The effects of the bacterial interaction with visible-light responsive titania photocatalyst on the bactericidal performance

The widespread use of antibiotics and the emergence of more resistant and virulent strains of microorganisms [1-3] have caused an urgent need to develop alternative sterilization technologies. Using the superb photocatalytic effect of titanium dioxide (TiO2) is a conceptually feasible technology for this material is easy and inexpensive to produce in industrial scale. Photocatalytic TiO2 substrates have been shown to eliminate organic compounds and to function as disinfectants [4]. Upon ultraviolet (UV) light excitation, the photon energy excites valence band electron and generates pairs of electrons and holes (electron-vacancy in valence band) that diffuse and are trapped on or near the TiO2 surface. These excited electrons and holes have strong reducing and oxidizing activity and react with atmospheric water and oxygen to yield reactive species such as hydroxyl radicals (.OH) and superoxide anions (O2-) [5]. These radicals, .OH and O2- are extremely reactive upon contact with organic compounds. Complete oxidation of organic compounds and bacterial cells to carbon dioxide could be achieved [6,7]. Reactive oxygen species (ROS), such as .OH, O2-, and hydrogen peroxide (H2O2) generated on the light irradiated TiO2 surfaces, were shown to operate in concert to attack polyunsaturated phospholipids in bacteria [4]. Traditional TiO2 photocatalyst, however, is effective only upon irradiation of UV-light at levels that would also induce serious damage to human cells. This greatly restricts the potential applications of TiO2 substrates for use in our living environments. Recently, nitrogen or metal ion-doped anatase based TiO2 photocatalysts have been identified to be active upon visible-light illumination [8,9], offering the possibility to overcome this problem.It is believed that nanometer-sized anatase phase particles have large surface area are efficient for the decomposition of pollutants in air and in water [10]. Furthermore, it is also found that the presence of anata