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PREPARATION, CHARACTERIZATION OF CHITOSAN DERIVATIVES AND

APPLICATION IN REMOVAL OF HEAVY METAL IONS FROM WATER

A THESIS SUBMITTED FOR THE DONGRUN-YAU SCIENCE

AWARD (CHEMISTRY)，2016

By

Group Members: LI MINZHANG

YANG YANRU

WANG ZEKAI

Supervisor: WANG CHANGLI

QINGDAO NO.2 MIDDLE SCHOOL

QINGDAO, CHINA

DECEMBER 9, 2016

论文题目：PREPARATION, CHARACTERIZATION OF

CHITOSAN DERIVATIVES AND APPLICATION IN

REMOVAL OF HEAVY METAL IONS FROM WATER

参赛队员姓名：李敏章杨燕如王泽凯

中学：山东省青岛第二中学

省份：山东省

国家/地区：中国

指导教师姓名：王昌丽

2016 年 12 月

i

ABSTRACT

The pollution caused by growth in industrialization and urbanization, is becoming more and

more severe, and heavy metal pollution has become a global problem. Heavy metal

contamination in water is a potential health hazard due to their possible reactivity, mobility and

toxicity. Heavy metals may enter the food chain by plant uptake, permeation into the water bodies

or be uptaken by aquatic organisms that serve as food.

Adsorption, an effective separation technology based on the affinity of adsorbents, is widely

used in water treatment. This inspired many workers to seek more economic and efficient

adsorbents.

Chitosan, a derivative of chitin is a versatile biopolymer with metal uptake capabilities. Chitin

is the second abundant natural biopolymer after cellulose and is distributed in the shells of

crustacean, which is waste product from marine food processing. Huge amounts of crab and

shrimp shells have been abandoned as wastes by worldwide seafood companies. Thus, the

utilization of chitosan results in alleviating the solid waste problem by converting the dumped

crustacean shell into an invaluable asset.

Chitosan is recognized excellent metal ligand, forming stable complexes with many metal ions.

In particular, chitosan is considered one of the best natural environment-friendly chelators for

heavy metal ions. However, the fatal defect of chitosan is that chitosan solids can graduately

dissolve in strong acid solutions.

By chemical modification, it prevents chitosan solids from dissolution in acidic media,

improving mechanical strength, and increasing the porosity and surface area.

Considering the above, epichlorohydrin-crosslinked chitosan resin (ECHC), epichlorohydrin-

crosslinked carboxymethyl-chitosan resin (ECHCMC), EDTA-modified epichlorohydrin-

crosslinked chitosan resin (EDTAEC), and thiourea-modified O-carboxymethyl-chitosan resin

(TUCMC) were designed and synthesized. FTIR-ATR and SEM were used to identify the

structures and characteristics of the resins. Adsorption experiments were utilized to testify

adsorption capacity of the synthesized resins for heavy metals ions (Pb2+, Cd2+). ICP-OES was

employed to determine the concentration of metal ions in solution.

Experimental data showed that EDTA-modified epichlorohydrin-crosslinked chitosan resin has

better adsorption capacity for Pb2+ and the maximum adsorption capacity for Pb2+ was 0.95

ii

mmol/g, and ECHCMC resin has relatively strong adsorption capacity for both Pb2+ and Cd2+

with the maximum adsorption capacity of 0.77 and 0.40 mmol/g, respectively.

The kinetic parameter of the Pb2+ adsorption process of EDTAEC was obtained, and the results

indicated that adsorption process for Pb2+ followed the Lagergren pseudo second order model. In

the reusability experiments, the EDTAEC resin showed that the adsorption capacity was not

significantly changed up to three cycles. Therefore, the resin could be easily regenerated and

efficiently reused.

In the present study, sorption performance of four cross-linked chitosan derivatives in multi-

component system was investigated in order to evaluate the uptake ability for the metal ions.

Infra-red spectrometry has been applied to study adsorption mechanisms that may be helpful

for synthesizing better adsorption property of modified chitosan.

The results revealed that the novel resin EDTAEC has outstanding performance on adsorption

of Pb2+, Cd2+, Cu2+, Ni2+, and Cr3+ from aqueous solutions. Order of metal chelation for 1mmol/g

was as follows: Cu2+> Pb2+> Ni2+> Cd2+> Cr3+. Metal chelating ability of EDTAEC for Cu2+ and

Pb2+ was higher than that of the other three resins. TUCMC adsorbed heavy metal ions in the

following order: Cu2+ > Ni2+ > Cd2+. ECHCMC indicated that it has binding capacities of 0.19

mmol/g for Cu2+ and ca. 0.05mmol/g Pb2+, Cd2+, Ni2+ and Cr3+. ECHC, as expressed by the order

of its affinity, was in the order of Cu2+>Cr3+> Ni2+> Pb2+> Cd2+. ECHC is more efficient in

scavenging Cr3+ from metal mixture solution as compared to other resins.

The novel chitosan chelating resin (EDTAEC) that we synthesized in this project showed great

potential in the field of removal of heavy metals from water.

Our experimental results approved that grafting of specific functional groups onto the chitosan

backbone allows sorption performances to be improved due to the appearance of new sorbing

functions. Hence, an efficient way to get chelating resin is to modify chitosan structure, and the

resins synthesized have been testified that they can efficiently adsorb heavy metals in aqueous

medium, which has drawn more and more attention.

Keywords: Chitosan resin; Chemical modification; Epichlorohydrin-crosslinked chitosan;

Heavy metal ions; Chemical adsorption

iii

DECLARATION

The research work embodied in the entitled, “PREPARATION,

CHARACTERIZATION OF CHITOSAN DERIVATIVES AND APPLICATION

IN REMOVAL OF HEAVY METAL IONS FROM WATER” is an original work

carried out under the supervision of the instructor. The work has not been submitted

in part or full for publication. The extent of information derived from existing

literature has been indicated in the thesis at appropriate places, giving the source of

information. If there is any inaccuracy, this team is accountable for all liabilities.

Signature:

Date:

iv

ACKNOWLEDGEMENT

We wish to express our sincere gratitude to our tutor WANG Changli for providing

patient guidance throughout my research project.

We thank Dr. LI Xiancui of the Institute of Oceanology, Chinese Academy of

Sciences (IOCAS), who co-supervised this work and provided the laboratory for the

study. He was an inspiration to us throughout this study.

We also wish to extend our thanks to Mr. LIU Wei, Institute of Oceanology, Chinese

Academy of Sciences, for assisting us with Scanning Electron Microscopy. We are also

grateful to Dr. YU Ying, Testing and Analysis Center, Institute of Oceanology, for

assisting us with FTIR-ATR and ICP-OES analysis.

We would also like to express my grateful thanks to Associate Professor, V.

Thiyagarajan, The Swire Institute of Marine Science and School of Biological Sciences,

The University of Hong Kong, for his constructive criticism, suggestions and positive

thought.

Special thanks are due to SUN Xianliang, the President of Qingdao No. 2 Middle

School for his support.

We wish to express our deepest appreciation to our loving parents for their blessing

and encouragement.

v

TABLE OF CONTENTS

Abstract iDeclaration iiiAcknowledgement ivTable of Contents vAbbreviation viList of Tables viiList of Figures viiiChapter I Introduction 1Chapter II Literature review 4 Motivation for research 12Chapter III Synthesis and characterization of epichlorohydrin-crosslinked

chitosan resin 13

3.1 Introduction 13 3.2. Materials and methods 13 3.3 Results and discussion 14Chapter IV Preparation and characterization of epichlorohydrin-crosslinked

carboxymethyl-chitosan 19

4.1 Introduction 19 4.2. Materials and methods 19 4.3 Results and discussion 20Chapter V Preparation and characterization of a novel bioadsorbent EDTA-

modified epichlorohydrin-crosslinked chitosan 26

5.1 Introduction 26 5.2. Materials and methods 26 5.3 Results and discussion 27Chapter VI Synthesis of thiourea-modified O-carboxymethyl -chitosan 32 6.1 Introduction 32 6.2. Materials and methods 33 6.3 Results and discussion 34Chapter VII Physicochemical characterization of four crosslinked chitosan

derivatives 38

7.1 Introduction 38 7.2. Materials and methods 40 7.3 Results and discussion 42Chapter VIII Evaluation of sorption performance and adsorption mechanism of

four crosslinked chitosan derivatives 44

8.1 Introduction 44 8.2. Materials and methods 45 8.3 Results and discussion 47Summary 58References 60

vi

ABBREVIATION

ATR Attenuated Total Reflectance

CM-chitosan Carboxymethyl-chitosan

DD Degree of Deacetylation

ECH Epichlorohydrin

ECHC Epichlorohydrin-crosslinked chitosan

ECHCMC Epichlorohydrin crosslinked carboxymethyl-chitosan

EDTA Ethylenediamine Tetraacetic Acid

EDTAEC EDTA-modified Epichlorohydrin-crosslinked chitosan

FTIR Fourier Transform Infrared Spectroscopy

ICP Inductively Coupled Plasma

OES Optical Emission Spectrometry

SEM Scanning Electron Microscopy

TUCMC Thiourea-modified O-carboxymethyl-chitosan

vii

LIST OF TABLES

Table 2.1 Approximate chitin content in various living species 5

Table 2.2 Applications of Chitin and its derivatives 10

Table 3.1 Peaks of FTIR-ATR spectra of Chitosan and ECHC and their assignment 17

Table 4.1 Peaks of FTIR-ATR spectra of Chitosan and ECHCMC and their assignment 24

Table 5.1 Peaks of FTIR-ATR spectra of Chitosan and EDTAEC and their assignment 30

Table 6.1 Peaks of FTIR-ATR spectra of Chitosan and TUCMC and their assignment 37

Table 7.1 Comparison of physical capacities of synthesized chitosan chelating resins 42

Table 7.2 Comparison of adsorption capacities of synthesized chitosan resins for metal ions 43

Table 8.1 Co-adsorption data of four resins in multiple-metals aqueous solution 48

viii

LIST OF FIGURES

Figure 2.1 Scheme for chitin and chitosan production 6

Figure 2.2 Structural comparisons of functional groups on chitin, chitosan and cellulose 8

Figure 3.1 Flowchart of synthesis of the epichlorohydrin-crosslinked chitosan 15

Figure 3.2 Synthetic pathway of epichlorohydrin crosslinked chitosan resin 15

Figure 3.3 SEM of chitosan microspheres, modified with epichlorohydrin 16

Figure 3.4 FTIR-ATR spectra of chitosan (A) and ECHC (B) 18

Figure 4.1 Flowchart of synthesis of epichlorohydrin crosslinked carboxymethyl-

chitosan

21

Figure 4.2 Synthetic pathways of epichlorohydrin crosslinked carboxymethyl-chitosan 22

Figure 4.3 Scanning electron micrograph of epichlorohydrin-crosslinked carboxymethyl

chitosan

23

Figure 4.4 FTIR-ATR spectra of chitosan (A), ECHC (B) and ECHCMC (C) 25

Figure 5.1 Flowchart of synthesis of EDTA-modified epichlorohydrin-crosslinked

chitosan

28

Figure 5.2 Synthetic routes of EDTA-modified epichlorohydrin-crosslinked Chitosan 28

Figure 5.3 Scanning electron micrograph of EDTAEC 29

Figure 5.4 FTIR-ATR spectra of chitosan (A), ECHC (B) and EDTAEC (C) 30

Figure 6.1 Flowchart of synthesis of thiourea-modified O-carboxymethyl-chitosan 34

Figure 6.2 Synthetic pathway of thiourea-modified O-carboxymethyl-chitosan 34

Figure 6.3 Scanning electron micrograph of thiourea-modified O-carboxymethyl-chitosan 36

Figure 6.4 FT-IR spectra of chitosan (A), CM-Chitosan (B) and TUCMC (C) 36

Figure 7.1 Chemical structures of four crosslinked-chitosan derivatives 39

Figure 7.2 The synthesized crosslinked chitosan derivatives 39

Figure 8.1 Adsorption performance of four resins in multiple-metals aqueous solution 47

Figure 8.2 Sorption of Pb2+, Cd2+, Cu2+, Cr3+ and Ni2+ from metal ion mixtures on four

resins

48

Figure 8.3 Effect of contact time on the uptake of Pb2+ with initial concentration 0.01 M by

EDTAEC

51

Figure 8.4 Pseudo-second-order kinetic plots for the adsorption of Pb2+ by EDTAEC 51

Figure 8.5 The air-dried spent cross-linked chitosan beads after sorption of multi-metal ions 52

Figure 8.6 FTIR spectra of ECHC beads and ECHC-metal complexation 53

Figure 8.7 FTIR spectra of ECHCMC beads and ECHCMC-metal complexation 54

Figure 8.8 FTIR spectra of EDTAEC beads and EDTAEC-metal complexation 55

Figure 8.9 FTIR spectra of TUCMC beads and TUCMC-metal complexation 56

1

Chapter I INTRODUCTION

Water is one of the most important necessities for the sustenance and continuation of life in

plants and animals. Of all the water available on earth, only less than 2.5% is fresh water

required for human activities. So it is important to have a supply of good quality water for

living beings to perform various activities.

With the rapid development of economy and the modern industry, water pollution caused

by oil spillage and industrial wastewater discharge (Mark, 2011; Dvoˇrák et al., 2013) has

drawn extensive attention, including heavy metal ions, organic dyes and other toxic pollutants.

The harmful contaminants inflict great threat on environment and human being (Govers et al.,

2014; Li et al., 2016). Disposal of water contamination has always been a major

environmental issue all over the world.

In recent years, the heavy metal ions concentration besides other pollutants has increased to

a dangerous level in water resources. Trace amounts of contaminates will result in high

volumes of contaminated water which threaten human health and other living organisms.

Heavy metals have a number of industrial applications due to their technological importance

but the wastewater released from these industries creates a permanent toxic effect on

environment and human beings (Xiong et al., 2009). The source of heavy metal contamination

is from various industrial activities, such as mining operations, metal plating, electric devices

manufacturing units, abandoned waste disposal sites and others includes natural weathering

processes, waste emissions, atmospheric depositions (Bhattacharyya, 2006). Thus, the

treatment of wastewater is an issue for paramount importance. The removal of heavy metal

ions from wastewater is always a challenging task for environmentalists, due to their trace

quantities, and they form complexes with natural organic matter (Wana et al., 2010).

Discharge of heavy metals like Pb (II), Hg (II), Cr (VI), Cd (II), Ni(II) and Cu (II) accumulate

in living organisms, causing disorder and cannot be degraded or destroyed by the organisms

(Bailey, 1999). Wastewater released from industries often contains a considerable amount of

toxic metals that would endanger public health and environment if discharged without

adequate treatment.

Lead is present in several minerals principally in galena, PbS, the main source for lead

production. Lead is one of the most commonly used metal, suitable for batteries due to the

resistance to corrosion and the reversible reaction between lead oxide and sulfuric acid, which

can be recycled. Other uses of the metals are for radiation shielding, ammunition, cable

2

sheathing and pipework etc. Lead compounds are used as pigments in paints and ceramics,

catalysts, antibacterial substances and wood preservatives. The major reason for lead

pollution in the environment is due to anthropogenic factor of industrial applications such as,

in electroplating etc. (Ngah, 2002). Lead in the atmosphere comes mainly from the oxidation

of gasoline in internal combustion engines.

