ED Sciences Chimiques
Magnetochiral nanocomposites: from natural to synthetic strategies towards the observation of the magnetochiral dichroism phenomenon
by Matheus MENDES (Institut de Chimie & de Biologie des Membranes & des Nano-objets)
The defense will take place at 14h00 - B6 Amphiteather Institut Européen de Chimie et de Biologie (IECB) - 2 Rue Robert Escarpit 33607 PESSAC FRANCE
in front of the jury composed of
- Emilie POUGET - Directrice de recherche - Université de Bordeaux - Directeur de these
- Wiktor LEWANDOWSKI - Professeur - Faculty of Chemistry, University of Warsaw - Rapporteur
- Cornelia MEINERT - Directrice de recherche - Institut de Chimie de Nice (ICN/CNRS UMR7272) - Examinateur
- Elizabeth HILARD - Directrice de recherche - ICMCB – UMR5026 - Examinateur
- Mathieu GONIDEC - Chargé de recherche - ICMCB – UMR5026 - Examinateur
- Miguel COMESANA-HERMO - Chargé de recherche - ITODYS - Université Paris Cité - Rapporteur
In this project, magnetochiral nanocomposites will be studied to detect their response to circular dichroism (CD), magnetic circular dichroism (MCD) and potentially magnetochiral dichroism (MChD). In simplified words, MChD is a cross effect between natural circular dichroism (NCD) observed in chiral materials, and magnetic circular dichroism (MCD) observed in simple achiral magnetic materials. MChD is typically studied in the UV-visible region on single crystals, where the magnetic and chiral properties are situated on the same site, typically metal-based transitions in chiral coordination complexes, of which several examples are known in literature. On the other hand, MChD on the nanoscale has been rarely studied, even if self-assembly of chiral objects tends to enhance the chiral response, compared to that of discrete molecules. Therefore, this Ph.D. project aims to develop strategies to synthesize magnetochiral- responsive synthetic systems and explore alternative natural materials as models to compare with those synthetic materials. Four strategies are envisaged, two of them based on synthetic nanostructures and the others on natural-based materials. The first approach (I) counts on using a helical silica nanotemplate that is intrinsically chiral by its morphology to act as a chiral template for the growth of magnetic NPs, as we expect that the helicoidal-shaped organization of the magnetic NPs can give origin to CD signals. The second approach (II) counts on the synthesis of Cobalt (II) and Nickel (II) single magnetic NPs by classical coprecipitation technique in the presence of chiral ligands, we expect that the functionalization of the magnetic NPs with the chiral ligand can induce chirality to the core of the nanoparticle by creating some kind of distortion/asymmetry on the vicinity of the crystalline structure. Among the chosen natural materials, the third approach (III) concerns the use of possible natural magneto chiral responsive material such as magnetotactic bacteria (BMT) since that is a living organism that intrinsically possesses chirality and because of its ability to synthesize magnetic NPs (Magnetite – Fe3O4) by biomineralization. Finally, the forth approach (IV) concerns the use of chiral functionalized clay minerals with amino acids as nanotemplates for the growing of magnetic NPs, originating an overall magnetochiral interlayered nanostructure.
Synthesis and densification of zirconia at low temperature : A synergy between chemistry and sintering
by Yoan DENIS (ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux)
The defense will take place at 14h00 - Amphithéâtre de l'ICMCB 87 Avenue du Dr Albert Schweitzer, ICMCB, 33600, Pessac, France
in front of the jury composed of
- Catherine ELISSALDE - Directrice de recherche - ICMCB - Directeur de these
- Anne LERICHE - Professeure des universités - Université Polytechnique des Hauts-de-France - CERAMATHS - Rapporteur
- Capucine SASSOYE - Maîtresse de conférences - Sorbonne Université - LCMCP - Rapporteur
- César STEIL - Ingénieur de recherche - LEPMI - Examinateur
- Cyril AYMONIER - Directeur de recherche - ICMCB - Examinateur
- Gilles PHILIPPOT - Maître de conférences - Université de Bordeaux - ICMCB - CoDirecteur de these
In the light of today's economic and ecological challenges, reducing the energy cost of ceramic forming processes is a major challenge for society. In this context, reducing sintering temperatures is a major challenge. In addition to environmental considerations, it also addresses the need to optimize the properties of (multi)materials by controlling their microstructure, and to develop ceramic/metal or ceramic/polymer composites or assemblies. In this context, yttria-stabilized zirconia is a material of major interest. Its remarkable properties (mechanical, ionic conduction, optical) have resulted in numerous applications in a wide range of fields (biomedical, aeronautics, energy, etc.). Conventionally, yttria-stabilized zirconia is sintered at high temperatures (~1400°C), but the development of non-conventional sintering processes has enabled these temperatures to be significantly reduced. It is now possible to densify yttria-stabilized zirconia by Spark Plasma Sintering (SPS) at temperatures of ~1100°C. To further lower sintering temperatures, solvent-assisted processes have been developed over the past fifteen years. Hydro/solvothermal sintering and the Cold Sintering Process (CSP) enable to densify many materials at temperatures below 300°C. Optimal densification of zirconia, however, remains unattainable using these processes alone, with an average relative density of ceramics reported in the literature around 65%. The aim of this thesis is to optimize the low-temperature densification of zirconia and yttria-stabilized zirconia, mainly by hydro/solvothermal sintering and/or CSP. Two strategies focusing on chemistry and powder reactivity have been developed. The first is based on the use of yttria-stabilized zirconia nanoparticles synthesized in supercriticals fluids medias, where the sizes (<10 nm) and crystallinity of the nanoparticles obtained are assumed to enhance reactivity with regard to sintering. The resulting powders were tested using two unconventional processes: CSP and SPS. The second strategy is based on the use of reactive precursors such as yttrium and zirconium hydroxides or oxo-hydroxides, which were sintered by hydro/solvothermal sintering and CSP. Promising results have been obtained, notably via CSP, with relative densities of 83% achieved for ceramics with a monoclinic structure at sintering temperatures as low as 500°C. With value of 6.5 GPa, Vickers hardness appears promising for these relatively porous monoclinic zirconia ceramics, obtained at low temperatures. Controlling the nanostructure at low temperatures via CSP-specific dissolution/precipitation mechanisms is crucial to the optimization of the mechanical properties. Yttria-stabilized zirconia ceramics with 95 wt% of tetragonal phase were subsequently obtained by reactive sintering from yttrium-containing hydroxide precursors. However, these CSP results revealed a compromise between densification and stabilization of the tetragonal phase content for yttria-stabilized zirconia. The original strategy based on reactive sintering led to an in-depth study to identify the levers influencing sintering (pressure and temperature conditions, nature of the solvent), and to understand the mechanisms underlying densification, notably with the contribution of in situ impedance spectroscopy. In conclusion, this thesis demonstrates the full potential of these solvent-assisted sintering processes for low-temperature zirconia densification.
