View source for Titanium dioxide

{{Short description|Chemical compound}}
{{cs1 config|name-list-style=vanc}}
{{Use dmy dates|date=August 2021}}
{{Chembox
| Verifiedfields = sleep
| Watchedfields  = changed
| verifiedrevid  = 476992554
| Name           = Titanium dioxide
| ImageFile      = Rutile-unit-cell-3D-balls.png
| ImageCaption   =  [[Unit cell]] of titanium dioxide (rutile form)<BR /> {{colorbox|#d3d3d3}} Titanium {{colorbox|#ee2010}} Oxygen
| ImageSize      = 
| ImageName      = Titanium(IV) oxide
| ImageFile1     = Titanium(IV)_oxide.jpg
| ImageSize1     = 
| ImageName1     = The unit cell of rutile
| IUPACName      = Titanium dioxide<br/>Titanium(IV) oxide
| OtherNames     = {{Unbulleted list|Titania|[[Rutile]]|[[Anatase]]|[[Brookite]]}}
| SystematicName = 
| Section1       = {{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 24256
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 15FIX9V2JP
| ChEMBL_Ref = {{ebicite|changed|EBI}}
| ChEMBL = 1201136
| InChI = 1/2O.Ti/rO2Ti/c1-3-2
| InChIKey = GWEVSGVZZGPLCZ-TYTSCOISAW
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 32234
| SMILES = O=[Ti]=O
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/2O.Ti
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = GWEVSGVZZGPLCZ-UHFFFAOYSA-N
| CASNo = 13463-67-7
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 26042
| RTECS = XR2775000
| KEGG_Ref = {{keggcite|changed|kegg}}
| KEGG = C13409
}}
| Section2       = {{Chembox Properties
| Formula = {{chem|TiO|2}}
| MolarMass = 79.866&nbsp;g/mol
| Appearance = White solid
| Odor = Odorless
| Density = {{ubl
 | 4.23&nbsp;g/cm<sup>3</sup> (rutile)
 | 3.78&nbsp;g/cm<sup>3</sup> (anatase)
 }}
| MeltingPtC = 1843
| BoilingPtC = 2972
| Solubility = Insoluble
| BandGap = 3.21{{nbsp}}eV (anatase)<ref name="Zanatta">{{cite journal |last1=Zanatta |first1=A.R. | title= Temperature-dependent optical bandgap of TiO2 under the Anatase and Rutile phases |journal=Results Phys. |date=May 2024 |volume=60 |pages= 107653–5pp |doi=10.1016/j.rinp.2024.107653 |doi-access=free }}</ref>  
3.15{{nbsp}}eV (rutile)<ref name="Zanatta">{{cite journal |last1=Zanatta |first1=A.R. | title= Temperature-dependent optical bandgap of TiO2 under the Anatase and Rutile phases |journal=Results Phys. |date=May 2024 |volume=60 |pages= 107653–5pp |doi=10.1016/j.rinp.2024.107653 |doi-access=free }}</ref> 
| RefractIndex = {{ubl
 | 2.488 (anatase)
 | 2.583 (brookite)
 | 2.609 (rutile)
 }}
| MagSus = +5.9·10<sup>−6</sup>{{nbsp}}cm<sup>3</sup>/mol
}}
| Section3       = 
| Section4       = {{Chembox Thermochemistry
| DeltaHf = −945&nbsp;kJ·mol<sup>−1</sup><ref name=b1>{{cite book |author= Zumdahl, Steven S.|title =Chemical Principles 6th Ed. |publisher= Houghton Mifflin Company |year= 2009 |isbn= 978-0-618-94690-7|page=A23}}</ref>
| Entropy = 50&nbsp;J·mol<sup>−1</sup>·K<sup>−1</sup><ref name=b1/>
 }}
| Section5       = 
| Section6       = 
| Section7       = {{Chembox Hazards
| ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics0338.htm ICSC 0338]
| NFPA-H = 1
| NFPA-F = 0
| NFPA-R = 0
| NFPA-S =
| FlashPt = not flammable
| IDLH = Ca [5000{{nbsp}}mg/m<sup>3</sup>]<ref name=PGCH>{{PGCH|0617}}</ref>
| REL = Ca<ref name=PGCH/>
| PEL = TWA 15{{nbsp}}mg/m<sup>3</sup><ref name=PGCH/>
}}
| Section8       = {{Chembox Related
| OtherAnions =
| OtherCations = [[Zirconium dioxide]]<br/>[[Hafnium dioxide]]
| OtherFunction = [[Titanium(II) oxide]]<br/>[[Titanium(III) oxide]]<br/>[[Titanium(III,IV) oxide]]
| OtherFunction_label = [[Titanium]] [[oxide]]s
| OtherCompounds = [[Titanic acid]]
}}
}}

'''Titanium dioxide''', also known as '''titanium(IV) oxide''' or '''titania''' {{IPAc-en|t|aɪ|ˈ|t|eɪ|n|i|ə}}, is the [[inorganic compound]] derived from [[titanium]] with the chemical formula {{chem|TiO|2}}. When used as a [[pigment]], it is called '''titanium white''', '''Pigment White 6''' ('''PW6'''), or '''[[Colour Index International|CI 77891]]'''.<ref name=Ullmann>{{Ullmann|author=Völz, Hans G. |display-authors=etal |title=Pigments, Inorganic|year=2006|doi=10.1002/14356007.a20_243.pub2}}</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>[http://minerals.usgs.gov/minerals/pubs/commodity/titanium/myb1-2014-titan.pdf "Titanium"] in ''2014 Minerals Yearbook''. USGS</ref><ref>{{cite web |url=http://minerals.usgs.gov/minerals/pubs/mcs/2015/mcs2015.pdf|title=Mineral Commodity Summaries, 2015|website=U.S. Geological Survey|publisher=U.S. Geological Survey 2015}}</ref><ref>{{cite web |url=http://minerals.usgs.gov/minerals/pubs/mcs/2016/mcs2016.pdf|title=Mineral Commodity Summaries, January 2016|website=U.S. Geological Survey|publisher=U.S. Geological Survey 2016}}</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>{{cite news |url=https://www.bloomberg.com/features/2018-quest-for-billion-dollar-red/|title=The Quest for the Next Billion-Dollar Color|last=Schonbrun|first=Zach|work=Bloomberg.com|access-date=2018-04-24}}</ref>
{{TOC limit|3}}

==Structure==
In all three of its main dioxides, [[titanium]] exhibits [[Octahedral molecular geometry|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. RuO<sub>2</sub> and ZnF<sub>2</sub>.

Molten titanium dioxide has a local structure in which each Ti is coordinated to, on average, about 5 oxygen atoms.<ref name="Ald">{{Cite journal |last1=Alderman |first1=O. L. G. |last2=Skinner |first2=L. B. |last3=Benmore |first3=C. J. |last4=Tamalonis |first4=A. |last5=Weber |first5=J. K. R. |year=2014 |title=Structure of molten titanium dioxide |journal=Physical Review B |language=en |volume=90 |issue=9 |page=094204 |bibcode=2014PhRvB..90i4204A |doi=10.1103/PhysRevB.90.094204 |issn=1098-0121 |doi-access=free}}</ref> This is distinct from the crystalline forms in which Ti coordinates to 6 oxygen atoms.

[[File:Anatase crystal structure.png|alt=A ball-and-stick chemical model of an anatase crystal|left|thumb|Structure of [[anatase]]. Together with rutile and brookite, one of the three major [[polymorphism (materials science)|polymorph]]s of TiO<sub>2</sub>.]]

