Research Article The Roll of NaPSS Surfactant on …downloads.hindawi.com/journals/jnm/2016/9747931.pdfResearch Article The Roll of NaPSS Surfactant on the Ceria Nanoparticles Embedding

Research ArticleThe Roll of NaPSS Surfactant on the Ceria NanoparticlesEmbedding in Polypyrrole Films

Simona Popescu Mihaela Micircndroiu Daniela Cabuzu and Cristian Picircrvu

University Politehnica of Bucharest 313 Splaiul Independentei Sector 6 060042 Bucharest Romania

Correspondence should be addressed to Cristian Pırvu c pirvuchimupbro

Received 27 October 2015 Revised 8 April 2016 Accepted 14 April 2016

Academic Editor Paulo Cesar Morais

Copyright copy 2016 Simona Popescu et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Ceriumoxide nanoparticles (CeO2NPs) in crystalline formhave been synthesized by a coprecipitationmethod CeO

2nanoparticles

were then embedded in polypyrrole (PPy) films during the electropolymerization of pyrrole (Py) on titanium substrate Theinfluence of poly(sodium 4-styrenesulfonate) (NaPSS) surfactant used during polymerization on the embedding of CeO

2NPs

in polypyrrole films was investigated The new films were characterized in terms of surface analysis wettability electrochemicalbehaviour and antibacterial effect The surface and electrochemical characterization revealed the role of surfactant on PPy dopingprocess cerium oxide incorporation In the presence of surfactant CeO

2NPs are preferentially embedded in the polymeric film

while without surfactant the ceria nanoparticles are quasiuniformly spread as agglomerates onto polymeric filmsThe antibacterialeffect of studied PPy films was substantially improved in the presence of cerium oxide and depends by the polymerizationconditions

1 Introduction

Nowadays titanium still represents a solution for the choiceof base-implant materials in orthopedic and dental field dueto its excellent properties that refers to corrosion resistanceand mechanical properties Many studies have confirmedthe necessity of titanium implants pretreatments in order toaccelerate the process of its integration within the surround-ing tissue by designing a new titanium-based material witha bioactive surface [1ndash5] The novelty in this domain camealways from the ingenuity of methods that have developedin a dynamic way

Among the variety of methods used to modify thetitanium surface in a ldquofriendlyrdquo way the deposition of anadherent biocompatible polymer film on titanium repre-sents a simple and efficient alternative [6ndash10] In this waythe reactivity of polymer surface could be further impliedin the process of biologically active molecules grafting [1112] Another advantage is related to protection of the metalagainst corrosion and avoiding the problem of ions releasein the surrounding tissue [13 14] Moreover these polymershave the doping ability with different molecules during their

polymerization thus improving the surface properties forappropriate application [15ndash17] The choice of polypyrrole(PPy) as conducting polymer for metallic substrate coating isbased on its simple electrochemical polymerization directlyonto metallic substrates [18 19] Other important propertiessuch as high electronic conductivity good stability regardingthe resistance against corrosion in aqueous solution andgood biocompatibility with respect to several cells types invitro and in vivo were also highlighted in literature [20ndash23]

Besides aspects related to biocompatibility a majorimportance was focused on antibacterial activity since theever-increasing resistance of pathogens towards antibioticsrepresents major postimplantation problems Bacteria areable to adapt rapidly to new unfavorable environmentalconditions hence their resistance to antimicrobial moleculesincreased substantially Considering this issues in the lastyears the metal oxide nanoparticles have gained attention indeveloping of new drug delivery systems and antibacterialagents [24ndash26] Metal oxide NPs are an important class ofinorganic compounds due to their special properties in dif-ferent domains optical magnetic electronic properties andmedicine Among them cerium oxide (CeO

2) became more

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2016 Article ID 9747931 12 pageshttpdxdoiorg10115520169747931

2 Journal of Nanomaterials

and more utilized as antioxidant providing an efficientprotection against free radicals and as antimicrobial agent[27ndash29] The small size of particles allows the interactionwith biological entities (proteins DNAmolecules and mem-branes)

In this respect as a polymeric matrix PPy has beenalready subjected to incorporation of different antibacterialsubstances such as silver nanoparticles [30 31] biodegradablecompounds such as dextrin or chitosan [32 33] PEG [34] orother carotenoid compounds like torularhodin [35]

The idea of combining a polymer with nanoparticles tocreate a compositematerial represents a promising alternativesince these materials combine both the unique propertiesof nanoparticles with those of the polymer resulting in anew material with specific properties The incorporationof ceria particles in polypyrrole film requires some specialprecautions These particles are stabilized by electrostaticsforces and are extremely sensitive to perturbations of pHionic strength and concentration that may dramaticallymodify their thermodynamic stability The low stabilityoccurs due to high surface-to-volume ratio for particles andfrom the strong reactivity of the surface chemical sites tophysicochemical changes Therefore for some applicationsthe challenge is to find appropriate conditions to prepareCeO2polymeric composite in which ceria nanoparticles are

dispersed homogeneously in a polymer matrix [36]Literature contains one study about the incorporation

of CeO2in dodecyl sulfate doped polypyrrole films (PPy-

DS) deposited on gold electrode It was concluded thatCeO2NPs have the ability to modify the morphology of

electrodeposited PPy-DS thin films but without highlightingthe film morphology and the influence of the surfactant onceria nanoparticles distribution into the polymeric film [37]

In the present study poly(sodium 4-styrenesulfonate)(NaPSS) was selected as surfactant based on previous studies[38 39] and it is expected to provide a goodCeO

2distribution

and a better embedding in the polymer nanocomposite filmdeposited on titanium surface Two PPy-CeO

2composite

films obtained with and without NaPSS were studied com-paratively in terms of surface properties electrochemicalstability and antibacterial activity

2 Experimental Part

21 Synthesis of CeO2 Nanoparticles For the synthesisof CeO

2nanoparticles we applied a simple hydroxide

mediated approach that uses cerium nitrate hexahydrate(Ce(NO

3)3sdot6H2Ogt 995 Aldrich Chemicals USA) as start-

ingmaterial and sodium hydroxide as precipitating agent Allthe chemical reagents were used without purification

The starting solutions were 01M Ce(NO3)3sdot6H2O and

03M NaOH prepared with double distilled water Firststep consists in adding dropwise the NaOH solution for 3hours under continuous stirring at room temperature untila pinkish precipitate is obtainedThe vigorous stirring is veryimportant because it influences the product particle size andits distribution

Precipitation of a pinkish white precipitate

Stirring at room temperature (3 hours)

+

Washing with ethanol and water(3 times)

NaOH (03M)

Centrifugation(8000 rpm 15min)

Ce(NO3)3middot6H2O (01M)

Drying of the precipitatein oven (80∘C 1h)

Annealed in furnace (270∘C 24h)

CeO2 particles

Figure 1 Synthesis of CeO2nanoparticles

The apparition of a pinkish precipitate suggests the oxi-dation of Ce(OH)

3into Ce(OH)

4that occurs in the presence

of dissolved oxygen while the pH was maintained around 9Finally it became a light yellow suspension characteristic forCeO2

The reactions during the synthesis are the following

Ce (NO3)

3sdot 6H2O(s) 997888rarr Ce3+

(aq) + 3NOminus

3(aq) + 6H2O (1)

2Ce3+(aq) +1

2

O2+ 6OHminus

pHasymp9997888997888997888997888rarr 2CeO

2+ 3H2O (2)

In another step the yellow precipitate was centrifugedthree times washed well with ethanol and distilledH

2O three

times and then dried in an oven at 80∘C for 1 hour followedby an annealing process at 270∘C for 24 h The resultingprecipitate is a light yellow precipitate that was furtheranalyzed through XRD Figure 1 presents the schematicdiagram for CeO

2particles synthesis

22 Preparation of Titanium Substrate before Polymer FilmsElectrodeposition Commercially pure Ti discs of 10mmdiameter and 1mm thickness (996 purity grade 2 Good-fellow Cambridge Ltd UK) were used The surface of testspecimens was polished with SiC paper to grade 4000 andthenwashedwith a large amount of water followed by acetoneand finally rinsed with distilled water and dried in air at roomtemperature

23 Synthesis of PPy Films and PPy-CeO2 with and withoutSurfactant Synthesis of polymeric films was performed by

Journal of Nanomaterials 3

potentiodynamic polymerization method Polypyrrole filmswere electrodeposited on titanium substrate (TiPPy) froman aqueous solution containing freshly distilled pyrrole (Py04molsdotdmminus3 purchased from Merck purity gt 98) andoxalic acid (02molsdotdmminus3) as support electrolyte Nanocom-posite films were obtained by adding cerium oxide nanopar-ticles (CeO

2NPs 40 120583gsdotmLminus1) in the electrolytic solution

(TiPPy-CeO2NPs) CeO

2NPs were ultrasonically dispersed

prior to the proper electrosynthesis step In order to modifythe surface characteristics of the polymer films NaPSS(01molsdotdmminus3) was added in the polymerization solution(TiPPy-NaPSS) The optimal surfactant concentration wasestablished in a previous work [38] The surfactant was alsointroduced along with CeO

