Surface areas of kaolin, α-Fe2O3 and hydroxy-Al montmorillonite

Adsorption of eight organic molecules on kaolin, alpha-Fe2O3, and hydroxy-Al montmorillonite was studied to examine the effect of sorbate area on the values of the surface area of these materials. For each sorbent, the number of molecules at monolayer coverage per gram produced a single hyperbola when plotted as a function of the area occupied by an adsorbate. The equations of the hyperbolas are: NA = 22.23 A(0.098) for the kaolin\NA = 53.70 A(-0.399) for alpha-Fe2O3 and NA = 161.81 A(0.322) for the hydroxy-Al montmorillonite. These equations give accessible surface areas and not the true surface areas of the solids studied, which remain elusive.