My research activity is focused on the rational development of advanced functional materials/objects with enhanced properties. With a combined approach of material chemistry, surface chemistry and organic/organometallic chemistry, I aim at designing specific objects (either nano-objects or bulk materials) with a control of their physical and chemical features at the nanoscale to obtain highly efficient materials (outperforming state of art systems) via the establishment of a reliable structure-property relationship. A major effort is thus directed towards the full characterization of the as-obtained objects using for example advanced NMR techniques. My research activity is very collaborative and is mainly built around three main axes.
My first research axis is devoted towards the preparation of nanostructured hybrid silica materials in which the distribution and the localization of the organic/organometallic moieties is controlled at the nanoscale.
My second research axis is devoted to i) the development of mono- or pluri-metallic nanoparticles of controlled size, composition and crystallinity in solution and ii) their transformation into metal-oxide nanoparticles and/or their selective introduction into nanostructured oxides or their deposition onto inorganic supports.
My third research axis is mainly directed towards the development of devices for micro-/nano-electronic applications using surface chemistry as a methodological tool for the functionalization of 2D supports (wafers).
To develop advanced catalytic materials, specific silica-based materials containing surface organic fragments are prepared by sol-gel process using a templating route as this synthetic route leads to well-defined systems where both the spatial distribution of the surface-ligand and the nature of the silicon surface-species is controlled.
Supported complexes yielded by the direct synthesis of hybrid silica supports
With these tailored hybrid supports in hand, the selective coordination of late transition metal complexes onto the surface ligands was achieved while avoiding side reactions with the surface silanols. As an example, Ir-NHC supported systems were obtained and their catalytic performances in hydrogenation of various substrates outperformed those of molecular analogues in solution (1 to 2 order of magnitude higher TON and TOF). These remarkable performances were attributed to the effective Ir-site isolation onto the silica surface that prevented bimolecular processes of deactivation as classically encountered when using Ir molecular complexes in solution.
Illustrative scheme of supported Ir-NHC complexes.
The presence of interactions between the organometallic centers and the silica surface using advanced NMR techniques was demonstrated and found to play a key role during catalysis.
The design of advanced functional materials was also extended to other application fields as for example, the development of hyperpolarizing matrices. The underlying idea of this project is to provide solid matrices that would allow the polarization of metabolites and tracers by Dynamic Nuclear Polarization (DNP) while delivering a pure solution of hyperpolarized metabolites ready for infusion into humans for MRI applications (early diagnosis of prostate cancers for example). It is worth noting that state of the art formulations of samples to hyperpolarize metabolites require in many case the use of glassy agents such as DMSO or glycerol and are polluted by potentially toxic organic radicals (TEMPO for instance) that prevent their easy use for in-vivo applications. In this context, tailored functional silica-based materials (powder, monoliths or nanoparticles) containing immobilized TEMPO radicals were developed in collaboration with with Prof. L. Emsley in EPFL, Prof. Copéret in ETHZ, Prof. G. Bodenhausen in ENS-Paris and Prof. S Jannin & Dr. A. Lesage in the Very High Fields RMN Center. The resulting solids exhibited unprecedented performances in d-DNP, providing pure hyperpolarized solutions.
In parallel, the development of recyclable luminescent materials for domestic lightening in collaboration with Dr. Olivier Maury and Dr. F. Riobé from the Laboratory of Chemistry in ENS Lyon was also undertaken. The aim of this project is to provide a straightforward synthetic route (low temperature and a minimum of synthetic steps) to prepare highly luminescent and recyclable materials that could be introduced in classical domestic lightening devices.
This very recent research project has already led to very promising results as we were able to prepare highly and fully recyclable luminescent materials.
Photographs of luminescent materials containing lanthanides complexes (red for Eu, Green for Tb), a blue emitter and a mixture of the three.
