Application of Zero-valent Iron Nanoparticles for Environmental Clean Up - Advanced Materials for Agriculture, Food and Environmental Safety - page 401

list of bimetallic iron nanoparticles which have been reported to exhibit a
high ei cacy for transformation of various chlorinated compounds, along
with their predominant degradation mechanism. Generally, two methods
are used for preparation of bimetallic nanoparticles. One method includes
consecutive reduction of the second metal ions and subsequent deposi-
tion onto i rst metal particle, i.e., iron. h is method leads to formation of
nanoparticles with core-shell structure. Another method involves simulta-
neous reduction of two metal ions, resulting in formation of alloy structure
nanoparticles [78, 79].
h e reason behind the enhanced reaction kinetics of bimetallic iron
nanoparticles may be attributed to the catalytic ef ect of the second metal,
which not only acts as catalyst but also enhances the surface area of
nanoparticles [80]. h e second metal also collects hydrogen gas produced
during the corrosion of iron and dissociates it into atomic hydrogen, which
is considered as a strong reductant for dehalogenation reactions [77].
Furthermore, the deposition of second metal creates many galvanic cells
on the surface of iron, which accelerates corrosion of iron and enhances
the kinetics of the redox reactions [81].
In bimetallic nanoparticles, the loading of second metal plays a cru-
cial role in determining the rate of reaction. He et al. [82] found that
the dechlorination ei ciency of nFe 0 /Pd for polychlorinated biphenyls
increases as the loading of second metal (Pd in this case) increases. Singh
et al. [35] also noticed a similar ef ect while studying dechlorination of
γ-HCH in the presence of stabilized nFe 0 /Pd. h e most likely explanation
for this enhanced rate is: (a) concomitant increase in the amount of hydro-
gen adsorbed on Pd surface with the increases in Pd content, which in
turn promotes the rate and extent of dechlorination, and (b) higher catalyst
loading increase in the total number of galvanic cells, increasing the rate
of iron corrosion, thus increasing degradation rate. However, beyond cer-
tain limits, the increase in Pd loading shows a declining ef ect on dechlo-
rination ei ciency. Wang et al. [38] suggested that the excessive amount of
Pd on nFe 0 hinders the formation of hydrogen by nFe 0 corrosion, thereby
reducing the dechlorination rate.
An important concern associated with the use of bimetallic nanopar-
ticles is the dislodgement of secondary metal with the corrosion of iron. As
the secondary metals are the reactive sites, this issue is a major setback in
the use of iron-based bimetallic nanoparticles for targeting contaminants.
In view of this, two regenerative approaches were investigated by Zhu
and Lim [83] for the recycling and reutilization of Pd/nFe 0 particles. One
approach utilized HCl and the other employed NaBH 4 for regeneration of
Pd. Pretreatment of aged nanoparticles with HCl served the purpose of