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Title Development of magnetic separation using modified magnetic chitosan for removal of pollutants in solution
Author(s) Sakti, Satya Candra Wibawa
Citation 北海道大学. 博士(環境科学) 甲第11984号
Issue Date 2015-09-25
DOI 10.14943/doctoral.k11984
Doc URL http://hdl.handle.net/2115/60077
Type theses (doctoral)
File Information Satya_Chandra.pdf
Hokkaido University Collection of Scholarly and Academic Papers : HUSCAP
博 士 論 文
Development of magnetic separation using modified magnetic
chitosan for removal of pollutants in solution
(溶液中の汚染物質除去のための修飾マグネティック
キトサンを用いた磁性分離法の開発)
北海道大学大学院環境科学院
Satya Candra Wibawa Sakti
(2015)
CONTENTS
CHAPTER 1. General Introduction ............................................................................... 1 1.1. Water Pollution ............................................................................................................ 2 1.2. Treatment of heavy metal ion polluted water .............................................................. 2 1.3. Magnetic separation for water decontamination .......................................................... 6 1.4. Chitosan as polymeric matrix for magnetic component .............................................. 8 1.5. Modification of magnetic chitosan .............................................................................. 9 1.6. References .................................................................................................................... 13 CHAPTER 2. A novel pyridinium functionalized magnetic chitosan with pH-
independent and rapid adsorption kinetics for magnetic separation of Cr(VI) .................................................................................................... 20
Abstract ........................................................................................................................... 21 2.1. Introduction .................................................................................................................. 22 2.2. Materials and Methods ................................................................................................. 24
2.2.1. Materials ....................................................................................................... 24 2.2.2. One-pot preparation of magnetic chitosan (MC) .......................................... 24 2.2.3. Amination of magnetic chitosan with diethylenetriamine ............................ 25 2.2.4. Quaternarization of diethylenetriamine functionalized magnetic chitosan
with pyridine .................................................................................................. 25 2.2.5. Characterization ........................................................................................... 26 2.2.6. Adsorption of Cr(VI) .................................................................................... 26 2.2.7. Desorption of Cr(VI)..................................................................................... 28
2.3. Results and Discussion ................................................................................................ 29 2.3.1.Characteristics of pyridinium-diethylenetriamine functionalized
magnetic chitosan .......................................................................................... 29 2.3.2. Effect of pH on Adsorption of Cr(VI) .......................................................... 36 2.3.3. Adsorption kinetics study ............................................................................. 38 2.3.4. Adsorption isotherm study ............................................................................ 41 2.3.5. Comparison with other magnetic chitosan based adsorbents ....................... 44 2.3.6. Effect of ionic strength.................................................................................. 47 2.3.7. Reuseability of pyridinium-diethylenetriamine functionalized magnetic
chitosan .......................................................................................................... 47 2.4. Conclusions .................................................................................................................. 48 2.5. References .................................................................................................................... 49 CHAPTER 3. A rapid magnetic separation of Cu(II) in aqueous solution
containing humic acid by a high reusability dendrimerized magnetic chitosan ...................................................................................... 56
Abstract ........................................................................................................................... 57 3.1. Introduction .................................................................................................................. 58 3.2. Materials and Methods ................................................................................................. 60
3.2.1. Materials ....................................................................................................... 60 3.2.2. Preparation of magnetic chitosan microparticle (MC) .................................. 60 3.2.3. Surface dendrimerization of magnetic chitosan with ethylenediamine ....... 60 3.2.4. Characterization ........................................................................................... 61 3.2.5. Adsorption of Cu(II) ..................................................................................... 62 3.2.6. Effect of humic acid on adsorption of Cu(II) ................................................ 62 3.2.7. Desorption of Cu(II) ..................................................................................... 63
3.3. Results and Discussion ................................................................................................ 64 3.3.1. Characteristics of dendrimerized magnetic chitosan microparticle .............. 64 3.3.2. Effect of pH on Adsorption of Cu(II) ........................................................... 69 3.3.3. Adsorption kinetics study ............................................................................. 72 3.3.4. Adsorption isotherm study ............................................................................ 74 3.3.5. Effect of humic acid on adsorption of Cu(II) by MCE-G2 ........................... 76 3.3.6. Reuseability of dendrimerized magnetic chitosan ........................................ 80
3.4. Conclusions .................................................................................................................. 81 3.5. References .................................................................................................................... 82 CHAPTER 4. A novel quaternized dendrimer magnetic chitosan for a rapid
magnetic separation of humic acid in aqueous solution ...................... 86 Abstract ........................................................................................................................... 87 4.1. Introduction .................................................................................................................. 88 4.2. Materials and Methods ................................................................................................. 90
4.2.1. Materials ....................................................................................................... 90 4.2.2. Quaternization of diethylenetriamine functionalized magnetic chitosan
with GTMAC .............................................................................................. 91 4.2.3. Characterization ........................................................................................... 91 4.2.4. Adsorption of humic acid.............................................................................. 92 4.2.5. Desorption of humic acid .............................................................................. 94 4.3. Results and Discussion ................................................................................. 95 4.3.1. Characteristics of quaternized diethylenetriamine functionalized
magnetic chitosan ........................................................................................ 95 4.3.2. Effect of pH on adsorption of humic acid ..................................................... 99 4.3.3. Adsorption kinetics study ............................................................................. 101 4.3.4. Adsorption isotherm study ............................................................................ 104 4.3.5. Reuseability of quaternized diethylenetriamine functionalized magnetic
chitosan ........................................................................................................ 106 4.3.6. Pilot scale of magnetic separation of humic acid.......................................... 107
4.4. Conclusions .................................................................................................................. 108 4.5. References .................................................................................................................... 109
CHAPTER 5. General Conclusions................................................................................. 113 ACKNOWLEDGEMENTS ............................................................................................. 116
1
CHAPTER 1
General Introduction
2
1.1. Water Pollution
Water is the most important chemical compound on the earth and the most
essential for all living creature in the world. It is also one of the most precious
resources for human civilization. However, rapid population growth, climate change
and the deterioration of environment affects on the quality of water supply.
Conserving and providing clean and accessible fresh water become one of the goals
for this century. Although water is considered as the most precious resources,
pollution of water source such as river, lake and sea continuously occurs. Water
pollution alters the property of water to hazardous toward environment and makes it
undrinkable.
Water pollutions are usually classified into: (1) organic pollutants such as
natural organic matters, oil [1], dyes [2], plastics [3–5] and pesticides [6,7], (2)
inorganic pollutants such as salts [8], heavy metal ions [9,10], acid [11,12], (3) water
soluble nutrients including nitrates [13,14] and phosphates, (4) water soluble
radioactive materials such as thorium [15], uranium [16], cesium [17] and strontium
[18], (5) hazardous microorganism such as viruses [19], protozoa [20] and bacteria
[21] and (6) suspended sediments. The discharge of these pollutants into the
environments causes serious health risk. Water pollution with heavy metal ions has
become the most serious problem on environments due to their mobility in water and
toxicity. Unlike organic pollutant, heavy metal ions are non-biodegradable and
accumulated on the environment.
1.2. Treatment of heavy metal ions in polluted water
Metals classified as heavy metal have the density of more than 5 g�cm-3 [22].
Based on their roles on biological system, heavy metal ions are classified into the
3
essential and non-essential metals. Metals, such as Cu, Fe, Mn, Ni and Zn, which are
required by living creatures for their life, are considered as an essential heavy metal.
On the other hand, As, Cd, Hg and Pb, which are not required by living creatures at
any level, are classified as a non-essential heavy metal. Some metals have both
properties of essential and non-essential depending on the concentration such as Cr
and Se. Table 1.1 shows the sources of heavy metal pollution and their effects on the
human health.
Table 1.1. Sources of heavy metal pollution and its effects toward human body.[23–31]
Heavy Metal Sources Effects on human body
As Pesticide, wood preservative Visceral cancer, vascular disease
Cd Paint, electroplating, plastic stabilizer, fertilizer Carcinogenic, kidney problem
Cr Steel industry, electroplating tanneries, leather industry
Carcinogenic, headache, nausea, diarrhea
Cu Pesticide, fertilizer Insomnia, liver damage, carcinogenic
Hg Precious metal mining, coal combustion
Kidney problem, nervous problem and circulatory problem
Ni Industrial effluents, steel alloys batteries
Dermatitis, carcinogenic and nausea
Pb Combustion of Pb containing fuels, battery, herbicide and insecticide
Damage of fetal brain, nervous system problem
The exposure to heavy metal ions even at low level leads to serious problem
towards human health. Therefore, the removal of heavy metal ions from water
becomes a great of interest. Various kinds of treatments have been investigated for
water purification and decontamination from heavy metal ion. These treatments
include chemical precipitation, ion exchange, and membrane filtration etc (Fig. 1.1.)
4
Fig. 1.1. Conventional methods for purification and decontamination of wastewater
Removal of heavy metal ion in drinking
and waste water
Chemical precipitation
Complexes
Hydroxides
Sulfides
Membrane filtration
Ultrafiltration
Nanofiltration
Reverse osmosis
Ion Exchange Electrochemical treatment
Electroflotation
Electrocoagulation
Electrodeposition
Coagulation Floatation
Dissolve floatation
Ion floatation
Precipitation floatation
Adsorption
5
Each treatment method has its advantages and disadvantages. Chemical
precipitation of heavy metal ion from wastewater probably is the most traditional and
the simplest method. The method can be applied in large scale and remove the heavy
metal ions effectively. However, this method requires large amount of chemicals and
also produces plenty of sludge for which the handling is difficult [32]. Removal of
pollutants by membrane filtration technique requires high-cost operation and
maintenance. The ion exchange method has shown higher effectiveness in the
removal of heavy metal ions [33]. As similar to the membrane filtration method, ion
exchange method is relatively high-cost. The electrochemical method can reduce the
amount of chemicals used for the decontamination of polluted water [34]. However,
the treatment for large amount of wastewater by this method seems to be difficult. In
a similar way to chemical precipitation method, coagulation method also produces
large amount of sludge, which is difficult to be handled [35]. Adsorption is the most
popular method on water decontamination due to its effectiveness and simplicity
[36,37]. However, adsorption process mostly depends on the quality of adsorbent.
Regeneration of adsorbent, decrease in its performances, kinetic rate during water
treatments are the important issues related to the adsorption process. The separation of
saturated adsorbent from treated water, the recollection and reuse of adsorbent are the
important steps in water treatment. After the adsorption process is completely
accomplished, it is difficult for the adsorbent to be separated and recollected using
common separation process such as filtration and sedimentation because adsorbent
may block the pores of the filter and membrane and become one of the cause of the
secondary pollution if the adsorbent will not be recollected.
6
1.3. Magnetic separation for water decontamination
Magnetism, which is a physical property, becomes an interesting feature to be
applied to the material separation in recent years [38]. Depending on the difference of
the ways of the application of the magnetism, magnetic separation for water
decontamination can be classified into: (1) direct magnetic separation, (2) magnetic
flocculation and (3) magnetic separation assisted by a magnetic material. The direct
magnetic separation is to separate magnetic materials such as hematite [39] and the
ores [40] by a magnet. The direct magnetic separation was also successfully applied
to the removal of radioactive waste composite because the majority of radionuclides
in waste sludge are paramagnetic materials such as plutonium, uranium and rhodium,
which form magnetic compounds in wastewater [41].
Magnetic flocculation is conducted on the basis of the formation of magnetic
floc from non-magnetic pollutant with Fe3+ ion so that the products could be collected
by using an external magnet. For example, arsenic ion (As(V)), which is non-
magnetic in natural water, can form magnetic floc with magnetite in the presence of
polymeric ferric sulfate [42]. Phosphate was successfully removed from water by
magnetic flocculation with magnetite particles in the presence of polyaluminium
chlorides (PACs) as coagulant [43]. The removal of algae, which consequently led to
the decrease of chemical oxygen demand (COD), total nitrogen and phosphorous in
natural water, have been successfully achieved [44].
Separation of pollutants by magnetic materials becomes popular and
interesting in recent years (Fig. 1.2). The removal of pollutants from wastewater by
using a conventional adsorbent has several limitations especially in the recollection of
adsorbents after adsorption process. By introducing magnetic property into
conventional adsorbents, recollection after separation could be achieved so easily that
7
the lost of adsorbents could be lowered. Depending on the type of the host compound
for the magnetic material, magnetic adsorbents can be classified into three groups: (1)
inorganic magnetic adsorbent, (2) organic magnetic adsorbents and (3) inorganic-
organic magnetic adsorbent. On inorganic magnetic adsorbents, silica and clay are
used as a host for magnetic component. Magnetic montmorillonite prepared by the
insertion of ferric ion in the montmorillonite structure showed the adsorption ability
towards methylene blue [45]. Magnetic sepiolite was applied to magnetic separation
of herbicides in the water [46]. Alginate and chitosan are the common organic
compounds used for coating of magnetic components due to their affinity towards
some pollutants such as heavy metal ions or dyes [47–51]. In order to enhance the
performance on the removal and stability, the combination of inorganic and organic
modification was attempted. The further modification of magnetic silica by
introducing active organic groups such as amine [52,53], thiol [54]or carboxylates
[55] showed the higher affinity toward pollutants, especially heavy metal ions in
comparison with unmodified magnetic silica. Introducing hydrophobic groups on
magnetic silica also increases the affinity toward aromatic compounds [56].
Fig. 1.2. Separation of pollutant with magnetic material, its recollection and reuse.
8
1.4. Chitosan as polymeric matrix for magnetic component
A polymeric material as a host for the magnetic component should have
several features such as effective active sites for pollutants, mechanical strength and
the functional groups to be modified easily [57]. Polysaccharides such as chitosan and
chitin have received much attentions, especially in water decontamination. Several
review articles have been published on application of chitosan and its derivatives as
adsorbents for water pollutant in wastewater [58–61]. Chitosan is a biopolymer,
which is obtained from deacetylation of chitin. Chitin is one of the most abundance
biopolymer in nature, which can be found in crustacean shells such as prawns, crab
and shrimps. In comparison with other synthetic polymers, chitosan has superior
features to be used as a host for the magnetic component. Chitosan is biodegradable,
non toxic, and cheap [62]. Moreover, chitosan can be dissolved easily in acidic
aqueous solution so that the use of toxic and dangerous organic solvent could be
avoided. Due to the presence of large amount of amine groups as well as hydroxyl
and carbonyl groups, chitosan has a high affinity towards pollutants such as heavy
metal ions [62], radionuclides [63] and dyes [61]. Furthermore, the presence of those
organic groups makes it possible for chitosan to be modified easily.
Fig. 1.3. Structure of chitin and chitosan.
