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All content in this area was uploaded by Faiz Bukhari Mohd Suah on Aug 26, 2019
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Malaysian Journal of Analytical Sciences, Vol 23 No 4 (2019): 625 - 636
DOI: https://doi.org/10.17576/mjas-2019-2304-08
625
MALAYSIAN JOURNAL OF ANALYTICAL SCIENCES
Published by The Malaysian Analytical Sciences Society
ADSORPTION OF MALACHITE GREEN ONTO MODIFIED CHITOSAN–
SULFURIC ACID BEADS: A PRELIMINARY STUDY
(Penjerapan Malakit Hijau ke atas Manik Kitosan-Asid Sulfurik Terubahsuai: Satu Kajian Awal)
Suhaila Mohd Yusoff1, Wan Saime Wan Ngah1, Faizatul Shimal Mehamod2, Faiz Bukhari Mohd Suah1*
1School of Chemical Sciences,
Universiti Sains Malaysia, 11800 Minden, Pulau Pinang, Malaysia
2School of Fundamental Science,
Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia
*Corresponding author: fsuah@usm.my
Received: 2 July 2018; Accepted: 9 July 2019
Abstract
The removal of malachite green (MG) from aqueous solutions by cross–linked chitosan–sulfuric acid (H2SO4) beads was
investigated. Solubility and swelling tests were performed in order to determine the stability of the chitosan–H2SO4 beads in
acidic solution, basic solution and distilled water. Different parameters affecting the adsorption capacity such as initial pH (pH 2-
12), agitation period (10-60 minutes) and initial concentrations of MG (5-30 mg/L) were studied. In addition, the adsorption
capacities of MG onto chitosan–H2SO4 beads were determined too. In order to describe adsorption isotherm of chitosan–H2SO4
beads, the sorption data were analyzed using linear form of Langmuir and Freundlich equation. It was found that Langmuir
isotherm showed higher conformity than Freundlich isotherm (30.96>2.23). A kinetic study indicated that pseudo–second–order
kinetic equation correlates well with the experimental data. FT–IR analysis established there was an interaction between MG and
chitosan–H2SO4 beads. It can be concluded that chitosan–H2SO4 beads were favorable absorbers and could be used as alternate
adsorbents for removal of MG in water treatment process.
Keywords: adsorption, chitosan–H2SO4 beads, isotherm, kinetics, malachite green
Abstrak
Penyingkiran malakit hijau (MG) daripada larutan akueus oleh manik kitosan-asid sulfurik (H2SO4) berangkai-silang telah dikaji.
Ujian keterlarutan dan pengembangan dijalankan untuk menentukan kestabilan manik kitosan-H2SO4 di dalam larutan asid,
larutan alkali dan air suling. Parameter berbeza yang mempengaruhi muatan penjerapan seperti pH awal (pH 2-12), tempoh
putaran (10-60 minit) dan kepekatan awal MG (5-30 mg/L) dikaji. Sebagai tambahan, muatan penjerapan bagi MG terhadap
kitosan-H2SO4 turut ditentukan. Bagi menentukan isoterma penjerapan manik kitosan-H2SO4, data penjerapan telah dianalisis
menggunakan persamaan linear Langmuir dan Freundlich. Didapati isoterma Langmuir lebih sesuai berbanding isoterma
Freundlich (30.96>2.23). Kajian kinetik menunjukkan persamaan tertib-pseudo-kedua berhubung baik dengan data kajian.
Analisis FT-IR mengesahkan terdapat interaksi diantara MG dan manik kitosan-H2SO4. Dapat disimpulkan bahawa kitosan-
H2SO4 adalah penjerap pilihan dan boleh digunakan sebagai penjerap alternatif bagi menyingkirkan MG dalam proses perawatan
air.
