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In Situ Chemical Oxidative Graft Polymerization of Aniline from Fe3O4 Nanoparticles

M. Hatamzadeh1, M. Johari-Ahar2, M. Jaymand2*

1-PolymerLaboratory,FacultyofChemistry,PayameNoorUniversity,Tabriz,I.R.Iran2-ResearchCenterforPharmaceuticalNanotechnology,TabrizUniversityofMedical

Sciences,Tabriz,I.R.Iran

(*)Correspondingauthor:m_jaymand@yahoo.com(Received: 12 Dec. 2011 and Accepted: 20 Mar. 2012)

Abstract:This study aims at exploring an effective route in the in situ graft polymerization of aniline from Fe3O4 nanoparticles. To this goal, Fe3O4 magnetic nanoparticles were prepared by coprecipitation method using ammonia solution as the precipitating agent, and were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thereafter, polyaniline (PANI) grafted magnetite nanoparticles were successfully synthesized by the in situ chemical oxidative polymerization of aniline monomer by ammonium peroxodisulfate (APS) from the surfaces of the aminopropyl magnetite nanoparticles with a dispersion polymerization method. The chemical grafting of polyaniline from magnetite nanoparticles were confimed by using FT-IR, ultraviolet-visible (UV-Vis) spectroscopy and thermogravimetric analysis (TGA), and also the dispersion state of Fe3O4 nanoparticles in the polyaniline matrix was examined by TEM. In comparison to the pure polyaniline, the polyaniline/Fe3O4 nanocomposite shows to have higher decomposition temperature.Keywords: Magnetic nanoparticles, Surface modification, Polyaniline, In situ polymerization, Nanocomposite.

Int. J. Nanosci. Nanotechnol., Vol. 8, No. 1, March 2012, pp. 51-60

1. INTRODUCTION

Inrecentyears,nanoscaledmagneticparticleshaveattracted much attention. These nanocrystallinedparticleswithahighsurface/volumeratiopossesssome extraordinary physical and chemicalproperties[1,2].Therefore,magneticnanoparticlescan be applied tomany industrial and biologicalfields,suchas improvedMRIdiagnosticcontrastagents, cell separation, tumor hyperthermia,retinal detachment therapy, and magnetic field-guidedcarriersforlocalizingdrugsorradioactivetherapies[3-5].AmagneticFe3O4powder,whichisnontoxicandeasy tobe synthesized,hasbeenintensivelyinvestigated.Thepreparationmethodsof magnetic Fe3O4 powders mainly include

coprecipitation, microwave thermal hydrolysis,plasma thesis, laser ablation, micron-scalecapsule,andglycothermalprocess[6,7].However,ironblackparticlesarenaturallyhydrophilicdueto plentiful hydroxyls on the particle surface.Additionally, Fe3O4 nanoparticles, like othernanoparticles,possesshighsurfaceenergy,whichmayresultintheagglomerationofparticleswhenFe3O4 nanoparticles are dispersed in organicsolvent and matrices. Therefore, the surfacecoatingormodificationof iron blackparticles isveryimportantinmanyapplications[8-10].Composites of conducting polymers containingmagnetic nanoparticles had attracted considerableattentionduetotheiruniquemagneticandelectricalproperties. They had many potential applications

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in electrochromic device, electromagneticinterference shielding, non-linear optical systemsand microwave absorbers [11-13]. Polyaniline(PANI) is a conducting polymer that showspotentialforfutureuseduetoitsgoodprocessibility,environmental stability, unique active conductionmechanism and reversible control of conductivityboth by charge-transfer doping and protonation.Potential applications of PANI include secondarybatteries, electromagnetic interference shielding,molecular sensors, nonlinear optical devices, andmicroelectronicdevices[14-17].Many polymerizationmethods have been appliedto prepare magnetic polymer microspheres,such as emulsion polymerization, precipitationpolymerization,andsuspensionpolymerization.Xueet al. [18], obtained PANI/Fe3O4 nanocompositesthrough mechanical mixing the DBSA–PANIpowder and theHCl–PANI–Fe3O4 powder.Wan’sgroup[19,20],preparedthePANInanocompositescontaining Fe3O4 nanoparticles by blending thePANI in N-methyl-2-pyrrolidone (NMP) withiron(II)sulfateaqueoussolution,andprecipitatingFe2+ intomagnetite, and allowed themonomer toreactwithFeCl2•4H2OandFeCl3•6H2O,followingbytreatmentwithKOHaqueoussolution.Inthepresentwork,magnetite(Fe3O4)nanoparticlesweresynthesizedbychemicalprecipitationmethod.Thereafter,anilinehadbeeninsituchemicaloxidativegraftfromtheaminogroupsonthesurfacesofaminopropyl magnetite nanoparticles directly with thefaciledispersionpolymerizationmethod.

