View of Study of effect of temperature on the synthesis of carbon nanotubes by floating catalyst method

Study of Effect of Temperature on the Synthesis of Carbon Nanotubes by Floating Catalyst Method

Ravindra RAJARAO and Badekai RAMACHANDRA BHAT

^*

Catalysis and Materials Division, Department of Chemistry, National Institute of Technology Karnataka, Surathkal, Mangalore-575 025, India

Abstract

Carbon nanotubes (CNTs) were grown by floating catalyst method using acetylene as carbon precursor and ferrocene as catalyst precursor. The CNTs were grown in the temperature range of 700 - 1150°C. The prepared CNTs were purified by acid treatment and air oxidation methods. The purified CNTs were characterized by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The purity of CNTs was determined by thermal analysis and X-ray diffraction method. The yield, diameter and length of grown CNTs were same at all temperatures. The crystalline perfection of CNTs increases as the temperature increases. Our results indicated that the synthesis temperature could affect the degree of graphitization of CNTs.

Keywords: Carbon nanotubes, Floating catalyst method, Double stage CVD, Effect of temperature

Introduction

Since the discovery by Iijima,⁽¹⁾ carbon nanotubes (CNTs) have drawn much attention and intensive research has been carried out. This great interest is due to CNTs unique microstructure, low density and they posses excellent mechanical and electrical properties, that enable them to be applied in many promising fields, such as; mechanical reinforcements in polymer composites,⁽²⁾ nanoelectronics devices,⁽³⁾ hydrogen storage,⁽⁴⁾ biosensors,⁽⁵⁾ fuel cells,⁽⁶⁾ field emitters⁽⁷⁾ and as catalyst supports.⁽⁸⁾

Until now various synthesis methods have been developed for the production of CNTs, including are arc discharge,⁽¹⁾ laser ablation,⁽⁹⁾ chemical vapor deposition (CVD)⁽¹⁰⁾ and so on. The main disadvantage of arc discharge and laser ablation method is that they are uncontrolled in the process parameters.

Compared with arc discharge and laser ablation method, CVD is simple, cheap and parameters are easily controlled. The CVD method requires both the metal catalyst (Ni, Co and Fe) and a carbon source to produce CNTs. The introduction of a catalyst divides CVD methods into floating catalyst methods group, using a catalyst in the gas phase and fixed catalyst methods group with supported catalyst. The main advantage of floating catalyst method is that it does not require the stage of catalyst

preparation as in the case of fixed catalyst method because the catalyst particles are continuously formed in the reactor and catalyst deactivation problem is avoided. Generally, organometallic compounds formed by transition metal (Ni, Co or Fe) are mainly used as precursors in the floating catalyst method.

In this paper, we investigated the CNT synthesis by floating catalyst method by using ferrocene as catalyst precursor and acetylene as carbon precursor. The effect of temperature on the synthesis of CNTs was also studied. The CNTs synthesised were characterised by using scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The purity of CNTs was determined by thermal analysis and X-ray diffraction studies.

Materials and Experimental Procedures

In order to synthesise CNTs, the apparatus (Figure 1) consists of two stage furnace system fitted with quartz tube (25 mm Inner Diameter, 1200mm Length). Argon gas was used as carrier gas and acetylene gas was used as carbon precursor.

The amount of carbon deposit was studied at different flow rates at 850°C for better yield. We investigated the effect of temperature on the quality of CNTs synthesised at gas flow rates of acetylene (15 sccm)

Corresponding author: Ph: +91 824-2474000 Extn. 3204 Fax: +91 824-2474033 Email: chandpoorna@yahoo.com (B. R. Bhat)

 

 

and argon taken in th quartz reac to 230°C, furnace reac Acetylene g the furnace argon flow as a black f was collecte

Figure 1. S A c

R H The nanoparticle treatment w eliminate th with distille oven at 100 to remove t The analysed by TA) to dete purity of s were again method (XR Kα radiatio of sample.

obtained by (SEM, SUP electron mi relative int obtained by 1000, He-N

Results an

In o TGA was TGA profil purified sam

(500 sccm).

he quartz b ctor. The pre

after the t ched to desire as flow was was cooled . Carbonace film onto the

ed.

