Escherichia coli inactivation by N, S co-doped commercial TiO2 powders under UV and visible light

Commercial anatase TiO2 powders (Tayca TKP101, TKP102) were ground with thiourea and annealed at 400 and 500 °C. Diffuse reflectance spectra (DRS) showed that the doping with thiourea shifted the TiO2 absorption towards the visible region. The absorption was observed to increase with increasing annealing temperature. Using the Kubelka–Munk relations, it was possible to determine the band-gap of the doped TiO2. Doped Tayca TiO2 TKP101 showed a band-gap of 2.12 and 2.24 eV calcined at 400 and 500 °C, respectively. Doped Tayca TiO2 TKP102 calcined at 400 and 500 °C showed in both cases a band-gap of 2.85 eV. X-ray photoelectron spectroscopy (XPS) revealed that these doped TiO2, TKP101 annealed at 400 °C and TKP102 annealed at 400 and 500 °C present interstitial N-doping while doped TKP101 annealed at 500 °C showed a peak characteristic of substitutional N-doping. S-doped materials calcined at 500 °C presented only anionic S-doping. Nitrogen adsorption studies (BET) showed a loss of specific surface area (SSA) in annealed TiO2 samples. N- and S co-doped materials showed suitable photocatalytic activity under UV illumination towards Escherichia coli inactivation and also under visible light irradiation (400–500 nm). Applying different annealing temperatures led to a variety of structures for N and S incorporated in the crystalline network. TiO2 upon annealing showed a varying degree of hydroxylation and particles sizes. This seems to affect the trapping and transfer of the charge carriers generated under light and the semiconductor performance.