Journal of Hazardous Materials 283 (2015) 164170

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Journal of Hazardous Materials

journa l homepage: www.e lsev ier .com/ locate / jhazmat

Conduc ol ftreatm

Md. Mom a,

a Department o traliab Samadha Pac

h i g h l i g h t s

Anion exchange property of polypyrrole lms exploited in developing a treatment method for Acid Red 1. An environmentally friendly treatment method for Acid Red 1 without generating any toxic by-products. Acid Red 1 is anodically entrapped and cathodically liberated at polypyrrole lms. Analytical characteristics of Acid Red 1-entrapped polypyrrole lms.

a r t i c l

Article history:Received 15 MReceived in reAccepted 18 JuAvailable onlin

Keywords:ElectrochemicDye entrapmePolypyrrole lAcid Red 1Environmenta

1. Introdu

Azo dyestile applicaease of synthigh solubicolours [4]exhibit varThis becom

CorresponE-mail add

http://dx.doi.o0304-3894/e i n f o

ay 2014vised form 17 July 2014ly 2014e 29 July 2014

al treatmentntliberationms

lly friendly treatment

a b s t r a c t

In this paper, we demonstrate conducting polypyrrole lms as a potential green technology for electro-chemical treatment of azo dyes in wastewaters using Acid Red 1 as a model analyte. These lms weresynthesisedbyanodicallypolymerisingpyrrole in thepresenceofAcidRed1asa supportingelectrolyte. Inthis way, the anionic Acid Red 1 is electrostatically attracted to the cationic polypyrrole backbone formedto maintain electroneutrality, and is thus entrapped in the lm. These Acid Red 1-entrapped polypyr-role lms were characterised by electrochemical, microscopic and spectroscopic techniques. Based on atwo-level factorial design, the solution pH, Acid Red 1 concentration and polymerisation duration wereidentied as signicant parameters affecting the entrapment efciency. The entrapment process willpotentially aid in decolourising Acid Red 1-containing wastewaters. Similarly, in a cathodic process, elec-trons are supplied to neutralise the polypyrrole backbone, liberating Acid Red 1 into a solution. In thiswork, following an entrapment duration of 480min in 2000mgL1 Acid Red 1, we estimated 21% of thedye was liberated after a reduction period of 240min. This allows the recovery of Acid Red 1 for recyclingpurposes. A distinctive advantage of this electrochemical Acid Red 1 treatment, compared to many othertechniques, is that no known toxic by-products are generated in the treatment. Therefore, conductingpolypyrrole lms can potentially be applied as an environmentally friendly treatment method for textileefuents.

2014 Elsevier B.V. All rights reserved.

ction

are among the most widely used groups of dyes in tex-tions [1]. This is mainly due to their cost effectiveness,hesis and intense colouring properties. Owing to theirlity in water [2], potential carcinogenicity [3], intenseand non-reactive nature [5], azo dyes are known to

ious adverse effects upon aquatic ora and fauna [2].es an even more severe issue in environments where

ding author. Tel.: +61 2 9850 8300; fax: +61 2 9850 8313.ress: Danny.Wong@mq.edu.au (D.K.Y. Wong).

existence of dyes persists for a long period of time. Their intensecolours in an aqueous system also inevitably decrease the amountof sunlight penetration, causing a reduction in the rate of photo-synthesis, which in turn affects various life forms in the water body[6].

