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SYNTHESIS AND CHARACTERIZATION OF MAGNETITE AND MAGNETITE/STARCH NANOCOMPOSITE THIN FILMS FOR

ELECTROCHEMICAL APPLICATIONS

Khoh Wai Hwa

Master of Science 2011

! 'usat Kbidmat Alaklº, ºnai A6ad<<rat UMVEILSITI MALAYSIA SARANVAK

SYNTHESIS AND CHARACTERIZATION OF MAGNETITE AND MAGNETITE/STARCH NANOCOMPOSITE THIN FILMS FOR

ELECTROCHEMICAL APPLICATIONS P. KHIDMAT MAKLUMAT AKADEMIK

viii IIIIlii1111 111111 1111 I

1000248313

KHOH WAI HWA

A thesis submitted in fulfillment of the requirement for the Degree of

Master of Science (Advanced Materials and Nanotechnology)

Faculty of Resources Sciences and Technology UNIVERSITI MALAYSIA SARAWAK

2011

Acknowledgements

I would like to take this opportunity to extend my deepest appreciation to many

people who have made it possible for me to complete this study.

First of all, I would like to express my gratitude to my supervisor, Assoc. Prof.

Dr. Pang Suh Cem, from Faculty of Resource Science and Technology, UNIMAS, for his

advice, moral and financially support, and encouragement throughout this study. I would

also like to thank Dr. Chin Suk Fun for her constructive comments on this thesis.

I would like to acknowledge all the lab assistants and staffs from Faculty of

Resource Science and Technology, UNIMAS for their kind assistance in making my

project a success. Special thanks for Dr Lim Poh Teen who was kindly taught us in

operating TEM and also technician from Faculty of Engineering who helped us in

operating FESEM.

Special thanks also to all my friends (Cindy Tan, Sze Yun, Boon Hong, Chian Ye,

Miss Tay, Swee Kim, Irene Foo Xiang yun, Chen Lim, Yean Yuan and Hui Ling) who

have assisted me in various aspects. Last but not least, my deepest appreciation also goes

to my lovely family everlasting support.

ii

Abstract

(The aims of this study were to investigate the effects of synthesis conditions on the

capacitive behaviors of magnetite and magnetite/starch nanocomposite thin films. In

addition, the relationship between the microstructure of thin films and their

electrochemical properties was elucidated. Magnetite nanocomposite in the form of stable

colloidal suspension was synthesized by the co-precipitation of Fe (II) and Fe (III) ions in

the ammonium hydroxide solution at 80°C under inert atmosphere. Nanocomposite of

magnetite/starch nanocomposites in the form of colloidal suspension were synthesized by

the same co-precipitation approach in the presence of dissolved starch in different

aqueous solvents such as NH4OH and NaOH (6 wt %) /urea (5 wt %)-Both magnetite

and magnetite/starch nanocomposite thin films were subsequently prepared by drop-

coating the magnetite colloidal suspensions onto pre-cleaned stainless steel plates. The

relative film thicknesses were controlled by the volume of the colloidal suspension used

per unit area of film formed. The synthesis parameters such as the type of solvent used,

calcination temperature and starch content were observed to affect the microstructure and

the surface morphology of magnetite and magnetite/starch nanocomposite thin films and

subsequently their electrochemical properties. The synthesis conditions, in particular, the

calcination temperature have substantial effects on the capacitive behavior of both

magnetite and magnetite/starch nanocomposite thin films. The specific capacitance of

magnetite and magnetite/starch nanocomposite thin films were observed to increase

substantially with increased calcination temperature, with optimum calcination

temperature observed at 300°C. A maximum specific capacitance of 89 F/g and 124 F/g

III

were obtained for magnetite and magnetite/starch nanocomposite (> 2 wt% of starch

content) thin films of optimum thickness that had been calcined at 300°C. The magnetite

thin films possessed lower specific capacitance due to its comparatively lower specific

surface area. The cyclic voltammograms of magnetite thin film in 1.0 M Na2SO4 aqueous

electrolyte were observed to be the most rectangular in shape as compared to those in 1.0

