Titanium dioxide

Titanium dioxide, also known as titanium(IV) oxide or titania Template:IPAc-en, is the inorganic compound derived from titanium with the chemical formula Template:Chem. When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891.<ref name=Ullmann>Template:Ullmann</ref> It is a white solid that is insoluble in water, although mineral forms can appear black. As a pigment, it has a wide range of applications, including paint, sunscreen, and food coloring. When used as a food coloring, it has E number E171. World production in 2014 exceeded 9 million tonnes.<ref>"Titanium" in 2014 Minerals Yearbook. USGS</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It has been estimated that titanium dioxide is used in two-thirds of all pigments, and pigments based on the oxide have been valued at a price of $13.2 billion.<ref>Template:Cite news</ref> Template:TOC limit

Structure

File:Anatase crystal structure.png

Structure of anatase. Together with rutile and brookite, one of the three major polymorphs of TiO₂.

In all three of its main dioxides, titanium exhibits octahedral geometry, being bonded to six oxide anions. The oxides in turn are bonded to three Ti centers. The overall crystal structures of rutile and anatase are tetragonal in symmetry whereas brookite is orthorhombic. The oxygen substructures are all slight distortions of close packing: in rutile, the oxide anions are arranged in distorted hexagonal close-packing, whereas they are close to cubic close-packing in anatase and to "double hexagonal close-packing" for brookite. The rutile structure is widespread for other metal dioxides and difluorides, e.g. RuO₂ and ZnF₂.

Molten titanium dioxide has a local structure in which each Ti is coordinated to, on average, about 5 oxygen atoms.<ref name="Ald">Template:Cite journal</ref> This is distinct from the crystalline forms in which Ti coordinates to 6 oxygen atoms.

Synthetic and geologic occurrence

Synthetic TiO₂ is mainly produced from the mineral ilmenite. Rutile, and anatase, naturally occurring TiO₂, occur widely also, e.g. rutile as a 'heavy mineral' in beach sand. Leucoxene, fine-grained anatase formed by natural alteration of ilmenite, is yet another ore. Star sapphires and rubies get their asterism from oriented inclusions of rutile needles.<ref name="BuildingBlocks451-3">Template:Cite book</ref>

Mineralogy and uncommon polymorphs

Titanium dioxide occurs in nature as the minerals rutile and anatase. Additionally two high-pressure forms are known minerals: a monoclinic baddeleyite-like form known as akaogiite, and the other has a slight monoclinic distortion of the orthorhombic α-PbO₂ structure and is known as riesite. Both of which can be found at the Ries crater in Bavaria.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Akaogiite. mindat.org</ref> It is mainly sourced from ilmenite, which is the most widespread titanium dioxide-bearing ore around the world. Rutile is the next most abundant and contains around 98% titanium dioxide in the ore. The metastable anatase and brookite phases convert irreversibly to the equilibrium rutile phase upon heating above temperatures in the range Template:Convert.<ref>Template:Cite journal</ref>

Titanium dioxide has twelve known polymorphs – in addition to rutile, anatase, brookite, akaogiite and riesite, three metastable phases can be produced synthetically (monoclinic, tetragonal, and orthorhombic ramsdellite-like), and four high-pressure forms (α-PbO₂-like, cotunnite-like, orthorhombic OI, and cubic phases) also exist:

Form	Crystal system	Synthesis
Rutile	Tetragonal
Anatase	Tetragonal
Brookite	Orthorhombic
TiO2(B)<ref>Template:Cite journal</ref>	Monoclinic	Hydrolysis of K2Ti4O9 followed by heating
TiO2(H), hollandite-like form<ref>Template:Cite journal</ref>	Tetragonal	Oxidation of the related potassium titanate bronze, K0.25TiO2
TiO2(R), ramsdellite-like form<ref>Template:Cite journal</ref>	Orthorhombic	Oxidation of the related lithium titanate bronze Li0.5TiO2
TiO2(II)-(α-PbO2-like form)<ref>Template:Cite journal</ref>	Orthorhombic
Akaogiite (baddeleyite-like form, 7 coordinated Ti)<ref>Template:Cite journal</ref>	Monoclinic
TiO2 -OI<ref>Template:Cite journal</ref>	Orthorhombic
Cubic form<ref>Template:Cite journal</ref>	Cubic	P > 40 GPa, T > 1600 °C
TiO2 -OII, cotunnite(PbCl2)-like<ref name=du1>Template:Cite journal</ref>	Orthorhombic	P > 40 GPa, T > 700 °C