Several treatment methods for azo dyes have hitherto beenreported. These include microbial degradation [7], adsorbents(e.g. active carbon) [8,9], sacricial iron electrodes [10], electrol-ysis [11,12], electrocoagulation [13,14], ion-pair extraction [15],Fentons process and other advanced electrochemical oxidationprocesses [16,17]. However, there are severe limitations associ-ated with these methods. For example, there are disposal problemsconcerning spent carbon in using active carbon as an adsorbent

rg/10.1016/j.jhazmat.2014.07.0382014 Elsevier B.V. All rights reserved.ting polypyrrole lms as a potential toent of azo dyes in textile wastewaters

inul Haquea, Warren T. Smithb, Danny K.Y. Wongf Chemistry and Biomolecular Sciences, Macquarie University, Sydney, NSW 2109, Ausica Pty Ltd, Woonona, NSW 2517, Australiaor electrochemical

Md.M. Haque et al. / Journal of Hazardous Materials 283 (2015) 164170 165

[18,19]. Fenferric hydrproper dispbiological titation in dmajority ofmicrobiolog[21]. Notaboften produple, the elep-methyl rwill produ1,3,5-trihydamines, resthe originaldevelopingmentally fri

Among t3-[[4-(phendisodium saclassied atection Agenot only thdecolourisafor the carcconditions [

In the a lot of recity (up to 2[29,30]. Asusually invrole, to yielto neutralistoluene sulThe polypyductivity asthis entrapenabling pothe mobilitanions canshown in Fithe transpoether andmechanism

lms are selective towards the original counter anion used, and thesize of the counter anion controls the microstructure and porosityof the lms. The relation between the porosity of the membraneand afnity for certain anions suggests a memory effect in terms

ctivipingr theypyrhis pa poAcidallyhesilypyterisectr

apmectoriion errole

erim

ateri

d Rey, AuC a

equirsedwnitromin a

para

voltaope

, Auacco

3 cmacturarier elea AgscopdorflmscopeFig. 1. Structure of the azo dye, Acid Red 1.

tons process also generates appreciable quantity ofoxide sludge that requires further treatment beforeosal [20]. Meanwhile, microbial degradation-basedreatments are very slow processes due to their lim-ecomposing macromolecular dyes. In addition, thethese dyes are chemically stable and resistant to

ical attack as a result of low degradation efciencyly, chemical and electrochemical oxidation treatmentsce toxic by-products during operation. As an exam-ctrochemical oxidation of the azo dyes, azobenzene,ed, methyl orange, Orange G and Sunset Yellow FCFce 1,4-benzoquinone, pyrocatechol, 4-nitrocatechol,roxynitrobenzene, p-nitrophenol, hydrazine, aromaticpectively, which are carcinogenic and more toxic thandye molecules [15,22,23]. Therefore, there is a need foralternative treatments that are effective and environ-endly in removing dyes from textile efuents.he azo dyes, Acid Red 1 (5-(acetylamino)-4-hydroxy-ylamino)phenyl]azo]-2,7-naphthalenedisulfonic acidlt), the structure of which is shown in Fig. 1, has beens a non-biodegradable dye by the Environment Pro-ncy [24]. This is a potential environmental concern,at it generates aesthetical problems associated withtion of the water body, but there are also evidencesinogenic effect of its degradation products in anaerobic2527].

of seleentrapnels fothe pol

In trole asusingchemicto syntas a pocharacand sp1 entrtwo-faliberatpolypy

2. Exp

2.1. M

Aci(Sydneat 130until rdeionipurityfor 10

2.2. Ap

AllSystemSydneycal cellplate (manufMacqucounteative tospectro(EppenRed 1microseld of conducting polymers, polypyrrole has receivedognition in the last decade due to its high conductiv-000S cm1) [28] and mechanical and thermal stabilityshown in Fig. 2 below, the synthesis of polypyrroleolves electrochemical oxidation of its monomer, pyr-d a polymeric chain with a positive backbone. In ordere this charge, a counter anion, for example, that of p-fonate (pTS), is entrapped in the backbone structure.rrolepTS lm has long been known to exhibit con-high as 160S cm1 [31]. Many studies have shown thatment process is electrochemically reversible [30,32],lypyrrole to act as an anion exchanger, depending upony of the entrapped counter anion [33]. Clearly, mobilealso be easily liberated from the polymeric lm, asg. 2. In this respect, several researchers have describedrt of small organic molecules, for example, aza crowntosylate, across polypyrrole by an anion exchanging[3436]. These reports also found that the polypyrrole

