SREL Reprint #2158

Sorption of aromatics in the interlayer space of organo-clays

W. P. Gates, B. J. Teppen, and P. M. Bertsch

University of Georgia, Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802 USA

Summary: We have directly determined the orientation of TMPA in the interlayer of smectites using plane-polarized infrared (FTIR) spectroscopy. Plane-polarized IR results indicate that the orientation of trimethylphenylammonium (TMPA) in the interlayers of smectites is such that the phenyl-N bond is parallel to the 001 surface. For smectites with tetrahedral charge, the phenyl ring-plane is normal to the 001 surface but loses orientational preference as tetrahedral charge decreases and octahedral charge increases. The orientation dependence of TMPA with density and location of layer charge indicated that mineral structural factors are important in controlling solution-phase reactions at mineral surfaces. To better understand these factors, we studied the vapor phase sorption of benzene onto oriented films loaded with TMPA at 0, 25, 50, 75%, and 100% of the cation exchange capacity (CEC). For all smectites and at all TMPA loadings, two sorbed forms of benzene were noted and TMPA loading influenced which form dominated. At 100% CEC loadings, benzene sorption depended on the overall charge of the smectite. For all treatments, interlayer hydration waters associated with both Na+ and TMPA and hydration waters displaced by benzene were observed. An absorption band for C-C in-ring stretch at 1330 cm-1 was strongly dichroic at TMPA loadings of 25 and 50% and red-shifted to 1310 in TMPA-clays relative to Na-clays. Our results indicate that individual benzene molecules stacked preferentially with one another such that the benzene ring-plant was nearly normal (±20º) to the 001 face of the clay and apparently aligned with the phenyl ring of TMPA.

SREL Reprint #2158

Gates, W.P., B.J. Teppen, and P.M. Bertsch. 1997. Sorption of aromatics in the interlayer space of organo-clays. pp. 41-48 In: Industrial Minerals Symposium. Verlag der Gesellschaft fur Geowissenschaften e. V., Neubrandenburg, Germany.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).