Synthesis of iron-rich tri-octahedral clay minerals: A review

International audienceExamples in materials science and in geology show an interest for iron-rich tri-octahedral clay mineral synthesis in large amounts and with well-defined char- acteristics. This review summarizes previously reported methods and conditions for iron-rich tri-octahedral clay mineral synthesis. Two approaches of hydrothermal synthesis have been applied: using gel or solid precursors. The most common synthesis approach is the hydrothermal synthesis using gel precursor. The synthesis of 1:1 type clay minerals were performed in reducing conditions in neutral or alkaline pH at various temperature and time ranges. The experimental conditions for 2:1 type clay mineral synthesis were in most cases similar to 1:1 type clay minerals, with in addition acidic pH and oxidizing conditions. The most commonly used methods for identifying and characterizing these minerals are X-ray diffraction, infra-red and Mössbauer spectroscopies as well as transmission electron microscopy. The thermodynamic stability of synthesized phases, as well as the reason for elements adopting a definite configuration and distribution in solid phase remain open questions

Electron transfer at the mineral/water interface: Selenium reduction by ferrous iron sorbed on clay

International audienceThe mobility and availability of the toxic metalloid selenium in the environment is largely controlled by sorption and redox reactions, which may proceed at temporal scales similar to that of subsurface water movement under saturated or unsaturated conditions. Since such waters are often anaerobic and rich in Fe2+, we investigated the long-term (≤ 1 month) kinetics of selenite (Se(IV)O3 -) sorption to montmorillonite in the presence of Fe2+ under anoxic conditions. A synthetic montmorillonite was used to eliminate the influence of structural Fe. In the absence of aqueous Fe2+, selenite was sorbed as outer-sphere sorption complex, covering only part of the positive edge sites, as verified by a structure-based MUSIC model and Se K-edge XAS (X-ray absorption spectroscopy). When selenite was added to montmorillonite previously equilibrated with Fe2+ solution however, slow reduction of Se and formation of a solid phase was observed with Se K-edge XANES (x-ray absorption near-edge spectroscopy) and EXAFS (extended x-ray absorption finestructure) spectroscopy. Iterative transformation factor analysis of XANES and EXAFS spectra suggested that only one Se reaction product formed, which was identified as nano-particulate Se(0). Even after one month, only 75% of the initially sorbed Se(IV) was reduced to this solid species. Mössbauer spectrometry revealed that before and after addition and reduction of Se, 5% of total sorbed Fe occurred as Fe(III) species on edge sites of montmorillonite (≈ 2 mmol kg-1). The only change observed after addition of Se was the formation of a new Fe(II) species (15%) attributed to the formation of an outer-sphere Fe(II)-Se sorption complex. The combined Mössbauer and XAS results hence clearly suggest that the Se and Fe redox reactions are not directly coupled. Based on the results of a companion paper, we hypothesize that the electrons produced in the absence of Se by oxidation of sorbed Fe(II) are stored, for example by formation of surface H2 species, and are then 3 available for the later Se(IV) reduction. The slow reaction rate indicates a diffusion controlled process. Homogeneous precipitation of an iron selenite was thermodynamically predicted and experimentally observed only in the absence of clay. Interestingly, half of Fe was oxidized in this precipitate (Mössbauer). Since DFT calculations predicted the oxidation of Fe at the water-FeSe solid interface only and not in the bulk phase, the average particle size of this precipitate does not exceed 2 nm. A comparison with the Mössbauer and XAS spectra of the clay samples demonstrates that such homogenous precipitation can be excluded as a mechanism for the observed slow Se reduction, emphasizing the role of abiotic, heterogeneous precipitation and reduction for the removal of Se from subsurface waters

Elaboration and Characterization of Recycled PP/Clay Nanocomposites

In this paper, the elaboration and characterization of recycled polypropylene/Tunisian clay nanocomposites has been investigated. When recycled, polypropylene polymer is degraded and has poorer mechanical and rheological properties. To overcome this problem, we proposed to incorporate Tunisian clay nanoparticles in recycled polypropylene (rPP) matrix. The incorporation of Tunisian clay was performed in molten state using maleic anhydride grafted polypropylene (PP-g-MA) as compatibilizer. The dispersion of clay in rPP polymer was evaluated by scanning electron microscopy and Fourier transformed infrared spectroscopy. Thus, Tunisian clay was more dispersed in nanocomposites with the increase of Tunisian clay loading. In dead, the incorporation of silicate layers gave rise to a considerable increase of the static viscosity demonstrating the reinforcing effect of Tunisian clay nanofillers on rPP matrix. However, the increasing trend of morphological and rheological properties is lower when the clay content exceeds 5%

New Materials and Technologies for Wastewater Treatment

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Synthèse et caractérisation de phyllosilicates 2:1 de type saponite et d'organophyllosilicates 2:1

