Bulletin of the Chemists and Technologists of Macedonia, Vol. 25, No. 1, pp.

4550 (2006)
GHTMDD 482 ISSN 0350 0136
Received: March 20, 2006 UDC: 547.551.1 : 544.653
Accepted: June 6, 2006
Original scientific paper
ELECTROCHEMICAL POLYMERIZATION OF ANILINE IN PRESENCE
OF TiO
2
NANOPARTICLES
Irena Mickova, Abdurauf Prusi, Toma Grev, Ljubomir Arsov*
Faculty of Technology and Metallurgy, Ss Cyril and Methodius University,
P. O. Box 580, MK-1001 Skopje, Republic of Macedonia
*arsov@tmf.ukim.edu.mk
The electrochemical polymerization of aniline from acid aqueous solutions of 1 M H
2
SO
4
in presence of TiO
2

nanoparticles was performed by cyclic voltammetry. The heterogeneous polymerization of new synthesized materials
from aniline monomers and electrodeposited TiO
2
polymer coated nanoparticles was analyzed using electrochemical
techniques. During the repetitive cyclic voltammetry scans the presence of TiO
2
nanoparticles inhibits the polymer
related oxidation process and diminishes the degradation products in the composite materials. Good adhesion of
composite materials on the Pt electrode, with superior electro-active repetitive properties in relation with pure poly-
aniline, was demonstrated.
Key words: polyaniline; TiO
2
nanoparticles; cyclic voltammetry
EEKTPOXEMHCKA HOHMEPH3AHH1A HA AHHHH BO HPHCYCTBO
HA

HAHOHECTHHKH O TiO
2

Co noxom na nnxnnna no1axe1n|a e ncnn1ynana eex1oxexncxa1a nonxen:ann|a na annnn
no xncen nonn ac1non no nncyc1no na nanonec1nnxn o TiO
2
. Hexy xe1eoiena nonxen:ann|a e
cnn1e1n:nan non xoxno:n1en xa1en|a o annnncxn xonoxen n eex1oeno:n1nann nanonec1nn-
xn o TiO
2
. Do 1exo1 na nonexexa1na nnxn:ann|a nncyc1no1o na nanonec1nnxn o TiO
2
|a nnxnona
eaxnn|a1a na oxcnannona1a nonxen:ann|a, m1o yconyna naxaynane na eiaannonn noyx1n
no xoxno:n1nno1 xa1en|a. Hoxaana e ooa a1xe:nnnoc1 na xoxno:n1nno1 xa1en|a n: Pt-eex-
1oa1a, xaxo n neionn cynenonn eex1oax1nnnn cno|c1na no onoc na nonannnno1.
Knyunu :6npnnu: nonannnn; nanonec1nnxn o TiO
2
; nnxnnna no1axe1n|a
INTRODUCTION
In scientific terminology the term nanomate-
rials refers to substances consisting of particles
with dimensions in the order of 10
9
m (1 nanome-
ter). The novel materials at the nanolevel exhibit
new phenomena and characteristics, most of which
we just now begin to explore and understand. The
size scale, aspect ratio, and properties of nanoma-
terials provide advantages in a variety of applica-
tions, including electro-statically dissipative mate-
rials; advanced materials with combined stiffness
and strength, as well as automotive components
with enhanced mechanical properties [13].
Polyaniline is electro-conducting polymer
containing a system of conjugated double bonds,
and its properties combine semiconducting and
metal physics with the molecular and solid-state
chemistry. To make this polymer electrically con-
ductive it is necessary to introduce mobile charge
carriers. This can be done by oxidation or reduc-
tion reactions, commonly called doping and
dedoping, respectively, which can be performed
by different chemical or electrochemical process-
ing. Chemical doping-dedoping occurs when the
polymer is exposed to an oxidizing or reducing
agent, whereas electrochemical doping-dedoping
46 I. Mickova, A. Prusi, T. Grev, Lj. Arsov
Bull. Chem. Technol. Macedonia, 25, 1, 4550 (2006)
can be obtained by anodic and cathodic polariza-
tion in suitable electrolytes [46].
The nanostructured metal oxides are promis-
ing new materials for blending with polymers for
obtaining low weight nanocomposites with excel-
lent mechanical, electrical, thermal, and multifunc-
tional properties. The creation of nanocomposites
based on electro-conductive polymers and nanos-
tructured metal oxides, i.e. incorporation of inor-
ganic filler into polymer matrixes, can dramati-
cally improve their processibility [79].
The main goal in this work is to enlarge the
existing knowledge of the preparation of new ad-
vanced materials consisting of polymer matrix
with nanoparticles. The polymerization of aniline
in presence of TiO
2
nanoparticles was performed
by cyclic voltammetry. Comparative analysis of
the resulting voltammograms with and without of
TiO
2
demonstrated the creation of new composite
material.
EXPERIMENTAL
Electrodes. Pt disc with an area of 24 mm
2
,
sealed in glass, was used as a working electrode.
The electrode surface was machined flat and pol-
ished to a final smoothness of around 0.1 m on
successively finer grades of alumina powder lubri-
cated with distilled water. Than, the electrode was
cleaned in an ultrasonic bath and rinsed with etha-
nol. After each measurement the electrodeposited
film was chemically dissolved in concentrated
HNO
3
.
The counter electrode was a Pt coil with a
large surface; the reference electrode was a satu-
rated calomel electrode (SCE). All potentials pre-
sented in this work refer to the SCE reference elec-
trode.
Electrolytic cell. The electrolytic cell was
classical three compartments cell. The working
electrode was separated from the counter electrode
by a fine porosity fritted glass disc and from the
reference electrode by a Luggin capillary. The so-
lution in the cell was purged by argon for at least
15 min prior to the start of each experiment. In
every set of experiments, a new electrolyte was
used to avoid the influence of possibly formed
soluble species and olygomers.
Solutions and chemicals. Aqueous solutions
of 1 M H
2
SO
4
and 0.1 M aniline were prepared
with triply distilled water. Prior to use aniline
(Merck p.a.) was distilled to eliminate oxidized
impurities and stored in the dark place under an
argon atmosphere. Sulfuric acid (Merck p.a. 98 %)
was used as received. Commercially pure TiO
2

