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CARBON NANOTUBES

by

Rasikh Tariq

ME-113006 Student of: Mechanical Engineering

Mohammad Ali Jinnah University, Islamabad Campus

A project report submitted to the

Department of Mechanical Engineering

in partial fulfillment of the requirements for the course of

ENGINEERING MATERIALS [ME2413]

Faculty of Engineering and Applied Sciences

Mohammad Ali Jinnah University

Islamabad

<December, 2012>

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Copyright 2012 by MAJU Student

All rights reserved. Reproduction in whole or in part in any form requires the prior written permission of

<Rasikh Tariq > or designated representative.

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The Project is about Carbon Nanotubes- A gift of 21st century. The project was

selected only due to wide Umbrella of application of Carbon Nanotubes. As

according to National Science & Technology Council (USA), “Nanotechnology is

an enabling technology that will change the nature of almost every human-made

object in the next century”

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DECLARATION

It is declared that this is an original piece of my own work, except where otherwise

acknowledged in text and references. This work has not been submitted in any form for

another degree or diploma at any university or other institution for tertiary education and

shall not be submitted by me in future for obtaining any degree from this or any other

University or Institution.

Rasikh Tariq

ME-113006

December 2012

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ABSTRACT

As the size and complexity of today’s modern World increases, new techniques must be

developed to effectively design and to keep balance within the new technology. For this purpose,

we have should think of something new. That is, Carbon Nanotubes. With the discovery of

Carbon Nanotubes back in Cold War, it had deviated the mind of Scientists and Engineers

towards itselves. That is the reason to select this particular project. Carbon Nanotubes have

brought a new revolution in our Small homeland. Maybe, in the future it will be the substitute of

certain materials.

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Table of Contents

Chapter 1: Project Charter Purpose .......................................................................................9

Chapter 2: Project Executive Summary..................................................................................9

Chapter 3: Project Scope ..........................................................................................................9

Chapter 4: An Introduction to Nanotechnology ...................................................................10

Nanotechnology- Definition & Examples ..................................................................................10

History and Background of Nanotechnology .............................................................................10

References ..................................................................................................................................11

Chapter 5: An Introduction to Carbon Nanotubes (CNT’s) ...............................................11

Carbon Nanotubes- Definition ..................................................................................................11

What CNT’s are? ........................................................................................................................11

Allotropic Forms of Carbon ......................................................................................................12

Historical Perspective ................................................................................................................13

References ..................................................................................................................................13

Chapter 6: Synthesis of Carbon Nanotubes ..........................................................................14

Top Down Method .....................................................................................................................14

Bottom Up Method .....................................................................................................................14

Arc Discharge Method ...............................................................................................................14

References ..................................................................................................................................15

Chapter 7: Types & Structure of Carbon Nanotubes ..........................................................16

Single-wall Carbon Nanotubes ...................................................................................................16

Calculating Diameter of Carbon Nanotube ................................................................................17

Multi-wall Carbon Nanotubes ....................................................................................................17

References ..................................................................................................................................17

Chapter 8: Properties of Carbon Nanotubes ........................................................................18

Mechanical Properties of CNT’s ................................................................................................18

References ..................................................................................................................................19

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Chapter 9: Application of Carbon Nanotubes ......................................................................19

Carbon Nanotube and Energy ....................................................................................................19

Carbon Nanotubes in Health Care ..............................................................................................20

Carbon Nanotubes & the Environment ......................................................................................20

Structural Changes across the World .........................................................................................20

Carbon Nanotubes & Electronics ...............................................................................................20

References ..................................................................................................................................21

Chapter 10: Pakistan & Carbon Nanotubes ...........................................................................21

Research and Publications ..........................................................................................................21

References ..................................................................................................................................22

Chapter 11: Conclusion ............................................................................................................22

Future Prospectus .......................................................................................................................22

Harmful Aspects of Nanotubes ..................................................................................................22

References ..................................................................................................................................22

“Nanotechnology is an enabling technology that will change the nature of almost

every human-made object in the next century.”

National Science and Technology Council (USA)

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Chapter 1:

Project Charter Purpose

The purpose of the Project is:

Disseminate a brief summary of Carbon Nanotubes.

