synthesis and characterization of polyaniline...

International Journal of Advanced Science and Engineering Research www.ijaser.inVolume: 3, Issue: 1, 2018 ISSN: 2455-9288

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Copyright © 2018 by the Authors.This is an open access article distributed under the Creative Commons Attribution License, which permits 1unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

SYNTHESIS AND CHARACTERIZATION OF POLYANILINEENCAPSULATED GREEN CU2O NANOPARTICLES

K Gopalakrishnana* , C Rameshb

aDepartment of Physics, SSM College of Engineering, Komarapalayam – 638 316, Tamilnadu, India.bDepartment of Chemistry, SSM College of Engineering, Komarapalayam – 638 316, Tamilnadu,

India.(*Author for correspondence: E-mail: [email protected])

Abstract Polyaniline encapsulated copper oxide (Cu2O/PANI) nanocomposites are synthesized at roomtemperature through in-situ chemical polymerization method in acidic medium with the assistance of hydrogenperoxide as oxidant. The Cu2O/PANI nanocomposites are then investigated for physicochemical and electricalproperties through X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Visible spectroscopy(UV-Vis), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA), DC conductivityand thermal conductivity studies. The completion of polymerization of aniline in the formation ofnanocomposites is confirmed through the functional group assignments in FTIR spectrum. The presence of greenCu2O nanoparticles in the polyaniline matrix is established in nanocomposites through XRD studies. SEManalysis revealed that the nanocomposite particles are irregular in shape and the size ranged from 50 to 130 nm.Optical absorbance of nanocomposites demonstrates the shifting of characteristic peaks due to presence of greenCu2O nanoparticles in polyaniline matrix. The band gap analysis exhibits the narrow band gap direct transitionsemiconducting nature of the nanocomposites.Keywords: Polyaniline, Green Cu2O nanoparticles, Hydrogen peroxide, Nanocomposites, Band gap,Conductivity.

1. INTRODUCTIONNano-dimensional materials inspired great interest among researchers due to its unique

electronic, optical and conducting properties and its potential applications in nano-devices [1]. Theexhibition of such properties is very useful for the fabrication of optoelectronic devices namely LightEmitting Diodes (LEDs), solar cells, photocatalytic and photoconductive cells. Nanostructuredconducting polymer and the composites emerged as a novel field of research and development and itdirects to create new materials for modern and future technologies. On comparison, it is found thatmetal oxide/polymer nanocomposites shows improved properties than pristine metal oxide andconducting polymers [2- 5].

Cu2O nanoparticles are considered as potential materials in gas sensing, CO oxidation, photocatalysis, photochemical evolution of H2 from water, photocurrent generation and organic synthesis [6,7] because of its unique structural and optical band gap utility properties. In addition, naturally Cu2Ooccurs p-type semiconductor with a direct band gap of 2.17 eV [8]. Cu2O nanoparticles are preparedby various methods such as electro deposition [9], sonochemical method [10], thermal relaxation [11],liquid phase reduction [12], vacuum evaporation and green synthesis. Green synthesis method iswidely used to prepare the Cu2O nanoparticles owing to its environmental friendly and also eliminatesthe generation of substance hazardous to human health. Tridax procumbens leaves acquirebiomolecules such as carbohydrates and proteins which are used as reductants to react with copperions and as scaffolds to direct the formation of Cu2O nanoparticles in solution.

Conducting polymers are used as an alternate to metal oxide for optoelectronic applications.Amongst the family of conducting polymers, polyaniline is the most studied conducting polymer for


