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 TiO 2 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 TiO 2 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 TiO 2 valence band holes ( h VB + ) with the DCA molecules. Moreover, under visible light (400–500 nm) illumination of N, S co-doped TiO 2 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 TiO 2 powders illuminated with visible light and in the presence of singlet oxygen ( 1 O 2 ) quencher, TMP-OH, showed the formation of 1 O 2 . This suggests that superoxide radical ( O 2 − ) and its oxidation product, 1 O 2 , were responsible for E. coli inactivation by N, S co-doped TiO 2 nanoparticles under visible light.