Highly efficient bacteria inactivation and phenol degradation by visible light irradiated iodine doped TiO2

In this study visible light active iodine doped titanium dioxide samples prepared by sol–gel method were investigated. Photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray fluorescence spectroscopy (XFS), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and by Brunauer–Emmett–Teller (BET) surface area technique.Different iodine/titanium ratios (nI/nTi = 0.0–2.6) were applied during the synthesis and the optimum value was determined by phenol degradation under UV and VIS irradiations. The photocatalytic efficiency towards phenol degradation and the inactivation of Escherichia coli (E. coli) contaminated water under visible light illumination (conventional 24 W energy-saving compact fluorescence lamps) of the most active iodine-doped TiO2 (nI/nTi = 0.5; 79.5 m2/g; 98 wt% anatase) was compared with well known reference photocatalysts, that are Aeroxide P25 and Aldrich anatase (>85 nm primary crystallite size). Results showed that our iodine doped TiO2 was far more efficient at inactivating the E. coli and decomposing the phenol than Aeroxide P25. Electron spin resonance (ESR) measurements confirmed the formation of highly reactive OH radicals by the iodine doped titania under VIS irradiation. In contrast, singlet oxygen and superoxide radical ions were not detected. The performed experiments also proved that dissolved iodine was produced in very low concentrations (about 0.01–0.025 mg/L) from the irradiated titanium dioxide. The dissolved iodine could have some contribution to the phenol oxidation and the disinfection effects. This study demonstrated this property of iodine-doped titanias for the first time.

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► TiO2-I decomposes phenol with much higher efficiency than P25 under VIS irradiation.
► TiO2-I kills E. coli more effectively than P25 under visible light.
► Iodine doped TiO2 can generate OH radical under VIS irradiation.
► Dissolved iodine was derived from the irradiated titanium dioxide.