Role of dopant concentration, crystal phase and particle size on microbial inactivation of Cu-doped TiO₂ nanoparticles

The properties of Cu-doped TiO₂ nanoparticles (NPs) were independently controlled in a flame aerosol reactor by varying the molar feed ratios of the precursors, and by optimizing temperature and time history in the flame. The effect of the physico-chemical properties (dopant concentration, crystal phase and particle size) of Cu-doped TiO₂ nanoparticles on inactivation of Mycobacterium smegmatis (a model pathogenic bacterium) was investigated under three light conditions (complete dark, fluorescent light and UV light). The survival rate of M. smegmatis (in a minimal salt medium for 2h) exposed to the NPs varied depending on the light irradiation conditions as well as the dopant concentrations. In dark conditions, pristine TiO₂ showed insignificant microbial inactivation, but inactivation increased with increasing dopant concentration. Under fluorescent light illumination, no significant effect was observed for TiO₂. However, when TiO ₂ was doped with copper, inactivation increased with dopant concentration, reaching more than 90% (>3wt% dopant). Enhanced microbial inactivation by TiO₂ NPs was observed only under UV light. When TiO₂ NPs were doped with copper, their inactivation potential was promoted and the UV-resistant cells were reduced by over99%. In addition, the microbial inactivation potential of NPs was also crystal-phase-and size-dependent under all three light conditions. A lower ratio of anatase phase and smaller sizes of Cu-doped TiO₂ NPs resulted in decreased bacterial survival. The increased inactivation potential of doped TiO ₂ NPs is possibly due to both enhanced photocatalytic reactions and leached copper ions.