Molecular Structure Effects on Diffusion of Cations in Clays

Alanah Fitch, John Song and Jenny Stein
Department of Chemistry, Loyola University of Chicago, 6525 N. Sheridan Rd. Chicago, Illinois 60626

Abstract: The roles of molecular structure and charge are examined in the transport of cations within montmorillonite clay films. The series of Ru(NH3)63+, Co(NH3)3+, Co(en)33+, Co(sep)3+ and Co(bpy)33+ are examined in detail via electrochemical and spectrochemical methods. The electrochemical signal is enhanced both in minimizing the time required to develop the signal and in the magnitude of the signal for Ru(NH3)63+. In addition, the potential for the observed reduction peak is shifted negative and the current peak associated with reduction disappears with rinsing of the clay film. These observations are characteristic of a compound that is held by simple electrostatic charge characteristics. In contrast, the compounds Co(NH3)3+, Co(en)33+ and Co(sep)3+, while showing rapid and enhanced signal development, eventually evolve a signal that is diminished with respect to the bare electrode, consistent with a hydrophobic mode of retention. The signal for Co(bpy)33+ is slow to be observed, is diminished with respect to the bare electrode and is shifted positive in potential, all hallmarks of a strong, non-electrostatic mode of binding within the clay.

Key Words: Clay-modified electrodes • Co complexes • Diffusion • Transport

Clays and Clay Minerals; June 1996 v. 44; no. 3; p. 370-380; DOI: 10.1346/CCMN.1996.0440306
© 1996, The Clay Minerals Society
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