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Seminars of the Research Lines
Biomaterials and Bioinspired Materials
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20 June 2012, 12:00 h. Sala de Seminarios, 182
FeRh CORE-SHELL NANOPARTICLES: SYNTHESIS DESIGN
Catherine Amiens
Laboratoire de Chimie de Coordination, UPR, France |
| Remarkable control over the size, shape, organization and surface chemistry of colloidal nanocrystals of different materials: semiconductors, metals or even bimetallic systems, is now reach. This allows already a fine control of their physical properties. However, in the case of bimetallic nanocrystals, the control over the chemical distribution is still a challenge. As their properties will greatly depend on the chemical distribution: statistical or ordered alloy, core-shell distribution of both elements, it needs to be adjusted as a function of the application envisaged (catalysis, microelectronics or for biological applications). A first typical example is the FePt system, which presents in the bulk state the highest magnetic anisotropy known only when it adopts the ordered tetragonalL1,0 phase. When this chemical order is reached, the material is the best suited for applications such as ultrahigh density magnetic data storage. Unfortunately, this situation is never reached via solution phase synthesis. Another example is the coating of ferromagnetic seeds by noble metals in a core-shell arrangement to afford air protection, biocompatibility and allow for further functionalization of the nanoparticles. Here again, no straightforward route is available. It is thus of crucial importance to develop new routes for the control of the chemical distribution inside bimetallic nanoparticles.
This report will present our strategy for the synthesis of core-shell bimetallic nanocrystals based on a kinetic control of the chemical distribution. Finally the effect of surface chemistry on segregation patterns will be discussed.
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07 May 2012, 15:00 h. Salón de Actos
WATERBORNE CARBON FOR ENERGY STORAGE
Maria-Magdalena Titirici
Max-Planck Institute of Colloids and Interfaces, Potsdam, Germany |
| The production of sustainable functional nanostructured materials starting from, cheap natural precursors using environmentally friendly processes is one of the most attractive subjects in material science today.
One route towards such materials is provided by a technique called hydrothermal carbonization. The practical approach is very simple and consists in placing a biomass or biomass derivative inside an autoclave, in water, followed by hydrothermal treatment overnight at 160-200°C. Since the production of carbon materials in general implies harsher and multi-step methodologies, this process has clear advantages, being greener, economical, mild and fast.
Here, we wish to present our latest results on the production and characterization of nanostructured hydrothermal carbon and carbon composites and their use in energy storage, mainly as electrodes in Li Ion Batteries and Supercapacitors.
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29 February 2012, 12:00 h. Sala de Seminarios, 182
Influence of real effects on magnetic response of iron oxide nanocrystals
Jana Poltierova Vejpravova
Institute of Physics AS CR Magnetism of Nanosystems Group Czech Republic |
| Recently, iron oxide-based nanostructures attracted enormous attention due to their significant application potential in various fields like biomedicine, catalysis, magnetic separation and recording, spintronics etc. Except the well-known magnetite phase (Fe2+/Fe3+ spinel) and thermodynamically stable iron tri-oxide variants: the maghemite (γ) and the hematite (α), respectively, two metastabile polymorphs (ε and β) can be stabilized in form of nanocrystals. In spite of the fact that magnetic properties of the iron oxide nanoparticles are principally determined by their phase composition, the key magnetic characteristics are mostly driven by formation of the single-domain state. The talk aims to summarize on basic concept of superparamagnetism and discuss how to treat the so-called real effects, which can be observed in majority of the samples, recognized as 1. particle size distribution, 2. surface spin canting and 3. inter-particle interactions. The following experimental techniques will be also introduced: 1. advanced profile analysis of the diffraction data using Rietveld and Debye approach, 2. analysis of magnetization considering size distribution and inter-particle interaction, 3. frequency-dependent a.c. susceptibility, and 4. in field Mössbauer spectroscopy. |
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