Provide an introduction to some of the remarkable properties of Carbon Nanotubes

Provide a very short introduction to some of the risks and opportunities presented by

nanotechnology

Chapter 2:

Project Executive Summary

The project will lead us from the introduction of Nanotechonology to the advanced basis of

Carbon Nanotubes. Stating from Nanotechonology, historical perspective of Nanotechonlogy

then we had introduced Carbon Nanotubes. It’s unique structure and remarkable properties was

also a point of focous in this Project. Then comes, wide umbrella of applications of Carbon

Nanotubes and then at the last we had try to relate Carbon Nanotubes with Pakistan.

Chapter 3:

Project Scope

The project was selected based on importance of Carbon Nanotubes. This will be shocking that

in the current days of this World Carbon Nanotubes is one of the material that is under

observations and experiments of much of the Scientist and Engineers. The project in this

scenario -when most of the Scientist and Engineers are researching on Carbon Nanotubes – plays

a vital role. Carbon Nanotubes is entirely new discovery for the World, perhaps a gift of 21st

Century.

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Chapter 4

An Introduction to Nanotechnology

Introduction:-

Nanotechnology, or, as it is sometimes called, molecular manufacturing , is a branch of

engineering that deals with the design and manufacture of extremely small electronic circuits and

mechanical devices built at the molecular level of matter.

Definition:-

The Institute of Nanotechnology in the U.K. expresses it as:

"Science and Technology where dimensions and tolerances in the

range of 0.1 nanometer (nm) to 100 nm play a critical role."

Examples:-

Some typical examples of Nanotechonology is as follows:

Advanced drug delivery systems

New generation of lasers

Carbon Nanotube products

Nanoparticle reinforced materials

High hardness cutting tools

History & Background of Nanotechnology:-

Although Nanotechnology is a relatively recent development in scientific research, the

development of its central concepts happened over a longer period.

Around the same time, K. Eric Drexler developed and popularized the concept of

nanotechnology and founded the field of molecular nanotechnology. In 1979, Drexler

encountered Richard Feynman's 1959 talk There's Plenty of Room at the Bottom. The term

"Nanotechnology", originally coined by Norio Taniguchi in 1974, was unknowingly

appropriated by Drexler in his 1986 book Engines of Creation: The Coming Era of

Nanotechnology, which proposed the idea of a nanoscale "assembler" which would be able to

build a copy of itself and of other items of arbitrary complexity

The early 2000s also saw the beginnings of commercial applications of nanotechnology,

although these were limited to bulk applications of Nanomaterials, such as the Silver Nano

This DNA tetrahedron is an

artificially designed

nanostructure of the type made

in the field of DNA

nanotechnology. Each edge of

the tetrahedron is a 20 base pair

DNA double helix, and each

vertex is a three-arm junction.

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platform for using silver Nanoparticles as an antibacterial agent, Nanoparticle-based transparent

sunscreens, and carbon Nanotubes for stain-resistant textiles.

References:-

Nanoscale Phenomena (Fundamentals and Application) by Horst Hahn, Anatolia

Sidorenko & Ion Tiginyanu

Institute of Nanotechnology, U.K. (http://www.nano.org.uk/)

“Springer Handbook of Nanotechnology”, 2nd

edition by Bharat Bhushan.

What is Nanotechnology, An Introduction

(http://www.understandingnano.com/introduction.html)

Definition – What is Nanotechnology?

(http://www.nanowerk.com/nanotechnology/introduction/introduction_to_nanotechnolog

y_1.php)

http://www.nanotech-now.com/current-uses.html

A Brief History of Nanotechnology (http://www.charpan.com/a-brief-history-of-

nanotechnology)

Chapter 5

An Introduction to Carbon Nanotubes (CNT’s)

Definition:-

Carbon Nanotubes are fullerene molecules having a cylindrical or

toroidal shape.

What CNT’s are ?

Carbon Nanotubes (CNTs) are allotropes of carbon with a cylindrical

nanostructure. Nanotubes have been constructed with length-to-diameter

ratio of up to 132,000,000:1, significantly larger than for any other

material. These cylindrical carbon molecules have unusual properties,

which are valuable for nanotechnology, electronics, optics and other

fields of materials science and technology. In particular, owing to their

extraordinary thermal conductivity and mechanical and electrical

properties, Carbon Nanotubes find applications as additives to various structural materials. For

instance, Nanotubes form a tiny portion of the material(s) in some (primarily carbon fiber)

baseball bats, golf clubs, or car parts.

