Microporous polycarbazole with high specific surface area for gas storage and separation

Article abstract of DOI:10.1021/ja300438w

Microporous polycarbazole via straightforward carbazole-based oxidative coupling polymerization is reported. The synthesis route exhibits cost-effective advantages, which are essential for scale-up preparation. The Brunauer-Emmett-Teller specific surface area for obtained polymer is up to 2220 m² g^-1. Gas (H₂ and CO₂) adsorption isotherms show that its hydrogen storage can reach to 2.80 wt % (1.0 bar and 77 K) and the uptake capacity for carbon dioxide is up to 21.2 wt % (1.0 bar and 273 K), which show a promising potential for clean energy application and environmental field. Furthermore, the high selectivity toward CO₂ over N₂ and CH₄ makes the obtained polymer possess potential application in gas separation.

Full text of DOI:10.1021/ja300438w

Communication
pubs.acs.org/JACS
Microporous Polycarbazole with High Specific Surface Area for Gas
Storage and Separation
†
†,‡
§
†
‡
§
Qi Chen, Min Luo, Peter Hammershøj, Ding Zhou, Ying Han, Bo Wegge Laursen,
‡
,†
Chao-Guo Yan, and Bao-Hang Han*
†
National Center for Nanoscience and Technology, Beijing 100190, China
‡
College of Chemistry & Chemical Engineering, Yangzhou University, Yangzhou 225002, China
§
Nano-Science Center and Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
S Supporting Information
*
Polycarbazole with a good electroactivity and useful
12
ABSTRACT: Microporous polycarbazole via straightfor-
ward carbazole-based oxidative coupling polymerization is
reported. The synthesis route exhibits cost-effective
advantages, which are essential for scale-up preparation.
The Brunauer−Emmett−Teller specific surface area for
photophysical property is a suitable candidate for exploration
of porous organic polymers possessing special functions and
properties. Rigid conjugated backbone of polycarbazole is
beneficial for formation of a porous polymer with permanent
porosity and high physicochemical stability. Nitrogen-contain-
ing conjugated structure makes the polymer electron-rich,
which may enhance the interaction between specific sorbate
2
−1
obtained polymer is up to 2220 m g . Gas (H and CO )
2
2
adsorption isotherms show that its hydrogen storage can
reach to 2.80 wt % (1.0 bar and 77 K) and the uptake
capacity for carbon dioxide is up to 21.2 wt % (1.0 bar and
2c,5b
molecule and adsorbent.
In this communication, prepara-
tion of microporous polycarbazole via carbazole-based oxidative
coupling polymerization is reported (Scheme 1). The obtained
2
73 K), which show a promising potential for clean energy
application and environmental field. Furthermore, the high
selectivity toward CO over N and CH makes the
2
2
4
Scheme 1. Synthetic Route to Microporous Polycarbazole
CPOP-1
obtained polymer possess potential application in gas
separation.
ncreasing CO concentration in the atmosphere mainly
caused by the rapid consumption of fossil fuels has partly led
2
I
to the global climate change and some environmental issues,
1
which have drawn great attentions and concerns. Therefore,
CO2 capture and utilizing clean energy source, such as
hydrogen, are of interest to meet the energy and environmental
demands. As a response, much effort has been devoted to
2
3
explore suitable materials for CO capture or H storage.
2
2
Microporous organic polymers with the intrinsic properties
including large specific surface area, narrow pore size
distribution, high chemical stability, and low skeleton density
have exhibited potential applications in gas storage and
4
separation.
