Bimetallic Nanoparticles - Nanotechnologies for Water Environment Applications - page 159

CHAPTER 7
Bimetallic Nanoparticles
Hsing-Lung Lien
7.1 Introduction
The majority of elements are zero-valent metals that can be divided into three
categories: reactive metals (i.e., alkali and alkaline earth metals), transition metals, and
non-reactive metals (i.e., noble metals), based on their electron-donating ability.
Reactive metals such as sodium and lithium usually have very high reduction potentials
that serve as strong reducing agents (Table 7.1). However, due to their high reactivity
toward water and many other substances, applications of these metals are limited in
environmental remediation. On the other hand, both transition and noble metals are of
great interesting in environmental applications. As shown in Table 7.1, transition metals
such as iron have mild reduction reactions that lead transition metals themselves good
remedial reagents for long-term treatments. For noble metals such as palladium and
silver, they have long been known as catalysts in chemical engineering and have
received great attention in environmental remediation.
Since early 1990s, the rediscovery of zero-valent iron (ZVI) for the
transformation of chlorinated organic compounds has led to the development and
proliferation of a number of environmental applications, particularly in so far as
groundwater remediation is concerned (Gillham and Burris, 1992; Gillham and
O'Hannesin, 1992, 1994). Implementation of full or pilot scale in situ permeable
reactive barriers (PRBs) has been demonstrated as a promising environmental remedial
technology for remediation of groundwater contaminated with various contaminants
(Puls et al., 1998, 1999; Wilkin et al., 2003). PRBs involve the placement or formation
of a reactive treatment zone in the path of a contaminant plume, in which groundwater
passively moves while contaminants precipitate, adsorb or degrade. Reactive media that
can be applied to treatment zones include ZVI (Matheson and Tratnyek, 1994; Burris, et
al., 1998; Su and Puls, 1999; Dries, et al., 2005), other zero-valent metals (e.g., Zn, Al)
(Schreier and Reinhard, 1994; Boronina et al., 1995; Roberts et al., 1996; Arnold and
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