Environmental Engineering Reference
In-Depth Information
Fig. 6.3 Infrared spectra in the high (A) and low-frequency (B) regions for (a) MHA in KBr,
(b) MHA on g-Fe
2
O
3
, and (c) g-Fe
2
O
3
coated on g-Fe
2
O
3
is thiol or bisulfide, rather than a carbonyl, sulfate, or
sulfonate functionality. It also indicated that long chain hydrocarbon association
of amphiphiles is necessary for a densely packed monolayer, such as MHA on
g-Fe
2
O
3
.
To examine the nature of the packing of various surfactants on the g-Fe
2
O
3
particle surface and to investigate the stability of self-assembled layers to harsh
environments, leaching experiments were conducted by placing the treated
particles in acidic (pH 3) and alkaline (pH 10) media. These experiments showed
that the surface coatings with stearic acid and MHA are stable in aqueous
solutions over a pH range from 3 to 10 for a few days. No ferric ions were
leached into the solution, indicating that the surface coatings are tightly packed.
After the leachate was removed and the powder dried, the same values of critical
surface tension were obtained, suggesting that the surfactant layer prepared
with stearic acid and MHA remained stable under the test conditions. In
contrast, ferric ions were detected (by sodium thiocyanide titration) in leachate
of DTDPA-coated g-Fe
2
O
3
exposed to distilled water. These observations
confirm the packing information inferred from DRIFTS and film flotation.
It is important to note that a monolayer coating of MHA on g-Fe
2
O
3
only
reduced the saturation magnetization (M
s
) of magnetic particles marginally
(2 emu/g) from 52.7 emu/g of bare g-Fe
2
O
3
. The particles remained super-
paramagnetic after coating.
The magnetic particles fabricated with thio or disulfide groups have potential
applications in various areas. It is well known that thio and disulfide groups have
strong affinity with precious metals, such as gold, silver, and copper [73, 74]. The
fabricated magnetic particles of large surface area could, therefore, be used to
