Microporous organic polymers based on tetraethynyl building blocks with N-functionalized pore surfaces: synthesis, porosity and carbon dioxide sorption

Article abstract of DOI:10.1039/C6RA20765K

A series of microporous organic polymers (MOPs) based on tetraethynyl monomers such as tetrakis(4-ethynylphenyl)methane and tetrakis(4-ethynylphenyl)silane was synthesized via conventional Sonogashira-Hagihara coupling reaction. The resulting MOPs were ch

Full text of DOI:10.1039/C6RA20765K

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PAPER
Microporous organic polymers based on
tetraethynyl building blocks with N-functionalized
pore surfaces: synthesis, porosity and carbon
dioxide sorption†
Cite this: RSC Adv., 2016, 6, 113826
a
b
a
c
d
Hongjiang Zhang, Chong Zhang, Xunchang Wang, Zexiong Qiu, Xinmiao Liang,
d
a
b
a
a
a
Bing Chen, Jiawei Xu, Jia-Xing Jiang,* Yuda Li, Hui Li and Feng Wang*
A series of microporous organic polymers (MOPs) based on tetraethynyl monomers such as tetrakis(4-
ethynylphenyl)methane and tetrakis(4-ethynylphenyl)silane was synthesized via conventional
Sonogashira–Hagihara coupling reaction. The resulting MOPs were characterized by thermogravimetric
analyses, IR-spectra, scanning electron microscopies, and the Brunauer–Emmett–Teller (BET) method.
The incorporation of triphenylamine or azobenzene moieties into the polymer skeleton increases the
number of electron donating basic nitrogen sites in the porous frameworks. Thus, these MOPs could
exhibit efficient adsorption of Lewis acidic CO
2 2 2
molecules and display good CO -over-N selectivity. The
Received 17th August 2016
Accepted 15th November 2016
2
ꢀ1
triphenylamine-based polymer, TEPM-TPA, shows a high BET specific surface area up to 1072 m
g
ꢀ1
with a moderate CO
both TEPM-Azo and TEPS-Azo exhibit relatively high CO
respectively, due to the N -phobic feature of azo-based polymers.
2
uptake capacity of 2.41 mmol g at 273 K and 1.13 bar. As for separation of CO
2
,
DOI: 10.1039/c6ra20765k
2
-over-N selectivities of 70.8 and 64.7 at 273 K,
2
www.rsc.org/advances
2
14–16
and sensing materials.
MOPs generally possess large surface
Introduction
area, excellent chemical and thermal stability, tunable pore
6
In recent years, global warming has become a major issue in properties, low skeleton density, and synthetic diversity. These
1
climate change. Overwhelming scientic consensus has features could make MOPs became strong candidates for post-
correlated global warming to anthropogenic CO
Thus, one of the promising technologies to protect the envi- research interests.
ronment is to develop new efficient adsorbents for CO
capture an effective approach to modulate framework–CO
emission. combustion CCS, and they have been the subject of recent
2
4,17–29
The surface modication of MOPs is
interactions.
2
2
2
and storage (CCS). Traditional CO
2
capture is based on the It has been proved that the introduction of nitrogen function-
3
chemical adsorption of CO using amine-containing solvents.
2
alities into the backbone of MOPs could enhance CO and
2
However, because of high energy consumption, solvent regen- energy storage properties owing to Lewis-acid–Lewis-base elec-
eration, and the corrosion of the equipment, scientists are trostatic interactions of the nitrogen atoms with CO mole-
Therefore, synthesis of new MOPs using
2
17,20–23,30–34
seeking new materials for CCS.
cules.
Microporous organic polymers (MOPs) have drawn much nitrogen-rich monomers has attracted considerable scientic
attention due to their promising applications such as gas sepa- interest in recent years. A range of MOPs have been successfully
4–6
7–10
11–13
ration matrices, heterogeneous catalysis, supercapacitors,
developed for CCS applications based on various nitrogen-
containing building blocks, such as covalent triazine frame-
3
0–32
33,34
works,
MOPs,
benzimidazole-linked polymers,
carbazole-based
2
0,23
21
a
and triphenylamine-containing polymers. A recent
Key Laboratory for Green Chemical Process of Ministry of Education, School of
Chemical Engineering and Pharmacy, Wuhan Institute of Technology, Wuhan study by Patel and coworkers has shown that nitrogen–nitrogen
4
30073, P. R. China. E-mail: psfwang@wit.edu.cn
double bonds (azo-bond) in the porous polymer main chain can
b
School of Materials Science and Engineering, Shaanxi Normal University, Xi'an
play important roles in CO storage and separation applica-
2
7
10062, P. R. China. E-mail: jiaxing@snnu.edu.cn
35
tion. These new azo-functionalized MOPs demonstrated that
c
School of Materials Science and Engineering, Wuhan University of Technology, Wuhan
the p-conjugated azo-bond could act as an electron donor, and
4
30070, P. R. China
35–37
d
thus enhance host–guest interactions.
