Role of the support on the activity of silica-supported TiO2 photocatalysts: Structure of the TiO2/SBA-15 photocatalysts

Immobilization of TiO2 on silica materials has been commonly proposed in order to make easier the separation of the catalyst after the photocatalytic reactions in aqueous systems. The main drawback of the supported photocatalysts is that they usually show lower activities in comparison with powdered TiO2 materials. The aim of this work is to elucidate the structure of some silica-supported TiO2 photocatalysts recently developed as well as to evaluate the role that the porous structure of the support can play in the observed photocatalytic activities. In comparison with the use of an amorphous silica support, the use of the mesostructured silica SBA-15 produces an ordered structure in which TiO2 crystals of similar sizes, independently of titania loading, are located inside the mesoporous channels of the support. The photocatalytic treatment of several cyanide-containing compounds is analyzed and the results are explained in terms of the structure of every catalyst. Depending on the model compound, the characteristic structure of the TiO2/SBA-15 materials allows increasing up to eight times the activity achieved by the Degussa P25 TiO2. The main conclusion of this work is the strong influence of the textural properties of the support on the catalytic activity of immobilized TiO2 photocatalysts.