2NPs in the composition of poly-

merization solution to study its influence on nanoparticlesincorporation in the polymeric films (TiPPy-NaPSS-CeO

2

NPs) All solutions were prepared using ultra-pure deionizedMilli-Q water

The films electrosynthesis was carried out using onecompartment cell with three electrodes titanium as workingelectrode platinum counter electrode and AgAgCl andKCl reference electrode connected to an Autolab PGSTAT302N potentiostat with general-purpose electrochemical sys-tem software Polymerization was performed by applying 5consecutive cyclic voltammetric scans between 0 and 095Vversus AgAgCl using a 50mVsdotsminus1 scan rate

24 Methods for Polymer Nanocomposite CoatingsCharacterization

241 Surface Characterization Scanning electron microscopy(SEM) images were taking with FEI Nova NanoSEM 630FEG-SEM (SEM with Field Emission Gun) with ultra-highresolution characterization at high and low voltage in highvacuum The voltage of SEM analysis was 20 kV and themagnification of the images was between 1000x and 50000xThe elemental composition was investigated using Carl ZeissEvo 50 XVP scanning electron microscope (SEM) equippedwith energy dispersive X-ray analysis (EDAX) QuantaxBruker 200 accessory

X-ray diffraction (XRD) the crystalline nature of CeO2

particles was analyzed using a Rigaku Ultima IV X-ray dif-fractometer in Bragg Brentano parafocusing setup with highresolution using CuK120572 radiation (120582 = 0154 nm) The sourcewas operated at 40 kV and 40mA

The contact angle of a drop of water with the films surfacewas measured with a Contact Angle Meter-KSV InstrumentsCAM 100 equipment The hydrophilichydrophobic balanceof synthesized films was evaluated by measuring the staticcontact angle (120579) of a drop of water deposited on the studiedfilm surface Each contact angle value is the mean value from5 measurements The investigation was carried out at 25∘C

242 Electrochemical Characterization Electrochemical sta-bility evaluation was performed at room temperature usingpotentiostatic assembly with a single compartment and threeelectrodes working electrode (samples Ti TiPPy TiPPy-CeO2NPs TiPPy-NaPSS and TiPPy-NaPSS-CeO

2NPs) a

counter electrode (Metrohm Pt disk) and a reference electrode(Metrohm AgAgCl 3M KCl) connected to an AutolabPGSTAT 302N potentiostatgalvanostat The data were col-lected with NOVA 110 software

All electrochemical characterizations were made in anaqueous buffer testing solution composed of NaCl 874 gsdotLminus1NaHCO

3035 gsdotLminus1 Na

2HPO4sdot12H2O 006 gsdotLminus1 and

NaH2PO4006 gsdotLminus1at pH67The substanceswere purchased

from Sigma-Aldrich Corp (St Louis MO USA)Polarization curves were registered at plusmn200mV versus

OCP at a scan rate of 2mVs and corrosion parameters werecomputed based on Tafel plots 119894cor (corrosion current den-sity) 119877p (polarization resistance) 119864cor (corrosion potential)and Vcor (corrosion rate) For electrochemical experimentsthe electrode area exposed to the solution was 02826 cm2

Cyclic potentiodynamic polarization was performed start-ing fromminus05V to 05 Vwith a scan rate of 100mVs 10 cyclesin buffer solution

The electrochemical impedance spectra (EIS) were ac-quired in the frequency range of 01ndash105Hz in order to obtainNyquist plots by applying a small excitation amplitude of10mV

TheMott-Schottkymeasurements were made from a startpotential of minus05 V to an end potential of 05 V with a steppotential of 005V In this work a frequency of 10 kHz forMott-Schottky measurements was applied [40]

243 Antibacterial Activity Evaluation of Polymer Nano-composite Coatings The antibacterial activity of polymernanocomposite films was tested against human pathogenicmicrobial strain Escherichia coli ATCC 8738 The bacterialstrains were grown in Luria Bertani Agar (LBA) plates at 37∘Cwith the following composition peptone (Merck) 10 gsdotLminus1yeast extract (Biolife) 5 gsdotLminus1 NaCl (Sigma-Aldrich) 5 gsdotLminus1and agar (Fluka) 20 gsdotLminus1

The stock culture was maintained at 4∘C All aqueoussolutions were prepared with deionized water To exploitantibacterial potential of the samples Kirby-Bauer disk-diffusion method was performed [41] In brief sterile LBAplates were prepared by pouring the sterilizedmedia in sterilePetri plates under aseptic conditions The bacterial strain1mL was spread on agar plates and then sterile samples wereapplied on plate surface At the end of the incubation time(24 h) the diameter of microbial growth inhibition halo wasmeasured in millimeters [35]

3 Results and Discussion

31 Characterization of CeO2 Nanoparticles Powder

311 XRD Characterization The crystalline nature of CeO2

nanoparticles prepared according to hydroxide mediatedapproach can be deduced from the X-ray diffraction spectrashown in Figure 2 The XRD pattern of the heat treatedpowder was registered from 10 to 90 degrees 2120579120579 scan axiswith 002∘ angular step and 05 secstep The resulting pat-tern revealed the formation of well-crystallized single phasematerialThe chemical synthesized powder exhibits lines that


0

500

1000

1500

2000

2500

20 40 60 80

Inte

nsity

(au

)

2120579 (deg)

Meas data CeO2_Sinteza

Cerianite syn CeO2 00-043-1002

(111

)

(200) (220)

(311

)(2

22

)

(400

)

(331

)(4

20

)

(422

)Figure 2 XRD diffraction patterns of ceria nanoparticles (CeO

2)

1120583m

Figure 3 SEM image obtained on CeO2powder prepared by

hydroxide mediated approach

correspond to crystal planes (111) (200) (220) (311) (222)(400) (331) (420) and (422) that are characteristics forCeO

2

according to those of centered face cubic (CFC) fluoritestructuredCeO

2crystal No extra peaks corresponding to any

other secondary phases are observedThe crystal planes were in accordance with ICDD

(PDF2DAT) (CeO2Cerianite syn DB card number 00-043-

1002)The diffraction peaks in these XRD spectra indicate thepure cubic fluorite structure

312 SEM Characterization SEM images of CeO2powder

prepared by hydroxide mediated approach are shown inFigure 3 From the SEM images it was found that CeO

2

particles are characterized by a size of the powder in the range20ndash70 nmAlso therewere some visible aggregates formed byparticles quite agglomerated

32 Electrosynthesis of Polypyrrole Nanocomposite Thin Filmson Titanium Electrodes The CV curves from electrodepo-sition of PPy films on titanium substrate are presented inFigure 4

For all samples the current density gradually increasesin the successive CV cycles showing the electrodeposition

000 025 050 075 100

00

20

40

60

0001

0000

E (V versus AgAgCl)

E (V versus AgAgCl)08060402

times10minus3

i(A

cm

2) i

(Ac

m2)

TiPPy-NaPSSTiPPyTiPPy-CeO2 NPs TiPPy-NaPSS-CeO2 NPs

The first cycles

The 5th cycle

Figure 4 Cyclic voltammograms of PPy-nanocomposite filmselectrodeposition on titanium substrate

of polypyrrole or polypyrrole nanocomposite films ontotitanium substrate

The presence of NaPSS surfactant in the polymerizationsolution seems to improve Py polymerization rate The totalelectric charge used for polymerization is higher in thepresence of NaPSS (040Ccm2) comparing to PPy film(024Ccm2) as can be seen from Figure 5 If we considerthat the entire charge is used for polymerization process thiscan be an indication that the thickness of the polymer filmobtained in the presence of surfactant is higher During thepolymerization of pyrrole PSSminus has three different roles PSSminus(i) stabilizes the radical cation of the pyrrole monomer (ii)acts as a charge balancing dopant for PPy and (iii) rendersthe dispersion of the growing PPy chains in the final polymerfilm Small oxalate molecule dopants have a similar dopingfunction however they did not render the final complexdispersible [42]

By adding CeO2NPs in polymerization solution that

contains pyrrole monomer and oxalic acid (pH = 14) thetotal charge used for polymerization decreases to 020Ccm2In this pH conditions the ceria nanoparticles are positivelycharged according to literature [43] Py+ cationic radicalstability in the polymerization process was diminished andthus the electrodeposition rate decreased Electrostatic repul-sions between positive cerium oxide and PPy+ could resultin pushing positive CeO

2nanoparticles to the surface of

polymer film during polymerization Figure 6(a)Different behaviour can be observed when CeO

2NPs are

added in the pyrrole andNaPSS acid polymerization solutionIn the presence of surfactant the surface charge of CeO

2NPs

became negative as a consequence of adsorption of PSSminusanions on their surface [43] Thus due to the electrostaticinteractions between in this situation negatively chargedCeO2nanoparticles and cationic PPy+ matrix (doping) the


