Modified chitosan for the collection of reactive blue 4, arsenic and mercury from aqueous media

Article abstract of DOI:10.1016/j.carbpol.2014.09.027

In the present investigation a series of modified chitosan as adsorbents were synthesized free radically at 70°C using acryloylated chitosan (AC-chitosan) as macromer, 2-acrylamido-2-methyl-1-propansulfonic acid (AMPS), 2-(diethylamino) ethylmethacrylate (DAEMA) as co-monomers and N,N'-methylenebisacrylamide (N-MBA) as a crosslinker for using as adsorbents in effluent remediation. Their structures(¹H and¹³C NMR), thermal stability (TG/DTG), surface morphology (SEM), reactive blue 4 (RB4), toxicmetals such as arsenic (AsO^2-) and mercury (Hg²⁺) uptake, swellability and reusability were evaluated.The adsorption of RB4 (701 mg/g), and the uptake of AsO^2- (551 mg/g) and Hg²⁺ (455 mg/g) showed Lang-muir isotherm behavior with pseudo-first-order kinetics. The diffusion of water, RB4, AsO^2- and Hg²⁺ into the matrix followed non-Fickian mechanism. The evaluated changes in Gibbs free energy (δG°), entropy(δS°) and enthalpy (δH°) for adsorption indicated that the process was exothermic..

Full text of DOI:10.1016/j.carbpol.2014.09.027

Carbohydrate Polymers 117 (2015) 123–132
Contents lists available at ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
Modified chitosan for the collection of reactive blue 4, arsenic and
mercury from aqueous media
V. Dhanapala, K. Subramanianb,∗
a Department of Physical Sciences, Bannari Amman Institute of Technology, Erode Dt, Sathyamangalam 638 401, Tamil Nadu, India
b Department of Biotechnology, Bannari Amman Institute of Technology, Erode Dt, Sathyamangalam 638 401, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 July 2014
Received in revised form 9 September 2014
Accepted 11 September 2014
Available online 23 September 2014
In the present investigation a series of modified chitosan as adsorbents were synthesized free radically at
70 ◦C using acryloylated chitosan (AC-chitosan) as macromer, 2-acrylamido-2-methyl-1-propansulfonic
acid (AMPS), 2-(diethylamino) ethylmethacrylate (DAEMA) as co-monomers and N,Nꢀ-methylene
bisacrylamide (N-MBA) as a crosslinker for using as adsorbents in effluent remediation. Their structures
(1H and 13C NMR), thermal stability (TG/DTG), surface morphology (SEM), reactive blue 4 (RB4), toxic
metals such as arsenic (AsO2−) and mercury (Hg2+) uptake, swellability and reusability were evaluated.
The adsorption of RB4 (701 mg/g), and the uptake of AsO2− (551 mg/g) and Hg2+ (455 mg/g) showed Lang-
muir isotherm behavior with pseudo-first-order kinetics. The diffusion of water, RB4, AsO2− and Hg2+ into
the matrix followed non-Fickian mechanism. The evaluated changes in Gibbs free energy (ꢀG◦), entropy
(ꢀS◦) and enthalpy (ꢀH◦) for adsorption indicated that the process was exothermic.
Keywords:
Dyes
Toxic metals
Remediation
NMR
Adsorption thermodynamics
© 2014 Elsevier Ltd. All rights reserved.
1. Introduction
malformation. In addition, the organic monomethylmercury causes
damage to the brain and the central nervous system and reduction
Increased industrialization and urbanization globally have
resulted in the enormous discharge of industrial effluents with col-
ored pigments such as dyes from textile industries and toxic heavy
metal ions such as arsenic (As3+) from electronic, wood and leather
in root growth of aquatic plants. The unabsorbed dyes from the
textile dying effluents are having low biochemical oxygen demand
and high chemical oxygen demand values (Rajeswari et al., 2001).
Besides, they are threatening the aquatic life, agricultural culti-
vation and underground water even at trace levels. Hence it is
necessary to remove these toxic metal ions and dyes from the
effluent to the tolerable level before being discharged into land
and water using appropriate methods. Adsorption technique is the
widely used cost effective method in the effluent treatment. Gener-
ally activated carbon, natural clays (Tahir & Rauf, 2006), modified
clays (Baskaralingam, Pulikesi, Ramamurthi, & Sivanesan, 2006),
fly ash (Dhodapkar, Rao, Pande, & Kaul, 2006) etc. are considered
to be cost effective adsorbents to bring down the concentration of
unabsorbed dyes and toxic metal ions from effluents.
In recent years hydrogels are increasingly being used as adsor-
bents to remove dyes, toxic metal ions and other pollutants from
effluent (Paulino et al., 2006; Wang & Liu, 2013) which involves
physico-chemical interaction of dyes and chelation of toxic metal
ions. Hydrogels, a class of physico-chemically crosslinked three-
dimensional network hydrophilic polymers can imbibe and retain
considerable amount of water and water soluble substances with-
out dissolving and losing their structural integrity. Due to these
properties, they are finding widespread applications (Guilherme
et al., 2005) in bioengineering, biomedicine, agriculture, food
tanning industries (Nami Kartal & Imamura, 2005), mercury (Hg2+
)
from electro chemical, metal extraction and refining industries, etc.
seriously polluting soil and water bodies. The typical concentration
range of As3+ and Hg2+ metal ions reported for industrial effluents
were 0.25 to 100 mg/L and 0.1 to 100 mg/L, respectively (Dinesh
& Pittman, 2007Anoop Krishnan & Anirudhan, 2002). Such toxic
metal ions and dyes beyond certain concentration limits in effluents
can cause potential hazards such as skin, lung and kidney cancers
and affect digestive system (Rajeswari, Namasivayam, & Kadirvelu,
2001) of mankind and harmful to other living beings if improp-
erly handled. A very high exposure to inorganic arsenic can cause
infertility, skin disturbances, declined resistance to infections, heart
disruption, and DNA and brain damage (Musico, Santos, Dalida,
& Rodrigues, 2013). Inorganic mercury poisoning is associated
with psychological changes, spontaneous abortion and congenital
∗
Corresponding author. Tel.: +91 4295 226254/+91 9894372411;
fax: +91 4295 226666.
