Showing papers on "Noble metal published in 2006"
TL;DR: A number of applications are presented that take advantage of the electromagnetic field enhancement of the radiative properties of noble metal nanoparticles resulting from the surface plasmon oscillations.
Abstract: This tutorial review presents an introduction to the field of noble metal nanoparticles and their current applications. The origin of the surface plasmon resonance and synthesis procedures are described. A number of applications are presented that take advantage of the electromagnetic field enhancement of the radiative properties of noble metal nanoparticles resulting from the surface plasmon oscillations.
2,811 citations
TL;DR: The optical properties of noble metal nanoparticles, specifically gold, silver, and their combinations, prepared in solution through colloid chemical methods are shown to be mainly influenced by the surface plasmon resonance of conduction electrons.
Abstract: Metal nanoparticles can be used as building blocks for the formation of nanostructured materials. For the design of materials with specific (optical) properties, several approaches can be followed, even when starting from the very same basic units. In this article, a survey is provided of the optical properties of noble metal nanoparticles, specifically gold, silver, and their combinations, prepared in solution through colloid chemical methods. The optical properties are shown to be mainly influenced by the surface plasmon resonance of conduction electrons, the frequency of which is not only determined by the nature of the metal but also by a number of other parameters, such as particle size and shape, the presence of a capping shell on the particle surface, or the dielectric properties of the surrounding medium. Recent results showing how these various parameters affect the optical properties are reviewed. The results highlight the high degree of control that can now be achieved through colloid chemical synthesis.
1,514 citations
TL;DR: It is demonstrated that hydroxyl-terminated PVP is also a well-suited reductant for the aqueous synthesis of circular, triangular, and hexagonal nanoplates made of other noble metals including Pd, Au, and Pt.
Abstract: Poly(vinyl pyrrolidone) (PVP) has been extensively used in the solution-phase synthesis of many types of colloidal particles, where it is mainly considered as a steric stabilizer or capping agent with a major role to protect the product from agglomeration. In a recent study, we discovered that the hydroxyl end groups of PVP could also serve as a very mild reductant for kinetically controlled synthesis of Ag nanoplates with yields as high as 75%. Here we further demonstrate that hydroxyl-terminated PVP is also a well-suited reductant for the aqueous synthesis of circular, triangular, and hexagonal nanoplates made of other noble metals including Pd, Au, and Pt. The reduction kinetics of a metal salt by the hydroxyl end groups of PVP can be maneuvered in at least two different ways to facilitate the evolution of plate morphology: (i) by adjusting the molar ratio of PVP to the salt precursor and (ii) by altering the molecular weight of PVP. Unlike previously reported studies of Ag and Au thin plates, light was found to have a negligible role in the present synthesis.
584 citations
558 citations
TL;DR: In this paper, a tutorial review presents an introduction to the field of noble metal nanoparticles and their current applications and the origin of the surface plasmon resonance and synthesis procedures are described.
Abstract: This tutorial review presents an introduction to the field of noble metal nanoparticles and their current applications. The origin of the surface plasmon resonance and synthesis procedures are described. A number of applications are presented that take advantage of the electromagnetic field enhancement of the radiative properties of noble metal nanoparticles resulting from the surface plasmon oscillations.
527 citations
TL;DR: In this paper, a simplified mechanism for the catalytic oxidation of formaldehyde (HCHO) over 1% Pt/TiO2 was proposed, based on the behavior of adsorbed species on the surface at room temperature using in situ DRIFTS.
