Environmental Engineering Reference
In-Depth Information
Many kinds of bimetallic nanoparticles (e.g, Pd/Au, Pd/Fe, Ni/Fe) have been
designed for groundwater remediation (Wang and Zhang, 1997; Schrick et al., 2002; Tee
et al., 2005; Nutt et al., 2005, 2006; Wu and Ritchie 2006). Bimetallic Pd/Au
nanoparticles consist of two catalytic metals while bimetallic iron-based nanoparticles
are composed of a catalytic metal (e.g., Pd, Ni) and an electron-donating metal (i.e.,
iron). Bimetallic Pd/Au nanoparticles have been shown a very high catalytic activity
toward chlorinated organic compounds. It has been reported that bimetallic Pd/Au
nanoparticles significantly increased the catalytic activity by a factor of 152245 as
compared to palladium nanoparticles, alumina-supported palladium and palladium black
(Nutt et al., 2005). A synergistic effect of the Pd-on-Au bimetallic structure has been
proposed (Nutt et al., 2005). However, the long-term application of bimetallic Pd/Au
nanoparticles for groundwater remediation may be limited because an extra supply of
hydrogen gas as an electron donor is necessary (Siantar et al., 1996).
Bimetallic iron nanoparticles (e.g., Pd/Fe, Ni/Fe) can be synthesized by chemical
reduction or co-reduction:
M
2+
+ Fe
0
M
0
+ Fe
2+
(M
2+
= e.g., Pd
2+
, Ni
2+
)
→
(Eq. 7.7)
Numerous studies have focused on bimetallic iron nanoparticles. In general, the
enhanced reactivity of bimetallic iron nanoparticles is attributed to: (a) catalytic effects
of second metals (e.g., Pd, Ni) through a direct hydrogen reduction (Li and Farrell, 2000;
Schrick
et al.
, 2002); (b) a galvanic corrosion leading to the increase of corrosion rates
(Zhang
et al.
, 1998; Liou et al., 2005); and (c) the prevention of an oxide formation at
the iron surface (Schrick
et al.
, 2002).
Bimetallic Pd/Fe nanoparticles provide many specific features, including a small
particle size (1100 nm in diameter), high specific surface areas (~35 m
2
/g), and a
bimetallic structure with catalytic functionality. Based on these characteristics, they have
been demonstrated to have many advantages in the treatment of chlorinated organic
contaminants, including: (a) a high surface reactivity. The surface-area normalized rate
coefficients (
k
SA
) for the transformation of chlorinated ethylenes were 5.8429 times
higher than those of commercial grade iron particles (Lien and Zhang, 2001); (b)
complete dechlorination reactions with the elimination of toxic intermediates (Lien and
Zhang, 1999, 2001); and (c) durable and stable performance that have been confirmed
from field tests (Elliott and Zhang, 2001; Zhang, 2003).
Bimetallic Ni/Fe nanoparticles (Ni:Fe = 1:3) synthesized by co-reduction of
mixed Fe(II) and Ni(II) solution using sodium borohydride have a particle size in the
Search WWH ::
Custom Search