Environmental Engineering Reference
In-Depth Information
Cr(VI) adsorption may derive from two aspects: (a) active sites for Cr adsorption were
varied with the change of the surface area by doping another kind of metal. From BET
surface area measurements, it was observed that the surface areas of Al-, Cu-, or Mg-
doped -Fe
2
O
3
nanoparticles were 191, 175, 183 m
2
/g, respectively, and they were
increased as compared to the pure -Fe
2
O
3
(162 m
2
/g). Thus, the increased surface active
sites after doping Al, Cu and Mg resulted in the enhanced adsorption; and (b) the other
parameters (e.g., crystallinity, lattice arrangement, etc.) may also affect the adsorption,
in addition to the surface area, because the surface area of Ni- or Zn-doped -Fe
2
O
3
was
similar to that of the pure -Fe
2
O
3
but the adsorption efficiency after doping these two
metals decreased. Having considered the superior performance of Al-doped -Fe
2
O
3
on
the Cr(VI) adsorption, this material was continually examined in the follow-up studies.
Although the Cr(VI) adsorption was varied favorably with doping Al but the magnetic
properties was changed unfavorably with doping Al, the optimal dosage of Al needed to
be determined in terms of the adsorption capacity, adsorption rate and nanoparticle
separation.
88
86
84
82
80
78
76
74
72
70
Blank
Al-
Ni-
Cu-
Zn-
Mg-
Metal-doped maghemite
Figure 9.34
Adsorption efficiency of Cr(VI) by various metal-doped -Fe
2
O
3
.
The Cr(VI) uptake by the Al-doped -Fe
2
O
3
nanoparticles containing Al mol%
from 0 to 13.1 as a function of contact time was studied under the optimal conditions
(pH 2.5, shaking rate of 200 rpm). It was found that the Cr(VI) adsorption onto various
Al-doped -Fe
2
O
3
could reach equilibrium within 2 h. As shown in Table 9.7, both the
adsorption efficiency and the required equilibrium time increase with an increase in the
Al dosage, which is perhaps due to the presence of the pores after doping Al. By
correlating the surface area shown in Table 9.8 with the adsorption efficiency listed in
Table 9.7, it is easy to observe that the surface area increases with an increase in Al
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