Surface modified alumina powder having photocatalytic activity was studied. In order to control the amount of Ti introduced on the surface at the molecular level, the powder was prepared by chemical surface modification with a monofunctional titanate-based coupling agent, followed by partial oxidation of the modification group. The surface density of Ti introduced onto the surface was quantitatively increased with the concentration of the modifying reagent, and/or the repeat times of the modification. Furthermore, the relationship between the surface structure and the photocatalytic activity was discussed. The surface structure was measured by XPS and UV-Visible absorption spectrometry. The photocatalytic activity was determined by means of the degradation of Methylene Blue molecule in a water solution with UV irradiation. The photocatalytic activity appeared at the Ti surface density of 3.7nm-2. The optical absorption edge in UV of the sample shifted to long wavelenghts. The ability as a photocatalyst increased with the amount of Ti-O-Ti. It was recognized that the photocatalytic activity was related to the amount of Ti-O-Ti on alumina surface and the ability of UV absorption.
