Activated carbon

Activated carbon is the more general term which includes material derived from charcoal. It denotes a material which has an exceptionally high surface area, typically determined by nitrogen adsorption, and includes a large amount of microporosity. Sufficient activation for useful applications may come solely from the high surface area, though often further chemical treatment is used to enhance the adsorbing properties of the material.

Activated carbons are used in metal extraction, eg gold, water treatment, and many other applications.

As an example, an activated carbon may have a surface area in excess of 500 m² per gram, with 1000 m² per gram being readily achievable. A tennis court is about 260 m².

Under an electron microscope, the structure of activated carbons looks something like ribbons of paper which have been crumpled together, with a few wood chips thrown in for good measure. There are lots and lots of nooks and crannies, and many areas where flat surfaces of graphite-like material run parallel to each other, separated by a few nanometers or so. These micropores provide superb conditions for adsorption to occur, since adsorbing material can interact with many surfaces simultaneously. Tests of adsorption behaviour are usually done with nitrogen gas at 77K under high vacuum, but in everyday terms an activated carbon is perfectly capable of the equivalent of producing, by adsorption from its environment, liquid water from steam at 100 degrees Celsius and a pressure of 1/10,000 of an atmosphere.