Environmental Engineering Reference
In-Depth Information
OH
O
NH
2
Si(OR)
3
+
OH
OH
O
Si(OR)
3
NH
Figure 29.10
Schematic reaction pathway for synthesis of alkoxysilyl humic derivatives with mineral-adhesive properties not inherent
within the parent humic material.
OH
O
HO
SiO
2
+
HO
N
Si(OCH
3
)
3
OH
O
O
SiO
2
Si
N
MeO
O
Figure 29.11
Self-assembly of silanized humic derivatives into adlayers at the silica gel surface under ambient conditions in aquatic
environments.
support. The pertinent derivatives were produced via the incorporation of alkoxysilyl groups into the humic backbone by treat-
ing the parent humic material with 3-aminopropyltrialkoxysilane. The synthetic pathway appears in Figure 29.10.
The alkoxysilyl groups (Si-OAlk, where Alk is a hydrocarbon radical, e.g., -cH
3
) undergo hydrolysis upon contact with
water-producing silanol groups (Si-OH) capable of covalent bonding to mineral surfaces carrying hydroxyls. The formation of
Si-O-Si or Si-O-m (where m is a metal, e.g., Fe) bonds provides a phase switch of the humic derivatives and their immobili-
zation on the surface of mineral support. The corresponding reaction scheme is shown in Figure 29.11.
The covalent bonding is viewed as being of particular advantage in the proposed approach, since it precludes the facile
remobilization of the humic coating and any contaminants bound to that coating. The spatial homogeneity and morphology
