Titanium dioxide
Titanium dioxide (TiO2) is also a leading candidate for nanoremediation and wastewater treatment, although as of 2010 it is reported to have not yet been expanded to full-scale commercialization. When exposed to ultraviolet light, such as in sunlight, titanium dioxide produces hydroxyl radicals, which are highly reactive and can oxidize contaminants. Hydroxyl radicals are used for water treatment in methods generally termed advanced oxidation processes. Because light is required for this reaction, TiO2 is not appropriate for underground "in situ" remediation, but it may be used for wastewater treatment or pump-and-treat groundwater remediation.