M Na2SO3 and 0.25M Na3PO4 electrolytes over the potential range of 0 to 0.9 V (vs SCE)

iv

Sintesis dan Ciri-Ciri Magnetit dan Magnetit/Kanji Filem Nipis Nano- Komposit untuk Aplikasi Elektrokimia

Abstrak

Kajian ini bertujuan untuk menerangkan kesan keadaan sintesis ke atas tingkah laku

kapasitor di dalam magnetit/kanji filem nipis nano komposit. Kajian ini juga menjelaskan

hubungan di antara mikrostruktur filem nipis and sifat elektrokimianya. Kstabilan bahan

koloid magnetit telah disintesiskan dengan menggunakan pengenapan ion Fe(II) and Fe

(III) dalam larutan ammonium hidroksida pada suhu 80 °C dan tekanan atmosfera.

Kaedah pengenapan bagi magnetit dan magnetit/kanji nano-komposit telah disintesis

dengan menggunakan larutan yang berlainan seperti NH4OH dan NaOH (6 wt %) /urea (5

wt %). Kedua-dua magnetit dan magnetit/kanji filem nipis nano-komposit telah

disediakan dengan menitis koloid ke atas kepingan keluli. Ketebalan filem yang

berkenaan dikawal berdasarkan isipadu koloid yang digunakan per unit perimeter filem

yang dibentuk. Kesan parameter kaedah sintesis seperti jenis larutan yang digunakan,

suhu pembakaran and kandungan kanji ke atas mikrostrutur dan morfologi

magnetite/kanji filem nipis nano-komposit diikuti dengan sifat elektrokimia telah

diperhatikan. Keputusan menunjukkan keadaan sintesis terutamanya suhu pembakaran

mempunyai kesan yang nyata ke atas sifat kapasitor di dalam magnetit dan magnetit/kanji

nano-komposit filem nipis. Kapasitan spesifik magnetit and magnetit/ kanji filem nipis

nano-komposit telah diperhatikan untuk menambahkan perlahan-lahan dengan

menambah suhu calcinations sehingga suhu optimum pada 300°C. Kapasitan spesifik

maksimum bagi 89 F/g dan 124 F/g telah diperolehi (> 2 wt% daripada kandungan kanji)

berdasarkan ketebalan filem yang dibentuk pada 300°C. Filem nipis magnetit

V

menunjukkan kapasitan spesifik yang rendah disebabkan keluasan permukaan. Kitaran

voltamogram bagi magnetit filem nipis dalam larutan elektrolit 1M Na2SO4 juga

diperhatikan agar memperolehi bentuk segiempat tepat berbanding dalam 1M Na2SO3

and 0.25M Na3PO4 elektrolit ke atas lingkungan potensi 0 to 0.9 V (vs SCE) .

