The present work analyses the physicochemical phenomena responsible for the microstructure of Pd/SiO2 xerogel catalysts and of metal-free hybrid SiO2 xerogels synthesized by sol-gel process. The samples are synthesized by co-polymerizing tetraethoxysilane (TEOS) with 3-aminopropyltriethoxysilane or 3-(2-aminoethylamino)propyltrimethoxysilane in ethanol, the latter co-reactant possibly forming a complex with palladium. The analysis is conducted by following in situ the formation of the gels' nanostructure by Small-Angle X-ray Scattering (SAXS), by characterizing the microstructure of the final gels by beam-bending, and by analyzing the microstructure of the xerogels after desiccation, most notably by electron tomography. The in situ SAXS analysis shows that the nanometer structure of the gels forms via a reaction-induced phase separation. The microstructure of the hybrid xerogels is hierarchical, as assessed by electron microscopy, nitrogen adsorption and SAXS. Its structure is that of a microcellular foam at large scale, with pores a few hundred nanometers across, supported by elongated filaments, a few ten nanometers wide, each filament being made up by smaller structures, a few nanometers wide. The characteristics of the various structural levels depend on the nature and concentration of the co-reactant used. In the case of xerogel catalysts, electron tomography shows that Pd nanoparticles are regularly dispersed inside the silica, with distances between them comparable to the thickness of the skeleton. On the basis of the time-resolved SAXS and of the characterization of the xerogels, it is argued that a double phase separation process is responsible for the structuring of the gels, with a primary phase separation leading to the microcellular foam morphology, and a secondary phase separation being responsible for the substructure of the filaments. The large scale structure of the gels themselves, before desiccation, is analyzed by beam bending. This enables one to estimate the mechanical properties of the gels as well as the size of their largest pores. The microstructure of aerogels obtained by supercritical drying of the samples is also investigated. The comparison of the characterization data show that the nature and concentration of the co-reactant controls the amount of shrinkage that the gels undergo during desiccation, at the macroscopic scale as well as at the scale of the filaments.