==Synthetic and geologic occurrence==
Synthetic TiO<sub>2</sub> is mainly produced from the mineral [[ilmenite]].  [[Rutile]], and [[anatase]], naturally occurring TiO<sub>2</sub>, 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 sapphire (jewel)|Star sapphire]]s and [[ruby|rubies]] get their [[asterism (gemology)|asterism]] from oriented inclusions of rutile needles.<ref name="BuildingBlocks451-3">{{cite book |last=Emsley |first=John |title=Nature's Building Blocks: An A–Z Guide to the Elements |year=2001 |isbn=978-0-19-850341-5 |pages=451–53 |publisher=[[Oxford University Press]] |location=Oxford}}</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 crystal system|monoclinic]] [[baddeleyite]]-like form known as [[akaogiite]], and the other has a slight monoclinic distortion of the [[orthorhombic crystal system|orthorhombic]] [[lead dioxide|α-PbO<sub>2</sub>]] structure and is known as riesite. Both of which can be found at the [[Nördlinger Ries|Ries crater]] in [[Bavaria]].<ref>{{cite journal |doi=10.1126/science.1062342|year=2001|title=An ultradense polymorph of rutile with seven-coordinated titanium from the Ries crater.|volume=293|issue=5534|pages=1467–70|pmid=11520981|journal=Science|author1=El, Goresy|author2=Chen, M|author3=Dubrovinsky, L|author4=Gillet, P|author5=Graup, G|bibcode=2001Sci...293.1467E|s2cid=24349901}}</ref><ref>{{cite journal |doi=10.1016/S0012-821X(01)00480-0|title=A natural shock-induced dense polymorph of rutile with α-PbO2 structure in the suevite from the Ries crater in Germany|year=2001|author=El Goresy, Ahmed|journal=Earth and Planetary Science Letters|volume=192|pages=485|last2=Chen|first2=Ming|last3=Gillet|first3=Philippe|last4=Dubrovinsky|first4=Leonid|last5=Graup|first5=GüNther|last6=Ahuja|first6=Rajeev|bibcode=2001E&PSL.192..485E|issue=4}}</ref><ref>[https://www.mindat.org/min-35912.html 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 {{convert|600|-|800|C|-1}}.<ref>{{cite journal |last1=Hanaor |first1=Dorian A. H. |last2=Sorrell |first2=Charles C. |title=Review of the anatase to rutile phase transformation |journal=Journal of Materials Science |date=February 2011 |volume=46 |issue=4 |pages=855–874 |doi=10.1007/s10853-010-5113-0 |bibcode=2011JMatS..46..855H |s2cid=97190202 |url=https://hal.science/hal-02308408|doi-access=free }}</ref>

Titanium dioxide has twelve known polymorphs – in addition to rutile, anatase, brookite, akaogiite and riesite, three metastable phases can be produced synthetically ([[monoclinic crystal system|monoclinic]], [[tetragonal crystal system|tetragonal]], and orthorhombic ramsdellite-like), and four high-pressure forms (α-PbO<sub>2</sub>-like, [[cotunnite]]-like, orthorhombic OI, and cubic phases) also exist:

{| class="wikitable"
|-
! Form
! Crystal system
! Synthesis
|-
| [[Rutile]]
| [[Tetragonal crystal system|Tetragonal]]
|
|-
| [[Anatase]]
|[[Tetragonal crystal system|Tetragonal]]
|
|-
| [[Brookite]]
| [[Orthorhombic crystal system|Orthorhombic]]
|
|-
| TiO<sub>2</sub>(B)<ref>{{cite journal |author1=Marchand R. |author2=Brohan L. |author3=Tournoux M. |title= A new form of titanium dioxide and the potassium octatitanate K<sub>2</sub>Ti<sub>8</sub>O<sub>17</sub> |year= 1980|journal= Materials Research Bulletin|volume= 15|issue= 8|pages= 1129–1133|doi= 10.1016/0025-5408(80)90076-8}}</ref>
| [[Monoclinic crystal system|Monoclinic]]
| Hydrolysis of K<sub>2</sub>Ti<sub>4</sub>O<sub>9</sub> followed by heating
|-
| TiO<sub>2</sub>(H), [[hollandite]]-like form<ref>{{cite journal |title= New hollandite oxides: TiO<sub>2</sub>(H) and K<sub>0.06</sub>TiO<sub>2</sub>|year= 1989|journal= Journal of Solid State Chemistry|volume= 81|issue= 1|pages= 78–82 |doi= 10.1016/0022-4596(89)90204-1|author1= Latroche, M|author2= Brohan, L|author3= Marchand, R|author4= Tournoux|bibcode= 1989JSSCh..81...78L}}</ref>
|[[Tetragonal crystal system|Tetragonal]]
| Oxidation of the related potassium titanate bronze, K<sub>0.25</sub>TiO<sub>2</sub>
|-
| TiO<sub>2</sub>(R), [[ramsdellite]]-like form<ref>{{cite journal |title= Topotactic Oxidation of Ramsdellite-Type Li<sub>0.5</sub>TiO<sub>2</sub>, a New Polymorph of Titanium Dioxide: TiO<sub>2</sub>(R)|year= 1994|journal= Journal of Solid State Chemistry|volume= 113|issue= 1|pages= 27–36 |doi= 10.1006/jssc.1994.1337|bibcode= 1994JSSCh.113...27A|last1= Akimoto|first1= J.|last2= Gotoh|first2= Y.|last3= Oosawa|first3= Y.|last4= Nonose|first4= N.|last5= Kumagai|first5= T.|last6= Aoki|first6= K.|last7= Takei|first7= H.}}</ref>
|[[Orthorhombic crystal system|Orthorhombic]]
| Oxidation of the related lithium titanate bronze Li<sub>0.5</sub>TiO<sub>2</sub>
|-
| TiO<sub>2</sub>(II)-([[lead dioxide|α-PbO<sub>2</sub>]]-like form)<ref>{{cite journal |title= The structure of TiO<sub>2</sub>II, a high-pressure phase of TiO<sub>2</sub>|year= 1967|journal= Acta Crystallographica|volume= 23 |issue= 2|pages= 334–336|doi= 10.1107/S0365110X67002713|last1= Simons|first1= P. Y.|last2= Dachille|first2= F.|bibcode= 1967AcCry..23..334S}}</ref>
|[[Orthorhombic crystal system|Orthorhombic]]
|
|-
| [[Akaogiite]] ([[baddeleyite]]-like form, 7 coordinated Ti)<ref>{{cite journal |author1=Sato H |author2=Endo S |author3=Sugiyama M |author4=Kikegawa T |author5=Shimomura O |author6=Kusaba K |title= Baddeleyite-Type High-Pressure Phase of TiO<sub>2</sub>|year= 1991|journal= Science|volume= 251|issue= 4995|pages= 786–788|doi= 10.1126/science.251.4995.786|pmid= 17775458|bibcode= 1991Sci...251..786S|s2cid=28241170 }}</ref>
|[[Monoclinic crystal system|Monoclinic]]
|
|-
| TiO<sub>2</sub> -OI<ref>{{cite journal |author1=Dubrovinskaia N. A. |author2=Dubrovinsky L. S. |author3=Ahuja R. |author4=Prokopenko V. B. |author5=Dmitriev V. |author6=Weber H.-P. |author7=Osorio-Guillen J. M. |author8=Johansson B. |title= Experimental and Theoretical Identification of a New High-Pressure TiO<sub>2</sub> Polymorph|year= 2001|journal= Phys. Rev. Lett.|volume= 87|pages= 275501|doi= 10.1103/PhysRevLett.87.275501|pmid= 11800890|issue= 27 Pt 1|bibcode=2001PhRvL..87A5501D}}</ref>
|[[Orthorhombic crystal system|Orthorhombic]]
|
|-
| [[Cubic crystal system|Cubic]] form<ref>{{cite journal |author1=Mattesini M. |author2=de Almeida J. S. |author3=Dubrovinsky L. |author4=Dubrovinskaia L. |author5=Johansson B. |author6=Ahuja R. |title= High-pressure and high-temperature synthesis of the cubic TiO<sub>2</sub> polymorph|year= 2004|journal= Phys. Rev. B|volume= 70|pages= 212101|doi= 10.1103/PhysRevB.70.212101|issue= 21|bibcode= 2004PhRvB..70u2101M |title-link=cubic crystal system}}</ref>
| [[Cubic crystal system|Cubic]]
| P > 40&nbsp;GPa, T > 1600&nbsp;°C
|-
| TiO<sub>2</sub> -OII, [[cotunnite]]([[lead(II) chloride|PbCl<sub>2</sub>]])-like<ref name=du1>{{cite journal |title= Materials science: The hardest known oxide|year= 2001|journal= Nature|volume= 410|pages= 653–654|doi= 10.1038/35070650|pmid= 11287944|last1= Dubrovinsky|first1= LS|last2= Dubrovinskaia|first2= NA|last3= Swamy|first3= V|last4= Muscat|first4= J|last5= Harrison|first5= NM|last6= Ahuja|first6= R|last7= Holm|first7= B|last8= Johansson|first8= B|issue= 6829|bibcode= 2001Natur.410..653D |hdl= 10044/1/11018|s2cid= 4365291|hdl-access= free}}</ref>
|[[Orthorhombic crystal system|Orthorhombic]]
| P > 40&nbsp;GPa, T > 700&nbsp;°C
|}

