Estudo eletroquimico de corantes organicos com propriedades redox imobilizados sobre o fosfato de zirconio

AUTOR(ES)
DATA DE PUBLICAÇÃO

1997

RESUMO

Methylene Blue (MB) and Nile Blue (NB), a phenothiazine and a phenoxazine dyes respectively, were adsorbed on zirconium (IV) phosphate (ZP) by ion exchange reaction. The dyes were strongly retained and were not leached out from the matrix. The materials with adsorbed dyes (ZPMB e ZPNB) were incorporated into a carbon paste electrode and the electrochemical properties were investigated by cyclic voltammetry and amperometry techniques. The immobilized dyes presented very stable redox properties. The midpoint potentials (Em) were 150 mV vs SCE for MB and 50 mV vs SCE for NB .A shift of about 300 mV towards more positive potentials of Em, was observed compared with those obtained in aqueous solutions. These shifts suggest that the reduced forms of the dyes are more stable on the ZP matrix than the oxidised forms. A possible explanation for this behavior is the high acidity of the material, because the Em for the immobilized dyes is similar of that observed when these dyes are present in acid solutions. The composition and pH of the supporting electrolyte did not affect the midpoint potential, Em, it remained pratically constant, in contrast to those observed for these dyes in solution phase or adsorbed on carbon and silver electrodes. The almost constant Em for both materials in various pHs conditions are very important from practical point of view since they can be used to prepare chemical sensors for real samples, where the pH plays an important role and can not be changed in order to optimize the electrode response. The electrocatalytic properties of the modified electrodes were tested using ascorbic acid and the NADH cofactor. The ZPMB -modified electrode was used to study the electrochemical oxidation of ascorbic acid. Both, ZPMB e ZPNB -modified electrodes electrocatalyse the NADH oxidation, however it was observed that ZPNB was more efficient catalyst at a lower midpoint potential than ZPMB.

ASSUNTO(S)

voltametria cíclica

ACESSO AO ARTIGO

Documentos Relacionados