Cécile Machut

A convenient and fast microwave synthesis of gold-doped titanium dioxide materials was developed with the aid of commercially available and common cyclodextrin derivatives, acting both as reducing and stabilizing agents. Anatase titanium oxide was synthesized from titanium chloride by microwave heating without calcination. Then, the resulting titanium oxide was decorated by gold nanoparticles thanks to a microwave-assisted reduction of HAuCl₄ by cyclodextrin in alkaline conditions. The materials were fully characterized by UV-Vis spectroscopy, X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and N₂ adsorption-desorption measurements, while the metal content was determined by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The efficiency of the TiO₂@Au materials was evaluated with respect to two different photocatalytic reactions, such as dye degradation and hydrogen evolution from water.

In cyclodextrin (CD)-mediated aqueous biphasic catalysis, favoring contacts between the CD (“host”), the organic substrate (“guest”) and the water-soluble catalyst is crucial for the reaction to proceed efficiently at the aqueous/organic interface. Grafting the catalyst onto the CD backbone thus appears as an attractive approach to favor the molecular recognition of the substrate and its subsequent catalytic conversion into products. In this context, a new water-soluble β-CD-based phosphane was synthesized and characterized by NMR, tensiometric and ITC measurements. The β-CD-based phosphane consisted of a 3,3′-disulfonatodiphenyl phosphane connected to the primary face of β-CD by a dimethyleneamino spacer. Intra- and intermolecular inclusion processes of one of the two sulfophenyl groups into the β-CD cavity were identified in water. However, the association constant (K_a) related to the β-CD/sulfophenyl group couple was low. Accordingly, the inclusion process was easily displaced upon coordination to rhodium complexes. The efficacy of the resulting Rh-complex coordinated by β-CD-based phosphanes was assessed in Rh-catalyzed hydroformylation of higher olefins. The catalytic system proved to be far more successful and efficient than a system consisting of supramolecularly interacting phosphanes and CDs. The catalytic activity was up to 30-fold higher while the chemo- and regioselectivities remain rather unchanged.

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.

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.