16

90

Research ArticleReceived: 6 July 2009 Revised: 7 February 2010 Accepted: 29 March 2010 Published online in Wiley Online Library: 20 August 2010

(wileyonlinelibrary.com) DOI 10.1002/pi.2908

Synthesis by in situ chemical oxidativepolymerization and characterizationof polyaniline/iron oxide nanoparticlecompositeAslam Khan,a∗ Abdullah S Aldwayyan,a,b Mansour Alhoshana,c

and Mohamad Alsalhia,b

Abstract

Polyaniline (PANI) is a well-studied material and is the pre-eminent electrically conducting organic polymer with the potentialfor a variety of applications such as in batteries, microelectronics displays, antistatic coatings, electromagnetic shieldingmaterials, sensors and actuators. Its good environmental as well as thermal stability and electrical conductivity tunable byappropriate doping make PANI an ideal active material for several applications. In this paper, we report the synthesis ofwater-dispersible colloidal PANI/iron oxide composite nanoparticles using an in situ chemical oxidation polymerization methodin a micellar medium of sodium dodecylsulfate, where the cores (iron oxide) are embedded in a PANI matrix layer. Transmissionelectron micrographs showed evidence of the formation of an iron oxide core/PANI shell composite with a thin layer of PANIover the iron oxide cores. The results of thermogravimetric, Fourier transform infrared and UV-visible analysis indicated thatthe iron oxide nanoparticles could improve the composite thermal stability possibly due to the interaction between iron oxideparticles and PANI backbone. We believe that the synthetic route described can also be adapted for the assembly of hierarchicalstructures of other metal oxides or hydroxides onto various cores.c© 2010 Society of Chemical Industry

Keywords: iron oxide; polyaniline; in situ polymerization; composites

INTRODUCTIONThe preparation of iron oxide nanoparticles and their compos-ite nanomaterials has attracted both fundamental and practicalinterest because of their electronic, magnetic, catalytic, chemicaland biological properties. Application examples include mag-netic resonance imaging for medical diagnosis, high-densitymagnetic recording, controlled drug delivery, catalysis and en-ergy conversion.1 – 4 The ability to control the size, morphology,composition and surface properties is very important becausemany of these applications are directly dependent on theseproperties.5 – 9

Polyaniline (PANI) is one of the most technologically importantmaterials because of its environmental stability in a conductingform, unique redox properties and high conductivity.10 In recentyears, there has been increasing interest in the synthesis of conduc-tive organic/inorganic nanocomposites. There have been severalreports on the synthesis of PANI/inorganic nanocomposites.11 – 14

Yang et al.15 prepared a PANI/Fe3O4 nanoparticle compositeby polymerizing aniline in the presence of Fe3O4 nanopar-ticles with the use of ecofriendly oxidant H2O2 for catalysisapplication. The saturation magnetization of the as-preparedPANI/Fe3O4 composite was found to be Ms = 6.2 emu g−1.Denga et al.16 have reported the synthesis of core/shell PANI/Fe3O4

composites by in situ emulsion polymerization with an average di-ameter of 80 nm. These composites exhibited good electrical

and ferromagnetic properties in proportion to the percent-age of Fe3O4 and degree of doping. Lu et al.17 developeda method to synthesize well-dispersed PANI/Fe3O4 nanopar-ticles with aniline dimer/COOH polymerization. The core/shellPANI/Fe3O4 nanoparticles exhibited typical superparamagneticcharacteristics.

Hsieh et al.18 synthesized PANI/maghemite nanocompositesin a toluene/sodium dodecylsulfate (SDS)/water system usinga reverse micelle method, with the product exhibiting typi-cal superparamagnetic characteristics. The dispersed maghemitewas non-uniformly distributed in the PANI matrix. Moreover,the same group19 have reported the synthesis of PANI-coated SiO2/γ -Fe2O3 core/shell nanoparticles by combining

∗ Correspondence to: Aslam Khan, King Abdullah Institute for Nanotechnology,King Saud University, Riyadh 11451, Saudi Arabia.E-mail: aslamkhan@ksu.edu.sa

a King Abdullah Institute for Nanotechnology, King Saud University, Riyadh11451, Saudi Arabia

b Department of Physics and Astronomy, King Saud University, Riyadh 11451,Saudi Arabia

c Department of Chemical Engineering, King Saud University, Riyadh 11451,Saudi Arabia

