靛蓝磺化物还原隐色和氧化脱色的薄层光谱电化学研究

Thin-layer spectroelectrochemical study on reductive color-hiding and oxidative decolorization of indigo sulfonate

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(>-1.0VvsAg/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CC双键的断裂而转化为靛红磺酸,后者在1.0V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。

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 CC double bond of IC,and the ISA may be further electro-degraded to small molecules at more positive potentials.