Carbon nanotubes (CNTs)From preparation to applications

Ali Ahmadpour

Department of Chemical Engineering& Nanotechnology center

Ferdowsi University of Mashhad

2

Contents

•Introduction

•CNT Properties

•Preparation methods

•Applications

•Conclusions

3

World of Carbon Materials

Amorphous

Graphite

Diamond

Fullerene

Carbon nanotube

4

Fullerenes – 1985

Robert F. Curl Jr.

Richard E. Smalley

Sir Harold W. Kroto

In 1991 during the preparation of Fullerenes by Arc vaporization method, Iijima changed the current from AC to DC and CNTs was found.

5

Nanotubes

• Nanotubes are flat sheets of interlinked carbon

atoms which are rolled into cylinders with a few

nanometer diameter.

• Because tubes are hollow, gases can pass through

as well as between them. So a mass of carbon

nanotubes is rather like porous graphite.

6

CNT Structures

• Single wall (SWNT)

• Double-wall (DWNT)

• Multi-wall (MWNT)

7

Cont.• Carbon nanotubes are considered to be the

building blocks of future nanoscale

electronic and mechanical devices.

• SWNT is seamless, with either open or

capped ends. The diameter of is 0.7-2 nm

(100,000 times thinner than a human hair).

Length ~ microns

Diameter ~ 1- 30 nm

Interlayer distance ~ 0.34nm

8

Structures of SWNTs

Different Indexed CNTs

Ch = na1+ ma2

dt = |Ch| / π

a) Armchair

b) Zigzag

c) Chiral

n: Column

m: Row

10

Cont.

• All the parameters governing the structure of a SWNT can be uniquely determined by knowing the n and m values.

• The nanotubes of type (n,n), are commonly called armchair

nanotubes because of the \_/¯\_/ shape, perpendicular to the

tube axis, and have a symmetry along the axis with a short unit

cell (0.25 nm) that can be repeated to make the entire section

of a long nanotube.

• Another type of nanotube (n,0) is known as zigzag nanotube,

because of the \/ \/ shape perpendicular to the axis and as well

as the short unit cell (0.43 nm) along the axis.

• All the remaining nanotubes are known as chiral or helical

nanotubes and have longer unit cell sizes along the tube axis.

11

Three distinct types of

nanotube structures

Schematic models for SWNTs with the nanotube axis normal to the

chiral vector which, in turn, is along:

(a) the θ = 30°direction [an “armchair” (n, n) nanotube],

(b) the θ = 0° direction [a “zigzag” (n, 0) nanotube], and

(c) a general θ direction, with 0 < θ < 30° [a “chiral” (n,m) nanotube].

12

CNTs

قرار هايي را كه در يك رديفاتم. يك اليه گرافيت را در نظر بگيريد•دهندة مختصات يك نقطه در صفحه ـ كه نشان ( n,m )اند باگرفته

مربوط به ستون nبه طوري كه مختصات. كنيميابي مياست ـ مكان.ها باشدمربوط به رديف اتم mها و مختصاتاتم

. ده باشدك نانولوله مانند صفحة گرافيتي است كه به شكل لوله درآمي•تصل شده بسته به اينكه چگونه دو سر صفحه گرافيتي به يكديگر م

.باشند، انواع مختلفي از نانولوله ها را خواهيم داشت

13

Structural parameters for CNTs

14

Structure of different types of carbon nanotubes

(a) (2, 2), (b) (10, 10), (c) (5, 0), and (d) (5, 2).

15

Chirality

• CNTs could be either semiconducting or metallic

depending on their geometrical characteristics, namely

their diameter and the orientation of their hexagons with

respect to the nanotube axis (chiral angle).

• CNT exhibits extraordinary mechanical properties:

Young’s modulus over 1 Tera Pascal, as stiff as diamond,

and tensile strength ~ 200 GPa.

16

Properties

• Electrical Electrical conductivity (metallic)

Semi-conductivity

• Mechanical The strongest and most flexible molecular material

because of C-C covalent bonding and seamless hexagonal

network.

