MULTI WALLED CARBON NANOTUBES

(MWCNT) & GRAPHENE NANO-SHEETS

FOR DYES REMOVAL

M. H. Khedr, A. A. Fargali M. Bahgat and W.M.A.EL Rouby

Beni-Suif University

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

Roll up

Classification of CNTs:

Single-wall Carbon nanotubes (SWNTs,1993)

• one graphite sheet seamlessly wrapped-

up to form a cylinder

• typical radius 1nm, length up to mm

Classification of CNTs:

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

Classification of CNTs:

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)

CNTs Current Applications

•Technological applications – conductive and high-strength

composites – energy storage and conversion

devices – sensors, field emission displays – nanometer-sized molecular

electronic devices

• Pipe

• Wires

• Springs

• Gears

• Pumps

CNTs 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 but

still high temperature

Laser ablation apparatus

Chemical Vapor Deposition (CVD)

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

• Hydrocarbons: CH4, C2H2, etc.

• Temperature: First furnace 1050oC

Second furnace: 750oC

• Advantages:

Higher production of CNTs High Purity

Fewer by-Products Low Temperature

What is 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 [in the plane].

• Imagine a material more conducting than copper. This is how conductive graphene is.

• Imagine a machine that can test the same physics that scientists test in, say, CERN, but small enough to stand on top of your table. Graphene allows this to happen.

• Having such a material in hand, one can easily think of many useful things that can eventually come out. As concerns new physics, no one doubts about it already...''

Allotropes of Carbon

Diamond, graphite, lonsdalerite, C60, C70,

carbon, amorphous carbon, carbon nanotube

And Graphene

What is Graphene?

• Is a 2D structure and 1

atom thick

• Hexagonal array of sp2

carbon atoms.

– Sigma orbital = valence

band

– Pi orbital = conduction

band (2)

• C-C bond is 120° and ~

0.142nm bond length

• Is electrically “metallic”

What is Graphene?

Graphene: A Honeycomb Lattice

Types of Graphene:

• Theoretical graphene (1947 -present)

• Mechanically exfoliated/cleaved graphene (1997-2004)

• Epitaxially grown graphene (1986-2004)

• Chemically exfoliated and intercalated graphene (c.1980-2004)

• Chemical decomposition graphene (1997-still under development)

1. Drawing – mechanical exfoliation of 3D graphite crystals

2. Epitaxial growth – use of the atomic structure of substrate to grow graphene

3. Silicon Carbide Reduction – heating of silicon carbide to 1100C and reduce it to form graphene (5)

4. Other processes

– Hydrazine Reduction

– Sodium Reduction of Ethanol

– CVD (4)

• Transistors

• Sensors

• TEM

• Inert Coatings

• Nanoribbons and Semiconductors

• Integrated circuits

• Ultracapacitors

• Biodevices (6)

1- Preparation of Fe-Co/CaCO3

catalyst/support:

1- The support material

(CaCO3) Ball milled

10 hrs

2- Fe(NO3)3·9H2O +

Co(NO3)2·6H2O +

milled CaCO3

Ball milled

2 hrs

4- The paste dried in oven at 120oC for 12 hrs

3- The produced

fine powder

dispersed in a few drops of water and

mixed well to get a homogeneous paste

cooled and ground well to obtain a fine powder of

Fe-Co/CaCO3 catalyst/support mixture

Mass flow

controllerGas

regulator

CO

CO

N2

Purification

towerKanthal wire

Balance

Alumina tube

Tube furnace

Kanthal basket

Fig. 2.1: Schematic diagram for the reaction system

Mass flow

controllerGas

regulator

CO

CO

N2

Purification

towerKanthal wire

Balance

Alumina tube

Tube furnace

Kanthal basket

Mass flow

controllerGas

regulator

CO

CO

N2

Purification

tower

Mass flow

controllerGas

regulator

CO

CO

N2

Purification

tower

Mass flow

controllerGas

regulator

CO

CO

N2

Purification

tower

CO

CO

N2

Purification

tower

CO

N2

COCO

N2

Purification

towerKanthal wire

Balance

Alumina tube

Tube furnace

Kanthal basket

Fig. 2.1: Schematic diagram for the reaction system

C2H2

Flo

w

C2H2

C % = [W3 – (W1 – W2) / (W1 – W2)]*100 W1 is the initial weight of the catalyst (Fe - Co ),

W2 is the weight loss of catalyst at operating temperature,

W3 is the weight of carbon deposited and catalyst.

Influence of reaction time and temperature

on Carbon yield and morphology

400 oC

500 oC

600 oC

700 oC

800 oC

2. Influence of reaction time and temperature on Carbon yield:

Figure 2: Effect of growing

time on the deposited

carbon percent during

acetylene decomposition

over Fe- Co /CaCO3

catalyst/support at

different temperatures

(400-800 oC)

M. Bahgat, M. Khedr and M. Shaaban, Materials Technology: Advanced Performance Materials, 2008, 23, 13-18.

M. Bahgat, M. Khedr, M. Radwan and M. Shaaban, Mineral Processing and Extractive Metallurgy, 2007, 116, 217-220.

4. CNTs Purification:

purification process was achieved by using chemical oxidation method.

Specific amount

of the as-grown

carbon nanotubes

added to mixture of conc.