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the past 20 years due to its facile synthesis [13], chemical and environmental stability [14] and itsexcellent electronic properties. Polyaniline is also a promising material because of its intrinsicelectrical conductivity by doping with organic dopant [15] and it is used in making organic solar cell[16]. Conducting polyaniline contains conjugated π - electron system which plays a vital role inenhancing the electrical conductivity [17]. The unpaired electrons (π – electron) are formed atchemical bonding between the monomer units in conjugated polymers. Hence, it is possible to find theuse of conducting polyaniline in various applications such as battery electrodes, biosensors, andtransparent conductor and in effective corrosion protection [18, 19]. The various types of oxidant suchas ammonium peroxydisulfate (APS) ((NH4)2 S2O8), ferric chloride (FeCl3), potassium dichromate(K2Cr2O7), potassium iodate (KIO3) and hydrogen peroxide (H2O2) are used in the chemical synthesisof polyaniline in which ammonium peroxydisulfate (APS) is the commonly used oxidant and the useof APS is complicated to eliminate the inorganic products like ammonium sulfate [20]. H2O2 is used asoxidant in chemical polymerization of aniline under acidic condition for the preparation of polyanilineand it is due to its environmental friendliness and water as byproduct during oxidative polymerization.However, some catalysis like Fe, Cu etc is to be used to increase the reaction rate of polymerization ofaniline.

The improved thermal and conducting properties of Cu2O/PANI nanocomposites preparedwith conducting polyaniline and green Cu2O nanoparticles are reported. The appropriate addition ofgreen Cu2O nanoparticles as filler particles and their good dispersion into the polymer matrix enhancethe thermal stability and conducting properties and their performance. The research provides aneasygoing and effective route for the preparation of Cu2O/PANI nanocomposites and it may be used inthe fabrication of electronic devices.

2. MATERIALS AND METHODS2.1 Materials

The chemicals including copper (II) acetate monohydrate (Cu (CH3COO)2.H2O), glacial aceticacid (CH3COOH), aniline (C6H5NH2), ferrous chloride (FeCl2), hydrochloric acid (HCl), ammonia(NH3) and hydrogen peroxide (H2O2) of analytical grade were used as received from Merck withoutfurther purification. De-ionized water was used for all stages of experiment. Whattman filter paper(No. 42) was used for filtration process.

2.2. Preparation of Cu2O nanoparticles2.2.1 Preparation of Barfoed’s solution

Glacial acetic acid (1 mL) was dissolved in 50 mL deionized water and stirred for 10 minutes.Under stirring, copper (II) acetate monohydrate (3.325g) was added with the above solution and bluecoloured Barfoed’s solution was obtained.

2.2.2. Preparation of Tridax procumbens leaf extract

About 20g taxonomically authenticated healthy Tridax procumbens leaf were collected,washed thoroughly with double distilled water, cut into fine pieces and boiled with 100 mL doubledistilled water in Erlenmeyer flask for 8-10 min. The extract was then cooled at room temperature andfiltered.


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2.2.3. Preparation of green Cu2O nanoparticles

Initially, 10 mL of Tridax procumbens leaf extract was added to 10 mL of Barfoad’s solutionand the colour of the solution was changed from blue to brick-red after 10 minutes. The change ofcolour was indicated the formation of Cu2O nanoparticles. The solid product was filtered and washedwith ethanol and then dried at room temperature.

The addition of Barfoad’s solution to the leaf extract containing mild reducing agent such ascarbohydrates cause the bio-reduction of copper ions which further results in the formation of brickred precipitate of Cu2O. The reaction of cupric ion (Cu2+) in the acetate complex with aldehyde groupof carbohydrates reduces to cuprous ion and it then precipitates as Cu2O. The aldehyde group is thenoxidized to a corresponding carboxylic acid. The chemical reaction is represented in the followingequation:RCHO + 2Cu 2+ + 2H2O RCOOH + Cu2O +4H+

The reduction of Cu2+ to Cu+ plays a main role in the process and then Cu2O is generated through thehydrolysis of Cu+ according to the following reactions.Cu 2+ + H2O CuOH + H+

Cu2O + H2O2CuOHTherefore, by the inherent advantages of ready reactive solution with reducing agent, the Cu2O

nanoparticles are synthesized through the innovative and facile method.

