Generation of reactive oxygen species in titanates nanotubes induced by hydrogen peroxide and their application in catalytic degradation of methylene blue dye

• TiNTs are novel catalysts for degradation of dyes with hydrogen peroxide.
• TiNTs exhibit substantially higher catalytic activity than anatase TiO2 or P25.
• The dye is not only decolorized promptly but degraded readily as well.
• A detailed catalytic mechanism was proposed.

The present work describes the application of sodium (Na-) and hydrogen (H-) titanate nanotubes (TiNTs) as catalysts in oxidation reactions with aqueous hydrogen peroxide. By applying a combination of characterization techniques, it is shown that the interaction of TiNTs with H2O2 leads to a modification in the color and vibrational structure of the TNT, which can be attributed to the formation of superoxide radicals. Electron paramagnetic resonance measurements reveal that fraction of generated radicals increases asymptotically with H2O2 concentration. Catalytic tests of methylene blue discoloration revealed that TiNTs are very active in the discoloration of the dye, being the catalytic activity dependent on the concentration of H2O2. The analysis of the reaction products by electrospray ionization mass spectrometry showed that the dye was successively oxidized in different intermediate compounds. The effects of previous thermal treatment of the TiNTs were also investigated, and it was found that the active catalytic sites are progressively deactivated as the treatment temperature is increased. The overall results suggest that terminal groups present in the titanate structure, such as TiO:− are active catalytic sites that convert into highly reactive superoxide radicals upon interaction with H2O2 molecules.

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