Clay modified electrodes

Earlandite structure, 849 Electrical conductivity metal complexes, 133 tetracyanoplatinates anion-deficient salts, 136 Electrical properties metal complexes, 133-154 Electrocatalysis, 28 Electrochemical cells, 1 Electrochemistry, 1-33 hydrogen or oxygen production from water coordination complex catalysts, 532 mineral processing, 831 reduction, 831 Electrodeposi (ion of metals, 1-15 mineral processing difficulty, 831 Electrodes clay modified, 23 ferrocene modified, 20 nation coated, 15 polymers on, 16 polyvinylferrocene coated, 19 poly(4-vinylpyridine) coated, 17 redox centres, 17 Prussian blue modified, 21 surface modified, 15-31 Electrolysis... 

Y. Sallez, P. Bianco, and E. Lojou, Electrochemical behavior of c-type cytochromes at clay-modified carbon electrodes a model for the interaction between proteins and soils. J. Electroanal. Chem. 493, 37-49 (2000). 

Following on from SAQ 5.8, why would anyone employ a clay-modified electrode for an electrochemical analysis ... 

At first sight, a clay-modified electrode is an unlikely choice since its capacitance is so large. However, the area of such electrodes is usually huge (see below), and hence the large capacitance. 

So why have a clay-modified electrode at all Why not just have an ordinary electrode, but one which is made of a fine wire mesh ... 

Many analyses are performed with mesh electrodes, thereby increasing the surface area. However, there is an additional reason for using a clay-modified electrode. We saw above (in Worked Example 5.2) that electrode side reactions are a common enemy of accurate electroanalytical work. 

Organic polymers are widely used in modified electrodes [220], but inorganic materials such as zeoHtes, clays or microporous solids are attractive as replacements since they have much better stability, tolerance to high temperatures and oxidizing conditions, and chemical inertness. Due to the capability of clays to exchange intercalated ions, clay modified electrodes have been extensively studied. 

Y. Shih, J.-M. Zen and H.-H. Yang, Determination of codeine in urine and drug formulations using a clay-modified screen-printed carbon electrode, J. Pharm. Biomed. Anal., 29 (2002) 827-833. 

Mousty, C., Therias, S., Forano, C. and Besse, J. P. (1994). Anion-exchanging clay-modified electrodes - synthetic layered double hydroxides intercalated with electroactive organic-anions. J. Electro anal. Chem. 374, 63. 

Manisankar, P., Selvanathan, G. and Vedhi, C. (2006), Determination of pesticides using heteropolyacid montmoriUonite clay-modified electrode with surfactant. Talanta, 68(3) 686-692. 

A brief mention about gas evolution at clay modified electrodes, which is desirable in electrocatalysis, was made by Bard and co-workers [167, 168]. It should be noted that metal-bpy complexes and MV + bound on the internal and external surfaces of montmorillonite clay are electroinactve, and only about 15-30 % of the external electroactive species, which probably are present as ion pairs [170], reach the electrode [169]. 

J. R. White and A. J. Bard, Clay modified electrodes. Part IV. The electrochemistry and electron spin resonance of methyl viologen incorporated into montmorillonite films, J. Electroanal. Chem. 797,233-244(1986). 

Ghosh, P.K., Man, A.W.-H., andBard, A. J. 1984. Clay-modified electrodes Part II. Electrocatalysis at bis(2,2 -bipyridyl) (4,4 -dicarboxy-2,2 -bipyridyl)Ru(n)-dispersed ruthenium dioxide— hectorite layers. Journal of Electroanalytical Chemistry 169, 315-317. 

Yamagishi, A., and Aramata, A. 1984. A clay-modified electrode with stereoselectivity. Journal of the Chemical Society Chemical Communications 7, 452-453. 

Zen, J.-M., and Chen, P.-J. 1997. A selective voltammetric method for uric acid and dopamine detection using clay-modified electrodes. Analytical Chemistry 69, 5087-5093. 

Many crystals can be considered as built up of parallel layers, especially if the forces operative between layers are of less consequence than those acting within layers. In some materials such as graphite the layers may be monotonic, but in others such as micas or clay materials they may be several atoms deep. Much attention has been directed toward the study of reactions enhanced by molecular catalysts intercalated in smectite clays [66,67]. Because of the ability of these minerals to imbibe water, a solution-like environment can exist between layers and, provided the layers are sufficiently swollen to permit rapid diffusion of reactants, many reactions involving cations or neutral molecules can be carried out. Photocatalytic and photochemical reactions in/on clays or clay-modified materials (electrodes) have been studied and discussions of these experiments are presented in the monographs of Thomas [68] and of Kalyanasundaram [69] and in the... 

RC(0H)C02 The low yield UV photoaquation of [Ru(NH3)6] has been reported. The adsorption-desorption of [Ru(NH3)s] + on pyrolytic graphite electrodes coated with Nafion 125 and on clay-modified electrodes has been described. ... 

C.H. Lei, F. Lisdat, U. Wollenberger, and F.W. Scheller, Cytochrome c/clay-modified electrode. 

VOLTAMMETRIC DETERMINATION OF ORGANIC COMPOUNDS USING CLAY MODIFIED CARBON PASTE ELECTRODES... 

The reduction mechanism of nitro derivatives (nitrobenzene, dinocap, flunitrazepan and others) when a clay modified carbon paste electrode is used agrees well with that reported for the reduction of these compounds. Figs 1 and 2 show the voltammograms obtained by cyclic and by differential pulse scan rsdifferential pulse voltammetryrespectively, when a sepiolite modified carbon paste electrode was kept for 5 minutes in a solution containing (a) nitrobenzene or (b) dinocap. 

The behaviour observed for aniline and phenol when a clay modified carbon paste electrode is used, agrees well with the mechanisms put forwards by Lines for the oxidation of aniline and with the oxidation of phenol to quinone. " ... 

Based on our studies it is possible to conclude that clay modified carbon paste electrodes allow the efficient preconcentration of organic compounds for voltammetric measurement. 

Itaya, K., Chang, H. C., and Uchida, I. 1987. Anion-exchanged hydrotalcite-like-clay-modified electrodes. Inorg. Chem. 26 624-26. 

Mousty, C. Biosensing rqrplications of clay-modified electrodes a review Anal. Bioanal. Chem. 396(1), 315-325 (2010). doi 10.1007/s00216-009-3274-y... 

The self-assembly of the 2 1 smectite-type clay containing thiol groups on Au was performed in a chloroform suspension of clay [91]. The formation of a monolayer or a partial double layer was demonstrated from the frequency change. In other studies on the clay-modified electrodes, the clay-precoated QCM was used to examine the swelling of the clay films, and the adsorption and redox of the metal complexes. 

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