Periodic mesostructured nanocrystalline titania
Subtitle: synthesis, characterization and electrical properties.
Published: 2005
Language: eng
Number of pages: 135
Description: Periodic mesostructured nanocrystalline metal oxides templated by supramolecular mesophases are comprised of a uniform array of monodispersed mesopores with walls made of metal oxide nanocrystals. They often exhibit higher surface area and easier diffusion paths for guest molecules compared with earlier generation polydispersed mesoporous nanocrystalline metal oxides, along with their unique electronic, magnetic and catalytic properties. The subject of this thesis deals mainly with the development of novel synthetic pathways to periodic mesostructured metal oxides targeted for device applications. The materials of choice is periodic mesostructured nanocrystalline titania, denoted meso-nc-TiO2 and the goal is to determine how it compares chemically, electrically and optically to conventional nanocrystalline titania, denoted nc-TiO2.A kinetic study of the thermally induced amorphous-to-nanocrystalline anatase phase transition within 2D hexagonal meso-TiO2 thin films using time-resolved in-situ high temperature X-ray diffraction (HTXRD) in conjunction with HRSEM and HRTEM is also described. This study reveals that the framework of the liquid crystal templated mesostructure guides anisotropic, rod-shaped anatase nanocrystallites growth preferentially aligned along the channel axis. Investigation of the electrical properties of 2D hexagonal meso-nc-TiO2 is also reported. Using the electrochromic performance of a viologen modified meso-nc-TiO2 electrode, it is demonstrated that a well-ordered meso-nc-TiO2 electrode exhibits a similar conduction band edge and electron percolation behavior as nc-TiO 2 but with the benefit of a larger accessible surface area.Highly reproducible synthetic methods are introduced in this thesis for producing a thermally stable well-defined meso-nc-TiO2 in the form of monoliths and crack-free films. By tuning the film aging conditions, it is possible to make optically transparent crack-free thin film of either 2D hexagonal or 3D face-centered cubic meso-nc-TiO2. It is demonstrated that 1-butanol plays a pivotal role in the successful synthesis of meso-nc-TiO 2 due to the relatively hydrophobic nature of this solvent, which is able to create an enhanced phase separation between the template and titania precursor leading to a more well-defined mesostructure and robust titania framework. In addition, a novel low temperature synthetic route is introduced for making meso-nc-TiO2 under mild (100&deg;C) hydrothermal conditions, which provides a convenient pathway to a crack-free flexible meso-nc-TiO 2 thin film.
Notes: Source: Dissertation Abstracts International, Volume: 66-10, Section: B, page: 5391.

Thesis (Ph.D.)--University of Toronto, 2005.

Electronic version licensed for access by U. of T. users.