Cécile Machut

Understanding the role of cyclodextrins in the self-assembly, crystallinity, and porosity of titania nanostructures.

A series of mesoporous titania photocatalysts with tailorable structural and textural characteristics was prepared in aqueous phase via a colloidal self-assembly approach using various cyclodextrins (CDs) as structure-directing agents. The photocatalysts and the structure-directing agents were characterized at different stages of the synthesis by combining X-ray diffraction, N2-adsorption, field emission scanning electron microscopy, transmission electron microscopy, UV-visible spectroscopy, dynamic light scattering, and surface tension measurements. The results demonstrate that the cyclic macromolecules efficiently direct the self-assembly of titania colloids, resulting in a fine-tuning of the crystal phase composition, crystallite size, surface area, particle morphology, pore volume, and pore size. Depending on the chemical nature of the substituents in the cyclodextrin ring, synergistic or competitive effects arising from the adsorption capacity of these cyclic oligosaccharides onto titania surface, surface-active properties, and ability to aggregate in water by intermolecular interactions were found to substantially impact the characteristics of the final material. We propose that, in contrast to the native cyclodextrins, which tend to favor the local agglomeration of titania nanoparticles due to the strong intermolecular interactions, the substitution of hydroxyl groups by a relatively large number of methoxyl or 2-hydropropoxyl ones in the β-CD derivatives allows for creating smoother interfaces, thus facilitating the self-assembly of the colloids in a more homogeneous network. The photocatalytic activity of those titania materials was evaluated in the photodegradation of a toxic herbicide, phenoxyacetic acid, and was correlated to the structural and textural characteristics of the photocatalysts.

Hydroxypropyl-β-cyclodextrin as a versatile additive for the formation of metastable tetragonal zirconia exhibiting high thermal stability

Single-phase tetragonal zirconium oxides with enhanced phase stability were successfully synthesized by a precipitation procedure, using hydroxypropyl-β-cyclodextrin (HP-β-CD) as a new macromolecular additive. The samples were prepared in the presence of controlled amounts of HP-β-CD by precipitation of a zirconium oxychloride solution in an aqueous ammonia solution and then annealed at 600 °C to produce the pure tetragonal phase. The as-prepared ZrO2 particles are composed of nanocrystallites with coherent scattering region sizes of the order of 40 nm at temperatures as high as 600 °C. The formation of the t-phase was investigated at different stages of the process by XRD, TGA–TDA, FTIR and conductivity measurements. The process of crystallization of the hydrous zirconia precursor was found to be retarded by the binding of HP-β-CD to the zirconium metal centres, further leading to structure-controlled t-ZrO2 nanocrystals with increasing temperature up to 800 °C. The beneficial effect of HP-β-CD was related to its ability to be partially deprotonated in the aqueous ammonia solution and interact with the Zr(IV) species in the early stage of the synthesis. This hypothesis was supported by additional controlled syntheses of materials using other cyclodextrin derivatives.

Block copolymer–cyclodextrin supramolecular assemblies as soft templates for the synthesis of titania materials with controlled crystallinity, porosity and photocatalytic activity

Nanostructured titania materials with tunable porosity and crystalline framework were prepared in an aqueous phase by using a template-directed colloidal self-assembly strategy. The approach employs the supramolecular assemblies formed between the randomly methylated β-cyclodextrin and the block copolymer P123 as soft templates and the sol–gel synthesised TiO2 nanocrystals as building blocks. By combining X-ray diffraction, N2-adsorption, field emission scanning electron microscopy and UV-visible spectroscopy, we show that considerable control over crystallite size, polymorph content and particle morphology could be achieved by using a delicate balance between the composition and structure of the supramolecular template as well as the reaction conditions. The photocatalytic activity of these mesoporous TiO2 materials was evaluated in the photodegradation of a toxic herbicide, the phenoxyacetic acid (PAA), and was correlated to the structural and textural characteristics of the photocatalyst.

Synthesis, surface tension properties and antibacterial activities of amphiphilic D-galactopyranose derivatives.

Several amphiphilic d-galactopyranose derivatives were synthesized in which the glycosidic moiety was separated from the hydrophobic alkyl chain (along 8 or 12 carbon atoms) by a spacer arm (butyl, butynyl or benzyl) in order to increase their surfactant properties and to obtain new antibacterial compounds. The surface tensions of the products were analyzed by Critical Micelle Concentration (CMC) and γCMC measurements and the antimicrobial activities were assayed against 10 bacterial species by Minimum Inhibitory Concentration (MIC) determination in liquid broth. The introduction of an aliphatic spacer arm increased the amphiphilic properties of the compounds and the CMC values were 40-500 times lower than their analogs without spacer arm. In the same manner, the spacer arms significantly increased the antibacterial power of the compounds. The products 4d and 4e exhibiting a C12 alkyl chain and an aliphatic spacer arm (butyl and butynyl) were the best surfactants (CMC = 0.023 and 0.032 mmol/L, respectively) and presented also the best antibacterial activities (MIC = 15.62 and 3.91 μg/mL for Micrococcus luteus, respectively). But the antibacterial activity of the newly synthesized products seemed to depend more on the cell wall composition of the bacteria than only on the amphiphilic character of the compounds.

New supramolecular amphiphiles based on renewable resources

The complexation between esters derived from sorbitol and β-cyclodextrin was studied. Isosorbide dioleate and sorbitan trioleate formed well-defined inclusion complexes with β-cyclodextrin and these inclusion complexes exhibited surfactant behaviour.