Nanoparticulate materials
A substance that consists of nanoparticlesTiny particles which are between 1 and 100 nanometres (nm) in size. is described as being nanoparticulate materialsUseful substances containing nanoparticles.. A nanoparticulate substance has different propertiesThe characteristics of something. In chemistry, chemical properties include the reactions a substance can take part in. Physical properties include colour and boiling point. from the same substance in bulk (powders, lumps and sheets). This is because of the small size and large surface areaThe total area of all sides on a 3D shape. to volumeThe volume of a three-dimensional shape is a measure of the amount of space or capacity it occupies, eg an average can of fizzy drink has a volume of 330 ml. ratios of nanoparticles.
Properties and uses
Small sizes
Nanoparticulate materials are used in some paints, cosmetics and sunscreens. Sunscreens block harmful ultraviolet lightElectromagnetic radiation with a greater frequency than visible light but less than X-rays. Humans cannot see it but it can damage eyes and skin in high doses. from the sun reaching the skin. Titanium dioxide blocks ultraviolet light, so it is used in sunscreens. In bulk titanium dioxide is white â it is used as a pigment in white paint. However, nanoparticulate titanium dioxide has no colour and cannot be seen when it is spread on the skin. Many people prefer nanoparticulate sunscreen because it is not obvious that they are wearing it.
Question
One disadvantage of nanoparticulate sunscreens is that they tend to clump together, making them difficult to apply. Suggest another disadvantage of these sunscreens.
It may be more difficult to tell where you have applied the sunscreen if you can't see it on your skin.
The large surface area to volume ratios of nanoparticulate substances allows them to act as catalystA substance that changes the rate of a chemical reaction without being changed by the reaction itself.. Compared to the same substances in bulk, they may:
- catalyse reactions more efficiently
- catalyse different reactions
- produce different productA substance formed in a chemical reaction.
Self-cleaning window panes have nanoparticulate coatings. These catalyse the breakdown of dirt in the presence of sunlight.
Possible risks of nanoparticles
Some people are concerned that the small size of nanoparticles makes it possible to breathe them in, or for them to pass into cells. Once inside the body, they might catalyse reactions that are harmful. toxicPoisonous. substances could bind to them because of their large surface area to volume ratios, harming health if the nanoparticles do get into the body. Modern nanoparticulate materials have only become common recently, so it is difficult for scientists to determine their risks.
Worked example
Silver has antibacterial properties. Nanoparticulate silver is used in some dressings for wounds. Suggest a possible hazard to the environment of silver nanoparticles.
The silver nanoparticles could harm or kill useful bacteria in the environment when these dressings are thrown away after use.