E-mail address: drksubramanian@rediffmail.com (K. Subramanian).
http://dx.doi.org/10.1016/j.carbpol.2014.09.027
0144-8617/© 2014 Elsevier Ltd. All rights reserved.

124
V. Dhanapal, K. Subramanian / Carbohydrate Polymers 117 (2015) 123–132
industry, water purification, separation process, effluent treat-
ment etc. It has been reported (Bayramoglu, Yakup Arica, & Bektas,
2007) that the adsorption capacity of hydrogel can be improved
by introducing some natural preformed polymer such as alginates
(Dhanapal & Subramanian, 2014), chitosan, etc. during hydrogel
synthesis or by growing hydrophilic moiety on chitosan/alginates
by graft copolymerization of appropriate hydrophilic monomers.
Among the polysaccharides, chitosan, chitosan derivatives or chi-
tosan modified by methods such as radical grafting of monomers,
reinforcing with clay, blending with other polymers, IPN formation,
etc. were widely used as adsorbent materials for the removal of
dyes and toxic metal ions from effluents through adsorption or
chelation mechanism (Liu, Wang, Yu, & Meng, 2013; Wan Ngah,
Teong, & Hanafiah, 2011; Crini & Badot, 2008; Bayramoglu et al.,
2007). Chelation is the prevalent mechanism of collection of tran-
sition and post-transition metal ions by chitosan amino groups
precipitated in acetone and repeatedly washed with acetone, air
dried and stored for further use.
2.4. Synthesis of ACAD
Twenty two samples of ACADs as adsorbent materials with
different compositions designated by ACAD-0, ACAD-1, ACAD-2. . .
ACAD-20 and ACAD-21 were synthesized by radical copolymeriza-
tion by taking various amounts of AC-chitosan, AMPS and DAEMA
using N-MBA as a crosslinker and KPS as thermal initiator in a
50 mL stoppered borosilicate tube, at 70◦C after nitrogen purging.
Thus obtained ACADs were recovered by adding ice cold methanol
and washed repeatedly with methanol. Then the crosslinked gels
were cut into small pieces and dried to constant weight at 50◦C in
an air oven. Further, these ACADs were powdered and purified by
Soxhlet extraction using acetone–methanol (1:1 v/v), at 70◦C for
48 h. The purified ACADs were powdered, sieved and stored after
vacuum drying.
(Muzzarelli
& Rocchetti, 1974; Muzzarelli, 1977; Muzzarelli,
2011). Incorporation of highly hydrophilic hydrogel segments on
chitosan may improve the collection of metal ions and dyes from
aqueous medium through adsorption (Paulino et al., 2006; Wang
& Liu 2013). Hence, the present investigation involves linking of
hydrophilic segments by copolymerizing the monomers AMPS
and DAEMA in presence of a crosslinker N-MBA via the N-acryloly
group of chitosan by appropriate synthetic strategy to enhance the
adsorption or chelation capacity of modified chitosan.
2.5. Characterization techniques
The NMR spectra were recorded on Bruker Avance III 500 MHz
multi nuclei NMR spectrometer at 500 MHz for 1H and 125 MHz
for 13C (proton decoupled) in CD3COOD/D2O mixed solvents tak-
ing solvent peak as reference. TG/DTG studies were performed on
TGA Q 500 V20.10 Build 36 with a sample size of 1.5–3.5 mg under
air at a heating rate of 10 ◦C/min for the temperatures range from
ambient to 800◦C. The concentrations of dye and those of AsO2− and
Hg2+ metal ions were estimated spectrophotometrically on Perkin
Elmer Lambda 35 UV–vis absorption spectrometer at 575 nm for
dye and at 554 and 592 nm for metal ions complex with Rh B. SEM
micrographs of equilibrium swelled, lyophilized ACAD and AsO2−
adsorbed ACAD at different magnifications were recorded on ZEISS
EVO series SEM model EVO 50 microscope.
2. Experimental
2.1. Materials
AMPS, N-MBA (Aldrich) were purchased and used as received.
DAEMA (Aldrich) and acrylic acid (AA, Himedia, Mumbai) were
purified by column chromatography. Potassium persulphate (KPS,
NICE, Cochin) and chitosan were used after recrystallization in dis-
tilled water and re-precipitation, respectively. Hydrochloric acid
(HCl), potassium iodide (KI), RB4, rhodamine-B (RhB) (Himedia,
Mumbai), benzoyl chloride (BC), hydroquinone (HQ), N,Nꢀ-dimethy
formamide (DMF), dimethyl sulfoxide (DMSO), poly(vinyl alco-
hol) (PVA), mercury(II) chloride, sodium arsenite (Merck), acetone,
methanol, sodium hydroxide (NaOH), acetic acid (Rankem, New
Delhi) were of analytical grade and used as received.
2.6. Water uptake measurements
The degree of water uptake of ACADs were measured using tea
bag method (Dhanapal, Vijayakumar, & Subramanian, 2013) by
taking 0.1 g of sieved ACAD sample in 200 mL of deionized water
at 30◦C under equilibrium swelling conditions (6 h). The swelling
profiles ACADs were constructed by plotting the water uptake vs.
time at 30◦C. An average of three measurements were taken to
calculate equilibrium swelling (ES) using the following equation:
2.2. Synthesis of acryloyl chloride (ACOCl)
Ws − Wd
ACOCl was synthesized by reflexing AA (0.8 mol), BC (2.66 mol)
and HQ (2 g, polymerization inhibitor) in a 500 mL round bottom
flask at 80◦C for 2 h in nitrogen atmosphere and collecting the frac-
tion distilled at 90◦C (Siva Bharathi, Mohan Reddy, Ramachandra
Reddy, & Venkata Naidu, 2010). The liberated HCl was trapped in
0.1 N NaOH solution. The collected impure ACOCl was redistilled at
72◦C and the fraction (yield 65%) collected was used in subsequent
experiment.