The [[cotunnite]]-type phase was claimed to be the hardest known oxide with the [[Vickers hardness]] of 38&nbsp;GPa and the [[bulk modulus]] of 431&nbsp;GPa (i.e. close to diamond's value of 446&nbsp;GPa) at atmospheric pressure.<ref name=du1/> However, later studies came to different conclusions with much lower values for both the hardness (7–20&nbsp;GPa, which makes it softer than common oxides like corundum Al<sub>2</sub>O<sub>3</sub> and rutile TiO<sub>2</sub>)<ref>{{cite journal |author1=Oganov A.R. |author2=Lyakhov A.O. |title= Towards the theory of hardness of materials |year= 2010|journal= Journal of Superhard Materials |volume= 32|pages= 143–147|doi= 10.3103/S1063457610030019|issue= 3|arxiv= 1009.5477|bibcode=2010JSMat..32..143O|s2cid=119280867 }}</ref> and bulk modulus (~300&nbsp;GPa).<ref>{{cite journal |author1=Al-Khatatbeh, Y. |author2=Lee, K. K. M. |author3=Kiefer, B. |title= High-pressure behavior of TiO<sub>2</sub> as determined by experiment and theory|year= 2009|journal= Phys. Rev. B |volume= 79|page= 134114|doi=10.1103/PhysRevB.79.134114|issue= 13|bibcode= 2009PhRvB..79m4114A}}</ref><ref>{{cite journal |author1=Nishio-Hamane D. |author2=Shimizu A. |author3=Nakahira R. |author4=Niwa K. |author5=Sano-Furukawa A. |author6=Okada T. |author7=Yagi T. |author8=Kikegawa T. |title= The stability and equation of state for the cotunnite phase of TiO<sub>2</sub> up to 70 GPa|year= 2010|journal= Phys. Chem. Minerals |volume= 37|pages= 129–136|doi=10.1007/s00269-009-0316-0|issue= 3|bibcode= 2010PCM....37..129N|s2cid=95463163 }}</ref>

Titanium dioxide (B) is found as a [[mineral]] in magmatic rocks and hydrothermal veins, as well as weathering rims on [[perovskite]]. TiO<sub>2</sub> also forms [[lamella (materials)|lamellae]] in other minerals.<ref>{{cite journal |author1= Banfield, J. F.|author2=Veblen, D. R.|author3=Smith, D. J. |title= The identification of naturally occurring TiO<sub>2</sub> (B) by structure determination using high-resolution electron microscopy, image simulation, and distance–least–squares refinement|journal= American Mineralogist|url=http://www.minsocam.org/ammin/AM76/AM76_343.pdf |year= 1991 |volume= 76|page= 343}}</ref>

==Production==
[[File:Industrial key players in the production of titanium dioxide.png|thumb|Industrial key players in the production of titanium dioxide - 2022]]
The largest {{Chem|Ti||O|2}} pigment processors are [[Chemours]], [[Venator Materials|Venator]], {{Interlanguage link|Kronos International|lt=Kronos|de}}, and [[Tronox]].<ref>{{cite press release |url=https://www.businesswire.com/news/home/20170420006437/en/Top-5-Vendors-Global-Titanium-Dioxide-Market|title=Top 5 Vendors in the Global Titanium Dioxide Market From 2017-2021: Technavio|date=2017-04-20}}</ref><ref name="Hayes (2011)">{{cite web |last=Hayes|year=2011|first=Tony|title=Titanium Dioxide: A Shining Future Ahead|url=http://argex.ca/documents/Euro_Pacific_Canada_Titanium_Dioxide_August2011.pdf|publisher=Euro Pacific Canada|access-date=16 August 2012|page=5}}{{dead link|date=January 2018 |bot=InternetArchiveBot |fix-attempted=yes}}</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 {{Chem|Ti||O|2}} pigment demand for 2010 was 5.3 Mt with annual growth expected to be about 3–4%.<ref>Hayes (2011), p. 4</ref>

[[File:Evolution production dioxyde de titane.svg|thumb|lang=en|right|Evolution of the global production of titanium dioxide according to process]]
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 production|batch process]]; the chloride process is run as a [[continuous process]].<ref>{{Cite web|url=https://www.essentialchemicalindustry.org/chemicals/titanium-dioxide.html|title=Titanium dioxide|website=www.essentialchemicalindustry.org}}</ref>

===Chloride process===
{{Main|Chloride process}}
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|iron(II) sulfate pentahydrate]]. This process requires concentrated ilmenite (45–60% TiO<sub>2</sub>) or pretreated feedstocks as a suitable source of titanium.<ref name=jv>{{cite web |url=https://patentimages.storage.googleapis.com/c6/c1/7b/20176ebf24a65c/EP0869194A1.pdf|title=Process for preparing titanium dioxide|last=Vartiainen|first=Jaana|date=7 October 1998}}</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">{{cite book |last=Winkler |first=Jochen |title=Titanium Dioxide |year=2003 |isbn=978-3-87870-148-4 |pages=30–31 |publisher=Vincentz Network |location=Hannover}}</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">{{cite news |url=http://www.francoiscardarelli.ca/PDF_Files/Article_Cardarelli_MER_Process.pdf}}</ref>

===Becher process===
{{Main|Becher process}}
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, TiO<sub>2</sub> films are prepared by various specialized chemistries.<ref>{{cite journal |title=Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications|author1=Chen, Xiaobo |author2=Mao, Samuel S. |journal=Chemical Reviews|year=2007|volume=107|issue=7|pages=2891–2959|doi=10.1021/cr0500535|pmid=17590053}}</ref> Sol-gel routes involve the hydrolysis of titanium [[alkoxide]]s such as [[titanium ethoxide]]:
:Ti(OEt)<sub>4</sub> + 2 H<sub>2</sub>O → TiO<sub>2</sub> + 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)<sub>4</sub> → TiO<sub>2</sub> + 2 Et<sub>2</sub>O

