Membrane Gas Separation

6.3
Results and Discussion 
The synthesis parameters of the four silicalite - 1 crystals prepared in this work (Figure 
6.1 ) are summarized in Table 6.2 . The average length of MFI_80 and MFI_350 crystals 

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Glassy Perfl uorolymer–Zeolite Hybrid Membranes for Gas Separations
117
is 80 and 350 nm respectively. MFI_1500 are slabs (010) with frequent twin intergrowths; 
the average dimensions are ca. 1.4
×
0.65
×
1.5
μ
m ( a
×
b
×
c ). The MFI_dC5 crystals 
are aggregates of highly intergrown thin sheets with the minimum length along the b axis 
of less than 400 nm, and dimensions along a and c up to about 5 and 10
μ
m, respectively. 
The surface treatment makes the zeolites fl uorophilic, and this refl ects into a sharp 
increase in the water contact angle from 89 ° (calcined zeolite) to 140 – 150 ° (surface modi-
fi ed zeolite, Figure 6.2 ). N 
2
sorption experiments at 77 K indicate that the modifi ed zeolites 
are permeable, with about the same sorption capacity as the pristine calcined samples.
The hybrid membranes are designated as follows: e.g. AD60_1500_42 indicates a 
membrane containing Hyfl on AD 60 and 1500 nm silicalite - 1 crystals, in which the mass 
of the zeolite is 42% of the total; AF24_dC5_40 indicates instead a membrane containing 
Tefl on AF 2400 and MFI_dC5 crystals, in which the mass of the zeolite is 40% of the 
a
b
c
d
Figure 6.1 SEM pictures of the silicalite - 1 samples used in this work: (a) MFI_80, (b) 
MFI_350, (c) MFI_1500, (d) MFI_dC5. Scale bar is 1
μ
 m (a, b), 5
μ
 m (c) or 10
μ
 m (d)
Figure 6.2 Droplet of water on a layer of fl uorophilic 80 nm silicalite - 1 crystals
Table 6.2  Synthesis conditions of the four silicalite - 1 samples 
Sample
Molar composition
a
T
b
/ ° C
t
c
/h
Ref.
MFI_80
25 TEOS : 9 TPAOH : 0.1 Na 
2
O : 461 H 
2
O
96
72
10
MFI_350
25 TEOS : 5 TPAOH : 0.1 Na 
2
O : 1550 H 
2
O
98
60
10
MFI_1500
d
40 TEOS : 7.29 TPAOH : 3237 H 
2
O
130
12
11
MFI_dC5
d
40 TEOS : 7.49 dC5 : 12.5 K 
2
O : 18906 H 
2
O
175
120
11
a
TEOS: tetraethoxysilane; TPAOH: tetrapropylammonium hydroxide; dC5: bis - 1,5 - (tripropylammonium)pentane 
diiodide.
b
Synthesis temperature.
c
Synthesis time.
d
Autoclaves under rotation.

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118
Membrane Gas Separation