Electrochemical Synthesis of Polyaniline –Single W alled Carbon Nanotube
Platform for Heavy Metal Ion Sensing
Megha A. Deshmukh, Harshada K. Patil, Sumedh D. Gaikwad, Gajanan A. Bodkhe, Mahendra D. Shirsat*
Dept. of Physics, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad (MS) - INDIA
Email- mdshirsat.phy@bamu.ac.in
ABSTRACT: The combination of conducting polymer Polyaniline (PANI) and Single Walled Carbon Nanotubes (SWNTs) composite
materials shows admirable electrochemical and electrical properties. In the present investigation PANI/SWNTs composite was prepared by
electrochemical method using cyclic voltammetry (CV) technique with the answer of less efforts and less time consumption using Dodecyl
benzene sulphonic acid sodium salt (DBSA) as surfactant at room temperature. The resulting composite microstructure can be utilized for
the application of heavy metal ion sensing acting as a platform for better sensing performance and stability of the sensor, overcoming the
limitations of individual materials. Atomic Force Microscope (AFM) indicates that PANI is wrapped around the SWNTs, where SWNTs
acting as a backbone of resulting microstructure. Fourier Transform Infrared Spectroscopy (FTIR), UV-Visible Spectroscopy, Raman
Spectroscopy confirms the chemical bonding and formation of the composite material revealing towards the better chemical bonding and
microstructure formation.
K ey words: Electrochemical, Heavy Metal Ion, SWNTs, Polyaniline etc.
environmental stability, low cost, ease of synthesis and charge
control ability by charge transfer doping.
Pei-Fen Hsu et al. has reported that Polyviologen (PV) modified
glass carbon electrode for Cu (II) ion sensing but the sensing
ability is pH dependent because for higher pH solution of analyte,
sensor shows good response but PV films are not stable at high
pH level and interference due to other species is also an
unresolved issue [20]. Joanna Lim W ee Ling et al. suggested
that poly (4-vinylpyridine-co-aniline)-modified electrode is
suitable for cadmium ion sensing but interference due to other
ions was an unsolved issue [21].
Thus, we have premeditated to utilize the ultimate properties of
these two organic materials conducting polymer Polyaniline
(PANI) and SWNTs for the synthesis of platform for heavy metal
ion sensing by overcoming their limitations and drawbacks. We
have intended to synthesize PANI/SWNTs composite by
electrochemical method and then its modification by chelating
ligand which will be selective for particular metal ion. CNTs will
act as basic conduction backbone, which will not directly get in
contact with the analyte through which we can tackle the problem
of dislodging, surface infection due to analyte and hydrophobic
nature of CNTs. Chelating ligands have two or more than two
binding sites that serve the purpose of selective detection of
heavy metal ions by forming a ring like structure. π- π interaction
between conducting polymers and SWNTs will lead to enhance
charge carrying capacity resulting in faster signal transduction.
Many researchers have developed number of chemical methods
for the synthesis of conducting polymer/carbon nanotubes
composite. Benlin He et al. has reported PANI/SWNTs
composite but the process involved by reflux method at 1840C.
Overall procedure is very prolonged and temperature dependent
[22]. Ashok K. Sharma et al. has carried out PANI/CNT
composite synthesis via different routes but the procedure is also
time consuming and temperature dependent [23]. Tursun
Abdiryim et al. and Y u-Jeong LIM et al. has reported synthesis
of PANI/SWNT composite but the used methods are very tedious
and time consuming [24, 25]. Leila Nikzad et al. has done
synthesis of PANI/CNT composite but the whole procedure is
very lengthy and temperature dependent [26].
INTRODUCTION:
Now a day’s heavy metal ions are becoming severe risk to human
health because they get in direct contact with atmosphere through
biogeochemical processes, which cause serious risk to human
health [1-3]. There are continuous efforts has been taken place by
researchers to come up with simple, sensitive and accurate
methods for detection of heavy metal ions [4-6]. Variety of
organic materials viz. organic conducting polymers, carbon
nanotubes, metal oxides have attracted much more interest of
material scientists, chemists and physicists for the selective and
sensitive sensor systems.
Carbon Nanotubes (CNTs) play vital role in the current material
science research field, due to their superior electrical, mechanical,
chemical and structural properties which are superior to other
organic materials [7]. Li et al., Tan et al., Rao et al. and Gao et
al. has reported CNTs based heavy metal ion sensors are much
efficient for detection of heavy metal ions [8-14]. Changlun
Chen et al. and Shitong Y ang et al. has recommended that
oxidized MWCNTs become ideal material for the detection of Ni
(II) from aqueous solution [15-16]. Instead of all these novel and
attractive properties, CNTs also have some shortcomings like,
CNTs ion adsorption properties depends upon the isoelectric
point and pH of the analyte. At pH below the isoelectric point
desorption of metal ions increases which will affect performance
of the sensors [17-19]. CNTs are also weak adsorbents of analyte
due to their hydrophobic nature [19]. pH of the solution also
influences the performance of the sensor because it affects the
surface of functionalized CNTs [19].