The cotunnite-type phase was claimed to be the hardest known oxide with the Vickers hardness of 38 GPa and the bulk modulus of 431 GPa (i.e. close to diamond's value of 446 GPa) at atmospheric pressure.<ref name=du1/> However, later studies came to different conclusions with much lower values for both the hardness (7–20 GPa, which makes it softer than common oxides like corundum Al₂O₃ and rutile TiO₂)<ref>Template:Cite journal</ref> and bulk modulus (~300 GPa).<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Titanium dioxide (B) is found as a mineral in magmatic rocks and hydrothermal veins, as well as weathering rims on perovskite. TiO₂ also forms lamellae in other minerals.<ref>Template:Cite journal</ref>

Production

File:Industrial key players in the production of titanium dioxide.png

Industrial key players in the production of titanium dioxide - 2022

File:Evolution production dioxyde de titane.svg

Evolution of the global production of titanium dioxide according to process

The largest Template:Chem pigment processors are Chemours, Venator, Template:Interlanguage link, and Tronox.<ref>Template:Cite press release</ref><ref name="Hayes (2011)">{{#invoke:citation/CS1|citation |CitationClass=web }}Template:Dead link</ref> Major paint and coating company end users for pigment grade titanium dioxide include Akzo Nobel, PPG Industries, Sherwin Williams, BASF, Kansai Paints and Valspar.<ref name="Hayes 2011, p. 3">Hayes (2011), p. 3</ref> Global Template:Chem pigment demand for 2010 was 5.3 Mt with annual growth expected to be about 3–4%.<ref>Hayes (2011), p. 4</ref>

The production method depends on the feedstock. In addition to ores, other feedstocks include upgraded slag. Both the chloride process and the sulfate process (both described below) produce titanium dioxide pigment in the rutile crystal form, but the sulfate process can be adjusted to produce the anatase form. Anatase, being softer, is used in fiber and paper applications. The sulfate process is run as a batch process; the chloride process is run as a continuous process.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Chloride process

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In chloride process, the ore is treated with chlorine and carbon to give titanium tetrachloride, a volatile liquid that is further purified by distillation. The TiCl4 is treated with oxygen to regenerate chlorine and produce the titanium dioxide.

Sulfate process

In the sulfate process, ilmenite is treated with sulfuric acid to extract iron(II) sulfate pentahydrate. This process requires concentrated ilmenite (45–60% TiO₂) or pretreated feedstocks as a suitable source of titanium.<ref name=jv>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The resulting synthetic rutile is further processed according to the specifications of the end user, i.e. pigment grade or otherwise.<ref name="Production">Template:Cite book</ref>

Examples of plants using the sulfate process are the Sorel-Tracy plant of QIT-Fer et Titane and the Eramet Titanium & Iron smelter in Tyssedal Norway.<ref name="fc1">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Becher process

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} The Becher process is another method for the production of synthetic rutile from ilmenite. It first oxidizes the ilmenite as a means to separate the iron component.

Specialized methods

For specialty applications, TiO₂ films are prepared by various specialized chemistries.<ref>Template:Cite journal</ref> Sol-gel routes involve the hydrolysis of titanium alkoxides such as titanium ethoxide:

Ti(OEt)₄ + 2 H₂O → TiO₂ + 4 EtOH

A related approach that also relies on molecular precursors involves chemical vapor deposition. In this method, the alkoxide is volatilized and then decomposed on contact with a hot surface:

