What is Degussa (Evonik) P25? Crystalline composition analysis, reconstruction from isolated pure particles and photocatalytic activity test

Anatase and rutile crystallites were isolated from Degussa (Evonik) P25 by selective dissolution with a hydrogen peroxide–ammonia mixture and diluted hydrofluoric acid, respectively, and used as standard samples for calibration curves of X-ray diffraction analyses. The results showed that P25 contains more than 70% anatase with a minor amount of rutile and a small amount of amorphous phase. The composition anatase/rutile/amorphous could be determined by analysis of P25 mixed with an internal standard, nickel(II) oxide. However, it was also found that the composition of P25 used in this study was inhomogeneous and changed depending on the position of sampling from the same package. Comparison of activities of original P25 and reconstructed P25 with those of isolated anatase and rutile particles suggested a less-probable synergetic effect of the co-presence of anatase and rutile.