Water-mediated structuring of bone apatite

International audienceIt is well known that organic molecules from the vertebrate extracellular matrix of calcifying tissues are essential in structuring the apatite mineral. Here, we show that water also plays a structuring role. By using solid-state nuclear magnetic resonance, wide-angle X-ray scattering and cryogenic transmission electron microscopy to characterize the structure and organization of crystalline and biomimetic apatite nanoparticles as well as intact bone samples, we demonstrate that water orients apatite crystals through an amorphous calcium phosphate-like layer that coats the crystalline core of bone apatite. This disordered layer is reminiscent of those found around the crystalline core of calcified biominerals in various natural composite materials in vivo. This work provides an extended local model of bone biomineralization

Direct Synthesis of TiO 2

Molybdenum disulfide nanoparticles supported on titania were synthesized from aqueous solutions containing Ti and Mo precursor salts by an in situ redox reaction. The synthesis involves a redox process between Ti3+ and MoS42−, which proceeds readily under mild conditions in aqueous solution. Catalysts were made in a single step, yielding amorphous catalysts with high Mo content, or in two steps to obtain MoS2 supported on well-defined TiO2 with lower Mo content. Catalysts obtained by single-step reductive coprecipitation were highly active in the hydrodesulfurization of dibenzothiophene, exceeding the activity of an alumina-supported Co–Mo reference. In contrast to alumina-supported catalysts, the addition of Co as promoter did not enhance the catalytic activity of MoS2/TiO2 to the same extent (+30 %) as for alumina-supported Co–Mo catalysts. Instead, a change in selectivity towards hydrogenolysis products at the expense of hydrogenation products was observed. It is suggested that Ti may act as a promoter for MoS2 in hydrogenation reactions

From Living Light to Living Materials

International audienceDiatom cells are enclosed within porous silica walls that exhibit a wide variety of forms. Some of them exhibit photonic crystals properties arising from a periodic distribution of pores along these walls. Diatoms then play with solar light to protect the cell and improve its photosynthetic properties. These micro-algae also suggest that life is possible inside a glass box leading to the bio-inspired synthesis of living materials via the so-called sol-gel process

Synthèse et caractérisation de nanoparticules d'oxydes sous-stoechiométriques (vers des applications dans le domaine de l'énergie)

L objectif de ce travail a été de proposer de nouveaux matériaux à base d oxydes réduits de vanadium, molybdène et tungstène, à l échelle nanométrique, pour des propriétés liées au stockage de l énergie. Dans cette optique, 6 systèmes différents ont été élaborés : un système de nanoparticules de MoO2 de taille variant entre 2 et 100 nm ; des assemblages hiérarchiques cœur-coquille constitués de billes carbonées enrobées de nanoparticules de MoO2; des nanoparticules de haggite et de duttonite (deux oxyhydroxydes de vanadium réduits) et enfin des nanoparticules de deux bronzes différents de tungstène basés sur deux structures hexagonales différentes, l une découverte au cours de la thèse. Dans tous les cas, l innovation provient de la réduction des tailles de nanoparticules (jusqu à un ordre de grandeur inférieur aux tailles répertoriées), de la texturation d assemblages multi-échelle originaux, ou encore de la structure cristalline, la morphologie et la nature des faces exposées par les particules. Les propriétés physico-chimiques de tous ces systèmes ont été caractérisées (structure cristalline, morphologie, surface spécifique, propriétés optiques, électriques et électrochimiques). Les mécanismes de formation ont également été étudiés. Les propriétés électrochimiques mesurées ont enfin été discutées au regard des caractéristiques comparées des matériaux : taille des particules, texturation de la matière active (cas des C@MoO2), ouverture des sites d insertion sur l extérieur des particules (cas des bronzes). Ces travaux ont permis d évaluer le potentiel des matériaux en batteries au lithium ou au sodium et a ouvert des perspectives intéressantes sur des applications telles que la catalyse (MoO2 de 9 nm) ou encore les électrochromes (W-346).The aim of this work was to propose new nanomaterials based on reduced vanadium, molybdenum or tungsten oxides, with interesting properties for energy storage. In that purpose, 6 different systems were elaborated: MoO2 nanoparticles with diameters ranging from 2 to 100 nm; hierarchical core-shell assemblies based on carbonaceous cores decorated with MoO2 nanoparticles; haggite and duttonite (two vanadium oxyhydroxides) nanoparticles; and finally nanoparticles of two different tungsten bronzes based on two hexagonal structures of WO3, one having been discovered during this work. Each time, the innovation comes from the particles size reduction (up to 10 times smaller), from the texturation of original multi-scale assemblies, or even from the crystal structure, morphology and nature of the exposed faces. The physical and chemical properties of these systems were characterized (cristal structure, morphology, specific surface, optical, electrical and electrochemical properties). Synthesis mechanisms were also investigated. Finally, the differences of electrochemical properties were discussed considering materials characteristics: size of the particles, texturation of active materials, and accessibility of the insertion sites. This work enabled us to evaluate the materials potentialities towards lithium or sodium batteries, and opened new prospects for applications such as catalysis or electrochromic devices.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Structural and morphological Control of TiO2 nanoparticles by selective adsorption of organic molecules

Semiconducting nanocrystals with tailored shapes have been widely investigated in the past decades because of their many shape-dependant properties. Anatase, a metastable phase of the titanium dioxyde (TiO2), is one of the most interesting material in many applications, such as photocatalysis, photovoltaics, photo/electrochromics or sensors. [1] In addition to an influence of the nanoparticles size, recent works on the anatase phase demonstrated the effect of the expressed surfaces nature on the nanoparticles photoreactivity. [2] Sol-gel method has been used to obtain a wide range of anatase nanoparticles sizes and morphologies by the control of concentrations, ions in solution, solution acidity and aging parameters. [3] In order to avoid the brookite phase often obtained with the anatase phase, microwave heating was efficiently used. Furthermore, conventional heating method has been compared with hydrothermal and microwave activated synthesis. The precise morphological control has been achieved by selective adsorption of organic molecules during synthesis: different shapes of anatase nanoparticles have been synthesized. [4,5]. The influences of synthesis parameters and the organic molecules nature on the nanoparticles structure and morphology have been analysed with various techniques, such as XRD and HRTEM

Photocatalytic efficiency in aqueous and gaseous phase of various TiO2 powders

SSCI-VIDE+CARE+CGU:FDAInternational audienceNon

Twinning Driven Growth of Manganese Oxide Hollow Cones through Self-Assembly of Nanorods in Water

International audienc