2.3. Preparation of conducting polyanilineNon aqueous aniline monomer (2.79g) was dissolved in 300 mL of hydrochloric acid in which

0.0064g of FeCl2 dissolved in 75 mL de-ionized water was mixed and then the mixture was stirred atroom temperature. 68 mL (6 wt. %) of hydrogen peroxide was added drop by drop for 30 min and thestirring was continued until the completion of polymerization process. The end product is separated byfiltration process and dedoped with ammonia solution (5 wt. %) to obtain the emeraldine base (EB)form and washed, dried and stored in an air tight container. 0.75g of EB form of polyaniline wasdoped with 75 mL HCl and stirred for 3h for emeraldine salt form and the HCl doped PANI was thendried and collected for further characterization.

2.4. Preparation of Cu2O/PANI nanocompositesInitially a calculated amount (2.29g -75%) of non aqueous aniline monomer was dissolved in

300 mL of 1 N hydrochloric acid and mixed with 0.0064g of ferrous chloride dissolved in 75 mL ofwater. Under stirring, 68 mL (6 wt. %) of hydrogen peroxide was added drop by drop to thismixture for 30 min in which 0.57g (25%) of synthesized green Cu2O nanoparticles was added. Thereaction was continued for 23 h at constant stirring at room temperature. The green colored productwas filtered, washed and dried overnight.

2.5 CharacterizationFourier transform infrared (SHIMADZU) spectrum was recorded in the wavenumber range of

4000 - 400 cm−1 at the scanning rate of 25 scan / min with a resolution of 4 cm-1 using KBr pellet. TheX-ray diffraction (XRD) was carried in Philips analytical X-ray diffractometer operated at the voltageof 30 kV and the current 30 mA using Cu-Kα radiation (λ=1.5404Å) at the scanning range andscanning rate of 10° - 80° and 5°/ min respectively. The morphological properties were examined byLEO 1455 VP Scanning Electron Microscope (SEM) operating at 20 kV. The optical absorptionspectra were recorded in the range from 190 to 2500 nm using UV-1800 double beam UV-Vis


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spectrophotometer. Thermogravimetric analyzer (Universal V4.4A, TGA Q50 V20.5 Build 30)was applied for TG measurements from 25 °C to 600 °C under nitrogen atmosphere at the heating rateof 20 °C/min. The electrical conductivity of the compressed pellets of the samples wasdetermined by four probe resistivity technique. The pellets were prepared with area of cross section1.3368 cm2 and 1.5 mm in thickness, pressed for 2 min at hydraulic pressure of 160 MPa at roomtemperature.

3. RESULT AND DISCUSSION3.1. Fourier transform infrared spectroscopic analysis

FTIR Spectroscopy is used to study the interaction between polyaniline and Cu2Onanoparticles. The functional groups of prepared conducting polyaniline, green Cu2O nanoparticlesand Cu2O/PANI nanocomposites are monitored. From the Fig. 1 a-c, the spectrum a of polyanilineacquires the strong absorption bands at 1570, 1496, 1288, 1146 and 827 cm-1. The bands at 1570, 1496and 1288 cm-1 are assigned to the stretching mode of N=Q=N ring, N-B-N ring and C-N (Caromatic-N)deformation respectively [21] (where B refers to benzenoid ring and Q refers Quinonoid ring). Theband at 1146 cm-1 is assigned to C-N stretching vibration of secondary aromatic amine which plays adominant role in conductivity [22]. The observed band at 827 cm-1 attributes to the out-of-planevibration of C-H on 1, 4-disubstituted aromatic rings. The characteristic peak at 624 cm-1 in thespectrum b of green Cu2O nanoparticles shows the bending vibrations of the Cu2O crystal lattice. Theabsorption bands due to stretching vibrations of quinonoid and benzenoid rings in Cu2O/PANInanocomposites confirms the polymerization of aniline in the presence of green Cu2O nanoparticles.The band positions of polyaniline and green Cu2O nanoparticles are shifted in the lower and higherwavelength regions of Cu2O/PANI nanocomposites, and it shows the interaction between polyanilineand green Cu2O nanoparticles. Scheme1 illustrates the formation of Cu2O/PANI nanocomposites inpolyaniline matrix.

