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B. Gunawardana et al.
the total area of Ni/Fe metal surface. Hence, the reactivity of Ni/Fe bimetal for CP
dechlorination could be assessed only based on the observed dechlorination reaction
rates.
It was anticipated that the use of Ni as a catalyst would result in enhanced CPs
dechlorination by Ni/Fe bimetal. However, the use of Ni/Fe bimetal resulted in
only partial dechlorination of CPs tested. Partial dechlorination of CPs observed
with Ni/Fe could be a result of the formation of a permanent Ni coating as a
thin film on the ZVI surface during Ni/Fe preparation, which could cover the
ZVI reactive sites thus restricting the electron and CP molecules transfer process
for effective dechlorination. These aspects are discussed under Sect. 12.3.2-Ni/Fe
characterization.
12.3.2 Characterization of ZVI and Ni/Fe Material
The analysis of specific surface area of various materials showed that the specific
surface area of unmodified ZVI, acid pre-treated ZVI, and Ni/Fe were 0.212 ± 0.002,
0.910 ± 0.003, 2.696 ± 0.011 m
2 /g, respectively. An increase in the ZVI surface
area after each modification indicates the possibility of variations and changes of the
composition or morphology between the materials after respective modifications,
which could have influenced the CP dechlorination potential (Cwiertny et al. 2007).
The surface morphology and elemental distribution on the ZVI, Ni/Fe surfaces
and the presence and distribution of Ni on the bimetal particles were obtained using
the ESEM-EDS analysis (Fig. 12.2). The EDS analysis showed Fe, O, and C as the
main elements on the unmodified and acid pre-treated ZVI surfaces (Fig. 12.2a, b).
The EDS scans done in many small regions on the surface of the Ni/Fe bimetallic
particles did not show any evidence of scattered deposition of Ni over the ZVI surfaces. An example of an EDS scans done on small areas on the Ni/Fe particles are
shown in Fig. 12.2c [Fig. 12.2c; (i), (ii), and (iii) areas marked in red)]. However, the
EDS scans done on a wide area on the Ni/Fe surface demonstrated the presence of
deposited Ni [Fig. 12.2c (iv) area marked in red]. Prior to using for the preparation of
Ni/Fe bimetallic particles, the acid-washed ZVI surface was initially mainly covered
with magnetite. Due to magnetite’s high conductivity, Ni
0 could be rapidly deposited
as a thin layer on the surface of the acid pre-treated ZVI particles during the synthesis of Ni/Fe. The assumption underlying this hypothesis is that due to the high
conductivity of magnetite, the reduction of Ni
2+ to Ni
0 occurs instantaneously and
rapidly on a magnetite surface. Accordingly, based on the observations of this study,
we hypothesize that during the Ni/Fe synthesis and reductive Ni deposition process
(Fe
0
+ Ni
2+
→ Ni
0
+ Fe
2+ ), Ni has deposited on the ZVI, not as clusters/scattered
deposition of Ni particles scattered/dispersed in parts of the ZVI surface but as a thin
Ni film over the ZVI surface. A schematic diagram illustrating the behaviour of the
ZVI and oxide phases during the acid washing and Ni/Fe preparation is presented as
Fig. 12.3.
B. Gunawardana et al.
the total area of Ni/Fe metal surface. Hence, the reactivity of Ni/Fe bimetal for CP
dechlorination could be assessed only based on the observed dechlorination reaction
rates.
It was anticipated that the use of Ni as a catalyst would result in enhanced CPs
dechlorination by Ni/Fe bimetal. However, the use of Ni/Fe bimetal resulted in
only partial dechlorination of CPs tested. Partial dechlorination of CPs observed
with Ni/Fe could be a result of the formation of a permanent Ni coating as a
thin film on the ZVI surface during Ni/Fe preparation, which could cover the
ZVI reactive sites thus restricting the electron and CP molecules transfer process
for effective dechlorination. These aspects are discussed under Sect. 12.3.2-Ni/Fe
characterization.
12.3.2 Characterization of ZVI and Ni/Fe Material
The analysis of specific surface area of various materials showed that the specific
surface area of unmodified ZVI, acid pre-treated ZVI, and Ni/Fe were 0.212 ± 0.002,
0.910 ± 0.003, 2.696 ± 0.011 m
2 /g, respectively. An increase in the ZVI surface
area after each modification indicates the possibility of variations and changes of the
composition or morphology between the materials after respective modifications,
which could have influenced the CP dechlorination potential (Cwiertny et al. 2007).
The surface morphology and elemental distribution on the ZVI, Ni/Fe surfaces
and the presence and distribution of Ni on the bimetal particles were obtained using
the ESEM-EDS analysis (Fig. 12.2). The EDS analysis showed Fe, O, and C as the
main elements on the unmodified and acid pre-treated ZVI surfaces (Fig. 12.2a, b).
The EDS scans done in many small regions on the surface of the Ni/Fe bimetallic
particles did not show any evidence of scattered deposition of Ni over the ZVI surfaces. An example of an EDS scans done on small areas on the Ni/Fe particles are
shown in Fig. 12.2c [Fig. 12.2c; (i), (ii), and (iii) areas marked in red)]. However, the
EDS scans done on a wide area on the Ni/Fe surface demonstrated the presence of
deposited Ni [Fig. 12.2c (iv) area marked in red]. Prior to using for the preparation of
Ni/Fe bimetallic particles, the acid-washed ZVI surface was initially mainly covered
with magnetite. Due to magnetite’s high conductivity, Ni
0 could be rapidly deposited
as a thin layer on the surface of the acid pre-treated ZVI particles during the synthesis of Ni/Fe. The assumption underlying this hypothesis is that due to the high
conductivity of magnetite, the reduction of Ni
2+ to Ni
0 occurs instantaneously and
rapidly on a magnetite surface. Accordingly, based on the observations of this study,
we hypothesize that during the Ni/Fe synthesis and reductive Ni deposition process
(Fe
0
+ Ni
2+
→ Ni
0
+ Fe
2+ ), Ni has deposited on the ZVI, not as clusters/scattered
deposition of Ni particles scattered/dispersed in parts of the ZVI surface but as a thin
Ni film over the ZVI surface. A schematic diagram illustrating the behaviour of the
ZVI and oxide phases during the acid washing and Ni/Fe preparation is presented as
Fig. 12.3.