Mixed-phase TiO2 photocatalysts: Crystalline phase isolation and reconstruction, characterization and photocatalytic activity in the oxidation of 4-chlorophenol from aqueous effluents

Abstract

Anatase and rutile isolated from Degussa P25 and two other TiO2 commercial samples were used as starting materials for the preparation of different anatase/rutile physical mixtures for the photocatalytic oxidation of 4-chlorophenol from aqueous effluents. Degussa P25 was also used as reference active material. The samples were characterized by X-ray diffraction, nitrogen physisorption, Raman spectroscopy, high-resolution transmission electron microscopy and diffuse reflectance UV–vis spectroscopy. A special attention was given to the determination of the band gap energy, by using two methods: Tauc plots and derivative spectroscopy. The second method seems more accurate, eliminating a certain degree of subjectivity, inherent to the Tauc-plot method. The photocatalytic tests showed that Degussa P25 was the most active photocatalyst, followed closely by anatase separated from Degussa P25 and by commercial anatase. The addition of rutile to the anatase powder produced a decrease in the photocatalytic activity. The photocatalytic tests showed that the original Degussa P25 was more active than the anatase phase from its composition, which in turn performed better than the reconstructed P25 in the photocatalytic test given an evidence that the supposed synergistic effect does not operate in this particular case.