Polym Int 2010; 59: 1690–1694 www.soci.org c© 2010 Society of Chemical Industry

16

91

Synthesis and characterization of PANI/Fe3O4 nanoparticles www.soci.org

the sol–gel process and in situ polymerization method. Dinget al.11 prepared PANI/Fe3O4 nanorods using an in situ self-assembly process in a micelle system, i.e. dodecylbenzene-sulfonic acid. These formed stable nanocomposites and self-assembled as uniformly dispersed magnetic particles absorbedon the surface of the PANI nanorods, i.e. stable PANI/Fe3O4

nanorods/nanoparticles.The present contribution describes the synthesis of col-

loidal PANI/iron oxide composite nanoparticles (PANI/IONPs)by in situ oxidation polymerization in a micellar mediumwhere the cores (iron oxide) are embedded in a PANI ma-trix layer. The formation of PANI was confirmed using UV-visible spectroscopy. Transmission electron micrographs of thecomposite showed that the colloidal particles self-assembledto form a PANI layer over iron oxide cores. Also, thecharacterization of the polymer composite was carried outusing Fourier transform infrared (FTIR) spectroscopy, XRDand TGA.

EXPERIMENTALMaterialsAniline (Aldrich) was distilled under vacuum prior to use. SDS,ammonium persulfate (APS), ammonium hydroxide (25 wt%) andoleic acid were obtained from Sigma-Aldrich. All solutions wereprepared with twice-distilled water.

Preparation of magnetic nanoparticlesIron oxide nanoparticles were prepared as reported in previouswork.20 Amounts of 23.5 g of FeCl3·6H2O and 8.6 g of FeCl2·4H2Owere dissolved in 600 mL of deionized water under nitrogenwith mechanical stirring at 600 rpm at 85 ◦C and then 30 mLof 7.1 mol L−1 NH4OH was quickly added. To the resultingsuspension 16 mL of oleic acid was added dropwise over aperiod of 30 min. After several minutes, the magnetic precipitatewas separated by magnetic decantation and washed withdeionized water several times and with ethanol twice, and finallyevaporated to dryness to yield magnetic nanoparticle (Fe3O4)powder.

Preparation of Fe3O4/PANI nanocompositesFe3O4/PANI nanocomposites were prepared via an in situpolymerization21 of aniline in aqueous solution containing Fe3O4

magnetic fluid. The polymerization was carried out in a 100 mLthree-necked round-bottom flask equipped with a mechanicalstirrer, a nitrogen inlet and a condenser. Typically, Fe3O4 solu-tion in chloroform (0.15 mg mL−1) was injected into a solutioncontaining 3 g of SDS in 40 mL of distilled water and kept inan ultrasonication bath for 10 min. Then, 10.7 mmol of anilinemonomer was added dropwise to the surfactant solution con-taining Fe3O4 and was stirred for 2 h. APS (1.12 g, 5.3 mmol) wasdissolved in 20 mL of 1.5 mol L−1 HCl and added to this solu-tion. The reaction was carried out at 60 ◦C and stopped as thecolour of the solution turned light green. Further, the solutionwas allowed to stand for 2 h more at room temperature where-upon the colour of the solution turned from light green to darkgreen. To obtain the composite in solid form, the dispersed so-lution was first mixed with methanol and then centrifuged. Thecycle was repeated several times and then the precipitate thusobtained was dried under vacuum on a glass plate prior to fur-ther studies. The reaction was carried out again under the same

condition as above omitting Fe3O4 to obtain PANI nanoparticlesonly.

CharacterizationUV-visible absorption spectra of the polymer and polymercomposites were recorded over the range 250–800 nm, usinga PerkinElmer Lambda-40 spectrophotometer. Attenuated to-tal reflectance Fourier transform infrared (FTIR) spectra of thecleaned and dried precipitates were recorded with a BrukerVertex-80 spectrometer. Powder XRD patterns were obtainedwith a Rigaku Ultima IV X-ray diffractometer at a scanningrate of 0.02◦ s−1 from 0◦ to 70◦ with a Cu Kα source (wave-length of 1.54 Å). TGA was carried on using a PerkinElmerTGA-7 thermogravimetric analyser. Transmission electron mi-croscopy (TEM) studies were performed by depositing col-loidal particles on a carbon-coated copper grid and thendrying in air. A JEOL electron microscope (JEOL 2100) oper-ated at an accelerating voltage of 80 kV was used for thesemeasurements.