0 100 200

00

01

02

Char

ge (C

)

Time (s)

PPy PPy-NaPSS

1 cycle

2 cycles

3 cycles

4 cycles

5 cycles

PPy-CeO2 PPy-NaPSS-CeO2

Figure 5 Electrical charge evolution with polymerization time forpolymer nanocomposite films

compacting degree of the polymeric film is expected tobe improved Figure 6(b) In this case the total electricalcharge used for polymerization decreases from 040Ccm2to 032 Ccm2 The embedding of CeO

2NPs in PPy matrix

starts right from the first cycle when the titanium surfaceis positively charged by the decrease of the Fermi leveldue to electrode anodic polarization Moreover the nega-tively charged ceria nanoparticle and PSSminus could be directlyadsorbed on the positively charged titanium surface

These different interactions between PPy+ and posi-tivelynegatively charged CeO

2NPs are intended to bring

major changes in terms of morphology wettability electro-chemical stability and antibacterial activity of these polymernanocomposite films

33 Surface Characterization of PPy-Nanocomposite Films

331 SEMandEDAXAnalysis TheSEM images correspond-ing to surface of PPy-CeO

2NPs and PPy-NaPSS-CeO

2NPs

are illustrated in Figure 7 The surface morphology analysissustains and completes the expected changes in the polymericfilms structure due to the role played by the surfactant onCeO2NPs embedded in PPy films

Figure 7(a) reveals a quasiuniform spreading of CeO2

NPs agglomerates onto polymeric matrix This confirms thepresumed idea from anterior section sustaining thenanoparticles pushed from the inside to outside polymer filmsurface due to the electrostatic repulsion between positivelycharged CeO

2NPs and PPy+ as was represented in

Figure 6(a) CeO2NPs agglomeration can be associated

with (i) suggested electrostatic repulsions towards PPy+(ii) low stability occurred due to high surface-to-volumeratio and (iii) strong reactivity of the nanoparticles surfacechemical sites FromFigure 7(b) bothCeO

2NPs aggregates of

Table 1 EDAX analyzes for PPy film PPy-CeO2NPs film and PPy-

NaPSS-CeO2NPs film

SamplesElement

Ti C N O Ce S(Atomic)

TiPPy 5077 2155 972 1594 mdash mdashTiPPy-CeO

2NPs 3597 335 1064 1916 033 mdash

TiPPy-NaPSS-CeO2NPs 2407 4232 114 2042 032 128

hundreds nanometers and free nanoparticles with dimensionless than 50 nm can be observed

Comparatively in Figure 7(c) the surface morphologyof PPy-NaPSS-CeO

2NPs is presented CeO

2NPs aggregates

are less numerous than on PPy-CeO2NPs surface and their

sizes are also more reduced The small amount of CeO2NPs

aggregates on the surface could be an additional argument tothe fact that in the presence of surfactant negatively chargedCeO2NPs are preferentially embedded in the polymeric

film due to the electrostatic interactions with PPy+ (dopingprocess) mentioned above Figure 7(d) shows CeO

2NPs

aggregates with dimensions comprised between 150 nm and300 nm and the amount of nonassociated nanoparticlesbetween 50 nm and 80 nm seems to be greater

Moreover the most important information highlightedby EDAX analysis consists in proving of CeO

2NPs presence

oninto the polymer film Furthermore the cerium amountis almost the same about 032 at for both PPy-CeO

2

NPs and PPy-NaPSS-CeO2NPs film (Table 1) This means

that almost the same quantity of CeO2NPs is differently

distributed mainly on PPy surface for PPy-CeO2NPs film

and preferentially into polymer matrix for PPy-NaPSS-CeO2

NPs film as was concluded from electrochemical depositionand SEM analyses

The increasing in atomic for C and N elements (pro-vided by polypyrrole) for PPy-CeO

2NPs comparing with

PPy indicates a higher amount of polypyrrole Howeverthe corresponding electrical charge used for polymerizationwas diminished (from 024Ccm2 to 020Ccm2 Figure 5)suggesting a negative influence of CeO

2NPs over PPy doping

process In the presence of NaPSS and CeO2NPs (PPy-

NaPSS-CeO2NPs) the amount of PPy (suggested by an

increasing in atomic of C and N) sustains the presumptionmentioned in Section 32 according to which the thicknessof the polymer film obtained in the presence of surfactant ishigher

332 SurfaceWettability The surface wettability is an impor-tant feature for many applications that implies the surfaceinteraction with different biological entities such as bacteriaor cells

The contact angle measurements of the studied surfacesare presented in Table 2

PPy film has a low hydrophobic behaviour The presenceof CeO

2NPs on the polymeric film (PPy-CeO

2NPs) leads to

a decrease of the contact angle from 8661∘ to 7864∘


Ti substrate Ti substrate

Electrostaticinteraction

Repu

lsion

(a) (b)

CeO2 CeO2CeO2 CeO2

CeO2 CeO2CeO2

CeO2CeO2

CeO2

CeO2

CeO2

CeO2 CeO2

CeO2

CeO2

CeO2

CeO2

Z+Z+Z+

Z+Z+Z+Z+

Z+ Z+ Zminus

ZminusZminus

Zminus

ZminusZminus

Zminus

Zminus

Zminus

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+PPyZ+

PPyZ+ PPyZ+

PPyZ+

PSSminus

Figure 6 Electrostatic repulsions between positive cerium oxide and PPy+(a) electrostatic interactions between negatively charged CeO2

nanoparticles (in the presence of NaPSS) and cationic PPy+ matrix (b)

200 120583mCSSNT 100 kV 82mm times200 k LM(UL) 05262016

(a)

CSSNT 100 kV 81mm times251k SE(U) 05262016 200 120583m

(b)

200 120583mCSSNT 100 kV 82mm times200 k SE(U) 05262016

(c)

CSSNT 100 kV 82mm times200 k SE(U) 05262016 200 120583m

(d)

Figure 7 SEM images for PPy-CeO2NPs ((a) and (b)) and PPy-NaPSS-CeO

2NPs ((c) and (d)) nanocomposite films electrodeposited from

electrolytic aqueous solution containing pyrrole (04molsdotdmminus3) CeO2NPs (40 120583gsdotmLminus1) and NaPSS (01molsdotdmminus3)

However the hydrophilic property of polymeric film wasincreased when the polymerization was performed in thepresence of NaPSS surfactant The contact angles for films inwhich NaPSS is present (TiPPy-NaPSS and TiPPy-NaPSS-CeO2NPs) are very close (5215∘ and 5388∘) This can be

explained by the less influence of CeO2NPs on the wettability

of the polymer film due to its embedding in the polymermatrix Moreover the effect of CeO

2NPs bonded at the

surface upon wettability is insignificant due to adsorption ofNaPSS molecules on ceria nanoparticles


minus05 00 05

80

40

00

PPy PPy-NaPSS

Potential (DC)

(minus120596Z

998400998400)2

(1F

)2times109

PPy-CeO2 NPs PPy-NaPSS-CeO2 NPs

(a)

minus05 00 05Potential (DC)

07

14

21

TiLinear fit of Ti

(minus120596Z

998400998400)2

(1F

)2

times1011

(b)

Figure 8 Mott-Schottky diagrams for (a) TiPPy films and (b) uncoated titanium

Table 2 The contact angle measurements and standard deviationsfor PPy-nanocomposite films

Coating film Contact angle degrees SDTiPPy 8661 plusmn229TiPPy-NaPSS 5215 plusmn253TiPPy-CeO

2NPs 7864 plusmn188

TiPPy-NaPSS-CeO2NPs 5388 plusmn133

34 Electrochemical Characterization of PPy-NanocompositeFilms in Buffer Solution

341 Mott-Schottky Analysis In order to emphasize thechanges in polymer films during CeO

2andor surfactant

embedding in the structure of PPy the characterizations weresupplemented with Mott-Schottky analysis This techniquebased on capacitance versus potential measurements is acommon in situ method for investigation of polymeric filmssemiconductor properties Figure 8 presents the experimen-tal data and the fit of linear domains of Mott-Schottkydiagrams for all anodized samples A positive slope can beobserved for uncoated titanium typical for 119899-type semicon-ductor and negative slopes for polypyrrole coated titaniumtypical for 119901-type semiconductor

The flat band potential (119864fb) and charge carrier density(119873

119889) data calculated from Mott-Schottky diagrams show

significant changes in the semiconductor properties of thepolypyrrole films during CeO

2NPs incorporation Table 3

After insertion of CeO2inonto PPy film 119864fb is shifted in

negative direction with about 180mV confirming that CeO2

NPs are positively charged in acid aqueous polymerizationsolution 119873

119889of PPy film decreases in the presence of CeO

2

NPs from 763 sdot 1018mminus3 to 539 sdot 1018mminus3 sustaining thenegative influence of ceria nanoparticles over PPy dopinghighlighted by EDX analysis and electrochemical polymer-ization process