tivity measfour-point p

2.3. Electro

Each pomerised on0.2mol L1

for a duratlm was cain further csolution in

2.4. X-ray d

X-ray dicrystallinethese experty of the polypyrrole lms [37]. In other words, aftera particular anion in the polypyrrole lm, specic chan-anion are formed. This behaviour was used to explainroleanion lms selectivity towards the targeted anion.aper, we have demonstrated the application of polypyr-tential tool for treatment of azo dyes in textile efuents,Red 1 as a model dye. Initially, pyrrole was electro-oxidised in the presence of Acid Red 1 as a counter ionse an Acid Red 1-entrapped polypyrrole lm (denotedrroleAcid Red 1 lm). The lms obtained were thened by electrochemistry, scanning electron microscopyophotometry. Experimental conditions for Acid Rednt in polypyrrole lms were also optimised using aal experimental design. Finally, we have evaluated thefciency of Acid Red 1 after electrochemically reducingAcid Red 1 lms.

ental

als

d 1 and pyrrole were purchased from SigmaAldrichstralia). Pyrrole was always doubly vacuum distillednd then stored in a light protected bottle at 4 Ced for use. All aqueous solutions were prepared usingater puriedby aMilli Qwater system (Millipore). Highgen gas (BOC) was used to purge all analyte solutionst the beginning of an experiment.

tus

mmetric studies were performed using a MacLab/200rated by EChem and Chart software (eDaq Pty Ltd,stralia). A 50-mL vial was used as an electrochemi-mmodating a three-electrode system. A stainless steel1.5 cm) and a same-sized stainless steel mesh (bothed by Macquarie Engineering and Technical Services,University) were used as a working electrode and actrode, respectively. All potentials were recorded rel-|AgCl (in 3mol L1 KCl) reference electrode. UVvisibley was performed using a Bio Spectrophotometer, Australia). The morphology of the polypyrroleAcidwere analysed by a JEOL JSM-6480 scanning electronoperatedwithanacceleratingvoltageof10kV.Conduc-urements were performed using a locally constructedrobe.

polymerisation of polypyrroleAcid Red 1 lms

lypyrroleAcid Red 1 lm was galvanostatically poly-a stainless steel working electrode in the presence ofpyrroleandAcidRed1of concentration602000mgL1

ion from 20 to 480min. The polypyrroleAcid Red 1refully removed from the electrode before being usedharacterisation experiments. The remaining electrolytethe cell was also used in the entrapment analysis.

iffraction analysis

ffraction (XRD) analysis was conducted to identify thephase of the polypyrroleAcid Red 1 lm samples. Iniments, polypyrroleAcid Red 1 lms were placed on

166 Md.M. Haque et al. / Journal of Hazardous Materials 283 (2015) 164170

ction in the presence of the counter ion, pTS .

a Si waferX-ray diffraand an ano(=0.15405step size anof 420.

2.5. Fourier

Fourier tlyse polypycovering tholution andspectromet

2.6. Entrap

All expeend of eachmixture wato estimateof Acid Redbased on thtion (Cinitial)into considmass of themassof polyto Eq. (1).

q =Cnal

m

In our exdye-entrapting electroduration. Thanalysed atto Eq. (2).

%Liberation

2.7. Optimi

A two-fators in Acidincluded soand pyrrole

ults and discussion

ectrochemical characterisation of polypyrroleAcid Red 1

his work, we are exploiting the anion entrappingliberatingnism at a polypyrrole lm to develop a feasible treatmentd for dye molecules in textile efuents. We have cho-e azo dye, Acid Red 1, as a model analyte in this pilotInitially, cyclic voltammetry of 0.2mol L1 pyrrole was con-at a stainless steel electrode in the presence of 1500mgL1