Ti(OEt)₄ → TiO₂ + 2 Et₂O

Applications

Pigment

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First mass-produced in 1916,<ref>Template:Cite book</ref> titanium dioxide is the most widely used white pigment because of its brightness and very high refractive index, in which it is surpassed only by a few other materials (see list of indices of refraction). Titanium dioxide crystal size is ideally around 220 nm (measured by electron microscope) to optimize the maximum reflection of visible light. However, abnormal grain growth is often observed in titanium dioxide, particularly in its rutile phase.<ref name="ref1">Template:Cite journal </ref> The occurrence of abnormal grain growth brings about a deviation of a small number of crystallites from the mean crystal size and modifies the physical behaviour of TiO₂. The optical properties of the finished pigment are highly sensitive to purity. As little as a few parts per million (ppm) of certain metals (Cr, V, Cu, Fe, Nb) can disturb the crystal lattice so much that the effect can be detected in quality control.<ref>Template:Cite book</ref>Template:Full citation needed Approximately 4.6 million tons of pigmentary TiO₂ are used annually worldwide, and this number is expected to increase as use continues to rise.<ref name="Nano-scaled titania">Template:Cite book</ref>

TiO₂ is also an effective opacifier in powder form, where it is employed as a pigment to provide whiteness and opacity to products such as paints, coatings, plastics, papers, inks, foods, supplements, medicines (i.e. pills and tablets), and most toothpastes; in 2019 it was present in two-thirds of toothpastes on the French market.<ref name=frouville>Template:Cite news</ref> In paint, it is often referred to offhandedly as "brilliant white", "the perfect white", "the whitest white", or other similar terms. Opacity is improved by optimal sizing of the titanium dioxide particles.

Additive for food

Often used as color in food,<ref>Template:Cite book</ref> it is commonly found in ice creams, chocolates, all types of candy, creamers, desserts, marshmallows, chewing gum, pastries, spreads, dressings, cakes, some cheeses, and many other foods.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It is permitted in many countries, but was banned for use in food by the European Union in 2022. While permitted in the United States, Mars removed it from their Skittles confectionery in 2025, although a class-action lawsuit against the use of titanium dioxide in Skittles had been dismissed in 2022.<ref>Template:Cite news</ref>

Thin films

When deposited as a thin film, its refractive index and colour make it an excellent reflective optical coating for dielectric mirrors; it is also used in generating decorative thin films such as found in "mystic fire topaz".Template:Citation needed

Some grades of modified titanium based pigments as used in sparkly paints, plastics, finishes and cosmetics – these are man-made pigments whose particles have two or more layers of various oxides – often titanium dioxide, iron oxide or alumina – in order to have glittering, iridescent and or pearlescent effects similar to crushed mica or guanine-based products. In addition to these effects a limited colour change is possible in certain formulations depending on how and at which angle the finished product is illuminated and the thickness of the oxide layer in the pigment particle; one or more colours appear by reflection while the other tones appear due to interference of the transparent titanium dioxide layers.<ref>Template:Cite book</ref> In some products, the layer of titanium dioxide is grown in conjunction with iron oxide by calcination of titanium salts (sulfates, chlorates) around 800 °C<ref>Template:Cite book</ref> One example of a pearlescent pigment is Iriodin, based on mica coated with titanium dioxide or iron (III) oxide.<ref>Template:Citation</ref>

The iridescent effect in these titanium oxide particles is unlike the opaque effect obtained with usual ground titanium oxide pigment obtained by mining, in which case only a certain diameter of the particle is considered and the effect is due only to scattering.

Sunscreen and UV blocking pigments

In cosmetic and skin care products, titanium dioxide is used as a pigment, sunscreen and a thickener. As a sunscreen, ultrafine TiO₂ is used, which is notable in that combined with ultrafine zinc oxide, it is considered to be an effective sunscreen that lowers the incidence of sun burns and minimizes the premature photoaging, photocarcinogenesis and immunosuppression associated with long term excess sun exposure.<ref>Template:Citation</ref> Sometimes these UV blockers are combined with iron oxide pigments in sunscreen to increase visible light protection.<ref>Template:Cite journal</ref>

Titanium dioxide and zinc oxide are generally considered to be less harmful to coral reefs than sunscreens that include chemicals such as oxybenzone, octocrylene and octinoxate.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Nanosized titanium dioxide is found in the majority of physical sunscreens because of its strong UV light absorbing capabilities and its resistance to discolouration under ultraviolet light. This advantage enhances its stability and ability to protect the skin from ultraviolet light. Nano-scaled (particle size of 20–40 nm)<ref>Dan, Yongbo et al. Measurement of Titanium Dioxide Nanoparticles in Sunscreen using Single Particle ICP-MS Template:Webarchive. perkinelmer.com</ref> titanium dioxide particles are primarily used in sunscreen lotion because they scatter visible light much less than titanium dioxide pigments, and can give UV protection.<ref name="Nano-scaled titania"/> Sunscreens designed for infants or people with sensitive skin are often based on titanium dioxide and/or zinc oxide, as these mineral UV blockers are believed to cause less skin irritation than other UV absorbing chemicals. Nano-TiO₂, which blocks both UV-A and UV-B radiation, is used in sunscreens and other cosmetic products.

