Chemistry of Titanium Dioxide (TiO2): Structure, Properties & Uses
Titanium dioxide, also known as titanium(IV) oxide or titania, is an inorganic compound with the chemical formula TiO2. It is a white, odorless, water-insoluble solid valued for its exceptional whiteness, high refractive index, chemical stability, and ultraviolet-light-absorbing behavior.
What Is Titanium Dioxide?
Titanium dioxide is the oxide of titanium in the +4 oxidation state. Its IUPAC-style name is titanium(IV) oxide, and its CAS Registry Number is 13463-67-7. The compound has a molar mass of approximately 79.866 g/mol.
| Property | Value |
|---|---|
| Chemical formula | TiO2 |
| Other names | Titanium(IV) oxide, titania |
| CAS number | 13463-67-7 |
| Molar mass | 79.866 g/mol |
| Appearance | White, odorless powder |
| Water solubility | Practically insoluble |
Crystal Structures of TiO2
Titanium dioxide exists in three principal crystalline forms: rutile, anatase, and brookite. In each structure, titanium is coordinated by oxygen atoms, but the arrangement of the TiO6 octahedra differs, producing distinct physical and chemical behavior.
Rutile
Rutile is the most common and thermodynamically stable form of titanium dioxide. It has a tetragonal crystal structure and a high density of about 4.23 g/cm3. Its high refractive index makes it especially useful in pigments for paints, coatings, plastics, and paper.
Anatase
Anatase is also tetragonal but has a different arrangement of TiO6 octahedra. It is less dense than rutile, around 3.90 g/cm3, and is widely studied for photocatalysis because of its favorable electronic properties under ultraviolet illumination.
Brookite
Brookite is the least common of the three natural forms. It has an orthorhombic structure and a density of approximately 4.13 g/cm3. Although less commercially important than rutile and anatase, it is chemically significant in mineralogy and materials research.
Physical and Chemical Properties
Titanium dioxide is a stable, nonvolatile inorganic oxide. It is white because it reflects most visible light, while its very high refractive index allows it to scatter light efficiently and create opacity in products such as paints and plastics.
- State and appearance: White, odorless solid powder.
- Molar mass: About 79.87 g/mol.
- Density: Approximately 4.23 g/cm3 for rutile and 3.90 g/cm3 for anatase.
- Refractive index: Very high; rutile values are about 2.616 and 2.903, while anatase values are about 2.554 and 2.493.
- Solubility: Insoluble or practically insoluble in water.
- Thermal stability: Highly stable at elevated temperatures, with reported melting behavior around 1,843°C for TiO2.
Bonding and Oxidation State
In TiO2, titanium exists in the +4 oxidation state, while each oxygen atom is in the −2 oxidation state. The compound can therefore be represented as Ti4+ and two O2‐ ions, although the bonding has substantial covalent character rather than being purely ionic.
Key Chemical Reactions
Photocatalytic reaction
When TiO2 absorbs ultraviolet light, electrons are promoted from the valence band to the conduction band, creating electron–hole pairs that generate reactive oxygen species capable of breaking down organic contaminants.
Major Uses of Titanium Dioxide
- Paints and coatings: Whiteness, brightness, hiding power, and weather resistance.
- Plastics: White pigment and opacifier.
- Paper and printing inks: Brightness, opacity, and print quality.
- Cosmetics and sunscreens: Colorant and UV-filtering ingredient.
- Photocatalytic materials: Self-cleaning surfaces and disinfection technologies.
Frequently Asked Questions
What is the chemical formula of titanium dioxide?
The chemical formula is TiO2, meaning one titanium atom is combined with two oxygen atoms.
Is titanium dioxide the same as titanium?
No. Titanium is a metallic element, while titanium dioxide is its oxide, TiO2. Titanium metal is used in alloys and structural applications, whereas TiO2 is mainly used as a pigment, opacifier, and UV-filtering material.
What is the difference between rutile and anatase TiO2?
Rutile and anatase are different crystal structures of the same compound. Rutile is denser, more stable, and widely used in pigments, while anatase is often favored for photocatalytic applications.
Does titanium dioxide dissolve in water?
Titanium dioxide is practically insoluble in water under normal conditions.
Why is TiO2 used in sunscreen?
TiO2 absorbs and scatters ultraviolet radiation, helping protect skin from UVA and UVB exposure.