In-situ technologies for groundwater treatment: the case of arsenic - In-Situ Remediation of Arsenic-Contaminated Sites - page 16

Figure 1.5. Transmission electron microscopy (TEM) images of different iron nanoparticles manufactured
or purchased. (A) nZVI synthesized by reduction of aqueous Fe(II) with sodium borohydride (Wang and
Zhang, 1997); (B) nanoscale magnetite, purchased from Sigma-Aldrich; (C) NANOFER STAR, purchased
from NANO IRON, s.r.o.; (D) nZVI synthesized by the carbothermal reduction of aqueous Fe(II); (E) nZVI
synthesized by the reduction of aqueous Fe(II) using green tea polyphenols; and (F) nZVI synthesized by the
reduction of aqueous Fe(II) using sodium borohydride then annealed under vacuum (at least 10 − 6 mbar) at

500 ◦ C for 24 h (Crane and Scott, 2012).

takes place the process of aggregation, and the particles in the growing phase are surrounded by the
surfactant molecules (Colvin, 2003; Robinson et al ., 1989). In this way, the formation of particles
and their dimensions can be controlled in a simple way and without high costs (Colvin, 2003).
Another way to get lower size particles is by the use of ultrasound in the process of formation of
the nanoparticles, because this helps to their separation.
In recent years, there has been much investigation to produce nZVI at accessible prices whilst
maintaining reactivity and/or functionality. A method using hydrogen as a reducing agent for
iron oxide nanoparticles at 350-600 ◦ C was patented in 2006 (Uegami et al ., 2006). Another
material for large-scale field deployment of nZVI was produced by a company by the mechanical
attrition of macroscale Fe(0) in planetary ball mill systems (USEPA, 2010), although the method
is highly energy intensive and the particles exhibit a very high surface energy and are thus prone
to aggregation.
Transmission electron microscopy images of different iron nanoparticles manufactured or
purchased can be seen in Figure 1.5 (Crane and Scott, 2012).

1.6.3 Bimetallic nZVI particles
The chemical reactivity of nZVI can be improved by alloying them with a second metal such
as Pd, Pt, Ag, Ni or Cu. Some studies have been made recently in the preparation of Fe/Pt
(Zhang et al ., 1998), Fe/Ag (Xu and Zhang, 2000), Fe/Pd (Lien and Zhang, 2007), and Fe/Ni
(Barnes et al ., 2010). In these electrochemical couples, Fe(0) behaves as an anode, becoming
sacrificially oxidized to galvanically protect the second (nobler) metal. Chemical reduction of
sorbed contaminants at the bimetallic nZVI surface is believed to occur through either direct
electron transfer with the noble metal or through reaction with hydrogen produced by Fe(0)
oxidation. For the clean-up of chlorinated organic contaminants such as TCE or PCP, hydrogen is
observed to be the predominant driver for degradation, by breaking C-Cl bonds and swapping itself