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Carbon Nanotubes by Rasikh Tariq

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  • 1. 1
  • 2. CARBON NANOTUBES by Rasikh Tariq ME-113006 Student of: Mechanical EngineeringMohammad 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> 2
  • 3. Copyright  2012 by MAJU StudentAll rights reserved. Reproduction in whole or in part in any form requires the prior written permission of<Rasikh Tariq > or designated representative. 3
  • 4. The Project is about Carbon Nanotubes- A gift of 21st century. The project wasselected only due to wide Umbrella of application of Carbon Nanotubes. Asaccording to National Science & Technology Council (USA), “Nanotechnology isan enabling technology that will change the nature of almost every human-madeobject in the next century” 4
  • 5. DECLARATION It is declared that this is an original piece of my own work, except where otherwiseacknowledged in text and references. This work has not been submitted in any form foranother degree or diploma at any university or other institution for tertiary educati on andshall not be submitted by me in future for obtaining any degree from this or any otherUniversity or Institution.Rasikh TariqME-113006December 2012 5
  • 6. ABSTRACT As the size and complexity of today’s modern World increases, new techniques must bedeveloped 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 ofCarbon Nanotubes back in Cold War, it had deviated the mind of Scientists and Engineerstowards itselves. That is the reason to select this particular project. Carbon Nanotubes havebrought a new revolution in our Small homeland. Maybe, in the future it will be the substitute ofcertain materials. 6
  • 7. Table of ContentsChapter 1: Project Charter Purpose .......................................................................................9Chapter 2: Project Executive Summary..................................................................................9Chapter 3: Project Scope ..........................................................................................................9Chapter 4: An Introduction to Nanotechnology ...................................................................10 Nanotechnology- Definition & Examples ..................................................................................10 History and Background of Nanotechnology .............................................................................10 References ..................................................................................................................................11Chapter 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 ..................................................................................................................................13Chapter 6: Synthesis of Carbon Nanotubes ..........................................................................14 Top Down Method .....................................................................................................................14 Bottom Up Method.....................................................................................................................14 Arc Discharge Method ...............................................................................................................14 References ..................................................................................................................................15Chapter 7: Types & Structure of Carbon Nanotubes ..........................................................16 Single-wall Carbon Nanotubes...................................................................................................16 Calculating Diameter of Carbon Nanotube ................................................................................17 Multi-wall Carbon Nanotubes ....................................................................................................17 References ..................................................................................................................................17Chapter 8: Properties of Carbon Nanotubes ........................................................................18 Mechanical Properties of CNT’s ................................................................................................18 References ..................................................................................................................................19 7
  • 8. 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 ..................................................................................................................................21Chapter 10: Pakistan & Carbon Nanotubes ...........................................................................21 Research and Publications ..........................................................................................................21 References ..................................................................................................................................22Chapter 11: Conclusion ............................................................................................................22 Future Prospectus .......................................................................................................................22 Harmful Aspects of Nanotubes ..................................................................................................22 References ..................................................................................................................................22“Nanotechnology is an enabling technology that will change the nature of almostevery human-made object in the next century.” National Science and Technology Council (USA) 8
