Etude du transfert d'ions aux interfaces eau/huile contenant des ligands monoamides (@ ICSM au Laboratoire des ions aux interfaces actives, Bagnols sur céze @ synchrotron SOLEIL, Saclay）

Study of the ion transfer at water/oil interfaces containing monoamide ligands

• Auteur / Autrice : Xiaochuan Ma
• Direction : Jean Daillant, Luc Girard
• Type : Projet de thèse
• Discipline(s) : Sciences des Matériaux
• Date : Inscription en doctorat le 01/11/2023
• Etablissement(s) : université Paris-Saclay
• Ecole(s) doctorale(s) : École doctorale Interfaces : matériaux, systèmes, usages (Palaiseau, Essonne ; 2015-....)
• Partenaire(s) de recherche : Laboratoire : Synchrotron SOLEIL
• Partenaire(s) de recherche : Référent : Université de Versailles-Saint-Quentin-en-Yvelines

Mots clés

Mots clés libres

Extraction

Monoamide

Transfert d'ions

Extraction

Monoamide

Ion transfer

Résumé

Sonder par des méthodes innovantes les interfaces liquide/liquide (LL) impliquées dans l'extraction assistée d'ions et de l'eau vers une phase organique 'huile' et vice versa reste un challenge. Ce procédé biphasique d'extraction par solvant est à la base d'un grand nombre applications hydrométallurgiques de recyclage de métaux stratégiques. Bien que ces techniques soient mises en œuvre à grande échelle au niveau industriel, les mécanismes moléculaires et supramoléculaires pouvant être déterminant dans les cinétiques de transfert sont toujours relativement méconnus et ce malgré des décennies de recherche. Cela vient du fait que sonder des interfaces nanométriques enfouies et fluides, donc dynamique reste un défi. Nous avons mis en évidence une organisation de la concentration d'excès de surface en ligands qui peut être plus ou moins homogène selon la nature du ligand. Il est reconnu que la structure de ces interfaces doit être étudiée en fonction de plusieurs paramètres thermodynamiques pour pouvoir déterminer le paysage énergétique associée. C'est tout l'objectif de cette thèse en utilisant des techniques spécifiques (AFM, SHG) et apportant une information locale et sensible aux fluctuations de concentration interfaciale. Ce sujet de recherche fondamentale qui requiert plutôt une formation de chimie-physique en solution permettra au candidat d'appréhender en R&D des phénomènes physico-chimiques aux interfaces dans des domaines qui s'étendent bien au-delà de l'hydrométallurgie, comme la catalyse hétérogène, les réactions chimiques dans des fluides complexes, les échanges cellulaires en biologie.

The separation of ions by liquid-liquid extraction (LL) or solvent extraction is a key process used in various industrial hydrometallurgy applications, especially in the reprocessing of nuclear fuel and materials or assemblies (e.g., waste electronic and electrical equipment) containing strategic metals. To better understand ion transfer between an aqueous phase and an organic phase in this type of process, it is important to understand: i) the speciation of different ionic and molecular species in each of the two contacting phases (aqueous and organic phases), which define the differences in chemical potential between the two phases, and ii) all molecular and supramolecular interactions at the interface that give rise to potential barriers that can influence ion transfer kinetics (1). Our work over the past decade (2) has demonstrated the importance and complexity of approaching liquid/liquid interfaces at the molecular scale to understand ion transfer phenomena in cases where aggregation in the organic phase impacts their kinetics. Many experimental results on bulk phases exist and can now be structurally interpreted through molecular dynamics simulations. However, the same experimental/simulation approach at the interface containing liposoluble ligands complexing ions in the aqueous phase and in equilibrium with adjacent volumes has been little explored. Using radiation reflectivity techniques, we have raised the possibility of analyzing interfacial structures rich in diamide-type ligands in terms of interfacial monolayers or interphases. These different interfacial structures seem to be correlated with different ion transfer regimes, characterized as either diffusional or kinetic, and explain why the energy barrier for a system containing DMDOHEMA is higher than for DMDBTDMA, two systems of amphiphilic diamides with quite different ion transfer behaviors (3). The interfacial structure can indeed strongly impact the entropic gain in the formation of inverse ligand aggregates in the organic phase, aggregates that solvate pairs of hydrated ions in the organic phase. Preliminary atomic force microscopy (AFM) measurements on these same interfaces have recently revealed force jumps at contact and during ion transfer kinetics, physical characteristics that can be correlated with lateral inhomogeneities (or rafts) previously observed in submerged biological membranes. Finally, nonlinear optical analyses, such as second harmonic generation (SHG), a suitable technique for probing buried fluid interfaces, suggest molecular orientation fluctuations characterized by correlation lengths. These numerous observations lack statistical significance, and the variety of chemical parameters in terms of ligand nature or solvent has not yet been explored to establish reliable correlations. This is the subject of this thesis, focusing on families of malonamides and monoamides on which we have collected a large amount of macroscopic data and average interfacial responses at CEA and ICSM, and for which our approaches must be systematized. Kinetic measurements of acid and trivalent ion transfer will be correlated with X-ray and neutron reflectivity measurements, AFM, and SHG measurements on systems without chromophores but also possibly on ligands of the same family containing chromophores (work based on the thesis results of J. Wang), while varying concentrations on both sides of the critical aggregation concentrations. It is indeed recognized that the structure of these interfaces must be studied as a function of several thermodynamic parameters to determine the associated energy landscape (4). Finally, the 'stripping' aspect, i.e., ion transfer from the organic phase to the aqueous phase, will also be specifically studied, a point that has rarely been developed from a structural point of view at liquid/liquid interfaces.