Titanium dioxide is a molecule composed of one atom of titanium and two atoms of oxygen. Titanium dioxide absorbs ultraviolet light; this property makes titanium dioxide useful in sunscreens.
Titanium dioxide nanoparticles are photocatalysts, which means that they have the capability to use energy in light to catalyze reactions with other molecules at reduced temperatures. Although other photocatalytic materials are available, researchers have found that titanium dioxide provides the best performance in sunlight.
Another property of titanium dioxide is that it reflects all colors in the visible light spectrum, therefore the light reflected from titanium dioxide is white. This characteristic makes it useful as a white pigment in paints and may make for white residue on your skin when you slather on sunscreen.
Forming titanium dioxide nanoparticles allow researchers to form photocatalysts that are more effective because they have more surface area available to react with other molecules. Also, in the nanoparticle form, titanium dioxide can be used in creams and coatings that absorb UV without causing a white coating.
Note that titanium dioxide (a molecule composed of one atom of titanium and two atoms of oxygen) nanotubes are similar to carbon nanotubes in that they are hollow cylinders. But titanium dioxide nanotubes, instead of being composed of carbon atoms bonded together, are made up of titanium dioxide molecules bonding together to form the surface of a cylinder. The oxygen atoms bond to another titanium atom, and you end up with a cylindrical lattice in which each oxygen atom is bonded to two titanium atoms. This arrangement of oxygen atoms between each titanium atom results in a much more complicated nanotube structure.
Some companies use titanium oxide nanoparticles as part of a film that uses the energy in light to start the chemical reaction that kills bacteria on surfaces.
At Penn State, a team of researchers led by Craig Grimes has come up with an ingenious method of turning captured CO2 into methane. They use clusters of titanium dioxide nanotubes coated with a catalyst that helps convert carbon dioxide and water into methane using sunlight as the power source.
Researchers are also developing methods to use the photocatalytic properties of titanium dioxide nanoparticles to destroy cancer tumors. They are delivering titanium dioxide nanoparticles to cancer tumors using targeted drug delivery methods, then shining light on the tumor. The titanium dioxide nanoparticles use the energy from the light to add an electron to oxygen molecules, which proceed to destroy cancer cells.
Excerpted from Nanotechnology For Dummies (2nd edition), from Wiley Publishing