Search results for "noble"

Maximum Noble-Metal Efficiency in Catalytic Materials: Atomically Dispersed Surface Platinum

2014

International audience; Platinum is the most versatile element in catalysis, but it is rare and its high price limits large-scale applications, for example in fuel-cell technology. Still, conventional catalysts use only a small fraction of the Pt content, that is, those atoms located at the catalyst's surface. To maximize the noble-metal efficiency, the precious metal should be atomically dispersed and exclusively located within the outermost surface layer of the material. Such atomically dispersed Pt surface species can indeed be prepared with exceptionally high stability. Using DFT calculations we identify a specific structural element, a ceria ``nanopocket'', which binds Pt2+ so strongly…

Crosslinked Spherical Nanoparticles with Core-Shell Topology

2000

Core–shell microgels are crosslinked nanosized spherical particles with a chemical composition that is different on the surface compared to the core region. By employing a core with special optical properties, e.g., a core labeled either with organic dye molecules or noble metal clusters (see Figure), these particles are perfectly suited as optical tracers in diffusion measurements. Here, the shell may be important for several reasons: (i) as a protective coating to suppress any influence of the labels on particle mobility, (ii) to optically separate individual particles even at high concentrations, and (iii) to compatibilize the particles with e.g., polymeric chains. Recent developments in…

Oxide-based nanomaterials for fuel cell catalysis:the interplay between supported single Pt atoms and particles

2017

The concept of single atom catalysis offers maximum noble metal efficiency for the development of low-cost catalytic materials. Among possible applications are catalytic materials for proton exchange membrane fuel cells. In the present review, recent efforts towards the fabrication of single atom catalysts on nanostructured ceria and their reactivity are discussed in the prospect of their employment as anode catalysts. The remarkable performance and the durability of the ceria-based anode catalysts with ultra-low Pt loading result from the interplay between two states associated with supported atomically dispersed Pt and sub-nanometer Pt particles. The occurrence of these two states is a co…

Limits on the release of Rb isotopes from a zeolite based 83mKr calibration source for the XENON project

2011

The isomer 83mKr with its half-life of 1.83 h is an ideal calibration source for a liquid noble gas dark matter experiment like the XENON project. However, the risk of contamination of the detector with traces of the much longer lived mother isotop 83Rb (86.2 d half-life) has to be ruled out. In this work the release of 83Rb atoms from a 1.8 MBq 83Rb source embedded in zeolite beads has been investigated. To do so, a cryogenic trap has been connected to the source for about 10 days, after which it was removed and probed for the strongest 83Rb gamma-rays with an ultra-sensitive Germanium detector. No signal has been found. The corresponding upper limit on the released 83Rb activity means tha…

Amphiphilic Poly(organosiloxane) Nanospheres as Nanoreactors for the Synthesis of Topologically Trapped Gold, Silver, and Palladium Colloids

2003

Amphiphilic poly(organosiloxane) nanospheres with different core−shell architectures are employed as passive nanoreactors for the synthesis of noble metal colloids. The amphiphilic poly(organosiloxane) nanospheres, which have diameters between 15 and 40 nm, possess a hydrophilic interior and a hydrophobic shell. Dispersed in organic solvents such as toluene, it has been achieved to transfer hydrophilic noble metal salts through the solvent into the nanospheres by either liquid−liquid or solid−liquid phase transfer. Subsequently, reduction of the noble metal salt with lithium triethylborohydride led to the formation of 2−5 nm sized noble metal colloids. If the network density of the shell of…

Molecular-mediated assembly of silver nanoparticles with controlled interparticle spacing and chain length

2012

In the present work, we report on a one-pot method for the assembly of noble metal nanoparticles with tunable optical properties, assembly length and interparticle spacing. The synthetic colloidal route is based on the covalent binding among OH-terminated silver nanoparticles by means of dicarboxylic acids with a defined molecular length. As a result, the initially symmetric plasmon band of silver nanoparticles splits into two plasmonic modes when nanoparticles are assembled due to the strong near-field plasmon coupling. We noticed a very good correlation between the plasmon wavelength shift and the interparticle spacing that is represented by the universal scaling law of the surface plasmo…

Plasmonic Silver Nanorod Sensitivity: Experiment and Simple Theoretical Treatment

2013

We compare the plasmonic sensitivity of silver and gold nanorods with similar resonance wavelengths by monitoring the plasmon resonance shift of single noble metal nanorods upon changing the environment from water to sucrose solution. We find that silver nanorods have 1.2 to 2 times higher sensitivity than gold in good agreement with simulations based on the boundary-elements-method (BEM). To exclude the effect of particle volume on sensitivity, we test gold rods with increasing particle width at a given resonance wavelength. Using the Drude-model of optical properties of metal together with the quasi-static approximation (QSA) for localized surface plas-mons, we show that the dominant cont…

Back Cover: Maximum Noble-Metal Efficiency in Catalytic Materials: Atomically Dispersed Surface Platinum (Angew. Chem. Int. Ed. 39/2014)

2014

Atomically Precise Nanocluster Assemblies Encapsulating Plasmonic Gold Nanorods.

2018

The self-assembled structures of atomically precise, ligand-protected noble metal nanoclusters leading to encapsulation of plasmonic gold nanorods (GNRs) is presented. Unlike highly sophisticated DNA nanotechnology, this strategically simple hydrogen bonding-directed self-assembly of nanoclusters leads to octahedral nanocrystals encapsulating GNRs. Specifically, the p-mercaptobenzoic acid (pMBA)-protected atomically precise silver nanocluster, Na4 [Ag44 (pMBA)30 ], and pMBA-functionalized GNRs were used. High-resolution transmission and scanning transmission electron tomographic reconstructions suggest that the geometry of the GNR surface is responsible for directing the assembly of silver …

Le prince face aux communautés ecclésiales: René, Charles, Louis, Philippe et les autres...

2019

À côté de René d’Anjou, la France du milieu du XVe siècle connaît un certain nombre de princes attachés à l’intensité d’une vie spirituelle qui se déploie dans des communautés exclusivement cléricales ou mêlant étroitement – les paroisses par exemple – les clercs et les laïcs. Ces églises, dont les guerres et la dépopulation ont souvent compromis la situation matérielle, ne manquent pas d’attendre d’eux maintien voire extension des droits, sauvegarde et éventuellement secours, mais elles peuv...