Abstract: The performance of TiO2 supported noble metal (Pt, Rh, Pd and Au) catalysts was examined and compared for the catalytic oxidation of formaldehyde (HCHO). Among them, the Pt/TiO2 was the most active catalyst. The effects of Pt loading and gas hourly space velocity (GHSV) on Pt/TiO2 activity for HCHO oxidation were investigated at a room temperature (20 degrees C). The optimal Pt loading is 1 wt.%. At this loading, HCHO can be completely oxidized to CO2 and H2O over the Pt/TiO2 in a GHSV of 50,000 h(-1) at 20 degrees C. The 1% Pt/TiO2 was characterized using BET, XRD, high resolution (HR) TEM and temperature programmed reduction (TPR) methods. The XRD patterns and HR TEM image show that Pt particles on TiO2 are well dispersed into a size smaller than 1 nm, an important feature for the high activity of the 1% Pt/TiO2. The mechanism of HCHO oxidation was studied with respect to the behavior of adsorbed species on Pt/TiO2 surface at room temperature using in situ DRIFTS. The results indicate that surface formate and CO species are the main reaction intermediates during the HCHO oxidation. The formate species could decompose into adsorbed CO species on the catalyst surface without the presence Of O-2, and the CO was then oxidized to CO, with the presence of O-2. Based on these results, a simplified mechanism for the catalytic oxidation of HCHO over 1% Pt/TiO2 was proposed. (c) 2006 Elsevier B.V. All rights reserved.
502 citations
TL;DR: A selective review on the materials and construction principles used for bifunctional oxygen/air electrodes is given in this paper, which emphasizes the catalytically active materials used for the construction of these electrodes, which are a key component in electrically rechargeable air breathing electrochemical systems.
389 citations
TL;DR: Several supported metal (Ru, Rh, Pt, Pd, Ir, Ni, Co) catalysts were prepared and used for methane reforming with CO 2, while their activity was lower than that of Ni and Co as discussed by the authors.
295 citations
TL;DR: In this paper, the catalytic activity of supported noble metal catalysts (Pt, Rh, Ru, and Pd) for the WGS reaction is investigated with respect to the physichochemical properties of the metallic phase and the support.
274 citations
TL;DR: In this paper, Cadmium sulphide nanoparticles (6-12nm) are prepared by a precipitation process using different zeolite matrices as templates and characterized by UV-Vis, XRD, SEM, TEM and sorptometric techniques.
268 citations
TL;DR: In this article, the authors found that Dowex and Amberlyst, two low-cost solid acids often used as catalysts in a variety of reactions, exhibit reaction kinetics higher than the noble metal catalysts.
TL;DR: In this article, the degradation of oxalic acid has been studied in aqueous solution photocatalyzed by band-gap-irradiated TiO2, modified with nanosized platinum or silver particles.
Abstract: The commercially available TiO2-catalyst (Degussa P25) was modified with nanosized platinum and silver particles by the photoreduction method to obtain different noble metal loading (0.5 and 1 wt.%). The characterization of the synthesized catalysts was carried out by the BET method, XPS, TEM and the adsorption of the model pollutant. The degradation of oxalic acid has been studied in aqueous solution photocatalyzed by band-gap-irradiated TiO2, modified with nanosized platinum or silver particles. The photocatalytic activity of TiO2, modified with noble metal, is approximately double that of the semiconducting support. The adsorption properties of the catalysts, as well as the noble metal content on the surface of the support, influence the efficiency of the photocatalytic process. The reaction rate of photocatalytic degradation of the oxalic acid follows a zero kinetic order according to the Langmuir–Hinshelwood model. The increase of the quantum yield of the photodestruction reaction of the studied model pollutant is due to the formation of Schottky barriers on the metal–semiconductor interface, which serve as efficient electron traps, preventing the electron–hole recombination.
TL;DR: In this article, the formation and stability of surface species generated in the interaction of ethanol and water mixture with Al2O3 and CeO2-supported noble metal catalysts were studied by FT-IR, TPD and TPR methods.
TL;DR: In this article, a physical alternative to sulfide-silicate chemical partitioning was proposed to generate a noble metal-rich basaltic melt from a sulfide saturated source.
