MOLECULAR-STRUCTURE EFFECTS ON DIFFUSION OF CATIONS IN CLAYS

The roles of molecular structure and charge are examined in the transp ort of cations within montmorillonite clay films. The series of Ru(NH3 )(6)(3+), Co(NH3)(3+), Co(sep)(3)(3+), Co(Sep)(3+) and Co(bpy)(3)(3+) are examined in detail via electrochemical and spectrochemical methods . The electrochemical signal is enhanced both in minimizing the time r equired to develop the signal and in the magnitude of the signal for R u(NH3)(6)(3+). In addition, the potential for the observed reduction p eak is shifted negative and the current peak associated with reduction disappears with rinsing of the clay film. These observations are char acteristic of a compound that is held by simple electrostatic charge c haracteristics. In contrast, the compounds Co(NH3)(3+), Co(en)(3)(3+) 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 signa l for Co(bpy)(3)(3+) is slow to be observed, is diminished with respec t to the bare electrode: and is shifted positive in potential, all hal lmarks of a strong, non-electrostatic mode of binding within the clay.