22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Production of reactive oxygen and nitrogen species during driven dc
atmospheric pressure glow discharge generated in contact with liquid
P. Jamróz, A. Dzimitrowicz, K. Greda and P. Pohl
Wroclaw University of Technology, Faculty of Chemistry, Division of Analytical Chemistry and Chemical
Metallurgy, Wybrzeze Stanislawa Wyspianskiego 27, PL-50370 Wroclaw, Poland
Abstract: The stable atmospheric pressure glow discharges (APGDs) were generated in
contact with a flowing liquid cathode. As an anode, a gaseous argon and helium microjets
or a metallic electrode were applied. All discharges were operated in the ambient air
atmosphere at a supplied power lower than 40 W. The different atomic and molecular
species were excited in the core of these discharges. The emission spectra of the
investigated APGDs were dominated by the bands of the OH, N 2 , NO, and NH molecules.
In addition, the atomic O I and H and ionic O II emission lines were identified. The
mechanisms of the processes occurred in the interfacial discharge-liquid zones as well as in
the liquid phases and responsible for the production of the reactive species were discussed.
The production of H 2 O 2 , NO 3 -, NO 2 - as well as the OH radicals in the liquid phase and the
fall of the solution pH was confirmed.
Keywords: atmospheric pressure glow discharge, plasma – liquid interaction, reactive
oxygen species, reactive nitrogen species
1. Introduction
The cold atmospheric plasmas, sometimes called as the
non-thermal plasmas or the atmospheric pressure plasmas,
generated in and in contact with liquids are frequently
applied in the studies related to the environmental
protection and the biomedical engineering [1,2].
Apparently from the literature, it is possible to apply such
cold atmospheric plasmas in the water cleaning, the
sterilization, the bacteria inactivation as well as in the
environmental remediation processes and other
biochemical processes [1-5]. These plasma sources were
also applied as cheap and efficient excitation and atomic
sources in the analytical atomic spectrometry for the
elemental analysis [6].
So far, the different constructions of the cold
atmospheric plasma sources, e.g., the atmospheric
pressure glow discharge, the dielectric barrier discharge,
the corona plasma, the pulsed plasma, the transient spark
discharge and the plasma needles, have been successfully
employed in the various processes related to the emerging
field of the plasma medicine [1,2,5]. Among them, the
atmospheric pressure glow discharges generated in and in
contact with liquids were established to be the rich
sources of the various oxygen (ROS) and nitrogen (RNS)
chemically active species, e.g., hydrogen peroxide
(H 2 O 2 ), singlet oxygen (1O 2 ), ozone (O 3 ), hydroxyl
(OH), hydroperoxyl (O 2 H) and oxygen (O) radicals,
superoxide (O 2 -) ions, hydrogen peroxonitrate (ONOOH),
NO and NO 2 [3,4]. Being rich sources of the reactive
oxygen species and the reactive nitrogen species, the
atmospheric pressure glow discharges could also be
applied for the bio-decontamination and the purification
of the water samples in a continuous flow mode, which is
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rarely encountered in the literature. They could also be
used for the fast and cheap synthesis of the biocompatible
nanoparticles [4].
The main aim of the present work was to elucidate the
discharge-liquid interactions as well as the production of
the chemically reactive species in the discharge and in the
liquid phase of different atmospheric pressure glow
discharges generated in contact with flowing liquid
cathodes. The emission spectra of the discharge were
determined and compared in order to clarify what kind of
the elementary processes exist in the atmospheric pressure
glow discharge sources. The suitability of the described
atmospheric pressure glow discharge sources in the
biomedical engineering was also evaluated.
2. Experimental setup
The atmospheric pressure glow discharges were
generated in contact with liquid cathodes. A schematic
representation of the discharge systems used in the
present work is given in Fig. 1. The stable discharges
were resulted from applying high voltages (1000-1300 V)
to the electrodes.
1
OH
N2
NH
NO
N2+
OH
b)
Fig. 1. The experimental set-up (not to scale).
Atmospheric pressure glow discharges were obtained
by the direct-current (dc) discharge with a miniature
argon or helium gas flow passed through a steel nozzle
(internal diameter 0.5 mm) or a molybdenum rod anode
(outer diameter 2 mm).
