Optimization and assessment on indirect electrochemical reduction of indigo

Purpose An indirect electrochemical reduction and dyeing with indigo were carried out here to solve problems of low dye reduction rate and poor dyeing depth in the current electrochemical dyeing process. Design/methodology/approach Response surface analysis tests were performed to evaluate the effects of ferrous sulfate concentration, medium concentration, sodium hydroxide concentration and reduction time on the reduction efficiency of indirect electrochemical reduction of indigo. Findings The conditions obtained by design-expert optimization showed that the concentration of FeSO 4 ·7H 2 O has the most significant effect on the reduction performance of dye liquor. Under the optimized electrochemical reduction dyeing process, the rate of dye reduction could be reached 91.21 per cent and the K/S value of indirect electrochemical dyeing of indigo can be achieved to 12.96, which is increased by about 9.56 per cent compared with that of Na 2 S 2 O 4 dyeing with the same color fastness basically. Research limitations/implications The recyclability and biodegradability of the dye remain to be explored. Practical implications The strategy presented here can be developed to replace a substantial part of electrochemical dyeing with optimized product quality and reduced environmental pollution in denim production. Social implications The strategy presented here can be developed to replace a substantial part of electrochemical dyeing with optimized product quality and reduced environmental pollution in denim production. Originality/value Application of the Fe(II)-DGS-Abal B complex media system in the indirect electrochemical reduction of indigo.