Study of hydrogen adsorption by spiral carbon nano fibers synthesized from acetylene

Article abstract of DOI:10.1080/15533170500471441

A spiral carbon nanofiber of 30 to 40 nm diam and 20 μm average lengths has been synthesized by catalyst chemical vapor deposition method using Ni or Fe-Ni alloy as catalyst. The purpose of synthesis of carbon nano fibers was to use it for hydrogen adsorption. Catalysts used affected the morphology of carbon nano material (CNM) where as purification and ball milling of CNMs affected the hydrogen adsorption. The hydrogen adsorption is found to be 0.296wt% and 0.334wt% at hydrogen pressure of 11 Kg/cm² with as grown and purified CNMs with nitric acid respectively. After the ball milling of CNMs, their hydrogen storage capacity decreased to 0.222wt%. Copyright

Full text of DOI:10.1080/15533170500471441

Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, 36:37–42, 2006
Copyright # 2006 Taylor & Francis Group, LLC
ISSN: 0094-5714 print/1532-2440 online
DOI: 10.1080/15533170500471441
Study of Hydrogen Adsorption by Spiral Carbon Nano Fibers
Synthesized From Acetylene
Sandesh V. Jaybhaye and Maheshwar Sharon
Nanotechnology Research Center, Birla College, Kalyan, India
Madhuri Sharon
Nanobiotechnology Research Center, Birla College, Kalyan, India
L. N. Singh
Dr. Ambedkar Technological University, Lonere, India
[2]
been limited. The discovery of carbon nano tubes (CNTs)
A spiral carbon nanofiber of 30 to 40 nm diam and 20 mm in 1991 has opened a Pandora box of its various applications.
average lengths has been synthesized by catalyst chemical vapor
This has created the necessity to develop economical process
[3,4]
deposition method using Ni or Fe-Ni alloy as catalyst. The
purpose of synthesis of carbon nano fibers was to use it for
hydrogen adsorption. Catalysts used affected the morphology of
carbon nano material (CNM) where as purification and ball
[5]
to synthesize CNMs. Arc discharge
and laser ablation
are principle methods for obtaining high quality CNMs of
various forms such as CNTs, carbon nanofiber(CNFs),
milling of CNMs affected the hydrogen adsorption. The carbon nanobeads (CNBs), single-walled carbon nanotubes
hydrogen adsorption is found to be 0.296 wt% and 0.334 wt% at
hydrogen pressure of 11 Kg/cm with as grown and purified
(SWCNTs), multi-walled carbon nanotubes (MWCNTs). But
chemical vapor deposition (CVD) process
2
[6–10]
seems to
CNMs with nitric acid respectively. After the ball milling of
CNMs, their hydrogen storage capacity decreased to 0.222 wt%.
have become plausible method for large-scale production of
CNTs. Sharon and his group have developed a method for
large-scale production of CNMs by the catalyst chemical
Keywords acetylene, CNMs, hydrogen adsorption, spiral carbon
nanofiber, ball milling, CCVD process
[11]
vapor deposition (CCVD) process
One dimensional nano carbon including CNFs,
from natural sources.
[12,13]
[14]
[15–17]
MWCNT,
natural source
SWCNT and CNMs obtained from
11]
have been reported to be promising candi-
[
dates for hydrogen adsorption. In this paper the effect of acid
treatment and ball milling of spiral carbon nano fibers
INTRODUCTION
The depletion of energy resources and maintenance of
environmental pollution are essential problem that are closely
related to the sustainable development of human society and
(SCNF) synthesized from acetylene by CCVD process to
store hydrogen is reported.
demand for prompt solution. A fuel cell to combat this EXPERIMENTAL
problem has drawn the attention of many workers. Hydrogen
Synthesis of CNMs
For the synthesis of carbon nanomaterial, it is necessary to
is regarded as one of the most fascinating candidates for the
[1]
fuel cell because end product is non-polluting water. Due
to difficulties in storing hydrogen, its application as fuel has use a catalyst particle of nanosize range. For this purpose we
[18]
adopted the method discussed elsewhere.
The catalyst i.e.,
Ni or Fe-Ni alloy was prepared by urea decomposition pro-
cedure (Figure 3f). In conventional production method of
Financial support by the BRNS and University of Mumbai are CNMs, aromatic compound mainly benzene are used as the
Received 20 July 2005; accepted 28 October 2005.
[
19–22]
gratefully acknowledged. We are also thankful to Dr. Naresh
Chandra (Principal), my colleagues of Chemistry Department and
all the Nano Technology Laboratory Researchers for their support.
Address correspondence to Sandesh V. Jaybhaye, Nanotechnology
Research Center, Birla College, Kalyan 421 307, India. E-mail:
jaysandesh@yahoo.co.in
carbon source. Acetylene is also a source of carbon for
nano fiber production.
acetylene by CCVD process. The pyrolysing apparatus was
[23–25]
The CCNFs was prepared from
[26]
same as described earlier and presented in Figure 1. In
this method one-meter long quartz tube kept inside the
37

