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Characterization of Polyaniline for Optical and Electrical Properties

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Vadiraj K T at JSS University
Vadiraj K T
S.L.Belagali
S.L.Belagali
S.L.Belagali
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Semiconductors have the conducting properties in between conductors and insulators. They have wide range of applications in the field of electronics and communications. Silicon compounds are mainly used as semiconducting materials, but the method of production is costly. Hence, the organic semiconductors can be considered, because of cheap raw materials for synthesis and their mode of construction or design. The organic semiconductors like polyaniline (Pani) can be considered because of its aromatic ring and lone pair of electrons on nitrogen for conducting electricity. It is a cheap, easily synthesizable and environmentally stable compound, with exciting electrochemical, optical and electrical properties. The synthesis was done by oxidation of aniline using hydrochloric acid and ammonium persulphate (APS), which forms an emeraldine salt. It was characterized by FT-IR, XRD, SEM NIR and UV-Vis Spectrophotometer.
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IOSR Journal of Applied Chemistry (IOSR-JAC)
e-ISSN: 2278-5736.Volume 8, Issue 1 Ver. II. (Jan. 2015), PP 53-56
www.iosrjournals.org
DOI: 10.9790/5736-08125356 www.iosrjournals.org 53 |Page
Characterization of Polyaniline for Optical and Electrical
Properties
Vadiraj K T1, S.L. Belagali2
1, 2Department of Studies in Environmental Science, University of Mysore, Mysore, India
Abstract: Semiconductors have the conducting properties in between conductors and insulators. They have
wide range of applications in the field of electronics and communications. Silicon compounds are mainly used
as semiconducting materials, but the method of production is costly. Hence, the organic semiconductors can be
considered, because of cheap raw materials for synthesis and their mode of construction or design. The organic
semiconductors like polyaniline (Pani) can be considered because of its aromatic ring and lone pair of electrons
on nitrogen for conducting electricity. It is a cheap, easily synthesizable and environmentally stable compound,
with exciting electrochemical, optical and electrical properties. The synthesis was done by oxidation of aniline
using hydrochloric acid and ammonium persulphate (APS), which forms an emeraldine salt. It was
characterized by FT-IR, XRD, SEM NIR and UV-Vis Spectrophotometer.
Keywords: Semiconductors, Silicon, Pani, environmentally stable, FT-IR XRD
I. Introduction
Semiconductor nano particles have attracted much interest during the past decade in both fundamental
reaches and technical applications due to their unique size and optical and electrical properties1.
Polymer based semiconductors are in the ogre of development because of their easy and cheap
synthetic procedures. The optical, chemical and electrical properties have provided a tremendous scope in the
field electrical conductivity compared to metallic counter parts. Conductive polymers like polyacetylene and
polyaniline have been subjected to numerous investigations in the past two decades 2,3.
Polyaniline is an excellent example of a conjugate polymer. The nanofibers of polyaniline can be
specifically synthesized for the application like rechargeable batteries4, biosensors5, corrosion protection layers6,
separation membranes7 and for molecular electronic materials. It is a cheap, easily synthesizable and
environmentally stable compound, with exciting electrochemical, optical and electrical properties.
Several methods like hard templates8, soft templates9, seeding10, electrochemical synthesis11 have been
reported. We synthesized the polyaniline by oxidation of aniline using hydrochloric acid and ammonium
persulphate (APS), which forms an emeraldine salt which shows excellent optical and electrical properties.
These properties were characterized by FT-IR, XRD, SEM NIR and UV-Vis Spectrophotometer.
II. Materials And Methods
2.1 Reagents:
The reagents required were procured from Merck chemicals. Aniline was first distilled before the
use. The catalyst, hydrochloric acid and oxidant ammonium persulphate (APS) were used as they were.
The water used was double distilled and demineralised.
2.2 Synthesis of polyaniline nanofibers:
First aniline was distilled and stored in a clean bottle. 2ml of distilled aniline was dissolved in
1N 100ml hydrochloric acid. Exactly weighed 6g of ammonium persulphate (APS), the oxidant was
dissolved in 100ml 1N hydrochloric acid. About 20ml of APS solution was added to the aniline solution
drop wise with constant stirring and kept for 24 hours undisturbed.
