Ferric-oxalate-gluconate based redox mediated electrochemical system for vat dyeing

The voltammetric behaviour of the ferric-oxalate-gluconate system is investigated along with some electrochemical dyeing results. The results are compared with the conventional ferric-triethanolamine-gluconate system on a glassy carbon electrode. The ferric-triethanolamine redox system is stable and exhibits quasi-reversible redox behaviour in alkaline medium. The ferric-oxalate system undergoes hydrolysis and precipitates above pH 8. Vat dyeing requires the stability of the redox system in alkaline solutions. The ferric-oxalate redox system alone cannot satisfy this requirement. However, in the presence of excess gluconate, both systems exhibit stability in alkaline media. Mechanistic studies indicate the formation of ferrous-gluconate as the reducing agent for vat dyeing from these mediator systems. Electrochemical dyeing was also carried out in the mediator system under investigation. Colour depth was characterized by the Kubelka-Munk value (K/S) and CIE Lab-coordinates for the dyed fabrics and was found to be comparable with samples dyed using sodium dithionite as the reducing agent.