Titanium dioxide(TiO2) plays a central role in energy and en-vironmental research, finding applications indye-sensitized solar cells,lithium ion batteries,as an active layer in chemical sensors,as a catalyst,inself-cleaning coatings,and for water purification.In 1985,Matsunaga and colleagues observed the antimicrobial
activity of TiO2.In particular,microbial cells could be killed by the contact with a TiO2–Pt catalyst under illumination with near UV light.When TiO2 is irradiated with photons of energy equal to or higher than its band-gap(3.15 eV for anatase,3.05 eV forrutile crystalline phase,electron–hole pairs are generated.They can
induce the formation of reactive oxygen species(ROS),such as OH, O2
·− and H2O2 on its surface(in contact with water).These species are directly involved in the oxidation processes that remove organic compounds and microorganisms in water.All
three ROS exhibit bactericidal activity but some studies have em-
phasized that the hydroxyl radical would be the most important oxidant species responsible for the attack of the bacterial cell wall,leading to modifications of membrane permeability and cell death.