Fabrice Leroux

Fine tuning between organic and inorganic host structure: new trends in layered double hydroxide hybrid assemblies

Driven by the scientific challenges involved in the creation of nanostructures providing access to new materials with unusual properties, the study of hybrid materials based on Layered Double Hydroxides (LDHs) has developed considerably during the last decade. This feature article is intended to give a broad overview of organic–inorganic hybrid assemblies based on LDH materials including their synthesis and characterization, and pointing out their potential applications. The LDH interlayer gap supplies an interesting, constrained environment arising from the anisotropic accommodation of the guest molecule at the nanoscale. Particularly, this article underlines the importance of compatibility between the two components, i.e. the organic and inorganic parts, in terms of charge distribution and molecular size for the polymerization process of interleaved molecules. Exfoliation and staging phenomena are also described. Through several examples of the shape and function of interlayer organic anions, hybrid LDH materials are described for their potential properties in optic devices, as drug delivery systems, and also as nano- and macro-fillers in polymer nanocomposites and cements, respectively. Eventually, LDH hybrid materials merge into even more complex systems for which topical applications are listed.

Delamination and restacking of layered doublehydroxides

Layered double hydroxides recovered after exfoliation have been characterized by solid state chemistry techniques. The nature of the recovered materials is highly dependant on the drying process; when gently dried, a well-ordered phase is obtained, either by freeze-drying or reconstruction, but the material becomes amorphous after evaporation of the solvent. Delamination was used to prepare interstratified LDHs, making this technique a new route to the formation of a wide range of tunable materials.

Understanding the role of co-solvents in the dissolution of cellulose in ionic liquids

The dissolution of microcrystalline cellulose in 1-butyl-3-methylimidazolium acetate [C4C1Im][OAc] was studied using a solid–liquid equilibrium method based on polarized-light optical microscopy from 30 to 100 °C. We found that [C4C1Im][OAc] could dissolve as much as 25 wt% of cellulose at temperatures below 100 °C. The structure of the composite phase obtained after cooling a solution of 16 wt% of cellulose in [C4C1Im][OAc] was analyzed by low angle X-ray diffraction showing the absence of microcrystalline cellulose, but depicting an extensive long range isotropic ordering. With the aim of improving the dissolution of cellulose in the ionic liquid, dimethyl sulfoxide, DMSO, was added as a co-solvent. It was observed that it enhances the solvent power of the ionic liquid by decreasing the time needed for dissolution, even at low temperatures. In order to understand what makes DMSO a good co-solvent, two approaches were followed. Firstly, we studied experimentally the mass transport properties (viscosity and ionic conductivity) of [C4C1Im][OAc] + DMSO mixtures at different compositions and, secondly, we assessed the molecular structure and interactions around glucose, the structural unit of cellulose, by means of molecular dynamics simulations. As expected, DMSO dramatically decreases the viscosity and increases the conductivity of the mixtures, but without inducing cation–anion dissociation in the ionic liquid. These results were confirmed by molecular simulation as it was found that the presence of a 0.5 mole fraction concentration of DMSO does not significantly affect the hydrogen-bond network in the ionic liquid. Furthermore, molecular dynamics shows that in the [C4C1Im][OAc] + DMSO equimolar mixture, DMSO does not interact specifically with glucose. We conclude that DMSO improves the solvation capabilities of the ionic liquid because it facilitates mass transport by decreasing the solvent viscosity without significantly affecting the specific interactions between cations and anions or between the ionic liquid and the polymer. The behavior of DMSO as a co-solvent was compared with that of water and it was found that water molecules are more probably found near glucose than those of DMSO, thus interfering with ionic liquid–glucose interactions, which might explain the unsuitability of water as a co-solvent for cellulose in ionic liquids.

Electrochemical insertion of lithium in catalytic multi-walled carbon nanotubes

Electrochemical lithium insertion was studied into purified and heat-treated catalytic multi-walled carbon nanotubes. It appears that the irreversible capacity for the MWNTs is relatively large, but decreasing with annealing temperature. This clearly shows that the intrinsic entanglement and the microtexture of the nanotubes must be responsible for this drawback of any potential application as an anode. The crucial role of the charge cut-off on the «traditional» intercalation was underlined and the reversible capacity was assigned to particular Li sites by high resolution NMR spectroscopy.

Synthesis and characterization of a polystyrene sulfonate layered double hydroxide nanocomposite. In-situ polymerization vs. polymer incorporation

Vinyl benzene sulfonate (styrene sulfonate — VBS) and polystyrene sulfonate (PSS) are incorporated into layered double hydroxides (LDH) of nominal composition ZnnAl(OH)2(1+n)Cl·nH2O by exchange and templating reaction, respectively. PSS adsorption leads to a delamination process of the LDH 2D-host structure. A hydrothermal treatment improves greatly the crystallinity of the PSS–LDH nanocomposite. The interactions between VBS and the host structure are evaluated by 13C CP-MAS solid state NMR spectroscopy. The electrostatic binding between the sulfonate group and the inner-surface of the LDH host structure causes some shifts in the resonance lines, although the shifts are independent of the LDH layer charge density. In-situ polymerization of VBS molecules between LDH sheets is reached after soft heat treatment. Its completion requires a good matching between the layer charge density and the projected surface area of the guest molecule as exemplified by a Zn to Al ratio of 2. In comparison to the pristine material, the change from Oh to Td aluminium site is substantially reduced for PSS–LDH nanocomposite and absent for the material prepared after the polymerization reaction.

Zn2Al layered double hydroxides intercalated and adsorbed with anionic blue dyes: a physico-chemical characterization.

