ABSTRACT
Activated carbons are unique and versatile adsorbents. Their adsorbent properties are essentially attributed to their large interparticulate surface area, universal adsorption effect, high adsorption capacity, a high degree of surface reactivity and a favorable pore size which makes the internal surface accessible and enhances the adsorption rate. The most widely used activated carbons have a surface area of about 800 to 1500 m
/g. This surface area is contained predominantly within micropores which have effective diameter less than 2 nm. In fact, a particulate of active carbon is made up of a complex network of pores that have been classified into micropores (diam. < 2 nm), mesopores (diam. between 2 and 50 nm), and macropores (diam. > 50 nm). Most of the adsorption on active carbons takes place in micropores and only small amount in mesopores, the macropores acting only as conduits for the passage of the adsorbate into the interior mesopores and the micropore surface. The pore size distribution in a given carbon depends on the type of the raw material and the method and conditions under which the carbon has been prepared. The large surface area of active carbons is the result of the activation process in which a carbonaceous char with little internal surface is oxidized in an atmosphere of air, carbon dioxide, or steam at a temperature of 800 to 900
°
C. This results in the oxidation of some of the regions within the char in preference to others so that a preferential etching takes place, as the combustion proceeds, causing an increase in surface area.
