Lect 4 carbon age

Prof. Mohamed Khedr

Faculty of Postgraduates for advanced

Sciences, Beni-Suif University

Carbon Age

Carbon

• Melting point: ~ 3500oC

• Atomic radius: 0.077 nm

• Basis in all organic componds

• 10 mill. carbon componds

Nanocarbon

• Fullerene

• Tubes

• Cones

• Carbon black

• Horns

• Rods

• Foams

• Nanodiamonds

• Graphene

M. Khedr, A. Farghali, A. Moustafa and M. Zayed, International Journal of Nanoparticles, 2009, 2, 430-442.

M. Khedr, K. Abdel Halim and N. Soliman, Materials Letters, 2009, 63, 598-601.

Carbon black

Large industry

- mill. tons each year

• Tires, black pigments,

plastics, dry-cell batteries,

UV-protection etc.

• Size: 10 – 400 nm

”The most symmetrical large molecule”

• Discovered in 1985

- Nobel prize Chemistry 1996, Curl, Kroto, and Smalley

Epcot center, Paris

~1 nm

Architect: R. Buckminster

Fuller

• C60, also 70, 76 and 84. - 32 facets (12 pentagons and 20 hexagons)

- prototype

Fullerene

Graphene…….!!!

• “Imagine a piece of paper but a million times thinner. This is how thick graphene is.

• Imagine a material stronger than diamond. This is how strong graphene is.

• Graphene is the strongest, yet thinnest possible material

you can imagine.

• It's so strong that It would take something

the size of an elephant, balanced on a pencil,

to break through a sheet of graphene the

thickness of a piece of paper.

Diamond, graphite, lonsdalerite, C60, C70,

carbon, amorphous carbon, carbon nanotube

Allotropes of Carbon

What are carbon

nanotubes? • Tubes with walls made of carbon (graphite)

• Nanometers in diameter

• Up to tens of micrometers in height

• Extremely good strength and field emission

properties

Classification of CNs:

single layer

• Single-wall Carbon nanotubes

(SWNTs,1993)

– one graphite sheet seamlessly wrapped-up to

form a cylinder

– typical radius 1nm, length up to mm

(10,10) tube

(From R. Smalley´s web image gallery) (From Dresselhaus et al., Physics World 1998)

Classification of CNs:

ropes • Ropes: bundles of SWNTs

– triangular array of individual SWNTs

– ten to several hundreds tubes

– typically, in a rope tubes of different diameters

and chiralities

(From R. Smalley´s web image gallery) (From Delaney et al., Science 1998)

Classification of CNs:

many layers

• Multiwall nanotubes (Iijima 1991)

– russian doll structure, several inner shells

– typical radius of outermost shell > 10 nm

(From Iijima, Nature 1991) (Copyright: A. Rochefort, Nano-CERCA, Univ. Montreal)

Why Carbon nanotubes so

interesting ? • Technological applications

– conductive and high-strength composites

– energy storage and conversion devices

– sensors, field emission displays

– nanometer-sized molecular electronic devices

• Basic research: most phenomena of mesoscopic physics observed in CNs

– ballistic, diffusive and localized regimes in transport

– disorder-related effects in MWNTs

– strong interaction effects in SWNTs: Luttinger liquid

– Coulomb blockade and Kondo physics

– spin transport

– superconductivity

Important History • 1991 Discovery of multi-wall carbon nanotubes by S. Iijima

• 1992 Conductivity of carbon nanotubes J. W. Mintmire, B. I. Dunlap and C. T.

White

• 1993 Structural rigidity of carbon nanotubes G. Overney, W. Zhong, and D.

Tománek

• 1993 Synthesis of single-wall nanotubes by S Iijima and T Ichihashi

• 1995 Nanotubes as field emitters By A.G. Rinzler, J.H. Hafner, P. Nikolaev, L.

Lou, S.G. Kim, D. Tománek, P. Nordlander, D.T. Colbert, and R.E. Smalley

• 1997 Hydrogen storage in nanotubes A C Dillon, K M Jones, T A Bekkendahl, C

H Kiang, D S Bethune and M J Heben

• 1998 Synthesis of nanotube peapods B.W. Smith, M. Monthioux, and D.E. Luzzi

• 2000 Thermal conductivity of nanotubes Savas Berber, Young-Kyun Kwon, and

David Tománek

• 2001 Integration of carbon nanotubes for logic circuits P.C. Collins, M.S. Arnold,

and P. Avouris

• 2001 Intrinsic superconductivity of carbon nanotubes M. Kociak, A. Yu.

Kasumov, S. Guéron, B. Reulet, I. I. Khodos, Yu. B. Gorbatov, V. T.

Volkov, L. Vaccarini, and H. Bouchiat

Classification of nanotube models, (a) armchair, (b) zigzag

and (c) chiral SWNTs.

• Structure of carbon nanotubes

Nanotube’s characteristic •Seemless cylindrical molecules

•Diameter as small as 1 nm.

•Length: a few nm. to serveral micron

•As a monoelemental polymer: Carbon atoms

only

•As hexagonal network of carbon atoms

•CNTs are single molecules comprised of

rolled up graphene sheets capped at each

end.

