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.

Tin oxide films have been prepared by physical vapor deposition of Sn followed by thermal oxidation and by spray pyrolysis of SnCl 4 or SnCl 4 ‚5H 4 O mixed with CH 3 OH. Phase changes and surface morphologies during the syntheses were monitored by X-ray diffraction and scanning electron microscopy. Electrical resistance and UV-visible transmittance of tin oxide films prepared by both methods were measured. The peak shapes of the Auger Sn M 4 N 45 N 45 transition of the prepared tin oxide films were compared to those of commercial SnO and SnO 2 and used to determine rough values of the oxidation state of Sn. Oxygen/tin ratios in the films were determined from analyses of scanning Auger microprobe and X-ray photoelectron spectroscopy and are all less than 2. Auger depth profiles with thermally oxidized tin oxide films on glass substrates show an overlapping region between the tin oxide film and the substrate. These films were tested as sensors for CH 2 Cl 2 in O 2 . The mixed phase (SnO‚SnO 2 ) tin oxide films prepared by temperature-programmed thermal oxidation of Sn showed better sensing behavior to CH 2 Cl 2 than single phase (SnO or SnO 2 ) films.

ChemInform Abstract is investigated using the following analytes: methyl viologen dication (I), heptyl viologen (II), Ru(NH3)63+ (III), Fe(CN)63-(IV) and Cu2+. It is found that zeolites mixed with carbon paste give more reproducible and robust electrodes than films of zeolite/polystyrene on Pt or glassy carbon. Electrodes modified with zeolite Y concentrate (I), (III), and Cu2+ from dilute solutions, whereas (II) and (IV) are excluded from the zeolite (due to charge and size, resp.). The zeolite A, having smaller pore size, accommodates only Cu2+. Enhancement factors (ratio of faradaic peak current at the zeolite modified, electrode to that of the unmodified electrode), selectivity and competition among pairs of analytes are investigated and the electroanalytical applicability is discussed.

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