Sylvie Masse

Contribution of multi-nuclear solid state NMR to the characterization of the Thalassiosira pseudonana diatom cell wall

A major issue in the study of biosilicification processes is the harsh chemical conditions required for silica dissolution, which often lead to denaturation of the associated bio-organic matter. In order to demonstrate the potential of solid state NMR for investigating silicified materials of natural origin, this technique was applied to isotopically enriched Thalassiosira pseudonana diatom cells. 29Si, 1H,31P, 13C and 15N solid state NMR studies were performed on whole cells, SDS-extracted and H2O2-cleaned silica shells. Cross-polarization techniques were useful for identifying the presence of mobile and rigid molecules, allowing loosely bound and silica-entrapped species to be discriminated. Successive cleaning procedures efficiently eliminated weakly associated organic matter. The H2O2-cleaned silica shell still contained carbohydrates (mainly chitin) and proteins as well as lipids. This suggests that the role of lipids in diatom shell formation may have been underestimated so far, demonstrating the potential of solid state NMR for studying composite biomaterials.

A SPECTROSCOPIC NMR INVESTIGATION OF THE CALCIUM SILICATE HYDRATES PRESENT IN CEMENT AND CONCRETE

NMR spectroscopy is applied to study microstructure of calcium silicate hydrates present in cement and concrete. It is shown that 29Si NMR gives information on the siliceous skeleton of the hydrates. 1H NMR, using CRAMPS techniques, allows to discriminate between protons linked to silicon atoms or to calcium atoms. A first investigation of reference compounds indicates that 43Ca NMR will be powerful to determine calcium atom sites in the structure.

Modification of the Stöber Process by a Polyazamacrocycle Leading to Unusual Core−Shell Silica Nanoparticles

In the view of designing functional nanoparticles, the encapsulation of 1,4,7,10-tetraazacyclododecane (cyclen) within silica nanoparticles using the Stöber process was studied. In the presence of cyclen and tetraethoxysilane (TEOS), silica particles exhibiting an unusual core-shell structure were obtained. On then basis of TEM, DLS, and NMR data, we suggest that the particle core is constituted of hybrid primary nanoparticles resulting from cyclen-silica interactions, whereas the shell formation results from further condensation of unreacted silica precursors. Control experiments performed with the zinc-cyclen complex and ammonia addition suggest that cyclen-TEOS interactions arise from the activation of the silicon alkoxide hydrolysis with the polyazamacrocycle amine groups. These data are discussed in the context of silica biomineralization mechanisms, where polyamine/silica interactions have been shown to play a major role. Moreover, the possibility to control the size and the structure of these nanoparticles makes them promising materials for pharmaceutical applications.

Bacteria survival and growth in multi-layered silica thin films

A layer-by-layer approach was used to build up silica thin films (<500 nm) compatible with Escherichia coli bacteria immobilization and spatially confined growth.

Surface reactivity of hydroxyapatite nanocoatings deposited on iron oxide magnetic spheres toward toxic metals

HYPOTHESIS Hydroxyapatite and magnetite are two environmentally-friendly mineral phases that have fruitful properties for remediation process. The formation of magnetic core@sorbent shell nanostructures should provide efficient materials for toxic metal removal from aqueous media. However the nanoscale confinement of hydroxyapatite may influence its reactivity. EXPERIMENTS Fe3O4@Hydroxyapatite nanocomposites were prepared by surface-controlled precipitation of hydroxyapatite layers from 10 nm to 150 nm in thickness on iron oxide spheres. The surface reactivity of the core-shell particles toward selected inorganic ions of environmental relevance (Pb(II), Y(III), Eu(III), Sb(III)) was studied by batch sorption experiments, X-ray diffraction and electron microscopy. FINDINGS The reactivity of the hydroxyapatite coating varied from partial cation exchange to dissolution/transformation of the shell. The nature and extent of the reactions depended significantly on the hydroxyapatite layer structure but was not significantly influenced by the magnetic core. These novel nanocomposites should be useful for environmental applications.

