PREPARATION, CHARACTERIZATION, AND POTENTIAL-DEPENDENT OPTICAL-ABSORPTION SPECTROSCOPY OF UNSUPPORTED LARGE-AREA TRANSPARENT NANOCRYSTALLINE TIO2 MEMBRANES

We describe preparation, characterization, and the potential-dependent optical absorption spectroscopy of an unsupported large-area transparent nanocrystalline TiO2 membrane. Regarding preparation, an aqueous sol of 10 nm nanocrystallites is used to deposit a TiO2 gel film on an ammonium chloride pellet. This salt pellet is then sublimed by heating under reduced pressure to yield an unsupported film. Firing of this film, at temperatures sufficiently high to fuse the constituent crystallites, leads to formation of a mechanically robust 2 x 2 cm transparent membrane. Characterization by electron microscopy and electron diffraction reveals the above to be a 2 mu m thick nanoporous-nanocrystalline anatase structure. Measurement of potential-dependent optical absorption spectra has proved possible, following formation of an ohmic contact using silver epoxy, for both underivitized membranes and membranes derivitized by adsorption of a redox dye. Results obtained are consistent with those for transparent nanocrystalline anatase films supported on conducting glass. Some implications of these findings are discussed, as are possible applications for such membranes.