Environmental Engineering Reference
In-Depth Information
black and activated carbon (Yue and Economy, 2005). This is due to the fact that most
of the internal surface of activated carbon is in the form of micropores that cannot be
accessed by large humic acid molecules, whereas the surface on nano-size carbon black
is more accessible.
Carbon nanobeads that were prepared by the detonation of a TNT-RDX
explosive were functionalized with N-β-aminoethyl-γ-aminopropyltrimethoxysilane, and
then with carbon disulfide and phenylisothiocyanate to form ethylenediamine,
dithocarbamate, and thioureido-functional groups on their surface (An and Zeng, 2003).
These nanoadsorbents have diameters in the range of 4-8 nm. Their adsorption with
metal ions was strongly dependent on the pH and functional groups on the surface of the
adsorbent. Dithiocarbamate nanoadsorbents exhibited high affinities (> 90% removed)
with metal ions of Cu
2+
and Ag
+
at pH 3, Au
3+
, Pd
2+
, Pt
4+
, Co
2+
, and Ni
2+
below pH 4,
and Zn
2+
and Fe
3+
below pH 6. In most cases, more than 95% of metal ions were
removed in less than 10 minutes at an appropriate solution pH (An and Zeng, 2003).
Park et al. (2000) used carbon nanofibers (CNFs) synthesized from the
interaction of ethylene/hydrogen mixtures over Cu-Ni powdered catalysts for the
removal of alcohols from water. These CNFs have diameters in the range of 4.6-17.5
nm and surface areas of 60-257 m
2
/g. It was found that the CNFs referred to as 'platelet'
CNFs have higher affinities with ethanol, butanol, and pentanol than activated carbon,
even though the 'platelet' CNFs have a surface area that is almost an order of magnitude
smaller than that of activated carbon (Park et al., 2000).
It is expected that the huge potential of carbon nanotubes, fullerenes, and
nanoporous carbon can be employed for contaminant separation in the near future.
However, before being applied in the environment, several issues need to be solved.
First, the biggest current drawback for application of special carbon nanotubes is cost.
The price for carbon nanotubes is still too high, ranging from $2.50/g for MWNTs (85%
purity) to $1900/g for SWNTs (90% purity) (Nanolab). This high cost is related to the
low production throughput, as to date no large-scale manufacture of CNTs (defined as
10000 tons per plant per year) is operational (See and Harris, 2007). It is expected that a
powerful synthesis method will be developed to produce cheaper CNTs in the coming
years. Second, the toxicity and fate and transport of carbon nanotubes and fullerenes are
another shortcoming. A review related to fate and transport, uptake and ecotoxicity of
CNTs and C
60
was conducted (Nowack and Bucheli, 2007). Pristine fullerenes and
untreated CNTs are insoluble in water, but derivatized fullerenes and CNTs with
ionizable or hydrophilic groups exhibit much greater water solubility and interaction
with their host molecules. Unfortunately, CNTs and fullerenes were found to be ingested
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