Kata kunci: penjerapan, manik kitosan-H2SO4, isoterma, kinetik, malakit hijau
Introduction
Discharges of various types of waste product and the rapid growth of different chemical industries have become the
main causes of environmental contamination and degradation to the country. Dyes, which are widely used in
ISSN
1394 - 2506
Suhaila et al: ADSORPTION OF MALACHITE GREEN ONTO MODIFIED CHITOSAN–SULFURIC ACID
BEADS: A PRELIMINARY STUDY
626
different industries, can inhibit light penetration into water, retard photosynthetic activity, prevent the growth of
biota and have a tendency to chelate metal ions. Dyes are classified according to their chemical properties and
solubility. Dyes can be categorized as an acid dye, basic dye, direct dye, mordant dye, disperse dye, reactive dye
and vat dye [1]. Basic dyes are the most commonly used in many industries and have become one of the main
sources of severe water pollution. Malachite green (MG) is an example of a basic dye used to dye wool, silk, cotton
and leather in textile industries and also as a strong anti-fungal, anti-bacterial and anti-parasitic agent in fish farming
[1, 2]. Nowadays, MG is considered as a highly controversial compound due to its genotoxic and carcinogenic
properties [3].
Adsorption has been found to be the most promising way to remove MG from wastewater because it uses low-cost
adsorbents, which could be found in nature or are by-products [4]. Chitosan is one of the unindustrialized adsorption
methods for the removal of dyes and heavy metal ions, even at low concentrations [5]. Chitosan is a type of natural
polyaminosaccharide composed of poly(β-1–4)-2-amino-2-deoxy-D-glucopyranose and can be produced through
deacetylation of chitin. Chitin is the second most abundant polymer in nature after cellulose that can be extracted
from crustacean shells such as prawns, crabs and cell walls of fungi [6]. This nontoxic and biodegradable chitosan is
an ideal adsorbent due to the presence of the amine (–NH2) and hydroxyl (–OH) groups that serve as the adsorption
sites for many adsorbates [7, 8].
In spite of chitosan’s good adsorption capability, it also can be physically and chemically modified [9 –11].
Accordingly, the physical modification of chitosan can provide support and increase the availability of the binding
sites because the chitosan has low mechanical properties and low specific gravity [12, 13]. Therefore, efforts have
been made to improve its chemical stabilities by cross-linking the chitosan to create a very stable and strong
chitosan even in acidic and basic solutions.
Many studies have been reported for utilizing modified chitosan for application in MG removal, such as chitosan–
ionic liquid beads [14], chitosan nanoparticles [15, 16], chitosan oligosaccharide [17], chitosan composite [18],
chitosan–bentonite beads [19] and chitosan foam [20]. These approaches seem to be effective for removing MG but
some improvement in existing methods is desirable. All of these modified chitosan’s are difficult to prepare, time-
consuming and unstable, especially the chitosan foam. Therefore, a simple approach has been taken in this study
which is using a modified chitosan with sulfuric acid (H2SO4) to remove MG from an aqueous solution. The method
to prepare this modified chitosan is relatively straightforward and not expensive.
In this preliminary study, chitosan–H2SO4 beads are used to remove MG dye in aqueous solution. The influences of
initial pH, agitation time, adsorbent dosage and initial concentrations of MG on the adsorption process were studied.
These are the basic parameters to determine the suitability and optimal conditions of the prepared cross-linked
chitosan beads as an adsorbent. The pseudo-first-order and pseudo-second-order kinetics models were used to
determine the adsorption rate during the adsorption process. The Langmuir and Freundlich isotherm models were
used to evaluate the equilibrium adsorption capacity data for the adsorption of MG onto chitosan–H2SO4.
Materials and Methods
Materials
Samples of chitosan flakes (M.W. 100,000－150,000 g/mol) with a degree of deacetylation of 72.55% were
supplied by Chito–Chem (M) Sdn. Bhd., Malaysia. MG was purchased from Fluka (Malaysia). Sodium hydroxide
pellets, NaOH, hydrochloric acid 37.0%, HCl, acetic acid, CH3COOH, were purchased from Sigma-Aldrich
(Malaysia). All the reagents used throughout the experiments are analytical–reagent grade and used without any
further purification. Distilled deionized water was used to prepare all solutions.
