Determination of hydroxyls density in the silica-mesostructured cellular foams by thermogravimetry

Thermogravimetry was applied to determine the surface hydroxyls coverage in the mesostructured cellular foams (MCFs) calcined at different temperatures and then rehydroxylated by contacting with water vapor or liquid. The TG measurements were performed by heating MCFs in air stream using a three-step temperature program: (i) at rate of 5 degrees C min(-1) from 25 to 200 degrees C; (ii) held at 200 degrees C for 30 min; and (iii) heating at rate of 10 degrees C min(-1) up to 1100 degrees C. The hydroxyls content was calculated from weight loss during third step. The hydroxyls density appeared to depend strongly on the calcination temperature and the subsequent contact with water vapor. When MCFs were exposed for a short period (ca. 1 min) to moist air the hydroxyls content increased rapidly, more in the samples calcined at 300 degrees C than 500 degrees C, to attain surface densities of 4.75 and 1.6 OH nm(-2), respectively. The 2-h contact with water vapor resulted in slower further increase of hydroxyls densities, to values of 5.45 and 2.9 OH nm-2, for samples calcined at 300 and 500 degrees C, but longer contacts had no significant effect. A similar trend was also observed when sample was treated with liquid water. (c) 2005 Elsevier B.V. All rights reserved.