Electrical conductivity and alcohol sensing studies on polythiophene/ tin oxide nanocomposites

Journal of Science: Advanced Materials and Devices 5 (2020) 84e94

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Journal of Science: Advanced Materials and Devices
journal homepage: www.elsevier.com/locate/jsamd

Original Article

Electrical conductivity and alcohol sensing studies on polythiophene/
tin oxide nanocomposites
Ahmad Husain, Sharique Ahmad, Faiz Mohammad*
Department of Applied Chemistry, Zakir Husain College of Engineering and Technology, Faculty of Engineering and Technology, Aligarh Muslim University,
ALIGARH, 202002, India

a r t i c l e i n f o

a b s t r a c t

Article history:
Received 26 August 2019
Received in revised form
15 January 2020
Accepted 16 January 2020
Available online 25 January 2020

Conducting polymer-based sensors have short response time at room temperature besides their good
electrical conductivity. However, the poor electrical conductivity retention at a higher temperature and
the failing reproducibility of sensors which are based on conducting polymers are an area of concern. To
this end, we are reporting the preparation of polythiophene (PTh) and polythiophene/Tin oxide (PTh/
SnO2) nanocomposites by an in-situ chemical oxidative polymerisation. The as-prepared materials were

characterized by FTIR, SEM, UV-vis absorbance spectroscopy, TEM and XRD techniques. PTh/SnO2-3 (i.e.
PTh/SnO2 nanocomposite containing 15% SnO2 nanoparticles) showed the highest DC electrical conductivity (9.82 Â 10À3 S,cmÀ1) in addition to a maximal stability as a function of DC electrical conductivity retention under accelerated isothermal and cyclic ageing conditions. We utilized PTh/SnO2-3 to
fabricate a novel pellet-shaped sensor for the selective detection of some of the higher alcohols, such as
butan-1-ol (1 alcohol), butan-2-ol (2 alcohol), and 2-methyl propanol (3 alcohol) at room temperature.
PTh/SnO2-3 exhibited the highest response in terms of variation in DC electrical conductivity and
maximal reproducibility for butan-1-ol. Finally, the sensing mechanism was explained by the adsorption
edesorption process of alcohol vapours on the large surface area of the PTh/SnO2 nanocomposites where
electronic interactions between the lone pairs of electrons of alcohol molecules with the polarons of PTh
cause the change in the DC electrical conductivity.
© 2020 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.
This is an open access article under the CC BY license ( />
Keywords:
PTh/SnO2 nanocomposites
Electrical conductivity
Alcohol sensor.

1. Introduction
Nowadays, the development of highly efficient chemical/gas/
vapour sensors becomes essential because of the increasing
concern about environmental protection [1e6]. An ideal sensor
should be reliable, selective and reversible in order to be employed
practically in various applications. A perfect sensor exhibits good
selectivity, i.e. it responds to the target analyte only in the presence
of additional interfering species [7e10]. One of the most common
types of sensors is the chemiresistor, whose electrical resistance is
highly sensitive to the different chemical environments. The advantages of using the four-point interdigital electrodes are the
minimisation of the contact resistance and the enhancement of the
sensing response of the chemiresistor [7]. The most conventional

* Corresponding author.

E-mail address: (F. Mohammad).
Peer review under responsibility of Vietnam National University, Hanoi.

sensors are based on inorganic semiconductor metal oxides, such as
SnO2, TiO2, ZnO, WO3 etc. because of their good sensing response,
cost-effective design and simple sensing mechanism [8,9]. Usually,
these types of sensors could only be used at higher temperatures
which cause a variation in the sensing response due to the possibility of structural deformation. Also, working at high temperature
is power consuming and may cause safety problems during the
detection of flammable gases which might catch fire at elevated
temperatures [9,10]. Therefore, enormous efforts have been
employed for the fabrication of a sensor working at low temperature or room temperature with a high sensitivity and a short recovery time [5e7,10].
Recently, conducting polymers (CPs), employed as gas sensors
at room temperature conditions, allow the detection and monitoring of various analytes, which can be a safer alternative as
compared to sensors working at elevated temperatures [7]. The
interaction with the analyte species significantly influences the
redox characteristics of the conducting polymers resulting in a
modification in their work function, resistance and electrochemical potential [1,7,10]. Safer detection of several combustible

/>2468-2179/© 2020 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi. This is an open access article under the CC BY license
( />

A. Husain et al. / Journal of Science: Advanced Materials and Devices 5 (2020) 84e94

gases at room temperatures is possible if we employ sensors
based on conducting polymers. This field today include several
conducting polymers, such as polyacetylene, polyaniline, polypyrrole, polyparaphenylenes, polythiophenes. These polymers
consist of a spine of the extended p-conjugated structure and an
arrangement of alternating single and double bonds (sp2 hybridised structure). This leads to the delocalisation of the p-electrons
along the whole polymer chain, therefore providing these conducting polymers with their characteristic optical and electrical

properties [11e14]. The main problems related to the sensors
based on CPs are their irreversibility and long-time instability. To
overcome these problems, nanocomposites of CPs with semiconducting inorganic nanoparticles could be a potential candidate. The incorporation of nanoparticles in the conducting
polymers induces high sensitivity and selectivity, which leads to
the further improvement in their performance as a gas sensor
[10,15e23]. Offering a superior shape and size control as
compared to the one-step redox process, the most commonly
employed method for nanocomposite fabrication is the in-situ
polymerization [10,16e19]. Among the different conducting
polymers available nowadays, polythiophene (PTh) based nanomaterials are ones of the most widely used contenders in the field
of sensors due their outstanding electrical, optical,
thermal, mechanical properties and their environmental stability
[18e23].
Over the years, tin oxide (SnO2) has been one of the most
favourable sensing materials owing to its good sensitivity towards
the most common reducing and oxidising gases besides its chemical and thermal stability and its bandgap of 3.6 eV [20,23e27]. But,
like other inorganic semiconductors, it also works at high temperature. Hence, nanocomposites of conducting polymers with
SnO2 nanoparticles have been synthesised having the properties of
both the constituents, i.e. low working temperature with high
sensitivity, reversibility, selectivity and long-time stability
[20,21,23,26].
Herein, we prepared the nanocomposites of polythiophene with
different weight percentage viz. 5%, 10% and 15% of SnO2 nanoparticles by the cost-effective in-situ chemical oxidative technique in
a chloroform solvent using anhydrous FeCl3 as both the oxidant and
dopant. The structural, chemical and optical properties of the PTh and
PTh/SnO2 nanocomposites were examined by Fourier Transformed
Infra-Red (FTIR), UV-VIS absorbance spectroscopy, Scanning Electron
Microscopy (SEM), Transmission Electron Microscopy (TEM) and XRay Diffraction (XRD) techniques. We have also explored DC electrical
conductivity to investigate the butan-1-ol (1 alcohol), butan-2-ol (2
alcohol), and 2-methyl propan-2-ol (3 alcohol) vapour sensing