3
8
S. V. JAYBHAYE ET AL.
Ball Milling
CNM, were cut to smaller sizes using centrifugal ball
milling. CNM was Ball Milled in Zirconia jar using Zirconia
balls of weight 3.36 g for 1 h at 300 rpm. Weight ratio of
CNM to ball was 1 : 5.
Characterization by SEM, TEM and XRD
Scanning Electron Microscope (SEM) observation was con-
ducted on FEI quanta 200, Transmission Electron Microscope
FIG. 1. Schematic showing the apparatus for the preparation of CNMs using (TEM) observation conducted on a Philips CM200 and XRD
CCVD.
study conducted on a Philips Panalytical Xpert.
furnace has been used. Ni or Fe-Ni alloy particle was kept in
quartz boat and placed inside the tube furnace. Hydrogen gas
was passed in to the furnace tube at the flow rate of 0.4 or
0
.6 cc/min. to create inert atmosphere. After 5 min. of
passing gas the pyrolysis was tried at 750 8C and 850 8C. As
soon as the temperature reached, the acetylene gas was
allowed to pass very slowly at a flow rate of 0.4 cc/min. for
1
h. and heating was continued for 2–3 h. At constant set temp-
erature in an inert atmosphere of hydrogen. The furnace was
allowed to cool down to room temperature, and then the pyro-
lised material was collected from the furnace.
Purification
The crude product (CNMs) obtained from acetylene con-
tained amorphous carbon and metal particles as impurities.
To remove the impurities the crude product was soaked in
either conc. Nitric acid or conc. HCl for 3 h. The CNM was
then washed with water till neutral pH. Finally it was rinsed
with acetone to remove the traces of water and then dried in
an oven at 150 8C. The purified sample was heated up to
700 8C in hydrogen atmosphere for 2 h to oxidize the amor-
phous carbon. The product was characterized by using SEM,
TEM and XRD studied for its hydrogen adsorption capacity.
FIG. 3. (a) SEM photograph of as grown CNTs obtained from acetylene at
7
50 8C over Ni catalyst; (b) SEM photograph of purified CNTs with conc.
HCL obtained from acetylene at 750 8C over Ni; (c) SEM photograph of as-
grown CNTs obtained from acetylene at 750 8C over Fe-Ni catalyst; (d)
SEM photograph of purified CNTs with HNO
50 8C over Fe-Ni catalyst; (e) SEM photograph of purified CNTs with
HNO3 by refluxing at 150 8C obtained from acetylene at 750 8C over Fe-Ni cat-
FIG. 2. A schematic diagram showing the measurement of hydrogen alyst; (f) SEM photograph of Ni catalyst obtained by urea decomposition
absorption.
method.
3
obtained from acetylene at
7

HYDROGEN ADSORPTION ON CARBON NANOFIBERS
39
Then hydrogen gas was filled in the sample cell at the
desired pressure and left over night to measure whether there
was any decrease in the pressure. Two sets of hydrogen adsorp-
tion were done: one was blank where sample did not have any
CNMs and the other was sample cell loaded with purified
CNMs. Both these experiments confirmed that there was no
leakage.
The sample cell was then filled with hydrogen at 11.0 Kg/
2
cm . The change in the pressure of hydrogen was then
measured as rise in temperature of the sample cell. This was
obtained from achieved by heating the sample cell. This rate of change in
FIG. 4. (a) SEM photograph of purified CNTs with HNO
3
acetylene at 750 8C over Ni catalyst; (b) TEM photograph of purified CNTs hydrogen pressure with temperature was used as a blank
3
with HNO obtained from acetylene at 750 8C over Fe-Ni catalyst.
experiment. Then 5.0 g of CNFs was placed inside the
sample cell. The sample cell was heated up to 150 8C for
degassing under vacuum, and left over night. Next day the
Measurement of Hydrogen Adsorption
2
Hydrogen adsorption study was carried out with an appar- sample cell was filled with hydrogen at 11.0 Kg/cm left for
atus shown in Figure 2. This apparatus enabled us to calculate 2 h to observe whether there was any change in hydrogen
the hydrogen adsorption capacity of CNMs by measuring the pressure at room temperature. Then the sample cell was gradu-
decrease in hydrogen pressure. Since volume of the container ally heated up to 170 8C and the change in hydrogen pressure
was fixed (470 cc) this decrease in pressure was used as the with temperature was noted. A graph was plotted between the
quantity of hydrogen adsorbed by the CNMs. For each exper- changes in pressure of hydrogen (i.e., when the carbon sample
iment, 5 g samples were used in a sample cell.
was present in the pressure vessel and when there was no
A leak test of apparatus was done before starting each exper- carbon sample in the pressure vessel) at various temperatures.
iment. For this purpose, the sample cell holder was evacuated The difference in pressure was then plotted against tempera-
and then left overnight to see whether there was any leakage. ture.
3
FIG. 5. XRD of CNMs obtained from acetylene purified with HNO acid obtained from acetylene at 750 8C over Fe-Ni catalyst.