Abstract: During partial melting in the earth’s mantle, the noble metals become fractionated. Os, Ir, Ru, and Rh tend to remain in the mantle residue whereas Pt, Pd, and Re behave mildly incompatible and are sequestered to the silicate melt. There is consensus that sulfide plays a role in the fractionation process; the major noble metal repository in the mantle is sulfide, and most primitive mantle melts are sulfide-saturated when they leave their mantle sources. However, with sulfide–silicate partitioning, the fractionation cannot be modeled properly. All sulfide–silicate partition coefficients are so extremely high that a silicate melt segregating from a mantle source with residual sulfide should be largely platinum-group elements free. We offer a physical alternative to sulfide–silicate chemical partitioning and provide a mechanism of generating a noble metal-rich melt from a sulfide-saturated source: Because sulfide is at least partially molten at asthenospheric temperature, it will behave physically incompatible during melt segregation, and a silicate melt segregating from a mantle residue will entrain molten residual sulfide in suspension and incorporate it in the basaltic pool melt. The noble metal abundances of a basalt then become independent of sulfide–silicate chemical partitioning. They reflect the noble metal abundances in the drained sulfide fraction as well as the total amount of sulfide entrained. Contrary to convention, we suggest that a fertile, sulfide-rich mantle source has more potential to generate a noble metal-enriched basaltic melt than a refractory mantle source depleted by previous partial melting events.
TL;DR: In this paper, ZnO nanoparticles were modified by depositing different amount of noble metal Ag or Pd on their surfaces with a photoreduction method, and the results showed that after an appropriate amount of Ag and Pd is deposited on the ZnOs surfaces, the X-ray photoelectron spectroscopy (XPS) spectrum shifts to higher binding energy, indicating that the content of surface hydroxyl oxygen (O H ) increases.
Abstract: In this paper, ZnO nanoparticles were modified by depositing different amount of noble metal Ag or Pd on their surfaces with a photoreduction method. The as-prepared ZnO samples were principally characterized by X-ray photoelectron spectroscopy (XPS) and surface photovoltage spectroscopy (SPS), and their activity was evaluated by a photocatalytic degradation reaction of phenol solution. The effects of noble metal modification on surface composition, photoinduced charge transfer behavior and photocatalytic activity of ZnO samples were mainly investigated. The results show that, after an appropriate amount of Ag or Pd is deposited on the ZnO surfaces, the O 1s XPS spectrum shifts to higher binding energy, indicating that the content of surface hydroxyl oxygen (O H ) increases. And the SPS intensity greatly decreases, indicating that the photoinduced electrons are easily captured by adsorbed oxygen via noble metal clusters so that the recombination of photoinduced electron and hole pairs is effectively inhibited. These are responsible for the enhancement in the photocatalytic activity. Moreover, the effects of Pd modification on photocatalytic activity is greater than that of Ag, which can be explained by means of surface hydroxyl content as well as charge separation situation.
TL;DR: In this article, the optical properties of noble metal clusters are measured and compared in the size range 1.4-7 nm in diameter, and a complete theoretical description of these optical properties through the same semi-quantal model for the three metals is given.
Abstract: The optical properties of noble metal clusters are measured and compared in the size range 1.4–7 nm in diameter. The clusters of copper, silver and gold are produced by the same experimental technique, the deposition of preformed clusters in a transparent matrix. The size dependence is found to be different for the three metals. As the size decreases, the surface plasmon resonance is only slightly blue-shifted for silver, more strongly blue-shifted and damped for gold while this peak resonance vanishes for copper. We show that these results cannot be interpreted by a simple classical theory. Since ab initio calculations are not possible in this size range, we obtain a complete theoretical description of these optical properties through the same semi-quantal model for the three metals.
TL;DR: The activity and selectivity of alumina-supported Pt, Pd, and Pt-Pd catalysts in the hydrodesulfurization of dibenzothiophene (DBT) and 4,6-dimethyldibenzethiophene(4,6)-DM-DBT were investigated, and all final, hydrocarbon products and partially hydrogenated intermediates were analyzed as discussed by the authors.
