#### Size of Nanoparticles

• ###### Compare the size of nanoparticles with the sizes of atoms and molecules
• 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

#### Uses

• ###### Describe how the properties of nanoparticulate materials are related to their uses including surface area to volume ratio of the particles they contain, including sunscreens
• 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:

Example

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.

#### Risks

• ###### Explain the possible risks associated with some nanoparticulate materials
• The use of nanoparticles in science is in its early stages so there are still a lot of unknown factors and potential risks.
• In particular there is a lack of understanding on how they may affect health.
• Although there haven’t been any serious shortterm side effects, there could be longterm side effects which we haven’t detected yet as they haven’t been in use long enough.
• Even a small amount of toxicity in a particular nanoparticle would be multiplied due to the high surface area to volume ratio.
• This coupled with the fact that they are not easily disposed of by the body are a cause for caution in the medical application of nanoparticles.

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### Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.