Vanessa Prevot

Hybrid derivatives of layered double hydroxides

The intercalation of a series of organic anions into ZnAl- and CuCr- hydrotalcite-like compounds and Cu 2 (OH) 3 (CH 3 COO) H 2 O has been performed. The organic anions differ by the anionic function (carboxylate, sulfonate and phosphonate) or by the substituted groups on the aromatic ring (OH, Cl, NH 2 , NO 2 ). The various hybrid phases were thermally treated in order to graft the anions onto the hydroxylated layers of the host structure. The CuCr- Layered Double Hydroxide (LDH) displays a reactivity higher than the ZnAl- compound with regard to the sulfonate and phosphonate groups. The grafting of aromatic carboxylates with OH groups substituted in para or meta positions is also evidenced. The characterization of all the compounds were realized using X-ray powder diffraction, infrared spectroscopy and thermogravimetry analyses.

Hybrid and biohybrid layered double hydroxides for electrochemical analysis.

AbstractLayered double hydroxides (LDH) are lamellar materials that have been extensively used as electrode modifiers. Nanostructured organic–inorganic materials can be designed by intercalation of organic or metallic complexes within the interlayer space of these materials or by the formation of composite materials based on biopolymers (alginate or chitosan) or biomolecules, such as enzymes. These hybrid or biohybrid materials have interesting properties applicable in electroanalytical devices. From an exhaustive review of the literature, the relevance of these hybrid and biohybrid LDH materials as electrode materials for electrochemical detection of species with an environmental or health impact is evaluated. The analytical characteristics (sensitivity and detection limit) of LDH-based amperometric sensors or biosensors are scrutinized. Figure(Bio) Hybrid LDH based modified electrodes

Characterization of hemoglobin immobilized in MgAl-layered double hydroxides by the coprecipitation method.

Hemoglobin was immobilized in Mg(2)Al-Layered Double Hydroxides (LDH) by coprecipation method at pH 9.0. Interactions between Hb and LDH particles were investigated by X-ray diffraction patterns, FTIR, UV-vis, circular dichroism, and fluorescence spectroscopies. Morphology and porosity of Mg(2)Al-Hb(cop) biohybrid are analyzed from SEM and TEM images and permeability measurement. The direct electron transfer of immobilized Hb was studied by cyclic voltammetry, and the electrocatalytic activity was evaluated at glassy carbon modified with this Mg(2)Al-Hb(cop) biohybrid. Even though the percentage of electroactive Hb was less than 2%, this bioelectrode showed a low detection limit (1.5 x 10(-8) M) and a very high sensitivity (37 A/M cm(2)) for the amperometric detection of H(2)O(2).

Glyphosate and glufosinate detection at electrogenerated NiAl-LDH thin films.

An amperometric sensor based on Ni(1-x)Al(x)(OH)(2)NO(3x).nH(2)O layered double hydroxide (LDH) has been developed for the electrochemical analysis in one step of two herbicides: glyphosate (N-(phosphonomethyl)glycine, Glyp) and glufosinate ((DL-homoalanine-4-yl)-methylphosphinic acid, Gluf). NiAl-LDH was prepared by coprecipitation or by electrodeposition at the Pt electrode surface. Inorganic films were fully characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. Adsorption isotherms of Glyp onto this inorganic lamellar material have been established. Electrocatalytic oxidation of Glyp and Gluf is possible at the Ni(3+) centres of the structure. The electrochemical responses of the NiAl-LDH modified electrode were obtained by cyclic voltammetry and chronoamperometry at 0.49V/SCE as a function of herbicide concentration in 0.1M NaOH solution. The electrocatalytic response showed a linear dependence on the Glyp concentration ranging between 0.01 and 0.9mM with a detection limit of 1muM and sensitivity 287mA/Mcm(2). The sensitivity found for Gluf was lower (178mA/Mcm(2)).

Synthesis Route to Supported Gold Nanoparticle Layered Double Hydroxides as Efficient Catalysts in the Electrooxidation of Methanol

This work describes a new one-step method for the preparation of AuNP/LDH nanocomposites via the polyol route. The novelty of this facile, simple synthesis is the absence of additional reactants such as reductive agents or stabilizer, which gives the possibility to obtain phase-pure systems free of undesiderable effect. The AuNP formation is confirmed by SEM, TEM, PXRD, and XAS; moreover, the electrochemical characterization is also reported. The electrocatalytic behavior of AuNP/LDH nanocomposites has been investigated with respect to the oxidation of methanol in basic media and compared with that of pristine NiAl-Ac. The 4-fold highest catalytic efficiency observed with AuNP/LDH nanocomposites suggests the presence of a synergic effect between Ni and AuNP sites. The combination of these experimental findings with the low-cost synthesis procedure paves the way for the exploitation of the presented nanocomposites materials as catalysts for methanol fuel cells.

