Structural stabilization and characterization of active peroxo species on TiO2-nanotube based materials in mild catalytic wet peroxide oxidation process

Amorphous TiO2 based nanotubes (TN) obtained through alkaline hydrothermal restructuring of P25 were treated with various acids and functionalized with hydrogen peroxide in order to tailor formation of structurally distinctive titanium peroxo species. Obtained solids were used as catalysts in the catalytic wet peroxide oxidation (CWPO) of model methyl orange (MO) aqueous solution under mild conditions. With the usage of 2 g/L of peroxide modified TN/ClO(4)p 0.01 catalyst and double stoichiometric amount of hydrogen peroxide, 50 ppm MO solution was purified up to 93% during 1 h at 40 degrees C. No decay of catalyst activity was observed in 5 consecutive runs using the same catalyst batch. O-17 NMR and TPD/MS analyses have revealed that catalytic activity of TN/ClO(4)p 0.01 sample can mainly be assigned to bidentate eta(2) surface peroxo species whose amount during 5 consecutive catalytic runs is almost constant, namely 5.9 x 10(-7) and 5.2 x 10(-7) mol/m(2) prior and after usage, respectively. In addition, it has been observed that considerable amount of thermally labile oxygen species is used during 5 consecutive runs. From O-17 NMR analysis we have observed that these species can be attributed to two coordinated (OTi2) oxygen formed on the place of terminal intra/interlayered - OH groups. Former can serve as structural stabilizing agents which enable formation of new eta(2) surface peroxo species during CWPO runs. To the best of our knowledge, this study is the first attempt to explain the possibility for eta(2) peroxo species structural stabilization during CWPO under mild conditions.