Advanced Nanocrystal-Dispersed Coatings from Metal Oxide Gels with Hot-Water Treatment under External Fields

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External fields of vibrations and electric voltages affected the nanostructure of titania crystallites formed on SiO_2-TiO_2 gel coatings during hot-water treatment. Without the external fields granular anatase nanocrystals of 30-50 nm in size were formed on the coatings during the hot-water treatment, whereas the shape of the precipitates became sheetlike by applying a vibration to the substrate during hot-water treatment. Similar changes in shape of the precipitates on the coatings were also observed, and ramiform (branchlike) crystallites were formed at the negative electrode by applying an electric field between the substrates. The sheetlike and ramiform crystallites are mainly composed of a hydrated titania, m(TiO_2)・nH_2O, with the lepidocrocite-like layered structure with a d-spacing of 0.6-0.8 nm. Titania nanosheets are characterized by a large surface-to-volume ratio, which gives rise to the excellent wettability for water and antifogging properties. Processing temperatures fo … More r the preparation of the coatings can be lowered at about 60℃ under atmospheric pressure, so that the coatings have a great potential for applications to various substrates including organic polymers with poor heat resistance.The addition of supramolecular assemblies of CTAB, P123, and F127 in the SiO_2-TiO_2 gel films permits the formation porous film structure and highly dispersion of anatase nanocrystals in the whole films after hot-water treatment. When the anatase nanocrystal-dispersed, porous films were irradiated with UV light, residual surfactants were completely eliminated due to the photocatalytic effects of the nanocrystals.SiO_2-TiO_2 spherical microparticles of about 0.7 μm in diameter have been prepared by the sol-gel method. Anatase nanocrystals were formed in the microparticles and their specific surface area was increased after a hot-water treatment at 90℃. Particulate, thick films were electrophoretically deposited on indium-tin oxide (ITO)-coated glass substrates using the anatase nanocrystal-precipitated SiO_2-TiO_2 microparticles.Hot water treatments were also found to be effective to form nanostructure as well as nanocrystals for Al_2O_3, SnO_2 and ZnO gel films at low temperatures. Cubic SnO_2 and hexagonal ZnO crystallites were precipitated by the hot water treatment, whereas AlO(OH) crystallite were formed on the Al_2O_3 film. With respect to ZnO gel coatings, the electric voltage and type of substrates showed a significant influence on the crystal habit of ZnO on the negative electrode. Hexagonal columnar and petal-like crystallites, which were oriented in the C-axis direction, were formed ITO-coated glass substrate and Si wafer, respectively. Less