Abstract
When H2O molecules desorb from the TiO2 surfaces during UV light irradiation, the vibrational spectroscopies, FT-IR and NIR, revealed that the H-bond interaction between H2O molecules decreased. This observation clearly suggests that the photo-induced high wettability of TiO2 surface is closely related to the decrease in the surface tension of H2O clusters to form H2O thin layers. The partial elimination of the hydrocarbons from the TiO2 surfaces by photocatalytic oxidation was seen to be another major factor, providing free spaces on the surface where the H2O clusters could spill over and spread out to form the thin H2O layers. The superhydrophilic properties of the TiO2 photocatalyst surfaces by a lessening in the amount of H2O adsorbed on the surfaces can be expressed as hydrophobic compared with the initial state before UV light irradiation. Moreover, the temperature changes of the TiO2 powder samples during UV light irradiation were found to show a good correspondence with the changes in the contact angle of H2O droplets on the TiO2 thin film surfaces. Especially, the time scale for hydrophilic conversion on the TiO2 surfaces under UV light irradiation was in good agreement with the decrease in the amount of H2O molecules adsorbed on the surfaces but not the amount of the hydrocarbons eliminated by the photocatalytic oxidation reactions, showing that the adsorption and desorption of H2O molecules are generally sensitive to the temperature changes of solid surfaces.
Published Version
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