Nanotube’s characteristic

• Young’s modulus of elasticity ~ 1 TPa

(Tera = 1012)

• Tensile strength > 60 GPa

(Steel ~ 2 GPa)

• Conductivity of CNTs ~ 109 A/cm2

(Copper 106 A/cm2 )

Charge Storage

Lithium Ion Batteries

Ultra Capacitors

Applications

M. Khedr, M. Bahgat, M. Radwan and H. Abdelmaksoud, Journal of materials processing technology, 2007, 190, 153-159.

M. Bahgat, M. Khedr, M. Nasr and E. Sedeek, Metallurgical and Materials Transactions B, 2007, 38, 5-11

Applications

Flat screen displays Plasma TV

M. Khedr, M. Bahgat, M. Nasr and E. Sedeek, Colloids and surfaces A: Physicochemical and engineering aspects, 2007,

302, 517-524.

M. Bahgat, M. Khedr, M. Nasr and E. Sedeek, Materials science and technology, 2006, 22, 315-320.

Transistor

• Vacuum tubes - Nobel prize 1906, Thomson.

IBM, 1952.

• Semiconductor, Si-

based

- Nobel prize 1956, Shockley,

Bardeen, and Brattain.

- 2000, Kilby.

Applications

M. Hessien and M. Khedr, Materials research bulletin, 2007, 42, 1242-1250.

K. S. Abdelahalim, A. M. Ismail, M. H. Khedr and M. F. Abadir, in First Afro-Asian Conference on Advanced Materials and

Technology, Nov. 13-16, Cairo - EGYPT, Editon edn., 2006.

Applications

Electric devices K. Abdel Halim, M. Khedr, M. Nasr and A. El-Mansy, Materials research bulletin, 2007, 42, 731-741.

M. Khedr, M. Sobhy and A. Tawfik, Materials research bulletin, 2007, 42, 213-220.

Applications

Hydrogen storage

2 H2(g) + O2(g) → 2 H2O (l) +

energy

H2 (200 bar) H2 (liquid) LaNi5H6

Mg2NiH

3.16 wt% 1.37 wt%

M. H. Khedr, A. A. Farghali and A. Abdel-Khalek, Journal of analytical and applied pyrolysis, 2007, 78, 1-6.

A. A. Farghali, M. H. Khedr and A. A. Abdel Khalek, Journal of materials processing technology, 2007, 181, 81-87.

Applications

Atomic Force Microscopy M. Khedr, A. Omar and S. Abdel-Moaty, Materials Science and Engineering: A, 2006, 432, 26-33.

M. Khedr, A. Omar and S. Abdel-Moaty, Colloids and surfaces A: Physicochemical and engineering aspects, 2006, 281, 8-14.

• Carbon Nano-tubes

are extending our

ability to fabricate

devices such as:

• Molecular probes

• Pipes

• Wires

• Bearings

• Springs

• Gears

• Pumps

Current Applications

Structural clothes: waterproof tear-resistant

compat jackets: that use carbon nanotubes as ultrastrong fibers and to monitor the

condition of the wearer.

concrete: They increase the tensile strength, and halt crack propagation.

polyethylene: Researchers have found that adding them to increases the polymer's

elastic modulus by 30%.

sports equipment: Stronger and lighter tennis rackets, bike parts, golf balls, golf clubs,

golf shaft and baseball bats.

space elevator: This will be possible only if tensile strengths of more than about 70 GPa

can be achieved.

Bridges: For instance in suspension bridges (where they will be able to replace steel), or

bridges built as a "horizontal space elevator".

buckypaper- a thin sheet made from nanotubes that are 250 times stronger than steel and

10 times lighter that could be used as a heat sink for chipboards, a backlight

chemical nanowires: Carbon nanotubes additionally can also be used to produce

nanowires of other chemicals, such as gold or zinc oxide. These nanowires in turn can be

used to cast nanotubes of other chemicals, such as gallium nitride.

computer circuits: A nanotube formed by joining nanotubes of two different diameters

end to end can act as a diode.

conductive films: A 2005 paper in Science notes that drawing transparent high strength

swathes of SWNT is a functional production technique are developing transparent,

electrically conductive films of carbon nanotubes to replace indium tin oxide(ITO) in

LCDs, touch screens, and photovoltaic devices.

electric motor brushes: Conductive carbon nanotubes have been used for several years

in brushes for commercial electric motors. They replace traditional carbon black, which is

mostly impure spherical carbon fullerenes.

light bulb filament: alternative to tungsten filaments in incandescent lamps.

magnets: MWNTs coated with magnetite

optical ignition: A layer of 29% iron enriched SWNT is placed on top of a layer of explosive

material such as PETN, and can be ignited with a regular camera flash.

solar cells: GE's carbon nanotube diode has a photovoltaic effect. Nanotubes can replace

ITO in some solar cells to act as a transparent conductive film in solar cells to allow light to

pass to the active layers and generate photocurrent.

superconductor: Nanotubes have been shown to be superconducting at low temperatures.

ultracapacitors: MIT is researching the use of nanotubes bound to the charge plates of

capacitors in order to dramatically increase the surface area and therefore energy storage

ability.

displays: One use for nanotubes that has already been developed is as extremely fine

electron guns, which could be used as miniature cathode ray tubes in thin high-brightness

low-energy low-weight displays.

transistor: developed at Delft, IBM, and NEC.

Chemical air pollution filter: Future applications of nanotube membranes include filtering carbon

dioxide from power plant emissions.

biotech container: Nanotubes can be opened and filled with materials such as

biological molecules, raising the possibility of applications in biotechnology.

hydrogen storage: Research is currently being undertaken into the potential use of

carbon nanotubes for hydrogen storage. They have the potential to store between 4.2

and 65% hydrogen by weight.

water filter: Recently nanotube membranes have been developed for use in filtration.