Preparations of chitosan beads and chitosan–H2SO4 beads
Chitosan beads were prepared by dissolving 2.0 g of chitosan flakes in 60 mL of 5% (v/v) acetic acid. The viscous
solution was left overnight before dropping into 500 mL of 0.50 M NaOH solution using a dropper. The aqueous
NaOH solution was under continuous stirring with the speed of 300 rpm. The chitosan hydrogel beads were allowed
to immerse in 0.50 M NaOH solution for 15 minutes. Then, the formed chitosan beads were filtered with filter paper
2.5 µm of pore size (Whatman 42) and rinsed many times with distilled water. Eventually, the extensively washed
Malaysian Journal of Analytical Sciences, Vol 23 No 4 (2019): 625 - 636
DOI: https://doi.org/10.17576/mjas-2019-2304-08
627
chitosan beads were then added into 100 mL of 0.50 M sulfuric acid solution and were stirred at 200 rpm for 24
hours at room temperature. After 24 hours the solution was filtered and the cross–linked beads were washed several
times using distilled water. The chitosan–H2SO4 beads were allowed for drying. The beads were then ground using
mortar and sieved to a constant size approximately (< 250 µm) before used. The structure of chitosan–H2SO4 beads
before and after MG adsorption obtained was confirmed by a Perkin–Elmer FT–IR System 2000 Model
spectrometer.
Solubility and swelling test of chitosan beads and chitosan–H2SO4 beads
The solubility of chitosan–H2SO4 beads was tested in 5% (v/v) acetic acid, 0.10 M NaOH and distilled water.
Approximately 0.05 g of the beads was weighed and transferred into a 50 mL of these three solutions and were left
stirring for 24 hours. After 24 hours, the solubility of the beads in these solutions was observed.
In the swelling test, both chitosan beads and chitosan–H2SO4 beads were studied. About 0.05 g of the beads was
weighed and transferred into a glass tube with a diameter of 5 mm and a height of 100 mm. Three tubes were
prepared. The level of the beads was marked before filling with 1 mL of 5 % (v/v) acetic acid, 0.10 M NaOH and
distilled water. They were left for 24 h. After that, the height of the beads in all three solutions was calculated. The
percentage swelling was calculated using the following equation:
(1)
where, S is the percentage of swelling (%), ht is the height of swollen beads or chitosan–H2SO4 beads at time t (cm),
ho is the initial height of chitosan beads or chitosan–H2SO4 beads (cm).
Batch adsorption experiments
A stock solution of 500 mg/L of MG was prepared freshly by dissolving approximately 0.25 g of MG in a 250 mL
beaker with distilled water. The solution was transferred into a 500 mL volumetric flask. A series of experiments
were conducted in 250 mL beaker using 0.05 g of chitosan–H2SO4 beads and left shaking for 30 minutes using
Heidolph Unimax 1010 shaker. The absorbance of MG was obtained before and after adsorption at the maximum
wavelength of 224 nm using a UV–Vis spectrophotometer (Perkin Elmer Lambda 35).
The effect of initial pH of the solution on the adsorption of MG onto chitosan–H2SO4 was performed in the pH
range of 2-12. Six sets of 100 mL of MG solutions with concentration of 10 mg/L were prepared.
Adsorption equilibrium analysis was performed at optimum condition where the pH is 6 and the agitation time is 30
minutes for chitosan–H2SO4 beads. Isotherm studies were accomplished with a constant amount of chitosan–H2SO4
beads and varying the initial concentration of MG in the range of 0–70 mg/L. The adsorption capacity (qe) at
equilibrium was calculated using the following equation:
(2)
where qe is the adsorption capacity at equilibrium (mg/g), Co is the initial concentration of MG (mg/L), Ce is the
final concentration of MG (mg/L), v is the volume of MG (mL), m is the weight of the beads used (g). For batch
kinetics studies of MG onto adsorbent was also studied. About 0.05 g of chitosan–H2SO4 beads were equilibrated at
optimum condition. The beads and 10 mg/L of MG solutions were placed in 250 mL beakers and stirred
continuously. The concentration of MG in solution was determined each time based on the differences of MG
concentration in the solution before and after adsorption. Three replicates analyses have been done for each
adsorption study and the average was reported.
In addition, several parameters were optimized too. Effect of adsorbent dosage (percentage removal) was calculated
using the following expression:
Suhaila et al: ADSORPTION OF MALACHITE GREEN ONTO MODIFIED CHITOSAN–SULFURIC ACID
BEADS: A PRELIMINARY STUDY
628
(3)
where Co is the initial concentration of MG (mg/L) and Cf is the final concentration of MG (mg/L).
Models for adsorption equilibrium isotherms used in this study were Langmuir and Freundlich isotherm models.