CeO2nanoparticles insertion performed in the presence

of surfactant has not caused a shifting of 119864fb minus192mV forPPy-NaPSS and minus191mV for PPy-NaPSS-CeO

2 Moreover

the presence of anionic surfactant in the polypyrrole film isclearly evidenced by a shifting of 119864fb in cathodic directionwith about 300mV and an increase of the charge carrierdensity of PPy film from 763 sdot 1018mminus3 to 952 sdot 1018mminus3Furthermore the increase of 119864fb of PPy-NaPSS film afterCeO2NPs insertion from 952 sdot 1018mminus3 to 1548 sdot 1019mminus3

shows that in this situation the negative effect of ceriananoparticles on the doping process is not observed in thepresence of surfactant Thus the influence of surfactant isprevalent on the doping process due to the presence of theadsorbed surfactant cage around ceria nanoparticles

342 Electrochemical Impedance Spectroscopy Electrochem-ical impedance spectroscopy performed at open circuitpotential in buffer solution was discussed in terms of Nyquistplots (Figure 9)

The equivalent electric circuits used to fit the EIS datawith Nova software are represented in Figure 10 For PPyand PPy-CeO

2NPs films a two-time constant circuit was

used (Figure 10(a)) where 119877s is solution resistance 119877ct1is the resistance responsible for the ion transfer throughpolymeric film connected in parallel with a constant phaseelement CPE

1 and 119899 is the phase change values 119877ct2 is the

resistance responsible for the electron transfer and CPE2is

the second constant phase element for electric double layerAnother constant phase element CPE

3was introduced for


Table 3 Charge carrier density (119873119889) and flat band potential (119864fb) fromMott-Schottky diagrams

Electrical parameters PPy PPy-CeO2NPs PPy-NaPSS PPy-NaPSS-CeO

2NPs

119864fb (V) 0108 minus0075 minus0192 minus0191119873

119889(mminus3) 7630 sdot 1018 5395 sdot 1018 0952 sdot 1019 1548 sdot 1019

Table 4 Electric parameters from fitting experimental EIS data

Parameters Polymeric-nanocomposite filmsPPy PPy-CeO

2NPs PPy-NaPSS PPy-NaPSS-CeO

2NPs

119877s (Ω cm2) 119 251 117 160

119877ct1 (Ω cm2) 832 515 6810 sdot 10+3 4370 sdot 10+3

CPE1(Ωminus1 cmminus2 s119899) 396 sdot 10minus3 799 sdot 10minus6 1860 sdot 10minus3 1370 sdot 10minus3

119899

10773 0360 0868 0785

119877ct2 (Ω cm2) 56 117 mdash mdash

CPE2(Ωminus1 cmminus2 s119899) 9750 sdot 10minus6 4050 sdot 10minus3 mdash mdash

119899

20342 0790 mdash mdash


119899


200 400 600 800 1000

200

400

600

800

1000

0

PPyFitted PPy

PPy-NaPSSFitted PPy-NaPSS

Z998400998400

(Ωcm

2 )

Z998400 (Ω cm2)

PPy-CeO2 NPsFitted PPy-CeO2 NPs

2 NPsPPy-NaPSS-CeO2 NPsFitted PPy-NaPSS-CeO

Figure 9 Nyquist spectra for PPy-nanocomposite filmsTi in buffersolution

lower frequency corresponding to capacitive behaviour ofthese films [40]

On the other hand for more compact PPy-nanocom-posite films PPy-NaPSS and PPy-NaPSS-CeO

2NPs the EIS

data were fitted with an equivalent electric circuit with one-time constant (Figure 10(b)) where 119877s is solution resistance119877ct1 is charge transfer resistance and CPE

1is constant phase

element

Electric parameters obtained from fitted experimentalEIS data with proposed equivalent circuits are presented inTable 4

The presence of the cationic oxide CeO2NPs in polymer-

ization solution is reflected by the values of the electron trans-fer resistance (119877ct2) For PPy-CeO2 NPs film 119877ct2 is higher(117Ω cm2) comparing with that of PPy film (56Ω cm2)This observation is in accordance with charge carrier density(119873119889) values obtained from Mott-Schottky analysis which are

superior for PPy film than PPy-CeO2NPs However 119877ct1

associated with ion transfer resistance decreases when CeO2

NPs were added in the polymeric film probably due to apresumed increase in ionic film permeability as was reportedin literature [37]

Also in NaPSS presence the charge transfer resistanceincreased with one order of magnitude compared to those ofpolymeric films without surfactant which could suggeststhat the resulted PPy-NaPSS films are more compact andstable On the other hand 119873

119889values obtained from Mott-

Schottky analysis indicated an increase in PPy doping processin the presence of surfactant Thus although PPy filmwhich resulted in the presence of surfactant should be moreconductive the resistance values are higher This behaviourcan be explained on the base of parallel adsorption processesof PSSminus on titanium surface at the beginning of anodicpolymerization that leads to a possible partial passivation ofthe substrate

The embedding of CeO2NPs into PPy-NaPSS-CeO

2NPs

film shows a decreasing of charge transfer resistance from681 kΩsdotcm2 to 437 kΩsdotcm2 probably due to the similar pro-cesses presented above 119899 value of constant phase element isalso slightly reduced from 086 to 078 sustaining a reductionin capacitive behaviour of the polypyrrole film due to ionicpermeation


Rs

Rct1 Rct2

CPE1 CPE2

CPE3

(a)

Rs

Rct1

CPE1

(b)

Figure 10 The equivalent circuits used to fit EIS data for (a) PPy and PPy-CeO2NPs films and (b) PPy-NaPSS and PPy-NaPSS-CeO

2NPs

films

minus015 000 015 030

PPy PPy-NaPSS

E (V versus AgAgCl)

i(A

cm

2)

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8


Figure 11 Tafel diagrams for PPy-nanocomposite films on Ti inbuffer solution

343 Tafel Diagrams Figure 11 shows the set of polarizationcurves recorded for PPy-nanocomposite films in buffer solu-tion

The electrochemical parameters computed with Novasoftware are presented in Table 5

The polarization resistance (119877p) values obtained fromTafel analysis performed in dc current depend on manysurface features such as film conductivity associated withthe doping process film permeability substrate passivationconnected with surfactant adsorption and titanium oxideformation119877p values from Tafel plots for PPy and PPy-CeO

2NPs

films are different than the 119877ct values obtained from EIS (per-formed in ac current) with about one order of magnitudeThese different results obtained by different techniques couldbe due to the effect of electrical imposed perturbations onthe coating properties The EIS analysis is performed at freepotential with small perturbation amplitude of 10mV and thefilm properties are not importantly affected On the contrary

Tafel analysis is performed in plusmn200mV perturbation stim-ulating reductionoxidation processes (undopingdoping) ofthe polypyrrole film which involve insertionrepulsion ofanions and cations intothrough the polymeric film asrepresented in (3) and (4) [40] One has

PPy + 119899Aminus oxidation997888997888997888997888997888997888rarr [(PPy)119899+ (Aminus)

119899] + 119899eminus (3)

[(PPy)119899+ (Aminus)119899] + 119899C+ + 119899eminus

reduction997888997888997888997888997888997888997888rarr [(PPy) (Aminus)

119899(C+)119899]

(4)

These insertionrepulsion processes lead to increase ofPPy film permeability and the electrolyte can reach moreeasily to the surface of titanium substrate promoting theresistive TiO

2oxide layer formation between PPy film and

Ti For PPy-NaPSS and PPy-NaPSS-CeO2NPs films 119877p

values obtained from Tafel plots are in a good correlationwith those obtained from EIS data sustaining once againthe stability and the less permeability of PPy-NaPSS filmsconferred by the presence of surfactant The PSSminus mobilityduring potential perturbation is reduced comparing withoxalate anionThus the film remains more compact avoidingthe electrolyte insertion

35 Antibacterial Activity In Figure 12 the influence ofCeO2NPs bonded in PPy matrix on antibacterial activity of

polymeric film was representedThe presence of uniform spreading CeO

2NPs agglomer-

ates onto polymeric matrix (PPy-CeO2) improves the anti-

bacterial activity of the polymeric film being in accordancewith the literature data which specified that the nanoparticlesof CeO

2have a good antibacterial effect on Escherichia coli

[44]PPy-NaPSS-CeO

2NPs film has a slightly lower antibac-

terial activity than PPy-CeO2NPs film The different doping

process in the presence ofNaPSS and the better embedding ofnegatively charged CeO

2NPs lead to a small amount of CeO

2

NPs on the polymer surfaceThus the role of the surfactant becomes determinant

during polymerization and the interaction between CeO2

NPs and PPy films has a strong influence on antibacterialactivity If the nanoparticles are on the polymer surfacethe antibacterial effect is improved but if nanoparticles are


Table 5 Electrochemical parameters from Tafel diagrams

Electrochemical parameters PPy PPy-CeO2NPs PPy-NaPSS PPy-NaPSS-CeO

2NPs

119864cor (mV) minus138 minus125 minus135 minus167119894cor (120583Acm

2) 19390 12321 53300 22268Vcor (mmyear) 0169 0107 0464 0194119877p (kΩ) 4617 6206 1083 1060

