Activated carbon is an adsorbent, which was used as early as a few hundred years BC. It was used for medical purposes and as a purifying agent. Whereas the beginnings of activated carbon's industrial applications date back to 1900,when it was used as decolourising solution in making syrup in the sugar sector. Carbons also stirred up an interest during the World War; for the first time they were being used in gas masks to protect against dangerous gases and vapours.
Activated carbon is a black, porous, amorphic sorbent. Its sorption capacity, specific surface area (reaching up to 2500 m2/g), size and distribution of pores or granularity makes activated carbon an excellent and universal adsorbent.
There are many theories concerning microscopic structure of activated carbon and its impact on the functioning of this sorbent. The basic structural unit of activated carbon is hexagonal structure of graphite, that is the form of numerous small graphite platelets. The platelets are connected with each other by chemical bonds, creating crevices, cracks and pockets, in which the pollutants are absorbed.
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Availability of the internal structure of activated carbons increases the speed of the adsorption process and makes it more efficient. The most commonly used activated carbons have surface area within the limits of 800 – 1500 m2/g. The surface area of these carbons is mainly characterized by the presence of micropores with their effective diameter smaller than 2 nm. As a matter of fact, activated carbons are composed of a complicated network of pores, classified as follows:
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Adsorption on the surface of activated carbons occurs mostly in micropores and in small parts in mezopores, while the macropores only function as channels through which the adsorbate flows into mesopores and on the surface of micropores. The distribution of pore sizes in a given carbon depends on the type of raw material used as well as on the methods and conditions of its production.