This technique can purportedly reduce desalination costs by 75%.

Mechanical oscillator: fastest known oscillators (> 50 GHz).

nanotube membrane: Liquid flows up to five orders of magnitude faster than predicted

by classical fluid dynamics.

slick surface: slicker than Teflon and waterproof.

Properties unusual current conduction mechanism: that make them ideal components of

electrical circuits. Currently, there is no reliable way to arrange carbon nanotubes into a

circuit.

The major hurdles that must be jumped for carbon nanotubes to find prominent places in

circuits relate to fabrication difficulties. The production of electrical circuits with carbon

nanotubes are very different from the traditional

IC fabrication process. The IC fabrication process is somewhat like sculpture - films

are deposited onto a wafer and pattern-etched away. Because carbon nanotubes are

fundamentally different from films, carbon nanotube circuits can so far not be mass

produced.

atomic force microscope in a painstaking, time-consuming process. Perhaps the best

hope is that carbon nanotubes can be grown through a chemical vapor deposition

process from patterned catalyst material on a wafer, which serve as growth sites and

allow designers to position one end of the nanotube. place the nanotubes from solution

to determinate place on a substrate.

Even if nanotubes could be precisely positioned, there remains the problem that, to this

date, engineers have been unable to control the types of nanotubes—metallic,

semiconducting, single-walled, multi-walled—produced. A chemical engineering solution

is needed if nanotubes are to become feasible for commercial circuits.

Production Methods

• Arc discharge

• Laser ablation

• Chemical Vapor Deposition

(CVD)

Arc–Discharge Process

• High-purity graphite rods

under a helium

atmosphere.

• T > 3000oC

• 20 to 40 V at a current in

the range of 50 to 100 A

• Gap between the rods

approximately 1 mm or

less

•Lots of impurities:

graphite, amorphous

carbon, fullerenes

Arc-discharge apparatus

Laser Ablation Process

• Temperature 1200oC

• Pressure 500 Torr

• Cu collector for carbon

clusters

• MWNT synthesized in

pure graphite

• SWNT synthesized

when Co, Ni, Fe, Y are

used

• Laminar flow

• Fewer side products

than Arc discharge

Laser ablation apparatus

CVD in Gas Phase Process

• Catalysts: Fe, Ni, Co, or alloys of the three metals

• Hydrocarbons: CH4, C2H2, etc.

• Temperature: First furnace 1050oC

Second furnace: 750oC

• Produce large amounts of MTWNs

Comparison of Nanotube

Production Technology

The CVD method has been reported to be the most selective in

CNTs formation

It can produce relatively large amounts of CNTs at lower cost

because it proceeds under mild conditions.

The CVD process makes it possible to control the purity of

product, the size and growth density of CNTs by regulating the

reaction parameters and catalyst composition as well as by

modifying .

The CNTs can also be readily isolated using chemical means

(HCl, HNO3, and HF), or ultra-sound treatment and heating.

it suitable for large area, irregular-shaped substrates and

multiple-substrate coatings,

It the most widely utilized duo to their versatility, and

industrial scalability

Controlling The yield %, and type of CNTs

• The yield %, and type of CNTs deposited depends on

support type ,percentage and type of metal loading, reaction

temperature, time, catalyst particles size, carrier gas flow

rate and finally the carbon source “ CO, CO2, CH4, C2H6,

C2H4 and C2H2”

• C2H2 exhibits very high carbon feed stock and very high

activity in producing metal carbide compared to CH4 and

CO

• Finally, acetylene is more reactive than other hydrocarbons

at the same reaction temperature, leading to CNTs of good

quality.

Selecting the materials of the present study;

• Ferrites have continued to attract attention over years.

• As magnetic materials, Ferrites cannot be replaced by any other

materials.

• Ferrites are relatively inexpensive, stable and have a wide range of

technological applications in the fabrication of high quality filters, high

frequency circuits and operating devices.

• Recently, ferrites are reported to be good catalysts for many chemical

processes. Among these processes, the decomposition of CO2 was

investigated as a process of both industrial and environmental

importance .

• Because CO2 is a a major component of the greenhouse gases, which

caused the global worming, Freshly reduced copper ferrite was selected

as a catalyst for the decomposition of CO2.

CO2 Catalytic decomposition Over freshly reduced CuFe2O4

• CO2 was allowed to decompose spontaneously

to carbon at 400-600oC during the reoxidation

of nano-crystallite metallic phase of Cu & Fe

compacts, produced from the reduction process.

• XRD analysis obtained for all samples

produced from the reduction-reoxidation

experiments at different temperatures indicates

that all samples contain the iron austenite and

magnetite phases, which reveals that CO2

decomposes during the reoxidation process to

carbon and oxygen forming the austenite and

magnetite.

• Deposited carbon was detected by C-analysis.

• Carbon in the form of Nano-tubes was detected

by SEM.

• For more evidence, carbon nano-tubes were

isolated by suspention in acetone, TEM was

used to prove the formation of Carbon Nano-

tubes.

200 nm

Production of

carbon nanotubes

using nanosized

metallic iron

• A catalyst of the composition 40%Fe2O3:60%Al2O3, was prepared by wet

impregnation method A certain amount of nanosized iron oxide powder was

mixed with Al2O3 powder and stirred for 1 hrs at 60 oC. The impregnate was

then dried in an oven at 100 oC for 3 hrs, calcined at 400 oC for 4 hrs in a box

muffle furnace.

