22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Analysis of the active species generated in the DBD surface treatment reactor
S. Kodama and H. Sekiguchi
Tokyo Institute of Technology, Depart of Chemical Engineering, JP-153-8550 O-okayama, Meguro-ku, Tokyo, Japan
Abstract: Plasma emission during the DBD surface treatment of lemon peel was analysed
by spectroscopy to understand the effect of active species generated in plasma on the
essential oil extraction. A peak attributed to the emission of OH radical was observed, and
the existence of the peak suggests the decomposition of surface layer of the peel and
enhances the essential oil extraction.
Keywords: DBD, surface treatment, spectroscopy
1. Introduction
DBD easily generates a non-thermal atmospheric
pressure plasma by application of a high-voltage AC or a
pulse to the reactor. The DBD reactor generally consists
of two electrodes separated by at least one insulating
dielectric barrier. The DBD has advantages in surface
processing and plasma chemistry because of its low gas
temperature, low power consumption, and use of simple
equipment.[1, 2]
We have reported the treatment of lemon peel aiming to
enhance the extraction of essential oil.[3] From the
surface analysis of the plasma-treated peel, it was
supposed that the surface layer of the peel was damaged
and etched by the discharge, and the treatment forms
small defects as shown in Fig. 1. The essential oil
evaporation during steam distillation was enhanced by
flowing through the defects. In this study, plasma
emission during the DBD surface treatment of lemon peel
was analysed by spectroscopy to understand the effect of
active species generated in plasma on the essential oil
extraction.
1 mm, alumina plate) so that the position of the plasma to
be fixed. The gap distance between the dielectrics was 5
mm. A lemon peel sample was removed from a fruit and
sliced to be the size of 10 mm × 10 mm × 4 mm, and
placed between two dielectric plates. For the controlled
experiment, an aluminium piece (5 mm × 10 mm × 4 mm)
was placed there. The plasma emission was monitored by
a CCD camera (Hamamatsu C4880-49-24A), equipped
with spectrometer (Hamamatsu C5094) and image
intensifier (Hamamatsu V3346U-04). The image
intensifier was equipped with a streak camera
(Hamamatsu C7700-01). The wavelength was calibrated
by the illumination from a low-pressure mercury lamp
(Hamamatsu L937-02).
Fig. 2. Schematic diagram of the plasma reactor
Fig. 1. Modification of sample surface by DBD treatment
2. Experimental
The experimental setup used in this study is shown in
Figs. 2 and 3. 10 ml/min of argon gas was introduced to
the plasma reactor during the treatment for all
experimental conditions. A 50 Hz AC high voltage power
supply was connected to the electrodes equipped in the
reactor and supplied up to 40 kV pp (peak-to-peak). The
applied voltage and discharge current were monitored
with an oscilloscope (LeCroy WaveSurfer 44Xs), a highvoltage probe (Tektronix P6015A) and a current probe
(Tektronix P6021). The electrodes were smaller in size
(φ3 mm) compared to the dielectrics (50 mm × 50 mm ×
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Fig. 3. Schematic diagram of the experimental setup
3. Results and discussion
The plasma emission spectra in the presence of lemon
peel and aluminium piece are shown in Fig. 4. The spectra
were essentially the same for that in the presence of
aluminium piece (control). However, a small peak around
309 nm was observed as shown in Fig. 5. This peak is
supposed to be attributed to the OH radical emission,
suggesting that the water vapor, which evaporated from
the defects generated on the lemon peel, was excited and
1
formed OH radical. The surface of lemon peel is covered
with hydrophobic (wax) layer, and it prevents from the
evaporation of moisture from the skin. It is expected that
the plasma generated in the applied voltage 40 kV has
enough power to decompose the surface layer (wax layer)
of the lemon peel, and the extraction of essential oil
during the steam distillation process enhanced by the
production of defects. However, the plasma generation
conditions are required to be normalized for the
application because it is strongly affected by the
experimental conditions such as gap distance, sample size
etc.
steam distillation process enhanced by the production of
defects.
5. References
[1] H.-E. Wagner, R. Brandenburg, K. V. Kozlov, A.
Sonnenfeld, P. Michel, J. F. Behnke, Vacuum, 71, 417
(2003)
[2] Z. Falkenstein, J. J. Coogan, J. Phys. D: Appl. Phys.,
30, 817 (1997)
[3] S. Kodama, B. Thawatchaipracha, H. Sekiguchi,
Plasma Process. Polym. 11, 126 (2014)
Fig. 4. Plasma emission spectra of lemon peel treatment
and control experiment
Fig. 4. Locally enlarged plasma emission spectra
4. Conclusion
Plasma emission during the DBD surface treatment of
lemon peel was analyzed by spectroscopy. A peak
attributed to the emission of OH radical was observed at
309 nm, suggesting that the water vapor, which
evaporated from the defects generated on the lemon peel,
was excited and formed OH radical. It is expected that the
plasma generated in the applied voltage 40 kV has enough
power to decompose the surface layer (wax layer) of the
lemon peel, and the extraction of essential oil during the
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