Effects of surface charge and particle morphology on the sorption/desorption behavior of water on clay minerals

In situ DRIFT spectroscopy is used in the current study to follow sorption/desorption of water vapor on several clay minerals that vary in surface charge and morphological character. Spectra of the dried sorbents indicate the significant effect of those factors on both liquid and vapor phase water remaining within the particles. Changes in the IR bands recorded during exposure to water vapor at 50% RH confirm the assignment of those bands to water. They also indicate that the dynamics of liquid phase sorption/desorption for all the sorbents investigated is consistent with the concept of capillary condensation within nanometer scale pores that was advanced in previous studies conducted with 1,2-dihaloethanes. The intraparticle accumulation of the vapor phase water, however, was found to be profoundly affected by both surface charge and particle morphology. These differences are attributed to the high polarity and hydration capabilities of water molecules. Band area changes documented during a second sorption/desorption cycle are nearly identical to those occurring during the first with regard to both timing and extent. They also confirm that some liquid phase water is retained by the sorbents even after five days of desorption and amounts of sorbed vapor phase water increase over the course of the experiments.