Electrochemical Reduction Of Indigo Research Articles

Electrochemical reduction of indigo by combination of sodium borohydride and copper salt

PurposeThe purpose of this study is to improve the performance of sodium borohydride in reducing indigo at room temperature, the divalent copper ion complex was combined with electrochemical technology for the reduction of indigo by sodium borohydride.Design/methodology/approachAccording to the K/S value of the dyed cloth sample, find a more suitable ligand for the copper ion in the catholyte. Response surface analysis tests were performed to evaluate the effects of sodium borohydride concentration, sodium hydroxide concentration and copper sulfate pentahydrate concentration on the reduction potential of the dye solution and the K/S value of the dyed fabric samples.FindingsSodium gluconate was found to be a more suitable ligand for copper ions in catholyte. The effects of NaOH concentration as well as the interaction of NaBH4 and NaOH on the reduction potential of the catholyte and the K/S value of the dyed fabric samples were extremely significant. The optimal concentrations of NaBH4, NaOH and CuSO4•5H2O were 0.5, 2.5 and 0.65 g/L. In the case of the optimized condition, the absolute value of the reduction potential was 968, and the K/S value was 11.92, which is comparable with that of the conventional reduction process with sodium dithionite.Originality/valueThe divalent copper ion complex combined with electrochemical technology was applied in the process of reducing indigo with NaBH4 at room temperature.

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 %).

Electrochemical reduction of indigo in fixed and fluidized beds of graphite granules

Reducing agents required in the dyeing process for vat and sulfur dyes cannot be recycled and lead to problematic waste products. The electrochemical reduction of indigo on a fixed bed cathode consisting of graphite granules has been investigated by spectrophotometric experiments in laboratory cells. Experiments yield information about the kinetics and show the possibility of this process for production of water soluble leuco indigo, which offers environmental benefits. The influence of noble metals deposited on the granules and of different pretreatment methods of the graphite is demonstrated. In addition, the immobilization of quinoid molecules on the graphite surface has been investigated.

Electrolytic Reduction of Indigo in Pyridine Application to the Determination of Dissolved Oxygen

AbstractThe electrochemical reduction of indigo in pyridine as solvent has been investigated in connection with the determination of oxygen dissolved in pyridine, using polarography, cyclic voltammetry, controlled electrode potential electrolysis and coulometry. In the absence of protons, the total current of the first and second reduction waves for an unsaturated solution of indigo (LiClO4 as background electrolyte) apparently represents a one‐electron transfer. In the presence of an excess of available protons (added as pyridinium nitrate), indigo is reduced in a reversible two‐electron process to indigo white (leucoindigo). The rapid conversion of indigo white to indigo by oxygen in pyridine solution can be used to determine coulometrically the concentration of oxygen in pyridine via measurement of the indigo produced on adding the pyridine‐oxygen sample to a solution of in situ electrolytically generated indigo white. The latter approach indicated a general method for the determination of dissolved oxygen in nonaqueous solvents.