<p>Advances in nanomaterials research have stoked interests in the design of dispersible catalysts for specific organic transformations, with higher reaction efficiency or lower burden in post-reaction waste processing. Multicomponent heterogeneous catalysts generally offer higher catalytic performance than single-component catalysts, with metal–substrate interactions (MSI) playing a key role in their performance. This thesis focuses on silver–iron-oxide particles as heterogeneous catalysts, starting with a literature survey (Chapter 1) followed by the synthesis and catalytic properties of two novel types of Ag–Fe₃O₄ particles that show strong potential for mediating C(sp²)–H arylation reactions (Chapters 2 and 3). Silver and especially iron oxide are much less expensive than other types of metals, and the magnetic properties of the Fe₃O₄ support transferability and reuse of the active catalytic species which enables us to reduce the ratio of catalyst to reactant. These features address multiple goals outlined by the principles of green chemistry. The arylation of heterocyclic compounds is frequently used in the preparation of organic dyes, polymers, and pharmaceutical intermediates, and is a useful benchmark reaction for comparing our cross-coupling catalyst with those from prior reports. </p> <p>In Chapter 2, we describe the synthesis of colloidal silver–iron-oxide (SIO) and investigate its conversion into an efficient catalyst for C(sp²)–H arylation using novel modes of activation. This includes electrochemical activation using mild cathodic potentials, and photoactivation using a white light source. Both methods dramatically improve the efficacy of colloidal SIO as a catalyst for the cross coupling of diazonium salts with heteroaromatic rings at room temperature. High-resolution transmission electron microscopy analysis reveals that the SIO particles are primarily composed of colloidal Ag that are coated with nanosized islands of Fe₃O₄. The SIO catalysts are magnetically responsive and can be collected and reused multiple times, without requiring reactivation. The SIO is susceptible to acid degradation but can be preserved with neutralization by added base during reaction cycling. </p> <p>In Chapter 3, we describe a second-generation catalyst in which Fe₃O₄ microspheres serves as the supporting substrate for Ag islands, with synthetic control over Ag size distribution. This material does not require any activation for cross-coupling catalysis, which can be attributed to better charge transfer between the Ag islands and Fe₃O₄ substrate. A comparison of Ag–Fe₃O₄ microspheres with different Ag/Fe ratios suggests that catalytic activity correlates with smaller particle sizes, where the strongest charge-transfer interactions are likely to occur. The role of MSI between Ag and Fe₃O₄ was further explored using X-ray absorption spectroscopy. The second-generation Ag–Fe₃O₄ catalysts are far more robust than the previous version and are better able to withstand acidic degradation, with less mass loss after multiple reaction cycles and no loss in catalytic function. Lastly, we have found that Ag–Fe₃O₄ microspheres can also be an efficient catalyst for the reduction of nitro groups into amines, and describe progress toward the one-pot conversion of  nitroarenes into  cross-coupling products.  </p>

Les émulsions représentent une large gamme de produits alimentaires, cosmétiques et pharmaceutiques. Pour assurer leur stabilité, une interface chargée de tensioactif est nécessaire. Cette interface constitue une barrière contre la coalescence mais gène la libération des principes actifs encapsulés. Dans cette thèse, une nouvelle méthode d’émulsification est développée. Elle consiste à utiliser des ultrasons à hautes fréquences (UHF) (1,7MHz) qui permettent d’avoir des émulsions stables sans émulsifiants tout en évitant les effets mécaniques violents de la cavitation acoustique présente aux basses fréquences. L’étude des répartitions granulométriques a montré une diminution significative de la taille des gouttelettes d’huile au cours du temps de traitement par ultrasons de hautes fréquences. Le suivi du pH des émulsions montre une forte diminution et une charge de surface importante des gouttelettes est enregistrée ce qui montre une accumulation d’ions OH- à l’interface l'huile/eau conduisant à la stabilité des gouttelettes dans l'émulsion. La conductivité des émulsions diminue durant l’émulsification traduisant une baisse de la quantité d’ions en solution, ce qui indique la formation de la couche contre ions (charge positive) autour de la structure des OH-. Les résultats montrent une stabilisation électrostatique des émulsions obtenue par la formation d’une double couche ionique autour des gouttelettes d’huile. Contrairement aux procédés d’émulsification standard, les émulsions faites par ce procédé montrent une stabilité de 30 jours à 37°C. L’utilisation des émulsions sans émulsifiant faites par UHF pour la vectorisation de CoQ10 montre une prolifération cellulaire plus élevée que dans le cas des émulsions avec émulsifiant. Une étude approfondie des émulsions sans émulsifiant par diffusion des rayons X aux petits angles (SAXS) et par résonance magnétique nucléaire (RMN) a été réalisée et comparée à des émulsions contenant un ou plusieurs émulsifiants. L’étude SAXS montre clairement l’absence de micelles de tensioactifs pour les émulsions sans émulsifiants et les résultats de la RMN montrent l’absence de la signature des tensioactifs et des phospholipides dans les émulsions faites par ultrasons de hautes fréquences. Par ailleurs, la RMN montre l’absence d’interaction entre des différents constituants de l’émulsion et aussi l’absence de structure néoformées / Emulsions are systems containing two immiscible liquids, one dispersed as droplets (dispersed phase) throughout the other (continuous phase). When emulsifier is added, it may interact with the other formulations compounds creating new emulsion properties. Therefore, it becomes difficult to study the role of oil phase alone on emulsion properties. In this thesis, emulsifier free emulsion was developed with high frequency ultrasounds (HFU) generated by piezoelectric ceramic transducer vibrating at 1.7 MHz. pH measurement showed significant decrease and negative electrophoretic mobility showed the accumulation of OH- at oil/water interface leading to droplets stability in the emulsion. Emulsions conductivity showed a decrease of the ions quantity in solution, which indicated formation of positive charge layer around OH- structure. They constituted a double ionic layer around oil particles providing emulsion stability. This study showed a strong correlation between turbidity measurement and proportion of emulsified oil. Unlike standard emulsification methods, emulsions made this process demonstrates stability for 30 days at 37 °C. The use of emulsions without emulsifier made by HFU for vectoring CoQ10 shows a higher cell proliferation in the case of emulsion without emulsifier. A study of emulsions without emulsifer by small angle X-ray scattering (SAXS) and nuclear magnetic resonance (1H NMR) was performed and compared to emulsions containing emulsifiers. NMR analysis showed no interactions between different compounds and the HFU manufacturing process did not cause chemical degradation or neoformed compounds. SAXS showed a thin interface between two phases with different electronic density (water/oil) for emulsions with and without emulsifiers. For emulsion with emulsifiers SAXS showed surfactant micelles diffusion signal which doesn’t appear in the emulsion without emulsifiers