behaviour of PTh and PTh/SnO2-3 along with their conductivity
retaining ability in the accelerated isothermal and cyclic ageing
conditions of all the samples.
2. Experimental
Thiophene (E.Merck, India), Tin Oxide nanoparticles (Platonic
Nanotech Pvt. Ltd India) and butan-1-ol, butan-2-ol, 2-methyl
propan-2-ol, chloroform, anhydrous ferric chloride, acetone,
methanol were purchased from Fisher Scientific, India.
A simple and cost-effective in-situ chemical oxidative polymerisation technique was employed for the preparation of PTh
and PTh/SnO2 nanocomposites with a varying weight percentage
of SnO2 nanoparticles. In this method, chloroform and anhydrous
FeCl3 were utilized as the solvent and the oxidant, respectively. In
the usual procedure, 2 mL (25.00 mmol) of thiophene (i.e.
monomer) was transferred into 40 mL of solvent (chloroform)
followed by a ultrasonication process for 25 min. Further, a known
amount of SnO2 nanoparticles (5%, 10% and 15%) was added to

85

60 mL of chloroform and then ultrasonicated for 30 min. After
that, the solution containing the SnO2 nanoparticles was transferred into the thiophene solution. Then, this mixture was subjected to the ultrasonication for the total duration of 90 min.
During the ultrasonication process, the thiophene molecules were
adsorbed on the surface of the SnO2 nanoparticles. After that,
16.24 g (100 mmol) of ferric chloride was dissolved in 100 mL of
chloroform and stirred for 20 min untill a homogeneous suspension was made. Then, the dropwise addition of the as-prepared
FeCl3 suspension to the thiophene and SnO2 mixture was
accompanied by constant stirring with a magnetic stirrer for 20 h.
Then, the resulting PTh/SnO2 nanocomposite was subjected to the
filtration process in addition to being washed quite a few times
with methanol and after that by distilled water and lastly using

acetone. In the course of washing, as soon as the methanol was
added, there was a visible change in the colour of the materials
from black to brown to be observed. Finally, the synthesised
materials were dried in a vacuum oven at 60  C for 18 h. After the
drying was completed, the materials were crushed into a very fine
powders and kept in the desiccator for further experiments. The
PTh/SnO2 nanocomposites comprising 5%, 10% and 15% SnO2 were
identified as PTh/SnO2-1, PTh/SnO2-2 and PTh/SnO2-3 respectively. Polythiophene (PTh) nanoparticles were also synthesised
without adding SnO2 nanoparticles by employing an identical
process.
A variety of methods was employed for the investigation of the
morphology, the formation and chemical composition of the PTh
and PTh/SnO2 nanocomposites. X-ray diffraction patterns, FTIR
spectra, UV-VIS spectra, SEM and TEM studies were carried out by
employing the Bruker D8 diffractometer with Cu-Ka radiation at
1.5418 Å, the PerkinElmer 1725 instrument on KBr pellets, the
Shimadzu UVÀVIS spectrophotometer (model 1601), the JEOL-JSM,
6510-LV (Japan) and the JEM 2100, JEOL (Japan), respectively.
The DC electrical conductivity and sensing experiments were
carried out with the help of the 4-in-line probe instrument
attached with a PID controlled oven (Scientific Equipment, Roorkee,
India). The following equation was employed for the evaluation of
the DC electrical conductivity:

s ¼ ½ln2ð2S = Wފ = ½2pSðV = Iފ

(1)

where: s, I, V, W and S are used for the DC electrical conductivity (in
S,cmÀ1), current (in A), voltage (in V), the thickness of the pellet (in

cm) and the probe spacing (in cm), respectively [28]. The pellets
utilised for the DC electrical conductivity and sensing measurements were made by 250 mg of materials with the support of a
hydraulic pressure machine operating at a pressure of 70 kN
applied for 3 min. In order to assess the DC electrical conductivity
retaining aptitude in the accelerated isothermal situation, the
pellets were subjected to heat at 40  C, 60  C, 80  C, 100  C and
120  C in an air oven. Then, the DC electrical conductivity was
calculated at the particular temperature at an interval of 4 min in
the accelerated ageing experiments. In order to assess the stability
under cyclic ageing conditions, the DC electrical conductivity experiments were carried out for four successive cycles within a wide
range of temperature ranging from 40  C to 120  C.
3. Results and discussion
3.1. FTIR studies
FTIR spectra of PTh, PTh/SnO2-1, PTh/SnO2-2 and PTh/SnO2-3
are presented in Fig. 1. The spectrum of PTh reveals a wide-ranging
absorption band at nearby 3427.9 cmÀ1 which may be accredited to
the eOH stretching vibrations. The strong peaks at 1634.8 cmÀ1 and


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A. Husain et al. / Journal of Science: Advanced Materials and Devices 5 (2020) 84e94

Fig. 1. FT-IR spectra of: (a) PTh, (b) PTh/SnO2-1, (c) PTh/SnO2-2 and (d) PTh/SnO2-3.

