AbstractDie Schönheit von Opalen beruht auf einer dichten, hochgeordneten Packung von SiO2‐Kugeln mit einem Durchmesser von einigen hundert Nanometern. Solche geordneten Nanostrukturen sind typische Beispiele für so genannte photonische Kristalle, die sowohl durch die bekannten Mikrostrukturierungsmethoden als auch durch Selbstorganisation hergestellt werden können. Opale stehen für den Selbstorganisationszugang zu diesen strukturierten Medien, die zu neuen Materialien in der Photonik, Photokatalyse und anderen Gebieten führen können. Die Selbstorganisation hat viele Arten von Defekten zur Folge, die zu den überraschenden und sehr individuellen Erscheinungsformen natürlicher Opale führen, aber auch Schwierigkeiten bei der technischen Anwendung von Opalsystemen verursachen.

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The beauty of opals results from a densely packed, highly ordered arrangement of silica spheres with a diameter of several hundred nanometers. Such ordered nanostructures are typical examples of materials called photonic crystals, which can be formed by known microstructuring methods and by self-assembly. Opals represent a self-assembly approach to these structured media; such an approach can lead to novel materials for photonics, photocatalysis, and other areas. Although self-assembly leads to many types of defects, resulting in the surprising and very individual appearance of natural opals, it causes also difficulties in technological applications of opal systems.

In this study, in-situ XANES measurements of the Ru L-III-edge of one commercially available and a novel PtRu colloid catalyst, synthetized at the Max-Planck-Institut fur Kohlenforschung, Muhlheim (Ruhr), Germany, at room temperature and at 80 degrees C in an atmosphere of 10% H-2 in N-2 are presented. During the process of heating at operating temperature, clear sample-specific changes are observed that can be correlated to structure and perfomance of the respective catalysts. The commercially available catalyst JM HiSpec 6000, Johnson Matthey company, and the freshly prepared novel colloid catalyst EUP-AA-25 show a reduction of the oxidation state of the Ru ions at operating temperature, demonstrating the existence of ruthenium sites which are accessible only under operating conditions. On the other hand, when examining the novel colloid catalyst extracted after 500 hours at working conditions, then declared as EUP-AA-21, no changes are observed while heating in a hydrogen containing atmosphere any more, indicating that the formerly active sites have been permanently blocked.

Chloride residues on the surface of fuel cell catalysts arc known to decrease the catalytic activity, especially for O-2 reduction. Using Armand's ligand, which contains the chloride free DCTA anion, for the colloidal stabilisation of nanoscopic Pt and PtRu catalysts precursors (< 2 nm size) leads to PEMFC catalysts with improved activity compared to commercial E-TEK catalysts as evidenced by both methanol oxidation and CO-stripping voltametric studies.

We present X-ray absorption spectroscopy (XAS) data, ultraviolet photoelectron spectra (Hei) and metastable impact electron spectra (MIES) of cobalt nanoparticles (typically 4 to 10 nm), prepared by CO2(CO)(8) thermolysis and pre-stabilized by smooth oxidation. We find that the particles consist of a core-shell system with a dominantly f.c.c. core and a shell in which Co-C and Co-O coordination is likely to occur. This corresponds well to the results from electron spectroscopy, that stabilization occurs via formation of (Co-COx) and (Co-O) groups formed during the oxidation procedure and appears sensitive to the reaction conditions. Peptization of the pre-stabilized particles with KorantinSH surrounds the particles with a dense organic shell, stable up to about 250degreesC. The carbonic acid molecules of the shell are oriented predominantly perpendicular to the surface of the particles, their carboxyl functional group linking the shell with the cobalt particles. This result is also supported by the XAS data, where it is observed that, during peptization, Co-C coordination is partly replaced by Co-O coordination. In order to arrive at these statements, auxiliary measurements on bare and gas-exposed cobalt films, also reported here, were required. Copyright (C) 2004 John Wiley Sons, Ltd.