V1

Pusat Khidmat N[aklumat Akademik IfNTN'ERS1T1 MALAYSIA SARAW"ak

TABLE OF CONTENTS

Title

Acknowledgements

Abstract

Abstrak

Table of Contents

List of Tables

List of Figures

List of Abbreviations

List of Symbols

CHAPTER 1 INTRODUCTION

1.1 Background

1.2 Objectives of Study

CHAPTER 2 LITERATURE REVIEW

2.1 Background

2.2 Current Status and Preparation Methods of

Magnetite Nanoparticles

2.2.1 Co-precipitation

2.2.2 Thermal Decomposition

2.2.3 Sonochemical Synthesis

2.2.4 Sol-Gel Process

2.2.5 Biosynthesis

2.2.6 Other Methods

Page

1

11

111

V

vii

X111

xiv

xvii

xviii

I

4

5

6

6

11

14

15

16

19

vii

2.3 Applications of Magnetite 25

2.3.1 Industrial Applications 25

2.3.2 Electrochemical Applications 26

2.3.3 Biomedical Applications 27

2.3.4 Environmental Remediation Applications 31

2.4 Surface-Modified Magnetite Nanoparticles 32

2.4.1 Dextran-Coated Magnetite 34

2.4.2 Starch-Coated Magnetite 34

2.5 Electrochemical capacitors (ECs) 38

CHAPTER 3 PREPARATION AND CHARACTERIZATION OF

NANOPARTICULATE MAGNETITE XEROGELS

AND THIN FILMS

3.1 Introduction 40

3.2 Materials and Methods 41

3.2.1 Preparation of Magnetite Colloidal Suspension 41

3.2.2 Preparation of Magnetite Thin Films and 42

Xerogels

3.2.3 Characterization of Magnetite Colloidal 43

Suspension

3.2.3.1 Visual Observations 43

3.2.3.2 Scanning UV-VIS Spectroscopy 43

3.2.4 Characterization of Magnetite Xerogels and 43

Thin Films

viii

3.2.4.1 Fourier Transformed Infrared 43

(FT-IR) Spectrometer

3.2.4.2 Field Emission Scanning Electron 44

Microscope (FESEM)

3.2.4.3 Nitrogen Adsorption-Desorption 44

(BET) Analyzer

3.2.5 Electrochemical Characterization of Magnetite 44

Thin Films

3.3 Results and Discussion 45

3.3.1 Characterization of Magnetite Colloidal Suspension 45

3.3.1.1 Stability of Magnetite Colloidal 45

Suspension by Visual Observations

3.3.1.2 Scanning UV-VIS Spectrophotometer 48

3.3.2 Characterization of Magnetite Xerogels and 50

Thin Films

3.3.2.1 Fourier Transformed Infrared (FT-IR) 50

Spectrometer

3.3.2.2 Field Emission Scanning Electron 56

Microscope (FESEM)


(BET) Analysis

3.3.3 Electrochemical Characterization of Magnetite 63

Thin Films

ix

3.3.3.1 Effect of Calcination Atmosphere 63

3.3.3.2 Effect of Relatives Film Thickness 64

3.3.3.3 Effect of Calcination Temperature 69

3.3.3.4 Effect of Electrolyte Composition 74

3.3.3.5 Effect of Long Term Cycling 76

3.4 Conclusions 78

CHAPTER 4 PREPARATION AND CHARACTERIZATION OF

MAGNETITE/STARCH NANOCOMPOSITE

XEROGELS AND THIN FILMS

4.1 Introduction 79

4.2 Materials and Methods 82

4.2.1 Preparation of Magnetite/Starch Nanocomposite 82

Colloidal Suspension and Xerogels

4.2.2 Preparation of Magnetite/starch Nanocomposite 83

Thin Films and xerogels

4.2.3 Characterization of Magnetite/starch 84

Nanocomposite


(FT-IR) Spectroscope

4.2.3.2 Scanning Electron Microscope 84

(SEM)/Field Emission Scanning

Electron Microscope (FESEM)

X


(BET) Analysis

4.2.3.4 Electrochemical Characterization 85

of Magnetite/Starch Nanocomposite

Thin Films

4.3 Results and Discussion 86

4.3.1 Preparation of Magnetite/Starch Colloidal 86

Suspension

4.3.2 Characterization of Magnetite/starch 88

Nanocomposite


(FT-IR) Spectroscopy

4.3.2.2 Scanning Electron Microscope 97

(SEM)/Field Emission Scanning

Electron Microscope (FESEM)


