ORIGINAL PAPER

Synthesis, characterization and application of cellulose/polyaniline nanocomposite for the treatment of simulatedtextile effluent

V. Janaki • K. Vijayaraghavan •

Byung-Taek Oh • A. K. Ramasamy •

Seralathan Kamala-Kannan

Received: 11 January 2013 / Accepted: 11 March 2013 / Published online: 23 March 2013

� Springer Science+Business Media Dordrecht 2013

Abstract The aim of the study was to analyze the

potential application of cellulose/polyaniline (Ce/Pn)

nanocomposite for the treatment of synthetic reactive

dye bath effluent. The Ce/Pn composite was synthe-

sized by chemical oxidative polymerization of aniline.

A central composite experimental design, a most

popular design of response surface methodology, was

applied to optimize the level of variables, namely,

cellulose and polyaniline, to get the best response on

dye removal. Biological transmission electron micros-

copy studies reveal that the cellulose particles were

uniformly distributed on the nanocomposite. The

results of the batch experiment studies indicate that

Ce/Pn nanocomposite removed 95.9, 91.9, 92.7, and

95.7 % of RBBR, RO, RV, and RBK, respectively,

and it decolorized 82 % of dye bath effluent. However,

the presence of the salts reduced the adsorption rate of

the dyes. The Langmuir model and pseudo first-order

rate expression exhibited satisfactory fit to adsorption

data of single component.

Keywords Cellulose � Nanocomposite �Polyaniline � Reactive dyes � Response surface

methodology

Introduction

Dyes usually have a synthetic origin and are exten-

sively used in several industries, such as textile, food

processing, leather tanning, and as additives in petro-

leum products. The synthetic dyes are classified into

two broad categories, such as anionic (direct, acid, and

reactive) and cationic (basic), based on chromophore

structure (Netpradit et al. 2004). The anionic reactive

dyes are typically characterized by azo-based chro-

mophores containing N=N double bonds. Due to their

high solubility, colorfastness, and ease of application

anionic reactive dyes are extensively used in textile

and dyeing industry, which constitutes 20–30 % of the

total dye market (Tanyildizi 2011). However, hydro-

xyl ions present in the dye bath can compete with the

cellulose substrate, resulting in a higher percentage of

hydrolyzed dyes that can no longer react with the

cellulose fiber. Thus, 10–50 % of the initial dye load

will be present in the wastewater, giving rise to a

highly colored effluent (Vijayaraghavan et al. 2009;

Janaki et al. 2012a). It has been established that some

V. Janaki � A. K. Ramasamy (&)

Department of Chemistry, Periyar University,

Salem 636011, Tamil Nadu, India

e-mail: drakramasamy@yahoo.in

K. Vijayaraghavan

Department of Chemical Engineering, Indian Institute

of Technology Madras, Chennai 600036, India

B.-T. Oh � S. Kamala-Kannan (&)

Division of Biotechnology, Advanced Institute

of Environment and Bioscience, College

of Environmental and Bioresource Sciences, Chonbuk

National University, Iksan 570752, South Korea

e-mail: kannan@jbnu.ac.kr

123

Cellulose (2013) 20:1153–1166

DOI 10.1007/s10570-013-9910-x

of these reactive dyes cause aesthetic problems and

may reduce some photosynthetic process in aquatic

ecosystem (Kunz et al. 2002). Thus, removal of

reactive dyes from wastewater is important for eco-

logical conservation. Among the numerous existing

techniques, adsorption is considered as one of the most

fascinating methods due to simple and ease of

operation (Nandi et al. 2009). Recently, several studies

have been focused on application of nanomaterials and

nanocomposites in adsorption processes (Chen 2011;

Janaki et al. 2012b; Konicki et al. 2012). Compared

with the micron-sized adsorbents, the nano-sized

adsorbents exhibit high adsorption rate because of

high specific surface area with little internal diffusion

resistance (Chang et al. 2006).

Natural biopolymeric materials are gaining more

attention in wastewater treatment because of its low

cost, biodegradability, and biocompatability. Among

the various natural biopolymeric materials, cellulose is

considered as an abundant and environment-friendly

biopoymeric material. Cellulose is a linear homopoly-

mer of b1 ? 4 linked b-D-glucopyranose units (Glc)

aggregated to form highly ordered structures (Klemm

et al. 1998). The hydroxyl groups present in each Glc

unit interact with one another forming intra and

intermolecular hydrogen bonds (Oh et al. 2005), thus

leading to low adsorption capacities. Hydrogen bonds in

cellulose can be modified by chemical transformations

and used for the removal of several pollutants from

aqueous solution (Anirudhan et al. 2009; Zhu et al.

2011). So far, two main chemical approaches can be

used to modify the cellulose. One is the direct

modification of cellulose, where useful functional

groups attached to cellulose through variety of chem-

istries (O’Connell et al. 2008). The other is cellulose

based composites, where functional groups of active

polymer are introduced into the weak cellulose polymer

backbone during polymerization process. Remarkably,

several cellulose-based composite has been synthesized

and are proven to have high adsorption capacity for dyes

(Zhu et al. 2011; Zhou et al. 2012).

Polyaniline, a semi-flexible, low cost, and environ-

mentally stable conducting polymer, has wide appli-

cation in material sciences (Janaki et al. 2012c).

Polyaniline carries several functional groups (amine,

imine, and secondary amino groups) and is expected to

have interactions with negatively charged anions

because of its innate cationic nature (Zheng et al.

