Environmental Engineering Reference
In-Depth Information
Fig. 6.4 Interactions involved in silanation. [6]
to hydrolyze surface metal species to obtain the maximum density of bindings
between coupling agent and surface. The interactions and competition between
the solvent-solute, solvent-substrate, and solute-substrate dictate both cover-
age and quality of the resultant film. The last (but not the least) parameter (not
included in Fig. 6.4) that needs to be considered is the post-curing during which
thermal dehydration enhances chemical binding between substrate and cou-
pling molecules and lateral polymerization among the coupling molecules,
resulting in a robust film.
In our laboratory, we synthesized and studied the silanation of superpar-
amagnetic (g-Fe
2
O
3
) particles with focus on characterization of the coated
organic films, such as organo-amine functional groups (3-aminopropyl
triethoxy silane (APTES)). The characteristics investigated included the state
of the amine groups, the binding of silane on magnetic particles, and the
stability of the film [6].
APTES were silanized on g-Fe
2
O
3
from both water and toluene solutions.
The presence of N
1s
and Si
2p
bands on XPS spectra of synthesized particles
suggests that APTES has deposited on g-Fe
2
O
3
from both solutions. The
two bands of nitrogen centered at 399.4 and 401.3 eV are attributed to the
protonated and non-protonated amines, respectively. The fraction of amines
protonated is larger in the films silanized from water (26%) than that from
toluene (17%), indicating the stronger interaction of amine groups with
g-Fe
2
O
3
in water than in toluene. Band-fit analysis revealed that the proportion
of oxygen in Si-O environment is higher for the film silanized in water (24%)
than in toluene (14%), suggesting a higher degree of hydrolysis of APTES on
g-Fe
2
O
3
from water. The XPS analysis also suggests the deposition of APTES
as monolayers, and the moderate increase in the number of APTES molecules
on g-Fe
2
O
3
from aqueous solutions is attributed to the increased APTES