==Applications==

===Pigment===
{{Main|Titanium white}}
First mass-produced in 1916,<ref>{{cite book|title=The Secret Lives of Colour|last=St. Clair|first=Kassia|publisher=John Murray|year=2016|isbn=978-1-4736-3081-9|location=London|page=40|oclc=936144129}}</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&nbsp;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">{{cite journal| last1=Hanaor| first1=D. A. H. | last2=Xu| first2=W.|last3=Ferry|first3=M.|last4=Sorrell|first4=C. C. | title= Abnormal grain growth of rutile TiO<sub>2</sub> induced by ZrSiO<sub>4</sub>| journal= [[Journal of Crystal Growth]]| year= 2012| volume=359| pages=83–91| url= https://hal.archives-ouvertes.fr/hal-02315198/document/#page=2 | doi=10.1016/j.jcrysgro.2012.08.015|arxiv=1303.2761| bibcode=2012JCrGr.359...83H | s2cid=94096447 }}
</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 TiO<sub>2</sub>. 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>{{cite book |title=Kemira pigments quality titanium dioxide |last=Anderson |first=Bruce |year=1999 |location=Savannah, Georgia |pages=39}}</ref> Approximately 4.6 million tons of pigmentary TiO<sub>2</sub> are used annually worldwide, and this number is expected to increase as use continues to rise.<ref name="Nano-scaled titania">{{cite book |last=Winkler |first=Jochen |title=Titanium Dioxide |year=2003 |isbn=978-3-87870-148-4 |pages=5 |publisher=Vincentz Network |location=Hannover, Germany}}</ref>

TiO<sub>2</sub> is also an effective [[opacifier]] in powder form, where it is employed as a pigment to provide whiteness and [[Opacity (optics)|opacity]] to products such as [[paint]]s, [[coating]]s, [[plastic]]s, [[paper]]s, [[ink]]s, [[food]]s, [[Dietary supplement|supplements]], [[medicine]]s (i.e. pills and tablets), and most [[toothpaste]]s; in 2019 it was present in two-thirds of toothpastes on the French market.<ref name=frouville>{{cite news |title=Deux dentifrices sur trois contiennent du dioxyde de titane, un colorant au possible effet cancérogène|language=fr|trans-title=Two out of three toothpastes contain titanium dioxide, a possibly carcinogenic colouring material|author=Margaux de Frouville|url=https://www.bfmtv.com/sante/deux-dentifrices-sur-trois-contiennent-du-dioxyde-de-titane-un-colorant-au-possible-effet-cancerogene-1660942.html |publisher=BFMTV.com |date=28 March 2019}}</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.

===Food additive===
In food, 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>{{cite web|url=https://healthknight.com/titanium-dioxide-e171-side-effects-benefits |title=Titanium Dioxide (E171) – Overview, Uses, Side Effects & More |date=10 April 2022 |publisher=HealthKnight |access-date=2022-06-09}}</ref>

===Thin films===
When deposited as a [[thin film]], its refractive index and colour make it an excellent reflective optical coating for [[dielectric mirror]]s; it is also used in generating decorative thin films such as found in "mystic fire topaz".

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>{{cite book|author=Koleske, J. V. |title=Paint and Coating Testing Manual|url=https://books.google.com/books?id=ri6FkY2xvgcC&pg=PA232|year=1995|publisher=ASTM International|isbn=978-0-8031-2060-0|page=232}}</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&nbsp;°C<ref>{{cite book|author=Koleske, J. V. |title=Paint and Coating Testing Manual|url=https://books.google.com/books?id=ri6FkY2xvgcC&pg=PA229|year=1995|publisher=ASTM International|isbn=978-0-8031-2060-0|page=229}}</ref> One example of a pearlescent pigment is Iriodin, based on mica coated with titanium dioxide or iron (III) oxide.<ref>{{citation |url= http://pearl-effect.com/index.php?option=com_content&view=article&id=92&Itemid=62 |archive-url= https://web.archive.org/web/20120117030508/http://pearl-effect.com/index.php?option=com_content&view=article&id=92&Itemid=62 |archive-date= 17 January 2012 |title= Pearlescence with Iriodin |work= pearl-effect.com}}</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 [[Cosmetics|cosmetic]] and [[skin care]] products, titanium dioxide is used as a pigment, sunscreen and a [[thickener]]. As a sunscreen, ultrafine TiO<sub>2</sub> is used, which is notable in that combined with [[zinc oxide nanoparticle|ultrafine zinc oxide]], it is considered to be an effective sunscreen that lowers the incidence of [[Sunburn|sun burns]] and minimizes the premature [[photoaging]], [[photocarcinogenesis]] and [[immunosuppression]] associated with long term excess sun exposure.<ref>{{Citation|last1=Gabros|first1=Sarah|title=Sunscreens And Photoprotection|date=2021|url=http://www.ncbi.nlm.nih.gov/books/NBK537164/|work=StatPearls|place=Treasure Island (FL)|publisher=StatPearls Publishing|pmid=30725849|access-date=2021-03-06|last2=Nessel|first2=Trevor A.|last3=Zito|first3=Patrick M.}}</ref> Sometimes these UV blockers are combined with iron oxide pigments in sunscreen to increase visible light protection.<ref>{{Cite journal|last1=Dumbuya|first1=Hawasatu|last2=Grimes|first2=Pearl E.|last3=Lynch|first3=Stephen|last4=Ji|first4=Kaili|last5=Brahmachary|first5=Manisha|last6=Zheng|first6=Qian|last7=Bouez|first7=Charbel|last8=Wangari-Talbot|first8=Janet|date=2020-07-01|title=Impact of Iron-Oxide Containing Formulations Against Visible Light-Induced Skin Pigmentation in Skin of Color Individuals|journal=Journal of Drugs in Dermatology |volume=19|issue=7|pages=712–717|doi=10.36849/JDD.2020.5032|issn=1545-9616|pmid=32726103|doi-access=free}}</ref>

Titanium dioxide and zinc oxide are generally considered to be less harmful to [[coral reef]]s than sunscreens that include chemicals such as [[oxybenzone]], [[octocrylene]] and [[octyl methoxycinnamate|octinoxate]].<ref>{{Cite web|title=US Virgin Islands bans sunscreens harming coral reefs|url=https://www.downtoearth.org.in/news/wildlife-biodiversity/us-virgin-islands-bans-sunscreens-harming-coral-reefs-70158|access-date=2021-03-06|website=www.downtoearth.org.in|date=April 2020 |language=en}}</ref>