Versatile microporous organic polymers such as polyfluor-
5
6
7
ene, poly(phenylene−ethynylene), polyphenylene, polyi-
8
9
10
mide, polybenzimidazole, polythiophene, and the other
11
hypercrosslinked polymers were obtained smoothly through a
template-free chemical process by selection of proper building
blocks and polymerization reactions, which show efficient
preparation and high flexibility in the molecular design. Since
the capability of microporous organic polymers for the gas
storage and separation is affected by multiple factors such as
material nature, specific surface area, pore structure, and
material morphology, it is still a challenge to develop
microporous organic polymers with potential use and good
performance for the gas storage and separation.
carbazole-based porous organic polymer (CPOP) possesses a
large specific surface area, a high gas uptake capacity, a good
selectivity toward CO over N or CH , and an intrinsic
2
2
4
photoluminescence property.
Oxidative coupling polymerization of carbazole-based build-
ing block exhibits cost-effective advantages such as cheap
catalyst, room temperature reaction, high yield and single
monomer used in the polymerization, which are essential for
Received: January 14, 2012
Published: March 28, 2012
©
2012 American Chemical Society
6084
dx.doi.org/10.1021/ja300438w | J. Am. Chem. Soc. 2012, 134, 6084−6087

Journal of the American Chemical Society
Communication
scale-up preparation of porous materials with potential
application. Since the building blocks show a great influence
on the porosity, specific surface area, and gas adsorption
capacity of the porous organic polymers, design and/or
selection of specific monomer is very important. We have
reported that the monomers with propeller-like nonplanar
13
conformation, such as tetraphenylethylene and hexaphenyl-
7
b
benzene, are good building units to form microporous
conjugated polymers. Therefore, a propeller-like building block
containing three carbazole moieties, 1,3,5-tri(9-carbazolyl)-
benzene (TCB), is selected as the monomer, which is
commercially available or can be easily synthesized by
copper-promoted N-arylation reaction between carbazole and
1
,3,5-tribromobenzene. Oxidative coupling polymerization of
TCB was promoted smoothly by anhydrous FeCl in dry
3
chloroform under nitrogen protection at room temperature.
After polymerization, the desired polymer CPOP-1 was fully
washed with methanol and concentrated HCl solution and was
obtained in 95% yield followed by Soxhlet extraction with
methanol and tetrahydrofuran. The polymer is chemically
stable, even when exposed to dilute solutions of acid and base,
such as HCl and NaOH. Thermal analysis (see Supporting
Information, Figure S1) shows that the material is stable up to
Figure 2. Nitrogen adsorption−desorption isotherms and the pore
size distribution calculated by NLDFT (inset) of CPOP-1.
The pore size distribution (PSD) analysis based on the non-
local density functional theory (NLDFT) approach has been
used extensively to characterize a wide variety of porous
materials although it does have limitations. PSD of the polymer
calculated from the adsorption branch of the isotherms with the
NLDFT approach indicates that CPOP-1 exhibits a dominant
pore diameter centered at about 0.62 nm. Listed in Table S2
(see Supporting Information) are the key porosity parameters
derived from the isotherm, such as the BET and Langmuir
specific surface area, micropore surface area, and pore volume.
Microporous polycarbazole with a high specific surface area
and a narrow pore distribution may interact attractively with
small gas molecules through improved molecular interaction,
which inspire us to investigate its gas (H and CO ) uptake
400 °C under nitrogen and has no evidence for distinct glass
transition for the polymer below the thermal decomposition
temperature due to the nature of its cross-linking structures as
shown in Figure S2 (see Supporting Information). The
structure of CPOP-1 was clearly characterized at the molecular
13
13
level by C CP/MAS NMR spectrum. The C NMR
spectrum for the obtained polymer with assignment of the
resonances is shown in Figure 1. The signal peak at 141.2 ppm
2
2
capacities. On the basis of the hydrogen (77 K) and carbon
dioxide (273 K) physisorption isotherms measured with a
pressure up to 1.13 bar, CPOP-1 exhibits hydrogen storage of
2
1
.80 wt % at 1.0 bar and carbon dioxide uptake of 21.2 wt % at
.0 bar (Figure 3). Both hydrogen storage capacity and carbon
Figure 1. 13C CP/MAS NMR spectrum of CPOP-1.
corresponds to the substituted phenyl carbons binding with
nitrogen atom. The high-intensity peak at 125.5 ppm is ascribed
to the signal peak of other substituted phenyl carbons. The
signal peak for unsubstituted phenyl carbons is located at 120.8
and 109.2 ppm, respectively.