0

5

30

25

20

15

10

Inhi

bitio

n zo

ne (m

m)

Ti PPy PPy-CeO2 PPy-NaPSS-CeO2

Figure 12 Antibacterial activity of PPy-nanocomposite films onEscherichia coli

preponderantly embedded into PPy film the antibacterialactivity is slightly decreased

The results obtained from antibacterial activity of PPy-nanocomposite films on Escherichia coli confirm and sustainthe observations arising out from the surface and electro-chemical analysis regarding CeO

2NPs bonding intoonto

polymeric matrix

4 Conclusions

CeO2nanoparticles with dimension of tens nanometers were

synthesized by a coprecipitation method The influence ofNaPSS surfactant on the embedded CeO

2NPs in polypyrrole

films was investigated CeO2nanoparticles with dimension

of tens nanometers were synthesized by a coprecipitationmethod and embedded in polypyrrole films in presence ofNaPSS surfactant

From surface and electrochemical characterization itwas highlighted that NaPSS surfactant and CeO

2NPs play

an important role in PPy doping process NaPSS presenceimproves CeO

2NPs embedding into PPymatrixThe adsorp-

tion of PSSminus anions on the nanoparticles surface leads tonegatively charged CeO

2NPs and improves the electrostatic

interactions with cationic PPy+ matrix (doping)In the presence of surfactant CeO

2NPs are preferentially

embedded in the polymeric film while without surfactantthe ceria nanoparticles are quasiuniformly spread as agglom-erates onto polymeric films

This different distribution of ceria nanoparticles intoonto polypyrrole influences the film stability and even itspossible applications

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

This work was supported by a project of CNCS-UEFISCDIPN2-2532014-NANOCOAT The authors wish to thankMs Cristina Nicolescu for XRD analysis and Ms CameliaUngureanu for antibacterial activity analysis

References

[1] J L Chen C Chen Z Y Chen J Y Chen Q L Li andN Huang ldquoCollagenheparin coating on titanium surfaceimproves the biocompatibility of titanium applied as a blood-contacting biomaterialrdquo Journal of Biomedical MaterialsResearch Part A vol 95 no 2 pp 341ndash349 2010

[2] M Geetha A K Singh R Asokamani and A K Gogia ldquoTibased biomaterials the ultimate choice for orthopaedicimplants-a reviewrdquo Progress in Materials Science vol 54 no 3pp 397ndash425 2009

[3] W Ma S-H Wang G-F Wu et al ldquoPreparation and in vitrobiocompatibility of hybrid oxide layer on titanium surfacerdquoSurface and Coatings Technology vol 205 no 6 pp 1736ndash17422010

[4] S Mei H Wang W Wang et al ldquoAntibacterial effects andbiocompatibility of titanium surfaces with graded silver incor-poration in titania nanotubesrdquo Biomaterials vol 35 no 14 pp4255ndash4265 2014

[5] Y-H Lee G Bhattarai S Aryal et al ldquoModified titanium sur-face with gelatin nano gold composite increases osteoblast cellbiocompatibilityrdquo Applied Surface Science vol 256 no 20 pp5882ndash5887 2010

[6] K Gulati S Ramakrishnan M S Aw G J Atkins D MFindlay andD Losic ldquoBiocompatible polymer coating of titaniananotube arrays for improved drug elution and osteoblastadhesionrdquo Acta Biomaterialia vol 8 no 1 pp 449ndash456 2012

[7] S K Mishra and S Kannan ldquoDevelopment mechanical evalu-ation and surface characteristics of chitosanpolyvinyl alcoholbased polymer composite coatings on titanium metalrdquo Journalof the Mechanical Behavior of Biomedical Materials vol 40 pp314ndash324 2014


[8] S K Mishra J M F Ferreira and S Kannan ldquoMechanicallystable antimicrobial chitosan-PVA-silver nanocomposite coat-ings deposited on titanium implantsrdquo Carbohydrate Polymersvol 121 pp 37ndash48 2015

[9] K Ishihara and J Chol ldquoBiocompatible polymer assembly onmetal surfacesrdquo Metals for Biomedical Devices pp 283ndash3022010

[10] H Chen L Yuan W Song Z Wu and D Li ldquoBiocompat-ible polymer materials role of protein-surface interactionsrdquoProgress in Polymer Science vol 33 no 11 pp 1059ndash1087 2008

[11] G Helary F Noirclere J Mayingi and V Migonney ldquoA newapproach to graft bioactive polymer on titanium implantsimprovement of MG 63 cell differentiation onto this coatingrdquoActa Biomaterialia vol 5 no 1 pp 124ndash133 2009

[12] G Tan L Zhou C Ning et al ldquoBiomimetically-mineralizedcomposite coatings on titanium functionalized with gelatinmethacrylate hydrogelsrdquo Applied Surface Science vol 279 pp293ndash299 2013

[13] A de Leon and R C Advincula ldquoConducting polymers withsuperhydrophobic effects as anticorrosion coatingrdquo in Intelli-gent Coatings for Corrosion Control A Tiwari L Hihara andJ Rawlins Eds pp 409ndash430 2015

[14] P Zarras and J D Stenger-Smith ldquoElectro-active polymer(EAP) coatings for corrosion protection ofmetalsrdquo inHandbookof Smart Coatings for Materials Protection A S H MakhloufEd pp 328ndash369 Woodhead Cambridge UK 2014

[15] D D Ateh P Vadgama and H A Navsaria ldquoCulture of humankeratinocytes on polypyrrole-based conducting polymersrdquo Tis-sue Engineering vol 12 no 4 pp 645ndash655 2006

[16] Y Li K G Neoh L Cen and E T Kang ldquoPorous and elec-trically conductive polypyrrole- Poly (vinyl alcohol) compositeand its applications as a biomaterialrdquo Langmuir vol 21 no 23pp 10702ndash10709 2005

[17] G M Spinks V Mottaghitalab M Bahrami-Samani P GWhitten and G G Wallace ldquoCarbon-nanotube-reinforcedpolyaniline fibers for high-strength artificial musclesrdquoAdvanced Materials vol 18 no 5 pp 637ndash640 2006

[18] E De Giglio M R Guascito L Sabbatini and G ZamboninldquoElectropolymerization of pyrrole on titanium substrates for thefuture development of new biocompatible surfacesrdquo Biomateri-als vol 22 no 19 pp 2609ndash2616 2001

[19] K Idla O Inganas and M Strandberg ldquoGood adhesionbetween chemically oxidised titanium and electrochemicallydeposited polypyrrolerdquo Electrochimica Acta vol 45 no 13 pp2121ndash2130 2000

[20] X Wang X Gu C Yuan et al ldquoEvaluation of biocompatibilityof polypyrrole in vitro and in vivordquo Journal of BiomedicalMaterials ResearchmdashPart A vol 68 no 3 pp 411ndash422 2004

[21] S T Earley D P Dowling J P Lowry and C B BreslinldquoFormation of adherent polypyrrole coatings on Ti and Ti-6Al-4V alloyrdquo Synthetic Metals vol 148 no 2 pp 111ndash118 2005

[22] Z Weiss D Mandler G Shustak and A J Domb ldquoPyrrolederivatives for electrochemical coating of metallic medicaldevicesrdquo Journal of Polymer Science Part A Polymer Chemistryvol 42 no 7 pp 1658ndash1667 2004

[23] MMındroiu C Ungureanu R Ion and C Pırvu ldquoThe effect ofdeposition electrolyte on polypyrrole surface interaction withbiological environmentrdquo Applied Surface Science vol 276 pp401ndash410 2013

[24] S M Dizaj F Lotfipour M Barzegar-Jalali M H Zarrintanand K Adibkia ldquoAntimicrobial activity of the metals and metal

oxide nanoparticlesrdquo Materials Science and Engineering C vol44 pp 278ndash284 2014

[25] R Gokulakrishnan S Ravikumar and J A Raj ldquoIn vitroantibacterial potential of metal oxide nanoparticles againstantibiotic resistant bacterial pathogensrdquoAsian Pacific Journal ofTropical Disease vol 2 no 5 pp 411ndash413 2012

[26] MMoritz andM Geszke-Moritz ldquoThe newest achievements insynthesis immobilization and practical applications of antibac-terial nanoparticlesrdquoChemical Engineering Journal vol 228 pp596ndash613 2013

[27] A S Karakoti N A Monteiro-Riviere R Aggarwal et alldquoNanoceria as antioxidant synthesis and biomedical applica-tionsrdquo The Journal of The Minerals Metals amp Materials Societyvol 60 no 3 pp 33ndash37 2008

[28] V Shah S ShahH Shah et al ldquoAntibacterial activity of polymercoated cerium oxide nanoparticlesrdquo PLoS ONE vol 7 articlee47827 2012