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics,
Wuhan Institute of Physics and Mathematics, Chinese Academy of Science, Wuhan
Cooper and coworkers applied Sonogashira–Hagihara
4
†
1
30071, P. R. China
coupling chemistry to prepare a series of MOPs with controllable
pore dimensions and surface areas by varying building blocks.
Electronic supplementary information (ESI) available. See DOI:
0.1039/c6ra20765k
38
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Impressively, the use of tetraethynyl monomers such as tetra- Synthesis
2
8
kis(4-ethynylphenyl)methane
and tetrakis(4-ethynylphenyl)
0
4
,4 -Diiodoazobenzene (4). 4-Iodoaniline (6 g, 27.4 mmol),
KMnO (10.5 g, 6.26 mmol) and CuSO $5H O were added to
29
silane is prominent for the generation of 3D-porous assem-
blies. Their strong covalent linkage leads to high chemical and
thermal stability. In this work, we have rationally designed and
synthesized a series of nitrogen-rich MOPs by copolymerization
4
4
2
a degassed solution of dichloromethane (160 mL) and stirred at
room temperature for 3 days. The reaction mixture was ltered
through Celite and the solvent was evaporated under reduced
pressure. The crude product was puried on a silica gel column
using a petroleum ether/dichloromethane (3 : 1 by volume)
mixture as eluent. An orange solid of 4 was isolated in 15% yield
0.89 g). H NMR (300 MHz, CDCl ), d (TMS, ppm): 7.84 (d, 4H),
.61 (d, 4H).
0
of tetraethynyl monomers with tris(4-iodophenyl)amine or 4,4 -
diiodoazobenzene via Sonogashira–Hagihara coupling reaction.
The highly cross-linked porous structure can substantially
increase the surface area of the resulting polymer networks and,
on the other hand, the incorporation of azobenzene or triphe-
nylamine groups from the building block into the polymer
skeleton could enhance the binding affinity between the
1
(
3
7
Polymerization
capture capacity. As we expected, azo-based polymers All of the polymer networks were synthesized by palladium-
exhibited excellent CO adsorption selectivity against N
. This catalyzed Sonogashira–Hagihara cross-coupling poly-
adsorbent and CO
2
molecules, and thus lead to the increase of
CO
2
2
2
unique property of TEPM-Azo and TEPS-Azo, along with their condensation of arylethynylenes and aryl halides. The molar
chemical and thermal stability, makes them ideal candidates for ratio of ethynyl to halogen functionalities in the monomer feed
38
post-combustion CO separation.
was set at 1.5 : 1 according to the reported procedure. The
2
purication of the polymers was conducted in air with yield of
8
0–90%. A typical procedure for TEPM-Azo is given below:
Tetrakis(4-ethynylphenyl)methane (81 mg, 0.195 mmol),
0
Experimental
Materials
4,4 -diiodoazobenzene (113 mg, 0.26 mmol), tetrakis
(
(
triphenylphosphine)palladium(0) (15 mg), and copper(I) iodide
10 mg) were dissolved in a mixture of anhydrous DMF (5 mL)
All the reagents, unless otherwise specied, were purchased
from Sigma-Aldrich Co., Acros, and Tokyo Chemical Industry
Co., Ltd. and were used without further purication. All the
solvents were further puried under nitrogen ow. Tetrakis(4-
ethynylphenyl)methane (1), tetrakis(4-ethynylphenyl)silane (2)
and tris(4-iodophenyl)amine (3) were prepared according to the
and triethylamine (5 mL). The reaction mixture was heated to
9
mixture was cooled to room temperature, and the precipitated
polymer networks was ltered and washed four times with
dichloromethane, water, methanol, and acetone to remove any
unreacted monomer or catalyst residues. The product was
ꢁ
0
C and stirred for 72 h under nitrogen atmosphere. The
28,29,39
previously reported method.