The porosity parameters of CPOP-1 were studied by
sorption analysis using nitrogen as the sorbate molecule.
Nitrogen adsorption−desorption isotherm of CPOP-1 meas-
ured at 77 K is shown in Figure 2, in which the fully reversible
isotherm shows a rapid uptake at low pressure (0−0.1 bar)
indicating a permanent microporous nature. The microporous
polycarbazole exhibits a combination of type I and II nitrogen
Figure 3. Gas adsorption isotherms of CPOP-1 (H
73 K).
at 77 K; CO at
2
2
2
14
dioxide uptake ability of CPOP-1 are exceptionally high.
Actually, the adsorption capacities are among the best reported
results for porous organic polymers under the same conditions.
Moreover, they can be competitive with other kinds of porous
materials such as activated carbons and metal−organic
sorption isotherms according to the IUPAC classification.
The increase in the nitrogen sorption at a high relative pressure
above 0.9 may arise in part from interparticulate porosity
associated with the meso- and macrostructures of the samples
15
and interparticular void. The specific surface areas calculated
2c,17
in the relative pressure (P/P ) range from 0.01 to 0.1 according
frameworks with even higher BET specific surface area.
0
16
to the previous reports (see Supporting Information, Table
As far as we know, at 1.0 bar and 77 K, the hydrogen storage
value of CPOP-1 is the highest one among the reported porous
materials. Comparison of the high gas (H and CO ) uptake
S1 and Figure S3) show that the Brunauer−Emmett−Teller
2
−1
(
BET) specific surface area of CPOP-1 is up to 2220 m g .
2
2
6
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Journal of the American Chemical Society
Communication
capacities of various porous materials with CPOP-1 at low
pressure is listed in Tables S3 (see Supporting Information).
These data prove that, besides the specific surface area, the
molecular structure and chemical nature of the porous
polymers also play crucial roles in the gas uptake capacity of
microporous polymers. Therefore, selection of proper building
blocks is an important premise for synthetic porous polymer
designing.
S5). As expected, CPOP-1 has a nonordered, amorphous
structure proved by the X-ray diffraction (XRD) measurement
(see Supporting Information, Figure S6). Figures S7 and S8
(Supporting Information) show scanning electron microscopy
(SEM) image and high-resolution transmission electron
microscopy (TEM) image of CPOP-1, respectively. The
TEM image is indicative of porous structures of the materials,
which is similar to some reported amorphous microporous
7b,13
In light of high CO capture capacity, large surface area, and
organic polymers.
SEM analysis of CPOP-1 displays that
2
small pore size for CPOP-1, it is reasonable to study the
selective uptake of CPOP-1 for small gases (CO , CH , and
the polymer consists of aggregated particles with submicrom-
eter sizes.
2
4
N ) to evaluate its potential use in gas separation. In particular,
In conclusion, preparation of fluorescent microporous
polycarbazole CPOP-1 via carbazole-based oxidative coupling
polymerization is reported. The preparative strategy exhibits
cost-effective advantages. The BET specific surface area for the
2
the CO /CH separation is one of very important processes in
2
4
natural gas upgrading since the contamination of CH with
4
CO will reduce the energy content of natural gas and cause
2
8
b,18
2
−1
equipment corrosion.
