Chemistry Reference
In-Depth Information
7
Advantages of electrocatalytic reactions in
textile applications: example - electrocatalytic
oxidation of sodium dithionite at a
phthalocyanine and porphyrin cobalt(II)-
modified gold electrode
P. WESTBROEK
7.1
Introduction
Sodium dithionite has several applications as a reducing agent, for example
in the reduction of textile dyes for dyeing processes. This reduction is crucial
for the process because the oxidised form of most of these dyes (indigo,
indanthrenes, etc.) is virtually insoluble in aqueous solutions. However,
sodium dithionite is relatively unstable and reacts with oxygen, potentially
causing a rapid decline in its concentration during processing
1,2
.This can
have a serious influence on the actual reduced dye concentration and on
the quality and reproducibility of the dyed textile product.
In Chapters 3-6, the development of sensors to measure concentrations
of chemical components important in the textile industry is discussed for
hydrogen peroxide in bleaching
3-6
, sodium dithionite
7-10
and sulphite
8,10
in
dyeing, as well as the dyes themselves such as indigo
10
and indanthrenes
7,9
.
These investigations focused primarily on voltammetric and amperometric
detection of these components using rotating-disc
3-9
, ultramicro
5
and wall-
jet electrodes positioned in flow-through cells
10
.To support the insight into
the analytical determination of the concentration of the above-mentioned
chemicals, the mechanism
11-13
, kinetics
11-14
and reagent transport proper-
ties
8,11-14
of the oxidation/reduction reactions used for their analytical
detection was also discussed in those chapters. The reason for initiating
the above-mentioned investigations on sodium dithionite and associated
dye sensor development was that the poor detection limit of about
5 ¥ 10
-4
mol l
-1
is not low enough to use this sensor in waste-water monitor-
ing. For that purpose, the sensor should be able to detect lower concentra-
tions, which can be obtained by electrocatalysis.
In this chapter, it will be shown that the detection of sodium dithionite
on bare gold electrodes can be improved by electrocatalysis using a
cobalt(II)tetrasulphonated phthalocyanine, sodium salt (CoTSPc) or a
5,10,15,20-tetrakis-(4-sulphonatophenyl)porphyrin cobalt(II), tetrasodium
salt (CoTSPor) as catalyst. The selection of these catalysts was based on
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