Abstract: The surface reduction behavior of nine monoazo dyes at the static mercury drop electrode has been studied by means of adsorptive square wave voltammetry. 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 the first step is a quasireversible reduction followed by a totally irreversible reduction. For those dyes having strong electron-repelling groups 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 observed. The second step gradually separates from the first step as the pHvalue of the solution increases. For those azo dyes having methoxy or hydroxy substituents, two peaks are observed; one is quasireversible, the other is totally irreversible. The second irreversible step gradually overlaps the first step as the pHvalue 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. The surface reduction behavior is quantitatively explained by the proposed models. The kinetic parameters for these surface reactions are obtained by non-linear least squares(COOL) analysis of the voltammograms. These techniques are useful for both establishing mechanism and chemical analysis.

Key words: Square wave voltammetry, Monoazo dyes, Surface electrochemical reaction, Reaction mechanism and kinetics