Advances in Chemical Engi neering and Science , 20 1 1, 1, 37-44
doi:10.4236/aces.2011.12007 Published Online April 2011 (http://www.scirp.org/journal/aces)
Spectroscopic, Kinetic Studies of Polyaniline-Flyash
Composite
Raju Khan, Puja Khare, Bimala Prasad Baruah, Ajit Kumar Hazarika, Nibaran Chandra Dey
North East Institute of Science & Technology, Council of Scientific & Industrial Research, Jorhat, India
Received December 21, 2010; revised February 2, 2011; accepted Marc h 3, 2011
Abstract
Polyaniline-fly ash (PANI-FA) composites were prepared by oxidative polymerization of aniline with fly ash
in presence of ammonium persulphate (APS). The PANI-FA composites were prepared with different con-
centrations of fly ash to aniline ratio. The composites, so prepared, were characterized by UV-vis spectros-
copy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and thermogra-
vimetric analysis (TGA). The thermal stability was studied by TGA and total weight loss of PANI, FA and
PANI-FA composites having FA composition of 0.02%, 0.1%, 0.5% and 1.0% were found to be 82%, 39%,
67% 65%, 62% and 61%, respectively. The UV-vis spectroscopy of the PANI-FA polymeric composite
shows absorption maxima at 315 and 350 nm (due to π-π* transition of the benzenoid rings), and 578-712 nm
(due to charge transfer excitations of the quinoid structure), which are characteristic of emeraldine base.
FTIR spectra of the PANI-FA composite is similar to that of pure polyaniline (PANI) but with the bands for
C = N, C = C and C-N shifted to lower wave numbers, i.e., 1585, 1494, 1327 and 1113 cm−1 due to strong
interaction of Fe2O3 and PANI matrix. SEM shows the complexation of metal oxide with emaraldine base of
PANI, significantly changing the aggregate state of polymeric molecular chain.
Keywords: Polyaniline, Fly-Ash, TGA, UV-Vis Spectroscopy, FT-IR, Kinetic Study and SEM
1. Introduction
Polyaniline (PANI) can be synthesized chemically or
electrochemically in an acidic medium. For chemical
synthesis, an appropriate oxidant is required. There are
three forms of PANI, namely fully oxidized pernigrani-
line, half-oxidized emeraldine base (EB) and fully re-
duced leucoemeraldine base (LB). Emeraldine is said to
be the most stable form of PANI and also the most con-
ductive form when doped (emeraldine salt) [1]. PANI is
a versatile substance which has potential applications in
corrosion prevention, as sensors, in electronics and elec-
trochromic devices, and in batteries [2-6]. Conducting
polymers are attractive alternative to conventional in-
organic gas sensors due to potentially lower costing,
simpler packing and compatibility with flexible sub-
strates [7,8]. Polyaniline (PANI), with unique electrical
and optical properties, is a promising candidate for
wide range of potential applications [9,10]. The changes
in electrical and optical properties of PANI induced
through interaction of oxidizing or reducing agents make
it suitable for sensing applications [11-16]. However, the
processing difficulty and poor stability due to polymer
degradation, have to be overcome for its successful ap-
plications.
Furthermore, the developments of organic-iorganic
nanocomposites are expected to play an important role as
gas sensing materials. Efforts are continuing to engineer
organic-inorganic materials with enhanced physical and
optical properties for gas sensing applications. Nano-
composite thin films of polymer-inorganic nanoparticles
are reported to have porous morphology caused by sol-
id-state polymerization [17]. This porous morphology
has added advantage for sensing application due to en-
hanced penetration of bio-molecules into the polymer
matrix.
North East India produces a large quantity of fly ash
from its coal-fired power plant. In India, substantial part
of electric power (about 65%) is generated from coal or
lignite fired thermal power stations. One of the major
pollutants generated in a coal based thermal power plant
is flyash. Silica (SiO2), alumina (Al2O3), iron oxide
(Fe2O3) and titanium oxide (TiO2) are major constituents
of FA. These metal oxides have been used in one way or