A high voltage (HV) positive bias direct current (dc)
power supply with a maximum power output of 200 W,
working in the discharge current range within 0-100 mA,
was used. Additionally, a ballast resistor (R=10 kΩ)
working in the anode circuit was applied to stabilize the
discharge current. Atmospheric pressure glow discharges
were operated in the ambient air atmosphere at a
discharge current of 40 mA. A peristaltic pump (Lab
Craft, France) was applied to deliver the water sample
solutions into the discharge zone.
The water sample solutions, treated by both
atmospheric pressure glow discharges, were collected into
10-mL stoppered glass tubes and directly analysed by the
chemical methods of the analysis (using the UV-Vis
absorption spectrophotometry as well as the fluorescence
method).
Additionally, a production yield of the reactive species
in the plasma gaseous phase was investigated using the
optical emission spectroscopy. For this purpose, a JY
Triax 320 monochromator (with holographic gratings:
1200 and 2400 grooves per mm and a R-928P
photomultiplier) and a miniaturized CCD spectrometer
(Blue Wave UV2) with optical fibers were applied. The
emission of the atmospheric pressure glow discharges was
measured in the discharge-liquid interfacial zone.
3. Results and discussion
The typical emission spectra of the atmospheric
pressure glow discharges (APGDs) are presented in Figs.
2a, 2b and 2c in the range of 200-900 nm.
As can been see on the Fig. 2, the NO, N 2 and OH
species were easily excited in all analysed discharges.
a)
2
N2
Na
H
O II
c)
Ar
H
O
O
Fig. 2. The emission spectra of atmospheric pressure glow
discharges generated in contact with flowing liquid
cathodes in the range of a) 200-400nm b) 400-600 nm and
c) 600-900 nm
The most prominent was the (0-0) band of the OH
radical at 306.4 nm belonging to the A2Σ-X2Π system and
the (0-0) band at 337.1 nm of the N 2 molecule belonging
to the second positive system (C3Π u -B3Π g ). In the 200270 nm spectral region, numerous bands of the NO
molecule, belonging to the γ-system (A2Σ+-X2Π), were
also observed. The atomic hydrogen (H) lines of the
Balmer series (at 656.2, 486.1 and 434.1 nm) as well as
the atomic oxygen (O I) at 777.2, 777.4 and 844.6 nm and
the ionic oxygen (O II) at 441.5, 459.1, 459.6, 467.4,
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466.6 and 470.7 nm emission lines were noted for all the
investigated discharges. The (0-0) and (1-1) bands of the
NH molecule (the A3Π-X3Σ- system) with the band heads
at 336.0 and 337.0 nm were also identified especially in
the case of the atmospheric pressure glow discharge
operated with the argon microjet. The relatively weak
bands of the N 2 moleculte (the B3Π g -A3Σ+ u system) in the
range of 650-750 nm were excited in the case of the
atmospheric pressure glow discharge system with both the
argon or helium microjets. Additionally, only for the
discharge system with the argon microjet numerous
atomic argon (Ar I) emission lines in the spectral range of
650-800 nm (with the excitation energies within 13-15
eV) as well as the weak (0-0) and (0-1) bands of the N 2 +
molecule (the B2Σ+ u -X2Σ+ g system) at 391.4 and 427.8
nm, respectively, were noted. It should be noted that the
intensities of the NO and N 2 molecular band heads
observed for the atmospheric pressure glow discharge
with the helium microjet were higher in comparison to
those obtained with the atmospheric pressure glow
discharge system with the argon microjet or the pin
electrode. On the other hand, the most intense emission of
the OH molecule was noted in the systems with the pin
electrode and the argon microjet. Moreover, the studied
atmospheric pressure glow discharge sources were
established to produce an intensive UV radiation.
The OH radicals with an oxidation potential of 2.80 V
were probably generated in the interfacial zone as a result
of the processes of water dissociation and/or their ions
(e.g. H 2 O+) coming from the sputtering/ionization
processes of the water molecules [3, 4] e.g.:
(1)
H 2 O + e = H + OH + e
H 2 O+ + e = H + OH
(2)
H 2 O+ + H 2 O = H 3 O+ + OH
(3)
The formation of the OH radicals in the liquid phase
was confirmed using the chemical dosimetry method with
terephthalic acid. A LED diode (working at 310 nm) was
applied as a light source to excite the product of the
reaction of terephthalic acid with OH radicals, i.e., 2hydroxyterephthalic acid. The fluorescence signal of the
latter compound was detected at 425 nm and confirmed
the production of the OH radicals in the liquid phase.
