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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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Synthesis and adsorption studies, Chem. Eng. J. 241 (2014) 175–183.

[43] R. Karthik, S. Meenakshi, Removal of Cr(VI) ions by adsorption onto sodium

alginate-polyaniline nanofibers., Int. J. Biol. Macromol. 72C (2014) 711–717.

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coaly activated carbon in single and binary systems, Desalination. 249 (2009)

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[45] S.T. Akar, Y. Yetimoglu, T. Gedikbey, Removal of chromium (VI) ions from

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and modification, Desalination. 244 (2009) 97–108.

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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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from wastewater using simulated flue gas: Sequent additions of fly ash, lime

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[9] Y.N. Thakare, A.K. Jana, Performance of high density ion exchange resin

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[10] Q. Yang, N.M. Kocherginsky, Copper removal from ammoniacal wastewater

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[11] N.M. Kocherginsky, Q. Yang, Big Carrousel mechanism of copper removal

from ammoniacal wastewater through supported liquid membrane, Sep. Purif.

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[12] Y. Li, X. Zeng, Y. Liu, S. Yan, Z. Hu, Y. Ni, Study on the treatment of copper-

electroplating wastewater by chemical trapping and flocculation, Sep. Purif.

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[13] B. Wang, K. Wang, Removal of copper from acid wastewater of bioleaching

by adsorption onto ramie residue and uptake by Trichoderma viride, Bioresour.

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[14] X.S. Wang, L. Zhu, H.J. Lu, Surface chemical properties and adsorption of Cu

(II) on nanoscale magnetite in aqueous solutions, Desalination. 276 (2011)

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[15] N.M. Alves, J.F. Mano, Chitosan derivatives obtained by chemical

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[16] O. Monteiro, C. Airoldi, Some Thermodynamic Data on Copper-Chitin and

Copper-Chitosan Biopolymer Interactions., J. Colloid Interface Sci. 212 (1999)

212–219.

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functionalized magnetic chitosan with pH-independent and rapid adsorption

kinetics for magnetic separation of Cr(VI), J. Environ. Chem. Eng. (2015).

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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

and chitosan by layer-by-layer deposition, Colloids Surfaces A Physicochem.

Eng. Asp. 450 (2014) 121–129.

[20] L. Fan, C. Luo, X. Li, F. Lu, H. Qiu, M. Sun, Fabrication of novel magnetic

chitosan grafted with graphene oxide to enhance adsorption properties for

methyl blue., J. Hazard. Mater. 215-216 (2012) 272–9.

[21] K. Petcharoen, a. Sirivat, Synthesis and characterization of magnetite

nanoparticles via the chemical co-precipitation method, Mater. Sci. Eng. B. 177

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[22] J. Zawadzki, H. Kaczmarek, Thermal treatment of chitosan in various

conditions, Carbohydr. Polym. 80 (2010) 394–400.

[23] Y.-T. Zhou, C. Branford-White, H.-L. Nie, L.-M. Zhu, Adsorption mechanism

of Cu2+ from aqueous solution by chitosan-coated magnetic nanoparticles

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(2009) 244–252.

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[24] L. Zhou, Y. Wang, Z. Liu, Q. Huang, Characteristics of equilibrium, kinetics

studies for adsorption of Hg(II), Cu(II), and Ni(II) ions by thiourea-modified

magnetic chitosan microspheres, J. Hazard. Mater. 161 (2009) 995–1002.

[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)

by immobilizing Saccharomyces cerevisiae on the surface of chitosan-coated

magnetic nanoparticles from aqueous solution, J. Hazard. Mater. 177 (2010)

676–682.

[28] G. Huang, C. Yang, K. Zhang, J. Shi, Adsorptive Removal of Copper Ions

from Aqueous Solution Using Cross-linked Magnetic Chitosan Beads, Chinese

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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.