Research Journal of Applied Sciences, Engineering and Technology 4(18): 3386-3390, 2012
ISSN: 2040-7467
© Maxwell Scientific Organization, 2012
Submitted: March 31, 2012
Accepted: April 17, 2012
Published: September 15, 2012
Investigation on Synthesis of Zinc Oxide-Polyethylene Oxide Composite
Nano-Fibers by Electrospinning Method
F. Ashrafi and S.A. Babanejad
Department of Chemical, Faculty of Science, Payame Noor University, Tehran, Iran
Asstract: Studying on nano-fibers is an interesting investigation because of their very small diameter and this
gives them a very extent surface area in relation to their volume. Surface interaction of nano fibers is greater
than different structure of materials because of their extent surface area. Geometrically, nano-fibers arranged
in one dimensional materials category. These one dimensional structures have special properties comparing to
other materials, because of their high flexibility and inelasticity characteristics. If the core of nano-fiber is filled
by nano particles then they will have a nano-fibers structure. In this study electrospinning method has selected
for nano fiber and nano composite synthesis, among the different methods. Essentially, electrospinning process
is based on tensioning a polymer solution under high voltage. Firstly, nano particles of zinc oxide have
processed by chemical method and then these they were used in synthesis of zinc oxide-polymer composite
nano-fibers. These synthetic composite nano fibers were studied by Raman scattering, UV-Visible and IR
spectroscopy, also by Scanning Electronic Microscopy (SEM) and Transmission Electronic Microscopy (TEM).
The results of Raman characterization affirm formation of ZnO nano particles in the form of Poly Vinyl
Pyrrolidone (PVP) polymer fibers. SEM images show that the synthesized nano fibers PEO/ZnO have an
average diameter of 277 nm. SEM images have shown also, the diameter of these nano fibers is not the same
along their length, i.e., they have not the same cross section along the length of nano fiber.
Keywords: Composite nano-fiber, electrospinning, nano particles, raman scattering spectroscopy, SEM
INTRODUCTION
Although, nano-fibers synthesis by electrospinning
method is the results of research and evolution of ideas of
different researchers in several decades, but
electrospinning is a process developed by Formhals
(1934) to create polymer fibers via the electrostatic force
(Formhals, 1934). Formhals was reported the results of
different experiments for polymeric fibers synthesis by
using electrostatic forces, in1934-1944. Vonnegut and
Neubauer (1952) were able to produce streams of highly
electrified uniform droplets of about 0.1 mm in diameter
(Vonnegut and Neubauer, 1952). Drozin investigated the
dispersion of a series of liquids into aerosols under high
electric potentials (Drozin, 1955). Simons patterned a
method for producing of light nano-textiles (simons,
1966). Baumgarten has made a device for electrostatic
spinning of acrylic microfibers of about 0.5 to 1.1 : in
diameter (Baumgarten, 1971). Then, during afterward
years, particularly in recent years, electrospinning method
was developed and extended for producing nano-fibers
from different type of polymers (Ramakrish et al., 2005;
Huang et al., 2003; Chronakis, 2005).
Nano-fibers have very interesting flexibility and
inelasticity characteristics, because they have a high
surface area per mass unit. For example, this may be
about 10000 to 1000000 (Song et al., 2005). Their large
surface area, leads to provide a high capacity for binding
to different types of nano particles. Nowadays, synthesis
of polymer and composite polymer nano-fibers, because
of their considerable applications, is much more desirable.
There are many techniques for synthesizing polymer and
composite polymer nano-fibers, in this study
electrospinning method was used (Huang et al., 2003).
Electrospinning process consists of creating a high
voltage between a reservoir containing polymer solution
and having a capillary of maximum 0.3 mm in diameter
and the target metallic plate where nano-fiber will be
collect. High voltage between polymer solution and
collecting plate causes an electrical force which creates a
stream from inside of capillary to collector. In order that
the fluid can flow, electrical force must overcome surface
tension of polymer. The fluid in the end of capillary takes
the shape of tailor cone, as critical voltage was reached,
then the flow of polymer begins from the end of cone.
Instability in flexibility cause narrowing of flow and
forms nano-fiber over metallic plate.
Zinc oxide is a semiconductor which due to its wide
bond gap (3.37 eV) (Morkoc et al., 1994) and interesting
optical properties (nonlinear) (Michelotti et al., 2003), has
Corresponding Author: F. Ashrafi, Department of Chem.ical, Faculty of Science, Payame Noor University, Tehran, Iran
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Res. J. Appl. Sci. Eng. Technol., 4(18): 3386-3390, 2012
Table 1: Materials properties and electrospinning process conditions for PEO polymeric nano-fibers
Materials properties
Electrospinning process conditions
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------Surface stress
Electrical conductivity
Temperature Rate of feeding
(mL/h)
Solvent
(dyne/cm)
(mS/m)
Sample No.
