Download Synergistic effect of sterilization by microwave-excited atmospheric-pressure plasma jet using photo-catalyst TiO2 with H2O2 and distilled water

Synergistic effect of sterilization by microwave-excited atmosphericpressure plasma jet using photo-catalyst TiO2 with H2O2 and distilled
water.
H. Wk. Lee1, Y. S. Seo1, S. K. Kang1, H. J. Seo2, J. Choi1, Seung-Jin Park1, Jae-Yoon Sim1, S. M. Jeon2 and J. K.
Lee1
1
Department of Electronic and Electrical Engineering, Pohang University of
Science and Technology, Pohang, 790-784, S. Korea
2
Department of Chemical Engineering, Pohang University of Science and
Technology, Pohang, 790-784, S. Korea
Abstract: A microwave-excited atmospheric-pressure plasma jet is applied to
inactivate Gram-positive bacteria, S. mutans using photo-catalyst TiO2 with H2O2.
Unlike UV-based sterilization methods, a significant synergy on the bactericidal
effect is observed when the plasma is combined with TiO2 and H2O2 at a time.
All the bacteria samples used in ~4´107 CFU/ml of concentration are destructed
within 30 seconds. A kinetic simulation shows plenty of electrons having more
than 5 eV in the high-frequency discharge, which can dissociate O-O and O-H
bond in H2O2 and water molecules. This indicates that OH radical may contribute
dominantly in this experiment. We conclude that the energetic electrons as well
as UV photons from the plasma are likely to significantly contribute to the fast
disinfection via effective interaction with TiO2 and H2O2 or H2O.
Keywords: list 3-5 relevant keywords
1. Introduction
Sterilization has been one of common research
topics in biomedical applications [1]. Many
researchers employed H2O2 based on
conventional UV method with photo catalyst
such as TiO2 to enhance bactericidal effect [2].
Low temperature plasma has been proposed as a
noble sterilizer which is more effective than UV
method, and the atmospheric non-thermal
plasmas with TiO2 have also been suggested to
enhance the inactivation of bacterial spores, B.
subtilis [3].
In this study, a low-temperature microwaveexcited plasma technology using the coaxial
transmission line resonator atmospheric pressure
plasma jet (APPJ) [4] and either TiO2 or H2O2
(3 % H2O2 solution) or both is presented as a
new powerful sterilization method.
2. Results and discussion
Figure 1. (a) Survival curve of S. mutans according to the
treatment method and time, and (b) survival curve of S. mutans
for observing temperature and UV effect. Simulation result of (c)
electron temperature, (d) percentage of high energy electron
and (e)O radical emission intensity by OES measurement .
Figure 1 (a) shows the result of Streptococcus
mutans(S. mutans) sterilization experiment.
While TiO2 with plasma case (TP treatment) did
not show significant sterilization effect, H2O2
with plasma case (HP treatment) significantly
promote the sterilization efficacy (filled square).
In particular, the plasma treatment of using both
H2O2 and TiO2 (HTP treatment) resulted in
outstanding inactivation of S. mutans, all the
bacteria were killed in 30 s. It should be noted
that there was significantly synergistic
bactericidal action of the HTP treatment in
comparison with two cases, TiO2 with APPJ (TP
treatment) and H2O2 with APPJ.
Figure 1 (b) shows the effect of heat, UV and
charged particles produced from the APPJ. A
quartz was located between the APPJ and the
sample to block the charged particles and other
chemical species, and pass UV only. In the case
of only UV, three log-reductions were achieved
in 60 s, while the HTP treatment induced the
destruction of all the bacteria in 30 s (25 s for
grounded case). This indicates clearly that the
charged particles of the plasma as well as UV
photons significantly interact with H2O2 and
TiO2 and consequently contribute to enhance the
sterilization process by photo-catalyst with
H2O2.
It is well-known that TiO2 needs more than 3.2
eV for photolysis, and the bond energies of O-O
and O-H on H2O2 are 146 (~1.51 eV) and 418.4
(~4.35 eV) kJ/mol, respectively. In the
computational study based on particle-in-cell
method, The percentage of energetic electrons
more than 5 eV was 53.8 % in the 900-MHz
discharge compared to 6 % in the 13.56-MHz
discharge (Fig. 1(c)) [5]. A recent work also
showed that microwave (2.45 GHz) plasma can
generate a majority of energetic electrons (Fig. 1
(d)) [6]. The analysis of optical emission spectra
also supports the result (Fig. 4c). The intensity
of atomic oxygen lines at 777 nm of the HTP
treatment was increased almost two-fold on
average from the only plasma treatment (Fig.
1(e)).
In summary, a synergistic effect on Grampositive bacteria sterilization by the microwaveexcited APPJ with TiO2 and H2O2 was observed.
The energetic electrons more than 5 eV with UV
photons in the APPJ may contribute to activate
the photo-catalyst, TiO2 nanoparticles and
dissociate the bonds of H2O2. As a result, the
ROS generation is more enhanced and the
outstanding rapid disinfection is achieved.
Acknowledgement
The authors thank Prof. T. H Chung and H. M.
Joh of Dong-A university for the OES
measurement. This work was supported by Midcareer Researcher Program through NRF grant
funded by the MEST (2011-0015395) and the
Korea Ministry of Education, Science, and
Technology through its Brain Korea 21 program.
References
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(2005)
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(2010)
[4] J. Choi et al., Plas. Sour. Sci. Tech., 18, 025029,
(2010)
[5] F. Iza et al., Phys. Rev. Lett., 99, 075004 (2007)
[6] Y. S. Seo et al., IEEE Trans. Plasma Sci., 38,
5540307, (2010)