1440.6 cmÀ1 may be related to the stretching modes of vibrations of
C]C and CeC present in thiophene rings, respectively. The peak at
1189.8 cmÀ1 may be related to the in-plane stretching vibration of
the CeH bond. Out of plane bending modes of vibrations of CeH
bonds are observed at 1105.4 cmÀ1 and 1024.1 cmÀ1. The band

that appeared at 782.9 cmÀ1 could be assigned to a CeH out of
plane deformation mode of the thiophene ring because of polymerization. The bending vibration mode related to the CeS bond of
thiophene ring could possibly be observed at 631.5 cmÀ1. The peak
at 470.2 cmÀ1 corresponds to a deformation mode of the CeSeC
bond. The peaks at 2852.6 cmÀ1 and 2928.3 cmÀ1 could be ascribed
to the stretching vibrations of the CeH bond. A new peak observed
at 699.7 cmÀ1 in the spectrum of PTh/SnO2-3 is due to a SneOeSn

antisymmetric and symmetric vibration mode and indicates the
presence of SnO2 nanoparticles. The peaks at around 1730 cmÀ1 to
1740 cmÀ1 in all the materials may be due to the >C]O stretching
vibration of acetone which was used during washing. The FTIR
spectra of PTh/SnO2-3 display similar bands like those of PTh with
slightly shorter wavenumbers. In the spectrum of PTh/SnO2-3, the
bands appeared at 3427.9 cmÀ1, 2928.3 cmÀ1, 2852.6 cmÀ1,
1634.8 cmÀ1, 1440.6 cmÀ1, 1319.7 cmÀ1, 1189.8 cmÀ1, 1105.4 cmÀ1,
1024.1 cmÀ1, 782.9 cmÀ1, 631.5 cmÀ1 and 470.2 cmÀ1 and move to
3426.8 cmÀ1, 2922.1 cmÀ1, 2852.2 cmÀ1, 1630.5 cmÀ1, 1436.2 cmÀ1,
1310.9 cmÀ1, 1175.8 cmÀ1, 1102.6 cmÀ1, 1022.5 cmÀ1, 781.3 cmÀ1,
595.8 cmÀ1 and 461.8 cmÀ1, respectively, after the incorporation of
the SnO2 nanoparticles into the PTh matrix showing some electronic (coulombic) interaction between PTh and SnO2 nanoparticles. The shifting of the bands towards the smaller
wavenumbers may be an indication of a successful polymerisation
of thiophene monomers on the large surface area of the SnO2
nanoparticles. The maximal shift among the peaks was observed
for the bending vibration mode of CeS bonds, which was shifted
from 631.5 cmÀ1 to 595.8 cmÀ1. This peak shift could be a result of
the strong coulombic interaction between the lone pair on the
sulphur atom of the thiophene and the Snþ4 ions of the SnO2
nanoparticles. These results were found to be consistent with the
previously published literature data [12,21e23,28e30].

3.2. X-ray diffraction (XRD) analysis
In Fig. 2, XRD patterns of PTh, PTh/SnO2-1, PTh/SnO2-2 and
PTh/SnO2-3 are revealed. In the case of PTh, a wide diffraction
peak observed within the range of 2q values from 10 to 20
designates the amorphous nature of the polymer [28,30]. The
presence of the SnO2 nanoparticles in PTh/SnO2-3 is confirmed by
the peaks observed at 2q values of 26.76 , 34.06 , 38.14 , 51.98 ,
54.86 , 62.6 , 66.21, 71.82 and 78.58 , which relate to the (110),
(101), (200), (211), (220), (310), (301), (202) and (321) planes of
the SnO2 nanoparticles, respectively [27,31]. In the case of the
SnO2 nanoparticle, the main peaks were observed at 2q ¼ 26.60 ,
33.80 , 37.90 , 51.80 , 54.70 , 61.90 and 65.90 [27]. In case of
PTh/SnO2-3, the characteristic peaks of the SnO2 nanoparticle are
shifted to slightly higher angles which signifies the coulombic
interaction involving the lone pairs of electrons of the sulphur
atom in PTh and the Snþ4 ions of the SnO2 nanoparticle. The
result indicates the polymerisation of thiophene over the surface
of the SnO2 nanoparticle, which enhances the DC electrical conductivity and the sensing ability of PTh.
3.3. Scanning electron micrographic (SEM) studies

Fig. 2. XRD patterns of: (a) PTh, (b) PTh/SnO2-1, (c) PTh/SnO2-2 and (d) PTh/SnO2-3.

Fig. 3 depicts the morphologies of PTh and PTh/SnO2-3. The
SEM micrographs of PTh revealed that the sample's surface
consists of flat nanorods interconnected with each other resulting in a slightly porous morphology. In the case of PTh/SnO2-3,
the absence of free SnO2 nanoparticles may be related to the
successful encapsulation of the SnO2 nanoparticles in the PTh
matrix. The observed morphology of PTh/SnO2-3 revealed a flaky
or thin sheet-like structure interlinked with each other, which
gives a highly porous surface. The modification in morphology

suggests that there may be some electronic interactions between
PTh and SnO2. The highly porous and large surface area plays a
tremendous role in the sensing mechanism of chemiresistors
because the adsorption of the analyte gas/vapour is considered to
be the first step, then the interaction between the polarons and
the analyte takes place. This electronic interaction leads to an
alteration in the DC electrical conductivity due to the


A. Husain et al. / Journal of Science: Advanced Materials and Devices 5 (2020) 84e94

87

Fig. 3. SEM micrographs of PTh and PTh/SnO2-3 at different magnifications.

neutralisation or decrease/increase in the mobility of polarons
depending on the types of the analyte gas/vapour [7,10].
3.4. Transmission electron micrographic (TEM) studies
In Fig. 4, TEM images of PTh and PTh/SnO2-3 are presented. The
TEM micrograph of PTh revealed the formation of nanorods with a
flaky structure, which may also be seen in the SEM image of PTh.

The TEM micrograph of PTh/SnO2-3 indicates the successful polymerisation of thiophene on the surface of the SnO2 nanoparticles.
The TEM image of the PTh/SnO2-3 revealed that SnO2 nanoparticles
(black coloured parts) are successfully captured within the PTh
matrix (grey coloured background).
3.5. UVevisible absorbance spectroscopy
The UVÀvis absorption spectra related to PTh and PTh/SnO2-3
are depicted in Fig. 5. In the case of PTh, the band detected at
348 nm may correspond to the pÀp* electronic transition of the

benzenoid rings [22]. For PTh/SnO2-1, PTh/SnO2-2 and PTh/SnO2-3,
the characteristic band of pure PTh is red-shifted to 354, 366 and

Fig. 4. TEM micrographs of PTh and PTh/SnO2-3.

Fig. 5. UVevis absorbance spectra of: (a) PTh, (b) PTh/SnO2-1, (c) PTh/SnO2-2 and (d)
PTh/SnO2-3.


