Titanium Dioxide Nanotubes
Harvest Solar Energy

Nanotubes, which just means "very small tubes", that are made of Titanium dioxide have the interesting property of being able to trap energy from sunlight and pass it on to chemicals that land on it.

Titanium Dioxide (TiO2) is white powdery substance. The name may be unfamiliar but we see this chemical all around us. It is the white pigment used in paint, toothpaste, sunscreen lotion and it is used as a food coloring. The white crust of Smarties is a layer of Titanium Dioxide.

What Is A Photocatalyst?

A catalyst is a chemical that speeds up a reaction, but does not get used up in the reaction. In effect, it just sits there but makes things happen faster. A photocatalyst is a catalyst that acts that way in the presence of sunlight.

How Does It Work?

A catalyst interrupts the bonds between existing molecules and allows new bonds to form. In the case of Titania it is also able to absorb energy from sunlight that can be transferred to the substances it is acting on.

Water molecules hit the surface of the Titania and break up. They do this because of the way the Titania affects the covalent bonds in the water molecule. This leaves groups of Hydrogen and Oxygen atoms on the surface of the Titania.

If the Titania has been exposed to sunlight, it has absorbed some of that energy it is available to the Hydrogen and Oxygen atoms. Because of the nature of chemical bonding, the most stable situation that can result is if the atoms attached to the surface of the Titania absorb that extra energy. They do this by forming the higher energy Hydrogen gas (H2) and Oxygen gas (O2).

Once in gas form, these atoms float away and the surface is open again for more water molecules to be split. We can see this process in action in the following series of pictures:

Why Nanotubes?

If Titania can act to harness energy from the sun, why does it need to be built into these very small tubes? In order to be effective, the Titania needs to be able to both act on a lot of water molecules and be exposed to a large amount of sunlight. The way to do both these things is to have a large surface area. This is achieved by creating tiny little tubes called nanotubes.

Have a look at the following picture and consider which has more surface:

The Ideal Situation

With this knowledge, it is possible to envision clean fuel being produced literally out of thin air. We can see a future where both our electricity and the fuel for our vehicles is made at no cost to either our pockets or the environment.

The technology is still in its early stages. Conversion rates of sunlight to Hydrogen are still quite low and there are issues related to the collection and use of the gases that need to be resolved. However the goal of a completely clean energy supply for our world is one worth striving for.

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