Adsorptive removal of hazardous methylene blue by fruit shell of Cocos nucifera

Abstract

In this work, fruit shell of Cocos nucifera (FSCN) treated with H3PO4 has been tested as a low cost adsorbent for the removal of methylene blue (MB) from aqueous solution in batch and column process. The adsorption of MB onto FSCN was affected by the initial solution pH, dye concentration, temperature, column internal diameter and adsorbent dose. The adsorption equilibrium data was fitted well to the Langmuir model and the maximum adsorption capacity was found to be 20.74 mg/g at 40°C. Kinetic studies showed that the dynamical data fitted well to the pseudo-second order kinetic model. The values of thermodynamic parameters such as the Gibbs free energy (ΔG°), the enthalpy (ΔH°) and the entropy (ΔS°) indicated that the adsorption process was spontaneous and endothermic in nature. The dye was desorbed efficiently through the 1M CH3COOH solutions and 76.2 % (10 mg/L) dye was recovered.

Full text

Environmental Engineering and Management Journal February 2014, Vol.13, No. 2, 231-240
http://omicron.ch.tuiasi.ro/EEMJ/
“Gheorghe Asachi” Technical University of Iasi, Romania
ADSORPTIVE REMOVAL OF HAZARDOUS METHYLENE BLUE
BY FRUIT SHELL OF Cocos nucifera
Pijush Kanti Mondal1, Rais Ahmad1, Rajeev Kumar1,2
1Aligarh Muslim University, Department of Applied Chemistry, Environmental Research Laboratory, Aligarh 202002, UP, India
2Department of Environmental Sciences, Faculty of Meteorology, Environment and Arid Land Agriculture,
King Abdulaziz University, Jeddah, 21589, Saudi Arabia
Abstract
In this work, fruit shell of Cocos nucifera (FSCN) treated with H3PO4 has been tested as a low cost adsorbent for the removal of
methylene blue (MB) from aqueous solution in batch and column process. The adsorption of MB onto FSCN was affected by the
initial solution pH, dye concentration, temperature, column internal diameter and adsorbent dose. The adsorption equilibrium
data was fitted well to the Langmuir model and the maximum adsorption capacity was found to be 20.74 mg/g at 40ºC. Kinetic
studies showed that the dynamical data fitted well to the pseudo-second order kinetic model. The values of thermodynamic
parameters such as the Gibbs free energy (ΔGº), the enthalpy (ΔHº) and the entropy (ΔSº) indicated that the adsorption process
was spontaneous and endothermic in nature. The dye was desorbed efficiently through the 1M CH3COOH solutions and 76.2 %
(10 mg/L) dye was recovered.
Key words: adsorption, kinetics, methylene blue, thermodynamics
Received: April, 2011; Revised final: March, 2012; Accepted: March, 2012
 Author to whom all correspondence should be addressed: E-mail: olifiaraju@gmail.com; Phone: +91- 9997063442; Fax: +91-571 2400528
1. Introduction
Aquatic toxicity, phototoxicity and metal
bioavailability of synthetic dyes, represent a serious
threat to human health, living resources, and
ecological systems (Nasuha and Hameed, 2011).
Methylene blue (MB) is one of the most common
dyeing material used for wood, silk and cotton. MB
causes eye burns and may be responsible for eternal
injury to the eyes. On inhalation, it can give rise to
short period of rapid or difficult breathing, while
ingestion through the mouth produces a burning
sensation and may cause nausea, vomiting, profuse
sweating, mental confusion and methemoglobinemia
(Auerbach et al., 2010; Clifton and Leikin, 2003).
Therefore attention must be focused on treatment of
the MB containing effluents.
The adsorption method is widely used in the
scavenging of synthetic dyes from the wastewater
without producing secondary degradation products
(Diaconu et al., 2010). This technology has an
advantage of low operating cost and dye species are
transferred to a solid phase and subsequently can be
recovered by elution. Various kind of adsorbents
have been used for the scavengigng of dyes from
aqeous solutions such as activated carbons, industrial
by-products, clays, zeolites, agricultural wastes,
polymeric materials etc. (Crini, 2006; Diaconu et al.,
2010; Figueiredo and Freitas, 2012; Nasuha and
Hameed, 2011; Suteu et al., 2009; Suteu and Rusu,
2012; Wang et al., 2009, 2011). Thus, there is still
need to develop new low cost materials for the
adsorption of dyes. Agricultural byproducts are the
best materials for this purpose. Since the adsorption
of dye ions takes place mainly on the surface, pre-
treatment would be an effective approach to enhance
the dye sorption capacity of the adsorbent by
increasing the active sites which are responsible for