Photocatalytic behavior of nanosized TiO2 immobilized on layered double hydroxides by delamination/restacking process

IntroductionEfficient immobilization of TiO2 nanoparticles on the surface of Mg2Al-LDH nanosheets was performed by delamination/restacking process.Experimental partThe structural and textural properties of as-prepared nanocomposite were deeply analyzed using different solid-state characterization techniques such as: X-ray powder diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopies, chemical analysis, X-ray photoelecton spectroscopy, N2 adsorption–desorption, and electronic microscopy.Results and discussionThe photocatalytic properties of immobilized TiO2 nanoparticles on Mg2Al were investigated using the photodegradation of two model pollutants: Orange II and 4-chlorophenol, and compared with pure colloidal TiO2 solution.ConclusionIt appears that Orange II photodegradation was systematically faster and more efficient than 4-chlorophenol photodegradation regardless of the medium pH. Moreover under slightly basic conditions, even if the TiO2 photocatalytic efficiency decreases, photodegradation performed in presence of easily recovered TiO2/Mg2Al1.5 nanocomposite gives rise to comparable or better results than pure TiO2.

Direct electron transfer and enhanced electrocatalytic activity of hemoglobin at iron-rich clay modified electrodes.

The possible role of structural iron in clays to promote direct electron transfer of hemoglobin (Hb) was investigated. Clays containing different amounts of iron situated in octahedral or tetrahedral sites have been used to modify glassy carbon electrodes: nontronite, synthetic montmorillonite, and saponite. A synthetic montmorillonite containing non-iron impurities was used as a reference. Interactions between Hb and these clays were studied with the establishment of adsorption isotherms and by the analysis of X-ray diffraction patterns, FTIR, and UV-vis spectra of the Hb-clay samples. The electrochemical behavior of clay modified electrodes (CME) was characterized by cyclic voltammetry in the presence of Hb in solution or adsorbed within the clays. Nontronite, which contains the highest amount of structural iron, enhanced significantly direct electron transfer of Hb. Finally, the electrocatalytic behavior of Hb-Nontronite CME in the presence of hydrogen peroxide was also studied, and the H(2)O(2) calibration curve was recorded under amperometric conditions for different bioelectrode configurations.

Enhancing atrazine biodegradation by Pseudomonas sp. strain ADP adsorption to Layered Double Hydroxide bionanocomposites.

To mimic the role of hydroxide minerals and their humic complex derivatives on the biodegradability of pesticides in soils, synthetic Mg(R)Al Layered Double Hydroxides (LDH) and Mg(R)Al modified by Humic substances (LDH-HA) were prepared for various R values (2, 3 and 4) and fully characterized. Adsorption properties of LDH and LDH-HA toward Pseudomonas sp. strain ADP were evaluated. The adsorption kinetics were very fast (<5 min to reach equilibrium). The adsorption capacities were greater than previously reported (13.5×10(11), 41×10(11) and 45.5×10(11) cells/gLDH for Mg(2)Al, Mg(3)Al and Mg(4)Al, respectively) and varied with both surface charge and textural properties. Surface modification by HA reduced the adsorption capacities of cells by 2-6-fold. Biodegradation kinetics of atrazine by Pseudomonas sp. adsorbed on both LDHs and LDH-HA complexes were measured for various solid/liquid ratios and adsorbed cell amounts. Biodegradation activity of bacterial cells was strongly boosted after adsorption on LDHs, the effect depending on the quantity and properties of the LDH matrix. The maximum biodegradation rate was obtained in the case of a 100 mg/mL Mg(2)Al LDH suspension (26 times higher than that obtained with cells alone).

Fate and ecotoxicological impact of new generation herbicides from the triketone family: An overview to assess the environmental risks

Triketones, derived chemically from a natural phytotoxin (leptospermone), are a good example of allelochemicals as lead molecules for the development of new herbicides. Targeting a new and key enzyme involved in carotenoid biosynthesis, these latest-generation herbicides (sulcotrione, mesotrione and tembotrione) were designed to be eco-friendly and commercialized fifteen-twenty years ago. The mechanisms controlling their fate in different ecological niches as well as their toxicity and impact on different organisms or ecosystems are still under investigation. This review combines an overview of the results published in the literature on β-triketones and more specifically, on the commercially-available herbicides and includes new results obtained in our interdisciplinary study aiming to understand all the processes involved (i) in their transfer from the soil to the connected aquatic compartments, (ii) in their transformation by photochemical and biological mechanisms but also to evaluate (iii) the impacts of the parent molecules and their transformation products on various target and non-target organisms (aquatic microorganisms, plants, soil microbial communities). Analysis of all the data on the fate and impact of these molecules, used pure, as formulation or in cocktails, give an overall guide for the assessment of their environmental risks.

Layered Double Hydroxide Nanoclusters: Aqueous, Concentrated, Stable, and Catalytically Active Colloids toward Green Chemistry

Increasing attention has been dedicated to the development of nanomaterials rendering green and sustainable processes, which occur in benign aqueous reaction media. Herein, we demonstrate the synthesis of another family of green nanomaterials, layered double hydroxide (LDH) nanoclusters, which are concentrated (98.7 g/L in aqueous solvent), stably dispersed (transparent sol for >2 weeks), and catalytically active colloids of nano LDHs (isotropic shape with the size of 7.8 nm as determined by small-angle X-ray scattering). LDH nanoclusters are available as colloidal building blocks to give access to meso- and macroporous LDH materials. Proof-of-concept applications revealed that the LDH nanocluster works as a solid basic catalyst and is separable from solvents of catalytic reactions, confirming the nature of nanocatalysts. The present work closely investigates the unique physical and chemical features of this colloid, the formation mechanism, and the ability to act as basic nanocatalysts in benign aqueous reaction systems.