• The catalysts was reduced at 500 oC at 1l/min in H2 flow and CNTs were

synthesized at the same reduction temperature by flowing 10%C2H2:90%H2

to know the most effective crystal size of iron oxide that give the highest

percentage yield of CNTs at 500 oC.

• The effect of growth temperature on the percentage yield was

also examined for iron oxide with crystal size 35 nm by

carrying out the acetylene decomposition reaction at

temperature 400, 500, 600 and 700 oC.

• The synthesized CNTs were cooled in H2 flow and the weight

of deposited CNTs was detected using weight gain technique.

• C, % = (W1 – W2) / W2 ]*100

• where W2 is the initial weight of the catalyst (Fe ) and W1 is

the weight of carbon deposited and catalyst.

• The structure and morphology of the synthesized CNTs were

characterized using XRD and HTEM

Samples of nanosized iron oxides (supported in alumina) were reduced at 500 oC and subjected to H2/C2H2 flow to get the most effective crystal size of the catalyst that give the highest percentage yield of CNTs. The highest percentage yield (228 %) was found for samples with average crystal size of 35 nm.

Effect of crystal size of iron oxide catalyst on the Carbon

yield%

0

50

100

150

200

250

0 5 10 15 20 25 30 35

35 nm

100 nm

150 nm

Carb

on

yie

ld (%

)

Time (min.)

• TEM analysis of the produced

CNTs over iron produced from

the complete reduction of iron

oxide with crystal size 35nm

.Graphitic structures with a

central channel (CNTs) of internal

diameter 53-93 nm and its length

is about 1-10 µm and CNTs were

formed with a helix and curved

shape structure.

• The presence of catalytic

nanoparticles at the tip of the

produced CNTs suggests that the

CNT production occurred via tip-

growth mechanism

(a)

(b

)

TEM images of CNTs produced from the decomposition of

acetylene over freshly reduced iron oxide with crystal size

35 nm at 500 oC.

1µm

200 nm

• TEM image of carbon produced

from the decomposition of

acetylene over the iron

produced from the complete

reduction of iron oxide with

crystal size 150 nm shows that

A nonhomogeneity of the

carbon products was observed

(amorphous carbonaceous

structures) were observed in the

sample. It was also observed

that iron particles were kept in

carbon capsules.

• Generally, when metallic iron

particles increase in size, the

formation of nonselective forms

of carbon is favored.

TEM images Carbon produced from the decomposition

of acetylene over freshly reduced iron oxide with crystal

size 150 nm at 500 oC

0.5µm

XRD patterns of the catalysts after

acetylene decomposition shows

that there are two major peaks,

one is near 2θ = 26o Minor

asymmetric peak near 43.5o

indicating the well graphitized

nature of the CNT. The other

peaks are due to catalytic

impurities, metallic iron phases

and support (Al2O3 ). These

results suggest that the growth

mechanism of carbon nanotube

was the tip growth mechanism. 0

20

40

60

80

100

20 30 40 50 60 70 80

Inte

nsi

ty (

a.u

)

2-Theta scale

XRD patterns of iron oxide catalyst with average

crystal size 35 nm after decomposition of

acetylene at (a) 500 oC (b) 600 oC

0

10

20

30

40

50

60

inte

nsi

ty (

a.u

) ( a)

( b)

A series of decomposition experiment were carried out at 400-700 oC using the iron produced from the reduction of iron oxide samples with lowest crystal size (35 nm). Two modes of decomposition rate can be observed. The first one at lower decomposition temperature, 400 and 500 oC, where the percentage yield 220 % and 228 % was recorded, respectively. Increasing the temperature to 600 and 700 oC increase in the decomposition rate and percentage yield of 426 and 407 % were observed at 600 and 700 oC, respectively.

The effect of temperature on the catalytic decomposition

of acetylene over freshly reduced iron oxide with average

crystal size 35 nm

0

100

200

300

400

500

0 5 10 15 20 25 30 35

400 C

500 C

600 C

700 C

Carb

on

yie

ld (

%)

Time (min.)

o

o

o

o

o

the relation ship between the acetylene decomposition

temperature and the carbon yield % over freshly reduced iron

oxide with average crystal size 35 nm

200

250

300

350

400

450

350 400 450 500 550 600 650 700 750

Carb

on

yie

ld (

%)

Decomposition temperature ( C) o

The activation energy value was found to be (12.5 kJ mol-1) indicates that the decomposition of acetylene on the catalyst surface is probably a physisorption process.

Fig. 11: Arrhenius plot of CNTs synthesis over freshly reduced nanosized Fe2O3

-2

-1

0

1

2

3

4

5

6

0.001 0.0011 0.0012 0.0013 0.0014 0.0015

ln d

r/d

t

1/T (k)

Ea =12.5 kJ/ mol

The presence of catalytic nano particles at the tip of the produced CNTs and its

appearance on the XRD- pattern suggests that the CNT production occurred via a tip-growth mechanism where the supported metals particles detach and move at the head of the growing nanotube

TEM images of CNTs produced from the decomposition of

acetylene over freshly reduced iron oxide with crystal size

35 nm at 500 oC.

catalytic nano particles

The rate is higher at the early stage then it

decrease with time and still active even

after 30 minutes of reaction which indicate

that the catalyst is very active toward the

decomposition of acetylene which is used as

a source of carbon

Kinetics of acetylene

decomposition over reduced

SHF

catalyst for the

production of carbon

nanotubes

• Catalyst of the composition 40SHF:60Al2O3 is prepared by wet

impregnation method as follows: aqueous solutions of SHF with

the required amount, was mixed with Al2O3 powder and stirred for

1 hrs at 60 oC to remove dissolved oxygen and to achieve a

homogeneous impregnation of catalyst in the support. The

impregnate was then dried in an oven at 100 oC for 3 hrs, calcined

at 400 oC for 4 hrs in a box muffle furnace.

