Diane Rébiscoul

This study introduces a novel, safer, and more efficient method for the preparation of mixed oxide powders (ThO2/CeO2 as surrogates for UO2/PuO2) homogeneously distributed at a nanoscale using aqueous multicolloidal sols. The latter were obtained either by mixing salts in solution or by mixing monoelemental sols. Combining Small and Wide Angles X-ray Scattering with Pair Distribution Function techniques, size, shape and the interactions of the various colloids were studied as a function of pH and amount of complexing agent in solution. The data obtained allowed for the selection of sols that remained stable for several months. The latter were then freeze-dried to induce assembly of the colloids forming ordered structures (e.g., body-centered cubic or lamellar phases). Depending on the organization of the resulting colloid stacking, driven by their surface charge, Scanning Electron Miscroscopy and High-Resolution Transmission Electron Microscopy highlight that the materials obtained after thermal treatment exhibit an assembly of monodisperse ThO2 and CeO2 nanocrystallites of few nanometers with a homogeneous distribution at the microscale and nanoscale depending on the experimental conditions. This method addresses key challenges of nuclear Mixed Oxide nuclear fuel fabrication, such as radioactive dust or heterogeneous actinide distribution, thus opening promising prospects for the development of advanced Gen-IV nuclear fuels.

This work reports the first upcycling valorization of rice husk ash industrial waste into well-ordered and antiseptic hybrid mesostructured silica with potential for human health protection.

Probing electrolytes behavior at the atomic level provides valuable insights into understanding the reactive transport of electrolyte solutions in nanoconfinement and help explaining and predicting the macroscopic properties of industrial or natural nanoporous materials. In this study, we focused on the behavior of water and ions in 2.6 nm silica nanocylinders filled with electrolyte solutions, XCl at 1M with X = Li, Na and Cs, monovalent cations presenting various kosmotropic/chaotropic properties. Using a combination of experiments and theoretical modeling, we analyzed the water dynamics based on three primary effects: the confinement, the electrolyte, and the interfacial ions-porous material surface interaction. Comparing the water dynamics obtained with divalent cations previously studied by Baum et al., we highlight that monovalent cations present weaker interactions with silica surfaces than divalent cations. This significantly impacts the water dynamics in addition to the confinement and electrolyte effects. This study pinpoints the importance of ions behavior within the interfacial layer and its impact on water transport in nanoconfinement.

The controlled synthesis of metal organic nanosheets (MONs) still remains a challenge for scientists and is of primary interest in many research areas. In this study, we have developed a simple and reproducible one-pot synthesis method leading to tunable cobalt-based hybrid materials consisting of nanosheets with a well-defined morphology. The synthesis is performed via a solvothermal process assisted by primary amines acting as surfactants. The obtained materials are composed of ultrathin nanosheets with a rectangular morphology (width of about 50 nm and length greater than 100 nm). The different analysis techniques used show that the nanosheets are constituted by the alternation, in their width, of inorganic fringes (cobalt hydroxide) and organic ones (dicarboxylic acid) and that amine molecules stabilize their surface. 3D organisation of the nanosheets can be achieved at a synthesis temperature above 190 °C due to the interaction of alkyl chains of the stabilising amines. A multiparametric study based on SAXS experiments and TEM and PXRD analyses has highlighted the control of structural parameters by variations of some synthesis conditions. The inter-fringe distances are tunable from 1.0 nm to 1.5 nm through the length of the dicarboxylic linker and the distances between nanosheets can be modulated by the length of the alkyl chain of the primary amines. This efficient one-pot process seems to be very promising for the synthesis of tunable multiscale nanostructured MONs and can be implemented in many research areas, opening the way for various applications.

Plasma polymerized (PP) thin films deposited in a soft or intermediate plasma discharge from hexamethyldisiloxane (HMDSO) were developed as sensors for the detection of volatile organic compound (VOC) vapors. Energy dispersive X-ray spectroscopy (EDX) and X-ray reflectometry (XRR) were performed to determine the organosilicon films’ elemental composition and density. Spectroscopic ellipsometry measurements were carried out to determine the refractive index of the films. Quartz crystal microbalance (QCM) and ellipsometry coupled to vapor sorption were used to investigate the sorption mechanism of several VOC vapors into the films as a function of the plasma deposition conditions. The density and the refractive index of the PP-HMDSO films increased with the plasma energy due to a different chemical composition and different proportion of free volumes in the material network. The PP-HMDSO films showed different affinities towards the VOC vapors depending on the plasma discharge energy. The films elaborated in the lowest plasma energy revealed a good sensitivity towards the VOCs, especially toluene (one of the BTEX vapors), compared to the other films deposited under higher plasma energy. In addition, the selectivity between toluene and other non-BTEX VOCs such as heptane and ethanol decreased to become zero while increasing the plasma energy.

Plasma polymerized (PP) thin films deposited in a soft or intermediate plasma discharge from hexamethyldisiloxane (HMDSO) were developed as sensors for the detection of volatile organic compounds (VOCs) vapors. Energy dispersive X-ray spectroscopy (EDX) and X-ray reflectometry (XRR) were performed to determine the organosilicon films elemental composition and density. Spectroscopic ellipsometry measurements were carried out to determine the refractive index of the films. Quartz crystal microbalance (QCM) and ellipsometry coupled to vapor sorption were used to investigate the sorption mechanism of several VOCs vapors into the films as a function of the plasma deposition conditions. The density and the refractive index of the PP-HMDSO films increased with the plasma energy due to a different chemical composition and different proportion of free volumes in the material network. The PP-HMDSO films showed different affinities towards the VOCs vapors depending on the plasma discharge energy. The films elaborated in the lowest plasma energy revealed a good sensitivity towards the VOCs especially toluene (one of the BTEX vapors) compared to the other films deposited under higher plasma energy. In addition, the selectivity between toluene and other non-BTEX VOCs such as heptane and ethanol decreased to become zero while increasing the plasma energy.