Lead is well known to be accumulative poison through water intake or food chains and can

cause brain damage and dysfunction of the kidneys, the liver and the central nervous system

in human beings, especially in children (Ng, 2003). Due to its toxicity, the upper limit for lead

in drinking water recommended by WHO is 0.05mg/l (Harikishore, 2010).

Cadmium exists in nature principally as sulphide ore greenockite, CdS. Many types of

soluble forms of cadmium exist in water. Cadmium enters the environment from wastewater

released from industries such as surface treatment, cement production, mining and from metal

processing units (Jha et al., 1988).

Anthropogenic sources of cadmium emission to the air are mainly from uncontrolled

burning of waste on dumpsites, recovery of metal, steel and cement production etc. Aquatic

inputs of cadmium are mostly from iron and steel production and to the soil. The contribution

of Ni-Cd batteries also plays a big role to cadmium emission from municipal solid waste.

Cadmium in the effluents is absorbed and accumulated by micro-organism. Eventually

cadmium will be transferred to human beings via the food chain and once the cadmium

ingested in the body its expulsion is very difficult. It causes damage even at very low

concentration (Izadiyar, 2010). Cadmium toxicity has a lot of adverse effects on human

beings, which causes renal dysfunction, lung diseases, bone degeneration & lesions, increased

blood pressure, and several types of cancers (Sankararamakrishanan, 2007). Due to its

toxicity, cadmium removal from aqueous effluents has been classified as a priority in the last

decade.

Disposal of water contamination has always been a major environmental issue all over the

world. Treatment methods have been continuously exploring for decade years, such as

precipitation (Al-Harahsheh et al., 2014; Mbamba et al., 2015), flotation (Saththasivam et al.,

2016), membrane technologies (Lin et al., 2015; Neoh et al., 2015), oxidation-reduction (Li et

al., 2014), photocatalytic degradation (Murgolo et al.,2015), adsorption (Bi et al., 2013), etc.

Chemical precipitation is the most traditional, and simple method for water purification

(Grimshaw, 2011). It involves addition of chemicals to facilitate their removal by

sedimentation. However, this method is inappropriate for large solution volumes with very

low concentrations of metal ions. In spite of its advantages, chemical precipitation requires a

3

large amount of chemicals to reduce metals to an acceptable level for discharge. The

precipitation method produces a large amount of sludge, which transforms an aquatic

pollution problem to a solid waste problem. In addition, chemical precipitation is usually

inefficient to deal with low concentration of heavy metals.

Coagulation-flocculation processes are widely used techniques can be employed to deal

with wastewater laden with heavy metals. In spite of its merits, coagulation-flocculation has

limitations such as high operational cost due to chemical consumption. The increased volume

of sludge generated from coagulation flocculation may hinder its adoption as a global strategy

for wastewater treatment.

Among the methods, adsorption has been wildly concerned by researchers in virtue of its

uncomplicated operation, high removal rate, less secondary pollution, as well as low-cost.

Various absorbents were studied and applied in water treatment. Activated carbon has proved

to be most popular and widely used adsorbent for the removal of heavy metals and other

pollutants from wastewater, because of their great capacity to adsorb pollutants. However,

activated carbon presents several disadvantages. It is non-selective, quite expensive, and the

higher the quality, the greater the cost. The regeneration of saturated carbon by thermal and

chemical procedure is also expensive. This forced many workers to search for more economic

and efficient adsorbents.

Due to the problems mentioned above, research interest into the production of alternative

sorbents to replace the costly activated carbon has intensified in recent years. A sorbent can

be regarded as low cost if it requires little processing, is abundant in nature, or is a by-product

or waste material from another industry.

Chitosan, produced by alkaline deacetylation of chitin, is considered one of the most

abundant polysaccharides on the earth especially in coastal regions and well-known for

renewable, nontoxic, biocompatible and degradable (Bhatnagar et al., 2009). As the only

natural alkaline and cationic polysaccharide, chitosan has great potentials in wastewater

treatment, because its amine and hydroxyl groups act as active sites for heavy metal and

anionic organic pollutants (Crini et al., 2008).

4

Chapter II LITERATURE REVIEW

Chitin is a non-toxic and biodegradable polymer of N-acetyl-glucosamine and

glucosamine.

2.1 Discovery of Chitin and Chitosan

Chitin is the most abundant natural biopolymer and the most abundant nitrogen-bearing

biopolymer and is second only to cellulose on earth (Singh and Ray, 2000). It is mainly found

as a component of the exoskeletons of crustaceans and insects and also from cell walls of

fungi (Wu, 2005). Chitin was first described by the French scientist, Braconnot (1811), when

he isolated it from mushrooms using diluted alkali, he called it “fungine”. Later, Odier (1823)

isolated the same substance from insects and called it chitin, using the Greek word for “tunic

envelope”.

Rouget first reportedly discovered Chitosan in 1859 when he boiled chitin in a very

concentrated potassium hydroxide solution making it soluble in organic acid (Muzzarelli,

1977). It was not until 1894 that this substance was named ‘Chitosan’ by Hoppe-Seyler.

During 1930’s and 1940’s these biopolymers gained much interest within the oriental world,

mainly in applications in the field of medicine and water purification. During 1970’s the

interest in these bio-macromolecules renewed at a brisk pace. Pioneering work of Muzzarelli

during 1980’s has greatly advanced our understanding of these materials. Today we know that

chitin and chitosan are found in abundance in nature and are renewable sources and this has

attracted much interest in developing new applications from these simple substances.

2.2 Sources of chitin and chitosan

Considering the annually total production, chitosan and chitin is second ubiquitous natural

polymer after cellulose. Chitin is the most abundant nitrogen-containing biopolymer found on

earth. Traditionally, chitin is produced from crustaceans, even though the largest source of

chitin is fungi (Muzzarelli, 1977). At least 10 gigatons (1 × 1013 kg) of chitin are synthesized

and degraded each year in the biosphere (Jollès and Muzzarelli, 1999). Chitin can be extracted

from different sources, such as from crustacean shells (crabs, cuttlefish, shrimp and crayfish)

and can also be prepared from squid pens. Another source is from the exoskeleton of insects,

bacteria, and some fungi.

Chitin forms a part of the supporting tissue and exoskeleton of arthropoda and is an

essential cell wall component of some plants and most fungi (Muzzarelli, 1977). Chitin in

nature is usually associated with protein (animal) or polysaccharides (yeast, fungi)

5

(Muzzarelli, 1977). In the crustacean exoskeleton, it is bound to polypeptides (proteins) and

calcium carbonate, which function as inorganic fillers. Marine benthic animals are also rich

sources of chitin. Chitosan is converted from chitin, which is a structural polysaccharide

found in the skeleton of marine invertebrates, insects and some algae.

The aquatic species that are rich in chitinous material (10-55 % on a dry weight basis)

include squids, crabs, shrimps, cuttlefish and oysters. It has been found that shrimp and crab

processing waste contains 14-27% and 13-15% on a total mass and dry weight basis,

respectively (No et al., 1989).

Table 2.1 Approximate chitin content in various living species

Species Weight % chitin by

dry body weight

Fungi 5-20%

Worms 20-38%

Squids/Octopus 3-20%

Scorpions 30%

Spiders 38%

Cockroaches 35%

Water Beetle 37%

Silk Worm 44%

Hermit Crab 69%

Edible Crab 70%

Chitosan is one of the most available polysaccharides with positive charges found in nature

(Xing et al., 2005, Shepherd et al., 1997; Krisana et al., 2004). The annual biosynthesis of

chitin has been estimated from 109 to 1011 tons. The traditional and commercial sources of

chitin are the shells of crab, shrimp and krill, all of which are waste product from marine food

processing (Devlieghere et al., 2004). Chitin content in various sources is given in Table 2.1

(Allan et al., 1978). The worldwide annual production of crustacean shells has estimated to be

1.2×106 tons and the production of chitin from this waste can be considered as a major

additional source of commercial income (Knorr, 1991; Roberts,1992). It accounts for

approximately one third of the dry weight of the waste shells. Amongst several sources, the

exoskeleton of crustaceans consists of 15-20% chitin, protein (15-40%), and calcium

carbonate (35-55%) by dry weight.

2.3 Preparation of chitin and chitosan

Commercially, chitin is extracted from the exoskeleton of crustaceans (Muzzarelli et al.,

1986). The industrial development of chitin and chitosan was brought about in the mid-80s.

6

Due to its insolubility in common solvents, the uses of chitin are limited (Kumar, 2000).

Chitosan is obtained by partially deacetylating chitin, removing acetyl groups from the

polysaccharide leaving free amine groups (Khan et al., 2002). The production of chitosan is a

multi-step process including the grinding, deproteinization, demineralization, discoloration

and deacetylation as follow:

Figure 2.1 Scheme for chitin and chitosan production

2.3.1 Production of chitin

Chitin can be extracted from many natural sources, however the main commercial source of

chitin is shrimp, crab and prawn waste. Extraction of chitin from crustacean shells is a time

consuming process that involves extensive demineralization and deproteinization treatments.

Many processes have been implemented with various treatment times, temperatures,

concentrations of acid and alkali solvents, and solid-to-solvent ratios. Crustacean shells are

first crushed into a pulverous powder to make a greater surface area available for the

heterogeneous processes to follow. An initial treatment of the shell with 5% sodium

hydroxide dissolves various proteins, leaving behind chitin, lipids and calcium salts (mainly

as CaCO3). Treatment with 5% hydrochloric acid hydrolyzes lipids; dissolves calcium salts

(demineralization) and other minor inorganic constituents. This is performed at or below

ambient temperatures for 2-3 hours (Wiles, 2000). Chitin thus obtained can be hydrolyzed

using 50% sodium hydroxide at high temperature to convert the amide functionality into the

amino group to provide chitosan. Alternatively, if isolation of chitin is not desired, the

7

acid-base sequence may be reversed to directly produce chitosan.

2.3.2 Chemical Conversion of Chitin to Chitosan

Chitosan is commonly prepared by deacetylating-chitin using 40-50% aqueous alkali such

as sodium and potassium hydroxide under heterogeneous conditions at 100-160°C for a few

hours (Campbell, 2003). This can give chitosan with a degree of deacetylation, which

determines the content of free amino groups in the polysaccharides, between 0.70 and 0.95.

For complete deacetylation, the alkaline treatment can be repeated. When deacetylation is

conducted with dilute alkali (20 or 30% sodium hydroxide) at gentle refluxing, DD levels of

33 and 45% can be obtained.

2.4 Chemical structures of chitin and chitosan

The structure of chitin, chitosan, and cellulose is shown in Figure 2.1. Both chitin and

chitosan have a similar chemical structure to cellulose with linear glycosidic backbone

connected by -(1-4) glycosidic bonds.

Chitin consists of linear repeating primary units of 2-acetamido-2-deoxy-D-glucopyranose

with a molecular weight ranging from about 10,000 to 2 million Daltons. These units are

combined by 1-4 glycosidic linkages, forming a long chain linear polymer without side chains.

Chitin is chemically identical backbone with cellulose, except that the secondary hydroxyl

group on the alpha carbon atom of the cellulose molecule is substituted with acetamide

groups.

Chitosan is a modified natural polymer derived from chitin. Chitosan is a

heteropolysaccharide composed of β-(1-4)-2-deoxy-2-amino-D-glucopyranose units (75-85%),

and of β-(1-4)-2-deoxy- 2-acetamido -D-glucopyranose units (Yasser and Ahmed, 2002).

Chitosan and cellulose differ at carbon-2, where the hydroxyl group of cellulose is replaced

by an amino group in chitosan (Muzzarelli, 1985). The high percentage of nitrogen on

chitosan gives it greater reactivity and therefore, greater commercial appeal (Muzzarelli,

1973).

Chitin and chitosan are similar in their chemical structure. The main difference is the

presence of an N-acetyl group attached at the C2 location in chitin. Either an acetamide group

(-NHCOCH3) or an amino group (-NH2) is attached to the C-2 carbon of the glucopyran ring.

When more than 70% of the C-2 attachment is amine group, the material is termed chitosan.

Removal of most of the acetyl groups of chitin by treatment with strong alkali yields chitosan

(Peniston and Johnson, 1980). The N-acetyl group becomes a NH2 amine group in chitosan. In

reality, the range of deacetylation is commonly 70 to 99%. The repeating units of the chitosan

8

backbone are glucosamine and N-acetylated glucosamine (2-acetylamino-2-deoxy-D

-glucopyranose).

(a)

O

HONH2

NHHO

OO

O

HONH2

O

CH3O

OH

OH

NH2HO

OO

H

OH

1

23

4

5

OH

6

n (b)

(c)

Figure 2.2 Structural comparisons of functional groups on chitin (a), chitosan (b), and cellulose (c)

2.5 Physicochemical characteristics of chitosan

Chitosan occurs as odorless substance. It is an amorphous solid and off-white in color. The

properties of chitosan vary considerably depending on the source and production process.

Most of the commercial polysaccharides like cellulose, pectin, alginic acid etc. are neutral

or acidic. But chitosan is an abundant basic polysaccharide. Its pH comes around 8 and this

basic nature makes it unique for different applications (Austin et al., 1981).

Among these physical and chemical characters of chitosan, its solubility and chemical

activity are of most concern because they are the main factors impacting its various

applications.

2.5.1 Physicochemical properties

Chitosan can be characterized in terms of its quality, intrinsic properties such as purity,

molecular weight, viscosity, and degree of deacetylation and physical forms.

2.5.1.1 Solubility of chitosan

The solubility of chitosan is very important for its utilization, such as for chemical

modification. Neither chitin nor chitosan are soluble in neutral water.

Chitosan readily dissolves in dilute mineral or organic acids by protonation of free amino

groups at pH below about 6.5. This cationic nature is the basis of a number of applications of

chitosan. Acetic and formic acids are most widely used in research and applications of

9

chitosan. Generally, the solubility of chitosan decreases with an increase in molecular weight.

Oligomers of chitosan with a degree of polymerization (DP) of 8 or less are water-soluble

regardless of pH.

2.5.1.2 Degree of deacetylation (DD)

The DD is the proportion of glucosamine monomer residues in chitin. It has a striking

effect on the solubility and solution properties of chitin. A number of methods have been

employed to measure the DD, such as IR spectroscopy, UV spectroscopy and so on. However,

one of the most frequently used methods is infrared spectroscopy because of its simplicity.

2.5.1.3 Molecular weight

Molecular weight of the chitosan obtained at the end of the production process depends on

process parameters such as time, temperature and concentration of HCl and NaOH used. The

MW determination of chitosan samples can be performed by various techniques such as

viscometer and gel permeation chromatography. Average molecular weight of chitosan is

around 1.2×105 Daltons.

2.5.1.4 Surface activity of chitosan:

Pure chitosan has low surface activity which can be described by the chemical structure.

