Abstract
Abstract In this study, alumina and titania nanostructures were prepared by template methods, where Tris-(8-hydroxyquinoline) gallium (Gaq3) organic nanowires and polystyrene (PS) nanosphere monolayer, respectively were used as the templates. The dissertation is divided into two parts. The growth mechanism, photoluminescence (PL) and photocatalysis of the nanostructures are discussed. In the first part, Gaq3 nanowires prepared by thermal evaporation were used as the templates. Atomic layer deposition (ALD) was employed to coat Al2O3 on the Gaq3 nanowires. Toluene and low temperature heating were then used to remove Gaq3 nanowires, and therefore alumina nanotubes were formed. The wall and thickness of the nanotubes were very uniform and could be well controlled. The growth of Al2O3 by ALD on the nanowires involved reaction of hydroxyl group on the nanowires with the precursor of alumina. In addition, PL spectra and their stability of Gaq3-Al2O3 core-shell nanowires in different gases were examined. No difference of PL spectra of Gaq3 and Gaq3-Al2O3 core-shell nanowires could be observed. The core-shell nanowires showed the highest degradation rate in oxygen among all gases. On the other hand, water acted only as a catalyst to provide oxygen and argon was protective. In the second part, TiO2 nanohoneycomb and nanowires were prepared by means of PS nanosphere monolayer. The nanohoneycombs were fabricated by titanium tetrachloride in different solvents, i.e., t-butanol, ethanol, and water. Because of higher affinity between t-butanol and polystyrene nanospheres, the nanohoneycomb prepared by t-butanol shows the better morphology. Besides the absorption due to the band gap of TiO2, the absorption in visible light was also obtained due to the defects of nanohoneycomb. Nanohoneycomb has better photocatalytic activity than that of thin film because of its higher surface area. Subsequently, as the precursor, titanium tetrachloride was replaced by TiO2 nanoparticles. In this case, TiO2 nanowires were formed. Different from V-L-S (vapor-liquid-solid) mechanism, the growth of the nanowires involved a precipitation process. In the beginning of the process, TiO2 nanoparticles reacted with silicon substrate to form titanium silicide. Titanium silicide was then oxidized to form TiO2 and SiO2. TiO2 nanowires were precipitated from the silica matrix to reduce the energy. Finally, the photocatalysis of the nanowires was also examined. They had higher activity for decomposition of rhodamine B than nanoparticles. It may be due to recombination of electrons and holes and the band gap widening.