  • 9. Chapter 1: Project Charter PurposeThe 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 nanotechnologyChapter 2: Project Executive SummaryThe project will lead us from the introduction of Nanotechonology to the advanced basis ofCarbon Nanotubes. Stating from Nanotechonology, historical perspective of Nanotechonlogythen we had introduced Carbon Nanotubes. It’s unique structure and remarkable properties wasalso a point of focous in this Project. Then comes, wide umbrella of applications of CarbonNanotubes and then at the last we had try to relate Carbon Nanotubes with Pakistan.Chapter 3: Project ScopeThe project was selected based on importance of Carbon Nanotubes. This will be shocking thatin the current days of this World Carbon Nanotubes is one of the material that is underobservations and experiments of much of the Scientist and Engineers. The project in thisscenario -when most of the Scientist and Engineers are researching on Carbon Nanotubes – playsa vital role. Carbon Nanotubes is entirely new discovery for the World, perhaps a gift of 21stCentury. 9
  • 10. Chapter 4 An Introduction to NanotechnologyIntroduction:-Nanotechnology, or, as it is sometimes called, molecular manufacturing , is a branch ofengineering that deals with the design and manufacture of extremely small electronic circuits andmechanical 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 therange 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 This DNA tetrahedron is an  New generation of lasers artificially designed  Carbon Nanotube products nanostructure of the type made  Nanoparticle reinforced materials in the field of DNA  High hardness cutting tools nanotechnology. Each edge of the tetrahedron is a 20 base pairHistory & Background of Nanotechnology:- DNA double helix, and eachAlthough Nanotechnology is a relatively recent development in scientific research,three-arm junction. vertex is a thedevelopment of its central concepts happened over a longer period.Around the same time, K. Eric Drexler developed and popularized the concept ofnanotechnology and founded the field of molecular nanotechnology. In 1979, Drexlerencountered Richard Feynmans 1959 talk Theres Plenty of Room at the Bottom. The term"Nanotechnology", originally coined by Norio Taniguchi in 1974, was unknowinglyappropriated by Drexler in his 1986 book Engines of Creation: The Coming Era ofNanotechnology, which proposed the idea of a nanoscale "assembler" which would be able tobuild a copy of itself and of other items of arbitrary complexityThe 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 10
  • 11. platform for using silver Nanoparticles as an antibacterial agent, Nanoparticle-based transparentsunscreens, 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 ortoroidal shape.What CNT’s are ?Carbon Nanotubes (CNTs) are allotropes of carbon with a cylindricalnanostructure. Nanotubes have been constructed with length-to-diameterratio of up to 132,000,000:1, significantly larger than for any othermaterial. These cylindrical carbon molecules have unusual properties,which are valuable for nanotechnology, electronics, optics and otherfields of materials science and technology. In particular, owing to theirextraordinary thermal conductivity and mechanical and electricalproperties, Carbon Nanotubes find applications as additives to various structural materials. Forinstance, Nanotubes form a tiny portion of the material(s) in some (primarily carbon fiber)baseball bats, golf clubs, or car parts. 11
  • 12. Allotropic forms of CARBON Crystalline Amorphous Diamond Coal Graphite Charcoal Fullerene Lampblack 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 All 8 allotropes of Carbon themselves into "ropes" held together by van der Waals forces, more specifically, pi- stacking.Applied quantum chemistry, specifically, orbital hybridization best describes chemical bondingin Nanotubes. The chemical bonding of Nanotubes is composed entirely of sp2 bonds, similar tothose of graphite. These bonds, which are stronger than the sp3 bonds found in alkanes anddiamond, provide nanotubes with their unique strength. 12
  • 13. Historical Perspective:-The history of Carbon Nanotubes is often misconstrued. A number of people consider 1991 asthe year when these tubes were discovered. Sumio Iijima is attributed with the discovery of thesetubes. 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 wereprinted in Soviet Journal of Physical Chemistry. Mr V. M. Lukyanovich and V. Radushkevichare 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 nothave access to much of Soviet Press during the period of Cold war. Had there been some sort ofways to exchange between the two super powers, scientist might have agreed unanimously uponthe existence of these tubes much earlier.Iijima also discovered the molecules in 1991 when he was studying the synthesis of fullerenes byusing electric arc discharge technique. A paper was also published in 1976. It also showed theexistence of these tubes. Koyama, Oberlin, and Endo did the paper. There is a TEM image of thistube in this publication. This tube consisted of single wall of graphene. Mr Endo later called thisas 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 13
  • 14. Chapter 6 Synthesis of Carbon NanotubesWe 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 temperaturein the resulting plasma is sufficient to vaporize the graphite. In fullerene synthesis the requiredplasma 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. 14
  • 15. 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 forelectrodes if the portions of higher fullerenes are increased. Finally, electrodes made of coal canbe 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 theoutput of fullerene decreaseson larger dimensions. Thiseffect is caused by thefullerene’s sensitivity towardradiation: while travelingtoward cooler parts of theapparatus, the fullerenemolecules are exposed to veryintensive UV - rays emitted bythe arc plasma. They get excited, and the resulting triplet state with a lifetime in the range of μ sgives rise to an increased reactivity toward other carbon clusters C n. The latter can be explainedwith the open - shell structure of the excited fullerene.As larger electrodes generate larger plasma zones, they also emit more radiation. Hence more ofthe initially formed fullerenes react with other carbon clusters present in the apparatus, and theyields of cage - like structures decrease rapidly.References:-  Kroto, H. W., Heath, J. R., OBrien, 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) 15
