Techn. Universiẗat, Diss., 2002--Berlin.

Techn. Universiẗat, Diss., 2004--Berlin.

Techn. Universiẗat, Diss., 2001--Berlin.

Shape and size control as well as the control of the assembly of nanostructures are current challenges in nano sciences. Focussing on metal nanostructures all of these aspects have been addressed in the frame of the present work. It was possible to develop a new aqueous seeded growth method that produces gold nanoparticles with adjustable diameters over a large range of sizes. The spherical particles obtained show very low polydispersities and a good long term stability. Furthermore it was possible to reveal the growth mechanism of these particles utilizing electron microscopy and optical investigations coupled with theoretical calculations. It was found that there is a formation of small nucleation sites on the surface of the seeds in the beginning of the growth process. These sites then subsequently grow into "blackberry-like" intermediate particles. A final intraparticle ripening step leads to smooth and uniform spherical gold nanoparticles. By correcting the dielectric function of gold for charging and the free mean path effect and taking into account the particle size distribution it was possible to accurately model the optical properties of the gold sols obtained using Mie theory. By controlling the concentration of chloride ions it was possible to influence both the ripening of the "blackberry-like" shaped particles and the morphology of gold nanoparticles. An increased concentration of the chloride ions in the standard citrate reduction procedure leads to larger and elongated particles, whereas the complete removal of the chloride ions made it possible to obtain star shaped, decahedral and \"desert-rose\" shaped particle morphologies. Using the layer-by-layer technique gold nanoparticles of different sizes could be immobilized on glass substrates. The surface-enhanced Raman scattering intensity of these mixed films were about 60% higher than compared to a film made of a single particle size. The optical properties were further investigated by comparing experimentally obtained UV/Vis spectra with generalized Mie theory simulations. Additionally it could be shown that tetrazole and its derivatives are suitable stabilizing agents in the aqueous synthesis of silver nanoparticles. It was found that depending on the tetrazole derivative used the tendencies of the nanoparticles to agglomerate vary significantly. Different agglomeration stages have been investigated by UV/Vis and Raman spectroscopy. The removal of the ligands used and a resulting improvement of the applicability of the silver nanostructures as SERS substrates is still a challenge. In the last part of this work the focus was changed from the optical properties of noble metal nanoparticles to their catalytic properties. Therefore gold and palladium nanoparticles have been successfully immobilized on highly porous zinc oxide aerogels. It was possible to synthesize sponge-, flake-, and ribbon-like zinc oxide gels with high specific surface areas. The facile approach of generating mixed metal oxide/noble metal aerogels is very promising for the preparation of highly selective and highly active heterogenous catalysts. First catalytic investigations of a sponge-like palladium loaded zinc oxide aerogel toward the semi-hydrogenation of acetylene showed very high selectivities of up to 85%.

Metallfluoride sind dank ihrer hohen chemischen und thermischen Stabilität, insbesondere bei Reaktionen unter Beteiligung von hoch korrosiven Gasen (HF, HCl, Cl2, F2) den entsprechenden Oxiden überlegen. Über den Sol-Gel Prozess synthetisierte Produkte weisen oft spezifische, zum Teil sehr unterschiedliche Eigenschaften im Vergleich zu klassisch hergestellten Verbindungen auf. In dieser Arbeit wurde der Sol-Gel Prozess zur Herstellung von binären Fluoriden (AlF3, MgF2, CaF2, CuF2 und FeF3) genutzt und zum Teil weiter entwickelt sowie das Synthesepotential dieser Methode als Zugang für komplexe Fluoride (KMgF3, K3AlF6), für Metallfluorid-geträgerte „nano Edelmetall-Systeme (Pd/AlF3, Pt/AlF3, Pd/CaF2, Pd/MgF2) und für Gast–Wirt–Metallfluorid-Systeme (CuF2/AlF3, FeF3/AlF3) untersucht. Die Eigenschaften der als kompakte Materialien hergestellten Metallfluorid Systeme wurden mit Hilfe spektroskopischer Methoden untersucht und dabei insbesondere deren Oberflächeneigenschaften bestimmt. Die neuen Materialien wurden für die Nutzung akademisch und industriell bedeutsamer Katalysereaktionen evaluiert und mit klassischen Katalysatoren verglichen. Es konnte gezeigt werden, dass der Sol-Gel Prozess für Fluoride zu neuartigen Materialien mit außergewöhnlichen Eigenschaften führt. Insbesondere infolge der Synthese-bedingten Vergrößerung der spezifischen Oberflächen um einen bis zu 20-fachen Faktor im Vergleich zu klassisch hergestellten Fluoriden konnten auch eine Reihe von katalytisch interessanten Metallen (Pd, Pt) in die nanoskopischen Festkörperfluoride eingebracht werden. Die TEM Aufnahmen zeigen, dass z. B. 2-5 nm große Palladiumpartikel sehr homogen in ca. 80 nm große CaF2- bzw. 20 nm große AlF3-Matrices in nur einem einzigen Reaktionsschritt eingeführt werden können. Die neuen Materialien wurden in verschiedenen katalytischen Reaktionen getestet und zeigten sich in mehreren Fällen den „Standard Katalysatoren“ überlegen. / Because of their high chemical and thermal stabilities, metal fluorides have found to be advantageous over metal oxides in such cases where reactions involving generation of corrosive acids like HCl and HF are concerned. The Sol-gel method is known for the synthesis of materials with considerably different properties to those prepared by classical routes. In this work, sol-gel route has been employed for the synthesis of binary fluorides (AlF3, MgF2, CaF2, CuF2 and FeF3), hydroxyfluorides [AlF3-x(OH)x, MgF2-x(OH)x] complex fluorides (KMgF3, K3AlF6), metal fluoride supported nanoscopic noble metals (Pd, Pt) and host-guest fluoride systems (CuF2/AlF3, FeF3/AlF3). Besides the successful synthesis of metal fluorides described above, the present thesis deals with investigation of their bulk and surface properties using various analytical and spectroscopic methods (XRD, BET, NH3-TPD FTIR-pyridine adsorption, XPS, microscopic studies) as well as with their catalytic properties for the reactions of academic and industrial interest. Metal fluorides prepared via sol-gel method have shown to possess extraordinary surface properties in terms of surface area, particle size, porosity, Lewis acidity and distortion in their structures as compared to those of classical methods like aqueous synthesis or impregnations. A homogeneous dispersion of Pd nanoparticles supported on high surface area metal fluoride prepared by this method was confirmed by XRD, XPS and TEM imaging. Catalytic properties of these materials have been investigated for dehydrofluorination of hydrofluorocarbons, isomerization of citronellal, hydrodehalogenation of chlorodifluoromethane, Suzuki cross coupling and oxidative fluorination of benzene.