Civil Engineering Reference
In-Depth Information
than offset by a lowering of the energy because of the absence of dangling
bonds at the edges of the graphene sheets. Such cylindrical carbon mole-
cules have novel properties that make them potentially useful in a wide
variety of applications in water and health care.
The as-grown or acidifi ed CNTs have shown potential as a sorbing media
for removal of various contaminants from water. The as-grown CNTs have
got defect sites (originated during synthesis), which make them a suitable
adsorbent for uptake of contaminants. However, it is noteworthy that such
CNTs do not pose any selectivity towards uptake of specifi c contaminants.
On the other hand, the surface area of as-grown CNTs lies in the range of
50-100 m 2 /g, which is not signifi cant in comparison to activated charcoal or
activated alumina (where the surface area is up to 1000 m 2 /g), which are
being extensively used in water decontamination because of being cheaper
and having easy availability. However, some of the work carried out by
researchers using as-grown and functionalized CNTs are cited below.
Peng et al. (2005) developed a novel adsorbent, ceria supported on CNTs
(CeO 2 -CNTs), for the removal of arsenate from water. Under natural pH
conditions, an increase from 0 to 10 mg/L in the concentration of Ca (II)
and Mg (II) results in an increase from 10 to 81.9 and 78.8 mg/g in the
amount of As (V) adsorbed, respectively. The adsorption was shown to be
pH-dependent. The effi cient regeneration of the loaded adsorbent was
carried out and the adsorption mechanism was suggested.
Y. H. Li et al. (2003a) used aligned carbon nanotubes (ACNTs) for the
removal of fl uoride from water. The adsorption slightly depends on the
solution pH value. The highest adsorption capacity of ACNTs occurs at pH
7 and reaches 4.5 mg/g at equilibrium fl uoride concentration of 15 mg/L.
Y. H. Li et al. (2003b) studied the removal of cadmium (II) with as-grown
and surface-oxidized CNTs. Cadmium (II) adsorption capacities for three
kinds of oxidized CNTs increase owing to the functional groups introduced
by oxidation compared with the as-grown CNTs. The cadmium (II) adsorp-
tion capacity of the as-grown CNTs is only 1.1 mg/g, while it reaches 2.6,
5.1 and 11.0 mg/g for the H 2 O 2 -, HNO 3 - and KMnO 4 -oxidized CNTs, respec-
tively, at the cadmium (II) equilibrium concentration of 4 mg/L. Adsorption
of cadmium (II) by CNTs was strongly pH-dependent and the increase of
adsorption capacities for HNO 3 - and KMnO 4 -oxidized CNTs is more
obvious than that of the as-grown and H 2 O 2 -oxidized CNTs at lower pH
regions. Analysis revealed that the KMnO 4 -oxidized CNTs hosted manga-
nese residuals, and these surely contributed to cadmium sorption to a yet-
undefi ned extent.
Li et al. (2002) found that CNTs show exceptional adsorption capability
and high adsorption effi ciency for lead removal from water. The adsorption
is signifi cantly infl uenced by the pH value of the solution and the nanotube
surface status, which can be controlled by their treatment processing. The
￿ ￿ ￿ ￿ ￿ ￿
Search WWH ::




Custom Search