Environmental Engineering Reference
In-Depth Information
nitrophenol and chlorophenol (Marczewski, 2007) or the Langmuir and Langmuir-
Freundlich models for the adsorption of NPE (Liu et al., 2006). In particular, it should be
noted that the adsorption model of NPE onto CMK-3 changes from the Langmuir-
Freundlich model to the Langmuir model when the adsorption temperature increases
from 15 to 35
o
C.
The adsorption kinetics of contaminants on mesoporous carbon was discovered
to obey the pseudo-second-order kinetic model. All adsorption of dyes (i.e., methylene
blue and neutral red) (Yuan et al., 2007), nonylphenol ethoxylate (Liu et al., 2006),
nitrobenzene, 4-nitrophenol, 4-chlorophenol (Marczewski, 2007), and arsenic (Gu and
Deng, 2007b) onto mesoporous carbon follow this model.
10.4.1.3 Effect of Surface Chemistry
Mesoporous carbon can be prepared from many different starting materials and
using different methods. As such, the characteristics of mesoporous carbon depend
strongly on the kinds of starting materials used. It is reported that the oxygen element on
OMCs decreases as the temperature increases, and that the polyaromatic order of the
outer surface and the mesopore surface of the OMC materials increases during heat-
treatment (Darmstadt et al., 2002). In agreement with this result, Kim et al. (2005)
confirmed that the material changes to more aromatic and finally condenses to aromatic
rings at temperatures above 550
o
C. In addition, the surface functional groups of the
OMC materials decrease with increasing temperature, in which the amount of acidic
groups on the surface is higher than that of the basic groups. Accordingly, the pH of the
surface is quite low (less than 5); however, this value increases slightly with an increase
in temperature. Influenced by the surface chemistry, the adsorption of methyl mercaptan
onto three ordered mesoporous carbon materials showed different capacities (Kim et al.,
2005). For instance, the physical adsorption of methyl mercaptan in micropores over 850
o
C-OMC and 1100
o
C-OMC is more contributable to the adsorption capacity of methyl
mercaptan, compared to that for 600
o
C-OMC.
10.4.2 Mesoporous Activated Carbon
10.4.2.1 Silica Sol Mediated Carbon (SMC)
Hyeon and co-workers synthesized mesoporous carbons by using silica sol
particles as templates, and then employed them for the adsorption of bulky dyes and
humic acids (Han et al., 2000; Han et al., 2003). These mesoporous carbons possessed
pore sizes in the range of 10-100 nm, a high pore volume of greater than 4 cm
3
/g, and a
high surface area of more than 1000 m
2
/g. The adsorption capacity of SMCs for humic
acids and dyes was 16 times and 10 times higher than that of commercial activated
carbon, respectively. Moreover, the adsorption rate of humic acids on SMC was faster
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