ꢁ
dried in vacuum for 24 h at 100 C. Yield: 80.1%. Apparent BET
surface area: 564 cm g
Measurements
3
ꢀ1
.
The NMR spectra were recorded on an Agilent 300-MR NMR
spectrometer. Thermogravimetric analysis (TGA) was per-
Result and discussion
Synthesis and characterization
formed by
a
differential thermal analysis instrument
(
Q1000DSC + LNCS + FACSQ600SDT) over the temperature
ꢁ
0
range from 30 to 1000 C with a heating and cooling rate of The synthesis of 4,4 -diiodoazobenzene (monomer 4) is shown in
ꢁ
ꢀ1
1
0 C min under nitrogen. Solid state magic angle spinning Scheme 1. Starting from the commercially available 4-iodoani-
1
3
0
C CP/MAS NMR measurements were carried out on a Varian line, 4,4 -diiodoazobenzene was prepared by the oxidative
Innity-Plus 300 MHz NMR spectrometer at a MAS rate of 10 coupling of two equivalents of 4-iodoaniline in the presence of
kHz. The FT-IR spectra were collected in transmission on CuSO $5H O and KMnO under nitrogen atmosphere in
4
2
4
40
a Tensor 27 FT-IR spectrometer (Bruker) using KBr disks. The dichloromethane. The polymer networks in this study were
polymer morphology was achieved using a eld-emission synthesized by palladium-catalyzed Sonogashira–Hagihara
scanning electron microscopy (SEM) (JSM-7001F, JEOL, Tokyo, coupling polycondensation. The polymerization reactions were
ꢁ
Japan). Powder X-ray diffraction measurement (PXRD) was performed at a xed reaction temperature (90 C) and the reac-
carried out on an X-ray diffractometer (D/Max-3c). The tion time (72 h). The molar ratio of ethynyl to iodine function-
measurements of the surface area and pore-size distributions alities in the monomer feed was xed at 1.5 : 1 since maximum
(
(
PSDs) of the samples were performed on an ASAP 2420-4 surface areas was observed at this ratio based on the previous
Micromeritics) volumetric adsorption analyzer by means of reports. The general synthetic routes to the polymer networks
38
nitrogen adsorption and desorption at 77.3 K. Samples were are shown in Scheme 1. The polymer networks are insoluble in
ꢁ
ꢀ5
degassed at 120 C for 15 h under vacuum (10 bar) before common organic solvents due to their highly cross-linked
analysis. The surface areas were calculated in the relative structures and the rigid skeleton. The FT-IR spectra revealed
pressure (P/P ) range from 0.05 to 0.20. PSDs and pore volumes no residual trace of the specic vibration bands related to
0
ꢀ
1
28
were derived from the adsorption branches of the isotherms terminal alkynes at around 3280 cm
,
therefore suggesting
1
3
using the nonlocal density functional theory (NL-DFT). Gas high conversion of the starting monomers (Fig. S1†). The
C
sorption isotherms were measured on an ASAP 2420-4 as well.
solid-state NMR (CP/MAS) measurements were carried out to
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0
Scheme 1 Synthetic routes to 4,4 -diiodoazobenzene (4) and the polymer networks.
study the local structures of these polymers (Fig. S2†). All of the materials measured at 77.3 K are shown in Fig. 2a. The polymer
carbon signals with a chemical shi exceeding 110 ppm are networks exhibited Type I isotherms with a steep nitrogen gas
related to aromatic carbon atoms of the building phenylene uptake at low pressure according to the International Union of
groups in the framework. The peak at around 91 ppm in the Pure and Applied Chemistry (IUPAC) classication, suggesting
18
NMR spectra is assigned to the sp carbons in alkyne bonds, thus that micropores are dominant in these polymer networks. The
suggesting that this cross-coupling reaction is effective for gradual increase in N uptake (P/P
¼ 0.05–0.9) at 77.3 K is due
A well-resolved peak to the presence of mesopores in the polymers. The signicant
2
0
41,42
the synthesis of these polymer networks.
is detected at 65 ppm associated with the quaternary carbon hysteresis between adsorption and desorption was observed in
atom in tetrakis(4-ethynylphenyl)methane, indicating that the isotherms for all the polymer networks in the whole range of
tetrakis(4-ethynylphenyl)methane is the main building units in relative pressure, which is in agreement with the fact that all the
41,42
the polymer networks TEPM-TPA and TEPM-Azo.