Basically, the preparation of magnetic chitosan can be accomplished at least in
two steps. The first step is the synthesis of a magnetic component and the second is
9
dispersion of magnetic component in chitosan matrix by coating or encapsulating. In
many published papers about the application of magnetic chitosan for water
decontamination, magnetite (Fe3O4) is mostly used as a magnetic component due to
its easiness on preparation and high magnetic saturation [64]. In order to increase the
stability of the obtained magnetic chitosan, crosslinking is conducted right after
dispersion of the magnetic component on chitosan solution with glutaraldehyde [65]
or epichlorohydrine [66] as the crosslinking agents. Another method, to prepare
magnetic chitosan, is by the process of oxidation-crosslinking method. The ferrous
ion is distributed in chitosan matrix to form Fe2+-chitosan complex followed by
partial oxidation of Fe2+ under alkali condition to obtain magnetite particles inside the
chitosan matrix [67]. The water/oil emulsion method is also frequently employed for
the preparation of magnetic chitosan. At first magnetite was distributed in chitosan
matrix and then the mixture was dropped in the dispersion medium containing
emulsifier and followed by crosslinking process [68].
1.5. Modification of magnetic chitosan
In all processes for the preparation of magnetic chitosan, crosslinking step is
one of the most important step, especially to stabilize the obtained magnetic chitosan.
However, crosslinking agent reacts to connect one active group with other active
group of chitosan. Consequently, the number of available active groups for pollutants
decreases to reduce the affinity toward pollutants. In order to increase the stability and
adsorption performance of magnetic chitosan, more adequate modification of
magnetic chitosan should be conducted. Modification of magnetic chitosan can be
classified into physical and chemical modifications.
10
Physical modification of magnetic chitosan was conducted by forming
magnetic chitosan into various shapes. Powder [69], nanoparticles [51] and beads [70]
of magnetic chitosan for water decontamination have been prepared. Powdered
magnetic chitosan is the most common shape due to its easiness on preparation
without any special treatments. Nanoparticles of magnetic chitosan has higher surface
area, which led to higher adsorbing capacity toward water pollutants [51]. Magnetic
chitosan into beads enhances diffusion properties of magnetic chitosan due to its high
porosity of magnetic chitosan, which allows water pollutants to diffuse into the
interior of the beads so that high adsorption capacity towards pollutants could be
achieved [70].
Chemical modification of magnetic chitosan was performed by introducing
organic functional groups such as amine, hydroxyl and carbonyl groups. Modification
with various organic group containing nitrogen and sulfur was widely performed with
various agents. Alkylamine compounds were introduced to magnetic chitosan surface
in order to increase its contents of amine, which decreased during crosslinked step
[71,72]. Their applications on magnetic separation of Cu, Cr, Zn, Hg were also
reported [71,73]. Introducing sulfur compounds such as thiourea, xanthate and thiols
increased the affinity of magnetic chitosan toward Ag, Pb, Cu, and Zn [74,75].
In this study, Cr(VI), Cu(II) and humic acid were selected as the pollutant to
be treated with modified magnetic chitosan. Removal of Cr(VI) by magnetic chitosan
have been published in several articles [65,66,76]. However, most of magnetic
chitosan were only effective in lower pH due to the protonation of amine groups,
though Cr(VI) exists not only in the acidic but also in neutral and basic wastewater.
Therefore, magnetic chitosan which could be applied on removal of Cr(VI) in wider
range of pH was required. Modification of magnetic chitosan with pyridinium groups
11
makes it positively charged in wider range of pH so that could be applied effectively
in wider range of pH. Chitosan based materials are well known as the effective
adsorbents for Cu(II) ion. Its performance depends on the amount of amine groups on
its structure. In the preparation of magnetic chitosan, amine groups are consumed to
crosslink the chitosan which leads to decreasing of available amine groups for the
removal of Cu(II). Since modification by dendrimer on the surface of magnetic
chitosan increases the amount of amine groups the removal of Cu(II) could be
enhanced. Removal of humic acid by chitosan and magnetic chitosan has been
reported in several published papers [77–80]. However, its performance on removal
of humic acid depends on the pH of solution. Introducing quaternary ammonium
groups on the magnetic chitosan will make the magnetic chitosan positively charged
in the wider range of pH. Due to the presence of quaternary ammonium groups,
humic acid could be removed effectively in wider range of pH.
The objectives of this study are: (1) to prepare pyridinium, dendrimer and
quaternary ammonium magnetic chitosan and (2) to evaluate its application for
magnetic separation of Cr(VI), Cu(II) and humic acid, respectively. Introducing of
pyridinium groups, dendrimer structure and quaternary ammonium groups made the
magnetic chitosan more effective for magnetic separation of Cr(VI), Cu(II) and humic
acid, respectively. Moreover, modified magnetic chitosan can be recollected easily by
a magnet and reused for several adsorption-desorption cycles which made it the
economical magnetic adsorbent for removal of pollutants in water.
This thesis consists of five chapters. In Chapter 1, the general introduction of
preparation of magnetic materials and its application on water treatment are described
with previous studies. The short review on the application of magnetic chitosan for
magnetic separation of pollutant on water were also explained.
12
In Chapter 2, a novel pyridinium functionalized magnetic chitosan were
synthesized for magnetic separation of Cr(VI). In comparison with unfunctionalized
magnetic chitosan, pyridinium magnetic chitosan could remove Cr(VI) ion in wider
range of pH. The adsorption rate was very fast and the equilibrium state could be
achieved within 5 min. The interaction of pyridinium magnetic chitosan with Cr(VI)
was confirmed to be the electrostatic interaction by the competitive adsorption with
NaCl. The regeneration study showed that the pyridinium magnetic chitosan could be
used for 10 times adsorption-desorption cycles.
In Chapter 3, a dendrimerized magnetic chitosan was used for magnetic
separation of Cu(II) in the solution. Dendrimerization was conducted in order to
increase the contents of amine groups that are important to adsorp Cu(II) from the
solution. The effect of initial pH, contact time, initial Cu(II) concentration and the
presence of humic acid on magnetic separation of Cu(II) from water were also
investigated. The equilibrium state could be achieved within 5 min. The presence of
humic acid increases the adsorption capacity towards Cu(II) slightly.
In Chapter 4, the quaternarization product of dendrimerized magnetic
chitosan, which was obtained in the previous chapter, were employed for magnetic
separation of humic acid in the solution. The quaternarization step was conducted to
introduce the active quaternary amine group on the surface of dendrimerized magnetic
chitosan. The effect of initial pH, contact time, initial concentration of humic acid on
the magnetic separation of humic acid were evaluated. In order to investigate the
feasibility of quaternary ammonium dendrimerized magnetic chitosan for the practical
application, the regeneration study was conducted. The reusability could be achieved
until 10 times adsorption-desorption cycles.
13
In Chapter 5, the results of each chapter are summarized. The potential
application of each prepared magnetic material for the magnetic separation of water
pollutant on solution is also proposed.
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20
CHAPTER 2
A novel pyridinium functionalized magnetic chitosan with
pH-independent and rapid adsorption kinetics for magnetic
separation of Cr(VI)
21
Abstract
A novel pyridinium-diethylenetriamine magnetic chitosan (PDFMC) has been
prepared and used for magnetic separation of Cr(VI) from aqueous solution. The
PDFMC was characterized by using an X-ray Diffractometer (XRD), a fourier
transform infrared (FTIR) spectrometer, a thermo gravimetric analyzer (TGA) and a
scanning electron microscope (SEM), while the magnetic property was examined by
the magnetic property measurement system magnetometer (MPMS). The PDFMC
worked well on removal of Cr(VI) in any condition of acidic, neutral and basic
solutions with the capacity (qmax) of 176 mg�L-1 (at pH 3, acidic), 124 mg�L-1 (pH 6,
near-neutral), and 86 mg�L-1 (pH 9, basic) based on the Langmuir isotherm model.
Kinetics study showed that the removal of Cr(VI) followed the pseudo-second order
model with an extremely fast removal rate (the complete adsorption within 5 min).
Regeneration of PDFMC could be conducted by simply washing with a mixture of
NaOH and NaCl solution and the adsorbent could be used for 10 cycles of adsorption-
desorption of Cr(VI) without any significant loss. The fast removal rate, applicability
in a wider range of pH and easy regeneration and reusability makes the PDFMC a
prospective material for magnetic separation of Cr(VI) from aquatic environments.
22
2.1. Introduction
Hexavalent chromium (Cr(VI)) is one of the heavy metal ions with a high
toxicity even in low concentrations. Cr(VI) causes DNA damage [1], is carcinogenic
[2], and mutagenic in human cells [3]. In aqueous solution, Cr(VI) exists as oxyanions
such as HCrO4- and Cr2O4
2- which depend on the pH. Cr(VI) widely used in various
industry such as electroplating [4], leather tanning [5], and textile [6]. Hence
effluents from these industry are the major source of Cr(VI) pollution. Several
methods have been developed to remove Cr(VI) from water such as liquid extraction
[7], chemical precipitation [8], electrodialysis [9], photocatalysis [10] and membrane
filtration [11,12]. However these methods have several disadvantages including the
requirement of large amounts of organic solvent, high cost and far from ideal for
technical application. Adsorption [13] have been the widely used techniques to
remove not only Cr(VI) but also other hazardous substances from water. Many
investigations have been done in the development of adsorbent and its application
toward Cr(VI) [14]. However, adsorption has a limitation in the recollection of
adsorbent after binding with Cr(VI) and a possibility of the secondary pollution with
the adsorbent itself.
Magnetic separation has been shown to be a promising method to separate
hazardous substances from water and to be superior in its performance in comparison
with previous common methods. Magnetic separation can be achieved simply by
applying a magnetic force toward magnetic particles. Among the magnetic particles,
magnetite (Fe3O4) has been used widely in water remediation [15]. However,
magnetite shows the lower affinity toward heavy metal ions, especially Cr(VI) in
comparison with other common adsorbents. Coating of magnetite with silica [16],
23
alumina, as well as organic polymers/non-polymers is one approach to enhance the
performance of magnetite [17].
Chitosan can be considered as a prominent organic polymer for the coating of
magnetite. Chitosan has abundant amounts of the amine (-NH2) group, which has a
great affinity toward heavy metal ions and then could be an adsorbent for Cr(VI). The
preparation methods of magnetic chitosan have been reported with various methods
such as magnetite synthesis followed by coating [18], the incorporation of Fe(II) in
chitosan followed by oxidation [19], and layer by layer assembly [20]. However, most
of those methods are complex and require multistep preparation and purification.
Although adsorption of Cr(VI) on chitosan based materials has been reported in
several papers, there are still some limitations in the application of the chitosan based
materials because chitosan can be applied only in the acidic solution where –NH2
groups of chitosan are protonated. As increasing pH, amine groups become less active
towards Cr(VI). On the other hand, Cr(VI) discharged from industry to environments
could be present in solution with various pHs, for example tanning waste water in pH
3 (acid) [21], leachate waste water in pH 6-7 (near neutral) [22] and cooling tower
water and coal mine water in pH 9 (basic) [23,24]. Due to those reasons, magnetic
chitosan, which could be applied to the separation of Cr(VI) from waste water with
various pH, is strongly required.
For practical reasons, magnetic chitosan for the removal of Cr(VI) has to be
produced via a simple method, could be applied in the wider range of pH and
effective even in short contact time. With the focus of fulfilling these demands, we
developed a magnetic chitosan with simply a single step (one pot method).
Additionally, quarternization of the amine groups of magnetic chitosan by introducing
the pyridinium group was conducted in order to enhance the performance of magnetic
24
chitosan to adsorb Cr(VI) without pH-dependency. The adsorption characteristics
including kinetics and adsorption isotherm, and reusability were also evaluated.
2.2. Materials and Methods
2.2.1. Materials
Low molecular weight chitosan (molecular weight: 50-190 kDa) was
purchased from Sigma-Aldrich (Japan). Iron (II) chloride tetrahydrate (FeCl2�4H2O,
99-102%), iron (III) chloride hexahydrate (FeCl3�6H2O, ≥ 99%), 1,2-dibromoethane
(C2H4Br2, ≥ 98%), sulfuric acid (H2SO4, 95%), potassium chromate (K2CrO4, >99%)
and 1,5-diphenylcarbazide (C13H14N4O) were purchased from Wako Pure Chemical
Industries. Ltd (Osaka, Japan). Sodium hydroxide (NaOH), glacial acetic acid
(CH3COOH, 99%), glutaraldehyde solution (25 wt.%), ethanol (C2H5OH, 99.5%),
methanol (CH3OH, >99.8%), acetone (>99.5%), diethylenetriamine (C4H13N3, >98%)
and pyridine (C5H5N, ≥99.5%) were obtained from Junsei Chemical Co. Ltd. (Tokyo,
Japan). Hydrochloric acid (HCl, 35-37%) was purchased from Kanto Chemical Co.
Ltd. (Tokyo, Japan). All reagents were analytical grade and used without any prior
treatment.
2.2.2. One-pot preparation of magnetic chitosan (MC)
One gram of low molecular weight chitosan was dissolved in 50 mL of 3
vol.% acetic acid solution with sonication for 120 min. One gram of FeCl3�6H2O and
0.375 g of FeCl2�4H2O were added into the chitosan solution with continuous
sonication and then 10 mL of 25 wt.% glutaraldehyde solution were added drop-wise
into Fe2+/Fe3+-chitosan solution. The obtained red-brownish gel was soaked in 500
25
mL of 5 mol�L-1 NaOH solution for 25 min, washed with deionized water until the pH
reached to 7 and then was dried in freeze dryer FDU-1200 (EYELA, Japan) for 24 h.
2.2.3. Amination of magnetic chitosan with diethylenetriamine
Amination of MC with diethylenetriamine to obtain diethylenetriamine
functionalized magnetic chitosan (DFMC) was performed in two steps. First, one
gram of MC was immersed in 20 mL of methanol. 1,2-Dibromoethane (1.67 mL) was
added drop wisely into the mixture and the mixture was refluxed with continuous
stirring for 24 h. The solid product was separated by using an external magnet and
then washed with ethanol and deionized water several times. Next, the solid product
resulted from the first step was immersed in 20 mL methanol. Diethylenetriamine
(8.33 mL) was added to the mixture drop wisely. The mixture was refluxed for 24 h
with continuous stirring. The obtained product was separated with an external magnet,
washed with ethanol and deionized water several times and dried in an oven for 24 h
at 40 oC.
2.2.4. Quaternarization of diethylenetriamine functionalized magnetic chitosan
with pyridine
Quaterization of DFMC with pyridine to obtain PDFMC was performed in
two steps. First, one gram of DMFC was immersed in 20 mL of methanol. 1,2-
Dibromoethane (2.37 mL) was added into the mixture drop wisely. The mixture was
then refluxed for 24 h. The solid product was separated from the mixture using an
external magnet, washed with acetone and dried in an oven at 40 oC for 12 h.
Secondly, the solid product was stirred in 500 mL of 10 wt.% NaCl solution for 6 h
and then washed with deionized water, ethanol and acetone several times and then
26
dried at room temperature. The pyridinium functionalized magnetic chitosan (PFMC)
was prepared by the similar method to MC as a precursor instead of DMFC.
