We report on Pt selectively photodeposited on oxides sites of Ti-, and W-carbon composites. The change of the lattice parameter strongly suggests that the metal center alloys with the metal centers of the oxides with a concomitant change of electronic properties favorable for oxygen reduction reaction in acid medium.

The oxygen reduction reaction (ORR) was investigated on carbon (XC-72) supported platinum nanoparticles, generated via the carbonyl chemical route and on oxide composites supported platinum generated via the UV-photo-deposition technique in sulfuric acid medium. The behavior of Pt/C was examined using a careful dosing of the catalyst loading spanning the range from 4.3 to 131 μg cm−2. The ORR electrochemical response of Pt/C (in line with recent literature data) is put into contrast with the Pt/oxide-composite systems. Our results point out that it is possible to use smaller amounts of catalyst for the ORR when platinum atoms interact with the oxide (anatase) surface of the substrate composite. Evidence of the incipient metal–substrate interaction is discussed in the light of the results of XRD experiments.

Conducting polymer coated graphitized active carbon as fuel cell catalysts support improves both the catalytic performance and stability. The PANi coating prevent aggregation and the loss of particles and shows improved long-term stability. X-ray diffraction indicated the Pt/Ru alloy is homogeneous and lacks Pt-core Ru-shell structure. The superior fuel cell performance and better electrocatalytic stability observed for Pt-Ru/P1ACg are attributed from its high degree of Pt-Ru alloy, and high active surface area. This study unveils a new design of durable catalysts by coating a layer of conducting polymer on carbon support which improves catalytical activity, CO tolerance and stability over other catalysts based on the current art.

The cluster-like RuxSey (x approximate to 2, y approximate to 1) compound can be prepared by simple pyrolysis of the carbonyl complex Ru4Se2(CO)(11) in inert gas. We have observed this process in situ using X-ray diffraction. The clusters exhibit a disordered hcp-type structure with an average size of 1.7 nm. Selenium is probably coordinated at the surface of ruthenium nanoparticles. Up to 430 degrees C, these nanoparticles are stable in an inert ambient, except for a certain growth in size. Above this temperature, the system splits into two phases: hcp-type ruthenium particles, which are probably free of Se, and a ruthenium-diselenide phase: RuSe2. Using density functional theory (DFT), we studied the surface structure of RuSe2 and found a preference for Se-rich surfaces. Transferring to the nanoparticles, this might correspond to the picture of a Ru core and either a RuxSey- or a pure Se shell (adsorbate layer).

Narrowly dispersed Pb-doped zinc sulfide nanoparticles were synthesized at room temperature using a chemical method in which the nanoparticle surfaces were passivated using mercaptoethanol. The maximum intensity of the broad green luminescence (∼530 nm) from these nanoparticles was observed at an optimum dopant concentration of 0.104 Pb wt%. The emission intensity was found to depend on the synthesis pH conditions, thus yielding maximum intensity at 5.0 pH. Comparatively lower emission intensities were observed for the other pH values (2.5–9.0 pH range). This may be due to the pH-dependent Cl− (as well as Na+) incorporation into the ZnS matrix, which possibly helps in inducing required density of impurity (donor/co-activator) states in the energy gap of ZnS nanoparticles. X-ray diffraction analysis using Debye functional analysis showed that the particle size is 2.8±0.3nm.

Ruthenium oxide-like (RuxOy) nanoparticles were prepared by the decomposition of carbonyl precursors in organic solvents under mild conditions. CO oxidation over the reduced particles was studied by combined in Situ X-ray diffraction and gas-phase analysis. For a sample prepared in dichlorobenzene, in a flow of CO/O-2 = 0.55, oxidation of CO started at ca. 70 degrees C with the simultaneous formation of amorphous surface oxide. On further heating. the CO? production increased proportionally with the rate of formation Of Surface oxide. Below ca. 130 degrees C the catalyst can be reversibly reduced in CO to the disordered precursor state, average size ca. 2.8, run. After catalytic performance for 3 It at 180 degrees C, reduction in CO of partially oxidized RuxOy is accompanied by a burst of CO2 partial pressure and induces particle growth to similar to 5 run due to the exothermic heat of the reaction. These results are comparable to earlier results for ruthenium single-crystal surfaces studied under low pressure conditions. (c) 2005 Elsevier Inc. All rights reserved.

