Solvation and Ion Specificity in Complex Media

Abstract : The object of this thesis was to create models for two applications which readily appear in separation chemistry, namely the solid-liquid and the liquid-liquid extractions. The benefit of modelling in both cases is twofold. Studying the fundamental properties of ions and their solvation properties in the complex media, and simplifying the expression for important effects, enables us to construct the framework which can be used by both chemists in the laboratory, as well as the chemical engineers in the process design. For two applications we adapted two different systems, both of which can be considered as complex. The model system to study the solid-liquid separation were TiO$_{mathrm{2}}$ nanotubes dispersed in the aqueous solution. This system was studied by the means of Classical Density Functional Theory coupled with the charge regulation method, within the Grand-canonical ensemble. Indeed, the method proved to be successful in establishing the full description of the charge properties of TiO$_{mathrm{2}}$ nanotubes. In this case, we were interested in obtaining the description of ion inside the charged nanotubes under influence by the electric field (exhibited by nanotubes). Calculations predicted effects such as the difference in surface charge between the outer and the inner surface, or the violation of electroneutrality inside the nanotubes. It was demonstrated that the model was in the agreement with the experimental data. Moreover, the method can be directly used to predict titration for various techniques. A simple generalization of the proposed approach can be used to study the actual adsorption efficiency of the solid-liquid separation process. The model system to study the liquid-liquid extraction process included three distinct parts. The three parts were devoted to the cases on non-ionic, acidic ion exchangers, and finally the synergistic mixtures of extractants. Simple bulk statistical thermodynamics model, in which we incorporated some of the well-established concepts in colloidal chemistry provided a soft-matter approach for the calculation of actual engineering-scale processes. Were have expanded a classical simple equilibria approach to broader, more intuitive polydisperse aggregates formation that underlines the liquid-liquid extraction. The key finding can be presented as a current opinion or newly-proposed paradigm: at equilibrium, many aggregates completely different in composition but similar in free energy coexist. With obtained polydispersity, we were equipped with a tool to study a more 'global' behavior of liquid-liquid extraction. This urged us to pass our considerations of historical extraction isotherms to extraction 'maps'. Great care was devoted to the study of synergy since it is a 60-year old ongoing question in the separation industrial and science community. To our best knowledge, the first quantitative rationalization total synergistic extraction was proposed within this thesis. Underlying effects of enthalpy and entropy control on the organic phase structuring were decoupled and studied in detail. Hopefully, this thesis demonstrated the importance of mesoscopic modelling to assist both chemists and chemical engineers in practical examples.
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Mario Spadina. Solvation and Ion Specificity in Complex Media. Other. Université Montpellier, 2019. English. ⟨NNT : 2019MONTS020⟩. ⟨tel-02299118⟩

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