High tensile strength (Young modulus)

Strength to weight ratio 500 times > Al; similar

improvements over steel and titanium; 10 times more

than graphite/ epoxy.

Maximum strain 10- 30% higher than any material.

Low weight

High flexibility

17

Cont.

• Thermal

High thermal conductivity ~ 3000 W/m.K in the axial

direction with small values in the radial direction.

• Chemical reactivity

Chemical reactivity of a CNT is comparable with a

graphene sheet, enhanced as a direct result of the

curvature of the CNT surface.

Small nanotube diameter results in increased

reactivity.

• Optical activity

Optical activity of chiral nanotubes disappears if the

nanotubes become larger.

18

Cont..

• Storage

Gas storage (hydrogen, methane,…)

Gas separation

Waste water treatment, air pollution control

Energy storage

19

Cont...Flexibility

20

Preparation Processes

• Electric Arc-Dischargeo High current are passed through 2 opposing graphite electrodes

in an inert atmosphere (He). Carbon atoms evaporate from the anode (3000°C) and grow on the cathode.

o Product: Mainly MWNTs [SWNTs by using electrode impregnated with metals (Co, Ni, Fe,…)]

• Laser Ablation (Vaporization)o An intense laser pulse ablate a carbon target containing

metals. Target is heated in a furnace (1200°C) and inert atmosphere.

o Product: Mainly ropes of SWNTs

• Chemical Vapor Deposition (CVD)o Thermal decomposition (500-1000°C) of hydrocarbons (CH4) in the

presence of a catalyst containing transition metals (Fe, Mo,…).

o Product: SWNTs and MWNTs

o Large-scale production of nanotubes

21

Cont.

• High-pressure CO conversion (HiPCO)

• Plasma CVD

• Microwave CVD

• Electrochemical

22

Iijima

(DC

(CNTS(amorphous

23

CNT FabricationCarbon Arc or Arc Discharge

24

K1473

.

Inert tube Quartz tube Target

Argon flow Laser beam Witness plates

25

CNT FabricationLaser Ablation or Pulsed Laser Vaporization (PLV)

26

TEMSWNTarc-discharge ( a PLV ( b

27

Gas inlet

Quartz tube

Gas

outlet

Quartz

boatOven 720℃

Sample

28

CNT FabricationChemical Vapor Deposition (CVD)

29

CO

•COFe(CO)5

SWNT

1-10200-

800

•Fe(CO)5

Furnace

Cold CO

+ Fe (CO)5

Cooling water

Hot co

30

CNT FabricationHigh-pressure CO conversion (HiPCO)

• Method is similar to CVD

• Carbon source is carbon monoxide

• Catalytic particles are generated in-situ

• Thermal decomposition of iron pentacarbonyl in a

reactor heated to 800 - 1200°C

• High pressure to speed up the growth (~10 atm)

• Bulk production of SWNTs

31

Growth mechanism

32

33

SWNT bundle

34

Cont.

35

Applications

• Diodes and transistors for computing

• CNT quantum wire interconnects

• Capacitors

• Data Storage

• Field emitters for instrumentation

• Flat panel displays

• Oscillators

• CNT based microscopy: AFM, STM …

• Nanotube sensors: force, pressure, chemical …

• Biosensors

36

• Molecular gears, motors, actuators

• Batteries, Fuel Cells: H2, Li storage

• Nanoscale reactors, ion channels

• Biomedical

• Lab on a chip

• Drug delivery

• DNA sequencing

• Artificial muscles, bone replacement, bionic

eye, ear ...

• coatings for prosthetics and surgical

implants

Cont.

37

• Gene therapy

• Nano-pipet

• Nano-capsule

• Nano-tweezer

• Use in composite materials

• Oil absorbent

• Catalyst support

• CNT ceramics

• CNT based plastic packaging

Cont..

