3D study of morphology and dynamics of zeolite nucleation

The principle aspects and constrains of the dynamics and kinetics of zeolite nucleation in hydrogel systems are analyzed on the basis of a model Na-rich aluminosilicate system. A detailed time-series EMT-type zeolite crystallization study in the model hydrogel system is performed in order to elucidate the topological and temporal aspects of zeolite nucleation. A comprehensive set of analytical tools and methods is employed to analyze the gel evolution complementing the primary methods of transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR) spectroscopy. TEM tomography reveals that the initial gel particles exhibit a core-shell structure. Zeolite nucleation is topologically limited to this shell structure and the kinetics of nucleation is controlled by the shell integrity. The induction period extends to the moment when the shell is consumed and the bulk solution can react with the core of the gel particles. These new findings, in particular the importance of gel particle shell in zeolite nucleation, can be used to control the growth process and properties of zeolites formed in hydrogels

Ceramiques tritigenes a base d'orthosilicate de lithium: preparation sol-gel, mobilite du lithium et relachement du tritium

SIGLEINIST T 74813 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

ÉVOLUTION SPATIOTEMPORELLE DES FORMATIONS VEGETALES DU PARC NATIONAL DE BELEZMA DE LA REGION EST DE L’ALGERIE

Au sud de la méditerranée et précisément en Algérie, l’évolution de la végétation est en régression, cela a induit une raréfaction des forêts climaciques. Dans la partie Nord-Est du pays se trouve le massif forestier du Belezma qui appartient au secteur du tell constantinois séparant les hautes plaines constantinoises des monts des Aurès. Ce massif qui est caractérisé au plan floristique par un paysage hétérogène, constitué de feuillus, de conifères sempervirents et d’espèces caducifoliées, n’a pas fait exception à l’état de régression écologique prédominant dans la région, dont les causes seraient le produit de plusieurs facteurs conjugués entre eux: la sécheresse, les incendies et le surpâturage.De ce fait, il est essentiel de disposer d’informations sur l’état de dégradation et de changement des surfaces forestières, afin d’adopter des mesures appropriées à la gestion de cet environnement naturel. On s’est alors proposé à identifier et à évaluer au moyen des nouvelles technologies (SIG et télédétection) la dégradation de l’aire protégée du « Parc National de Belezma ».Cette analyse diachronique pour la période allant de 1987 à 2014, a révélé que 52,4% de la surface du parc a subi des changements avec un taux annuel évalué à 2%. Ceci fait ressortir le caractère inquiétant de la situation et les menaces qui pèsent sur l’avenir de ces essences. La cédraie a régressé au profit d’une chênaie et les sites où dominait le matorral à chêne vert dense ont été remplacés soit par un matorral plus clair, soit par un matorral à genévrier de Phénicie. Ces changements seraient attribués au phénomène de dépérissement qui a touché particulièrement la cédraie et à la pression anthropique (incendies, surpâturage, coupes illicites…) exercée sur l’ensemble de la végétation

Template extraction from surface-functionalised zeolite β nanoparticles

International audienc

Investigation of the Crystallization Stages of LTA-Type Zeolite by Complementary Characterization Techniques

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Flavonol dye molecules in zeolite beta nanocrystals for biodiagnostic applications

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Site-Specific Anchoring of a Flavonol Dye into Zeolite β Nanoparticles

International audienceThe structural and electronic properties of the accessible CuI site of a faujasite-type zeolite have been studied, by use of large cluster models and a density functional theory-based methodology. We demonstrate that the local ideal C3 symmetry of the CuI site II is broken. The CuI cation is bonded to the zeolite framework by one bond of about 2.26 Å and two shorter ones of 2.07 Å. We demonstrate that only one cation position exists at this site. This result is also confirmed by a molecular electrostatic potential analysis. We show that local properties at site II, as well as the global properties of the solid (frontier orbitals), do not depend on the Al and cation distribution and only slightly on the cocation nature. Taking into account the present results and well-known experimental data, we propose that specific catalytic behaviors are correlated with local response properties, such as the local acid strength or, in other reactions, specific local architecture or confinement

Site-specific anchoring of a flavonol dye into zeolite beta nanoparticles

Microporous zeolite nanoparticles have been used as a host for the confinement of 3-hydroxyflavone (3-OHF), leading to stable fluorescent colloids that may constitute a first step in the development of future biomarkers. Prior to the dye inclusion, the host physicochemical properties (porosity and crystalline structure) have been extensively studied. In particular, conditions for obtaining a template-free host have been established. It has been shown that standard calcination procedures, required to reveal the micropores, cannot be straighforward applied since they leave a non-negligible concentration of template residues in the host. Afterward, structural and chemical characterization, as well as simulation of 3-OHF-loaded zeolite beta colloids enabled to determine the presence and location of [(3-OHF)Al] chelates in the zeolite micropores. Characterization of the dye loading by independent techniques involving elemental analysis, pore volume, and crystalline structure investigations highlighted the determinant impact of prior calcination treatments and the presence in the zeolite micropores of trapped solvent molecules simultaneously with the dye

From basic research to industrial applications

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