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Daqiang Yuan, Weigang Lu, Dan Zhao, and Hong-Cai Zhou*
For several decades, porous materials have
been exploited for their applications in gas
storage.[1] Recently, several metal–organic
frameworks (MOFs) with high surface area
and gas-uptake capacity have been reported.[2]
However, most of them suffer from limited stability, which hampers their practical
application. Here we show a series of porous
polymer networks (PPNs) with exceptionally
high surfaces area and gas-uptake capacities.
For example, PPN-4 has Brunauer–Emmett– Figure 1. a) Synthetic route for PPN-3 (X: Adamantane), PPN-4 (X: Si), PPN-5 (X: Ge), and
Teller (BET) and Langmuir surface areas PAF-1 (X: C). b) The default noninterpenetrated diamondoid network of PPN-4 (black, C; pale
of 6461 and 10063 m2 g−1, respectively. Its grey, H; grey, Si).
total hydrogen, methane, and carbon dioxide
shown in Figure 1. It needs to be pointed out that most of the
storage capacities are 158 mg g−1 (77 K, 90 bar), 389 mg g−1
porous organic polymers are noncrystalline, including the PPNs
(295 K, 55 bar), and 2121 mg g−1 (295 K, 50 bar), respectively.
reported here (Figure S1-S3, Supporting Information).
Combined with its superior stability, PPN-4 is a very promising
Conventional Yamamoto homo-coupling reaction for polycandidate for gas storage applications.
merization was carried out at 80 °C with dimethylformamide
Compared with MOFs, porous organic polymers offer supe(DMF) as the solvent, which is proven efficient in synthesizing
rior stability by replacing chemically susceptible coordination
PAF-1. However, when the same reaction condition was applied
bonds with robust covalent bonds.[3] Our strategy is based on the
to tetrakis(4-bromophenyl)silane or tetrakis(4-bromophenyl)synthesis of PAF-1, which is a porous organic polymer obtained
admantane, the surface areas of the synthesized materials were
through Yamamoto homo-coupling of a tetrahedral monomer,
much lower than the calculated data (Table S1, Supporting
tetrakis(4-bromophenyl)methane.[4] PAF-1 possessed high surface
Information).[5a,6] With the assumption that reduced temperaarea (BET: 5600 m2 g−1, Langmuir: 7100 m2 g−1), as well as excellent H2 and CO2 storage capacities. The high surface area was
ture would slow the reaction to yield polymers with higher
molecular weight and avoid any unwanted side reactions, we
hypothetically attributed to the default diamondoid framework
adopted an optimized Yamamoto homo-coupling procedure, in
topology imposed by the tetrahedral monomers, which provides
which the reactions were carried out at room temperature in
wide openings and interconnected pores to efficiently eliminate
a DMF/THF (THF: tetrahydrofuran) mixed solvent. Using this
“dead space”.[5] Thus, the study of PAF-1 analogues by replacing
procedure, we were able to synthesize PPN-3, PPN-4, and PPN-5
the central carbon with other quadricovalent building centers
with exceptionally high surface areas (Table S1, Supporting
(adamantane, silicon, and germanium) may provide not only
Information). The surface area of PPN-3 synthesized through
better understanding of the network, but also even higher surface
this procedure is much higher than the value previously
area given the more expanded tetrahedral monomers (Table S1,
reported, and the surface area of PPN-4 is close to the value
Supporting Information). The general synthetic route and default
predicted based on the molecular model, indicating the superinon-interpenetrated diamondoid structural model of PPN-4 are
ority of this optimized procedure. The two criteria discussed in
the literature have been strictly followed to decide the pressure
range for applying the BET analysis (Figure S4-S13, Supporting
[+]
[+]
Dr. D. Yuan, Dr. W. Lu, Prof. H.-C. Zhou
Information).[7] With BET surface area of 6461 m2 g−1 and
Department of Chemistry
Langmuir surface area of 10063 m2 g−1, PPN-4 possesses, to
Texas A&M University
the best of our knowledge, the highest surface area among all
College Station, Texas, 77842, USA
E-mail: zhou@mail.chem.tamu.edu
reported porous materials, so far.[8] In addition, most of the
Dr. D. Zhao
pores in PPN-4 sit within the microporous or microporous/
Chemical Sciences and Engineering Division
mesoporous range (Figure 2b), which serves remarkably for gas
Argonne National Laboratory
storage purposes.