nanoparticles with size of 21 nm were used as re-
ceived. The suspension of 0.01 M TiO
2
nanoparti-
cles was prepared in 1 M H
2
SO
4
by vigorous stir-
ring for two hours. The final solution consisting of
1 M H
2
SO
4
, 0.1 M aniline and 0.01 M TiO
2
, was
ultrasonically treated before the measurements in
order to destroy potential agglomerates of TiO
2

particles in the solution.
Apparatus. The electrochemical measure-
ments were carried out with a HEKA Model 488
potentiostat/galvanostat interfaced with a PC.
RESULTS AND DISCUSSION
The general formula for ideal polyaniline
(PANI) materials in their base forms consists of three
benzenoid (C
6
NH
4
NH) units denoted B and
one quinoid (N=C
6
H
4
=NC
6
H
4
) unit denoted Q,
so that they can be written as [(BB)
y
(QB)
1y
]
n
.
The y value accounts to the oxidation state of the
polymer: leucoemeraldine (completely reduced,
y = 1), emeraldine salt (half reduced, y = 0.5) and
pernigraniline salt (completely oxidized, y = 0)
states [1012].
In order to determine all existing redox reac-
tions during the electrochemical polymerization
and film deposition, cyclic voltammetry measure-
ments were first performed in one larger potential
region, starting from cathodic potential of 0.4 V
(when hydrogen evolution on electrode surface
occurs), up to +1 V (when degradation products in
polymer film begin to be formed) [1314]. Fig. 1
shows typical voltammograms recorded during the
continuously applied cyclic voltammetric scans on
the virgin Pt electrode immersed in aqueous solu-
tions of H
2
SO
4
containing aniline and TiO
2
nano-
particles.
As it can see from Fig. 1, in each forward
scan 5 anodic and in each reverse scan 4 cathodic
peaks appear. The intensity of the current in the
anodic peaks; A, B, C and D, as well as in cathodic
peaks A1, B1, C1 and D1 increases in each next
cycle as a result of regular growth of polymer film
on electrode surface. The voltammogram shapes
are similar to the voltammogrames obtained during
the electro-polymerization of polyaniline without
presence of nanoparticles, reported in our previous
works [15].
Electrochemical polymerization of aniline in presence of TiO2 nanoparticles 47
Inac. xc+. cxuon. Matc0ouuja, 25, 1, 455O (2OO6)







