INFLUENCE OF WATER ON ADSORPTION OF TRIETHYLSILANOL ONTO SILICA

The adsorption of triethylsilanol (TES) on silica from a heptane solut ion has been studied in situ by microcalorimetry with a special attent ion to the water content of the adsorbent. In a first step, controlled rate transformation analysis, which allows one to distinguish between physisorbed and chemisorbed water, is used to prepare silica samples with a known surface concentration of water. Adsorption isotherms and displacement enthalpies (of the solvent by the solute) are then determ ined. A decrease of both affinity and displacement enthalpy is observe d when the water surface concentration on silica is decreased. Moreove r, irreversibility of adsorption (attributed to the formation of silox ane bonds) is observed only when physisorbed water is present: the sil oxane bond formation seems to be catalyzed by the surface water.