Physics and chemistry of photocatalytic titanium dioxide: visualization of bactericidal activity using atomic force microscopy

Abstract

When titanium dioxide (TiO₂) is exposed to near-ultraviolet light, it exhibits strong bactericidal activity. Anatase phase of TiO₂ film was prepared by anodizing pure titanium coupons (substrate). Atomic force microscopy (AFM) technique was used to image the transformation of titanium surface to TiO₂ surface on anodization. We observed wide distribution of TiO₂ particles ranging from submicron to nanometre sizes, fully covering the substrate forming a thin film on anodizing. With the formation of a thin film of TiO₂, we observed strong bactericidal activity. Bactericidal activity was attributed to the well-known photocatalytic property of the semiconductor TiO₂. Here we present some arguments for reasoning out why certain semiconducting metal oxides exhibit photocatalytic properties and some do not. We also present some of the important elementary reaction steps considering adsorbed oxygen and water molecule as necessary molecules for the photooxidation process. Other reactions involved in producing reactive oxygen species and hydroxyl radical are presented to understand the process involved in photocatalytic biocidal activity. Finally, we present visualization of photocatalytic bactericidal activity of TiO₂ using AFM.