Addition- MOPs contain both meso- and microporosity. As shown in
ally, the azo-linkage formation was further conrmed by the
presence of characteristic signals for the –C–N]N–C– bond at
35
around 152 ppm in NMR spectra of azo-based polymers. TGA
measurements were carried out to evaluate the thermal stability
of these polymers (Fig. S3†). All the polymer networks exhibit
good stability, showing less than 5% weight loss at around
ꢁ
4
80 C under nitrogen ow. Powder X-ray diffraction measure-
ments suggested that all the polymer networks are amorphous
solid in nature (Fig. S4†). The SEM images of the obtained
polymer networks are shown in Fig. 1. For the polymer networks,
similar morphology can be observed to be solid submicrometer
particles with different size range from 10 to 100 nm.
Porosity measurements
In order to study the porosity of these polymer networks,
sorption analysis using nitrogen as the sorbent molecules was
Fig. 1 SEM images of TEPM-TPA (a), TEPM-Azo (b), TEPS-TPA (c),
carried out. Nitrogen adsorption/desorption isotherms of these TEPS-Azo (d), scale bars: 1 mm.
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Fig. 2 (a) Nitrogen adsorption/desorption isotherms (the adsorption branch is labeled with filled symbols and desorption branch is labeled with
open symbols); (b) pore size distribution curves calculated by NL-DFT for the polymer networks.
Fig. 2b, similar PSD proles based on the adsorption branch of with tetrakis(4-ethynylphenyl)methane, the absolute CO uptake
2
ꢀ1
the isotherm using nonlocal density functional theory (NL-DFT) capacity of the polymer decreases from 2.41 mmol g for TEPM-
ꢀ1
were found for the obtained polymer TEPM-TPA and TEPS-TPA. TPA to 1.78 mmol g for TEPM-Azo. This could be explained by
Both polymers show abundant micropore structures with the decrease of surface area and pore volume for the polymer
2
micropore diameters centered at around 1.1 nm. As for the networks as mentioned above (Table 1). The CO uptake of
ꢀ
1
polymer TEPM-Azo and TEPS-Azo, the PSDs are relative broader 2.41 mmol g for TEPM-TPA is comparable to that of many
in the range of 1.1–2.1 nm compared with those of TEPM-TPA reported MOPs produced by Sonogashira–Hagihara coupling
and TEPS-TPA, indicating that much more mesopores and/or reaction at the same conditions, such as the conjugated
macropores in these two polymers. Besides, TEPM-Azo and microporous PAE networks without nitrogen-containing
41,43–47
TEPS-Azo show a spot mesopores peaks at around 5 nm. The building blocks and their metalized derivatives,
PSD curves of the polymer networks are in good agreement with tetraphenylmethane-based hypercrosslinked porous aromatic
ꢀ1
48
the shape of the nitrogen isotherms (Fig. 2a) and suggest that frameworks (2.27 mmol g
for PAF-32-OH), the tri(4-
the pores of the polymer networks are dominated by micro- ethynylphenyl)amine-based porous aromatic frameworks
ꢀ
1
42
pores. The contribution of microporosity to the networks can be (1.19–2.50 mmol
g
), the triazine-functionalized CMPs
ꢀ1
49
calculated as the ratio of the micropore volume over the total (2.62 mmol g for TNCMP-2), the phenolsulfonephthalein-
pore volume. As shown in Table 1, the ratios indicated that containing CMPs (2.77 mmol g
ꢀ1
50
for BFCMP-2), but still
polymer networks TEPM-TPA, TEPS-TPA, TEPM-Azo, and TEPS- lower than that of other tetrakis(4-ethynylphenyl)methane-
ꢀ
1
ꢀ1
Azo possess a ratio of 0.63, 0.74, 0.79, and 0.90, respectively. based MOPs (3.77 mmol g , 5.07 mmol g , and 4.28 mmol
ꢀ
1
51,52
The BET specic surface areas of TEPM-TPA and TEPS-TPA
g
for F-MOP-1, F-MOP-2, and HEX-POP-3, respectively),
, respectively, which are higher imine-linked porous polymer frameworks (e.g. 6.1 mmol g for
the
2
ꢀ1
ꢀ1
are 1072 and 937 m
g
2
ꢀ1
2
ꢀ1
53
than those of TEPS-Azo (564 m g ) and TEPM-Azo (598 m g
)
PPF-1),
the benzimidazole-incorporated porous polymer
containing the azobenzene building block. It should be
noted that TEPM-TPA and TEPS-TPA exhibit comparable
surface area to the most of reported conjugated microporous
poly(aryleneethynylene) (PAE) networks by Sonogashira–Hagi-
Table 1 Summary of pore properties for the polymer networks
a
BET
b
c
d
S
S
Micro
ꢀ1
V
Micro
V
Total
S
Micro
/
Micro
V /
26
2
ꢀ1
2
3
ꢀ1
3
ꢀ1
hara cross-coupling chemistry.