Schematic re A-Argon gas cylinder. C-Q Reaction zone H-Water bubb e as grow es which w with 5N HC he acid, final

ed water. Th 0°C. This wa the amorphou e as grown y Thermogra ermine the am sample after

characterise RD, JEOL JD on, λ=1.5418 The microstr y using sca PRA 40VP C

icroscope (T tensities of y Raman sp Ne laser excit

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performed i les of as grow mple by acid

RAJA . 100 mg of boat and pla eheater furna temperature

ed temperatur allowed for

to room tem ous material e walls of qua

presentation s cylinder. B Quartz tube. D e. F-Quartz bo bler.

wn products were remove Cl at 80°C lly the sampl he samples w

as followed b us carbon.

and purified avimetry (TG

mount of me r purification d by using X DX 8P diffrac

8A˚) to deter ructure of th anning electr Carl Zeiss) an TEM, CM20

D-band and ectroscopy ( tation line at

ion

mate the purit in air. Figur wn product a d treatment an

ARAO, R. and f ferrocene w aced inside

ace was hea in the seco re (700-1150

10 min. Fina mperature in l was deposi artz tube, wh

of CVD set B-Acetylene D-Pre heater.

oat. G-Contro

contain i ed by an a for 30min.

les were was were dried in by air oxidat

d samples w GA, SDT Q

etal present n. The samp X-ray diffract ctometer with

rmine the pu he samples w

ron microsc nd transmiss 00 Philips). T

d G-band w (Renishaw, R

633.0 nm).

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were 600 and ples tion Cu urity were ope sion The were RM

mple, the d its tion

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Fig

Fig

CN

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ntain iron p rified sample e absence of n content w move from mple was ag

ttern (Figure .0°, 43.5° an d (004) diffr CPDS card o other notic observed in

gure 2. TGA carb

gure 3. XRD p Figure NTs grown at

AT, B.

s grown samp efore 500°C

amount of oss after 500 particles of shows loss o f amorphous was present

acid treatm gain analyse e 3) contains nd 53.5°, ind raction plane

files, no 41 eable peaks the XRD pat

A analyses o bon deposits g

pattern of purifi 4 shows SEM t 700°C, 850

ple shows th indicating t amorphous 0°C. The as g f 24% in w

only after 500 carbon and which was ment. The pu ed by XRD

s characteris dexed with ( es of hexago 1-1487), resp

induced by ttern.

f as grown grown at 850°C

fied product gro M images of 0°C, 1000°C

he little or no the presence carbon and grown CNTs weight. The 0°C indicates only 1% of s unable to urity of the . The XRD stic peaks at (002), (101) onal graphite pectively.⁽¹¹⁾ catalyst can

and purified C

own at 850°C f the purified

and 1150°C d

f

t

n

d

d

 

for 10 min remained al The diamet their twistin the length o but the len several ten CNTs was observed fr the crystalli of CNTs als

Figure. 4. S (

Figure. 5. T ( The have shown at around 13 The D-band G-band is d The quality peak intens The value increases fr

n. The leng most same at ter of CNTs ng morpholo of the CNT f ngth can be ns of micro further con rom TEM th ization perfe so increases

SEM images (a) 700°C (b)

TEM images (a) 700°C (b) e Raman sp n in the figure

325cm^-1 (D-b d is due to d due to the g y of CNTs ca sity ratio of of I_D/I_G ratio rom 700°C t

gth and diam t all the grow s was 20-40n ogy it is diffi

from the SEM estimated to ometers. The nfirmed by T hat as temper ection of the

(Figure 5).

of purified pr 850°C (c) 100

of purified pr 850°C (c) 100 pectra obtain e 6. All spect band) and 157

disordered st graphitic stru an be identifi f the D-peak

o decreases to 1150°C.

