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5. Size and shape distributions of primary crystallites in titania aggregates

Author

Grulke, Eric A., Yamamoto, Kazuhiro, Kumagai, Kazuhiro, Häusler, Ines, Österle, Werner, Ortel, Erik, Hodoroaba, Vasile-Dan, Brown, Scott C., Chan, Christopher, Zheng, Jiwen, Yamamoto, Kenji, Yashiki, Kouji, Song, Nam Woong, Kim, Young Heon, Stefaniak, Aleksandr B., Schwegler-Berry, D., Coleman, Victoria A., Jämting, Åsa K., Herrmann, Jan, Arakawa, Toru, Burchett, Woodrow W., Lambert, Joshua W., and Stromberg, Arnold J.

Published
2017
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12. Customizing New Titanium Dioxide Nanoparticles with Controlled Particle Size and Shape Distribution: A Feasibility Study Toward Reference Materials for Quality Assurance of Nonspherical Nanoparticle Characterization.

Author

Pellegrino, Francesco, Ortel, Erik, Mielke, Johannes, Schmidt, Roland, Maurino, Valter, and Hodoroaba, Vasile-Dan

Subjects
TITANIUM dioxide nanoparticles, PARTICLE size distribution, REFERENCE sources, QUALITY assurance, FEASIBILITY studies
Abstract

An overview is given on the synthesis of TiO2 nanoparticles with well‐defined nonspherical shapes (platelet like, bipyramidal, and elongated), with the focus on controlled, reproducible synthesis, as a key requirement for the production of reference materials with homogeneous and stable properties. Particularly with regard to the nanoparticle shapes, there is a high need of certified materials, solely one material of this type being commercially available since a few months (elongated TiO2). Further, measurement approaches with electron microscopy as the golden method to tackle the nanoparticle shape are developed to determine accurately the size and shape distribution for such nonspherical particles. A prerequisite for accurate and easy (i.e., automated) image analysis is the sample preparation, which ideally must ensure a deposition of the nanoparticles from liquid suspension onto a substrate such that the particles do not overlap, are solvent‐free, and have a high deposition density. Challenges in the synthesis of perfectly monodispersed and solvent‐free TiO2 nanoparticles of platelet and acicular shapes are highlighted as well as successful measurement approaches on how to extract from 2D projection electron micrographs the most accurate spatial information, that is, true 3D size, for example, of the bipyramidal nanoparticles with different geometrical orientations on a substrate. [ABSTRACT FROM AUTHOR]

Published
2022
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20. Characterization of the inner structure of porous TiO 2 nanoparticle films in dye sensitive solar cells (DSSC) by focused ion beam (FIB) tomography and transmission Kikuchi diffraction (TKD) in the scanning electron microscope (SEM)

Author

Wollschläger, Nicole, primary, Palasse, Laurie, additional, Häusler, Ines, additional, Dirscherl, Kai, additional, Oswald, Frédéric, additional, Narbey, Stéphanie, additional, Ortel, Erik, additional, and Hodoroaba, Vasile-Dan, additional

Published
2017
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29. Shape engineered TiO2nanoparticles in Caenorhabditis elegans: a Raman imaging based approach to assist tissue-specific toxicological studies

Author

Iannarelli, Luca, primary, Giovannozzi, Andrea Mario, additional, Morelli, Federica, additional, Viscotti, Francesco, additional, Bigini, Paolo, additional, Maurino, Valter, additional, Spoto, Giuseppe, additional, Martra, Gianmario, additional, Ortel, Erik, additional, Hodoroaba, Vasile-Dan, additional, Rossi, Andrea Mario, additional, and Diomede, Luisa, additional

Published
2016
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31. Synthese templatiert poröser Metalloxidfilme: Von kontrollierter Einstellung der Morphologie zu maßgeschneiderten Katalysatormaterialien

Author

Ortel, Erik, Kraehnert, Ralph, and Technische Universität Berlin, Fakultät II - Mathematik und Naturwissenschaften

Subjects
540 Chemie und zugeordnete Wissenschaften, Butadienhydrierung, Katalysatorfilme, Novel metal nanoparticle, Templatierung, Butadiene hydrogenation, ddc:540, Porous metal oxide, Templating, Edelmetall-Nanopartikel, Catalytic coating, Poröse Metalloxide
Abstract