The obtained green polyaniline was washed with 1N hydrochloric acid to remove unreacted
aniline, then with distilled water to remove APS in the material, then with acetone to remove any organic
impurities. The filtered material was dried at 600C for 5 hours and stored in air tight container.
III. Characterization
The synthesized polymer was used to study the morphology through XRD. The XRD pattern was
recorded with the help of Rigaku miniflex II desktop X-Ray diffractometer using Cu –Kα X-ray of wave length
1.54Å. UV visible spectrophotometer was used for the analysis of band gap using the instrument Beckman
Coulter DU730 LSUV/Vis Spectrophotometer. To confirm the analysis UV Visible spectrophotometer NIR
spectra of the polymer was recorded. The Fourier Transfer Infrared spectrum was used for the analysis of
Characterization of Polyaniline for Optical and Electrical Properties
DOI: 10.9790/5736-08125356 www.iosrjournals.org 54 |Page
functional groups of the polymer, by dissolving Polyaniline in dimethyl sulphoxide (DMSO) with the help of
Perkin Elmer Spectrum Version 10.03.09.
IV. Results And Discussion
Polyaniline was characterized for various parameters for knowing the required properties. During
these experiments at most care was taken to reduce the error while analysis.
4.1. XRD analysis
In the Fig. 1, shows the X-ray diffraction pattern of Polyaniline at room temperature with four
diffraction peaks at 9.270, 15.160, 20.650 and 25.190 respectively.
Fig. 1 XRD pattern of emaraldine salt Polyaniline
Polymer is semi crystalline in nature as the patterns show sharp peaks, because of the presence of
benzenoid and quinonoid group in the Polyaniline. The interplanar crystalinity distance and crystal size
were calculated by Bragg’s Law and Debye Scher er equation.
where k= Bragg’s constant (0.9) and β is the full width half maximum (FWHM)12.
From the XRD pattern, it was found that the crystallinity of Polyaniline was 36.15% and the crystal
size was found to be 2.10nm.
4.2. UV-Visible spectrum Analysis
Ultra violet and visible spectra were recorded from the synthesized Polyaniline using Beckman Coulter
DU730 LS UV/Vis Spectrophotometer. Dimethyl sulphoxide(DMSO) was used as solvent during the analysis.
The Fig. 2 shows the UV-Visible pattern of Polyaniline. The spectrum has 2 peaks, one at 272 nm and
other one at 400 nm. The first peak represents the presence of aniline moiety. The second peak represents the
presence of benzenoid group and lone pair of electrons of nitrogen. This in turn leads to π-π* interactions of the
molecule and this shows that it is a conducting polymer.
Fig 2 UV-Visible spectrum of Polyaniline
The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are
separated by band gap which are fundamentally important, which it determines the electrical conductivity and
optical absorbance of polyaniline.
The band gap has been calculated by absorbance co-efficient data as a function wave length using Tauc
relation
αhϑ = B ( ϑh - Eg )n
Characterization of Polyaniline for Optical and Electrical Properties
DOI: 10.9790/5736-08125356 www.iosrjournals.org 55 |Page
where α is the absorbance coefficient hϑ is the photon energy, B is the band gap tailing parameter, Eg is a
characteristics energy which is termed as optical band gap and n is the transition probability index with discrete
value like 1/2, 3/2, 2 or more depending on transition of direct or indirect or forbidden band gap. The absorption
coefficient (α) at corresponding wavelength was calculated by using Beer Lambert’s relation.
where l is the path length and A is the absorbance.
The plot (αhϑ)1/2 vs hϑ was linear function existence of indirect allowed in transition in Polyaniline.
Extrapolation of linear dependence of the relation to yield corresponding band gap Eg. The value of the optical
energy of Pani synthesized obtained from Fig 3 is 3.73eV and this is due to π-π* transition from valance band to
conduction band at 381 nm and formation of polar on at 532 nm.