Ce travail est consacré à la synthèse de phyllosilicates 2:1 de type saponite en milieu fluoré par voie hydrothermale et d'organophyllosilicates 2:1 par voie douce. Les différents paramètres gérant l'intégration de l'aluminium dans les couches tétraédriques du feuillet font l'objet d'une étude détaillée. En milieu basique, la saponite est obtenue dans une large gamme de taux de substitution tétraédrique. En milieu acide, ce taux est relativement faible. Un mécanisme de formation du feuillet est proposé. Un hydroxyde double lamellaire en milieu basique et un acide polysilicique en milieu acide sont à l'origine de la formation d'un phyllosilicate. Des matériaux hybrides lamellaires de divers types sont également synthétisés : un organo-aluminosilicate lamellaire différent d'un phyllosilicate, un organo-magnésoaluminosilicate apparenté à un phyllosilicate 2:1. Un mécanisme de formation du feuillet est aussi proposé. Ces matériaux se sont révélés intéressants dans la rétention de cations de métaux lourds.The present work deals with the hydrothermal synthesis of 2:1 phyllosilicate with a saponite type-like structure in fluoride medium and the soft and direct synthesis of 2:1 organophyllosilicates. The effects of the different parameters controlling the presence of aluminum in the tetrahedral sheet were studied. Saponite was only obtained for a low substitution rate of aluminum in fluoride and acidic medium, whereas high substitution rate in basic medium has been provided a saponite-like structure. A proposition of a formation mechanism is given. In basic medium, the 2:1 phyllosilicate structure is induced by the hydrotalcite formation and in acidic medium by the polysilicic acid formation.Different kind of hybrid lamellar materials were also prepared : a lamellar organoaluminosilicate having no phyllosilicate structure, a lamellar organomagnesoaluminosilicate having, as inorganic parent, a 2:1 phyllosilicate structure. A formation mechanism was proposed. These materials are very interesting in the chelating of heavy metal cations.MULHOUSE-SCD Sciences (682242102) / SudocSudocFranceF

Insights on the influence of the precursors on the sol–gel synthesis of hybrid organic–inorganic saponite-like materials

International audienceLamellar organic–inorganic hybrid materials, especially talc- and saponite-like structures, have been broadly investigated over the past decades because of the combination of the thermal and mechanical properties of the inorganic part with the possibility to finely tune hydrophilic–hydrophobic balance, ion exchange capacity, and properties through the choice of the silicon source. These compounds are generally produced by coprecipitation or hydrothermal synthesis methods, allowing the formation of well-crystallized particles but it is time and energy consuming. Recently, hybrid organic–inorganic lamellar materials have been synthesized using sol–gel method, which is attractive as it is a one-step method performed under mild conditions, with low energy consumption and short formation times. The originality of this research stands in the study of the influence of the reactants on the formation of saponite-like hybrids and especially on the role of the aluminum source in the sol–gel synthesis of hybrid organic–inorganic lamellar materials. The obtained materials have been characterized by X-ray diffraction, Fourier transform infrared, and solid-state nuclear magnetic resonance spectroscopies and thermogravimetric analysis, and it was shown that hydrotalcite-like compounds can be obtained beside saponite-like compounds depending on the aluminum source.De nombreuses études ont été menées récemment sur les matériaux hybrides organiques–inorganiques de structure lamellaire, de types talc et saponite, notamment, dans le contexte de la combinaison des propriétés thermiques et mécaniques de la fraction inorganique, d'une part, avec la possibilité d'adapter la balance hydrophile/hydrophobe, la capacité d’échange cationique ainsi que les propriétés associées au choix de la source de silicium, d'autre part. Ces composés sont généralement synthétisés par co-précipitation ou par synthèse hydrothermale, ce qui permet la formation de particules bien cristallisées, mais demande beaucoup de temps et d’énergie. Plus récemment, ces matériaux ont été synthétisés par la méthode sol–gel, qui permet d'obtenir des matériaux de grande pureté en des temps très courts avec une faible nécessité énergétique. L'originalité de ce travail repose sur l’étude de l'influence des réactifs sur la formation de matériaux hybrides organiques–inorganique de structure de type saponite, notamment le rôle de la source d'aluminium dans la synthèse par voie sol–gel de matériaux hybrides organiques–inorganiques de structure lamellaire. Les matériaux synthétisés ont été analysés par DRX, IR-TF, RMN du solide et ATG, ce qui a permis de découvrir que des composés similaires à des hydrotalcites peuvent être obtenus selon la source d'aluminium employée

Elaboration d'hybrides organiques-inorganiques de structure de type phyllosilicate 2:1 et leurs applications

Cette thèse décrit la synthèse et l'étude d'hybrides organique-inorganiques de type talc. La synthèse dont est inspiré ce travail a été décrite pour la première fois par Fukushima & Tani en 1995. Celle-ci est particulièrement attractive du fait des conditions de synthèse douce. Ainsi ce travail décrit la recherche des conditions optimales de synthèse sur l'exemple su N-phénylaminométhyl - TLH. Par la suite, nous décrivons la synthèse d'une large série d'hybrides organiques-inorganiques de structure de type talc. De nombreuses techniques de caractérisation sont ensuite employées pour décrire précisément la structure de ces matériaux. Enfin, le dernier chapitre illustre l'application comme renfort de ces matériaux hybrides.This thesis describes the synthesis and study of organic-inorganic talc like hybrid. The synthesis is inspired frome the work of Fukushima & Tani in 1995. This synthesis is particularly attractive because of soft conditions. Thus this work describes the search for optimum conditions of synthesis on the example N- phenylaminomethyl - TLH. Subsequently, we describe the synthesis of a wide range of organic-inorganic talc like hybrid. Many characterization techniques are then used to precisely describe the structure of these materials. The last chapter illustrates the application as a reinforcement of these hybrid materials.MULHOUSE-SCD Sciences (682242102) / SudocSudocFranceF

Diatomaceous earth, an attractive materials towards sustainable chemistry

Congrès du : 06.12.2007 au 07.12.200