Photocatalytic water disinfection on oxide semiconductors: Part 1-basic concepts of TiO2 photocatalysis

Water disinfection (removal of microbial agents) using sunlight is an emerging technology, which has the capacity to address the global shortage of drinking water. Therefore, intensive investigations in many laboratories aim to develop photocatalyst for water disinfection. The research is focused on titanium dioxide (TiO2), which is the most promising candidate for high performance photocatalyst able to address the commercial requirements. The present work (Part 1) considers the effect of defect disorder on semiconducting and photocatalytic properties of TiO2 (rutile) in water disinfection using solar energy. It is shown that photocatalytic properties of TiO2 in water are closely related to the light induced reactivity of TiO2 with water leading to the formation of active species, such as OH*, H2O2 and O-2(-), which have the capacity to oxidise microorganisms. It is also shown that the ability of TiO2 to form the active radicals is closely associated with the presence of point defects in the TiO2 lattice and the related semiconducting properties. Therefore, photocatalytic properties of TiO2 may be modified in a controlled manner by changes in its defect disorder. Consequently, defect chemistry may be used as the framework in the development of TiO2 with controlled properties that are desired for solar water disinfection. The following work (Part 2) considers the structure of bacteria and their reactivity/photoreactivity with TiO2 in aqueous environments. Both Part 1 and 2 bring together the concepts of TiO2 photocatalysis and the concepts of microbiology in order to derive the theoretical models that are needed for the development of high performance photocatalysts for solar water disinfection.