Showing papers on "Mesoporous material published in 1976"

Specificity in the adsorption of nitrogen and water on hydroxylated and dehydroxylated silicas

Abstract: Adsorption isotherms of nitrogen (at −196°C) and water (at 25°C) were determined on nonporous, mesoporous and microporous silicas outgassed at temperatures of 25 and 1000°C. The isotherms are analyzed by the BET, FHH, and αs methods, and the adsorption characteristics are related to the extent of surface hydroxylation and the porosity of each sample. A small change in the surface concentration of hydroxyl groups produced by exposing the nonporous silica (TK 800) to water vapor did not affect the BET-nitrogen area to any significant extent, but the uptake of water was enhanced and the low-pressure hysteresis removed. Outgassing the nonporous and mesoporous samples at 1000°C resulted in only a small change in texture. In contrast, the microporous gel underwent a drastic reduction in BET-area, although the isotherm shape and αs-plot show that the micropore structure was not destroyed. Values for the fractional surface coverage, θw, by the BET-monolayer of water are found to range between ∼0.1 and 0.9, the lowest values being obtained with the dehydroxylated silicas (irrespective of pore size) and the highest values obtained with the partially hydroxylated, microporous gels. The FHH analysis indicates that the development of the nitrogen multilayer is not much affected by surface dehydroxylation.