Gap (cm)
Voltage (kV) (oC)
DMF
37.10
1.090
1
15.0
14
25
0.5
polyethylene oxide
2
17.5
14
25
0.5
3
20.0
14
25
0.5
PEO, Mw . 400000
been the aim of much more investigations consisting
semiconductors. A significant characteristic of ZnO is its
high electron-cavity dependency energy, which results in
extreme stability of electron-cavity dependency (Chen
et al., 1998). It is well known that semiconductors of
small dimension, because of quantum restrictions, may
have very interesting optical properties (Dong et al.,
2006; Schwartz et al., 2003). These properties and actual
applications of ZnO, results in much more studies for
providing nano structures of ZnO, so that synthesis of
ZnO nano structures as nanorods and nanowires, nano
particles and nano composite fibers are widely reported
(Jiang et al., 2005; Müller and Wei, 1994; Karanth and
Fu, 2005; Vayssieres, 2003; Sui et al., 2007).
In this approach we have provided nano particles of
ZnO and then have synthesized zinc oxide-polymer
composite nano-fibers by using Polyethylene Oxide
(PEO) as polymer basis. The structure and characteristic
of nano composite fibers were studied by Raman
scattering, UV-Visible and IR spectroscopy, also by
Scanning Electronic Microscopy (SEM) and Transmission
Electronic Microscopy (TEM).
C
C
C
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MATERIALS AND METHODS
This study was performed in Payame Noor
University, Tehran, Iran, as a research project on
synthesis of polymeric nano-fibers and nano composites
in 2010 and 2011.
Materials: Polyethylene Oxide (PEO) (Mw . 400000),
N, N-Dimethylformamide (DMF), Zinc acetate dihydrate
((CH3COO)2 Zn.2H2O) and Tetramethylammonium
Hydroxide (TMAH).
Electrospinning system: The system which have used in
this study consist of following sections: stainless steel
rotary cylindrical collector, high voltage system (23 kV,
100 mA, accuracy . 100 V), polymer solution feeding
system (using a micro-pump for uniform output of either
polymer or polymer composite solution, minimum output
flow = 1 mL/h). This system has been placed inside of a
hood, for preventing any propagation of nano-fibers in air.
This electrospinning system have been designed and
mounted in nano-fiber and nano composite laboratory of
Tarbiat Modarres University.
Method of synthesizing ZnO-polyethylene oxide
composite nano-fibers: Synthesis of these composite
nano-fibers was performed four stages as following:
Providing suitable polyethylene oxide solution for
electrospinning process, polymer powder was added
gradually into DMF solvent and agitate by a stirrer at
25ºC for 1 h. Materials properties and electrospinning
process conditions were indicated in Table 1.
Providing ZnO nano particles, firstly we have
prepared 0.5 M zinc acetate by dissolving required
amount of CH3COO)2 Zn.2H2O in DMF solvent.
Then we add TMAH solvent within an interval of 20
min, by burette, for hydrolyzing initial solution in
proportionality 1 to 1/4 of zinc acetate to TMAH.
Note that, this step performs inside a bath of cold
water and was agitated by a stirrer throughout the
process.
For preparing polymeric composite solution, obtained
solution of ZnO nano particles (stage 2) was added to
polyethylene oxide solution (stage 1) in different
volume proportions. Then, this composite solution
was agitated by a magnetic stirrer for 1 h in order to
obtain a homogeny distribution of nano ZnO nano
particles in solution.
Electrospinning process was performed by charging
the micro-pump with composite solution (prepared in
stage 3).
Injecting this solution by micro-pump and
introducing start up voltage for initiating electrospinning
process, causes that polymeric solution induced by
repulsion forces of similar electrical charges via electrode
of high voltage source and attractive forces due to
grouping of opposite charges over rotary electrode, spout
towards rotary cylindrical collector. The spouting
composite traversing its pathway towards collector
undergoes instability in flexibility, so that, while
achieving collector, will traverse a spiral pathway and will
collected over stainless steel rotary cylindrical collector.
During process, the diameter, length and shape of nanofibers may be controlled by voltage changes, distance
between two electrodes, the rate of polymer solution
injection and the velocity of rotary electrode.