The EU Scientific Committee on Consumer Safety considered nano sized titanium dioxide to be safe for skin applications, in concentrations of up to 25 percent based on animal testing.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The risk assessment of different titanium dioxide nanomaterials in sunscreen is currently evolving since nano-sized TiO₂ is different from the well-known micronized form.<ref name=":2">Template:Cite journal</ref> The rutile form is generally used in cosmetic and sunscreen products due to it not possessing any observed ability to damage the skin under normal conditions<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and having a higher UV absorption.<ref name=":3">Template:Cite journal</ref> In 2016 Scientific Committee on Consumer Safety (SCCS) tests concluded that the use of nano titanium dioxide (95–100% rutile, ≦5% anatase) as a UV filter can be considered to not pose any risk of adverse effects in humans post-application on healthy skin,<ref name="Eur Acad Dermatol Venereol">Template:Cite journal</ref> except in the case the application method would lead to substantial risk of inhalation (ie; powder or spray formulations). This safety opinion applied to nano TiO₂ in concentrations of up to 25%.<ref name=":4">Template:Cite journal</ref>

Initial studies indicated that nano-TiO₂ particles could penetrate the skin, causing concern over its use. These studies were later refuted, when it was discovered that the testing methodology couldn't differentiate between penetrated particles and particles simply trapped in hair follicles and that having a diseased or physically damaged dermis could be the true cause of insufficient barrier protection.<ref name=":2" />

SCCS research found that when nanoparticles had certain photostable coatings (e.g., alumina, silica, cetyl phosphate, triethoxycaprylylsilane, manganese dioxide), the photocatalytic activity was attenuated and no notable skin penetration was observed; the sunscreen in this research was applied at amounts of 10 mg/cm2 for exposure periods of 24 hours.<ref name=":4" /> Coating TiO₂ with alumina, silica, zircon or various polymers can minimize avobenzone degradation<ref>Template:Cite journal</ref> and enhance UV absorption by adding an additional light diffraction mechanism.<ref name=":3" />

Template:Chem is used extensively in plastics and other applications as a white pigment or an opacifier and for its UV resistant properties where the powder disperses light – unlike organic UV absorbers – and reduces UV damage, due mostly to the particle's high refractive index.<ref>Polymers, Light and the Science of TiO₂ Template:Webarchive, DuPont, pp. 1–2</ref>

Other uses of titanium dioxide

In ceramic glazes, titanium dioxide acts as an opacifier and seeds crystal formation.

It is used as a tattoo pigment and in styptic pencils. Titanium dioxide is produced in varying particle sizes which are both oil and water dispersible, and in certain grades for the cosmetic industry. It is also a common ingredient in toothpaste.

The exterior of the Saturn V rocket was painted with titanium dioxide; this later allowed astronomers to determine that J002E3 was likely the S-IVB stage from Apollo 12 and not an asteroid.<ref name=Jorgensen>Template:Cite journal</ref>

Titanium dioxide is an n-type semiconductor and is used in dye-sensitized solar cells.<ref>Template:Cite journal</ref> It is also used in other electronics components such as electrodes in batteries.<ref>Template:Cite journal</ref>

Research

Patenting activities

File:Relevant patent families describing titanium dioxide production from ilmenite, 2002–2021.png

Relevant patent families describing titanium dioxide production from ilmenite, 2002–2021.

File:Public Institutions patent activity in titanium dioxide production.png

Academic and public institutions having significant patent activity in titanium dioxide production, 2022.