18mol L1) Acid Red 1 as a supporting electrolyte. We havestainless steel electrode in this work solely because it is

nomical material for construction of bigger-size electrodeseces

ed. Hial wV astribuFig. 2. Schematic diagram for pyrrole oxidation and polypyrrole redu

(111) before being analysed on an XPert Pro MPDctometer (Philips, Netherlands). A voltage of 40kVde current of 40mA were applied. A Cu K radiationnm)wasused inacontinuous scanningmodewith0.02

d 0.5 s set time for collecting the data in a 2 scan range

transform infrared spectroscopic analysis

ransform infrared spectroscopy (FTIR) was used to ana-rrole lms. The spectra were obtained over 16 scanse 4000650 cm1 wave number range at 4 cm1 res-at 25 C using a Thermo Scientic Nicolet iS10 FTIR

er.

ment and liberation experiments

riments were carried out at room temperature. At thepolymerisation experiment, the pyrrole and Acid Red 1s analysed by UVvisible spectrophotometry at 530nmthe nal concentration of Acid Red 1. The percentage1 entrapped in a polypyrrole lm was then evaluatede difference (in mgL1) between the initial concentra-and the nal concentration (Cnal) of Acid Red 1. Taking

eration the total solution volume (V in L) and the initialpolypyrrole lm (m in g), the mass of Acid Red 1 perpyrrolelm(q inmgg1)was thenevaluatedaccording

Cinitial

V (1)

periments, Acid Red 1 was cathodically liberated fromped polypyrrole lms placed in a 0.1M KNO suppor-

3. Res

3.1. Ellms

In tmechamethosen thstudy.ducted(0.00used aan ecowhen nobtainpotent0.64was at3lyte by applying 0.80V (versus Ag|AgCl) for differente resultant solution was again spectrophotometrically530nmtodetermine the liberation efciency according

= CnalCnal Cinitial 100 (2)sation experiments

ctorial design was used to identify the signicant fac-Red 1 entrapment in polypyrrole lms. These factorslution pH, adsorption time, Acid Red 1 concentrationconcentration.

Fig. 3. Cyclic1500mgL1 Asary. Trace (a) in Fig. 3 shows the cyclic voltammogramere, an oxidation peak at 0.76V was observed as theas scanned from 1.0V to 1.0V, and a reduction peak atthe potential was scanned backward. The former peakted to the oxidation of pyrrole to form polypyrrole withvoltammetry of 0.2M pyrrole at a stainless steel electrode incid Red 1 as supporting electrolyte; scan rate 100mVs1.

Md.M. Haque et al. / Journal of Hazardous Materials 283 (2015) 164170 167

Fig. 4. ScannpolypyrroleA

a positivelywhile the lform an unshown in trpeak betwe(versus Ag|Aence of 1.0cyclic voltatrolytewithno Acid Redtrode in 0.1Based on trpositive thatial of 0.8potential, wment and libelow.

In ourpolypyrrole1500mgL

deviation o218S cm

dopedwithless mobileleads to less

3.2. Scannin1 lms

Scanningface morphtypical cauof such lmlms polymNotably, theand valleyshigh degree

3.3. FTIR of

Next, thThe spectraare shown i

TIR sp

Fig.nd 1

r resud thg oftivelye abswithm1

oupsIR spabs

stretond

t 345efore, thepresenceof thesepeaks inFig. 5(a)provides furtherce of Acid Red 1 entrapment in polypyrrole.

D analysis of polypyrroleAcid Red 1 lmsing electron micrograph of the electrolyte-facing surface of acid Red 1 lm.

charged backbone with entrapped Acid Red 1 anion,atter peak arose from the reduction of polypyrrole tocharged, Acid Red 1 liberated lm. The voltammogramace (a) is comparable to that of a very broad oxidationen 0.1 and 0.6V and a sharper reduction peak at 0.7VgCl) for the formation of polypyrrole lms in the pres-