TL;DR: In this paper, the optimal proportions of Pt-Cu and Pd-Cu in bimetallic catalysts on activated carbon, obtained by wetness impregnation, have been found.
Abstract: The increasing pollution of natural sources of drinking water encourages the development of new emerging technologies and processes for water remediation. This work deals with the study of catalytic reduction of contaminated waters containing nitrates (60 ppm) in a continuous reactor working at room temperature and atmospheric pressure and using hydrogen as reducing agent. Optimal proportions of Pt-Cu and Pd-Cu in bimetallic catalysts on activated carbon, obtained by wetness impregnation, have been found. Besides, novel catalysts obtained from copper nanoparticles doped with Pd or Pt and supported on activated carbon, have also been studied. For all catalysts the Pt-Cu pair seems to be more selective in the transformation of the nitrates ions to nitrogen compared to Pd-Cu pair. Furthermore, considering the noble metal amount, the bimetallic nanosphere catalysts are more active (between 20 and 50) than the impregnated ones. The catalysts have been characterized by hydrogen chemisorption, BET, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. During the reaction, a considerable amount of the noble metal in its oxidised form has been detected. Based on this result an additional step to the generally accepted reaction mechanism of the nitrate reduction has been proposed.
TL;DR: In this paper, a cobalt-ethylene diamine complex on carbon was used for four-electron reduction of molecular oxygen, and the Quinone groups introduced by nitric acid treatment, in addition to increasing the dispersion of the chelate complexes, played a role in forming the active site for oxygen reduction.
TL;DR: In this paper, the current literature concerning the catalytic destruction of dioxins and of related model compounds is reviewed, and several different catalyst formulations have been tested, but V-rich vanadia-tungsta-titania catalysts seem to be mostly applied and allow reducing the dioxin concentration well below the limits of 0.1 n TEQ/Nm 3, as required by the EU directives.
Abstract: The current literature concerning the catalytic destruction of dioxins and of related model compounds is reviewed. Several different catalyst formulations have been tested, but V-rich vanadia-tungsta-titania catalysts seem to be mostly applied and allow reducing the dioxins concentration well below the limits of 0.1 ng TEQ/Nm 3 , as required by the EU directives. Other catalysts (in particular the noble metal-based ones) seem to be less efficient, due to deactivation effects and/or a considerable amount of polychlorinated by-products formation during oxidation activity. The coupled de-NO x and dioxin destruction systems compete with activated carbon adsorption for efficiency in PCDD/F removal from gases.
TL;DR: A novel plasma reduction method has been developed to reduce supported noble-metal ions without the use of any reducing chemicals, and it is shown that the supported metal ions are completely reduced to metallic species.
Abstract: A novel plasma reduction method has been developed to reduce supported noble-metal ions without the use of any reducing chemicals. H2PtCl6, PdCl2, AgNO3, and HAuCl4 supported on nonporous TiO2 and porous γ-Al2O3 and HZSM-5 were reduced using an Ar glow discharge plasma. Optical absorption spectra and X-ray photoelectron spectroscopy show that the supported metal ions are completely reduced to metallic species. Transmission electron microscopy shows that the prepared metals are amorphous clusters and homogeneously distributed with nanoscale sizes. X-ray diffraction also confirms that the plasma-reduced metals exist as small crystallites or amorphous clusters. Thermal annealing of plasma-reduced samples at elevated temperature transforms the clusters into crystals with a slight increase in particle sizes, but the sizes are still smaller than those of H2-reduced metals. O2 glow discharge plasma can also reduce noble-metal ions, accompanied by production of a small amount of oxides. Plasma reduction is very p...
TL;DR: Cyclometalated platinum(II) complex has been successfully incorporated into the (3-aminopropyl) triethoxysilane-modified channels of ordered mesoporous silica SBA-15 that has large pore hexagonal channels, and it is demonstrated that the olefins in the nano-channels of Sba-15 can be enriched 8 times higher than those in the homogeneous solution.
