Comparison of the photocatalytic efficiencies of bare and doped rutile and anatase TiO2 photocatalysts under visible light for phenol degradation and E. coli inactivation

Abstract

This study aimed at comparing the photocatalytic efficiencies of various TiO2 based photocatalysts for phenol degradation and bacteria inactivation under illumination with visible light. Commercial undoped anatase and rutile (both from Aldrich), Aeroxide P25 (Evonik Industries), nitrogen-doped anatase (Sumitomo TP-S201, Sumitomo Chemical Inc.), nitrogen and sulphur co-doped anatase (Kronos VLP7000, Kronos Titan GmbH), and our custom-synthesized nitrogen- and iron-doped TiO2, as well as nitrogen and sulphur co-doped Aeroxide P25 and silver- and gold-deposited Aeroxide P25 were studied. The photocatalytic efficiency of different types of titanium dioxide based photocatalysts was determined by inactivation of Escherichia coli K12 bacteria and by phenol decomposition. Electron spin resonance (ESR) in combination with spin trapping was used to get insight into the reactive oxygen species (ROS)-mediated photocatalytic processes in the presence of TiO2-based photocatalysts. ESR results confirmed that titanias which generated OH radicals were efficient in E. coli disinfection, whereas titanias that were unable to produce OH radicals did not reveal significant bactericidal action. Three of our home-made titanias (iron-, nitrogen-, nitrogen/sulphur) as well as the commercial nitrogen/sulphur codoped Kronos VLP7000 TiO2 showed higher efficiency of phenol degradation than the well-established reference photocatalyst, Aeroxide P25, but showed much lower (if any) activity for bacteria inactivation, including Kronos VLP7000, which revealed extremely high efficiency for phenol decomposition. Interestingly undoped Aldrich rutile (with large particles - 100–700nm) had the highest efficiency for inactivation of E. coli and also had fairly high activity of phenol degradation.