2.2.5. Characterization
Fourier transform infra-red (FTIR) spectra were measured on a FTIR 4100
(JASCO, Japan) using the KBr disc technique. X-ray diffractograms were recorded on
the Miniflex X-ray diffractometer (Rigaku, Japan) with Cu Kα radiation (λ 0.154 nm)
at 30 kV and 15 mA in the range of 10 – 70o. Morphological structures of adsorbents
were examined by using a scanning electron microscope (JSM-6360LA, JEOL,
Japan). The magnetic properties of adsorbents were investigated at room temperature
by using the magnetic performance measurement system (MPMS, Quantum Design,
Japan). Thermogravimetric analysis was performed on a Thermoplus TG 8210
(Rigaku, Japan). Samples were heated from room temperature to 500 oC at a rate of 5
oC�min-1 under constant helium flow. Carbon, hydrogen and nitrogen content were
measured by using a CHN Corder MT-6 Elemental Analyser (Yanaco, Japan). The
zeta potentials of adsorbents were measured using a DelsaTM Nano HC Zeta Potential,
which was equipped with a DelsaTM Nano AT Autotitrator (Backman Coulter Inc,
USA).
2.2.6. Adsorption of Cr(VI)
Adsorption tests were performed in a batch system on a Bioshaker VBR-36
(Taitec, Japan). Adsorbent 50 mg was added to 20 mL of 100 mg�L-1 Cr(VI) solution
at various pHs (from 2 to 10). The initial pH of Cr(VI) solution was adjusted with 0.1
mol�L-1 HCl solution or 0.1 mol�L-1 NaOH solution. The mixtures were shaken for 2 h
and the adsorbents were separated from the mixtures with an external magnet. The
27
remaining Cr(VI) ion in the solution was analyzed with a UV-Vis spectrophotometer
V-550 (JASCO, Japan) at 540 nm using diphenylcarbazide method, and the Cr(VI)
ion adsorbed was calculated using Eq.2.1.
𝑄 = (𝐶0 − 𝐶𝑒) ∙ 𝑉𝑊 (2.1)
Where Q represents the amount of Cr(VI) ion adsorbed on the adsorbent, C0 and Ce
are the initial and equilibrium concentration of Cr(VI) in the solution (mg�L-1),
respectively, V is the volume of Cr(VI) solution (L) and W is the weight of the
adsorbent (g).
The kinetics of adsorption was examined by varying the contact time from 5 to
80 min at a constant pH. The kinetics models such as pseudo-first order and pseudo-
second order were applied and the rate constants were calculated. Similar work was
carried out by varying the initial Cr(VI) concentration (in a range of 50-300 mg�L-1) to
determine the maximum adsorption capacity of each adsorbent. The Langmuir [25],
Freundlich [26] and Temkin [27] models were applied to evaluate the experimental
data.
The Freundlich isotherm model assumes that the surface of adsorbent is
heterogeneous and adsorption is multilayer interaction [26]. The Freundlich isotherm
model can be expressed as:
𝑞𝑒 = 𝑘𝐹(𝐶𝑒)1𝑛 (2.2)
where qe is the amount of Cr(VI) adsorbed per a mass unit of adsorbent at equilibrium
(mg�g-1); kF is the constant of Freundlich isotherm model related to adsorption
capacity; Ce is the concentration of Cr(VI) in solution at equilibrium (mg�L-1) and 1/n
is the dimensionless parameter which describes the intensity of adsorption.
28
The Langmuir isotherm model assumes that the surface is homogenous and
the adsorption takes place as a monolayer without any interaction between the
adsorbates [25]. The Langmuir isotherm model can be expressed as:
𝑞𝑒 = 𝑞𝑚.𝑘𝐿.𝐶𝑒1+(𝑘𝐿.𝐶𝑒) (2.3)
where qe is the amount of Cr(VI) adsorbed per a mass unit of adsorbent at equilibrium
(mg�g-1); kL is a constant of Langmuir isotherm model related to the affinity of the
binding sites and Ce is the concentration of Cr(VI) in solution at equilibrium (mg�L-1).
The Temkin isotherm model was developed by assuming: (1) due to the
interaction of adsorbate-adsorbate, the heat of adsorption decreases linearly rather
than logarithmically with the coverage and (2) the adsorption process is characterized
by a uniformed distribution of binding energies [27]. The Temkin model can be
expressed by:
𝑞𝑒 = 𝑞𝑚𝑎𝑥 ln(𝑘𝑇. 𝐶𝑒) (2.4)
Where qe is the amount of Cr(VI) adsorbed per a mass unit of adsorbent at
equilibrium (mg�g-1); kT is the binding constant of Temkin isotherm model (L�g-1) and
Ce is the concentration of Cr(VI) in solution at equilibrium (mg�L-1).
The effect of ionic strength on the removal of Cr(VI) was investigated by
shaking 20 mL of 100 mg�L-1 Cr(VI) solution containing 50 mg adsorbents at pH 3, 6
and 9 in the presence of NaCl for 2 h. The concentration of NaCl in Cr(VI) solution
was varied from 0.1 to 1 mol�L-1.
2.2.7. Desorption of Cr(VI)
Repeated adsorption-desorption steps were conducted to examine the
reusability of PDFMC, PFMC and MC. Adsorption experiments were performed by
contacting adsorbents with Cr(VI) solution at pH 3, 6 and 9 (volume: 20 mL,
29
adsorbents weight: 50 mg, the initial Cr(VI) concentration: 100 mg�L-1 and contact
time: 120 min). After equilibrium, the adsorbent was separated from solution by using
a magnet and then 20 mL of 10 wt.% NaCl in 0.01M NaOH solution which was
contacted with adsorbent to desorb Cr(VI). After each cycle, adsorbent was washed
with distilled water several times, followed with 10 wt.% NaCl solution.
2.3. Results and Discussion
2.3.1. Characteristics of pyridinium-diethylenetriamine functionalized magnetic
chitosan
2.3.1.1. Morphology
The synthesis route of PDFMC is shown in Scheme 2.1. The SEM images of
MC, PFMC and PDFMC is shown in Fig. 2.1. The structure of MC, PFMC and
PDFMC were examined by using X-ray diffractometer (XRD) and the results are
shown in Fig. 2.2. For MC, all diffraction peaks indicate the cubic spinel of Fe3O4
(JCPDS, No 79-0418). It indicates that the magnetic particle in the chitosan matrix is
Fe3O4. These results are in agreement with previously reported magnetite chitosan
prepared by different methods [28,29]. In comparison with MC, the diffraction peaks
of PFMC and PDFMC have no significant difference. It means that there is no change
in the structure of Fe3O4 during functionalization with pyridine.
In order to understand the amount of pyridinium groups in PDFMC, elemental
analysis (carbon, hydrogen and nitrogen) was performed and the results are listed in
Table 2.1. Introducing pyridinium groups in MC to obtain PFMC increased N amount
from 4.02% (2.9 mmol�g-1) to 4.94% (3.5 mmol�g-1), which was equal to 0.66 mmol
pyridinium�g-1. In order to increase the number of attached pyridinium, the amination
step was performed. Amination of MC to obtain diethylenetriamine (DETA)
30
functionalized magnetic chitosan (DFMC) has increased the amine number, equal to
1.18 mmol DETA�g-1.
Fig. 2.1 SEM images of MC (a), PFMC (b) and PDFMC (c).
Due to that reason, the amount of attached pyridinium on PDFMC is higher than that
of PFMC. The higher amount of attached pyridinium (1.76-2.13 mmol pyridinium�g-1)
on chitosan polymer prepared by the reaction of chitosan with alkyl pyridinium
halides has been reported by Kathalikkattil et al. [30]. The higher amount of attached
pyridinium in chitosan polymersynthesized by Kathalikkattil et al. [30] is due to a
higher amine group amount in chitosan polymer than on MC or DFMC.
a b
c
31
Scheme 2.1. Preparation of pyridinium functionalized magnetic chitosan.
32
Fig. 2.2. X-ray diffractograms of bare Fe3O4, MC, PFMC and PDFMC.
33
Table 2.1. Elemental compositions of MC, PFMC and PDFMC.
Adsorbent C (%) H (%) N (%) DETA
(mmol�g-1) Pyridinium (mmol�g-1)
Magnetite
(mg�g-1)
MC 37.74 6.56 4.02 - - 228.5
PFMC 39.33 6.48 4.94 - 0.66 219.3
DFMC 33.3 5.28 5.67 1.18 - 212.7
PDFMC 39.4 7.14 7.50 1.18 1.31 203.5
2.3.1.2. Magnetic properties
Magnetic properties of synthesized bare magnetite (Fe3O4), MC, PFMC and
PDFMC were examined by using MPMS and the results are shown in Fig. 3. The
magnetization of each sample reaches the maximum value when the applied magnetic
field is 10,000 Oe. The saturation magnetization (Ms) of Fe3O4, MC, PFMC and
PDFMC are 49; 15.6; 13.7 and 13.6 emu�g-1, respectively. The Ms value for Fe3O4 is
relatively lower than the reported magnetite (94.4 emu�g-1)[31]. It’s probably due to
the differences in size, shape and homogeneity of the magnetite surface [19]. MC has
a lower Ms value than that of bare Fe3O4 due to the presence of a thick chitosan
polymer layer. Fe3O4 particle in MC exhibits magnetic properties while chitosan layer
itself has no magnetic property. The Ms value of MC is slightly different with other
results in published reports [32,33]. Further modification of MC using pyridine to
obtain PFMC and diethylenetriamine followed by pyridine to obtain PDFMC has
decreased the magnetization value due to the presence of those non-magnetic organic
moieties in the surface.
34
Fig. 2.3. Magnetization (MH) curve of MC, PFMC and PDFMC (room
temperature).
-60
-40
-20
0
20
40
60
-10000 -7500 -5000 -2500 0 2500 5000 7500 10000
Mag
neti
zati
on (e
mu.
g-1)
Magnetic field (Oe)
Magnetite
MC
PFMC PDFMC
35
2.3.1.3. Fourier transform infrared (FTIR) spectra
For the spectra of MC, the characteristic band appeared at 1644 cm-1 (amide
I). The absorption band for –NH2 group appeared at 1539 cm-1. Vibration of –OH
group in pyranose ring appeared as a broadening peak around 3300 cm-1. Comparing
the FTIR spectra of MC and PDFMC, a peak at 1487 cm-1 can be observed in the
latter. This peak indicates C=C aromatic from pyridinium groups. Similar peaks also
appeared on the PFMC spectra, which indicate the presence of pyridinium groups.
2.3.1.4. Thermogravimetric analysis
Thermogravimetric analysis (TGA) was performed in a non-oxidizing
condition (He) to avoid the combustion effects of the samples in the presence of O2 at
high temperatures. TGA curves of bare Fe3O4, MC, PFMC and PDFMC are shown in
Fig. 2.4. The TGA curve of bare Fe3O4 shows that until the temperature reaches 500
oC, the mass loss of bare Fe3O4 is only about 6% due to the desorption of physically
and chemically adsorbed water molecules [34]. At the temperature below 200 oC, the
mass loss of MC, PFMC and PDFMC was 7-15% due to the evaporation of adsorbed
water molecules from the inner polymer [35]. The degradation of organic layers on
MC, PMFC and PDMFC begins at temperature 210-230 oC. This degradation is
related to the decomposition of organic moieties including pyridinium and
diethylenetriamine and the opening of the pyranose ring [36]. At the final
temperature (500 oC), the weight loss of MC, PFMC and PDFMC are 42, 45 and 50%,
respectively.
36
Fig. 2.4. TGA curve of synthesized bare Fe3O4, MC, PFMC and PDFMC.
2.3.2. Effect of pH on Adsorption of Cr(VI)
The effect of the initial pH of Cr(VI) solution on adsorption process is shown
in Fig. 2.5. The adsorption of Cr(VI) by MC has reached its maximum condition at
pH 2, decreasing with the increase of pH. Since the amino groups of chitosan are
protonated at a low pH, adsorption of Cr(VI) by chitosan based material mainly is due
to the electrostatic interaction [37]. This result can be interpreted that the adsorption
of Cr(VI) by MC is dependent on the pH of Cr(VI) solution. Previous studies by
Thinh et al. [29], Hu et al. [38] and Yu et al. [39] have shown similar results. On the
other hand, adsorption of Cr(VI) by PDFMC has no significant difference in the wider
range of pH. This result indicates that the adsorption of Cr(VI) by PDFMC was less
effected by the pH of Cr(VI) solution in comparison with MC and also PFMC. This
phenomenon can be explained that the pH of Cr(VI) affects both the speciation of
40
60
80
100
0 100 200 300 400 500
Wei
ght (
%)
Temperature (oC)
Magnetite
MC
PFMC
PDFMC
37
Cr(VI) and the surface charge of adsorbents (Fig. 2.5). Under high acidic condition,
Cr(VI) is stable as H2CrO4. As pH increases, the predominant species of Cr(VI) is
HCrO4- with Cr2O7
2- as coexisting species. In neutral and alkali conditions, the
predominant species of Cr(VI) are CrO42- and Cr2O7
2-. Adsorption of Cr(VI) by
PDFMC is favorable in the range of pH (2-11) due to the presence of pyridinium
moieties in its surface. Pyridinium moieties are quartenary amine which can bind
Cr(VI) through electrostatic interaction.
Fig. 2.5. Speciation of Cr(VI) and adsorption of Cr(VI) by MC, PFMC and PDFMC in various pH (Cr(VI) initial concentration: 100 mg�L-1, adsorbent dose: 2.5 g�L-1, contact time: 120 min).
The zeta potential measurement of MC, PFMC and PDFMC as the function of
pH is shown in Fig. 2.6. It has been shown that MC is positively charged in acidic
solution with the surface potential 18.88 mV at pH 3. This data indicate that amino
groups on the surface of MC are protonated. As increases of pH, the surface of MC
becomes less positively charged with 0 mV at pH 8.8 in comparison with MC. Both
0
0.2
0.4
0.6
0.8
1
0
20
40
60
80
100
0 2 4 6 8 10 12R
atio
of C
r(VI
) Spe
cies
Adso
rbed
Cr(
VI) (
%)
pHHCrO₄⁻ CrO₄²⁻ Cr₂O₇²⁻ H₂CrO₄
PFMC
PDFMC
MC
38
of PFMC and PDFMC are more positively charged and have zeta potential 26.3 mV
and 35.5 mV pH 3, respectively. This confirms the presence of pyridinium moiety,
which always has a positive charge in the wider pH region.
Fig. 2.6. Zeta potentials of MC, PFMC and PDFMC.