-30
-15
0
15
30
-0.4 0.0 0.4 0.8 1.2
19
16
F
D1
C1
B1
A1
D
C
B
A
E (V) SCE
I

(
m
A
)

Fig. 1. Cyclic voltammograms from16 to 19 cycle registered
on Pt electrode in solution consisting 1 M H
2
SO
4
+ 0.1 M
anilin + 0.01 M TiO
2
(v = 5 mV/s)
The only difference is the smaller intensity of
the current peaks, especially of the redox peaks
B/B1 and C/C1, that can be associated with the
degradation products in the polymer matrix. The 4
redox peaks are assigned as: A/A1 semiquinone
radical cations, i.e. polaron states of PANI (0/+1),
B/B1 benzoquinone/hydra-quinone, C/C1 p-ami-
nophenol/quinoneimine, and D/D1 quinoid diradi-
cal dications, i.e. bipolaron state of PANI (+1/+2)
[15]. The anodic peak F has the same intensity in
each repetitive cycle and it originates from de-
sorbed hydrogen that is beeing accumulated on the
electrode surface during the cathodic polarization.
In literature data some controversy still exist
over the interpretation of the middle peaks B/B1
and C/C1 in PANI films [16,17]. They also appear
when the cyclic voltammetry measurements were
performed with higher anodic potential limits
through the redox peaks D/D1. For anodic poten-
tials before the appearance of the anodic peak D,
the only redox process on electrode surface is
characterized with the redox peaks A/A1. The po-
tential position of these redox peaks doesnt shift
with increasing cycle number, even after 500 cy-
cles, confirming the repetition of the reversible
redox reactions independent on the thickness of
the film. When the redox peaks D/D1 are reached,
the degradation of PANI films begin. For limit an-
odic potentials that are more positive then the re-
dox peaks D/D1, the middle peaks B/B1 and C/C1
gradually grow and in each next cycle the irre-
versibility of redox reactions increase. This is
manifested by gradually shifting the peaks A and
D towards anodic and peaks A1 and D1 towards
cathodic direction. The degradation products mani-
manifested by peaks B/B1 and C/C1 are soluble in
aqueous solutions and the formed PANI film begin
to peel off from electrode surface.
The PANI films can be more applicable and
effective if the potential range of anodic and ca-
thodic polarization is larger, and if the number of
repetitive cycles of redox reactions without ap-
pearance of degradation products is bigger. These
conditions can be achieved by introducing the
nanoparticles in polymer matrix that will form
composite polymer materials, diminishing the
possibility of formation of degradation products.
Shown in Figs 2 and 3 are comparative volt-
ammograms of PANI films, with and without
polymer coated nanoparticles of TiO
2
deposited on
electrode surface, for two different values of cycli-
zation rate.






-2
0
2
4
-0.2 0.0 0.2 0.4 0.6 0.8
2
1
A1
A
C1
B1
C B
A1
A
E (V) SCE
I

(
m
A
)

Fig. 2. Cyclic voltammograms of 8-th cycle registered on Pt
electrode in the solution of: 1) 1 M H
2
SO
4
+ 0.1 M aniline;
2) 1 M H
2
SO
4
+ 0.1 M aniline + 0.01 M TiO
2
(v = 20 mV/s)







-6
-3
0
3
6
9
-0.2 0.0 0.2 0.4 0.6 0.8
C1
C
B1
B
A1
A
A1
A
2
1
E (V) SCE
I

(
m
A
)

Fig. 3. Cyclic voltammograms of 8-th cycle registered on Pt
electrode in the solution of: 1) 1 M H
2
SO
4
+ 0.1 M aniline;
2) 1 M H
2
SO
4
+ 0.1 M aniline + 0.01 M TiO
2
(v = 50 mV/s)
E (V) SCE
I

