COMPUTER-SIMULATION OF THE ADSORPTION OF ARGON ON THE SURFACE OF TITANIUM-DIOXIDE .2. AMORPHOUS SURFACE

Computer simulation of the adsorption of Ar on three different models of the amorphous surface was carried out by the grand canonical ensemble Monte Carlo method. One, called the Bernal surface (BS), is the surface of a dense random packing of oxide ions. Another is the corrugated Bernal surface (CBS) that is obtained by random deletion of surface oxide ions from BS. The third is a partially melted surface (MS) which is obtained by computer simulation of surface melting on the (100) face of rutile. The isotherm and the integral molar energy of adsorption on CBS are very close to the corresponding experimental data of Drain and Morrison (DM) for Ar on rutile. The isotherm is type II (BDDT classification) and has a long linear portion in the supermonolayer region. The computer-simulated isotherm on BS has no such linear portion (and thus does not obey the BET equation). It is suggested that the characteristic shape of the type II isotherm with the long linear portion which is employed for determination of specific surfaces of adsorbents by the BET method is the consequence of surface corrugation. In the submonolayer region, the computer-simulated isotherms of Ar adsorption on BS and CBS are very close to DM. This is achieved, however, by adjusting the well-depth parameters of the Ar/oxide ion interatomic interaction potential. The computer-simulated isotherm on MS deviates considerably from DM.