Practical and environment-friendly indirect electrochemical reduction of indigo and dyeing

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 (Na 2 S 2 o 4)", 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.

Indigofera tinctoria leaf powder as a promising additive to improve indigo fermentation prepared with sukumo (composted Polygonum tinctorium leaves)

“…On contact with atmospheric oxygen, it oxidises to a blue form (Clark et al 1993;Głowacki et al 2012). Fermentation by bacterial, chemical and electrochemical reduction, and catalytic and electrocatalytic hydrogenation can be used to reduce indigo (Chavan 2015;Yi et al 2020;Nakagawa et al 2021). Industrial dyeing commonly involves the reducing agent sodium dithionate (Głowacki et al 2012).…”

Sodium dithionite mediated one-pot, tandem chemoselective reduction/cyclization for the synthesis of pyrrole fused N-heterocycles

“…Sodium dithionite (Na 2 S 2 O 4 ) is largely used in the textile industry and for the preparation of dyes. 5 However, Na 2 S 2 O 4 has never been employed in the reduction of a nitro group in industry. Despite being a cheap (30$ per kg, ©Thermo Fisher), non-toxic, greener and more sustainable alternative to conventional metal-acid reduction, the use of Na 2 S 2 O 4 in the reduction of nitro groups remains underexplored and limited to only a few recent reports.…”

Cleaner Dyeing Technology for Denim Fabrics with Excellent Utilization of Indigo Based on Inert Gas Protection

“…11 However, no method has yet been successfully used for large-scale dyeing that replaces Na 2 S 2 O 4 , such as conventional fermentation, 12 biological reduction, 13 using glucose as the reducing agent, or electrochemical reduction. 14 Herein, we report the use of different N 2 protection approaches to overcome the problems of energy hunger and pollution caused by the conventional denim dyeing process of indigo reduced by Na 2 S 2 O 4 . First, we demonstrate the feasibility of applying such an efficient approach to use N 2 protection.…”

“…Consequently, developing dyeing and finishing technologies with high fixation rates, low energy consumption, and quick processes suitable for denim dyeing is critical to clean dyeing and sustainable denim production . However, no method has yet been successfully used for large-scale dyeing that replaces Na 2 S 2 O 4 , such as conventional fermentation, biological reduction, using glucose as the reducing agent, or electrochemical reduction …”