Gegenstand der vorliegenden Arbeit ist die Synthese von templatiert porösen Metalloxidfilmen mit kontrolliert einstellbaren Eigenschaften in Bezug auf Porenstruktur und Materialzusammensetzung für den Einsatz als neuartige Modellkatalysatoren. Für die Schaffung von porösen Katalysatorschichten mit definierter Mesoporenstruktur wurde im Rahmen dieser Arbeit eine Serie neuer amphiphiler Polymertemplate mit der Struktur PEO-PB-PEO entwickelt. Mittels SAXS-Untersuchungen konnte nachgewiesen werden, dass die PEO-PB-PEO-Template bereits bei geringen Polymerkonzentrationen stabile Mizellen in Lösung ausbilden. Die Templatierung mit solchen „vorgeformten“ PEO-PB-PEO-Mizellen ermöglichte eine gezielte Kontrolle der Porenmorphologie. Anhand von mesoporösen TiO2-Filmen wurde demonstriert, dass i) über die Länge der Polymerblöcke der eingesetzten PEO-PB-PEO-Template die Porengröße von 7 nm bis 21 nm im Durchmesser eingestellt werden kann, ii) durch eine Variation des eingesetzten Mengenverhältnisses von Polymer-zu-Oxidvorstufen eine gezielte Einstellung der Porenwanddicke unabhängig von der templatierten Porengröße in einem weiten Wanddicke von ca. 4 nm bis 23 nm möglich ist und iii) eine Kombination aus zwei verschiedenen amphiphilen Polymertemplaten mit unterschiedlichen Blocklängen die Schaffung bimodaler Mesoporensysteme erlaubt. Ferner wurde gezeigt, dass das PEO-PB-PEO-Polymer erfolgreich TiO2-Nanokristalle zu lokal geordneten mesoporösen TiO2-Filmen templatiert mit nahezu sphärischen Mesoporenformen, wohingegen molekulare Oxid-Vorstufen zu ellipsoiden stark abgeflachten Poren führen. Desweiteren demonstriert diese Arbeit die Synthese von neuartigen geordnet mesoporösen IrO2-Katalysatorfilmen basierend auf PEO-PB-PEO-Mizellen und einer Ir-Acetat-Vorstufe. Eine systematische Untersuchung der IrO2-Filmentwicklung während der thermischen Behandlung ermöglichte die Identifizierung der optimalen Kalzinierbedingungen zur Bildung eines IrO2-Films mit intakter Mesoporenstruktur, hoher innerer Oberfläche und gleichzeitig nanokristallinen Porenwänden. Ein weiterer Schwerpunkt der Arbeit war die Synthese von porösen Katalysatorschichten mit geträgerten Edelmetall-Nanopartikeln. Basierend auf einer unkonventionellen pH-neutralen TiO2-Vorstufe, dem Titan(IV)-bis(ammoniumlactato)-dihydroxid, wurde ein Konzepte zur Präparation von Pd-NP geträgerten mesoporösen TiO2-Filmen ausgearbeitet, welche eine gezielte Einstellung von sowohl Pd-NP-Größe, Pd-Beladung als auch der Porenstruktur unabhängig voneinander erlaubt. Templatiert mesoporöse Katalysatorschichten in der Zusammensetzung Pd/TiO2, Pt/TiO2, Au/TiO2, Pd/Al2O3, Pt/Al2O3, Pd/ZrO2, Pt/ZrO2 sowie Pd/CeO2 wurden auf einen alternativen Weg synthetisiert. Damit wurde eine Toolbox von neuen Präparationswegen geschaffen, die die Synthese von mesoporösen Katalysatorfilmen mit variierter Zusammensetzung von aktivem Metall und Trägeroxid ermöglichen. Die Aktivität und Selektivität der entwickelten Katalysatoren wurde experimentell anhand einer Modellreaktion, der Gasphasenhydrierung von Butadien nachgewiesen. Der mesoporöse Katalysatorfilm der Zusammensetzung Pd/Al2O3 zeigte dabei die höchste Raum-Zeit-Ausbeute an Butenen., Aim of the present work was the development of synthesis methods for metal oxide coatings with controlled pore structure and material composition as a new type of model system for heterogeneous catalysis. To control the materials pore structure a set of new structure-directing agents was deployed, i.e. amphiphilic triblock copolymers with PEO-PB-PEO structure. SAXS studies proof that PEO-PB-PEO forms stable micelles in solution already at very low polymer concentrations. Templating of mesopores with such "pre-formed" PEO-PB-PEO micelles therefore allows precise control over the obtained pore system. Using TiO2 films as example it is demonstrated that i) the pore size is determined by the molecular mass of the template polymer (pore diameter between 7 nm and 21 nm), ii) the thickness of pore walls can be controlled independent of pore size by changing the polymer to precursor ratio (wall thickness between 4 and 23 nm) and iii) the micelle formation of the PEO-PB-PEO template polymers is sufficiently distinct from that of other commercial polymers (e.g. PPO-PEO-PPO Pluronics), so that a combination of both polymers facilitates bimodal porosity via dual micelle templating. Moreover, PEO-PB-PEO can be used in combination with different oxide building-blocks. The polymers successfully template crystalline and locally ordered mesoporous TiO2 films employing either TiCl4 or redispersed TiO2 nanocrystals as metal oxide precursors. Moreover, it is shown that the employed building block strongly influences the obtained pore shape. While TiCl4-based films exhibit elliptical pore shapes, films based on TiO2 nanocrystals feature a pore structure with mesopore shapes close-to-spherical. Furthermore, it is shown for the first time that Iridium oxide, one of the most stable OER catalysts, can be synthesized as crystalline IrO2 films with ordered mesoporosity. Analytical studies of the Iridium oxide films during their thermal treatment clearly identifies the synthesis pathways and conditions that are essential to achieve a stable IrO2 catalyst, which possesses templated mesopore structure, crystalline pore walls and a large surface area. A major focus of this work was placed on the synthesis of porous catalytic coatings containing active noble-metal nanoparticles with adjustable particle size. Colloidal synthesis methods provide access to unsupported metal nanoparticles with narrow size distribution. Hence, a new approach for the preparation of supported catalysts was developed that relies on co-assembly of preformed colloidal metal particles, pore templates and a metal-oxide precursors. The synthesis employs titanium(IV) bis(ammonium lactato) dihydroxide as unconventional water-soluble precursor. The synthesis approach is illustrated for mesoporous and hierarchical porous Pd/TiO2 catalysts prepared from colloidal solutions of palladium nanoparticles. Moreover, templated mesoporous catalyst layers with varied composition in terms of support oxide and noble metal (Pd/TiO2, Pt/TiO2, Au/TiO2, Pd/Al2O3, Pt/Al2O3, Pd/ZrO2, Pt/ZrO2 and Pd/CeO2) were synthesized by an alternative route that employs molecular metal precursors. The combination of developed synthesis methods provides a toolbox for the precise synthesis of catalyst with controlled pore structure and composition. Activity and selectivity of the developed catalysts were studied employing gas-phase hydrogenation of butadiene as test reaction. In the present investigation, mesoporous Pd/Al2O3 catalysts provided the highest space-time yield to butenes.