[29] C H Baker ldquoHarnessing cerium oxide nanoparticles to protectnormal tissue from radiation damagerdquo Translational CancerResearch vol 2 pp 343ndash358 2013

[30] F Liu Y Yuan L Li et al ldquoSynthesis of polypyrrole nanocom-posites decorated with silver nanoparticles with electrocatalysisand antibacterial propertyrdquo Composites Part B Engineering vol69 pp 232ndash236 2014

[31] M B Gonzalez L I Brugnoni M E Vela and S B SaidmanldquoSilver deposition on polypyrrole films electrosynthesized insalicylate solutionsrdquo Electrochimica Acta vol 102 pp 66ndash712013

[32] E N Zare M M Lakouraj and M Mohseni ldquoBiodegrad-able polypyrroledextrin conductive nanocomposite synthesischaracterization antioxidant and antibacterial activityrdquo Syn-thetic Metals vol 187 no 1 pp 9ndash16 2014

[33] M Cabuk Y Alan M Yavuz and H I Unal ldquoSynthesis char-acterization and antimicrobial activity of biodegradable con-ducting polypyrrole-graft-chitosan copolymerrdquo Applied SurfaceScience vol 318 pp 168ndash175 2014

[34] C Ungureanu C Pirvu M Mindroiu and I DemetresculdquoAntibacterial polymeric coating based on polypyrrole andpolyethylene glycol on a new alloy TiAlZrrdquo Progress in OrganicCoatings vol 75 no 4 pp 349ndash355 2012

[35] CUngureanu S Popescu G Purcel et al ldquoImproved antibacte-rial behavior of titanium surface with torularhodin-polypyrrolefilmrdquoMaterials Science and Engineering C vol 42 pp 726ndash7332014

[36] K-Q Liu C-X Kuang M-Q Zhong Y-Q Shi and F ChenldquoSynthesis characterization and UV-shielding property ofpolystyrene-embedded CeO

2nanoparticlesrdquo Optical Materials

vol 35 no 12 pp 2710ndash2715 2013[37] C Benmouhoub J Agrisuelas N Benbrahim et al ldquoInflu-

ence of the incorporation of CeO2nanoparticles on the ion

exchange behavior of dodecylsulfate doped polypyrrole filmsAc-electrogravimetry investigationsrdquo Electrochimica Acta vol145 pp 270ndash280 2014

[38] C Pirvu M Mindroiu S Popescu and I Demetrescu ldquoElec-trodeposition of polypyrrolepoly(Styrene Sulphonate) com-posite coatings on Ti6Al7Nb alloyrdquo Molecular Crystals andLiquid Crystals vol 521 pp 126ndash139 2010

[39] M Mindroiu R Ion C Pirvu and A Cimpean ldquoSurfactant-dependent macrophage response to polypyrrole-based coatingselectrodeposited on Ti

6Al7Nb alloyrdquo Materials Science and

Engineering C vol 33 no 6 pp 3353ndash3361 2013


[40] C Pirvu C C Manole A B Stoian and I DemetresculdquoUnderstanding of electrochemical and structural changes ofpolypyrrolepolyethylene glycol composite films in aqueoussolutionrdquo Electrochimica Acta vol 56 no 27 pp 9893ndash99032011

[41] J H Jorgensen and J D Turnidge Susceptibility Test MethodsDilution and Disk Diffusion Methods ASM Press 2015

[42] R Bouldin S Ravichandran A Kokil et al ldquoSynthesis ofpolypyrrole with fewer structural defects using enzyme catal-ysisrdquo Synthetic Metals vol 161 no 15-16 pp 1611ndash1617 2011

[43] A Sehgal Y Lalatonne J-F Berret and M MorvanldquoPrecipitation-redispersion of cerium oxide nanoparticleswith poly (acrylic acid) toward stable dispersionsrdquo Langmuirvol 21 no 20 pp 9359ndash9364 2005

[44] Y Kuang X He Z Zhang et al ldquoComparison study on theantibacterial activity of nano-or bulk-cerium oxiderdquo Journal ofNanoscience and Nanotechnology vol 11 no 5 pp 4103ndash41082011

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


and more utilized as antioxidant providing an efficientprotection against free radicals and as antimicrobial agent[27ndash29] The small size of particles allows the interactionwith biological entities (proteins DNAmolecules and mem-branes)

In this respect as a polymeric matrix PPy has beenalready subjected to incorporation of different antibacterialsubstances such as silver nanoparticles [30 31] biodegradablecompounds such as dextrin or chitosan [32 33] PEG [34] orother carotenoid compounds like torularhodin [35]

The idea of combining a polymer with nanoparticles tocreate a compositematerial represents a promising alternativesince these materials combine both the unique propertiesof nanoparticles with those of the polymer resulting in anew material with specific properties The incorporationof ceria particles in polypyrrole film requires some specialprecautions These particles are stabilized by electrostaticsforces and are extremely sensitive to perturbations of pHionic strength and concentration that may dramaticallymodify their thermodynamic stability The low stabilityoccurs due to high surface-to-volume ratio for particles andfrom the strong reactivity of the surface chemical sites tophysicochemical changes Therefore for some applicationsthe challenge is to find appropriate conditions to prepareCeO2polymeric composite in which ceria nanoparticles are

dispersed homogeneously in a polymer matrix [36]Literature contains one study about the incorporation

of CeO2in dodecyl sulfate doped polypyrrole films (PPy-

DS) deposited on gold electrode It was concluded thatCeO2NPs have the ability to modify the morphology of

electrodeposited PPy-DS thin films but without highlightingthe film morphology and the influence of the surfactant onceria nanoparticles distribution into the polymeric film [37]

In the present study poly(sodium 4-styrenesulfonate)(NaPSS) was selected as surfactant based on previous studies[38 39] and it is expected to provide a goodCeO

2distribution

and a better embedding in the polymer nanocomposite filmdeposited on titanium surface Two PPy-CeO

2composite

films obtained with and without NaPSS were studied com-paratively in terms of surface properties electrochemicalstability and antibacterial activity

2 Experimental Part

21 Synthesis of CeO2 Nanoparticles For the synthesisof CeO

2nanoparticles we applied a simple hydroxide

mediated approach that uses cerium nitrate hexahydrate(Ce(NO

3)3sdot6H2Ogt 995 Aldrich Chemicals USA) as start-

ingmaterial and sodium hydroxide as precipitating agent Allthe chemical reagents were used without purification

The starting solutions were 01M Ce(NO3)3sdot6H2O and

03M NaOH prepared with double distilled water Firststep consists in adding dropwise the NaOH solution for 3hours under continuous stirring at room temperature untila pinkish precipitate is obtainedThe vigorous stirring is veryimportant because it influences the product particle size andits distribution

Precipitation of a pinkish white precipitate

Stirring at room temperature (3 hours)

+

Washing with ethanol and water(3 times)

NaOH (03M)

Centrifugation(8000 rpm 15min)

Ce(NO3)3middot6H2O (01M)

Drying of the precipitatein oven (80∘C 1h)

Annealed in furnace (270∘C 24h)

CeO2 particles

Figure 1 Synthesis of CeO2nanoparticles

The apparition of a pinkish precipitate suggests the oxi-dation of Ce(OH)

3into Ce(OH)

4that occurs in the presence

of dissolved oxygen while the pH was maintained around 9Finally it became a light yellow suspension characteristic forCeO2

The reactions during the synthesis are the following

Ce (NO3)

3sdot 6H2O(s) 997888rarr Ce3+

(aq) + 3NOminus

3(aq) + 6H2O (1)

2Ce3+(aq) +1

2

O2+ 6OHminus

pHasymp9997888997888997888997888rarr 2CeO

2+ 3H2O (2)

In another step the yellow precipitate was centrifugedthree times washed well with ethanol and distilledH

2O three

times and then dried in an oven at 80∘C for 1 hour followedby an annealing process at 270∘C for 24 h The resultingprecipitate is a light yellow precipitate that was furtheranalyzed through XRD Figure 1 presents the schematicdiagram for CeO

2particles synthesis

22 Preparation of Titanium Substrate before Polymer FilmsElectrodeposition Commercially pure Ti discs of 10mmdiameter and 1mm thickness (996 purity grade 2 Good-fellow Cambridge Ltd UK) were used The surface of testspecimens was polished with SiC paper to grade 4000 andthenwashedwith a large amount of water followed by acetoneand finally rinsed with distilled water and dried in air at roomtemperature

23 Synthesis of PPy Films and PPy-CeO2 with and withoutSurfactant Synthesis of polymeric films was performed by




(TiPPy-CeO2NPs) CeO





2









2NPs) a


















0

500

1000

1500

2000

2500

20 40 60 80

Inte

nsity

(au

)

2120579 (deg)



(111

)

(200) (220)

(311

)(2

22

)

(400

)

(331

)(4

20

)

(422


2)

1120583m




2








2




000 025 050 075 100

00

20

40

60

0001

0000

E (V versus AgAgCl)


times10minus3

i(A

cm

2) i

(Ac

m2)


