Layered double hydroxides: where should research stress on for massive scaling up?

International audienceFor more than half a century, layered double hydroxides (LDHs) have attracted great attention from the scientific community. These materials belong to a rare anionic clay group and have demonstrated amazing physicochemical properties, leading to disruptive, cost-effective and eco-friendly applications for health, environment and agriculture. However, LDHs are not widely used in daily items, nor are they massively applied in industry despite their very good potential for large-scale development. This study looks at the current shortcomings preventing the industrial implementation of LDH powders while evidencing and discussing the strategies to encourage research to bridge the gaps on this topic

Étude du mécanisme d'échange et de la structure des matériaux hydroxydes doubles lamellaires (HDL) par diffraction et diffusion des rayons X

La maîtrise des performances des matériaux HDL (Hydroxydes Doubles lamellaires) nécessite une compréhension de plus en plus fine de leur structure ainsi que des relations entre structure, morphologie et propriétés d'emploi. Des mesures en diffraction et diffusion des rayons X (rayonnement synchrotron) haute résolution enregistrées à grand Q permettent d'aborder de manière plus précise la description structurale et la microstructure de ces matériaux mal cristallisés notamment vial'analyse de la fonction de distribution de paires (PDF). D'autre part, des mesures réalisées in situ en solution par diffraction des rayons en dispersion d'énergie (EDXRD) ont permis de révéler la formation de composés HDL bi-intercalés porteurs de nombreuses potentialités dans le domaine des matériaux multifonctionnels. Des mesures EDXRD ont également été appliquées à l'étude du mécanisme de formation de nanocomposites HDL-polymère qui représente un domaine d'application important des matériaux HDL

Thermooxidative degradation of crosslinked EVA/EPDM copolymers: Impact of Aluminium TriHydrate (ATH) filler incorporation

International audienceThis study focuses on the thermal oxidation of model composites of insulating materials based on a cross-linked mixture of EVA (Ethylene Vinyl Acetate) and EPDM (Ethylene Propylene Diene Monomer) highly loaded (60 wt %) with ATH (Aluminium TriHydrate) filler. A thorough analysis of the material is performed, focusing not only on the polymer but also on the ATH filler. This preliminary study is essential firstly to determine the possible influence of a large amount micrometric filler incorporation on the structure of crosslinked EVA/EPDM materials, and secondly on the thermooxidative degradation mechanisms at different levels and scales (chemical structure, microstructure and architecture, degradation profile, functional properties …). The structure of both the polymer and the filler are modified during the processing step of the composite. It is shown that the reactivity of the ATH fillers leads to the probable intercalation of some segments of the polymer into the interlayer space of the ATH, and to a much less dense polymer network in the composite compared to the unfilled material. Then, the role of the added ATH filler on the thermooxidative degradation and on the resistance of the composite to ageing is studied. After thermooxidative ageing, there is only a very limited accelerator effect of ATH on the oxidation rate of the polymer within the composite compared to the unfilled material, but significant difference between materials with or without ATH filler in terms of oxidation profile or insulating properties. Nevertheless, a noticeable effect on the mechanical properties is highlighted: the mechanical properties of the unfilled materials are retained all through the oxidation process while these properties reduce drastically in the case of filled composites. The significant loss of mechanical properties occurring in the filled composites can be explained by the combination of three factors: only 40 wt % of polymer in the composite, a low density polymer network within the composite, and de-cohesion process between the ATH filler and the polymer matrix upon thermooxidative degradation

Structural Insight into Iodide Uptake by AFm Phases

International audienceThe ability of cement phases carrying positively charged surfaces to retard the mobility of 129I, present as iodide (I−) in groundwater, was investigated in the context of safe disposal of radioactive waste. 125I sorption experiments on ettringite, hydrotalcite, chloride-, carbonate- and sulfatecontaining AFm phases indicated that calcium−monosulfate (AFm−SO4) is the only phase that takes up trace levels of iodide. The structures of AFm phases prepared by coprecipitating iodide with other anions were investigated in order to understand this preferential uptake mechanism. X-ray diffraction (XRD) investigations showed a segregation of monoiodide (AFm−I2) and Friedel's salt (AFm−Cl2) for I−Cl mixtures, whereas interstratifications of AFm−I2 and hemicarboaluminate (AFm−OH−(CO3)0.5) were observed for the I−CO3 systems. In contrast, XRD measurements indicated the formation of a solid solution between AFm−I2 and AFm−SO4 for the I−SO4 mixtures. Extended X-ray absorption fine structure spectroscopy showed a modification of the coordination environment of iodine in I−CO3 and in I−SO4 samples compared to pure AFm−I2. This is assumed to be due to the introduction of stacking faults in I−CO3 samples on one hand and due to the presence of sulfate and associated space-filling water molecules as close neighbors in I−SO4 samples on the other hand. The formation of a solid solution between AFm−I2 and AFm−SO4, with a shortrange mixing of iodide and sulfate, implies that AFm−SO4 bears the potential to retard 129I

New insights into two ciprofloxacin-intercalated arrangements for layered double hydroxide carrier materials

International audienceThis paper describes the intercalation of ciprofloxacin (CIP), a bactericidal antibiotic, into the interlayer space of layered double hydroxides (LDHs). To counter the problem of bacterial resistance and also to improve the properties of the CIP drug, the drug carrier approach promises significant benefits. Through the tight control over the synthesis parameters, particularly the amounts of CIP with respect to aluminum ions, two different LDH-CIP-intercalated structures were obtained with significantly different interlayer distances, namely, 21 and 32 Å. The samples were fully characterized in terms of composition, structure, and morphology. Interestingly, the structure with the largest interlayer distance incorporated both CIP anions and Al(CIP)3 complex, exhibiting the possibility to increase the CIP drug loading beyond the anionic-exchange capacity of the LDH carrier. In vitro release in a simulated intestinal fluid (phosphate-buffered solution at pH 7.5) confirmed that LDH was a potentially efficient carrier to deliver CIP in a sustained manner via the anion- exchange mechanism. Different release rates were observed depending on the intercalated structure, which were also influenced by the morphological characteristics

Investigation about iron(III) incorporation into layered double hydroxides: Compositional and structural properties of Mg2FeyAl(1−y)(OH)6-Cl and Zn2FeyAl(1−y)(OH)6-Cl

International audienceLayered Double Hydroxides (LDH) and related nanocomposites have attracted much attention for biomedical applications and the development of LDH drug carriers composed by endogenous metals such as iron is of obvious interest. However, most of the studies reported so far on iron-containing LDH, mainly focusing on the applications, suffer from insufficient data about the synthesis and the characterization of these materials. In this study, it is addressed compositional and structural properties of two series of LDH materials, Mg2FeyAl(1−y)-Cl and Zn2FeyAl(1−y)-Cl with a M2+/M3+ molar ratio (R) equal to 2 and 0 ≤ y ≤ 1. By combining crystal-chemical reasoning, Rietveld refinements and pair distribution function analysis (PDF), it was possible to differentiate between contributions from crystalline and amorphous components. Concerning Mg-series, for y > 0.5, the compositions were found to slightly deviate from those expected with an increase in the value of R tending to 3. For Zn-series, more heterogeneous samples were obtained with the presence of amorphous 2-line ferrihydrite clearly demonstrated by PDF analysis. As well as providing a reliable approach to the characterization of Fe-LDH, this study gives useful elements for better understanding and interpreting the results reported in the literature regarding these phases