Fe3+--gluconate and Ca2+-Fe3+--gluconate complexes as mediators for indirect cathodic reduction of vat dyes ? Cyclic voltammetry and batch electrolysis experiments

Abstract

The indirect cathodic reduction of dispersed vat dyes CI Vat Yellow 1 and CI Vat Blue 5 was investigated by cyclic voltammetry and with batch electrolysis experiments. 0.01molL−1 solutions of the complexes Fe3‰+--gluconate and Ca2‰+-Fe3‰+--gluconate were studied. The addition of dispersed dyestuff to the mediator solution lead to a catalytic current. While the cathodic peak currents of both complexes is comparable, Fe3‰+-DGL shows higher enhancement factors, which are defined as quotient of catalytic peak current and cathodic peak current of the mediator system (Ip)c/(Ip)d. In the presence of 0.5gL−1 of dispersed vat dye enhancement factors of 1.8 were determined at scan rates of 0.005–0.010Vs−1. Galvanostatic batch reduction experiments with use of a laboratory multi-cathode cell confirmed the favourable properties of the Fe3‰+-DGL in comparison to the binuclear Ca2‰+-Fe3‰+-DGL. With use of the Fe3‰+-DGL mediator complete dyestuff reduction could be achieved. The batch reduction process was followed experimentally by photometry and redox potential measurement in the catholyte.