Ahmad et al./Environmental Engineering and Management Journal 13 (2014), 2, 231-240
232
the adsorption (Allen et al., 2005; Huang and Huang,
1996). Pre-treatments could modify the surface
characteristics/ groups either by removing or
masking the groups or by exposing more dye-binding
sites. Furthermore untreated agricultural materials
release organic compounds and causes high BOD and
COD problems (Gupta et al., 2010). Many chemicals
such as KMnO4, NaOH, H2SO4, HNO3, H3PO4,
NaHCO3, CaCl2, H2O2 etc. have been used for the
treatment of adsorbents to enhance their adsorption
capacity (Bekaroo and Mudhoo, 2011; Crini, 2006;
Gupta et al., 2010; Mittal et al., 2010; Nasuha and
Hameed, 2011; Sharma and Uma, 2010). Among all
of them, Sulfuric acid is low cost chemical and
widely used for the chemical activation of biomass.
According to Esteghlalian et al. (1997), dilute acid
pretreatment using sulfuric acid can achieve high
reaction rates and improve cellulose hydrolysis
(Esteghlalian et al., 1997).
The Cocos nucifera is a versatile tree crop and
produced worldwide around 54 billion nuts per
annum. India is one of the highest producers of
coconut in the world with an annual production of 13
billion nuts. The fruit shell of Cocos nucifera is very
hard about 35% of the fruit mass (Cazetta et al.,
2011). Therefore, fruit shell of Cocos nucifera is one
such byproduct of its fruit and considered to be a
waste. Several research have explored the adsorption
properties of Cocos nucifera based adsorbents such
as Coconut coir dust (Macedo et al., 2006), Coconut
bunch waste (Hameed et al., 2008b), C. nucifera L.
activated carbon, (Sharma et al., 2010), C. nucifera
L. shell powder (Bekaroo and Mudhoo, 2011) etc. In
this study, H3PO4 activated fruit shell of Cocos
nucifera has been used for the removal of MB from
aqueous solution in batch and column process. From
the primary study, it was observed that treated FSCN
showed approximately 31% higher adsorption as
compared to untreated FSCN. Adsorption studies
were conducted under various experimental
conditions, such as pH, contact time, initial dye
concentrations and temperature. The data from the
adsorption experiments was fitted with different
kinetics and isotherm models to elucidate the
adsorption mechanism.
2. Materials and methods
2.1. Adsorbate methylene blue
Methylene blue (MB), MF: C16H18N3SCl;
FW: 319.85 g/mol, C.I.: 52015, was supplied by the
CDH Ltd. India. The stock solution was prepared by
dissolving 1 g MB in 1 L double distilled water. The
experimental solutions were prepared by diluting the
stock MB solution with distilled water in accurate
proportions.
2.2. Preparation of adsorbent and characterization
The fruit shell of Cocos nucifera (FSCN) was
collected locally and thoroughly washed with double
distilled water to remove dirt and unwanted particle.
The shell was dried at 60 °C, crushed and sieved into
100-150 BSS mesh particle size. The powdered
material was soaked into 1.0 M H3PO4 solution for
24 h to remove the impurities and for chemical
activation of adsorbent surface. Activated shell
powder was then thoroughly washed with double
distilled water until the sample was neutralized and
dried in the oven at 60 °C for 36 h. Finally, the
resulting material was stored in vacuum desiccator
for further adsorption studies.
The surface morphology of adsorbent was
examined by the scanning electron microscopy
(SEM) using Leo 435 VP model. The FTIR spectra
of activated shell before and after MB adsorption
were recorded in the frequency range of 400–4000
cm−1 using FTIR spectrophotometer (Inter-spec 2020,
Spectro lab, UK) in KBr pellets.
2.3. Batch adsorption studies
2.3.1. Equilibrium and kinetic studies
Adsorption equilibrium studies were carried
out by taking 0.05 g of FSCN with 50 mL of MB
solution with different initial concentrations (5-20
mg/L) in 250 mL volumetric flasks at 20, 30 and 40
ºC at 200 rpm. The concentration of dye remaining in
supernatant solution was determined UV-visible
spectrophotometer (Elico, Sl-164) at 665 nm. The
adsorption capacity of FSCN for MB was calculated
by (Eq. 1):