by Float meter of CN wth temperatu

nm, because icult to meas M micrograp o be more t e formation TEM. It can rature increa graphitic w

roducts grown 00°C (d) 1150

roducts grown 00°C (d) 1150 ned from CN

tra show 2 ba 75cm^-1 (G-ban

tructure and ucture of CN ied by using k to G-peak as temperat The I_D/I_G va

ting Catalyst NTs

ures.

e of sure phs, than of n be

ases walls

n at 0°C

n at 0°C NTs ands nd).

the NTs.

the k.⁽¹²⁾

ture alue

wa fig per Th dia

Fig

Fig

Tab

exp Th

t Method as plotted ve

ure 7. The rfection incr

e table 1 giv ameters of CN

gure 6. Rama (a) 70

gure 7. Plot of ble 1. Summa CNTs a

Reactio Temperatur 700 850 1000 1150 The ca plained based e VLS mode

ersus temper e plot show eases linearl ves summary NTs and ID/I

an spectra of p 0°C (b) 850°C

f ID/IG ratio ve ary of reaction and ID/IG valu

n e (°C)

D C

atalytic grow d on vapour-l

el consists of

rature as sh ws that the

ly with the t of reaction t IG values.

purified produ C (c) 1000°C

ersus reaction n temperature,

es

Diameter of CNTs (nm)

20-30 25-35 20-25 20-30 wth of CNT liquid-solid (V

f the followi

hown in the crystalline temperature.

temperature,

ucts grown at (d) 1150°C

temperature , diameters of

ID/IG

ratio 1.10 0.83 0.53 0.31 Ts has been

VLS) model.

ing steps: (i) t

f

 

a carbon so transition m carbide is fo the nanopa carbon prec Vap decompositi quartz tube deposit on th Carbons resu adsorb on t form a misc as the carb form the CN image for th they form th (Figure 9a a catalytic par is produced growing tub particle. Pr carbons accu dissolves ins carbons can tube with a growth rate sheets build higher temp during grow

Figure 8.

Figure 9. Gr

ource is dec metal nanopa formed by dif articles (iii) cipitates to fo porised ferr ion in the gas in the reacti he quartz tub ulted from th the iron nan cible alloy. In ons saturate, NTs. Figure 8 he carbon nan

he graphitic s and 9b). As th

rticle, a close d (Figure 9c a be was limi robably main umulated on t side the tube.

n arrive at the a higher diffu of nanotube d up with a l perature, the wth.

Supporting T nanotube grow

rowth model o

RAJA composed on

articles (ii) l ffusion of ca after over orm CNTs.

rocene mole phase or on t ion zone, iro be wall which he decomposit noparticles a n catalytic iro

, they start t 8 shows the s notube growth sheets on the he graphite sh ed tip with th and 9d). The

ted by size nly via bulk the surface of

As the tempe e reaction site usion rate. C es increases a

less defect. T e nanotubes

TEM image wth model

of CNTs

ARAO, R. and n the surface

liquidised m arbon atoms i

saturation;

ecules unde the surface of on nanopartic h acts as catal

tion of acetyle and dissolves on nanopartic to precipitate supporting T h model. Initia

catalytic part heets lifts off he inside hol e diameter of

of the cataly k diffusion, f catalytic part erature increa e of the grow onsequently and the graph Therefore at can align be

for the car

d RAMACHA e of

metal into the

ergo f the cles lyst.

ene, s to cles,

e to TEM ally, ticle f the llow f the ytic the ticle ases, wing the hitic the etter

rbon

Co

by the gro sam CN res tem

Ac

Re Go als CE

Re

1. I

2. W

3. B

4.

5. O

6. W

7. Y

ANDRA BHA

onclusions

The CN using floatin e effect of own CNTs.

me at all the NTs was up sults indicate mperature inc

cknowledge

The au search and D overnment of

o to SAIF ECRI for prov

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