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Nanotubes are members of the fullerene

structural family. Their name is derived

from their long, hollow structure with the

walls formed by one-atom-thick sheets of

carbon, called graphene. These sheets are

rolled at specific and discrete ("chiral")

angles and the combination of the

rolling angle and radius decides the

Nanotube properties; for example, whether

the individual Nanotube shell is a metal or

semiconductor. Nanotubes are categorized

as single-walled Nanotubes (SWNTs) and

multi-walled Nanotubes (MWNTs).

Individual Nanotubes naturally align

themselves into "ropes" held together by van

der Waals forces, more specifically, pi-

stacking.

Applied quantum chemistry, specifically, orbital hybridization best describes chemical bonding

in Nanotubes. The chemical bonding of Nanotubes is composed entirely of sp2 bonds, similar to

those of graphite. These bonds, which are stronger than the sp3 bonds found in alkanes and

diamond, provide nanotubes with their unique strength.

Allotropic forms of CARBON

Crystalline

Diamond

Graphite

Fullerene

Amorphous

Coal

Charcoal

Lampblack

All 8 allotropes of Carbon

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Historical Perspective:-

The history of Carbon Nanotubes is often misconstrued. A number of people consider 1991 as

the year when these tubes were discovered. Sumio Iijima is attributed with the discovery of these

tubes. However the reality is quite different.

If we go back in history, in the year 1952, we will see that clear pictures of these tubes were

printed in Soviet Journal of Physical Chemistry. Mr V. M. Lukyanovich and V. Radushkevich

are credited for that publication. However, the journal was published in Russian Language.

Hence, this discovery went rather under the radar. Western scientist and literature writers did not

have access to much of Soviet Press during the period of Cold war. Had there been some sort of

ways to exchange between the two super powers, scientist might have agreed unanimously upon

the existence of these tubes much earlier.

Iijima also discovered the molecules in 1991 when he was studying the synthesis of fullerenes by

using electric arc discharge technique. A paper was also published in 1976. It also showed the

existence of these tubes. Koyama, Oberlin, and Endo did the paper. There is a TEM image of this

tube in this publication. This tube consisted of single wall of graphene. Mr Endo later called this

as single walled Nanotube.

References:-

“Carbon nanotubes, preparation and properties", edited by T.W.Ebbesen, CRC Press

(1996).

"Carbon Nanotubes and Related Structures: New Materials for the Twenty-First

Century" , Peter J F Harris, Cambridge University Press (1999).

"Carbon Nanotubes", by S. Reich, C. Thomsen, J. Maultzsch, Wiley-VCH, 2004.

“The Science & Technology of Carbon Nanotubes” by Kazuyoshi Tanaka, Tokio

Yamabe & Kenichi Fukui.

Timeline of Carbon Nanotubes (http://www.pa.msu.edu/cmp/csc/nttimeline.html)

http://www.damascusfortune.com/history-of-carbon-nanotubes.html

History of Carbon Nanotubes (http://www.cnanotech.com/2012/08/07/history-of-carbon-

nanotubes.html)

http://www.personal.reading.ac.uk/~scsharip/Carbon%20Nanotubes.html

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Chapter 6

Synthesis of Carbon Nanotubes

We can Synthesis Carbon Nanotubes by two approaches:

Arc Discharge Method:-

When high voltage is applied to two graphite electrodes, an arc flashes over between them

(provided they are not positioned too far from each other) and an arc develops. The temperature

in the resulting plasma is sufficient to vaporize the graphite. In fullerene synthesis the required

plasma is generated between two pointed graphite electrodes that barely touch each other

(contact arc). The resultant particles rise from the plasma zone and deposit on the reactor walls.

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The yields of fullerene are about 15% with C 60 constituting about 80% of the fullerene material.

Graphite “soiled” with other elements (B, Si, or Al) turns out to be a suitable material for

electrodes if the portions of higher fullerenes are increased. Finally, electrodes made of coal can

be used in these syntheses too; only do the yields drop to 4 – 6% of the employed carbon.

Usually electrodes with a diameter of less than 6 mm are used for the arc method because the

output of fullerene decreases

on larger dimensions. This

effect is caused by the

fullerene’s sensitivity toward

radiation: while traveling

toward cooler parts of the

apparatus, the fullerene

molecules are exposed to very

intensive UV - rays emitted by

the arc plasma. They get excited, and the resulting triplet state with a lifetime in the range of μ s

gives rise to an increased reactivity toward other carbon clusters C n. The latter can be explained

with the open - shell structure of the excited fullerene.

