Environmental Engineering Reference
In-Depth Information
can be attributed to an increase in the number of the adsorption sites as well as the
endothermic nature of this specific adsorption (Lin and Teng, 2002).
Though activated carbon is an excellent adsorbent for various contaminants,
ordered mesoporous carbon has been developed due to its advantages. Creating
uniformity within the pore size, shape and volume has steadily increased over recent
years because it can lead to superior application properties. For example, a material
with uniform micropores, such as zeolites, can separate molecules on the basis of their
size by selectively removing a small molecule from a mixture containing molecules too
large to enter its pores (Davis, 2002). Ordered mesoporous carbon has been actively
investigated for its potential applications as catalyst supports, electrochemical materials
and gas separation media. Recently, its application in the field of environmental
engineering has been realized. Iron-modified ordered mesoporous carbon was prepared
by in-situ polymerization of acrylic acid in a template, followed by carbonization and
template and final iron impregnation (Gu and Deng, 2007). This novel type of
adsorbents was used to adsorb different contaminant including arsenic from the aqueous
phase. Batch experiments showed that the pH level of the solution had a major impact
on arsenic sorption. It was also found that the presence of anions (i.e., PO
4
3-
and SiO
3
2-
)
could significantly decrease the sorption of both arsenate and arsenite. Arsenite
oxidation to arsenate was observed in alkaline solutions, with or without anions being
present. The oxidation of arsenite was attributed to both direct and catalytic reactions
with the surface functional groups on the ordered mesoporous carbon (Gu and Deng,
2007).
11.2.2.2 Buckminster Fullerenes
Fullerenes C
60
/C
70
(buckyballs) have been of great interest to scientists in many
different areas since their first discovery (Kroto et al., 1985). It is a typical allotrope of
carbon uniquely closed to form ball like structure having a size of ~1 nm diameter. A
typical SEM and HRTEM image of fullerene is shown in Figure 11.12. It has been of
tremendous interest due to its very good catalytic and sorption properties. Though the
pore within itself doesn't exist in its pristine state (unless functionalized by breaking the
wall), it has been categorized here as nanoporous materials considering its bulk
structure. Due to strong van der Waals force combined with its
interaction, these
materials always remain as highly aggregated state, making them an unique type of
porous carbon with very large surface area. Moreover, once these materials are
functionalized, C=C of the carbon cage gets break down and making again precisely
controlled porous cage. For example a carbon derivatives based on these fullerene have
found to have (a) a super high BET surface area of 3142 m
2
/g; (b) a high micropore
(pores < 2 nm) volume of 0.92 cm
3
/g; (c) a very narrow pore size distribution with pores
predominantly in the range of 0.4-3 nm; and (d) an ultra-high carbon purity of near
100% (Loutfy et al., 2002). Similarly, hollow porous carbon nanospheres with a large
π−π
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