Intrinsic photocatalytic activity of anatase and rutile TiO2 for the bleaching of methylene blue

The influence of the crystal structure of TiO2 on the photocatalytic activity was investigated. Methylene blue decolourization was used as a test reaction to give an indication of the number of excited electron-hole pairs available for photocatalytic reactions. The anatase crystal phase in Degussa P25 was partially converted to rutile with the use of heat treatments. X-ray diffraction was used to determine the rutile to anatase ratio in the heat treated material and the crystallite size. The surface area of the catalyst particles was determined with BET measurements, and the morphology observed with scanning electron microscopy. It was found that the change in crystal structure plays an important role, but only at very high conversion degrees of anatase to rutile. The reaction rate normalized to the surface area remains constant up to a very large percentage of rutile.