Vulcan XC-72 carbon-supported Pt-Ni alloy nanoparticle catalysts with different Pt/Ni atomic composition were prepared via the carbonyl complex route and their structure was studied by X-ray diffraction spectroscopy at wide angles (WAXS) and Debye function analysis (DFA). The very good agreement between the WAXS pattern and DFA simulation revealed that all the as-prepared Pt-Ni alloy catalysts have a unique and highly disordered face-centered cubic structure (solid solution) and that the lattice parameter decreases with the increase of the Ni content in the alloys. Transmission electron microscopy (TEM) images indicated that the as-prepared Pt-Ni alloy nanoparticles were well dispersed on the surface of the carbon support with a narrow particle size distribution and that their mean particle size slightly decreased with the increase in Ni content. Energy-dispersive X-ray analysis (EDX) confirmed that the catalyst composition was nearly the same as that of the nominal value. Thus, a comparative study was made for the oxygen reduction reaction (ORR) using the thin-film rotating ring-disk electrode method to the behavior of Pt based catalysts on the same carbon support, having the same metal loading, the same disordered structure, and a similar particle size. As compared to the Pt/C catalyst, the bimetallic catalysts with different Pt/Ni atomic ratios exhibited an enhancement factor of ca. 1.5 to 3 in the mass activity and of ca. 1.5 to 4 in the specific activity for the ORR and a lower production of hydrogen peroxide in pure perchloric acid solution. The maximum activity of the Pt-based catalysts was found with ca. 30 similar to 40 at. % Ni content in the alloys, which could originate from the favorable Pt-Pt interatomic distance. The ring-current measurements on all the catalysts showed similar behavior for hydrogen peroxide production. The enhanced electrocatalytic activity of as-prepared Pt-Ni alloy catalysts for the ORR is attributed to the high dispersion of the alloy catalysts, to their disordered structure, and to the favorable Pt-Pt mean interatomic distance caused by alloying.

Silver nanoparticles in the size range of 2-5 nm were synthesized extracellularly by a silver-tolerant yeast strain MKY3, when challenged with 1 mM soluble silver in the log phase of growth. The nanoparticles were separated from dilute suspension by devising a new method based on differential thawing of the sample. Optical absorption, transmission electron microscopy, x-ray diffraction and x-ray photoelectron spectroscopy investigations confirmed that metallic (elemental) silver nanoparticles were formed. Extracellular synthesis of nanoparticles could be highly advantageous from the point of view of synthesis in large quantities and easy downstream processing.

Structural and stability studies of bimetallic Pt-Sn (3:1) nanoparticles were performed in situ via X-ray diffraction at wide angles (WAXS). The homemade bimetallic catalyst (Pt-Sn) ccomp (ecomp = from carbonyl complex) was synthesized in mild conditions from a Pt-carbonyl chemical precursor. A relatively narrow size distribution (2.4 +/- 0.9 nm) of such a bimetallic catalyst supported onto carbon Vulcan XC72 was obtained at room temperature. Its electrochemical behavior was compared to that of a commercial catalyst. The WAXS study revealed that such a catalyst, prepared via the carbonyl route, has a certain degree of surface disorder (high Debye parameter, B), which enhances the electrocatalytic activity for hydrogen adsorption. Furthermore, WAXS also demonstrated that the structural stability of this bimetallic catalyst is maintained at the annealing temperature employed (500 degreesC), although the particle size increases from 1.6 to 2.2 nm. Electrochemical underpotential deposition studies, via copper deposition, also provide information concerning the state of the nanoparticulate surface of the various platinum-based catalysts investigated.

The use of microbes as producers of semiconductor nanocrystals is demonstrated. When torulopsis yeast is challenged with lead, it builds intracellular spherical crystallites of PbS, 2-5 nm in diameter (see Figure for an HR-TEM image) and pure by X-ray diffraction. The crystals, which can be isolated by freeze-thawing, show a sharp absorption maximum at 330 nm, corresponding to a bandgap of 3.75 eV.

Zinc sulphide quantum dots chemically capped with thioglycerol having two different sizes have been synthesized. The particles have a disordered sphalerite structure and are slightly contracted by 1% against the bulk. Small angle X-ray scattering investigations reveal that powders of these nanocrystallites are mass fractals that aggregate via a reaction-limited process to form irregular but rather dense networks with a fractal dimensionality of Df = 2.7 and 2.1, respectively.

Cadmium sulfide nanoparticles were synthesized intracellularly by a Schizosaccharomyces pombe strain when challenged with 1 mM cadmium in solution. The nanoparticles, a known semiconducting material, exhibited an absorbance maximum at 305 nm. X-ray scattering data showed that the nanoparticles had a Wurtzite (Cd(16)S(20))-type hexagonal lattice structure and most of the nanoparicles were in the size range of 1-1.5 nm. The nanoparticles were used in the fabrication of a heterojunction with poly (p-phenylenevinylene). The diode exhibited approximately 75 mA/cm(2) current at 10 V when forward biased and the breakdown occurred at approximately 15 V in the reverse biased mode. These characteristics are considered ideal for a diode.