Between 2002 and 2022, there were 459 patent families that describe the production of titanium dioxide from ilmenite. The majority of these patents describe pre-treatment processes, such as using smelting and magnetic separation to increase titanium concentration in low-grade ores, leading to titanium concentrates or slags. Other patents describe processes to obtain titanium dioxide, either by a direct hydrometallurgical process or through the main industrial production processes, the sulfate process and the chloride process.<ref name=":6">Template:Cite journal</ref> The sulfate process represents 40% of the world’s titanium dioxide production and is protected in 23% of patent families. The chloride process is only mentioned in 8% of patent families, although it provides 60% of the worldwide industrial production of titanium dioxide.<ref name=":6" />

Key contributors to patents on the production of titanium dioxide are companies from China, Australia and the United States, reflecting the major contribution of these countries to industrial production. Chinese companies Pangang and Lomon Billions Groups hold major patent portfolios.<ref name=":6" />

Photocatalyst

Nanosized titanium dioxide, particularly in the anatase form, exhibits photocatalytic activity under ultraviolet (UV) irradiation. This photoactivity is reportedly most pronounced at the {001} planes of anatase,<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> although the {101} planes are thermodynamically more stable and thus more prominent in most synthesised and natural anatase,<ref>Template:Cite journal</ref> as evident by the often observed tetragonal dipyramidal growth habit. Interfaces between rutile and anatase are further considered to improve photocatalytic activity by facilitating charge carrier separation and as a result, biphasic titanium dioxide is often considered to possess enhanced functionality as a photocatalyst.<ref>Template:Cite journal</ref> It has been reported that titanium dioxide, when doped with nitrogen ions or doped with metal oxide like tungsten trioxide, exhibits excitation also under visible light.<ref name=Visible>Template:Cite journal</ref> The strong oxidative potential of the positive holes oxidizes water to create hydroxyl radicals. It can also oxidize oxygen or organic materials directly. Hence, in addition to its use as a pigment, titanium dioxide can be added to paints, cements, windows, tiles, or other products for its sterilizing, deodorizing, and anti-fouling properties, and is used as a hydrolysis catalyst. It is also used in dye-sensitized solar cells, which are a type of chemical solar cell (also known as a Graetzel cell).

The photocatalytic properties of nanosized titanium dioxide were discovered by Akira Fujishima in 1967<ref name=fujishima/> and published in 1972.<ref>Template:Cite journal</ref> The process on the surface of the titanium dioxide was called the Template:Ill.<ref name=fujishima>"Discovery and applications of photocatalysis – Creating a comfortable future by making use of light energy". Japan Nanonet Bulletin Issue 44, 12 May 2005.</ref> In thin film and nanoparticle form, titanium dioxide has the potential for use in energy production: As a photocatalyst, it can break water into hydrogen and oxygen. With the hydrogen collected, it could be used as a fuel. The efficiency of this process can be greatly improved by doping the oxide with carbon.<ref>Template:Cite news</ref> Further efficiency and durability has been obtained by introducing disorder to the lattice structure of the surface layer of titanium dioxide nanocrystals, permitting infrared absorption.<ref>Cheap, Clean Ways to Produce Hydrogen for Use in Fuel Cells? A Dash of Disorder Yields a Very Efficient Photocatalyst. Sciencedaily (28 January 2011)</ref> Visible-light-active nanosized anatase and rutile has been developed for photocatalytic applications.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

In 1995 Fujishima and his group discovered the superhydrophilicity phenomenon for titanium dioxide coated glass exposed to sun light.<ref name=fujishima/> This resulted in the development of self-cleaning glass and anti-fogging coatings.

Nanosized TiO₂ incorporated into outdoor building materials, such as paving stones in noxer blocks<ref>Advanced Concrete Pavement materials Template:Webarchive, National Concrete Pavement Technology Center, Iowa State University, p. 435.</ref> or paints, could reduce concentrations of airborne pollutants such as volatile organic compounds and nitrogen oxides.<ref>Hogan, Jenny (4 February 2004) "Smog-busting paint soaks up noxious gases". New Scientist.</ref> A TiO₂-containing cement has been produced.<ref>TIME's Best Inventions of 2008. (31 October 2008).</ref>

Using TiO₂ as a photocatalyst, attempts have been made to mineralize pollutants (to convert into CO₂ and H₂O) in waste water.<ref name="Mineralize Pollutants">Template:Cite book</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> The photocatalytic destruction of organic matter could also be exploited in coatings with antimicrobial applications.<ref>Template:Cite journal</ref>

