Doctoral dissertation
Catalytic wet peroxide oxidation of water dissolved organic pollutants under mild conditions
Views: 2 | Downloads: 0
Abstract
Peroxo species decorated amorphous TiO2-based materials, namely nanosheets, nanotubes, nanorods and rice-like morphology, have been obtained through alkaline hydrothermal restructuring of different Ti-based precursors. Obtained materials were tested in catalytic wet peroxide oxidation (CWPO) of methyl orange (MO) under mild conditions, where prevalent catalytic activity has been attributed to TiO2-based nanotubes characterized with high specific surface area and high amount of surface peroxo species.
Low-temperature thermal treatment of the TiO2 based nanotubes has revealed loss in the amount of ion-exchangeable OH groups, and consequently in the amount of peroxo species, which causes lowering of the catalytic activity. In contrast, by applying optimal acid treatment catalytic activity increased and with the usage of 2 g/L of peroxide-treated TN/ClO4p 0.01 material, and double stoichiometric amount of H2O2, 50 ppm MO solution was purified up to ~93 % during 90 min at 40 °C with adsorption of only ~1 %. Catalytic performance remained constant during 5 consecutive runs using the same batch of the material.
With detailed O2 TPD/MS, temperature-dependent UV/Vis DR, in-situ Raman, 1H MAS and 17O NMR analyses it has been proposed that peroxide treatment induces complete changes in the material, although high catalytic activity can directly be ascribed to end-on η2 peroxo species whose amount remains almost constant during 5 consecutive runs, namely 5.9*10-7 mol O2/m2 and 5.2*10-7 mol O2/m2 prior and after usage. Remaining thermally labile two-coordinated oxygen species, detected with O2 TPD/MS and 17O NMR and used during CWPO of MO without affecting high catalytic activity, is proposed to serve as a place for novel peroxo species formation through creation of terminal Ti-O•- radicals and OH groups.