Fig. 3 Relation between (αhϑ)1/2 and hϑ for the polyaniline
4.3 FT-IR Spectrum
According to Fig 4, in the analysis of Fourier Transfer Infrared spectra, the main characteristic peaks of
PANI appeared at 3436, 2998, 1436, 1311, 1020, 952 and 698 cm−1. The peak at 3436 cm−1 is attributed to the
stretching mode of N–H band. C-H sp3 stretch and C=C stretch mode for benzenoid group was which occurred
at 2998cm-1 and 1436cm-1 respectively, while the peak at 1020 cm-1 was attributed for quinonoid unit of
polyaniline. The peaks at 952cm-1 and 698 cm-1 represent the C-H and C-C bands of benzenoid group13.
Fig. 4 FT-IR Spectrum of polyaniline
4.4. SEM Analysis
Polyaniline was subjected to Scanning Electron Microscopy to understand the structural make up. This
was recorded using Hitachi SEM Insrtument. Polyaniline was fibrous in nature and the length is around 800nm,
which shows that the material is in good shape as a nano fiber and can be further processed for needful
applications.
Characterization of Polyaniline for Optical and Electrical Properties
DOI: 10.9790/5736-08125356 www.iosrjournals.org 56 |Page
Fig. 5 SEM image of Polyaniline
V. Conclusion
Polyaniline is said to be one of the organic conductor. The optical properties show that it can
even acts as an organic semiconductor. The morphology of polymer studied by XRD shows that, crystal
size was 2.10nm which is helpful for the π-π* transition, was studied through UV-Visible
spectrophotometer. By this study, the band gap of the polymer was calculated through the Tauc’s rela tion
which was found to be 3.73eV.
The properties of polyaniline show that, it is a potent p type semiconductor, which could be used
in hybrid solar cell, where it may the conjugated with any inorganic n -type semiconductor like cadmium
sulphide or zinc oxide. By this one can expect a good output in the field of photovoltaics.
Acknowledgement
One of the Authors Mr. Vadiraj K.T. is thankful to UGC for providing financial support and UPE for
providing instrumentation facility
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... The presence of a band at 785 nm indicates the conducting phase of PANI (viz., PANI-ES) [68,69]. These transitions are presented schematically in Fig. S2 (Supplementary information). ...
... The calculated optical bandgap for PANI (ES) obtained from the Tauc plot is 3.2 eV, and for pure PVA hydrogel (for direct band gap,5.62eV, for indirect band gap, 5.05eV), are presented in Fig. 4b [64] and Verdiraj et al. [69]. Therefore, it may be concluded that all the samples possess semiconducting property. ...
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... Where A is the edge width parameter, ν is the frequency of incident photon, n is the power coefficient determines the possible electronics transitions and E g is the bandgap energy, α is the absorption coefficient [59,60]. The bandgap energy values of PANI, GNP and PANI-GNP were obtained by extrapolating the linear portion of αhν 2 into the E = hν axis in the αhν 2 versus hν plot ( figure 7). ...
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... CPs are large molecules (macromolecules) that are made up of smaller molecules (monomers) that can be linked together in various ways, resulting in microstructures [4]. Polyaniline (PANI), polypyrrole (PPY), and polythiophene (PTh) have complex dynamic structures and are a few CPs that have captivated smart materials research [5][6][7][8][9]. PANI is used in advanced polymeric materials because of its modifying abilities, favorable electrical conductivity, processing ease, unique redox properties, different oxidation states, wide applicability, environmental stability, low cost, and electron richness [10][11][12][13][14]. ...
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... The obtained XRD patterns were in agreement with other studies [36][37][38]. The obtained synthesized polymer is a semi-crystalline in nature as the patterns showed sharp peaks, because of the presence of benzenoid and quinonoid group in the Polyaniline [39]. ...