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A. Husain et al. / Journal of Science: Advanced Materials and Devices 5 (2020) 84e94

372 nm, respectively, that could be accredited to a growth in the
degree of conjugation of PTh due to the creation of a well-organised
network by the coulombic interaction of PTh with SnO2 nanoparticles. The significant red shift in the PTh/SnO2-3 spectra may be
related to the boosted DC electrical conductivity as a consequence
of the easiness in the mobility of polarons (charge carriers) through
the prolonged p-conjugation in PTh/SnO2-3.
3.6. DC electrical conductivity studies
The theory of polaron and bipolaron could explain the fundamental mechanism of the electrical conductivity in the intrinsically
conducting polymers [11,12]. The generation of polarons and
bipolarons depends upon the intensity of the oxidation process. At
a lower oxidation level polarons are generated while a higher
oxidation level favours the production of bipolarons. These are
charge carriers and behave like holes. The number and the mobility
of these charge carriers through the extended p-conjugated system
determine the magnitude of the electrical conductivity of conducting polymers. As the temperature rises, the electrical conductivity is expected to rise due to a greater mobility of the charge
carriers. But it was witnessed that at higher temperatures, the
electrical conductivity decreases and some times is lost entirely due

to the loss of dopants and the degradation of polymers which break
the p-conjugation. In the case of nanocomposites of conducting
polymers, the electrical conductivity was found to increase even at
a higher temperature and to behave like in a semiconductor
because of the better alignment of the polymer chains, the thermal
stability and the increase in the p-conjugation extent [13e17].
In this paper, the PTh and PTh/SnO2 nanocomposites, having 5%,
10% and 15% of SnO2 nanoparticles, were examined for their initial
DC electrical conductivities which were evaluated by employing a
standard four-in-line probe technique. The calculated DC electrical
conductivities of PTh and PTh/SnO2 nanocomposites were found in
a similar range to those exhibited by semiconductors. The DC
electrical conductivity of PTh was found to be 5.59 Â 10À4 S,cmÀ1,
whereas the conductivities were found to be about 1.43 Â 10À3,
4.73 Â 10À3 and 9.82 Â 10À3 S,cmÀ1 for PTh/SnO2-1, PTh/SnO2-2
and PTh/SnO2-3, respectively. The DC electrical conductivity related
to PTh/SnO2 rises with the loading of SnO2 nanoparticles, as
depicted in Fig. 6a. It may be supposed that the DC electrical conductivity of PTh was considerably enhanced after the incorporation
of SnO2 nanoparticles due to the following two reasons: (1) the
polymerization of thiophene monomer on the large surface area of
the SnO2 nanoparticles resulted in the formation of an efficient
system in PTh which increases and stabilises the extended pconjugation; (2) the electronic interaction between the lone pairs
of sulphur of polythiophene with the Snþ4 ions causes an increase
in the number and in the mobility of charge carriers (polarons) in
the PTh chains (Fig. 6b). Thus, a greater amount of SnO2 nanoparticles in the PTh matrix provides a greater surface area where
charge carriers can move freely without any hindrance which
boosts the electrical conductivity.
3.6.1. Stability under isothermal ageing conditions
The DC electrical conductivity retaining aptitude of PTh, PTh/
SnO2-1, PTh/SnO2-2 and PTh/SnO2-3 was examined under accelerated isothermal ageing conditions, and results are represented in

Fig. 7. The following equation was employed for the calculation of
the relative DC electrical conductivity at a particular temperature:

sr;t ¼

st
s0

(2)

Fig. 6. (a) Initial DC electrical conductivities of PTh, PTh/SnO2-1, PTh/SnO2-2, PTh/
SnO2-3 nanocomposites and (b) the possible interaction between PTh and SnO2
nanoparticles in the PTh/SnO2 nanocomposite leading to the creation of additional
polarons and electronic pathways vital for boosted electrical conductivity.

where sr,t, st and so symbolise the relative DC electrical conductivity at time t, the DC electrical conductivity at time t and the DC
electrical conductivity (in S,cmÀ1) at time zero, respectively
[28,30].
The isothermal stability of PTh/SnO2 nanocomposites as a
function of the retention of DC electrical conductivity was observed
to be far better than that of PTh. It is obvious from Fig. 7a that PTh is
fairly well stable at 40 and 60  C. In the case of PTh, direct heating at
high temperatures (i.e. at 80, 100 and 120  C) resulted in a regular
dropping of conductivity which may be caused by the damage of
materials and the loss of the doping agent. PTh/SnO2-1 shows good
stability at 40, 60 and 80  C and behaves like a semiconductor, i.e.
an increase in the conductivity with the increasing temperature
(Fig. 7b). PTh/SnO2-2 shows a gain in conductivity with a high
stability at 40, 60, 80 and 100  C as depicted in Fig. 7c. The most
significant gain in conductivity with the highest stability at 40, 60,

80, 100 and 120  C was observed in the case of PTh/SnO2-3 (Fig. 7d).
The effect of the amount of SnO2 nanoparticles in the PTh matrix on
the stability of DC electrical conductivity at different temperatures
signifies the electronic interaction between PTh and SnO2, which
increases the mobility of polarons as the temperature rises.
Consequently, it could be established that PTh/SnO2-3 displayed
the maximal stability and the utmost gain in conductivity among
the PTh/SnO2 nanocomposites expressed as a function of the DC
electrical conductivity under isothermal ageing condition. PTh/
SnO2-3 can be used as a semiconducting material at a temperature
of 120  C. Thus, the incorporation of a small amount of SnO2
nanoparticles in the PTh matrix can lead to a greater DC electrical
conductivity, which is stable at a higher temperature and the material shows a stable semiconducting behaviour as compared to the
pristine PTh. Hence, the PTh/SnO2-3 composite can be considered a
potential candidate in electrical and electronic applications within
a wide range of temperature starting from room temperature to


A. Husain et al. / Journal of Science: Advanced Materials and Devices 5 (2020) 84e94

Fig. 7. Relative electrical conductivity versus time of (a) PTh, (b) PTh/SnO2-1, (c) PTh/SnO2-2 and (d) PTh/SnO2-3 under the isothermal ageing environments.

Fig. 8. Relative electrical conductivity of: (a) PTh, (b) PTh/SnO2-1, (c) PTh/SnO2-2 and (d) PTh/SnO2-3 under cyclic ageing conditions.

89


RT
0.5 M

Resistance change

Conductivity change

Filaments

Pellet
8.

7.

Polythiophene, polypyrrole,
polyaniline derivatives
Polystyrene/polyaniline
nanoblend
PTh/SnO2 nanocomposite
6.

chemical oxidative and melt
processing
chemical oxidative

Resistance change
Thin film

ClO4 doped polypyrrole
5.

