Fundamental Study and Practical Applications of Composite Colloidal Nanostructures

In recent years, nanomaterials, defined as materials with a size of < 100 nm in at least one axis, have attracted widespread interest due to their promise in many applications. Due to their small sizes, nanoparticles exhibit unique properties not found in their bulk counterparts, such as superparamagnetism in magnetic nanoparticles, as well as quantized plasma oscillations leading to well-defined extinction peaks in metal nanoparticles. Although many fabrication techniques exist to produce these unique materials, colloidal nanomaterials are of particular importance due to their low cost and ready scalability, and their easy suspension in solutions. Current research focuses on improving syntheses and developing new types of materials with novel properties, as well as studying the underlying mechanisms behind their growth in solution. One area of investigation involves producing composite nanomaterials, which contain two or more different nanoscale components. By making a composite material, it is possible to produce a material which possesses the properties of all of its components, or even a material with entirely new properties. Composite materials can also be produced as intermediates, often with one material acting as a sacrificial template which is later removed, to produce a material with a morphology unattainable with conventional synthesis. In this work, a variety of uses have been explored for colloidal nanoscale composites. First, the mechanism for the seeded growth of 2D silver nanoplates was studied through a marker experiment. Prior to growth, a thin layer of gold was deposited on the plate edges, which defined the original boundary of the nanoplate seed, allowing easy observation of the direction of growth and making it possible to explain previously observed shape transitions during this process. In later work, gold microplates were conjugated to amine-terminated magnetic nanoparticles to create a material which was both anisotropic, magnetic, and highly reflective. This composite was studied as a micron-size actuated mirror system, which was found to have a fast magnetic response and good optical contrast between the "on" and "off" states. Finally, a gold-titania core-shell composite was developed, which proved resistant to high-temperature sintering and was able to photocatalytically produce hydrogen from ethanol.