Much has been written in mainstream and scientific sources about technologies that purify air or provide self-cleaning properties to clothing and other items by harnessing the oxidative power of light. Titanium dioxide (TiO₂) provides these exciting benefits, expanding its utility beyond its long history as a white colorant in paint and a common ingredient in cosmetics, sunscreens, ceramic tile, windows, and cement. When exposed to the correct wavelength and intensity of light, TiO₂ acts as a photocatalyst and oxidizes diverse contaminants that cause stains, odors, and air pollution. It also kills bacteria, fungi, and other microorganisms.

TiO₂ is a semiconductor and a photocatalytic material. It exists as anatase, rutile, and brookite polymorphs. All possess photocatalytic activity, but the anatase form (Figure 1) has proved to be the most effective photocatalyst for cleaning or purifying applications.