Abstract:

Thin-layer cyclic voltammetry and double potential step UV-Vis spectroelectrochemical method were used to study the reductive color-hiding and oxidative decolorization of indigo sulfonate（IC）in a long-path thin-layer electrochemical cell to understand the reaction mechanism in the two cases.IC was electro-reduced to its leuco form via a 2e^-/2H⁺ reversible reaction at appropriate potentials not lower than -1.0 V（vs Ag/AgCl/saturated KCl）.The leuco-IC can be electrochemically reoxidized to IC with a rate constant an order of magnitude higher than that in the electro-reduction，or it can be chemically reoxidized by dissolved oxygen，leading to a decrease in electro-reduction efficiency.For the oxidative decolorization of IC，a complex electrochemical-chemical-electrochemical（ECE）mechanism was proposed，in which the oxidized intermediate formed in the first step decomposes to isatin sulfonic acid（ISA）upon cleavage of the center C=C double bond of IC，and the ISA may be further electro-degraded to small molecules at more positive potentials.