Abstract
Indigo has been widely used as a dye in the industrial dyeing due to its good color fastness in dyeing cellulose fibers. However, excess reducing agent, “insurance powder (Na2S2O4)”, was always used in the actual production of the factory, sparking serious pollution (water pollution and air pollution). Herein, we developed a practical and environment-friendly indirect electrochemical reduction of indigo, and applied this method for cloth dyeing. The electrochemical device was designed in the combination of source of electro-catalytic reduction and dyeing. The iron-triethanolamine-calcium gluconate (Fe-TEOA-Ca) complex played a role of key intermediate, and ultrasonic wave was found to speed up the indirect electro-catalytic process. The electrochemical performance of intermedia was improved by calcium ion addition. Washed with oxalic acid solution, the dyed fabric could achieve the level of color fastness in industry standard. Generally speaking, our method leads to a green route for indigo reduction using electrochemistry, which may change the crafting process of indigo dyeing in industry.
Highlights
Indigo has been widely used as a dye in the industrial dyeing due to its good color fastness in dyeing cellulose fibers
Direct electro-chemical reduction leads to a straightforward way for indigo reduction, while the efficiency is too poor to satisfy the practical use of industry as the mass-transfer between indigo solution and cathodes[14,15]
After the complement of electrochemical reduction, the catholyte was transferred to dyeing tank for dyeing by a water pump
Summary
Indigo has been widely used as a dye in the industrial dyeing due to its good color fastness in dyeing cellulose fibers. We developed a practical and environment-friendly indirect electrochemical reduction of indigo, and applied this method for cloth dyeing. Indigo has shown great application in the dyeing industry due to its good color fastness in dyeing cellulose fibers, especially in the light resistance, water washing and chlorine bleaching process[1,2]. In the dyeing process (Fig. 1a), indigo needs firstly to be reduced to a water-soluble leuco indigo. We developed a practical and environment-friendly indirect electrochemical reduction of indigo, and applied this method to cloth dyeing (Fig. 1c). After washing with oxalic acid solution, the dyed fabric could achieve the level of color fastness in industry standard This method provides a green route for indigo reduction and dyeing with indirect electrochemistry
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