Polycrystalline anatase TiO2 films were deposited by rf reactive magnetron sputtering on polyethylene terephthalate (PET) or polyimide (PI) films with different buffer layers, such as SiO2 or Zn2SnO x (ZTO), between the TiO2 film and the substrate. Such TiO2/(SiO2 or ZTO)/(PET or PI) sheets with high transmittance in the visible region of light showed high photo-decomposition ability towards CH3CHO under UV irradiation by a black light centered at 352 nm. When SiO2 was used as the buffer layer, a "nano-pore layer" was observed clearly over the full area of the polymer substrate close to the buffer layer after UV irradiation, whereas such degradation was suppressed drastically when ZTO was used as the buffer layer. Such photocatalytic sheets also demonstrated photo-induced hydrophilicity upon UV irradiation, with the contact angle to pure water becoming around 5° under UV irradiation. After additional deposition of SiO2 on the outermost surface of the TiO2 films by reactive sputtering under rather a high total gas pressure of 3.0 Pa, the photo-induced hydrophilicity was maintained for more than 98 days in the dark. Such three-layered SiO2/TiO2/ZTO films on PET or PI substrates could be promising flexible photocatalytic sheets that retain photo-induced hydrophilicity.
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