- Nanoparticles are between 1 and 100 nanometres (nm) in size and usually contain only a few hundred atoms.
- One nanometre is one billionth of a metre, so 1 nm = 1 x 10-9 m.
- Atoms and simple molecules are around 100 times smaller than this.
- Nanoparticles are much smaller than fine particles which have diameters of between 100 and 2500 nm.
Diagram showing the size of nanoparticles relative to other objects and substances
- Nanoparticles have different properties than the chemicals from which they are made.
- Fullerenes for example, which are nanoparticles made of carbon, behave very differently to larger compounds of carbon.
- One of the most interesting features of nanoparticles is their very high surface area to volume ratios.
- As particles decrease in size, their surface area increases in relation to their volume.
- The surface area to volume ratio is an important feature in catalysis and surface chemistry.
- The higher the ratio then the more surface area is available for reaction, hence the better the catalyst.
- The ratio is calculated using the following formula:
A scientist develops two nanoparticles of different shapes and sizes. One is cube shaped and has sides of 8 nm and the other is spherically shaped and has a diameter of 6 nm. Determine which nanoparticle would make the most effective catalyst.
For the Cube
A cube has six faces, so the surface area = 6 x 8 x 8 = 384 nm2
Volume = 8 x 8 x 8 = 512 nm3
Surface area to volume ratio = 384 ÷ 512 = 0.75
For the Sphere
Surface area = 4πr2 = (4)(3.14)(32) = 113.04 nm2
Surface area to volume ratio = 113.04 ÷ 112.75 = 1.00
The sphere has a higher surface area to volume ratio than the cube hence it would be the more effective catalyst.
- The main industrial application of nanoparticles is in catalysis due to their high surface area to volume ratios.
- Titanium dioxide is a good example of how the same chemical has different properties in bulk and nanoparticle form.
- Titanium dioxide in nanoparticle form is used in sunscreens as it blocks UV light but leaves no white marks on the skin.
- The same chemical in bulk form is used as a white pigment in paints.
- Fullerenes are used in the medicine and drug design as they are more easily absorbed than other particles and can deliver drugs to target areas more effectively.
- Fullerenes are also used in electronic circuitry and as coatings for artificial limbs and joints.
- Nanoparticles of silver are sprayed onto the fibres of medical clothing and surgical masks which gives them the flexibility of a material but with the added benefit of the antibacterial properties of silver metal.