universiti putra malaysia effect of hydrogen flow...

UNIVERSITI PUTRA MALAYSIA

EFFECT OF HYDROGEN FLOW RATE ON THE QUALITY OF CARBON NANOTUBES PRODUCED USING THE FLOATING CATALYST

CHEMICAL VAPOR DEPOSITION METHOD

RAJA NOR IZAWATI RAJA OTHMAN

FK 2007 10

EFFECT OF HYDROGEN FLOW RATE ON THE QUALITY OF CARBON NANOTUBES PRODUCED USING THE FLOATING CATALYST CHEMICAL

VAPOR DEPOSITION METHOD

By


Thesis submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfilment of the Requirement for the Degree of Master of Science

February 2007

DEDICATED TO

MOHD HANY SUAIB

WAN AHMAD NABIL MOHD HANY

WAN NURIN DAMIA MOHD HANY

2

Abstract of thesis presented to the Senate of Universiti Putra Malysia in fulfillment of the requirement for the degree of Masters of Science

EFFECT OF HYDROGEN FLOW RATE ON THE QUALITY OF CARBON

NANOTUBES PRODUCED USING THE FLOATING CATALYST CHEMICAL VAPOR DEPOSITION METHOD

By


February 2007

Chairman: Associate Professor Fakhru’l-Razi Ahmadun, PhD Faculty : Engineering

Well aligned multi walled carbon nanotubes (MWNTs) was successfully synthesized by

floating catalyst chemical vapor deposition method (CVD) involving the catalytic

decomposition of benzene upon the surface of iron particle. Two sources of hydrogen

were employed and varied; H2* that carried benzene vapor and H2** that supplied fresh

hydrogen into the electrical furnace to analyze the effects they had on quantity as well as

the morphology and structure of the produced CNTs. Total hydrogen flow rate was kept

constant to allow constant residence time. Reaction time was also varied to study the

growth rate of the products. The remaining parameters such as reaction temperature

(850°C), ferrocene sublimation temperature (120°C), and mass of ferrocene (200 mg)

were kept constant throughout the reaction. Argon (300 ml/min flow rate) was flown into

the system before reaction to provide an inert atmosphere in the furnace. It was also

flown after reaction to prevent product oxidation. The quantity of CNTs produced was

highest (0.08g) when the reaction time and supply of benzene were maximized (t = 50

min, H2*=350 ml/min, and H2**= 0 ml/min).

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The structure of the selected CNT samples was then further characterized via the means

of Electron Microscopy (SEM, TEM, and HRTEM) as well as X Ray Diffractometer. By

using TEM, measurement of 50 tubes per sample revealed CNTs of outer diameter (OD)

from 5 to 55 nm and inner diameter (ID) from 5 nm to 25 nm for all conditions studied.

At H2* = 150 ml/min, H2** = 250 ml/min, and t = 50 min, mean OD and ID of 18.64 nm

and 4.85 nm with standard deviation of 18.64 nm and 4.85 nm, respectively were

obtained.

XRD results revealed formation of sharp and narrow peaks at around 26° position (2θ),

which confirms the presence of highly crystallized CNTs for all samples. The values of

the intershell spacing of the wall (d002) are between 0.338 nm to 0.342 nm. The values of

full width at half maximum (FWHM) of the peaks of 0.7144, 0.2273, and 0.0200 was

obtained when H2*=350 ml/min, H2*=250 ml/min and H2*=150 ml/min, respectively at

50 min reaction time. The reduction in the FWHM value indicated the CNTs exhibit more

crystalline graphite as more H2** was supplied.

4

Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah Master Sains

KESAN ALIRAN GAS HIDROGEN KE ATAS KUALITI NANOTIUB KARBON MELALUI KAEDAH PEMANGKIN TERAPUNG-PENGURAIAN WAP KIMIA

Oleh


Febuari 2007 Pengerusi: Profesor Madya Fakhru’l-Razi Ahmadun, PhD Fakulti: Kejuruteraan