(BET) Analysis

4.3.2.4 Electrochemical Characterization of 110

Magnetite/starch Nanocomposite

Thin Films

4.4 Conclusions 115

R1

CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions

5.2 Recommendations for Future Studies

116

117

REFERENCES 119

xii

List of Tables Page

Table 2.1 Temperature of decomposition (TD) of different precursors and

boiling temperature (TB) of various solvents used for the preparation

of magnetite nanoparticles. 12

Table 2.2 Average diameter, standard deviation and composition of reaction

mixtures for the synthesis of the magnetite nanoparticles 21

Table 2.3 Summary reviews on the preparation and applications of

starch-magnetite particles. 36

Table 3.1 Characteristic absorption peaks of magnetite xerogel and thin film

samples 53

Table 3.2 Characteristic absorption peaks of Fe-O bond in magnetite sample

prepared by the co-precipitation method. 54

Table 3.3 Fe-O absorption peaks of magnetite xerogels calcined at 300°C

in nitrogen or air atmosphere respectively. 55

Table 3.4 A summary of reviews on methods of preparation of magnetite

thin films. 67

Table 3.5 Effect of microstructure on the charge capacity and capacitance of

magnetite thin film prepared from alkaline suspension. 73

Table 4.1 Characteristic absorption peaks of magnetite, native sago starch,

magnetite/starch xerogels prepared from Approach A and B without

heat treatment. 93

Table 4.2 Characteristic absorption peaks of magnetite/starch xerogels (MSI)

calcined at different temperatures. 94

Table 4.3 Characteristic absorption peaks of magnetite/starch xerogels (MS2)

calcined at different temperatures. 95

Table 4.4 Fe-O Absorption Peaks of magnetite xerogels, MS 1 xerogel and

MS2 xerogels and calcined at 300°C in nitrogen or air atmosphere 97

Table 4.5 Effect of microstructure on the charge capacity and capacitance of

magnetite and MS2 thin film with 2 wt% of starch calcined at 300°C

in nitrogen atmosphere. 115

xiii

List of Figures Page

Figure 2.1 Potential biomedical applications of magnetic nanoparticles 28

Figure 3.1 Magnetite colloidal suspensions at pH range of 1-12 (a) freshly

prepared, (b) after aging for 8 hours. 47

Figure 3.2 UV-VIS spectra of freshly prepared magnetite colloidal suspensions

at pH 1-12, and the effect of aging at (b) pH 2 and (c) pH 10.49

Figure 3.3 Effect of aging on the absorbance of magnetite colloidal suspensions

at pH 2 and pH 10 (measured at ß, 1118, C = 360 nm). 50

Figure 3.4 FTIR spectra of magnetite xerogel and thin film samples. 53

Figure 3.5 FTIR spectra of magnetite xerogels calcined at different temperatures. 54

Figure 3.6 FTIR spectra of magnetite xerogels calcined at 300°C in (a) nitrogen

and (b) air. 55

Figure 3.7 FESEM micrographs of magnetite thin films prepared from

(a) acidic sol, (b) alkaline sol, and calcined at 300°C in nitrogen for

1 hour (200,000 x magnification). 56

Figure 3.8 SEM micrographs and EDX spectra of magnetite thin films calcined

at (a) 100°C, (b) 300°C, and (c) 500°C, in nitrogen atmosphere for

1 hour (100,000 x magnification). 58

Figure 3.9 Nitrogen adsorption-desorption isotherms of magnetite xerogels

calcined at various temperatures. 59

Figure 3.10 Effect of calcination temperature on the specific surface area and

total pore volume of magnetite xerogels derived from alkaline sol. 62

Figure 3.11 Effect of calcination temperature on the specific surface area (SSA)

and pore size distribution of magnetite xerogels derived from alkaline

colloidal suspension. 62

Figure 3.12 Cyclic Voltammograms (CV) of magnetite thin films heat treated

under different calcination atmospheres. 64

Figure 3.13 Cyclic Voltammograms (CV) of magnetite thin films prepared by

drop coating at different relative film thickness. 68

Figure 3.14 Effect of relative film thickness on the charge capacity of magnetite

thin films prepared from acidic sol with 7.0 x 10-2 wt% of

methycellulose added as a binder. 68

X1V

Figure 3.15 Effect of deposition time on the charge capacity of magnetite thin

films using the electrophoretic deposition technique (EPD). 69

Figure 3.16 Cyclic voltammograms of magnetite thin films prepared from

a) alkaline sol, b) acidic sol, and calcined at different temperatures. 72

Figure 3.17 Effect of calcination temperature on the charge capacity of magnetite