Langmuir isotherm model used is applicable for monolayer sorption on to a surface with finite number of identical
sites and is given by:
(4)
where Q is the maximum adsorption at monolayer (mg/g), Ce is the equilibrium concentration of MG (mg/L), qe is
the amount of MG adsorbed per unit weight of chitosan–H2SO4 beads at equilibrium concentration (mg/g) and b is
the Langmuir constant related to the affinity of binding sites (mL/mg) and is a measure of the energy of adsorption.
A linearized plot of Ce/qe against Ce gives Q and b.
Freundlich isotherm model is an empirical isotherm for non–ideal adsorption on heterogeneous surfaces as well as
multilayer adsorption and is expressed as [21]:
(5)
where KF and n are Freundlich constant that indicates adsorption capacity (mg/g) and intensity, respectively. KF and
n can be obtained from linear plot of log qe against log Ce.
The critical features of a Langmuir isotherm can be expressed in terms of dimensionless constant separation factor,
RL which can be expressed as:
(6)
where RL is the separation factor parameter. Co is the initial concentration (mg/L) and b is the Langmuir constant
(L/mg).
Meanwhile adsorption kinetic models used in this study were pseudo–first–order and pseudo–second–order. The
linear form of pseudo–first–order rate equation is expressed as Equation 7 [22]:
(7)
where qe and qt (mg/g) are the amount of MG absorbed onto adsorbent at equilibrium and at time t (min),
respectively and k1 (min–1) is the rate constant of pseudo–first–order adsorption. The straight-line plots of log (qe–qt)
against t will yield the values of rate constant, k1 and qe from the slope and intercept, respectively.
The pseudo–second–order equation is based on the assumption that chemisorption is the rate determining step and is
expressed as given by Equation 8 [23]:
(8)
where h = k2
can be regarded as the initial adsorption rate (mg/g/min) as t approaches to zero, and k2 (g/min/mg)
is the rate constant of pseudo–second–order adsorption.
Malaysian Journal of Analytical Sciences, Vol 23 No 4 (2019): 625 - 636
DOI: https://doi.org/10.17576/mjas-2019-2304-08
629
Results and Discussion
Solubility and swelling test of chitosan and chitosan–H2SO4 beads
Chitosan is known for its stability in acidic media. Therefore, physical and chemical alterations were carried out to
increase the adsorption capacity and improve the stability of chitosan–H2SO4 beads. According to Ngah et al. [10],
the primary group of amine causes the chitosan beads to have higher hydrophilicity triggering chitosan to be easily
soluble in dilute acetic solution to yield a hydrogel. Based on Table 1, it can be seen that the chitosan beads were
insoluble in both distilled water and alkaline solution but completely dissolved in acidic medium giving a viscous
solution. The chitosan–H2SO4 beads were insoluble in all three media studied. This is due to the ionic cross-linking
modification with sulfuric acid greatly reinforcing the chemical stability of chitosan in acidic solution. Both the
chitosan beads and chitosan–H2SO4 beads do not dissolve in neutral and alkaline media because there is less H+ ion
present to protonate the amino group of chitosan. The insolubility of the chitosan–H2SO4 beads is important because
it is the main indicator to determine the optimum pH for the adsorption process and as a sign that it can be used in
all media.
Table 1. Solubility effect of chitosan beads and chitosan–H2SO4 beads
Adsorbent
Solubility Effect
5% (v/v) Acetic Acid
Distilled Water
0.1 M NaOH
Chitosan beads
Soluble
Insoluble
Insoluble
Chitosan–H2SO4 beads
Insoluble
Insoluble
Insoluble
The percentage of swelling is the most important to understand the crystalline nature of the adsorbent. From Table
2, the percentage of swelling of chitosan–H2SO4 beads was much lower than the percentage of swelling observed
for chitosan beads. The swelling ability of chitosan–H2SO4 beads depended on the degree of cross-linking. The
percentage of swelling will be much lower at a higher cross-linking density [11]. In this study, chitosan beads are
soluble in acidic medium but have a higher percentage of swelling in neutral and alkaline medium. However,
chitosan–H2SO4 beads show the highest percentage in both acidic and neutral medium but a lower percentage of
swelling in alkaline medium. This proved that the reduction in the swelling percentage of chitosan can be attributed
to ionic linkages formed between the protonated amine groups (
) of chitosan and
ions of sulfuric acid,
which increased the chemical stability of the beads in acidic medium.
