(592e) Atomic Layer Deposition of Nanoscale Metal Oxide Layers On TiO2 Nanoparticles Using a Micro-Jet Assisted Fluidized Bed Reactor

The gas-phase fluidization behavior of nanoparticles has been rapidly developing in recent years. Atomic layer deposition (ALD) is a gas-phase reactive process by which nanoscale functional layers can be chemically bonded to the surfaces of fine particles. It is well known that shear forces must be imparted to the nanoparticles in order to overcome attractive interparticle forces and break apart large nanoagglomerates which form due to van der Waals and other attractive forces. A high-pressure micro-nozzle within the bed allows for the delivery of large shear forces and enables the use of glass reactors to monitor the fluidization behavior of powders during ALD processes. ALD is typically performed under vacuum conditions (~1 Torr), but has recently been demonstrated at atmospheric pressure. Nozzle diameter, pressure and relative flow rate are studied at a variety of conditions to optimize nanoparticle fluidization behavior at several operating pressures between vacuum and atmospheric. Since metal oxides are typically deposited using water as an oxygenation source, liquid bridging of hydrophilic nanoparticles is problematic, especially under non-vacuum operating conditions. To mitigate water uptake, isopropanol is studied as a drying agent, as a reactive precursor, or both. Hydrophilic TiO2 particles are used as the substrate of choice, and SiO2 ALD layers are applied in order to passivate the photoactive substrate for usage as pigments in paints or UV absorbers in sunscreens. The performance of the coated particles using the micro-jet assisted fluidization technique is presented in the context of the respective application.