9700 S. Cass Avenue, Argonne, IL 60439, USA
Similar to previously reported PPNs, PPN-3, PPN-4, and
[+] D.Y. and W.L. contributed equally to this work.
PPN-5 are off-white powders, insoluble in common organic solvents. No residual bromine is observed based upon elemental
DOI: 10.1002/adma.201101759
Adv. Mater. 2011, 23, 3723–3725
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COMMUNICATION
Highly Stable Porous Polymer Networks with Exceptionally
High Gas-Uptake Capacities
3723
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small pores caused by network interpenetration. This network interpenetration may also
account for the reduced experimental surface
areas of PPN-3 and PPN-5 compared with
the calculated data (Table S1, Supporting
Information). Thermogravimetric analysis
(TGA) data show the three polymers possess
good thermal stability and high decomposition temperatures of more than 450 °C in a
nitrogen atmosphere (Figure S14, Supporting
Information). In addition, PPN-4 retains its
structural integrity after being exposed to
air for one month, as indicated by virtually
no drop of N2 uptake capacity at 77 K
(Figure S15, Supporting Information).
The exceptionally high surface area combined with excellent stability make PPN-4 a
very attractive candidate for gas storage applications, particularly in H2, CH4 and CO2 for
clean energy purposes. To evaluate its gas
storage capacity, high-pressure excess adsorption of H2, CH4 and CO2 within PPN-4 were
measured at 77 K (liquid nitrogen bath) or
295 K (room temperature). As shown in
Figure 2c, the excess H2 uptake of PPN-4 at
77 K and 55 bar can reach 91 mg g−1 (8.34 wt%)
(total uptake: 158 mg g−1, 13.6 wt%, 80 bar),
which is by far the highest among all amorphous materials, and is also comparable to the
best value reported in MOFs (Table 1). The
isosteric heat of adsorption for H2 is around
4 kJ mol−1 (Figure 2d), which fits within the
range of physisorption and indicates that the
high surface area may be the sole factor in
determining this high H2 uptake capacity.[9]
Figure 2. a) 77 K N2 sorption isotherms of PPN-3, PPN-4, and PPN-5. b) Pore size distribution
Unlike MOFs, whose H2 uptake capacity will
of PPN-3, PPN-4, and PPN-5. c) Excess and total H2 adsorption isotherms of PPN-4 at 77 K.
decrease after several uptake-release cycles,
d) Isosteric heat of adsorption for H2 in PPN-4. e) Excess and total CO2 adsorption isotherms
the H2 uptake capacity of PPN-4, even being
of PPN-4 at 295 K. f) Excess and total CH4 adsorption isotherms of PPN-4 at 295 K.
exposed to air for several days, can be simply
regenerated by heating under vacuum. The
analyses (Table S2, Supporting Information), indicating the
excellent physicochemical stability and impressively high delivery
completion of the reaction and the efficiency of Yamamoto
capacity (71 mg g−1, 77 K, from 1.5 bar to 55 bar) make PPN-4 the
homo-coupling. Surprisingly, trace amounts of nitrogen were
currently leading material for cryogenic H2 storage application.
detected in PPN-3 and PPN-5 (0.14 wt% and 0.11 wt%, respecA high-pressure CO2 adsorption isotherm was also measured
tively), which likely comes from trapped 2,2′-bipyridine within
at 295 K to evaluate the capability of PPN-4 for CO2 capture.
Table 1. Gas sorption data for PPNs and selected porous materials.