The selectivity of CPOP-1 toward
obtained polymer is higher than 2000 m g . Gas (H and
2
CO over CH and N was investigated by collecting pure-
component physisorption isotherms at 273 K (Figure 4). The
CO ) adsorption isotherms show that the hydrogen storage can
2
4
2
2
reach to 2.80 wt % (1.0 bar and 77 K) and uptake capacity for
carbon dioxide is up to 21.2 wt % (1.0 bar and 273 K), which
can be competitive with the best reported results for porous
organic polymers, activated carbons, and metal−organic
frameworks under the same conditions. Furthermore, the
good selectivity of the polymer toward CO over N and CH
2
2
4
makes it have a promising potential application in gas
separation. Because of its good performance for the gas storage
and separation, CPOP-1 with a large specific surface area
exhibits potential use for clean energy applications and
environmental field. Various microporous carbazole-based
polymers have been prepared by this facile method and the
related porosities and gas sorption analysis are under study.
ASSOCIATED CONTENT
■
*
S
Supporting Information
Details of experimental materials and measurements; synthetic
procedures for monomer TCB and polymer CPOP-1; thermal
analysis and model structure of CPOP-1; BET specific surface
Figure 4. Gas adsorption isotherms (CO , triangle; N , circle; and
2
2
CH , square) of CPOP-1 (273 K).
4
CO uptake shows a nearly linear increase with the pressure
area of CPOP-1 calculated over different pressure ranges; CO
adsorption isotherms of CPOP-1 at different temperatures and
isosteric heat of CO adsorption for CPOP-1; comparison of
2
2
whereas that of CH or N has no apparent increase trend. At
4
2
−1
2
73 K and 1.0 bar, the CO uptake is up to 4.82 mmol g . In
2
2
the gas (H and CO ) uptake capacities of various porous
comparison, the CH and N uptake of CPOP-1 under the
2
2
4
2
−1
materials with CPOP-1 at low pressure; optical properties and
same conditions is 0.13 and 0.19 mmol g , respectively. The
estimated ideal CO /CH and CO /N adsorption selectivity is
1
XRD plot of CPOP-1; SEM and TEM images of CPOP-1; H
2
4
2
2
NMR, 13C NMR, and MS of monomer TCB. This material is
available free of charge via the Internet at http://pubs.acs.org.
3
3 and 25, respectively. The isosteric heat of adsorption CO is
2
calculated based on adsorption isotherms of CO at different
2
temperatures (273 and 291 K) from 0 to 1.13 bar through the
19
AUTHOR INFORMATION
Clausius−Clapeyron equation (see Supporting Information,
■
Figures S4a−c). It can be observed that the isosteric heat of
Corresponding Author
hanbh@nanoctr.cn
−1
CPOP-1 is about 27 kJ mol at zero coverage and drops to 23
kJ mol− as the uptake reaches 130 mg g . The isosteric heat
1
−1
−1
11c
Notes
value is higher than HCP materials (20−24 kJ mol ) or
−1
9b
The authors declare no competing financial interest.
porous polybenzimidazole BILP-1 (19.7−26.5 kJ mol ), and
can be comparable to some CMP materials (25−33 kJ
−
1
2c
ACKNOWLEDGMENTS
mol ). The high selectivity toward CO over N or CH
2
2
4
■
can be ascribed to the electron-rich polycarbazole network and
high charge density at the nitrogen sites of CPOP-1 might
facilitate more favorably the interaction with the polarizable
CO2 cm,9bolecules through local-dipole−quadrupole interac-
The financial support of the Ministry of Science and
Technology of China (Grant 2011CB932500), National
Science Foundation of China (Grants 91023001,
60911130231, and 21002017), and the Chinese Academy of
Science (Grant KJCX2-YW-H21) is acknowledged. The
authors also acknowledge the financial support from the
Danish-Chinese Center for Molecular Nanoelectronics funded
by the Danish National Research Foundation and the Danish
Agency for Science, Technology and Innovation.
2
tions.
The microporous polycarbazole CPOP-1 exhibits strong
photoluminescence properties and shows a green-yellow
emission with a maximum wavelength at about 545 nm and a
shoulder peak at 495 nm (see Supporting Information, Figure
6
086
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Journal of the American Chemical Society
Communication
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