RESULTS AND DISCUSSIONPANI/IONP composite was fabricated in aqueous SDS solutionin an acidic environment, with APS as the oxidant. After stirringthe SDS surfactant in distilled water to form micelles, colloidaliron oxide (oleic acid-capped) nanoparticles were injected intothe surfactant solution and sonicated for 10 min to ensurefull insertion of the colloidal particles into the inner core ofthe surfactant. Further, a known amount of aniline monomerwas added dropwise to the reaction solution while stirringwith a magnetic stirrer. An appropriate amount (5.3 mmol) ofAPS was added to the mixture solution, the colour of thesolution turning dark brown to light green and finally to darkgreen indicating the formation of the emeraldine salt form ofPANI. The whole process of composite formation is shown inScheme 1.

To investigate the reversible redox behaviour of the PANI/IONPcomposite, UV-visible absorption analysis was conducted withvariation of the pH values of the dispersion solution of thecomposite. Figure 1 shows the UV-visible absorption spectra ofthe PANI/IONP composite and PANI alone, dispersed in waterat two pH values. The UV-visible spectrum of the compositeat pH = 3 shows the presence of the polaron band transitionat about 420 nm and the π –π∗ transition of the benzenoidrings at 320–350 nm.22 As the pH of the solution is increasedto pH = 12, the polaron band at 420 disappears, and a strongabsorption band at 620 nm appears which is attributed to excitontransition from the benzene ring to the quinoid ring along thePANI chain. The inset of Fig. 1 shows the UV-visible spectrum of thedispersed PANI particles (at pH = 12) synthesized in the absenceof IONPs exhibiting peaks at 620 and 350 nm, characteristic of theemeraldine form of PANI. There is no significant change observedin the composite spectrum as compared to polymer alone (PANI)at the same pH.

Figure 2 shows the FTIR spectra of PANI, Fe3O4 and thecomposite. The main characteristic bands for PANI are at1515 and 1458 cm−1 which are assigned to the C C bondstretching of quinoid and benzenoid rings, respectively. Bandsat 1257 and 1164 cm−1 are due to C N stretching and in-plane bending of the C–H bond, respectively. In the case ofthe composite, the main peaks are observed at 1034, 1123,

Polym Int 2010; 59: 1690–1694 c© 2010 Society of Chemical Industry wileyonlinelibrary.com/journal/pi

16

92

www.soci.org A Khan et al.

Aniline monomer APS

Surfactant micelle

Polyaniline-ironoxide NPs

Removesurfactant

= Iron oxide nanoparticles

60° C

Scheme 1. Schematic of PANI/IONP (shell/core) formation.

1294, 1400, 1455, 1633, 630 and 558 cm−1. The peaks at 630and 558 cm−1, which are characteristic of Fe–O bond stretching(Fig. 2(b)), clearly indicate the presence of Fe3O4 in the polymermatrix, while the shift in the main peaks arises because ofthe interaction of Fe3O4 with the nitrogen atom of the anilinering.

The presence of IONPs in the dispersed composite was furtherconfirmed from powder XRD studies (Fig. 3). In the case ofPANI (only) particles (Fig. 3, inset), two broad bands appear at2θ values of 22.3◦ and 26◦ indicating the formation of lowlevel of crystalline phase in the polymer.23 For the PANI/IONPcomposite, the peak appearing at 22.3◦ representing the (020)Bragg reflection is stronger, implying that the molecular chains ofthe PANI prepared in the micellar medium are in a much moreordered state in the presence of IONPs and the crystallinity ofthe PANI in the composite is higher than that of PANI alone.Further, five strong bands appear with maximum intensity at30.1◦, 35.4◦, 42.9◦, 57.5◦ and 62.7◦ representing Bragg reflectionsfrom (220), (311), (400), (511) and (440) planes of iron oxide.24

This means that the IONPs have grown in all five planes.This finding confirms that the PANI coating does not influencethe crystalline structures of the IONPs embedded in PANIlayers.