Material
PPN-4
PAF-1
UMCM-2
PCN-68
MOF-210
NU-100
a)77
3724
Excess H2
uptake [mg g−1]
Total H2
uptake [mg g−1]
Excess CO2
uptake [mg g−1]
Total CO2
uptake [mg g−1]
Excess CH4
uptake [mg g−1]
Total CH4
uptake [mg g−1]
Reference
91 (55 bar)a)
158 (80 bar)a)
1710 (50 bar)b)
2121 (50 bar)b)
269 (55 bar)b)
389 (55 bar)b)
This work
bar)a)
1300 (40
bar)c)
bar)c)
ND
ND
[4a]
69 (46 bar)a)
116 (72 bar)a)
ND
ND
ND
ND
[2c]
73.2 (28 bar)a)
130 (100 bar)a)
1393 (55 bar)c)
1740 (50 bar)c)
390 (100 bar)c)
446 (100 bar)c)
[2e]
86 (55 bar)a)
167 (80 bar)a)
2396 (50 bar)c)
2870 (50 bar)c)
264 (80 bar)c)
475 (80 bar)c)
[2f ]
a)
c)
c)
ND
ND
[2g]
75.3 (48
bar)a)
99.5 (70 bar)
a)
120 (48
164 (70 bar)
2043 (40 bar)
1585 (40
2315 (40 bar)
K; b)295 K; c)298 K.
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Experimental Section
Synthesis of PPN-4: To a solution of 2,2′-bipyridyl (226 mg, 1.45 mmol),
bis(1,5-cyclooctadiene)nickel(0) (Ni(COD)2, 400 mg, 1.45 mmol), and
1,5-cyclooctadiene (COD, 0.18 mL, 1.46 mmol) in anhydrous DMF/
THF (24 mL/36 mL) add tetrakis(4-bromophenyl)silane (210 mg,
0.32 mmol), and the mixture was stirred at room temperature under
argon atmosphere overnight. Then, the mixture was cooled in ice bath,
6 mol/L HCl solution (20 mL) was added, the resulting mixture was
stirred for another 6 h. the precipitate was collected, then washed with
Methanol (6 × 10 mL), and H2O (6 × 10 mL), respectively, and dried in
vacuo to produce PPN-4 as off-white powder (95 mg, 0.28 mmol, 89%).
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
This work was supported by the U.S. Department of Energy (DOE
DE-SC0001015, DE-FC36-07GO17033, and DE-AR0000073), the National
Science Foundation (NSF CBET-0930079 and CHE-0911207), and the
Welch Foundation (A-1725). We acknowledge Dr. Vladimir Bakhmoutov
for his help in solid state NMR, Dr. Michael Pendleton for his help in
Adv. Mater. 2011, 23, 3723–3725
SEM image, Mei Cai and Eric Poirier for their help in high pressure
hydrogen adsorption measurement. We acknowledge the Laboratory for
Molecular Simulation of Texas A&M University for providing the Material
Studio 5.5 software.
Received: May 10, 2011
Revised: June 14, 2011
Published online: July 6, 2011
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COMMUNICATION
Thanks to the exceptionally high surface area, PPN-4 can adsorb
2121 mg g−1 CO2 at 50 bar (Figure 2e), which is also among the
highest of porous materials reported to date (Table 1). Although
it is hard to compare the volumetric methane uptake capacity of
PPN-4 with PCN-14 due to the lack of material density data, the
gravimetric methane uptake capacity of PPN-4 (total: 273 mg g−1
at 295 K and 35 bar) (Figure 2f) is much higher than that of
PCN-14 (total: 188 mg g−1 at 290 K and 35 bar).[10]
In conclusion, a series of porous polymer networks (PPNs)
with excellent physiochemical stability have been synthesized
with optimized Yamamoto homo-coupling procedure. Among
them, PPN-4 possesses a BET surface area of 6461 m2 g−1,
which transcends all reported porous materials to date. In addition, its H2, CH4, and CO2 uptake capacities are also among
the highest reported so far. We believe PPN-4 represents a great
stride in the adsorption-based gas storage realm, and its largescale application is anticipated.
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