As larger electrodes generate larger plasma zones, they also emit more radiation. Hence more of

the initially formed fullerenes react with other carbon clusters present in the apparatus, and the

yields of cage - like structures decrease rapidly.

References:-

Kroto, H. W., Heath, J. R., O'Brien, S. C., Curl, R. F. & Smalley, R. E. Nature 318,

162−163 (1985).

The Royal Swedish Academy of Sciences

(http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1996/press.html)

http://www.gitam.edu/eresource/nano/nanotechnology/tem.htm

Carbon Nanotubes, Production Methods for Carbon Nanotubes Including Arc

Discharge, Laser, Chemical Vapor Depsition and Ball Milling by Cheap Tubes

Inc(http://www.azonano.com/article.aspx?ArticleID=1561)

Arc-discharge method

(http://www.rsc.org/publishing/journals/prospect/ontology.asp?id=CMO:0002240&MSI

D=b9nr00268e)

Arc-Discharge and Laser Ablation

(http://www.iue.tuwien.ac.at/phd/pourfath/node15.html)

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Chapter 7

Types & Structure of Carbon Nanotubes

Carbon Nanotubes have two divisions-divided based on different structures.

Single-wall Carbon Nanotubes (SWNT):-

SWNTs have a diameter of close to 1 nm with a tube length that can be many thousands of times

longer. The structure of a SWNT can be conceptualized by wrapping a one-atom-thick layer of

graphite called graphene into a seamless cylinder. The way the graphene sheet is wrapped is

represented by a pair of indices (n, m) called the

chiral vector. The integer’s n and m denote the

number of unit vectors along two directions in

the honeycomb crystal lattice of graphene.

If m=0, the Nanotubes are called

"zigzag".

If n=m, the Nanotubes are called

"armchair".

Otherwise, they are called "chiral".

Carbon Nanotubes

Single -wall Carbon Nanotubes

Multi-wall Carbon Nanotubes

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Calculating Diameter of Carbon Nanotube:-

The diameter of Carbon Nanotube cannot be measured directly. To measure diameter of Carbon

Nanotubes we use “m” and “n” vector.

Where a = 0.246 nm.

Multi-wall Carbon Nanotube (MWNT):-

SWNTs are an important variety of carbon nanotube because most of their properties change

significantly with the (n,m) values, and this dependence is non-monotonic . In particular, their

band gap can vary from zero to about 2 eV and their electrical conductivity can show metallic or

semiconducting behavior. The most basic building block of these systems is the electric wire,

and SWNTs with diameters of an order

of a nanometer can be excellent

conductors.

There are two models, which can be

used to describe the structures of multi-

walled nanotubes. In the Russian Doll

model, sheets of graphite are arranged

in concentric cylinders, e.g. a (0, 8)

single-walled nanotube (SWNT) within a larger (0, 17) single-walled nanotube. In the Parchment

model, a single sheet of graphite is rolled in around itself, resembling a scroll of parchment or a

rolled newspaper.

References:-

EXOHYDROGENATED SINGLE-WALL CARBON NANOTUBES

(http://www.ncnr.nist.gov/staff/taner/nanotube/exohydrogen.html)

Carbon Nanotubes (http://www.cnanotech.com/)

Types of Carbon Nanotubes (http://people.bath.ac.uk/tl258/Types.html)

What is a Carbon Nanotube? ( http://www.docstoc.com/docs/2250435/What-is-a-

Carbon-Nanotube)

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Chapter 8

Properties of Carbon Nanotubes

Some of the common properties of Carbon Nanotubes in comparison with other materials is

shown in the table below:

Material Young Modulus

(GPa)

Yield Strength

(MPa)

Density (g/cm3)

High Strength Steel 200 <2000 8.19

Carbon Fibers 425 1600 1.75

Aluminum Alloy 70 483 2.8

Copper (99.9% Cu) 130 220 8.92

Brass - 200+ 5.3

Carbon Nanotubes 1250 11000-63000 0.037-1.34

Properties SWNT Comparison

Density 0.037-1.34 g/cm3

Al 2.7g/cm3

Tensile strength Upto 63 GPa Steel <2GPa

Current density ≈109 A/cm

2 Cu <10

6 A/cm

2

Heat transmission ≈ 4000 W/mK Diamond ≈ 4000 W/mK

Temperature stability Upto 2800 oC in vaccum Metal in μchips <1000

oC

Mechanical Properties of Carbon Nanotubes:-

Carbon nanotubes are the strongest and stiffest materials yet discovered in terms of tensile

strength and elastic modulus respectively. This strength results from the covalent sp2 bonds

formed between the individual carbon atoms. In 2000, a multi-walled carbon nanotube was

tested to have a tensile strength of 63 GPa.

