Article

Zeolite-modified electrodes with analytical applications*

Pure and Applied Chemistry (Impact Factor: 3.39). 01/2011; 83:325-343. DOI: 10.1351/PAC-CON-10-07-08

ABSTRACT Zeolite-modified electrodes (ZMEs) have been widely investigated because of their chemical, physical, and structural characteristics (shape, size, and charge selectivities; phys-ical and chemical stabilities; high ion-exchange capacity; hydrophilic character; etc.), which make them of high interest in the design of electroanalytical systems. The paper presents recent literature data about fundamental and practical aspects related to the obtaining and applications of ZMEs. Some new ZMEs based on carbon paste incorporating soluble pheno -thiazinic dyes adsorbed on X-type zeolites are assessed comparatively, and the influence of some experimental parameters on the electrochemical response of these electrodes was inves-tigated. The kinetic parameters for the heterogeneous electron-transfer process correspon-ding to the surface-immobilized mediators were determined, and all observed differences were used as evidence of the influence of the mediator structure and of the zeolite nature on the electrochemical activity of the new electrodes and on their electrocatalytic properties toward β-nicotinamide adenine dinucleotide (NADH) or ascorbic acid (AA) electro-oxida-tion and H 2 O 2 electroreduction. Zeolites are crystalline, microporous, aluminosilicate materials with well-defined structures. Generally, they contain silicon, aluminum, and oxygen in their framework and cations, water, and/or other mole-cules within their pores. Zeolites have the capacity to be completely hydrated and dehydrated without damage to the crystalline lattice [1]. A general formula of aluminosilicate zeolites is: M a D b T c [Al (a+2b+3c) Si [x–a+2b+3c)] O 2x ]mH 2 O, where M, D, T are mono-, di-, and trivalent extra-framework cations which maintain the electrical neu-trality [2]. Many zeolites occur naturally as minerals, and are extensively mined in many parts of the world. Others are synthetic, and are made commercially for specific uses, or produced by research scientists trying to understand more about their chemistry. Natural zeolites form where volcanic rocks and ash layers react with alkaline groundwater. Their structure has more acid-resistant silica to hold the structure together; they are rarely pure and are con-taminated to varying degrees by other minerals, metals, quartz, or other zeolites. For this reason, natu-*Paper based on a presentation made at the 2 nd Regional Symposium on Electrochemistry: South East Europe (RSE SEE-2), Belgrade, Serbia, 6–10 June 2010. Other presentations are published in this issue, pp. 253–358.

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