.5 × 10-2 M) are γ-irradiated in the presence of colloidal gold (∼6 × 10-5 M; mean particle size, 15 nm). The hydroxymethyl radicals, •CH2OH, which are generated in these solutions, reduce Au(I) in Au(CN)2-, and the reduced gold is completely deposited on the gold seeds to yield larger particles. The particle growth is followed spectrophotometrically and by electron microscopy. A mechanism is proposed in which the radicals transfer electrons to the gold particles and Au(CN)2- is subsequently reduced by the stored electrons directly at the surface of the particles. In further steps of particle enlargement, Au(CN)2- is reduced in solutions in which the gold particles synthesized in the preceding step serve as seeds, the result being larger and larger gold particles up to 120 nm. The reduction yield is discussed with respect to side reactions of the radicals, such as mutual deactivation and gold-catalyzed H2 formation. The rad...
TL;DR: In this article, the superparamagnetic properties of the MgFe2O4 spinel ferrite nanoparticles with the particle size from about 6 to 18 nm were studied.
Abstract: Superparamagnetism is a unique and important aspect of magnetism in nanoparticles. The superparamagnetic properties of the MgFe2O4 spinel ferrite nanoparticles with the particle size from about 6 to 18 nm are studied. The blocking temperature is a function of the particle size and increases with increasing particle size. The coercivity of MgFe2O4 nanoparticles also is a function of the particle size below the blocking temperature. When the temperature rises above the blocking temperature, the nanoparticles show nonhysteresis magnetization behaviors. With these interesting superparamagnetic properties, MgFe2O4 nanoparticles have potentials for applications such as ferrofluids, magnetocaloric refrigeration, and the contrast agents for magnetic resonance imaging.
TL;DR: In this article, a self-organization of magnetic cobalt nanoparticles into 2D superlattices is reported, which can be used for data storage devices and sensors.
Abstract: The synthesis of nanoparticles, characterized by a low size distribution, is a new challenge in solid-state chemistry. Due to their small size, nanoparticles exhibit novel materials properties that differ considerably from those of the bulk solid state. In this emerging field, finely divided magnetic nanoparticles are desirable owing to their broad range of applications, especially in data storage devices and sensors. A great deal of work on large magnetic nanoparticles has been carried out, but, although the magnetic properties of isolated atoms are well understood, there are still questions about the development of magnetic order on a macroscopic scale. The creation of perfect nanometer-scale magnetic crystallites identically replicated with long-range order in a state that can be manipulated and understood in terms of a pure macromolecular substance is an ultimate challenge in present materials research and could help us to understand the formation of ferromagnetism. To develop this application, it is crucial to be able to control the spatial arrangement of these nanoparticles in 2D or 3D arrays. Recently, in our laboratory spontaneous arrangement of particles either into monolayer organized hexagonal networks or into 3D face-centered cubic (fcc) arrangements was observed with silver sulfide and silver nanosized clusters. Similar arrangements with metal particles such as gold or silver and CdSe semiconductors have been reported elsewhere. Here, we report, for the first time, self-organization of magnetic cobalt nanoparticles into 2D superlattices. The magnetic properties of isolated and organized particles are compared. Reverse micelles are water in oil droplets stabilized by a monolayer of surfactant (e.g., sodium bis(2-ethylhexyl)sulfosuccinate, usually called Na(AOT)). The diameter of the droplets is controlled by the volume of solubilized water and varies from 0.5 to 18 nm. In this liquid solution, as a result of Brownian motion, collision between droplets induces exchange between water pools. In a previous paper we demonstrated that nanosized cobalt particles can be produced by using reverse micelles as a microreactor. Cobalt particles are obtained by mixing two micellar solutions having the same diameter ([AOT] = 0.25 M): one contains 10 M Co(AOT)2 (cobalt bis(2-ethylhexyl)sulfosuccinate) and the other one 2 10 M sodium tetrahydroborate (NaBH4, sodium borohydride). After mixing, the micellar solution remains optically clear and its color immediately turns from pink to black, indicating the formation of colloidal particles. The synthesis is performed in 3 nm diameter reverse micelles. The average diameter of cobalt nanoparticles, determined by transmission electron microscopy (TEM), is 6.4 nm with a polydispersity of 21 % (Fig. 1a). The particles are very well dispersed and no aggregation occurs. However the particles are very readily oxidized. High-resolution TEM of the particles after synthesis shows a well-developed crystalline phase. The spacing distance of the lattice fringes is 2.15 which is consistent with the bulk value of fcc cobalt. No trace of oxide shell is observed on the surface. To form superlattices, the cobalt nanocrystallites are extracted from the reverse micelles. Trioctylphosphine (4 mL/ mL) is added to the micellar solution containing the cobalt nanoparticles. The solvent is then evaporated at 40 C under vacuum and a solid mixture of trioctylphosphine-coated nanoparticles and surfactant is obtained. The surfactant is removed by ethanol addition and a black solid remains, which is easily redispersed in pyridine. This surface treatment is carried out under nitrogen in a glove box to avoid oxidation. At the end of the process, the coating is thick enough to prevent the particles from being oxidized. The coated particles can be stored without taking any precautions for at least one week without any aggregation or oxidation. The size of the coated particles redispersed in pyridine can be determined by TEM (Fig. 1b). A size selection is made by extraction of the nanoparticles from reverse micelles (Fig. 1). The average size decreases from 6.4 nm to
TL;DR: In this paper, an Fe2O3−SiO2 composite was prepared by a gelation method that adopts tetraethoxysilane and iron(III) nitrate as starting materials.
