Adsorption Study of Hydroxylated Silica Surface
over a Wide Temperature Range

B. V. Kuznetsov and A. K. Ya. Mukhammed

Faculty of Chemistry, Moscow State University, Moscow, 119899 Russia

Received May 5, 1996

Abstract—The differential heats and isotherms of adsorption of acetonitrile on macroporous silica were mea-
sured at 292–433 K using a calorimeter in a vacuum adsorption setup. The isosteric heats were calculated from
the isotherms, and the temperature coefficients for differential heats of adsorption, entropy of adsorbed aceto-
nitrile, and differential entropy of adsorption were calculated from the calorimetric data. The applicability of
the BET equation at different temperatures was checked, and the average lifetime of an acetonitrile molecule
on the surface was evaluated by the Frenkel equation. Based on the experimental data obtained and calculation
results, it was concluded that the energy contribution of active sites capable of donor-acceptor interaction, on
the one hand, and that of the field of dispersion forces, on the other, vary reversibly with increasing adsorption
temperature or, in other words, the mechanism of adsorption changes. This change is found to be dramatic and
its temperature boundary lies somewhat above the normal boiling point of acetonitrile.

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