ES =
(1)
Wd
where Ws and Wd are the weights of the swollen and the dry
polymer samples, respectively.
2.7. Column mode adsorption of metal ions and dye
Separate stock solutions of AsO2− and Hg2+ were prepared by
dissolving 1.733 and 1.350 g of sodium arsenite and mercury(II)
chloride, respectively in 1000 mL deionized water. A series of RB4
solution of different concentrations (1, 2, 3, 4 and 5 × 103 mg/L)
were prepared. The adsorption studies of AsO2−, Hg2+ and dye
from their respective solutions were performed on all ACAD sam-
ples at different swelling time, temperature and pH. The adsorption
experiments were done using separate identical glass columns of
2 cm diameter and 86 cm length. The columns were filled with
10 g of powdered and sieved adsorbents (ACADs) without voids.
Then, the synthetic effluent prepared using metal ion/or dye were
eluted through these columns at a constant flow rate (2 mL/min) at
30◦C. The effluent solutions were collected at different time inter-
vals and the concentration of metal ions and dye in the collected
2.3. Synthesis of AC-chitosan
A chitosan solution prepared by dissolving ten grams of puri-
fied chitosan powder in 50 mL of 1% acetic acid solution taken in
a 250 mL round bottom flask was charged with 75 mL DMSO and
the mixture was heated to 100◦C to facilitate complete dissolu-
tion of chitosan. To this 20 mL of DMF and 1.5 mL of pyridine were
added under continuous stirring over a period of 5 min and then
cooled to 0◦C. In sequence, 3 mL of ACOCl in 5 mL DMF were drop
wise added to this solution with constant stirring and left aside for
2 h at 0◦C (Jayakumar, Prabaharan, Reis, & Mano, 2005; Pourjavadi,
Jahromi, Seidi, & Salimi, 2010). The AC-chitosan thus formed was

V. Dhanapal, K. Subramanian / Carbohydrate Polymers 117 (2015) 123–132
125
fractions were estimated spectrophotometrically. An average of
2.10. Adsorption kinetics
triplicate was taken for metal ions and dye concentrations. Sim-
ilarly the adsorption capacity of virgin chitosan was tested for
these adsorbates. The simultaneous removal (Tastan, Ertugrul, &
Donmez, 2010) of dye and metal ions was also tested using a syn-
thetic composite effluent containing RB4 (5.3 × 10−4 mol), AsO2−
(1.1 × 10−3 mol) and Hg2+ (1.23 × 10−3 mol). Besides, the adsorp-
tion capacity of ACADs (showed maximum uptake behavior) were
also compared to the reported (Bayramoglu et al., 2007; Pourjavadi
et al., 2010) values on other adsorbents and virgin chitosan. The
amount of dye and metal ions uptake were calculated as per the
mass balance in the following equation:
The metal ions and RB4 adsorption kinetics will be influenced
by adsorption reactions, and the mass transfer steps that gov-
ern the transfer of metal ions/dye from the respective effluents
to the adsorption sites. Hence the kinetics of AsO2−, Hg2+ and
RB4 adsorptions were tested using pseudo-first and second order
kinetic models based on Eqs. (5) and (6), respectively.
ꢀ
ꢁ
k1
log q − q = log q −
t
(5)
(6)
(
)
e
t
e
2.303
dqt
2
= k2 q − q
(
)
c
t
dt
v
w
qe = C − C
mg/g
(2)
(
)
e
i
where qe and qt (mg/g) are amounts of AsO2−/or Hg2+/or RB4
adsorbed at equilibrium and at time ‘t’, respectively, k1 (min−1) and
k2 (g/mg/min) are the rate constants for pseudo-first and second
order kinetics, respectively.
where qe, Ci, v and w are the equilibrium amount of metal ion/dye
adsorbed onto the adsorbents (mg/g), the initial concentration of
metal ion/dye in the dye effluent (mg/L), the equilibrium concen-
tration of the metal ion/dye in solution (mg/L), the volume of the
metal ion/dye solution (L) and the weight of the adsorbent (g),
respectively.
2.11. Thermodynamics of adsorption
The practical applicability and spontaneity of the adsorption
process was evaluated by measuring the changes in thermody-
namic parameters such as ꢀG◦, ꢀH◦ and ꢀS◦, since they are the
actual indicators of adsorption process. The values of ꢀG◦, ꢀH◦
and ꢀS◦ for AsO2−, Hg2+ and RB4 adsorptions were determined
graphically using the following equation:
2.8. Estimation of adsorbed metal ions and RB4 dye in treated
effluent
To estimate the amount of AsO2− ions, 20 mL of eluate contain-
ing residual AsO2− ion was taken in 50 mL standard flask. To this
4 mL each of KI solution and con. HCl were added and then the
mixture was shaken gently, followed by the addition of 8 mL of
0.05% RhB. Then this was made up-to 50 mL with distilled water
and then left aside for 15 min and then its absorbance was measured
at 554 nm. For the estimation of Hg2+, 2 mL each of 10.8 M H2SO4
and 0.15 M KI solution were added to 20 mL of eluate containing
residual Hg2+ was taken in a 50 mL standard flask and shaken for a
min. Subsequently 2 mL of RhB (5 × 0−4 M) and 5 mL of 1% PVA were
added to the above solution and made up-to 50 mL, and left aside
for 10 min and the absorbance of complex formed was measured
at 592 nm (Ajai, Sunita,& Gupta, 2000; Yow loo et al., 2012). The
amount of metal ions, dye uptake and its molar absorption coeffi-
cient values were calculated using Beer–Lambert law equation (Ajai
et al., 2000; Yow loo et al., 2012).
