Simultaneous determination of the spectroscopic and adsorption isotherms of water on silica

The changes in the near infrared spectra of the porous 96% silica glass-water system were determined, simultaneously with the vapour pressure and the adsorbate concentration, during a complete adsorption cycle. The heating effect of the analyzing undispersed infrared beam was eliminated. From the absorbance vs concentration plots it is inferred that the “free” silanol groups are the main adsorption centres and the ratio of H2O to OH is 1:1 in the monolayer. The results indicate that the Corning 7,930 porous silica has micropores and a portion of the adsorbed water exists in an unperturbed state over the entire concentration region.