Synthesis, characterization and application of … characterization and...of these reactive dyes...
Transcript of Synthesis, characterization and application of … characterization and...of these reactive dyes...
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: [email protected]
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: [email protected]
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
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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
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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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