The chitosan polysaccharide having cationic amine group (-NH3) and an alcoholic hydroxyl

group (-OH). The chitosan self-aggregates could be formed in acetate buffer solutions by

intra- and inter-molecular hydrophobic interactions.

2.5.1.5 Viscosity

Viscosity is an important characteristic of chitosan. Viscosity of chitosan is highly

dependent on the degree of deacetylation, molecular weight, concentration of solution, ionic

strength, pH, and temperature.

The processes involved in the extraction of chitosan also affect the viscosity of chitosan.

For instance, chitosan viscosity decreases with an increased time of demineralization. Another

characteristic of chitosan is its high viscosity in an acidic environment.

2.5.2 Chemical properties

Chitosan has three reactive groups, including primary and secondary hydroxyl groups at the

C-2, C-3 and C-6 positions (Furusaki et al., 1996) on each repeat unit, and the amino group on

each deacetylated unit. Chitosan undergoes the typical reactions of amines, of which

N-acetylation and Schiff reaction are the most important. Chitosan forms aldimines and

ketimines respectively with aldehydes and ketones at room temperature. Chitosan can also be

modified by either cross-linking or graft copolymerization. A number of chemically modified

chitosan derivatives are listed in the literature (Muzzarelli, 1985).

10

2.5.2.1 Complex formation of chitosan

A significant unique reaction involving amine groups is complex formation. To be specific,

chitosan is known to have good ability of interacting with metals in various environments.

Researches indicated that chelate process is related to the physical state of chitosan, degree of

deacetylation, pH, metal content and distribution of amino groups.

2.5.2 Derivatives of chitosan

Chitosan is a linear polyamine and it can be widely derivatized because a large amount of

the amine groups on the C-2 position and hydroxide groups on the C-3 and C-6 positions.

Alkylation: Alkylated chitosan is an outstanding surfactant and can absorb hydrophobic

molecules.

Carboxymethylchitosan: The carboxymethylchitosan (CM-chitosan) is a highly developed

chitosan derivatives. The carboxymethylation can be carried on C-2, C-3 and C-6.

Graft copolymerization: PEG can be grafted on chitosan and bring the good water

solubility to the copolymer.

Table 2.2 Applications of Chitin and its derivatives (Khor, 2001; Majeti and Kumar, 2000)

Application Areas Specific Use Health Care Burn and Wound dressing

Tissue Engineering Drug and gene delivery

Food and Beverages Preservative agent Food additive and natural thickener Food processing (e.g. sugar)

Agriculture Seed coating Fertilizer Antimicrobial agent

Waste and Water Treatment Removal of metal ions Flocculating agent for polluted water Treating food waste

Cosmetic and Diet-aids Oral health care Dietary aid (fat binding properties) Cosmetic component

Product Separation Membrane separation Chromatographic columns Encapsulating adsorbents

2.6 Uses of chitosan

In the past decades chitosan products have been largely manufactured and applied in

diverse fields ranging from waste management, agriculture to biotechnology.

By changing the degree of acetylation of chitin and the level of viscosity, a wide range of

chitosan forms can be produced. Chitosan is a versatile polymer with applications in waste

treatment (Savant and Torres, 2000), food processing (Ahmed and Pyle, 1999), medical and

11

pharmaceutical industries (Lee and others, 2001), and agriculture (Peter, 1995).

MOTIVATION FOR RESEARCH

1. Research background

Environmental pollution has become more and more serious, especially regarding heavy

metal ions. Heavy metals, mainly from industrial activities such as metal plating facilities,

mining operations, fertilizer and electronic device manufactures are a serious threat to human

beings and the environment, due to their highly toxicity and persistence after being released

into the natural environment. The amount of heavy metals produced from metal industries,

agricultural activities, and waste disposal has increased dramatically. They must be removed

from the polluted water in order to meet increasingly stringent environmental quality

standards.

Many methods including chemical precipitation, electrodeposition, ion exchange,

membrane separation, and adsorption have been used to treat waste water. Among these

techniques, adsorption has been recognized as one of the most popular methods due to its

simplicity of operation, cost effectiveness, high efficiency, easy recovery, regeneration

capacity and sludge-free operation. Many conventional adsorbents are used for removal of

toxic metals, such as activated carbon (Kalpakli et al., 2007), and cellulose.

However, most absorbents are relatively expensive, low adsorption capacity and poor

reusability which have restricted their applications. Likewise, the defects of synthetic organic

absorbents (such as non-biodegradability and non-renewability) are still to be solved before

their widespread application.

Therefore, fungible and effective adsorbents are required for the disposal of heavy

metal-contaminated water.

As effective biosorbent, chitosan has drawn much attention due to its low cost compared to

activated carbon and its high contents of amino and hydroxyl functional groups on chitosan

chains serve as coordination sites. This biopolymer represents an attractive alternative to other

biomaterials because of its physico-chemical characteristics, chemical stability, high reactivity,

excellent chelation behavior and high selectivity toward pollutants.

As mentioned before, the polycationic nature of chitosan makes it available for chelation

with metal. Chitosan acts as a powerful chelating agent owing to the presence of amino

groups within its backbone. Chitosan has been reported as an excellent chelator of many

harmful metals ions (copper, nickel, chromium, cadmium, manganese, cobalt, lead, mercury,

zinc, uranium and silver) from wastewater. The amino groups of chitosan are readily available

12

for chemical reactions with acids. In solution, the chitosan amine groups are protonated

resulting in a positively charged polymer which readily reacts with negatively charged

colloids such as alginate, carrageenan and pectin by electrostatic interactions between -COO-

or -SO3- in the polyanion and forming large polymeric complexes (Mireles et al., 1992).

2. Project significance and values

The project significance and values are embodied in following aspects:

a. Natural chitosan has been modified by several methods in order to enhance the

adsorption capacity for various types of pollutants. The grafting of specific functional groups

onto a chitosan backbone allows sorption performances to be improved due to the appearance

of new sorbing functions. This simple technique of modification of the structure of the

chitosan allows the uptake capacity and sorption kinetics to be increased.

b. Huge amounts of crab and shrimp shells have been abandoned as wastes. Thus, the

utilization of chitosan results in alleviating the solid waste problem by converting the

otherwise dumped crustacean shell into an invaluable asset.

c. The advantages of chemical modification are

(i) It prevents chitosan solids from dissolution in acid solutions

(ii) Mechanical strength of chitosan solids can be improved which provides resistance to

chemical degradation.

(iii) It may increase the porosity and surface area of chitosan solids.

13

Chapter III Synthesis and Characterization of Epichlorohydrin-

Crosslinked Chitosan Resin

3.1 INTRODUCTION

Increasing industrialization worldwide had caused serious pollution all around the world,

especially in the aquatic environment. Wastewaters produced by humans are frequently laden

with toxic heavy metals such as lead, cadmium, mercury, etc. The soluble form of these heavy

metals is very dangerous because it is easily transported to plants and animals. Hence, to

remove toxic heavy metals from wastewaters has become increasingly focused.

Adsorption using low-cost adsorbents is recognized as an emerging technique and a large

variety of adsorbents have been developed and tested. Chitosan, as one of the most frequently

reported biosorbents, has been investigated by many researchers for removal of heavy metals

from aqueous solution. Modifications of chitosan can make it more selective and effective for

several metal ions, especially heavy metal ions. Homogeneous cross linked materials are easy

to prepare with relatively inexpensive reagents and are available in a variety of structures with

a variety of properties.

(1) They are insoluble in acidic and alkaline mediums as well as organic solvents. Cross

linked gels are very stable hydrophilic polymers. They become more resistant to shear, high

temperature and low pH compared to their parent polysaccharide.

(2) After crosslinking, they maintain their properties, original characteristics and strength in

acidic and basic solutions. These characteristics are important for an adsorbent so that it can

be used in a lower pH environment.

(3) After adsorption, the crosslinked materials can also be easily regenerated by washes

using a solvent or by solvent extraction.

In this work, a crosslinked chitosan resin with epichlorohydrin was synthesized and

characterized by Fourier transform infrared (FT-IR) spectroscopy and a scanning electron

microscope.

3.2. MATERIALS AND METHODS

3.2.1 Instrumentation

Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) was

used to identify the functional groups in the synthesized resin and the original chitosan. The

morphological characterization of chitosan bead was performed by images acquired using a

scanning electron microscope (S-3400N, Hitachi, Japan), operated 5.00 kV after coated with

14

Au to make the samples conductive.

3.2.2 Chemicals

Chitosan with 80 meshes, 96% degree of deacetylation and average-molecular weight of

1.5×105 was purchased from Qingdao Baicheng Biochemical Corp. (China). Formaldehyde,

epichlorohydrin and other chemicals and reagents were from Sigma Chemicals Co. All the

other reagents were analytical grade and distilled water was used to prepare all the solution.

3.2.3 Synthesis of the epichlorohydrin crosslinked chitosan

A 5% chitosan solution was prepared by immersing 10g chitosan in 190 ml 2% aqueous

acetic acid solution to swell for 24 h. The mixture was poured into the dispersion medium,

consisting of 167 mL paraffin liquid and 2.0 mL Span80. During this process, the dispersion

medium was vigorously stirred at 60oC.

After 30 min, a 9.74-mL formaldehyde solution was added to the dispersion medium and

then stirred for 1 h to protect the amino group. At the end of this period, 5% NaOH was added

drop-wise to keep pH 10 of the mixture, and then added 7.3 ml of crosslinking reagent

epichlorohydrin. The reaction was carried out at 70°C for 2 h under gentle agitation.

Chitosan beads were filtered and washed with water to give the crosslinked microspheres,

which were suspended in 1 M HCl for 9 h to remove the protective group. After filtration and

washing with water, the microspheres were immersed in 1 M NaOH aqueous solution for 5 h

for conversion to base chitosan resin.

Finally, the crosslinked chitosan beads were collected and washed consecutively with water

and ethanol. The product was dried in vacuum and kept under vacuum for further analysis.

3.3 RESULTS AND DISCUSSION

3.3.1 Synthesis of the epichlorohydrin crosslinked chitosan

Crosslinked chitosan beads were prepared by using an organic suspension medium and

crosslinking technique. The process of synthesis of epichlorohydrin crosslinked chitosan resin

is shown in Figure 3.1.

15

Figure 3.1 Flowchart of synthesis of the epichlorohydrin-crosslinked chitosan

Figure 3.2 Synthetic pathway of epichlorohydrin crosslinked chitosan resin (ECHC)

16

It is well known that chitosan is soluble in an acidic solution. So in most cases, it is applied

with crosslinking products. The methods for producing spherical particles with crosslinking

agent, such as glutaraldehyde, were reported. Aldehyde reacts with amino groups of chitosan

to form the Schiff base. Glutaraldehyde makes chitosan resin more hydrophobic and would

cause the properties of chitosan change.

Among the crosslinking agents, the most popular is epichlorohydrin. It can form stable

chemical bonds with amino groups or hydroxyl groups under a certain condition. The results

from SEM showed that the tensile strength of the crosslinked chitosan was considerably

improved. Then it is reasonable to believe that chitosan beads crosslinking with

epichlorohydrin have superior properties to those with glutaraldehyde.

Epichlorohydrin is widely used in chemical industries as intermediates for synthesis of

many products. One bifunctional molecule, which contains two functional groups, is highly

reactive with hydroxyl groups.

One of the advantage of epichlorohydrin is that it does not eliminate the cationic amine

function of chitosan, which is the major adsorption site attracting the pollutant during

adsorption.

In the reaction, the amino group was protected by forming chemical unstable Schiff base

with formaldehyde first, because the crosslinking reagent, epichlorohydrin, can form stable

chemical bonds with amino groups.

Finally the Schiff base was hydrolyzed under low pH solution and converted into the amino

groups.

3.3.2 Morphology

Figure 3.3 SEM of chitosan microspheres, modified with epichlorohydrin Morphology of epichlorohydrin crosslinked chitosan microspheres was examined by

scanning electron microscopy (SEM). A sample SEM micrograph is given in Figure 3.3.

Analysis reveals some interesting features about the texture and morphology of ECHC.

17

ECHC beads have a spherical shape, smooth structure and nonporous appearance.

Microsphere size was evaluated, and the related results show that the mean diameter of the

particles was ca. 220µm.

3.3.3 FTIR-ATR spectra of chitosan and ECHC

The FTIR spectra of ECHC and chitosan are shown in Figure 3.4. FTIR analysis shows that

the adsorption band around 3300cm-1 in all spectra, revealed the stretching vibration of –NH2

and -OH groups in chitosan and ECHC. Bands near 1634 and 1554cm-1 in the spectrum of the

resin ECHC are assigned to C=N of Schiff base moiety and N-H of ECHC moiety,

respectively. Compared with chitosan, the differences in the spectra of ECHC were observed.

Figure 3.4 exhibits the strengthened characteristic peaks of C-H at 2923, 2876cm-1, which

indicates that more methylene groups appeared in ECHC resin. It could be appreciated that a

specific band appears at 1320 cm-1 for N-acetylglucosamine. The reaction of chitosan with

epichlorohydrin can occur at the more reactive hydroxyl group at C6 or the amino group at C2

of chitosan. However, N-substitution is reported to be preferable to O-substitution. The fact

that the intensity of the adsorption band around 1057 cm-1 was substantially increased in the

spectrum of ECHC, and the intensity of characteristic peak of C–N at 1375cm-1 is similar,

indicates that epichlorohydrin has reacted with the hydroxyl group of chitosan at C6.

Table 3.1 Peaks of FTIR-ATR spectra of Chitosan and ECHC and their assignment

-OH C-H Amide II N-H C-H amide II C-N C-O-C C-O C-O

Chitosan 3352 2867 1650 1589 1416 1374 1315 1150 1024

ECHC 3284 2923

2876

1634 1554 1414 1375 1316 1150 1057

Above all, chitosan has crosslinked with epichlorohydrin and the crosslinking takes place

only between hydroxyl groups of chitosan molecules at C6 and epichlorohydrin, due to the

amino group protected by forming a Schiff base with formaldehyde.

18

Wavenumbers (cm-1)

Figure 3.4 FTIR-ATR spectra of chitosan (A) and ECHC (B)

19

Chapter IV Preparation and characterization of Epichlorohydrin crosslinked carboxymethyl-chitosan

4.1 INTRODUCTION

Chitosan, as one of the most frequently reported biosorbents, has been investigated by

many researchers for removal of heavy metals from aqueous solution. Modifications of

chitosan can make it more selective and effective for several metal ions, especially heavy

metal ions. In addition, grafting new functional groups such as carboxymethyl group onto

cross-linked chitosan backbone was regarded as a simple and efficient way to facilitate the

adsorption capacity of chitosan for many heavy metals.

The grafting of specific functional groups onto a chitosan backbone allows sorption

performances to be improved due to the appearance of new sorbing functions. This simple

technique of modification of the structure of the chitosan allows the uptake capacity and

sorption kinetics to be increased.

In this work, Epichlorohydrin crosslinked carboxymethyl-chitosan resin was synthesized

and characterized by Fourier transform infrared (FT-IR) spectroscopy and a scanning electron

microscope.

