TiO2

TiO2, or titanium dioxide, is an inorganic compound widely used as a white pigment and UV blocker. It combines brightness, a high refractive index, and chemical stability, making it a staple in paints, coatings, plastics, papers, cosmetics, and sunscreens. It has also been used as a food additive (E171) in some regions, though regulatory status varies and some jurisdictions have restricted its use in food.

TiO2 occurs in several crystal forms. Rutile is the most stable phase at ambient conditions and provides strong opacity as a pigment; anatase is also a common pigment form and more active as a photocatalyst. Brookite is rare. Pigment-grade TiO2 is produced as rutile or anatase crystals, with particle sizes optimized for coverage and brightness.

Industrial production proceeds mainly via two routes: the sulfate process and the chloride process. The sulfate process uses titanium-bearing ores such as ilmenite and refines them to hydrous TiO2 pigments, while the chloride process converts titanium tetrachloride to high-purity rutile TiO2. The chloride route yields higher color purity and opacity and is favored for high-end pigments.

In addition to pigments, TiO2 is a semiconductor used in photocatalysis, environmental remediation, and energy applications. Anatase-rich samples are generally more photoactive than rutile and are studied for water splitting and pollutant degradation, as well as self-cleaning surfaces. TiO2 is also used in dye-sensitized solar cells and as a UV-absorbing layer in sunscreens.

Safety and regulation: TiO2 is considered chemically stable and of low acute toxicity in many consumer uses, though inhalation of fine powders can pose health risks to workers. In nanoscale form, safety assessments continue. The food use of TiO2 (as E171) has been banned in the European Union since 2022; other jurisdictions regulate nanoparticle exposure and labeling differently.