Abstract: An Fe2O3−SiO2 composite was prepared by a gelation method that adopts tetraethoxysilane and iron(III) nitrate as starting materials. The dried gel was treated at increasing temperatures, and the samples were characterized by XRD, TEM, magnetic susceptibility measurements, and EPR and Mossbauer spectroscopies. Nanometer size (3−4 nm) X-ray-amorphous iron(III) oxide particles are observed in the samples treated at low temperature. These particles display superparamagnetic behavior in the Mossbauer spectra and susceptibility measurements, and their magnetic moments indicate antiferromagnetic clustering. The occurrence of two sites for iron ions, one in the bulk and one on the surface of nanoparticles, is suggested by EPR and Mossbauer spectroscopies. Heating of the samples to higher temperatures (T > 700 °C) gives rise to a small increase of the particle size. Simultaneously XRD and TEM exhibit the formation of γ-Fe2O3 crystalline particles, Mossbauer spectra reveal a large change in the magnetization, magne...
TL;DR: In this paper, nonaggregated nanoparticles of titania are obtained through hydrolysis at 60 °C of titanium butoxide in the presence of acetylacetone and para-toluenesulfonic acid.
Abstract: Monodisperse nonaggregated nanoparticles of titania are obtained through hydrolysis at 60 °C of titanium butoxide in the presence of acetylacetone and para-toluenesulfonic acid. After the particles are dried, the resulting xerosols can be dispersed without aggregation in water−alcoholic or alcoholic solutions at concentrations higher than 1 M. The characterizations of the nanoparticles were carried out in solution by using quasi-elastic light scattering (QELS); FTIR; 13C, 17O, and 1H NMR and in solid state by X-ray diffraction, transmission electron microscopy (TEM), FTIR, thermogravimetry−dynamic thermal analysis (TG−DTA), 13C cross-polarization−magic angle spinning (CP−MAS) NMR. The mean size of the anatase oxide core can be adjusted in the 1−5 nm range by a careful tuning of the synthetic conditions. The protection of these particles toward aggregation is ensured through the complexation of the surface by acetylacetonato ligands and through an adsorbed hybrid organic−inorganic layer made with acetylace...
TL;DR: The field of long-circulating microparticulate drug carriers is reviewed, and the protective effect of certain polymers including poly(ethylene glycol) on nanoparticulated carriers (liposomes, nanoparticles, micelles) is considered in terms of statistical behaviour of macromolecules in solution.
Abstract: The field of long-circulating microparticulate drug carriers is reviewed. The protective effect of certain polymers including poly(ethylene glycol) on nanoparticulate carriers (liposomes, nanoparticles, micelles) is considered in terms of statistical behaviour of macromolecules in solution. Using liposomes as an example, the mechanism is discussed assuming that surface-grafted chains of flexible and hydrophilic polymers form dense 'conformational clouds' preventing other macromolecules from interaction with the surface even at low concentrations of the protecting polymer. The scale of the protective effect is interpreted as the balance between the energy of the hydrophobic anchor interaction with the liposome membrane core or with the particle surface and the energy of the polymer chain free motion in solution. The possibility of using protecting polymers other than poly(ethylene glycol) is analysed, and examples of such polymers are given, based on polymer-coated liposome biodistribution data. General requirements for protecting polymers are formulated. Sterically protected nanoparticles and micelles are considered, and differences in steric protection of liposomes and particles are discussed. The problem of the preparation of drug carriers combining longevity and targetability is analysed. The biological consequences of steric protection of drug carriers with surface-grafted polymers are discussed, and possible clinical applications for long-circulating pharmaceutical carriers are considered.
