Environmental Engineering Reference
In-Depth Information
expected for treating large quantities of water, the size below about 0.3 mm causes opera-
tional problems [25]. In adsorption-based puriication of water, adsorbents in powder
form, especially in nanoscale, have several practical limitations: (i) low hydraulic conduc-
tivity in packed bed, (ii) dificulty in solid-liquid separation, and (iii) risk of leaching of
the NPs along with treated water [12]. Besides, the presence of coexisting ions in water can
cause ion-induced aggregation of NPs and thereby reduce the reactivity. These limitations
might be overcome by anchoring the NPs on suitable matrices. Anchoring can be done in
situ or ex situ on natural or synthetic templates. A few examples in this direction are being
reviewed.
19.4.2.1 Natural Polymers as Support Matrix
Natural cellulose ibers are gaining interest as templates because of their nanoporous sur-
face features, low cost, and environment friendly nature. They have been used as a sub-
strate for the in situ synthesis of metal and metal oxide NPs [12,102,103]. An example is
shown in Figure 19.5. These kinds of composites are also interesting as adsorbent media
for puriication of water owing to potential synergistic properties that may arise from the
combination of materials such as the inherent properties of the ibers, in particular lex-
ibility and strength, and also the high adsorption properties of the surface-loaded NPs.
However, the possible reduction in the adsorption capacity, due to blockage of adsorption
sites by the interactions between the supporting media and the biopolymer, cannot be
ruled out completely.
Recently, Yu et al. [104] have synthesized nanoscale hydroxyapatite supported on cel-
lulose ibers. The nanocomposites (cellulose@hydroxyapatite) were prepared by mixing
NaOH/thiourea/urea/H 2 O (8:6.5:8:77.5 by weight) solution with cellulose. The composites
were tested for their ability to remove luoride from water. The adsorbent was found to be
capable of removing luoride to a level below the World Health Organization-prescribed
c3
12k
c1
a
b
10k
8k
c4
c2
Mn
O
6k
4k
Mn
Mn
2k
9/7/2009
12:39:02 PM
HV
5.00 kV
spot
3.0
mag
det
LV D
WD
5.7 mm
HFW
tilt
0
5 µm
37.3 µm
8000×
Mn
0.90
1.80
2.70
3.60
4.50
5.40
6.30
7.20
KeV
FIGURE 19.5
(a) Energy-dispersive x-ray spectrum of manganese oxide-impregnated cellulose ibers. (b) Field emission
SEM (FESEM) micrographs of 4.64% Mn-loaded cellulose ibers. Inset of panel b shows FESEM micrographs of
pristine cellulose. Photographs of manganese oxide-impregnated cellulose ibers at various manganese oxide
loading: (c1) 0% Mn, (c2) 0.39% Mn, (c3) 0.66% Mn, and (c4) 3.7% Mn. (From S.M. Maliyekkal, K.P. Lisha, and
T. Pradeep, J. Hazard. Mater. , 181, 986, 2010.)
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