- Particles can be placed into one of three categories according to their diameter which are coarse, fine and nano particles.
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
- Nanoparticles have different properties than the bulk 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 ratio.
- 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:
Formula triangle for calculating the surface area – volume ratio
A scientist develops two nanoparticles of different shapes and sizes. One is cube shaped and has sides of 8 nm and the other is spherical 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
Volume = 4/3 πr3 = 4/3 x 3.14 x 33 = 112.75 nm3
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.