Abatement of organics and Escherichia coli by N, S co-doped TiO2 under UV and visible light. Implications of the formation of singlet oxygen (1O2) under visible light

Nitrogen and sulfur co-doping has been achieved in the commercial TiO2 nanoparticles of anatase TKP 102 (Tayca) by grinding it with thiourea and calcinating at 400 °C. The successful substitutional N-doping and cationic/anionic S-doping were validated by XPS measurements. Diffuse reflectance spectroscopy (DRS) showed a marked broadening of the absorption spectrum of the doped material towards the visible range.Phenol and dichloroacetate (DCA) oxidation and Escherichia coli inactivation were achieved under UV illumination using the N, S co-doped TiO2 powders. Electron spin resonance (ESR) spin-trapping experiments showed that under UV light irradiation, the OH radicals were the main species responsible for photo-degradation of phenol and E. coli abatement. Photo-degradation of DCA was found to be due a direct interaction of the TiO2 valence band holes (hVB+) with the DCA molecules.Moreover, under visible light (400–500 nm) illumination of N, S co-doped TiO2 a complete inactivation of E. coli bacteria was observed. In contrast, under such conditions, phenol was only partially degraded, whereas DCA was not at all affected. ESR experiments performed with N, S co-doped TiO2 powders illuminated with visible light and in the presence of singlet oxygen (1O2) quencher, TMP-OH, showed the formation of 1O2. This suggests that superoxide radical (O2−) and its oxidation product, 1O2, were responsible for E. coli inactivation by N, S co-doped TiO2 nanoparticles under visible light.