M/VCCq eoe


(1)
where qe is the adsorption capacity (mg/g) at
equilibrium, Ce is the MB concentration (mg/L) at
equilibrium, V is the volume (L) of solution, and M is
the mass (g) of FSCN.
The kinetic studies were performed by taking
0.05 g adsorbent and 50 mL of 10 mg/L
concentration of dye solution in 250 mL flasks at 30
ºC. The mixtures were agitated at 200 rpm at the
regular time interval (15, 30, 45, 60, 90, 120, 150,
180 and 210 min). After a particular time (means a
fixed time for each flask), each solution was
centrifuged and the dye remained in the solution was
analyzed by spectrophotometry.
2.3.2. Effect of pH on MB adsorption
The influence of solution pH on the MB
adsorption was studied over the pH range from 2-9.
The pH was adjusted using dilute NaOH and HCl
solutions. In this study, 50 mL dye solution of 10
mg/L was agitated with 0.05 g adsorbent for 180 min
at 30 °C. The concentration of MB left in the
supernatant solution was analyzed by
spectrophotometry.
2.4. Column adsorption studies
Column adsorption is the real process used in
industries for wastewater purification while batch

Adsorptive removal of hazardous Methylene blue by fruit shell of Cocos nucifera
233
adsorption studies are used to finds the optimum
experimental conditions for maximum adsorption
(Mittal et al., 2010). In the present work, column
adsorption studies were performed using glass
column of 25 cm length by varying adsorbent dose
(0.5 and 1 g) and internal diameters of column (0.4
and 1 cm). MB solution of 10 mg/L at the flow rate
of 2 mL/min was then passed through each column
until the effluent concentration matches with loaded
dye concentration.
2.5. Column regeneration
Regeneration studies help to elucidate the
recycling nature of the spent adsorbent. The
regeneration study was performed in the column (25
cm in length and 1 cm in internal diameter) packed
with 1 g of FSCN. Then the column was loaded with
the dye solution of concentration 10 mg/L at the flow
rate of 2 mL/min. The column was operated until the
effluent concentration matched the concentration of
the loaded dye. After complete saturation of the
adsorbent, distilled water was passed through the
column to remove traces of unadsorbed dye.
Afterwards the efficiency of 1 M CH3COOH and
NaOH solution was tested as an eluent to desorb the
MB dye form saturated CNFS.
3. Result and discussion
3.1. Characterization of adsorbent
The SEM micrographs of FSCN before and
after treatment are shown in Fig. 1. SEM images
clearly show that the chemical treatment of CNFS
significantly alters the surface texture and enhanced
physical characteristics. It can also be seen from the
image that the surface is more irregular and porous
than the parent one, which provides a good platform
for MB adsorption
FTIR spectra of FSCN before and after
adsorption are shown in Fig. 2. The broad band
around 3412 and strong peak at 1052 cm−1 are due to
the –OH vibrations (Nasuha and Hameed, 2011),
shifted to lower wavelength i.e. 3368 and 1029 cm−1
after MB. The peak at 2899 cm−1 is assigned to C–H
asymmetrical stretching of methyl groups on the
surface. The intensity of absorption band at 1712 and
1604 cm−1 corresponds to carbonyl group stretching
vibration of ketones, aldehydes, lactones or carboxyl
groups also decrease to 1701 and 1602 reveled the
strong interaction between the adsorbent surface and
MB (Song et al., 2011). The peak observed at 1509
cm−1 can be attributed to aromatic compound group.
The peaks at 1461, 1322 and 1271 cm−1 are attributed
to the CH2 scissoring mode of vibration, CH3 and C-
OH, respectively, shifted to higher wavelength (1495,
1332, and 1276 cm−1).
This may be due to high electron density
induced by the MB adsorption. After adsorption, two
new peaks appeared at 2922 and 1171 cm−1
corresponding to aliphatic C–H and C-N groups of
MB. On the basis of above observations, it can be
concluded that–OH and C=O groups of CNFS were
mainly involved in the complexation of MB on the
adsorbent surface (Nasuha and Hammed, 2011; Song
et al., 2011).
The adsorption of MB onto FSCN surface can
be explained on the basis on of weak and strong
forces. The weak interactions occur due to the van
der Waals forces while the strong interactions occur
due to (i) hydrogen bonding interaction between the
nitrogen and sulphur groups of MB and FSCN
surface (ii) hydrophobic–hydrophobic interaction
between the hydrophobic parts of MB and FSCN,
and (iii) π-π interaction between bulk π systems on
FSCN surface and MB molecule with C=C double
bonds or benzene rings. On the basis of FTIR
analysis, a proposed mechanism for the adsorption of
the MB onto FSCN is shown in Fig. 3.
a) b)
Fig. 1. SEM image of FSCN at 1 KX magnification (a) before treatment and (b) after acidic treatment

