The degradation of organic dyes by corona discharge Page: 6 of 16
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A concentration of 6 (ig/mL of dye in water was used in all
cases. This concentration was chosen because it was found to
show best results without overloading the sensitivity of the
detector. Absorbance was measured continuously using a
submersible fiber optic cell, supplied with the PC600
colorimeter. Current between the two electrodes (stainless
steel and platinum) was measured continuously, using a
picoammeter. Typically, 5 - 15,000 Volts were used which
resulted in a current of Ca . 10 to 50 p.A. Current
fluctuations of Ca. 10% were often present, largely due to
rigorous stirring. When the magnetic stirrer bar was
removed, or the stirrer was turned off, current fluctuated
only slightly. All experiments were carried out with one
control. Controls consisted of aliquots of mixed solutions
of dye which were stirred adjacent to the exposed fractions,
but without current between the electrodes.
Several experiments were carried out exposing methylene
blue, malachite green, and other dyes to corona discharge in
the presence of air, using the reaction vessel shown in
Figure 1. All dyes were dissolved in water as described in
Methods. In the presence of air and at ambient temperature,
methylene blue lost most of its color (absorbance) within
four hours of exposure to 10 kV and 20 |1A or corona
discharge. Figure 2 shows the change in absorbance of a
6.0 jlg/ml. solution of methylene blue at 664 nm both with and
without (control) exposure to corona discharge.
Approximately half of that absorbance was lost within one
hour under these conditions. There was little or no change
in absorbance after 4.5 hours of exposure to corona
discharge. The experiment was ended after 24 hours.
Malachite green (Figure 3) and new coccine (Figure 4)
behaved in a similar manner in the presence of corona
discharge and under the same conditions.
Experiments were also performed under different
atmospheric conditions (in the presence of N2, O2, He,
individually) to determine their effect on reaction rates.
Results from these experiments indicated dyes reacted rapidly
only in the presence of oxygen and corona discharge to form
colorless solutions (Figures 2-4) . For these and in
subsequent experiments, methylene blue was chosen rather than
all three dyes.
Experiments were performed to measure the effect of
current on bleaching rate of methylene blue (Figure 5) .
Current was adjusted by changing the voltage. Reaction rates
were measured as a function of current by following the loss
of color. The reaction rate increased with increasing
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Goheen, S.C.; McCulloch, M.; Durham, D.E. & Heath, W.O. The degradation of organic dyes by corona discharge, article, February 1, 1992; Richland, Washington. (digital.library.unt.edu/ark:/67531/metadc1092124/m1/6/: accessed January 16, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.