(
m
A
)

E (V) SCE
E (V) SCE
I

(
m
A
)

I

(
m
A
)

48 I. Mickova, A. Prusi, T. Grev, Lj. Arsov
Bull. Chem. Technol. Macedonia, 25, 1, 4550 (2006)
In both diagrams the formation of new com-
posite materials on the base of PANI/TiO
2
is indi-
cated by shifting of the anodic peak A toward the
anodic direction, and the cathodic peak A1 toward
the cathodic direction. These shifts are more pro-
nounced for faster sweep rates, indicating notable
change in electrochemical behavior of newly syn-
thesized composite materials.
Taking into account the values of the redox-
charges under current peaks A and A1 for both
PANI films and PANI/TiO
2
composite materials
(Fig. 2. and Fig. 3.), it can be concluded that the
PANI films are much thicker comparing with
PANI/TiO
2
. The presence of TiO
2
nanoparticles in
the composite films decrease the electrical conduc-
tivity of the film resulting in a strong increase on
the peaks separation potential of the redox couple
A/A1. In addition, the redox couples B/B1 and
C/C1 of degradation products are inhibited, which
is the main advantages of the composite film.
Shown in Fig. 4 is the separation potential of
the redox couple A/A1, for both the PANI films
and PANI/TiO
2
composite films, as a function of
the sweep rate.
0
150
300
450
600
750
0 50 100 150 200
v (mV/s)

E

(
m
V
)
2
1

Fig. 4. Dependence of potential difference between peaks A
and A1 of sweep rate in solution of: 1) 1 M H
2
SO
4
+ 0.1 M
aniline; 2) 1M H
2
SO
4
+ 0.1 M aniline + 0.01 M TiO
2

According to the Nernst equation,
(mV)
59

n
E E E
C A
= =
during the cyclisation, for reversible redox proc-
esses the separation potential E between anodic
and cathodic peaks should be the same for all
sweep rate. For irreversible redox processes, as the
sweep rate is increased, the rate of mass transport
increases and becomes comparable to the rate of
electron transfer. The most noticeable effect of this
process is the increase of the potential of peak
separation E. As it can seen in Fig. 4, the separa-
tion potentials between anodic and cathodic peaks
in both cases increased with the sweep rate, but
these increases are more pronounced in composite
PANI/TiO
2
than in PANI films. It is evident that
the irreversibility of redox couple A/A1 in
PANI/TiO
2
composite films is higher than in PANI
films.
Table 1 lists some characteristic electroche-
mical parameters, for various sweep rate, taken
from registered voltammograms.
T a b l e 1
Current intensities in cathodic and anodic peaks
for various values of sweep rate registered
on Pt electrode
1 M H
2
SO
4
+
0.1 M aniline
1 M H
2
SO
4
+
0.1 M aniline +
0.01 M TiO
2

v v
1/2
I
A
I
C
I
A
/I
C
I
A
I
C
I
A
/I
C

(mV/s) (mV/s)
1/2
(mA) (mA) (mA) (mA)
5 2.23 0.21 0.22 0.95 0.15 0.15 1.00
10 3.16 0.82 0.79 1.03 0.42 0.37 1.13
20 4.47 2.57 1.93 1.36 1.00 0.78 1.28
50 7.07 7.48 5.15 1.45 2.26 1.90 1.18
100 10.00 14.8 10.4 1.42 3.80 3.48 1.09
200 14.14 26.1 19.6 1.33 6.11 5.93 1.03
v sweep rate, I
A
anodic current, I
C
cathodic current