2. EXPERIMENTAL

2.1. Materials

Aniline purchased from Merck (Darmstadt,Germany), was dried with NaOH and fractionallydistillated under reduced pressure from sodium orCaH2. Ammonium peroxodissulfate (APS) fromMerckwasrecrystallizedatroomtemperaturefromEtOH/water.Analyticalgradeofferricchloridehexa-hydrate(FeCl3•6H2O),ferrouschloridetetra-hydrate(FeCl2•4H2O),ammoniumhydroxide(NH4OH,25%ofammonia),aminopripyltriethoxysilane(APTES),p-toluen sulphonic acid, chloform, methanol and

N-methyl-2-pyrrolidone(NMP)wereobtainedfromMerckandwereusedwithoutfurtherpurification.

2.2. Synthesis of Fe3O4 nanoparticles

Avolumeof150mLofdeionizedwaterwasplacedinaround-bottomedflask;subsequently,thewaterwas deoxygenated by bubbling N2 gas for 30minutes.Thereafter,20mLofferrouschloride,0.1M,and40mLofferricchloride,0.1M,wereadded.After the solutionwas heated to 80°C, 10mL ofNH4OH (25% of ammonia)was rapidly added toitundervigorousstirringandimmediatelyafter,ablackprecipitateappeared.Theresultingsuspensionwas maintained at 80°C for 2 hours while beingstirred and then cooled to room temperature.Theprecipitated particles are washed five times withwater and methanol and dried overnight undervacuumatroomtemperature.

2.3. Surfaces modification of Fe3O4 nanoparticles by amino pripyl triethoxy silane

The introductionof -NH2 groupsonto the surfaceof Fe3O4 nanoparticles was achieved through thereaction between amino pripyl triethoxy silane(APTES)andthehydroxylgroupsonthenanoparticlesurface. The process started with dispersing ofcertain amount (1g) ofFe3O4 nanoparticles in thechloroform solvent (100 ml) under 20 minutesultrasonication, into which the coupling agentAPTES(1mL)wasadded.Thedispersedsolutionwasthentransferredtoa250mLtree-neckround-bottom flask equipped with condenser, droppingfunnel, gas inlet/outlet, and a magnetic stirrer,under bubbling N2 gas. The solution temperaturewasmaintainedat70°Cfor12hoursunderstirringand N2 protection. The particles were recoveredby centrifugation at 6000 rpm for 10 minutes.Theparticleswere thenredissolved inchloroformsolventandreprecipitatedbycentrifugationwhichwasrepeateduntilthesolutionwasclear.Thesolidproductwasdriedovernightundervacuumatroomtemperature.

2.4. In situ chemical oxidative polymerization of aniline from Fe3O4 nanoparticles

About 1 g of modified nanoparticles (Fe3O4-

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APTES) dispersed in 100mL, p-toluen sulphonicacid (1.0 mol L-1),aqueoussolutionofaniline(0.50mol L-1)withultrasonicvibrationsfor30minutes.Themixturewasvigorouslystirredandtemperaturewas reduced to 5°C. Thereafter, 50 mL aqueoussolutionofammoniumperoxodissulfate (1.10molL-1)was drop-added into the dispersionwithin 30minutesunderstirring.Themixturewasstirredforanother4hoursat5°C.Theproductwasfilteredandwashedwithwaterandacetoneeachforthreetimesin turn. The resulting products, polyaniline/Fe3O4 nanocomposite,weredriedatroomtemperaturefor48hoursundervacuum.TheobtainedproductwasextractedwithN-methyl-2-pyrrolidone(NMP)inaSoxhletapparatusfor24hourstoremoveungraftedpolyaniline. 2.5. CharacterizationFourier transform infrared (FT-IR) spectra of thesampleswereobtainedonaShimadzu8101MFT-IR (Shimadzu, Kyoto, Japan). The samples wereprepared by grinding the dry powders with KBrand compressing the mixture to form disks. Thediskswerestoredinadesiccatortoavoidmoistureabsorption. The spectra were recorded at roomtemperature. Transmission electron microscopeimages(TEM)wereperformedonaPhilipsCM10-THmicroscope(Phillips,Eindhoven,Netherlands)with a 100 kV accelerating voltage. The samples

