Environmental Engineering Reference
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confirms the strong potential of oxidized MWNTs for remediation of heavy metal ions
from industrial wastewater (Chen and Wang, 2006).
Recently, Hyung et al. (2007) investigated the aqueous stability of MWNTs in
the presence of natural organic matter (NOM). MWNTs were readily dispersed as an
aqueous suspension in both model NOM (Suwannee River NOM (SR-NOM)) solutions
and natural surface water (actual Suwannee River water with unaltered NOM
background), and remained stable for over 1 month. Microscopic analyses suggested that
the suspension consisted primarily of individually dispersed MWNTs. Concentrations of
MWNTs suspended in the aqueous phase, quantified using thermal optical transmittance
analysis (TOT), ranged from 0.6 to 6.9 mg/L as initial concentrations of MWNTs and
SR-NOM were varied from 50 to 500 mg/L and 10 to 100 mg/L, respectively. Suwannee
River water showed a similar MWNT stabilizing capacity as compared to the model SR-
NOM solutions. For the same initial MWNT concentrations, the concentrations of
suspended MWNTs in SR-NOM solutions and Suwannee River water were considerably
higher than that in a solution of 1% sodium dodecyl sulfate, a commonly used surfactant
to stabilize CNTs in the aqueous phase. These findings suggest that dispersal of carbon-
based nanomaterials in the natural, aqueous environment might occur to an unexpected
extent following a mechanism that has not been previously considered in environmental
fate and transport studies (Hyung et al., 2007).
Pyrzynska et al. (2007) investigated CNT and graphitized carbon as adsorbents
for solid phase extraction of dicamba and 2,4,5-T, two phenoxyalkanoic acid herbicides.
These adsorbents have much greater adsorption capability than that of C-18 bonded
silica, which was also tested for comparison studies. The adsorption capacity increases
remarkably at lower pH of the sample solution. Freundlich isotherms were applied to
analyze the data. These studies suggest that carbon nanotubes have great application
potential in environmental analysis (Pyrzynska et al., 2007). Wang et al. (2005) reported
radionuclide 243Am(III) sorption to uncapped MWNTs under the influence of different
243Am(III) solution concentrations, ionic strengths, and pHs. The sorption was found to
be strongly dependent on pH values and weakly dependent on the ionic strength in the
experimental conditions. The results showed that MWNTs can adsorb 243Am(III) with
extraordinarily high efficiency by forming very stable complexes. Chemisorption or
chemicomplexation were predicted to be the main mechanism of 243Am(III) sorption on
the surface of MWNTs. This clearly signifies the great potential of using MWNTs for
remediation of its analogue lanthanides and actinides from industry wastewater (Wang et
al., 2005).
Yang et al. (2006) for the first time studied adsorption of polycyclic aromatic
hydrocarbons (PAHs), such as naphthalene, phenanthrene, and pyrene, onto different
carbon nanomaterials, including fullerenes, SWNTs, and MWNTs. All adsorption
isotherms were nonlinear and were fitted well by the Polanyi-Manes model (PMM).
Through both isotherm modeling and constructing "characteristic curve," Polanyi theory
was useful to describe the adsorption process of PAHs by the carbon nanomaterials. The
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