Vendredi 25 novembre 2016 : Thèse de Audrey IRANZO
La thèse se déroulera le Vendredi 25 novembre 2016 en Amphi Concorde : Campus UPS-RANGUEIL à 10h
Intitulé de la Thèse :
"Ultrasounds assisted electrosynthesis of zero valence iron nanoparticles : study of the deposit growth and dispersion by acoustic waves"
M. Théo TZEDAKIS - UT3 - Université de Toulouse 3 Paul Sabatier : Directeur de thèse
M. Fabien CHAUVET - Université de Touloulouse 3 Paul Sabatier : Co-directeur de thèse
M. Emmanuel MAISONHAUTE - Université Pierre-Marie Curie : Rapporteur
M. Paul KENIS - University of Illinois Urbana Champaign : Rapporteur
Mme Béatrice BISCANS - CNRS Université de Toulouse : Examinateur
Mme Rosaria FERRIGNO - Université Claude Bernard Lyon 1 : Examinateur
M. Marc VERELST - Université de Toulouse 3 Paul Sabatier : Invité
This study concerns the coupling of the ultrasounds with the electrodeposition process for the synthesis of zero-valent iron nanoparticles ; it is structured in two sections. The first focuses on the material of the electrode substrate used for the iron electrodeposition and aims to determine its influence on both the deposit growth and its dispersion by ultrasonication.
The interfacial and the adhesion energies of the deposit on the substrate are controlled by both the surface energy and the roughness of the substrate, therefore a particular focus is put on the influence of these two properties. Two materials of different surface energies (gold and vitreous carbon), as well as various roughnesses, are tested. The affinity of the gold and vitreous substrates with the metallic iron deposit is correlated with the energy required for its formation. The voltamperometric studies reveal, indeed, that a higher overpotential is necessary to produce the iron deposit on the vitreous carbon substrate than on the gold substrate. This difference impacts the deposit morphology (on the gold substrate the iron deposit forms a thin and continuous layer whereas, a 3D growth is favored on the vitreous carbon substrate) but also the deposit adhesion. Indeed, experiments performed to study the effect of ultrasound on the iron electrodeposit, reveal its progressive and complete dispersion for the vitreous carbon case while no dispersion is obtained with the gold substrate. Finally, results show that the substrate roughness is also a control parameter for the deposit adhesion and thus for its dispersion by ultrasonication. To sum up, this first part of the study has enabled to determine the optimal parameters (ultrasounds power and duration, roughness and surface energy of the substrate) for a fast and complete dispersion.
The second axis of the present study expects to synthesize iron micro/nanoparticles ; to this end, the electrodeposition of ramified deposits has been investigated in a Hele-Shaw cell integrating a vibrating element (piezoelectric diaphragm), expected to allow both the deposit formation and its fragmentation. Experiments reveal that the hydrogen bubbles, formed by the co-reduction of the free proton during the iron electrodeposition, strongly influence the fragmentation process. Using high frequencies and high amplitudes vibrations, the bubbles oscillate with surface deformations, inducing interface velocity sufficiently high (≈ 4 m/s) to allow the fragmentation of the deposit into particles of sizes ranging between 1 µm and 100 nm.
These particles have a high specific surface due to their dendritic morphology. The understanding and the optimization of the synthesis in the vibrating Hele-Shaw cell, coupled with the possibility to apply a flow of iron precursor solution, and an in-situ magnetic separation allow the proposal of a new electrochemical synthesis of micro/nanoparticles in microchannels.