Polymer (m g ) (m g ) (cm g ) (cm g ) SBET (%) VTotal (%)
TEPM- 1072
TPA
TEPM- 598
901
552
787
489
0.446
0.267
0.396
0.236
0.708
0.338
0.536
0.261
84.05
92.3
62.99
78.99
73.88
90.42
Gas uptake of CO
2 2 4
, H , and CH
Because of the considerable porosity and nitrogen-rich features,
Azo
we were interested in assessing their performance in gas uptake. TEPS-
The CO
uptake of the polymer networks were measured up to TPA
TEPS-
937
564
83.99
86.7
2
1.13 bar at 273, 283, and 298 K, respectively (Fig. 3a and b, S5,†
Azo
and Table 2). It can be seen that the CO uptake capacity
enhances monotonically with increasing CO pressure. TEPM-
TPA exhibited the highest CO uptake at both 273 and 298 K,
adsorbing 2.41 and 1.39 mmol g
2
a
Surface area calculated from N
) range from 0.05 to 0.20. Micropore surface area
calculated from the N adsorption isotherm using the t-plot method
based on the Harkins–Jura equation. The micropore volume derived
2
adsorption isotherm in the relative
2
b
pressure (P/P
0
2
2
ꢀ1
c
at 1.13 bar among the
d
resulting four polymers. When azobenzene is copolymerized from the t-plot method. Total pore volume at P/P
0
¼ 0.988.
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Fig. 3 (a) CO
2
adsorption isotherms collected at 273 K up to 1.13 bar for the polymer networks; (b) CO
2
adsorption isotherms collected at 298 K;
(
c) volumetric H
2
sorption curves collected at 77.3 K; (d) CH adsorption isotherms collected at 273 K.
4
ꢀ
1
54
network of PPN-101 (5.1 mmol g ), the microporous poly-
H2 and CH4 are important potential clean fuels for auto-
ꢀ
1
55
carbazole of CPOP-1 (4.8 mmol g ), and the nanoporous azo- motive technology; therefore, we also investigated the uptake
ꢀ
1
36
linked polymer of ALP-1 (5.36 mmol g ). To determine the capacities of these two gases by volumetric methods. The
binding affinity between the polymer network and CO mole- hydrogen sorption performance for the polymers networks was
cules, the isosteric heats of adsorption (Qst) were calculated from measured at 77.3 K up to a pressure of 1.13 bar. All adsorption
the CO adsorption isotherms at 273, 283, and 298 K by using
2
2
the Clausius–Clapeyron equation. As illustrated in Fig. 4, the Qst
values of the obtained MOPs are in the range from 22 to 33 kJ
ꢀ1
mol at the near zero coverage. TEPM-Azo shows the highest
ꢀ1
Qst of 33 kJ mol among the polymers, which could be attrib-
uted to the high nitrogen content from azo groups in the skel-
eton of MOPs leading to a strong induce-dipole force with CO
2
35–37
molecules.
TEPS-Azo shows somewhat lower Qst values than
TEPM-Azo. We suspect that even though the azo framework is
same in both, TEPS-Azo with tetrakis(4-ethynylphenyl)silane
units in the structure generated diminish basicity in the
nitrogen species compared with those in TEPM-Azo with no Si
56
(
silicon is acidic in nature). As for triphenylamine-containing
polymers, the Qst value of TEPS-TPA is lower than that of
TEPM-TPA, which is further support the above results in the
case of azo-based polymers.