thin films derived from alkaline and acidic sols. 73

Figure 3.18 Cyclic voltammograms of magnetite thin films calcined at 300°C

in various aqueous electrolytes (a) 1M Na2SO3, (b) 1M Na2SO4,

(c) IM Na3PO4.75

Figure 3.19 Qa/Qc ratio and effect of long term cycling on the charge capacity

of magnetite thin films in alkaline medium that calcined at 300°C. 77

Figure 4.1 FTIR spectra of magnetite and native sago starch 91

Figure 4.2 FTIR spectra of magnetite/starch nanocomposite xerogels

(1 wt% starch) prepared under various synthesis conditions without

heat treatment. 92

Figure 4.3 FTIR spectra of magnetite/starch xerogels (MS 1) (1 wt% starch)

calcined at different temperatures in nitrogen atmosphere. 94

Figure 4.4 FTIR spectra of magnetite/starch xerogels (MS) (1 wt% starch)

and calcined at different temperatures in nitrogen atmosphere. 95

Figure 4.5 FTIR spectra of a) MSI xerogel, and b) MS2 xerogel and calcined

at 300°C in nitrogen or air atmosphere respectively. 96

Figure 4.6 SEM micrograph and EDX spectra of MSlsamples and calcined at

a) 100°C, b) 300°C and c) 500°C in nitrogen atmosphere at 100,000x 99

Figure 4.7 SEM micrograph and EDX spectra of MS2 and calcined at a) 100°C,

b) 300°C and c) 500°C in nitrogen atmosphere at I 00,000x magnification. 100

Figure 4.8 SEM micrograph of a) MS 1 with 2 wt% starch, b) MS2 with 2 wt%

starch and c) MS2 with 4 wt% starch calcined at 300°C in nitrogen

atmosphere at 100,000x magnification and the corresponding

EDX spectra. 101

Figure 4.9 Nitrogen adsorption-desorption isotherms of MSI (1 wt% starch)

calcined at various temperatures in nitrogen. 103

Figure 4.10 Nitrogen adsorption-desorption isotherms of MS2 (1 wt% starch)

calcined at various temperatures in nitrogen. 103

Figure 4.11 Nitrogen adsorption-desorption isotherms of MSI with 1-4 wt%

xv

starch calcined at 300°C in nitrogen. Figure 4.12 Nitrogen adsorption-desorption isotherms of MS2 with 1-4 wt%

starch calcined at 300°C in nitrogen.

Figure 4.13 Effect of calcination temperature on the specific surface area

(SSA) and pore size distribution of MS1.

104

104

106

Figure 4.14 Effect of calcination temperature on the specific surface area

(SSA) and pore size distribution of MS2.106

Figure 4.15 Effect of wt% starch on the specific surface area (SSA) and pore

size distribution of MS1 calcined at NOT in nitrogen atmosphere. 108

Figure 4.16 Effect of starch wt% on the specific surface area (SSA) and pore

size distribution of MS2 calcined at 300°C in nitrogen atmosphere. 109

Figure 4.17 Effect of starch wt% on the specific surface area (SSA) of MS1 and

MS2 xerogels calcined at 300°C in nitrogen atmosphere. 109

Figure 4.18 Cyclic voltammograms of magnetite thin film and MS2 thin films

with various contents of starch and calcined at 300°C,

1.0 M Na2SO4 aqueous electrolytes. 112

Figure 4.19 Effect of starch wt% on the specific capacitance and charge capacity

of MS2 calcined at 300°C in nitrogen atmosphere. 113

Figure 4.20 Effect of calcination temperature on the specific capacitance and

charge capacity of MS2 with 2 %wt of starch. 113

xvi

List of Abbreviations

AAS Aq atm BET CV 1D 2D 3D DC DLS DTA EC EDLC EPD ESR Fe203 Fe304 FESEM FTIR IUPAC Min MS 1 MS2 S SAMS SCE SEM SPION SQUID TEM TGA UV-Vis Vs. VSM XRD

