Abstract: In the present study, particulate suspensions of nanosized(particle size less than 10nm) anatase and rutile TiO₂ under UV irradiation in a loop
photoreactor catalyzed the oxidation of a typical organic contaminant: phenol. Both nanosized anatase and rutile TiO₂ have a much higher photocatalytic
activity than bulk TiO₂ (particle size more than 100nm), however, anatase shows a higher selectivity for complete mineralization: the concentration of
p-quinone as intermediate of this photocatalytic reaction is at lower level than those of rutile. Species adsorbed by titanium dioxide such as H₂O and OH
play a significant role in the photodegradation of phenol as well as particle size . With the decrement of particle size especially less than 15nm,
the photocatalytic activity of TiO₂ increases dynamically.

Key words: titania, nanocrystalline, photocatalysis, degradation