Interlamellar Adsorption of Carbon Dioxide by Smectites

The adsorption of CO 2 at low temperature (~ -70°C) on thin films of homoionic smectites was studied by X-ray diffraction and by i.r. absorption. An increase in the d 001 spacings of these clay films upon adsorption of CO 2 was observed. In addition, a dichroic effect was readily discernible by comparing the i.r. spectra at two different orientations of the smectite films; i.e. with the film normal and tilted 35° with respect to the i.r. beam. The CO 2 stretching vibration at 2350 cm -1 was used for the i.r. study. These observations conclusively show that CO 2 intercalates the smectite structure rather than being adsorbed only in pores between clay tactoids—the limiting process proposed by other investigators. Adsorption isotherm data from earlier surface area studies are re-examined here through application of the Dubinin equation. Again, intercalation is demonstrated by convergence of the plotted experimental data for smectites containing large monovalent interlayer cations toward a pore volume that is near the calculated theoretical value for a monolayer of intercalated CO 2 . Scanning electron photomicrographs of Li- and Cs- smectites provide additional evidence that aggregation differences are not responsible for the large observed difference in BET surface areas obtained for these smectites with CO 2 as the adsorbate. At low magnification, visual differences in macro-aggregates are apparent, but at high magnification no significant differences are observed in the micro-structure of individual aggregates where the major amount of gas adsorption really occurs. L’adsorption à basse température (~ -70°C) du CO 2 sur des films fins de smectites homoioniques a été étudiée par diffraction X et par absorption infrarouge. On a observé une augmentation des espacements d 001 de ces films d’argile lors de l’adsorption du CO 2 . De plus, un effet dichroïque est facilement discernable en comparant les spectres infrarouges pour deux orientations différentes des films de smectite, à savoir l’incidence normale et une incidence oblique pour laquelle le plan du film fait un angle de 35° avec le faisceau infrarouge. La vibration d’élongation du CO 2 à 2350 cm -1 a été utilisée lors de l’étude infrarouge. Ces observations montrent d’une façon concluante que le CO 2 s’intercale dans la structure de la smectite au lieu de s’adsorber seulement dans les pores existant entre les tactoïdes d’argile—ce que d’autres auteurs ont considéré comme un phénomène limitant. Les clichés