Inactivation of Goose Parvovirus, Avian Influenza Virus and Phage by Photocatalyst on Polyethylen Terephthalate Film under Light Emitting Diode (LED)

The biocidal action of the TiO2 photocatalyst has been now well recognized from massive experimental evidences, which demonstrates that the photocatalytic disinfection process could be technically feasible. However, the understanding on the photochemical mechanism of the biocidal action largely remains unclear. In particular, the identity of main acting photooxidants and their roles in the mechanism of killing microorganisms is under active investigation. It is generally accepted that reactive oxygen species (ROS) and OH radicals play the role. The aim of this study is to determine how the OH radical, acting either independently or in collaboration with other ROS, is quantitatively related to the inactivation of E. coli. The steady-state concentrations of OH radicals ([*OH]ss) in UV-illuminated TiO2 suspensions could be quantified from the measured photocatalytic degradation rates of p-chlorobenzoic acid (a probe compound) and its literature bimolecular rate constant with OH radicals. The results demonstrated an excellent linear correlation between [*OH]ss and the rates of E. coli inactivation, which indicates that the OH radical is the primary oxidant species responsible for inactivating E. coli in the UV/TiO2 process. The CT value of OH radical for achieving 2 log E. coli inactivation was initially found to be 0.8x10(-5) mg min/l, as predicted by the delayed Chick-Watson model. Although the primary role of OH radicals in photocatalytic disinfection processes has been frequently assumed, this is the first quantitative demonstration that the concentration of OH radicals and the biocidal activity is linearly correlated.

Particularly in microbiological laboratories and areas in intensive medical use, regular and thorough disinfection of surfaces is required in order to reduce the numbers of bacteria and to prevent bacterial transmission. The conventional methods of disinfection with wiping are not effective in the longer term, cannot be standardized, are time- and staff-intensive and use aggressive chemicals. Disinfection with hard ultraviolet C (UVC) light is usually not satisfactory, as the depth of penetration is inadequate and there are occupational medicine risks. Photocatalytic oxidation on surfaces coated with titanium dioxide (TiO2) might offer a possible alternative. In the presence of water and oxygen, highly reactive OH-radicals are generated by TiO2 and mild ultraviolet A (UVA). These radicals are able to destroy bacteria, and may therefore be effective in reducing bacterial contamination. Direct irradiation with UVC however can produce areas of shadow in which bacteria are not inactivated. Using targeted light guidance and a light-guiding sheet (out of a UVA-transmittant, Plexiglas, for example), as in the method described in the present study, bacterial inactivation over the entire area is possible. The effectiveness of the method was demonstrated using bacteria relevant to hygiene such as Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Enterococcus faecium. For these bacteria, a reduction efficiency (RE) more than 6log10 steps in 60 min was observed. Using Candida albicans, a RE of 2log10 steps in 60 min was seen. Light and scanning electron microscopic examinations suggest that the germ destruction achieved takes place through direct damage to cell walls caused by OH-radicals.

Photocatalytic TiO(2) powders impart ultraviolet light-induced self-cleaning and antibacterial functions when coated on outdoor building materials. For indoor applications, however, TiO(2) must be modified for visible-light and dark sensitivity. Here we report that the grafting of nanometer-sized Cu(x)O clusters onto TiO(2) generates an excellent risk-reduction material in indoor environments. X-ray absorption near-edge structure using synchrotron radiation and high-resolution transmission electron microscopic analyses revealed that Cu(x)O clusters were composed of Cu(I) and Cu(II) valence states. The Cu(II) species in the Cu(x)O clusters endow TiO(2) with efficient visible-light photooxidation of volatile organic compounds, whereas the Cu(I) species impart antimicrobial properties under dark conditions. By controlling the balance between Cu(I) and Cu(II) in Cu(x)O, efficient decomposition and antipathogenic activity were achieved in the hybrid Cu(x)O/TiO(2) nanocomposites.