Fig. 4 Isosteric heats of adsorption for CO
adsorption isotherms collected at 273, 283, and 298 K.
2
calculated from the
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Table 2 Summary of gas uptakes values for the polymer networks
d
e
Henry law selectivity
IAST selectivity
a
b
b
c
H
(wt%)
2
uptake
CH
(mmol g
4
uptake
CO
(mmol g
2
uptake
CO
(mmol g
2
uptake
ꢀ
1
ꢀ1
ꢀ1
Polymer
)
)
)
CO
2
/N
2
CO
2
/CH
4
CO
2
/N
2
2 4
CO /CH
TEPM-TPA
TEPM-Azo
TEPS-TPA
TEPS-Azo
1.4
0.81
0.55
0.65
0.52
2.41
1.78
1.97
1.71
1.39
1
1.14
0.99
26.3
70.8
20.5
64.7
4.6
4.6
3.9
4.3
36.9
121.1
30.5
5.1
6.3
4.9
6.5
0.91
1.08
0.88
111.9
a
b
c
Data collected by volumetric H
2
sorption method at 77.3 K and 1.13 bar. Data collected at 273 K and 1.13 bar. Data collected at 298 K and 1.13
d
e
bar. Adsorption selectivity based on the Henry's law. Calculated from ideal adsorbed solution theory (IAST) by using the CO
adsorption isotherms collected at 273 K.
2 2 4
, N , and CH
49
isotherms show a gradual rise and reached a maximum of 0.88– functionalized CMPs (9.0–25.2 at 298 K), and the amide-
.4 wt% for hydrogen uptake (Fig. 3c). The H uptake sorption functionalized CMPs (8.5–12 at 298 K) under the similar condi-
properties of polymer networks can be correlated with the tions. Moreover, they are also comparable to the best azo-
1
2
61
37
micropore volume and micropore surface area, which was also polymers ever reported like azo-COPs, tri(4-ethynylphenyl)
observed in other MOPs. Triphenylamine-based polymer amine-containing polymers (72 and 63.9 for PAF-34 and PAF-
42
networks exhibit higher H adsorption capacity than azo-based 34-OH, respectively), tetrakis(4-ethynylphenyl)methane-based
2
polymer networks under the same conditions because of their porous aromatic frameworks PAF-18-OH, PAF-26-COOH, and
4
1,46
lager surface areas and narrower pore sizes. The CH uptakes at their metalized derivatives (16–73 at 298 K).
As for separation
adsorption selectivity was about
TEPM-TPA having the highest micropore volume and highest from 3.9 to 4.6 for the four polymers at 273 K. The results
4
4 2 4
273 K up to 1.13 bar (Fig. 3d) were also conducted. As expected, of CH , the calculated CO /CH
ꢀ
1
surface area shows the largest CH
4
uptake of 0.81 mmol g
.
are comparable to that of most other reported porous
organic polymers, such as tetrakis(4-ethynylphenyl)methane-
based porous materials PAF-26 (4–9 at 298 K),
tetraethynylspirobiuorene-containing porous organic polymers
POP (3.4–4.8 at 298 K), the carbazole-based microporous
organic polymer of Cz-POF (4.4–7.1 at 273 K), the nanoporous
41
Selective CO capture over N and CH
2
2
4
57
We also investigated the CO
2
sorption selectivity over N
2
and CH
4
6
0
to assess their potential application in gas separation. The CO
2
,
62
N , and CH adsorption isotherms were measured at 273 K up to covalent triazine-based frameworks (5–7 at 273 K), the tetra-
2
4
63
1
.13 bar (Fig. S6†). The selectivity of the polymer networks was armed triphenylamine-containing MOPs (3.5–4.3 at 273 K),
estimated using the ratios of the Henry's law constant calculated and the azo-containing polymer networks ALP (8 at 273 K)
from the initial slopes of the single-component gas adsorption under the same conditions. The CO /CH
isotherms collected at 273 K at low pressure coverage less than resultant polymers is considerably lower than that of CO
36
2
4
selectivity of the
/N
2
2
60
0
.15 bar, which is typical partial pressure of CO
shown in Table 2, TEPM-Azo and TEPS-Azo exhibit relative high
CO /N
selectivity ratios of 70.8 and 64.7 at 273 K, whereas CO
TEPM-TPA and TEPS-TPA show poor selectivities of 26.3 and by using ideal adsorbed solution theory (IAST) at a standardized
0.5, respectively. These results suggested that the azo-based temperature of 273 K. The method allows for the determination
polymer is efficient for CO /N
separation as expected because of the selectivities as a function of pressure, and has been
of the “N -phobicity” of the azo-linkage.