ꢀS0
R
ꢀH0
RT
ln Kd
=
−
(7)
where Kd is the distribution coefficient of the adsorbate (Kd = qe/Ce),
which is a measure of adsorption capacity of ACAD, R is the univer-
sal gas constant (8.314 J/K/mol) and T is the absolute temperature
(K). The plot of ln Kd vs. 1/T yields a straight line with-ꢀHo/R and
ꢀSo/R as slope and intercept, respectively.
3. Result and discussion
3.1. Mechanism of polymerization
The mechanism for the formation of ACAD by free radical graft
copolymerization is shown in Scheme 1. The termination of grow-
ing polymer radical may occur either by coupling or disproportion-
ation route or by chain transfer mechanism involving monomer,
polymer or by primary radical (Dhanapal & Subramanian, 2014).
If termination occurs through disproportionation terminal double
bonds may be introduced in the dead polymer, unlike the termina-
tion by coupling which will produce saturated polymer.
2.9. Adsorption isotherm modeling
In any adsorption experiment the equilibrium adsorption
isotherm data can explain the interactive behavior between adsor-
bate and adsorbents, and the isotherm data will be useful for the
selection of an adsorbent for a particular adsorbate. The equilibrium
relationship between an adsorbate and adsorbent was correlated
by several expressions (Dhanapal & Subramanian, 2014) which are
used to describe isotherm modeling. In the present investigation
the isotherm data were fitted for the Langmuir and Freundlich
models as per Eqs. (3) and (4), respectively, since majority of
adsorbent–adsorbate systems obeyed these two models.
3.2. 1H and 13C NMR analysis
The representative 1H and 13C NMR spectra of chitosan and AC-
chitosan are displayed in Fig. 1. The 1H NMR spectrum of chitosan
(Fig. 1(a)) showed a signal at 4.7 ppm corresponding to the C1
H
1
qe
1
qm
1
proton of the glucosamine ring, while the signals between 3.05 and
4.20 ppm correspond to the hydrogen atoms bonded to C2, C3, C4,
C5 and C6 carbons of the glucosamine unit. The observed 1H NMR
signals (Fig. 1(b)) in the range 5.93–6.95 ppm for AC-chitosan are
attributed to the olefinic and amide protons in NH CO CH CH2
group, which indicate the presence of acryloylated amino group in
the glucosamine ring (Pourjavadi et al., 2010). These signals were
absent in the 1H NMR of chitosan (Fig. 1(a)). The signals at 11.5,
2.2 and 4.78 ppm are due to solvent peaks of residual protons in
the deuterated solvents. Similarly the resonance signal at 97.2 ppm
in the 13C NMR spectra of chitosan (Fig. 1(c)) and AC-chitosan
(Fig. 1(d)) is assigned to C1 atom of chitosan and AC-chitosan. The
=
+
(3)
(4)
qmKLCe
log qe = log KF + N log Ce
where qm is the equilibrium monolayer adsorption capacity (mg/g)
and the KL (L/mg, Langmuir constant) value is essentially equilib-
rium constant. The variation of KL with temperature can be used
to estimate the enthalpy change accompanying adsorption and the
affinity between the adsorbent and adsorbate. KF is Freundlich con-
stant, which predicts the quantity of dye adsorbed (mg/g) per g of
polymer under equilibrium. The values of N indicate the degree of
non-linearity between solution concentration and adsorption

126
V. Dhanapal, K. Subramanian / Carbohydrate Polymers 117 (2015) 123–132
Scheme 1. Mechanism for formation of ACAD.
resonance signals in the region 55–79 ppm correspond to C2 C6
atoms of chitosan and AC-chitosan. The signals at 179.2, 129.6
and 138.7 ppm are attributed to the carbons of >C O, CH2 and
CH of acryloylamido group, respectively and those at 19.2 and
177.2 ppm are due to solvent. The average degree of substitution
(DS, acrylolylation) was calculated from the integrals of the 1H
NMR signals of acryloyl and C1 H protons using the following
equation:
assigned to decomposition via the sulfonate and amide groups,
olefinic bonds, etc. (Diao, Yan, Qiu, Lu, Lu & Lin, 2010; Zhu et al.,
2012). The weight loss around 345–350◦C was more likely due to
the degradation initiated via decarboxylation of carboxylate anion,
scission of crosslinks (Dhanapal et al., 2013) etc. The weight loss
at 395 and 405◦C were due to the degradations of methacrylate
moiety and of the stabilized product formed during earlier stage
of thermal degradations (Diao et al., 2010) in ACAD-0 and ACAD-
13. The degradation of ACAD-13 around 480◦C was more likely
due to a complex process involving dehydration of gulcoseamine
rings, decomposition of acetylated and deacetylated units of chi-
tosan (Zhu et al., 2012). These thermal features of ACAD-13 in air
indicated that the modified chitosan was thermally stable enough
to withstand the adverse environmental conditions in air for con-
tinuous and prolonged applications.
Integral of protons of-CO-CH = Ch /3
(
)
2
DS =
(8)
Integral of proton C1
and the value of DS was found to be 0.282.