ED Sciences et environnements
Platinum contamination trajectory in french hydrosystems since the beginning of the 20th century: a multi-scale spatio-temporal approach
by Maxime CHASTANET (Environnements et Paléoenvironnements Océaniques et Continentaux)
The defense will take place at 14h00 - Amphithéâtre B18N Allée Geoffroy Saint Hilaire Bâtiment B18N 33615, Pessac
in front of the jury composed of
- Jörg SCHÄFER - Professeur - Université de Bordeaux - Directeur de these
- Sebastien RAUCH - Full professor - Chalmers University of Technology - Rapporteur
- Jérôme VIERS - Professeur - Université Toulouse III - Paul Sabatier - Rapporteur
- Charlotte CATROUILLET - Maîtresse de conférences - Institut de Physique du Globe de Paris - Examinateur
- Liliane JEAN-SORO - Chargée de recherche - Université Gustave Eiffel - Examinateur
- Frédérique EYROLLE - Senior Researcher - Autorité de Sûreté Nucléaire et de Radioprotection - Examinateur
Platinum (Pt) is a critical element for technologies due to its scarcity and recent uses. These new uses, particularly in catalytic converters for combustion vehicles and in pharmaceutical compounds used in chemotherapy, led to an increase in Pt releases into the environment, making it an emerging contaminant. However, the temporal evolution (or trajectory) of Pt concentrations in river environments remains poorly understood, requiring multi-scale approaches, both spatial and temporal. Sediment cores collected downstream of major French rivers have been used to analyze Pt trajectories since the 20th century and define baseline levels in the sediments of the Garonne, Loire and Rhône Rivers, ranging from 0.6 to 1.6 µg kg-1. An historical Pt contamination was also revealed in the Seine River (> 10 µg kg-1), linked to industrial activities during the 20th century. Since the 2000s, emerging Pt signals have been observed in the Loire and Rhône Rivers while the legacy of historical contamination tends to mask this emergence in the Seine River. Estimated fluxes show that the Rhône River exports 21 kg yr-1 of particulate Pt, compared with ~2 kg yr-1 for the Loire and Seine Rivers. Sediment cores are therefore essential tools for characterizing the Pt temporal evolution in contrasting watersheds. For the Garonne River, it was not possible to find a site where a sediment core covering the last century could be collected. The analysis of its trajectory was made possible by coupling old deposits (<1950) from a sediment core and SPM taken from a monitoring network (~30 years) and selected to represent flood conditions. This approach allowed to (i) define a baseline for quantifying natural annual fluxes and (ii) identify anomalies and estimate anthropogenic fluxes that can be explained for most events by emissions from road traffic and/or cancer treatments. Other anomalies could not be explained, suggesting additional sources and/or processes to be investigated. In order to better identify the Pt sources and transfer processes, one strategy was to change scale by focusing on a small urban river draining the Bordeaux Metropole area (Jalle de Blanquefort), which had been monitored monthly for a year and sampled at high frequency during a storm event. This study demonstrates the role of meteorological conditions: under normal conditions, Pt is found mainly in dissolved form, supported by medical Pt discharges from WWTP. Under rainy conditions, Pt is mainly in particulate form, resulting from road runoff. This type of intense event (~4h) can contribute up to a third of the annual flux of particulate Pt, demonstrating the importance of monitoring first-flush waters. Based on general medical practices in oncology and the spatialization of cancer incidence and treatment data, a conceptual model of medical Pt emissions (Ptmed) was developed. The emissions distribution could be influenced not only by population density, but also by an age group (> 60 years old), particularly on the coast and in major cities. It is estimated that 67 % of the Ptmed national flux is emitted in the main hydrosystems, into which are discharged between 2 and 46 kg year-1 of Ptmed. As a first estimate, French hydrosystems may have exported 223 kg of Ptmed to coastal environments in 2023. This model will require adjustments to reduce uncertainties, spatialization of incidence data, WWTP treatment efficacies, and Ptmed reactivity along the land-sea continuum.