Electrochemical deposition

Thin film

butan-1-ol, butan-2-ol and
2-methyl propan-2-ol

[37]
25  C
e

[35]
30  C and 120  C

Quartz crystal
microbalance (QCM)
technique
Resistance change
Thin film
Polyaniline
4.

Electrodeposition

Resistance change
3.

chemical oxidative

Pellet

methanol, ethanol, 1-propanol,

2-propanol
methanol, ethanol, 1-propanol,
1-butanol, 1-pentanol
methanol, ethanol, 1-propanol

[36]

[33,34]
25  C
2-17 mg L-1 and 2e60 ppm

RT

[32]
e
3000 ppm

2000 ppm
Conductivity change
Pellet

Polythiophene/graphene
nanocomposite
Polyaniline
2.

chemical oxidative

0.15e2.01% and 0.61e17.62%
(mass/mass)

1600e4800 ppm

[30]
RT

[15]

butan-1-ol, butan-2-ol and
2-methyl propan-2-ol
ethanol, methanol, sec-butanol,
tert-butanol, iso-propanol
methanol, ethanol, propanol,
butanol, heptanol
methanol, ethanol, 1-propanol
and 2-propanol
Conductivity change
Pellet
TiO2@PPy nanocomposite
1.

chemical oxidative

Analyte
Technique
Type of sensor
Method of Preparation of
material

A sensor may be defined as a device which can detect and
measure a physical quantity and can give a clear output for it. The

DC electrical conductivities of conducting polymers (PTh) and
their nanocomposites could be altered by changing the dopants as
well as the composition of fillers [16,17,28,30]. The polarons act as
the charge carriers and the electrical conductivity is governed by
the ease of movement of these polarons along with the conjugated
system of the polymer back-bone. The electrical conduction could
significantly be modified by any type of interaction with the
polymer chain that can affect the quantity and the mobility of
these charge carriers either alongside the polymer chain or by a
tunnelling/hopping mechanism. The porous structure of PTh/
SnO2-3 permits the penetration of analyte gas molecules into the
PTh film. Then, the analyte gas molecules get adsorbed on the
surface of PTh/SnO2-3 and interact with polarons of PTh, causing a
change in the electrical conductivity. This phenomenon occurs
significantly in nanocomposite materials in which the electrical
conductivity is explained through the transfer of electrons between fillers (nanoparticles) and polymers. Therefore, robust
sensor consequences are detected for conducting polymer nanocomposites with various oxidising as well as reducing gases/vapours. For that reason, the highly porous structure and the large
surface area of sensors which provide a greater extent of
adsorption of analyte molecules on the sensor surface are beneficial because adsorption is considered to be the first step in
sensing. The chemical/gas/vapour sensing characteristics of PTh in
terms of a change in electrical conductivity is based on the above
theory [7,10,28,30].

Table 1
Comparison of our present study with other existing alcohol sensing studies based on conducting polymers.

3.7. Sensing

Conc. analyte

where: sT and s40 stand for the DC electrical conductivity
(S,cmÀ1) at temperature T ( C) and at 40  C, i.e. at the start of each
cycle, respectively [28,30]. The relative DC electrical conductivity
of each sample was evaluated for four succeeding cycles. In the
case of PTh (see Fig. 8a), the outcome reveals that the conductivity
increased steadily for the initial two cycles and follows a regular
rising trend in the number along with the mobility of the charge
carriers (polarons and bipolarons) at elevated temperatures. But,
for the third and fourth cycles the conductivity decreases due to
the material damage and the loss of conjugation. PTh/SnO2-1
(Fig. 8b) and PTh/SnO2-2 (Fig. 8c) show a gain in the electrical
conductivity with good stability for three successive cycles. PTh/
SnO2-3 (Fig. 8d) displayed the maximal upsurge in conductivity
with an excellent stability and reversibility. Therefore, PTh/SnO2-3
can be a potential candidate for applications in various technological fields where electrical conductivity retention for several
repetitions is required even at higher temperatures. As a consequence, it may be concluded that PTh/SnO2-3 presents the utmost
stable semiconducting behaviour among all samples under cyclic
ageing environments.

1M

(3)

Material

sT
s40

S. No

sr ¼

Worki-ng Temp.

3.6.2. Stability under cyclic ageing conditions
The DC electrical conductivity retaining aptitude of PTh, PTh/
SnO2-1, PTh/SnO2-2 and PTh/SnO2-3 was also examined by a cyclic
ageing method within the temperature range of 40e120  C, and is
represented in Fig. 8. The following equation was employed for the
calculation of the relative DC electrical conductivity (sr):

RT

Ref.

120  C due to its higher DC electrical conductivity and excellent
isothermal stability.

This study

A. Husain et al. / Journal of Science: Advanced Materials and Devices 5 (2020) 84e94

chemical oxidative

90


A. Husain et al. / Journal of Science: Advanced Materials and Devices 5 (2020) 84e94

91

1-pentanol [36]. Segal et al. prepared a polystyrene/polyaniline
nano blend and studied its sensing properties towards methanol,
ethanol and 1-propanol [37]. A comparative study of our work with
the literature based on the method of preparation, the form of
sensor, sensing techniques, analyte concentration and operating
temperature etc. is presented in Table-1.
As evident from Table-1, the majority of reported literature
data suggests that lower alcohols like methanol and ethanol were
more selective than higher alcohols. But, very little work has been
done on the selective sensing among the higher alcohols containing different side chains viz. primary, secondary and tertiary
alcohols. In this work, we studied the sensitivity, reversibility and
selectivity of some higher alcohols containing different
parent chains, i.e. butan-1-ol (1 alcohol), butan-2-ol (2 alcohol)
and 2-methyl propan-2-ol (3 alcohol). In our best knowledge, this
is the first attempt to utilise PTh/SnO2 nanocomposite for this type
of study.

Fig. 9. DC electrical conductivity alteration of PTh/SnO2-3 on exposure to 1, 2 and
3 alcohols vapours followed by ambient air with respect to time.