Ultrasound-Assisted Synthesis of Mesoporous Zirconia-Hydroxyapatite Nanocomposites and Their Dual Surface Affinity for Cr3+/Cr2O72– Ions

Zirconia-hydroxyapatite nanocomposites were prepared by sol-gel deposition of zirconium oxide from a zirconium alkoxide in the presence of apatite colloidal suspension under ultrasonication. The material porosity evolves from mainly microporous zirconia to mesoporous hydroxyapatite, with decreasing surface area and increasing pore volume. XRD studies indicate that the apatite phase is well-preserved within the composite materials. The homogeneous dispersion of apatite colloids within the zirconia network was supported by TEM observations and nitrogen sorption measurements. (31)P solid-state NMR studies suggest that partial dissolution of apatite may have occurred during the preparation, leading to the adsorption of phosphate species on zirconia particles. This is confirmed by XRD studies of nanocomposites after thermal treatment that demonstrate the preferred formation of tetragonal over monoclinic ZrO(2) in the presence of hydroxyapatite. In order to investigate the surface properties of these novel materials, the adsorption of Pb(2+), Cr(3+), and Cr(2)O(7)(2-) was evaluated. Metal cations were preferentially adsorbed on apatite-rich composites, whereas Cr(2)O(7)(2-) shows a good affinity for the zirconia-rich phases. Zirconia-apatite materials showed the most promising performance in terms of recyclability. These nanocomposites that combine microporosity, mesoporosity and dual sorption properties for these species appear as interesting materials for metal ion remediation and may also find applications as biomaterials.

Evolution of C-rich SiOC ceramics

Abstract Carbon-rich Si–O–C polymer-derived ceramics (PDCs) were investigated by various spectroscopic techniques, in order to characterize the evolution of their predominantly amorphous microstructure upon thermal treatment up to 1450°C. Particular attention was addressed to modifications of the excess free carbon phase present in these materials. Surprisingly, the carbon clusters exhibited high stability above the pyrolysis temperature. Despite the high volume fraction of carbon, only a very limited carbothermal reduction process was detected. This study is divided into two parts: PartI deals with characterization tools that reveal a rather low lateral resolution and are hence termed here as integral spectroscopic techniques, i.e., solid-state NMR and Raman spectroscopy. In contrast, PartII illustrates the experimental results obtained from the very same materials characterized by spectroscopic and imaging techniques with high lateral resolution, i.e., electron energy-loss spectroscopy (EELS), high-resolution transmission electron microscopy (HRTEM), and energy-filtered TEM. In addition to materials characterization, emphasize of both papers is also to compare the information gained by either integral or local spectroscopy techniques and to highlight the strengths and weaknesses of either approach.

Design of gold nanoshells via a gelatin-mediated self-assembly of gold nanoparticles on silica cores

A gelatin-mediated self-assembly of gold nanoparticles on silica particles has been performed during gold ion reduction using ascorbic acid as reductant and PVP as stabilizer. Gold nanoshells with near infrared photothermal properties have been successfully designed.

Tricalcium Silicate Hydration at High Temperature. A 29Si and 1H NMR Investigation

A systematic study of pure tricalcium silicate (C3S) samples hydrated in hydrothermal conditions from room temperature to 160°C has been done, in order to follow the hydration kinetics and the evolution of the calcium silicate hydrates (C-S-H) structure. MAS and CPMAS 29Si NMR allowed to determine the silicate skeleton of the hydrates. It was shown that the increase of synthesis temperature and time of hydration lengthen the silicate chains of C-S-H, based on dimers linked together by bridging SiO4 tetrahedra, like in tobermorite structure. When silica fume is added to anhydrous C3S, C-S-H phases result from two complexe chemical reactions: C3S hydration and silica fume reaction with calcium ions, especially those coming from portlandite dissolution. Some careful CRAMPS experiments allowed us to distinguish the Ca-OH protons of C-S-H and those of portlandite and to follow the two reaction kinetics.

Growth of gold nanoparticles at gelatin-silica bio-interfaces

The growth of gold nanoparticles via chemical reduction of HAuCl4 dispersed in gelatin-silicate mixtures was studied. Gelatin leads to densely packed nanoparticles whereas open colloidal aggregates with tight boundaries are formed within silica. Within the bio-hybrid systems, gold species are located within the gelatin-silicate particles and/or within the gelatin phase, depending on the preparation conditions. These various localizations and their impact on the final nanoparticle structure are discussed considering attractive and repulsive electrostatic interactions existing between the three components. These data suggest that bio-hybrid systems are interesting and versatile interfaces to study crystallization processes in confined environments.