3.3. Thermogravimetric (TG) analysis
The representative TG thermograms of ACAD samples shown in
Fig. 2(a) indicated multistep degradations. The initial weight loss
up to 100◦C was attributed to loss of moisture and other volatile
impurities present in ACAD. The degradations of ACAD-0 (pre-
pared without AC-chitosan) and ACAD-13 around 245–250◦C was
3.4. Water, metal ions uptake and dye adsorption
The water, metal ions and dye uptake studies for all ACAD
samples revealed that the sample ACAD-13 had adsorbed higher

V. Dhanapal, K. Subramanian / Carbohydrate Polymers 117 (2015) 123–132
127
Fig. 1. Representative 1H (Chitosan, (a), AC-chitosan (b)) and 13C (chitosan (c), AC-chitosan (d)) NMR spectra.
amounts of Hg2+(455 mg/g) AsO2− (551 mg/g) and RB4 (701 mg/g)
at 30◦C compared to those observed for other samples. Hence, the
extent of metal ions, dye and water uptake profiles with respect to
time were given only for ACAD-13 and chitosan (Fig. 2(b)). These
values for virgin chitosan were 223, 257 and 323 mg/g, respectively
for identical experimental conditions. The significant difference
in the adsorption capacities of virgin and modified chitosan was
more likely due to its increased swellability and three dimensional
network structures due to hydrophilic segments and crosslink-
ing, respectively. During the simultaneous removal of toxic metal
ions and RB4, the RB4 adsorption was not affected by toxic metal
ions even though the effluent contained considerable amount of
Hg2+ and AsO2− metal ions. Here only 233 and 275 mg/g of Hg2+
and AsO2−, respectively were chelated/adsorbed and these values
were much less than those observed when they were present sep-
arately. This may be attributed to a competition for the metal ions
to get chelated and dye molecules to get adsorbed at the reactive
sites of adsorbent. Hence the chelation of AsO2− and Hg2+ were
significantly altered due to the extent of metal ion-ligand interac-
tion and competition between dye and metal ions for the active
sites of adsorbent. It is worth noting that the adsorption capacity
of ACAD-13 was significantly higher than the reported values for
other materials (Bayramoglu et al., 2007; Pourjavadi et al., 2010; Liu
et al., 2013; Wan Ngah et al., 2011;) and virgin chitosan. Crini et al.,
2008
3.5. SEM
The surface morphological features of equilibrium swelled
lyophilized ACAD-13, ACAD-21, metal ion adsorbed ACAD-13 were
probed using SEM and the typical representative SEM micrographs
are given in Fig. 3. Analysis of these micrographs implied the forma-
tion of pores and porous network structures during freeze drying of
synthesized ACAD. These were attributed to water loss by evapora-
tion and crosslinks in ACAD-13. The distribution of pores massively
in the freeze dried samples (Figs. 3(b and d)) indicated uptake of
water and AsO2− throughout the bulk of the material and presence
of void volume. The average diameter of the pores calculated by
assuming spherical shape for these pores was found to be 6 ␮m.
The uneven pores sizes (Fig. 3(b)) may be due to the heterogene-
ity in the adsorbent. These pores may be the areas, where water,
metal ions permeate and form secondary bond with dyes and metal
ions (Pourjavadi & Barzegar, 2009). The influence of crosslinker on
the surface morphological features of the adsorbent was explained
using the SEM micrograph of ACAD-21 (prepared without
crosslinker) and it is given in Fig. 3(c). In the absence of crosslinker
few pores were observed on the surface of ACAD-21, and less extent
of water and metal ions uptake for ACAD-21 were also corroborated
by the lack of pores structure and void volume. Analysis of Fig. 3(d)
implied the adsorption/chelation of AsO2− on ACAD-13 which can
be well supported by the presence of highly heterogeneous pores

128
V. Dhanapal, K. Subramanian / Carbohydrate Polymers 117 (2015) 123–132
Fig. 2. TG/DTG traces (a) of ACAD-0 and ACAD-13, (b) water, RB4, AsO2− and Hg2+ uptake profiles for ACAD-13 and virgin chitosan, effect of (c) N-MBA and pH (d) on dye
and toxic metal 00ions uptake of ACAD-13.
was identified by comparing the R2 (Table 2) values of the plot
‘log (qe − qt) vs. t’ and t/qt vs. t, respectively (Fig. 4(b–d)). This anal-
ysis implied that the dye and metal ion uptake followed pseudo
first-order kinetics. The rate constants of adsorption determined
from the slopes of profiles in Fig. 4(b–d) decreased with tem-
perature, indicating that enhanced temperature does not favor
the adsorption of RB4/metal ions which may be attributed to the
decrease in activation energy.
within the sample before adsorption (Fig. 3(b)) while the pores
were observed to be packed with metal ion after adsorption. The
porous structure appeared to be the predominant cause for the high
swellability, and dye and metal ions uptake.
3.6. Adsorption isotherms
The adsorption data for Hg2+ and AsO2− metal ions and RB4 dye
on ACAD-13 were tested for Langmuir, and Freundlich isotherms
models by curve fitting as shown in Fig. 4 The correlation coef-
ficient of (R2) Langmuir isotherm (Fig. 4(a)) for these adsorbates
indicated mono layer uptake. This was also supported by the nearly
identical adsorption values for these adsorbates measured experi-
mentally and calculated theoretically under equilibrium conditions
on ACAD-13 for Langmuir adsorption. Hence, it appears that the
Langmuir model described well the uptake of metal ion and RB4 on
ACAD-13 and the calculated isotherm parameters qm and KL from
the slope and intercept of the Langmuir plot 1/qe vs. 1/Ce (Fig. 4(a))
are given in Table 1. The KL and qm values for organic dye seems to
be more due to more interaction of organic dye with organic matrix
than the metal ions (inorganic) interaction with organic matrix.
3.8. Thermodynamics of adsorption
The effect of temperature on the adsorption process can be
understood by analyzing the change in thermodynamic parame-
ters such as ꢀG◦, ꢀH◦ and ꢀS◦ for metal ions and dye as per Eq. (9)
and their values are given in Table 3. The negative values of ꢀG◦ for
the temperatures 303, 313 and 323 K indicated that the metal ions
and RB4 adsorption on ACAD-13 were spontaneous. The average
negative ꢀH◦ value for the above temperatures indicated adsorp-
tion was exothermic which may be due to the weak interactions
such as hydrogen bonding, salt-like interaction, etc. between the
adsorbent and adsorbate. The positive ꢀSo value for the adsorption
may be attributed to the increased randomness at the solid-solution
interface (Dhanapal & Subramanian, 2014) due to the increased seg-
mental mobility of the swollen polymer and release of hydrated
water molecules from the dye and metal ions.