TGA of PANI, Fe3O4 and PANI composite was carried outunder nitrogen atmosphere in order to see the effect of theFe3O4 content on the thermal stability of the composite (Fig. 4).The thermograms of the various samples show three majorweight losses: the first at 100 ◦C due to the loss of water;the second in the range 230–380 ◦C due to the loss of thedopant from the polymer matrix; and the third major loss from380 to 700 ◦C attributed to the destruction of the polymericbackbone. As seen from the TGA curves, the rate of weightloss for PANI (third weight loss occurs at 421 ◦C; Fig. 4(a)) ismuch faster, while the rate of weight loss for the PANI/IONPcomposite (third weight loss occurs as 476 ◦C; Fig. 4(b)) is slower.PANI alone is thermally stable up to 230 ◦C. However, whenthe conducting polymer is synthesized by incorporating Fe3O4

moieties in the reaction system along with surfactant, it isobserved that the thermal stability of the polymer increasesto 260 ◦C. This shows that in situ polymerization of aniline in

300 400 500 600 700 8000.0

0.2

0.4

0.6

0.8

1.0

300 400 500 600 700 8000.25

0.30

0.35

0.40

0.45

0.50

Abs

orba

nce

(a.u

.)

Wavelength (nm)

Abs

orba

nce

(a.u

.)

Wavelength (nm)

Figure 1. UV-visible spectra of PANI/IONP composite dispersed in waterat two pH values (dotted curve, pH = 3; solid curve, pH = 12). The insetshows the UV-visible spectrum of PANI only at pH = 12.

the presence of Fe3O4 leads to a conducting polymer of betterthermal stability. These results indicate that there is possiblysome interaction between Fe3O4 particles and polymer backbone.The FTIR spectra shown in Fig. 2 also support this conclusion.The characteristic absorption band of C–N in PANI alone is at1257 cm−1, while the absorption peak of C–N in the PANI/IONPcomposite shifts to 1294 cm−1. This result also agrees with theprevious conclusion.

The magnetic properties of the samples were investigatedwith an alternating gradient magnetometer at room temper-ature. The hysteresis loop of IONPs shown in Fig. 5(a) revealsferromagnetic behaviour, with a saturation magnetization (Ms)value of ca 60 emu g−1. The Ms value of the PANI/IONP com-posite particles synthesized using our method is 8.5 emu g−1

(Fig. 5(b)), which is much lower than that of the pure IONPs. Asshown in Fig. 5, the magnetic hysteresis loop of the PANI/IONPcomposite sample is an S-type curve through the coordinateorigin, it exhibit negligible coercivity.19 The results indicate

wileyonlinelibrary.com/journal/pi c© 2010 Society of Chemical Industry Polym Int 2010; 59: 1690–1694

16

93

Synthesis and characterization of PANI/Fe3O4 nanoparticles www.soci.org

1000150020002500300035004000

Wavenumber cm-1

050

100

150

200

250

Tra

nsm

ittan

ce [%

]

(b)

(c)

(a)

Figure 2. FTIR spectra of (a) PANI, (b) PANI/IONP composite and (c) Fe3O4nanoparticles.

10 20 30 40 50 60 700

100

200

300

Inte

nsity

(a.

u.)

2θ (degrees)

440511400

311

220

Figure 3. Powder XRD pattern of PANI/IONP composite particles. The insetshows the XRD pattern of the PANI (only) particles synthesized using APSas the oxidizing agent.

PANI/IONP composite particles have the properties of superpara-magnetism.

We further pursued a TEM investigation to learn about theparticle sizes of PANI and PANI/IONP composite as formed inthe aqueous solution using the method described. We recordedTEM images of samples dried on a carbon-coated copper grid.The micrograph in Fig. 6(a) indicates that the sizes of the ironoxide particles range from 10 to 15 nm. Figure 6(b) indicatesthat PANI is generated in the form of largely spherical particleshaving a wide distribution of particle sizes with average particlediameter below 100 nm. The TEM study of the PANI/IONPcomposite (Fig. 6(c)) reveals the formation of aggregated particles,with a PANI layer surrounding a cluster of aggregated IONPsof average dimension of 15 nm, resulting in clusters of well-separated composite particles of diameter greater than 50 nm.A closer look at the TEM micrograph indicates the formationof a PANI shell around the IONPs with self-assembly of IONPsdistinguishable by dark cores surrounded by greyish shells of PANI(Fig. 6(d)).

100 200 300 400 500 600 700

94

95

96

97

98

99

100

(c)

(b)

(a)

Wei

ght l

oss

(%)

Temperature (°C)

Figure 4. TGA of (a) PANI particles, (b) PANI/IONP composite and (c) IONPs.

-15000 -10000 -5000 0 5000 10000 15000

-60

-40

-20

0

20

40

60

(b)

(a)

M e

mu

g-1

H (Oe)

Figure 5. Magnetic hysteresis loops of (a) IONPs and (b) PANI/IONPcomposite.