2012). However, the use of polyaniline in adsorption

process could be limited by the massive aggregation of

molecules. This drawback of using polyaniline may be

overcome by preparing polyaniline composites such as

polyaniline/chitosan, polyaniline/carbon nanotube,

and polyaniline/bacterial extra cellular polysaccha-

rides. Polyaniline/chitosan composite removed

95.4 % of Congo Red, 98.2 % of Coomassie Brilliant

Blue, and 99.8 % of Remazol Brilliant Blue R from

aqueous solution (Janaki et al. 2012c). Zeng et al.

(2012) reported that polyaniline/carbon nanotube

composite effectively removed Malachite Green from

wastewater. Polyaniline/bacterial extracellular poly-

saccharides composites significantly decolourized the

complex Remazol dye effluent (Janaki et al. 2012a).

In the last decade, there has been considerable

interest in the synthesis of polymeric nanocomposites

that are composed of different biological and chemical

polymers. This becomes an important area in com-

posite research because of its application in different

scientific fields including environmental sciences.

Polyaniline/sawdust nanocomposite removed 96.8 %

of Acid Violet 49 from aqueous solution at pH 3–4

(Baseri et al. 2012). Starch/polyaniline nanocomposite

significantly removed reactive dyes and decolorized

reactive dye bath effluent (Janaki et al. 2012b). Thus, it

is noteworthy to make nanocomposite of two polymers

cellulose and polyaniline. However, to our knowledge

cellulose/polyaniline (Ce/Pn) nanocomposite has

never been used for the removal of dyes and decol-

orization of dye bath effluent. Hence, the objectives of

the present study were to (a) synthesis and characterize

Ce/Pn nanocomposite under optimized condition for

maximum adsorption, (b) evaluate the potential of

Ce/Pn nanocomposite for the removal of reactive dyes

and decolorization of reactive dye effluent, (c) assess

the experimental variables and salts affecting optimal

removal of dyes, and (d) explore adsorption isotherms

and kinetic models to identify the possible mechanism

of dye removal.

Materials and methods

Materials

Commercial cellulose was purchased from Sigma-

Aldrich (St. Louis, MO, USA) and was used as received.

Aniline monomer was distilled under reduced pressure

before polymerization. Ammonium peroxydisulfate

1154 Cellulose (2013) 20:1153–1166

123

(initiator), Remazol Brilliant Blue R (RBBR)

(C22H16N2Na2O11S3, molecular weight: 626.54, kmax:

595 nm), Reactive Orange 16 (RO) (C20H17N3

Na2O11S3, molecular weight: 617.54, kmax: 490 nm),

Reactive Black 5 (RBK) (C26H21N5Na4O19S6, molec-

ular weight 991.82, kmax: 597 nm), and Remazol

Brilliant Violet 5R (RV) (C20H16N3Na3O15S4, molec-

ular weight 735.58, kmax: 577 nm), as well as all the

auxiliary chemicals were also procured from Sigma-

Aldrich.

Synthesis of Ce/Pn nanocomposite

Ce/Pn composite was prepared by in situ chemical

oxidative polymerization method (Janaki et al.

2012b). In brief, 0.5 g of cellulose was dissolved in

20 mL of nanopure purified water (conductiv-

ity = 18 lX/m, TOC \ 3 ppb) (Barnstead, Waltham,

MA, USA), to which aniline (0.2 M) dissolved in 1 M

HCl was introduced and stirred for 15 min to attain a

homogenous solution. Ammonium peroxydisulfate

(4.4 g) solution in 1 M HCl was added drop wise into

the above mixture with constant stirring at 2 �C to

maximize the yield of polyaniline. The solution

mixture was stirred for additional 5 h for completion

of polymerization and kept in a refrigerator overnight.

The molar ratio of oxidant to monomer was main-

tained at 1:2. After centrifugation, the resulting

greenish-black precipitate was extensively washed

with nanopure water followed by methanol until the

supernatant became colorless. The resulting compos-

ite was freeze-dried under vacuum at -80� C for 24 h.

The mechanism of polymerization between polyani-

line and cellulose is schemed in Fig. 1.

Response surface methodology

Central composite design (CCD), one of the widely

accepted response surface method for experimental

design, was employed to Ce/Pn nanocomposite syn-

thesis. The main objective of CCD is to optimize the

level of variables to get the best response. This method

is well suited to fitting a quadratic surface, and works

well for process optimization with minimum number

of experiments, and also to analyze the interaction

between parameters (Branchu et al. 1999). In our study

the amount of polyaniline (X1) and the cellulose (X2)

were considered as dependent variables, and the

percentage of removal was taken as the responses.

The total number of experiments can be determined by

the following equation

N ¼ 2k þ 2K þ x0 ð1Þ

where N is the number of variables and x0 is the

number of repetition of experiments at the central

value. The variables are determined from the low and

higher coded values as -1 and ?1, respectively. The

experimental range and the coded levels are presented

in Table 1. For statistical analysis the independent

variables were coded according to the following

equation:

Xi ¼ Zi � Z�i� �

=dZi ð2Þ

where Zi is the uncoded value of the ith independent

variable, Zi* represents the ith independent value at

centre point, and dZi is the step change of the variable.

The response in this study was the percentage of

removal of dyes. The response developed from the

experiment was correlated by quadratic equation as

follows:

Y ¼ b0 þXn

i¼1

biXi þXn

i¼1

biiX2i þ

Xn�1

i¼1

Xn

j¼iþ1

bijXiXj

ð3Þ

where Y is the predicted responses, b0 is the constant

coefficient, bi is the linear coefficient, bij is the

interaction coefficient, bii is the quadriatic coefficient,

and Xi and Xj represent the coded values. The

applicability of the polynomial model can be deter-

mined by the coefficient determination of R2. The

Design Expert 8.0, trial version, was used for the

experimental design, statistical, and regression anal-

ysis of data.

