Nanotechnology for domestic water purification - Nanotechnology in Eco-efficient Construction - page 377

Table 16.2 Overview of the important synthesis procedures for CNTs (adapted
with permission from Balasubramanian and Burghard, 2005)

Synthesis
method

Type of CNT
with yield

Maximum
production rate Principle

Arc
discharge

Carbon atoms are
generated through an
electric arc discharge at
T

Both SWNT and
MWNT can be
produced;
yield: about
30% by
weight

120 g per day

3000°C between two
graphite rods. Catalyst
metal particles (Fe, Co,
Ni) required

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Laser
ablation

Generation of atomic
carbon at T

Mainly SWNT
can be
formed; yield:
about 70%
(expensive
method)

50 g per day

3000˚C
through laser irradiation
of graphite containing
catalyst metal particles
(Fe, Co, Ni)

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Chemical
vapour
deposition

Decomposition of gaseous
hydrocarbon source is
catalysed by catalyst
metal particles (Fe, Co,
Ni). Spray pyrolysis
method with liquid
precursor such as
benzene

Both SWNT and
MWNT can be
formed; yield:
about 60%

50 kg per day

ferrocene can
be used directly where
patterned substrate with
catalyst impregnation is
not required.
Temperature of synthesis
is about 750-1000°C

+

with particular length, diameter and alignment. Each of the parameters is
critical toward the nature as well as yield of CNTs (Dasgupta et al. , 2008).
This synthesis route provides CNTs with a high degree of alignment because
the catalyst particle (iron in the case of ferrocene precursor) is generated
in situ . Also the method is economical with no requirement of substrate
preparation as well as less involvement of trained manpower compared to
the other two synthesis routes.
A self-standing tubular macrogeometry of aligned carbon nanotubes with
very high surface area (

￿ ￿ ￿ ￿ ￿ ￿

90 m 2 /g) was developed with optimization of spray
pyrolysis parameters. The macrogeometry of aligned CNTs is shown in Fig.
16.6, and Fig. 16.7 shows the scanning electron microscope (SEM) image
depicting the highly aligned CNTs along the thickness of cylinder. It has
the usual advantages of a membrane where, based upon the principle of
size exclusion, the water purifi cation can take place.

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