3.7. Adsorption kinetics
The degree of metal ions and dye uptake were tested with the
pseudo-first and second order kinetic models and the better model

V. Dhanapal, K. Subramanian / Carbohydrate Polymers 117 (2015) 123–132
129
Fig. 3. SEM micrographs of as synthesized ACAD-13 (a), freeze dried ACAD-13 (b), ACAD-21(c) and AsO2− adsorbed ACAD-13 (d).
Table 1
Langmuir and Freundlich adsorption isotherm parameters for ACAD-13/RB4, ACAD-13/AsO2− and ACAD-13/Hg2+ systems.
Langmuir isotherm parameters
Adsorbent code
Adsorbate
qm (mg/g)
KL (L/mg)
R2
ACAD-13*
RB4
676
494
421
4.127
2.869
1.843
0.986
0.987
0.981
AsO2−
Hg2+
Freundlich isotherm parameters
Adsorbent code
ACAD-13*
Adsorbate
KF (mg/g)
N
R2
RB4
4.81
7.19
8.06
0.405
1.29
1.53
0.931
0.923
0.891
AsO2−
Hg2+
The composition of ACAD-13
*
was (AMPS (0.15 M), DAEMA (0.1 M), AC-chitosan (150 mg) and N-MBA (0.012 M)) and ACAD-0 (AMPS (0.15 M), DAEMA (0.1 M), AC-chitosan (0 mg) and N-MBA (0.012 M))
and ACAD-21 (AMPS (0.15 M), DAEMA (0.1 M), AC-chitosan (150 mg) and N-MBA (0 M)). KPS (0.009 M) were taken in all the experiments for a polymerization volume of
40 mL.
3.9. Diffusion mechanism
intercept of the plot log (Mt/M ) vs. log (t), respectively, at differ-
∞
ent temperatures. In case of adsorption/or release from swellable
matrices, if n = 0.45–0.5 then transport is nearly Fickian, whereas
for 0.5 < n < 1 the diffusion is non-Fickian. In the present investiga-
tion the values of n were found to be in the range of 0.66–0.74 for
dye, metal ions solutions and pure water. These values indicated
that the diffusion of dye/metal ions and water from the swollen
polymer followed non-Fickian (Dhanapal & Subramanian, 2014)
mechanism.
The dye/metal ions and water uptake kinetics of ACAD-13 can
be more quantitatively understood by fitting the initial swelling
data (up-to 60%) of ACAD-13 in the following power law (Dhanapal
& Subramanian, 2014) equation:
Mt
= ktn
(9)
M
∞
where Mt is the amount of the water/or dye/or metal ion adsorbed
by swollen polymer at time t, M is the amount of the water/or
3.10. Desorption and reusability of adsorbent
∞
dye/or metal ion adsorbed after infinite time, k is the swelling
constant related to the structure of network and n is the diffusion
exponent. The values of n and k were calculated from the slope and
In order to find the predominant mechanism for metal ions
uptake, the pure water was eluted through metal ions adsorbed

130
V. Dhanapal, K. Subramanian / Carbohydrate Polymers 117 (2015) 123–132
2.8
(b)
RB 4
(a)
RB 4
AsO2-
Hg2+
303 K (R2= 0.986)
313 K (R2= 0.987)
323 K (R2= 0.996)
2.6
2.4
2.2
2.0
6
4
2
0.003
0.002
0.001
10
20
30
40
50
60
Contact time (min)
1/Ce (L/mg)
AsO2-
(c)
(d)
Hg2+
2.6
2.4
2.2
2.0
1.8
1.6
1.4
303 K (R2= 0.988)
313 K (R2= 0.985)
323 K (R2= 0.986)
2.6
303 K (R2= 0.992)
313 K (R2= 0.983)
323 K (R2= 0.991)
2.4
2.2
2.0
15
30
45
60
10
20
30
40
50
60
Contact time (min)
Contact time (min)
Fig. 4. Langmuir adsorption isotherms (a) and pseudo-first-order adsorption kinetic plots at different temperatures for ACAD-13/RB4 (b), ACAD-13/AsO2− (c) and ACAD-
13/Hg2+ (d) system.
Table 2
Pseudo-first and second order kinetics parameters for adsorption of ACAD-13/RB4, ACAD-13/AsO2− and ACAD-13/Hg2+ systems at different temperatures.
Adsorbent code
ACAD-13
Adsorbate
RB4
Kinetic model
T (K)
parameters(qe = mg/g, k1 = min−1 and k2 = g/mg/min)
R2
303
313
323
303
313
323
303
313
323
303
313
323
303
313
323
303
313
323
qe = 689.2, k1 = 4.2
qe = 304.4, k1 = 1.7
qe = 282.5, k1 = 1.3
qe = 525.4, k1 = 3.4
qe = 312.6, k1 = 2.6
qe = 178.2, k1 = 1.6
qe = 385.5, k1 = 3.2
qe = 311.3, k1 = 2.6
qe = 141.3, k1 = 1.6
qe = 77. 3, k2 = 5.23
qe = 42.2, k2 = 4.65
qe = 31.7, k2 = 4.50
qe = 51.5, k2 = 4.67
qe = 21.4, k2 = 3.25
qe = 18.9, k2 = 2.45
qe = 45.8, k2 = 3.45
qe = 20.4, k2 = 2.34
qe = 18.9, k2 = 2.10
0.998
0.999
0.998
0.988
0.985
0.986
0.992
0.983
0.991
0.977
0.974
0.987
0.852
0.911
0.883
0.889
0.747
0.778
Pseudo-first order
AsO2−
Hg2+
RB4
Pseudo-second order
AsO2−
Hg2+
16 mg/g of AsO2− and Hg2+, respectively. The differences were more
likely attributed to the more metal ions uptake in three dimen-
sional network ACAD-13 and the reduction in the concentration
of free amino group available for metal chelation compared to
ACAD-13 and metal ions adsorbed/chelated virgin chitosan packed
columns under identical conditions over a known and constant
period of time. The amount of metal ions leached from ACAD-13
and virgin chitosan were found to be 189, 31 and 156 (mg/g), and

V. Dhanapal, K. Subramanian / Carbohydrate Polymers 117 (2015) 123–132
131
Table 3
Thermodynamic parameters for adsorption of ACAD-13/RB4, ACAD-13/AsO2− and ACAD-13/Hg2+ systems at different temperatures.