Characterization of Ce/Pn nanocomposite

The morphology and surface characters of Ce/Pn

nanocomposite were obtained from biological trans-

mission electron microscopy (Bio-TEM) (H-7650,

HITACHI, Japan). The Fourier transform infrared

(FTIR) spectra of the Ce/Pn nanocomposite were

obtained on a Perkin–Elmer FTIR spectrophotometer

(CA, USA) in the diffuse reflectance mode at a

resolution of 4 cm-1 in KBr pellets. The influence of

atmospheric water and CO2 was always subtracted.

X-ray diffractograms (XRD) of the Ce/Pn composite

before and after adsorption of dyes were obtained

Cellulose (2013) 20:1153–1166 1155

123

using a Cu Ka incident beam (k = 0.1546 nm),

monochromated by a nickel filtering wave at a tube

voltage of 40 kV and tube current of 30 mA. The

scanning was done in the region of 2h from 4 to 80� at

0.04� min-1 with a time constant of 2 s. Thermo

gravimetric analysis (TGA) of cellulose, polyaniline,

and Ce/Pn nanocomposite was performed by using DT

Q600 V20.9. Build 20, Universal V4.5A TA instru-

ments over the temperature range of 25–800 �C at a

heating rate of 10 �C/min under nitrogen atmosphere.

Determinaton of pHpzc of Ce/Pn nanocomposite

The pHpzc is an important parameter that plays a

crucial role in the adsorption processes as it shows the

characteristics of the adsorbent. In our study, the

determination of pHpzc was carried out by potentio-

metric mass titration (Bourikas et al. 2003). The

aqueous suspension containing different masses of

Ce/Pn nanocomposite in the range of 0.1–0.3 g L-1

was brought into contact with a 0.03 M KNO3

solution. The suspensions were equilibrated for 24 h

to reach an equilibrium pH value. Surface sites of the

nanocomposite were deprotonated with small volume

Fig. 1 Schematic

representation of cellulose

and polyaniline

polymerization

Table 1 Full factorial CCD matrix and observed dye

adsorption

Run Aniline (M) Cellulose (g) Dye removal (%)

1 0.20 0.22 65.0

2 0.06 0.50 42.0

3 0.10 0.70 49.0

4 0.20 0.50 74.0

5 0.20 0.50 73.8

6 0.20 0.50 74.1

7 0.10 0.30 62.0

8 0.20 0.78 42.0

9 0.30 0.30 44.0

10 0.20 0.50 74.1

11 0.34 0.50 44.0

12 0.20 0.50 74.0

13 0.30 0.70 41.0

1156 Cellulose (2013) 20:1153–1166

123

of 1 M KOH solution, and the samples were titrated

with 0.1 M HNO3 solution. The pH was recorded after

each addition of acidic solution as a function of its

volume. A similar titrating procedure was followed for

the blank solution without Ce/Pn nanocomposite. The

potentionmetric curves were obtained by plotting

the graph between the equilibrium pH and the volume

of acid solution added to the suspension. The pHpzc

was determined from the common intersection point

of the potentiometric curve of the blank with the

corresponding curves of suspension containing differ-

ent amount of Ce/Pn nanocomposite.

Preparation of synthetic Remazol dye effluent

Synthetic dye effluent was prepared by dissolving

equal amount (0.5 mM) of four reactive dyes RBBR,

RO, RB, and RV in distilled water to produce the stock

solution of 2 mM concentration. The stock solution

was diluted to desired proportions to produce solutions

of different initial dye stuff concentrations.

Batch experiments

Batch adsorption experiments were carried out typi-

cally by adding 0.2 g of Ce/Pn nanocomposite with

100 mL of dye solution or effluent. If necessary the pH

of the solution was initially adjusted and controlled

using 0.1 M NaOH or HCl. The flasks were stirred at a

constant speed of 150 rpm at 25 ± 2 �C in a rotary

shaker. After the attainment of equilibrium, the

supernatant was separated by centrifugation at

9,000 rpm for 10 min, and the total dye concentration

was analyzed using a UV–vis spectrophotometer (UV-

1800, Shimadzu, Japan) at their corresponding wave-

lengths after appropriate dilution.

Desorption studies

Desorption experiment was carried out according to

Janaki et al. (2012c) with minor modification. Briefly,

freeze-dried, dye laden Ce/Pn nanocomposite (0.2 g)

was mixed with 100 mL of 0.1 M NaOH, and the

mixture was agitated on a rotary shaker (150 rpm) at

25 ± 2 �C for 12 h. After desorption, the supernatant

was centrifuged, with the remaining procedure being

the same as for the sorption experiments.

Data evaluation

The dye uptake in the single system was calculated

from the difference between the dye concentrations in

the supernatant using the following mass balance

equation:

Q ¼ VðC0 � CfÞM

ð4Þ

where Q is the dye uptake (mg g-1), C0 and Cf are the

initial and final dye concentrations in the solution

(mol L-1), respectively, V is the volume of the

solution (L), and M is the mass of Ce/Pn nanocom-

posite (g).

Single dye adsorption isotherms were modeled

using the Langmuir and Freundlich models. The

Langmuir isotherm is based on the assumption that

adsorption takes place at specific homogenous sites

within the adsorbent. It is then assumed that all the

sites are energetically equivalent, and once these sites

are occupied, no further adsorption can take place at

that site. The Langmuir isotherm also represents that

adsorption proceeds through monolayer coverage, and

there is no interaction between adsorbed molecules.

