It is well known that Degussa P25, a very famous titania powder sample, is composed of anatase and rutile crystallites, but, as far as the authors know, there have been no reports on correct quantitative analyses for the crystal composition. Recently, the author's group succeeded in isolation of anatase crystalline phases from P25 [1]. Using this pure anatase as well as rutile [2], calibration curves (Figure) for the X-ray diffraction peaks were obtained to determine the ratio of anatase, rutile and amorphous phase to be 78 : 14 : 8.
Reconstitution of P25 was performed by mixing isolated pure anatase and rutile particles with a commercial amorphous titania in the above-mentioned ratio. An XRD pattern, BET surface area and a diffuse reflection spectrum of the reconstituted sample were almost the same as those of the original sample. The reconstituted sample showed the photocatalytic activities, in four reaction systems, which are almost the same as those by the original sample, even when the sample suspension was preparing only by putting two powders into an aqueous solution. This suggests that there is negligible synergetic effect by the co-presence of anatase and rutile in P25.

[1] Trans. Mater. Res. Soc. Jpn. 2007, 32, 401.
[2] J. Phys. Chem. B, 105, 2417-2420 (2001).