Nanosized titanium dioxide is found in the majority of physical [[sunscreen]]s 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&nbsp;nm)<ref>Dan, Yongbo et al. [https://www.perkinelmer.com/CMSResources/Images/44-171045APP_011990_01-NexION-350D-TiO2-NPs-in-Sunscreen.pdf Measurement of Titanium Dioxide Nanoparticles in Sunscreen using Single Particle ICP-MS]. 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 type|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-TiO<sub>2</sub>, 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>{{Cite web|url=https://ec.europa.eu/health/scientific_committees/consumer_safety/docs/sccs_o_136.pdf|title=Health_scientific_committees}}</ref> The risk assessment of different titanium dioxide nanomaterials in sunscreen is currently evolving since nano-sized TiO<sub>2</sub> is different from the well-known micronized form.<ref name=":2">{{Cite journal|date=2010|title=Sunscreens with Titanium Dioxide (TiO<sub>2</sub>) Nano-Particles: A Societal Experiment|journal=Nanoethics|pmc=2933802|last1=Jacobs|first1=J. F.|last2=Van De Poel|first2=I.|last3=Osseweijer|first3=P.|volume=4|issue=2|pages=103–113|doi=10.1007/s11569-010-0090-y|pmid=20835397}}</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>{{Cite web|last=cosmeticsdesign-europe.com|title=Scientists encourage 'safer' rutile form of TiO<sub>2</sub> in cosmetics|url=https://www.cosmeticsdesign-europe.com/Article/2013/09/26/Scientists-encourage-safer-rutile-form-of-TiO2-in-cosmetics|access-date=2021-03-06|website=cosmeticsdesign-europe.com|date=25 September 2013 |language=en-GB}}</ref> and having a higher [[UV protection|UV absorption]].<ref name=":3">{{Cite journal|date=29 March 2006|title=Characteristics of silica-coated TiO<sub>2</sub> and its UV absorption for sunscreen cosmetic applications|url=https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/abs/10.1002/sia.2313|journal=Wiley Analytical Science|doi=10.1002/sia.2313|via=Wiley Online Library|last1=Jaroenworaluck|first1=A.|last2=Sunsaneeyametha|first2=W.|last3=Kosachan|first3=N.|last4=Stevens|first4=R.|volume=38|issue=4|pages=473–477|s2cid=97137064 }}</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">{{Cite journal |last1=Dréno |first1=B. |last2=Alexis |first2=A. |last3=Chuberre |first3=B. |last4=Marinovich |first4=M. |date=2019 |title=Safety of titanium dioxide nanoparticles in cosmetics |journal=Journal of the European Academy of Dermatology and Venereology |language=en |volume=33 |issue=S7 |pages=34–46 |doi=10.1111/jdv.15943 |issn=0926-9959 |pmid=31588611 |s2cid=203849903 |doi-access=free |hdl-access=free |hdl=2434/705700}}</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 TiO<sub>2</sub> in concentrations of up to 25%.<ref name=":4">{{Cite journal|date=7 November 2016|title=OPINION ON additional coatings for Titanium Dioxide (nano form) as UV-filter in dermally applied cosmetic products|url=https://ec.europa.eu/health/scientific_committees/consumer_safety/docs/sccs_o_202.pdf|journal=Scientific Committee on Consumer Safety (SCCS)|publisher=European Commission|via=ec.europa.eu}}</ref>

Initial studies indicated that nano-TiO<sub>2</sub> 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]], [[Silicon dioxide|silica]], cetyl phosphate<!--Q27292009-->, [[Silicone#Personal care|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&nbsp;mg/cm2 for exposure periods of 24 hours.<ref name=":4" /> Coating TiO<sub>2</sub> with alumina, silica, [[zircon]] or various [[polymer]]s can minimize [[avobenzone]] degradation<ref>{{Cite journal|title=Preparation of rutile TiO<sub>2</sub>@avobenzone composites for the further enhancement of sunscreen performance|url=https://pubs.rsc.org/en/content/articlelanding/2016/ra/c6ra23282e#!divRelatedContent&articles|journal=RSC Advances|bibcode=2016RSCAd...6k1865W|via=Royal society of chemistry|last1=Wang|first1=Can|last2=Zuo|first2=Shixiang|last3=Liu|first3=Wenjie|last4=Yao|first4=Chao|last5=Li|first5=Xiazhang|last6=Li|first6=Zhongyu|year=2016|volume=6|issue=113|page=111865|doi=10.1039/C6RA23282E}}</ref> and enhance UV absorption by adding an additional light diffraction mechanism.<ref name=":3" />

{{Chem|Ti|O|2}} 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>[http://www2.dupont.com/Titanium_Technologies/en_US/tech_info/literature/Plastics/PL_B_Polymers_Light_Science.pdf Polymers, Light and the Science of TiO<sub>2</sub>] {{Webarchive|url=https://web.archive.org/web/20170329071755/http://www2.dupont.com/Titanium_Technologies/en_US/tech_info/literature/Plastics/PL_B_Polymers_Light_Science.pdf |date=29 March 2017 }}, DuPont, pp. 1–2</ref>

===Other uses of titanium dioxide===
In [[ceramic glaze]]s, titanium dioxide acts as an opacifier and seeds [[crystal]] formation.

It is used as a [[tattoo]] pigment and in [[styptic pencil]]s. 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>{{cite journal |bibcode= 2003DPS....35.3602J |last1= Jorgensen |first1= K. |last2= Rivkin |first2= A. |last3= Binzel |first3= R. |last4= Whitely |first4= R. |last5= Hergenrother |first5= C. |last6= Chodas |first6= P. |last7= Chesley |first7= S. |last8= Vilas |first8= F. |title= Observations of J002E3: Possible Discovery of an Apollo Rocket Body |journal= [[Bulletin of the American Astronomical Society]] |date= May 2003 |volume= 35 |page= 981}}</ref>

==Research==

===Patenting activities===
[[File:Relevant patent families describing titanium dioxide production from ilmenite, 2002–2021.png|thumb|Relevant patent families describing titanium dioxide production from ilmenite, 2002–2021.]]
[[File:Public Institutions patent activity in titanium dioxide production.png|thumb|Academic and public institutions having significant patent activity in titanium dioxide production. 2022]]
Between 2002 and 2022, there were 459 [[Patent family|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|sulfate process]] and the [[chloride process]].<ref name=":6">{{Cite journal |date=2023 |title=Patent Landscape Report : Production of titanium and titanium dioxide from ilmenite and related applications |url=https://www.wipo.int/publications/en/details.jsp?id=4651&plang=EN |access-date=2023-11-13 |website=www.wipo.int |publisher=[[WIPO]] |doi=10.34667/tind.47029 |language=en |author1=World Intellectual Property Organization. |series=Patent Landscape Reports }}</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 Group Vanadium Titanium & Resources|Pangang]] and [[Lomon Billions]] Groups hold major patent portfolios.<ref name=":6" />