used for transmission electron microscopyobservations were prepared by dispersing thepowders in distilled water followed by ultrasonicvibrationfor15minutes,thenplacingadropofthedispersionontoacoppergridcoatedwithalayerofamorphouscarbon.X-raydiffraction(XRD)spectrawas obtained with a Siemens D 5000 (Aubrey,Texas,USA),X-raygenerator(CuKαradiationwithλ=1.5406Å)with a 2θ scan range of 2 to 80° atroomtemperature.ThethermalpropertiesofthesampleswereobtainedwithaTGA-PLSTA1640 (PolymerLaboratories,Shropshire,UK).About10mgof the samplewasheatedbetween25and800°Catarateof10°Cmin-1 underflowingnitrogen.Theultraviolet-visible(UV-Vis) spectra of the samples were measured usinga Shimadzu 1601 PC, UV-Vis spectrophotometer(Shimadzu,Kyoto,Japan)inthewavelengthrange300-1100nm.

3. RESULTS AND DISCUSSION

In the present work, the magnetic nanoparticleswereproducedviatheinsitusynthesisofchemicalcoprecipitation technique by adding ferric (Fe3+) and ferrous (Fe2+) salts into the alkali solutionundernonoxidizingenvironment.Thisisthemostcommonsyntheticroutetoobtainmagnetiteparticlecomparewithothers,suchasoxidationofFe2+,sol-

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Figures, Scheme and Table

Scheme 1: Synthetic route of the in situ chemical oxidative graft polymerization of

aniline from Fe3O4 nanoparticles

Figure 1: XRD pattern of bare Fe3O4 nanoparticles

Scheme 1: Synthetic route of the in situ chemical oxidative graft polymerization of aniline from Fe3O4 nanoparticles

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gel method and water-in-oil microemulsions, invirtueofitssimplicityandproductivity.Thereafter,polyaniline(PANI)graftedmagnetitenanoparticlesweresynthesizedbytheinsituchemicaloxidativepolymerizationofanilinemonomerwithammoniumperoxodisulfate (APS) from the surfaces of theaminopropyl magnetite nanoparticles with adispersion polymerization method. The overallmethodologyissummarizedinScheme1.

3.1. Characterization of Fe3O4 nanoparticles

X-ray diffraction (XRD) pattern of Fe3O4 nanoparticles is illustrated in Figure 1. The peakintensity can be used to quantify the proportionof iron oxide forms in a mixture by comparingexperimentalpeakandareferencepeakintensity.ItwasfoundfromtheX-raypatternsthattherewereaseriesofcharacteristicpeaksat2.964(220),2.523(311),2.088(400),1.704(422),1.609(511),1.479(440),and1.276(533).ThedvaluescalculatedfromtheXRD,patternwaswell indexed to the inverse cubic spinel phase ofFe3O4. The average crystallite size D, calculatedusing the Debye-Scherrer formula D=kλ/(βcosθ)was roughly about 23 nm.The equation uses thecorrectedreferencepeakwidthatangleθwhereλistheX-raywavelength,βisthecorrectedwidthoftheXRDpeakatfullwidthathalfmaximum(fwhm)andK isa shape factorwhich isapproximatedas

0.9formagnetite.Figure2showstheTEMimageofthesynthesizedFe3O4 nanoparticles. It is clear that the Fe3O4 nanoparticleshavesphericalmorphologyandgoodmonodispersity.Thesizedistributionof theFe3O4 nanoparticles is narrow.However, because of thelarge specific surface area, high surface energy,and magnetization of Fe3O4 nanoparticles, someof theprimarynanoparticleswereaggregated intosecondaryparticlesduringtheprocessofdrying.

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Figure 2: Transmission electron microscope image of Fe3O4 nanoparticles

Figure 2: Transmission electron microscope image of Fe3O4 nanoparticles

Figure 3 shows the FT-IR spectra of unmodified(a) and modified (b) Fe3O4 nanoparticles. It can

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Figures, Scheme and Table

Scheme 1: Synthetic route of the in situ chemical oxidative graft polymerization of

aniline from Fe3O4 nanoparticles

Figure 1: XRD pattern of bare Fe3O4 nanoparticles

Figure 1: XRD pattern of bare Fe3O4 nanoparticles

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be seen that the FT-IR spectrum of unmodifiedFe3O4 nanoparticles appeared absorption bandsat 570 cm−1 resulting from the oxygen-metalstretching vibration and the bands around 1623and3388cm-1aredue to thehydroxylgroups inthe Fe3O4 nanoparticles. FT-IR andXRD spectraconfirmed that synthesis of Fe3O4 nanoparticleswassuccessfullycarriedout.Itiswellknownthat,ingeneral,inorganicparticleshavehydroxylgroupson their surface,which canreactwithalkoxysilanes.Therefore,silanecouplingagent is suitable for the introductionof functionalgroups onto the surface of inorganic particles.Figure(3-b)showstheFT-IRspectrumofmodifiedFe3O4 nanoparticles. The modification of Fe3O4 nanoparticles with amino pripyl triethoxy silane(APTES),confirmedby theFe-O-Si transmittancepeakat1115cm-1andtheC–Hstretchingvibrationat2816and2938cm-1.