• Approximately 50 mg of a catalyst sample was introduced in to

cylindrical alumina cell closed with one end, the cell with the

catalyst placed in the central region of a longitudinal furnace.

• The catalyst was reduced at different temperature 500, 550, 600,

and 650 oC at 1l/min in H2 flow and CNTs were synthesized via two

type of experiments by flowing 10C2H2:90H2

E N2

H2

C2H2

Reduction & decomposition system

• The synthesized CNTs were cooled in H2 flow and

the weight of deposited CNTs was detected using

weight gain technique.

• The activity of catalyst was measured by yield %

of carbon deposited which can be calculated from

the following relation,

C% = [W3 – (W1 – W2) / (W1 – W2)]*100.

• Where W1 is the initial weight of the catalyst, W2

is the weight loss of catalyst at operating

temperature, and W3 is the weight of carbon

deposited and catalyst.

• The structure and morphology of the synthesized

CNTs were characterized using high resolution

transmission electron microscopy (HRTEM)

• The kinetics of synthesis of CNTs were investigated through two types of experiments, the first was done at constant reaction time 30 min and rate gas flow of 10 C2H2: 90 H2, samples were reduced at 500-650 oC and subjected to C2H2 flow at each temperature. The optimum conditions for the higher yield % were found to be 600 oC which give 262.4 yield %

• The second type of experiments was done at variable decomposition temperature 500-800 oC and constant reduction temperature (600 oC). This was done at the same experimental conditions. The highest yield % was found at reduction and decomposition temperature 600 and 700 oC respectively.

Kinetics of acetylene decomposition over reduced

SHF catalyst for the production of CNTs

Reaction temperature dependence for the yield % at variable

reduction and decomposition temperature.

yield % at (a) 500 oC, (b) 550 oC, (c) 600 oC, (d) 650 oC.

b

500nm

a

200nm

ــــــــــ

TEM images of CNFs produced on SHF reduced at

600 oC by the decomposition of acetylene at 500 oC.

Not only CNTs but also CNFs

Crystal size and the phase content for completely reduced SHF

compacts as obtained from XRD analysis.

Reduction temperature oC ) )

phases content phases content

( % )

Crystal size

(nm)

500 Sr4Fe6O13,

Fe21.4O32,

FeO,

Fe (metal)

50

50

50

12.5

62.1

32.2

23.7

43.2

550 Fe (metal),

FeO,

Sr2Fe2O3

50

50

20.8

98.2

36.2

31.8

600 Fe (metal),

Fe21.4O32,

Fe2O3,

FeO,

Sr2Fe2O5,

SrO

50

6.25

10.4

6.25

6.1

4.17

104

20

77.6

• The activation energies for the first and second experiments were found to be 26.3 and 5.2 kJ/mol respectively,

Arrhenius plot of CNTs synthesis on reduced SHF supported

on alumina at different reduction temperature.

Arrhenius plot of CNTs synthesis on reduced SHF supported

on alumina at different decomposition temperature.

• Surface area measurements

• The catalyst has curie temperature around 500 oC, the catalyst

has different behaviors below and above these temperature.

Reduction temperature 500 oC 550 oC 600 oC 650 oC

Surface area

(m2g-1)

76.55 64.39 77.84 57.56

Total pore volume

( Ccg-1)

0.03788 0.0319

4

0.0368 0.02699

Average pore diameter

(nm)

19.79 19.84 18.91 18.76

Micro pore volume

(Ccg-1)

0.08814 0.0748

9

0.08045 0.0668

Adsorption energy

( kJmol-1)

2.429 2.208 2.357 2.217

The surface area measurements for the SHF supported on

alumina with the molar ratio 40 (SrFe12O19): 60Al2O3.

TEM images of CNTs produced on SHF

reduced at 600 oC by the decomposition of

acetylene at 600 oC

50nm

200 nm

_____

Catalyst Wt % Time

(min)

T ( oC)

Carbon

source

Carrier

gas

Rate flow Yield % Observation

Fe-Ni/

MgO

2:98 30 1000 C2H2 N2 10:90cm3\min 112 Good crystallinity

Fe-Ni/

MgO

2:98 60 800 C2H2 N2 10:90cm3\min 104 Excellent quallity

Fe-Ni/

MgO

20:80 30 800 C2H2 N2 10:90cm3\min 240 High quality and

density

Fe-Ni/

MgO

30:70 30 800 C2H2 N2 10:90cm3\min 260 High quality and

density

Co-Mo/

MgO

5:95 30 800 C2H2 H2 10:100sccm 6 SWNTs

Co-Mo/

MgO

10:90 30 800 C2H2 H2 10:100sccm 27

Co-Mo/

MgO

40:60 30 800 C2H2 H2 10:100sccm 576 MWNTs

Fe/

AL2O3

40:60 90 700 C2H2 H2 10:100sccm Low L. 2m m D. 40-50 nm

Ni/

AL2O3

40:60 90 700 C2H2 H2 10:100sccm

Fe –Ni/

AL2O3

40:60 90 700 C2H2 H2 10:100sccm 121 L. 4 µ m D. 20 nm

Fe –Co/

CaCO3

5:95 60 700 C2H2/ C2H4 N2 30ml/min 358 Spongy and very soft

Fe –Co/

MgO

5:95 60 700 C2H2/ C2H4 N2 30ml/min 229

Catalyst Carbon source Temperature (oC)