HNO3 &H2SO4

(3:1 by volum)

refluxed oil bath

for 4 hrs

at 120 °C

cooling to room

temperature the reaction mixture is

diluted with distilled water

filtered through

a filter paper

(3 μm porosity)

washing drying at 100 °C.

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

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.

6. Effect of acid treatment on MWCNTs

a

b

Figure 6 : TEM (a) and SEM (b) image of CNTs

synthesized at 600 oC and oxidized in

concentrated acid for 4 hrs.

MWCNT Oxidized MWCNT

Scheme 1: Schematic preparation of the functionalized carbon

nanotubes.

Figure 8: FTIR spectra of MWCNTs

synthesized at 600 oC and then oxidized in

concentrated acid for 4 hrs.

3. Effect of operating temperature on MWCNTs morphology:

a

15 nm

60 nm

22 nm

b

Figure 3 : TEM image of the synthesized

MWCNTs at 600 oC (a) and 700 oC (b).

Walls of MWCNT with thickness about 36

nm the inner and outer diameter of the

tube about 28 and 112 nm respectively

Internal diameters of approximately

12–15 nm and external diameters of

55–60 nm.

M. Bahgat, M. Khedr and S. Abdel-Moaty, Materials Technology: Advanced Performance Materials, 2007, 22, 139-146.

M. Bahgat and M. Khedr, Materials Science and Engineering: B, 2007, 138, 251-258.

Graphene preparation:

1-Preparation of graphite oxide “Hummers method” 10 g Natural

Graphite

powders

The mixture was

stirred for 40 min

Treated by 5%

HCl twice

placed (0 ◦C)

concentrated

H2SO4 (230 mL)

KMnO4 (30 g) was

added gradually with

stirring and cooling

solution temperature was not

allowed to go up to 20 ◦C

distilled water (460 mL)

was added slowly to an

increase in temperature

to 98 ◦C

temperature was

held at 353 ◦C

for 30 min

The solution was

held at room temperature

for 24 h

filtered, Washed

and dried at 110 ◦C

for 24 h

distilled water (1.4 L)

and 30% H2O2 solution

(100 mL) were

added after the reaction

the mixture was filtered

and washed with 5% HCl

The reaction product was dried

under vacuum at 50 ◦C for 24 h

Graphite oxide

2-Preparation of graphene “Hummers method”

Added to distilled water

and sonicated for 30 min

50 µ of hydrazine

hydrate was added

The solution was

treated with microwave

900 W for 3 min “On

and Off”

The solution was

filtered, washed and

dried at 60 oC 24h

Graphene

Graphene characterizations

SEM of graphene sheets prepared by hummer method

M. Bahgat, A. Farghali, W. El Rouby and M. Khedr, Journal of analytical and applied pyrolysis, 2011, 92, 307-313.

A. Farghali, M. Moussa and M. Khedr, Journal of alloys and compounds,2010, 499, 98-103.

SEM of graphene sheets decorated with CoFe2O4 nanoparticles

Graphene characterizations

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.

TEM of graphene sheets decorated with CoFe2O4 nanoparticles

Graphene characterizations

M. Bahgat, A. Farghali, W. El Rouby and M. Khedr, Journal of analytical and applied pyrolysis, 2011, 92, 307-313.

A. Farghali, M. Moussa and M. Khedr, Journal of alloys and compounds,2010, 499, 98-103.

Organic dyes Removal:

0.05 g oxidized CNTs or graphene was added 50 ml of dye solution dye solution of increased

initial concentrations (C0) from 50 to 400 mg/L.

temperature control box to

maintain water temperature

(298, 313,323K) equilibrium 5 ml separated

(UV-Vis) spectrophotometer (Jasco 530)

Organic dyes Removal:

X-ray diffraction pattern for Fe, Co supported on CaCO3.

( 1: CaCO3, 2: Fe2O3, 3: CoO)

X-Ray analysis for Catalyst:

FTIR spectra for CNTs:

a

b

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

HNO3/H2SO4

MWCNT Oxidized MWCNT

schematic preparation of the functionalized carbon nanotubes.

3369

3369

1569 1704 1146 674 596

871

1428 2916

2916

2848

2848

Electron microscope examination for CNTs

TEM for nonoxidized CNTs TEM for oxidized CNTs

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

Electron microscope examination for CNTs

Electron microscope examination for Graphene

SEM of prepared graphene

Adsorption studies:

Effects of dye concentration on the adsorption of methyl

green dye (CNTs = 0.1 g/100 ml and T = 298 K).

The amount of dye

adsorbed per unit of CNT

mass increased as initial

dye concentration

increased due to the

increase in the driving

force of the concentration

gradient for mass transfer

with the increase in initial

dye concentration.

Adsorption studies:

Effects of CNTs dosage on the adsorption of methyl green dye

(dye concentration = 4.36 x 10-5 M and T = 298 K).

Adsorption Isotherm:

Adsorption isotherms of methyl green

onto MWCNTs at different

temperature.

Adsorption isotherms of methyl green

onto Graphene at different

temperature.

Electron microscope examination for CNTs

• The adsorption capacity of methyl green onto MWCNTs and

Graphene nano-Sheets

298 K 313 K 323 K

MWCNTs 119.05 mg/g-1 160.12 mg/g-1 181.2 mg/g-1

Graphene 203.51 mg/g-1 258.39 mg/g-1 312.80 mg/g-1