Nanotiub karbon menjajar pelbagai dinding (MWNTs) telah berjaya disintesis dengan

menggunakan kaedah pemangkin terapung-penguraian wap kimia, (floating catalyst

chemical vapor deposition (CVD)) yang melibatkan penguraian bermangkin benzena di

atas permukaan zarah ferum. Dua sumber gas hidrogen telah digunakan dan

dipelbagaikan, H2* yang membawa wap benzene dan H2** yang membekalkan hidrogen

segar ke dalam sistem untuk menganalisa kesan kadar aliran tersebut terhadap kuantiti,

morfologi, dan struktur nanotiub karbon yang terhasil. Masa tindakbalas juga

dipelbagaikan untuk mengkaji kadar pertumbuhan produk. Nilai parameter yang

selebihnya seperti suhu tindakbalas (850°C), suhu pemejalwapan ferosin (120°C), dan

jisim ferosin (200 mg) dikekalkan sepanjang tindakbalas. Gas argon (kadar aliran

sebanyak 300 ml/min) digunakan sebagai gas lengai semasa tempoh pemanasan relau

sebelum tindakbalas dan semasa tempoh penyejukan relau selepas tindakbalas untuk

mengelakkan pengoksidaan produk. Kuantiti maksimum nanotiub karbon (0.08g)

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diperolehi apabila masa tindakbalas dan pembekalan benzena adalah pada tahap

maksimum (t = 50 min, H2*=350 ml/min, dan H2**= 0 ml/min).

Struktur CNT yang terpilih kemudiannya dicirikan dengan menggunakan mikroskopi

electron (SEM, TEM, and HRTEM) dan X Ray Diffractometer. Dengan menggunakan

TEM, pengiraan 50 tiub untuk setiap sampel menunjukkan garis pusat luar (OD) CNT

diperolehi adalah dari 5 ke 55 nm dan garis pusat dalam (ID) CNT dari 5 ke 25 nm untuk

semua keadaan yang dikaji. Pada H2* = 150 ml/min, H2** = 250 ml/min, dan t = 50 min,

purata OD dan ID diperolehi adalah 18.64 nm and 4.85 nm dengan nilai piawai deviation

masing-masing sebanyak 18.64 nm and 4.85 nm.

Keputusan XRD menunjukkan penghasilan puncak yang tajam dan sempit pada posisi

26°, iaitu 2θ. Nilai jarak di antara dinding dalaman (d002) adalah di antara 0.338 nm dan

0.342 nm. Nilai full width at half maximum (FWHM) puncak diperolehi adalah 0.7144,

0.2273, dan 0.0200 apabila H2*=350 ml/min, H2*=250 ml/min dan H2*=150 ml/min,

masing-masing pada masa tindakbalas tertinggi iaitu 50 minit. Pengurangan di dalam

nilai FWHM menunjukkan CNT mempunyai lebih tahap kekristalan grafit apabila lebih

H2** dibekalkan.

6

ACKNOWLEDGEMENTS

I am deeply grateful to Allah S.W.T. for giving me the strength and patience that enables

me to complete this study.

I would like to extend my gratitude and appreciation to the supervisory committee;

Chairman, Associate Professor Dr. Fakhru’l-Razi Ahmadun; Committee Members, Dr

Salmiaton Ali and Dr Suraya Abdul Rashid for providing invaluable advice, untiring

assistance, encouragement, motivation, and support that enabled me to complete the

Masters program smoothly and efficiently.

I also wish to thank Universiti Putra Malaysia for financial support.

My heartfelt and sincere appreciation goes to my children; Wan Ahmad Nabil and Wan

Nurin Damia, my parents (Raja Othman Raja Abdul Hamid, Fatimatul Rahni Chik, Suaib

Haron, and Khadijah Abdul Rahman), Ayunda Sanusi, other relatives and friends who

always encouraged and supported me during the study period. Last but not least, my

special thanks to my husband, Mohd Hany Suaib, for his love, constant encouragement,

sacrifices, patience, and understanding that enable me to finish the study successfully.

7

I certify that an Examination Committee has met on 14 February 2007 to conduct the final examination of Raja Nor Izawati Raja Othman on her Master of Science thesis entitled “Effect of Hydrogen Flow Rate on the Quality of Carbon Nanotubes Produced Using the Floating Catalyst Chemical Vapor Deposition Method” in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian Malaysia (Higher Degree) Regulations 1981. The Committee recommends that the candidate be awarded the relevant degree. Members of the Examination Committee are as follows: Robiah Yunus, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Chairman) Thomas Choong Shean Yaw, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Internal Examiner) Tinia Idaty Mohd. Ghazi, PhD Lecturer Faculty of Engineering Universiti Putra Malaysia (Internal Examiner) Subhash Bhatia, PhD Professor Faculty of Engineering Universiti Sains Malaysia (External Examiner)

