Electrocatalytic recycling of indigo dye from waste denim fabric: an engineering approach toward efficient denim dye reuse

The denim fabric industry has experienced exponential growth and escalating concerns regarding sustainable production and recycling practices. The wide utilization of indigo dye in denim manufacturing presents significant challenges owing to its intricate chemical structure and inherent resistance to degradation. Improper disposal of waste denim fabric and the release of indigo dye impose severe ecological ramifications. In this study, we explore the productive application of electrochemistry to recycle indigo dye from waste denim fabric while repurposing the electrolyte for denim dyeing. Notably, the separation of indigo from waste denim textiles reaches 82.34%. It is calculated that 21.59 g of indigo can be recovered from 1 kg of denim waste. Recovered indigo can be reused for cotton yarn dyeing. In the experiment, indigo was recovered from 0.03 square meters of denim waste, and the K/S value of the yarn was up to 2.997 after five dyeing cycles. The loss of fabric strength after recycling is as low as 13.32%, which has little effect on secondary fabric recycling. Our recycling method reduces the waste of 978.41 g of waste fabric and 21.59 g of indigo per kilo compared to conventional treatment. This research provides compelling scientific evidence supporting adopting a closed-loop system within denim production, underlining the potential for environmentally conscious and economically viable practices in the industry.