F\-CATALYZED CHEMICAL TREATMENT OF SILICA XEROGELS
377
TABLE 6
Gelation Times and Yields for the Xerogels S1+6
TABLE 7
Yields for the Xerogels ST1+6 and ST3ꢀ,4
Gelation time
(min)
Mass of xerogel
obtained (g)
Yield
(%)
Mass of xerogel
obtained (g)
Yield
(%)
Xerogel
Xerogel
S1
S2
S3
S4
S5
S6
10
86;10ꢁ
1
86;10ꢁ
10
2.07
2.35
1.88
2.13
1.71
2.24
77
87
70
79
63
83
ST1
ST2
ST3
ST3ꢀ
ST4
ST4ꢀ
ST5
ST6
1.6
1.7
1.7
1.7
1.6
1.7
1.69
1.7
80
85
85
85
80
85
84
85
26;10ꢁ
previously dried during 24 hours at 1003C under
a 0.1 mmHg vacuum. Hydrophilicity was then measured in
ꢃ
\ꢀ
a desicrator containing a saturated aqueous NaBr solution 490 m )g . Mean pore diameter: 200 A. SAXS: power law,
(60% humidity rate at equilibrium).
!3.7; D "2.3. E "0.20.
ꢀ
ꢆꢇꢄ
\ꢀ
ꢂ
S6 (THF, HCl). IR (KBr): 946, 1082, 1218, 3510 cm
.
ꢃꢅ
ꢃ
ꢁ
NMR CP-MAS Si d: !91 (Q ), !100 (Q ), !109 (Q )
Silica Xerogels Preparation
ppm. Porosimetry (nitrogen, 77 K). Speci"c area:
Tetramethoxysilane (7.0 mL; 49.3 mmol) and solvent
(16.0 mL) were mixed with catalyst (1.0 mmol) and water (2
equiv, 98.7 mmol, pH 7). The mixture was stirred until
a homogeneous solution was obtained and geli"ed during
stirring. Gel was left for aging for 1 week under ambient
temperature (223C), and then crushed, washed "ve times
with 20.0 mL of ethylic ether, and dried under vacuum at
1003C for 24 hours to give a white powder. For mass and
ꢃ
\ꢀ
460 m )g . Mean pore diameter: 15 A. SAXS: power law,
!2.5; D "3.5(!). E "0.22.
ꢀ
ꢆꢇꢄ
Chemical ¹reatment
In a typical experiment, the xerogel (1.00 g) was poured
into a 50-mL monocol #ask, surrounded by a refrigerant.
The reagents, solvent (20.0 mL), H O (39.0 mL), and an
aqueous molar solution of catalyst (0.3 mL, 0.3 mmol) were
ꢃ
added. The suspension was heated until methanol re#ux for
4 days without stirring. The suspension was then "ltered
yield (calculated for SiO ) see Table 6.
ꢃ
and the residue washed 3 times using 20.0 mL of H O, THF,
acetone, and diethyl ether and dried for 24 hours under
vacuum (2 mmHg) at ambient temperature. For mass and
Silica Xerogels Characterization
ꢃ
S1 (EtOH, NH ). IR (KBr): 956, 1082, 1213, 2997,
ꢁ
\ꢀ
ꢃꢅ
ꢁ
ꢂ
3422 cm . NMR CP-MAS Si d: -101 (Q ), !110 (Q )
ppm. Porosimetry (nitrogen, 77 K). Speci"c area:
ꢃ
\ꢀ
700 m )g . Mean pore diameter: 80 A. SAXS: Porod be-
Silica Xerogels Characterization after Chemical ¹reatment
ꢃ
\ꢀ
havior. S "630 m )g . l "31. l "82. E "0.15.
\ꢀ
ꢂ
ST1 (EtOH, NH ). IR (KBr): 959, 1082, 1189, 3476 cm
.