Conducting polymers are also unconventional organic materials,
which are also fascinated by the researchers in advanced
applications due to their idyllic chemical, mechanical, electrical
properties, good process ability,
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Thus, the objective of the present investigation is to fabricate
better sensing platform using simple but novel synthesis method
for the application of heavy metal ion sensing. The platform is
based on the composite of single walled carbon nanotubes
(SWNTs) and Polyaniline (PANI) composite which have better
electrical, mechanical and chemical properties.
MATERIALS AND METHODS:
Aniline of reagent grade purchased from Sigma Aldrich
(Bangalore, India), Dodecyl benzene sulphonic acid sodium salt
(DBSA)-purified procured from Kemphasol (Bombay) used as
surfactant and organic solvent to form fine suspension of
SWNTs, H2SO4 HPLC grade obtained from Rankem (India),
COOH functionalized SWNTs were purchased from Nanoshel
LLC. Stainless Steel (SS type 304, 0.5mm thick, and area 1*1
cm2) substrates were purchased from SSD Enterprises,
Aurangabad.
Fig. 1 CVs of growth of PANI and PANI/SW NTs
composite films
In the voltammogram of PANI and PANI/SWNTs can be
observed that both the voltammogram are slightly similar in
shape but there is only difference in current densities and
oxidation and reduction peaks. PANI curve shows current density
for six cycles up to 0.06 Amp. However, voltammogram of
PANI/SWNTs shows rapid change in the current densities due
the incorporation of SWNTs up to 0.16 Amp. It can also be
observed that voltammogram of PANI/SWNTs shows clear and
extra reduction peaks compared to PANI which shows the
tendency of material to acquire electrons. More the positive
potential greater the affinity of material towards electrons. The
transfer of electrons in the material shows the reduction potential,
which is very useful to store the energy of material in the reduced
compound. The reduction potential helps to increase conductivity
and stability of organic materials. Thus, PANI/SWNTs show
more conductivity and stability.
Synthesis of PANI and PANI/SW NTs composite by
electrochemical method: For the preparation of PANI-SWNTs
composite by electrochemical method, 20wt. % of SWNTs with
respect to Aniline monomer was dissolved in 0.5 ml of DBSA
and then ultrasonicated for 4 hours at room temperature in order
to disperse SWNTs bundles uniformly. Then, 0.25M of aniline
monomer was dissolved in 0.5M H2SO4 and stirred for 20 min.
This content was transferred to the flask containing ultrasonicated
suspension of SWNTs. The reaction mixture of (Aniline, H 2SO4 +
SWNTs) was put for ultra-sonication for 20 min at room
temperature to form an electrolyte of PANI-SWNTs composite.
The PANI electrolyte was also prepared by same method
mentioned above but without incorporation of SWNTs.
PANI and PANI/SWNTs composite films were deposited on SS
substrate by electrochemical polymerization method using cyclic
voltammetry (CV) technique, at the scan rate of 0.1 V/S between
0.1 to 1.0V for 10 segments for composite in a solution of 0.5M
H2SO4 + 0.25M aniline dissolved SWNTs. Electrochemical
polymerization was carried out in a three electrode system with a
SS substrate working electrode, platinum (Pt) plate counter
electrode and Ag/AgCl reference electrode. The electrochemical
polymerization of
PANI and PANI/SWNTs composite were
observed by dark green colored coating on SS (working
electrode). After deposition the films were rinsed with distilled
water and then dried at room temperature.
Raman spectroscopy analysis of PANI and PANI/SW NTs
composite structures: Below Fig.2 shows the Raman spectra of
pure PANI and PANI/SWNTs composite. The spectra show the
typical D&G bands at 1328 cm -1 and 1598 cm -1 respectively.
The intensity of D & G bands is observed to
G
D
D
RESULTS AND DISCUSSION
Electrochemical
polymerization
of
PANI
and
PANI/SW NTs composite: Fig. 1 shows the typical CV growth
of PANI and PANI/SWNTs composite. Continuous potential
scanning at 0.1 V/S in the potential range from 0.1 to 1.0V gives
a thin uniform dark green colored coating on the SS substrate.
The oxidation of aniline monomer starts at 0.1V in the
voltammogram. The CV recorded during continuous
scan shows the current increases with increasing each successive
cycle of the voltammogram, which confirms that the synthesized
films were electrically conductive and electro active. Thickness
of the film increases with increasing no. of cycles.
