Studies on the Surface Properties of the Surface-Treated Silica Gels by the n-Pentanol through the Adsorption of Various Kinds of Vapours and the Heat of Immersion

Abstract

The surface properties of silica gels treated with n-pentanol were investigated by the adsorption of argon at 77°K, water vapour at 288°K and n-heptane at 273°K and by the heat of immersion of water and n-heptane at 298°K on the samples having various numbers of surface groups. The following results were confirmed: (1) For the silica gel samples which were untreated or had a small number of surface groups, the shape of isotherms of water vapour adsorption was the type II in BET classification, whereas it was the type I for the samples with a large number of surface groups. (2) The shape of isotherms of n-heptane adsorption was the type II for both the untreated and surface-treated samples. The existence of many capillary pores less than 20Å in diameter was suggested, since the volume of pores larger than 20Å in diameter appeared to be exactly the same for both the untreated and surface-treated silica gels. (3) The surface areas obtained from the absorption of argon, water and n-heptane showed a linear dependence on the number of surface groups. From their slopes, it was concluded that each of the surface groups covered 1.5 unreacted silanol and these surface groups would presumably be distributed on the surface of silica gels uniformly. (4) The heat of immersion of water showed a linear relation with the monolayer adsorption value obtained from water vapour adsorption.