3.2. Characterization of PANI/Fe3O4 nano-composite

Figure 4 shows the FT-IR spectrum of PANI/Fe3O4 nanocomposite. The FT-IR spectrum ofnanocompositeisbasicallythesameduetostrongabsorptionbyPANIandweakabsorptionofFe3O4. The main characteristics peaks are assigned asfollow:thebandat3472cm-1isattributabletoN-Hstretchingmode,C=N andC=C stretchingmodefor the quinonoid and benzenoid units occur at1561and1614cm-1.Thebandsaround1304and1218 cm-1havebeenattributed toC-Nstretchingmode for benzenoid units and the band at 573cm-1 is assigned to the oxygen-metal stretchingvibration.Figure5givesUV–VisabsorptionspectraofrawFe3O4nanoparticles(d),modifiednanoparticles(a),neatPANI(b),PANI/Fe3O4nanocompositebefore(e) and after (c) extracting with NMP solvent.

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Figure 2: Transmission electron microscope image of Fe3O4 nanoparticles

Figure 3: FT-IR spectra of unmodified Fe3O4 nanoparticles (a) and modified Fe3O4 nanoparticles by silane coupling agent (b)

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Figure(6-b)showsthatthePANIwascharacterizedbytwoelectronictransitionsrespectivelyataround341.5and633.5nm.Theabsorptionbandaround341.5 nm is attributed to π-π* transition of thebenzenoid ring,while thepeakaround633.5nmcorrespondstochargetransferfromthebenzenoidrings to the quinoid rings [14]. It is found fromFigure (6-c and 6-e) that the absorption peak at

341.5nmcorrespondingtoPANIhasaredshiftinPANI/Fe3O4nanocomposite, andvaryingdegreesof red shift increase with the ferrite content thepercentage of nanoparticles in nanocomposites.The percentage of nanoparticles in the PANImatrix increased with extracting of PANI/Fe3O4 nanocomposite with NMP solvent, because withextracting the ungrafted PANI chains removed

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Figure 3: FT-IR spectra of unmodified Fe3O4 nanoparticles (a) and modified Fe3O4

nanoparticles by silane coupling agent (b)

Figure 4: FT-IR spectra of PANI/Fe3O4 nanocomposite

Figure 4: FT-IR spectra of PANI/Fe3O4 nanocomposite

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Figure 3: FT-IR spectra of unmodified Fe3O4 nanoparticles (a) and modified Fe3O4

nanoparticles by silane coupling agent (b)

Figure 4: FT-IR spectra of PANI/Fe3O4 nanocomposite

Figure 5: UV-Vis spectra of modified nanoparticles (a), polyaniline (b), extracted PANI/Fe3O4 (c), Fe3O4

nanoparticles (d) and unextracted PANI/Fe3O4 nanocomposite (e)

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fromnanocompositesample.Theseresultssuggestthat there may be interaction between Fe3O4 particlesandPANIchains.

3.3. Thermal stability of PANI and PANI / Fe3O4 nanocomposite

The characteristic thermogravimetric analysis(TGA) curves of the Fe3O4 nanoparticles (a),modified Fe3O4 nanoparticles (b), PANI/Fe3O4 nanocomposite(c)andpurePANI(d)areshowninFigure6.TGAresultsindicatetheimprovementofthethermalstabilityforPANI/Fe3O4nanocompositecompared with the neat PANI. This is differentfrom the results ofKumar et al. [21],who foundthe decomposition temperature of the PANInanocomposites with Cu3O4 nanoparticles waslower than that of the pure one.However, Karimet al. [22], observed that the thermal stability ofPANI was relatively enhanced by forming thenanocompositeswithtitaniumdioxide.

