Photocatalytic water disinfection on oxide semiconductors: Part 2 – structure, functional properties and reactivity of microbial agents

Worldwide, waterborne diseases resulting from ingestion of contaminated drinking water carrying infectious microbial agents kill some 2 million people annually. Disinfection of drinking water aimed at the removal and inactivation of microbiological agents typically requires the consumption of energy, which to date is mainly generated from fossil fuels. The titanium dioxide (TiO2) based photo-induced oxidising system (POS) is one of the most promising candidates for the disinfection of water using solar energy. Progress in photocatalytic water disinfection requires understanding both concepts of TiO2 semiconductors as well the biochemistry of microorganisms. The aim of the present study is to introduce workers in the solid state sciences to relevant basic concepts and terminology of microbial biochemistry. We review the structure of the bacterial cell envelope, which is the major target of the TiO2 based POS. We outline how attack by the POS leads to the production of additional reactive species commonly referred to in the biological literature as reactive oxygen species both at the surface and the inside of the cell and develop a unifying model of the molecular mechanisms underlying the biocidal activity of the TiO2 POS.