4.2 MATERIALS AND METHODS

4.2.1. Instrumentation






4.2.2. Chemicals



epichlorohydrin, monochloroacetic acid and other chemicals and reagents were from Sigma

Chemicals Co. All the other reagents were analytical grade and distilled water was used to

prepare all the solution.

20

4.2.3 Synthesis procedures:

Preparation of crosslinked carboxymethyl-chitosan resin is shown in Figure 4.1.

A 5% chitosan solution was prepared by immersing 10g chitosan in 190 ml 2% aqueous

acetic acid solution to swell for 24 h. The mixture was poured into the dispersion medium,

consisting of 167 mL of paraffin liquid and 2.0 mL Span80. During this process, the

dispersion medium was vigorously stirred at 60oC.

After 30 min, a 9.74 mL formaldehyde solution was added to the dispersion medium and

then stirred for 1 h to protect the amino group. At the end of this period, 5% NaOH was added

drop-wise to keep pH 10 of the mixture, and then added 7.3 ml of crosslinking reagent

epichlorohydrin. The reaction was carried out at 70°C for 2 h under gentle agitation.

Chitosan beads were filtered and washed with water to give the crosslinked microspheres,

which were suspended in 1 M HCl for 9 h to remove the protective group. After filtration and

washing with water, the microspheres were immersed in 1 M NaOH aqueous solution for 5 h,

and then was filtered and washed with deionized water to neutral.

72.5g epichlorohydrin crosslinked chitosan beads were immersed in a solution consisting of

100 ml ethanol and 4g NaOH to alkalize for 3 h. 7.2 grams of monochloroacetic acid was

dissolved in 25 ml of isopropanol, and then added drop-wise to the flask containing the

alkalized chitosan. The reaction continued 4 h at room temperature and then the mixture was

filtered to remove the solvent. The product was washed twice with 75% ethanol and the resin

was dried at 60oC for 3 h and 7.3g of ECHCMC was obtained.

4.3. RESULTS AND DISCUSSION

4.3.1 Synthesis of Epichlorohydrin crosslinked carboxymethyl-chitosan (ECHCMC)

21

Figure 4.1 Flowchart of synthesis of epichlorohydrin crosslinked carboxymethyl-chitosan

22

Figure 4.2 Synthetic pathways of epichlorohydrin crosslinked carboxymethyl-chitosan

The procedure and synthesis mechanism of Epichlorohydrin crosslinked carboxymethyl

-chitosan (ECHCMC) was provided in Figure 4.1 and 4.2. The synthesis of ECHCMC was

based on carboxymethylation of epichlorohydrin-crosslinked chitosan resin (ECHC).

Concerning carboxymethylation of ECHC, the accessible reaction site was amino group,

due to C6 OH group crosslinked with epichlorohydrin. In the mildly alkaline medium, only

the amine groups will be activated and N-substitution will take place most probably.

4.3.2 Morphology

Morphology of epichlorohydrin crosslinked carboxymethyl-chitosan (ECHCMC)

microspheres was examined by scanning electron microscopy (SEM). The SEM micrograph

is given in Figure 4.3.

SEM micrograph shows some interesting features about the texture and morphology of

ECHCMC, compared with ECHC. The beads have a spherical shape, rough and uneven

surface structure and porous internal structure. The sample contained heterogeneously

23

distributed pores, and obviously different pore sizes

The microsphere size was evaluated, and the related results show that the mean diameter of

the particles was ca. 230µm.

Figure 4.3 Scanning electron micrograph of

epichlorohydrin-crosslinked

carboxymethylchitosan

4.3.3 FTIR-ATR spectra of chitosan and ECHCMC

FTIR-ATR spectra of ECHCMC and the attribution of characteristic peaks are shown in

Figure 4.4 and Table 4.1.

Figure 4.4 shows the basic characteristics of chitosan at 3352 cm-1 (O-H stretching and

N-H stretching), 2867 cm-1 (C–H stretching in methylene), 1650 cm−1 (C=O of NH C=O

stretching), 1589 cm-1 (N–H bending), 1154 cm-1 (bridge-O-stretch), and 1024 cm-1 (C-OH

stretching). The spectrum of ECHCMC beads displays a number of absorption peaks, an

indication of different types of functional groups present in the crosslinked beads. The broad

and strong band ranging from 3200 to 3600 cm-1 indicates the presence of OH and N-H

groups, which is consistent with the peak at 1055 cm-1 assigned to C-OH and C-N stretching

vibration. The peaks at 2923cm-1 can be assigned to asymmetric and symmetric CH2 groups.

Compared with the peaks of chitosan, the bands at 1597 cm-1 and 1404 cm-1 corresponding

24

to the carboxyl group (which overlaps with N–H bend) and -CH2COOH group, respectively

are intense in spectrum of ECHCMC indicating carboxymethylation on both the amino and

hydroxyl groups of chitosan. The peaks at the 1055 cm-1 (C–O stretch) also increase. When

–COOH becomes –COONa, its absorption peak will shift to 1598 cm-1, no bands at 1730 cm-1

for –COOH will be observed in the spectrum.

Table 4.1 Peaks of FTIR-ATR spectra of Chitosan and ECHCMC and their assignment

-OH C-H C=N

C=O

N-H C-H amide II C-N C-O-C C-O C-O

Chitosan 3352 2867 1650 1589 1416 1374 1315 1150 1024

ECHC 3284 2923

2876

1634 1554 1414 1375 1316 1150 1057

ECHCMC 3260 2923 - 1574 1404 - 1320 - 1055

Comparing with the spectra of ECHC, the difference in spectra of ECHCMC was observed.

Figure 4.4 exhibits the strengthened characteristic peaks of C-H at 2923, 2876cm-1, which

indicates that more methylene groups appeared in ECHCMC resin. The carboxymethylation

reaction of chitosan can occur at the more reactive hydroxyl group at C6 or the amino group

at C2 of chitosan. However, hydroxyl group at C6 is crosslinked with epichlorohydrin already.

The sharper band at 1574, 1404 and 1320 cm-1, corresponding to the bending vibration of

aliphatic secondary amine, confirmed the introduction of carboxymethyl group into the ECHC

backbone at –NH2 group of chitosan, namely the NH2 group of chitosan was involved in the

reaction.

25

Wavenumbers (cm-1)

Fig.4.4 FTIR-ATR spectra of chitosan (A), ECHC (B) and ECHCMC (C)

The FTIR-ATR analysis results of the derivatives show that a large amount of the

characteristic group (carboxyl group) exists in the product, and the carboxymethylation

reaction takes place mainly between amino groups of chitosan molecules at C2 and

monochloroactic acid.

The information above indicates the success of carboxymethylation process of the

epichlorohydrin crosslinked chitosan derivative.

26

Chapter V Preparation and characterization of a novel bioadsorbent EDTA-modified Epichlorohydrin crosslinked Chitosan

5.1. INTRODUCTION

Heavy metal ions in wastewater can bring harmful effects to human beings, as well as to

animals and plants. As a result, efficient removal of heavy metal ions from various water

resources has been a crucial issue by employing appropriate adsorbents.

Many researchers demonstrated that chitosan is an excellent natural adsorbent for metal

ions with much higher selectivity than usual commercial chelating resins and with a high

loading capacity (Inoue et al., 1988; 1993; 1994).

The large number of primary amine groups and hydroxyl groups at the sixth position with

high reactivity enables a variety of chemical modification on the backbone of chitosan (Kurita,

1986). Hence, it is very desirable to modify chitosan by grafting new functional groups on the

cross-linked chitosan to preserve or enhance the adsorption capacity.

Because a number of organic ligands containing amino-acetic acid groups (-NHCH2COOH)

are known to form stable complexes with a variety of metal ions, carboxylic acids (such as

ethylenediaminetetraacetic acid) represent promising candidates for the preparation of

environmental friendly adsorbents. Supposedly, the introduction of EDTA residues into

chitosan could significantly enhance the adsorption ability. Chemical modification of chitosan

with chelating agents such as ethylenediaminetetraacetic acid (EDTA), which form very

strong chelates with metal ions, may produce adsorbents with excellent metal binding

properties.

To date, no report has been identified on grafting EDTA onto epichlorohydrin crosslinked

chitosan resin.

In the present work, we prepared epichlorohydrin crosslinked chitosan chemically modified

with functional group ethylenediamine-N,N,N’,N’-tetraacetic acid (EDTA). The novel

biosorbent was synthesized and characterized by Fourier transform infrared (FT-IR)

spectroscopy and a scanning electron microscope.



Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES, Thermo-Fisher)

was used to determine the concentration of metal ions. Fourier transform infrared

27

spectroscopy with attenuated total reflectance (FTIR-ATR) was used to identify the functional

groups in the synthesized resin and the original chitosan.

5.2.2. Chemicals

Chitosan with 80 mesh, 96% degree of deacetylation and average-molecular weight of


epichlorohydrin and other chemicals and reagents were from Sigma Chemicals Co. All the

other reagents were analytical grade and distilled water was used to prepare all the solution.

5.2.3. Synthesis of EDTA-modified Epichlorohydrin crosslinked Chitosan

Preparation of EDTA dianhydride

EDTA anhydride was synthesized according to Tülü et al. (1999). 10.0g of EDTA (34mmol)

was suspended in 16ml of pyridine; then 14.0g of acetic anhydride (0.14mmol) was added and

the mixture was stirred vigorously at 65oC for 24h. The product was filtered, washed with

acetic anhydride and diethyl ether, and dried in vacuum for 24h.

Synthesis of EDTA-modified Epichlorohydrin crosslinked Chitosan

To improve its reactivity, epichlorohydrin crosslinked chitosan was functionalized with

EDTA. The epichlorohydrin crosslinked chitosan (ECHC) was chemically modified with

EDTA anhydride according to according to Nagib et al. (Figure 5.1), the reaction showed in

Fig. 1 for EDTAEC. A total of 6.4g of ECHC was suspended in 100 ml of 10 vol% aqueous

acetic acid solution. The mixture was diluted to four times with methanol. Afterwards,

approximately 4g of EDTA anhydride suspended in methanol was added to this solution and

stirred for about 24 h at room temperature to allow the reaction with ECHC to proceed.

After filtration, the precipitate was mixed with ethanol and stirred for a further 12h. After

filtering again, the precipitate was mixed with a dilute sodium hydroxide solution at pH 11

and stirred for 12 h to remove the unreacted EDTA. The precipitate was further washed

several times with deionized water. The repeated washing was followed by decantation using

a centrifuge until the solution became neutral. It was then mixed with 0.1 M hydrochloric acid

solution and washed with deionized water. After stirring in ethanol followed by filtration, the

final product was dried in vacuum to obtain 6.7g white microbeads and stored in a desiccator.


5.3.1. Synthesis of EDTA-modified Epichlorohydrin crosslinked Chitosan

The flowchart and the mechanisms of synthesis of EDTA-modified epichlorohydrin

crosslinked Chitosan are shown in Figure 5.1 and Figure 5.2, respectively.

28

Figure 5.1 Flowchart of synthesis of EDTA-modified epichlorohydrin-crosslinked Chitosan

(EDTAEC)

OHN

HO

O

NHO

O OH

O

O

+ H3C O CH3

O O

2pyridine

N2, 65oC, 24hO

NN

O

O

O

O

O

EDTA EDTA anhydride

+ CH3COOH4

ON

N

O

O

O

O

O

EDTA anhydride

+room temp

24h

O

OOH

O

N

OHO

N

HO

O

H

O

HO

HH

CH2H

NH2

O

H

O

HO

O

H

O

HO

HH

CH2 H

NH2

O

H

O

O

H

O

OH

HH

CH2H

H2NH

O

OH

O

H

O

OH

HH

CH2H

H2NH

O

n

+

O

H

O

HO

HH

CH2H

O

H

O

HO

O

H

O

HO

HH

CH2 H

NHO

H

O

O

H

O

OH

HH

CH2H

H

O

OH

O

H

O

OH

HH

CH2H

HNH

O

nNH

O

OOH

O

N

OHO

N

HO

O

OHO

O

N

OOH

N

OH

HN

O

OHO

O

N

OOH

N

OH

Figure 5.2 Synthetic routes of EDTA-modified Epichlorohydrin-crosslinked chitosan

(EDTAEC)

The procedure and synthesis mechanism of EDTAEC were shown in Figure 5.1 and 5.2,

29

respectively. The synthesis of EDTAEC began with epichlorohydrin-crosslinked Chitosan

Resin (ECHC). Concerning structure of ECHC, the accessible reaction site was amino group

due to C6 OH group already crosslinked with epichlorohydrin. In the mildly alkaline medium,

only the amine groups will be activated and N-substitution will take place.

5.3.2 Morphology

Morphology of EDTA-modified Epichlorohydrin-crosslinked Chitosan (EDTAEC)

microspheres was examined by scanning electron microscopy (SEM). The SEM micrograph

is given in Figure 5.3.

SEM analysis reveals some features about the fine structure and morphology of EDTAEC.

The EDTAEC beads have a spherical shape, relatively smooth surface structure and

nonporous appearance.

After magnification, some interesting structure appeared on the surface of EDTAEC

microsphere.

The grafting of EDTA on the backbone of ECHC resulted in the remarkable change of the

surface (see Figure 5.3). Many fissures on the surface EDTAEC microsphere appeared.

The size of microsphere was evaluated, and the related results show that the mean diameter

of the particles was ca. 200µm.

Figure 5.3 Scanning electron micrograph of EDTAEC

30

5.3.3 FTIR-ATR spectra of chitosan and EDTAEC

The FTIR-ATR spectra of EDTAEC and chitosan are shown in Figure 5.4.

Wavenumbers (cm-1)

Figure 5.4 FTIR-ATR spectra of chitosan (A), ECHC (B) and EDTAEC (C)

Table 5.1 Peaks of FTIR-ATR spectra of Chitosan and EDTAEC and their assignment

-OH C-H Amide II N-H C-H amide II C-N C-O-C C-O C-O

Chitosan 3352 2867 1650 1589 1416 1374 1315 1150 1024

ECHC 3284 2923

2876

1634 1554 1414 1375 1316 1150 1057

EDTAEC 3267 2927 1621 1377 1318 1152 1057

FTIR analysis shows that the basic characteristics of chitosan at: 3352 cm-1 (O-H stretching

and N-H stretching), 2867 cm-1 (C–H stretching in methylene), 1650 cm−1 (C=O of NH C=O

stretching), 1589 cm-1 (N–H bending), 1154 cm-1 (bridge-O-stretch), and 1024 cm-1 (C-OH

stretching). Compared with chitosan, the spectrum of ECHCMC beads displays remarkable

difference among the three spectra. The broad and strong band at 3267 cm-1 indicates the

presence of OH and N-H groups, which is consistent with the peak at 1057 cm-1 assigned to

31

C-OH and C-N stretching vibration. The peak at 2927 was assigned to asymmetric and

symmetric CH2 groups.