===Photocatalyst===
Nanosized titanium dioxide, particularly in the anatase form, exhibits [[photocatalysis|photocatalytic activity]] under ultraviolet (UV) irradiation. This photoactivity is reportedly most pronounced at the {001} planes of anatase,<ref>{{cite journal |author=Liang Chu |journal=Scientific Reports |volume=5 |pages=12143 |title=Anatase TiO<sub>2</sub> Nanoparticles with Exposed {001} Facets for Efficient Dye-Sensitized Solar Cells |doi=10.1038/srep12143 |pmid=26190140 |pmc=4507182 |bibcode=2015NatSR...512143C |year=2015}}</ref><ref>{{cite journal |author= Li Jianming and Dongsheng Xu |title=tetragonal faceted-nanorods of anatase TiO<sub>2</sub> single crystals with a large percentage of active {100} facets |journal= Chemical Communications |volume=46 |issue=13 |pages=2301–3 |year=2010 |doi=10.1039/b923755k |pmid=20234939}}</ref> although the {101} planes are thermodynamically more stable and thus more prominent in most synthesised and natural anatase,<ref>{{cite journal |author= M Hussein N Assadi |title= The effects of copper doping on photocatalytic activity at (101) planes of anatase TiO 2: A theoretical study |url=https://www.researchgate.net/publication/304714130 |journal= Applied Surface Science |volume= 387 |pages=682–689|year=2016|bibcode=2016ApSS..387..682A|doi=10.1016/j.apsusc.2016.06.178 |arxiv= 1811.09157|s2cid= 99834042 }}</ref> as evident by the often observed tetragonal dipyramidal [[crystal habit|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>{{cite journal |title=Sand Supported Mixed-Phase TiO<sub>2</sub> Photocatalysts for Water Decontamination Applications |journal= Advanced Engineering Materials |year=2014 |volume=16|issue=2 |pages=248–254|doi=10.1002/adem.201300259 |arxiv=1404.2652 |last1= Hanaor |first1= Dorian A. H. |last2= Sorrell |first2= Charles C. |bibcode= 2014arXiv1404.2652H|s2cid= 118571942 }}</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>{{cite journal |author1=Kurtoglu M. E. |author2=Longenbach T. |author3=Gogotsi Y. |year= 2011|title= Preventing Sodium Poisoning of Photocatalytic TiO<sub>2</sub> Films on Glass by Metal Doping|journal= International Journal of Applied Glass Science|volume= 2|issue= 2|pages= 108–116|doi= 10.1111/j.2041-1294.2011.00040.x}}</ref> The strong [[redox|oxidative potential]] of the [[electron hole|positive holes]] oxidizes [[water]] to create [[hydroxyl radical]]s. 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>{{cite journal |doi=10.1038/238037a0|title=Electrochemical Photolysis of Water at a Semiconductor Electrode|year=1972|journal=Nature|volume=238|pages=37–8|pmid=12635268|issue=5358|bibcode= 1972Natur.238...37F|last1=Fujishima|first1=Akira|last2=Honda|first2=Kenichi|s2cid=4251015}}</ref> The process on the surface of the titanium dioxide was called the {{ill|Honda-Fujishima effect|ja|本多-藤嶋効果}}.<ref name=fujishima>[https://web.archive.org/web/20050608091634/http://www.nanonet.go.jp/english/mailmag/2005/044a.html "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>{{cite news |work=Advanced Ceramics Report|date=1 December 2003|url=http://www.highbeam.com/doc/1G1-110587279.html|archive-url=https://web.archive.org/web/20070204161415/http://www.highbeam.com/doc/1G1-110587279.html|url-status=dead|archive-date=4 February 2007|title=Carbon-doped titanium dioxide is an effective photocatalyst|quote=This carbon-doped titanium dioxide is highly efficient; under artificial visible light, it breaks down chlorophenol five times more efficiently than the nitrogen-doped version.}}</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>[https://www.sciencedaily.com/releases/2011/01/110128165212.htm 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>{{cite journal |last=Karvinen|first=Saila|title=Preparation and Characterization of Mesoporous Visible-Light-Active Anatase|journal=Solid State Sciences|volume=5 2003|issue=8|pages=1159–1166|bibcode=2003SSSci...5.1159K|year=2003|doi=10.1016/S1293-2558(03)00147-X}}</ref><ref>{{Cite journal |last1=Bian |first1=Liang |last2=Song |first2=Mianxin |last3=Zhou |first3=Tianliang |last4=Zhao |first4=Xiaoyong |last5=Dai |first5=Qingqing |date=June 2009 |title=Band gap calculation and photo catalytic activity of rare earths doped rutile TiO2 |url=https://linkinghub.elsevier.com/retrieve/pii/S1002072108602707 |journal=Journal of Rare Earths |language=en |volume=27 |issue=3 |pages=461–468 |doi=10.1016/S1002-0721(08)60270-7}}</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-fog]]ging coatings.

Nanosized TiO<sub>2</sub> incorporated into outdoor building materials, such as paving stones in [[noxer block]]s<ref>[http://www.cptechcenter.org/publications/task15/task15_vol2/track12am.pdf Advanced Concrete Pavement materials] {{Webarchive|url=https://web.archive.org/web/20130620080135/http://www.cptechcenter.org/publications/task15/task15_vol2/track12am.pdf |date=20 June 2013}}, National Concrete Pavement Technology Center, Iowa State University, p. 435.</ref> or paints, could reduce concentrations of airborne pollutants such as [[volatile organic compound]]s and [[nitrogen oxide]]s.<ref>Hogan, Jenny (4 February 2004) [https://www.newscientist.com/article/dn4636 "Smog-busting paint soaks up noxious gases"]. ''New Scientist''.</ref> A TiO<sub>2</sub>-containing cement has been produced.<ref>[http://content.time.com/time/specials/packages/0,28757,1852747,00.html TIME's Best Inventions of 2008]. (31 October 2008).</ref>

Using TiO<sub>2</sub> as a photocatalyst, attempts have been made to mineralize pollutants (to convert into CO<sub>2</sub> and H<sub>2</sub>O) in waste water.<ref name="Mineralize Pollutants">{{cite book |last=Winkler |first=Jochen |title=Titanium Dioxide |year=2003 |isbn=978-3-87870-148-4 |pages=115–116 |publisher=Vincentz Network |location=Hannover}}</ref><ref>{{cite journal |doi=10.1016/j.apcatb.2003.11.010|title=TiO<sub>2</sub>-assisted photocatalytic degradation of azo dyes in aqueous solution: Kinetic and mechanistic investigations|year=2004|last1=Konstantinou|first1=Ioannis K|last2=Albanis|first2=Triantafyllos A|journal=Applied Catalysis B: Environmental|volume=49|issue=1 |pages=1–14|bibcode=2004AppCB..49....1K }}</ref><ref>{{cite journal |last1=Hanaor |first1=Dorian A. H. |last2=Sorrell |first2=Charles C. |title= Sand Supported Mixed-Phase TiO<sub>2</sub> Photocatalysts for Water Decontamination Applications |journal= Advanced Engineering Materials |year=2014 |volume=16 |issue=2 |pages=248–254 |doi=10.1002/adem.201300259 |arxiv=1404.2652|s2cid=118571942 }}</ref> The photocatalytic destruction of organic matter could also be exploited in coatings with antimicrobial applications.<ref>{{cite journal |last1=Ramsden|first1=Jeremy J.|title=Photocatalytic antimicrobial coatings|journal=Nanotechnology Perceptions|date=2015|volume=11|issue=3|pages=146–168|doi=10.4024/N12RA15A.ntp.15.03|doi-access=free}}</ref>

====Hydroxyl radical formation====
Although nanosized anatase TiO<sub>2</sub> does not absorb visible light, it does strongly absorb [[ultraviolet|ultraviolet (UV) radiation]] (''hv''), leading to the formation of hydroxyl radicals.<ref name=":1">{{cite book|title=Kirk-Othmer Encyclopedia of Chemical Technology|last1=Jones|first1=Tony|last2=Egerton|first2=Terry A.|date=2000|publisher=John Wiley & Sons, Inc.|isbn=978-0-471-23896-6|language=en|chapter=Titanium Compounds, Inorganic|doi=10.1002/0471238961.0914151805070518.a01.pub3}}</ref> This occurs when photo-induced valence bond holes (h<sup>+</sup><sub>vb</sub>) are trapped at the surface of TiO<sub>2</sub> leading to the formation of trapped holes (h<sup>+</sup><sub>tr</sub>) that cannot oxidize water.<ref name=":8">{{cite journal |last1=Hirakawa|first1=Tsutomu|last2=Nosaka|first2=Yoshio|date=23 January 2002|title=Properties of O2•-and OH• formed in TiO<sub>2</sub> aqueous suspensions by photocatalytic reaction and the influence of H2O2 and some ions|journal=Langmuir|volume=18|issue=8|pages=3247–3254|doi=10.1021/la015685a}}</ref>
:TiO<sub>2</sub> + ''hv'' → e<sup>&minus;</sup> + h<sup>+</sup><sub>vb</sub>
:h<sup>+</sup><sub>vb</sub> → h<sup>+</sup><sub>tr</sub>
:O<sub>2</sub> + e<sup>&minus;</sup> → O<sub>2</sub><sup>•&minus;</sup>
:O<sub>2</sub><sup>•&minus;</sup> + O<sub>2</sub><sup>•&minus;</sup>+ 2{{H+}} → H<sub>2</sub>O<sub>2</sub> + O<sub>2</sub>
:O<sub>2</sub><sup>•&minus;</sup> + h<sup>+</sup><sub>vb</sub> → O<sub>2</sub>
:O<sub>2</sub><sup>•&minus;</sup> + h<sup>+</sup><sub>tr</sub> → O<sub>2</sub>
:{{OH-}} + h<sup>+</sup><sub>vb</sub> → HO•
:e<sup>&minus;</sup> + h<sup>+</sup><sub>tr</sub> → 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|thumb|Synthetic single crystals of TiO<sub>2</sub>, ca. 2–3 mm in size, cut from a larger plate]]

