Oxidative power of aqueous non-irradiated TiO2-H2O2 suspensions: Methylene blue degradation and the role of reactive oxygen species

• Non-irradiated TiO2-H2O2 suspensions can degrade MB.
• Degussa P25 shows the highest degradation of MB among five TiO2 catalysts.
• Degradation of MB takes place at the catalysts surface.
• EPR spin trapping verified the formation of highly oxidative ROS.

In the present study, the degradation of methylene blue in non-irradiated TiO2-H2O2 suspensions was investigated. Five commercially available catalysts were characterized (BET surface area, zeta potential, hydrodynamic diameter) and their oxidative power was assessed by means of the degradation of methylene blue. A subsequent EPR study was made to verify and identify potential oxidative radicals. The results showed that all suspensions could degrade methylene blue significantly stronger compared to hydrogen peroxide alone. A broad variation between the different catalysts in their capability to adsorb dye molecules was found which was essential for decomposition of methylene blue in darkness. The highest degradation rate of all samples was found for Degussa P25 at neutral pH. EPR studies of this sample verified the presence of oxygen centred radicals namely hydroxyl (OH) and superoxide radicals (O2−/OOH). Non-irradiated TiO2-H2O2 systems show great potential not only in dye removal applications but also in the field of disinfection where low concentrations of hydrogen peroxide are required and irradiation may not be feasible.

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