In-Depth Experimental and Computational Investigations for Remarkable Gas/Vapor Sorption, Selectivity, and Affinity by a Porous Nitrogen-Rich Covalent Organic Framework

Article abstract of DOI:10.1021/acs.chemmater.8b04683

Porous nitrogen-rich covalent organic frameworks (COFs) are most challenging materials for selective CO₂ capture, separation, and conversion for a substantive impact on the environment and clean energy application. On the other hand, separation of industrial cyclic congeners (benzene/cyclohexane) by the host-guest interaction through ?-electron-rich and -deficient centers in a COF is the key. On the basis of the strategic design, a triazine-based benz-bis(imidazole)-bridged COF (TBICOF) has been synthesized under polycondensation conditions and structurally characterized by various analytical techniques. Because of the presence of a benz-bis(imidazole) ring, TBICOF exhibits permanent stability and porosity in the presence of acid and base monitored by the wide-angle X-ray pattern and N₂ sorption studies. The enhanced CO₂ uptake of 377.14 cm³ g^-1 (73.4 wt %) at 195 K confirms its high affinity toward the framework. CO₂ sorption is highly selective over N₂ and CH₄ because of very strong interactions between CO₂ and triazine and benz-bis(imidazole)-functionalized pore walls of TBICOF as clearly evident from the isosteric heat of adsorption and ideal adsorbed solution theory calculation, which is higher than other reported functionalized metal-organic frameworks or COFs. Interestingly, TBICOF also behaves as a heterogeneous organocatalyst for chemical fixation of CO₂ into cyclic carbonates under ambient conditions. The ?-electron-deficient triazine and benz-bis(imidazole) moieties have been utilized for selective sorption and separation of benzene (641.9 cm³ g^-1) over cyclohexane (186.2 cm³ g^-1). Computational studies based on density functional theory and grand canonical Monte Carlo molecular simulations further support the selectivity of CO₂ (over N₂ and CH₄) and benzene (over cyclohexane).

Full text of DOI:10.1021/acs.chemmater.8b04683

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Article
In-depth Experimental and Computational Investigations
for Remarkable Gas/Vapor Sorption, Selectivity and Affinity
by a Porous Nitrogen-Rich Covalent Organic Framework
Prasenjit Das, and Sanjay K. Mandal
Chem. Mater., Just Accepted Manuscript • Publication Date (Web): 05 Feb 2019
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In-depth Experimental and Computational Investigations for
Remarkable Gas/Vapor Sorption, Selectivity and Affinity by
a Porous Nitrogen-Rich Covalent Organic Framework
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Prasenjit Das and Sanjay K. Mandal*
Department of Chemical Sciences, Indian Institute of Science Education and Research Mohali, Sector 81, Manauli PO,
S.A.S. Nagar, Mohali, Punjab 140306, India
ABSTRACT: Porous nitrogen-rich covalent organic frameworks (COFs) are most challenging materials for selective CO2 capture,
separation and conversion for substantive impact on the environment and clean energy application. On the other hand, separation of
industrial cyclic congeners (benzene/cyclohexane) by host-guest interaction through -electron rich and deficient centers in a COF is
the key. Based on the strategic design, a triazine-based benz-bis(imidazole) bridged COF (TBICOF) has been synthesized under
polycondensation conditions and structurally characterized by various analytical techniques. Due to the presence of a benz-
bis(imidazole) ring, TBICOF exhibits permanent stability and porosity in the presence of acid and base monitored by wide angle x-
ray (WAX) pattern and N2 sorption studies. The enhanced CO2 uptake of 377.14 cm3g-1 (73.4 wt%) at 195 K, confirms its high affinity
towards the framework. CO2 sorption is highly selective over N2 and CH4 due to very strong interactions between CO2 and triazine
and benz-bis(imidazole) functionalized pore walls of TBICOF as clearly evident from isosteric heat of adsorption and ideal adsorbed
solution theory calculation, which is higher than other reported functionalized MOFs or COFs. Interestingly, TBICOF also behaves
as a heterogeneous organocatalyst for chemical fixation of CO2 into cyclic carbonate under ambient conditions. The -electron
deficient triazine and benz-bis(imidazole) moieties have been utilized for selective sorption and separation of benzene (641.9 cm3g-
1) over cyclohexane (186.2 cm3g-1). Computational studies based on density functional theory (DFT) and Grand Canonical Monte
Carlo (GCMC) molecular simulations further support selectivity of CO2 (over N2 and CH4) and of benzene (over cyclohexane).
product obtained is utilized in industrial and pharmaceutical
INTRODUCTION
applications.8,9 Utilizing a suitable material serving as both
The rapid change in the climate by global warming owing to
adsorbent and catalyst for CO2 capture and chemical fixation
extensive carbon dioxide emission into the atmosphere by
would be highly desirable.
anthropogenic activities such as industrialisation, fossil-fuel
Covalent organic frameworks (COFs), an emerging class of
power plants, deforestation and automobile toxic emissions has
new porous crystalline materials, have been exploited as
been a serious issue in the present day world.1,2 The industrial
excellent aspirants for CO2 capture and sequestration.10,11 COFs
revolution and population expansion is creating environmental
provides almost all the merits of metal-organic frameworks
imbalance leading to scarcity problems for the future
(MOFs), such as structural diversity, easy surface engineering
generation. The development of efficient technologies or
with ordered pore distribution, tailorable functionality, and high
strategies that can capture CO2 efficiently and mitigate the
thermal and chemical stability. These features make them
dilemma is more challenging and urgent task in the present
excellent candidates for high gas uptake, selectivity and
situation.3 Under this canvas, carbon capture and sequestration
reusability.12-14 Various CO2-philic moieties containing
(CCS) technologies play a crucial role to tackle this urgent
heteroatoms have been incorporated into COFs to improve CO2
global issue by adequate capture and storage of pre- and post-
capture and selectivity through Lewis acid-base interactions.15-
combustion CO2 to decrease the emission in an efficient and
19
On the other hand, heterocyclic rings were extensively used
durable manner.4-6 The CCS is much more essential to sustain
in porous organic polymers (POPs) only; however, very
climate change for fossil-fuel combustion in humid conditions.
recently crystalline COFs with such rings have also been
Furthermore, post-combustion capture of flue gas (15:85 v/v
reported.20-24 However, a combination of both triazine and benz-
CO2/N2) and pre-combustion capture of landfill gas (10-50 %
bis(imidazole) moieties in the same COF with nitrogen rich
CH4 over CO2) are required in order to avoid pipeline
surfaces has not been reported for CO2 capture, separation and
corrosion.7 On the other hand, the catalytic conversion of waste
chemical fixation. Furthermore, the incorporation of such
CO2 into workable industrial products is a pompous and
moieties within the framework can be utilized for the
alternative strategy for CO2 fixation. The cycloaddition of CO2
exploitation of these materials as selective adsorbents for
to cyclic carbonates is an atom economy process, which is one
electron-rich benzene (Bz) over cyclohexane (Cy) by favorable
of the basic principles of green chemistry; moreover, the
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OHC
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CHO
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NH2
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Mesitylene:NMP:Dioxane
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, 60 o
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ic a
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.4HCl
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HN
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Figure 1. Synthesis of TBICOF and model monomer.
 interactions. This addresses an industrially important
chemical separation of a liquid phase hydrocarbon mixture of
Bz/Cy.25 Their separation cannot be feasible by conventional
methods due to their markedly similar boiling points (Bz, 353.3
K; Cy, 353.9 K) and very similar kinetic diameters.26
RESULTS AND DISCUSSION
Synthesis and Structural Characterization. TBICOF was
synthesized by the polycondensation reaction between tri(4-
formylphenoxy)cyanurate (TFPC),27 1,2,4,5-tetraminobenzene
Herein, we report a new porous, highly stable, nitrogen rich
triazine based and benz-bis(imidazole) bridged COF, TBICOF,
to showcase its applications in (a) highly selective CO2
sorption, (b) separation over N2 (flue gas) and CH4 (landfill gas)
followed by ideal adsorbed solution theory (IAST), and (c)
chemical fixation of CO2 to make various cyclic carbonates at
ambient conditions. As anticipated, TBICOF has been found to
be very efficient and selective for the separation of benzene
over cyclohexane (about 44 at 298 K for an equimolar Bz/Cy
mixture). Both DFT and GCMC molecular simulation have
provided excellent support to the experimental results for the
high CO2 uptake, selectivity and interaction site with host
TBICOF. Similarly, the strong interaction and selectivity of Bz
over Cy with TBICOF was preferentially observed.
o
(TAB) and imidazole at 120 C in a mesitylene/NMP/dioxane
(2:1:1) mixture for 3 days with 88% yield (Figure 1 and Scheme
S1). For the synthesis of TBICOF, several solvothermal
methods have been screened (WAX patterns and maps are
shown in Figure S1). It has been observed that the paramount
crystallinity was obtained using the mesitylene/NMP/dioxane
(2:1:1) mixture. Thus, the synthesis of crystalline TBICOF via
a cascade reaction without any additional catalyst is remarkable
compared to the multistep synthesis of amorphous
benzimidazole-based organic polymers.20-22 As shown in
Scheme S2, the formation of benzimidazole ring in TBICOF
include three steps: (i) formation of imine-linked intermediate,
(ii) ring closing to form benzimidazoline intermediate, and (iii)
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Figure 2. Structure analysis of TBICOF: (a) Experimental (red) and Pawley refinement (blue) showing very minimal difference
(black line) with Rp and Rwp of 1.92% and 3.16%, respectively, for hexagonal AA stacking with space group P6/m. (b) Simulated
PXRD pattern for AA structure (purple). (c) AB structure (cyan). (d) ABC structure (violet). (e) AA structure of TBICOF. (f)
Pawley refinement structure (Color code; carbon: grey, oxygen: red, nitrogen: blue, hydrogen: yellow). (g) AB structure of
TBICOF. (h) ABC structure of TBICOF.
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acceptor-less dehydrogenation of benzimidazoline intermediate data for simulated pattern (blue line) were indexed and well
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(irreversible). The first step is the rate determining step, through
which the crystalline COF structure can be formed by reversible
formation of imine linkages. It is noteworthy that the imidazole
used in the reaction acts as an additional base (a
dehydrogenating agent) to facilitate the aromatization in the
third step.24,28 For comparison, a model monomer (Yield: 90%)
was also synthesized following the same condensation route
except 1,2-diaminobenzene (DAB) was used instead of TAB
fitted by implementing the X-cell program of Pawley
refinement and matched with the experimental PXRD
pattern (red dots) with a minimum difference (black line)
(Figure 2a). An excellent fit was obtained with good Rp
(1.92) and Rwp (3.16) and cell parameters a = b = 36.0252
Å and c = 3.4032 Å, which are obtained from the simulated
pattern. Moreover, in the experimental WAX profile, the
strong peak at 2.5o (100), indicates that the highly periodic
structure is present in the COF. These diffraction peaks are
at 2 = 2.5o, 5.3o, 10.76, 14.3, 17.5o and 25.1o with d values
33.9, 15.8, 7.15, 6.18, 5.1 and 3.45 Å, corresponding to the
(100), (200), (210), (330), (430) and (001) facets,
respectively (Bragg’s equation, 2dsin = n, where n = 1
and  = 0.154 nm). Also, the strong - stacking of the 2D
sheets (001 facet) was observed with an interlayer distance
of 3.4 Å at 2 = 25o. This confirms that TBICOF has the
AA stacking; however, the simulated PXRD patterns of
AB and ABC were inconsistent with the experimental
result. The model monomer shows the crystallinity in
WAX patterns and WAX 2D map (Figure S12).
Microscopic Analysis and Stability Test. Several
microscopic techniques, such as field emission scanning
electron microscopy (FESEM), scanning transmission electron
microscopy (STEM), high resolution transmission electron
microscopy (HRTEM) and atomic force microscopy (AFM),
have been utilized to ascertain the surface property of TBICOF.
