Page 24 - Carbon Nanotubes

CATALYTIC PRODUCTION AND PURIFICATION OF
NANOTUBULES HAVING FULLERENE-SCALE DIAMETERS

J.
V. I[vANov,~** A. FONSECA," B.NAGY,"+ LUCAS," P. LAMBIN," D. BERNAERTS~ and
A.
X. B. ZHANG~
"Institute for Studies of Interface Science, FacultCs Universitaires Notre Dame de la Paix,
61 rue de Bruxelles, B-5000 Namur, Belgium
bEMAT, University of Antwerp (RUCA), Groenenborgerlaan 171, B-2020 Antwerp, Belgium
(Received 25 July 1994; accepted in revisedform 13 March 1995)
Abstract-Carbon nanotubules were produced in a large amount by catalytic decomposition of acetylene
in the presence of various supported transition metal catalysts. The influence of different parameters such
as the nature of the support, the size of active metal particles and the reaction conditions on the formation
of nanotubules was studied. The process was optimized towards the production of nanotubules having
the same diameters as the fullerene tubules obtained from the arc-hscharge method. The separation of
tubules from the substrate, their purification and opening were also investigated.
Key Words-Nanotubules, fullerenes, catalysis.

1. INTRODUCTION production. The synthesis of the nanotubules of vari-
ous diameters, length and structure as dependent on
The catalytic growth of graphitic carbon nanofibers the parameters of the method is studied in detail. The
during the decomposition of hydrocarbons in the elimination of amorphous carbon is also investigated.
presence of either supported or unsupported metals,
has been widely studied over the last years[ 1-61.
The main goal of these studies was to avoid the 2. EXPERIMENTAL
formation of "filamentous" carbon, which strongly
poisons the catalyst. More recently, carbon tubules The catalytic decomposition of acetylene was car-
of nanodiameter were found to be a byproduct of ried out in a flow reactor at atmospheric pressure. A
arc-discharge production of fullerenes [7]. Their cal- ceramic boat containing 20-100 mg of the catalyst
culated unique properties such as high mechanical was placed in a quartz tube (inner diameter 4-10 mm,
length 60-100 cm). The reaction mixture of 2.5-10%
strength[ 81, their capillary properties [ 91 and their
remarkable electronic structure [ 10-121 suggest a CzH2 (Alphagaz, 99.6%) in N, (Alphagaz, 99.99%)
wide range of potential uses in the future. The catalyti- was passed over the catalyst bed at a rate of
cally produced filaments can be assumed to be ana- 0.15-0.59 mol C2H2 g-lh-' for several hours at tem-
peratures in the range 773-1073 K.
logous to the nanotubules obtained from arc- The catalysts were prepared by the following
discharge and hence to possess similar properties [ 51, methods. Graphite supported samples containing
they can also be used as models of fullerene nano- 0.5-10 wt% of metal were prepared by impregnation
tubes. Moreover, advantages over arc-discharge fibers of natural graphite flakes (Johnson-Matthey, 99.5%)
include a much larger length (up to 50pm) and a with the solutions of the metal salts in the appropriate
relatively low price because of simpler preparation. concentrations: Fe or Co oxalate (Johnson-Matthey),
Unfortunately, carbon filaments usually obtained in Ni or Cu acetate (Merck). Catalysts deposited on
catalytic processes are rather thick, the thickness SiO, were obtained by porous impregnation of
being related to the size of the active metal particles. silica gel (with pores of 9 nm, S, 600 m2g1, Janssen
The graphite layers of as-made fibres contain many
defects. These filaments are strongly covered with Chimica) with aqueous solutions of Fe(IJ1) or Co(I1)
nitrates in the appropriate amounts to obtain 2.5
amorphous carbon, which is a product of the thermal wt% of metal or by ion-exchange-precipitation of the
decomposition of hydrocarbons [ 131. The catalytic same silica gel with 0.015 M solution of Co(I1) nitrate
formation of thin nanotubes was previously (Merck) following a procedure described in Ref. [ 151.
reported[ 141. In this paper we present the detailed The catalyst prepared by the latter method had 2.1
description of the catalytic deposition of carbon on wt% of Co. All samples were dried overnight at 403 K
various well-dispersed metal catalysts. The process and then calcined for 2 hours at 173 K in flowing
has been optimized towards the large scale nanotubes
nitrogen and reduced in a flow of 10% H, in Nz at
773 K for 8 hours.
*To whom all correspondence should be addressed. Zeolite-supported Co catalyst was synthesized
+Permanent address: Laboratory of Organic Catalysis,
Chemistry Department, Moscow State University, 119899, by solid-state ion exchange using the procedure
Moscow, Russia. described by Kucherov and SlinkinC16, 171. COO
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