Environmental Engineering Reference
In-Depth Information
effective for the adsorptive removal of large molecules such as dyes and natural organic
matters (NOMs), which are difficult to eliminate with activated carbon.
10.4.1 Ordered Mesoporous Carbon
10.4.1.1 Adsorption Capacity
Ordered mesoporous carbons (OMCs) have exhibited excellent affinities for
macromolecule pollutants such as dyes and surfactants from aqueous solutions (Liu et al.,
2006; Yuan et al., 2007). To this end, Yuan et al. (2007) reported that the adsorption of
OMCs for methylene blue and neutral red were much higher than those of microporous
carbon. OMCs prepared from SBA-15 as a hard template exhibited a maximum
adsorption capacity of approximately 287 for methylene blue and 265 mg/g for neutral
red. This capacity is attributed to the pore system of OMCs, which is mainly composed
of mesopores that allow large dye molecules to diffuse easily into their pore structure.
The adsorption of methylene blue generally prefers larger mesopores and higher-pore-
volume materials, resulting in the multilayer adsorption of this compound onto OMCs.
In contrast to methylene blue, neutral red is preferably adsorbed into relatively narrower
mesopores (Yuan et al., 2007). In another study, mesoporous carbon CMK-3 prepared
using SBA-15 as the template was found to be an effective adsorbent to remove
nonylphenol ethoxylate (NPE) surfactant from aqueous solution (Liu et al., 2006). In this
case, NPE adsorption decreased when the temperature increased. At 15, 25, and 35
o
C,
the maximum amounts of NPE adsorbed onto CMK-3 were 923, 720, and 463 mg/g,
respectively.
The surface modification of OMCs can make them become more effective in the
removal of various contaminants, including cations or anions. For example, the
adsorption of arsenic (Gu and Deng, 2007a; Gu and Deng, 2007b; Gu et al., 2007) on
iron-containing OMC was investigated. At a initial arsenic concentration of 9.98 mg/L,
the removal percentage of As(V) (95%) and As(III) (80%) was optimum in the pH range
of 3.0-7.0 and 6.0-9.5, respectively (Gu et al., 2007), although the adsorption of both
As(V) and As(III) significantly decreased in the presence of anions (e.g. PO
4
3-
and
SiO
3
2-
) (Gu and Deng, 2007a). Jung et al. (2008) attempted to functionalize CMK-3 with
carboxymethylated polyethyleneimine (CMPEI) for uranium removal. Estimated with
the Langmuir model, the maximum adsorption capacity of uranium on CMPEI/CMK-3
was about 151.5 mg U/g, three times higher than that for PEI-coated silica.
10.4.1.2 Adsorption Isotherms and Kinetics
The adsorption isotherm of OMCs could be described by the Langmuir model for
the adsorption of arsenic and uranium (Gu and Deng, 2007b; Jung et al., 2008), the
Freundlich and Langmuir-Freundlich models for the adsorption of nitrobenzene,
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