Adsorbent code
Adsorbate
AsO2−
T (K)
ꢀG◦ (kJ/mol)
ꢀH◦(kJ/mol)
ꢀS◦ (J/mol/K)
R2
−47.43
303
313
323
303
313
323
303
313
323
−21.1734
−6.53991
−4.59294
−41.3379
−20.6205
−4.66825
−21.4211
−9.72515
−3.76919
15.45
0.987
−66.16
−48.44
Hg2+
RB4
21.99
15.12
0.988
0.997
virgin chitosan. Further, the reliability of adsorbent for the repeated
usage in effluent treatment was tested by evaluating its reusabil-
ity by several adsorption-desorption cycles using 0.01 M HCl as
desorption agent. About 98% of metal ions and dye were recovered
for more than five adsorption–desorption cycles. Hence ACAD-13
can be used repeatedly without losing its adsorption capacities for
prolonged application.
conditions. The surface morphology by SEM on ACAD confirmed
the presence of pores and network structures. The equilibrium
dye adsorption at different dye/metal ion concentrations implied
predominantly Langmuir isotherm model with pseudo-first order
kinetics. The diffusion of water, dye and toxic metal ions into the
matrix followed non-Fickian mechanism. The values of ꢀG◦, ꢀH◦
and ꢀS◦ for RB4, AsO2− and Hg2+ adsorption/chelation indicated
that the adsorption was spontaneous and exothermic for the cho-
sen ACAD-13. These features demonstrated that ACAD-13 can serve
as a potential adsorbent for the effective removal of reactive dyes
and toxic metal ions from the aqueous media.
3.11. Effect of AC-chitosan and N-MBA concentration in the feed
and pH on uptake
Analysis of dye, metal ions and water uptake characteristics of
all ACAD samples revealed that the ACAD-13 had adsorbed max-
imum dye and metal ions under ambient conditions but ACAD-0
had adsorbed pure water to the extent of 1189 g/g. However the
uptake of metal ions/dye and thermal stability of ACAD-0 were
significantly reduced due to low crosslink density and the lack of
coordination sites.
The influence of crosslinker concentration on water uptake pro-
file is shown Fig. 2(c). The uptake behavior of ACAD was directly and
inversely proportional to crosslinker concentrations for low and
high concentrations of crosslinker, respectively. For the crosslinker
concentration 0.012 M, water, dye, AsO2− and Hg2+ ions uptake
were enhanced to the maximum values of 1055 g/g and 701, 551and
455 mg/g, respectively which were reduced to 532 g/g and 412, 307,
524 mg/g, respectively without crosslinker.
The pH of the effluent affects the adsorption behavior of an
adsorbent and its effect was investigated over a pH range of 2–12
and the results are displayed in Fig. 2(d). The functional groups on
the surface of adsorbent may be altered by the variation in pH of
dye effluent. It was obvious that the adsorption/chelation capacity
increased with increasing pH of dye/metal ions in effluents, and
significant enhancement on adsorption was observed when the pH
value reached 6.5 and further increase of pH beyond 8 had reduced
the dye/metal ion uptake. In acidic pH most of the SO3− groups on
the surface of the adsorbent exist as SO3H, which lead to a com-
petition between hydrogen ion and RB4/or AsO2−/or Hg2+ to seek
the active site on the adsorbent. In basic pH (>9) the electrostatic
repulsive force between adsorbent and adsorbate may minimize
the dye/metal ions uptake.
Acknowledgments
The authors thank the management of Bannari Amman Institute
of Technology, Sathyamangalam for encouraging research work by
extending the required facilities and IIT Madras (SAIF) for providing
NMR characterization facilities.
References
Ajai, P., Sunita, G., & Gupta, V. K. (2000). A new system for the spectrophotometric
determination of arsenic in environmental and biological samples. Analytica
Chimica Acta, 408, 111–115.
Anoop Krishnan, K., & Anirudhan, T. S. (2002). Removal of mercury(II) from aqueous
solutions and chlor-alkali industry effluent by steam activated and sulphurised
activated carbons prepared from bagasse pith: Kinetics and equilibrium studies.
Journal of Hazardous Materials, 92, 161–183.
Baskaralingam, P., Pulikesi, M., Ramamurthi, V., & Sivanesan, S. (2006). Equilib-
rium studies for the adsorption of acid dye onto modified hectorite. Journal of
Hazardous Materials, 136, 989–992.
Bayramoglu, G., Yakup Arica, M., & Bektas, S. (2007). Removal of Cd(II), Hg(II) and
Pb(II) Ions from aqueous solution using p(HEMA/Chitosan) membranes. Journal
of Applied Polymer Science, 106, 169–177.
Crini, G., & Badot, P. M. (2008). Application of chitosan, a natural aminopolysaccha-
ride, for dye removal from aqueous solutions by adsorption processes using
batch studies: A review of recent literature. Progress in Polymer Science, 33,
399–447.
Dhanapal, V., & Subramanian, K. (2014). Recycling of textile dye using double net-
work polymer from sodium alginate and superabsorbent polymer. Carbohydrate
Polymers, 108, 65–74.
Dhanapal, V., Vijayakumar, V., & Subramanian, K. (2013). Synthesis and evaluation
of trimethylolpropane triacrylate crosslinked superabsorbent polymers for con-
serving water and fertilizers. Journal of Applied Polymer Science, 129, 1350–1361.