Yield %

3Co:3Mo/SiO2

CO 800 1

1.7Co:85Mo/ MgO

CO 1000 2 SWNTs

1.7Co:85Mo/ MgO

CH4 1000 15 MWNTs

5Co:5Mo/ MgO CH4 1000 80% SWNTs and

20% MWNTs

1Mo:9Fe/SiO2

CO 850 40

1Mo:9Fe/SiO2 C2H4 850 SWNTs and MWNTs

with a ratio of 3:7

Catalyst Reduction

temperature

(oC)

Decomposition

temperature

(oC)

Time

(min.)

Carbon

source

Carrier

gas

Rate

flow

L/min.

Yield

%

Freshly

reduced

SrFe12O19 supported on

Al2O3

500 500

30

C2H2

H2

10/90

171.3

550 550 272.3

600 600 367

650 650 329

Second Experiment

Catalyst Reductio

n

T (oC)

Decompositio

n

T (oC)

Time

(min.)

Carbon

source

Carrie

r

gas

Rate

flow

L/min.

Yield

%

Freshly

reduced

SrFe12

O19 supported on

Al2O3

600

500

30

C2H2

H2

10/90

230.2

600 367

700 436.9

800 180.7

Catalytic decomposition

of acetylene over

CoFe2O4/ BaFe12O19 core

shell

• Catalyst of the composition 40 catalyst:60Al2O3 is prepared by wet impregnation method as follows: aqueous solutions of catalyst with the required amount, was mixed with Al2O3 powder and stirred for 1 hrs at 60 oC to remove dissolved oxygen and to achieve a homogeneous impregnation of catalyst in the support. The impregnate was then dried in an oven at 100 oC for 3 hrs, calcined at 400 oC for 4 hrs in a box muffle furnace.

• Approximately 50 mg of a catalyst sample was introduced in to cylindrical alumina cell closed with one end, the cell with the catalyst placed in the central region of a longitudinal furnace.

• The catalyst was reduced at different temperature 500, 600, 700 and 800 oC at 1l/min in H2 flow and CNTs were synthesized via two type of experiments by flowing 10C2H2:90H2

1. Catalyst characterization

Figure 1 . XRD patterens for CoFe2O4/BaFe12O19 core shell reduced

at different temperatures

(1) Iron, Fe (2) Cobalt, Co (3) Barium peroxide, BaO2

(4) Barium oxide, BaO .

Figure 2. SEM of CoFe2O4 / BaFe12O19 core shell reduced, at

different temperatures, (A) 700 oC (81 % reduction)

(B) 500 oC (72 % reduction)

The difference in reduction temperatures lead to difference in phases formed

during reduction process at those temperatures (500-800oC).

500 oC 600 oC 700 oC 800 oC

Surface area (m2/g) 82.24 124.1 66.96 36.29

Total pore volume (cc/g) 0.040 0.0629 0.032 0.018

Adsorption energy (kJ/mol) 2.58 2.9 2.342 2.250

Average pore diameter (nm) 19.83 20.29 19.38 19.95

Micro pore volume (cc/g) 0.077 0.105 0.0712 0.0429

Surface area increases by decreasing reduction temperatures till 600oC, then any further

decrease in temperatures from 600 to 500oC leads to a decrease in the surface area, as

shown in Figure which shows fine structure containing microspores of sample reduced

at 600oC.

Figure . SEM of CoFe2O4 / BaFe12O19 core shell

reduced at 600 oC.

2. Surface area measurements

Table 1.

Effect of different reduction temperatures of CoFe2O4/ BaFe12O19 core shell on surface area measurements.

3. Effect of reduction temperature on the formation of carbon nanotubes

Figure . Carbon yields (%)

as a function of time at

different reduction and

decomposition

temperatures.

Figure . Carbon yields (%) as a function of temperatures of CoFe2O4 / BaFe12O19 core shell reduced, at

different temperatures and decomposed the C2H2 at the same temperature.

Figure . TEM of CoFe2O4 / BaFe12O19 core shell reduced, at different temperatures,

(a) 700 oC (81 % reduction ) (b) 800 oC (84.5 % reduction)

Figure 5. TEM of CoFe2O4 / BaFe12O19 core shell reduced and decomposed the C2H2 at the same

temperature

(a) 700 oC ( 81 % reduction and 267% carbon yield )

(b) 500 oC ( 72 % reduction and 141% carbon yield )

It is supposed that acetylene decomposes at different temperatures 500-

800°C on the top of a supported catalyst

The dissolved carbon diffuses in the catalyst, precipitates on the rear

side and forms a nanotubes

The carbon diffuses through the catalyst due to a thermal gradient

formed by the heat release of the exothermic decomposition of acetylene

The formation of carbon nanotubes and formation of carbon fibers by tip

growth mode

4. Effect of decomposition temperature on the formation of carbon

nanotubes and kinetics

Figure. Carbon yields (%) as a function of temperatures of CoFe2O4 / BaFe12O19

core shell reduced, at 700oC and decomposed the C2H2 at different temperatures

500-800 oC .

FT-IR spectra analysis at Figure , revealed four peaks at 283.48, 269.02, 256.48

and 1577.49 cm-1 that indicating the presence of multiwalled carbon nanotubes

as shown in the TEM micrograph.

