Takeuchi Masato, Sakamoto Kenji, Martra Gianmario, Coluccia Salvatore, Anpo Masakazu
Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1, Gakuen-cho, Sakai, Osaka 599-8531, Japan.
J Phys Chem B. 2005 Aug 18;109(32):15422-8. doi: 10.1021/jp058075i.
The physicochemical properties of the H(2)O molecules adsorbed on TiO(2) surfaces during UV light irradiation were fully investigated by near-infrared (NIR) absorption spectroscopy. It was found that the H(2)O molecules adsorbed on the TiO(2) surfaces desorb during UV light irradiation by the heating effect of the light source. Since the amount of the H(2)O adsorbed on the TiO(2) surfaces decreased, the distribution of the hydrogen bonds within the H(2)O molecules decreased, resulting in a decrease in the surface tension of the H(2)O clusters. The decrease in the surface tension of H(2)O under UV light irradiation was found to be one of the most important driving forces in which the H(2)O clusters on the TiO(2) surface spread out thermodynamically, forming H(2)O thin layers. The partial elimination of the hydrocarbons from the TiO(2) surface by the photocatalytic complete oxidation was seen to be the other important factor, providing free spaces on the surface where the H(2)O clusters could spill over and spread out to form the thin H(2)O layers. Moreover, the temperature changes of the TiO(2) powder samples during UV light irradiation were found to show a good correspondence with the changes in the contact angle of the H(2)O droplets on the TiO(2) thin film surfaces. Especially the time scale for the hydrophilic conversion on the TiO(2) surfaces under UV light irradiation was in good agreement with the decrease in the amount of H(2)O molecules adsorbed on the TiO(2) surfaces but not the amount of the hydrocarbons eliminated by the photocatalytic oxidation reactions, showing that the adsorption and desorption of H(2)O molecules are generally quite sensitive to the temperature changes of solid surfaces.
通过近红外（NIR）吸收光谱对紫外光照射下吸附在TiO₂表面的H₂O分子的物理化学性质进行了全面研究。结果发现，吸附在TiO₂表面的H₂O分子在紫外光照射下因光源的加热效应而解吸。由于吸附在TiO₂表面的H₂O量减少，H₂O分子内氢键的分布减少，导致H₂O团簇的表面张力降低。发现紫外光照射下H₂O表面张力的降低是TiO₂表面的H₂O团簇热力学上展开形成H₂O薄层的最重要驱动力之一。光催化完全氧化使TiO₂表面的碳氢化合物部分消除被认为是另一个重要因素，它在表面提供了自由空间，H₂O团簇可以溢出并展开形成薄的H₂O层。此外，发现紫外光照射期间TiO₂粉末样品的温度变化与TiO₂薄膜表面上H₂O液滴的接触角变化具有良好的对应关系。特别是紫外光照射下TiO₂表面亲水性转变的时间尺度与吸附在TiO₂表面的H₂O分子数量的减少一致，但与光催化氧化反应消除的碳氢化合物数量不一致，这表明H₂O分子的吸附和解吸通常对固体表面的温度变化相当敏感。
