Marie-Alexandra Neouze

We report on the catalytic activity for the cycloaddition of CO₂ to cyclic organic carbonates of recently developed ionic nanoparticle networks (INN). The combination of high imidazolium content and ability to coordinate to CO₂ molecules within the 3D network makes the hybrid INN materials highly promising heterogeneous catalysts for CO₂ activation reactions. The catalytic activity of INN powders and gels was investigated with various starting epoxides. Quantitative conversion was reached with epichlorohydrin. The influence of mono or bis(imidazolium) bridging ligands and methylation at the C2 position in the aromatic ring of the organic cation could be highlighted by evaluation of the activity with the less reactive propylene oxide as the starting epoxide. Finally, the influence of the type of inorganic nanoparticle support was also studied by preparing heterobimetallic silica‐zinc oxide nanoparticle networks. Promising results were obtained with various epoxides. Conversion or selectivity up to 100 % could be obtained. The catalyst could be reused owing to the good thermal stability of the hybrid inorganic‐organic INN. After four reaction runs the catalyst still proved to be active.

A newly arising challenge in the field of nanoparticle research concerns the control and the understanding of the interparticle interactions and interparticle properties. This should allow the development of materials based on nanoparticle assemblies which represents a great opportunity to exploit nanoparticle collective properties. Although some nanoparticle networks have been reported, few works are addressing the highly exciting problem of forming bis-nanoparticle assemblies in which two different types of nanoparticles are present. In this article we report an original synthesis pathway for the formation of an ionic bis-nanoparticle network, silica/silver, based on the formation of an imidazolium bridging unit. The reaction used for the formation of the bridging imidazolium can be considered as click-like chemistry. The synthesis of the metal/metal oxide hybrid composite material starts from the formation of a metal oxide nanoparticle modified with an imidazole ligand. This composite formation is therefore very general and could be extended to other metal/metal oxide composites.

Titania nanoparticle networks were synthesized by the reaction between imidazole and alkyl halide functionalized anatase nanoparticles. The reaction produced imidazolium bridging units between the nanoparticles that were observed by the means of CP MAS ¹⁵N NMR spectroscopy. The porous characteristics of the obtained nanoparticle network were investigated with nitrogen sorption experiments. From these experiments, a high surface area originating from small mesopores was observed. These results were confirmed by small-angle X-ray diffraction experiments.

Recently we published the synthesis of new hybrid materials, ionic silica nanoparticles networks (ISNN), made of silica nanoparticles covalently connected by organic bridging ligands containing imidazolium units owing to a “click-chemistry-like” reaction. Among other techniques small-angle X-ray scattering (SAXS) experiments were carried out to get a better picture of the network extension. It turned out that the short-range order in ISNN materials was strongly influenced by the rigidity of the bridging ligand, while the position of the short-range order peaks confirmed the successful linking of the bridging ligands. The photoluminescence experiments reported in this communication revealed strongly enhanced emission in the hybrid material in comparison with neat imidazolium salts. Moreover the shift of the emission maximum toward longer wavelengths, obtained when varying the aromatic ring content of the bridging ligand, suggested the existence of strong π−π stacking in the hybrid material. Experiments revealed a stronger luminescence in those samples exhibiting the higher extent of short-range order in SAXS.

Recently nanoparticles ionic networks were reported in the frame of the remarkable development of new inorganic–organic hybrid materials based on nanoparticles assembly. In this article a layer-by-layer deposition method for the formation of imidazolium-based assemblies of photocatalytic titania nanoparticles is presented. This provides a new route for the controlled processing of this promising class of materials.

In the parallel dramatic development of both nanoparticles and ionic liquids for materials chemistry, remarkable synergy was observed when combining nanoparticles and one type of ionic liquid, namely imidazolium moieties. This feature article highlights the main steps in the use and understanding of such combinations. It starts with a presentation of the use of imidazolium based ionic liquids as synthesis media for the preparation of nanoparticles, under various classical and non-classical processes. Then, the interactions taking place between the nanoparticle surfaces and functionalized or non-functionalized imidazoliums are reviewed. A step-by-step description of the way to new hybrid materials, based on this combination of imidazolium units and nanoparticles, follows. The multiple role of the imidazolium moiety is evidenced. Finally, the main fields of application for the new hybrid materials will be presented.

Metathesis reactions in acetone were performed on ionic silica networks based on imidazolium chloride bridging units. The salts investigated were NaBF₄, KPF₆ and LiN(SO₂CF₃)₂. XRD experiments and NMR analysis were used to follow the anion metathesis. For all compounds the thermal stability of the hybrid material was maintained after metathesis. SAXS experiments confirmed that the anion metathesis only very slightly affected the short-range order of the network. However, the yield of the metathesis reaction, depending on the length of the imidazolium based ligand, was evaluated by EDX analyses. The anion metathesis reaction provides a tailoring tool for hybrid material hydrophobicity.