Abstract: Cyclometalated platinum(II) complex has been successfully incorporated into the (3-aminopropyl) triethoxysilane-modified channels of ordered mesoporous silica SBA-15 that has large pore hexagonal channels. Studies on the 1O2 generation conclusively demonstrates that the olefins in the nano-channels of SBA-15 can be enriched 8 times higher than those in the homogeneous solution as the diffusion quantum yield of singlet oxygen (1O2) is assumed to be unit. The platinum(II) complex loaded in the channel of SBA-15 is stable, and the photosensitized oxidation occurs efficiently. No obvious degradation and leaching of photosensitizers is observed even after 10 runs. Only a simple filtration is needed for the recycled use of the expensive noble metal catalysts. This versatile system is a good example of photochemical reactions occurring in the mesoporous silica molecular sieve. SBA-15 not only provides a support for the photosensitizer, but also acts as a nano-reactor to facilitate the photooxidation.
TL;DR: In this paper, the authors used co-sputtering of noble metals together with polytetrafluorethylene (PTFE) as a method for producing antibacterial metal/polymer nanocomposite coatings, where the precious metals are only incorporated in a thin surface layer.
Abstract: In this work, we used co-sputtering of noble metals together with polytetrafluorethylene (PTFE) as a method for producing antibacterial metal/polymer nanocomposite coatings, where the precious metals are only incorporated in a thin surface layer. Moreover, they are finely dispersed as nanoparticles, thus saving additional material and providing a very large effective surface for metal ion release. Nanocomposite films with thickness between 100 and 300 nm were prepared with a wide range of metal filling between 10 and 40%. The antimicrobial effect of the nanocomposite coatings was evaluated by means of two different assays. The bactericidal activity due to silver release from the surface was determined by a modification of conventional disc diffusion methods. Inhibition of bacterial growth on the coated surface was investigated through a modified proliferation assay. Staphylococcus aureus and S. epidermidis were used as test bacteria, as these species commonly cause infections associated with medical polymer devices. The antibacterial efficiency of the coatings against different bacteria was demonstrated at extremely small noble metal consumption: Au: ~1 mg m−2 and Ag: ~0.1 g m−2. The maximum ability for having an antibacterial effect was shown by the Ag–Au/PTFE nanocomposite, followed by the Ag/PTFE nanocomposite.
TL;DR: In this paper, visible light induced hydrogen generation over dye-sensitized M/TiO 2 photocatalysts has been achieved in the presence of electron donors such as triethanolamine, acetonitrile and triethylamine.
Abstract: In the present study, visible light induced hydrogen generation (>420 nm) over the dye-sensitized M/TiO 2 (M = Pt, Ru and Rh) photocatalysts has been achieved in the presence of electron donors such as triethanolamine, acetonitrile and triethylamine. The significant enhancement of quantum yield was achieved via noble metal loading and subsequent dye sensitization of M/TiO 2 . The highest quantum yield for hydrogen generation was 10.27% under irradiation with a wavelength longer than 420 nm. The strong adsorption of dye eosin has been found to enhance this high efficient hydrogen generation, which is supported by the comparsion results of dye eosin adsorption per square nanometer on noble metal loading TiO 2 , UV–vis adsorption spectra, activity tests and stability tests. In addition, improvement of adsorption of dye on the catalyst, for example, by multidentate co-ordination complexion, may result in higher photocatalytic efficiency of hydrogen generation under visible light illumination.
TL;DR: In this paper, stable mono and bimetallic nanoparticles have been prepared from colloids developed by a simple and reproducible method, based on a reduction-by-solvent process.
TL;DR: This result shows the utility of an engineered peptide as a molecular erector in the directed immobilization of a nanoscale hybrid entity (SAQDs) over selected regions (Au) on a fairly complex substrate ( au and Pt micropatterned regions on silica).