R. KHAN ET AL. 38
the other in the preparation of nanocomposites. For ex-
ample, Al2O3 and Fe2O3 have been used as catalyst sup-
port for the production of organic-inorganic porous na-
nocomposites. In this paper we are using natural compo-
sition of metal oxides for the preparation of PANI-FA
composite, which forms morphologically porous marix
and have improved thermal stabilty. The incorporation of
FA into the polymeric network introduces uniform po-
rosity and is expected to be advantageous for gas sensing
and biosensing applications.
2. Experimental
2.1. Chemical and Reagents
Aniline (25% v/v in water), acetone, ammonium persul-
phate, dimethylformamide (DMF) and hydrochloric acid
were all products of Sigma-Aldrich Chemicals. Only
freshly vacuum-distilled aniline was used for the synthe-
sis of PANI. EDX study showed that the main constitu-
ents of the FA used in this study are as follows: silica
as SiO2 ~ 50%, alumina as Al2O3 ~ 30%, calcium oxide
as CaO ~ 5%, iron oxide as Fe2O3 ~ 4%, magnesium
oxide as MgO ~ 2% and titanium oxide as TiO2 ~ 2%.
2.2. Synthesis of Polyaniline-Fly Ash Composites
For preparation of Polyaniline-Fly Ash (PANI-FA)
composite, the procedure for the synthesis of composite
was followed [18]. 0.1 M aniline was prepared in 2 M
HCl solution. 100 mL of this aniline solution was stirred
and FA was added in the solution with vigorous stirring
(0%, 10%, 20%, 30%, and 40% FA to aniline w/w ratio).
The mixture was kept in an ice bath with continuous stir-
ring. Then 0.1 mol of ammonium persulphate (APS) was
added slowly to the aniline solution until the reaction
mixture turned green. The reaction mixture was then
stirred for 8 h. The product was collected by filtration
and washed with water and acetone until the washing
was colourless. The collected samples were dried at room
temperature and preserved for further studies.
2.3. Characterization of PANI, FA and PANI-FA
Composites
All the UV-vis absorbance experiments were per-
formed at room temperature with UV-vis Specord-200
using quartz cuvettes. The UV-vis sample solution was
prepared by dissolving 0.005 g of a PANI composite in
10 mL dimethylformamide (DMF) and experimental
wavelength scanned between 200 to 800 nm. The infra-
red spectra of the PANI, FA and PANI-FA polymer
composite were recorded on Perkin Elmer system 2000
FT-IR spectrometer using KBr pallets at room tempera-
ture in the region of 3600-4000 cm−1. Scanning electron
microscopy (SEM) analysis was performed with a Hita-
chi X-650 scanning electron microanalyser which has an
operating voltage window of 5 - 40 kV. Micrographs
were obtained for samples of the composites mounted on
aluminium stubs using conductive glue and coated with a
thin layer of gold. Experiments were carried out in a Le-
co TGA 701 thermal analysis system with 0.5 gm each of
fly-ash samples in a stream of nitrogen with a flow rate
of 40 mL·min−1 and linear heating rate of 10℃·min−1.
The weight loss (thermogravimetric TG signals) and the
rate of weight loss (differential thermogravimetric DTG
signals) as a function of time or temperature were rec-
orded.
3. Results and Discussion
3.1. FTIR Properties
FTIR spectra of PANI, FA & PANI-FA composite are
shown in Figure 1. FTIR band at 2982-3463 cm−1 cor-
responds to N-H stretching with hydrogen bonded amino
groups and free O-H stretching vibration and is attributed
to the N-H stretching vibrations of the leucoemeraldine
component. The characteristic absorption band observed
for PANI-flyash at 3463 cm−1 and 1690 cm−1 are assigned
to the N-H stretching vibration mode, and NH2 deforma-
tion in aniline unit respectively. The absorption band
2925 cm−1 and 2830 cm−1 are assigned to the aromatic sp2
hybridized C-H stretching vibration mode and aliphatic
hydrocarbon C-H stretching due to -CH2- bonded with
aniline unit. Strong peak at 2355 cm−1 was associated
with -NN in diazonium salts. The absorption bands ob-
Figure 1. FTIR spectra of chemically synthesized of (a)
PANI; (b) FA; (c) and composite of polyaniline-flyash, PA-
NI-FA (0.02); (d) PANI-FA (0.1); (e) PANI-FA (0.5) and (f)
PANI-FA (1.0).