_________________________________ HASANAH MOHD. GHAZALI, PhD Professor/Deputy Dean School of Graduate Studies Universiti Putra Malaysia Date:

8

This thesis submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfilment of the requirement for the degree of Master of Science. The members of the Supervisory Committee are as follows: Fakhru’l-Razi Ahmadun, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Chairman) Salmiaton Ali, PhD Lecturer Faculty of Engineering Universiti Putra Malaysia (Member) Suraya Abdul Rashid, PhD Lecturer Faculty of Engineering Universiti Putra Malaysia (Member)

______________________ AINI IDERIS, PhD Professor/Dean School of Graduate Studies Universiti Putra Malaysia

Date:

9

DECLARATION I hereby declare that the thesis is based on my original work except for quotations and citation, which has been duly acknowledged. I also declare that it has not been previously or concurrently submitted for any other degree at UPM or other institutions.

___________________________________


Date:

10

TABLE OF CONTENTS

Page

DEDICATION 2 ABSTRACT 3 ABSTRAK 5 ACKNOWLEDGEMENTS 7 APPROVAL 8 DECLARATION 10 LIST OF TABLES 13 LIST OF FIGURES 14 LIST OF ABBREVIATIONS/NOTATIONS/GLOSSARY OF TERMS 16 CHAPTER

1 INTRODUCTION 17 1.1 Background 17 1.2 Objectives and Scopes of Work 21 1.3 Thesis Outline 22

2 LITERATURE REVIEW 23 2.1 Introduction 23 2.2 History: Fullerenes and Carbon Nanotubes 24 2.3 Carbon Nanotube Properties and Application 27 2.3.1 Mechanical properties 28 2.3.2 Electronic Properties 29 2.3.3 Other physical properties 30 2.3.4 Application of carbon nanotubes 31 2.4 Major Carbon Nanotube Synthesis Methods and

comparison 33 2.4.1 Arc discharge 33 2.4.2 Laser vaporization 35 2.4.3 Chemical Vapor Deposition 37 2.4.4 Comparison of the Nanotube Synthesis Method 48

2.5 Growth mechanism of Carbon Nanotube 49 2.6 Effects of hydrogen in CVD 52 2.7 Current product market and future market outlook

for carbon nanotubes 56

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3 RESEARCH METHODOLOGY 60 3.1 Introduction 60 3.2 Materials 60 3.3 Experimental Apparatus 61 3.4 Experimental Procedure 63

3.4.1 Raw Material and Equipment Set Up 63 3.4.2 Reaction and Product Collection 63

3.5 Experimental Parameters 66 3.6 Sample Analysis and Characterization 69

3.6.1 Mass Analysis 69 3.6.2 Structural Analysis 69

4 RESULTS & DISCUSSION 72

4.1 Introduction 72 4.2 Product formation 72

4.2.1 Product collection and observation 73 4.2.2 Discussion on product distribution 76

4.3 Mass Analysis 82 4.3.1 Mass distribution 83

4.3.2 Empirical correlation on the mass of CNTs 87 4.4 Structural Analysis 93

4.4.1 SEM Observations and Discussion 94 4.4.2 TEM Observations and Discussion 99 4.4.3 CNT Characterizations 106 4.4.4 HRTEM and XRD observation and analysis 112

5 CONCLUSION AND RECOMMENDATIONS 117

5.1 Conclusions 117 5.2 Recommendations 119

REFERENCES 121 APPENDICES 135 BIODATA OF THE AUTHOR 175

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LIST OF TABLES

Table Page

2.1 Comparison of arc-discharge, laser ablation, and CVD methods 49

2.2 CNT price list for the year of 2006 57

3.1 Experimental runs and the combination of the varied parameters 68

4.1 Empirical relations between mass of CNT obtained and H2* flow rate at different reaction time 90

4.2 Outer diameter distribution of CNTs produced at different reaction conditions. 107 4.3 Inner diameter distribution of CNTs produced at different reaction conditions. 110 4.4 Numerical analysis on the microstructure of the CNTs synthesized

at t = 50 min 115

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LIST OF FIGURES

Figure Page

2.1 The chiral vector OA or Ch=na1 + ma2 is defined on the honeycomb lattice of carbon atoms by unit vectors a1 and a2 and the chiral angle θ with respect to the zigzag axis. Along the zigzag axis θ = 0°. Also shown are the lattice vector OB = T of the 1D nanotube unit cell and the rotation angle ψ and the translational τ which constitute the basic symmetry operation R = (ψ│τ) for the carbon nanotube. The diagram is constructed for (n,m) = (4,2). (Dresselhaus et al., 1995) 26