N
ꢀ
ꢁ
ꢆꢇꢄ
ꢁ
ꢃꢅ
ꢃ
ꢁ
NMR CP-MAS Si d: !90 (Q ), !100 (Q ), !108 (Q )
\ꢀ
S2 (EtOH, HCl) IR (KBr): 935, 1087, 1196, 3466 cm
NMR CP-MAS
Porosimetry (nitrogen, 77 K). Speci"c area: 5 m )g
.
ppm. Porosimetry (nitrogen, 77 K). Speci"c area:
ꢃꢅ
ꢁ
ꢂ
Si d: !99 (Q ), !106 (Q ) ppm.
ꢃ
\ꢀ
590 m )g . Mean pore diameter: 100 A. SAXS: Porod be-
ꢃ
\ꢀ
.
ꢃ
\ꢀ
havior. S "650 m )g . l "29. l "90. E "0.11.
SAXS: power law, !3.5; D "2.5. E "0.12.
N
Q
N
ꢆꢇꢄ
ꢀ
ꢆꢇꢄ
S3 (MeOH, NH ). IR (KBr): 969, 1073, 1175, 2855,
\ꢀ
ST2 (EtOH, HCl). IR (KBr): 968, 1093, 1218, 3476 cm
.
ꢁ
NMR CP-MAS ꢃꢅSi d: !101 (Qꢁ), !110 (Qꢂ) ppm. Po-
\ꢀ
\ꢀ
ꢂ
\ꢀ
ꢃꢅ
ꢃ
ꢁ
3730 cm . NMR CP-MAS Si d: !91 (Q ), !100 (Q ),
ꢃ
rosimetry (nitrogen, 77 K). Speci"c area: 5 m )g . SAXS:
\ꢀ
!110 (Q ) ppm. Porosimetry (nitrogen, 77 K). Speci"c area:
ꢃ
Porod behavior. S "6 m )g
.
l "3550. l "23.
ꢁ
ꢀ ꢁ
ꢃ
650 m )g . Mean pore diameter: 65 A. SAXS: Porod be-
E
"0.11.
ꢆꢇꢄ
ꢃ
\ꢀ
havior. S "580 m )g . l "34. l "70. E "0.24.
N
Q
N
ꢆꢇꢄ
ST3 (MeOH, NH ). IR (KBr): 968, 1098, 1218, 3259,
ꢁ
\ꢀ
ꢂ
S4 (MeOH, HCl). IR (KBr): 940, 1087, 1224, 3488 cm
NMR CP-MAS Si d: !90 (Q ), !101 (Q ), !110 (Q )
ppm. Porosimetry (nitrogen, 77 K). Speci"c area: 5 m )g
SAXS: power law, !3.8; D "2.2. E "0.13.
.
\ꢀ
ꢂ
\ꢀ
ꢃꢅ
ꢃ
ꢁ
3466 cm . NMR CP-MAS Si d: !91 (Q ), !100 (Q ),
ꢃꢅ
ꢃ
ꢁ
!109 (Q ) ppm. Porosimetry (nitrogen, 77 K). Speci"c area:
300 m )g . Mean pore diameter: 200 A. SAXS: Porod be-
ꢃ
\ꢀ
.
ꢃ
ꢃ
\ꢀ
havior. S "200 m )g . l "96. l "68. E "0.14.
ꢀ
ꢆꢇꢄ
ꢁ
Q
N
ꢆꢇꢄ
ꢀ
S5 (THF, NH ). IR (KBr): 957, 1104, 1213, 2979,
3673 cm . NMR CP-MAS Si d: !92 (Q ), !99 (Q ), 3444 cm . NMR CP-MAS Si d: !92 (Q ), !101 (Q ),
!108 (Q ) ppm. Porosimetry (nitrogen, 77 K). Speci"c area: !111 (Q ) ppm. Porosimetry (nitrogen, 77 K). Speci"c area:
ST3 (MeOH, NH ). IR (KBr): 968, 1098, 1186, 3259,
ꢁ
ꢁ
\ꢀ
ꢂ
ꢃꢅ
ꢃ
ꢁ
\ꢀ
ꢃꢅ
ꢃ
ꢁ
ꢂ