Search results for "noble metal"
showing 10 items of 44 documents
Cd12Ag32(SePh)36: Non-Noble Metal Doped Silver Nanoclusters
2019
While there are numerous recent reports on doping of a ligand-protected noble metal nanocluster (e.g., Au and Ag) with another noble metal, non-noble metal (e.g., Cd) doping remains challenging. Here, we design a phosphine-assisted synthetic strategy and synthesize a Cd doped Ag nanocluster, Cd12Ag32(SePh)36 (SePh: selenophenolate), which exhibits characteristic UV–vis absorption features and rare near-infrared (NIR) photoluminescence at ∼1020 nm. The X-ray single crystal structure reveals an asymmetric two-shell Ag4@Ag24 metal kernel protected by four nonplanar Cd3Ag(SePh)9 metal–ligand frameworks. Furthermore, the electronic structure analysis shows that the cluster is a 20-electron “supe…
Photoelectron spectra from first principles: from the many-body to the single-particle picture
2008
We derive a many-body method to evaluate photoelectron spectra of atoms, molecules and clusters from first principles. The excitation energies and the spectroscopic factors are calculated from the linear-response time-dependent density functional theory. The method is applied to noble metal anions, anionic clusters and to neutral small molecules. Our approach shows significant improvement over a simple single-particle treatment and gives an insight into the necessary conditions under which the single-particle picture holds. The consideration of the spectroscopic factor is shown to be crucial for the correct description of inner valence photoelectron peaks.
Review of gas diffusion cathodes for alkaline fuel cells
2009
Abstract This paper gives a technical background to alkaline fuel cells (AFCs), introducing the advantages and drawbacks of the technology. AFCs offer the potential for low cost, mass producible fuel cells, without the dependency on platinum based catalysts and (currently) expensive membrane electrolytes. The AFC uses relatively low cost electrolytes based on aqueous bases such as potassium hydroxide. The inherent CO 2 sensitivity of the electrolyte can be addressed by filtering out the CO 2 from the air intake using a simple scrubber and periodically replacing the liquid electrolyte. A review of the state-of-the-art in gas diffusion cathode development is given. The overall cell performanc…
Separation of Nanoparticles by Gel Electrophoresis According to Size and Shape
2007
We demonstrate the separation of gold and silver nanoparticles according to their size and shape by agarose gel electrophoresis after coating them with a charged polymer layer. The separation is monitored optically using the size- and shape-dependent plasmon resonance of noble metal particles and confirmed by transmission electron microscopy (TEM). Electrophoretic mobilities are quantitatively explained by a model based on the Henry formula, providing a theoretical framework for predicting gel mobilities of polymer coated nanoparticles.
Laser-Ablation-Induced Synthesis of SiO2-Capped Noble Metal Nanoparticles in a Single Step
2010
Here we describe a simple, powerful technique based on the laser ablation of a target immersed in a water solution of a metal salt. With this method, nanoparticles of different metals and alloys can be processed very quickly. Both the target and the salt solution can be chosen to produce metal nanoparticles of different sizes, surface-oxidized nanoparticles (silica-silver, for example), or even more complex structures to be defined by the researcher on one or more steps because the technique combines the advantages of both physical and chemical methods. We have applied this technique to the fabrication of inert silica-metal (silver, gold, and silver-gold) nanoparticles with a strong surface…
On the Interaction of Carbon Nanowires with Noble Metals through a Study of Their Surface-Enhanced Raman Spectra
2008
This paper deals with the interaction of linear carbon chains (polyynes) with silver and gold surfaces in the form of nanometer-sized clusters. Surface-enhanced Raman signals have been detected rev...
Effects of Crystal Field Splitting and Surface Faceting on the Electronic Shell Structure
1992
The shell structure of the valence electrons is clearly observed in all alkali and noble metal clusters containing up to hundreds of atoms[1 – 4]. It is seen in the abundances of the clusters, in the ionization potential and in the polarizability. The shell structure of the valence electrons is closely related to the shell model of nuclei, but is simpler owing to the negligibly small spin-orbit interaction. The ability to produce all sizes of metal clusters has made the metal clusters a test ground for the super-shell structure[5].
Spectroscopic evidence for a new type of surface resonance at noble metal surfaces
2020
We investigated the surface and bulk properties of the pristine (110) surface of silver using threshold photoemission by excitation with light of 5.9 eV. Using a momentum microscope, we identified two distinct transitions along the $\overline{\mathrm{\ensuremath{\Gamma}}}\overline{\mathrm{Y}}$ direction of the crystal. The first one is a so far unknown surface resonance of the (110) noble-metal surface, exhibiting an exceptionally large bulk character that has so far been elusive in surface sensitive experiments. The second one stems from the well-known bulklike Mahan cone oriented along the $\mathrm{\ensuremath{\Gamma}}L$ direction inside the crystal but projected onto the (110)-surface cu…
A solar photothermo-catalytic combined process for the VOCs combustion and the subsequent CO2 valorization using noble metal-free catalysts
2023
We here investigated a solar photothermo-catalytic combined process where the toluene (as volatile organic compound model) was first oxidized to CO2 which was subsequently converted into solar fuels in a second reactor. For this aim two noble-metal free catalytic systems were used, namely MnOx-ZrO2, which gave the best results for the toluene removal, and brookite TiO2-CeO2 mixed oxides which were the most efficient in the subsequent CO2 conversion. This latter reaction was further improved by the addition of small amounts of copper-based materials on brookite-ceria, acting as co-catalysts. The key point for both the examined reactions was the synergism between the thermocatalytic and the p…
The abundance of Au, Pt, Pd, and the mode of heavy metal fixation in highly polluted sediments from the Rhine River near Mainz, West Germany
1984
The Au, Pt and Pd contents of the sediments of Ginsheimer‐Altrhine River, a channel of the Rhine river which drains one of the most industrialized regions of western Europe, have been determined by flameless atomic absorption spectrophotometry. The abundances of these noble metals range from 96–460 ppb Au; 734 ppb‐31 ppm Pt and 32 ppb‐4 ppm Pd. The extremely high concentrations, particulary those of Pt and Pd, are attributed to their use in industry and are due to the formation and concentration of metal‐organic complexes, mainly at the interface between an extremely reducing and an oxidizing aquatic environment. Differential thermal analyses of the polluted sediments in comparison to the p…