Hydroxyl radical formation

Although nanosized anatase TiO₂ does not absorb visible light, it does strongly absorb ultraviolet (UV) radiation (hv), leading to the formation of hydroxyl radicals.<ref name=":1">Template:Cite book</ref> This occurs when photo-induced valence bond holes (h⁺_vb) are trapped at the surface of TiO₂ leading to the formation of trapped holes (h⁺_tr) that cannot oxidize water.<ref name=":8">Template:Cite journal</ref>

TiO₂ + hv → e⁻ + h⁺_vb

h⁺_vb → h⁺_tr

O₂ + e⁻ → O₂^•−

O₂^•− + O₂^•−+ 2Template:H+ → H₂O₂ + O₂

O₂^•− + h⁺_vb → O₂

O₂^•− + h⁺_tr → O₂

Template:OH- + h⁺_vb → HO•

e⁻ + h⁺_tr → recombination

Note: Wavelength (λ)= 387 nm<ref name=":8"/> This reaction has been found to mineralize and decompose undesirable compounds in the environment, specifically the air and in wastewater.<ref name=":8"/>

File:TiO2crystals.JPG

Synthetic single crystals of TiO₂, c. 2–3 mm in size, cut from a larger plate

Nanotubes

Anatase can be converted into non-carbon nanotubes and nanowires.<ref>Template:Cite journal</ref> Hollow TiO₂ nanofibers can be also prepared by coating carbon nanofibers by first applying titanium butoxide.<ref name=chiral>Template:Cite journal</ref>

• Chiral TiO2 nanofibers 2.jpg

  SEM (top) and TEM (bottom) images of chiral TiO₂ nanofibers<ref name=chiral/>

• TiO2nanotube.jpg

  Titanium oxide nanotubes, SEM image

• The army of titanium dioxide nanotubes.jpg

  Nanotubes of titanium dioxide (TiO₂-Nt) obtained by electrochemical synthesis. The SEM image shows an array of vertical self-ordered TiO₂-Nt with closed bottom ends of tubes.

Solubility

Titanium dioxide is insoluble in water, organic solvents, and inorganic acids. It is slightly soluble in alkali, soluble in saturated potassium acid carbonate, and can be completely dissolved in strong sulfuric acid and hydrofluoric acid after boiling for a long time.<ref>Template:Citation</ref>

Health and safety

Widely-occurring minerals and even gemstones are composed of TiO₂. All natural titanium, comprising more than 0.5% of the Earth's crust, exists as oxides.<ref name="auto">Template:Cite journal</ref>

Food additive

As of 2024, titanium dioxide is considered safe by the US FDA as a color ingredient for oral human consumption as long as it is 1% or less of the total food composition.<ref name="fda">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> A 2021 ban by the EU EFSA has been criticized as based on errors regarding the safety of titanium dioxide (E171) particles as a food additive,<ref>Template:Cite journal</ref> and according to a 2022 review, existing evidence does not support a direct DNA damaging mechanism for titanium dioxide.<ref>Template:Cite journal</ref>

Government policies

TiO₂ whitener in food was banned in France from 2020, due to uncertainty about safe quantities for human consumption.<ref>Template:Cite news</ref>

In 2021, the European Food Safety Authority (EFSA) ruled that as a consequence of new understandings of nanoparticles, titanium dioxide could "no longer be considered safe as a food additive", and the EU health commissioner announced plans to ban its use across the EU, with discussions beginning in June 2021. EFSA concluded that genotoxicity—which could lead to carcinogenic effects—could not be ruled out, and that a "safe level for daily intake of the food additive could not be established".<ref>Template:Cite news</ref> In 2022, the UK Food Standards Agency and Food Standards Scotland announced their disagreement with the EFSA ruling, and did not follow the EU in banning titanium dioxide as a food additive.<ref>Template:Cite news</ref> Health Canada similarly reviewed the available evidence in 2022 and decided not to change their position on titanium dioxide as a food additive.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The European Union removed the authorization to use titanium dioxide (E 171) in foods, effective 7 February 2022, with a six months grace period.<ref>'amending Annexes II and III to Regulation (EC) No 1333/2008 of the European Parliament and of the Council as regards the food additive titanium dioxide (E 171)'. Commission Regulation (EU) 2022/63, 14 January 2022</ref>