Compared with the peaks of chitosan and ECHC, the bands at 1554 cm-1 and 1414 cm-1

corresponding to the carboxyl group (which overlaps with N–H bend) and -CH2COOH group,

respectively are disappeared in spectrum of EDTAEC, while the intensity of the peaks at the

1621 cm-1 (C –O stretch) and 1377cm-1 (C-N) increase considerably. The reason is that when

–COOH becomes –COONa, its absorption peak will shift to 1621 cm-1, and no bands at 1730

cm-1 for –COOH will be observed in the spectrum.

The sharper bands at 1621, and 1377 cm-1 confirmed the introduction of EDTA group into

the ECHC backbone at –NH2 group of chitosan.

Results from IR spectrograph suggest that EDTA was grafted on to the molecular skeleton

of ECHC successfully. And so far the EDTAEC resin has not been reported after information

retrieval. It is most probably a novel bioabsorbent.

32

Chapter VI Synthesis of Thiourea-Modified O-Carboxymethyl-Chitosan

6.1. INTODUCTION

Wastewaters produced by humans are frequently laden with toxic heavy metals such as lead,

copper, cadmium, etc. The soluble form of these heavy metals is very dangerous because it is

easily transported and more readily available to plants and animals. Hence, to remove toxic

heavy metals from wastewaters has become increasingly focused.

Chitosan, as one of the most frequently reported biosorbents, has been investigated by

many researchers for recovery of heavy metals from aqueous solution. The high nitrogen

content of this abundant natural biopolymer exceeds a 7% (w/w) proportion which explains

the ability of the biosorbent to remove metal ions from dilute solutions. Free electronic

doublet of nitrogen is responsible for the sorption of many cations: copper, lead and cadmium.

Chitosan is also a versatile material which can be easily modified by grafting new specific

functional groups on the backbone of the polymer. Transformations occur on several

functional groups of chitosan but more specifically on –CHOH and –NH2 groups depending

on the substitution mechanism.

Modifications of chitosan can make it more selective and effective for several metal ions,

especially heavy metal ions. The treatment induces new linkages between the chitosan chains

allowing the polymer to be highly resistant to dissolution even in harsh solutions such as

hydrochloric molar solutions.

Carboxymethylation was regarded as a simple and efficient way to facilitate the adsorption

capacity of chitosan for many heavy metals. In addition, grafting new functional groups such

as thiourea onto cross-linked chitosan backbone can also improve its selectivity and

adsorption ability. The grafting of new chelation groups on chitosan backbone is assumed to

increase sorption capacities owing to the coordination chemistry of grafted functional groups:

sulfur compounds are well-known for their affinity for heavy metals.

Sorbents with donor N and more especially S atoms in their functional groups are thus

performing resins. Muzzarelli and Tanfani showed dithiocarbamate chitosan is effective at

removing metal ions even in acid solutions. Guibal et al. had prepared a thiourea derivative of

chitosan which shows a greater selectivity for platinum.

In this work, we modified chitosan by both carboxymethylation and grafting sulfur groups

(thiourea). Thiourea-modified chitosan resin was synthesized and characterized by Fourier

transform infrared (FT-IR) spectroscopy.

33








6.2.2. Chemicals


1.5×105 was purchased from Qingdao Baicheng Biochemical Corp. (China). Glutaraldehyde,

thiourea, monochloroacetic acid and other chemicals and reagents were from Sigma

Chemicals Co. All the other reagents were analytical grade and deionized water was used to

prepare all the solution.

6.2.3 Synthesis procedures:

Thiourea-modified O-carboxymethyl-chitosan was prepared through two steps as showed

in Figure 6.1:

1) O-carboxymethyl-chitosan was prepared according to Zhu et al. 2g chitosan was

immersed in 25 ml of 50 wt% NaOH solution to swell and alkalize for 24 h. Five grams of

monochloroacetic acid was dissolved in 25 ml of isopropanol, and then added drop-wise to

the flask containing the alkalized chitosan after filtration for 20 min. The reaction continued 8

h at room temperature and then the mixture was filtered to remove the solvent.

The filtrate obtained was dissolved in 100 ml of water, and 2.5M HCl was added to it to

adjust its pH to 7. After this solution was centrifuged to remove the precipitate, 400 ml of

anhydrous ethanol was added. The precipitate was washed with absolute ethanol and dried in

vacuum. 2.3g of O-carboxymethyl-chitosan was obtained and kept under vacuum for further

application.

2) 3.0g of thiourea was dissolved in 60 ml distilled water，and then 17 ml of (50%)

glutaraldehyde solution was added to thiourea solution in a round flask. The mixture was

heated on a water bath for 3h at 50oC.

After reaction, 1.36g of carboxymethyl-chitosan was dissolved in 30 ml distilled water, and

then added to the mixture to the flask and heated for 8h at 70oC. Thiourea-modified chitosan

resin was formed, and washed several times with dilute sodium hydroxide, deionized water

and acetone respectively, and then the resin was dried at 70oC for 3h.

34

Finally, 3.2g of the thiourea-modified carboxymethyl chitosan resin was obtained.

6.3. RESULTS AND DISCUSSIONS

6.3.1 Synthesis of Thiourea-Modified O-Carboxymethyl-Chitosan Derivative

The process of synthesis of Thiourea-Modified O-Carboxymethyl-Chitosan is shown in

Figure 6.1.

Figure 6.1 Flowchart of synthesis of Thiourea-modified O-carboxymethyl-chitosan

Figure 6.2 Synthetic pathway of thiourea-modified O-carboxymethyl-chitosan

Thiourea-modified O-carboxymethyl-chitosan (TUCMC) was synthesized through two

steps as showed in Figure 6.1. The synthesis mechanism of TUCMC was provided in Figure

6.2. The O-carboxymethylation of chitosan is the key step to succeed in preparation of

TUCMC. The high degree of O-carboxymethylation was obtained by using a strong base

medium, pointing out the importance of alkaline conditions for O-carboxymethylation. A

35

sufficiently strong base is needed to allow chloroacetate penetration on the whole TMC chain,

avoiding side reactions between NaOH and chloroacetate (Barros et al., 2013).

Concerning carboxymethylation, isopropanol as reaction medium led to better results,

achieving degrees of O-carboxymethylation to the extent of 85%. This might be related to a

better conformation of chitosan in isopropanol offering higher accessibility to the reaction

sites.

The reaction conditions are responsible to attain the N versus O selectivity of

carboxyalkylation and degree of substitution (DS). To proceed with the reaction of

carboxymethylation of chitosan in the solvent as water/isopropyl alcohol, chitosan is first

activated by soaking it in the alkaline solution. At high alkali concentrations (more than 25%

aqueous NaOH), alkylation with monochloroacetic acid gives mixed N- and O-alkyl

chitosan derivatives with substitution at the C6 and C3 OH groups and also some substitution

on the C2- NH2 groups. The ease of substitution is in the order OH- 6 > OH-3 > NH2-2.

Yields of carboxymethyl-chitosan prepared in the mixed solvents were higher than in water

alone or in isopropanol alone. The highest yields were close to 100% at water/isopropanol

ratios between 1/4 and 1/1 at 50 °C. The carboxymethyl groups were mostly substituted on

the –OH groups, with a small amount on the –NH2 groups. The 6-OH group had the highest

degree of substitution.

6.3.2 Morphology

Morphology of thiourea-modified O-carboxymethyl-chitosan resin was examined by

scanning electron microscopy (SEM). The SEM micrograph is shown in Figure 6.3.

Some interesting features about the texture and morphology of TUCMC were revealed by

SEM micrograph analysis. The produced particles have an irregular shape, network structure

and porous internal structure and it can also be observed that TUCMC particles have irregular

surface structure. The particle size was evaluated, and the related results show that the mean

diameter of the particles was ca. 80µm.

As showed by SEM of the cross-sectional morphologies of TUCMC in Figure 6.3, the

sample contained interconnected and heterogeneously distributed pores, and obviously

different pore sizes.

36

Figure 6.3 Scanning electron micrograph of Thiourea-modified O-carboxymethyl-chitosan

6.3.3 FTIR-ATR spectra of chitosan and TUCMC

The FTIR-ART spectra of TUCMC and the attribution of characteristic peaks were shown

in Figure 6.4 and Table 6.1.

Wavenumbers (cm-1)

Figure 6.4 FT-IR spectra of chitosan (A), CM-Chitosan (B) and TUCMC (C)

37

Table 6.1 Peaks of FTIR-ATR spectra of chitosan and TUCMC and their assignment

-OH C-H C=N

C=O

N-H C-H amide II C-N C-O-C C-O C-O-O

Chitosan 3352 2867 1650 1589 1416 1374 1315 1150 1024

CM-chitosan 3285 2880 1581 1409 1379 1317 1148 1061

TUCMC 3320 2933

2870

1633 1555 1397 1369 1317 1198 1028

As seen from Figure 6.4 and Table 6.1, the basic characteristic peaks of chitosan are at

3352 cm-1(O–H stretch), 2923-2867 cm-1 (C–H stretch), 1589-1600cm-1 (N–H bend), 1154

cm-1 (bridge-O stretch), and 1024cm-1 (C–O stretch) (Brugnerotto et al., 2001 and Shigemasa

et al., 1996). Compared with the peaks of chitosan, the bands at 1597–1650 cm-1 and

1414-1401 cm-1 corresponding to the carboxyl group and S=C (which overlaps with N–H

bend) and -CH2COOH group, are intense in spectrum of TUCMC indicating

carboxymethylation on hydroxyl groups of chitosan. The peaks at the 1154–1029 cm-1 (C–O

stretch) also increase, and it is one of the characteristics of O-carboxymethyl-chitosan.

In Figure 6.4, comparing the spectrum of TUCMC with raw chitosan, the new band near

1397cm-1 corresponds to COO– stretching vibration. The band near 1033cm-1 is weakened,

and the band near 1155cm-1 disappears, which means that the carboxymethylation process

has happened on the –C–OH. Bands near 1633 and 1555cm-1 are assigned to v-C=N of

Schiff’s base moiety and -C–N of thiourea moiety, respectively. And the broad peak of

1633cm-1 is a result of the overlapping of peaks of C=N, –COOH and –COO−. In addition,

the spectrum shows no characteristic bands related to free aldehydic group near 1720cm-1 for

glutaraldehyde. The information above indicates the success of the modification process of

the thiourea-modified chitosan derivative.

38

Chapter VII PHYSICOCHEMICAL CHARACTERIZATION OF FOUR CROSSLINKED CHITOSAN DERIVATIVES

7.1. INTRODUCTION

In past decades, it is confirmed that chitosan is an excellent natural adsorbent for metal ions

with much higher selectivity and a high loading capacity than usual commercial chelating

resins. The grafting of specific functional groups onto a chitosan backbone allows sorption

performances to be improved due to the appearance of new sorbing functions and by an

improvement in diffusion properties. The simple technique of modification of the structure of

the chitosan allows the uptake capacity and sorption kinetics to be increased (Guibal et al.

2002). The advantages of chemical modification are:

(a) It prevents chitosan solids from dissolution in strong acid solutions

(b)Mechanical strength of chitosan solids can be improved which provides resistance to

chemical degradation.

(c) It may increase the porosity and surface area of chitosan solids.

Based on chitosan four bioadsorbents have been synthesized and characterized. The

structures of four crosslinked chitosan derivatives are shown in Figure 7.1.

O

H

O

HO

HH

CH2H

NH2

O

H

O

HO

O

H

O

HO

HH

CH2 H

NH2

O

H

O

O

H

O

OH

HH

CH2H

H2NH

O

OH

O

H

O

OH

HH

CH2H

H2NH

O

n

ECHC

O

H

O

HO

HH

CH2H

NH

O

H

O

HO

O

H

O

HO

HH

CH2 H

NH

O

H

O

O

H

O

OH

HH

CH2H

HNH

O

OH

O

H

O

OH

HH

CH2H

HNH

O

O

HO

O

OH

O

OH

O

HO

n

ECHCMC

39

EDTAEC

TUCMC

Figure 7.1 Chemical structures of four crosslinked-chitosan derivatives

A

B

C

D

(A) Epichlorohydrin-crosslinked chitosan resin (ECHC); (B) Epichlorohydrin-crosslinked carboxymethyl-chitosan resin (ECHCMC); (C) EDTA-modified epichlorohydrin-crosslinked chitosan resin (EDTAEC); (D) Thiourea-modified O-carboxymethyl-chitosan resin (TUCMC)

Figure 7.2 The synthesized crosslinked chitosan derivatives

40

Physiochemical characteristics of resin will affect remarkably on the absorption capacity.

Therefore, the aim of this study was to investigate the physicochemical properties and

adsorption properties of these promising materials in more detail.




was used to determine the concentration of metal ions. pH meter (PHS-25).

7.2.2. Chemicals

Chemicals and reagents were purchased from Sigma Chemicals Co. All the reagents were

analytical grade and deionized water was used to prepare all the solution. Standard solutions

of Lead and Cadmium for ICP-OES were obtained from Beijing NCS Analytical Instruments

Co. Ltd. Pb(NO3)2, and Cd(NO3)2 were used and 0.1M HNO3 and 0.1M NaOH were used for

pH adjustment.

7.2.3 Swelling Test of Cross-linked Chitosan Beads

Cross-linked chitosan derivatives were tested with regard to their solubility in distilled

water. 0.1g of cross-linked chitosan derivatives were taken in a 10 ml graduated cylinder and

dipped in 8 ml distilled water for 5 hours in a closed environment until the volume did change

anymore. The expansion coefficient of these bioabsorbents was calculated from the following:

where K is the expansion coefficient; V0 is the volume of dry beads; V is the volume of the

swelling crosslinked chitosan derivatives.

7.2.4 Determination of bulk density

Bulk density is determined by measuring the volume of a known mass of the powder

sample that has been passed through a screen into a graduated cylinder.

The resins were sieved where the particle size fraction 0.1–0.4mm was kept.

After about 2 ml of dry resin was transferred carefully to graduated cylinder, the volume

was measured accurately without compacting. Calculate the bulk density, in g per mL, by the

formula:

Where is the bulk density g/ml; W is the weight of resin; V is the volume of the

resin.

41

Generally replicate determinations are desirable for the determination of this property.

7.2.5 Determination of skeletal density

The skeletal density was measure by the following procedure:

Add 5 ml of n-heptane to a 10 ml graduated cylinder accurately and then weigh to get the

mass (W1). Add exactly 0.2g of dry resin (W) and 3 ml n-heptane. After 2 hours, add more

n-heptane to the level of 5 ml and weigh it (W2), Calculate the skeletal density, in g per mL,

by the formula:

(dt=0.6830 the density of n-heptane g/cm3)

Wheres is the skeletal density.

7.2.6. Determination of water uptake of modified Chitosan derivatives

Water uptake of the crosslinked Chitosan derivatives was determined at 37oC after

equilibration in distilled water. The preliminary tests lead to the equilibrium time required for

complete swelling and was shorter than 60 h. Therefore, the experiments were carried out

considering the water uptake calculation after equilibration in distilled water for 72 h. The

weight of swollen samples was determined after removal of the surface liquid with lint-free

tissue paper. Water uptake was then calculated according to the following Equation:

Where, Wu, Wf and W0 are water uptake, final weight and the initial weight of the sample,

respectively.