TL;DR: In this article, a new class of metal nanoparticles has been identified from heterogeneous silver colloids, which are relatively large, faceted nanocrystals that are able to enhance the efficiencies of surface optical processes by as much as 14−15 orders of magnitude.
Abstract: A rapid screening and enrichment method is reported for exploring the size and shape diversities (libraries) of nanometer-scale colloidal particles. With the use of surface-enhanced Raman scattering, a new class of metal nanoparticles has been identified from heterogeneous silver colloids. These particles are relatively large, faceted nanocrystals that are able to enhance the efficiencies of surface optical processes by as much as 14−15 orders of magnitude. The population of these novel nanoparticles is only about 0.1−1% in standard colloid preparations but can be enriched to about 10−15% by size-selective fractionation. This new class of nanoparticles could find potential uses in optoelectronic devices, ultrasensitive chemical sensors, and single-molecule detection.
TL;DR: Polymeric latex particles with strongly differing surface properties were synthesized as models for colloidal drug carriers for tissue-specific drug targeting via the intravenous route and protein-nanoparticle interactions were studied.
Abstract: Plasma protein adsorption patterns on colloidal drug carriers acquired after iv administration depend on their surface characteristics and are regarded as key factors for their in vivo organ distribution. Polymeric latex particles with strongly differing surface properties were synthesized as models for colloidal drug carriers for tissue-specific drug targeting via the intravenous route. Physicochemical char- acterization was performed for size, surface charge density, zeta potential, and surface hydrophobicity. The interactions with human plasma proteins were studied by way of two- dimensional polyacrylamide gel electrophoresis (2-D PAGE). Considerable differences in protein adsorption on the latex particles were detected with regard to the total amount of surface-bound protein on the various particle types as well as specific proteins adsorbed, for example, fibrinogen, albumin, and a recently identified plasma glyco- protein. Possible correlations between protein adsorption patterns and the physicochemical characteristics and topog- raphy of the polymeric surfaces are shown and discussed. Knowledge about protein-nanoparticle interactions can be utilized for the rational design of colloidal drug carriers and also may be useful for optimizing implants and medical devices. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 478-485, 1998.
Book•
01 Aug 1998
TL;DR: In this paper, size and morphology control of Nanoparticle growth in Organized Surfactant Assemblies (M. Hodes, et al.). Oriented growth of nanoparticles at organized assemblies.
Abstract: Electrodeposited Quantum Dots: Size Control by Semiconductor-Substrate Lattice Mismatch (G. Hodes, et al.). Oriented Growth of Nanoparticles at Organized Assemblies (F. Meldrum). Electrodeposition of Superlattices and Nanocomposites (J. Switzer). Size and Morphology Control of Nanoparticle Growth in Organized Surfactant Assemblies (M. Pileni). Synthesis of Silicon Nanoclusters (R. Bley & S. Kauzlarich). Two-Dimensional Crystal Growth of Fullerenes and Nanoparticles (D. Guldi). Metal Colloids in Block Copolymer Micelles: Formation and Material Properties (L. Bronstein, et al.). Plasma-Produced Silicon Nanoparticle Growth and Crystallization Process (J. Dutta, et al.). Electron Transfer Processes in Nanostructured Semiconductor Thin Films (P. Kamat). Template Synthesis of Nanoparticles in Nanoporous Membranes (J. Hulteen & C. Martin). Morphology-Dependent Photocatalysis with Nanoparticle Aggregates (M. Tomkiewicz & S. Kelly). Zeta Potential and Colloid Reaction Kinetics (P. Mulvaney). Semiconductor Nanoparticles in Three-Dimensional Matrices (S. Romanov & C. Sotomayor-Torres). Charge Transfer at Nanocrystalline Metal-Oxide Semiconductor/Solution Interfaces: Mechanistic and Energetic Links Between Electrochromic/Battery Interfaces and Photovoltaic/Photocatalytic Interfaces (B. Lemon, et al.). Nanoparticle-Mediated Monoelectron Conductivity (S. Carrara). Heterosupramolecular Chemistry (X. Marguerettaz, et al.). Nanoclusters in Zeolites (J. Nagy, et al.). Nanoparticles and Nanostructured Films: Current Accomplishments and Future Prospects (J. Fendler & Y. Tian). Index.
TL;DR: In this article, a gamma radiolysis method was used to synthesize capped copper nanoclusters by optimizing various conditions like metal ion concentration, polymer or surfactant concentration and pH.
