ELECTROCHEMICAL REDUCTION BEHAVIOR OF VAT AND SULFUR DYES: A COMPARATIVE STUDY

In the application of vat and sulfur dyes, a large amount of hazardous by-products are generated from chemical reducing agent decomposition such as sodium dithionite and sodium sulfide. The substitution of these non-regenarable by-products by cathodically regenerable reducing agents offers great ecological advantages. In this study, indirect electrochemical reduction of the most popular Vat dye (CI Vat Blue 1) and Sulfur dyes (CI Sulfur Black 1) was studied in a divided electrochemical cell connected with a separated dye bath. The redox properties of the tested dyes were studied by the mean of potentiometry at imposed low current and by controlling the evolution of the redox potential. The colorcoordinates and the colorfastness of the samples were investigated and compared with the conventional dyeing process. The electrochemical process proposed in this study permitted an improved understanding of the dyestuff reduction behavior at a molecular level. The electrochemical reduction of CI Vat Blue 1 showed better performance. The CI Sulfur Black 1 has almost good advantage, but with different reduction behavior and more complications because of different reducible sites in its molecule.