Antibacterial efficacy of photocatalytic reaction on titanium dioxide-coated ceramic air filters

Titanium dioxide (TiO2) photocatalysis generates reactive oxygen species such as ・OH and ・O2-, which can effectively eliminate organic compounds. In the present study, we evaluated the antibacterial and antifungal effects of TiO2-coated ceramic air filters in both laboratory and hospital settings. Photocatalysis with the TiO2-coated ceramic filter effectively inactivated all 4 pathogenic organisms tested. Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans. After the photocatalysis reaction for 4 h under UV-A (365nm, 250μW/㎠) irradiation, the percentage reductions of the number of E. coli, P. aeruginosa, S. aureus, C. albicans cells were 99.9%, 98.9%, 97.7% and 99.9%, respectively, indicating that Gram-negative bacteria are more susceptible to such photocatalysis than Gram-positive bacteria. Scanning electron microscopic analysis showed damage to the cytoplasmic membrane and cell wall by photocatalysis : consistent with above observations, the morphological change of Gram-negative E. coli was greater than that of Gram-positive S. aureus. Further, an air cleaner equipped with a TiO2-coated ceramic filter significantly decreased the number of bacteria floating in hospitals. These results indicate that air cleaners with TiO2-coated ceramic filters could be useful in reducing the incidence of nosocomial infections