M KNO3 [38]. In contrast, trace (b) shows a featurelessmmogram obtained in the Acid Red 1 supporting elec-out any pyrrole. Notably,Wang et al. [39] also observed1 oxidation/reduction peaks at a glassy carbon elec-mol L1 Na2SO4 solution between 1.0V and 1.0V.

ace (a), an oxidation potential of 0.88V, which is moren the oxidation peak potential, and a reduction poten-0V, which is more negative than the reduction peakere selected to be the respective potential for entrap-

beration of Acid Red 1 at polypyrrole lms in our studies

work, we have also measured the conductivity ofAcid Red 1 lms formed in 0.2M pyrrole and1 of Acid Red 1 solution to be 18S cm1 (with a standardf 1.2 S cm1; N=7). Our results are comparable to

1 obtained by Wang et al. [40] using polypyrrole lmsdifferent sulfonic acids. ClearlyAcidRed1 is bulkier andthan smaller aromatic sulfonates such as pTS, and this

Fig. 5. F

lm in1490 aSimilaassignebendinrespec[43] thof S O2600 clene grthe FTteristicstrongcorresppeak a1. Thereviden

3.4. XR

well ordered polypyrrole lms of lower conductivity.

g electron microscopic study of polypyrroleAcid Red

electron microscopy was employed to study the sur-ology of the polypyrroleAcid Red 1 lms. Fig. 4 showsliower like structures on the electrolyte-facing surfaces, similar to those previously observed at polypyrroleerised in the presence of p-toluene sulfonic acid [41].lm surface is not at, but consists of a series of peaks

with considerable surface roughness associated with aof lm porosity.

polypyrroleAcid Red 1 lms

e polypyrroleAcid Red 1 lms was analysed by FTIR.of a polypyrroleAcid Red 1 lm and Acid Red 1 alonen Fig. 5. The FTIR spectrum of a polypyrroleAcid Red 1

In this ementary tepolypyrroleterns of polDianix Red.a dye sandwperpendicubased on Br

= 2d sin where dein our wordiffractionRed 1 lm,2 diffractiopolypyrroledistinct peawhich alsoectra of (a) a polypyrroleAcid Red 1 lm and (b) Acid Red 1 alone.

5(a) shows three groups of weak bands at (1) 1660,410 cm1, (2) 1050 cm1, (3) 980 and 898 cm1.lts were observed by Zhang et al. [42] and they haveese three groups of bands to ring stretching, N Hpolypyrrole, in-plane and out-of-plane C H bending,. In addition, according to Zhang et al. [42] and Li et al.orption peaks at 898, 1256 cm1 indicate the couplingthe stretching vibration of the pyrrole ring, and that at

corresponds to the stretching vibration mode of methy-in the long alkyl chains of Acid Red 1. In comparison,

ectrum of Acid Red 1 alone in Fig. 5(b) shows charac-orption bands at 750, 1256 cm1 corresponding to theching vibration of S O group and the peak at 1750 cm1

ing to C O stretching of Acid Red 1. A broad and intense0 cm1 arose from the OH stretching band of Acid Redxperiment, XRD analysis was carried out as a comple-chnique for examining the entrapment of Acid Red 1 inlms. Previously, Ferreira et al. [44] analysed XRD pat-

ypyrrole synthesisedwith the dyes Remazol Black B andIn their work, they proposed a structure consisting ofiched between two polypyrrole chains separated by a

lardistance termed d-spacing,which canbeevaluatedaggs law [44] in Eq. (3),

(3)

notes the Cu K radiation wavelength (=0.15405nmk) and sin is derived from the lowest 2 signal in apattern. The diffraction patterns of a polypyrroleAciddepicted in Fig. 6(a), shows a sharp peak at the lowestn angle of 8.62. For comparison, the XRD patterns of aNO3 lm alone, shown in Fig. 6(b), do not reveal anyks. The result of Acid Red1 alone is displayed in Fig. 6(c),shows a 2 peak at 8.62, supporting the origin of this

168 Md.M. Haque et al. / Journal of Hazardous Materials 283 (2015) 164170

Fig. 6. XRD paAcid Red 1.

