N, S co-doped and N-doped Degussa P-25 powders with visible light response prepared by mechanical mixing of thiourea and urea. Reactivity towards E. coli inactivation and phenol oxidation

Degussa P-25 powder was mixed mechanically with thiourea and urea and then annealed during 1 h at 400 °C. Diffuse reflectance spectroscopy (DRS) revealed that treated powders absorb visible light (between 400 and 550 nm) and by Kubelka–Munk relations it was possible to estimate their band-gap energies, being 2.85 and 2.73 eV to thiourea and urea treated powders, respectively. X-ray photoelectron spectroscopy (XPS) showed in the case of thiourea treated P-25, hints of interstitial N-doping and anionic S-doping. On the other hand, P-25 treated with urea showed only the presence of interstitial N-doping. Atomic concentrations measured by XPS showed highest content of N species on TiO2 surfaces in urea treated P-25 (2.7 at%) while thiourea treated powders presented low concentrations of N and S (0.61 and 0.68 at%, respectively). Specific surface area (SSA) was measured by BET method, obtaining values of 52 and 46 m2 g−1 for undoped P-25 and undoped P-25 annealed at 400 °C during 1 h. N, S co-doped and N-doped P-25 showed SSA of 42 and 40 m2 g−1, respectively. We suggest that probably OH radical is not directly involved in oxidative processes taking place when N, S co-doped Degussa P-25 was exposed to visible light.