Table 2. Swelling behavior of chitosan beads and chitosan–H2SO4 beads in different medium
Adsorbent
Percentage of Swelling (%)
5% (v/v) Acetic Acid
Distilled Water
0.1 M NaOH
Chitosan beads
Soluble
164
104
Chitosan–H2SO4 beads
125
81.5
71
Effect of initial pH
Figure 1 shows the effect of different pH for the adsorption of MG onto chitosan–H2SO4 beads. It can be seen that
dye adsorption was unfavorable at pH < 4. As the pH of the system decreased, the –NH2 groups that surround the
adsorbent surface are protonated. The number of negatively charged adsorbent sites decreased and the number of
positively charged surface sites increased, which did not favor the adsorption of positively charged dye cations due
to electrostatic repulsion. This would cause repulsion between the –NH3+ groups on the adsorbent surface and the –
N+(CH3)2 groups of MG. Lower adsorption of MG at acidic pH is due to the presence of excess H+ ions competing
with dye cations for the adsorption sites of chitosan–H2SO4 beads [12]. With the increase in pH, the number of H+
ions decreased and the adsorbent surface carried more negative charge resulting in greater attraction between the
adsorbent and the cationic form of the adsorbate. Therefore, pH 6 was chosen as the optimum condition for
following adsorption experiments.
Suhaila et al: ADSORPTION OF MALACHITE GREEN ONTO MODIFIED CHITOSAN–SULFURIC ACID
BEADS: A PRELIMINARY STUDY
630
Figure 1. Effect of initial pH on the adsorption of MG onto chitosan–H2SO4 beads
Effect of adsorbent dosage
The effect of adsorbent dosage is illustrated in Figure 2. The percentage removal increases with the increasing
adsorbent dosage from 8 to 17% for an adsorbent dosage of 0.01 g to 0.10 g. However, the adsorption capacity,
which is the amount of MG adsorbed per unit weight decreased with increasing adsorbent dosage. Percentage
removal is increased because the availability of adsorption surface is increased yet the decrease in adsorption
capacity with increase adsorbent dosage is due to saturation of adsorption sites.
Figure 2. Effect of adsorbent dosage on the adsorption of MG onto chitosan–H2SO4 beads
0.0
1.0
2.0
3.0
4.0
5.0
0 5 10 15
Adsorption capacity,
qe (mg/g)
Initial pH
0
10
20
30
40
50
60
70
0
2
4
6
8
10
12
14
16
18
0 0.02 0.04 0.06 0.08 0.1 0.12
Removal (%)
Adsorption capacity,
qe (mg/g)
Adsorbent dosage (g)
qe
%
Removal
Malaysian Journal of Analytical Sciences, Vol 23 No 4 (2019): 625 - 636
DOI: https://doi.org/10.17576/mjas-2019-2304-08
631
Effect of agitation period
It is necessary to determine the optimum agitation period required for the adsorption of MG because it represented
the time required for the adsorbate to reach an equilibrium state after contact with the adsorbent. The optimum
period can be observed in Figure 3 by looking at a rapid adsorption capacity within the first 10 minutes, then a
decrease before slowly becoming constant at 30 minutes. The initial rapid phase during the first 10 minutes was due
to the availability of adsorption sites for the uptake of MG. Meanwhile, after 30 minutes the adsorption became
constant because of the quick exhaustion of the adsorption sites [13]. As a result, the equilibrium time of 30 minutes
was selected for additional studies.
Figure 3. Effect of agitation time on the adsorption of MG onto chitosan–H2SO4 beads
Adsorption equilibrium isotherms
An adsorption isotherm is an expression that shows the relationship between the amounts of adsorbate adsorbed per
unit weight of adsorbent (qe, mg/g) and the concentration of adsorbate in the bulk solution (Ce, mg/L) at 300 K
under equilibrium conditions. The Langmuir and Freundlich models are often used to describe equilibrium
adsorption isotherms. The Langmuir isotherm usually indicates individual chemical adsorption (chemisorption) and
reflects a relatively high affinity between adsorbate and the adsorbent within a low concentration range [1].