7.2.7 Evaluation of the porosity

The porosity (P) was expressed in the following formula:

Where s is the skeletal density (g/ml), H is water uptake of the resins (%).

7.2.8 Determination of absorption capacity

A sample of 0.1g dry resin was swelled in a 250 mL Erlemeyer flask containing 50mL of

deionized water for 1 hour. 50mL of 0.02 M Pb(NO3)2 and Cd(NO3)2 solutions, was

separately added, where the concentration of the metal ion became 0.01M. The mixture of the

flask was equilibrated for 12 h on a rotary shaker at 200rpm and 25◦C. The metal ion

42

concentration has been determined before and after the treatment using ICP-OES. The

difference in the amount of metal ion was considered as a function of metal ion uptake of the

investigated resin.

The following equation was used to calculate the polymer absorption capacity in mmol/g

polymer.

Where Qe is the maximum metal uptake capacity (mmol/g); Ci, the initial metal

concentration (mmol/L); Cf the final metal concentration (mmol/L); V the volume of solution

(L); M, the dry resin loading (g).


7.3.1 Comparison of physical capacities of four resins

The results of the expansion coefficient, bulk density, skeletal density, water uptake, and

the porosity of the four synthesized resins are available in Table 7.1.

Table 7.1 Comparison of physical capacities of synthesized chitosan chelating resins

Expansion

Coefficient( K)

Bulk Density

(g/cm3)

Skeletal Density

(g/cm3)

Water Uptake

(%)

Porosity

(%)

ECHC 1.857 0.4585 0.5452 53.133 38.19

ECHCMC 2.000 0.6270 1.1562 59.200 62.65

EDTAEC 2.143 0.4979 0.7747 67.984 62.19

TUCMC 1.286 0.3730 1.5929 40.723 52.25

The expansion coefficient is one of acting factors of sorption capacity. The swelling can

make the gap between the macromolecular skeleton increases, and small molecules can easily

diffuse into the interior. It will improve the utilization rate of chelating ligands.

The expansion coefficient, bulk density and porosity of the chitosan were depicted in Table

7.1. Compared with ECHC, the bulk density of ECHCMC and EDTAEC increased obviously

from 0.4585 to 0.627g/cm3, while the porosity increased from 38.19% to 62.65%, and

expansion coefficient increased from 1.857 to 2.143. It is indicated that physical properties of

chitosan have changed remarkably after grafting with carboxymethyl and EDTA group.

Among the four resins, TUCMC has the lowest bulk density and water uptake, and the highest

skeletal density. As to the new resin EDTAEC, it has the highest expansion coefficient, water

uptake and porosity. The presence of hydrophilic amino and amide groups is known to

43

increase the hydrophilicity of the system and consequently they increase the equilibrium

swelling values of the samples in aqueous medium (Kandile et al., 2009).This means that the

novel resin has the characteristics of porous and high water absorption and swelling.

7.3.2 Comparison of adsorption capacities of four resins for metal ions

Table 7.2 Comparison of adsorption capacities of synthesized chitosan resins for metal ions

ECHC ECHCMC EDTAEC TUCMC

Pb2+ (mmol/g) 0.42 0.77 0.95 0.32

Cd2+(mmol/g) 0.20 0.40 0.16 0.18

Table 7.2 showed the adsorption capacity of four synthesized crosslinked derivatives for

Pb2+ and Cd2+. By comparative analysis of the maximum adsorption capacity of resins for

Pb(II) and Cd(II), among the four resins, ECHCMC is very effective at removing Cadmium

with sorption capacity exceeding 0.40mmol/g from aqueous solutions. Additionally, excellent

uptaking capacity of the novel resin EDTAEC for Pb(II) was 0.95mmol/g. ECHCMC resin

has the relatively strong adsorption capacity for both Pb2+ and Cd2+ with the maximum

adsorption capacity of 0.77 and 0.40 mmol/g, respectively. In addition, EDTAEC could be

used for the selective absorption of Pb from aqueous solution by analysis of the data in Table

7.2. In the following study, EDTAEC was singled out for further research.

44

Chapter VIII EVALUATION Of SORPTION PERFORMANCE AND ADSORPTION MECHANISM OF FOUR CROSSLINKED CHITOSAN

DERIVATIVES

8.1. INTRODUCTION

Heavy metal contamination in aquatic systems is one of the most critical environmental

issues today because these natural resources may impact human health through the food chain.

Heavy metals are released into the aqueous environment through a variety of sources such as

microelectronics and usage in fertilizers paints, pigments, batteries, and the like. These would

endanger public health and the environment if discharged improperly. The heavy metals play

a dual role as essential nutrients and toxic chemicals in plant production and human health.

Trace metals such as Cd, Cr, Cu, Hg, Pb and Ni are mainly regarded as responsible for water

pollution from the viewpoints of phytotoxicity of undesirable entrance into the food chain.

Toxic heavy metals are of concern due to their harmful effects and long-term persistence in

the environment. The hazards associated with the pollution of water bodies caused by heavy

metals have led to the development of various wastewater reclamation technologies such as

chemical precipitation, membrane separation, advanced oxidation process, electrochemical

technique, biological treatment, and adsorption. Among all treatments that are proposed,

adsorption is recognized as an effective and economical method for the removal of pollutants

from wastewaters. However, the removal of heavy metal ions from wastewater is always a

challenging task for environmentalists, so some researchers have attempted to develop

effective performance adsorbents for the disposal of heavy metal ions.

Chitosan have received great attention over the past few decades due to its outstanding

adsorption behavior toward various toxic heavy metals from aqueous solutions because they

possess a number of different functional groups such as hydroxyls and amines to which metal

ions can bind either by chemical or by physical adsorption. Nevertheless, chitosan has some

defects (i.e. low acid stability, inadequate mechanical strength and low thermal stability)

which restrict its application.

Chemical modification of chitosan can prevent chitosan solids from dissolution in acidic

media, improving mechanical strength, and increasing the porosity and surface area and

45

promoting its applications for heavy metal contaminate removal.

In the present study, epichlorohydrin-crosslinked chitosan resin (ECHC),

epichlorohydrin-crosslinked carboxymethyl-chitosan resin (ECHCMC), EDTA-modified

epichlorohydrin-crosslinked chitosan resin (EDTAEC), and thiourea-modified

O-carboxymethyl-chitosan resin (TUCMC) were designed and synthesized.

Moreover the effects of process variables, adsorption kinetics in single-component system

and sorption performance of four cross-linked chitosan derivatives in multi-component

system were investigated.

Finally, infra-red spectrometry has been applied to investigate adsorption mechanisms.

The main objective is to provide information about the most important features of chitosan-

based adsorbents that may be helpful for synthesizing better adsorption property of modified

chitosan.




was used to determine the concentration of metal ions. pH meter (PHS-25). Fourier transform

infrared spectroscopy with attenuated total reflectance (FTIR-ATR) was used to identify the

functional groups in cross-linked bead and cross-linked chitosan-metal complex. These

figures show the chemical modifications of cross-linked chitosan and the modifications due to

adsorption of metal.

8.2.2. Chemicals

Chemicals and reagents were purchased from Sigma Chemicals Co. All the reagents were

analytical grade and deionized water was used to prepare all the solution. Standard solutions

of Lead and Cadmium for ICP-OES were obtained from Beijing NCS Analytical Instruments

Co. Ltd. Pb(NO3)2, Cd(NO3)2, Cu(NO3)2, Ni(NO3)2 and Cr(NO3)3 were used and 0.1M HNO3

and 0.1M NaOH were used for pH adjustment.

8.2.3 Sorption experiments in multiple metals aqueous solution

1mmol of each of Pb2+, Cd2+, Cu2+, Cr3+ and Ni2+ metal ion mixture was dissolved in 500

ml deionized water.

A sample of 0.1g dry resin was swelled in a 250 mL Erlemeyer flask containing 50mL of

deionized water for 1 hour. 50mL of 0.002 M multiple-metals solution, was separately added,

46

where the concentration of the metal ion became 0.001M. The mixture of the flask was

equilibrated for 12 h on a rotary shaker at 200rpm and 25◦C.

After shaking, the sample was filtered through Whatman No. 2 filter. The filtrate was

gathered in a plastic bottle and stored until analysis, while the sorbent loaded with metal was

washed thoroughly with deionized water to remove the traces of unreacted metal ions. These

beads were air dried. Dried spent sorbent was collected for FTIR analysis. Metal solution

without sorbent was also shaken for 12 h, filtered and analyzed to take one accurate measure

of the initial metal concentration.

The metal ion concentration has been determined before and after the treatment using

ICP-OES. The difference in the amount of metal ion was regarded as a function of metal ion

uptake of the investigated resin.

The following equation was used to calculate the polymer chelation capacity in mmol/g

polymer.

Where Qe is the maximum metal uptake capacity (mmol/g); Ci, the initial metal

concentration (mmol/L); Cf the final metal concentration (mmol/L); V the volume of solution

(L); M, the dry resin loading (g).

8.2.4 Kinetic studies on EDTAEC

For the kinetics study, a single metal concentration (0.002mmol/L) was used and the

mixture was shaken for 60, 120, 180, 240, 300, 330 and 360 min.

The experimental method and calculation were described in section 8.2.3.

8.2.5. Desorption and reusability

Metal ions-loaded modified chitosan resin was collected and washed with deionized water

to remove any unabsorbed metal ions. Then batch desorption experiments were carried out

using various concentrations of HCl solutions. The resin after desorption was rinsed with

deionized water, dried and then reused in an adsorption experiment. The process was

replicated for five times.

8.2.6 Infrared Spectroscopy for Characterization

Experiment was on cross-linked chitosan derivatives and newly formed resin-metal

complex beads. Adsorption is a surface phenomenon; this technique is suitable to observe the

47

chemical changes occurring on the surface induced by either chemical modification or by

heavy metal adsorption. FTIR characterization of chitosan powder and chitosan metal

complex beads was characterized with Thermo Fisher Nicolet iS50 FT-IR spectrophotometer

Spectrum instrument with attenuated total reflectance (ATR).

8.2.6. Statistical analysis

Triplicate measurements were carried out and metal free were used as controls. The results

were reported as mean±standard deviation. The data were analyzed using statistic software

Sigmaplot 12.5.


8.3.1 Evaluation of sorption performance in multiple-metals aqueous solution

The amounts of sorption of heavy metals from water on cross-linked chitosan derivatives

were measured. Experiments were performed at an initial concentration of 1 mmol/L of each

metal in multiple-metal solution.

The co-sorption data of Pb2+, Cd2+, Cu2+, Cr3+ and Ni2+ from multiple-metal system on four

resins were presented in table 8.1, Figure 8.1 and Figure 8.2.

Figure 8.1 Adsorption performance of four resins in multiple-metals aqueous solution

48

Table 8.1 Co-adsorption data of four resins in multiple-metals aqueous solution (mmol/g)

(±RSD%, relative standard deviation)

ECHC ECHCMC EDTAEC TUCMC

Pb2+ 0.0222±0.43 0.0632±0.60 0.1704±0.58 0.0048±0.21

Cd2+ 0.0205±0.07 0.0507±0.86 0.0569±0.51 0.0311±0.60

Cr3+ 0.0964±0.26 0.0400±0.20 0.0533±0.57 0.0000±0.48

Cu2+ 0.1253±0.30 0.1907±0.56 0.3692±0.68 0.2724±0.44

Ni2+ 0.0230±0.28 0.0460±0.87 0.0731±1.09 0.0579±0.23

Figure 8.2 Sorption of Pb2+, Cd2+, Cu2+, Cr3+ and Ni2+ from metal ion mixtures on four resins

The sorption of heavy metals including Pb2+, Cd2+, Cu2+, Ni2+ and Cr3+ from aqueous

streams by raw and chemically modified chitosan has been widely studied. Most of these

studies either obtained the sorption isotherms or purely compared the selectivity series based

on the results of single-metal systems or binary-component systems.

Considering metal ion mixtures, the novel resin EDTAEC has outstanding performance on

adsorption of Pb2+, Cd2+, Cu2+, Ni2+, and Cr3+ from aqueous metal ion solutions (Table 8.1 and

Figure 8.2). Order of metal chelation for 1mmol/g was as follows: Cu2+> Pb2+> Ni2+> Cd2+>

49

Cr3+. Metal chelating ability of EDTAEC for Cu2+ and Pb2+ was higher than that of the other

three resins.

TUCMC has binding capacities of more than 0.057 mmol/g for Ni2+ and 0.031mmol/g Cd2+,

with the exception of chromium, and is more efficient in scavenging Cu2+ from metal mixture

solution as compared to other resins. TUCMC beads adsorbed heavy metal ions in the

following order: Cu2+ > Ni2+ > Cd2+.

The result of metal ion sorption of ECHCMC indicated that it has binding capacities of

0.19 mmol/g for Cu2+ and ca. 0.05mmol/g Pb2+, Cd2+, Ni2+ and Cr3+.

Comparing the uptake capacity for the metal ions, the performance of ECHC, as expressed

by the order of its affinity, was in the order of Cu2+>Cr3+> Ni2+> Pb2+> Cd2+. Table 8.1 and

Figure 8.2 showed that ECHC is more efficient in scavenging Cr3+ from metal mixture

solution as compared to other resins.

By comparison of sorption performance of four resins, a conclusion could be reached that

the resins based on chitosan exhibit selective binding towards of Cu(II), Cd(II), Ni(II), Cr(III)

and Pb(II) ions in aqueous medium.

The lone pair electrons present on the amino nitrogen can establish dative bonds with

transition metal ions. Some hydroxyl groups in chitosan derivatives may function as second

donors; hence, hydroxyl groups can be involved in coordination with metal ions.

Table 8.1 shows remarkably that EDTAEC is of higher capacity for sorption of Pb(II) than

the others from multi-component metals solutions, and the adsorption performance of

EDTAEC for Pb(II) is more attractive to study.

8.3.2 Adsorption performance of EDTAEC for Pb2+

8.3.2.1 Reusability of EDTAEC

After adsorption of Pb (II) by EDTAEC, the loaded sorbent was resuspended in 20 mL of

0.1 M HCl. After this suspension was shaken for 6 h at room temperature, sorbents were

separated by filtration and washed with distilled water until neutralization and then dried.

Then, the sorption process was repeated by using the regenerated adsorbent. It was observed

that after three cycles there is no change in Pb (II) sorption capacity of EDTAEC. In

desorption experiments, it has been observed that almost total recovery of Pb (II) occurs,

suggesting that the EDTAEC is regenerable and can be used several times.

50

8.3.2.2 Kinetic studies on EDTAEC for Pb2+

The adsorption behavior of Pb (II) on the studied resin at initial concentration 0.01 M, pH

6.5 and 25◦C as a function of contact time is shown in Figure 8.3. It can be seen that the

maximum uptake of Pb (II) could be achieved within 6 h and maximum uptake capacity

reached 0.95 mmol/g. The good adsorption capacity of Pb (II) is mostly attributed to graft

EDTA in the structure of the epichlorohydrin-crosslinked chitosan resin.

