Nathalie Marcotte

Azoic Dye Hosted in Layered Double Hydroxide: Physicochemical Characterization of the Intercalated Materials

Intercalation compounds were obtained by introduction of guest methyl orange (MO) into the interlayer space of host Mg/Al and Ni/Al layered double hydroxides (LDHs). Three synthesis methods of organic anion-LDH intercalation compounds, i.e., coprecipitation, reconstruction of the MII(Al)O mixed oxides, and anion exchange of LDH, were compared. The former method gives rise to a highly organized MO-intercalated Mg/Al LDH with an interlayer spacing of 2.43 nm and up to seven (00l) reflection orders. Reconstruction of the mixed oxide by intercalation with MO in the restored LDH was only achieved with Mg(Al)O. In this case, a competitive adsorption of MO on the external surface of the crystals was also seen. On the other hand, intercalation compounds exhibiting interlayer spacing of 2.43 nm were obtained with both Mg- and Ni-containing LDH using the anionic exchange method. The equilibrium and kinetic adsorption properties of the compounds were analyzed by UV-visible spectroscopy in anionic exchange experiments. According to the pseudo-second-order adsorption model, the amounts of adsorbed MO reach 3.82 and 2.83 mequiv/g for Mg- and Ni-containing LDHs, respectively, which are close to their respective anionic exchange capacity. The adsorption rates are on the same order of magnitude for the two LDHs (0.10-0.44 g mmol(-1) min(-1)), the equilibrium being reached in less than 60 min. The decomposition of MO by combustion of the organic moieties under an oxidizing atmosphere is delayed in Mg-containing MO-LDH hybrids when compared to the free MO molecule, showing that the thermal stability of MO species is enhanced after intercalation. In Ni-containing LDH, the main decomposition step of MO occurs 300 degrees C below that of Mg-containing LDH. This was rationalized in terms of a catalysis by the Ni-containing oxides formed during the thermal treatment. So these materials exhibit several advantages useful for the development of eco-friendly processes for the removal of dyes from effluents of textile, plastic, and paper industries.

Efficient mesoporous silica–titania catalysts from colloidal self-assembly

Mesoporous silica-titania materials of tunable composition and texture, which present a high catalytic activity in the mild oxidation of sulfur compounds, have been obtained by combining the spray-drying process with the colloidal self-assembly of α-chitin nanorods (biopolymer acting as a template) and organometallic oligomers.

Stable aqueous colloids of ZnS quantum dots prepared using double hydrophilic block copolymers

Stable aqueous colloids of ZnS nanoparticles have been synthesised using zinc acetate, sodium sulfide and asymmetric double hydrophilic block copolymers PAA-b-PAM (polyacrylic acid-block-polyacrylamide) with various block molecular weights: MPAA = 1000, 3000, 5000 g mol−1 and MPAM = 10 000, 15 000, 30 000 g mol−1, respectively. The synthesis involves the formation of precursor hybrid polyion complex (HPIC) micelles, in which the micelle core is composed of Zn2+ ions complexed by polyacrylate blocks, while the corona is constituted by the stabilising neutral PAM blocks. The addition of S2− ions in the micelle solutions yields ZnS nanoparticles with a diameter of 3–4 nm. The ZnS nanoparticle size is weakly dependent on the copolymer block length, while the particle size distribution correlates with the copolymer asymmetry degree in such a way that a higher MPAM/MPAA ratio yields particles with a narrower size distribution. Characterisation by XRD and SEAD revealed that ZnS has a cubic sphalerite structure with the cell parameter a = 5.25 ± 0.05 A that is smaller than that of the bulk material (a = 5.406 ± 0.05 A). The obtained colloids present photoluminescent properties with an emission band peaking at 410 nm and exhibit a blue-shift of the band-gap energy in the UV-visible absorption spectra due to the quantum-confinement effect.

Nanocomposites from Natural Templates based on Fatty Compound-Functionalised Siloxanes

This work describes the synthesis of new, environmentally friendly, robust and biocompatible organic–inorganic hybrid materials based on fatty acid methyl ester-functionalised silica. The hydrosilylation reaction was used to covalently anchor 10-undecenoic methyl ester to a cyclic and acyclic backbone based on methylsiloxane repeating units. These as-synthesised amphiphilic precursors exhibit a self-assembling ability as shown by the formation of nanoobjects evidenced by fluorescence experiments, transmission electronic microscopy (TEM) and dynamic light scattering (DLS) analyses. Spherical nanocomposites featuring unprecedented flexibility, hydrophobicity and improved hydrolytic and thermal properties were built using sol–gel condensation of tetraethoxysilane (TEOS) controlled by these new self-assembling nanobuilding blocks. The textural characteristics and the morphology of these composite materials were dependent on the type of catalyst (acidic or basic) and the nature of the solvent (polar or apolar) used during the sol–gel polymerisation. This strategy opens new opportunities for advanced applications in various fields of nanochemistry and biomaterials.

Single-Step Dispersion of Functionalities on a Silica Surface

A new process for coating a mesoporous silica gel with a mixture of the grafting reagents para-aminophenyltrimethoxysilane and phenyltrimethoxysilane is thoroughly analyzed. The dilution of para-aminophenylsilane with phenylsilane at different ratios allows the density of the functional amino groups present on the silica surface to be controlled, while keeping constant the overall number of grafts. Furthermore, the choice of a rigid linker prevents undesirable interactions between the active function and the inorganic support that could alter the function reactivity. This simple and new method, which results in the improvement of the dispersion of a functionality in a one-pot synthesis, could be particularly interesting in the field of supported catalysis and molecular recognition. The dispersion of the functional groups of the synthesized hybrid solids is investigated using a pyrene derivative covalently linked to the free amino groups of the para-aminophenylsilanes by analyzing the excimer and monomer fluorescence properties of the probe.

Structural characterization of azoic dye hosted layered double hydroxides

Abstract The removal of methyl orange (MO) from an aqueous solution was performed using layered double hydroxides (LDHs) in a move to develop cleaning processes of effluents contaminated with dye molecules. The intercalation of the guest anionic MO species into host MII/AlIII LDHs differing by the nature of the divalent cations (MII = Mg, Ni or Zn) was achieved by anionic exchange of the initially NO3– present in the interlayer space and led to MO/LDH intercalation compounds. The exchange process was followed by XRD and UV-visible absorption spectroscopy at different stages. Almost all MO in solution is uptaken by the Mg-containing LDH in the concentration range corresponding to its anionic exchange capacity (AEC). A lower exchange is reached with the Ni- and Zn-containing LDHs, for which the diffusion of MO is limited due to a larger crystallite size. MO–Zn/Al LDH intercalation compounds exhibit the highest crystallinity and display a remarkable stacking of the layers at maximal MO exchange. This behaviour can be assigned to the higher intrinsic charge density of the host layers in agreement with its lower MII/AlIII molar ratio (ZnII/AlIII ≈ 1.5 whereas MgII/AlIII and NiII/AlIII = 2). The maximum amount of MO retained by the different LDHs is higher for Mg-containing LDH, than for Ni- and Zn-containing LDH, reaching respectively 1.15, 0.84 and 0.77 g/g.