In our previous work, we reported that the binary polypyrrole/
titania (TiO2@PPy) nanocomposites serves as an alcohol sensor
which selectively detects butan-2-ol in the presence of other alcohols like butan-1-ol and 2-methyl propan-2-ol vapours [15]. In
another study, we used a polythiophene/graphene nanocomposite
as a highly selective and reversible ethanol sensor with a lower
detection limit of 400 ppm at room temperature [30]. Athawale
et al. utilised polyaniline and its substituted derivatives as sensing
materials for the detection of alcohol vapour viz. methanol, ethanol,
propanol, butanol and heptanol [32]. Ayad et al. reported the

detection of methanol, ethanol, 1-propanol and 2-propanol using
polyaniline thin films by the quartz crystal microbalance technique
[33,34]. Babaei et al. reported that PPy-ClO4 films could be
employed as an aliphatic alcohol vapour sensor. The sensor
showed the highest sensitivity for methanol as compared to
ethanol, 1-propanol and 2-propanol [35]. Hatfield et al. used polythiophene, polypyrrole and polyaniline derivatives to fabricate an
n-alcohol sensor, i.e. methanol, ethanol, 1-propanol, 1-butanol and

Fig. 10. DC electrical conductivity alteration of PTh on exposure to 1, 2 and 3 alcohols vapours followed by ambient air with respect to time.

3.7.1. Sensing response as a function of change in DC electrical
conductivity
The sensitivity of PTh and PTh/SnO2-3 towards higher
alcohols such as butan-1-ol (1 alcohol), butan-2-ol (2 alcohol)
and 2-methyl propan-2-ol (3 alcohol) was investigated by
quantifying the alterations in their DC electrical conductivity at
room temperature through exposing them in the environment of
alcohol vapour for 50 s followed by ambient air for another 50 s
(Fig. 9 & Fig. 10). The concentration of the aqueous solutions of
each of the alcohols tested was 0.5 M. When PTh/SnO2-3 was
exposed in the environment of alcohol vapour, a decrease in the
overall DC electrical conductivity was detected with the increasing
exposure time. As soon as the pellet was removed from the alcohol
vapour environment and kept in the ambient air, the conductivity
started to increase with respect to time. Different kinds of alcohols
displayed different behaviours in the alcohol vapours environment
and air. In the case of 1 alcohol, the DC electrical conductivity
change was found to be maximal while it was minimal in the case
of 2 alcohol. The DC electrical conductivity change in the environment of 1 alcohol, 2 alcohol and 3 alcohol was found to be
7.7 Â 10À3 S,cmÀ1, 5.6 Â 10À3 S,cmÀ1 and 2.5 Â 10À3 S,cmÀ1,

respectively. The decrease in the electrical conductivity may be
attributed to the charge transfer between alcohol (i.e. the lone
pairs of electrons of alcohol molecules) and the polarons of PTh.
When the lone pairs of electrons on the oxygen atom in alcohol
molecules interact with the polarons of PTh, the mobility of the
polarons (charge carriers) decreases and some polarons may also
get neutralised which causes a decrease in the DC electrical conductivity. As soon as the pellet was kept in ambient air, the molecules of alcohol get desorbed, and the electrical conductivity
started to rise. When the PTh pellet was exposed to the environment of 1 alcohol, 2 alcohol and 3 alcohol, the change in
electrical conductivity was detected to be 3.2 Â 10À4 S,cmÀ1,
2.5 Â 10À4 S,cmÀ1 and 1.2 Â 10À4 S,cmÀ1, respectively. In the case
of PTh/SnO2-3, the change in the electrical conductivity (sensing
response) in the environment of 1 alcohol, 2 alcohol and
3 alcohol was 24.06, 22.4 and 20.8 times of the change in conductivity of PTh, respectively. Thus, PTh/SnO2-3 exhibits superior
sensing efficacy compared to PTh. The significant improvement in
the sensing efficiency of PTh/SnO2-3 may be attributed to the
higher electrical conductivity and highly porous and large surface
area which provides a greater number of active sites in which the
adsorption of analyte vapours takes place.
3.7.2. Reproducibility test
The sensors based on PTh and PTh/SnO2-3 were also tested for
their reproducibility. The reproducibility of the sensing response of


92

A. Husain et al. / Journal of Science: Advanced Materials and Devices 5 (2020) 84e94

Fig. 11. Reversibility of PTh/SnO2-3 on alternate exposure to 1, 2 and 3 alcohols vapours followed by ambient air with respect to time.

PTh and PTh/SnO2-3 was measured by first exposing the pellet of

the sample in alcohol vapours for 30 s and after that 30 s in ambient
air for a total duration of 180 s (Fig. 11). PTh/SnO2-3 shows excellent
reproducibility in the environment of 1 alcohol due to the greater
extent of adsorption and complete desorption of the analyte vapour
in the ambient air. While in the environment of 2 alcohol and
3 alcohol, PTh/SnO2-3 shows relatively low reversibility because of
the considerably lower extent of adsorption and partial desorption.
In contrast, PTh exhibits poor reproducibility in the environment of
1 alcohol, 2 alcohol as well as 3 alcohol due to the slow rate of
adsorption and the very poor rate of desorption.

However, PTh shows some reversible nature in 1 alcohol
vapour due to the ease of adsorption and the interaction between
polarons and lone pairs of the oxygen atom of the alcohol molecules (Fig. 12).
The sensor-based on PTh/SnO2-3 shows the highest electrical
conductivity change (sensing response) and reproducibility in case
of 1 alcohol which may be explained by the following points: (1)
due to the linear structure of 1 alcohol, the extent of adsorption is
very high and the lone pairs of electrons of the oxygen atom of the
alcohol molecules can freely interact with the polarons of PTh; (2)
this interaction causes a decrease in the mobility as well as the

Fig. 12. Reversibility of PTh on alternate exposure to 1, 2 and 3 alcohols vapours followed by ambient air with respect to time.


A. Husain et al. / Journal of Science: Advanced Materials and Devices 5 (2020) 84e94

Fig. 13. Recommended mechanism of interaction of different alcohols with PTh/SnO2
nanocomposites.