3.2. Structural analysisFig. 2 a-c illustrates the XRD patterns for conducting polyaniline, green Cu2O nanoparticles

and Cu2O/PANI nanocomposites. The XRD spectrum a of PANI demonstrates a characteristic broadpeak at 13.90° signifying the completion of polymerization process and shows that the polyanilinepossess partly crystalline structure [23]. The spectrum b of crystalline nature of green Cu2Onanoparticles contains five major peaks which are clearly distinguishable and all of them are perfectlyindexed to crystalline green Cu2O nanoparticles. The peak positions are matched with standard JCPDSdata (file No.05-0667) and the formation of green Cu2O nanoparticles are confirmed. The peaks at29.53°, 36.34°, 42.22°, 61.30° and 73.47° are assigned to the corresponding crystal planes of 110, 111,200, 220 and 311 of crystalline green Cu2O nanoparticles. The sizes of Cu2O particles are determinedfrom the width of the XRD peak position using Scherrer formula and its size are found to be in therange of 15-30 nm. The spectrum c of Cu2O/PANI nanocomposites confirms the presence of peaks ofpolyaniline and crystalline peaks of green Cu2O nanoparticles at 13.90°, 29.53°, 36.34°, 42.22°,44.50°, 60.20°, 61.30°, 73.47°, 75.0° and 87.32° with little shift in their peak positions. Theincorporation of peaks of green Cu2O nanoparticles into polyaniline indicates polyaniline undergoesinterfacial interactions with crystallite green Cu2O nanoparticles. The presence of green Cu2Onanoparticles in polymer matrix improves the crystalline behavior of the nanocomposites.Nanocomposites show more crystalline nature than that of polyaniline indicating the advantage of bothCu2O and polyaniline to form new advanced materials. The calculated sizes in the range of 50-130 nmof the Cu2O/PANI nanocomposites are increased as compared that of green Cu2O nanoparticles. Thecalculated values are well agreed with that of the values measured from SEM images. Increases of


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particle sizes of nanocomposites are due to encapsulation of green Cu2O nanoparticles in the polymermatrix.

3.3. Morphological analysisScanning Electron Microscopy (SEM) is used for analyzing the morphology of Cu2O/PANI

nanocomposites. The SEM images of conducting polyaniline, green Cu2O nanoparticles andCu2O/PANI nanocomposites are shown in Fig. 3 a-c. The image a shows the partial crystalline natureof conducting polyaniline owing to agglomerated nano-dimensional particles distributed partiallyregular in the structure of cauliflower like morphology. The image b of Cu2O nanoparticlesdemonstrates the well separated irregular cubic and hexagonal like shapes of green Cu2O nanoparticleswithout agglomeration. Cu2O/PANI nanocomposites expose that many aggregation of agglomeratedCu2O nanoparticles exist in the polymer matrix of cauliflower like structure as shown in image 3 c.This indicates the encapsulation of polyaniline on Cu2O nanoparticles and also represents theincreased size of the particles in nanocomposites.

3.4 Optical studiesOptical spectroscopy is an important technique to understand the conducting states

corresponding to the absorption bands of inter and intra gap states of conducting polymers [24]. Fig. 4a-c shows the optical absorbance with respect to wavelength for conducting polyaniline, green Cu2Onanoparticles and Cu2O/PANI nanocomposites. The conducting polyaniline spectrum illustrates themajor absorption peaks at 330, 347, 451 and 691 nm. The observed bathochromic shift at 330 nm isdue to the π –π* transition of benzenoid ring which is related to the extent of conjugation between theadjacent phenylene rings in the polymeric chain and the forced planarization of π-system induced byaggregation. It leads to increased conjugation and thus lowers the band gap [25] which is well agreedwith the band gap result obtained in the prepared polyaniline. The peak at 451 nm is due to polaron -π* transition and shift of electron from benzenoid ring to quinonoid ring. The peak at 691 nm is due toπ - polaron transition [26]. The spectrum of Cu2O nanoparticles shows the major peak at 257 nm. Thepeaks of both polyaniline and Cu2O nanoparticles are noticed in Cu2O/PANI nanocomposites withsome shift in their position indicating the incorporation of Cu2O nanoparticles filler in the polyanilinematrix. Such shifts in the characteristic peak positions of nanocomposites are related with surfacemodifications of Cu2O nanoparticles. The transition of π-π* of benzenoid ring and the formation ofpolaron band in the nano-composite are responsible to increase the electrical conductivity of thenanocomposites [27]. The bathochromic shift in the nanocomposites is due to particle size in the nanoregime. The particle size calculated from XRD analysis for Cu2O nanoparticles and nanocompositesare in good agreement with the results obtained from the optical studies. The estimation of size of theparticles is confirmed further by evaluating it with Meulenkamp equation [28]. According toMeulenkamp, the wavelength λ½ at which the absorption is 50% of that excitonic peak and is directlyrelated to the size of the particle using the fitted expression