R. KHAN ET AL. 39
served at 1567 and 1482 cm−1 in PANI is assigned re-
spectively to the non-symmetric vibration mode of C=C
in quinoid and benzenoid ring system in polyaniline. The
C-N stretching vibration mode in aromatic amine nitro-
gen (quinoid system) in doped polyaniline is found at
1290 cm−1, corresponding to the oxidation or protonation
state. The absorbance peak at 1233 cm−1 is attributed to
C-N stretching vibration mode in benzenoid ring system
of polyaniline due to the conducting protonated form. In
plane vibration of C-H bending mode in N = Q = N,
Q-N+H-B or B-N+H-B (where Q = quinoid and B = ben-
zenoid) is observed at 1146 cm−1. The presence of this
absorption band is expected due to the polymerization of
PANI, i.e., polar structure of the conducting protonated
form. The absorption bands at 874 and 799 cm−1 are at-
tributed to the aromatic ring and out of plane C-H de-
formation vibrations for 1, 4-disubstituted aromatic ring
system[19].
In FTIR spectrum of purified FA, the characteristic
3426 cm−1 band indicating the stretching vibration of the
-OH group appears due to some components with an
-OH group or crystal lattice water on the surface of FA.
Broadening in characteristic peaks range 2750 - 3463
cm−1 is associated with N-H stretching vibration of
PANI. The decrease in broadening of FTIR bands in
the range 2750 - 3463 cm−1 was due to covalent and hy-
drogen bonding between –NH2 and –OH group of PANI
and FA respectively. The very sharp FTIR peak at 1632
cm−1 was associated with C = O stretch in –HNCOCH3
group of PANI-FA matrix. The IR spectra of PANI
composite in presence of FA exhibit new absorption
peaks distinctly at 1522, 1447, 1280, 1196 and 641 cm–1
which could be assigned to the presence of various metal
oxides in the composite. The peak around 1113 cm−1
may be attributed to the presence of silica within the
composite. The FTIR peaks at 1030 cm−1 for the FA
corresponds to the internal SiO4 tetrahedra, especially the
Si-O-Si chain structure. The peaks at 1030 - 1196 cm−1
of the FA correspond to a cyclic Si-O-Si structure. The
FA indicates the FTIR spectra of Fe2O3, where the bands
around 540-466 cm−1 are assigned to Fe-O stretch. It can
be seen that the FTIR spectra of the PANI-FA composite
is similar to that of pure PANI where the bands for C=N,
C=C and C-N are all shifted to lower wave numbers, i.e.
1585, 1494, 1327 and 1113 cm−1 due to strong interac-
tion of Fe2O3 and PANI [20].
3.2. UV-Vis Properties
The UV-vis absorption spectra of PANI and PANI-FA
composite are shown in Figure 2. Two absorption
bands are observed in the wavelength region from 315 to
350 nm and a small band at 578 to 712 nm for the PANI
(Figure 2(b)). PANI always exhibits a π-π* transition,
300 400 500 600 700 800
0.0
0.5
1.0
0
2
4
6
8
1
dc
a
b
e
Absorbance
W avelength (nm )
Figure 2. UV-vis spectra of chemically synthesized of (a)
PANI-FA (1.0), (b) PANI, (c) PANI-FA (0.5), (d) PANI-FA
(0.1) and (e) FA.
usually closer to 315 nm [21]. Partially oxidized PANI
and its oligomers display an additional absorption at
around 712 nm associated with the quinoid (oxidized)
units [22]. These peaks are characteristic of the PANI
emeraldine base [23,24] and indicate that nanostructured
PANI composites are stabilized in the emeraldine base
redox state. The peak at 315 nm is attributed to π – π*
transition of benzoid rings and the peak at 712 nm is at-
tributed to the charge transfer excitation of the quinoid
structure. In the spectra of pure FA, peaks are observed
in the regions at 258-289 nm but were found absent in
the region 600-700 nm (Figure 2(e)). PANI–FA pre-
pared without aging show clear similarity in their UV-vis
spectra particularly with the complete absence of the
absorption maxima at 320 and 630 nm which is asso-
ciated with the stabilization of the composite in the eme-
raldine form. Comparatively, PANI–FA composite show
clear similarity in their UV-vis spectra particularly with
the presence of the absorption maxima at 315 and 610
nm which is associated with the stabilization of the
composite in the emeraldine form. Comparison of the
PANI and PANI-FA composite spectra shows that FA
stabilizes the polyanilines in its emeraldine form.
3.3. TGA Properties
TGA is widely used to study all physical process involv-
ing the weight changes such as to measure the diffusion
characteristics and the moisture uptake of a sample. The
thermo gravimetric profiles of PANI, FA and PANI-FA
polymer composite is shown in Figure 3. Total weight
loss of PANI, FA and PANI-FA polymer composite
PANI-FA (0.02), PANI-FA (0.1), PANI-FA (0.5) and