From these values, it can concluded that the
current peaks for redox couple A/A1 are much
lower in the case of PANI/TiO
2
composite films,
indicating that appreciably less quantity of electro
active PANI species are present in this film. Ana-
lyzing the current peaks I
A
and I
C
as a function of
sweep rate, (plots: I
A
v and I
C
v, as well as
I
A
v
1/2
and I
C
v
1/2
), clearly show a better linearity
of current peaks I
A
and I
C
vs v than the current
peaks I
A
and I
C
vs v
1/2
. Such a behavior indicates
that the slowest step in the redox processes is dif-
fusion of ions in the polymer films. This conclu-
sion is in accordance with many literature results
where the diffusion constants of ions in various
electro-conducting polymer films is in order from
10
9
to 10
10
cm
2
/s, and for diffusion of ions in
electrolytic solutions, in order from 10
5
cm
2
/s [7,
8, 18]. In addition, the calculated values of redox
charges (under current peaks A and A1) for dop-
Electrochemical polymerization of aniline in presence of TiO2 nanoparticles 49
Inac. xc+. cxuon. Matc0ouuja, 25, 1, 455O (2OO6)
pimg and dedopping processes were determined as
~55 mF/cm
2
(for PANI films), and ~20 mF/cm
2

(for PANI/TiO
2
composite films).
Taking into account that the usual values for
redox capacitance of electro-conductive polymer
films are mainly located in the region from 300
400 F/g, or 50 65 Ah/kg, for PANI with an ap-
proximately density of 1.6 g/cm
3
, the polymer
film thickness in Fig. 2, after 8 cycles, can be es-
timated to be approximately 2 m. The polymer
thickness of PANI/TiO
2
composite films is much
lower, but for more precise determination of this
value the additional investigations, especially the
density of composite material, are needed.
Concerning the reversibility/irreversibility of
the redox couple A/A1 in both films (PANI and
PANI/TiO
2
), the diagnostic tests showed existence
of quasi-reversible systems. For reversible proc-
esses: E = 59/n (mV), the position of peaks po-
tential are independent of sweep rate, and the ratio
(I
A
/I
C
) = 1 and I
A
and I
C
are proportional with v
1/2
.
For totally irreversible processes there is no ap-
pearance of reverse peaks and for quasi reversible
processes, I
A
and I
C
increase with v
1/2
, but are not
proportional to it, E is greater than 59/n (mV)
and increases with increasing v, the ratio (I
A
/I
C
) = 1,
provided
A
=
C
= 0.5, and the potential position
of the cathodic peak E
C
shifts negatively with in-
creasing v. In our case, all diagnostic tests for both
PANI and PANI/TiO
2
films fit well to quasi-
reversible systems. In addition, for all investigated
sweep rates, the current ratios (I
A
/I
C
) of PANI/TiO
2

composite films are close to 1, indicating ap-
proximately equal transfer coefficients of anodic

A
and cathodic
C
processes.
CONCLUSIONS
From comparative cyclic voltammetry meas-
urements on Pt electrode in electrolytes consisting
of 1 M H
2
SO
4
+ 0.1 M aniline and 1 M H
2
SO
4
+
0.1 M anilin + 0.01 M TiO
2
, the following conclu-
sions can be drawn.
The electrodeposition of PANI and PANI
with TiO
2
nanoparticles occurs in the same poten-
tial range, approximately 0.7 V (SCE).
The presence of TiO
2
nanoparticles inhibits
the polymer-related oxidation process and the
characteristic redox peaks for PANI significantly
diminish in intensity and shift from primary poten-
tial positions. The oxidation peaks A shift towards
anodic and reduction A1 towards cathodic direc-
tion. These separations of peaks potential are lar-
ger for faster sweep rate indicating that the build-
ing of composite materials is a complex process
depending of many parameters. The most impor-
tant parameters are: diffusion of the TiO
2
nanopar-
ticles from electrolyte solution to electrode sur-
face, their migration in the polymer backbone dur-
ing the film thickness growth (number of per-
formed scans), and charge transfer in the polymer
chain depending on existing energetic barriers
provoked by TiO
2
nanoparticles.
The redox processes in both PANI films
and PANI/TiO
2
composite films are quasi reversi-
ble. The irreversibility of PANI/TiO
2
composite
films are higher because the nanoparticles of TiO
2

decreased the electrical conductivity of the com-
posite film.
Studies of the mechanism for incorporation
of metal-oxide nanoparticles in polymer backbone
and formation of composite (PANI/TiO
2
) compos-
ite materials are in progress.
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