Characterization of activated carbons from peach stones through the mixed geometry model

A good characterization of the pore size distribution of activated carbons is of crucial importance for gas separation and gas storage applications of microporous materials. It has been recently shown that characterization methods of activated carbons can be improved by considering the porous space as represented by a mixture of pores of different geometries, slit and triangular geometry. The triangular geometry was included as a necessity of considering the simultaneous interaction of an adsorbed molecule with three graphite walls to account for high observed values of the isosteric heat of adsorption at low pressures. Places where such interaction with three graphitic walls occurs can be clearly seen in some high resolution digitalized TEM images of activated carbons published in the literature. Many lignocellulosic substances have been used in the literature as the precursor material in the preparation of activated carbons. In the present work we use peach stones, which are very abundant in the region of Cuyo (Argentina), as well as in any other regions in the world where peaches are extensively cultivated, processed and canned. Different samples of activated carbons from this precursor are obtained through different processing methods. N2 adsorption isotherms at 77 K are measured for these samples and fitted by using the mixed geometry model, obtaining the corresponding PSDs. Finally these characterization results are correlated to the preparation procedures for the different samples. The analysis of results reveals that the mixed geometry model provides a more consistent picture of the sample characteristics than the pure slit geometry model, reinforcing the conclusions of previous studies. The same analysis allows to determine clearly some general trends relating the preparation method with the morphological and adsorptive characteristics of the AC.