Decolorization Study of Indigo Carmine by Atmospheric Pressure Microplasma
Naoto Masamura, Marius Blajan and Kazuo Shimizu
Organization for Innovation and Social Collaboration, Shizuoka University,Jyouhoku, Hamamatsu, 432-8561, Japan
E-mail：shimizu@cjr.shizuoka.ac.jp

Power supply

AC(2) Decomposition rate forvarious carrier gases

Carrier gas

Air

60

Flow rate [L/min. ]10TargetIndigo carmine

Concentration [mg/L]

10Treatment volume [ml]200

Introduction
In recent years, associated with industrial
development, water pollution became
aserious problem. Plasma could be used as watertreatment technology for the decompositionof organic compound and sterilization ofbacteria.
Conventional technologies requires expensive
processes or the usage of chemicals for water
treatment. Microplasma is an ecological andeconomical technology to be applied for water
treatment due to the low cost and low
discharge voltage[1].

Methods
Microplasma Electrode and Mechanism

A neon transformer was used as the AC highvoltage power supply. The carrier gases were
supplied in case of the air from an air pumpand in case of N2, Ar and O2 from gas
cylinders. It flowed above the reactor andpassed through the holes of electrodes.
Indigo carmine was used as the target to be
decomposed. The treated sample was analyzed
by UV-VIS, ozone monitor and ESR(ElectronSpin Resonance).

Electrode Feature

5040
30
20
100O2Air

5.6

8.0

5.4

7.5
5.2

7.0
6.5

5.0

6.0

4.8

5.5

4.6
4.4

4.5

05

10

4.0
1.0

1.1

1.2

1.3

Fig. 4 `Power consumption of microplasma
electrode using AC power supply.

0.6

no treatment
0.4

10 min. treatment

0.3

300

400

500

O

SO3H

600

700

SO3HHNHNO

Indigo carminemg/LIndigo carmine
solutionppm

Water pumpOzone monitor

Fig. 3 An experimental setup
for water treatment.

3420

3440

34603480

an ESR measurement.

OUV-VIS-50

0.1

Isatin sulfonic acid

Fig. 5 Chemical reaction of indigo carmine
promoted by microplasma treatment.
Electrodes

0Fig. 9 OH signal detected by3ESR

50

0.2

O
2・OH, OHV probe

100

3500

Magnetic field [G]

20 min. treatment

HN

HO3S

200-200
3400

The decrease of 610 nm and 300 nm peaks
suggested that organic compounds containedin indigo carmine solution was decomposedduring microplasma treatment.

Flow meter(4)ESR analysis

-150

0.5

Oscilloscope

Air pump

The pH value was changed to the acidproperty. It saturated at about 4.8.

-100

Fig. 4 Absorbance of the indigo carmine
solution before and after microplasma
treatment (Vd=1.0 kV).

HV

microplasma treatment.

Intensity [a.u.](1)Observation ofindigo carmine solution absorbanceWavelength [nm]Current
probe

35150

Results

200

Experimental Setup

30Fig. 7 pH value changed by theMicroplasma electrodes power consumption isless than 10 W as shown in Fig. 4. Thus
microplasma is ecological technology.

0Fig. 2 Emission of microplasma(Vd=1.0kV).

152025Treatment time [min. ]Discharge Voltage [kV]

Absorbance [a.u.]

Microplasma
electrodes
areperforated
metallic plates covered with a dielectric layer
and faced together with a spacer of 100 μm.
Microplasma electrodes were placed at small
distance above the water thus gas is flown
towards the water surface to react with thetarget to be decomposed. Various active
species such as ozone, OH radical etc. weregenerated by microplasma. Microplasma wasgenerated at relatively low discharge voltage
as a typical dielectric barrier discharge.

N2

The decomposition rate was calculatedby the absorbance value. In the case of
air and oxygen were higher due to theactive species of oxygen origin.
(3)The change of the pH value

8.5

5.0

Fig. 1Mechanism of water treatment
by microplasma.

ArFig. 6 The decomposition rate of indigo
carmine for various carrier gases(Vd=1.0kV).

pH

Power Consumption [W]9.0

Decomposition rate [%]Table.1 Experimental parameters.

Indigo carmine has the H type chromophoricgroup which gives the blue color. Double bond
(C=C) was cut thus OH radicals and ozone
presence lead to the formation of a new bond2(C=O). As a result, Indigo carmine wasdecomposed to as a by-product of plasma
treatment process be isatin sulfonic acid.

Spin trap agent 5,5-dimethyl-1-pyrroline
N-oxide was used to perform ESR analysis.
Generated OH radical by microplasma wereobserved at 3450, 3460, 3430, 3480 gauss.

Conclusions
Microplasma could be used as an ecologicaland economical technology. Water treatmentusing microplasma was carried out.
1. Indigo carmine was decomposed after
microplasma treatment and decomposition
rate was reacted to 70% with thetreatment time.
2. OH radical was one of the causes of indigo
carmine decomposition. It was dissolved in
the water as confirmed by using ESR
analysis.
3. Active species of oxygen origin were themost effective for decomposition process.

Reference[1] Y. Shen, L. Lei, X. Zhang. M. Zhou and Y.
Zhang,
EnergyConversion
andManagement 49 pp. 2254-2263(2008).