2.3.3. Adsorption kinetics study
Kinetics study was performed by examining the effect of contact time on
adsorption of Cr(VI) by MC, PFMC and PDFMC over the range from 5 to 180 min
with three initial pH (3, 6 and 9) of Cr(VI) solution. The adsorption capacity sharply
increased within the first five minutes and no significant increasing until 3 h. Pseudo-
-20
-10
0
10
20
30
40
0 2 4 6 8 10Zeta
Pot
entia
l (m
V)
pH
PDFMC
PFMC
MC
39
first order [40] and pseudo-second order [41] have been used to evaluate experimental
data for the investigation of the adsorption process of Cr(VI) by MC, PFMC and
PDFMC. Pseudo-first order can be expressed as follows:
𝑞𝑡 = 𝑞𝑒 (1 − 𝑒𝑥𝑝(−𝑘𝑝1𝑡)) (2.5)
Equation (2.5) can be linearized as:
𝑙𝑛(𝑞𝑒 − 𝑞𝑡) = 𝑙𝑛 𝑞𝑒 − (𝑘𝑝1. 𝑡) (2.6)
While pseudo-second order can be expressed as follows:
𝑞𝑡 = 𝑘𝑝2.𝑞𝑒2.𝑡1+(𝑞𝑒.𝑘𝑝2.𝑡) (2.7)
and can be linearized as:
𝑡𝑞𝑡
= ( 1𝑘𝑝2.𝑞𝑒2
) + 𝑡𝑞𝑒
(2.8)
qe and qt are the amounts of Cr(VI) adsorbed at equilibrium and time t, kp1 and kp2 are
pseudo-first and second order rate constant, respectively. The effect of contact time
on adsorption of Cr(VI) by MC, PFMC and PDFMA are shown in Fig. 2.7. The
parameters obtained by using each kinetics model are listed in Table 2.2.
40
Fig. 2.7. Effect of contact time on adsorption of Cr(VI) PDFMC at pH 3, pH 6 and pH
9 (Cr(VI) initial concentration: 100 mg�L-1, adsorbent dose: 2.5 g�L-1).
From the correlation coefficient and the qe value calculated from the pseudo-
first order are not in agreement with the experimental data. On the other hand, higher
correlation coefficient (≥0.999) can be obtained when the experimental data are
plotted to the pseudo-second order model. The adsorption capacities obtained from
the pseudo-second order model are closer to the experimental data. It can be
concluded that the adsorption of Cr(VI) by MC, PFMC and PDFMC follows the
pseudo-second order model. The suitability of the pseudo-second order on adsorption
of Cr(VI) by magnetic cellulose [42], alginate nanofiber [43], activated carbon [44],
montmorillonite clay [45] and biomass [46] have been reported. The PDFMC has a
30
35
40
45
50
0 30 60 90
Adso
rbed
Cr(
VI) (
mg.
g-1 )
Contact time (min)
pH 3 pH 6 pH 9
41
fine and rigid structure, moreover post-synthesis for functionalization formed the
active pyridinium groups in the vicinity of surface. The active pyridium groups on the
surface of PDFMC are available in the binding with Cr(VI) without a large barrier.
The electrostatic/ion-exchange mechanism and the specific structure of PDFMC
might lead to the fast removal rate of Cr(VI).
Table 2.2. The pseudo-first and second order kinetics model for adsorption of Cr(VI)
by MC, PFMC and PDFMC at different pH.
Adsorbent
s pH
Pseudo-first order Pseudo-second order
R2 qe
(mg�g-1)
kp1
(min-1) R2
qe
(mg�g-1)
kp2
(g�mg-1�min-1)
MC
3 0.892 1.56 0.010 1.000 39.6 0.072
6 0.069 2.45 0.003 0.996 26.2 0.051
9 0.090 2.76 0.003 0.952 16.3 0.008
PFMC
3 0.047 1.83 0.002 0.999 45.9 0.022
6 0.070 2.71 0.005 1.000 45.5 0.352
9 0.021 1.77 0.001 0.997 28.5 0.025
PDFMC
3 0.576 4.37 0.008 1.000 47.7 0.045
6 0.938 2.48 0.010 1.000 49.4 0.057
9 0.112 3.43 0.002 0.999 50.1 0.067
2.3.4. Adsorption isotherm study
In order to evaluate the adsorption capacity of MC, PFMC and PDFMC, the
widely used Freundlich, Langmuir and Temkin isotherm models have been applied in
this study. The interaction between Cr(VI) and the surface of MC, PFMC and
42
PDFMC could be understood by plotting the experimental data to the modeling data
as shown in Fig. 2.8.
The calculated parameters and linear regression coefficient (R2) value of each
isotherm model are shown in Table 2.3. The R2 value shows that the experimental
data of adsorption of Cr(VI) by MC, PFMC and PDFMC at pH 3, 6 and 9 are fitted
well with the Langmuir isotherm model. Lower R2 value had been obtained from the
Freundlich and Temkin isotherm models. From these data it can be considered that
the bonding sites on MC, PFMC and PDFMC are homogenous. Chi-square (x2)
analysis have been performed to select the optimum adsorption isotherm as suggested
by Ho [47]. The results obtained from chi-square analysis are in agreement with the
regression analysis, From these two analyses, it could be concluded that the
experimental data well suited with Langmuir model rather than Freundlich or Temkin
model.
43
Fig. 2.8. Non-linear Freundlich, Langmuir and Temkin isotherm for the adsorption of
Cr(VI) onto PDFMC.
As shown in Table 2.3, the monolayer adsorption capacity of MC, PFMC and
PDFMC decreases as the pH increases. In basic solution (pH 9), the monolayer
adsorption capacity of MC, PFMC and PDFMC are about a half of the monolayer
adsorption capacity in acidic solution (pH 3). The reason of this phenomena can be
explained by speciation of Cr(VI) on solution. In acidic solution, the predominant
species of Cr(VI) is HCrO4- while in basic solution is CrO4
2-. In acidic solution, a
pyridinium of PFMC/PDMC or an ammonium group of MC to adsorp HCrO4- is
required for adsorption of HCrO4-. On the other hand, to stabilize electrostatic
0
40
80
120
160
200
0 50 100 150 200
q e(m
g.g-
1 )
Ce (mg.L-1)
pH 3 pH 6 pH 9Langmuir Freudlich Temkin
44
interaction, two pyridinium or ammonium groups are required for a CrO42-. In the
other words, the interaction of Cr(VI) with PFMC/PDFMC depends on the speciation
of Cr(VI) since the surface of PFMC/PDFMC does not change significantly.
Table 2.3. The Freundlich, Langmuir and Temkin isotherm model parameters for adsorption of Cr(VI) by MC, PFMC and PDFMC at different pH.
Adsorbent pH Freudlich Langmuir Temkin
R2 KFa 1/n R2 KLb qmaxc R2 KTd qmaxe
MC
3 0.906 29.2 0.16 0.995 2.4 56.3 0.948 87.5 6.8
6 0.981 8.1 0.29 0.997 0.1 34.1 0.979 10.2 4.5
9 0.971 4.6 0.32 0.996 0.041 27.8 0.987 1.1 4.7
PFMC
3 0.962 38.9 0.21 0.996 1.4 80.3 0.986 30.64 11.9
6 0.950 29.1 0.15 0.989 0.822 55.6 0.982 289.1 5.5
9 0.928 27.1 0.12 0.997 14.4 45.7 0.970 969.3 4.1
PDFMC
3 0.994 19.2 0.54 0.999 0.073 175 0.967 2.2 26.1
6 0.954 20.3 0.38 0.992 0.087 123 0.990 1.1 23.8
9 0.949 22.8 0.27 0.993 0.185 86.5 0.982 3.9 13.5
a KF in (mg�g-1)(L�mg-1)1/n d KT in L�mg-1
b KL in L�mg-1 e qmax in mg�g-1
c qmax in mg�g-1
2.3.5. Comparison with other magnetic chitosan based adsorbents
In order to evaluate the performance the PDFMC to adsorp Cr(VI) ion, the
comparison with other magnetic chitosan based material has been done and listed in
Table 2.4. Due to the importance of its application, three parameters have been
compared namely with working pH, equilibrium time and maximum capacity (qmax).
45
The qmax of MC, which was synthesized via the one-pot method, toward Cr(VI) has
similar value with magnetic chitosan nanoparticle which was synthesized via co-
precipitation followed by the coating method [29]. Both of these two materials have
been applied in a similar acidic solution. However, MC reached the equilibrium state
20 times faster than magnetic chitosan nanoparticle did. PDFMC showed superior
features on the adsorption of Cr(VI) in acidic conditions compared to other
functionalized magnetic chitosan in terms of equilibrium time and qmax. The
adsorption mechanism of Cr(VI) ion onto the magnetic chitosan probably consist of
two steps: (1) mass transfer of the Cr(VI) ion from bulk solution onto the surface of
magnetic chitosan particles and (2) the binding of Cr(VI) with ammonium/pyridinium
group on the surface of adsorbent. Originally, the ammonium/pyridinium group exists
as an ion pair with Cl- ion, and then Cr(VI) ion that reached to the magnetic chitosan
will bind to ammonium/pyridinium group by the electrostatic interaction as replacing
Cl- (ion-exchange with Cr(VI) ion). The fast removal rate of Cr(VI) by PDFMC
should be attributed not only to the electrostatic/ion-exchange mechanism but also to
its structure. The PDFMC has a fine and rigid structure, moreover post-synthesis for
functionalization formed the active pyridinium groups in the vicinity of surface. The
active pyridium groups on the surface of PDFMC are available in the binding with
Cr(VI) without a large barrier. The electrostatic/ion-exchange mechanism and the
specific structure of PDFMC might lead to the fast removal rate of Cr(VI). In basic
solutions, quaternary ammonium magnetic chitosan reported by Elwakeel [48] has the
qmax value of 1.7 times larger than that with PDFMC and 3.2 times larger than that
with PFMC. It can be understood because quaternary ammonium magnetic chitosan
has higher amounts of active groups (ammonium group, 3.5 mmol�g-1) than PDFMC
(pyridinium, 1.3 mmol�g-1) and PFMC (pyridinium, 0.66 mmol�g-1). However, both of
46
PDFMC and PFMC can reach the equilibrium state 16 times faster than quaternary
ammonium magnetic chitosan does.
Table. 2.4. Comparison adsorption of Cr(VI) by MC, PFMC and PDFMC with other reported magnetic chitosan based materials.
No Adsorbent pH teq
(min)
qmax
(mg�g-1) Ref
1 Quarternary ammonium
magnetic chitosan
8 80 145 [48]
2 Magnetic chitosan-GO
nanoparticle
3 150 82.1 [49]
3 Magnetic chitosan
nanoparticle
3 180 55.8 [29]
4 Ethylenediamine magnetic
chitosan
2 6-10 51.8 [38]
5 Magnetic ionic
liquid/chitosan/graphene
oxide
3-4 40 145 [50]
6 Crosslinked magnetic
chitosan antranilic acid
glutaraldehyde Schiff base
2 120 58.4
[51]
7 PDFMC 3 5 175
This study 6 5 123
9 5 86.5
47
2.3.6. Effect of ionic strength
The effect of ionic strength on adsorption of Cr(VI) expressed in Fig. 2.9
showed that NaCl had a significant effect on adsorption of Cr(VI) by PDFMC. At pH
3, in the presence of 0.1 mol�L-1 NaCl, the ability of PDFMC to remove Cr(VI) from
the solution dropped from 98.3% to 75.8%, while at pH 6 and 9 the ability dropped to
70.8% and 50.5%, respectively. A similar trend was observed when MC and PFMC
were used as adsorbents in the place of PDFMC. As the NaCl concentration increases,
the ability of MC, PFMC and PDFMC to remove Cr(VI) decreased. It can be
explained that Cl- from dissolution of NaCl in solution competed with Cr(VI) to
interact with pyridinium and ammonium groups in the adsorbent surface. This result
indicates that ion exchange interaction is the mechanism of the removal process of
Cr(VI) by MC, PFMC and PDFMC.
2.3.7. Reuseability of pyridinium-diethylenetriamine functionalized magnetic
chitosan
Reusability of an adsorbent is important property for practical applications. In
this study, a mixture of the solution of 0.01 mol�L-1 NaOH-0.1 mol�L-1 NaCl was used
as a regeneration desorption agent. Adsorbed Cr(VI) can be released from PDFMC in
alkali and high ionic strength solutions due to the competition of OH- and Cl- with
Cr(VI), which weaken the Cr(VI)-pyridinium interaction. The PDFMC has the ability
to adsorp Cr(VI) from acidic, near neutral and basic solutions until 10 cycles without
any significant loss. Besides, more than 98% of PDFMC can be recollected easily
from each cycle by using an external magnet. This result indicates that PDFMC can
be used repeatedly for the removal of Cr(VI).
48
Fig. 2.9. Effect of NaCl on adsorption of Cr(VI) PDFMC at pH 3, pH 6 and pH 9
(Cr(VI) initial concentration: 100 mg�L-1, adsorbent dose: 2.5 g�L-1, contact time: 120
min).
2.4. Conclusions
Pyridinium group was successfully attached on MC to obtain PFMC and
PDFMC. The application of PFMC and PDFMC as adsorbents for Cr(VI) in acidic,
near neutral and basic conditions have been studied. The isotherm studies showed that
the Langmuir isotherm was the best model to describe the experimental data.
pH 9pH 6
pH 30
20
40
60
80
100
0 0.1 0.5 1
Adso
rbed
Cr(
VI) (
%)
Concentration of NaCl (mol�L-1 )
49
Adsorption processes were extremely fast to reach the equilibrium state within 5 min.
The kinetics studies showed that the experimental data fitted well with the pseudo-
second order model. Due to the presence of magnetite, both of PFMC and PDFMC
can be separated and recollected easily from the solution by a magnet. The adsorbent
could be regenerated by simply washing with NaCl in basic solution and both PFMC
and PDFMC could be used for five times without any significant loss of their
performances.
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[43] R. Karthik, S. Meenakshi, Removal of Cr(VI) ions by adsorption onto sodium
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[46] A.K. Giri, R. Patel, S. Mandal, Removal of Cr (VI) from aqueous solution by
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56
CHAPTER 3
A rapid magnetic separation of Cu(II) in aqueous solution
containing humic acid by dendrimerized magnetic chitosan
with a high reusability
57
Abstract
A second generation of dendrimerized magnetic chitosan (MCE-G2) has been
synthesized by using ethylenediamine as an amine source and methyl acrylate as a
bridging agent. The MCE-G2 was characterized by using a Fourier Transform Infra-
Red spectrophotometer (FTIR), an X-ray Difrractometer (XRD) and a Thermo
Gravimetric Analyzer (TGA). The morphology and the amount of nitrogen were
examined by using a Scanning electron microscope (SEM) and CHN analyser. The
magnetic property of MCE-G2 was investigated by using the Magnetic Property
Measurements System (MPMS). The kinetics of the removal of Cu(II) in the solution
was very fast and could reach the equilibrium stage within 5 min in the both of
absence and presence of humic acid in the solution. Based on the Langmuir isotherm
model, the qmax of MCE-G2 was 72.9 mg�g-1 and slightly increased by the presence of
humic acid in the solution. The regeneration studies showed that MCE-G2 could be
used to remove Cu(II) for 10 cycles without any significant decreases on its
performance. Due to the combination of its fast kinetics for the removal, easiness on
recollection and high regeneration features make the MCE-G2 as an economical and
effective as the magnetic material for removal of Cu(II).
58
3.1. Introduction
Increasing of industrial activities resulted in increase in the use heavy metals.