Under excessive tensile strain, the tubes will undergo plastic deformation, which means the

deformation is permanent.

CNTs are not nearly as strong under compression. Because of their hollow structure and high

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aspect ratio, they tend to undergo buckling when placed under compressive, torsional, or bending

stress.

References:-

“Carbon Nanotubes” by Valetin N.Popov & Philippe Lambin- NATO Science Series

Physical Properties of Carbon Nanotubes (http://www.pa.msu.edu/cmp/csc/ntproperties/)

http://www.makeitfrom.com/material-data/

Tensile strength of single-walled carbon nanotubes directly measured from their

macroscopic ropes

(http://apl.aip.org/resource/1/applab/v77/i20/p3161_s1?isAuthorized=no)

Measurements of near-ultimate strength for multiwalled carbon nanotubes and

irradiation-induced crosslinking improvements

(http://www.nature.com/nnano/journal/v3/n10/full/nnano.2008.211.html)

Chapter 9

Application of Carbon Nanotubes

Carbon Nanotubes is the “Technology of the Future”. It had wide domain of uses and

applications. Some of them are:

Carbon Nanotube & Energy:-

Carbon Nanotube technology also holds promise for a wide range of energy-related applications.

Batteries:-

Electrodes made of carbon nanotubes can be ten times thinner and lighter than

amorphous carbon electrodes and their conductivity is more than one thousand times

greater. In some cases, such as electric vehicles, the reduction in weight can make a

significant reduction in battery power requirements. Carbon nanotubes have been used in

supercapacitors producing a power density of 30kw/kg (compared to 4kw/kg for

commercially available devices). Such supercapacitors could drastically reduce the time

it takes to recharge devices such as laptops and cell phones.

Solar Cells:-

Researchers at Georgia Tech Research Institute have created solar cells consisting of

100- micrometer-high towers built of CNTs grown on iron-coated silicon wafers. There

are 40,000 of these towers in each square centimeter of the surface; Each tower is an

array of millions of vertically aligned CNTs. These cells absorb more light as it reflects

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off the sides of the towers. Unlike typical solar cells that have peak efficiency when the

sun is at 90º, these cells have two peaks at 45° and operate with relatively high efficiency

during most of the day. This makes them particularly appropriate for applications in

space because it eliminates the requirement of having a mechanical means of orienting

the cells to face the sun.

Carbon Nanotube & Health Care:-

A potential building material for medical Nanodevices is the graphene sheet, which can form

carbon Nanotubes. Carbon fullerenes and Nanotubes can be used for sensors or manipulators of

medical Nanorobots. They can also be used to create electrically conductive polymers and tissue

engineering constructs with the capacity to provide controlled electrical stimulation. We have

also developed Electromechanical Nanothermometer.

Carbon Nanotube & the Environment:-

The environmental risks of Nanotubes are still unclear. Naturally occurring carbon is benign, and

is largely unregulated, but Nanotubes interact with the environment differently. There have been

several studies performed to test the effects of carbon Nanotubes on living systems.

Fruit fly larvae fed a diet containing Nanotubes appeared to develop normally.

One study showed that CNTs delay embryo development in zebrafish, but the fish

otherwise appeared normal.

Mice lungs became inflamed when exposed to Nanotubes. However, the inflammation

subsided within a few months; this has stark parallels to the affect of asbestos on human

lungs.

Some human tumor cells seem to proliferate more rapidly in the presence of Nanotubes.

Structural Changes across the World:-

Because of the carbon Nanotube's superior Mechanical properties, many structures have been

proposed ranging from everyday items like clothes and sports gear to combat jackets and

space elevators. However, the space elevator will require further efforts in refining carbon

Nanotube technology, as the practical tensile strength of carbon Nanotubes can still be

greatly improved.

Carbon Nanotube & Electronics:-

Nanotube-based transistors, also known as carbon nanotube field-effect transistors

(CNTFETs), have been made that operate at room temperature and that are capable of digital

switching using a single electron. The first nanotube integrated memory circuit was made in

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2004.Large structures of carbon nanotubes can be used for thermal management of electronic

circuits.