R. KHAN ET AL. 40
(a)
(b)
Figure 3. Thermo gravimetric analysis (TGA) of chemically
synthesized of (Figure 3(a)) and DTG of (Figure 3(b)) PANI,
FA and composite of polyaniline-flyash PANI-FA (0.02),
PANI-FA (0.1) PANI-FA (0.5) and PANI-FA (1.0).
PANI-FA (1.0) are 82%, 39%, 67%, 65%, 62% and 61%,
respectively. Decrease in ultimate weight loss indicates
the interaction of PANI with the metal oxides such as
Al2O3, Ti-O-Ti and SiO2 present in FA. FTIR spectra of
these composites also show strong interaction of SiO2,
Fe2O3 and PANI. This may be due to the Van der-Walls
binding of PANI-FA polymer composites.
The thermogram of PANI indicates three major stages
of weight loss. In the first stage, 3% - 4% weight loss at
temperature up to 125˚C is associated with the loss of
water molecules from the polymer matrix [1]. The weight
loss at second stage that commences after 125˚C until
225˚C (about 9-12%) is due to the removal of the acid
dopant bound to the polyaniline chain and low molecular
weight oligomers. A slow and somewhat gradual weight
loss profile observed starting at 225˚C onward, represent
degradation of the skeletal polyaniline chain structure
after the dopant has been removed [25]. Above 600℃,
the results obtained are associated with the residues only.
The thermogram of fly ash indicates four major stages of
weight loss (Figure 3(b)). PANI and composite PANI-
FA(0.02) and PANI-FA(0.1) exhibit similar pattern, with
a small variation in degradation temperature, while ther-
mograms of PANI-FA(0.5) and PANI-FA (1.0) show
similar pattern with FA. In the first stage, 3-4% weight
loss at temperature up to 125˚C is associated with the
loss of water molecules [26]. In the second stage corres-
ponding to temperature zone 125º - 400˚C, the weight
loss (about 9-12%) is due to the evolution of thermally
labile compounds and the breaking of aliphatic structures
with low dissociation bonds in the carbonaceous matrix
of FA. In the third stage that commences after 400˚C
until 700˚C, maximum weight loss occurs (21%) due to
release of shoot particles attached with SiO2 system of
FA [9,16]. Above, 700˚C gradual decreases were ob-
served due to thermal degradation of mineral matter of
fly ash. The weight loss of PANI, fly-ash and composi-
tions of PANI-FA (0.02), PANI-FA (0.1), PANI-FA (0.5)
PANI-FA (1.0) have been found 82%, 38.9%, 67% 65%,
62% and 61%, respectively. A decrease in weight loss of
composite is observed with the increasing FA content. It
indicates the interaction of polyaniline with mineral
matter of the FA. As indicated earlier, SiO2, Fe2O3 and
Al2O3 are the major oxides present in the FA. FTIR
spectra of these composites confirm strong interactions
with metal oxides SiO2, Fe2O3 and polyaniline in the
composite matrix.
3.4. Kinetic Properties
The activation energies of PANI, FA and PANI-FA
composites were determined by the integral method [27].
It is assumed a first order reaction [28,29]. Applying Arr-
henius equation for reactions, it can be expressed as

 
dd exp1
x
tAERT x

 (1)
where A is pre-exponential factor, E is the activation
energy, T is temperature in K, R is gas constant, t is time
and x is weight loss fraction or decomposition during
pyrolysis which can be calculated by



00tf
x
WW WW  (2)
where W0 is the original mass of the test sample, Wt is the
mass at time t or at temperature T and Wf is the final
mass at the end of pyrolysis.
The constant heating rate during pyrolysis is H = dT/dt
for H being the heating rate. Rearranging the Equation (1)
and integration gives


2
lnln 1ln12
x
TARHERTEERT

  


(3)

R. KHAN ET AL. 41
The expression


ln1 2
A
RRTEHE

in Equa-
tion (3) is essentially constant for most of the values of E
and temperature range of the pyrolysis. By plotting the
left side of Equation (3) against 1/T, a straight line is
obtained indicating the process to be of first order reac-
tion (Figure 4). From the slope, –E/R, the activation
energy E can be determined. Pre-exponential factor A
was determined by substituting the T in the intercept
(Equation (3)) with temperature at which

