Chemistry Reference
In-Depth Information
4.3.3 Metal Modified POFs
The CH
4
uptake ability is related to the surface area of POFs, measurement pressure,
and temperature. One research has attracted our attention, at 1 bar and 273 K, the
CH
4
uptake of PAF-1 is 1.12 mmol g
−
1
[
29
]. Matthew reported that 5 %_Li@PAF-1
exhibited higher CH
4
storage capacities with value of 1.30 mmol g
−
1
(273 K,
1.22 bar) [
31
]. However, the surface area of 5 %_Li@PAF-1 is only 479 m
2
g
−
1
,
which is extremely lower than 5,600 m
2
g
−
1
of PAF-1. Thus, it provides very useful
information for us to design and synthesize effective adsorbents to satisfy the CH
4
storage requirement.
Recently, we have successfully designed and synthesized a carboxyl-functional-
ized PAF material, PAF-26-COOH [
51
]. Post-metalation of PAF-26-COOH yields
a series of PAF-26-COOM derivatives (M
=
Li, Na, K, Mg). The porosity and pore
size are tuned and achieved via this post-metalation method. N
2
adsorption measure-
ments indicate the surface areas of PAF-26-COOM derivatives decrease compared
with original PAF-26-COOH (Fig.
4.7
a). The dependence of uptakes per effective
V
total
versus pressure for the PAF-26 series toward CH
4
is also calculated. It can be
found that the CH
4
uptakes per effective
V
total
of PAF-26-COOM increased, with
values from 34 mg cm
−
3
(PAF-26-COOH) to 46 mg cm
−
3
(PAF-26-COOLi, 35 %
increased), 54 mg cm
−
3
(PAF-26-COOMg 35 % increased), 56 mg cm
−
3
(PAF-
26-COONa, 65 % increased) and 60 mg cm
−
3
(PAF-26-COOK, 76 % increased)
(Fig.
4.7
b). Based on the above results, we can conclude that introduction of metal
active centers would greatly promote gas adsorption capacity.
Compared with H
2
storage, CH
4
storage has promising feasibility to achieve the
DOE target because CH
4
storage could be performed at room temperature. For prac-
tical application, the POFs should satisfy some basic demands such as high surface
area, inexpensive synthesis, mass production under mild condition, etc. In addition,
the design and synthesis of POFs could be conducted by theoretical simulation.
Fig. 4.7 a
N
2
adsorption-desorption isotherms measured at 77 K for PAF-26-COOH, PAF-26-
COOLi, PAF-26-COONa, PAF-26-COOK and PAF-26-COOMg;
b
CH
4
uptakes per effective
V
total
for PAF-26-COOH, PAF-26-COOLi, PAF-26-COONa, PAF-26-COOK and PAF-26-COOMg
samples at 273 K and 101 kPa