The first cycles

The 5th cycle








2NPs are


2NPs



0 100 200

00

01

02

Char

ge (C

)

Time (s)

PPy PPy-NaPSS

1 cycle

2 cycles

3 cycles

4 cycles

5 cycles




2NPs in PPy matrix








2NPs







2NPs aggregates of


NaPSS-CeO2NPs film

SamplesElement



2NPs 3597 335 1064 1916 033 mdash





2NPs aggregates





2NPs



2NPs presence


2







2NPs comparing with










2NPs) leads to





Repu

lsion

(a) (b)

CeO2 CeO2CeO2 CeO2

CeO2 CeO2CeO2

CeO2CeO2

CeO2

CeO2

CeO2

CeO2 CeO2

CeO2

CeO2

CeO2

CeO2

Z+Z+Z+

Z+Z+Z+Z+

Z+ Z+ Zminus

ZminusZminus

Zminus

ZminusZminus

Zminus

Zminus

Zminus

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+PPyZ+

PPyZ+ PPyZ+

PPyZ+

PSSminus




(a)


(b)


(c)


(d)







2NPs bonded at the



minus05 00 05

80

40

00

PPy PPy-NaPSS

Potential (DC)

(minus120596Z

998400998400)2

(1F

)2times109


(a)


07

14

21

TiLinear fit of Ti

(minus120596Z

998400998400)2

(1F

)2

times1011

(b)




2NPs 7864 plusmn188




2andor surfactant










2




2 Moreover










3was introduced for




2NPs






2NPs

119877s (Ω cm2) 119 251 117 160

119877ct1 (Ω cm2) 832 515 6810 sdot 10+3 4370 sdot 10+3


119899

10773 0360 0868 0785



119899



119899


200 400 600 800 1000

200

400

600

800

1000

0

PPyFitted PPy


Z998400998400

(Ωcm

2 )

Z998400 (Ω cm2)






2NPs the EIS


1is constant phase

element











2NPs



Rs

Rct1 Rct2

CPE1 CPE2

CPE3

(a)

Rs

Rct1

CPE1

(b)


2NPs

films

minus015 000 015 030

PPy PPy-NaPSS

E (V versus AgAgCl)

i(A

cm

2)

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8






2NPs




119899] + 119899eminus (3)



119899(C+)119899]

(4)







2NPs agglomer-




[44]PPy-NaPSS-CeO





2







2NPs


2) 19390 12321 53300 22268Vcor (mmyear) 0169 0107 0464 0194119877p (kΩ) 4617 6206 1083 1060

0

5

30

25

20

15

10

Inhi

bitio

n zo

ne (m

m)






polymeric matrix

4 Conclusions



2NPs in polypyrrole




2NPs play









Competing Interests


Acknowledgments


References




























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






(TiPPy-CeO2NPs) CeO





2









2NPs) a


















0

500

1000

1500

2000

2500

20 40 60 80

Inte

nsity

(au

)

2120579 (deg)



(111

)

(200) (220)

(311

)(2

22

)

(400

)

(331

)(4

20

)

(422


2)

1120583m




2








2




000 025 050 075 100

00

20

40

60

0001

0000

E (V versus AgAgCl)


times10minus3

i(A

cm

2) i

(Ac

m2)


The first cycles

The 5th cycle








2NPs are


2NPs



0 100 200

00

01

02

Char

ge (C

)

Time (s)

PPy PPy-NaPSS

1 cycle

2 cycles

3 cycles

4 cycles

5 cycles




2NPs in PPy matrix








2NPs







2NPs aggregates of


NaPSS-CeO2NPs film

SamplesElement



2NPs 3597 335 1064 1916 033 mdash





2NPs aggregates





2NPs



2NPs presence


2







2NPs comparing with










2NPs) leads to





Repu

lsion

(a) (b)

CeO2 CeO2CeO2 CeO2

CeO2 CeO2CeO2

CeO2CeO2

CeO2

CeO2

CeO2

CeO2 CeO2

CeO2

CeO2

CeO2

CeO2

Z+Z+Z+

Z+Z+Z+Z+

Z+ Z+ Zminus

ZminusZminus

Zminus

ZminusZminus

Zminus

Zminus

Zminus

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+PPyZ+

PPyZ+ PPyZ+

PPyZ+

PSSminus




(a)


(b)


(c)


(d)







2NPs bonded at the



minus05 00 05

80

40

00

PPy PPy-NaPSS

Potential (DC)

(minus120596Z

998400998400)2

(1F

)2times109


(a)


07

14

21

TiLinear fit of Ti

(minus120596Z

998400998400)2

(1F

)2

times1011

(b)




2NPs 7864 plusmn188




2andor surfactant










2




2 Moreover










3was introduced for




2NPs






2NPs

119877s (Ω cm2) 119 251 117 160

119877ct1 (Ω cm2) 832 515 6810 sdot 10+3 4370 sdot 10+3


119899

10773 0360 0868 0785



119899



119899


200 400 600 800 1000

200

400

600

800

1000

0

PPyFitted PPy


Z998400998400

(Ωcm

2 )

Z998400 (Ω cm2)






2NPs the EIS


1is constant phase

element











2NPs



Rs

Rct1 Rct2

CPE1 CPE2

CPE3

(a)

Rs

Rct1

CPE1

(b)


2NPs

films

minus015 000 015 030

PPy PPy-NaPSS

E (V versus AgAgCl)

i(A

cm

2)

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8






2NPs




119899] + 119899eminus (3)



119899(C+)119899]

(4)







2NPs agglomer-




[44]PPy-NaPSS-CeO





2







2NPs


2) 19390 12321 53300 22268Vcor (mmyear) 0169 0107 0464 0194119877p (kΩ) 4617 6206 1083 1060

0

5

30

25

20

15

10

Inhi

bitio

n zo

ne (m

m)






polymeric matrix

4 Conclusions



2NPs in polypyrrole




2NPs play









Competing Interests


Acknowledgments


References




























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0

500

1000

1500

2000

2500

20 40 60 80

Inte

nsity

(au

)

2120579 (deg)



(111

)

(200) (220)

(311

)(2

22

)

(400

)

(331

)(4

20

)

(422


2)

1120583m




2








2




000 025 050 075 100

00

20

40

60

0001

0000

E (V versus AgAgCl)


times10minus3

i(A

cm

2) i

(Ac

m2)


The first cycles

The 5th cycle








2NPs are


2NPs



0 100 200

00

01

02

Char

ge (C

)

Time (s)

PPy PPy-NaPSS

1 cycle

2 cycles

3 cycles

4 cycles

5 cycles




2NPs in PPy matrix








2NPs







2NPs aggregates of


NaPSS-CeO2NPs film

SamplesElement



2NPs 3597 335 1064 1916 033 mdash





2NPs aggregates





2NPs



2NPs presence


2







2NPs comparing with










2NPs) leads to





Repu

lsion

(a) (b)

CeO2 CeO2CeO2 CeO2

CeO2 CeO2CeO2

CeO2CeO2

CeO2

CeO2

CeO2

CeO2 CeO2

CeO2

CeO2

CeO2

CeO2

Z+Z+Z+

Z+Z+Z+Z+

Z+ Z+ Zminus

ZminusZminus

Zminus

ZminusZminus

Zminus

Zminus

Zminus

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+PPyZ+

PPyZ+ PPyZ+

PPyZ+

PSSminus




(a)


(b)


(c)


(d)







2NPs bonded at the



minus05 00 05

80

40

00

PPy PPy-NaPSS

Potential (DC)

(minus120596Z

998400998400)2

(1F

)2times109


(a)


07

14

21

TiLinear fit of Ti

(minus120596Z

998400998400)2

(1F

)2

times1011

(b)




2NPs 7864 plusmn188




2andor surfactant










2




2 Moreover










3was introduced for




2NPs






2NPs

119877s (Ω cm2) 119 251 117 160

119877ct1 (Ω cm2) 832 515 6810 sdot 10+3 4370 sdot 10+3


119899

10773 0360 0868 0785



119899



119899


200 400 600 800 1000

200

400

600

800

1000

0

PPyFitted PPy


Z998400998400

(Ωcm

2 )

Z998400 (Ω cm2)






2NPs the EIS


1is constant phase

element











2NPs



Rs

Rct1 Rct2

CPE1 CPE2

CPE3

(a)

Rs

Rct1

CPE1

(b)


2NPs

films

minus015 000 015 030

PPy PPy-NaPSS

E (V versus AgAgCl)

i(A

cm

2)

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8






2NPs




119899] + 119899eminus (3)



119899(C+)119899]

(4)







2NPs agglomer-




[44]PPy-NaPSS-CeO





2







2NPs


2) 19390 12321 53300 22268Vcor (mmyear) 0169 0107 0464 0194119877p (kΩ) 4617 6206 1083 1060

0

5

30

25

20

15

10

Inhi

bitio

n zo

ne (m

m)






polymeric matrix

4 Conclusions



2NPs in polypyrrole




2NPs play









Competing Interests


Acknowledgments


References




























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0 100 200

00

01

02

Char

ge (C

)

