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.

摘要：

自制长光程薄层电化学池，对靛蓝磺化物（IC）的还原隐色和氧化脱色过程及其逆过程进行循环伏安和双电势阶跃UV-Vis光谱电化学测量。结果表明，IC在不至过低的电势下（>-1.0 V vs Ag/AgCl/饱和KCl），可通过2e^-/2H⁺可逆反应还原为隐色体，其逆向电氧化过程的速率常数大于电还原速率常数1个数量级以上;隐色体也可被溶解氧化学氧化，导致电还原效率降低。在IC的电氧化脱色方面，提出一种复杂的电化学-化学-电化学机理，氧化生成的中间体通过水解发生中心C=C双键的断裂而转化为靛红磺酸，后者在1.0 V以上的较高电势下进一步被不可逆电氧化降解为一系列小分子。