The influence of thermal treatment of silica gel on surface-molecule interactions I. Finite coverage region

Adsorption isotherms of n-octane, benzene, toluene, and chloroform were determined by a gas chromatographic method on the surface of silica gel heated at 200, 400, and 800 degrees C. From the isotherms, the film pressure of the adsorbates was determined, and then the components of silica surface free energy were calculated. It was determined that the thermal treatment provided almost no changes in nonspecific interactions and a considerable decrease in acid-base ones; however, electron-acceptor interactions were always stronger than electron-donor ones. Based on these data, the surface concentration of adsorption sites was estimated. The adsorption energy distribution function (chi) was also determined for silica gels according to the asymptotically corrected condensation approximation method. The influence of the thermal treatment on distribution of adsorption sites was demonstrated for adsorbates possessing various types of interactions. (C) 1998 Academic Press.