Indirect Electrochemical Reduction of Indigo and Dyeing

The method of electrochemical reduction utilizes electrons as agent to achieve the reduction of indigo, vat dyes and pollution emissions, as well as the recycling of electrolyte. In this study, Ca2+-Fe3+-triethanolamine (TEA) redox system was used as the mediator to achieve the indirect electrochemical reduction of indigo. The optimization of parameter was analyzed by reduction efficiency (RE) and current efficiency (CE). The result showed that indigo could be reduced by electrochemical method and the best optimization recipe was 20 g/L NaOH + 5 g/L Fe2(SO4)3 + 30 g/L TEA + 5 g/L Calcium gluconate + 3 g/L indigo in 1 A·dm-2 current density at 50°C. This work suggested that Ca2+-Fe3+-TEA redox system in reduction of indigo was an effective way with higher CE (75.9 %).