Enhancement of photocatalytic activity of rutile titanium dioxide single crystals by ordering surface oxygen defects

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Photocatalytic activity of titanium dioxide is normally discussed in terms of band theory. There are, however, other factors that are also important for the photocatalytic activity, especially when surface oxygen is involved in the reaction. In this study we investigated the relation between the surface condition of rutile titanium dioxide single crystals and the photocatalytic activity: (1) Effect of crystallographic orientation of as-received (polished) surface on the photocatalytic activity, (2) Effect of surface treatment on the photocatalytic activity and contact angle, (3) Structural analysis of (001) surface, etc. We find that (001) surface is the most active surface among the low index surfaces of rutile titanium dioxide, that the activity decreases as the surface is heated or treated in HF solution, and that multiple parallel grooves must be introduced in certain direction on the low active surface before the activity is regained.