atomic adsorption spectroscopy aqueous atmosphere Brunauer-Emmet-Teller analysis cyclic voltammograms one dimension two dimensions three dimensions direct current dynamic light scattering differential thermo analysis electrochemical capacitor electrochemical double-layer capacitor electrophoretic deposition equivalent series resistance hematite magnetite Field emission scanning electron microscopy Fourier Transform Infrared Spectrometer International union of pure and applied chemistry minute Magnetite/starch nanocomposite prepared by Approach A Magnetite/starch nanocomposite prepared by Approach B

solid self-assembled monolayers saturated calomel electrode scanning electron microscopy supermagnetic iron oxide nanoparticles superconducting quantum interference device transmission electron microscopy thermogravimetric analysis ultraviolet-visible versus vibrating sample magnetometer X-ray diffractometry

XVII

Lists of Symbols

> < %

a B

Y

A

mA µA A/cm2

mA/cm2 µA/cm2 A A C mC µC C/cm2 mC/cm2 µC/cm2 °C cm cm2 cm3 cm2 /g

cm3/g E Eq

eV e F mF µF F/cm2 mF/cm2 µF/cm2 g mg µg g/cm2 mg/cm2 µg/cm2 g/cm3

more than less than percentage alpha beta gamma ohm ampere miliampere (10 3)

microampere (10"6) ampere per centimeter square miliampere per centimeter square microampere per centimeter square electrode area Armstrong (10-10) Coulomb miliCoulomb (10"3) microCoulomb (10-6) Coulomb per centimeter square miliCoulomb per centimeter square microCoulomb per centimeter square degree Celsius or Centigrade centimeter centimeter square centimeter cube centimeter square per gram centimeter cube per gram potential applied to the electrode equation electron volt electron farad milifarad (10-3) microfarad (10-6) farad per centimeter square milifarad per centimeter square microfarad per centimeter square gram milligram (10'3)

microgram (10"6)

gram per centimeter square milligram per centimeter square microgram per centimeter square gram per centimeter cube/density

XVlll

mg/cm3 Flg/cm3

g/L g/mL mg/L mg/mL µg/L µg/ML g/mol mg/mol µg/mol i K L mL µL m mm µm nm m2 m3 m 2/g

m3/g M MS pH Qa/Qc

S

TB Tý Td

v AT mV mV/s wt

milligram per centimeter cube/density microgram per centimeter cube/density gram per liter

gram per milliliter miligram per liter miligram per milliliter microgram per liter microgram per milliliter gram per molar miligram per molar microgram per molar current kelvin litre

militre (10"3)

microlitre (10"6)

meter millimeter (10"3)

micrometer (10-6)

nanometer (10"9)

meter square meter cube meter square per gram meter cube per gram molar saturation magnetization negative logarithm of the hydrogen ion concentration anodic and cathode charge ratio second boiling temperature curie temperature temperature of decomposition voltage temperature change milivoltage (10"3)

milivoltage per second weight

xix

Chapter 1

Introduction

1.1 Background

As our society becomes more technologically advanced, electronic products are featuring

more sophisticated functions, more compact in sizes and lighter weights. Sources of power for

operating these products have to be more powerful, which means higher power and energy

density. To meet these requirements, researches have focused significant attention on the

fabrication of nanoscale electronics using inexpensive and abundant novel materials with

specific characteristics.

Nanostructured material is a very important aspect of nanotechnology and modem

materials science. Nanosized particles and/or nanostructured materials have dimensions

within the 1-100 nm range. These nano-materials often exhibit very interesting electrical,

optical, magnetic, and chemical properties, which are absent in bulk samples, due to their high

surface area to volume ratios (Fendler, 2001; Hyeon, 2003). The ability to control the size and

shape of nanoparticles, as well as the extended arrangement of nanopartilces in 1 D, 2D and

3D are of crucial importance in nanoscience and nanotechnology (Mera et al., 2007).