Table 1Experimental

Factor

1234

peak in Fig.from Eq. (3)between twthe chains.

3.5. Optimi

Initially,tal conditioour work, widentify theues, but als[45]. We haas X1), pyrrtion (CAcid R24 factorialadopted. Taemployed iresults andlevelwere aunder the cof Acid Redated using Eeach conditputation ofX3X4, X1X2Xare shown iaverage of tfactor, whilexpression

tE =Effec

2sp/

where sp is

sp =m

i=

and m is thwork), nF iWhen the a

X1X

2X1X

3X1X

4X2X

3X2X

4X3X

4X1X

2X3

X1X

3X4

X2X

3X4

X1X

2X3X

4Ave

rage

dye

entr

apped

/mgg

1Var

iance

DF

++

++

++

+

32.2

231

.13

1

++

++

+

6.

276.

161

+

+

+

+

+

38.9

69.

721

+

+

+

++

8.00

24.5

01

+

+

+

++

+

480.

6087

3.62

1

+

+

+

+45

0.46

2670

.34

1

+

+

+

+49

0.75

1225

.13

1+

+

+

+

46

0.94

2538

.28

1+

+

+

++

95

.87

123.

561

++

+

++

65.5

859

.08

1

+

+

+

+

+98

.44

65.9

01

+

+

+

92.5

210

7.90

1+

++

+60

0.56

2051

.20

1

++

+

+

52

0.93

3862

.33

1

++

+

+

66

0.75

2346

.13

1+

++

++

++

++

+54

0.53

3532

.20

123

21.2

222

38.3

322

62.0

623

62.8

923

71.7

724

28.1

923

01.8

522

61.3

823

50.7

422

96.5

223

42.1

224

25.0

124

01.2

823

00.4

522

91.5

722

35.1

523

61.4

924

01.9

623

12.6

2366

.82

4663

.34

4663

.34

4663

.34

4663

.34

4663

.34

4663

.34

4663

.34

4663

.34

4663

.34

4663

.34

20.

91

86.6

91

39.2

262

.43

80.2

193.

055

9.63

140

.59

38.1

37

0.3

2.6

12

3.34

17.

47.

810

.03

24.1

37

.45

17.

574.

778

.79

0.2

11

.89

1.4

10.

630.

811.

950

.61

.42

0.39

0.7

1t*

(16)

=2.

12tterns of (a) polypyrroleAcid Red 1, (b) polypyrroleNO3 and (c)

factors and their levels employed in a 24 factorial design.

Denition Label Low level () High level (+)Solution pH X1 2 12Cpyrrole/mol L1 X2 0.1 0.6CAcid Red 1/mgL1 X3 60 2000Time/min X4 20 480

6(a). Accordingly, a d-spacing of 10.3 A was estimated. This distance suggests that, Acid Red 1 is sandwichedo polymer chains, and it may act as a bridge between

sation of entrapment parameters

it is necessary to determine the optimum experimen-ns for Acid Red 1 entrapment in polypyrrole lms. Ine have used a two-level factorial design not only tosignicant factors and determine their optimal val-

o to study possible interactions among these factorsve considered factors including solution pH (denotedole concentration (Cpyrrole; X2), Acid Red 1 concentra-ed 1; X3) and polymerisation time (X4). Accordingly, adesign for four factors (16 experiments in total) wasble 1 shows the experimental factors and their levelsn the 24 factorial design. Based on earlier experimentalpractical operation conditions, a low () and a high (+)ssigned to each factor. Following electropolymerisationonditions specied for each run, the percentage weight

1 adsorbed per weight of polypyrrole lm was evalu-q. (1). Two replicate measurements were conducted ation and the average results obtained at different com-effects and interactions (X1X2, X1X3, X1X4, X2X3, X2X4,3, X1X3X4, X2X3X4, X1X2X3X4) for a 24 factorial designn Table 2. Also, in Table 2, the Effect row represents thehe high (+) and the low () values of each experimentale tE represents a signal-to-noise ratio calculated by the

tnF

a pooled standard deviation,

1(degrees of freedom variance)mi=1degrees of freedom

e number of experimental conditions (m=16 in thiss the number of experimental replications (nF =32).bsolute value of tE is larger than the tabulated t-value T

able

2M

odel

mat

rix

and

the

resu

ltsof

the

24fa

ctor

iald

esig

n.