Abstract: Adsorption studies of a genetically engineered gold-binding peptide, GBP1, were carried out using a quartz-crystal microbalance (QCM) to quantify its molecular affinity to noble metals. The peptide showed higher adsorption onto and lower desorption from a gold surface compared to a platinum substrate. The material specificity, that is, the preferential adsorption, of GBP1 was also demonstrated using gold and platinum micropatterned on a silicon wafer containing native oxide. The biotinylated three-repeat units of GBP1 were preferentially adsorbed onto gold regions delineated using streptavidin-conjugated quantum dots (SAQDs). These experiments not only demonstrate that an inorganic-binding peptide could preferentially adsorb onto a metal (Au) rather than an oxide (SiO2) but also onto one noble metal (Au) over another (Pt). This result shows the utility of an engineered peptide as a molecular erector in the directed immobilization of a nanoscale hybrid entity (SAQDs) over selected regions (Au) on a fairly complex substrate (Au and Pt micropatterned regions on silica). The selective and controlled adsorption of inorganic-binding peptides may have significant implications in nano- and nanobiotechnology, where they could be genetically tailored for specific use in the development of self-assembled molecular systems.
TL;DR: A series of noble metal catalysts (Ru, Rh, Ir, Pt, and Pd) supported on alumina-stabilized magnesia (Spinel) were used to produce syngas by methane reforming with carbon dioxide as mentioned in this paper.
TL;DR: It is demonstrated that the shape of PbSe nanocrystals can be controlled systematically by seeding their growth with noble metal nanoparticles (Au, Ag, or Pd) and varying the seed and precursor concentrations.
Abstract: We demonstrate that the shape of PbSe nanocrystals can be controlled systematically by seeding their growth with noble metal nanoparticles (Au, Ag, or Pd) and varying the seed and precursor concentrations. Cylinders (quantum rods), cubes, crosses, stars, and branched structures were produced in high yield at 150 °C in reaction times of a few minutes. Although their absorption spectrum does not exhibit sharp features, the quantum rods exhibit significant photogeneration efficiency, enabling infrared sensitization of a polymeric photoconductive nanocomposite.
TL;DR: The photocatalytic activity of strontium titanate (SrTiO3) perovskite films has been examined and compared with that of commercially available titania (TiO2, Degussa P25) in the degradation of a model pollutant, Victoria Blue dye as discussed by the authors.
Abstract: The photocatalytic activity of strontium titanate (SrTiO3) perovskite films has been examined and compared with that of commercially available titania (TiO2, Degussa P25) in the degradation of a model pollutant, Victoria Blue dye. The effects of pH, synthesis temperature, and Sr/Ti ratio in the synthesis of the perovskite were examined. SrTiO3 was prepared using Ag, Pt, or Au and characterized using optical and surface analysis methods. We found no clear evidence of substitution of the noble metal into the SrTiO3 lattice, and most metal existed as zerovalent metal deposits. Addition of Ag to SrTiO3 showed the most promising catalytic activity toward dye degradation. Degradation of the dye under UV−visible light was also observed to be enhanced only for Ag−SrTiO3.
TL;DR: In this paper, the authors consider the application of IPMC with water as the solvent, and show that the applied electric potential must be limited to less than 1.3V at room temperature to avoid electrolysis.
Abstract: Ionic polymer-metal composites (IPMCs) consist of a perfluorinated ionomer membrane (usually Nafion® or Flemion®) plated on both faces with a noble metal such as gold or platinum and neutralized with a certain amount of counterions that balance the electrical charge of anions covalently fixed to the backbone ionomer. IPMCs are electroactive materials with potential applications as actuators and sensors. Their electrical-chemical-mechanical response is dependent on the cations used, the nature and the amount of solvent uptake, the morphology of the electrodes, the composition of the backbone ionomer, the geometry and boundary conditions of the composite element, and the magnitude and spatial and time variation of the applied potential. With water as the solvent, the applied electric potential must be limited to less than 1.3V at room temperature, to avoid electrolysis. Moreover, water evaporation in open air presents additional problems. These and related factors limit the application of IPMCs with water a...