Adsorption of Water Vapour on Rutile and Silica-Coated Rutile

Abstract

Adsorption isotherms of water vapour have been determined at 25°C on pure rutile (surface area 22 m².g⁻¹) and on two samples of the rutile coated with different amounts of dense silica (0·6 & 2·6 wt% SiO₂). With each adsorbent, the adsorption measurements were made after outgassing at temperatures of 298, 373, 423 and 573 K, and finally at 298 K in the case of the pure rutile. An upward displacement of the isotherms with an increase in the outgassing temperature was found with each system but a pronounced change in isotherm character was found only with pure rutile. It is concluded that ligand water is incorporated into the surface structure of rutile, thus providing additional sites for the physisorption of water in the hydrogen-bonded form. The addition of 0·6 wt% of silica appeared to be sufficient to block off the cationic sites and the resulting surface then became remarkably similar to that of precipitated silica.