Three different anionic blue organic dyes have been intercalated into the structure of Zn(2)Al layered double hydroxides, using the co-precipitation method at constant pH. Using the same synthetic procedure, Zn(2)Al-Cl has been prepared and used as an adsorptive phase to retain the blue dyes from an aqueous solution. All the organic/inorganic (O/I) hybrid LDH compounds were analyzed by X-ray powder diffraction (XRPD), thermal analysis (TG/DTA), elemental analysis, solid state (13)C nuclear magnetic resonance (CPMAS (13)C NMR), and Fourier transform infrared spectroscopy (FTIR). In the adsorption experiments, Gibbs free energy DeltaG values for the temperatures in a range between 10 and 40 degrees C were found to be negative, which indicates that the nature of adsorption is spontaneous and shows the affinity of LDH material towards the blue anionic dyes. Additionally a decrease in DeltaG values at higher temperature further indicates that this process is even more favorable at these conditions. The enthalpy DeltaH values were between physisorption and chemisorption, and it may be concluded that the process was a physical adsorption enhanced by a chemical effect, characterized by a combined adsorption/intercalation reaction, making these O/I assemblies reminiscent of the Maya blue.

Chapter 13.1 Layered Double Hydroxides

Publisher Summary This chapter describes layered double hydroxides. Among the group of minerals referred to as nonsilicate oxides and hydroxides, the layered double hydroxides (LDH) have many physical and chemical properties that are surprisingly similar to those of clay minerals. Their layered structure, wide chemical compositions (because of variable isomorphous substitution of metallic cations), variable layer charge density, ion-exchange properties, reactive interlayer space, swelling in water, and rheological and colloidal properties make LDH clay-like. However, because of their anion-exchange properties, LDH were referred to as “anionic clays.” Most metals in the first transition series can be incorporated into the hydroxyl sheet of the hydrotalcite-like structure. Thus, the formation of mixed metal-Al secondary precipitates may be a general reaction mechanism for transition metal adsorption to clay minerals.

Poly(styrene sulfonate) layered double hydroxide nanocomposites. Stability and subsequent structural transformation with changes in temperature

Poly(styrene sulfonate)–Zn2Al(OH)6·nH2O (PSS–LDH) layered double hydroxide nanocomposites have been prepared by the polymer templating method or by an exchange reaction followed by in situ polymerization of the monomers. The two well-defined samples were characterized by a combination of techniques and the polymerization of styrene sulfonate evidenced by 13C CP-MAS experiments. The nanocomposites were further characterized by in situ XRD measurements at different temperatures. The basal spacing differs in the two samples; it is stable up to 450 °C for the material synthesized by the polymer templating method, whereas a large contraction is observed for the other sample. Grafting reactions were not observed during thermal treatment. The pristine chlorine LDH material first underwent a contraction attributed to the loss of intracrystalline water molecules followed by an expansion before the breakdown of the lamellar framework at 200 °C. The microstructural transformations and the nature of the by-products are independent of the atmosphere. In contrast, drastic changes occur in the nanocomposites. A ZnS-like phase is evidenced by EDX analysis and an EXAFS study at the sulfur K-edge after treatment at 600 °C under a nitrogen atmosphere; ZnS was observed to crystallize at higher temperatures. For the templating assisted nanocomposite, an intermediate phase Zn3O(SO4)2 was observed in air. The organic moiety is found to delay the crystallization of the metal oxides, ZnO (zincite) and ZnAl2O4 (gahnite); treatment under N2 atmosphere also shows this trend.

Organic inorganic dye filler for polymer : Blue-coloured layered double hydroxides into polystyrene

A series of blue dye molecules, Evans blue (EB), Chicago sky blue (CB), Niagara blue (NB) were incorporated by direct co-precipitation within the galleries of negatively charge layered double hydroxide (LDH). The materials of cation composition Zn/Al = 2 lead to well-defined organic inorganic assemblies. The molecular arrangement of the interleaved dye molecule is proposed by 1D electronic density projection along the stacking direction for the hydrothermally treated samples with alternatively a highly inclined orientation of EB and CB and a parallel-bilayer arrangement for NB. Blue coloured LDH assemblies were subsequently dispersed into polystyrene (PS). It was found that the hybrid fillers do not interfere in the radical polymerization of styrene, giving rise to similar molecular weight and polydispersity than filler free PS, while higher glass transition temperatures were obtained for the nanocomposites. This was consistent with the rheological behaviour with the observation for LDH/NB filler based nanocomposite of shear thinning exponent different from zero, underlining frictional interaction between filler and PS chain. The absorption maximum slightly blue-shifted for the hybrid filler in comparison to the corresponding organic dye was found unmodified for the PS nanocomposite, thus giving rise to blue coloured plastic films, reminiscent somehow of the blue Maya effect.

The 2D Rancieite-type manganic acid and its alkali-exchanged derivatives: Part I — Chemical characterization and thermal behavior

Abstract The 2D Rancieite type manganic acid was prepared by reduction of KMnO 4 in acidic medium. Its ion exchange behavior allows to prepare alkali derivatives. All compounds were characterized with use of a combination of X-ray diffraction, chemical analyses, TGA, magnetic measurements and spectroscopic techniques. The evolution of their chemical composition versus temperature was studied between 180 and 400 °C. It shows that the dehydration process is partly reversible in these compounds whereas the weak reduction is irreversible. The 2D Rancieite-type manganic acid is readily different from a Birnessite-type phyllomanganate, as shown by several features: the interlayer distance, the ion exchange capacity, the thermal behavior, the interlayer cation content, the manganese average oxidation state, the magnetic behavior and the IR spectrum.