  • 16. Chapter 7 Types & Structure of Carbon NanotubesCarbon Nanotubes have two divisions-divided based on different structures. Carbon Nanotubes Single -wall Carbon Multi-wall Carbon Nanotubes NanotubesSingle-wall Carbon Nanotubes (SWNT):-SWNTs have a diameter of close to 1 nm with a tube length that can be many thousands of timeslonger. The structure of a SWNT can be conceptualized by wrapping a one-atom-thick layer ofgraphite called graphene into a seamless cylinder. The way the graphene sheet is wrapped isrepresented by a pair of indices (n, m) called thechiral vector. The integer’s n and m denote thenumber of unit vectors along two directions inthe 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". 16
  • 17. Calculating Diameter of Carbon Nanotube:-The diameter of Carbon Nanotube cannot be measured directly. To measure diameter of CarbonNanotubes 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 changesignificantly with the (n,m) values, and this dependence is non-monotonic . In particular, theirband gap can vary from zero to about 2 eV and their electrical conductivity can show metallic orsemiconducting behavior. The most basic building block of these systems is the electric wire,and SWNTs with diameters of an orderof a nanometer can be excellentconductors.There are two models, which can beused to describe the structures of multi-walled nanotubes. In the Russian Dollmodel, sheets of graphite are arrangedin concentric cylinders, e.g. a (0, 8)single-walled nanotube (SWNT) within a larger (0, 17) single-walled nanotube. In the Parchmentmodel, a single sheet of graphite is rolled in around itself, resembling a scroll of parchment or arolled 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) 17
  • 18. Chapter 8 Properties of Carbon NanotubesSome of the common properties of Carbon Nanotubes in comparison with other materials isshown in the table below:Material Young Modulus Yield Strength Density (g/cm3) (GPa) (MPa)High Strength Steel 200 <2000 8.19Carbon Fibers 425 1600 1.75Aluminum Alloy 70 483 2.8Copper (99.9% Cu) 130 220 8.92Brass - 200+ 5.3Carbon Nanotubes 1250 11000-63000 0.037-1.34Properties SWNT ComparisonDensity 0.037-1.34 g/cm3 Al 2.7g/cm3Tensile strength Upto 63 GPa Steel <2GPaCurrent density ≈109 A/cm2 Cu <106 A/cm2Heat transmission ≈ 4000 W/mK Diamond ≈ 4000 W/mKTemperature stability Upto 2800 oC in vaccum Metal in μchips <1000 oCMechanical Properties of Carbon Nanotubes:-Carbon nanotubes are the strongest and stiffest materials yet discovered in terms of tensilestrength and elastic modulus respectively. This strength results from the covalent sp2 bondsformed between the individual carbon atoms. In 2000, a multi-walled carbon nanotube wastested to have a tensile strength of 63 GPa.Under excessive tensile strain, the tubes will undergo plastic deformation, which means thedeformation is permanent.CNTs are not nearly as strong under compression. Because of their hollow structure and high 18
  • 19. aspect ratio, they tend to undergo buckling when placed under compressive, torsional, or bendingstress.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 NanotubesCarbon Nanotubes is the “Technology of the Future”. It had wide domain of uses andapplications. 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 19
  • 20. 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 formcarbon Nanotubes. Carbon fullerenes and Nanotubes can be used for sensors or manipulators ofmedical Nanorobots. They can also be used to create electrically conductive polymers and tissueengineering constructs with the capacity to provide controlled electrical stimulation. We havealso developed Electromechanical Nanothermometer.Carbon Nanotube & the Environment:-The environmental risks of Nanotubes are still unclear. Naturally occurring carbon is benign, andis largely unregulated, but Nanotubes interact with the environment differently. There have beenseveral 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 Nanotubes 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 20
  • 21. 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 NanotubesUniversity 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. ShamaliaShahzadi, Dr. Rehana Sharif & Dr. Khaleeq.International Islamic University, Islamabad:-International Islamic University Islamabad (IIUI) is offering BS, MS, PHD Programs inNanotechnology.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 andTechnology (NUST) are offering Programs in Nanotechnology. 21
  • 22. 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 ConclusionsFuture Prospectus:-Number of Engineers and Scientist are working on Carbon Nanotubes. They believe thatNanotubes is a gift of 21st Century. On monthly basis research papers are publishing on CarbonNanotubes. And they believe that Carbon Nanotubes will take place of number of materials thatare currently in progress.Harmful Aspects of Carbon Nanotubes:-Carbon nanotubes have unexpected negative impact on environment. Although, Carbonnanotubes are stronger than steel, harder than diamond, light as plastic and conduct electricitybetter than copper. Earlier findings have shown that carbon nanotubes are harmful for cells in thehuman body, more or less having the same effect on them as a spear has on game. Finding thatthe 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/) 22
  • 23.  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/) 23

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