Due to their toxicities even at low concentration, the presence of heavy metal ions in
environmentals have been an important concern. Copper is one of the major heavy
metal pollutants in water. The sources of copper pollutant are effluents from mining
[1], electroplating [2] and printed circuit board industry [3]. Even though copper is
essential on human body as a micronutrient but at elevated level copper could be
considered as a toxin [4], a mutagen [5] and a carcinogen [6]. The permissible level of
Cu(II) in industrial effluent settled by the United States Environmental Protection
Agency (US EPA) is 13 mg�L-1 [7]. Chemical precipitation [8], ion exchange [9],
membrane filtration [10,11], flocculation [12] and adsorption [13] are the well known
technologies, which have been applied to remove Cu(II) ion in industrial effluents.
Adsorption is the most popular methods due to its high effectiveness in the removal of
Cu(II) to the permissible limits. However, adsorption has several disadvantages on the
removal of Cu(II) such as lower regeneration, lost of adsorbents and high cost on the
preparation of adsorbents.
Removal of heavy metal ion by using magnetic materials becomes popular
recently due to its better performance, especially in recollection after removal of
heavy metal ions in comparison with previous methods. Recollection of magnetic
materials can be performed easily and simply by using a magnet. Iron oxide,
especially magnetite (Fe3O4) is the most popular magnetic material for water
treatment. However, magnetite itself has a low affinity towards Cu(II) [14]. Coating
magnetite with a polymer such as chitosan is one method to enhance its performance
on removal of Cu(II).
59
Chitosan or poly(β-1-4)-2-amino-2-acetamido-2-deoxy-D-glucopyranose is a
biopolymer which is obtained from deacetylation of chitin or poly(β-1-4)-2-
acetamido-2-deoxy-D-glucopyranose. Chitin is the second most abundant biopolymer
in nature which could be found in crustaceans shells such as shrimp, crab and prawn
[15]. The high amount of amine group on its structure make chitosan bind Cu(II) ion
effectively via chelating [16]. However, recollection of chitosan after removal process
is difficult to be conducted and there is some possibility of the secondary pollution by
chitosan itself. Application of chitosan to the industrial water treatment has difficulty
due to the fouling effects.
Various methods have been proposed to synthesize magnetic chitosan, such as
one pot method [17], oxidation of Fe2+ in chitosan matrix [18], layer by layer
assembly [19] and direct coating via crosslinking [20]. However, all of those methods
require a crosslinking agent, for example glutaraldehyde, which consumes free amine
groups to connect one chitosan to others. In the other hand, the ability of magnetic
chitosan toward Cu(II) depends on the amount of amine group on its structure.
In this study, magnetic chitosan has been prepared by a coating method.
Magnetite was coated with chitosan, followed by crosslinking. In order to increase
the content of amine groups, dendrimerization with ethylenediame was repeatedtly
conducted. The adsorption behavior of MCE-G2 towards Cu(II) ion was evaluated in
batch experiments. The effect of pH, contact time and initial Cu(II) concentration
were investigated. The effect of humic acid in the solution on the kinetics and
isotherm of the adsorption behavior toward Cu(II) were also examined. Repeating
adsorption-desorption cycles of Cu(II) in the presence or absence of humic acid were
performed in order to investigate the reuseability of MCE-G2.
60
3.2. Materials and Methods
3.2.1. Materials
Chitosan (molecular weight: 50-190 kDa) was purchased from Sigma-Aldrich
(Japan). Magnetite (Fe3O4) was purchased from Kishida Kagaku (Osaka, Japan).
Glutaraldehyde solution (25 wt.%), methyl acrylate (C4H6O2, ≥99%),
ethylenediamine (C2H8N2, ≥99%), diethylenetriamine (C4H13N3, >98%), ethanol
(C2H5OH, 99.5%), sodium hydroxide (NaOH), glacial acetic acid (CH3COOH, 99%),
were obtained from Junsei Chemical Co. Ltd. (Tokyo, Japan). Hydrochloric acid
(HCl, 35-37%) was purchased from Kanto Chemical Co. Ltd. (Tokyo, Japan). Copper
(II) nitrate trihydrate (Cu(NO3)2�3H2O, 99.9%) was purchased from Wako Pure
Chemical Industries. Ltd (Osaka, Japan). Sodium salt of humic acid was purchased
from Aldrich (Milwaukee, USA). All reagents were used without any prior treatment.
3.2.2. Preparation of magnetic chitosan microparticle (MC)
Typically, one gram of low molecular weight chitosan was dissolved in 50 mL
of 3 vol.% acetic acid solution with sonication. Magnetite powder (Fe3O4, 0.75 g) was
added into the chitosan solution with continuous mechanically stirring and then 5 mL
of 25 wt.% glutaraldehyde solution was added drop wisely. The obtained black gel
was allowed to stand at room temperature for 24 h to achieve total formation of gel. It
was then rinsed with deionized water and dried in an freeze dryer FDU-1200
(EYELA, Japan).
3.2.3. Surface dendrimerization of magnetic chitosan with ethylenediamine
Dendrimerization of MC with ethylenediamine to obtain the first generation of
ethylenediamine functionalized magnetic chitosan (MCE-G1) was conducted as
61
follows: Firstly, one gram of magnetic chitosan was refluxed in 25 mL of 10 vol.%
methyl acrylate in ethanol solution for 3 days. The solid product was collected by a
magnet and washed with ethanol. Next, the solid product obtained from previous step
was refluxed in 25 mL of 15 vol.% ethylenediamine in ethanol solution for another
three days, separated by a magnet, washed with ethanol and deionized water and dried
in an freeze dryer. The second generation of ethylenediamine functionalized magnetic
chitosan (MCE-G2) was synthesized by repeating the two-steps above. The
diethylenetriamine functionalized magnetic chitosan (MCD) was also synthesized by
similar method with diethylenetriamine as a modifier instead of ethylenediamnie.
3.2.4. Characterization
Fourier transform infrared spectra of MC, MCS-G1, MCE-G2 and MCD were
recorded in a FTIR 4100 (JASCO, Japan) in the range 600 – 4000 cm-1 using KBr
disk technique. Surface morphology was examined by a scanning electron microscopy
(JSM-6360LA, JEOL, Japan). The X-ray diffractograms were collected on a Miniflex
X-ray diffractometer (Rigaku, Japan) operated at 30 kV and a current of 15 mA with
Cu-Kα radiation (λ= 0.154) in the range 10-70o. The adsorbent are further
characterized by the magnetic performance measurement system (MPMS, Quantum
Design, Japan) at room temperature. Thermogravimetric analysis was conducted on a
Thermoplus TG 8210 (Rigaku, Japan) operated from room temperature to 500 oC at a
rate of 5 oC�min-1 with constant flow of helium. The total carbon, hydrogen and
nitrogen contents were measured by CHN Corder MT-6 Elemental Analyzer (Yanaco,
Japan).
62
3.2.5. Adsorption of Cu(II)
Adsorption of Cu(II) ions was investigated by experiments in batch. About a
0.05 g of adsorbents was suspended into a 20 mL of 100 mg�L-1 Cu(II) solution and
equilibrated by using a Bioshaker VBR-36 (Taitec, Japan). The initial pH of Cu(II)
solution was adjusted by using 0.1 mol�L-1 of HNO3 or 0.1 mol�L-1 NaOH solution.
After reaching equilibrium state, the adsorbents were separated by using a magnet and
metal ion concentrations in supernatant solution before and after adsorption were
measured with a A-2000 Atomic Absorption Spectrophotometer (AAS, Hitachi,
Japan). The adsorption capacity of adsorbent (Q, mg�g-1) was calculated by a mass
balance relationship (Eq. 3.1)
𝑄 = (𝐶0 − 𝐶𝑒) ∙ 𝑉𝑊 (3.1)
where C0 and Ce are the initial and equilibrium concentration of Cu(II) in the solution
(mg�L-1), V is the volume of Cu(II) solution (L) and W is the mass of the adsorbents.
Similar batch experiments were conducted to study the effect of contact time (in the
range 1-180 min) and of the initial concentration of Cu(II) (in the range of 10-300
mg�L-1).
3.2.6. Effect of humic acid on adsorption of Cu(II)
The effect of humic acid (HA) on adsorption of Cu(II) was conducted by
equilibrating 0.05 g of adsorbent with 20 mL of 100 mg�L-1 Cu(II) solution containing
25 and 50 mg�L-1 of HA for 120 min. The adsorbent was separated by using a magnet
and the concentration of Cu(II) was measured by AAS.
63
3.2.7. Desorption of Cu(II)
For desorption experiments, 0.05 g of adsorbents were shaken with 20 mL of
100 mg�L-1 Cu(II) solution at pH 6 for 2 h. Cu(II)-adsorbents were magnetically
collected, rinsed with deionized water three times, and them suspended in 20 mL of
Na2EDTA and shaken for 2 h. The adsorbents were then rinsed with deionized water
three times and contacted again with the fresh solution of Cu(II). The amount of
Cu(II) in the supernatants was measured by AAS. This adsorption-desorption steps
was repeated several times to examine reusability of the adsorbents.
Scheme 3.1. Dendrimerization of magnetic chitosan.
64
3.3. Results and Discussion
3.3.1. Characteristics of dendrimerized magnetic chitosan microparticle
3.3.1.1. Morphology
The dendrimerization route of MC to obtain MCE-G1, MCE-G2 and MCD is
shown in Scheme 1. The morphology of magnetic chitosan before (MC) and after
dendrimerization (MCE-G1, MCE-G2 and MCD) were investigated by scanning
electrone microscopy which in Fig. 3.1. For MC, magnetite was dispersed in chitosan
matrix. The similar morphology were obtained after dendrimerization of MC to obtain
MCE-G1, MCE-G2 and MCD. The presence of magnetite in each adsorbent was also
investigated by X-ray diffractometry. Fig. 3.2 shows the comparative diffractogram of
the magnetic chitosan before (MC) and after dendrimerization (MCE-G1, MCE-G2
and MCD). All peak of diffractogram were analyzed and indexed by using the
database from Joint Committee on Powder Diffraction Standard (JCPDS). Peaks of
MC corresponded to (220), (311), (400), (422), (511) and (440) planes of Fe3O4
(JCPDS, No 79-0418). All of those peaks were in agreement with diffraction peaks of
the bare Fe3O4, indicating that Fe3O4 was successfully incorporated in chitosan
matrix. The similar results were obtained for MCE-G1, MCE-G2 and MCD. Based on
these results it can be concluded that Fe3O4 was stable during dendrimerization steps.
Comparative elemental analysis of MC, MCE-G1, MCE-G2 and MCD was
conducted. MC contained nitrogen (2.2 mmol�g-1) due to the existence of amino group
on chitosan structure. MCE-G1 and MCD contained 4.6 and 5.2 mmol�g-1 nitrogen,
respectively, due to the presence of ethylenediamine and diethylenetriamine in
addition of amine group of chitosan. The larger amount of nitrogen was contained in
the MCE-G2 (8.6 mmol�g-1), which confirmed that repeating step of dendrimerization,
increased the nitrogen content.
65
Fig. 3.1. SEM images of pure magnetite (a), chitosan (b), MC (c), MCE-G1 (d), MCD
(e) and MCE-G2 (f).
a b
c d
e f
66
Fig. 3.2. X-ray diffractograms of magnetic materials.
67
3.3.1.2. Fourier Transform Infrared (FTIR) and Thermogravimetric (TG) analyses
For the FTIR spectrum of Fe3O4 in Fig. 3.3, characteristic bands appeared at
1634 and 3432 cm-1 which were assigned to the stretching and vibration bending of
the hydroxyl group, respectively [21]. New peaks appeared on a spectra of MC at
1539 cm-1 and 1644 cm-1. The peak at 1539 cm-1 corresponded to –NH2 group and the
peak at 1644 cm-1 corresponded to amide I. Similar peaks also appeared in spectra of
MCE-G1, MCE-G2 and MCD because all of those adsorbents have similar peak
which mainly was –NH2 group.
Fig. 3.3. FTIR spectra of magnetic materials.
68
The TGA curves (Fig. 3.4) indicates that Fe3O4 is relatively stable up to 500 oC
with very small mass lost (<1%) due desorption of physically adsorbed water. From
Fig. 3.4, significant mass loss started at temperature 210-230 oC. Those mass losses
were due to the decomposition of organic moieties (ethylenediamine and
diethylenetriamine) and the opening of pyranose ring of chitosan matrix [22]. The
TGA results confirmed that the higher generation of the dendrimerization became, the
more amount the organic contents were.
Fig. 3.4. Themogravimetric analysis of magnetic materials.
69
3.3.1.3. Magnetic properties
Magnetic properties of Fe3O4, MC, MCE-G1, MCE-G2 and MCD were
measured at room temperature at the magnetic field ranging from -20.000 to 20.000
Oe. The saturation magnetization (Ms) value of Fe3O4 (46.8 emu�g-1) was relatively
lower than the theoretical value (96.4 emu�g-1) due to the differences in size, synthesis
method and inhomogeneity of surface [18]. Comparative magnetization curve (Fig.
3.5) showed that non-magnetic chitosan layer on MC decreased the Ms value in
comparation with Ms value of Fe3O4. Dendrimerization of MC by using
ethylenediamine and diethylenetriamine were also decreased the Ms value. The
decrease in Ms value was caused by the presence of non-magnetic organic moieties
on the surface of MCE-G1, MCE-G2 and MCD. The magnetic measurement
confirmed that the Ms value decrease when the dendrimerization was increased to
higher generation.
3.3.2. Effect of pH on adsorption of Cu(II)
The result of the removal performance of Cu(II) by MC, MCE-G1, MCE-G2
and MCD in aqueous solution with initial pH 1 until 8 are presented in Fig. 3.6. The
removal of Cu(II) in aqueous solution with higher pH than 8 was not conducted due to
the precipitation of Cu(II) to form Cu(OH)2. At lower pH, the removal efficiency of
Cu(II) was low due to the protonation of amine group of chitosan or dendrimer
brances. Protonated amine (-NH3+) has positive charge that could prevent Cu(II) ion
to approach the active site on surface of adsorbents via the electrostatic repulsion.
Hence at low pH, the removal of Cu(II) was less favorable. As the pH increases, the -
NH3+ group will be deprotonated and form –NH2 which made the electrostatic
repulsion between the surface of adsorbents and Cu(II) less attractive. Due to that
70
phenomenon, the removal of Cu(II) was favorable at higher pH. In order to avoid the
precipitation of Cu(II) at high pH and electrostatic repulsion at low pH, pH 6 was
selected for the further adsorption experiments.
Fig. 3.5. Magnetic property of magnetic materials.
71
Fig. 3.6. Adsorption of Cu(II) by magnetic material in various pH (Cu(II) initial
concentration: 100 mg�L-1, adsorbent dose: 2.5 g�L-1, contact time: 120 min)
0
20
40
60
80
100
0 2 4 6 8
Cu(
II) A
dsor
bed
(%)
pH
MC
MCE-G1 MCD
MCE-G2
72
3.3.3. Adsorption kinetics study
The adsorption kinetics study was conducted to understand the effect of the
contact time on removal performance of Cu(II) by MC, MCE-G1, MCE-G2 and
MCD. The kinetic experiments of adsorption were conducted at contact time varied 1
to 180 min. As shown in Fig. 3.7, more than 50% of Cu(II) in the solution could be
removed within 3 min. It was found that the adsorption equilibrium of Cu(II) could be
reached within 5 min and no significant increase could not be found on the
performance until 180 min.