CONCLUSIONSA PANI/IONP was successfully synthesized via in situ polymeriza-tion of aniline in SDS aqueous solution containing iron oxidenanoparticles. Both the colloidal PANI and PANI/IONP compos-ite particles were formed in their emeraldine salt form. Usingthe method described we could fabricate PANI particles withsizes of the order of 100 nm, whereas those of the compos-ite had an average size greater than 50 nm. FTIR results showthe presence of characteristic band stretching of Fe–O bond at630 and 558 cm−1 which are clear evidence for the presence ofFe3O4 in the polymer matrix. The magnetic Fe3O4 nanoparticlescan improve the thermal stability of the PANI/IONP compos-ite due to interactions between Fe3O4 particles and polymerchains.

Polym Int 2010; 59: 1690–1694 c© 2010 Society of Chemical Industry wileyonlinelibrary.com/journal/pi

16

94

www.soci.org A Khan et al.

Figure 6. TEM micrographs of (a) colloidal IONPs, (b) PANI nanoparticles and (c) PANI/IONP composite. (d) Expanded view of (c).

ACKNOWLEDGEMENTFinancial support from the King Abdullah Institute for Nanotech-nology research fund is gratefully acknowledged.

REFERENCES1 Tartaj P, Morales MD, Veintemillas-Verdaguer S, Gonzalez-Carreno T

and Serna CJ, J Phys D 36:182–197 (2003).2 Sun C, Lee JSH and Zhang M, Adv Drug Deliv Rev 60:1252–1265 (2008).3 Li P, Miser DE, Rabiei S, Yadav RT and Hajaligol MR, Appl Catal B

43:151–162 (2003).4 Sun S, Murray CB, Weller D, Folks L and Moser A, Science

287:1989–1992 (2000).5 Boal AK, Das K, Gray M and Rotello VM, Chem Mater 14:2628–2636

(2002).6 Woo K, Hong J, Choi S, Lee HW, Ahn JP, Kim CS, et al, Chem Mater

16:2814–2818 (2004).7 Sun SH, Zeng H, Robinson DB, Raoux S, Rice PM, Wang S, et al, J Am

Chem Soc 126:273–279 (2004).8 Shafi KVPM, Ulman A, Yan X, Yang NL, Estournes C, White H, et al,

Langmuir 17:5093–5097 (2001).9 Teng XW and Yang H, J Mater Chem 14:774–779 (2004).

10 Kingsborough RP and Swager TM, Adv Mater 10:1100–1104 (1998).

11 Ding X, Han D, Wang Z, Xu X, Niu L and Zhang Q, J Colloid Interface Sci320:341–345 (2008).

12 Bae WJ, Kim KH, Jo WH and Park YH, Macromolecules 37:9850–9854(2004).

13 Kinyanjui JM, Harris-Burr R, Wagner JG, Wijeratne NR andHatchett DW, Macromolecules 37:8745–8753 (2004).

14 Koh HD, Changez M, Lee JP and Lee JS, Macromol Rapid Commun30:1583–1588 (2009).

15 Yang C, Du J, Peng Q, Qiao R, Chen W, Xu C, et al, J Phys Chem B113:5052–5058 (2009).

16 Denga J, Hea CL, Peng Y, Wang J, Longa X, Li P, et al, Synth Met139:295–301 (2003).

17 Lu X, Yu Y, Chen L, Mao H, Gao H, Wang J, et al, Nanotechnology16:1660–1665 (2005).

18 Hsieh TH, Ho KS, Huang CH, Wang YZ and Chen ZL, Synth Met156:1355–1361 (2006).

19 Hsieh TH, Ho KS, Bi X, Han YK, Chen ZL, Hsu CH, et al, Eur Polym J45:613–620 (2009).

20 Khan A, Mater Lett 62:898–902 (2008).21 Jang J, Ha J and Kim S, Macromol Res 15:154–159 (2007).22 Huang WS and MacDiarmid AG, Polymer 34:1833–1845 (1993).23 Yan F and Xue GJ, Mater Chem 9:3035–3039 (1999).24 Wang L, Luo J, Maye MM, Fan Q, Rendeng Q, Engelhard MH, et al,

Mater Chem 15:1821–1832 (2005).

wileyonlinelibrary.com/journal/pi c© 2010 Society of Chemical Industry Polym Int 2010; 59: 1690–1694