Photocatalytic activity of TiO2/SiO2 systems

Silica-supported TiO2 powders were synthesized by a wet method under mild conditions. The aim of thework was the preparation of TiO2/SiO2 additives for photocatalytic cements. Three types of commercialSiO2 were used as supports: Cabot, Axim and Fly Ash. Cabot silica was ultra-pure whereas the othertwo silica contained different percentages of various oxides. The TiO2/SiO2 samples, denoted TiO2/Cabot,TiO2/Axim and TiO2/Fly Ash, were prepared by boiling suspensions obtained by addition of silica to asolution of TiCl4 in water (volume ratio 1:10). The photocatalytic activity was evaluated in a gas–solidsystem both in batch and in continuous reactors using 2-propanol as probe molecule. SEM-EDX analysisrevealed that titanium dioxide was quantitatively deposited on silica. TiO2/Axim and TiO2/Fly Ash werescarcely active whereas a good photoactivity was exhibited by the TiO2/Cabot sample both in the batchand in the continuous system. Consequently only the last sample was tested for both NOx abatement andfor 4-nitrophenol photodegradation in a liquid–solid system.