SURFACE REDUCTION STUDY OF MONOAZO DYES BY ADSORPTIVE SQUARE-WAVE VOLTAMMETRY

The surface reduction behavior of nine monoazo dyes at the static merc ury drop electrode has been studied by adsorptive square wave voltamme try. Three types of surface reduction behavior are seen among the nine azo dyes. Two of them are modeled as a two-step mechanism in which th e first step is a quasi-reversible reduction followed by a totally irr eversible reduction. For those dyes having strong electron-donating gr oups such as amino or dimethylamino, the second reduction occurs at a potential almost the same as that of the first, and only one peak is o bserved. The second step gradually separates from the first step as th e pH-value of the solution increases. For those azo dyes having methox y or hydroxy substituents, two peaks are observed; one is quasi-revers ible, the other is totally in irreversible. The second, irreversible s tep gradually overlaps the first step as the pH-value of the solution decreases. The third type voltammogram of these monoazo dyes displays a single irreversible peak that is modeled as a four-electron one-step irreversible reduction. These surface reduction behaviors are quantit atively explained by the proposed models. Kinetic parameters for these surface reactions are obtained by non-linear least squares (COOL) ana lysis of the voltammograms. These techniques are useful both for estab lishing mechanisms and chemical analysis.