To conclude, this first research axis led to the development of new organic-inorganic hybrid materials in the field of catalysis but also beyond catalysis applications (hyperpolarization of biological tracers or luminescence). In the former domain, well-defined heterogeneous catalysts containing unique M-NHC catalytic sites were developed. These materials show high performances in the targeted catalytic reactions. We were able to demonstrate the beneficial presence of interactions between the organometallic centers and the silica surface by advanced solid-state NMR characterization using Dynamic Nuclear Polarization (DNP). These interactions have a major impact of the chemical structure of resulting surface-sites and play a key role for catalytic performances. Recently, we showed that it was possible to secure the isolation of the catalytically active surface leading to remarkable catalytic performances (TON and TOF) which are much greater than those of molecular counterparts in solution.
Mono- or pluri-metallic nanoparticles of controlled size, composition and crystallinity in solution nanoparticles are obtained using an organometallic approach in which transition metal complexes are decomposed at low temperature in the presence of organohydrogenosilane precursors under H2 pressure. The silane precursor plays the role of stabilizing agent, avoiding the aggregation of the as-obtained metallic nanoparticles into bulk metal. The nature of the silane also allows controlling the hydrophilic or hydrophobic character of the nanoparticles, allowing their dispersion into polar or non-polar solvents.
Principle of the synthesis of metallic nanoparticles using silanes.
This methodology was found to be very versatile, allowing the preparation of very small nanoparticles (< 2 nm) with a narrow size distribution. It was found compatible with many complexes (whatever their oxidation degree) and the use of H2 was often found un-necessary. Using this procedure, any kind of transition metal particles were successfully obtained (Pt, Pd, Ru, Rh, Ni, Fe, Co…). They were found very small and very stable in solution (at least several months!). Surprisingly, they could be advantageously used as catalysts in solution with remarkable performances with no agglomeration in the course of reaction. For example, gold nanoparticles were used for the epoxidation of trans-stilbene and more recently Co nanoparticles were found extremely active in olefin hydrosilylation. With the same protocol, the replacement of silane precursors by alkyltinhydrides allowed the preparation of alloyed nanoparticles exhibiting specific metal-tin phases. As an example, small crystalline Pt3Sn and Pd2Sn nanoparticles were obtained
TEM micrographs and Pt3Sn nanoparticles’ size histograms as a function of the number of Sn equivalents: a) 1 equiv., b) 0,5 equiv., c) 0,3 equiv. (left) ; TEM diffraction micrographs and modelling of two nanoparticles of different sizes (right).
From these as-obtained nanoparticles, heterogeneous catalysts were easily prepared by simple impregnation of the colloidal solution onto oxide supports. Among the results obtained recently, it was found that the as-obtained catalysts were more active and stable than those prepared by a more conventional protocol (impregnation of a solution of metal salts, evaporation of the solvent and further reduction). This difference in the catalytic properties was attributed to the concomitant deposition of silicates (related to the presence of the starting silane ligands) that modifies the interactions between the metal particle and the oxide support.
This axis has mainly consisted in the development of industrially relevant methodologies for the doping of wafers (silicon and germanium) at the nanometer-scale either with p (boron atoms) or n dopants (phosphorus and antimony atoms). To reach this goal, original precursors containing main group and metalloid elements (B, P, Si, Sb...) were first developed. Their chemical structure was finely tuned i) for fast grafting onto non-deoxidized wafers (no need of HF treatments as generally needed) and ii) for an optimized diffusion of the dopant (no need of an extra capping layer of oxide to prevent volatilization of the dopant during the diffusion step. These grafting procedures allowed to drastically modify the electrical properties of the as-obtained doped wafers at the nanoscale to fit the development of nano-transistors.
My research group currently includes:
Other projects I am involved in include:
The development of silica supported heterobimetallic complexes via surface organometallic chemistry. This project is headed by Dr. Clément Camp within the MMAGICC team in the CP2M Laboratory and Mr. Leon Escomel (shared PhD Student) is working on this topic.
2 positions (1 PhD position and 1 Postdoctoral fellowship) are currently open in my research group so don’t hesitate to contact me if you are interested!
43 Bd du 11 Nov. 1918
(B. P. 82007)
69616 Villeurbanne CEDEX FRANCE
+33 (0)4 72 43 17 67 (team PCM)
+33 (0)4 72 43 17 94 (team MMAGICC)
+33 (0)4 72 43 17 56 (Communication)