Conductivity of clay-modified electrodes: alkali metal cation hydration and film preparation effects

145

Abstract--Clay-modified electrode research indicates that adsorbed complexes are electroactive if the adsorption sites are clay edges. Interlayer adsorbed complexes may be electroactive ifa charge shuttle is added or if interlayer swelling is large. Conductivity of the film towards anionic species depends upon the swelling of the clay, which depends on the electrolyte concentration and speciation. The diffusion coefficients measured by electrochemical experiments agree well with alternative measurements.

Section: Conductivity Of Clay-modified Electrodesmentioning

confidence: 97%

Section: Conductivity Of Clay-modified Electrodesmentioning

confidence: 99%

Clay-Modified Electrodes: A Review

Fitch

1990

145

“…In order to study diffusion in clays, we have developed the technique of clay-modified electrodes (CME) where the gradient driving transport is unaffected by hydraulic considerations Fitch and Fausto 1988;Fitch and Edens 1989;Lee and Fitch 1990;Fitch 1990aFitch , 1990bWieglos and Fitch 1990;Edens et al 1991;Fitch and Du 1992;Subramanium and Fitch 1992;Fitch and Lee 1993;Fitch and Subrarnanium 1993;Stein and Fitch 1995;Fitch et al 1995). In this method, a well-ordered clay gel is formed on a flat glass surface in which a Pt wire is embedded.…”

Section: Introductionmentioning

confidence: 99%

Molecular Structure Effects on Diffusion of Cations in Clays

Fitch

Song

Stein

1996

Abstract--The roles of molecular structure and charge are examined in the transport of cations within montmorillonite clay films. The series of Ru(NH3)6 3+, Co(NH3) 3+, Co(en)33+, Co(sep) 3+ and Co(bpy)3 3+ are examined in detail via electrochemical and spectrocbemical 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)6 3+. 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)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 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.

“…The results for these ratio studies have been compared to other studies that measure the interlayer spacing through X-ray diffraction (XRD). The correlation between the ratio values and XRD values is excellent (Norrish 1954, Lee andFitch 1990).…”

Section: Introductionmentioning

confidence: 93%

Effect of Clay Type on the Diffusional Properties of a Clay-Modified Electrode

Stein¹

1996

Abstract--The response of two swelling clays (SWy-1 and SAz-1) and of one non-swelling clay (KGa-1) and of a series of mixtures of these clays to different electrolyte concentrations was examined using clay-modified electrode techniques. A non-interacting probe ion, Fe(CN)6 3-, was monitored via reduction for its arrival at a Pt electrode coated with thin films of the day mixtures. The three clays had both different temporal responses and different equilibrium currents. For SWy-1 the currents were developed over time and were dependent upon the electrolyte of the bathing solution, which was consistent with X-ray diffraction data literature for the interlayer dimension. Similar behavior was found for SAz-1, but for KGa-1, currents were instantaneous and were independent of the bathing electrolyte. This suggests that the pores controlling the probe ion transport were between particle or pinhole in nature. When mixtures of the clays were examined, it was found that KGa-1 caused defects within the structures of the mixed clay films. The SWy-1 mixture was not as affected by these disruptions as was the SAz-1 mixture.