The kinetic of adsorption is an important characteristic that defines the efficiency of

sorption. In order to evaluate the kinetic mechanism that controls Pb (II) adsorption process of

EDTAEC, the pseudo-first- and pseudo-second-order-kinetic models were applied.

The Lagergren pseudo-first-order model (Lagergren, 1898) is expressed as:

where k1 is the pseudo-first-order rate constant (h−1) of adsorption; and qe and qt (mmol/g)

are the amounts of metal ion adsorbed at equilibrium and at time t (h), respectively. Straight

line plots of log(qe-qt) against t were used to determine the rate constant, k1 and correlation

coefficient R2 values for Pb (II) under different concentration range conditions. On the other

hand, the pseudo-second-order equation (Deng et al., 2007) is expressed as:

where k2 is the pseudo-second-order rate constant of adsorption (g/(mmol h−1)). The kinetic

parameters for pseudo-second-order model were determined from the linear plots of t/qt

versus t. The validity of each model is checked by comparing the R2 values. The adsorption of

Pb (II) on the resin perfectly fits pseudo-second-order model (see Figure 8.4). The first-order

kinetic process has been used for reversible reaction with an equilibrium being established

between liquid and solid phases (Low, 2000).

Whereas, the pseudo-second-order kinetic model assumes that the rate-limiting step may

be chemical adsorption (Crini, 2007). In this case, the adsorption behavior of Pb (II) implies

the adsorption rate may be controlled by intraparticle diffusion.

51

1 2 3 4 5 6 70.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Upt

ake

(mm

ol/g

)

Time (h)

Figure 8.3 Effect of contact time on the uptake of Pb (II) with initial concentration 0.01 M by EDTAEC at 25◦C.

0 1 2 3 4 5 60

1

2

3

4

5

6

7

t/qt (

h,g

/mm

ol)

t (h)

Equation y = a + b*x

Weight No Weighting

Residual Sum of Squares

0.28964

Pearson's r 0.98888

Adj. R-Square 0.97346

Value Standard Error

C Intercept 1.74404 0.21896

C Slope 0.7822 0.05261

Figure 8.4 Pseudo-second-order kinetic plots for the adsorption of Pb2+ by EDTAEC

8.3.3 Infrared Spectroscopy for characterization and mechanism of adsorption

FTIR spectra have widely been used as a tool to detect the presence of certain functional

groups or chemical bonds on a solid surface in material modifications because each specific

chemical bond often shows a unique energy adsorption band.

In this study, Infra-red (IR) techniques are used to identify the active sites in chelate

52

formation. After filtration, the sorbent loaded with metal was washed thoroughly with

deionized water to remove the traces of unreacted metal ions. These air-dried spent sorbents

were collected for FTIR analysis (Figure 8.5).

(1) ECHCMC (2) TUCMC (3) EDTAEC (4) ECHC

Figure 8.5 The air-dried spent cross-linked chitosan beads after sorption of multi-metal ions

8.3.3.1 Infrared Spectroscopy for characterization of ECHC-metal complexation

FTIR studies were made on ECHC beads before and after being in contact with multi-metal

ions of solution. FTIR spectra (Figure 8.6) show that there is a remarkable difference between

two samples.

Infrared spectrum analysis reveals that the band at 3290cm-1 is due to the elongation of

N−H and O−H bonds; therefore it can be assigned to several functional groups present in the

sample as −NH2 primary amines, R2NH secondary amines and alcoholic group. The band at

2922cm-1 is due to C−H (−CH3, >CH2) bond elongation. The band at 1642cm-1 is

characteristic of the >C=O bond of an amide which was expected, since the chitosan was

prepared from chitin by partial deacetylation. The bands at 1375 cm-1 (signal of C-N bond)

and at 1554 cm-1 (signal of N-H bond) changed very much in intensity and the signal of C-OH

at 1025 cm-1 increased remarkably.

The difference between the IR spectra of ECHC before and after the heavy metal ions

were adsorbed that the wide band at 3290 cm-1 assigned to amines changed very much in

intensity due to vibration of the N−H bond is modified while forming a bond between the

nitrogen (by its free pair of electrons) and the metal. The band at 1642 cm-1 also assigned to

N−H bond decreased considerably in intensity and was displaced to 1531 cm-1.

53

Wavenumbers (cm-1)

A: ECHC beads B: ECHC-metal complexation

Figure 8.6 FTIR spectra of ECHC beads and ECHC-metal complexation

There are several bands in the IR spectrum that neither present a reduction in their intensity

nor change position this indicates that the metal does not associate with the functional groups

that generate these bands. Results from IR spectrograph suggest that a coordination complex

is established between the chitosan and the metal with the participation of the amino and

secondary alcohol functional group. It suggests that the metal predominantly associates with

−NH2 and −OH of secondary alcohols. There is no participation of −CH2OH groups observed

since they are involved in the crosslinking.

8.3.3.2 Infrared Spectroscopy for characterization of ECHCMC-metal complexation

FTIR studies performed on association complex between metal ions and ECH-crosslinked

NO-carboxymethyl chitosan (Figure 8.7). Compared with the FTIR spectrum of ECHCMC,

the remarkable changes were that the band at 1404 cm-1 disappeared and considerably in

intensity and the band at 1055cm-1 was displaced to 1028 cm-1. FTIR spectra revealed that the

complexing sites are the carbonyl groups, and the hydroxyl and amino groups probably do not

participate in the formation of complex. The chelation sites mainly occurred at carboxyl

groups as indicated by FTIR spectra.

54

Wavenumbers (cm-1)

A: ECHCMC beads B: ECHCMC-metal complexation

Figure 8.7 FTIR spectra of ECHCMC beads and ECHCMC-metal complexation

8.3.3.3 Infrared Spectroscopy for characterization of EDTAEC-metal complexation

FTIR spectra of EDTAEC-metal commplexation show (Figure 8.8) strong band at 1377,

1318 and 1027cm-1 in comparison with EDTAEC. The band in EDTAEC bead when chelated

with lead metals shows a remarkable change in the spectra. Band at 3267 cm-1 is similar, but

the EDTAEC bead with metal show intensive band at 2922cm-1. the band of EDTAEC with

metals at 1596 cm-1 shows a sharp band of NH bending. Band at 1621cm-1 in EDTAEC

disappeared after forming associated complexation with metals. EDTAEC with metals

1308cm-1 assigned to metal binding at carbonyl groups. EDTAEC with lead metal show

intensive band at 1373 cm-1 attributed to binding of metal at C-N of EDTA unit.

Coordination of EDTAEC with metal ions showed the involvement of tertiary amine,

carbonyl and secondary hydroxyl group in chelate formation. Also shifts in the 1620cm-1 band

(-NH and C=O) to 1597 cm-1, and shift in 1062 cm-1 band (sec OH stretching) to 1027 cm-1

supported the above data. There was no shift in the band at 1030 cm-1 (primary OH), which

55

suggested that primary hydroxyl was not involved in chelate formation because they are

involved in the crosslinking.

FTIR indicated that the complexing main sites are the carbonyl, amines and secondary

alcohol functional groups, since the nitrogen of the amino group and the oxygen have a pair

of electrons that can add themselves to a cation by coordinated covalent bonds

Wavenumbers (cm-1)

A: EDTAEC beads B: EDTAEC-metal complexation

Figure 8.8 FTIR spectra of EDTAEC beads and EDTAEC-metal complexation

8.3.3.4 Infrared Spectroscopy for characterization of TUCMC-metal complexation

Experiment was performed on TUCMC bead and TUCMC-metal complex. FTIR analysis

was carried out to confirm the binding mechanism of metal. The FTIR spectra of TUCMC

before and after metal ions uptake is shown in Figure 8.9. The spectrum modification of

TUCMC is caused by adsorption of metal. From Figure 8.9, the wide band at 3309 cm-1

assigned to the stretching vibration of -OH, and the extension vibration of N-H.

A change in the intensity of the C-N stretches at 1319 and 1369 cm-1 was observed, while

the band at 1369 cm-1 decreased significantly. By comparison with the spectra, the signals of

carbonyl group and C=S group from TUCMC backbone increased significantly after forming

complex with metals. FTIR analysis revealed that carbonyl and C=S group take part in

complexation.

56

Wavenumbers (cm-1)

A: TUCMC beads B: TUCMC-metal complexation

Figure 8.9 FTIR spectra of TUCMC beads and TUCMC-metal complexation

8.3.4 Adsorption mechanism

The adsorption mechanism is of crucial importance for further understanding the process of

heavy metal ion removal onto different adsorbents and providing an orientation for the design

of the desorption strategy, but it is a very tedious and complicated work to identify the

adsorption mechanism of heavy metal ions. This aspect has not been adequately studied and

there is very little literature focusing on this topic.

Metal ions can be bound to the surface of a sorbent by several mechanisms including

complexation, ion exchange, chelation, adsorption and co-ordination. However, complexation

have been regarded as major mechanisms for metal ion sorption by sorbents containing

functional groups such as –C=O, -NH2 and -OH. It is accepted that amine sites in chitosan are

the principal reactive groups for metal ions, though hydroxyl groups (especially in the C-3

position) may contribute to sorption.

FTIR spectra of four cross-linked chitosan derivatives after metal ions sorption showed

similar major changes implying similar binding mechanism.

Based on the electron donating nature of the N, O and S containing groups in cross-linked

57

chitosan derivatives and the electron-accepting nature of the metal ions, makes the

resin–metal complex form in the surface of the adsorbent. The involvement of N and O atoms

in binding metal from heavy metal solution was evident in four resins by FTIR analysis.

Cd(II) adsorption onto cross-linked chitosan beads can be explained by complexation,

which interacted through the electron pair sharing between Cd2+ and N and O atoms of the

functional groups. Similarly, an adsorption mechanism for the binding of Pb(II), Cd(II), Cr(III)

and Cu(II) microspheres can also explain by complexation.

A lone pair of electrons of the nitrogen atom was donated to the shared bond between the

N atom and metals, resulting in the decreasing of the electron cloud density of the nitrogen

atom and the increasing of binding energy.

The attraction of the electron pair to the atom's nucleus was stronger in oxygen, and

nitrogen had a greater tendency to donate its pair of electrons to a metal ion to form a

complex through a coordinated covalent bond.

All four resins were effective in the removal of metal ions Cd(II), Pb(II), Ni(II), Cu(II) and

Cr(III) from multi-component solution at pH 7. EDTAEC was demonstrated favorable

efficiency in adsorption for heavy metal ion. Therefore, the EDTAEC is regarded as a

potential candidate in the industrial wastewater treatment.

58

SUMMARY

Environmental pollution has become more and more serious, especially regarding heavy

metal ions. Heavy metals are a serious threat to human beings and the environment, due to

their toxicity and persistence after being released into the natural environment. The amount of

heavy metals produced from metal industries, agricultural activities, and waste disposal has

increased considerably.

Disposal of water contamination has always been a major environmental issue all over the

world. Treatment methods have been continuously exploring for decade years, such as

precipitation flotation, membrane technologies, oxidation-reduction, photocatalytic

degradation, adsorption, etc. Among these methods, adsorption has been wildly concerned by

researchers in virtue of its simple operation, high removal rate, less secondary pollution, as

well as low cost. Various absorbents were studied and applied in water treatment. However,

most of inorganic absorbents remain in laboratories because of their expensive cost, low

adsorption capacity and poor reusability. Likewise, defects of synthetic organic absorbents are

still to be solved before their widespread application.

Chitosan is one of the most abundant polysaccharides on the earth especially in coastal

regions and well known for renewable, nontoxic, biocompatible and degradable. Chitosan has

great potentials in wastewater treatment, because its amine and hydroxyl groups act as active

sites for heavy metal and anionic organic pollutants.

However, the fatal defect of chitosan is that chitosan solids can graduately dissolve in acid

solutions.

By chemical modification, it prevents chitosan solids from dissolution in strong acidic

solutions, improving mechanical strength, and increasing the porosity and surface area.

In this project, epichlorohydrin-crosslinked chitosan resin (ECHC),

epichlorohydrin-crosslinked carboxymethyl-chitosan resin (ECHCMC), EDTA-modified

epichlorohydrin-crosslinked chitosan resin (EDTAEC), and thiourea-modified

O-carboxymethyl-chitosan resin (TUCMC) were designed and synthesized successfully.

FTIR-ATR, SEM were used to identify the structures and characteristics of the resins.

59

Adsorption experiments were used to testify of the adsorption capacity of the synthesized

resins for heavy metals ions Pb2+ and Cd2+. ICP-OES was utilized to determine the

concentration of metal ions in solution in this study.

Experimental data showed that EDTAEC has better adsorption capacity for Pb2+ and the

maximum adsorption capacity for Pb2+ was 0.95 mmol/g, and ECHCMC resin has relatively

strong adsorption capacity for both Pb2+ and Cd2+ with the maximum adsorption capacity of

0.77 and 0.40 mmol/g, respectively.

The kinetic parameter of the Pb2+ adsorption process of EDTAEC was obtained, and the

results indicated that the adsorption process for Pb2+ followed pseudo second order model. In

the reusability experiments, the EDTAEC resin showed that the adsorption capacity was not

significantly changed up to three cycles. Therefore, the resin could be easily regenerated and

efficiently reused.

In the present study, sorption performance of four cross-linked chitosan derivatives in

multi-component system was investigated in order to evaluate the uptake ability for the metal

ions. FTIR spectrometry has been applied to study adsorption mechanisms that may be

helpful for synthesizing better adsorption property of modified chitosan.

The results revealed that the novel resin EDTAEC has outstanding performance on

adsorption of Pb2+, Cd2+, Cu2+, Ni2+, and Cr3+ from aqueous solutions. Order of metal

chelation was as follows: Cu2+> Pb2+> Ni2+> Cd2+> Cr3+. Metal chelating ability of EDTAEC

for Cu2+ and Pb2+ was higher than that of the other three resins. TUCMC adsorbed metal ions

in the following order: Cu2+ > Ni2+ > Cd2+. ECHCMC indicated that it has binding capacities

of 0.19 mmol/g for Cu2+ and ca. 0.05mmol/g Pb2+, Cd2+, Ni2+ and Cr3+. ECHC, as expressed

by the order of its affinity, was in the order of Cu2+>Cr3+> Ni2+> Pb2+> Cd2+.

The novel chitosan resin (EDTAEC) that we synthesized in this project showed potential in

the field of removal of heavy metals from water. It is worthy of further research on the

adsorption mechanism, adsorption kinetic studies, optimizing the conditions to synthesize

highly efficient adsorption capacity of EDTAEC.

From this study, it can be concluded that the modification of chitosan’s structure is an

efficient way to discover new resin that can efficiently adsorb heavy metals in aqueous

medium.

60

REFERENCES Ahmed M, Pyle DL. (1999) Investigation of single protein adsorption on ion exchangers using confocal

laser scanning microscopy. Journal of Chemical Technology and Biotechnology. 74(3): 193-198.