It seems that the influence of the inorganicnanoparticles on the thermo stability of PANInanocomposites is very complex, its mechanismremainingtobeaddressed.AccordingtotheFigure(7-c),wecandrawtheconclusionthattheweight-lossaround470-650oCintheTGAcurveofPANI/Fe3O4nanocompositeisaresultofthedecompositionofPANIcovalentlyattachedtoFe3O4nanoparticles.Higher decomposition temperature of PANI/Fe3O4 nanocomposite(470-650oC)comparedwiththepurePANI(450-550oC), indicated thatnopolymersarenoncovalently adsorbed onto the surface of Fe3O4 nanoparticles.Theweightlossaround200-300oCmaybeduetothelossofaciddopant(p-toluensulphonicacid)boundtothepolyanilinechainsortheskeletalofpolyanilinechains decomposed after the elimination of dopantfrompolymerstructure.Theweightpercentofgraftedmodifier and grafted PANI are calculated from theTGA curves and summarized in Table 1.

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Figure 5: UV-Vis spectra of modified nanoparticles (a), polyaniline (b), extracted

PANI/Fe3O4 (c), Fe3O4 nanoparticles (d) and unextracted PANI/Fe3O4 nanocomposite

(e).

Figure 6: TGA thermograms of bare Fe3O4 nanoparticles (a), modified nanoparticles

(b), PANI/Fe3O4 nanocomposite (c) and pure PANI (d)

Table 1: Weight changes of the samples from TGA

Samples Initial wt. (%)

Residual wt. (%)

Grafted APTES(%)

Grafted PANI (%)

Fe3O4 100 99.14 - - PANI 100 9.53 - - Fe3O4-APTES 100 94.68 4.46 - PANI/Fe3O4 100 33.27 4.46 61.41

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Figure 5: UV-Vis spectra of modified nanoparticles (a), polyaniline (b), extracted

PANI/Fe3O4 (c), Fe3O4 nanoparticles (d) and unextracted PANI/Fe3O4 nanocomposite

(e).

Figure 6: TGA thermograms of bare Fe3O4 nanoparticles (a), modified nanoparticles

(b), PANI/Fe3O4 nanocomposite (c) and pure PANI (d)

Table 1: Weight changes of the samples from TGA

Samples Initial wt. (%)

Residual wt. (%)

Grafted APTES(%)

Grafted PANI (%)

Fe3O4 100 99.14 - - PANI 100 9.53 - - Fe3O4-APTES 100 94.68 4.46 - PANI/Fe3O4 100 33.27 4.46 61.41

Figure 6: TGA thermograms of bare Fe3O4 nanoparticles (a), modified nanoparticles (b), PANI/Fe3O4 nanocomposite (c) and pure PANI (d)

Table 1: Weight changes of the samples from TGA

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3.4. Transmission electron microscopy of PANI / Fe3O4 nanocomposite

The obtained nanocomposite was also examinedwithTEM (Figure 7),which showwell-dispersedFe3O4inthepolyanilinematrix.Someagglomerationof Fe3O4stillexists,althoughthegenerallyexcellentseparation of Fe3O4 particles is attributed to thegrowingof‘‘graftingfrom’’PANI,whichseparatesthepreviouslyagglomeratedFe3O4nanoparticles.

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Figure 7: Transmission electron microscope image of PANI/Fe3O4 nanocomposite

Figure 7: Transmission electron microscope image of PANI/Fe3O4 nanocomposite

4. CONCLUSIONS

Magnetite (Fe3O4) nanoparticles were synthesizedby chemical precipitation. TEM image shows thatthe Fe3O4 nanoparticles have spherical morphologyand good monodispersity. The PANI/Fe3O4 nanocomposite was synthesized by the chemicaloxidative polymerization of aniline from the aminogroupon thesurfaceofFe3O4nanoparticles.FT-IR,UV-Vis andTGA investigation provided direct andclearevidenceforthepresenceofPANIshellonnano-Fe3O4coreparticles.UV-Visspectroscopyshowsthatthe absorption peak at 341.5 nm corresponding toPANIhasaredshiftinthePANI/Fe3O4nanocomposite,and varying degrees of red shift increase with thepercentage of nanoparticles in nanocomposites.Thermogravimetricanalysis(TGA)indicatedthattheresulting nanocomposite displayed higher thermalstabilityincomparisontothepurePANI.

ACKNOWLEDGMENTS

WeexpressourgratitudetotheResearchCenterforPharmaceuticalNanotechnology,TabrizUniversityofMedicalSciencesandPayameNoorUniversityforsupportingthisproject.

ABBREVIATIONS

PANI: PolyanilineAPS: AmmoniumperoxodissulfateXRD: X-raydiffractionTEM: TransmissionelectronmicroscopyTGA: ThermogravimetricanalysisAPTES: AminopripyltriethoxysilaneNMP: N-methyl-2-pyrrolidone

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