neutralisation of the polarons, which is accountable for a decrease
in the DC electrical conductivity; (3) due to the branched structure
of 2 alcohol and 3 alcohol, the rate of adsorption becomes relatively slow, and the interaction between the polarons and the lone
pairs of alcohol molecules decreases due to a greater steric hindrance. The greater the crowding, the poorer will be the electrondonating capacity. That is why, in the case 3 alcohols, the
sensing response is minimal. Thus, PTh/SnO2-3 nanocomposite
may be used to fabricate a highly sensitive, selective and reproducible butan-1-ol (1 alcohol) sensor.
3.7.3. Proposed Mechanism for sensing
The sensing response (i.e. change in DC electrical conductivity)
of the tested pellets as a function of the difference in the DC electrical conductivity of PTh/SnO2-3 to different alcohol vapours viz
1 alcohol, 2 alcohol and 3 alcohol is based on the decline in the
DC electrical conductivity by exposing to the analyte vapour and
the return to the approximately initial value as soon as exposed to
the ambient air. The mechanism involved in the sensing aptitude of
PTh/SnO2-3 was defined by means of the variation in the DC electrical conductivity (i.e. sensing response) through an easily explicable adsorptionedesorption method of alcohol vapours at
ambient temperature on the surface of PTh/SnO2-3, as depicted in
Fig. 13. In the presence of the alcohol molecules, which is a source of
electrons, the lone pairs on the oxygen atom of the alcohol molecules interact with the polarons of PTh/SnO2-3. Consequently, the
mobility of the polarons retards, which spontaneously diminishes
the DC electrical conductivity. As soon as the pellet was kept in
the ambient air atmosphere, the alcohol molecules started to
desorb from pores of PTh/SnO2-3. Subsequently, the electrical
conductivity started to revert towards the original value. So, the
adsorptionedesorption method of alcohol molecules on the highly
porous and large surface area of PTh/SnO2-3 significantly alters the
mobility of the polarons which is the reason for the drop and rise in
the electrical conductivity in the environment of the alcohol vapour
and the ambient air in that order.
4. Conclusion
In this study, PTh and PTh/SnO2 nanocomposites were synthesised with different weight percentage viz. 5%, 10% and 15% of
SnO2 nanoparticles by the in-situ chemical oxidative method.

Different instrumental techniques such as FTIR, SEM, TEM, UV-vis
absorbance spectroscopy and XRD were utilised for the

93

characterization of the as-synthesised materials. We evaluated the
electrical properties comprehensively by studying the DC electrical
conductivity retention performances of all the materials under
accelerated isothermal as well as cyclic ageing conditions. Among
all materials, PTh/SnO2-3 was found to be the best semiconductor
showing an initial DC electrical conductivity of 9.82 Â 10À3 S,cmÀ1.
The PTh/SnO2-3 based sensor showed the best sensitivity, selectivity as well as reproducibility towards butan-1-ol (1 alcohol) as
compared to butan-2-ol (2 alcohol), and 2-methyl propan-2-ol (3
alcohol). In the case of PTh/SnO2-3, the change in DC electrical
conductivity (sensing response) in the environment of 1 alcohol,
2 alcohol and 3 alcohol was found to be 24.06, 22.4 and 20.8 times
the change in conductivity of PTh, respectively. The sensing
mechanism was successfully cited by the adsorption of the alcohol
vapours on the large surface area of PTh/SnO2 nanocomposites
followed by an electronic interaction between the polarons and the
lone pairs of electrons of the oxygen atoms of alcohol molecules
which cause a decrease in the DC electrical conductivity. Thus, this
study suggests that these PTh/SnO2 nanocomposites could be utilised as a semiconducting material in various electrical and electronic applications besides their sensing capability towards
different alcohol vapours tested in this study.
Declaration of Competing Interest
None.
Funding
This research did not receive any specific grant from funding
agencies in the public, commercial, or not-for-profit sectors.
Acknowledgements

Ahmad Husain thankfully acknowledges USIF, AMU.
References
[1] M. Khan, T. Anwer, F. Mohammad, Synthesis and sensing properties of sulfonated multi-walled carbon nanotube and graphene nanocomposites with
polyaniline, J. Sci. Adv. Mater. Dev. 4 (2019) 132e142, />j.jsamd.2019.02.002.
[2] N. Abraham, R.R. Krishnakumar, C. Unni, D. Philip, Simulation studies on the
responses of ZnO-CuO/CNT nanocomposite based SAW sensor to various
volatile organic chemicals, J. Sci. Adv. Mater. Dev. 4 (2018) 125e131, https://
doi.org/10.1016/j.jsamd.2018.12.006.
[3] C.M. Hung, D. Thi, T. Le, N. Van Hieu, On-chip growth of semiconductor metal
oxide nanowires for gas sensors: a review, J. Sci. Adv. Mater. Dev. 2 (2017)
263e285, />[4] K.R. Jawaher, R. Indirajith, S. Krishnan, R. Robert, S.K.K. Pasha, K. Deshmukh,
S.J. Das, Hydrothermal synthesis of CeO2-SnO2 nanocomposites with highly
enhanced gas sensing performance towards n-Butanol, J. Sci. Adv. Mater. Dev.
3 (2018) 139e144, />[5] S. Pandey, Highly sensitive and selective chemiresistor gas/vapor sensors
based on polyaniline nanocomposite: a comprehensive review, J. Sci. Adv.
Mater. Dev. 1 (2016) 431e453, />[6] M.H. Suhail, O.G. Abdullah, G.A. Kadhim, Hydrogen sulfide sensors based on
PANI/f-SWCNT polymer nanocomposite thin films prepared by electrochemical polymerization, J. Sci. Adv. Mater. Dev. 4 (2019) 143e149, https://
doi.org/10.1016/j.jsamd.2018.11.006.
[7] H. Bai, G. Shi, Gas sensors based on conducting polymers, Sensors 7 (2007)
267e307. www.mdpi.org/sensors.
[8] D. Kwak, Y. Lei, R. Maric, Ammonia gas sensors : a comprehensive review,
Talanta 204 (2019) 713e730, />[9] A. Dey, Semiconductor metal oxide gas sensors : a review, Mater. Sci. Eng., B
229 (2018) 206e217, />[10] T. Sen, S. Mishra, N.G. Shimpi, Synthesis and sensing applications of polyaniline nanocomposites : a review, RSC Adv. 6 (2016) 42196e42222, https://
doi.org/10.1039/C6RA03049A.
[11] F. Mohammad, Comparative studies on diffusion behaviour of electrochemically prepared polythiophene and polypyrrole : effect of ionic size of dopant,
Synth. Met. 99 (1999) 149e154.