The nonlinear form of Langmuir equation is defined as

Q ¼ Qmaxb Cf

1þ b Cf

ð5Þ

where Q is the equilibrium dye uptake (mmol g-1),

Qmax is the maximum adsorption capacity of the

adsorbent (mmol g-1), and b the Langmuir equilib-

rium constant (L mmol-1).

The Freundlich equation is an empirical equation

used to describe the heterogenous system. It assumes

that adsorption energy exponentially decreases on

completion of the sorptional centers of an adsorbent.

The nonlinear form of Freundlich is expressed as

Q ¼ KFðCfÞ1=nF ð6Þ

where KF is the Freundlich constant (mmol g-1)

(L mmol-1)1/n and nF the Freundlich model exponent.

Kinetics of reactive dyes onto Ce/Pn was exploited

using the pseudo first-order and pseudo second-order

equations which can be represented as

Pseudo first-order model:

Qt ¼ Qe 1� exp �k1tð Þð Þ ð7Þ

Cellulose (2013) 20:1153–1166 1157

123

Pseudo second-order model:

Qt¼Q2

ek2t

1þ Qek2tð8Þ

where Qe is the amount of dye sorbed at equilibrium

(mmol g-1), Qt is the amount of dye sorbed at time

t (mmol g-1), k1 is the rate constant of pseudo first-

order model (min-1), and k2 is the pseudo second-

order rate constant (g mmol-1 min-1).

To represent the dye removal in the effluent, two

parameters viz. percentage removal and extent of

decolorization were used (Vijayaraghavan et al. 2009).

The percentage removal can be represented as follows:

Removal ð%Þ ¼ ðAbsi � AbsfÞðAbsiÞ

� 100 ð9Þ

The extent of decolorization, QD (L g-1), can be

calculated from:

QD ¼ VðAbsi � AbsfÞ=M ð10Þ

where Absi and Absf are the initial and final absor-

bance of the dye effluent, respectively, V is the effluent

volume (L), and M is the mass of the Ce/Pn

nanocomposite used (g).

A modified form of the Freundlich model was used

to describe the isotherm data of dye effluent, which is a

plot of the final absorbance versus the extent of

decolorization, which can be represented as follows:

QD ¼ KFðAbsfÞ1=nF ð11Þ

The concentration term in the conventional model

(Freundlich 1907) was replaced by an absorbance

term, which is indicative of the color.

All the model parameters were evaluated by nonlin-

ear regression using the Sigma plot (version 8.0, SPSS,

USA) software. Duplicate experiments were considered

for all the operating variables studied, and only the

average values were considered. Blank experiments

were carried out concurrently to ensure that the sorption

of dye on the walls of flasks was negligible.

Results and discussion

Characterization of Ce/Pn nanocomposite

TEM micrograph of the cellulose, polyaniline and

Ce/Pn nanocomposite is shown in Fig. 2a–c. The

celluose were uniformly distributed on the polyaniline

particles and formed Ce/Pn nanocomposite. The shape

of the composite was irregular and mostly present in

aggregates. The surface of the composite was rough or

porous, providing good possibility for adsorption of

dyes and other pollutants. The FTIR spectrum of the

Ce/Pn nanocomposite is presented in Fig. 3a. The

absorption peak at 3,408, 3,398 and 3,204 cm-1 could

be assigned to the O–H and N–H stretching vibrations

of polymeric compounds. The characteristic peaks at

1,570 and 1,482 cm-1 is associated with C–C stretch-

ing vibrations of benzenoid and quinoid moieties in

polyaniline (Saikia et al. 2010). The band at

2,900 cm-1 could be ascribed to N–H bending, and

a pick at 1,304 cm-1 correspond to the C–H stretching

vibration with aromatic conjugation. The bands at

1,244 and 1,108 cm-1 are associated with the car-

bonyl bands (C–O ester) of cellulose (Zheng et al.

2012). In addition, the spectrum showed the presence

of aromatic (800 and 706 cm-1) and alkane (616 and

508 cm-1) peaks of cellulose and polyaniline, respec-

tively. The results indicate that cellulose is activated

by superfluous acids and combined successfully with

polyaniline. The intra and intermolecular hydrogen

bonds were broken and hydroxyl groups become

freely accessible for interaction with dye molecules.

XRD is the analytical technique widely employed to

analyze the nature of materials. Thus, to investigate

the nature of Ce/Pn nanocomposite, XRD analysis was

carried out, and the results presented in Fig. 3b. The

peaks at 2h = 20.4 and 25.3� were assigned to

emeraldine polyaniline, corresponding to the period-

icity parallel and perpendicular to polymer chains

(Pouget et al. 1991; Janaki et al. 2012c). The

characteristic peaks at 2h = 14.7, 16.4, and 22.6�corresponds to the crystal structure of the cellulose

(Montano-Leyva et al. 2011). The results indicate that

Ce/Pn nanocomposite had crystal structure and which

is expected to have high adsorption properties. Ther-

mal gravimetric curve of cellulose, polyaniline and

Ce/Pn nanocomposite is shown in Fig. 3c. A minor

weight loss of Ce/Pn nanocomposite was observed at

100 �C and it could be due to moisture present in

nanocomposite. First stage of weight loss was

observed at 200–478 �C indicating the degradation

of cellulose in Ce/Pn nanocomposite. Simultaneously,

the onset temperature of Ce/Pn nanocomposite

(62 �C) was slightly increased as compared to pure

cellulose (57 �C) and it represent the inclusion of

polyaniline in nanocomposite. However, a major

1158 Cellulose (2013) 20:1153–1166

123

weight loss of cellulose and Ce/Pn nanocomposite was

observed at 333 and 278 �C, and it was attributed by

the absence of inter molecular hydrogen bonds of

cellulose. The results suggest the dissociation of

cellulose macromolecules into smaller ones. The final

stage of weight loss in Ce/Pn nanocomposite was

observed at 478–700 �C and it represent the thermal-

oxidative degradation of the main polyaniline chains.

