Abstract: Mesoporous titania films are of intense and growing interest as components for photovoltaic and photoelectrochemical power conversion. Our group has introduced a method to prepare titania films with vertically oriented, 2D hexagonally close packed nanopores. However, for widespread commercial use of these materials, the geometry of the films must be controlled, including the pore size, the wall thickness, and crystallinity of the walls. Mesoporous titania thin film are synthesized by sol-gel chemistry in the presence of tri-block copolymer P123 ((EO)
20 (PO)
70 (EO)
20) template. The films are deposited on glass slides modified with cross-linked P123 to orient the pores normal to the substrate, and then the fresh films are either exposed to the air during aging, or contacted with an identical modified slide to sandwich the films and give complete orientation. The effects of the molar ratio of template P123 to titanium (R) and the micelle swelling agent butanol are investigated. The results indicate that wall thickness and pore size of the mesoporous titania thin films can be tuned without damaging the well ordered mesostructure by varying R and the amount of butanol. Furthermore, when the films are sandwiched, mesoporous titania thin films with channels perpendicular to the substrates can still be obtained even as R decreases and the amount of butanol increases. The only limitation on this seems to be when the system moves into a different region of the phase diagram (e.g. when close-packed globular micelle phases form). To further improve the properties of the mesoporous titania thin films, a post synthesis treatment approach is explored in which the films are heated slowly to a temperature below 400 °C for a prolonged time, followed by a short treatment at high temperature (> 400 °C). This approach is hypothesized to preserve mesopore order while giving larger crystallites, especially when thicker walls are produced by decreasing R, and we will present data to confirm the status of the films during the post-synthesis treatment.
Key words: mesoporous, titania, thin films, crystallization, energy