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Organically modified montmorillonite has been extensively used as nanofiller in studies of polymer layered silicate nanocomposites, promising materials for today's automotive industry because the nano-materials reduce the overall weight of vehicle. However, industrial applications have not followed suit primarily due to cost/performance issues. Supercritical carbon dioxide is promising as an aid in the production of a fully exfoliated polymer layered silicate nanocomposite but has not been fundamentally studied in this regard at present. As the first stage in studies of using supercritical carbon dioxide for aiding the production of thermoplastic elastomer nanocomposites, this thesis investigates the influence of this unique supercritical fluid on the microstructure and surface chemistry of five organically modified clays. Four alkyl-based quaternary ammonium surfactants with different number and length of chains attached and one aromatic quaternary ammonium surfactant were chosen to vary the degree of C02-philicity exhibited by the organoclay. In a high pressure batch vessel, the different organoclays were suspended in the supercritical solvent at temperatures of 50°C and 200°C and pressures of 7.6 MPa and 9.7 MPa for a fixed time and then removed after depressurization at 0.2 MPa/s or 4.8 MPa/s. The structures of these treated clays were characterized by XRD, TEM, DSC, TGA, FT -IR, and SEM, and their chemical properties were analyzed by various methods including atomic absorption spectroscopy, and contact angle measurement. The potential role of water to favor the interaction between scC02 and an organoclay was also investigated. Solute-solvent interactions plasticized the organic modifier while suspended in the supercritical fluid, which resulted in greater chain mobility and further cation exchange. The results indicate that surfactants exhibiting a paraffin-type conformation within the galleries of the clay were most likely to experience significant basal expansion, provided the tilt angle was not already close to being perpendicular to the silicate surface. For those organoclays demonstrating basal expansion, it was noted that the resulting particle size was increased due to enhanced porosity. Water proved useful in clay expansion in certain cases and primarily while operating conditions allowed the co-solvent to remain adsorbed to the clay surface. / Thesis / Master of Applied Science (MASc)

L'exploitation de l'énergie solaire présente une solution alternative efficace pour limiter la consommation de l'énergie fossile et résoudre ainsi les problèmes qui en découlent notamment la pollution et le changement climatique. La dissociation de l'eau par le procédé de la photocatalyse est considérée actuellement comme une méthode innovante pour la photogénération de l'hydrogène (H₂) à partir d'une ressource non carbonée. Les photocatalyseurs classiques mis en jeu ne sont malheureusement activables que sous l'irradiation de l'ultraviolet, ce qui limite leur activité catalytique sous la lumière solaire principalement formée par le visible. Grâce à ses propriétés optiques et électroniques, le phosphore noir (BP) est caractérisé par une bonne absorption lumineuse étendue sur le visible, et même l'infrarouge proche. Ainsi, il présente un candidat potentiel pour les procédés photocatalytiques. Ce travail présente une méthode alternative pour la synthèse d'un nanocomposite à base du BP assisté par le phosphure de nickel (Ni₂P). Cette méthode est basée sur la transition de phase induite par l'éthylènediamine en présence des ions nickel (Ni²⁺) pour la formation in-situ du Ni₂P en tant que co-catalyseur à la surface du BP formé. Les résultats obtenus montrent que l'activité photocatalytique du nanocomposite avec un ratio molaire Ni/P de 3 % atteint 406,08 μmol.g⁻¹.h⁻¹, qui est 185 fois plus élevé que le matériau sans co-catalyseur. Le plus important, le photocatalyseur a montré une efficacité quantique élevée allant jusqu'à 48,45 % à 360 nm et 7,90 % à 400 nm. La caractérisation du matériau synthétisé a prouvé que cette performance photocatalytique pourrait être expliquée par l'absorption lumineuse étalée sur le visible ainsi que l'efficacité de la séparation des porteurs de charges assurée par un contact intime entre le co-catalyseur et le matériau principal. Ce contact établi par une liaison covalente permet également d'avoir une stabilité notable. La stabilité du nanocomposite développé s'est manifestée par une capacité importante de réutilisabilité, ce qui lui permettrait d'être un photocatalyseur performant pour une application pratique. / The exploitation of solar energy presents an effective and an alternative solution to limit the consumption of fossil energy and to solve the correspondent problems, particularly the pollution and the climate change. The water splitting using the photocatalysis process is considered currently as an innovative method for the photogeneration of hydrogen (H₂) from a non-carbon resource. The involved conventional photocatalysts are unfortunately activable only under ultraviolet irradiation, which limits their catalytic activity under sunlight, mainly composed of the visible spectrum. Thanks to its optical and electronic properties, black phosphorus (BP) is characterized by a good light absorption including the visible and even the near-infrared spectrum. Thus, it presents a potential candidate for photocatalytic processes. This work presents an alternative method for the synthesis of a BP-based nanocomposite assisted by nickel phosphide (Ni₂P). This method is based on the ethylenediamine-induced phase transition in the presence of nickel ions (Ni²⁺) for the in-situ growth of Ni₂P as a co-catalyst on the surface of the as-synthesized BP. The obtained results show that the photocatalytic activity of the nanocomposite with Ni/P molar ratio of 3% reached 406.08 μmol.g⁻¹.h⁻¹, which is 185 times higher than the bare material. Most importantly, the photocatalyst showed a high quantum efficiency of up to 48.45% at 360 nm and 7.90% at 400 nm. The characterization of the synthesized material proved that this photocatalytic performance could be explained by the light harvesting efficiency including the visible light as well as the charge carrier separation efficiency ensured by the intimate contact between the co-catalyst and the main material. Also, this contact established by a chemical covalent bond provides a notable stability. The stability of the developed nanocomposite is manifested by a significant capacity for reusability, which would allow it to be a powerful photocatalyst in a practical application.