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Article
  • Nov 2011
Polyaniline-zinc sulphide nanocomposite has been synthesized by the chemical oxidative polymerization of aniline with ammonium peroxodisulphate as an initiator in presence of zinc sulphide nanoparticles. XRD, HRTEM, FTIR, UV-Vis spectroscopy and photoluminescence studies were done for the structural and optical characterization of the samples. The particle size of nanocomposites lies in between 6-11 nm. The d.c. conductivity of different PANI-ZnS samples have been investigated within a temperature range 77≤ T ≤ 300K. ZnS nanoparticles in the polyaniline matrix increases the conductivity by several orders.
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Modification of the Electrochemical and Corrosion Behavior of Stainless Steels with an Electroactive Coating
Article
  • May 1985
Electroactive polyaniline coatings have been deposited on ferritic stainless steels. The coatings appear to be deposited over the passive metal oxide film but can undergo electron transfer with the metal. Polyaniline immobilized on the alloys imparts a form of anodic protection which stabilizes the materials in mineral acids. Electrochemical and SEM characterization results are presented, and effects of coating application techniques are discussed. Oscillations in the open-circuit voltage occur in solutions containing a high enough concentration of chloride io to initiate pitting at potentials dictated by the coating. Inhibition of localized corrosion may also be obtainable for favorable systems.
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Polyaniline: Electrochemistry and application to rechargeable batteries
Article
  • Feb 1987
  • SYNTHETIC MET
The present study shows that: (1) reversible electrochemical oxidation of the leuucoemeraldine base form of polyaniline in the pH range ≈1 to ≈4 occurs initially with no deprotonation to give the emeraldine salt; continued oxidation occurs with spontaneous deprotonation to give the pernigraniline base (2) a rechargeable battery employing the analytically pure emeraldine base form of polyaniline as the cathode can be constructed. This battery shows very promising features such as a capacity of ≈148 Ah/kg, an energy density of ≈340 Wh/kg, coulombic recovery > 98%, good recyclability and satisfactory stand life.
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Polyaniline Nanofiber Synthesis by Co-Use of Ammonium Peroxydisulfate and Sodium Hypochlorite
Article
  • Jul 2008
The polymerization to polyaniline nanofibers was carried out in an aqueous system using aniline, 1 M HCl. and ammonium peroxydisulfate (APS) with additional use of sodium hypochlorite solution as a co-oxidant. The addition of sodium hypochlorite solution was made either before or after the addition of APS. This new method always produces polyaniline nanofibers with long length. Additional advantages of this new method are discussed. The effect of aniline concentration, hypochlorite concentration, different acid use, reaction temperature, and both aniline and hypochlorite purity on morphology and electrical property of the nanofibers synthesized by this new method was investigated.
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Synthesis of Polyaniline Nanofibers by “Nanofiber Seeding”
Article
  • Apr 2004
Seeding a conventional chemical oxidative polymerization of aniline with even very small amounts of biological, inorganic, or organic nanofibers (usually <1%) dramatically changes the morphology of the resulting doped electronic polymer polyaniline from nonfibrillar (particulate) to almost exclusively nanofibers. The nanoscale morphology of the original seed template is transcribed almost quantitatively to the bulk precipitate. These findings could have immediate impact in the design and development of high-surface area electronic materials.
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Polyaniline Nanofiber Composites with Metal Salts: Chemical Sensors for Hydrogen Sulfide
Article
  • Jul 2005
  • SMALL
A bulk synthetic method that yields uniform polyaniline nanofibers with narrow size distribution, which can be adjusted from 30 to 120 mm, was analyzed. The polyaniline nanofibers used as chemical sensors offers high surface area and small diameter, which facilitates the diffusion of molecules and dopants into the nanofibers. In this experiment, as a result new composite materials were formed from metal salts and polyaniline nanofibers, which show an enhanced response to hydrogen sulfide. The reaction between H2S and metal occurs with metal ions coordinated to polyaniline whereas a metal salt is added to polyaniline the metal cation coordinates both the imine and amine nitrogen atoms on the polyaniline chains. The mechanism of H2S with the metal salt to form the corresponding metal sulfide is offered. These new materials have great potential to control the response of conducting polymers to various chemicals along with other new applications.
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