Contaminant-Activated Visible Light Photocatalysis

Pristine titanium dioxide (TiO₂) absorbs ultraviolet light and reflects the entire visible spectrum. This optical response of TiO₂ has found widespread application as white pigments in paper, paints, pharmaceuticals, foods and plastic industries; and as a UV absorber in cosmetics and photocatalysis. However, pristine TiO₂ is considered to be inert under visible light for these applications. Here we show for the first time that a bacterial contaminant (Staphylococcus aureus-a MRSA surrogate) in contact with TiO₂ activates its own photocatalytic degradation under visible light. The present study delineates the critical role of visible light absorption by contaminants and electronic interactions with anatase in photocatalytic degradation using two azo dyes (Mordant Orange and Procion Red) that are highly stable because of their aromaticity. An auxiliary light harvester, polyhydroxy fullerenes, was successfully used to accelerate photocatalytic degradation of contaminants. We designed a contaminant-activated, transparent, photocatalytic coating for common indoor surfaces and conducted a 12-month study that proved the efficacy of the coating in killing bacteria and holding bacterial concentrations generally below the benign threshold. Data collected in parallel with this study showed a substantial reduction in the incidence of infections.