Fig. 3.7. Adsorption of Cu(II) by magnetic material in various contact time (Cu(II)
initial concentration: 100 mg�L-1, adsorbent dose: 2.5 g�L-1, pH: 6)
0
10
20
30
40
50
0 50 100 150 200
Cu(
II) A
dsor
bed
(mg.
g-1)
Contact time (min)
MC
MCE-G1
MCD
MCE-G2
73
In order to understand the removal mechanism of Cu(II), the experimental
data were evaluated by two well-known kinetic models namely the pseudo-first order
(PFO, Eq. 3.2) and the pseudo-second order (PSO, Eq. 3.3) as represented below.
𝐿𝑛(𝑞𝑒 − 𝑞𝑡) = 𝐿𝑛 𝑞𝑒 − (𝑘𝑝𝑓𝑜 ⋅ 𝑡) (3.2)
𝑡𝑞𝑡
= ( 1𝑘𝑝𝑠𝑜⋅𝑞𝑒2
) + 𝑡𝑞𝑡
(3.3)
qe and qt are the amount of Cu(II) adsorbed at equilibrium and time t, kpfo and kpso are
the rate constant of the PFO and the PSO, respectively. The kinetics parameter of
PFO and PSO models were all listed in Table 3.1. Based on the analysis of the
correlation coefficients (R2), the experimental data shown higher linearity with PSO
model in comparison with PFO model. This results indicated that the removal of
Cu(II) followed PSO model rather than PFO model. The qe value obtained from PSO
model was relatively closer to the experimental result in comparison with qe value
obtained from PFO model. The short equilibrium time in removal of Cu(II) by MC,
MCE-G1, MCE-G2 and MCD indicated the high affinity of these materials toward
Cu(II).
74
Table 3.1 The pseudo-first and second order kinetics model for adsorption of Cu(II) by MC, MCE-G1, MCE-G2 and MCD
HA Concentration
(mg�L-1)
Pseudo-first order Pseudo-second order
R2 Qe (mg�g-1)
kpfo (min-1) R2 Qe
(mg�g-1) kpso
(g�mg-1�min-1)
MC 0 0.422 1.7 0.0245 0.999 6.1 0.080 25 0.535 2.6 0.0284 1 9.1 0.0456 50 0.713 3.1 0.0352 1 11.3 0.0388
MCE-G1 0 0.703 9.4 0.0250 1 32.3 0.020 25 0.651 6.8 0.0381 1 37.1 0.0177 50 0.360 4.4 0.0221 1 38.3 0.0165
MCE-G2 0 0.688 12.5 0.0265 1 47.6 0.0138 25 0.344 4.8 0.0218 1 50.1 0.0107 50 0.480 5.5 0.0278 1 51.2 0.0100
MCD 0 0.721 11.4 0.0254 1 37.1 0.0161 25 0.304 4.3 0.0184 1 41.4 0.0149 50 0.450 6.1 0.0309 1 44.8 0.0138
3.3.4. Adsorption isotherm study
In preparation of dendrimerized magnetic chitosan, two types of amine
compound namely ethylendiamine and diethylenetriamine were used as modifiers.
The effect of different dendrimerization of the magnetic chitosan generation on
adsorption performance was also examined. The experimental data were evaluated
with two well known isotherm models namely the Freundlich and the Langmuir
models. The Langmuir model assumes that the adsorbent is structurally homogenous
and the adsorption can take a place as a monolayer without any interactions between
adsorbates. The Langmuir model can be described as follows:
75
𝐶𝑒𝑞𝑒
= 1𝐾𝐿•𝑞𝑚𝑎𝑥
+ 𝐶𝑒𝑞𝑚𝑎𝑥
(3.4)
where qe is the amount of Cu(II) ions adsorbed at the equilibrium (mg�g-1), Ce is the
concentration of Cu(II) ion in solution at the equilibrium (mg�L-1), qmax is the
maximum adsorption capacity of the adsorbent (mg�g-1) and KL is the Langmuir
adsorption constant (L�mg-1).
The Freundlich adsorption model is usualy used to describe the heterogenous
adsorption mechanism:
𝐿𝑛 𝑞𝑒 = 𝐿𝑛 𝑘𝐹 + 𝑛−1 𝐿𝑛 𝐶𝑒 (3.5)
where qe is the amount of Cu(II) ions adsorbed at the equilibrium (mg�g-1), Kf is the
constant of the Freundlich isotherm model which is related to adsorption capacity, n-1
is a dimensionless parameter which describes the intensity of adsorption and Ce is the
concentration of Cu(II) ions in solution at the equilibrium (mg�L-1). The fitting of
experimental data with the Freundlich and the Langmuir model was represented in
Tabel 3.2. The fitting results showed that the correlation coefficient (R2) of the
Langmuir model was higher than that of the Freundlich models. This results indicated
that the adsorption of Cu(II) by dendrimerized magnetic chitosan tough placed as
monolayer interaction. The maximum adsorption capacity of MC, MCE-G1, MCE-G2
and MCD based on Langmuir model was 29.1; 54.1; 58.4 and 72.9 mg�L-1,
respectively.
The first generation of magnetic chitosan dendrimerized with ethylenediamine
(MCE-G1) and with diethylenetriamine (MCD) showed slightly different results on
maximum adsorption capacity towards Cu(II) ion (qmax,MCD = 1.08 qmax, MCE-G1). This
is because the amount of nitrogen in MCD is almost the same to that in MCE-G1
([N]MCD = 1.11 [N]MCE-G1). The amount of adsorbed Cu(II) by dendrimerized
magnetic chitosan depended on the amount of nitrogen on the structure. In
76
comparison with MCE-G1, MCE-G2 showed higher maximum adsorption capacity
towards Cu(II) (qmax,MCE-G2 = 1.35 qmax, MCE-G1) due to the higher amount of amine
groups on its structure. By compraring the qmax and the amount of nitrogen, repeated
dendrimerisation with ethylenediamine resulted dendrimerised magnetic chitosan with
higher amount of nitrogen and qmax toward Cu(II) than one step dendrimerisation with
longer amine compound (diethylenetriamine).
Table 3.2 Freundlich, and Langmuir isotherm parameters for adsorption of Cu(II) by MC, MCE-G1, MCE-G2 and MCD in the presence of humic acid.
HA Concentration
(mg�L-1)
Freundlich Langmuir
R2 1/n Kfa R2 qmaxb Klc
MC 0 0.967 0.36 3.74 1 29.1 0.035 25 0.986 0.46 2.83 0.999 32.1 0.03 50 0.987 0.51 2.53 0.993 35.3 0.026
MCE-G1 0 0.977 0.38 7.23 1 54.1 0.044 25 0.972 0.40 8.31 0.999 63.4 0.039 50 0.981 0.44 6.88 0.999 67.3 0.034
MCE-G2 0 0.974 0.32 14.42 0.999 72.9 0.076 25 0.985 0.36 12.95 1 82.7 0.046 50 0.986 0.45 9.44 1 87.9 0.042
MCD 0 0.973 0.35 9.45 1 58.4 0.056 25 0.98 0.43 7.44 0.998 65.2 0.040 50 0.981 0.46 7.33 0.999 72.9 0.037
a Kf in (mg�g-1)(L�mg-1)1/n bqmax in mg�g-1 cKl in L�mg-1
3.3.5. Effect of humic acid on adsorption of Cu(II) by MCE-G2
Adsorption kinetics of Cu(II) with MCE-G2 in the absence and presence of
humic acid are shown in Fig. 3.8. It was found that more than 50% of Cu(II) in
77
solution could be removed by MCE-G2 within 3 min and the equilibrium state was
reached within 5 min. In the presence of humic acid, the equilibrium state was also
reached within 5 min. The experimental data were well fitted to the pseudo second-
order model rather than to the pseudo first-order model. The dendrimerised magnetic
chitosan has the high affinity toward Cu(II) in the solution regardless of with or
without humic acid. The experimental data of adsorption isotherm of Cu(II) in the
presence of humic acid were evaluated by using both of the Langmuir and the
Freundlich model. In the presence of humic acid, the experimental data were well
fitted to the Langmuir model rather than to the Freundlich model. According to the
Langmuir model (Tabel 3.2), the qmax of MCE-G2 toward Cu(II) slightly increases by
increasing of concentration humic acid in the solution. The qmax value increased from
72.9 mg�g-1 (0 mg�L-1 of humic acid), to 87.9 mg�g-1 (50 mg�L-1 of humic acid). The
effect of humic acid on Cu(II) adsorption by MCE-G2 could be described as follows
Firstly, HA forms a complex with Cu(II) via chelating with the carboxylate groups.
Next, as the humic-acid-Cu(II) complex was formed, the free carboxylate groups will
interact with protonated amine group of MCE-G2 via the electrostatic interaction so
than MCE-G2-(humic acid-Cu(II)) complex was formed. The comparison of
dendrimerised magnetic chitosan with other chitosan based adsorbents was listed in
Table 3.3.
78
Fig. 3.8. Effect of contact time on adsorption of Cu(II) by MCE-G2 in the presence of
humic acid (Cu(II) initial concentration: 100 mg�L-1, adsorbent dose: 2.5 g�L-1,
pH: 6)
0
20
40
60
0 50 100 150 200
Cu(I
I) A
dsor
bed
(mg.
g-1)
Contact time (min)
0 ppm HA25 ppm HA50 ppm HA
79
Fig. 3. 9. Isotherm adsorption of Cu(II) by MCE-G2 in the presence of humic acid
(Cu(II) initial concentration: 100 mg�L-1, adsorbent dose: 2.5 g�L-1, pH: 6)
0
20
40
60
80
100
0 100 200
Qe(
mg�
g-1)
Ce (mg� L-1)
0 ppm HA25 ppm HA50 ppm HALangmuirFreundlich
80
Table 3.3 Comparison of adsorption of Cu(II) by MCE-G2 with other reported chitosan based materials.
No Adsorbents Teq
(min)
qmax
(mg�g-1) Ref
1 Α-ketoglutaric chitosan-magnetic
nanoparticle 180 96.1 [23]
2 Thiourea modified magnetic chitosan
microsphere 180 66.7 [24]
3 Chitosan coated sand 240 8.2 [25]
4 Macroporous chitosan membrane 1440 19.9 [26]
5
Saccharomyces cerevisiae
Immobilized on chitosan coated
magnetic nanoparticle
60 144.9 [27]
6 Crossslinked magnetic chitosan beads 60 78.1 [28]
7 MCE-G2 5 72.9 This work
3.3.6. Reuseability of dendrimerized magnetic chitosan
In order to evaluate the feasibility of dendrimerized magnetic chitosan in
practical use, the regeneration and reuse experiment were conducted. Solution of 0.1
mol�L-1 EDTA, 0.1 mol�L-1NaOH and deionized water were used as desorption agent.
The EDTA solution was used to extract the Cu(II) from humic acid. Since the
interaction of humic acid with dendrimerized magnetic chitosan was via the
electrostatic interaction, the NaOH solution was used to weaken the electrostatic
interaction. The MCE-G2 could adsorp Cu(II) in aqueous solution with or without the
presence of humic acid until 10 cycles without any significant loss on its
81
performance. In other hand, almost all of MCE-G2 could be recollected by using an
external magnet.
For the preparation of magnetic chitosan, low molecular magnetic chitosan
(USD 577.3 kg-1) and magnetite (USD 28.36 kg-1) and glutaraldehyde (USD 33.37
kg-1) were used. In order to enhance the adsorption performance, dendrimerization
steps were conducted using ethylenediamine (USD 34.37 kg-1) and methyl acrylate
(USD 38.40 kg-1). The resulted product, dendrimerised magnetic chitosan, could
remove almost all of Cu(II) ion in the solution just within 5 min which requires much
less process cost. The MCE-G2 has maximum adsorption capacity of 2.5 times higher
than undendrimerised magnetic chitosan. Moreover, the MCE-G2 could also be used
for 10 cycles of adsorption-desorption without any significant decrease on its
performance. Considering the fast adsorption kinetics, high regeneration and cheap
preparation cost, the dendrimerised magnetic chitosan could be considered as an
economical adsorbent for Cu(II).
3.4. Conclusions
Dendrimerization of MC to obtain MCE-G1, MCE-G2 and MCD was
successfully conducted. The removal performance of dendrimerized magnetic
chitosan toward Cu(II) ion in the presence and absence of humic acid were examined.
The kinetic data showed that the equilibrium state was reached within 5 min and the
experimental data were well fitted to the pseudo-second order model. The removal of
Cu(II) with the dendrimerized magnetic chitosan was well described by the Langmuir
model. In the presence of humic acid in the solution, the qmax value of dendrimerized
magnetic chitosan was slightly increased. After reaching the equilibrium state, the
82
dendrimerized magnetic chitosan could be recollected easily by using a magnet and
could be used for 10 cycles of adsorption-desorption without any significant loss.
3.5. References
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(II) on nanoscale magnetite in aqueous solutions, Desalination. 276 (2011)
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functionalized by grafting: Synthesis and characterization, Chem. Eng. J. 203
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characterization of biobased magnetic nanoparticles double coated with dextran
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chitosan grafted with graphene oxide to enhance adsorption properties for
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[24] L. Zhou, Y. Wang, Z. Liu, Q. Huang, Characteristics of equilibrium, kinetics
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[25] M.-W. Wan, C.-C. Kan, B.D. Rogel, M.L.P. Dalida, Adsorption of copper (II)
and lead (II) ions from aqueous solution on chitosan-coated sand, Carbohydr.
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[26] a. Ghaee, M. Shariaty-Niassar, J. Barzin, a. Zarghan, Adsorption of copper and
nickel ions on macroporous chitosan membrane: Equilibrium study, Appl. Surf.
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[27] Q. Peng, Y. Liu, G. Zeng, W. Xu, C. Yang, J. Zhang, Biosorption of copper(II)
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[28] G. Huang, C. Yang, K. Zhang, J. Shi, Adsorptive Removal of Copper Ions
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86
CHAPTER 4
A novel quaternized dendrimer magnetic chitosan for a
rapid magnetic separation of humic acid in aqueous solution
87
Abstract
A quaternary ammonium second generation of dendrimerized magnetic
chitosan (QAMCE-G2) has been synthesized and employed for magnetic separation
of humic acid in the solution. QAMCE-G2 was characterized by using an X-ray
diffractometer (XRD), a scanning electron microscope (SEM), a Fourier transform
infrared sprectofotometer (FTIR) and a thermogravimetric analyzer (TGA). The
amount of quaternary ammonium group (QA) on its surface was measured by using
the CHN analyzer. The QAMCE-G2 could remove humic acid in the wider range of
pH in comparison with the MC. The removal rate was very fast and reached the
equilibrium within 10 min. The experimental data were well fitted to the Langmuir
isotherm model with the qmax: 77 mg�g-1. The saturated QAMCE-G2 could be
separated from the mixture easily by using a magnet. The regeneration study showed
that the QAMCE-G2 could be used for the magnetic separation of humic acid up to 10
times without any significant loss.