AIIan GG, Fox JR, Kong N. (1978) In Proc. First Int. Conf. Chtin/Chitosan, MIT Cambridge, pp 64-78.

Al-Harahsheh M, Batiha M, Kraishan S, and Al-Zoubi H. (2014). Precipitationtreatment of effluent acidic

wastewater from phosphate-containing fertilizerindustry: characterization of solid and liquid products.

Separation and Purification Technology. 123:190-199.

Austin PR, Brine CJ, Castle JE, Zikakis JP. (1981) Chitin: New facets of research. Science. 212:749-753.

Bailey SE, Olin TJ, Bricka RM and Adrian DD. (1999) A review of potentially low-cost sorbents for heavy

metals. Water Research. 33: 2469-2479.

Barakat MA (2008) Removal of Cu(II), Ni(II) and Cr(III) ions from wastewater using complexation

-ultrafiltration technique. Journal of Environmental Science and Technology. 1:151-156.

Barbara K. (2005) Membrane-based processes performed with use of chitin/chitosan materials. Separation

and Purification Technology. 41: 305-312.

Barros AAA, Alves A, Nunes C, Coimbra MA, Pires RA, Reis RL. (2013) Carboxymethylation of ulvan

and chitosan and their use as polymeric components of bone cements. Acta Biomaterial. 9(11):

9086-9097.

Bhatnagar A, and Sillanpää M (2009) Applications of chitin- andchitosan-derivatives for the detoxification

of water and wastewater - a short review. Advances in Colloid and Interface Science. 152: 26–38.

Bhattacharyya KG and Gupta SS (2006) Kaolinite, montmorillonite, and their modified derivatives as

adsorbents for removal of Cu(II) from aqueous solution. Separation and Purification Technology. 50:

388-397.

BI H, Yin Z, Cao, X, Xie X, Tan C, Huang X (2013) Carbon fiber aerogelmade from raw cotton: a novel:

efficient and recyclable sorbent for oils andorganic solvents. Advanced Materials. 25:5916-5921.

Campbell MA (2003) Characterization of chitosan as an antimicrobial solution and packaging film.

(Master’s Thesis (M.S.). Department of Packaging Science. Clemson University of South Carolina, 2003).

Master’s Thesis TS195.2, C36.

Chen X, Chen G and Yue PL (2002) Investigation on the electrolysis voltage of electrocoagulation.

Chemical Engineering Science. 57: 2449-2455.

Chen XG, Park HJ (2003) Chemical characteristics of O-carboxymethyl chitosans related to the preparation

conditions. Carbohydrate Polymers. 53: 355-359.

Crini G, and Badot P (2008) Application of chitosan, a naturalaminopolysaccharide: for dye removal from

aqueous solutions by adsorptionprocesses using batch studies: a review of recent literature. Progress in

Polymer Science. 33: 399-447.

Crini G, Peindy HN (2007) Removal of C.I. Basic Green 4 (Malachite Green) from aqueous solutions by

adsorption using cyclodextrin-based adsorbent: Kinetic and equilibrium studies. Separation and

Purification Technology. 53:97-110.

Deng L, Su Y, Su H, Wang X, Zhu X. (2007) Sorption and desorption of lead (II) from wastewater by green

algae Cladophora fascicularis. Journal of Hazardous Materials. 143: 220-225.

Devlieghere F, Vermeiren L and Debevere J (2004) New preservation technologies: Possibilities and

limitations. International Dairy Journal. 14 (4):273-285.

Dvoˇrák L, Svojitka J, Wanner J and Wintgens T (2013) Nitrification performance in a membrane bioreactor

treating industrial wastewater. Water Research. 47: 4412-4421.

Furusaki E, Ueno Y, Sakairi N, Nishi N and Tokura S (1996) Facile Preparation and Inclusion Ability of a

61

Chitosan Derivative Bearing Carboxymethyl-b-Cyclodextrin. Carbohydrate Polymers. 9:29-34.

Govers LL, Lamers LPM, Bouma TJ, Eygensteyn J, Brouwer JHFD, Hendriks AJ (2014). Seagrasses as

indicators for coastal trace metalpollution: a global meta-analysis serving as a benchmark: and a

Caribbean case study. Environmental Pollution. 195: 210-217.

Grimshaw P, Calo JM and Hradil G (2011) Cyclic electrowinning precipitation (CEP) system for the

removal of heavy metal mixtures from aqueous solutions. Chemical Engineering Journal. 175:103-109.

Guibal E，Janssoncharrier M， Saucedo I，Cloirec PL (2002) Enhancement of Metal Ion Sorption

Performances of Chitosan: Effect of the Structure on the Diffusion Properties. Langmuir. 11(2):591-598.

Harikishore, KRD, Harinatha, Y, Seshaiaha K and Reddy AVR (2010) Biosorption of Pb(II) from aqueous

solutions using chemically modified Moringa oleifera tree leaves. Chemical Engineering Journal. 162:

626-634.

Inoue K, Baba Y, Yoshizuka K (1993) Adsorption of metal ions on chitosan and crosslinked copper

(II)-complexed chitosan. Bulletin of the Chemical Society of Japan. 66: (5), 2915-2921.

Inoue K, Baba Y, Yoshizuka K, Noguchi H, Yoshizaki M (1988) Selectivity Series in the Adsorption of

Metal Ions on a Resin Prepared by Crosslinking Copper(II)-Complexed Chitosan. Chemistry Letters.

17(8): 1281-1284.

Inoue K, Yoshizuka K, Baba Y (1994) Biotechnology and Bioactive Polymers. Plenum Press, New York

p35.

Izadiyar MH and Yargholi B (2010) Study of cadmium absorption and accumulation in different parts of

four forages. American-Eurasian Journal of Agricultural and Environmental Science. 9: 231-238.

Jayakumar R, Prabaharan M, Nair SV, Tokura S, Tamura H, Selvamurugan N (2010) Novel carboxymethyl

derivatives of chitin and chitosan materials and their biomedical applications. Progress in Materials

Science. 55(7): 675-709.

Jha IN, Iyengar L and Prabhakara AVS (1988) Removal of cadmium using chitosan. Journal of

Environmental Engineering. 114: 962-974.

Jollès P, Muzzarelli RAA (1999) Chitin and Chitinases. Berlin, Germany:Birkhäuser Verlag.

Kalpakl YK, Koyuncu K (2007) Characterization of Activated Carbon and Application of Copper Removal

from Drinking Water. Annali Di Chimica. 97(11-12):1291-1302.

Kandile NG, Nasr AS (2009) Environment friendly modified chitosan hydrogels as a matrix for adsorption

of metal ions, synthesis and characterization. Carbohydrate Polymers. 78753-759.

Khan TA Peh, Khiang Peh, Ch’ng, Hung Seng (2002) Reporting degree of deacetylation values of chitosan:

the influence of analytical methods. Journal of Pharmacy and Pharmaceutical Science. 5(3): 205-212.

Knorr D (1991) Recovery and utilization of chitin and chitosan in food processing waste management.

Food Technology. 45: 114-122.

Krisana S, Khatcharin S, Tawun R, Nongnuj M, Werasak U, Supot H (2004) Solvation structure of

glucosamine in aqueous solution as studied by Monte Carlo simulation using ab initio fitted potential.

Chemical Physics Letters. 395(4-6):233-238.

Kurita K (1986) Chitin in Nature and Technology, Plenum Press, New York. p. 287.

Lagergren S (1898) About the theory of so-called adsorption of soluble substances. In: K. Sven.

Vetenskapsakad (Ed.) Zur theorie der sogenannten adsorption geloster Stoffe. Handlingar, Germany,

pp1-39.

Lee M, Nah JW, Kwon Y, Koh JJ, Ko KS, Kim SW (2001) Water-soluble and low molecular weight

chitosan-based plasmid DNA delivery. Pharmaceutical Research. 18: 427-31.

Li A, Lin R, Lin C, He BY, Zheng TT, Lu LB, Yang CK (2016) An environment-friendly and

62

multi-functional absorbent from chitosan for organic pollutants and heavy metal ion. Carbohydrate

Polymers. 148: 272-280.

Li T, Wang H, Dong W, Liu T, Ouyang F, Zhang Q (2014) Phosphate removal during Fe(II) oxidation in the

presence of Cu(II): characteristics and application for electro-plating wastewater treatment. Separation

and PurificationTechnology. 132: 388-395.

Lin PJ, Yang MC, Li YL, Chen JH (2015) Prevention of surfactant wetting with agarose hydrogel layer for

direct contact membrane distillation used in dyeing wastewater treatment. Journal of Membrane Science.

475: 511–520.

Low KS, LEE CK, LIEW SC (2000) Sorption of cadmium and lead from aqueous solutions by spent grain.

Process Biochemistry. 36: 59-64.

Majeti NV, Kumar RA (2000) Review of chitin and chitosan applications. Reactive and Functional

Polymers. 46: 1-27.

Mark S (2011) Oil spill: deep wounds. Nature. 472: 152–154.

Mbamba CK, Batstone DJ, Flores-Alsina X (2015). A generalised chemical precipitation modelling

approach in wastewater treatment applied to calcite. Water Research. 68: 342-353.

Mireles C, Martino M, Bouzas J, Torres JA (1992) Complex formation of chitosan and naturally occuring

polyanions. In Brine CJ, Sanford PA, Zikakis JP, editors. Advances in chitin and chitosan. New York:

Elsevier Applied Science.

Mourya VK, Nazma Inamdar and Ashutosh Tiwari (2010) Carboxymethyl chitosan and its applications.

Advanced Materials Letters. 1(1): 11-33.

Murgolo S, Petronella F, Ciannarella R, Comparelli R, Agostiano A, Curri ML (2015) UV and solar-based

photocatalytic degradation of organic pollutants by nano-sized TiO2 grown on carbon nanotubes.

Catalysis Today. 240: 114–124.

Muzzarelli RAA (1973) Natural chelating polymers: alginic acid, chitin and chitosan. Pergamon Press.

Muzzarelli RAA (1977) Chitin. Pergamon Press, New York.

Muzzarelli RAA (1985) Chitin. in The polysaccharides, Vol 3 (G.O. Aspinall, Ed.); Academic Press, New

York, pp.417-450.

Muzzarelli RAA, Jeauniaux C and Gooday G, Eds. (1986) Chitin in nature and technology. New York,

Plenum Press.

Muzzarelli, RAA (1978) In Proc. First Int. Conf Chitin. Chitosan MIT, Cambridge.

Neoh, CH., Noor, ZZ., Mutamim, NSA., & Lim, CK. (2015). Green technology inwastewater treatment

technologies: integration of membrane bioreactor withvarious wastewater treatment systems. Chemical

Engineering Journal: 283: 582-594.

Ng JCY, Cheung WH, McKay G (2003) Equilibrium studies for the sorption of lead from effluents using

chitosan. Chemosphere. 52: 1021-1030.

Ngah WWS, Ghani AS, Hoon LL (2002) Comparative adsorption of lead (II) on flake and bead types of

chitosan. Journal of the Chines Chemical Society. 49: 625-628.

No HK, Meyers SP (1995) Preparation and characterization of chitin and chitosan -A review. Journal of

Aquatic Food Product Technology. 4 (2): 27-50.

No HK, Meyers SP, Lee KS (1989) Isolation and characterization of chitin from crawfish shell waste.

Journal of Agricultural and Food Chemistry. 37(3): 575-579.

Peniston QP, Johnson E (1980) Process for the manufacture of chitosan. US patent 4,195,175.

Peter MG (1995) Applications and environmental aspects of chitin and chitosan. Journal of

Macromolecular Science-Pure and Applied Chemistry. 32:629-41.

63

Roberts GAF (1992) Chitin chemistry; Macmillan Press Ltd. London.

Sahin M, Nuriye Kocak, Gulsin Arslan, Halil Ismet Ucan (2011) Synthesis of Crosslinked Chitosan with

Epichlorohydrin Possessing Two Novel Polymeric Ligands and Its Use in Metal Removal. Journal of

Inorganic and Organometallic Polymers. 21:69-80.

Sankararamakrishanan N, Sharma AK, Sanghi R (2007) Novel chitosan derivative for the removal of

cadmium in the presence of cyanide from electroplating water. Journal of Hazardous Materials. 148:

353-359.

Saththasivam J, Loganathan K, Sarp S (2016) An overview of oil-water separation using gas flotation

systems. Chemosphere. 144: 671-680.

Savant VD, Torres JA (2000) Chitosan based coagulating agents for treatment of Cheddar cheese whey.

Biotechnology Progress. 16: 1091-1097.

Schatz C, Viton C, Delair T, Pichot C, Domard A (2003) Typical physicochemical behaviors of chitosan in

aqueous solution. Biomacromolecules. 4:641-648.

Seham Nagib, Inoue K, Yamaguchi T, Tamaru T (1999) Recovery of Ni from a large excess of Al generated

from spent hydrodesulfurization catalyst using picolylamine type chelating resin and complexane

types of chemically modified chitosan. Hydrometallurgy. 51:73-85.

Shahidi F, Arachchi JK, Jeon Y (1999) Food applications of chitin and chitosans. Trends in Food Science

and Technology. 10 (2): 37-51.

Shepherd R, Reader S, Falshaw A (1997) Chitosan functional properties. Glycoconjugate Journal.

14(4):535-42.

Singh DK, Ray AR (2000) Biomedical Applications of Chitin, Chitosan, and Their Derivatives. Journal of

Macromolecular Science - Polymer Reviews. C40, 1: 69-83.

Tülü M, Geckeler KE (1999) Synthesis and properties of hydrophilic polymers. Part 7. Preparation,

characterization and metal complexation of carboxy-functional polyesters based on poly(ethylene

glycol). Polymer International. 48:909-914.

Wana MW, Kan CC, Rogel BD, Dalida MLP (2010) Adsorption of copper (II) and lead (II) ions from

aqueous solution on chitosan-coated sand. Carbohydrate Polymers. 80: 891-899.

Wiles J (2000) The Effect of Relative Humidity on the Steady State Water Vapor Permeability of Chitosan

Films. Dissertation. Clemson, SC, USA: Clemson University, Department of Food Technology.

Wu T, Zivanovic S, Draughon FA, Conway WS, Sams CE (2005) Physiochemical Properties and

Bioactivity of Fungal Chitin and Chitosan. Journal of Agricultural and Food Chemistry. (53),

3888-3894.

Xing R, Liu S, Guo Z, Vu H, Wang P, Li C, Li Z, Li P (2005) Relevance of molecular weight of chitosan

and its derivatives and their antioxidant activities in vitro. Bioorganic and Medicinal Chemistry. 13:

1573-1577.

Xiong C, Yao C, Wang L, Jiajun K (2009) Adsorption behavior of Cd(II) from aqueous solutions onto

gel-type weak acid resin. Hydrometallurgy. 98: 318-324.

Zhu A, Chan-Park MB, Dai S, Li L (2005) The aggregation behavior of O-carboxymethyl chitosan in dilute

aqueous solution. Colloids and Surfaces. B43:143-149.

preparation, characterization of chitosan derivatives …€¦ · · 2018-03-20preparation,...

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