Ahmad et al./Environmental Engineering and Management Journal 13 (2014), 2, 231-240
234
Fig. 2. FTIR spectra of FSCN (a) before MB adsorption (b) after MB adsorption
Fig. 3. Proposed mechanism for the adsorption of MB onto FSCN surface
3.2. Effect of pH on MB adsorption
The adsorption of dyes is highly sensitive to
the solution pH because chage in solution pH may
affect the surface charge and the degree of ionization
of the material and dye (Garg et al., 2007). Fig. 4
illustrates the effect of the solution pH on MB
adsorption. It seems that adsorption increases with
the increase in solution pH. This behavior can be
explained on the basis of the change in charge of
FSCN surface. At lower pH, the H+ ion concentration
in the aqueous system increases and the surface of
FSCN acquires positive charge by adsorbing H+ ions.
The positively charged surface sites on FSCN do not
favor the adsorption of cationic dye due to the
electrostatic repulsion. As the pH of the solution
increases, the negatively charged sites increase by
adsorbing OH− ions. As the FSCN surface gets
negatively charged at higher pH, a significant high
electrostatic attraction exists between the negatively
charged surface of FSCN and cationic dye molecules,
leading to maximum dye adsorption. Similar results
were also reported for the adsorption of MB onto
wheat shells (Bulut and Aydın, 2006) and rice hull
(El-Halwany, 2010). The following reactions are
expected to occur at the solid/liquid interface (Eqs. 2-
5):



mediumacidicHFSCNHFSCN   (2)


)repulsionticelectrosta(
MBHFSCNMBH)FSCN(   (3)



mediumbasicOHFSCNOHFSCN   (4)


)eractionintticelectrosta(
MBOHFSCNMBOH)FSCN(   (5)