Figure. FT-IR spectra for CoFe2O4 / BaFe12O19 core shell

reduced at 700oC and decomposed the C2H2 at 600oC

(a) at range from 4000-500cm -1 (b) at range from 650-150

cm-1

TEM of CoFe2O4 / BaFe12O19 core shell reduced at 700 oC

and decomposed the C2H2 at 600 oC.

Arrhenius plots for CoFe2O4/BaFe12O19 core shell reduced at different

temperatures 500- 800oC.

Activation energy of 2.9

kJ/mol for the reaction

physisorption

Catalytic

decomposition of

acetylene over

CoFe2O4/ NiFe2O4

core shell

1. Catalyst characterization

The difference between reduction temperatures lead to slightly increase in the

rate of reduction from 76 % at 800 oC to 71% at 500 oC, which can be attributed to

grain size approximation.

SEM micrograph of nanocrystallite

CoFe2O4 /NiFe2O4 core shell reduced at

800 oC.

SEM micrograph of cobalt ferrite /nickel

ferrite core shell reduced at different

temperatures at final stages at 600oC.

500 oC 600 oC 700 oC 800 oC

Surface area (m2/g) 193.8 65.09 74.79 185.7

Total pore volume (cc/g) 0.0968 0.032 0.0356 0.0690

Average pore diameter (nm) 19.99 19.67 19.08 14.87

Photomicrograph of CoFe2O4 / NiFe2O4 core shell reduced at 500 oC

(X400).

2. Surface area measurements

Effect of different reduction temperatures of CoFe2O4/ NiFe2O4 core shell on

surface area measurements

3. Effect of reduction temperature on the formation of carbon nanotubes

Carbon yields

(%) as a

function of

time at

different

reduction and

decomposition

temperatures.

4. Effect of decomposition temperature on the formation of carbon

nanotubes and kinetics

Carbon yields (%) as a

function of temperatures of

CoFe2O4 / NiFe2O4 core

shell reduced, at different

temperatures and

decomposed the C2H2 at

the same temperature.

Photomicrograph of

CoFe2O4 / NiFe2O4

core shell reduced at

different

temperatures (X40).

(a)800 oC to give 76

% reduction and 153

% carbon yield.

(b)700 oC to give 73

% reduction and 158

% carbon yield.

(c)600 oC to give 72

% reduction and 217

% carbon yield.

(d)500 oC to give 71

% reduction and 157

% carbon yield.

Carbon yields (%) as a

function of temperatures of

CoFe2O4 / NiFe2O4 core shell

reduced, at 600oC and

decomposed the C2H2 at

different temperatures 500-

800 oC.

TEM micrograph of cobalt ferrite /nickel ferrite core

shell reduced at 600oC and decomposition temperature at

700oC.

TEM micrograph of cobalt ferrite /nickel ferrite core shell reduced at 600oC and

decomposition temperature at 800oC.

FT-IR spectra analysis at Figure , revealed three peaks at 256.48, 1571.7 and

1282.43 cm-1 that indicating the presence of multiwalled carbon nanotubes as

shown in the TEM micrograph.

FT-IR spectra for CoFe2O4 / NiFe2O4 core shell reduced at 700oC and

decomposed the C2H2 at 600oC

(a) at range from 4000-500cm -1 (b) at range from 650-150 cm-1

Activation energy of 2.1

kJ/mol for the reaction

Arrhenius plots for CoFe2O4/NiFe2O4 core shell reduced at different

temperatures 500- 800oC.

physisorption

SYNTHESIS AND

MODIFICATION OF MULTI

WALLED CARBON

NANOTUBES (MWCNT) FOR

WATER TREATMENT

APPLICATIONS

1- Preparation of C/S catalyst/support:

The support-catalyst were prepared by wet impregnation

method. A required amount of the support material (S)

was milled in a ball mill for 10 hrs in order to decrease

the crystallite size and increase the surface area.

Calculated ratios of the metal salts (C1(NO3)and C2(NO3)

were added into the ball mill with (S) and milled for

another 2 hrs. The produced fine powder dispersed in a

few drops of water, mixed well to get a homogeneous

paste of (S), C1(NO3) and C2(NO3). The mixture was

dried in oven at 120oC for 12 hrs, cooled and ground well

to obtain a fine powder of C1-C2/S catalyst/support

mixture

2- Carbon nanotubes preparation:

Approximately 0.5g of catalyst/support sample was introduced to

cylindrical alumina cell closed with one end, the cell with the catalyst

suspended by chain in a horizontal furnace and attached to the pan of a

fully automatic sensitive (0.1 mg) balance (K) (Perciza-Swiss) to

record the weight gain at all the time of the experiment.

catalyst/support preheated to different operating temperature in a flow

of nitrogen gas (70 ml/min). After 10 min the acetylene gas was

allowed to pass over the catalyst bed with a rate of 10 ml/min for 40

min. The acetylene gas flow was stopped; the product on the alumina

cell was cooled to room temperature while nitrogen flow was on. The

weight of the carbon deposited along with the catalyst was noted. The

percentage of carbon deposit (C%) obtained in each reaction was

determined using the following relationship:

C % = [W3 – (W1 – W2) / (W1 – W2)]*100

where W1 is the initial weight of the catalyst , W2 is the weight loss of

catalyst at operating temperature, and W3 is the weight of carbon

deposited and catalyst.

