Selective dissolution of TiO 2 crystalline phases: Physicochemical characterization and photocatalytic activity

In this study, different commercially available TiO2 powders (Degussa P25, pure anatase, and rutile) were submitted to selective dissolution treatments, with H2O2/NH4OH and 10% HF, known to remove rutile and anatase from physical mixtures. The aim was to check whether a particular separation method designed to remove a specific crystalline phase influences the properties of the other phase from the mixture or not. More precisely, we have studied how the HF dissolution method designed to selectively remove the anatase affected the physicochemical and photocatalytic properties of rutile. In a similar way, the changes in the anatase properties were studied, after the H2O2/NH4OH treatment, initially used to remove rutile from the mixture. All the samples were characterized by X-ray diffraction, nitrogen adsorption–desorption, transmission electron microscopy, diffuse reflectance (DR) ultraviolet–visible, and Raman spectroscopy. The photocatalytic activity of these powders was tested in the oxidation of p-chlorophenol from water. The selective treatment methods not only dissolved the target phase but also changed some physicochemical and the photocatalytic performances of the other TiO2 crystalline phase in a considerable manner. These aspects should be taken into account in the studies regarding the synergistic effects of anatase and rutile, especially in reconstructed TiO2 photocatalysts.