Abstract
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.
Highlights
Patients and visitors in healthcare facilities can acquire infections by direct or indirect contact with common surfaces that have become contaminated with pathogenic microbes[1]
For the first time, that a natural, bacterial contaminant (S. aureus) with very low levels of light absorption is inactivated on pristine TiO2 by the same mechanism
A strong secondary peak is observed in the O 1 s spectra, corresponding to oxygen in the model contaminants (Fig. 2g,h). These results indicate that contacting model contaminant with pristine TiO2 effects changes in electronic properties of photocatalyst similar to those obtained by doping TiO2 with elements such as carbon or nitrogen[24]; co-synthesizing TiO2 with light harvesters such as phosphorous or quantum dots[25]; or surface modifying TiO2 by, for example, surface hydrogenation[28]
Summary
Patients and visitors in healthcare facilities can acquire infections by direct or indirect contact with common surfaces (room door handles, bed rails, taps, sterile packaging, mops, ward fabrics and plastics, keyboards and telephones) that have become contaminated with pathogenic microbes[1]. For the first time, that a natural, bacterial contaminant (S. aureus) with very low levels of light absorption is inactivated on pristine TiO2 by the same mechanism In this mechanism, which we refer to as contaminant activated photocatalysis, the rate of photocatalytic degradation depends on the extent of visible light absorption. This new information is utilized to design transparent, contaminant activated photocatalytic coatings for prevention of healthcare-acquired infections
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