G
Fig.2 Raman spectra of PANI and PANI/SW NT composite
be increasing in the spectra of PANI/SWNT composite
Compared to pure PANI film revealing to the fact of
incorporation of SWNTs. The band at 1330 cm -1 show C-N+
vibrations at delocalized polaronic structures whose intensity
increases in the composite spectra due to SWNT dosage. The CN+ vibrations at 1330 cm -1 and C-C stretching vibrations at 1590
cm -1. These two sharper peaks show the S-S interaction between
PANI/SWNT during the process of polymerization.
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composite structure was done by modifying the composite
structure by EDTA using simply dip coating technique.
PANI/SWNTs composite was dipped in 0.01M EDTA solution
where EDC was used as activating agent in this solution for the
duration of 5 hours. After 5 hours film modified composite film
removed from the solution and rinsed thoroughly with distilled
water. Differential Pulse Voltammetry (DPV) technique was
used for the tracing of Cu++ ion in aqueous solution. EDTA
modified composite structure thin film was dipped in the solution
of Cu++ ion for 5 min. The concentration of Cu ions in the
solution was
1mM L-1.
Fourier Transform Infrared Spectroscopy of PANI and
PANI/SW NTs Composite: FTIR spectra of pure PANI and
PANI/SWNTs composite are shown in figure 3. The spectrum in
good agreement shows the C-H bending out of plane and in plane
at 860cm-1 and 1380cm-1. The peaks around 1425cm-1 and 1637
cm-1 show the emeraldine salt form of PANI and PANI/SWNTs
composite. The band around 3400 cm-1 shows the stretching of
N-H band of aromatic ring in PANI and PANI/SWNTs composite
structure. As compared to pure PANI, composite structure shows
reduction in the ratio of Benzoid to quinoid intensity indicating
the stabilized form of nanocomposite and correlated the result of
conductivity [27]. In the comparison of PANI and PANI/SWNT
composite spectrum, the composite spectrum shows the
appearance of special band at 1037Cm-1 which confirms the high
dosage of SWNTs in composite structure [28].This band also
contributes for the charge transfer and confirms the interaction
between SWNTs and quinoid ring of PANI [29].
Fig. 5 Differential pulse voltammogram of EDTA
modified PANI/SW NTs composite structure, recorded
for 1mM Cu++ ion concentration
Fig 6 shows the DPV voltammogram recorded for 1mM Cu++
ion concentrations. The resulting DPV shows the clear current
peak for the Cu ion accumulated modified composite structure
whether without accumulation of Cu ion i.e. reference curve does
not show any recognizable changes. In this technique the
potential was traced between -0.30 to -0.40 V. with the amplitude
of 0.05 V. The modified composite structure shows good affinity
towards Cu++ ions.
Fig. 3 FTIR of PANI and PANI/SW NTs composite
structure
Morphological and Structural Characterization of PANI
and PANI/SW NTs Composite: After electrochemical
deposition of PANI and PANI/SWNTs, films were examined by
AFM with non-contact mode. The fig. 5[A] shows a 3D view of
an area of 5*5µm AFM scan of electrochemically synthesized
PANI/SWNTs composite film and Fig 5 [B] shows 3D view of an
area of 3*3µm.
A
CONCLUSION
We have successfully synthesized and characterized
PANI/SWNTs composite formation which is possible due to
the donor acceptor phenomenon of two organic materials. The
method used for composite formation makes it possible for
aniline molecules to polymerize and deposit on the surface of
SWNTs uniformly, whereas SWNTs can completely wrapped
by PANI. The method reported in current investigation for the
synthesis of composite structure is simple to perform and fewer
efforts
consuming revealing towards reduction of time
consuming job. .An AFM study confirms that resulting PANI
/SWNTs composite film was a uniform with lower defect
density. Spectroscopic characterizations of consequential
composite structure confirm the better structure information by
chemical bonding between PANI and SWNTs molecules.
PANI/SWNTs composite structure which was further modified
by EDTA has been proved to be highly sensitive
and reliable for trace analysis of Cu++ ion in conjugation with
Differential Pulse Voltammetry (DPV) technique. The
detection limit of 1mM L-1 was obtained. Thus the proposed
PANI/SWNTs composite structure will offer easy way of
synthesis and its potential application for monitoring the heavy
metal ions.
B
Fig. 4 AFM scan image of PANI/SW NTs composite film
3D view of [A] composite structure [B] PANI structure
Fig. 5 (B) shows the morphological structure of PANI which
looks like cloudy structure whereas composite structure shows
the rod like structure which is due to incorporation of SWNTs.
The AFM scan image of PANI/SWNTs composite film signifies that the PANI molecules are completely bonded onto the
surface of SWNTs. This result in forming thin layer where
SWNTs acts as backbone of the PANI coated structure.
Electrochemical analysis of PANI/SW NTs Composite for
Cu ion Sensing: Electrochemical analysis of PANI/SWNTs
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ACK NOW LEDGEMENT
The authors are grateful to Department of Science and
Technology (DST)-SERB, New Delhi, India (Project No.
SB/EMEQ-042/2013).
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