A Study Of Electrochemical Reduction Of Indigo

Electrochemical reduction of vat dyes (including indigo and sulfur dyes) is a new attempt for dyeing. Based on the research and development of vat dyes at home and abroad, we chose the electrochemical reduction as research direction, indigo for raw materials. The mechanism of direct and indirect eleltrochemical reduction of indigo were discussed. The indirect electrolysis of indigo employing Fe-TEA as mediator on stainless steel cathode was mainly studied.ChapterⅠprovide the background for the research, including indigo’s character, production, and apparatus for indigo dyeing. The new dyeing methods and the application of electrochemical dyeing were also introduced.ChapterⅡfocuses on the experiment contents and methods.In chapterⅢ, the direct electrochemical reduction behavior of indigo on silver and glassy carbon electrode was discussed. The cathodal reduction experiment of indigo was carried out by cyclic voltammetry and linear sweep voltammetry. The influence of scan rate on the electrochemical behavior of indigo and the amount of electron were studied. The results showed that: (1) Direct electrochemical reduction of indigo was feasible in thermodynamics. (2)The electrochemical reduction of indigo on glassy carbon electrode is a two-electron process. (3) It was found that the leuco indigo was oxidized to solid indigo and deposited on the silver electrode. The thickness of coating and the size of indigo granule were increased gradually with the increasing of electro-oxidation time.In chapterⅣ, we studied the influence of electrode material, scan rate, the molar ratio of Fe(Ⅲ):TEA, pH and temperature to the indirect electrochemical reduction of indigo. The mechanism of indirect electrochemical reduction of indigo was dicussed. In addition, influencing factors on indirect electrolysis, including the current, the temperature, the concentration of NaOH and Fe(Ⅲ)-TEA were investigated with an orthogonal experiment.The results show that: (1) In graphite, silver, nickel and stain steel four kinds of materials, we choose stain steel as cathode material because of its advantages at price and machining. (2) There two mediators and two kinds of mechanism during indirect electrochemical reduction of indigo, one mediator is Fe(Ⅲ)-TEA, the other one is indigo radical. (3) The orthogonal electrolysis experiment showed that indigo can be reduced entirely in this system, high current efficiency (>40%) can be achieved in the optimized conditions and the concentration of Fe(Ⅲ)-TEA mediator was the main influencing factor under the corresponding reaction conditions.