CrIr

TaTi

W

Co Fe Ni Fe/Ni Ni/Co

Si wafer

Catalyst Layers

38

Light elements

39

Nanocomposites

40

CNT based Sensor

+ + + + + + + +

+ +

s Sio2

Nanotube

Pt contactPt contact

Gas molecules

MWNT based chemical sensor

41

Gas Sensors

• Gas detection instruments are increasingly neededfor industrial health and safety, environmentalmonitoring (detection of NO2 and CO) and processcontrol.

• The worldwide revenue of the gas sensors willexceed $2.5B by 2010.

42

Biosensors

CNT, though inert, can be functionalized at the tip with a probe molecule to be used as a sensor for food industry, medical and research purposes.

Schematic diagram of the CNT array biosensor

43

Hydrogen storage

44

Hydrogen storage with electrochemical

charge-discharge cycles

xOH)xHCNT(xeOHCNTeargch2

45

Fuel cells

46

SWCNTs in H2 fuel cells

47

AFM with CNT tip

48

CNT Applications

in Food industries

• Functionalized CNT: When CNT is attached by organic

functional groups, it can be dissolved into solution. This

will increase processability of CNT for device fabrication.

• Polymer-CNT Gas Sensor: vapor/gas sensor based on

carbon nanotube and polymer nanocomposites.

• Biosensors: Novel applications which makes possible

the reversibility of some redox-enzymes reactions, which

are irreversible at common electrodes.

49

Cont.

• Biological application: For protein crystallization and

bioreactors.

• Membrane synthesis using CNTs: For detection and

separation of enzymes, antibodies, proteins, vitamins,

minerals, and DNA.

• Conductive membrane: More separation of aromas and

nutritious from food substances.

50

CNTs Find New Applications as Heat

Sensors for Hot Chilli Peppers

• HPLC, which is currently used, requires bulky,

expensive equipment and detailed analysis of the

capsaicinoids.

• In the new method, the capsaicinoids are adsorbed

onto MWCNT electrodes. The current change is measured

as the capsaicinoids are oxidised by an

electrochemical reaction, and this reading can be

translated into Scoville units.

• The technique is called adsorptive stripping

voltammetry (ASV), and is a relatively simple

electrochemical method.

51

• CNTs are just the thing for cleaning up poisonous

pollutants. These tiny tubes mop up dioxins, the

hazardous and persistent by-products of a wide

range of industrial processes that contaminate

the air, soil, water and, thence, the food chain.

• CNTs attract much more dioxin than activated

carbon, currently used to clean up incinerator

gases.

Environmental

applications of CNTs

52

Purification of air

and water

• Another environmental catalysis includes

photocatalysis for air and water purification

and for heavy metal removal. The Base is CNT

and active material is nanostructured TiO2.

Environmentally toxic materials such as

volatile organic compounds and heavy metal

compounds become harmless by oxidation or

reduction processes.

53

Ethanol production

inside CNTs

• CNTs are increasingly

recognized as promising

materials for catalysis,

catalyst additives or

supports. Researchers in

China used CNTs loaded with

rhodium (Rh) nanoparticles

as reactors to convert a

gas mixture of CO and H2into ethanol (nanosized CNT

reaction vessel).

54

CNT Market

• Global CNT production capacity is ~ 2.5 tons per day.

• Bayer is planning to produce about 3,000 tons CNTs by

2012.

• The price of MWCNTs has fallen from tens of

thousands of dollars in just few years ago to

hundreds of dollars per kg.

• Recent market analyses forecast sales of all

nanotubes to reach 1-2 billion dollars annually

within the next four to seven years.

• In terms of dollar value, electronics devices will be

the largest end-use category, although composite

materials may account for greater volumes. These

volumes are expected to approach several thousand

metric tons per year.

55

Conclusions

CNTs have attracted much attention due to

their remarkable properties.

These materials will have a significant

contribution to the new science fields.

Complete experimental characterization of

CNTs is not an easy task, as there are

several parameters affecting the type and

structure of CNTs.

Theoretical methods of characterization is

necessary to have better control over the

CNT preparation step.

Future advancement of nanotube science and

technology requires much research works.