Adsorptive removal of hazardous Methylene blue by fruit shell of Cocos nucifera
235
Fig. 4. Effect of pH on MB adsorption (Adsorbent dose-
0.05g, Conc-10mg/L, V-50mL, Contact time- 180 min,
Temp.-30ºC)
3.3. Effect of contact time and kinetics
Studies on the effects of contact time on
sorptopn efficiency were performed in order to find
the time required for the complete saturation of the
adsorbent. The experiments reveal that adsorption
increases with any increase in time and the
equilibrium is attained within 150 min (Fig. 5). It
seemed that the adsorption consisted of two phases: a
primary rapid phase and a second slow phase. The
rapid adsorption was due to MB adsorption onto
FSCN surface while slow adsorption can be
attributed to the diffusion of dye molecules into the
pore of FSCN. Furthermore, coulombic repulsion
between adsorbed MB ions and the MB ions
approaching to the adsorbent surface also increases
the equilibrium time (Camacho et al., 2010).
Fig. 5. Effect of contact time on MB adsorption (Adsorbent
dose: 0.05g; Concentration: 10mg/L; Volume: 50mL;
Temperature: 30ºC)
In order to investigate the adsorption kinetics
of MB onto FSCN, pseudo-first order (Lagergren,
1898), pseudo-second order (McKay and Ho, 1999)
and Elovich (Elovich and Larinov, 1962) models
have been used to fit experimental data obtained
from the batch experiments. The linear equations for
pseudo-first order, pseudo-second order and Elovich
models are (Eqs. 6-8):
log (qe − qt) = log qe − (k1 t/2.303) (6)
t/qt = (1/k2qe
2) + (t/ qe) (7)
qt = (1/ β) ln (α β) + (1/ β) ln t (8)
where qe and qt are the amount of MB adsorbed at
equilibrium and time t (mg/ g), respectively. k1 and k2
are the rate constants for the pseudo-first order and
pseudo-second order kinetics models. α is the initial
adsorption rate (mg/g min) and β is related to the
extent of surface coverage and the activation energy
for chemisorption (g/mg).
From the experimental data in Fig. 5, the
linear equations were determined for pseudo-first
order, pseudo-second order and Elovich models,
respectively (Eqs. 9-11):
log (qe − qt) = 1.191 − 0.0138 t (9)
t/qt = 3.613 + 0.0845 t (10)
qt = 1.191 − 0.0138 ln t (11)
The values of determination coefficient (R2)
obtained from the linear equation for pseudo-first
order, pseudo-second order and Elovich equations are
0.873, 0.996, and 0.980, respectively. The value of R2
is higher for the pseudo-second order kinetic model
than for the pseudo-first order and Elovich model,
indicating that the adsorption of MB followed the
pseudo second-order kinetics model. Furthermore,
the calculated qe value is much closer to the
experimental qe value for the pseudo-second order
model. Therefore, the adsorption of MB onto FSCN
followed the pseudo-second order kinetic model.
Similar kind of results was also reported for MB
adsorption onto rejected tea (Nasuha and Hameed,
2011) and peanut husk (Song et al., 2011).
In order to assess the transportation of the
adsorbate particles to the adsorbent surface, kinetics
experimental data has been fitted to the intra-particle
diffusion model. The linear equation for intra-particle
diffusion model (Weber and Morris, 1963) is (Eq.
12):
qt = kd t1/2 + C (12)
where qt (mg/g) is concentration of MB in solid
phase at time t (min) and kd (mg/g min1/2) is the intra-
particle diffusion rate constant. The intercept of
linear plot of qt vs. t1/2 gives an idea about the
thickness of the boundary layer on the adsorbent
surface. The larger value of C, greater is the
boundary layer effect. Fig. 6 clearly shows two zones
for MB adsorption.
The First linear portion can be attributed to
fast adsorption of dye ions on vacant active sites of
the FSCN surface while second portion may be
attributed to slow diffusion of MB ions from the
surface into the inner pore (Panday et al., 1986). The
value of intra-particle constant (kd) for first linear
portion is 0.824 mg/g min1/2 much higher that kd for
second portion (0.2005 mg/g min1/2), indicative of
fast adsorption followed by slow one due to low dye
concentration.

Ahmad et al./Environmental Engineering and Management Journal 13 (2014), 2, 231-240
236
Fig. 6. Intra-particle diffusion model for MB adsorption
(Adsorbent dose- 0.05g, Conc-10mg/L, V-50mL,
Temp.-30ºC)
3.4. Effect of concentration and isotherm studies
The effect of initial dye concentration on
adsorption was studied at 20, 30 and 40 °C, and the
results are shown in Fig. 7. The adsorption of MB
onto FSCN increases with increase in solution
concentration and temperature. The larger adsorption
capacity at higher concentration is possibly due to the
greater driving force by the concentration gradient
(∆C = C0 −Ce). Furthermore, increase in temperature
may produce the swelling effect within the internal
structure of adsorbent enabling dye ions to penetrate
further and reduce solution viscosity (Ahmad and
Kumar, 2010). The interaction between MB and
FSCN can be estimated by the adsorption isotherm.
The data obtained from isotherm studies was tested
for their applicability to the Langmuir and Freundlich
isotherm models. The linear equations for Langmuir
and Freundlich models, respectively, are (Eqs. 13,
14):
(Ce/qe) = (1/qm b) + (Ce/qm) (13)
ln qe = ln Kf + (1/n) ln Ce (14)
where qe is the amount of dye adsorbed at
equilibrium (mg/g), Ce is the equilibrium
concentration of MB in solution (mg/L), qm and b are
the Langmuir constants related to adsorption capacity
and energy of adsorption. Kf (mg/g (L/mg)1/n) and n
are Freundlich constants related to adsorption
capacity of adsorbent and adsorption intensity.
The values of Langmuir and Freundlich
constant at different temperature calculated from
their respective plots (Fig. not shown) are given in
Table 1. The Langmuir isotherm best described the
experimental data, which is apparent from the higher
values of determination coefficient (R2) than those of
Freundlich model implying the monolayer coverage
and the surface homogeneity of the adsorbent.
Similar adsorption behaviors were also reported for
MB onto modified rejected tea (Nasuha and Hameed,
2011) and phosphate rock (Rubin et al., 2010).
Fig. 7. Effect of dye concentration on MB adsorption
(Adsorbent dose- 0.05g, Conc-10mg/L, V-50mL, Contact
time- 180min)
The maximum monolayer adsorption capacity
of the FSCN was found to be 20.74mg/g. The
comparison of the maximum monolayer adsorption
capacities of the various adsorbents with FSCN is
shown in Table 2.
The affinity between the MB ions and FSCN
can be calculated by substituting the value of
Langmuir adsorption constant, b (L/mg) in the
expression for the dimensionless separation factor,
RL, which is given by (Eq. 15):
RL = 1/ (1 + b C0) (15)
where C0 is the highest initial dye concentration
(mg/L). The value of RL indicates, either the shape of
adsorption isotherm is favorable (0 < RL < 1) or
unfavorable (RL > 1) or linear (RL = 1) or irreversible
(RL = 0) (Sadasivam et al., 2010). The values of RL at
different temperature have been found to be in the
range of 0–1, indicating the favorable adsorption
process (Table 1). Furthermore multi stage favorable
parameter (bC0) (Tseng and Wu, 2009) is given by
(Eq. 16):
bC0 = (1/RL) – 1 (16)
The values of bC0, which are from 0 to
infinite, can be divided into five intervals as
described in literature (Tseng and Wu, 2009).
When bC0 is zero, the isotherm is linear; when
it varies from 1 to 10, it is termed as favorable and
when its value is above 10, the isotherm is termed as
highly favorable (Konaganti et al., 2010). The values
of bC0 are in the range of 2.16-3.01 at 20-40 ºC
(Table 1) indicating the favorable MB adsorption
onto FSCN.
Smith and Caockley (1983) determined the
specific surface area of biomass by dye adsorption
method. The specific surface area of FSCN for
maximum monolayer adsorption of MB ions is
determined by (Eq. 17):