The Langmuir isotherm also assumes that the adsorbed layer is one molecule in thickness and that all adsorption
sites have equal energies and enthalpies of adsorption. The linearized Langmuir and Freundlich models plot at 300
K are shown in Figures 4 and 5, respectively. Table 3 shows the obtained values for the Langmuir and Freundlich
isotherms constants and coefficients of determination (R2). Overall, the experimental data fitted well with the
Langmuir isotherm model because the R2 values were very high. This showed that chitosan–H2SO4 beads had
homogeneous adsorption sites.
0
2
4
6
8
10
12
020 40 60 80
qe (mg/g)
Agitation period (minutes)
10 mg/L
20 mg/L
30 mg/L
Suhaila et al: ADSORPTION OF MALACHITE GREEN ONTO MODIFIED CHITOSAN–SULFURIC ACID
BEADS: A PRELIMINARY STUDY
632
Figure 4. Linearized Langmuir adsorption isotherm of MG onto chitosan–H2SO4 beads
Figure 5. Linearized Freundlich adsorption isotherm of MG onto chitosan–H2SO4 beads
Table 3. Langmuir and Freundlich isotherm constants and correlation for the adsorption of MG
onto chitosan–H2SO4 beads at 300 K
Langmuir
Freundlich
Q
(mg/g)
b
(L/mg)
R2
Kf
(mg/g)
n
R2
30.96
0.0730
0.9985
2.23
1.1287
0.9666
0.00
0.20
0.40
0.60
0.80
1.00
0246810 12
Ce/qe (g/L)
Ce (mg/L)
300 K
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 0.2 0.4 0.6 0.8 1 1.2
log qe
log Ce
300 K
Malaysian Journal of Analytical Sciences, Vol 23 No 4 (2019): 625 - 636
DOI: https://doi.org/10.17576/mjas-2019-2304-08
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It has been stated that the effect of isotherm shape with a view to predicting if an adsorption system is ‘favorable’ or
‘unfavorable’. It has been established that for favorable adsorption, 0 < RL < 1; unfavorable adsorption, RL > 1;
linear adsorption, RL = 1; and irreversible adsorption process if RL = 0. Based on Table 4, the RL values are in the
range of 0 < RL < 1, which reveals the adsorption of MG onto chitosan–H2SO4 beads is favorable.
Table 4. Values of RL for initial concentrations range from 0 to 30 mg/L at 300 K
Initial Concentration of MG
(mg/L)
RL value
5
0.7326
10
0.5780
15
0.4773
20
0.4065
25
0.3540
30
0.3135
Adsorption kinetics
The kinetics of adsorption is applied to determine the adsorption rate of MG uptake on the beads. The most
common kinetic models applied in adsorption studies are pseudo-first-order and pseudo-second-order. Figure 6
represents the pseudo-first-order kinetic plot for chitosan–H2SO4 beads.
Figure 6. Plot of pseudo–first–order kinetic model for the adsorption of MG onto chitosan–H2SO4 beads
The straight-line plots of t/qt against t were used to determine the rate constant, k2 and coefficient of determination,
R2. Figure 7 represents the pseudo-second-order plot for chitosan–H2SO4 beads. The results of kinetic parameters of
the pseudo-first-order and pseudo-second-order kinetic models for the adsorption of MG are given in Table 5. Based
on the R2 values shown in the table, it can be concluded that the pseudo-second-order kinetic model can be used to
represent the adsorption behavior over the whole range of contact time. Moreover, the calculated adsorption
-2
-1.6
-1.2
-0.8
-0.4
0020 40 60 80
log (qe - qt)
time (minutes)
10 mg/L
20 mg/L
30 mg/L
Suhaila et al: ADSORPTION OF MALACHITE GREEN ONTO MODIFIED CHITOSAN–SULFURIC ACID
BEADS: A PRELIMINARY STUDY
634
capacity (qe, calc) values were in agreement with the experimental adsorption capacity (qe, exp) value. This showed that
the uptake of MG onto chitosan–H2SO4 beads was rapid and favorable. The initial adsorption rate, h, of the pseudo-
second-order kinetic model increased as concentrations increased. The large number of adsorption sites available on
chitosan–H2SO4 beads might cause the rapid adsorption of MG at higher concentrations, possibly due to the
increase in the driving force for mass transfer, and thus, allowing MG molecules to reach the adsorbent surface in a
shorter period of time [24, 25].
