The reduction of dispersed indigo by cathodically formed 1,2,4-trihydroxynaphthalene

Electrochemical characteristics and dyeing properties of selected 9,10-anthraquinones as mediators for the indirect cathodic reduction of dyes

“…As shown in the literature, cyclic voltammetry is well suited to characterise AQs with regard to their electrochemical properties in the context of alkali soluble mediators [17,18,27,31]. From voltammograms, information about the suitability of a chosen AQ can be obtained.…”

“…The use of 1,8-dihydroxy-9,10-anthraquinone to enhance cathodic indigo reduction, reduction by glucose and bacterial indigo reduction, has been reported [27e30]. Soluble 9,10-anthraquinoids such as lawsone also have been applied as mediators for indirect cathodic indigo reduction [31].…”

Voltammetry and spectroelectrochemistry of solid indigo dispersed in carbon paste

“…The water-insoluble indigo is reduced by reducing agents such as sodium dithionite and iron(II) triethanolamine complex to soluble leucoindigo which, having penetrated into the material to be dyed, is oxidized back to the original indigo by oxygen. The reducing agents required in the dyeing process lead to problematic waste products, therefore electrochemical reduction processes, both direct [1][2][3][4] and indirect [5][6][7][8][9], are being developed as an environmentally-friendly alternative to the traditional chemical reduction. In addition, the electrochemical studies of indigo also focused on the redox properties of indigo [10][11][12][13][14][15], the electrochemical determination of indigo species [16][17][18][19][20][21][22][23], and the electro-oxidation of indigo for the treatment of textile wastewaters [24].…”

Comparison of sodium dithionite and glucose as a reducing agent for natural indigo dyeing on cotton fabrics

“…These ions can cause ecological problems, for example, SO 3 2-can be easily oxidized to SO 4 2-and the high concentration of SO 4 2-can cause corrosion in concrete pipes [9]. Thus, our approach in this work is to use glucose as a green reducing agent instead of Na 2 S 2 O 4 in natural indigo dyeing process.…”

“…In Thailand, indigo is called "Kramm" and indigo plants, Indigofera tinctoria, are grown mainly in the north-east areas such as Surin, Udon Thani, Kalasin and Sakon nakhon [2]. The water insoluble indigo pigments consist of a conjugated dicarbonyl system [3] that can be reduced to a leuco form by a reducing agent in an alkaline condition (pH 11-14) before applying on cellulosic fibers [4]. Only air oxidation is enough to convert a leuco dye to the original indigo pigment inside the fibers [5].…”