Intercalation Phenomena of Carbon Dioxide, Water or Ions in Smectite Clay

Abstract

Smectites, or swelling clays, are layered porous materials based on two-dimensional stacks of inorganic layers. The non-equivalent substitutions of atoms generate a negative charge on each layer surface which is balanced by exchangeable interlayer cations. These cations are responsible for the differences in the physicochemical behavior of smectites such as plasticity and swelling. The large scientific and technological interest in smectites is connected to their ability to swell, most commonly caused by their interactions with water (H2O) or carbon dioxide (CO2). Smectites are rarely found in nature without H2O, that’s why understanding this interaction is of paramount importance. While for CO2 the attracted interest in the scientific community in recent years, is partly because clays, being cheap, environmental friendly and abundant, can be used to capture anthropogenic CO2 and also because geological structures are used as storage sites. This thesis contains experimental studies on intercalation of H2O and CO2 in smectites. The study was systematically done in a synthetic smectite Mfluorohectorite, with M referring to the interlayer cations Li+, Na+ and Ni2+. The main objective of this work was to comprehend the role that the aforementioned cations play in the intercalation process. More specifically, how these cations influence: (i) the kinetics of intercalation of CO2 molecules when a fluorohectorite is exposed to different sets of CO2 pressure and temperature conditions; (ii) water intercalation/water vapor transport when a fluorohectorite is under different sets of relative humidity and temperature. The physical processes and phenomena described within this thesis were studied mainly by X-ray Diffraction. The results show the strong cation dependence on intercalation of H2O and CO2. For each cation-fluorohectorite system some unique features were observed, such as kinetics of intercalation of CO2 and H2O stable hydration states.