We used both localized and periodic calculations within the helm of Density Functional Theory (DFT) on a series of monovalent (Li+, Na +, K+, Rb+, Cs+), and divalent (Mg2+, Ca2+, Sr2+, Ba2+) cations, to monitor their effect on swelling of clays. The activity order obtained for the exchangeable cations among all the monovalent and divalent series studied is: Mg2+ > Ca2+ > Sr2+ > Ba2+ > Cs+ > Rb+ > Na+ > Li+ > K+. We studied two type of clays Montmorillonite and beidellite, with different surface structure and with/without water using periodic calculation. We have calculated the layer spacing at the first, second and third hydration shell of exchangeable cation, to compare with the experimental d-spacing values to correlate with humidity. A novel quantitative scale is proposed by the relative nucleophilicity of the active cation sites in their hydrated state through Fukui functions within the helm of hard soft acid base (HSAB) principle. Finally, the swelling mechanism is proposed.
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry