Synthesis of Microporous Nitrogen-Rich Covalent-Organic Framework and Its Application in CO2 Capture

Article abstract of DOI:10.1002/cjoc.201400550

An imine-based nitrogen-rich covalent-organic framework (COF) was successfully synthesized using two triangular building units under solvothermal reaction condition. The gas adsorption properties of the obtained microporous nitrogen-rich COF were investigated. The results indicated that the activated COF material presented good up take capabilities of CO₂ and CH₄ at 61.2 and 43.4 cm³·g^-1 at 1 atm and 273 K, respectively, showing its application potential in selective gas capture and separation.

Full text of DOI:10.1002/cjoc.201400550

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DOI: 10.1002/cjoc.201400550
Synthesis of Microporous Nitrogen-Rich Covalent-Organic
Framework and Its Application in CO Capture
2
†,a
†,a
b
a
a
a
Qiang Gao, Linyi Bai, Xiaojing Zhang, Peng Wang, Peizhou Li, Yongfei Zeng,
,c,d
,a,b,d
Ruqiang Zou,* and Yanli Zhao*
a
Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences,
Nanyang Technological University, 21 Nanyang Link, Singapore 637371
b
School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue,
Singapore 639798
c
Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, China
d
Singapore Peking University Research Centre for a Sustainable Low-Carbon Future, 1 Create Way, Singapore
38602
1
An imine-based nitrogen-rich covalent-organic framework (COF) was successfully synthesized using two tri-
angular building units under solvothermal reaction condition. The gas adsorption properties of the obtained micro-
porous nitrogen-rich COF were investigated. The results indicated that the activated COF material presented good
3
1
up take capabilities of CO and CH at 61.2 and 43.4 cm •g at 1 atm and 273 K, respectively, showing its applica-
2
4
tion potential in selective gas capture and separation.
Keywords CO capture, covalent-organic frameworks, crystalline structure, microporous materials, nitrogen-rich
2
[
6]
[7]
Introduction
porous carbons, metal-organic frameworks, and po-
[
8]
rous organic polymers, have been widely studied and
utilized as ideal materials for CO storage and separa-
The research has shown that global land temperature
[1]
2
has increased over the past 250 years. The main rea-
son of the increasing temperature can be attributed to
human activities, i.e. greenhouse gases generated pro-
duce heat in the atmosphere, hence leading to the Earth
warming. Greenhouse gases include nitrous oxide, car-
bon monoxide, methane, and the most important of all,
tion. Among these materials, nitrogen-rich porous ad-
sorbents show good regeneration properties without
sacrificing high separation efficiency. The incorporation
of amine groups into the porous backbone can effi-
ciently improve the affinity to CO and increase the CO
uptake capacity and selectivity. As such, nitrogen-rich
porous materials have been intensively investigated as
highly promising CO adsorbents.
Due to their compatible porosity, adjustable pore
size and large surface area, covalent-organic frame-
works (COFs) and conjugated microporous polymers
CMPs) have recently been employed as an important
group of porous materials for gas separation, energy
2
2
[
9]
[
2]
carbon dioxide. Emission of carbon dioxide comes
from daily activities like burning of fossil fuels to pro-
duce electricity, burning of gasoline to run vehicles,
cutting down and burning of trees to clear vegetation
and emission from industrial and manufacturing proc-
esses. The global warming will worsen as time goes by
due to the rapid rate of development in different coun-
tries. Therefore, it is important that new ways are im-
plemented to mitigate the emission of greenhouse gases
into the atmosphere, which include exploring physical
[10]
2
(
[
8]
transfer and catalysis. For the application of COF ma-
terials in CO storage and separation, however, it is still
2
necessary to improve the performance of the materials
in order to meet the requirements of practical applica-
tions. In this study, a novel imine-based nitrogen-rich
COF (N-COF) was designed and synthesized via the
Schiff base reaction of two triangular building units.
The gas adsorption properties of this N-COF were then
investigated.
and chemical adsorbents for CO
2
capture and storage
[
3]
(
CCS), and developing novel catalysts for CO con-
2
[
4]
version and utilization. Developing highly efficient
adsorbents has become an urgent task to meet the indus-
trial and environmental demands. Until now, various
porous materials with accessible pores, high surface
[
5]
areas and high pore volumes, such as porous silica,
*
E-mail: zhaoyanli@ntu.edu.sg, rzou@pku.edu.cn; Tel.: 0065-63168792; Fax: 0065-67911961
Received August 13, 2014; accepted September 16, 2014; published online XXXX, 2014.
These authors contributed equally to this work.
†
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201400550 or from the author.
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Gao et al.
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Experimental
General
tion branches using density functional theory (DFT)
method. Transmission electron microscopy (TEM) and
scanning electron microscopy (SEM) images were taken
by JEOL JEM 2010 microscope and JEOL JSM-6340F
FESEM, respectively. Molecular modeling of N-COF
was generated using the Materials Studio.
All reagents for syntheses and analyses were pur-
chased commercially and used as received. Fourier
transform infrared (FT-IR) spectra were recorded as
KBr pellets on a SHIMADZU IR Prestige-21 spec-
trometer. Thermogravimetric analyses (TGA) were car-
ried out on a TGA-Q500 thermo analyzer with a ramp
rate of 10 K/min from room temperature to 1023 K un-
der nitrogen atmosphere. Powder X-ray diffraction
Synthesis of precursors 2,4,6-Tris(4-aminophe-
[
1]
[2]
nyl)-1,3,5-triazine (1) and 1,3,5-triformylbenzene (2)
were synthesized according to the reported procedures.
1
13
The H NMR and C NMR spectra matched well with
those reported ones.
(
PXRD) patterns were recorded with a Bruker AXS D8
Advance diffractometer using nickel-filtered Cu Kα ra-
diation (λ＝1.5406 Å). The N , CH and CO sorption
Synthesis of nitrogen-rich COF (N-COF) 2,4,6-
Tris(4-aminophenyl)-1,3,5-triazine 1 (70 mg, 0.2 mmol)
and 1,3,5-triformylbenzene 2 (48 mg, 0.2 mmol) were
placed in a 25 mL Schlenk storage tube, which were
dissolved in a mixture solvent (10 mL, 1,4-dioxane∶
mesitylene＝10∶1, V∶V) and sonicated for 10 min.
After that, aqueous HOAc (0.75 mL, 6 mol•L ) was
added, and the mixture was degassed by three freeze-
pump-thaw cycles. Finally, the tube was sealed, heated
at 120 ℃ in an oven, and left undisturbed for 72 h. The
precipitate was collected through centrifugation, which
2
4
2
isotherms were measured on an autosorp-IQ instrument
from Quantachrome Instruments Corporation. The ni-
trogen adsorption and desorption isotherms were meas-
ured at 77 K. The samples were outgassed at 120 ℃
for 8 h before the measurements. Surface areas were
calculated from the adsorption data using Langmuir and
Brunauer-Emmett-Teller (BET) methods. The pore-
size-distribution curves were obtained from the adsorp-
－
1
Scheme 1 Synthetic procedure of N-COF
2
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Microporous Nitrogen-Rich Covalent-Organic Framework and Its Application in CO Capture
was washed with anhydrous THF for 3 times, and then
dried at 150 ℃ under vacuum for 24 h. A yellow
powder was obtained in 90% isolation yield.
(Figure 2b) of this hexagonal unit cell shows an excel-
lent agreement with the experimental PXRD pattern, not
only in the peak positions, but also in relative intensities.
The staggered model was also calculated (Figure 2d and
Figure S7 in the SI). However, the simulated PXRD
pattern of staggered structure (Figure 2c) did not match
the observed data. Therefore, the structure of N-COF
was proposed to have the eclipsed layer-sheet arrange-
ment.
Results and Discussion
The synthesis of imine-based N-COF material was
shown in Scheme 1, which was based on the condensa-
tion of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (1) and
1
,3,5-triformylbenzene (2) to result in the imine bond
formation under the solvothermal condition. The reac-
tion was completed in a Schlenk storage tube, instead of
disposable and flame-sealed glass ampule used in most
related reports. The product was insoluble in water as
well as conventional organic solvents. A simulated
structure of N-COF is shown in Figure 1. The SEM im-
ages of N-COF (Figure S1 in the Supporting Informa-
tion (SI)) show that N-COF crystallized with uniform
flower-like morphology. The TEM image (Figure S2 in
the SI) exhibits layer-sheet arrangement of N-COF. The
FT-IR spectrum of N-COF reveals a strong C＝N
1
stretch at 1690 cm (Figure S3 in the SI), indicating the
formation of imine bonds. The N-COF material displays
a high thermal stability of up to 450 ℃, which was de-
termined by TGA (Figure S4 in the SI).
Figure 1 Simulated structure of N-COF. C: blue, N: red, H:
gray.
The crystalline structure of N-COF was determined
and confirmed by PXRD analysis with Cu Kα radiation.
The experimental PXRD pattern (Figure 2a) indicates
that N-COF is a crystalline material with a long-range
structure. In the pattern, N-COF exhibits the most in-
tense peak at 5.54° corresponding to the reflection from
the (100) plane, while other diffraction peaks with 2 of
Figure 2 (a) Experimental PXRD pattern of N-COF; (b) simu-
lated PXRD pattern for the eclipsed structure; (c) simulated
PXRD pattern for staggered structure; (d) staggered structure. C:
blue, N: red.
9
.64°, 11.24°, 14.85°, and 25.58° can be attributed to
the (110), (200), (210), and (001) planes, respectively.
After geometrical energy optimization by using the the-
oretical universal force field to improve the shape of the
molecular building blocks, the unit-cell parameters and
simulated PXRD patterns of N-COF were achieved. The
eclipsed structure of N-COF was simulated using the
space group of P6 with the optimized parameters of a＝
b＝18.1590 Å and c＝3.4970 Å (Figure 1 and Figure S6
in the SI). Interestingly, the calculated PXRD pattern
The porosity and surface area of N-COF were de-
termined by N adsorption/desorption analysis at 77 K
2
(Figure 3). The obtained classic type I isotherm indi-
cates the microporous structure of the N-COF material.
The BET surface area of N-COF was calculated to be
2
1
3
1
1700 m •g , with a total pore volume of 0.84 cm •g
(p/p ＝0.98). Its pore size distribution (inset in Figure 3)
0
was calculated using DFT method, revealing a narrow
distribution of pore size at 1.1 nm.
Chin. J. Chem. 2014, XX, 1—5
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Gao et al.
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structure has been confirmed by both experimental ob-
servation and theoretical simulation. It has been demon-
strated that this microporous crystalline COF material
2
could act as a scaffold for selective CO capture. It is
expected that the present approach will boost the re-
search on employing nitrogen-rich COF materials for
gas adsorption and separation.
Acknowledgement
This research is supported by the National Research
Foundation (NRF), Prime Minister’s Office, Singapore
under its NRF Fellowship (NRF2009NRF-RF001-015)
and Campus for Research Excellence and Technological
Enterprise (CREATE) Programme-Singapore Peking
University Research Centre for
a
Sustainable
Low-Carbon Future, and the NTU-A*Star Centre of
Excellence for Silicon Technologies (A*Star SERC No.:
Figure 3 Nitrogen adsorption (open symbols) and desorption
1
12 351 0003).
(filled symbols) isotherms of N-COF measured at 77 K. Inset:
half pore-size distribution of N-COF.
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1
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1
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1
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[
(
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4
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