3- CNTs Purification:

CNTs purification process was achieved by using

Chemical oxidation method. Specific amount of the as-

grown carbon nano-tubes were added to a mixture of

concentrated nitric acid /sulfuric acid (3:1 by volume,

respectively). The mixture is refluxed in oil bath for 4

hrs at 120 °C. After cooling to room temperature, the

reaction mixture is diluted with distilled water and then

filtered through a filter paper (3 μm porosity). This

washing operation was repeated several times using

distilled water and followed by drying in a drier at 100

°C.

4-Adsorption of heavy metals and organic dyes:

Adsorption experiments were performed at 298 K.

Exactly 100 ml of metal or dye solution placed in a

beaker and 0.1g oxidized CNTs was added to the

solution and left on a magnetic stirrer for 5 min. to

ensure the dispersion. At different times, 5 ml of the

sample solution was withdrawn and filtered with filter

paper and the change in characteristic absorption at the

specific beaks measured using an ultraviolet-visible

(UV-vis) spectrophotometer (Jasco 530), from which the

concentration of heavy metals and dyes was inferred.

Results and dissections:

TEM image of the as prepared CNTs synthesized at 600 oC.

TEM image of the oxidized CNTs synthesized at

600 oC and refluxed in conc. Acid for 4 hrs.

SEM image of the oxidized CNTs synthesized at 600 oC and refluxed in concentrated acid for 4 hrs.

HNO3/H2SO4

MWCNT Oxidized MWCNT

schematic preparation of the functionalized carbon nanotubes.

FTIR spectra of (a) as grown MWNT , (b) acid treated purified MWNT.

b

a

b

Wave length

200 400 600

Inten

sity

0

1

2

3

Before adsorption

After adsorption

Adsorption Mn7+ by using functionalized CNTs.

Wave length

300 400 500 600 700 800

Inte

ns

ity

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

CrCl3 before adsorption

CrCl3 after 3hrs

CrCl3

after 8hrs

Wave length

300 400 500 600

Inte

nsity

0

1

2

3

K2CrO

4

K2CrO

4 after 4.5 hrs

K2CrO

4 after 20 hrs

Absorption peaks of Cr3+ and Cr6+ adsorbed by functionalized CNTs.

Wave length

300 400 500 600 700 800

Inte

nsi

ty

0.0

0.0

0.2

0.3

0.4

0.5

T. Blue

After adsorption

Wave length

300 400 500 600 700 800

Inte

nsi

ty

0

1Methylen blue

Methylen blue after adsorption

Wave length

300 400 500 600 700 800

Inte

nsi

ty

Methyl green

Methyl green after adsorption

Wave length

300 400 500 600 700 800

Inte

nsity

Bromopyrogallol red

Bromopyrogallol after adsorption

Absorption beaks of different dyes ( Tolludine blue,

Methyl green, Methylen blue, Bromopyrogallol red)

before and after adsorption on functionalized CNTs.

For nonpolar and/ or planer chemicals:

Adsorption decreased.

For polar chemicals : Adsorption increased.

Adsorption increased

O=C

HO

HOOC

COOH

OH

C=O

COOH HOOC

COOH

As-growing CNTs Acid treated Functionalized

Inner pores blocked Catalyst removed Functional group added

The effect of CNT functional groups on organic molecule adsorption

Reduction-Reoxidation System

11 12 13 14 15 16

log(d

r/d

t)

-1.0

-0.5

0.0

0.5

1.0

1.5

initial

meddle

final

104/T, K-1.

Activation energies of nano cryst. copper ferrite reduction

Gas-Solid reaction mechanisms

1-Gaseous diffusion mechanism

2-Interfacial chemical reaction mechanism

3-Solid state diffusion mechanism

Activation energies and controlling mechanisms of the reduction process

Stage Ea,

kJ/mol. Controlling mechanism

Initial 39.35 Interfacial chemical reaction with

some contribution to gaseous

diffusion mechanism

Intermediate 65.2

Interfacial chemical reaction

mechanism

Final 55.3 Interfacial chemical reaction

mechanism

time, min.

0 2 4 6 8 10 12 14 16 18 20[1-(

1-X

)1/2

] +

[X

+(1

-x)

ln (

1-X

)]

0.00

0.05

0.10

0.15

0.20

0.25

400 o

C

500 o

C

600 o

C

time, min.

0 20 40 60 80 100 120 140

1 -

(1-X

)1/2

0.2

0.3

0.4

0.5

0.6time, min.

0 50 100 150 200 250

1 -

(1-X

)1/2

0.4

0.6

0.8

1.0 c

b

a

CO2 Catalytic decomposition Over freshly reduced 220 nm CuFe2O4

Inte

nsit

y, a.u

.2 - theta, degree

20 30 40 50 60 70 80

R6O6

R6O5

R6O4

R5O6

R5O5

R5O4

R4O6

R4O5

R4O4

• CO2 was allowed to decompose spontaneously

to carbon at 400-600oC during the reoxidation

of nano-crystallite metallic phase of Cu & Fe

compacts, produced from the reduction process.

• XRD analysis obtained for all samples

produced from the reduction-reoxidation

experiments at different temperatures indicates

that all samples contain the iron austenite and

magnetite phases, which reveals that CO2

decomposes during the reoxidation process to

carbon and oxygen forming the austenite and

magnetite.

• Deposited carbon was detected by C-analysis.

• Carbon in the form of Nano-tubes was detected

by SEM.

• For more evidence, carbon nano-tubes were

isolated by suspention in acetone, TEM was

used to prove the formation of Carbon Nano-

tubes.