CO /N
selectivity between azo- and triphenylamine-based poly- in many MOPs. The adsorption data in Table 2 exhibit
2
in ue gas. As because of the higher polarizability of CH
In addition, the gas adsorption selectivity for mixtures of
: N (0.15 : 0.85) and CO : CH (0.05 : 0.95) were predicted
4 2
than that of N .
2
2
2
2
2
4
2
2
2
35–37
The differences in widely used to predict binary gas mixture adsorption behaviors
2
64,65
2
2
mer networks indicate that in addition to the function of the that the calculated IAST selectivities are higher than the values
surface area and pore size, the linkage is very important factor obtained from Henry's constant ratios, as observed for most
17,30,31
2 2 2
that affect CO uptake and the CO /N
selectivity. The calculated reported porous materials.
CO /N2 selectivities by both TEPM-Azo and TEPS-Azo are
2
signicantly higher than those of TEPM-TPA, TEPS-TPA, and
some other MOPs such as tetraethynylspirobiuorene-based
Conclusions
57
porous organic polymers POP (6.7–11.8 at 298 K), porous In summary, we have synthesized a series of microporous
hypercrosslinked aromatic polymers (PHAPs) using tetrahedral organic polymer networks by using Sonogashira–Hagihara
56
precursors (29.3–34.2 at 273 K), tetraphenylsilane-containing cross-coupling chemistry from two kinds of tetrahedral-shaped
porous covalent triazine polymer networks PCTP-2 (31.6 at 298 monomers of tetrakis(4-ethynylphenyl)methane and tetrakis(4-
5
8
K),
tetra(4-(N-carbazolyl)phenyl)silane-based polycarbazole ethynylphenyl)silane. The resulting polymer networks incorpo-
59
microporous polymer P-TCzPhSi (24.8 at 273 K), the nano- rated nitrogen-rich triphenylamine or azobenzene groups
porous azo-bridged polymers (30–43 at 273 K), the carbazolic present a high affinity to CO2 molecules, which has been
porous organic frameworks (19–37 at 273 K), the imine-linked signicantly veried by gas adsorption measurements. TEPM-
porous polymer frameworks (14.5–20.4 at 273 K), the triazine- TPA shows high BET specic surface area up to 1072 m g
36
60
53
2
ꢀ1
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ꢀ
1
with a moderate CO
2
uptake capacity of 2.41 mmol g at 273 K 19 S. Qiao, Z. Du, C. Yang, Y. Zhou, D. Zhu, J. Wang, X. Chen
and R. Yang, Polymer, 2014, 55, 1177–1182.
monomers for the construction of high surface area materials. 20 S. Qiao, Z. Du and R. Yang, J. Mater. Chem. A, 2014, 2, 1877–
In addition, TEPM-Azo and TEPS-Azo exhibit relative high CO2/ 1885.
selectivity of 70.8 and 64.7 at 273 K, respectively, which 21 X. Yang, M. Yu, Y. Zhao, C. Zhang, X. Wang and J. Jiang,
and 1.13 bar, which reinforce the benets of tetrahedral
N
2
compared to that of some other reported polymer networks.
J. Mater. Chem. A, 2014, 2, 15139–15145.
2
2
2
2
2
2 C. Gu, D. Liu, W. Huang, J. Liu and R. Yang, Polym. Chem.,
2015, 6, 7410–7417.
Acknowledgements
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This work was supported by Natural Science Foundation of
China (Grant No. 51103111, 21304055 and 21574077), Educa-
tion Ministry of China (Program for NCET-12-0714), Shaanxi
Innovative Team of Key Science and Technology (2013KCT-17),
the Fundamental Research Funds for the Central Universities
(GK201501002), the Scientic Research Foundation for the
Returned Overseas Chinese Scholars, the Open Fund of the
State Key Laboratory of Luminescent Materials and Devices
2014, 35, 1466–1496.
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