Effect of treatment on the adsorption capacity of activated carbon

The adsorption of p-cresol by three activated carbons, one untreated S.E.I. and the other two treated S.E.I., was carried out under controlled conditions. Such treatment led to a change in the point of zero charge (PZC) and the adsorption capacity (Q(max)) of the carbon concerned. The adsorption capacity and affinity (K-1) of each carbon was determined using the Langmuir homogeneous and binary models to compare the effects of different treatments on these and relative parameters. The variation of the model parameters with the solution pH was also studied. The fitted parameters obtained from both models showed the pH value had the most significant effect on the adsorption capacity (Q(max)) and the adsorption affinity (K-1) of a given carbon, with both quantities showing a decrease with increasing pH. It was found that the uptake of the molecular forms of the aromatic solute was dependent on the PZC of the carbons. Treatment with H-2 increased the PZC whilst treatment with H2SO4 led to a decrease in this factor. At higher pH (when the solute was in an ionic form), it was found that electrostatic forces played a significant role on the extent of adsorption. Under these conditions, the adsorption of the solute depended on the concentration of its anionic form. It was shown that the effect of pH must be considered from the viewpoint of its combined effect on the carbon surface and on the solute molecules.