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Synthesis, properties and application of polyindole/TiO2
nanocomposites
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2009 J. Phys.: Conf. Ser. 187 012058
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Synthesis, properties and application of polyindole/TiO2
nanocomposites
Vu Quoc Trung1
and Duong Ngoc Huyen2
1Faculty of Chemistry, Hanoi National University of
Education,
136 Xuan Thuy Road, Cau Giay District, Hanoi, Vietnam2Institute
of Engineering Physics, Hanoi University of Technology,
1 Dai Co Viet, Hanoi, Vietnam
E-mail: [email protected]
Abstract. Nanocomposites of polyindole (PIn) and TiO2 were
prepared by chemicalpolymerization. The morphology of nanocomposite
particles was studied by scanning electronmicroscopy and
transmission electron microscopy. The chemical structure of
conducting polymers in nanocomposites was characterized by FTIR and
Raman spectra. The thermalanalysis showed that all conducting
polymers in the nanocomposites were stable at more than600oC. The
corrosion protection of the nanocomposites was investigated.
Keywords: Nanocomposite, polyindole, titanium dioxide, corrosion
protection.
1. Introduction
In recent years, several conducting polymers have received
increasing attention as material coatings
for the protection of common metals against corrosion. In
particular, polyaniline and polypyrrole have
been found to sufficiently reduce the corrosion of steel and
other oxidizable metallic materials [13].
Several reports have been published on polyindole and its
derivatives although its close structural
similarities with polyaniline and polypyrrole [46].
Polyindole is an electroactive polymer, which can be usually
obtained after anodic oxidation of
indole in various electrolytes; electro-chemical oxidation of
indole in LiClO4 containing acetonitrile
electrolyte medium gives an electrochromic polymer film with
good air stability. In its doped state,polyindole has a green
colour and an electrical conductivity in the range of 1010 Scm,
depending on
the nature of the counter ion [7, 8]. It is also reported that
polyindole films have the advantages of
fairly good thermal stability, high redox activity and slow
degradation rate in comparison with
polypyrrole and polyaniline [9, 10]. However, there was a lack
of reports on the chemical
electrosynthesis of PIn or PIn composites.
In this paper, nanocomposites of polyidole and TiO2 were
prepared by chemical polymerization.
The morphology and properties of nanocomposite and were studied
by scanning electron microscopy
(SEM), transmission electron microscopy (TEM), FTIR, Raman
spectra and thermal gravimetric
analysis (TGA). The corrosion protection of the nanocomposites
was investigated.
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Experimental
1.1. Preparation of nanocomposites
All nanocomposites were chemically prepared as the procedure
described in Ref. [11]. Firstly, a
dispersion was prepared by mixing (for 30 minutes) of 10.0 g
TiO2 (Merk) and 1.0 mL indole
monomers (Guangzhou Jihuada Chemical, China) in 50.0 ml
distilled water. Then 4.5 g FeCl 3 (water-
free, Fluka Chemie) was added to the oxide particle dispersion
during stirring. After 2 hours of
stirring, the particles were cleaned by distilled water,
filtered, extracted for 10 hours and dried at 50oC
for several days under low pressure.
1.2. Characterization of nanocomposites
TGA of prepared samples was measured by Ghimashu-50 H with scan
rate of 10oC/min in ambient
conditions. The X-ray diffraction patterns of TiO2 and TiO2
nanocomposites were measured by
Simens D-5005. The chemical structure of the nanocomposites was
characterized by Fourier transforminfrared spectroscopy (FT-IR) and
Raman spectroscopy. FTIR spectra were performed by GBC Cintra
40-Nicolet Nexus 670 FT-IR. Raman spectra were measured by a
Laser Raman spectrophotometer
(Ramalog 9I, USA). The Van der Pauw method was used to measure
the dependencies of dark
conductivity on reciprocal temperature, as acquired on pressed
pellets. The electromagnetic shielding
features of the nanocomposites were performed by HP8720D Network
Analyzer (USA).
1.3. Investigation of metal corrosion inhibition [12]
The corrosion inhibition of the PIn/TiO2 nanocomposite was
performed by electrochemical methods
using potentiostatic technique. The electrochemical equipment
was AUTOLAP 30 composed from a
potentiostat in order to make a polarized potential or current.
A computer with suitable software
(GPES) controls the measurement system and analyses the obtained
data.
The solution containing typical eroded ion Cl- (using HCl 3%)
was used. The material for corrosioninvestigation was a cylinder
(horizontal section: 1 cm), made by the construction steel CT3
(TISCO
company, produced in Thainguyen, Vietnam) with standard: GOST
001-2001 - TCVN 1656-75 (C:
0.16 %; Mn: 0.62 %; Si: 0.15 %; P: 0.010 % and S: 0.042 %).
Before using, it was polished by rough
paper 1000, and then cleaned by distilled water and ethanol.
The sample of the PIn/TiO2 nanocomposite (marked DTC) was
prepared as a mixture of 0.1g
nanocomposite and 1.0 g polyvinyl alcohol (PVA). Then this
mixture was covered to be a thin film on
the surface of the steel. Three other samples were prepared for
comparison. The first one was made by
only 1.0 g PVA (marked D0). The second one was made by a mixture
of 0.1 g TiO2 and 1.0 g PVA
(marked DT). The third one was made by a mixture of 0.1 g PIn
and 1.0 g PVA (marked by DP). Then
these mixtures were covered on the surface of the steel as in
the case of the PIn/TiO2 nanocomposite.