Published
2012
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36. Nafion-Free Carbon-Supported Electrocatalysts with Superior Hydrogen Evolution Reaction Performance by Soft Templating.

Author

Bernsmeier, Denis, Bernicke, Michael, Ortel, Erik, Bergmann, Arno, Lippitz, Andreas, Nissen, Jörg, Schmack, Roman, Strasser, Peter, Polte, Jörg, and Kraehnert, Ralph

Subjects
WATER electrolysis, ELECTROCATALYSTS, NAFION, CARBON, HYDROGEN evolution reactions, ELECTRODES
Abstract

Efficient water electrolysis requires electrode coatings with high catalytic activity. Platinum efficiently catalyzes the hydrogen evolution reaction in acidic environments, but is a rare and expensive metal. The activity achieved per metal atom can be increased if small Pt particles are dispersed onto electrically conductive, highly accessible and stable support materials. However, the addition of Nafion, a typical binder material used in the manufacture of electrode coatings, can decrease catalytic activity by the blocking of pores and active surface sites. A new approach is reported for the direct synthesis of highly active Nafion-free Pt/C catalyst films consisting of small Pt nanoparticles supported in size-controlled mesopores of a conductive carbon film. The synthesis relies on the co-deposition of suitable Pt and C precursors in the presence of polymer micelles, which act as pore templates. Subsequent carbonization in an inert atmosphere produces porous catalyst films with controlled film thickness, pore size and particle size. The catalysts clearly outperform all Nafion-based Pt/C catalysts reported in the literature, particularly at high current densities. [ABSTRACT FROM AUTHOR]

Published
2017
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41. In-depth structural and chemical characterization of engineered TiO2 films.

Author

Ortel, Erik, Häusler, Ines, Österle, Werner, Narbey, Stéphanie, Oswald, Frédéric, Andersen, Inge H., Holzweber, Markus, Unger, Wolfgang E. S., and Hodoroaba, Vasile Dan

Subjects
*TITANIUM dioxide films, *CRYSTALLINITY, *DEPTH profiling, *METAL coating, *DYE-sensitized solar cells, *MAGNETRON sputtering
Abstract

Analytical routines for a comprehensive in-depth morphological, structural, and chemical characterization of functionalized TiO2 films by using different state-of-the-art analytical techniques are presented and discussed with the main objective to identify potential reference TiO2 coating parameters able to be certified at a later stage. TiO2 films fabricated by two different synthetic procedures as representative for two main large-scale applications were selected: (i) pulsed d.c. magnetron sputtering for photocatalytic applications and (ii) screen printing from preformed anatase nanoparticles. The screen-printed films were further loaded with a sensitizing dye for application as a dye-sensitized solar cell. Film properties such as microstructure and crystallographic texture of pulsed d.c. magnetron sputtering synthesized films were systematically studied by means of scanning nanobeam electron diffraction in a transmission electron microscope and the surface and inner morphology by scanning electron microscopy. The dye distribution over the depth of screen-printed TiO2 layers was analyzed before and after dye-loading by means of energy dispersive X-ray spectroscopy at scanning electron microscope, Auger electron spectroscopy and time-of-flight secondary ion mass spectrometry. The long-term goal of the present study is the improvement of quality of the TiO2 film parameters as measured by using different types of reference TiO2 coatings having specific parameters certified. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Published
2016
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