Environmental Engineering Reference
In-Depth Information
(a)
(b)
(c)
100
Fe/Pd colloid NPs
ZVI NP-containing nanofibrous mats
Fe/Pd NP-containing nanofibrous mats
100
120
80
80
ZVI NP-containing nanofibrous mats
Colloidal Fe/Pd nanoparticles
Fe/Pd NP-containing nanofibrous mats
Pd NP-containing nanofibrous mats
100
60
60
80
60
40
40
40
20
20
20
0
0
0
0
1
2
Reaction time (h)
3
4
10 20
TCE inital concentration (mg/l)
50
100
1
2
3
4
Reaction cycle number
figure 6.9 (a) remaining fraction of TCE as a function of time after treatment with Fe/Pd colloid NPs, ZVI NP-containing fibrous mats,
and Fe/Pd NP-containing nanofibrous mats. C 0 and C represent the initial and final concentration of TCE, respectively. The initial concentration
of TCE was 10 mg/l. (b) removal efficiency of TCE by Fe/Pd colloid NPs and ZVI NP- and Fe/Pd NP-containing nanofibrous mats with
different initial TCE concentrations. The reaction time was 1.5 h. (c) removal efficiency of TCE after treatment with the same Fe/Pd
NP-containing nanofibrous mats for the first, second, third, and fourth time. The reaction time was 1.5 h and the initial TCE concentration was
10 mg/l. reprinted with permission ref. [69], pp. 349-356. © 2012, Elsevier.
degradation of TCE. during the first 30 min, the degradation process reached a dynamic equilibrium, and the remaining fraction
of TCE treated with ZVI NP-immobilized nanofibrous mats with and without MWCNTs was estimated to be 0.034 and 0.086,
respectively. It should be noted that the major advantage of the MWCNTs within the nanofibers is to improve the mechanical
durability of the nanofibers. The presence of MWCNTs does not compromise the excellent capability of the immobilized ZVI
NPs to dechlorinate TCE. Moreover, it may be helpful to concentrate the hydrophobic chlorinated organic contaminants for
efficient remediation.
In another study, we investigated the feasibility of using bimetallic Fe/Pd NP-immobilized PAA/PVA electrospun nanofi-
bers to dechlorinate TCE [69]. Freshly synthesized Fe/Pd colloidal NPs and single-metal ZVI NP- and Pd NP-immobilized
nanofibrous mats were used as controls. As shown in Figure 6.9a, except Pd NP-immobilized nanofibrous mats, the other
three materials were able to degrade TCE, indicating that immobilized Pd NPs do not contribute to the dechlorination effect
of TCE. The slightly decreased remaining fraction of TCE may be ascribed to the adsorption of TCE onto the polymer nano-
fibers with a high specific surface area. It is noticeable that the remaining fraction of TCE treated with Fe/Pd colloid NPs and
ZVI NP- and Fe/Pd NP-immobilized nanofibrous mats were quite close at the initial TCE concentration of 10 mg/l. In order
to further investigate the enhanced dechlorination ability of Fe/Pd NP-immobilized nanofibrous mats, the initial TCE
concentration was increased to 20, 50, and 100 mg/l, respectively. It is clear that in all the cases, the efficiency of TCE dechlo-
rination using Fe/Pd NP-containing nanofibrous mats is above 90.6% (Figure  6.9b), much higher than that using ZVI
NP-containing nanofibrous mats and the Fe/Pd colloid NPs. reusability and recyclability assessment results showed that after
exposure to sodium borohydride aqueous solution for 10 min, nanofibrous mats can be regenerated. The regenerated Fe/Pd
NP-containing nanofibrous mats exhibited similar performance in the second, third, and fourth round of TCE dechlorination,
comparable to that of freshly prepared mats (Figure 6.9c).
6.5.4
environmental catalysis
The generated hybrid metal NP-containing polymer nanofibers can be used as an efficient catalyst to remediate heavy metal
ions. In our recent report, catalytic active Pd NP-immobilized electrospun PEI/PVA nanofibrous mats were fabricated for
catalytic transformation of hexavalent chromium (Cr(VI)) to trivalent Cr (Cr(III)) [72]. It is known that Cr(VI) has acute muta-
genicity and carcinogenicity, while Cr(III) is far less toxic. In the presence of formic acid used as a reducing agent, a piece of
Pd NP-immobilized PEI/PVA nanofibrous mat was immersed in a K 2 Cr 2 o 7 solution as a catalyst. Meanwhile, in order to eval-
uate the reusability of this catalyst, more reaction cycles were performed using the same mat. As shown in Figure 6.10, the
intensity of the characteristic absorption peak at 350 nm for Cr 2 o 7 2− decreased with time. At 12 min, the absorption peak com-
pletely vanished, indicating the complete transformation of Cr(VI). by comparison, in the presence of PEI/PVA nanofibrous
mats without Pd NPs (control group), the characteristic peak at 350 nm did not change considerably (Figure 6.10b). In addition, the
Cr(VI) solution treated by formic acid without any catalysts did not show any significant change in the absorption peak at 350 nm
within 25 min (Figure  6.10c). These results demonstrate that the excellent catalytic transformation of Cr(VI) to Cr(III) can
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