88
4.1. Introduction
Humic acid is one of widespread macromolecule on the earth. Together with
fulvic acid and humin, humic acid is the core of humic substances. It is produced from
the decomposes of natural organic matters. Humic acid consists of hydroxyphenyl,
hydroxybenzoic acid polymer and other aromatic substances [1], which are connected
with carbohydrate, fatty acid and peptides [2]. Humic acid has various types of
functional groups both of hydrophobic and hydrophilic group such as carboxylic,
hydroxyl, phenolic, carbonyl together with aromatic and aliphatic carbon in a
complex structure. Humic acid can be found in aquatic environment as well as in soil
[3]. The presence of humic acid in water could alter watercolor to yellowish-brown.
It’s not directly toxic but humic acid can form carcinogenic disinfectant by products
(DBPs) such as trihalomethan and haloacetic during chlorination of drinking water
[4]. The DBPs causes dizziness, headache and central nervous problems even in the
shortime exposure [5]. The United States of America-Environmental Protection
Agency (US-EPA) sets the permissible level of DBPs on drinking water to not exceed
0.08 mg�L-1 [6]. Due to the existence of various organic group on its structure, humic
acid could bind heavy metal ion in water [7,8], change its speciation [9,10] and
facilitate the distribution of heavy metal ion in water system. The United States
Environmental Protection Agency (US-EPA) set the maximum level of humic acid in
the drinking water, which should not exceed 2 mg�L-1. Moura et al. [11] and Imai et
al. [12] also reported that humic acid would present (3-28%) in the effluents from
industrial wastewater treatment. As a result of its ubiquity and effects on human
health, the treatment and removal of humic acid in the water become a big concern.
89
Fig. 4.1. Structure of humic acid.
Various technologies including chemical coagulation [13,14], membrane
separation [15,16], ion exchange [17] and adsorption [18] have been applied on
remediation of humic acid in water and wastewater. Even though chemical
coagulation has been adopted industrially, it requires high amount of chemicals, high
cost on its operation and regenerates huge amount of sludge. Membrane fouling by
humic acid becomes other issues on removal of humic acid by membrane technology
[19]. Membrane fouling by humic acid sometime shortens the lifetime of membrane
and requires frequent cleaning of the system. Adsorption is one of the most effective
methods on removal of humic acid. Due to its simplicity and cost-effectiveness,
adsorption of humic acid has been adopted industrially. Many adsorbents such as
activated carbon [20], clay [21–23], metal oxides [24], activated sludge [25], silica
[26,27] and chitosan [28,29] showed the affinity toward humic acid. However,
separation of saturated adsorbents after removal process would be time consuming
and difficult to be performed. Since humic acid could not be removed completely by
90
conventional method, developing a new technology to remove humic acid in water
effectively should be done.
Magnetic separation is one of alternative method to remove humic acid in
water. Due to its magnetic property, magnetic materials can be separated from non-
magnetic material by applying external magnetic field. The development of magnetic
separation relies on the development of magnetic material. Iron oxides such as Fe3O4,
Fe2O3, CuFe2O4 and ZnFe2O4 are widely used as a core of magnetic adsorbent.
Polymers such as chitosan, alginate [30] and silica [31,32] were applied as coating
materials. Chitosan, which is obtained from chitin attracts much attention as a coating
polymer due to its biodegradability, availability, non-toxicity and high content of
amine group. Magnetic chitosan and its modification products were successfully
applied for magnetic separation of heavy metal ion such as Cd [33], Cu [34], Cr [35],
Hg [36] and also some dyes [37–39].
Electrostatic interaction between solid materials with negatively charged
humic acid is reported to play the main role on removal of humic acid in water. In this
study, positively charged magnetic chitosan was synthesized by introducing
trimethylammonium groups on the surface of dendrimer modified magnetic chitosan.
The magnetic materials were characterized and apllied for removal of humic acid in
solution. The repeating adsorption-desorption were also conducted to evaluate its
regeneration factor.
4.2. Materials and Methods
4.2.1. Materials
Chitosan (molecular weight: 50-190 kDa) and glycidyltrimethylammonium
chloride (GTMAC, C6H14ClNO, ≥90%) were purchased from Sigma-Aldrich (Japan).
91
Magnetite (Fe3O4) was purchased from Kishida Kagaku (Osaka, Japan).
Glutaraldehyde solution (25 wt.%), methyl acrylate (C4H6O2, ≥99%),
ethylenediamine (C2H8N2, ≥99%), ethanol (C2H5OH, 99.5%), sodium hydroxide
(NaOH), glacial acetic acid (CH3COOH, 99%), were obtained from Junsei Chemical.
Co. Ltd. (Tokyo, Japan). Hydrochloric acid (HCl, 35-37%) was purchased from
Kanto Chemical Co. Ltd. (Tokyo, Japan). Sodium salt of humic acid was purchased
from Aldrich (Milwaukee, USA). All reagents were used without any prior treatment.
4.2.2. Quaternization of diethylenetriamine functionalized magnetic chitosan
with GTMAC
The quaternarization of MCE-G2 was performed as follows: a gram of the
MCE-G2 was immersed in 22.5 mL of 50 vol.% of ethanol. The GTMAC (2.5 mL)
was added into the mixture drop wisely. The mixture was stirred at room temperature
for 30 min followed by refluxing for 48 h. The obtained QAMCE-G2 was separated
from the mixture by using a magnet, washed with ethanol and water for several times
and dried at 40 °C for overnight.
4.2.3. Characterization
Fourier Transform Infra-Red (FTIR) spectra were measured by a FTIR 4100
(JASCO, Japan) using the KBr disc technique. X-Ray diffractograms were recorded
on the Miniflex X-ray Diffractometer (Rigaku, Japan) with Cu Kα radiation (λ 0.154
nm) at 30 kV and 15 mA in the range of 10 – 70o. Morphological structures of
adsorbents were examined by using a Scanning Electron Microscope (JSM-6360LA,
JEOL, Japan). Thermogravimetric analysis was performed by a Thermoplus TG 8210
(Rigaku, Japan). Samples were heated from room temperature to 500 oC at a rate of 5
92
oC�min-1 under the constant helium flow. Carbon, Hydrogen and Nitrogen content
were measured by using CHN Corder MT-6 Elemental Analyser (Yanaco, Japan).
The zeta potentials of adsorbents were measured using a DelsaTM Nano HC Zeta
Potential, which was equipped with a DelsaTM Nano AT Autotitrator (Backman
Coulter Inc, USA).
4.2.4. Adsorption of humic acid
Magnetic separation tests were performed in a batch system by a Bioshaker
VBR-36(Taitec, Japan). The QAMCE-G2 (50 mg) was added to 20 mL of 100 mg�L-1
humic acid solution at various pHs (from 2 to 8). The initial pH value of humic acid
solution was adjusted with 0.1 mol�L-1 HCl solution or 0.1 mol�L-1 NaOH solution.
The mixtures were shaken for 2 h and the QAMCE-G2 were separated from the
mixtures using an external magnet. The remaining humic acid in the solution was
analyzed with a UV-Vis spectrophotometer V-550 (JASCO, Japan) at 254 nm and the
humic acid adsorbed was calculated using Eq. 4.1.
𝑄 = (𝐶0 − 𝐶𝑒) ∙ 𝑉𝑊 (4.1)
where Q represents the amount of Cr(VI) ion adsorbed on the QAMCE-G2, C0 and Ce
are the initial and equilibrium concentration of humic acid in the solution (mg�L-1),
respectively, V is the volume of humic acid solution (L) and W is the weight of the
QAMCE-G2 (g).
The kinetics of adsorption was examined by varying the contact time from 5 to
80 minutes at a constant pH. The kinetic models such as the pseudo-first order (PFO)
[40] and the pseudo-second order (PSO) [41] models were applied and the rate
constants were calculated. Similar work was carried out by varying the initial humic
acid concentration (in a range of 50-300 mg�L-1) to determine the maximum
93
adsorption capacity of each adsorbent. The Langmuir [42] and Freundlich [43]
models were applied to evaluate the experimental data.
The Freundlich isotherm model assumes that the surface of adsorbent is
heterogeneous and adsorption is multilayer interaction [43]. The Freundlich isotherm
model can be expressed as:
𝑞𝑒 = 𝑘𝐹(𝐶𝑒)1𝑛 (4.2)
where qe is the amount of humic acid adsorbed per a mass unit of adsorbent at
equilibrium (mg�g-1); kF is the constant of Freundlich isotherm model which related to
adsorption capacity; Ce is the concentration of humic acid in solution at equilibrium (
mg�L-1) and 1/n is the dimensionless parameter which describes the intensity of
adsorption.
The Langmuir isotherm model assumes that the surface is homogenous and
the adsorption takes place as a monolayer without any interaction between the
adsorbates [42]. The Langmuir isotherm model can be expressed as:
𝑞𝑒 = 𝑞𝑚.𝑘𝐿.𝐶𝑒1+(𝑘𝐿.𝐶𝑒) (4.3)
where qe is the amount of humic acid adsorbed per a mass unit of adsorbent at the
equilibrium (mg�g-1); kL is a constant of Langmuir isotherm model related to the
affinity of the binding sites and Ce is the concentration of Cr(VI) in solution at the
equilibrium (mg�L-1).
94
4.2.5. Desorption of humic acid
Repeated adsorption-desorption steps were conducted to examine the
reusability of QAMCE-G2. Adsorption experiments were performed by contacting
magnetic material with humic acid solution at pH 6 (volume: 20 mL, adsorbents
weight: 50 mg, the initial humic acid concentration: 100 mg�L-1 and contact time: 120
min). After equilibrium, the adsorbent was separated from solution by using a magnet
and then contacted with 0.1M NaOH-0.1 M NaCl solution to leach humic acid. After
each cycle, the adsorbent was washed with distilled water several times followed with
deionized water.
Scheme 4.1. Preparation of quaternary ammonium magnetic chitosan materials.
95
4.3. Results and Discussion
4.3.1. Characteristics of quaternized diethylenetriamine functionalized magnetic
chitosan
4.3.1.1. Morphology
The preparation of QAMCE-G2 is shown in Scheme. 4.1. The surface
morphology of QAMCE-G2 was investigated by SEM (Fig. 4.2). The QAMCE-G2
has an irregular shape. It’s shown that the Fe3O4 was entrapped in chitosan polymer
layer. In comparison with the magnetite, the QAMCE-G2 has a similar shape. The
structure of the QAMCE-G2 was investigated by using XRD and the result is shown
in Fig. 4.3. All peaks were indexed based on the Joint Committee of Powder
Diffraction (JCPDs) database and it’s shown that all peaks of the QAMCE-G2 were
consistent with cubic spinel of Fe3O4 (JCPDs No 79-0418). In comparison with the
magnetite, the QAMC and the QAMCE-G1, the diffraction pattern of the QAMCE-
G2 had no significant different. These results indicated that the Fe3O4 core was stable
during dendrimerization and quaternarization step.
Fig. 4.2. SEM images of MC (a), QAMC (b), QAMCE-G1(c) and QAMCE-G2 (d).
a b
c d
96
In order to measure the amount of attached quaternary ammonium group (QA)
on the magnetic materials, the carbon, nitrogen and hydrogen analyses were
conducted. Quaternarization of the MC to obtain the QAMC increased the amount of
nitrogen from 3.04% to 4.33%, which is equal to 0.92 mmol QA�g-1. A higher amount
of QA attached on MCE-G1 and MCE-G2 to obtain QAMCE-G1 (1.74 mmol QA•g-1
) and QAMCE-G2 (2.35 mmol QA�g-1), respectively. This is because the MCE-G2
had a higher amount of amine group to react with GTAMC in comparison with the
MC and MCE-G1. This result confirmed that dendrimerization of MC to the higher
generation increased the number of attached quaternary ammonium group.
Fig. 4.3. X-ray diffractogram of magnetic materials.
Magnetite
QAMC
QAMCE-G1
QAMCE-G2
97
4.3.1.2. Fourier Transform Infrared (FTIR) Spectra
The FTIR spectra of the MC, the QAMCE-G1 and the QAMCE-G2 are shown
in Fig. 4.4. The broaden peak around 3291 cm-1 was associated to N-H stretching
overlapped with O-H stretching. Peaks at 1633 cm-1 and 1552 cm-1 were corresponded
to amide I and II, respectively. The presence of Fe3O4 was confirmed by the presence
of peak around 560 cm-1, which corresponded to the Fe-O bond. In comparison with
the spectrum of the MC, a new peak appeared at 1473 cm-1 on FTIR spectra of
QAMC, QAMCE-G1 and QAMCE-G2. This new peak corresponded to the
asymmetric bending of C-H of QA group[44]. The appearance of a peak around 1470
cm-1 indicated that quaternarization with GTAMC was successfully performed.
Fig. 4.4. FTIR spectra of magnetic materials
98
Tabel 4.1. Elemental composition of magnetic materials
ADSORBENT C (%) H (%) N (%) Quaternary ammonium Fe3O4
(mmol�g-1) (mg�g-1) Magnetite nd nd nd - 999.7 MC 31.07 4.96 3.04 - 317.6 QAMC 31.98 4.95 4.33 0.92 316 QMCE-G1 36.59 6.83 9.01 1.74 310.7 QAMCE-G2 42.72 9.78 15.31 2.35 305
4.3.1.3. Thermogravimetric analysis
Thermogravimetric analysis of the magnetite the MC, the QAMCE-G1 and
the QAMCE-G2 was performed under the inert condition (He) to avoid combustion of
organic moeities at higher temperature. The TGA curves of all magnetic materials are
shown in Fig. 4.5. In Fig. 4.5, It’s shown that the magnetite was relatively stable up to
500 °C. The small weight lost of magnetite (0.05%) occurred due to desorption of
physically adsorbed water [45]. Desorption of water molecules was also observed for
the MC, QAMCE-G1 and QAMCE-G2 below 200 °C. The further degradation of
MC, QAMCE-G1 and QAMCE-G2 started at 230 °C which were related with the
degradation of organic moieties (dendrimer and QA) and opening of pyranose ring of
chitosan [46]. At final temperature, the QAMCE-G2 lost a higher amount of weight in
comparison with the MC and QAMCE-G1, which indicate that the QAMCE-G2
contained a higher amount of organic layer in comparison with the MC and QAMCE-
G1. This result was in agreement with the C,H and N analyses data.
99
Fig. 4.5. TGA curve of magnetic materials
4.3.2. Effect of pH on adsorption of humic acid
The effect of the pH in the initial solution on magnetic separation of humic
acid was conducted in the pH range from 2 to 8 (Fig. 4.6.). In Fig. 4.6, it is shown
that the magnetic separation of humic acid by the MC was favorable in acidic
condition. Its performance decreased by increasing of pH. On the other hand,
magnetic separation of humic acid by quaternary ammonium magnetic materials
(QAMC, QAMCE-G1 and QAMCE-G2) was favorable in all range of pH studied.
