BASIC CONCEPTS AND AN OVERVIEW - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 16

hydrogen gas flow. In both methods, catalyst nanoparticles are formed through
thermal decomposition of organo metallic compounds, such as iron pentacarbonyl
and ferrocene. The reverse micelle method is promising, which contains catalyst
nanoparticles (Mo and Co) with a relatively homogeneous size distribution in a
solution. The presence of surfactant makes the nanoparticles soluble in an organic
solvent, such as toluene and benzene. The colloidal solution can be sprayed into
a furnace, at a temperature of 1200°C; it vaporizes simultaneously with the injec-
tion and a reaction occurs to form a carbon product. The toluene vapor and metal
nanoparticles act as carbon source and catalyst, respectively. The carbon product
is removed from the hot zone of the furnace by a gas stream (hydrogen) and col-
lected at the bottom of the chamber [55-56].

1.1.5.3.2 RECENT TRENDS IN THE SYNTHESIS OF CNT

Some researchers synthesized carbon nanotubes from an aerosol precursor.
Solutions of transition metal cluster compounds were atomized by electro hy-
drodynamic means and the resultant aerosol was reacted with ethane in the gas
phase to catalyze the formation of carbon nanotubes. The use of an aerosol of
iron penta carbonyl resulted in the formation of multi-walled nanotubes, mostly
6-9 nm in diameter, whereas the use of iron dodecacarbonyl gave results that
were concentration dependent. High concentrations resulted in a wide diameter
range (30-200 nm) whereas lower concentrations gave multi-walled nanotubes
with diameters of 19-23 nm. CNT synthesized by electrically arcing carbon rods
in helium (99.99%) in a stainless steel chamber with an inner diameter of 600 mm
and a height of 350 mm. The anode was a coal-derived carbon rod (10 mm in di-
ameter, 100-200 mm in length); the cathode was a high-purity graphite electrode
(16 mm in diameter, 30 mm in length). The helium gas functioned as buffer gas
and its pressure was varied in range of 0.033-0.076 MPa in the experiment. CNT
synthesized via a novel route using an iron catalyst at the extremely low tempera-
ture of 180 o C. The carbon clusters can grow into nanotubes in the presence of Fe
catalyst, which was obtained by the decomposition of iron carbonyl Fe 2 (CO) 9 at
250 o C under nitrogen atmosphere. SWNT have been successfully synthesized us-
ing a fluidized bed method that involves fluidization of a catalyst/support at high
temperatures by a hydrocarbon flow. A new method, which combines non-equi-
librium plasma reaction with template controlled growth technology, has been
developed for synthesizing aligned carbon nanotubes at atmospheric pressure and
low temperature. Multiwall carbon nanotubes with diameters of approximately
40 nm were restrictedly synthesized in the channels of anodic aluminum oxide
template from a methane hydrogen mixture gas by discharge plasma reaction at a
temperature below 200 o C. In a recent technique, Nebulized spray pyrolysis, large-
scale synthesis of MWNT and aligned MWNT bundles is reported. Nebulized
spray is a spray generated by an ultrasonic atomizer. A SEM image of aligned
MWNT bundles obtained by the pyrolysis of a nebulized spray of ferrocene-tolu-