Gels, chemical redox

Kerner W, Lindquist S-E, Pishko MV, Heller A. Amperometric glucose sensor containing glucose oxidase cross-linked in redox gels. In Turner APF, Alcock SJ (Eds), In Vivo Chemical Sensors Recent Developments. Cranfield Press, Cranfield UK, 1993. 

Once the multi-step reaction sequence is properly chosen, the bifunctional catalytic system has to be defined and prepared. The most widely diffused heterogeneous bifunctional catalysts are obtained by associating redox sites with acid-base sites. However, in some cases, a unique site may catalyse both redox and acid successive reaction steps. It is worth noting that the number of examples of bifunctional catalysis carried out on microporous or mesoporous molecular sieves is not so large in the open and patent literature. Indeed, whenever it is possible and mainly in industrial patents, amorphous porous inorganic oxides (e.g. j -AEOi, SiC>2 gels or mixed oxides) are preferred to zeolite or zeotype materials because of their better commercial availability, their lower cost (especially with respect to ordered mesoporous materials) and their better accessibility to bulky reactant fine chemicals (especially when zeolitic materials are used). Nevertheless, in some cases, as it will be shown, the use of ordered and well-structured molecular sieves leads to unique performances. 

This scheme can be extended to nonconducting or semiconducting nanoporous solids incorporating redox-active centers via chemical doping prompted by sol-gel methodologies (Domenech and Alarcon, 2002b, 2003 Domenech et al. 2004b-d). Eventually, the materials can be electrochemically modified (Rolison and Bessel, 2000). 

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