EFFECT OF ULTRASONIC TREATMENT ON HIGHLY HYDROPHILIC TIO2 SURFACES

Glass surfaces coated with polycrystalline titanium dioxide (TiO2) fil ms were found to exhibit a 0 degrees water contact angle when the surf aces were illuminated with UV light in the air. This highly hydrophili c surface was maintained for more than 1 week in the dark in air. Howe ver, ultrasonic treatment in pure water decreased the degree of surfac e hydrophilicity, yielding a contact angle of approximately 11 degrees . X-ray photoelectron spectroscopic measurements indicated that hydrox yl groups and molecular mater adsorption, which govern the surface wet tability, were partially removed from the surface by the ultrasonic tr eatment. The effect of ultrasonic treatment was ascribed to the genera tion of OH radicals that reoxidized the photoreduced surface, accompan ied by the removal of sm face-adsorbed water. This has been confirmed by adding acrylamide, a typical OH radical scavenger, to pure water to effectively suppress the hydrophilic-to-hydrophobic reconversion on t he TiO2 surface.