ABSTRACT
Graphitic structure and heteroatom content Activated carbon can be created from a wide range of natural and synthetic organic raw materials. The production process involves carbonization (heating in the absence of air to temperatures of about 800°C) and then activation in the presence of an activating agent, usually steam, at temperatures of between 850 and 1000°C. Wood-based carbons are often carbonized and activated in the same step in the presence of a dehydrating chemical such as phosphoric acid, usually at lower temperatures than steam activation.[30] The carbonization process removes most of the volatile components in the form of gaseous oxygen and hydrogen compounds. The remaining carbon atoms form graphite-like structures consisting of sheets of condensed aromatic ring systems. The sheets are held together by dispersion forces and may be flat or distorted into a more convoluted pore structure. The surface of these sheets forms the basal planes of the carbon. The activation step further enhances the pore and graphite plate structure, burning out any decomposition products remaining from the carbonization process and opening the pores. If the activation continues, walls between pores can be destroyed, leading to larger pores and a decreased volume of very small pores.[19] There are a number of representations of the structure of activated carbon in the literature.[30-32]
An alternative structure for chemically activated wood-based carbons is given by the NORIT-activated carbon manufacturing company at their website.[32] They describe a structure that is totally different from that of steam-activated carbons and claim that “…as a result of the relatively low process temperature, graphitic basal planes are not found in chemically activated carbons. Instead, each particle can be seen as a partly aromatic, partly aliphatic organic molecule, or a highly crosslinked polymer produced from an almost infinite number of different monomers. The pore walls are thus not flat but ‘rough,’ even in the micropores, and contain a relatively large amount of heteroatoms (mostly oxygen). As a result, chemically activated carbons are somewhat less hydrophobic than steam-activated carbons.” How ever, they provide no evidence nor cite any literature for this description.
