Effects of Halogen Ions on Degradation of Azo Dyes with Electrolysis

The degradation of azo dyes such as Orange I_??_IV was investigated in an electrolyte solution containing chloride or bromide ions as halide ions with electrolysis. In the presence of halide ions, the electrolyzed degradation was accomplished because of the generated electrophilic halonium ions as active species with electrolysis that involve initial attack at azo groups. It was presumed that these degradations were due to the molecular structure of dyes relating to the existence of azo-hydrazone equilibria in hydroxyazo dyes and electron-donating group in aminoazo dyes. In the case of an electrolyte solution containing chloride ion, the degradation of dyes was significantly influenced by the pH of this electrolyte and decrease with rising pH. The ability of degradation with electrolysis was larger in bromide ion than that in chloride ion and the pH of electrolyte had no influence on the degradation in the case of bromide ion, compared with chloride ion.