Photoinduced Hydrophilic Conversion Properties of Titania Nanosheets

Photoinduced hydrophilic conversion properties of titania nanosheets were investigated. A highly hydrophilic state was achieved on the monolayer film surface of titania nanosheets, the thickness of which is less than 1 nm. The hydrophilic conversion rate (k) for the monolayer film of titania nanosheets was proportional to the intensity (I) of irradiated light, suggesting that the hydrophilic conversion of the titania nanosheet surface proceeded under light-limited conditions even with a high concentration of photoexcited carriers. As the number of layers of titania nanosheets increased, the dependence behavior changed from k ∝ I^1.0 to k ∝ I^0.5, indicating that the recombination processes become dominant in the multilayer films of titania nanosheets. In-plane X-ray diffraction (XRD) analyses showed a very small but reproducible structural change of titania nanosheets upon UV irradiation.