Environmental Engineering Reference
In-Depth Information
APTES can be directly silanized onto magnetic particles from water or
toluene solutions and the process is characterized by XPS, IR, and zeta-poten-
tial measurements. APTES films formed on bare magnetic particles from
toluene are relatively stable in acid solution compared to the films formed
from water. Both films are unstable in alkaline solution.
Silica coatings on magnetic particles were achieved by both sol-gel and DLS
process. A uniform but porous silica layer was coated on magnetic particles by
sol-gel process. At low supersaturation level, non-uniform silica coatings were
formed by DLS process. A dense thin silica layer was coated on magnetic particles
by a novel two-step process, i.e., sol-gel followed by DLS coating. The chemical
stability of the two-step silica-coated magnetic particles was increased.
Mesoporous silica coating by a combination of DLS coating and the sol-gel
process with molecular templating on magnetic particles can dramatically
increase the surface area of the final composites. The templating mechanism
and the mesoporous silica-coated magnetic particles were studied by AFM,
DRIFTS, TEM, zeta-potential measurement, and leaching tests. The resultant
particles show paramagnetic property with strong saturation magnetization,
and the silica surface is amenable for various functionalizations.
The magnetic nanocomposite particles functionalized by silanation with
different reactive functional groups, such as -SH, -NH
2
, and -COOH, have
been proven to be effective for removal or recovery of heavy metal ions such as
Cu
2+
,Zn
2+
,Ni
2+
,Ag
+
, and Hg
2+
from aqueous solutions. Selective separa-
tion of different metal ions can be achieved by controlling the solution pH.
Loaded metal ions on the magnetic particles can be stripped off by acid wash-
ing. Magnetic nanocomposites particles with tailored functional groups have
potential applications in many scientific and technological applications of
different disciplines.
References
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Drainage-Full Scale. EPA Project Summary. EPA-600/S7-81-033.
3. Yamamura, S. (2000) Drinking Water Guidelines and Standards, World Health Organiza-
tion, Geneva, Switzerland, http://www.who.int/water_sanitation_health/dwq/arsenicun5.
pdf
4. Maximum Contaminant Level Goals and National Primary Drinking Water Regulation
for Lead and Copper; Proposed Rule (1996) http://www.epa.gov/EPA-WATER/1996/
April/Day-12/pr-20958DIR/pr-20958.txt.html
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5065.
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