Photocatalytic decolorization and mineralization of dyes with nanocrystalline TiO2/SiO2 materials

The application of photocatalytic technologies for the treatment of dyeing effluents from the textile industry has been shown to be economically competitive, especially when solar light drives the process. However, improvements in the catalysts are required to facilitate the separation stage. This work addresses the synthesis and characterization of nanocrystalline TiO2 (n-TiO2) incorporated into commercial silica particles and the activity of these materials in the photocatalytic treatment of three different azo dyes. The characterization of the n-TiO2/SiO2 photocatalysts shows differences in the average crystallite size that lead to significant differences in the values of the band gap energy of the semiconductor and also in activity. The molecular structure of the dyes also influences the kinetics of degradation, being almost independent of the TiO2 loading for Methyl Orange, which is opposite to the cases of Congo Red and Trypan Blue. This different behavior could arise from the existence of mass-transport restrictions hindering the complex dye molecules from reaching the titania nanocrystals located inside the porous structure of the silica particles.