4
0
S. V. JAYBHAYE ET AL.
RESULTS AND DISCUSSION
yield; rather it showed more deposition of amorphous carbon
Urea decomposition procedure for nano size catalyst prep- in quartz boat. This suggests that the residence time of the
aration yielded nano sized (40–60 nm) Ni or Fe-Ni alloy. acetylene in the reactor is controlling the amount of disorga-
These catalysts have been successfully used by the Sharon nized carbon coatings. It was found that a large amount of
[26,18]
group.
Acetylene introduced into the furnace at a flow tar-like liquid by-product was being condensed on the cooled
rate of 0.4 cc/min. was found to yield higher amount of part of the furnace outlet. This might be due to a part of acety-
CNMs when it was run for 30 minute. This procedure lene feed getting converted in to higher hydrocarbons by the
yielded 4 g of CNMs per liter acetylene. An increased flow catalytic action of nickel or Fe-Ni alloy as reported by
[27]
rate 0.6 cc/min. was not only decreased amount of CNMs Soneda et al.
but also produced more amorphous carbon. In trial, the acety-
As mentioned above, CNMs synthesized from SEM, TEM
lene flow rate was kept constant at 0.4 cc/min and hydrogen and XRD characterized acetylene by CCVD process for
flow rate was decreased. But this also could not increase the quality, structure and nature of carbon deposited on metal
FIG. 6. (a) Variation of change in pressure vs. temperature for adsorption/desorption of as-grown CNTs obtained from acetylene at 750 8C over Ni catalyst;
(
b) Variation of change in pressure vs. temperature for adsorption/desorption of purified CNTs with conc. HCL obtained from acetylene at 750 8C over Ni catalyst;
c) variation of change in pressure vs. temperature for adsorption/desorption of as-grown CNTs obtained from acetylene at 750 8C over Fe-Ni
(
catalyst; (d) variation of change in pressure vs. temperature for adsorption/desorption of purified CNTs with HNO
3
obtained from acetylene at 750 8C over
obtained from acetylene at 750 8C
Fe-Ni catalyst; (e) variation of change in pressure vs. temperature for adsorption/desorption of purified CNTs with HNO
3
over Fe-Ni catalyst and ball milled for 2 hrs.

HYDROGEN ADSORPTION ON CARBON NANOFIBERS
41
particles. The SEM images of Acetylene pyrolised on Ni as precursor in CCVD method. And 0.4 cc/min flow rate of
particle show large quantity of SCNFs as well as CNTs. acetylene was found to be more suitable for synthesis of
Figures 3a and 3b are SEM of SCNFs before and after purifi- CNM as it yielded 4 g of CNTs per gram of acetylene. Better
cation, whereas acetylene pyrolised on alloy (Fe-Ni) showed purification of as-grown CNFs was achieved when they were
comparatively more amount of CNTs than SCNFs in both soaked in nitric acid. Moreover purified CNMs showed more
unpurified and purified samples (Figures 3c and 3d). These hydrogen adsorption capacity. However ball milling of
results were consistent in all the trials.
CNMs to smaller unit decreased their capacity to adsorb
TEM of purified CNMs presented in Figure 4 shows that Ni hydrogen.
as a catalyst could produce more SCNFs (Figrue 4a) Whereas
CNMs deposited on Fe-Ni alloy shows large quantity of CNTs
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