Environmental Engineering Reference
In-Depth Information
(CH
2
)
3
SH
CH
3
O
Si
OCH
3
OCH
3
Methoxy group
+
OH
OH
Clay surface
Toluene
(reflux)
Δ
3 CH
3
OH
(CH
2
)
3
SH
HO
Si
O O
figure 16.2
schematic illustration of the functionalization with functional silane.
O
O
Si
(CH
2
)
3
-NH
2
O
O
Si
(CH
2
)
3
-NH
2
O
O
M
n
+
M
n
+
O
O
(CH
2
)
3
-NH
2
Si
O
Si
(CH
2
)
3
-NH
2
O
O
O
figure 16.3
Reaction mechanism between the modified sepiolite and the metal ions.
acid-activated sepiolite at initial pH 3, when the pH of solution reached 4.7, and ca. 2.7 mg Cr(VI) per gram of functionalized
natural sepiolite at initial pH 2, when the pH of the solution reached 2.5. Cr(VI) removal by the functionalized sepiolites was
mainly attributed to electrostatic attraction between the protonated mercapto groups and the negatively charged Cr(VI) species.
Besides the functional silane-containing thiol (-sH) groups, those containing amino (-nH
2
) groups were widely investi-
gated as surface modifiers. 3-Aminopropyltriethoxysilane (APTs) was used for the surface modification of sepiolite as an
adsorbent in the removal of various HmI such as fe, mn, Co, Zn, Cu, Cd, and ni from aqueous solutions (fig. 16.3) [68]. The
results showed that the amount adsorbed increases with solution pH in the pH range of 1.5 and 7.0, indicating that the modified
sepiolite adsorbed fe and mn ions more than other metal ions such as Co, Zn, Cu, Cd, and ni. It was also found that temperature
had an important effect on metal ion adsorption by the modified sepiolite.
smectite clay was used for pillaring and the organo-functionalization process in the present study. The pillaring ions were
obtained through chemical reaction of AlCl
3
·6H
2
O/naOH, Ti(OC
2
H
5
)
4
/HCl, Cr
3
(OH)
4
4+
/naOH and ZrOCl
2
·8H
2
O solutions.
The resulting materials were organo-functionalized with APTs to obtain the
S
Al/APs
,
S
Zr/APs
,
S
Ti/APs
, and
S
Cr/APs
samples [69]. The
adsorption affinity of the divalent metal Pb
2+
ions onto modified clays edge sites exhibited the following order:
S
>
S
>
S
>
S
>
S
Zr ASP
/
AlAPS
/
Cr APS
/
TiAPS
/
nat
mmT clay was intercalated with pyridine/APTs and dimethyl sulfoxide/3-aminopropyltri-ethoxysilane for mercury cation
adsorption from aqueous solutions [70]. The specific area of the natural mmT, 41.4 m
2
/g, increased after the immobilization
process to give 198.5 m
2
/g. Therefore, the adsorption capacity for mercury removal increased after the chemical modification.
Three organo-mmT, APTs-mmT, sds-mmT, and HdTmAB-mmT, were prepared by grafting with 3-aminopropyl-
triethoxysilane (APTs), or surface modification with HdTmAB and sds from the calcium-saturated mmT (Ca-mmT),
respectively [71]. The organo-mmT were used for the adsorption of sr(II). The adsorption capacity of APTs-mmT was 65.6
mg/g, much larger than those of Ca-mmT, sds-mmT, and HdTmAB-mmT (13.23, 26.85, and 3.91 mg/g, respectively) under
the chosen conditions. sr(II) removal by Ca-mmT was mainly by ion exchange; nevertheless, removal by sds-mT and APTs-mmT
