Application of Zero-valent Iron Nanoparticles for Environmental Clean Up - Advanced Materials for Agriculture, Food and Environmental Safety - page 396

• Reaction temperature: As per literature, the rise in tem-

perature has an accelerating ef ect on the reaction process.
h is can be attributed to an increase in the mobility of target
molecules with the increase in temperature, which in turn
enhances the rate of reaction [35]

• Natural Organic Matter: h e natural organic matter such as

humic acid plays an important role in contaminant reduc-
tion by virtue of its functional groups such as quinones [70].
Humic acids have high binding ai nity towards Fe 2+ and Fe 3+
[71] and also have a strong tendency for adsorption on iron
oxides surfaces [20, 72]. h e adsorption of humic acid inhib-
its iron corrosion, thereby prolonging the lifetime of nano
Fe 0 . On the other hand, adsorbed humic acid also transfers
electron from inner Fe 0 to Fe 3+ to facilitate reduction reac-
tion. In addition, humic acid complexation with dissolved
iron released from corrosion can regenerate reactive Fe 2+
to reduce redox amenable species [73]. In contrast to the
enhancing ef ect of humic acid, Liu et al. [74] reported that
humic acid competes with the contaminants for the reac-
tive sites on nFe 0 surface and alters the reduction potential of
neighboring surface sites, thus decelerating the contaminant
reduction rate.

h ese are some of the factors which have been widely investigated in nFe 0
mediated remediation. Besides these, other factors which determine the reac-
tivity of nFe 0 include dissolved oxygen, hardness, oxidation-reduction poten-
tial, ionic strength of groundwater, aquifer's hydraulic properties, etc. [75].

14.2.4.2 Bimetallic Iron Nanoparticles: Improving the

Reactivity of nFe 0

h e urge for enhancement of reaction kinetics and improvement in metal
usage has lead to the synthesis of bimetallic nanoparticles. Iron-based
bimetallic nanoparticles consist of a base metal, i.e., Fe 0 , as the reductant,
and a second metal such as Pd, Cu, Ni or Pt as the catalyst. h ese bimetallic
nanoparticles have reaction rates that are orders of magnitude higher than
the corresponding monometallic nanoparticles [26, 35, 64, 76]. Catalytic
hydrodechlorination is considered as the main pathway of contaminant
degradation in the case of bimetallic iron nanoparticles. Studies have
shown that this pathway leads to formation of a lesser amount of toxic
chlorinated intermediates during reaction [31, 77]. Table 14.2 shows the