2.2 (a) Schematic diagram of the arc-discharge apparatus (Ando et al.,

2004); and (b) HRTEM micrographs of CNTs produced via arc discharge (Iijima, 1991). 34

2.3 (a) Schematic diagram of the laser ablation apparatus (Ando et al., 2004); and (b) HRTEM micrographs of CNTs produced via laser ablation (Thess et al., 1996). 36 2.4 (a) Schematic diagram of the CVD apparatus (Ando et al., 2004); and (b) HRTEM micrographs of CNTs produced via CVD (Lee et al., 2003). 37

3.1 Schematic of CVD apparatus 61

3.2 CVD apparatus showing 1st furnace and benzene in Erlenmenyer

Flask 62

3.3 2nd furnace and tube that directs unreacted gas to fume hood 62

3.4 Outline of the experiments 64

3.5 Inlets to the CVD Apparatus 65 4.1 Images of the boats after reaction (a) Boat 3; (b) Boat 2; (c) Boat 1; (d) Overall view showing product distribution on each Boat 74

4.2 Carbon products from Boat 2 75 4.3 SEM images of the product obtained from (a) Wall, (b) Boat 1 and (c) Boat 2 76

14

4.4 Effects of varying H2* and H2** flow rate on mass of the products obtained for different reaction times; (a) 10 min, (b) 20 min, (c) 30 min, (d) 40 min, and (e) 50 min 84

4.5 Mass of CNT synthesized as H2* varies at different reaction time. 89 4.6 SEM images of CNTs produced at t = 10 min. 95 4.7 SEM images of CNTs produced at t = 20 min. 96 4.8 SEM images of CNTs produced at t = 30 min. 96

4.9 SEM images of CNTs produced at t = 40 min. 97 4.10 SEM images of CNTs produced at t = 50 min. 97 4.11 TEM images of CNTs produced at t = 10 min. 100 4.12 TEM images of CNTs produced at t = 20 min. 100 4.13 TEM images of CNTs produced at t = 30 min. 101

4.14 TEM images of CNTs produced at t = 40 min. 101 4.15 TEM images of CNTs produced at t = 50 min. 102 4.16 (a) Fe nanoparticles located at the end and middle of the tube;

(b) Fe nanoparticles formed in the middle of the tube; (c) CNT with open end; (d) CNT with bamboo structure. 104

4.17 Mean outer diameter at different H2* flow rate and reaction time. 109 4.18 Mean inner diameter at different H2* flow rate and reaction time. 111 4.19 HRTEM images showing the wall structures of CNTs for (a)

H2*=150 ml/min (b) H2*=250 ml/min and (c) H2*=350 ml/min at 50-min reaction time with their corresponding XRD peak 113

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LIST OF ABBREVIATIONS

Ar Argon

C Carbon

CNT Carbon Nanotube

CVD Chemical Vapor Deposition

d002 Interlayer spacings between walls

Fe Iron

FeCp Ferrocene

H2 Hydrogen

H2* Hydrogen that carries benzene vapor

H2** Hydrogen that is supplied directly to the furnace

HRTEM High resolution transmission electron microscopy

MWNT Multi walled nanotubes

SEM Scanning electron microscopy

SWNT Single walled nanotubes

TEM Transmission electron microscopy

VGCF Vapor grown carbon fibers

XRD X Ray Diffraction

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CHAPTER 1

INTRODUCTION

1.1 Background

Research in finding new materials has attracted the attention of scientists all over the

world due to the growing need of humankind to improve the quality of life. Research on

carbon materials especially has a lot to be explored due to its unique C-C bonding that

enables carbon to assume different structures such as one-dimensional nanotubes, two-

dimensional graphite, three-dimensional diamond, and even zero-dimensional fullerenes.

The discovery of multiwalled carbon nanotubes (1991) and single walled nanotubes

(1993), both by Iijima of NEC laboratories in Japan has stimulated researchers all over

the world to explore their much-anticipated extraordinary properties. As described by

Iijima (1991), multiwalled nanotubes (MWNTs) consist of two to seven concentric

graphene shells. As the name implies, single-walled nanotubes (SWNTs) consist of a

single graphene cylinder. Compared to MWNTs, SWNTs exhibit superior properties that

emerge from the strong one-dimensionality and crystalline perfection of the structure.