02 tf
WWW . From DTG (Figure 3(b)) of PANI,
FA and PANI-FA composite, it could be seen that the
reactions was not described by one first order reaction
but could be described in two consecutive first order
reactions instead. Equation (3) is applied separately to
each stage. The conversion of x was recalculated for each
reaction. From the slope of each line, the value of E can
be obtained for different stages (Table 1). DTG curve of
PANI and FA show two peaks. The first peak corres-
ponds to devolatilization of PANI and FA. Therefore, the
second one corresponds to thermal degradation of resi-
due of PANI and mineral matter of FA, respectively. The
overall, DTG curve shapes of PANI and its composites
are similar to a combination curve of its components
indicating that PANI is a dominant factor affecting the
thermal stability of the composite. The kinetic energy of
first peak of composite shift to higher sites with increas-
ing FA content in composites. The reaction with higher
activation energy means that the reaction needs more
energy from the surroundings. It indicates that the com-
posites are thermally more stable as compared to PANI
and FA. The kinetic energy of second peak of composite
was in between that of PANI and FA and also shift to
higher site with increasing FA content in the composite.
These facts indicate that some intimate interaction
among skeleton of PANI and mineral matter content of
FA makes the kinetic energy higher than that of PANI
itself.
3.5. Scanning Electron Microscopy
Scanning electron microscopy (SEM) in Figure 5 is
showing the general features of the original fly ash (Fig-
ure 5(a)). As it can be seen in the figure, the fly ash is
mainly constituted by compact or hollowed spheres but
with a regular smooth texture. Often, on the surface of
spheres the existence of solid deposits or small crystals
could be observed which could be soluble alkaline sul-
phates, dendritic shaped particles of iron minerals, mul-
lite crystals (Figures 5(g-i)) etc. Also, some quartz par-
ticles, residue of un-burnt coal or some vitreous un-
shaped fragments could be seen. SEM of PANI shows
porous, non-uniform structure (Figure 5(b)). PANI-FA
composite shows (Figures 5(c)-(f)) the formation of
rough micro structure having uniformly distributed metal
oxide embedded in the PANI-FA polymer matrix. The
concentration of increasing FA in polymer composite
is found to play an important role in the surface mor-
phology. The complexation of metal oxide with emaral
Table 1. Activation energy (KJ/Mol) of PANI, FA, and PA-
NI-FA composite during pyrolysis.
Temperature
(˚C) PANI FAPANI- FA (0.02)
PANI-
FA (0.1)
PANI-
FA(0.5)
PANI-
FA(1.0)
50 - 400 80.3980.2384.23 88.24 97.2999.23
500 - 800 47.3068.5048.83 50.08 53.4557.08
Figure 4. The activation energies of PANI-FA composites as
determined by the integral method.
1/T(K–1)
ln[-ln(1 - x)/T2]
1/T(K–1)
ln[-ln(1 - x)/T2]

R. KHAN ET AL. 42
(a) (b) (c)
(d) (e) (f)
(g) (h) (i)
Figure 5. Scanning electron micrograph (SEM) of chemical synthesized of (a) FA (b) PANI and (c-f) composite of polyani-
line-flyash PANI-FA (0.02), PANI-FA (0.1), PANI-FA (0.5) and PANI-FA (1.0), EDXA spectra from (g-i) composite of polya-
niline-flyash PANI-FA (0.1), PANI-FA (0.5) and PANI-FA (1.0).
dine base form of PANI significantly changes the aggre-
gate state of polymeric molecular chain. The incorpora-
tion of metal oxides into the polymeric network induces
uniform porosity and is expected to be advantageous for
gas and biosensing applications.
4. Conclusions
In this study we demonstrated a way to use the toxic
waste like fly ash (FA) to enhance the characteristic pro-
perties of polyaniline (PANI). Polyaniline fly-ash (PA-
NI-FA) composites were prepared by oxidative polyme-
rization of aniline with fly ash in presence of ammonium
persulphate. The morphology of new composite mate-
rials was studied by scanning electron microscopy
(SEM). SEM and EDXA pictures have been confirmed
the complexation of metal oxide with emaraldine base
form of PANI, significantly changing the aggregate state
of polymeric molecular chain. The increase of kinetic
energy as seen from TGA for the PANI-FA composite
compared to PANI and FA indicate strong complexation
of metal oxide with PANI emaraldine base.
5. Acknowledgements
Raju Khan is thankful to the Department of Science &
Technology (DST), Govt. of India, for financial support
under the Young Scientist Scheme project No. SR/FT-
P/CS-77/2007.
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