Cod

eX

valu

es

Run

Mea

nX1

X2

X3

X4

1+

2+

+

3+

+

4+

++

5+

+

6+

+

+

7+

+

+

8+

++

+

9+

+

10+

+

+

11+

+

+

12+

++

+

13+

++

14+

+

++

15+

+

++

16+

++

++

(+

)46

63.3

421

65.2

2400

.87

4205

.526

75.1

6

()

024

98.1

422

62.4

745

7.84

1988

.18

(+

)+

()

4663

.34

4663

.34

4663

.34

4663

.34

4663

.34

(+

)

()

4663

.34

332

.94

138.

4137

47.6

768

6.98

Effe

ct29

1.46

41.

6217

.346

8.46

85.8

7t E

3.3

71.

437

.93

6.95

DF,

deg

rees

offree

dom

.

Md.M. Haque et al. / Journal of Hazardous Materials 283 (2015) 164170 169

Fig. 7. Effect oAcid Red 1 ent

(denoted bylar factor orAccordinglytistically sigalso show tprediction e

Y = 291.46

= 291.46

3.5.1. Effectpolypyrrole

The pH otors inuensolution pHstudied betA 480-minsolution pHrole lms iapproximatRed 1 thenwas reporteducting pollms underwas observpyrrole [46role lmswfavour efc

iberatentra

Effectrisatrapmentrathecreas. Noed frtent690

ce ardye ction rrrolemostypyrr[47]ial df (a) pH, (b) polymerisation time and (c) Acid Red 1 concentration onrapment in polypyrrole lms.

Fig. 8. Ldye conc

3.5.2.polyme

Ent1 concshowswith intrationincreasthe ex51 toing forinitialcentrapolypyThis ison poltrationan initt*) at the 95% condence level, the effect of a particu-interaction between factors is considered signicant., the results in Table 2 reveal that X1, X3 and X4 are sta-nicant and X2 is not signicant. However, the resultshat none of the interactions is signicant. In this way, aquation for our system can be written as:

(

41.622

)X1 +

(468.46

2

)X3 +

(85.87

2

)X4

20.81X1 + 234.23X3 + 42.94X4

of solution pH on Acid Red 1 entrapment atlmsf the Acid Red 1 solutions is one of the important fac-

cing the entrapment process. The effect of the initial dyeonAcid Red 1 entrapment efciency at polypyrrolewasween pH 2 and 12 and the results are shown in Fig. 7(a).duration was allowed to entrap Acid Red 1 at different. In general, more Acid Red 1 was entrapped at polypyr-n the pH 24 range and a maximum was observed ately pH 4. However, this entrapment efciency of Aciddecreased with higher solution pH. Previously, pyrroled to be readily oxidised forming thick, smooth and con-ypyrrole lms in acidic media and almost insulatingneutral conditions [43]. However, no lm formation

ed in alkaline media owing to an inhibited oxidation of]. In this work, we observed that thin, fragile polypyr-ere formed in neutral and alkalinemedia,which did notient entrapment of Acid Red 1.

2000mgL

3.6. Liberat

A polypyple, polypyradical catiDuring oxidanionic Acielectroneutplied and pof Acid Redparticular ftextile efuin literatureprocess.