RESULTS AND DISCUSSION
Studying raman spectra of ZnO composite nano-fibers
synthesized by electrospinning method: There two
types of nano-fibers which were synthesized from
different ZnO nano particles solution with different
volume proportionality, by electrospinning method in the
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Res. J. Appl. Sci. Eng. Technol., 4(18): 3386-3390, 2012
Absorbence
Raman intensity (a.u)
(c)
(b)
T = 25 oC
T = 180 oC
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
200
300
400 500 600 700 800
Wave length (nm)
900
1000
(a)
Fig. 3: UV-visible spectra of ZnO nano particles, after
filtering the solution containing these nano particles
and drying in two different temperatures, 25 and
180oC, respectively
3000
2500
2000
1500
Raman shift (cm-1)
1000
500
Fig. 1: Raman spectra (a), (b) and (c) for ZnO-PEO composite
nano-fibers in relation with 15, 17.5 and 20 cm gaps,
respectively, for low concentrations of ZnO nano
particles
(f)
Raman peaks, Raman peaks due to ZnO nano particles,
also, are present. But in the region where the peaks of
ZnO nano particles must be appear, there is only a large
peak at 325 per cm. This peak was extended
asymmetrically towards the upper wave numbers and
overlap throughout the region. Thus, due to its high
intensity, any sign of vibrating mode of nano particles,
even, by increasing in ZnO nano particles concentration
the peaks, couldn’t be observed. This may be interpreted
as following:
Raman intensity (a.u)
C
Considering that ZnO molecules are polar and
asymmetric, peak intensity of this compound is
essentially weak.
(e)
Therefore, because of its low intensity and presence
of other impurities, probably, its Raman peak can’t
be observed.
C
(d)
3000
2500
2000
1500
Raman shift (cm-1)
1000
C
500
Fig. 2: Raman spectra (d), (e) and (f) for ZnO-PEO composite
nano-fibers in relation with 15, 17.5 and 20 cm gaps,
respectively, for high concentrations of ZnO nano
particles
same conditions, was studied. The spectra of low and high
concentration of ZnO nano particles were shown in
Fig. 1 and 2.
Because, these are Raman spectra, of composite
nano-fibers, we must expect that in addition to polymer
Reference Raman spectra of Aldrich Co., consider
much more peaks of vibrating modes, for PEO
molecules, in this region. In the other hand, vibrating
modes of ZnO lie, also, in the same region,
consequently, it may be probable overlap of these
vibrating modes results in a large peak which was
observed at 325 per cm.
If matrix spattering curves in a composite polymer is
not in accordance with the same one for material
which is composed, then the possibility of vibrating
phonon propagation occurs only for the substances
which have high luminescence. Generally, in such
substances, related peaks appear in different regions
of spectrum. In the case of our study, eventually,
such interpretation may be admissible.
Studying UV-visible spectrometry: Further, we have
noted that ZnO is a semiconductor with a wide gap bond
(3.37 eV). Considering the fact, we will study UV-visible
spectra of ZnO nano particles which have dried in 25 and
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Res. J. Appl. Sci. Eng. Technol., 4(18): 3386-3390, 2012
Fig. 4: SEM images obtained for ZnO-PEO nano-fibers; gap energy is 20 cm, voltage is 14 kV, rate of feeding is 0.5 mL/h, and
average diameter of fibers is 277 nm
180oC. UV-visible spectra of ZnO nano particles are
shown in Fig. 3.
The spectrum obtained in room temperature, shows
a peak at 968 nm which is not present in the spectrum
obtained in 180oC. Since ZnO is transparent at visible
wave length due to its wide gap bond, therefore, the
mentioned peak may be attributed to existent impurities.
As it can be observed, after drying in 180oC this peak
disappears and not any more present. Adsorption wave
length approximatively was placed at 364 nm which
predicts a gap energy of about 3.4 eV which is compatible
with gap energy of ZnO.
SEM images of ZnO-PEO nano-fibers: Studying SEM
images of ZnO-PEO nano-fibers, we can confirm
formation of fibrous structure of materials obtained from
electro spinning method and their nano scales. Synthesis
suitable nano fibers with adequate elongation and an
average diameter in nano scale, needs much more
investigations and experiments, providing different
samples with different concentrations and determination
of electrospinning conditions. Figure 4 shows SEM
50
Frequency
40
30
20
10
0
150
200
250
300
Fibers diameter (nm)
350
400
Fig. 5: Distribution diagram of diameter of nano-fibers; gap
energy is 20 cm, voltage is 14 kV, rate of feeding is 0.5
mL/h
images of ZnO-PEO composite nano-fibers which have
synthesized in our experimental conditions which are
explained above. Figure 5 shows distribution diagram of
ZnO-PEO composite nano-fibers in the same conditions
discussed above.
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CONCLUSION
Raman spectrometry shows that the spectrum of
polymer fibers is similar to polymer powder one and the
peaks present in both spectra haven’t so differences. This
represents that polymer solvent will evaporate during
electrospinning process and for this reason there is not
any sign in fibers spectra.
By Raman spectrometry we have satisfied formation
of ZnO nano-fibers composite in PEO polymer matrix.
The results obtained from UV-visible spectra show
that the range of adsorbed wave lengths, partly is due to
electronic transition of polymer molecules and partly is
due to inter-bonds transition of semiconductor nano
particles in composite.
SEM images show that synthesized nano-fibers of
ZnO polymer composite, have an average diameter of 277
nm and show also, the diameter of these fibers varies
along its length.
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