The Wettability Properties Of Oxygen-deficient TiO₂ Nanotube Array Films

The surface wettability properties is the basic properties of a solid surface, it has a wide application in the self-clean, anti-fog and oil-water separation. The surface wettability properties is determined by the synergy of the surface morphology and the surface free energy.This dissertation titled "The wettability properties of oxygen-deficient TiO₂ nanotube array films" focuses on the preparation and surface wettability properties of oxygen-deficient TiO₂ nanotube array films, mainly summarized the following two aspects work:（1） The TiO₂ nanotube array films were prepared by anodization, then annealed at different temperatures in different atmospheres to obtain oxygen-deficient TiO₂ nanotube arrays films, and studied the surface wettability properties of them. The experiment results show that the annealing atmosphere almost had no effect on the morphologies. But the surface contact angle decreased with the increased of the annealing temperature, and both showed superhydrophilic state. Deposing these samples in dark for a period of times could be changed from superhydrophilic to hydrophobic. After illumination 3 h under the simulated sunlight,they all returned to the superhydrophilic again. When repeated the experiment, the wetting switch was reversible, and the sample which annealed in Argon gas the wettability was changed obvious. Further characterization analysis revealed that the crystallinity of TiO₂ nanotube array films to be better with the increased of the annealing temperature, and the surface free energy of the samples were increased. But the samples annealed in different atmosphere and different temperature could be introduction of different concentration of oxygen vacancy（the sample annealed in Argon gas at 450 ℃, the oxygen vacancy concentration was largest）. The oxygen vacancy reduced the crystalline of the sample, then the surface free energy of samples were decreased. As a result, the contact angle of the samples which were annealed in different atmosphere were depended on the concentration of oxygen vacancies and its crystalline. In addition,the concentration of oxygen vacancy was larger, the sample’s surface activity was stronger, could adsorbed more organic matters, at the same time, the surface contact angle of the samples were bigger.（2） The experimental through low temperature liquid phase reduction TiO₂ nanotube array films which were prepared by anodization, NaBH4 as a reducing agent, controlled the reduction temperature and reduction time to studied the wettability properties ofoxygen-deficient TiO₂ nanotube array films. It was found that the contact angle of samples increased with the increased of reduction time; the contact angle of samples first increased then decreased with the increased of reduction temperature. After illumination 3h under the simulated sunlight, its contact angle were reduced obviously. Further characterization analysis revealed that the NaBH4 liquid phase reduction process could be introducted a large number of oxygen vacancy in TiO₂ nanotube array films. But oxygen vacancy reduced the crystalline of the sample, then the surface free energy of samples were decreased. Anatase TiO₂ is a hydrophilic material, undermining its crystalline will lead to the contact angle of the samples become bigger. But the oxygen vacancies could be introduction of hydroxyl on the surface of the samples, made the samples hydrophilic. As a result, the wettability of the samples were depended on the concentration of oxygen vacancies and its crystalline. With the increased of reduction time, the oxygen vacancy concentration of TiO₂ nanotube array films were increased, the contact angle of samples were increased. At the same time, with the increased of the concentration of oxygen vacancy, the surface activity of TiO₂ nanotube array films were increased, its could be adsorbed more organic matters, and reduced the surface free energy of the samples, then surface contact angle was bigger. When illumination the samples under the simulated sunlights, the contact angle of samples were decreased. Because the TiO₂ nanotube array films had a good photoactivity, which could degradation the organic matters, then the surface of the samples returned to high surface energy. As a result, the oxygen vacancy had obvious effect on the surface activity, and influenced the wettability switched.In conclusion, the results of this study has a beneficial reference in basic research and applied research based on the application of TiO₂ or other metal oxide nanometer functional thin film in self-clean, anti-fog, oil-water separation, photocatalytic and photoelectric conversion and so on.