Nanomorphology of activated carbon porosity: geometrical models confronted to experimental facts

Abstract For centuries, activated-carbons are widely used adsorbents the nanomorphology of which is still badly understood. Nevertheless, recent advances in the characterization of their microporosities and in their carbonaceous structures lead to experimental evidences in a common frame shared by those materials. By plotting their mean pore size calculated using the D.R. method vs. their corresponding specific microporous volume, activated carbons made from various precursors and activated by different conventional methods gather themselves according to three linear domains. In the same representation, activated carbons submitted to transient oxidative treatments lead also to linear behaviour but with very higher slopes. In the present study, simple geometrical models of porosity based on a BSU packing approach are proposed and tested on KOH and CO2 activated pitches and on a modified commercial coconut activated carbon. The conventional activation processes seem to concern mainly the slit-like porosity potentially available between adjacent BSU faces while transient oxidative treatments concern mainly a star-like porosity potentially available between the edges of adjacent BSU. As the proposed model could be unsuitable for other kinds of activated carbons, it will be tested on other materials for generalization.