Similar phenomenon was reported by Mo et al. (2009)

in the preparation of cellulose-polyaniline conductive

composites.

Response surface methodology

According to the central composite design, a total of 13

experiments including 5 replicates were designed, and

statistical significance of the model was evaluated

(Table 1). Five replicate runs at the centre point were

used to determine the experimental error in the synthesis

of Ce/Pn nanocomposite. To analyze the dye removal

capacity (%) of Ce/Pn composite, the second degree

polynomial equation was suggested by the software, and

the coded values are obtained according to Eq. 3.

Y ¼ 74:02� 2:89X1 � 6:06X2 þ 2:5X1X2 � 15:32X21

� 10:07X22

ð12Þ

where Y is the predicted responses and Xi is the coded

variables. The positive sign in front of the term

denotes the synergistic effect, whereas the negative

sign represents the antagonistic effect. The ANNOVA

results for response surface quadratic model are

presented in Table 2. Values of probability F less

than 0.05 represents the significant terms. From

Table 2, it reveals that X2, X12, and X2

2 were significant

model terms, whereas X1 and X1X2 were insignificant

model terms. The insignificant model terms were

excluded from the study to improve the integrity of the

model. The fitness of the model was examined by the

determination factor R2. The determination coefficient

R2 and the adjusted R-squared were calculated as

0.9468 and 0.9089, respectively. Both the values

showed a good correlation with each other, and the

higher values represents the good fitting of quadratic

equation over the whole system on the given exper-

imental condition. Coefficient of variance (CV%)

represents that the experiments were conducted more

precise and reliable, and the values (CV% = 7.63)

showed satisfactory results. Adequate precision mea-

sures the signal-to-noise ratio, and a value greater than

4 is desirable. The ratio 11.5 indicates an adequate

signal and this model can be used to navigate the

designed space. The 3D plots were drawn to analyze

the effect of variables viz aniline and cellulose on

removal of dyes, and the results are depicted in

Fig. 4a. The dye removal capacity of the Ce/Pn

nanocomposite was higher when the aniline and the

cellulose concentrations were 0.2 M and 0.5 g,

respectively. The amount of aniline is higher than

0.2 M resulting in the aggregation of the particles,

whereas the increased amount of cellulose may reduce

the potential of the adsorbent due to weak adsorbing

functional groups on its backbone. Thus, 0.2 M aniline

and 0.5 g of cellulose were used for the synthesis of

nanocomposite to get uniform distribution of the

particles and to increase the potential of the adsorbent.

Fig. 2 Transmission electron micrograph of cellulose (a), polyaniline (b) and Ce/Pn nanocomposite (c). The cellulose was uniformly

distributed on polyaniline particles without any aggregation

Cellulose (2013) 20:1153–1166 1159

123

Effect of pH on removal of dyes

pH is considered as one of the important parameter

controlling the adsorption processes. The adsorption

system usually depends on the degree of speciation of

adsorbate and the dissociation of functional group of

the adsorbent, which varies at different pH (Janaki

et al. 2012d). Thus, to investigate the optimal pH and

to reveal the adsorption mechanism, adsorption of

reactive dyes (RBBR, RO, RV and RBK) was carried

out at different pH ranging from 2 to 10. As can be

seen from the Fig. 4b, the maximum removal of

RBBR (94 %), RO (89 %), RV (84 %), and RBK

(98 %) were observed at pH 3. However, the removal

percentage drastically decreases with increase in pH

values. The higher removal percentage in acidic pH 3

were due to the electrostatic attraction between the

reactive dye anions (Dye-SO3-) and the positively

charged nitrogen (NH?.) moiety present in the

constituent polymer (Janaki et al. 2012b). In addition,

the polyaniline molecule exists in the doped state only

in acidic solution, which may further increase the

adsorption rate of dyes (Mahanta et al. 2009). As the

pH increases, the electrostatic interaction between the

dye molecule and the polymeric constituent was

hindered due to the dedoping of polyaniline molecules

and a marked decrease in negative charge of the dye

molecules. Moreover, the competition between the

OH- ions and reactive dye anions was also responsible

for lower adsorption capacity at neutral and alkaline

pH values. This was supported by the results obtained

in pHpzc studies, where the pHpzc value of the Ce/Pn

composite was calculated as 3.4 (Fig. 5a). It has been

well established that the surface charge of the

adsorbent was positive when the pH of the solution

is higher than pHpzc, whereas it is negative at pH lower

than pHpzc (Zheng et al. 2012). Thus, the adsorptions

of negatively charged reactive dye anions were highly

favored under acidic pH at 3. However, limited

adsorption was observed in neutral and alkaline pH

and it could be due to the van der Waal’s forces and

hydrogen bonding. Similar phenomenon was observed

in the treatment of various dyes using Pn/Ch compos-

ite (Janaki et al. 2012c).

Single solute adsorption

Adsorption isotherm and modeling

The adsorption isotherm reveals information about the

distribution of dye molecules between the liquid and

the solid phase when the adsorption process reaches an

equilibrium state (Buvaneswari and Kannan 2011).

