Activated charcoal is not the same substance as that found in charcoal bricks or burnt pieces of food.
The manufacture of activated charcoal makes it extremely adsorbent, allowing it to bind to molecules, ions, or atoms. In this way, it removes these from dissolved substances.
Making activated charcoal involves heating carbon-rich materials, such as wood, peat, coconut shells, or sawdust, to very high temperatures.
This ‘activation’ process strips the charcoal of previously absorbed molecules and frees up bonding sites again. This process also reduces the size of the pores in the charcoal and makes more holes in each molecule, therefore, increasing its overall surface area.