|Adsorption is the process where
molecules are concentrated on the surface of the activated carbon.
What makes molecules adsorb on
activated carbon ?
Adsorption is caused by
London Dispersion Forces, a type of Van der Waals Force which exists
between molecules. The force acts in a similar way to
gravitational forces between planets.
London Dispersion Forces are
extremely short ranged and therefore sensitive to the distance between
the carbon surface and the adsorbate molecule They are also additive,
meaning the adsorption force is the sum of all interactions between all
the atoms. The short range and and additive nature of these forces
results in activated carbon having the strongest physical adsorption
forces of any material known to mankind.
Gas Phase Adsorption -
This is a condensation process where the adsorption forces condense the
molecules from the bulk phase within the pores of the activated carbon.
The driving force for adsorption is the ratio of the partial pressure
and the vapour pressure of the compound.
Liquid Phase Adsorption
- The molecules go from the bulk phase to being adsorbed in the pores in
a semi-liquid state. The driving force for adsorption is the ratio
of the concentration to the solubility of the compound.