Thus, the adsorption of four reactive dyes (RBBR,

RBK, RV, and RO) onto Ce/Pn nanocomposite was

performed in the preselected dye concentration

Wavenumber cm -11000200030004000

% T

rans

mit

tanc

e

20

40

60

80

100

120

Cellulose Polyaniline Ce/Pn

1570

1482 1304

800610

10581108

2900

3408

15741134

804506

2 Theta (degree)20 40 60 80

Inte

nsit

y

5000

10000

15000

Ce/Pn Polyaniline Cellulose

22.6

14.7

25.320.4

Temperature (°C)200 400 600 800

Wei

ght

(%)

0

20

40

60

80

100

Cellulose Polyaniline Ce/Pn

(a)

(b)

(c)

Fig. 3 a FTIR spectra of cellulose, polyaniline and Ce/Pn

nanocomposite, b XRD spectra of cellulose, polyaniline and

Ce/Pn nanocomposite, c thermal gravimetric curve of cellulose,

polyaniline, and Ce/Pn nanocomposite

1160 Cellulose (2013) 20:1153–1166

123

(0–1 mM) at 25 �C, and the equilibrium characteris-

tics of adsorption were evaluated using Langmuir and

Freundlich models.

The theoretical parameters (Qmax, b, KF, and nF)

derived from their corresponding isotherms along with

regression coefficients are summarized in Table 3. On

comparing the R2 values (Table 3), the Langmuir

model describes the experimental data compared with

the Freundlich model. Also, Langmuir model helps to

estimate the maximum adsorption capacity of the

adsorbent, which could not be determined experimen-

tally. The Qmax value observed for RBBR, RBK, RV,

Table 2 Analysis of variance for the response surface quadratic model

Source Sum of squares Degrees of freedom Mean square F value P value Prob [ F

Model 2,481.05 5 496.20 24.94 0.0003

X1-Aniline 67.11 1 67.11 1.37 0.1088

X2-Cellulose 294.35 1 294.35 14.79 0.0063

X1X2 25.00 1 25.00 1.25 0.2992

X12 1,633.24 1 1,633.24 82.10 \0.0001

X22 705.77 1 705.77 35.48 0.0006

Residual 139.24 7 19.89 – –

Corrected total 2,620.28 12 – – –

0.30

0.40

0.50

0.60

0.70

0.10

0.15

0.20

0.25

0.30

40

50

60

70

80

Dye

rem

oval

A: Aniline B: Cellulose

pH2 4 6 8 10

Rem

oval

eff

icie

ncy

(%)

30

40

50

60

70

80

90

100

RBBRRORVRBK

(a)

(b)

Fig. 4 a Response surface graph of dye removal, b experimen-

tal curves corresponding to the influence of pH on dye removal.

Maximum removal of dyes was observed at pH 3

mL HNO3

pH

0

2

4

6

8

10

12

14

0.1 g0.2 g0.3 gBlank

Final dye concentration (mg L-1)

0 2 4 6 8 10 12

0.0 0.2 0.4 0.6

Upt

ake

(m m

ol g

-1)

0.0

0.2

0.4

0.6

0.8

RBBRRORVRBK

(a)

(b)

Fig. 5 a pHpzc of Ce/Pn nanocomposite, determined by

potentiometric mass titration method, b single component

isotherm of reactive dyes on Ce/Pn nanocomposite. Curves

were predicted by Langmuir model

Cellulose (2013) 20:1153–1166 1161

123

and RO were 0.671 (420.40 mg g-1), 0.612 (606.99

mg g-1), 0.547 (402.36 mg g-1), and 0.503 mmol g-1

(310.62 mg g-1), respectively. The adsorption capacity

values of all the four reactive dyes were higher to

those in previous published work. The modified cellu-

lose from flax shive exhibited a Qmax value of

204.08 mg g-1 (293 K) for Reactive Red 228 (Wang

and Li 2013). Similarly, adsorption of RBBR onto

polyaniline/chitosan composite exhibits inferior Qmax

value of 303.03 mg g-1 (Janaki et al. 2012c). Several

reasons may explain the high adsorption potential of the

Ce/Pn nanocomposite compared with other composites;

nanosized composite may have limited internal diffu-

sion resistance and high surface area when compared

with other micron-sized composites. Alternatively, the

changes in the surface morphology of the cellulose, pore

formation in cellulose (Lin et al. 2009), and distribution

of polyaniline/cellulose in the composite (without

aggregation) may increase the adsorption rate of dyes.

The constant b represents the affinity between the

adsorbent and adsorbate. Among the four dyes, higher

b value (2,925.01 L mmol-1) was observed for RV

indicating that RV has more affinity to the Ce/Pn

nanocomposite. KF represents the binding capacity

between the dye and Ce/Pn nanocomposite. Among the

four dyes, higher KF value was observed for RBBR

[1.0275 (mmol g-1) (L mol-1)1/n] indicating higher

binding capacity of RBBR to the Ce/Pn nanocomposite.

Based on the correlation coefficient values (R2),

Freundlich model exhibited the inferior correlation

compared with the Langmuir model. The applicability

of Langmuir model suggests monolayer coverage and

homogenous distribution of active sites on Ce/Pn

nanocomposite. The predicted Langmuir curves for

RBBR, RBK, RO, and RV are presented in Fig. 5b. The

results are in agreement with the previous study on the

treatment of various dyes from aqueous solution using

Pn/Ch composite (Janaki et al. 2012c).

Adsorption kinetics and modeling

To evaluate the adsorption rate and investigate the

possible mechanism governing the adsorption process,

kinetic models were applied to test the experimental

data. The kinetic experiments were carried out using

1 mM dye concentration (25 �C), and the important

parameters for both the models are listed in Table 3.