These two are often simply called Carbon Nanotubes (CNTs).

Realizing that these structures exhibits remarkable mechanical, electrical, and electronic

properties, the focus of the CNTs research has moved to the engineering aspect of it, i.e.

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the production of CNTs. In order to fully utilize of their special properties, it is important

to come out with a method for synthesis that can be controlled, relatively cheap, and

scaleable, so that the production of high quality of carbon nanotubes can be

commercialized. Arc discharge (Iijima, 1993) and laser vaporization (Thess et al., 1996)

methods have been used to produce CNTs of superior straightness and highly

crystallized. These two methods however suffer a high cost of manufacturing since they

involve with high operating temperature (>2727°C) and size constraint. Hence, these two

are not economical to produce CNTs on a large scale.

Chemical Vapor Deposition (CVD) technique has gained popularity as an alternative

production method due to its potential to produce CNTs on a large scale. With this

method, CNTs are produced via catalytic decomposition of hydrocarbons at relatively

lower temperatures, normally between 427°C to 1400°C in a furnace. Although the

technology had been applied to produce vapor grown carbon fibers (VGCFs) back in

1970s, the VGCFs produced are often of low quality, which formed spaghetti-like

structure (Teo et al., 2004). Driven by the need to produce CNTs on a large scale,

substantial and rapid progress was made in the development of CVD to establish it as a

highly controlled technology for the production of CNTs.

Baker et al. (1972), Oberlin et al. (1976) and Dai et al. (1996) each suggested three

different growth models for the formation of carbon filament or CNT. These authors

however agreed that the formation occurred as a consequence of the precipitation of

carbon through or on the catalyst. The growth would occur as long as the catalyst

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remained active, i.e. the catalyst was not covered by amorphous carbon or the formation

of carbide was prevented. Hence, the presence of catalyst deactivation agent would play

an important role in determining the amount of the CNTs formed. It could also prevent

catalyst poisoning that would eventually yield low purity CNTs.

Hydrogen is known to have significant effect in increasing the amount of CNTs formed

during CVD process. Cui et al. (1999) reported that the growth of CNTs flourished as the

percentage of H2 was increased in their CVD system. Bladh et al. (2000) observed that

the formation of SWNT was enhanced upon moderate addition of hydrogen to the

CO/Fe(CO)5 mixture. Both Neumayer et al. (2004) and Qiu et al. (2004) also reported the

presence of H2 in facilitating the growth of CNTs in their CVD system as well.

The presence of hydrogen also could prevent catalyst poisoning. As a result the as

synthesized CNTs would be of high purity with minimal side product formation. Both

Rao et al. (1998) and Satishkumar et al. (1998) observed that the use of H2 in the gas

flow with argon minimized the amorphous carbon coating on the CNT produced by their

CVD. Li et al. (2001) also observed that low flow-rate of methane accompanied by a

hydrogen co-flow could prevent amorphous formation. Venegoni et al. (2002) observed

encapsulated iron particles in all of their samples with a greater occurrence when

hydrogen was not introduced in the gas phase. Dong et al. (2004) reported formation of

nanoparticles on the surface of the CNTs when hydrogen was not introduced in their

CVD system.

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Previous work in synthesizing CNT at UPM involved synthesizing CNT via floating

catalyst CVD method that employed ferrocene as catalyst and benzene as hydrocarbon

precursors (Atieh, 2005). Hydrogen was used to bubble benzene into the reactor to obtain

CNT. Higher flow rate of hydrogen contributed to higher amount of benzene that would

enhance to the formation of amorphous carbon and encapsulated nanoparticles, as

highligted by this author (Atieh, 2005). Hence, the real effects exerted by hydrogen in

minimizing co-formation of amorphous carbon and encapsulated nanoparticles as

mentioned by other researchers (Rao et al., 1998; Satishkumar et al., 1998; Li et al.,

2001; Venegoni et al., 2002 and Dong et al., 2004) was not fully utilized. This study

seeks to improve the previous process based on the earlier findings.

In spite of the well known effects exerted by hydrogen, not much work has been

published on the CNT grown by adding fresh hydrogen to the benzene-ferrocene-

horizontal-floating catalyst CVD system. Ci et al. (2001) added thiophene to the similar

system and obtained mostly carbon nanofiber, not carbon nanotube, at unnecessarily high

operating temperature (>1000°C). The products obtained were of high impurity (presence

of carbonaceous product), which might be due to H2 that didn't effectively react with

excess carbon. This indicated the failure of H2 as purification agent and the inefficiency

of the parameters employed to control the CNTs growth in their system. The presence of

thiophene might explain such observations.