===Nanotubes===
[[File:TiO2nanotube.jpg|thumb|Titanium oxide nanotubes, [[Scanning electron microscope|SEM]] image]]
[[File:The army of titanium dioxide nanotubes.jpg|thumb|Nanotubes of titanium dioxide (TiO<sub>2</sub>-Nt) obtained by electrochemical synthesis. The SEM image shows an array of vertical self-ordered TiO<sub>2</sub>-Nt with closed bottom ends of tubes.]]
Anatase can be converted into [[non-carbon nanotube]]s and [[nanowire]]s.<ref>{{cite journal |doi=10.1016/j.cplett.2008.06.063 |title=The structure of multilayered titania nanotubes based on delaminated anatase |year=2008 |last1=Mogilevsky |first1=Gregory |last2=Chen |first2=Qiang |last3=Kleinhammes |first3=Alfred |last4=Wu |first4=Yue |journal=Chemical Physics Letters |volume=460 |issue=4–6 |pages=517–520 |bibcode= 2008CPL...460..517M}}</ref> Hollow TiO<sub>2</sub> nanofibers can be also prepared by coating [[carbon nanofiber]]s by first applying [[titanium butoxide]].<ref name=chiral>{{cite journal |doi=10.1088/1468-6996/16/5/054206 |pmid=27877835 |title=Hard-templating of chiral TiO<sub>2</sub> nanofibres with electron transition-based optical activity |journal=Science and Technology of Advanced Materials |volume=16 |issue=5 |pages=054206 |author=Wang, Cui |pmc=5070021 |year=2015 |bibcode=2015STAdM..16e4206W}}</ref>

=== 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>{{Citation |last=Wu |first=Yuan |title=15 - PREPARATION OF ULTRAFINE POWDERS BY REACTION–PRECIPITATION IN IMPINGING STREAMS III: NANO TITANIA |date=2007-01-01 |work=Impinging Streams |pages=301–315 |editor-last=Wu |editor-first=Yuan |url=https://www.sciencedirect.com/science/article/abs/pii/B9780444530370500458 |access-date=2024-11-15 |place=Amsterdam |publisher=Elsevier Science B.V. |isbn=978-0-444-53037-0}}</ref>[[File:Chiral TiO2 nanofibers 2.jpg|thumb|[[Scanning electron microscopy|SEM]] (top) and [[transmission electron microscopy|TEM]] (bottom) images of [[optical rotation|chiral]] TiO<sub>2</sub> nanofibers<ref name=chiral/>]]

==Health and safety==

Widely-occurring minerals and even gemstones are composed of TiO<sub>2</sub>. All natural titanium, comprising more than 0.5% of the Earth's crust, exists as oxides. <ref>{{cite journal |vauthors=Warheit DB, Donner EM |title=Risk assessment strategies for nanoscale and fine-sized titanium dioxide particles: Recognizing hazard and exposure issues |journal=Food Chem Toxicol |volume=85 |issue= |pages=138–47 |date=November 2015 |pmid=26362081 |doi=10.1016/j.fct.2015.07.001 |type=Review}}</ref> 

===Food additive===
As of 2006, titanium dioxide had been regarded as "completely nontoxic when orally administered".<ref name=Ullmann/> However, concerns persist.
==== Government policies ====
TiO<sub>2</sub> whitener in food was banned in France from 2020, due to uncertainty about safe quantities for human consumption.<ref>[https://www.reuters.com/article/us-france-food-additive/france-to-ban-titanium-dioxide-whitener-in-food-from-2020-idUSKCN1RT23D ''France to ban titanium dioxide whitener in food from 2020'']. Reuters, 2019-04-17</ref>

In 2021, the [[European Food Safety Authority]] (EFSA) ruled that as a consequence of new understandings of [[nanoparticle]]s, 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>{{cite news |last1=Boffey |first1=Daniel |title=E171: EU watchdog says food colouring widely used in UK is unsafe |url=https://www.theguardian.com/world/2021/may/06/e171-eu-watchdog-says-food-colouring-widely-used-in-uk-is-unsafe |work=the Guardian |date=6 May 2021 |language=en}}</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>[https://www.foodsafetynews.com/2022/03/uk-disagrees-with-eu-position-on-titanium-dioxide/ 'UK disagrees with EU position on titanium dioxide']. Food Safety News, 2022-03-09</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>[https://www.canada.ca/en/health-canada/services/food-nutrition/reports-publications/titanium-dioxide-food-additive-science-report.html 'Titanium dioxide (TiO2) as a food additive: Current science report']. Health Canada, 2022-06-20</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>[https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32022R0063 '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 (state)|New York]] were considering banning the use of titanium dioxide in foods.<ref name="NJTimesMay2023">{{Cite news |last=Smith |first=Dana G. |date=April 13, 2023 |title=Two States Have Proposed Bans on Common Food Additives Linked to Health Concerns |work=[[The New York Times]] |url=https://www.nytimes.com/2023/04/13/well/eat/food-additive-ban.html |url-status=live |access-date=November 15, 2023 |archive-url=https://web.archive.org/web/20231113022102/https://www.nytimes.com/2023/04/13/well/eat/food-additive-ban.html |archive-date=November 13, 2023}}</ref>

As of 2024, the [[Food and Drug Administration]] (FDA) in the United States permits titanium dioxide as a food additive.  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, alllowing 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="WebM">"Titanium Dioxide in Food: Safety and Side Effects"    26 Nov 2023 ''WebMD''  https://www.webmd.com/diet/titanium-dioxide-in-food</ref><ref>"Is Big Dairy Putting Microscopic Pieces of Metal in Your Food?" Tom Philpott  28 May 2014  ''Mother Jones'' https://www.motherjones.com/food/2014/05/nanotech-food-safety-fda-nano-material/</ref><ref>"Titanium Dioxide as a Color Additive in Foods" US  Food and Drug Administration https://www.fda.gov/industry/color-additives/titanium-dioxide-color-additive-foods</ref> despite growing scientific concerns.<ref>[https://www.wsj.com/health/wellness/titanium-dioxide-health-pizza-a363afab?st=s53luxolmkrjyu7&reflink=desktopwebshare_permalink Why Americans Are Eating a Sunscreen Ingredient in Their Frozen Pizza: Scientists are raising concerns about the use of titanium dioxide in food] by Andrea Petersen in the Wall Street Journal, June 11, 2024.</ref> 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>{{Cite web |last=Bedigan |first=Mike |date=2024-06-12 |title=Scientists raise alarm over sunscreen ingredient being found in cakes and candies |url=https://www.independent.co.uk/life-style/health-and-families/health-news/frozen-pizza-candy-titanium-dioxide-sunscreen-foods-b2561031.html |access-date=2024-06-13 |website=The Independent |language=en}}</ref>

====Industry response====
[[Dunkin' Donuts]] dropped titanium dioxide from their merchandise in 2015 after public pressure.<ref>{{cite web |title=Dunkin' Donuts to remove titanium dioxide from donuts|url=https://money.cnn.com/2015/03/10/news/companies/dunkin-donuts-titanium-dioxide/|website=CNN Money|date=March 2015}}</ref> 

