The adsorption isotherms of cyclohexanone and BzOH from cyclohexane onto silica gels, heated at various temperature (200-700? or treated with Me3SiCl were determine at 35? Some of the silica gels were studied by IR. After the surface of silica gels were treated with Me3SiCl, the free OH group disappeared, but the associated OH group did not change, and the adsorption of cyclohexanone and BzOH decreased slightly. This shows that the associated OH groups are not important in the adsorption from solns. On the surface of silica gel, only the free OH groups reacted with Me3SiCl and the amount of adsorption changed correspondingly with the degree of trimethylsilylation. Furthermore, the adsorption from solns. did not take place on the silica surface from which free OH had been removed entirely. These facts indicate that the free OH groups play the role of adsorption centers. Monomol. adsorption shows a max. on the surface of silica gel heated at 400? which suggests that the concentration of the free OH group may have a max. at this temperature

Key words: BENZENECARBOXYLIC ACID, ADSORPTION, SURFACE CHEMISTRY, CYCLOHEXANE, SILICA GEL, CYCLOHEXANONE, ISOTHERM, SOLUTION CHEMISTRY