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1.2 Objectives and Scope of Work

The objectives of this research are

1) To determine the operating conditions to synthesize CNTs of no side products as

well as of highest quality at a relatively low temperature.

2) To study the effects of adding fresh hydrogen into the system on the as produced

CNTs in terms of morphology and growth mechanism.

The scopes of the work are directed towards assessing the effects of operating parameters

on the quantity and quality of CNTs produced. The parameters considered in the study

are reaction time, amount of benzene, as well as flow rates of fresh hydrogen supplied.

The reaction involves catalytic decomposition of benzene at constant temperature, which

is 850°C in this reactor. Benzene is chosen due to its low boiling point which is 80°C

(Williamson, 1994). Hence, it is easily decomposed upon entering the low-temperature

reaction zone. Ferrocene is used since it does not need to be pretreated, i.e. can be readily

used upon purchase. The reaction is run under atmospheric pressure to eliminate its

dependency on pressure factor. The weighted sample is characterized by using SEM,

TEM, as well as HRTEM. XRD is further used to identity the crystallinity of the carbon

produced.

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1.3 Thesis Outline

The thesis consists of five chapters. Chapter 1 highlights the background of the problem

and the significance of the research work in the field of carbon nanotubes. Chapter 2

covers the literature reviews on the subject, where extensive review, analysis and

synthesis are given to the reported work of various authors. The review provides the basis

for the experimental and analysis section of the thesis. Chapter 3 is on the development of

the analytical methods. Chapter 4 presents the results and the discussions of the obtained

results. The mass of the pure CNTs produced as well as their outer and inner diameters

are reported. The optimized condition for producing high quality CNTs is suggested.

Chapter 5 presents the conclusion of the work and recommendation for future work.

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CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

Carbon is one of the three basic elements (C, H, and O) that form many kinds of

organisms with other elements to constitute life on earth. Among the pure elements in the

periodic table, carbon can assume different structures such as one-dimensional nanotubes,

two-dimensional graphite, three-dimensional diamond, and even zero-dimensional

fullerenes. The tubule morphology of carbon includes carbon fibers, whiskers, and

nanotubes. Other forms of carbon are glassy carbon, carbon blacks, amorphous carbon,

and liquid carbon (Dresselhaus et al., 1997).

Discovered in 1991 by Iijima, CNTs has attracted attention of scientists and researchers

all over the world due to its unique structure and properties. Since then, tremendous work

has been extensively done to study its unique properties. Due to its wide practical

application, massive work on the methods of its preparation/production has also been

studied to improve its yield in terms of quantity and also quality. This literature reviews

previous work on the synthesis of CNTs by different methods in details; special attention

will be given to ‘Chemical Vapor Deposition’ technique using ‘floating catalyst’ type.

Role of hydrogen in growth mechanism will be discussed in details.

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2.2 History: Fullerenes and Carbon Nanotubes

It was the Kroto-Smalley work (Kroto et al., 1985) that pioneered the field of nano-

structured carbon science era and further stimulated the search of finding new carbon

materials. In this experiment, graphite was laser-vaporized and a new structure was

accidentally found. Fullerenes or C60, a dominant structure of the product was detected by

mass spectrometry. They soon realized that it was a closed cluster containing precisely 60

carbon atoms, which would have a structure of unique stability and symmetry.

Iijima was the first to discover CNTs in 1991. This was multiwalled nanotube (MWNT),

which consisted of two to seven concentric graphene shells, and were embedded in the

fullerene by-product soot materials produced by the arc-discharge method. Researchers

and scientists were stimulated by the remarkable one dimensional quantum effects

predicted for their electronic properties (Iijima, 1991). The remarkable structure and

properties of CNTs also were predicted to give rise to some unique applications (Iijima,

1991).

Independently and at about the same time, Iijima (1993) and Bethune et al. (1993) both

synthesized single walled nanotube (SWNT). Iijima’s important contribution to CNTs

was that he connected his nanotube work to the ongoing fullerene studies. It was

observed that fullerene-like caps or hemisphere were formed at the end of nanotube. As

the name implies, single-walled nanotube (SWNT) consists of a single graphene cylinder.

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