Nanostrukturierte Materialien zeichnen sich dadurch aus, dass sie aus sehr kleinen Baueinheiten zusammengesetzt sind. Typischerweise liegt die Grössenordnung dieser Bausteine im Bereich von einigen Nanometern. Ein Nanometer entspricht 10-9 Meter. Dadurch bekommen nanostrukturierte Materialien oft verbesserte, vielfach sogar ganz neue Eigenschaften, die für viele heutige wie auch zukünftige Anwendungen von Vorteil sind.<br /> <br /> Ein Weg, um solche nanostrukturierte Materialien herzustellen, ist die sogenannte &bdquo;Templatierungsmethode&ldquo;. Das Templat besteht aus einem einzelnen Molekül, einer Ansammlung von Molekülen oder aus einem festen Objekt. Beim Aufbau des nanostrukturierten Materials wirkt das Templat als Schablone oder als Gussform und beeinflusst damit die Struktur des Endproduktes. Normalerweise besteht dieser Prozess aus mehreren Schritten. Zuerst wird der Raum um das Templat mit dem Ausgangsstoff umhüllt oder ausgefüllt, dann wird der Ausgangsstoff chemisch in das gewünschte Endprodukt umgewandelt, wobei das Templat die Endform kontrolliert und am Schluss wird das Templat entfernt. Das geschieht meistens durch Erhitzen. Als Ausgangsstoff können dabei einzelne Moleküle verwendet werden, die sich leicht in das Endprodukt umwandeln lassen, oder aber vorgeformte Partikelchen, die nur noch zur entsprechenden Form angeordnet werden müssen.<br /> <br /> In dieser Arbeit wurden poröse Metalloxid-Kügelchen hergestellt, die aus einem Gemisch aus Titanoxid und entweder Aluminium-, Gallium- oder Indiumoxid bestehen. Als Template wurden poröse Kunststoffkügelchen eingesetzt, die man sonst für Chromatographiezwecke braucht. Bei der Synthese wurden die Poren der Kunststoffkügelchen mit dem Ausgangsmaterial gefüllt und mit Wasser in ein amorphes Netzwerk umgewandelt. Danach werden die Kügelchen erhitzt, wobei das Kunststofftemplat zersetzt wird. Gleichzeitig wird das amorphe Gerüst in stabile, kristalline Wände umgewandelt, die die Form der Kügelchen auch dann noch behalten, wenn das Templat verschwunden ist. Mit einem ähnlichen Prozess wurden auch Kügelchen aus Cer-Zirkonoxid erhalten. Als Ausgangsstoff wurden dabei aber vorgeformte Cer-Zirkonoxid-Nanopartikel eingesetzt, die in die Poren der Kunststofftemplatkügelchen hinein diffundieren. Diese Cer-Zirkonoxid-Nanopartikel lassen sich auch für die Herstellung von porösen Pulvern verwenden, wobei dann nicht Polymerkügelchen, sondern hochgeordnete Ansammlungen von Block Copolymeren als Template verwendet werden.<br /> <br /> Form, Struktur und Eigenschaften all dieser Materialien wurden systematisch unter Anwendung verschiedenster Analysemethoden untersucht. Die auf Titanoxid-basierten Kügelchen wurden auch auf ihre photokatalytische Verwendung zum Abbau von umweltschädlichem 2-Chlorophenol untersucht. Die Cer-Zirkonoxid-Kügelchen wurden für die Herstellung von Wasserstoff aus Methanol getestet. Wasserstoff gilt als hoffungsvoller, sauberer Energieträger der Zukunft und kommt in Brennstoffzellen zum Einsatz. / Nanostructured materials are the materials having structural features on the scale of nanometers i.e. 10-9 m. the structural features can enhance the natural properties of the materials or induce additional properties, which are useful for day to technology as well as the future technologies<br /> <br /> One way to synthesize nanostructured materials is using templating techniques. The templating process involves use of a certain &ldquo;mould&rdquo; or &ldquo;scaffold&rdquo; to generate the structure. The mould is called as the template, can be a single molecule or assembly of molecule or a larger object, which has its own structure. The product material can be obtained by filling the space around the template with a &ldquo;precursor&rdquo;, transformation of precursor into the desired material and then removal of template to get product. The precursor can be any chemical moiety that can be easily transformed in to the desired material. Alternatively the desired material is processed into very tiny bricks or &ldquo;nano building blocks (NBB)&rdquo; and the product is obtained by arrangement of the NBB by using a scaffold. <br /> <br /> We synthesized porous metal oxide spheres of namely TiO2-M2O3: titanium dioxide- M-oxide (M = aluminum, gallium and indium) TiO2-M2O3 and cerium oxide-zirconium oxide solid solution. We used porous polymeric beads as templates. These beads used for chromatographic purposes. For the synthesis of TiO2-M2O3 we used metal- alkoxides as precursor. The pore of beads were filled with precursor and then reacted with water to give transformation of the precursor to amorphous oxide network. The network is crystallized and template is removed by heat treatment at high temperatures. In a similar way we obtained porous spheres of CexZr1-xO2. For this we synthesized nanoparticle of CexZr1-xO2 and used then for the templating process to obtain porous CexZr1-xO2 spheres. <br /> <br /> Additionally, using the same nanoparticles we synthesized nano-porous powder using self-assembly process between a block-copolymers scaffold and nanoparticles. <br /> <br /> Morphological and physico-chemical properties of these materials were studies systematically by using various analytical techniques <br /> <br /> TiO2-M2O3 material were tested for photocatalytic degradation of 2-Chlorophenol a poisonous pollutant. While CexZr1-xO2 spheres were tested for methanol steam reforming reaction to generate hydrogen, which is a fuel for future generation power sources like fuel cells. All the materials showed good catalytic performance.

Electron crystallography is an important technique for studying micro- and nano-sized materials. It has two important advantages over X-ray crystallography for structural studies: 1) crystals millions of times smaller than those needed for X-ray diffraction can be studied; 2) it is possible to; focus the electrons to form an image. The local atomic arrangement can be seen directly by high-resolution transmission electron microscopy (HRTEM). The crystallographic structure factor phases, which are lost in recording diffraction patterns, are present in HRTEM images and can be determined experimentally. The main disadvantages of electron crystallography compared to X-ray diffraction are that the data are difficult to collect, often incomplete and suffer from dynamic scattering. New methods need to be developed to overcome these problems. In this work, structure determination of several unique and complex porous materials including zeolites and mesoporous silica is demonstrated. None of the structures of these materials could be solved by X-ray crystallography. New techniques are also developed in order to overcome the disadvantages of electron crystallography. The new techniques include a digital sampling method for collecting precession electron diffraction data and a rotation method for automatic collection of complete 3D electron diffraction data. A number of practical issues concerning data collection and data processing are described and the data quality is analysed. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Submitted.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 214-220). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Molecular dynamics; hydrophobic zeolite; water; confined media. Includes bibliographical references (p. 71).

Thesis (Ph. D.)--Institute of Paper Chemistry, 1955. / Includes bibliographical references (p. 65).

Thesis (Ph. D.)--Institute of Paper Chemistry, 1962. / Includes bibliographical references (p. 85-86).

Thesis (Ph. D.)--Institute of Paper Chemistry, 1977. / Includes bibliographical references (p. 122-124).

Thesis (Ph. D.)--Institute of Paper Chemistry, 1975. / Includes bibliographical references (p. 102-104).