A three-electrode cell was used. A saturated calomen electrode
(SCE) was used as reference
electrode, Pt was the counter electrode and steel bar was the
working electrode. All chemicals werepure (PA, China).
2. Results and discussion
2.1. Morphology
Figure 1 shows the SEM image of the PIn/TiO2 nanocomposite
particles. The average size of the
nanocomposite particles was around 60 nm while the average size
of TiO2 particles was 50 nm. Figure
2 shows the TEM image of the PIn/TiO2 nanocomposite particles.
The black is TiO2 material and the
light is the PIn polymer. Generally, SEM and TEM images show
that the PIn/TiO 2 nanocomposite
particles presented with core-shell structure.
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Figure 1. SEM image of the PIn/TiO2
nanocomposite particles.
Figure 2. TEM image of the PIn/TiO2
nanocomposite particles.
2.2. Thermal analysis and conductivity of the PIn/TiO2
nanocomposite
Thermal analysis of the PIn/TiO2 nanocomposite was studied.
Below 120oC, the weight reduction is
originated from water inside samples (1.4%). In the range of
120-330oC, the weight reduction (3.2%)
is very small, corresponding to the decomposition of redundant
oligomers. At higher temperatures
(300-600oC), the change of weight (10%) is attributed to the
decomposition of the oxidized PIn.
Conductivity of the PIn/TiO2 nanocomposite was performed by
two-probe methods with the
pressed pellet from material powder. It showed that the
conductivity of the PIn/TiO 2 nanocomposite is
1.75 S.cm-1
. Low conductivity could be explained by the presence of
TiO2.
2.3. FTIR and Raman spectra
Chemial structure of PIn nanocomposites was characterized by
FTIR and Raman scatteringspectroscopy. The FTIR spectrum is of good
quality and the infra-red bands are well defined (figure
3). The spectrum associated with the oxidized PIn are
characterized by a very large adsorption band
located in the spectral domain between 3700 and 3100 cm-1
, which is characteristic of the OH groups
belonging to residual water molecules trapped in the polymer
matrix as well as water molecules
absorbed in PIn. The peaks at 3401, 2924, 1593, and 1312
cm-1
could be attributed to N-H stretching,
C-H (aromatic) stretching, C=C stretching and C-N stretching
(between two idole units), respectively.
Figure 3. FTIR spectrum of
PIn/TiO2 nanocomposite.
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300 600 900 1200 1500 1800
8000
16000
24000
32000
40000
1105
1330
1374 1
460
1613
410 5
10 6
31
148
RamanScattering/a.u
Wavenumber / cm-1
Figure 4. Raman spectrum of
PIn/TiO2 nanocomposite.
Figure 4 presents Raman spectrum of the PIn/TiO2 nanocomposite
measured at 514 nm with 1 mW
laser power. The peaks at 148, 410, 510, and 631 cm-1
correspond to the characteristic signals of TiO2.
The peaks at 1620, 1372, and 1107 cm-1
were attributed to C=C stretching, C-N stretching and C-H in
plane deformation.
2.4. Study of the corrosion inhibition
The potentiostatic method was applied to study the corrosion
inhibition of the eugenol derivatives. The
curves describing the dependent of the open circuit potential on
time (E 0vs. t) are showed in figure 5.
Value E0 is a parameter to appreciate the corrosion inhibition
of samples. It shows that all samples DT,
DP and DTC had higher E0 than that of D0. It means that these
samples could inhibit steel against
corrosion better than PVA. Among these samples, DTC had highest
E0 and, thermodynamically, E0
presented the best corrosion protection.
Figure 5. The plots of open circuit
potential of the test samples vs. time (in
solution of HCl 3%).
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Figure 6. Tefel curves of the test
samples (in solution of HCl 3%).
Do DT DP DTC
0.024
0.032
0.040
0.048
0.056
icorr
(mA/cm
2)
Sample Figure 7. Corrosion current density ofthe test
samples.
In a 3% solution of HCl, the corrosion inhibition of DTC
presented remarkably well by transferring
positively the Tafel plots (figure 5). Therefore, the corrosion
potential was also more positive. From
Tefel plots and GPES software, the corrosion current density was
determined (figure 6). All samples
containing TiO2, PIn and PIn/TiO2 nanocomposite have lower
corrosion current densities, in which
sample DTC performed the lowest current density.
Figure 8. Electrochemical
impedance spectroscopy of the test
samples (Z is the imaginary part
and Z is the real part).
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Figure 8 shows the electrochemical impedance spectroscopy (EIS)
of the test samples. The order of
the impedance is DTC >DP > DT >> D0. By using FRAS
software, resistances of the charge transfer
(Rct) and of the polarization (Rp) were determined (figure 9).
It shows both the resistances of thecharge transfer and of the
polarization of samples.
Figure 9. Resistance of charge
transfer (Rct) and of the
polarization (Rp).
Generally, from the results of EIS measurements were in the
agreement with open circuit potential
and corrosion current measurements. These results show that the
corrosion inhibition of the PIn/TiO 2
was the best.
3. Conclusions
In this paper, the PIn/TiO2 nanocomposites were prepared by in
situ polymerization. SEM and TEM
imagesshow that the composites are obtained with nanostructure.
The chemical structure of PPy in
nanocomposites was characterized by FTIR and Raman spectra. The
thermal analysis TGA showedthat PPy in the nanocomposites was
stable at around 600
oC. The corrosion inhibition of the PIn/TiO2
nanocomposite was investigated by the polarization and
electrochemical impedance methods. It
showed that the PIn/TiO2 nanocomposite can protect the mild
steel against corrosion. It is the
foundation for producing the environment-friendly paints.
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