Rapid adsorption was observed during the initial stage

(10 min), and it could be because of the availability of

more active sites present in the Ce/Pn composite. On

gradual occupancy of these active sites, the reaction

rate and the adsorption reduced. The time required to

attain this state of equilibrium was termed equilibrium

time (40 min), and it reflects the maximum adsorption

capacity of the Ce/Pn composite. In the case of pseudo

first-order model the calculated adsorption capacity Qe

values were quite closer to experimental value. The

correlation coefficient value of RBBR, RBK, RO, and

RV were 0.966, 0.962, 0.964, and 0.964 respectively.

Based on the correlation coefficient (R2) and adsorp-

tion capacity Qe values, the kinetic data were

preciously found to follow pseudo first-order model.

The kinetic data modeled with the pseudo second-

order model did not provide satisfactory fit to the

experimental data. The calculated equilibrium capac-

ities (Qe) did not agree with the experimental (Qe)

values. The difference in the Qe values could be due to

a time lag, possibly as a result of formation of

boundary layer on the surface of the polymer or by the

external resistance controlling the adsorption process.

Although the correlation coefficient values (R2) were

quite closer to unity, the difference in adsorption

capacity values (Qe) were higher indicating that the

pseudo second-order is not an appropriate model for

describing the kinetics involved. The predicted pseudo

first-order curves for RBBR, RBK, RO, and RV are

shown in Fig. 6a. Similar phenomenon was observed

for the treatment of Remazol dye effluent onto Pn/EPS

composite (Janaki et al. 2012a).

Treatment of dye effluent and modeling

Ce/Pn nanocomposite highly decolorizes the dye

effluent in acidic pH 3 with removal efficiency of

88 %. Similar trend was already reported in the

previous studies, where the reactive dye adsorption

decreases with increase in pH (Vijayaraghavan et al.

2008). Although the Ce/Pn nanocomposite shows

good performance in the acidic pH 3, all dye bath

experiments were carried at pH 5. Besides it is

impractical for large-scale application in industries

under acidic pH 3.

The important parameters along with the correlation

coefficients are listed in Table 4. The high correlation

coefficient (R2 = 0.869) indicated that the adsorption

isotherm of dye effluent followed the Freundlich

model. The KF and nF values were 0.902 L g-1 and

1162 Cellulose (2013) 20:1153–1166

123

0.474, respectively. The predicted Freundlich isotherm

curve is shown in Fig. 6b, which was in accordance

with the experimental data.

Influence of various salts in adsorption of dye effluent

Dyeing wastewater discharged from textile industries

typically contains various salts. A great deal of

research suggests that salts present in wastewater

may diminish the performance of dye adsorption

process (Mahmoodi et al. 2011; Shuang et al. 2012).

Thus, it is crucial to evaluate the influence of salts on

the adsorption of reactive dyes. Figure 6b shows the

influence of various salts (NaCl, NaNO3, Na2CO3, and

Na3PO4) on the adsorption of dye effluent onto Ce/Pn

nanocomposite. It is evident from Fig. 6b that the

addition of various salts decreases the decolorization

efficiency and the order was: control [ NaCl [NaNO3 [ Na2CO3 [ Na3PO4. In addition, the KF

values (0.902, 0.707, 0.672, 0.598, and 0.528 for

control, NaCl, NaNO3, Na2CO3, and Na3PO4, respec-

tively) follow the same order which represents the

binding capacity between the dye and the polymeric

material. The co-existing salts in the effluent increase

the ionic strength which affects the performance of

adsorption by their influence on hydophobicity, size,

and solubility of reactive dye molecules (Shuang et al.

2012). Theoretically, when the electrostatic forces

between the adsorbent and the adsorbate are attractive,

an increase in ionic strength will decrease the decol-

orization efficiency. As we discussed above, higher

electrostatic attraction between the positively charged

species (NH?�) present in the polymer and the negative

charged dye anions (Dye-SO3-) was responsible for

the dye adsorption. The decolorization efficiency also

Table 3 Adsorption isotherm and kinetic model constants for Reactive dyes onto Ce/Pn composite

Isotherm/Kinetic models Parameters RBBR RBK RO RV

Langmuir Qmax (mmol g-1) 0.671 0.612 0.547 0.503

b (L mmol-1) 2,314.8 2,340.5 35.51 2,925.01

R2 0.960 0.972 0.957 0.946

Freundlich KF (mmol g-1) (L mol-1)1/n 1.028 0.803 0.655 0.624

nF 0.152 0.127 0.243 0.128

R2 0.839 0.830 0.969 0.925

Qe(exp) (mmol g-1) 0.436 0.458 0.412 0.432

Pseudo-first order Qe(cal) (mmol g-1) 0.438 0.461 0.410 0.436

K1 (min-1) 0.050 0.049 0.054 0.049

R2 0.966 0.962 0.964 0.964

Pseudo-second order Qe (mmol g-1) 0.534 0.563 0.494 0.534

K2 (g mmol-1 min-1) 0.107 0.098 0.127 0.102

R2 0.981 0.981 0.981 0.978

Time (min)

Upt

ale

(m m

ol g

-1)

0.0

0.1

0.2

0.3

0.4

0.5

RBBRRORVRBK

Final absorbance

0 20 40 60 80 100

0 2 4 6 8 10

Ext

ent

of d

ecol

oriz

atio

n (L

g-1

)

0.0

0.5

1.0

1.5

2.0

ControlNaClNaNO3

Na2CO3

Na3PO4

(a)

(b)

Fig. 6 a Pseudo first-order predicted curves of reactive dyes

onto Ce/Pn nanocomposite, b influence of various salts on

adsorption of reactive dyes onto Ce/Pn nanocomposite

Cellulose (2013) 20:1153–1166 1163

123

followed same trend (Fig. 6b), and the possibilities for

the reduced efficiency values are as follows:

1. The change in adsorption capacity value is less

obvious for NaCl compared with Na3PO4, prob-

ably because NaCl did not affect the pH of the

system, and Na3PO4 altered the pH to 7.