References:-

“Development and Application of Carbon Nanotubes” by Morinobu Endo, Takuya

Hayashi, Yoong Ahm Kim, and Hiroyuki Muramatsu - Shinshu University and

Institute for Carbon Science and Technology.

“Carbon Nanotubes” By Chris Scoville, Robin Cole, Jason Hogg, Omar Farooque,

and Archie Russell.

The Latest Technology Research News (TRN)- Nanotubes Pack Power

(http://www.trnmag.com/Stories/2002/022702/Nanotubes_pack_power_022702.html)

Reviewing the Environmental and Human Health Knowledge Base of Carbon

Nanotubes(http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1940104/)

Biocompatibility and applications of Carbon Nanotubes in medical

Nanorobots(http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2676659/)

New study on Carbon Nanotubes gives hope for medical applications

(http://ki.se/ki/jsp/polopoly.jsp?l=en&d=130&a=98408)

Chapter 10

Pakistan & Carbon Nanotubes

University of Engineering & Technology, Lahore:-

UET is a leading University of Pakistan. They have a Research Center relating Nanotechnolgy.

Under this Center they had published 3 papers. The authors of those papers are Dr. Shamalia

Shahzadi, Dr. Rehana Sharif & Dr. Khaleeq.

International Islamic University, Islamabad:-

International Islamic University Islamabad (IIUI) is offering BS, MS, PHD Programs in

Nanotechnology.

Preston University, Islamabad:-

Preston University, Islamabad Campus is offering BS & MS programs in Nanotechnology.

Furthermore, Ghulam Ishaq Khan Insitute of Engineering and Technology (GIKI),

University of Punjab, Government Collage University, National University of Science and

Technology (NUST) are offering Programs in Nanotechnology.

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References:-

Department of PHYSICS (Nanotechnology), International Islamic University,

Islamabad (http://www.iiu.edu.pk/index.php?page_id=2173)

University of Engineering & Technology, Nanotechnology Research Center

(http://www.uet.edu.pk/nanotechnology/)

Dr. Khaleeq Publication Link

(http://www.uet.edu.pk/faculties/facultiesinfo/physics/Physics_faculty.html?RID=DrKhal

eeq1)

Dr. Rehana Sharif Publication Link

(http://www.uet.edu.pk/faculties/facultiesinfo/physics/Physics_faculty.html?RID=Dr._Re

hana_Sharif)

Preston University, Islamabad (http://www.preston.edu.pk/pinsat_intro.php)

Dr. Shamalia Shahzadi Publication

(http://www.uet.edu.pk/faculties/facultiesinfo/physics/Physics_faculty.html?RID=DrSha

mailaShahzadi)

Chapter 11

Conclusions

Future Prospectus:-

Number of Engineers and Scientist are working on Carbon Nanotubes. They believe that

Nanotubes is a gift of 21st Century. On monthly basis research papers are publishing on Carbon

Nanotubes. And they believe that Carbon Nanotubes will take place of number of materials that

are currently in progress.

Harmful Aspects of Carbon Nanotubes:-

Carbon nanotubes have unexpected negative impact on environment. Although, Carbon

nanotubes are stronger than steel, harder than diamond, light as plastic and conduct electricity

better than copper. Earlier findings have shown that carbon nanotubes are harmful for cells in the

human body, more or less having the same effect on them as a spear has on game. Finding that

the toxic effects on green algae are minimal was therefore a pleasant surprise.

References:-

Harmful Aspects of Carbon Nanotubes (http://www.bitsofscience.org/carbon-

nanotube-environment-toxicity-4038/)

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Effects of water-soluble functionalized multi-walled carbon nanotubes examined by

different cytotoxicity methods in human astrocyte D384 and lung A549 cells.

(http://www.ncbi.nlm.nih.gov/pubmed/20079395)

Carbon Nanotubes Dangerous to the Environment

(http://thefutureofthings.com/news/7409/carbon-nanotubes-dangerous-to-the-

environment.html)

Researchers Studying Effects of Carbon Nanotubes on Waterways and Algae Health

| Inhabitat - Sustainable Design Innovation, Eco Architecture, Green Building

(http://inhabitat.com/researchers-find-carbon-nanotubes-have-harmful-effects-on-

waterways-and-algae-health/)