½

The size of the particles evaluated from Meulenkamp equation is in good agreement with thevalues obtained from Scherrer’s method.

The optical energy plays a crucial role in the utilization of the materials in the optoelectronicapplications. The band gap of conducting polyaniline, green Cu2O nanoparticles and Cu2O/PANInanocomposites are measured from the absorbance coefficient data as a function of wavelength usingTauc relation. The optical band gap of conducting polyaniline, green Cu2O nanoparticles and


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Cu2O/PANI nanocomposites obtained from Fig. 5 a-c are 1.37 eV, 2.6 eV and 1.7 eV. The increase ofband gap of green Cu2O nanoparticles compared with its bulk band gap 2.17 eV is due to the effect ofbiomolecules of leaf extract on Cu2O. The decrease in band gap of Cu2O/PANI nanocomposites ascompared with Cu2O nanoparticles are due to the formation of polaron in the nanocomposites. Thelower band gap value originates from the quantum confinement effect which is caused by the nano-dimensional state of materials [29].

4. CONCLUSIONCu2O/PANI nanocomposites were successfully synthesized through in-situ chemical

polymerization method with the assistance of H2O2 as oxidant. The use of H2O2 as oxidant enabled thesynthetic route to prepare facile and eco-friendly green nanocomposites. The morphological andoptical, studies of conducting polyaniline, green Cu2O nanoparticles and Cu2O/PANI nanocompositeswere reported. The formation of nanocomposites in polyaniline matrix was confirmed through thefunctional groups assignments in FTIR spectrum. The nano-dimensional state and increased crystallinenature of the nanocomposites were ascertained through XRD analysis. The bands shift in its positionpresented in the UV-Visible absorption spectrum of Cu2O/PANI nanocomposites indicated the Cu2Onanoparticles embedded in polyaniline matrix and the distribution of green Cu2O nanoparticles in thematrix was further exposed in SEM images. The possibility of manipulating the properties of thenanocomposites could lead to the new applications in constructing the electronics devices.

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Figure Captions:

Fig. 1 FTIR spectra of (a) conducting polyaniline (b) green Cu2O nanoparticles & (c) Cu2O/PANInanocomposites.

Fig. 2 XRD patterns of (a) conducting polyaniline (b) green Cu2O nanoparticles & (c) Cu2O/PANInanocomposites

Fig. 3 SEM images with different magnification of (a) conducting polyaniline (b) green Cu2Onanoparticles & (c) Cu2O/PANI nanocomposites.

Fig. 4 UV –Vis spectra of (a) conducting polyaniline (b) green Cu2O nanoparticles & (c) Cu2O/PANInanocomposites.

Fig. 5 Relation between (αhυ) 2 and hυ for (a) conducting polyaniline (b) green Cu2O nanoparticles& (c) Cu2O/PANI nanocomposites.

Scheme1. Structure of Cu2O/PANI nanocomposites


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Fig. 1

Fig. 2


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Fig. 3

Fig. 4a


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Fig. 4b

Fig. 4c


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Fig. 5a

Fig. 5b


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Fig. 5c


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N

N

N

N

n

Cu2O

NH2

+ Cu2O

PolymerizationH2O2Aniline

Cu2O/PANI nanocomposite

Scheme1

synthesis and characterization of polyaniline...

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