Photocatalytic activity of MCM-organized TiO(2) materials in the oxygenation of cyclohexane with molecular oxygen

The photooxygenation of cyclohexane by molecular oxygen has been investigated on two mesoporous TiO(2) materials, which have been prepared using colloidal nanoparticles as building blocks. One of the structured systems (mpTiO(2)-50) is a mixture of 50% TiO(2) and 50% SiO(2); the second one (mpTiO(2)-100) is constituted by 100% of TiO(2). Both mpTiO(2)- 100 and mpTiO(2)-50 can induce cyclohexane photooxidation in repeated cycles, but with the former the yield in cyclohexanone is higher and only traces of cyclohexanol are observed. The results of experiments with different incident light intensities are reported: contrary to mpTiO(2)-50, the selectivity of mpTiO(2)-100 towards cyclohexanone is not significantly affected by the photonic flux. Based on the substrate conversion rates, incident photonic flux effects, photoluminescence and EPR spectra of the mesoporous materials, we infer that the photoreactivity of mpTiO(2)-100 and mpTiO(2)-50 is mainly controlled by textural effects. In particular, we propose that the inter-particle electron mobility that characterizes the mpTiO(2)-100 material, which is constituted exclusively of TiO(2) nanoparticles, entails a better utilization of electron traps for converting the photogenerated cyclohexyl-peroxide radicals to cyclohexanone.