Hydrophilic Sites on Silica Surface Modified in Gaseous and Liquid Phases

The methods of chromatography, adsorption, and potentiometic titration were used to determine the amount and energetics of the residual hydrophilic sites on the wide-porous silica surfaces modified in gaseous and liquid phases. The concentration of the residual hydrophilic sites on the silica surfaces modified by both methods was shown virtually to be the same. However, the activity of the hydrophilic sites on the sample modified in gaseous phase was significantly higher than that on the sample modified by liquid-phase method. Based on the comparison of the calculated isosteric heats of adsorption of water vapors on the studied modified sorbents with calorimetric heats, which are characteristic for the interaction of water molecules with vicinal and single hydroxyl groups of silica gel, the nature of the residual hydrophilic sites on the silica surfaces modified by these two methods was discussed.