Figure 7. Plot of pseudo–second–order kinetic model for the adsorption of MG onto chitosan–H2SO4 beads
Table 5. Kinetic parameters for the adsorption of MG onto chitosan–H2SO4 beads based on pseudo–first–order and
pseudo–second–order kinetic model
Pseudo–First–Order
Pseudo–Second–Order
Concentration
of MG
(mg/L)
qe, exp
(mg/g)
k1
(1/min)
R2
qe, calc
(mg/g)
k2
(g/mg
/min)
h
(mg/g
/min)
R2
qe, calc
(mg/g)
10
5.97
4.38 ×10-3
0.9335
0.61
0.17
5.97
0.9716
5.93
20
7.98
5.94 × 10-2
0.8227
1.06
0.25
16.10
0.9996
7.97
30
9.97
3.68×10-3
0.1768
0.85
23.89
1999.74
0.9999
9.15
FT–IR analysis
The FTIR spectra obtained for chitosan beads and chitosan–H2SO4 beads before and after adsorption were shown in
Figure 8. The broad peaks at 3428.58 cm–1 in chitosan beads can be assigned to stretching vibration of hydroxyl
group and N–H groups found in chitosan. The adsorption band at 1655.12 cm–1 is the N–H bending in primary
amine groups (–NH2). Other major band observed at 1383.14 cm–1 represents C–N stretching vibration. After the
cross–linking process, several changes were observed in the spectra obtained for chitosan–H2SO4 beads. The broad
peak at 3428.58 cm–1, shifted to 3423.52 cm–1 and eventually become broader. This showed that the –NH2 groups in
chitosan were protonated to –NH3+, as this broader band represented the stretching vibration of –NH3+. The
adsorption bands at 1635.05 and 1532.64 cm–1 represented the bending vibration of –NH3+ groups. The involvement
0.0
2.0
4.0
6.0
8.0
10.0
12.0
020 40 60 80
t/qt (g min / mg)
time (minutes)
10 mg/L
20 mg/L
30 mg/L
Malaysian Journal of Analytical Sciences, Vol 23 No 4 (2019): 625 - 636
DOI: https://doi.org/10.17576/mjas-2019-2304-08
635
of SO42– ions in the cross–linking process was confirmed by the presence of the adsorption bands at 1191.64 cm–1
that represented the sulfo groups. The band observed at 1076.47 cm–1 also confirmed the presence of S=O stretching
found in the SO42– ions. This FTIR spectra proved that the formation of chitosan–H2SO4 beads was through the
ionic interaction between the protonated amine groups (–NH3+) of chitosan and the SO42– ions of sulfuric acid. The
FTIR of chitosan–H2SO4 beads after adsorption showed there were no appearances of new bands. However, there
were adsorption bands at 887.59 and 855.15 cm–1 represented –NH3+ rocking vibrations. These spectral changes
shown that many amine groups were protonated to form –NH3+.
Figure 8. Infrared spectra for chitosan flakes and chitosan–H2SO4 before and after adsorption
Conclusion
This study demonstrated that chitosan–H2SO4 beads are a promising adsorbent for the removal of MG from aqueous
solutions. Chitosan–H2SO4 beads show a lower percentage of swelling than chitosan beads. The adsorption isotherm
could be well fitted by the Langmuir equation and the MG adsorption followed the pseudo-second-order equation.
The interaction between MG and chitosan–H2SO4 beads was confirmed by FTIR spectroscopy. Hence, it can be
concluded that chitosan–H2SO4 beads are effective adsorbents for the uptake of MG sorption studies. Based on
these findings, the prepared chitosan–H2SO4 beads can be used to remove MG from the wastewater, which is
currently being carried out. In addition, the chitosan–H2SO4 beads can also be prepared in membrane, microbead
and nanoparticle forms. It is expected that the removal of MG shall be increased with the use of different physical
shapes of the cross-linked chitosan–H2SO4.
Acknowledgement
Authors would like to thank Universiti Sains Malaysia for providing financial assistances through a bridging grant
(304/PKIMIA/6316215) and a short-term grant (304/PKIMIA/6315197).
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4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400.0
cm-1
%T
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chitosan-sulfuric acid after adsorp tion
3428.58
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899.48
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3423.52
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3422.13 2114.75
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