2. The coexisting salts may prevent the electro-

static interaction between the charges on the

Ce/Pn nanocomposite and the reactive dye

molecules, thereby mitigating the adsorption

phenomenon.

FTIR and XRD studies

Numerous studies have well established that FTIR is

a useful tool to understand the possible interaction

between the adsorbent and adsorbate. FTIR spectra

of the dye bath treated Ce/Pn composite is shown in

Fig. 7a. It is observed that after dye adsorption, the

adsorption peak assigned to O–H and N–H stretch-

ing vibrations of polymeric compounds have

shifted from 3,398 and 3,204 cm-1 to 3,450 and

3,219 cm-1. The absorption bands attributed to C–C

stretching vibrations of benzenoid and quinoid

moieties have shifted from 1,570 and 1,482 cm-1

to 1,578 and 1,494 cm-1. Also, the bands associated

with the carbonyl band shifted from 1,244 cm-1 to a

higher wave number, 1,250 cm-1. The results indi-

cate that different functional groups are involved in

the dye adsorption and that certain bonds were

formed between the Ce/Pn composite and dye

molecule which caused the changes in vibration

frequency of these chemical groups. The results are

consistent with previous studies reporting the

involvement various functional group in the adsorp-

tion of dyes onto polyaniline composites (Janaki

et al. 2012a, b, c). The XRD profile of the dye bath

treated Ce/Pn nanocomposite is presented in Fig. 7c.

The results indicate a minor change in the crystal-

line nature of the composite after the adsorption of

dyes. The changes in the nature of the adsorbent

indicate that diffusion into the pores of Ce/Pn

nanocomposite and adsorption by ionic interactions.

The results are in agreement with previous studies

reporting that the nature of the polyaniline compos-

ites changes after adsorption of reactive dyes (Janaki

et al. 2012b, c).

Desorption studies

To assess the potential of Ce/Pn nanocomposite for

several cycles and to further confirm the mechanism of

adsorption, desorption experiments were carried out

Table 4 Effect of salts on reactive dyes adsorption

Freundlich parameters Control NaCl NaNO3 Na2CO3 Na3PO4

KF (mmol g-1) (L mol-1)1/n 0.902 0.707 0.672 0.598 0.528

nF 0.474 0.400 0.412 0.452 0.491

R2 0.869 0.882 0.881 0.849 0.896

Wavenumber cm-1

400600800100012001400160018002000

% T

rans

mit

tanc

e

40

60

80

100

Control Eflluent treated

1570

1482 1304

1108

800

706616 508

260028003000320034003600380094

95

96

97

98

99

100

101

3398 3204

2900

2 Theta (degree)20 40 60 80

Inte

nsit

y

0

2000

4000

6000

8000

10000

12000

14000

Control Effluent treated

14.7

16.4

22.5 25.3

(a)

(b)

Fig. 7 a FTIR spectra of Ce/Pn nanocomposite before and after

dye bath effluent treatment, b XRD spectra of Ce/Pn nanocom-

posite before and after dye bath effluent treatment

1164 Cellulose (2013) 20:1153–1166

123

for four cycles. The results of the dye bath batch

experiment studies indicate that Ce/Pn nanocomposite

exhibit maximum adsorption of reactive dyes under

acidic pH 3, then it is logical to recover the dyes using

basic solution. Sodium hydroxide solution (0.1 N) was

used as eluant, and it showed satisfactory results with

an elution efficiency of 90 % for the reactive dye bath

effluent. Under basic conditions, the negatively

charged species (OH- ion) increase on the Ce/Pn

nanocomposite and causes the elution of dye anions

(Dye-SO3-) by electrostatic repulsion. The results

have further confirmed the ionic interaction between

the reactive dyes and Ce/Pn nanocomposite (Janaki

et al. 2012b). In the series of adsorption and desorption

cycles, a negligible reduction (4.3 %) in adsorption

capacity was observed, thus, indicating that it can be

regenerated and reused for several cycles.

Conclusion

In the present study, the application of Ce/Pn nano-

composite for the removal reactive dyes were evalu-

ated, and the conclusions are summarized below

• To the best of our knowledge, this is the first study

to report the potential application of Ce/Pn nano-

composite for the removal of reactive dyes from

aqueous solution and synthetic dye bath effluent.

• Characterization of the Ce/Pn nanocomposite

revealed that cellulose was uniformly dispersed

on the conducting polymer. The composite has the

characteristic features of both polyaniline and

cellulose.

• The Ce/Pn composite removed more than 90 % of

reactive dyes (RBBR, RO, RV, and RBK) from the

aqueous solution within 40 min. The high adsorp-

tion rate could be due to the changes in the surface

morphology of the cellulose and uniform distribu-

tion of polyaniline in the composite. The adsorption

followed Langmuir model and pseudo first-order

kinetics.

• The presence of salts in dye bath effluent had

minor effects on the adsorption process.

• The results of FTIR studies confirmed the involve-

ment of various functional groups in the adsorption

of dyes. Minor changes in the crystalline nature of

the Ce/Pn nanocomposite were observed after

adsorption of dyes.

• Easy availability, low cost, and relatively high

decolorisation efficiency represents an attractive

option for the treatment of reactive dye-based

textile effluents.

Acknowledgments The preparation of manuscript was

supported by the National Research Foundation of Korea

(NRF) grant funded by the government (MEST) (No.

2011-0020202).

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