Nanoparticles (OCR Gateway GCSE Chemistry)

• Particles can be placed into one of three categories according to their diameter:
  • Coarse particles (also called particulate-matter or dust)
  • Fine particles
  • Nanoparticles

The diameter in nanometres used to classify particles

• Nanoparticles are between 1 and 100 nanometres in size and usually contain only a few hundred atoms
• 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
• The research into the production and application of nanoparticles is called nanoscience

Diagram showing the size of nanoparticles relative to other objects and substances

• One of the most interesting features of nanoparticles is their very high surface area to volume ratio
• As particles decrease in size, their surface area increases in relation to their volume
• As the side of a cube decreases by a factor of 10, the surface area to volume ratio increases by a factor of 10
• This is why nanoparticles may have properties different from those for the same materials in bulk
• It may also mean that smaller quantities are needed to be effective than for materials with normal particle sizes
• Fullerenes (nanoparticles made of carbon) behave very differently to larger compounds of carbon like diamond and graphite
• 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

This diagram shows the surface area to volume ratio of three different sizes cubes

• 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 while also providing better coverage than other sun creams
• The same chemical in bulk form is used as a white pigment in paints
• Fullerenes are used in 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

• Nanoparticles have widespread uses and applications that can provide an immense advance in materials technology
• However, 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 short term side effects, there could be long term 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