In thismeasured0.1mol L1

a dened pprepared w2000mgL

the concenAcid Red 1increase inafterprolonlikely becaumatrix on tout from thobserved. In1 concentraed Acid Red 1 from dye entrapped polypyrrole lms at various initialtions after different time interval.

of initial Acid Red 1 concentration andion time on entrapmentent of Acid Red 1 is also affected by the initial Acid Redtion and polymerisation time of polypyrrole. Fig. 7(b)extent of Acid Red 1 entrapped at polypyrrole lmssing polymerisation time at various initial dye concen-tably, when the initial Acid Red 1 concentration wasom 60 to 2000mgL1 (0.002mol L10.078mol L1),of Acid Red 1 entrapped after 480min increased frommgg1. This is clearly attributed to an increased driv-ising from the concentration gradient with the higheroncentration. However, over the same Acid Red 1 con-ange, the relative percentage of entrappedAcid Red 1 atlms decreased from 68 to 44% (depicted in Fig. 7(c)).likely due to a limitednumber of active adsorption sitesole lms, which were saturated at a particular concen-. Fig. 7(c) also shows that equilibrium was attained atye concentration of 1500mgL1 with little change at1.

ion of Acid Red 1 from polypyrrole lms

rrole lmelectrolyte system involves the redox cou-rrole+

/polypyrrole [48], where polypyrrole+

is the

onic species and polypyrrole is the neutral species.ation, polypyrrole+

will electrostatically attract the

d Red 1 at the polypyrrole matrix so as to maintainrality. Similarly, during reduction, electrons are sup-olypyrrole becomes neutral, leading to the liberation1 from the polypyrrole lm to the solution. Indeed, thiseature distinguishes the potential treatment method ofents using polypyrrole lms frommany others reported. In this way, Acid Red 1 itself can be recovered in the

work, using UVvisible spectrophotometry, we havethe concentration of the liberated Acid Red 1 in

KNO3 after applying a reduction potential of 0.80V foreriod. This study was conducted on polypyrrole lmsith increasing Acid Red 1 concentrations from 60 to

1. The results obtained are shown in Fig. 8. In general,tration of Acid Red 1 liberated increased as the initialconcentration was increased. However, no signicantconcentration of liberated Acid Red 1 was observedging the reductionprocessbeyond180min. This ismostse Acid Red 1 entrapped deep in the multilayered lmhe stainless steel electrode would be unable to diffusee lm interfaces. Consequently, a low recovery rate wasthis experiment, in the presence of an initial Acid Red

tion of 2000mgL1, a maximum liberation rate of 21%

170 Md.M. Haque et al. / Journal of Hazardous Materials 283 (2015) 164170

was estimated following a reduction period of 240min. Improve-ment on the liberation rate requires further work that involves,for example, development of polypyrrole lms with high porosity,polypyrrolenanomaterial composite lms.

4. Conclusion

In this stproperty ofment methpyrrole atreadily entrvoltammetrtion to charesults suppsynthesisedthe entrapmcentration oentrapped Aapplying a relectropolydevelopedof dye efulms in thepublication

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Conducting polypyrrole films as a potential tool for electrochemical treatment of azo dyes in textile wastewaters1 Introduction2 Experimental2.1 Materials2.2 Apparatus2.3 Electropolymerisation of polypyrrole-Acid Red 1 films2.4 X-ray diffraction analysis2.5 Fourier transform infrared spectroscopic analysis2.6 Entrapment and liberation experiments2.7 Optimisation experiments

3 Results and discussion3.1 Electrochemical characterisation of polypyrrole-Acid Red 1 films3.2 Scanning electron microscopic study of polypyrrole-Acid Red 1 films3.3 FTIR of polypyrrole-Acid Red 1 films3.4 XRD analysis of polypyrrole-Acid Red 1 films3.5 Optimisation of entrapment parameters3.5.1 Effect of solution pH on Acid Red 1 entrapment at polypyrrole films3.5.2 Effect of initial Acid Red 1 concentration and polymerisation time on entrapment

3.6 Liberation of Acid Red 1 from polypyrrole films

4 ConclusionReferences