There are two fundamentally different approaches for the synthesis of nanoparticles and

nanostructured materials: "bottom-up" and "top-down". In the "bottom-up" approach, the

nanostructured building blocks are first forms, and then assemble them into the final material.

These techniques have been used extensively in the formation of structural composite

materials. The "top down" approach begins with a suitable starting material and then cut, mill

I

and shape the materials into the desired shape and order (Fendler, 2001). Both approaches are

currently being used in industry. The top down approach tends to produce a lot of waste

materials and requires lots of machinery and time consuming. The bottom up approach

appears to be more attractive as the desired features are constructed from fundamental

building blocks, usually spontaneously through self-assembly (Margolis, 2005).

Despite the wide range of practical applications of magnetite, each application requires

different material properties such as thermal, chemical and colloidal stability, magnetic

characteristic, particle shape and size, and low toxicity (Nedkov et al., 2006). Pure magnetite

particles may not be very useful in practical applications due to some inherent limitations.

Due to their high specific surface area, these particles tend to aggregate to minimize their total

surface energy. Besides, they undergo oxidation rapidly to form a-Fe2O3. As such, appropriate

surface coating agents are necessary to modify the surface properties of magnetite particles in

order to address these limitations (Hong et al., 2006; Dumitrache et al., 2005).

Recently, starch has been considered as a promising candidate material for surface

modification of magnetite nanoparticles. Starch possesses strong hydrophilic characteristic. It

is composed of repeating 1,4-cý-D glucopyranosyl units: the linear form amylose and highly

branched amylopectin (Kim et al., 2006). Simi & Abraham, (2007) have reported the

synthesis of nanosized cassava starch for drug delivery applications. The starch was modified

with different long-chain fatty acids to decrease its hydrophilicity by the graft polymerization

reaction between starch and long chain fatty acids. Grafted starch was made into nanoparticles

and subsequently stabilized by cross-linking with sodium tripolyphosphate.

2

All applications of magnetite require highly stable magnetite colloidal dispersion with

monodispersed nanoparticles of tunable size and regular shape (Pei et al., 2007). Magnetite

nanoparticles can be further functionalized with starch via chemical modifications of their

surfaces to improve their properties. However, producing magnetite nanoparticles with the

desired size and acceptable size distribution and magnetite/starch nanocomposite are still

great challenges in nanotechnology since the characteristics of magnetite nanoparticles are

strongly affected by the synthesis parameters (Laurent et al., 2008).

In this study, both magnetite and magnetite/starch nanocomposite were synthesized

and characterized for electrochemical applications. Sago starch was used because it is

abundant, cheap and environmental friendly (Lang et al., 2006). Chapter 2 provides an

overview of the recent development of synthesis methods and applications of magnetite,

magnetite/starch and other magnetite nanocomposite including a brief introduction of

electrochemical capacitor. Chapter 3 focused on the synthesis and characterization of

magnetite colloidal suspension and thin films. The effects of synthesis conditions and

microstructure on the electrochemical properties of magnetite thin films were investigated.

Synthesis and characterization of magnetite/starch nanocomposite thin films were reported in

Chapter 4. The relationship between microstructural parameters and electrochemical

properties of magnetite and magnetite/starch nanocomposite thin films was elucidated. The

electrochemical performance of the magnetite and magnetite/starch nanocomposite thin films

were then evaluated for potential applications as electrode material of electrochemical devices,

in particular, electrochemical capacitors.

3

1.2 Objective of Study

The main objectives of this study include:

- To synthesize magnetite and magnetite/starch nanoparticle in the form of stable colloidal

suspensions.

- To characterize the physical, chemical and electrochemical properties of magnetite and

magnetite/starch nanoparticle thin films.

- To elucidate the microstructure property relationship for the optimization of

electrochemical properties of magnetite and magnetite/starch nanocomposite thin films.

- To evaluate the utility of magnetite and magnetite/starch nanocomposite thin films for

potential electrochemical applications.

4

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