Environmental Engineering Reference
In-Depth Information
used for the dechlorination of TCE and polychlorinated biphenyls. The starch-modified
nanoparticles showed less agglomeration and were present as discrete particles as
opposed to dendritic flocs for unmodified particles. The starch-modified nanoparticles
remained suspended in water after 24 h, and only partial precipitation was observed after
48 h. In contrast, the bare nanoparticles agglomerated and precipitated within a few
minutes. Starch is a branched, hydrophilic polymer containing ~20% amylase units. It
was hypothesized that iron-starch interactions and formation of intra-starch iron clusters
played a fundamental role in nanoparticle dispersion and stabilization. A significant
improvement in the reactivity of the starch-modified Pd-Fe nanoparticles towards TCE
and polychlorinated biphenyls (PCB) was observed. The researchers reported a 37-fold
increase in the surface area normalized reaction rate (k
SA
) for TCE degradation using
starch-modified Fe-Pd nanoparticles as compared to bare particles.
Gu et al. (2005) examined a method to produce monodispersed submicron-sized
polymer coated Fe
2
O
3
particles referred to as “magnetic polymer particles.” They
conducted soap-free emulsion polymerization, during which Fe
2
O
3
nanoparticles were
heterocoagulated onto precipitated polymer nuclei and fixed to the nuclei through the
introduction of vinyl groups on the Fe
2
O
3
surface. To chemically fix the nanoparticles to
the polymer, a vinyl group was introduced into the primary surface modification reaction
with methacryloxypropyltrimethoxysilane (MPTMS) and
methacryloxypropyldimethoxysilane (MPDMS). The colloidal stability of the polymer
coated particles was improved by adding the ionic monomer, sodium p-styrenesulfonate
(NaSS), during polymerization. The researchers concluded that the addition of the ionic
surfactant to the soap-free emulsion polymerization might have improved the surface
potential and raised the dispersion stability of the polymer coated Fe
2
O
3
particles.
Further, it was observed that the NaSS addition changed the zeta-potential, and
consequently, raised the stability of the particles.
Jun et al. (2005) coated magnetite nanocrystals (4-12 nm) with a multifunctional
ligand system to provide high stability of the particles. The ligand, 2,3-
dimercaptosuccinic acid (DMSA), was used for the synthesis of the coated nanocrystals.
They found that the DMSA coated Fe
2
O
3
nanocrystals were fairly well dispersed in
aqueous media. DMSA forms a stable coating on the Fe
2
O
3
surface by chelation
through a carboxylic acid group. Further stabilization was achieved through
intermolecular disulfide cross-linking (Jun et al., 2005).
Ponder et al. (2000) synthesized supported Fe-nanoparticles using polymeric
resin, silica gel or sand as a support material. They studied the rates of remediation of
Cr(VI) and Pb(II) using both the modified and unmodified nZVI. Their modified
particles showed high reactivity for a longer time compared to unmodified nZVI.
Colloidal stability of the modified nZVI was not reported.
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