Lab. « Hétérochimie Fondamentale et Appliquée », Université Paul Sabatier
Toulouse, France
Description
Designing new nanomaterials with orginal properties and structures hopefully will allow to solve the currrent energy challenge. For energy storage devices (lithium-ion batteries), catalysts for low-cost raw materials refining, nanolabelling and nano-vectors for medecine, researchers need to create new nanomaterials for successful developments in the next decade. For all these potential applications, metal phosphide (MxPy) are actively investigated in the academic word and in the industry. Some of these materials are indeed semi-conductors (InP, GaP, Zn3P2…) or heterogeneous catalysts (MoP, VP, MnP, FeP, Ni2P…). Nanoscaling enhances some properties (such as the reactivity in catalysis) while other are completely transformed (luminescence, lithium ion storage), as illustrated below. Our group works both on the design of new preparation routes for nanoparticles, allowing size and shape control, and on the in depth understanding of the structure-property relationship. This gives rise to nanomaterials with original properties. In 2008, we developed a genuinely new synthetic route, base on the stoichiometric reaction of metal nanoparticles and white phosphorus (P4) in solution. The key of this route is to use P4, which is the most reactive of the phosphorus allotropes. We were recently able to vary the M:P ratio in order to obtain several MxPy phases. These results raised many mechanistic questions that will be further studied in the course of the project. Firstly, we will study how the phosphorus inserts into the metal nanoparticles. Does this step affect the nanoparticle morphology? To test this, nickel nanocubes will be prepared and reacted with P4. Secondly, we noticed that the reaction of nickel nanoparticles with a substoichiometry of P4 triggered a phase segregation (Ni/Ni2P) inside each nanoparticle, provided an unexpected access to core-shell nanoparticles.[6] We will try to generalize this phase segregation mechanism to bimetallic nanoparticle alloys M/M’. Ni/Pd alloys will be specifically studies because they are a good model system and they can be used in catalysis. Thirdly, the reactivity of gold nanoparticles will be probed. Preliminary results are contrasted on this case. They suggests that even though P4 is very reactive, it does not fully converts the gold nanoparticles into gold phosphide ones (Au2P3). A reaction limited to the surface was observed at 250°C and further heating at 320°C allowed to form crystalline Au2P3. In-depth study of this particular case will provide a rationale for gold specificity in this reaction. It will also pave the way for gold-alloyed metal phosphide and their applications in plasmonics. Further perspective deal with the preparation of metal phosphide nanoparticles with less common metals (rare earth) and ternary alloys incorporating other heteroatoms such as sulfur. Depending of the ongoing of the project that is broad because of the variety of metal studied, emphasis will be put on homogeneous and heterogeneous catalysis (C-C coupling reactions, selective hydrogenations, etc.) and/or on the use of these nanoparticles as building blocks for incorporation into advanced nanomaterials such as mesoporous oxides or carbon materials.
Requirements
Technical skills involved: synthesis under inert atmosphere, x-ray diffraction on powder, electron microscopy, inorganic material synthesis, nuclear magnetic resonnance, gas-phase chromatography, mass spectrometry. The candidate should have experience in some of these techniques and be willing to learn the others.
More information and applications
Contact : Dr. Nicolas Mézailles, mezailles@chimie.ups-tlse.fr
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