Voltammetric Response of Zeolite‐Modified Electrodes

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Abstract
As a prelude to using zeolites as supports for electrocatalysts, the voltammetric behavior of various analytes was examined at zeolite‐modified electrodes in aqueous solution. The following parameters were studied: preparation and characterization of electrodes, ability to concentrate or exclude analytes from dilute solution, linearity of response to concentration of analytes in solution, selectivity toward analytes of various sizes and charges, and the role of electrolyte cations in determining the response. The following analytes were used: methyl viologen dication (N,N′‐dimethyl‐4,4′bipyridyl), heptyl viologen, hexammineruthenium (III), hexacyanoferrate (III), and copper (II). Zeolites mixed with carbon paste gave more reproducible and robust electrodes than did films of zeolite/polystyrene on platinum or glassy carbon electrodes. Electrodes modified with zeolite Y concentrated methyl viologen, hexammineruthenium (III), and Cu(II) from dilute solution (0.1–10 mM), and cyclic voltammetric peak current was linear as a function of solution concentration after an equilibration period of 1h. Ferricyanide and heptyl viologen were excluded from the zeolite based on charge and size, respectively, and were therefore not concentrated from solution. The smaller pore zeolite A accommodated only Cu(II). Selectivity and competition among pairs of analytes were also examined. The peak current in cyclic voltammetry was also correlated with the mobility of electrolyte cations within the zeolite matrix, based on their charge, and their size relative to the size of the zeolite channels. Enhancement factors (defined as peak current at a modified electrode divided by that at an unmodified electrode) reached values in the range of 50, despite the loss of active surface area of the electrode caused by the modification.

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