TL;DR: Flexible membranes which are in contact with dispersed nanoparticles or colloids are theoretically studied and it is shown that if the membrane/particle interactions are attractive, the membrane curves away from the adsorption layers of small particles but wraps itself around large particles which become completely encapsulated.
Abstract: Flexible membranes which are in contact with dispersed nanoparticles or colloids are theoretically studied. For closed vesicles, the membrane/particle interactions change the "spontaneous" curvature of the membrane provided the surrounding solution contains more than one species of particles. If the membrane/particle interactions are repulsive, the membrane curves toward the larger particles. If the membrane/particle interactions are attractive, the membrane curves away from the adsorption layers of small particles but wraps itself around large particles which become completely encapsulated.
TL;DR: In this article, the dissolution rate was strongly dependent on particle size, and size selective etching of a mixture of ZnO particles was demonstrated, and the change of the particle size during etching can be modeled adequately by a Monte Carlo simulation, in which the known degree of polydispersity and the size dependence of the etch rate are taken into account.
Abstract: ZnO nanoparticles of about 30−60 A size in ethanolic solution were etched by addition of anhydrous acetic acid. Upon dissolution, the volume-weighted particle size decreased by about 10%. The polydispersity increased slightly. The dissolution rate was strongly dependent on particle size, and size selective etching of a mixture of ZnO particles was demonstrated. The change of the particle size during etching can be modeled adequately by a Monte Carlo simulation, in which the known degree of polydispersity and the size dependence of the etch rate are taken into account. On the basis of a comparison with work on the dissolution of silica nanoparticles and oxidic thin films, and on the etching of single-crystal ZnO, it is proposed that the size dependence is caused by variations of the chemical reactivity of the nanoparticles related to, for example, the concentration of defects and kink sites. Thus, dissolution provides a convenient method to investigate size-dependent chemical properties.
TL;DR: In this article, a method of the formation of composite polypyrrole films containing a highly dispersed three-dimensional array of platinum catalyst particles is presented, where PtCl{sub 4{sup 2{minus}} anions were trapped inside the polypryrole matrix during the electropolymerization of pyrrole.
Abstract: A new method of the formation of composite polypyrrole films containing a highly dispersed three-dimensional array of platinum catalyst particles is presented. PtCl{sub 4}{sup 2{minus}} anions were trapped inside the polypyrrole matrix during the electropolymerization of pyrrole. In the next step followed by solution exchange, PtCl{sub 4}{sup 2{minus}} anions were reduced to Pt{sup 0} particles with an average size of 10 nm. Metallic particles were incorporated in electrically conducting polypyrrole films in order to achieve multielectron-transfer processes in a three-dimensional matrix. These films were characterized using the electrochemical quartz crystal microbalance technique. The use of this technique allowed evaluation of the Pt{sup 0} loading inside the polymer film. The electropolymerization process was controlled by measuring frequency changes of piezoelectrodes. The presence of Pt{sup 0} particles in composite polypyrrole films and their uniform distribution were confirmed by energy-dispersive x-ray spectroscopy and x-ray diffraction. The size of the Pt{sup 0} particles was evaluated from transmission electron microscopy experiments. The electrocatalytic effect toward the methanol oxidation was observed. Larger surface area and higher catalytic activity were found for electrodes with dispersed Pt{sup 0} nanoparticles in the polymer evaluation of matrix than electrodes with electrodeposited Pt{sup 0} on the surface of the conductive polymer.
TL;DR: Conjugates between cytochrome c and colloidal Au particles have been prepared and it is shown that Cc molecules bound to 12-nm diameter Au nanoparticles prior to adsorption to aggregated Ag are more stable to changes in the orientation of the heme with respect to the surface.
Abstract: Conjugates between cytochrome c (Cc) and colloidal Au particles have been prepared. These conjugates, purified by centrifugation/resuspension, provide a reproducible means of positioning a biomolecule analyte between two metal surfaces: the metal nanoparticle to which the biomolecule is bound and an aggregated Ag sol used as a substrate for surface enhanced Raman scattering (SERS). SERS spectra for Ag:Cc:Au sandwiches made by addition of Cc:Au conjugates to aggregated Ag show that the protein retains its native conformation. Conjugation of Cc to colloidal metal nanoparticles prior to exposure to the SERS substrate can be used as a means of controlling protein orientation with respect to the substrate. In addition, Cc molecules bound to 12-nm diameter Au nanoparticles prior to adsorption to aggregated Ag are more stable to changes in the orientation of the heme with respect to the surface and to surface-induced heme spin state conversion than adsorbed, free Cc. These experiments show that protein:Au conju...