Nanoscale Carbon Materials for Contaminant Separation - Nanotechnologies for Water Environment Applications - page 273

difficult than that for the silica templates. One more interesting result pertaining to the
nanocasting method is that mesoporous carbon in turn can be used as a hard template for
the synthesis of an oxide.
The synthesis of OMCs using the nanocasting pathway can be performed based
on various silica molds, such as MCM-48, SBA-15, SBA-1, HMS, FDU-5, FDU-12,
SBA-16, and KIT-6 (Song et al., 2006). Moreover, diverse carbonaceous precursors can
be employed, including sucrose, phenol resin, furfuryl alcohol, acetylene, acrylonitricle,
pyrrole, benzene, acenaphthene, and poly(vinyl chloride) (Song et al., 2006). As such,
OMCs with diverse textures and morphology can be produced, for example: CMK-1
prepared by using MCM-48 and sucrose (Ryoo et al., 1999), CMK-3 produced by
employing SBA-15 and sucrose (Jun et al., 2000), and CMK-5 formed based on SBA-15
and furfuryl alcohol (Joo et al., 2001).
10.1.3.2 Mesoporous Activated Carbon
There are various ways to form mesoporous carbon with a disordered pore
structure referred to as mesoporous activated carbon (MAC). However, the most
common way involves a carbonaceous starting material being carbonized under a
nitrogen atmosphere at about 450 o C, then chemically treated with an acid or base or
mixed with a chemical compound such as salt or metal complex. Finally, the samples are
activated at a high temperature (800-1000 o C) under nitrogen or steam. Typically,
Yasuda and his co-workers synthesized MAC materials using the steam invigoration of
pitches mixed with a 1-3% proportion of rare-earth metal complexes (Tamai et al.,
1997). The resulting mesoporous carbons had high mesopore ratios of up to 80% and
pore sizes ranging from 20-50 nm. In another study, Gryglewicz et al. used the approach
in which sub-bituminous and high-volatile bituminous coal were exchanged with Ca and
Fe or impregnated with titanium oxide acetylacetonate, followed by carbonization and
activation with steam to produce mesoporous carbons with mesopore ratios ranging from
53.4 - 82.1% (Lorenc-Grabowska and Gryglewicz, 2007a).
Another approach was developed by Hyeon et al. using silica sol nanoparticles as
templates (Han and Hyeon, 1999a). The polymerization of resorcinol and formaldehyde
in the presence of a silica sol solution (Ludox HS-40 silica sol solution with an average
particle size of ca. 12 nm) was performed to produce resorcinol-formaldehyde (RF)
gel/silica nanocomposites. After carbonization to form a carbon phase, HF (hydrofluoric
acid) etching was used to remove the silica templates (see Figure 10.4). A nanoporous
carbon was obtained with a high surface area of about 1000 m 2 /g, pore volumes of 4
cm 3 /g, and the pore size predominantly ranging from 10 to 100 nm. To prevent
aggregation of the silica nanoparticles, surfactant-stabilized silica nanoparticles were
used as the template (Han and Hyeon, 1999b), resulting in a mesoporous carbon with a
narrow pore size distribution centered at 12 nm.