Adsorptive removal of hazardous Methylene blue by fruit shell of Cocos nucifera
237
Table 1. Langmuir and Freundlich isotherm model constants for the MB adsorption
Temp Langmuir Model Freundlich Model
ºC qm
(mg/g)
b
(L/mg) RL bC0 R
2 KF
(mg/g(L/mg)1/n) 1/n R2
20 16.80 0.108 0.316 2.160 0.9772 10.69 0.521 0.8802
30 19.64 0.110 0.325 2.110 0.9735 12.43 0.466 0.8944
40 20.74 0.150 0.249 3.016 0.9752 13.5 1 0.529 0.8866
Table 2. Comparison of maximum monolayer adsorption capacity of various adsorbents for MB removal
Adsorbent Adsorption capacity (mg g−1) Reference
Rejected tea 156 Nasuha et al. (2010)
Pumpkin seed hull 141.92 Hameed and El-Khaiary (2008)
Banana stalk waste 243.90 Hameed et al. (2008a)
jackfruit peel 285.71 Hameed (2009a)
papaya seeds 555.557 Hameed (2009b)
Coconut coir dust 14.36 Macedo et al. (2006)
Coconut bunch waste 70.92 Hameed et al. (2008b)
Banana peel 20.8 Ofomaja (2007)
Cocos nucifera L. activated carbon 20.62 Sharma et al. (2010)
Wheat shells 16.56 Bulut and Aydin (2006)
Rice husk activated carbon 14.34 Sharma and Uma (2010)
Neem leaf powder 3.67 Bhattacharyya and Sharma (2005)
Cocos nucifera 20.74 This study
S = (qm N A/ m) (17)
where qm is the maximum monolayer adsorption
capacity (mg/g), N is Avogadro's Number, A is the
area occupied by single dye ion (Aº2) and m the
molecular mass of MB.
The molecular mass of MB is 319.85 g/mol
and the cross sectional area is 108 Aº2 (Van den Hul
and Lyklema, 1968, Weng and Pan, 2006, 2007). The
specific surface area of FSCN was calculated as
42.26 m2/g based on Eq. (17).
3.4.1. Thermodynamics of MB adsorption
Thermodynamic studies have been performed
to find the nature of adsorption process.
Thermodynamic parameters such as standard free
energy change (ΔGº), enthalpy change (ΔHº) and
entropy change (ΔSº) are calculated using the
following equations (Eqs. 18-20):
Kc = Cae/Ce (18)
ΔGº = −RT ln Kc (19)
ln Kc = (ΔSº/R) − (ΔHº/RT) (20)
where, Kc is the equilibrium constant and Cae and Ce
are the equilibrium concentration of dye (mg/g) on
the adsorbent and solution, respectively. T is the
temperature in Kelvin and R is gas constant. The
negative ΔG° values 0.987, 1.669 and 2.714 kJ/ mol
for 293, 303 and 313 K, respectively, increases with
temperature, indicating the feasibility and
spontaneity of the MB adsorption onto FSCN.
The positive value of ΔH° (24.261 kJ/mol)
confirming the endothermic nature of the adsorption
process, while the positive value of ΔS° (85.978
J/mol K) revealed the increase in randomness at the
solid/solution interface during the adsorption of MB
onto FSCN (Smaranda et al., 2009).
The energy released by different forces during
adsorption process is unequal (Oepen et al., 1991; Qi
et al., 2007) and the energy associated with the
physical and chemical forces are van der Waals
forces (4–10 kJ/mol), hydrophobic bond forces (5
kJ/mol), hydrogen bond forces (2–40 kJ/mol),
coordination exchange (40 kJ/mol), dipole bond
forces (2–29 kJ/mol), and chemical bond forces (>60
kJ/mol). The enthalpy change for MB adsorption by
FSCN is 24.261 kJ/mol, suggesting that the physical
forces were involved for adsorption of MB.
3.5. Column adsorption studies
Fixed bed adsorption experiments were
performed by varying adsorbent dose (0.5 and 1g)
and column internal diameter (0.4 and 1cm) at the
flow rate of 2 mL/min. The breakthrough curves for
the MB adsorption onto FSCN are shown in Fig. 8.
The area between the ordinate and the breakthrough
curve gives the amount of adsorbate removed during
the test time.
Fig. 8 shows that breakthrough capacity
increase with increase in the adsorbent dose and with
reducing internal diameter of the column (Table 3).
This may be due to increase in number of theoretical
plates which provide more active sites and relatively
higher time for interaction between adsorbent and
dyes ions.