====Research as an ingestible nanomaterial====
Due to the potential that long-term ingestion of titanium dioxide may be toxic, particularly to cells and functions of the [[gastrointestinal tract]], preliminary research as of 2021 was assessing its possible role in disease development, such as [[inflammatory bowel disease]] and [[colorectal cancer]].<ref name="bar">{{cite journal |vauthors=Barreau F, Tisseyre C, Ménard S, Ferrand A, Carriere M |title=Titanium dioxide particles from the diet: involvement in the genesis of inflammatory bowel diseases and colorectal cancer |journal=Particle and Fibre Toxicology |volume=18 |issue=1 |pages=26 |date=July 2021 |pmid=34330311 |pmc=8323234 |doi=10.1186/s12989-021-00421-2 |doi-access=free |bibcode=2021PFTox..18...26B }}</ref>

Size distribution analyses showed that batches of food-grade TiO₂ always include a nano-sized fraction as inevitable byproduct of the manufacturing processes.<ref>
{{Cite journal |last1=Winkler |first1=Hans Christian |last2=Notter |first2=Tina |last3=Meyer |first3=Urs |last4=Naegeli |first4=Hanspeter |date=December 2018 |title=Critical review of the safety assessment of titanium dioxide additives in food |journal=Journal of Nanobiotechnology |language=en |volume=16 |issue=1 |page=51 |doi=10.1186/s12951-018-0376-8 |issn=1477-3155 |pmc=5984422 |pmid=29859103 |doi-access=free }}</ref>

Andrew Maynard, director of Risk Science Center at the [[University of Michigan]], rejected the supposed danger from use of titanium dioxide in food. He says that the titanium dioxide used by Dunkin' Brands and many other food producers is not a new material, and it is not a nanomaterial either. Nanoparticles are typically smaller than 100 nanometres in diameter, yet most of the particles in food-grade titanium dioxide are much larger.<ref>
[https://theconversation.com/dunkin-donuts-ditches-titanium-dioxide-but-is-it-actually-harmful-38627 Dunkin' Donuts ditches titanium dioxide – but is it actually harmful?] ''The Conversation''. 12 March 2015</ref>

===Inhalation===
Titanium dioxide dust, when inhaled, has been classified by the [[International Agency for Research on Cancer]] (IARC) as an [[list of IARC Group 2B carcinogens|IARC Group 2B carcinogen]], meaning it is ''possibly carcinogenic to humans''.<ref name=IARC>{{cite book|publisher= International Agency for Research on Cancer|year= 2006 |volume= 93|title=Titanium dioxide|url= http://monographs.iarc.fr/ENG/Monographs/vol93/mono93.pdf}}</ref><ref>{{cite web |url=https://www.ccohs.ca/headlines/text186.html|title=Titanium Dioxide Classified as Possibly Carcinogenic to Humans |date= August 2006|website=Canadian Centre for Occupational Health & Safety}}</ref> 
The US [[National Institute for Occupational Safety and Health]] recommends two separate exposure limits. NIOSH recommends that fine {{chem|Ti|O|2}} particles be set at an exposure limit of 2.4&nbsp;mg/m<sup>3</sup>, while [[ultrafine particle|ultrafine]] {{chem|Ti|O|2}} be set at an exposure limit of 0.3&nbsp;mg/m<sup>3</sup>, as time-weighted average concentrations up to 10 hours a day for a 40-hour work week.<ref>{{cite web |author= National Institute for Occupational Safety and Health |title= Current Intelligence Bulletin 63: Occupational Exposure to Titanium Dioxide (NIOSH Publication No. 2011-160) |publisher= National Institute for Occupational Safety and Health |url= https://www.cdc.gov/niosh/docs/2011-160/pdfs/2011-160.pdf}}</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 TiO<sub>2</sub> particles indicate that even at high exposure there is no adverse effect to human health.<ref>{{cite journal |vauthors=Warheit DB, Donner EM |title=Risk assessment strategies for nanoscale and fine-sized titanium dioxide particles: Recognizing hazard and exposure issues |journal=Food Chem Toxicol |volume=85 |issue= |pages=138–47 |date=November 2015 |pmid=26362081 |doi=10.1016/j.fct.2015.07.001 |type=Review}}</ref>

===Environmental waste introduction===
Titanium dioxide (TiO₂) is mostly introduced into the environment as [[nanoparticle]]s via wastewater treatment plants.<ref name=":5">{{cite journal |last1=Tourinho|first1=Paula S.|last2=van Gestel|first2=Cornelis A. M.|last3=Lofts|first3=Stephen|last4=Svendsen|first4=Claus|last5=Soares|first5=Amadeu M. V. M.|last6=Loureiro|first6=Susana|date=2012-08-01|title=Metal-based nanoparticles in soil: Fate, behavior, and effects on soil invertebrates|journal=Environmental Toxicology and Chemistry|language=en|volume=31|issue=8|pages=1679–1692|doi=10.1002/etc.1880|pmid=22573562|s2cid=45296995 |issn=1552-8618|doi-access=free}}</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. TiO<sub>2</sub> 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 TiO<sub>2</sub> (pH= 5.8) which renders it neutral and solution ion concentrations above 4.5 mM.<ref name=":0">{{cite book|title=Kirk-Othmer Encyclopedia of Chemical Technology|last=Swiler|first=Daniel R.|date=2005|publisher=John Wiley & Sons, Inc.|isbn=978-0-471-23896-6|language=en|chapter=Pigments, Inorganic|doi=10.1002/0471238961.0914151814152215.a01.pub2}}</ref><ref>{{cite journal |last1=Preočanin|first1=Tajana|last2=Kallay|first2=Nikola|year=2006|title=Point of Zero Charge and Surface Charge Density of TiO<sub>2</sub> in Aqueous Electrolyte Solution as Obtained by Potentiometric Mass Titration|journal=Croatica Chemica Acta|volume=79|issue=1|pages=95–106|issn=0011-1643}}</ref>

==See also==
*[[Delustrant]]
*[[Dye-sensitized solar cell]]
*[[List of inorganic pigments]]
*[[Noxer block]]s, TiO<sub>2</sub>-coated pavers that remove {{NOx}} pollutants from the air
*[[Suboxide]]
*[[Surface properties of transition metal oxides]]
*[[Titanium dioxide nanoparticle]]

==Sources==
{{Free-content attribution
| title = Production of titanium and titanium dioxide from ilmenite and related applications
| publisher = WIPO
| documentURL = https://www.wipo.int/edocs/pubdocs/en/wipo-pub-1077-23-en-patent-landscape-report-ilmenite.pdf
| license = CC-BY
}}

==References==
{{Reflist}}

==External links==
{{Wiktionary|titanium suboxide}}
{{Wikiquote}}
*[https://inchem.org/documents/icsc/icsc/eics0338.htm International Chemical Safety Card 0338]
*[https://www.cdc.gov/niosh/npg/npgd0617.html NIOSH Pocket Guide to Chemical Hazards]
*[https://www.ccohs.ca/headlines/text186.html "Titanium Dioxide Classified as Possibly Carcinogenic to Humans", Canadian Centre for Occupational Health and Safety, August, 2006] (if inhaled as a powder)
*[https://web.archive.org/web/20070112210620/http://www.threebond.co.jp/en/technical/technicalnews/pdf/tech62.pdf A description of TiO<sub>2</sub> photocatalysis]
*[https://www.usgs.gov/centers/national-minerals-information-center/titanium-statistics-and-information Titanium and titanium dioxide production data (US and World)]

{{Titanium compounds}}
{{Oxides}}
{{Molecules detected in outer space}}
{{Sunscreening agents}}
{{Authority control}}

[[Category:Dye-sensitized solar cells]]
[[Category:E-number additives]]
[[Category:Excipients]]
[[Category:Food colorings]]
[[Category:IARC Group 2B carcinogens]]
[[Category:Inorganic pigments]]
[[Category:Sunscreening agents]]
[[Category:Titanium(IV) compounds]]
[[Category:Transition metal oxides]]