Dhodapkar, R., Rao, N. N., Pande, S. P., & Kaul, S. N. (2006). Removal of basic dyes
from aqueous medium using a novel polymer: Jalshakti. Bioresource Technology,
97, 877–885.
4. Conclusions
Diao, H., Yan, F., Qiu, L., Lu, J., Lu, X., Lin, B., et al. (2010). High performance
cross-linked poly(2-acrylamido-2-methylpropanesulfonic acid)-based proton
exchange membranes for fuel cells. Macromolecules, 43, 6398–6405.
Dinesh, M., & Pittman, C. U., Jr. (2007). Arsenic removal from water/wastewater using
adsorbents—A critical review. Journal of Hazardous Materials, 142, 1–53.
Guilherme, M. R., Reis, A. V., Takahashi, S. H., Rubira, A. F., Feitosa, J. P. A., & Muniz, E.
C. (2005). Synthesis of a novel superabsorbent hydrogel by copolymerization of
acrylamide and cashew gum modified with glycidyl methacrylate. Carbohydrate
Polymers, 61, 464–471.
Jayakumar, R., Prabaharan, M., Reis, R. L., & Mano, J. F. (2005). Graft copolymerized
chitosan-present status and applications. Carbohydrate Polymers, 62, 142–158.
Liu, B., Wang, D., Yu, G., & Meng, X. (2013). Adsorption of heavy metal lons, dyes
and proteins by chitosan composites and derivatives—A review. Journal of Ocean
University of China, 12, 500–508.
Chitosan was modified by graft copolymerization using
hydrophilic water soluble acrylic monomers to enhance its adsorp-
tion/chelation capacity for the collection of RB4, toxic metal
ions AsO2− and Hg2+ from aqueous media. The observed adsorp-
tion/chelation capacity values of the modified chitosan were
significantly higher (701, 551 and 455 mg/g, respectively) than
those reported for chitosan and chitosan based other adsorbent
materials. The degree of acrylolylation determined by 1H NMR in
AC-chitosan was found to be 0.282. TG studies of ACAD revealed
that they are thermally stable under ambient environmental

132
V. Dhanapal, K. Subramanian / Carbohydrate Polymers 117 (2015) 123–132
Musico, Y. L. F., Santos, C. M., Dalida, M. L. P., & Rodrigues, D. F. (2013). Improved
removal of lead(II) from water using a polymer-based graphene oxide nanocom-
posite. Journal of Materials Chemistry A, 1, 3789–3796.
Siva Bharathi, Y., Mohan Reddy, M., Ramachandra Reddy, G., & Venkata Naidu, S.
(2010). Synthesis, characterization and compatibility studies of homopolymers
of poly(carboxy phenyl acrylate) and poly(carboxy methyl phenyl acrylate).
Malaysian Polymer Journal, 5, 95–108.
Muzzarelli, R. A. A. (1977). Chitin. Oxford: Pergamon Press.
Muzzarelli, R. A. A. (2011). Potential of chitin/chitosan-bearing materials for uranium
recovery: An interdisciplinary review. Carbohydrate Polymers, 84, 54–63.
Muzzarelli, R. A. A., & Rocchetti, R. (1974). The use of chitosan columns for the
removal of mercury from waters. Journal of Chromatography, 96, 115–121.
Nami Kartal, S., & Imamura, Y. (2005). Removal of copper, chromium, and arsenic
from CCA-treated wood onto chitin and chitosan. Bioresource Technology, 96,
389–392.
Paulino, A. T., Guilherme, M. R., Reis, A. V., Campese, G. M., Muniz, E. C., & Nozaki, J.
(2006). Removal of methylene blue dye from an aqueous media using superab-
sorbent hydrogel supported on modified polysaccharide. Journal of Colloid and
Interface Science, 301, 55–62.
Tahir, S. S., & Rauf, N. (2006). Removal of a cationic dye from aque-
ous solutions by adsorption onto bentonite clay. Chemosphere, 63, 1842–
1848.
Tastan, B. E., Ertugrul, S., & Donmez, G. (2010). Effective bioremoval of reactive dye
and heavy metals by Aspergillus versicolor. Bioresource Technology, 101, 870–
876.
Wan Ngah, W. S., Teong, L. C., & Hanafiah, M. A. K. M. (2011). Adsorption of dyes and
heavy metal ions by chitosan composites: A review. Carbohydrate Polymers, 83,
1446–1456.
Wang, J. J.,
& Liu, F. (2013). Enhanced adsorption of heavy metal ions onto
simultaneous interpenetrating polymer network hydrogels synthesized by UV
irradiation. Polymer Bulletin, 70, 1415–1430.
Pourjavadi, A., Jahromi, P. E., Seidi, F.,
& Salimi, H. (2010). Synthesis and
swelling behavior of acrylatedstarch-g-poly(acrylic acid) and acrylated starch-
g-poly(acrylamide) hydrogels. Carbohydrate Polymers, 79, 933–940.
Pourjavadi, A., & Barzegar, S. (2009). Synthesis and evaluation of pH and thermosen-
sitive pectin-based superabsorbent hydrogel for oral drug delivery systems.
Starch-Starke, 61, 161–172.
Rajeswari, S., Namasivayam, C., & Kadirvelu, K. (2001). Orange peel as an adsor-
bent in the removal of acide violet 17(acid dye) from aqueous solution. Waste
Management, 21, 105–110.
Yow loo, A. Y., Lay, Y. P., Kutty, M. G., Timpe, O., Behrens, M., & Abd-hamid, S. B. (2012).
Spectrophotometric determination of mercury with iodide and rhodamine B.
Sains Malaysiana, 41, 213–218.
Zhu, H. Y., Fu, Y. Q., Jiang, R., Yao, J., Xiao, L., & Zeng, G. M. (2012). Novel magnetic
chitosan/poly(vinyl alcohol) hydrogel beads: Preparation, characterization and
application for adsorption of dye from aqueous solution. Bioresource Technology,
105, 24–30.