Ahmad et al./Environmental Engineering and Management Journal 13 (2014), 2, 231-240
238
Fig. 8. Column adsorption studies plot for MB adsorption
Table 3. Breakthrough and exhaustive capacity of FSCN
for the removal of MB
Adsorbent
dose (mg)
Column
internal
diameter
(cm)
Breakthrough
capacity
(mg/g)
Exhaustive
capacity
(mg/g)
0.5 1.0 13 34
1.0 1.0 20 38.5
1.0 0.4 24.5 40
3.6. Desorption studies
In order to recover the adsorbed dye and
regenerate the adsorbent, 1 M NaOH and 1 M
CH3COOH solutions were used as eluent. In case of
1 M NaOH, no desorption of MB form saturated
adsorbent was observed while 76.2% dye was
recovered by 1M CH3COOH solution (Fig. 8, Inset).
The incomplete desorption of MB form saturated
FSCN can be explained on the basis of forces
(physical and chemical) involved in adsorption
process.
Those dye molecules bonded with the
physical forces get desorbed easily by 1M
CH3COOH while chemically bonded molecules were
not desorbed completely because of the strong
complexation between MB and FSCN surface.
3.7. Treatment of real wastewater
The adsorption efficiency of FSCN has been
tested for real wastewater containing MB collected
from Jalan Colour Company, New Delhi, India. The
initial dye concentration of this sample and their
correlated COD value was 50 mg/L and 375 mg
O2/L. After the adsorption treatment, the dye and
COD reduced to 20 mg/L and 150 mg O2/L. These
results indicate that FSCN is a very promising
adsorbent for the treatment of effluents containing
MB.
4. Conclusions
This study demonstrated that FSCN is an
excellent adsorbent for removal of MB from aqueous
solution and wastewater. The adsorption capacities of
FSCN for MB increased with increasing solution pH
and temperature. The kinetic data shows that the
pseudo second order kinetic model was fitted better
than the pseudo-first-order and Elovich kinetic
models. The equilibrium data is in good agreement
with the Langmuir isotherm, thus confirming the
monolayer adsorption process. The thermodynamic
study shows that the dye adsorption is spontaneous
and endothermic. Column adsorption studies exhibit
that with the increase of adsorbent doses and the
decrease the internal diameter of column resulted that
the breakthrough time was delayed.
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