This phenomenon could be explained on the basis of the surface charged of each
material. Based on the zeta potential data (Fig. 4.7), humic acid was negatively
100
charged in pH 2 until 8. The MC was positively charged in acidic condition and
negatively charged in basic condition with PZC of 6.4. Due to the presence of the
opposite charge between humic acid and the MC in acidic solution, electrostatic
attraction was favorably occurred. In higher pH, humic acid was attached on the MC
surface via week hydrogen bonding. On the other hand, the QAMCE-G2 was
positively charged in all range of the studied pH due to the presence of QA group on
its surface. Thus the electrostatic attraction intensively occurred in all range of the
studied pH and more than 97% of humic acid in the solution could be removed. The
similar results were obtained on magnetic separation of humic acid by the QAMC and
QAMCE-G1. However, the amounts of humic acid removed by QAMC and QAMCE-
G1 were relatively lower in comparison with the QAMCE-G2 due to their lower
amount of QA on its surface.
Fig. 4.6. Magnetic separation of humic acid in various pH (humic acid initial concentration: 100 mg�g-1, adsorbent dose: 2.5 g�L-1, contact time: 120 min)
0
20
40
60
80
100
0 2 4 6 8
HA
Ads
orbe
d (%
)
pH
QAMC QAMCE-G1QAMCE-G2 MC
101
Fig. 4. 7. Zeta potential of humic acid and magnetic materials.
4.3.3. Adsorption kinetics
The effect of contact time on magnetic separation of humic acid by the
QAMCE-G2 was investigated at the time range from 1 to 180 min and it is shown in
Fig. 4.8. In Fig. 4.8. it’s shown that humic acid could be removed with a fast
removal rate. Moreover, more than 85% of humic acid in solution could be removed
within 3 min. The equilibrium state could be achieved within 5 min, which was three
times faster than that MC (Fig. 4.9). In order to understand the adsorption process, the
experimental data were evaluated with two well-known kinetic models, namely the
pseudo-first order (PFO) [40] and the pseudo-second order (PSO) [41] model. The
PFO model could be expressed as follows:
-40
-20
0
20
40
0 3 6 9 12
Zeta
Pot
enti
al (m
V)
pHHA MC QAMC QAMCE-G1 QAMCE-G2
102
𝑞𝑡 = 𝑞𝑒 (1 − 𝑒𝑥𝑝(−𝑘𝑝1𝑡)) (4.4)
Equation (4.4) can be linearized as:
𝑙𝑛(𝑞𝑒 − 𝑞𝑡) = 𝑙𝑛 𝑞𝑒 − (𝑘𝑝1. 𝑡) (4.5)
While pseudo-second order can be expressed as follows:
𝑞𝑡 = 𝑘𝑝2.𝑞𝑒2.𝑡1+(𝑞𝑒.𝑘𝑝2.𝑡) (4.6)
and can be linearized as:
𝑡𝑞𝑡
= ( 1𝑘𝑝2.𝑞𝑒2
) + 𝑡𝑞𝑒
(4.7)
qe and qt are the amounts of humic acid adsorbed at the equilibrium and time t, kp1 and
kp2 are pseudo-first and second order rate constant, respectively. The parameters
obtained by using each kinetic model are listed in Table 4.2.
Based on the Table 4.2, the higher R2 value could be obtained by plotting the
experimental data to the PSO model in comparison with the PFO model. Moreover
the qe values obtained from the PSO model were closer with the experimental data.
MC, QAMC and QAMCE-G1 showed similar results with QAMCE-G2 on magnetic
separation of humic acid. These indicated that the magnetic separation of humic acid
by MC, QAMC, QAMCE-G1 and QAMCE-G2 followed the PSO model.
Tabel 4. 2. The PFO and PSO models for magnetic separation of humic acid.
Adsorbents
Pseudo-first order Pseudo-second order
R2 Qe kpfo
R2 Qe kpso
(mg�g-1) (min-1) (mg�g-1) (g�mg-1�min-1)
MC 0.586 6.4 0.06 0.999 29.9 0.007 QAMC 0.313 1.8 0.031 1 36.1 0.059 QAMCE-G1 0.531 1.4 0.055 1 39.4 0.068 QAMCE-G2 0.362 1.1 0.04 1 40.5 0.084
103
Fig. 4.8. Effect of contact time on magnetic separation of humic acid (humic acid initial concentration: 100 mg�g-1, initial pH: 6, adsorbent dose: 2.5 g�L-1)
Fig. 4.9. Humic acid solution treated with MC (above) and QAMCE-G2 (below) (humic acid initial concentration: 100 mg�g-1, initial pH: 6, adsorbent dose: 2.5 g�L-1)
0
10
20
30
40
0 50 100 150 200
HA
Ads
orbe
d (m
g.g-1
)
Contact time (min)
MCQAMCQAMCE-G1QAMCE-G2
104
4.3.4. Adsorption isotherm study
The effect of the initial concentration of humic acid on its magnetic separation
by the QAMCE-G2 is shown in Fig. 4.10. The Freundlich model and the Langmuir
model were used to evaluate the experimental data. The investigation of removal
mechanism of humic acid by the QAMCE-G2 was conducted by simply plotting the
experimental data on the Freundlich model and the Langmuir model. All isotherms
parameters were enlisted and shown in Table 4.3. Based on the Table 4.3, the
experimental data had a higher linearity with the Langmuir model in comparison with
the Freundlich model. This result indicates that the humic acid attached on surface of
the QAMCE-G2 as a monolayer. This phenomenon could be explained by
electrostatic interaction between the QAMCE-G2 and humic acid. Humic acid
interacted with the positively QA group on the surface of the QAMCE-G2 and made
the QA group not longer available for other humic acid molecule. In equilibrium
stage, the humic acid layer on the surface of the QAMCE-G2 will hinder other humic
acid molecule by the electrostatic repulsion. The similar results and mechanism were
obtained on the magnetic separation of humic acid by the MC, the QAMC and the
QAMCE-G1. However, due to the higher amount of QA, the QAMCE-G2 had a
higher qmax toward humic acid in comparison with the MC, the QAMC and the
QAMCE-G1. The comparison of the QAMCE-G2 on removal of humic acid with
other adsorbent is shown on Table 4.4.
Tabel 4.3. The Freundlich and Langmuir model for magnetic separation of humic acid
Adsorbent Freudlich Langmuir
R2 KFa n-1 R2 KLb qmaxc MC 0.989 1.42 0.532 1 0.01 35.9 QAMC 0.983 3.08 0.467 0.999 0.015 47.3 QAMCE-G1 0.974 5.07 0.435 0.999 0.02 59.3 QAMCE-G2 0.968 12.4 0.339 0.999 0.038 77
a Kf in (mg�g-1)(L�mg-1)1/n bqmax in mg�g-1 cKl in L�mg-1
105
Fig. 4.10. Effect of contact time on magnetic separation of humic acid (the initial concentration of humic acid: 100 mg•g-1, initial pH: 6, adsorbent dose: 2.5 g�L-1)
Tabel 4.4. Comparison of the QAMCE-G2 with other adsorbents
No Adsorbents teq (min) qmax
Ref (mg•g-1)
1 Magnetic polyaniline 400 36.3 [47] 2 Chitosan beads 50 44.8 [29]
3 Magnetic chitosan nanoparticle
60 29.3 [48]
4 Activated carbon 150 45.4 [49]
5 Activated greek bentonite
300 10.7 [50]
7 QAMCE-G2 5 77 This work
106
4.3.5. Reuseability of quaternized diethylenetriamine functionalized magnetic
chitosan
In order to evaluate the feasibility of the QAMCE-G2 as an economical
adsorbent, the regeneration experiment was conducted. The regeneration experiment
was conducted by repeating adsorption-desorption step and the results are showed in
Fig. 4.11. A mixture of 0.1 M NaOH-0.1 M NaCl solution was used as desorption
agent. The OH- and Cl- form desorption agent competed and replaced of humic acid to
bind with the QA group on the surface of the QAMCE-G2. The experimental result
showed that the QAMCE-G2 could be used for humic acid removal up to 10 times
without any significant lost on its performance. All of the QAMCE-G2 could be
recollected easily by using a magnet.
Fig. 4.11. Regeneration of magnetic material on magnetic separation of humic acid.
107
4.3.6. Pilot scale of magnetic separation of humic acid
In order to evaluate the feasibility of the QAMCE-G2 on magnetic separation
of humic acid, a scale up experiments was conducted (Fig. 4.12). The pilot
experiment was conducted by scaling up to 50 times in comparison with a previous
experiment. A mixture of 2.5 g of the QAMCE-G2 and 1 L of 100 mg�L-1 was stirred
for 10 min. The mixture was then pumped out by a circulator pump with a flow rate
of 1 ml�L-1 to a separating pipe which equipped with two magnet ( 0.4 T, 25 x 10 x 5
mm). The humic acid saturated QAMCE-G2 was attracted to the interior of separating
pipe while the liquid could pass through the separating pipe. The humic acid in the
solution could be removed with this system (98.72%). After all solution passed
through the separating pipe, the humic acid saturated QAMCE-G2 was recollected by
removing the magnet and let the pure water flew through the separating pipe. The
humic acid then was separated from the QAMCE-G2 by using 0.1 M NaOH-0.1 M
NaCl as a leaching agent . The recollected ratio of QAMCE-G2 was reached to
97.32%. A small number of the QAMCE-G2 was lost during magnetic separation.
108
Fig. 4.11. Scale up experiment of magnetic separation of humic acid by the QAMCE-G2 (QAMCE-G2: 2.5 g, Humic acid: 100 ppm, 1 L, contact time : 10 min, flow rate : 1 ml�s-1) 4.4. Conclusions
Quaternarization of MC, MCE-G1 and MCE-G2 with GTMAC to obtain
QAMC, QAMCE-G1 and QAMCE-G2 were successfully conducted. The QAMCE-
G2 could remove humic acid in solution with a fast rate and reached the equilibrium
within 10 min. The kinetics study showed that the experimental data followed the
pseudo-second order model. In comparison with the QAMC, the QAMCE-G2 had a
higher maximum capacity toward humic acid. The saturated QAMCE-G2 could be
recollected easily using a magnet. The regeneration study showed that the QAMCE-
G2 could be reused until 10 times without significant loss on its performance. The
QAMCE-G2 could be used for magnetic separation of humic acid in a larger scale
with high removal ratio of humic acid and recollection ratio of the QAMCE-G2.
109
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113
CHAPTER 5
General Conclusions
114
Magnetic separation of pollutants in water by using modified magnetic
chitosan was successfully developed. In order to enhance the performance of
magnetic chitosan on the removal of pollutants, several modified magnetic chitosan
materials were prepared and employed for the magnetic separation of pollutants. The
first modified magnetic chitosan was a novel pyridinium-diethylenetriamine magnetic
chitosan which is employed on the magnetic separation of Cr(VI) ion in the water.
Due to the presence of the pyridinium group on its surface, the pyridinium
diethylenetriamine magnetic chitosan could remove all Cr(VI) in all condition of the
acidic, neutral and basic solutions when other reported magnetic chitosan materials
only worked well in acidic solution. The interaction of Cr(VI) with the pyridinium
diethylenetriamine magnetic chitosan was dominated by electrostatic interaction
which achieved equilibrium stage within 5 min. The pyridinium diethylenetriamine
magnetic chitosan could be applied for five cycles of magnetic separation of Cr(VI) in
water.
In the removal of pollutants in water by magnetic chitosan, the presence of the
amine groups is important. On the other hand, the number of amine groups decreases
during crosslinking step. Due to that reason, preparation and application of amine-rich
magnetic chitosan became the next goal of my study. The second type of modified
magnetic chitosan was the dendrimerized magnetic chitosan. The repeating
dendrimerization of magnetic chitosan to obtain the dendrimerized magnetic chitosan
increased the total amount of amine groups. Due to the higher amount of amine
groups, the dendrimerized magnetic chitosan has a higher affinity toward Cu(II) ions
in the water. The presence of humic acid made the magnetic separation of Cu(II)
become more favorable due to the additional carboxylate groups which were provided
with humic acid to bind Cu(II) ions in water. The short contact time, less affect by
115
humic acid and a high regeneration were the advantages of dendrimerized magnetic
chitosan in comparison with other published materials. The third type of modified
magnetic chitosan was obtained by quaternarization of the second type of modified
magnetic chitosan. The quaternarization was conducted by introducing quaternary
ammonium groups on the surface of dendrimerized magnetic chitosan. The presence
of quaternary ammonium group enhanced its ability to remove humic acid in the
solution. Interaction of humic acid with the quaternary ammonium dendrimerized
magnetic chitosan was the electrostatic interaction, which was favorable in all pH
solutions and achieved the equilibrium stage within 5-10 min. The removal
performance of the quaternary ammonium dendrimerized magnetic chitosan toward
humic acid was stable until 10 cycles.
There are many published reports about the application of magnetic chitosan
on the removal of water pollutants. However, some issues such as its effectivity only
in specific conditions, requires longer contact time to reach equilibrium and low
regeneration factor should be solved. Modification of magnetic chitosan by
introducing the active organic group could enhance its ability as a magnetic material
for separation of pollutants. The combination of the effectivity in a wider range of pH,
requires shorter contact time and has a high regeneration made the modified magnetic
chitosan as a prospective material for magnetic separation of pollutants in the water.
116
ACKNOWLEDGEMENTS
I would like to express my deep gratitude to my supervisor, Prof. Shunitz
Tanaka for his extraordinary support, wisdom, guidance and kindness to me during
my doctorate program in his laboratory. I thank Prof. Nobuo Sakairi, Prof. Yuichi
Kamiya, Assoc. Prof. Kazuhiro Toyoda (Graduate School of Environmental Science,
Hokkaido University) and Prof. Hideyuki Itabashi (Gunma University) for their
valuable comments, discussion and advise on my research. My sincere thanks are
extended to Assoc. Prof. Taiki Umezawa (Graduate School of Environmental Science,
Hokkaido University) for his help on the FTIR measurements and Prof. Nuryono
(Universitas Gadjah Mada, Indonesia) for his collaboration.
Sincere thanks goes to my senior, Dr. Takahiro Sasaki (Muroran Institute of
Technology) and my research partner, Mr. Yasuyuki Narita for their warm support,
collaboration and hard work during our research on magnetic materials. I am grateful
Mr. Tomoaki Moriya, Ms. Aoi Nasu, Mr. Yasuhiro Akemoto, Ms. Sayaka Fujita, Ms.
Lina Mahardiani, Assist. Prof. Yoshihiro Mihara (Hokkaido Pharmaceutical
University), Dr. Devon Dublin, Dr. Adavan Kiliyankil Vipin and Mr. Masashi
Yoshitake (Institute for Electronics Science, Hokkaido University), for their support
and advise on my study. I thank Mr. Atfritedy Limin, Ms. Nongluck Jaito, Mr. Julius
Adam Velasco Lopez, Mr. Min Guo, Mr. Luo Weifeng, Mr. Haiki Mart Yupi and Dr.
Yustiawati for their warm friendship and support. For financial assistance, I
acknowledge the Directorate General of Higher Education (DGHE), Republic of
Indonesia for the DGHE Postgraduate Scholarship.
Finally, I would like to express my sincere gratitude to my father, mother,
sister, brother and Mr. Michel Hol for their everlasting support and assistance.