Time (s)

PPy PPy-NaPSS

1 cycle

2 cycles

3 cycles

4 cycles

5 cycles




2NPs in PPy matrix








2NPs







2NPs aggregates of


NaPSS-CeO2NPs film

SamplesElement



2NPs 3597 335 1064 1916 033 mdash





2NPs aggregates





2NPs



2NPs presence


2







2NPs comparing with










2NPs) leads to





Repu

lsion

(a) (b)

CeO2 CeO2CeO2 CeO2

CeO2 CeO2CeO2

CeO2CeO2

CeO2

CeO2

CeO2

CeO2 CeO2

CeO2

CeO2

CeO2

CeO2

Z+Z+Z+

Z+Z+Z+Z+

Z+ Z+ Zminus

ZminusZminus

Zminus

ZminusZminus

Zminus

Zminus

Zminus

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+PPyZ+

PPyZ+ PPyZ+

PPyZ+

PSSminus




(a)


(b)


(c)


(d)







2NPs bonded at the



minus05 00 05

80

40

00

PPy PPy-NaPSS

Potential (DC)

(minus120596Z

998400998400)2

(1F

)2times109


(a)


07

14

21

TiLinear fit of Ti

(minus120596Z

998400998400)2

(1F

)2

times1011

(b)




2NPs 7864 plusmn188




2andor surfactant










2




2 Moreover










3was introduced for




2NPs






2NPs

119877s (Ω cm2) 119 251 117 160

119877ct1 (Ω cm2) 832 515 6810 sdot 10+3 4370 sdot 10+3


119899

10773 0360 0868 0785



119899



119899


200 400 600 800 1000

200

400

600

800

1000

0

PPyFitted PPy


Z998400998400

(Ωcm

2 )

Z998400 (Ω cm2)






2NPs the EIS


1is constant phase

element











2NPs



Rs

Rct1 Rct2

CPE1 CPE2

CPE3

(a)

Rs

Rct1

CPE1

(b)


2NPs

films

minus015 000 015 030

PPy PPy-NaPSS

E (V versus AgAgCl)

i(A

cm

2)

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8






2NPs




119899] + 119899eminus (3)



119899(C+)119899]

(4)







2NPs agglomer-




[44]PPy-NaPSS-CeO





2







2NPs


2) 19390 12321 53300 22268Vcor (mmyear) 0169 0107 0464 0194119877p (kΩ) 4617 6206 1083 1060

0

5

30

25

20

15

10

Inhi

bitio

n zo

ne (m

m)






polymeric matrix

4 Conclusions



2NPs in polypyrrole




2NPs play









Competing Interests


Acknowledgments


References




























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






Repu

lsion

(a) (b)

CeO2 CeO2CeO2 CeO2

CeO2 CeO2CeO2

CeO2CeO2

CeO2

CeO2

CeO2

CeO2 CeO2

CeO2

CeO2

CeO2

CeO2

Z+Z+Z+

Z+Z+Z+Z+

Z+ Z+ Zminus

ZminusZminus

Zminus

ZminusZminus

Zminus

Zminus

Zminus

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+

PPyZ+PPyZ+

PPyZ+ PPyZ+

PPyZ+

PSSminus




(a)


(b)


(c)


(d)







2NPs bonded at the



minus05 00 05

80

40

00

PPy PPy-NaPSS

Potential (DC)

(minus120596Z

998400998400)2

(1F

)2times109


(a)


07

14

21

TiLinear fit of Ti

(minus120596Z

998400998400)2

(1F

)2

times1011

(b)




2NPs 7864 plusmn188




2andor surfactant










2




2 Moreover










3was introduced for




2NPs






2NPs

119877s (Ω cm2) 119 251 117 160

119877ct1 (Ω cm2) 832 515 6810 sdot 10+3 4370 sdot 10+3


119899

10773 0360 0868 0785



119899



119899


200 400 600 800 1000

200

400

600

800

1000

0

PPyFitted PPy


Z998400998400

(Ωcm

2 )

Z998400 (Ω cm2)






2NPs the EIS


1is constant phase

element











2NPs



Rs

Rct1 Rct2

CPE1 CPE2

CPE3

(a)

Rs

Rct1

CPE1

(b)


2NPs

films

minus015 000 015 030

PPy PPy-NaPSS

E (V versus AgAgCl)

i(A

cm

2)

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8






2NPs




119899] + 119899eminus (3)



119899(C+)119899]

(4)







2NPs agglomer-




[44]PPy-NaPSS-CeO





2







2NPs


2) 19390 12321 53300 22268Vcor (mmyear) 0169 0107 0464 0194119877p (kΩ) 4617 6206 1083 1060

0

5

30

25

20

15

10

Inhi

bitio

n zo

ne (m

m)






polymeric matrix

4 Conclusions



2NPs in polypyrrole




2NPs play









Competing Interests


Acknowledgments


References




























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




minus05 00 05

80

40

00

PPy PPy-NaPSS

Potential (DC)

(minus120596Z

998400998400)2

(1F

)2times109


(a)


07

14

21

TiLinear fit of Ti

(minus120596Z

998400998400)2

(1F

)2

times1011

(b)




2NPs 7864 plusmn188




2andor surfactant










2




2 Moreover










3was introduced for




2NPs






2NPs

119877s (Ω cm2) 119 251 117 160

119877ct1 (Ω cm2) 832 515 6810 sdot 10+3 4370 sdot 10+3


119899

10773 0360 0868 0785



119899



119899


200 400 600 800 1000

200

400

600

800

1000

0

PPyFitted PPy


Z998400998400

(Ωcm

2 )

Z998400 (Ω cm2)






2NPs the EIS


1is constant phase

element











2NPs



Rs

Rct1 Rct2

CPE1 CPE2

CPE3

(a)

Rs

Rct1

CPE1

(b)


2NPs

films

minus015 000 015 030

PPy PPy-NaPSS

E (V versus AgAgCl)

i(A

cm

2)

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8






2NPs




119899] + 119899eminus (3)



119899(C+)119899]

(4)







2NPs agglomer-




[44]PPy-NaPSS-CeO





2







2NPs


2) 19390 12321 53300 22268Vcor (mmyear) 0169 0107 0464 0194119877p (kΩ) 4617 6206 1083 1060

0

5

30

25

20

15

10

Inhi

bitio

n zo

ne (m

m)






polymeric matrix

4 Conclusions



2NPs in polypyrrole




2NPs play









Competing Interests


Acknowledgments


References




























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






2NPs






2NPs

119877s (Ω cm2) 119 251 117 160

119877ct1 (Ω cm2) 832 515 6810 sdot 10+3 4370 sdot 10+3


119899

10773 0360 0868 0785



119899



119899


200 400 600 800 1000

200

400

600

800

1000

0

PPyFitted PPy


Z998400998400

(Ωcm

2 )

Z998400 (Ω cm2)






2NPs the EIS


1is constant phase

element











2NPs



Rs

Rct1 Rct2

CPE1 CPE2

CPE3

(a)

Rs

Rct1

CPE1

(b)


2NPs

films

minus015 000 015 030

PPy PPy-NaPSS

E (V versus AgAgCl)

i(A

cm

2)

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8






2NPs




119899] + 119899eminus (3)



119899(C+)119899]

(4)







2NPs agglomer-




[44]PPy-NaPSS-CeO





2







2NPs


2) 19390 12321 53300 22268Vcor (mmyear) 0169 0107 0464 0194119877p (kΩ) 4617 6206 1083 1060

0

5

30

25

20

15

10

Inhi

bitio

n zo

ne (m

m)






polymeric matrix

4 Conclusions



2NPs in polypyrrole




2NPs play









Competing Interests


Acknowledgments


References




























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Rs

Rct1 Rct2

CPE1 CPE2

CPE3

(a)

Rs

Rct1

CPE1

(b)


2NPs

films

minus015 000 015 030

PPy PPy-NaPSS

E (V versus AgAgCl)

i(A

cm

2)

10minus3

10minus4

10minus5

10minus6

10minus7

10minus8






2NPs




119899] + 119899eminus (3)



119899(C+)119899]

(4)







2NPs agglomer-




[44]PPy-NaPSS-CeO





2







2NPs


2) 19390 12321 53300 22268Vcor (mmyear) 0169 0107 0464 0194119877p (kΩ) 4617 6206 1083 1060

0

5

30

25

20

15

10

Inhi

bitio

n zo

ne (m

m)






polymeric matrix

4 Conclusions



2NPs in polypyrrole




2NPs play









Competing Interests


Acknowledgments


References




























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






2NPs


2) 19390 12321 53300 22268Vcor (mmyear) 0169 0107 0464 0194119877p (kΩ) 4617 6206 1083 1060

0

5

30

25

20

15

10

Inhi

bitio

n zo

ne (m

m)






polymeric matrix

4 Conclusions



2NPs in polypyrrole




2NPs play









Competing Interests


Acknowledgments


References




























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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