ELECTROCHEMISTRY OF ALUMINA PILLARED CLAY-MODIFIED ELECTRODES

A simple method for preparing metal oxide pillared clay films on graph ite electrodes, based on the use of preformed pillared structures, is described. The films exhibited very good electroactivity when immersed in solutions containing redox active cationic species, e.g. Fe(bpy)(3 )(2+), Os(bpy)(3)(2+), Ru(NH3)(6)(3+) and methyl viologen. Aging a pil lared clay film, loaded with electroactive cations, in de-ionized wate r or varying the concentration of the supporting electrolyte have pron ounced effects on the voltammetric behavior of the pillared clay films . These effects demonstrate clearly the key role of ion-paired electro active cations for the electroactivity of pillared clay films. The pH dependence of the observed electroactivity for an alumina pillared cla y film arises in part from the binding of the electroactive cations at the surface hydroxyl groups of the alumina pillars. This binding favo rs further formation of electroactive ion pairs. The voltammetric resp onse from anionic redox couples, observed in acidic solutions, is attr ibuted to the amphoteric nature of the alumina pillars. Discrepancies in the voltammetric behavior of silica and alumina pillared montmorill onite are explained in the light of different degrees of attachment of the redox active cations to the surface hydroxyl groups of the two me tal oxide pillars. A model describing the charge transport in metal ox ide pillared clays is also presented.