Applied Organometallic ChemistryVolume 18, Issue 11 p. 566-572 Review A review—How nanoparticles emerged from organometallic chemistry Dedicated to Professor Helmut Bönnemann on the occasion of his 65th birthday S. S. Botha, S. S. Botha Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorW. Brijoux, Corresponding Author W. Brijoux [email protected] Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanyMax-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorR. Brinkmann, R. Brinkmann Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorM. Feyer, M. Feyer Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorH.-W. Hofstadt, H.-W. Hofstadt Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorG. Kelashvili, G. Kelashvili Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorS. Kinge, S. Kinge Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorN. Matoussevitch, N. Matoussevitch Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorK. S. Nagabhushana, Corresponding Author K. S. Nagabhushana [email protected] Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanyMax-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorF. Wen, F. Wen Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this author S. S. Botha, S. S. Botha Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorW. Brijoux, Corresponding Author W. Brijoux [email protected] Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanyMax-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorR. Brinkmann, R. Brinkmann Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorM. Feyer, M. Feyer Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorH.-W. Hofstadt, H.-W. Hofstadt Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorG. Kelashvili, G. Kelashvili Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorS. Kinge, S. Kinge Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorN. Matoussevitch, N. Matoussevitch Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorK. S. Nagabhushana, Corresponding Author K. S. Nagabhushana [email protected] Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanyMax-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this authorF. Wen, F. Wen Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz-1, D 45468 Mülheim an der Ruhr, GermanySearch for more papers by this author First published: 20 October 2004 https://doi.org/10.1002/aoc.808Citations: 9AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume18, Issue11Special Issue: XVth FECHEM Conference on Organometallic Chemistry, 10–15 August 2003, Zürich, SwitzerlandNovember 2004Pages 566-572 RelatedInformation

This work investigates in detail the interaction between colloidal core and protection shell for N(octyl)(4)Cl-stabilized cobalt particles of 2.5 rim average diameter. We have analyzed the electronic and geometric structure of these particles using the X-ray absorption near edge structure (XANES) spectra measured at both Cl and Co K edge as well as the extended X-ray absorption fine structure measured at the Co K edge. The metal XANES data are interpreted based on FEFF8 real space full multiple scattering calculations for a suitable reference system. On the basis of these results, we propose a detailed model describing how the protection shell is anchored to the core of the particle. To show the broad applicability of this model, it is then used on Palladium particles stabilized by the same technique.

A novel, size-selective preparation route leads to air stable ‘monodisperse’ colloidal cobalt nanoparticles via the thermolysis of Co2(CO)8 in the presence of aluminum alkyls. X-ray absorption near edge structure measurements have proved that this preparation pathway provides long term stable zerovalent magnetic Cobalt particles. In addition, these measurements show that the chemical nature of the surfactant used exerts a significant influence on the stability and the local electronic and geometric structure of the analyzed nanoparticles.

We present X-ray absorption near edge structure (XANES) measurements on N(butyl)4Cl- and N(octyl)4Cl-stabilized Pd colloids at both the Pd LIII- and the Cl K-edge. Metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (HeI) results for these colloids, deposited on silica substrates, are also shown. The results provide detailed insight into the mechanism of bonding between the protection shell and the colloidal core. Both XANES and MIES suggest that the chlorine is present on the inside of the protection shell, located between palladium core and N(alkyl)4 groups forming the protection shell. Moreover, the XANES results suggest a dependence of the equilibrium position of the chlorine between the metal core and the alkyl chain on the length of the alkyl chains. The possible motivation for such an effect is discussed on the basis of different models. MIES, in addition, provides information on the thermal stability of the shell-stabilized Pd colloids.

PEM fuel cell anode catalysts with an improved CO tolerance can be prepared from pre-synthesized bimetallic colloid precursors with particle sizes of 1-2 nm. The particles are supported on Vulcan XC72 and activated by thermal conditioning to remove the stabilizing organic shell. Various routes for colloid synthesis, some using also different organic stabilizers, are explored. NR4X-stabilized Pt/Ru- or Pt/Sn-Precursors of sizes below 2 nm and having a narrow particle size distribution are obtained via the co-reduction of platinum, ruthenium and tin salts, respectively, using alkalitriethylhydroborate. Go-reduction of organic metal salts using organoaluminum compounds without adding any further stabilizer leads to halogen-free, orgartoaluminum pre-stabilized polymetallic platinum colloids (e.g. Pt50Ru50/Al-acac-alkyl, particle size 1.2 +/- 0.3 nm). The ratio of platinum to second metal in the colloid can be easily adjusted by changing the stoichiometric ratio of the metal salts. The dispersivity of these colloids can be modified by adding alcohols or suitable surfactants. The size of organoaluminum-stabilized particles does not change during the thermal conditioning even at high metal loadings (20 wt % metal), avoiding an undesirable particle growth.