TiO2 nanoparticles have been synthesized at room temperature using a simple chemical precipitation route. Particles were further coated with polymer. Detailed structural analysis of the particles has been carried out. Wide-angle X-ray scattering (WAXS) and transmission electron microscopy (TEM) confirm that “as-synthesized” particles as well as annealed particles are nanoparticles having pure rutile phase. Thermal annealing at 1000 °C of 4.2 nm particles led to an increased size ∼20 nm in the same phase. The purity and composition of the particles were determined using energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (XPS), respectively.

Structural studies and stability of cluster-like particles of Ru-x and RuxSey were performed in situ via X-ray diffraction at wide angles (WAXS). Both materials have a similar particle size (1.4-1.6 nm) in the reduced state. Whereas Ru-x particles are rather sensitive to oxygen from air, the chemical stabilization, against oxidation, of such metallic centers is obtained by the coordination of selenium atoms. The role of selenium atoms is also to stabilize the nanostructural nature (geometric effect) of the compound, as demonstrated by the temperature measurements (up to 300 degreesC) in the gas phase, and to provide the electronic effect for electrocatalysis.

Copper and copper (I) oxide nanoparticles protected by self-assembled monolayers of thiol, carboxyl, and amine functionalities [X(CH(2))(n)-CH(3), where X can be -COOH, -NH(2), or -SH] have been prepared by the controlled reduction of aqueous copper salts using Brust synthesis. The optical absorption spectrum (lambda(max)=289 nm) is found to be invariant with the nature of the capping molecule while the particle shape and distribution are found to depend strongly on it. A comparison of the protection efficiency for different capping agents such as dodecanethiol (DDT), tridecylamine (TDA), and lauric acid (LA) suggests that although zerovalent Cu is initially formed for dodecanethiol, all other cases allow oxidation to Cu(2)O nanoparticles. Despite the variation in particle size and relative stability, nanoparticles have been found to form oxides after a few days, especially for the case of LA and TDA surface capping. For all the samples studied, the size has been found to be 4-8 nm by high-resolution transmission electron microscopy. The protective ability is found to be better for dodecanethiol SAM (similar to the case of Au and Ag nanoparticles), while the order of capping efficiency varies as Cu-DDT>Cu-TDA>Cu-LA. In the present study we also demonstrate a reversible metal-insulator transition (MIT) in capped nanoparticles of Cu using temperature-dependent electrical resistivity measurement. However, the LA-capped sample does not show any such transition, possibly due to the oxide formation.

Equilateral CdS nanocrystals with 10-nm sides are produced in a Cd(AOT)(2)/isooctane/water reverse micellar solution. The structures of individual nanocrystals are determined by TENT and HRTEM, and these data were compared with computer simulations and power spectra calculations. This shows that the particles are crystallized in a hexagonal (wurtzite) form. The thickness of these equilateral nanocrystals (around 5 nm) is estimated from optical measurements. These nanocrystals are not highly stable as the coated surfactant desorbs, and they coagulate, forming particles with a cubic structure (zinc blende).

Zinc sulphide nanoparticles have been synthesized in silica matrix using sol-gel method. It is observed that silica could be loaded with zinc sulphide over a very wide range of concentration without changing the nanoparticle size. A strongly luminescent zinc sulphide-silica composite, thermally stable even upto ∼700°C was thus obtained. Several techniques like UV absorption, photoluminescence, x-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetry and photoelectron spectroscopy have been performed to analyse the ZnS-silica composites.

Extremely small 1.4-nm size mercaptoethanol-stabilized ZnS clusters have been synthesized with narrow size distribution. The structure of these clusters was studied by wide-angle X-ray scattering. The scattering curves were compared with the calculated scattered intensity of a variety of model clusters (ZnS)(N) and different defect types via Debye functions. In the as-received state the pattern is best described by a fragment of the zinc blende lattice, with N approximate to 30, and a defective stacking of three to four (111) planes. A large improvement of the simulation is gained by introducing liquidlike disorder to the model structure. This raises the unanswered question of a "real" liquid state of these small clusters at room temperature, The cluster matrix is thermally stable to 583 K. Above this temperature the primary cluster coalesce to form larger particles. Annealed at 1013 K the particles grow to > 4.0 nm with a highly defective zinc blende structure.