It was presumed that the NO/NO 2 molecules were
produced in the discharge zone as a result of the reaction
of nitrogen coming from the air atmosphere with oxygen
[3], e.g.:
N 2 + O = NO + N
(4)
N + O 2 = NO + O
(5)
NO + O + M = NO 2 + M
(6)
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In the solutions treated by the discharges, the hydrogen
peroxide molecules (H 2 O 2 ) and the nitrate (NO 3 -) and the
nitrite (NO 2 -) ions were identified.
The source of H 2 O 2 was probably the oxidative
processes of water or other reactions [3,4,7], e.g.:
+ H2
2H 2 O* = H 2 O 2
(7)
OH + OH = H 2 O 2
(8)
The main sources of the nitrite and the nitrite ions were
nitric oxide (NO) and/or nitric dioxide (NO 2 ) [3,8]. These
species reacted with the OH radicals or water molecules,
e.g.:
(9)
NO + OH = HNO 2
NO 2 + OH = HNO 3
(10)
2NO 2 + 3H 2 O = NO 3 - + NO 2 - + 2H 3 O+
(11)
In each case, the growth of the concentration of the
H 3 O+ ions and consequently a drop of the pH in the
solutions treated by the discharges were also observed,
probably due to the reactions of nitrogen oxide with water
or the OH radicals (see reactions 9-11). The fall of the pH
in the solutions is rather connected with the enhanced
production of nitric acid (HNO 3 ).
Under the acidic conditions, hydrogen peroxonitrate
(ONOOH) with an oxidation potential of 2.44V could
also be produced from the nitrate ions (NO 2 -) and the
hydrogen peroxide molecules (H 2 O 2 ) [5, 9]:
(12)
NO 2 - + H 2 O 2 + H 3 O+ = ONOOH + 2H 2 O
The identified reactive species could act as oxidants in
the various biochemical and biotechnology reactions. In
order to confirm the role of the reactive species in the
selected biochemical systems, some additional
experiments would be performed.
4. Conclusions
The stable non-thermal direct current atmospheric
pressure glow discharges were generated in contact with
the flowing liquid cathodes using different kinds of the
anode system, i.e., the solid pin and argon or helium
gaseous microjets. The all atmospheric pressure sources
were operated in the open to air atmosphere.
The following species: N 2 , NH, NO, OH, H and O were
excited in the examined discharges. Additionally, the
atmospheric pressure glow discharge sources emitted the
relative strongly radiation in the UV range. Hydrogen
peroxide (H 2 O 2 ), the OH radicals in addition to the nitrate
(NO 3 -) and the nitrite (NO 2 -) ions were identified in the
water sample solutions treated by these discharges as a
result of the chemical reactions occurred in the interfacial
discharge-liquid zone. A growth of the concentration of
the H 3 O+ ions in the liquid phase was noted for all the
examined atmospheric pressure glow discharge systems.
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5. References
[1] A. Fridman and G. Friedman. Plasma Medicine,
Willey (2013).
[2] Y. Yang, Y. I. Cho and A. Friedman. Plasma
discharge in liquid. Water treatment and applications,
CRC Press Boca Raton (2012).
[3] P. Jamróz, K. Gręda, P. Pohl, W. Żyrnicki. Plasma
Chem Plasma Process., 34, 25(2014).
[4] P. Jamróz, K. Gręda and P. Pohl. Plasma Process.
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[5] Z. Machala, B. Tarabova, K. Hensel, E. Spetlikova, L.
Sikurova and P. Lukes. Plasma Process. Polym., 10, 649
(2013).
[6] K. Greda, P. Jamroz and P. Pohl. J. Anal. At.
Spectrom., 28, 1233 (2013).
[7] B. R. Locke and K. Y. Shih. Plasma Sources Sci.
Technol., 20, 034006 (2011).
[8] X. Liu, H. Zhang, D. Qin, Y. Yang, Y. Kang, F. Zou
and Z. Wu. Plasma Chem. Plasma Process., 35, 321
(2015).
[9] T. Shimizu, Y. Iwafuchi, G. E. Morfill and T. Sato.
New J. Phys., 13, 053025 (2011).
6. Acknowledgement
The work was financed by a statutory activity subsidy
from the Polish Ministry of Science and Higher Education
for the Faculty of Chemistry of Wrocław University of
Technology.
The project supported by Wroclaw Centre of
Biotechnology, the programme The Leading National
Research Centre (KNOW) for years 2014-2018 was also
acknowledged.
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