94

A. Husain et al. / Journal of Science: Advanced Materials and Devices 5 (2020) 84e94

[12] F. Mohammad, Compensation behaviour of electrically conductive polythiophene and polypyrrole, J. Phys. D Appl. Phys. 951 (1998) 951e959.
[13] M.O. Ansari, F. Mohammad, Thermal stability and electrical properties of
dodecyl-benzene-sulfonic-acid doped nanocomposites of polyaniline and
multi-walled carbon nanotubes, Compos. B. 43 (2012) 3541e3548, https://
doi.org/10.1016/j.compositesb.2011.11.031.
[14] M. Khalid, F. Mohammad, Preparation, FTIR spectroscopic characterization
and isothermal stability of differently doped fibrous conducting polymers
based on polyaniline, Synth. Met. 159 (2009) 119e122, />10.1016/j.synthmet.2008.08.005.
[15] A. Sultan, T. Anwer, S. Ahmad, F. Mohammad, Preparation, characterization,
and dynamic adsorption e desorption studies on polypyrrole encapsulated
TiO 2 nanoparticles, J. Appl. Polym. Sci. 43411 (2016) 1e11, />10.1002/app.43411.
[16] M.O. Ansari, F. Mohammad, Chemical Thermal stability, electrical conductivity and ammonia sensing studies on p -toluenesulfonic acid doped polyaniline : titanium dioxide (p TSA/Pani : TiO 2) nanocomposites, Sensor.
Actuator. B Chem. 157 (2011) 122e129, />j.snb.2011.03.036.
[17] S. Ahmad, M. Mujahid, F. Mohammad, Graphene/nickel oxide-based
nanocomposite of polyaniline with special reference to ammonia
sensing, ACS Omega 3 (2018) 9378e9387, />acsomega.8b00825.
[18] S. Bai, K. Zhang, J. Sun, D. Zhang, R. Luo, Polythiophene-WO 3 hybrid architectures for low-temperature H 2 S detection, Sensor. Actuator. B Chem. 197
(2014) 142e148, />[19] J. Huang, Y. Kang, T. Yang, Y. Wang, S. Wang, Preparation of polythiophene/
WO 3 organic-inorganic hybrids and their gas sensing properties for NO 2
detection at low temperature, J. Nat. Gas Chem. 20 (2011) 403e407, https://
doi.org/10.1016/S1003-9953(10)60196-X.
[20] S.S. Barkade, D.V. Pinjari, U.T. Nakate, A.K. Singh, P.R. Gogate, J.B. Naik,
S.H. Sonawane, A.B. Pandit, Process Intensification Ultrasound assisted synthesis of polythiophene/SnO 2 hybrid nanolatex particles for LPG sensing,
Chem. Eng. Process. Process Intensif. 74 (2013) 115e123, />10.1016/j.cep.2013.09.005.
[21] F. Kong, Y. Wang, J. Zhang, H. Xia, B. Zhu, Y. Wang, S. Wang, S. Wu, The preparation and gas sensitivity study of polythiophene/SnO 2 composites, Mater. Sci.
Eng., B 150 (2008) 6e11, />[22] A. Tripathi, S.K. Mishra, I. Bahadur, Optical properties of regiorandom polythiophene/Al 2 O 3 nanocomposites and their application to ammonia gas
sensing, J. Mater. Sci. Mater. Electron. 26 (2015) 7421e7430, />10.1007/s10854-015-3373-9.
[23] M. Xu, J. Zhang, S. Wang, X. Guo, H. Xia, Y. Wang, S. Zhang, W. Huang, S. Wu,

Gas sensing properties of SnO 2 hollow spheres/polythiophene inorganic e
organic hybrids, Sensor. Actuator. B Chem. 146 (2010) 8e13, />10.1016/j.snb.2010.01.053.

[24] J.P. Cheng, J. Wang, Q.Q. Li, H.G. Liu, Y. Li, A review of recent developments in
tin dioxide composites for gas sensing application, J. Ind. Eng. Chem. 44 (2016)
1e22, />[25] R. Li, S. Chen, Z. Lou, L. Li, T. Huang, Y. Song, Fabrication of porous SnO 2
nanowires gas sensors with enhanced sensitivity, Sensor. Actuator. B Chem.
252 (2017) 79e85, />[26] A. Beniwal, Chemical Electrospun SnO 2/PPy nanocomposite for ultralow ammonia concentration detection at room temperature, Sensor.
Actuator. B Chem. 296 (2019) 126660, />j.snb.2019.126660.
[27] G.E. Patil, D.D. Kajale, V.B. Gaikwad, G.H. Jain, Preparation and characterization
of SnO 2 nanoparticles by hydrothermal route, Int. Nano Lett. 2 (2012) 2e6,
/>[28] A. Husain, S. Ahmad, F. Mohammad, Thermally stable and highly sensitive
ethene gas sensor based on polythiophene/zirconium oxide nanocomposites,
Mater. Today Commun. (2019) 100574, />2019.100574.
[29] R. Venkatesan, L. Cindrella, Semiconducting composite of chalcone-bridged
polythiophene and titania, its ammonia vapor sensing property, Mater. Sci.
Semicond. Process. 34 (2015) 126e137, />2015.02.025.
[30] A. Husain, S. Ahmad, F. Mohammad, Synthesis, characterisation and ethanol
sensing application of polythiophene/graphene nanocomposite, Mater. Chem.
Phys. 239 (2020) 122324, />122324.
[31] O. Lupan, L. Chow, G. Chai, H. Heinrich, S. Park, A. Schulte, Growth of
tetragonal SnO 2 microcubes and their characterization, J. Cryst. Growth J. 311
(2008) 152e155, />[32] A.A. Athawale, M.V. Kulkarni, Polyaniline and its substituted derivatives as
sensor for aliphatic alcohols, Sensor. Actuator. B Chem. 67 (2000) 173e177.
[33] M.M. Ayad, N.L. Torad, Alcohol vapours sensor based on thin polyaniline salt
film and quartz crystal microbalance, Talanta 78 (2009) 1280e1285, https://
doi.org/10.1016/j.talanta.2009.01.053.
[34] M.M. Ayad, G. El-hefnawey, N.L. Torad, A sensor of alcohol vapours based on
thin polyaniline base film and quartz crystal microbalance, J. Hazard Mater.
168 (2009) 85e88, />[35] M. Babaei, N. Alizadeh, Methanol selective gas sensor based on nanostructured conducting polypyrrole prepared by electrochemically on interdigital electrodes for biodiesel analysis, Sensor. Actuator. B Chem. 183 (2013)

617e626, />[36] J.V.H.P. Neavesa, P.J. Hicks, K. Persaudb, P. Travers, Towards an integrated
electronic nose using conducting polymer sensors, Sensor. Actuator. B Chem.
18 (1994) 221e228.
[37] E. Segal, R. Tchoudakov, M. Narkis, A. Siegmann, Y. Wei, Polystyrene/polyaniline
nanoblends for sensing of aliphatic alcohols, Sensor. Actuator. B Chem. 104 (2005)
140e150, />