As of May 2023, following the European Union 2022 ban, the U.S. states California and New York were considering banning the use of titanium dioxide in foods.<ref name="NJTimesMay2023">Template:Cite news</ref>

As of 2024, the Food and Drug Administration (FDA) in the United States permits titanium dioxide as a food additive.<ref name=fda/> It may be used to increase whiteness and opacity in dairy products (some cheeses, ice cream, and yogurt), candies, frostings, fillings, and many other foods. The FDA regulates the labeling of products containing titanium dioxide, allowing the product's ingredients list to identify titanium dioxide either as "color added" or "artificial colors" or "titanium dioxide;" it does not require that titanium dioxide be explicitly named.<ref name=fda/> In 2023, the Consumer Healthcare Products Association, a manufacturer's trade group, defended the substance as safe at certain limits while allowing that additional studies could provide further insight, saying an immediate ban would be a "knee-jerk" reaction.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Industry response

Dunkin' Donuts dropped titanium dioxide from their merchandise in 2015 after public pressure.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Research as an ingestible nanomaterial

Size distribution analyses showed that batches of food-grade TiO₂, which is produced with a target particle size in the 200Template:En dash300Template:Nbspnm range for optimal pigmentation qualities, include a nanoparticle-sized fraction as inevitable byproduct of the manufacturing processes.<ref> Template:Cite journal</ref>

Inhalation

Titanium dioxide dust, when inhaled, has been classified by the International Agency for Research on Cancer (IARC) as an IARC Group 2B carcinogen, meaning it is possibly carcinogenic to humans.<ref name=IARC>Template:Cite book</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The US National Institute for Occupational Safety and Health recommends two separate exposure limits. NIOSH recommends that fine Template:Chem particles be set at an exposure limit of 2.4 mg/m³, while ultrafine Template:Chem be set at an exposure limit of 0.3 mg/m³, as time-weighted average concentrations up to 10 hours a day for a 40-hour work week.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Although no evidence points to acute toxicity, recurring concerns have been expressed about nanophase forms of these materials. Studies of workers with high exposure to TiO₂ particles indicate that even at high exposure there is no adverse effect to human health.<ref name="auto"/>

Environmental waste introduction

Titanium dioxide (TiO₂) is mostly introduced into the environment as nanoparticles via wastewater treatment plants.<ref name=":5">Template:Cite journal</ref> Cosmetic pigments including titanium dioxide enter the wastewater when the product is washed off into sinks after cosmetic use. Once in the sewage treatment plants, pigments separate into sewage sludge which can then be released into the soil when injected into the soil or distributed on its surface. 99% of these nanoparticles wind up on land rather than in aquatic environments due to their retention in sewage sludge.<ref name=":5"/> In the environment, titanium dioxide nanoparticles have low to negligible solubility and have been shown to be stable once particle aggregates are formed in soil and water surroundings.<ref name=":5"/> In the process of dissolution, water-soluble ions typically dissociate from the nanoparticle into solution when thermodynamically unstable. TiO₂ dissolution increases when there are higher levels of dissolved organic matter and clay in the soil. However, aggregation is promoted by pH at the isoelectric point of TiO₂ (pH= 5.8) which renders it neutral and solution ion concentrations above 4.5 mM.<ref name=":0">Template:Cite book</ref><ref>Template:Cite journal</ref>

See also

• Delustrant
• Dye-sensitized solar cell
• List of inorganic pigments
• Noxer blocks, TiO₂-coated pavers that remove Template:NOx pollutants from the air
• Suboxide
• Surface properties of transition metal oxides
• Titanium dioxide nanoparticle

External links

• International Chemical Safety Card 0338
• NIOSH Pocket Guide to Chemical Hazards
• "Titanium Dioxide Classified as Possibly Carcinogenic to Humans", Canadian Centre for Occupational Health and Safety, August, 2006 (if inhaled as a powder)
• A description of TiO₂ photocatalysis
• Titanium and titanium dioxide production data (US and World)