FESEM and STEM images of TBICOF showcased that the
condensation polymerization of TFPC and TAB afforded self-
assembly of nanosheets to form microflowers with uniform
thickness of 160 nm (Figures 3a,b and S13). Similarly, TEM
image of TBICOF depicted the similar self-assembly of
nanosheets, and the HRTEM image displayed uniformly
ordered porous hexagonal arrangement (Figures 3c-f and S14).
These exfoliated nanosheets make a ring-like assembly in mica
plate with a height of 12-15 nm and an average diameter of 150-
200 nm. This result is highly correlated with FESEM and
HRTEM data (Figures 3g-i and S15). Furthermore, an AFM
image provided the height thickness corresponding to 30-35
unit cell on the basis of their optimized AA stacking model.
Overall, the lateral sizes of TBICOF obtained from the SEM,
TEM and AFM data indicate that TBICOF has a high aspect
ratio in the 2D layers. On the other hand, the model monomer
displayed rod like morphology with thickness of 161 nm which
is correlating with the TBICOF diameter (Figure S16). The
high chemical stability of TBICOF was examined by
immersing in 3 N NaOH and 3 N HCl for 7 days and monitored
by the WAX and FESEM (Figures S17-S19).
o
using EtOH/dioxane (4:1) as a solvent at 60 C (Scheme S3).
9
FTIR spectra of TBICOF and its model monomer exhibit the
characteristic stretching frequency for the C=N bond of benz-
bis(imidazole) moiety at 1608 and 1609 cm-1, respectively,
confirming the completion of reaction (Figures S2-S3). The
formation of the model compound was further confirmed by
HRMS data with the observation of a peak at 706.2235 (cal.
[M+H]+, 706.2270) (Figure S4). The elemental analyses of
TBICOF and its model monomer confirmed the calculated
values of C, H and N close to the corresponding experimental
values. The high N value in this analysis indicates TBICOF is
nitrogen rich system. The solid-state absorbance spectra of
TBICOF and its model compound show two absorption bands
at 384 and 316 nm attributing to the * transition for the N-
containing conjugated -system, respectively (Figure S5). For
investigating the thermal stability, the thermogravimetric
analysis (TGA) of TBICOF and its model compound was
carried out. A major weight loss near 400 oC for TBICOF from
this analysis demonstrates that it is highly stable in comparison
with its model monomer (Figure S6). The 13C CP-MAS NMR
spectrum of TBICOF (Figure S7) confirming its atomic
precision construction (exhibits signals from 100-200 ppm for
eight different carbon centres). The peaks corresponding to
imidazole unit and triazine ring appeared around 153.03 and
173.1 ppm for TBICOF, while 152.8 and 173.4 ppm for its
model monomer (Figure S8). Additional signal of TBICOF in
the aromatic region are consistent with the building block. The
1H and 13C NMR spectra of model compound in d6-DMSO also
show characteristic signals at 7.62 ppm and 152.8 ppm,
respectively, confirming the formation of a benzimidazole ring.
Structure Solution of TBICOF. In order to ascertain
the periodical structure of TBICOF, simulation of PXRD
was carried out using Reflex module in Accelrys BIOVIA,
Materials Studio 2017R2 software package. The powder
diffraction pattern of TBICOF exhibits well-defined
diffraction peaks, confirming the crystalline nature of the
framework (Figure 2a). Most of the COFs are constructed
by the three-connected ligand with ditopic linker having
hexagonal layered structure.29-31 Considering the
hexagonal system for TBICOF, both eclipsed structure
(AA) and staggered structures (AB and ABC) were
optimized using the DFT-D calculation (CASTEP
method) using space group P6/m and simulated PXRD
patterns were generated (Figure 2 and Figures S9-S11,
Table S1-S3). The unit cell parameters for hexagonal
system differ in ‘c’ axis, where eclipsed (AA) and
staggered (AB and ABC) structures have a = b = 36 Å, c =
3.4 Å (AA) or 6.8 Å (AB) or 10.2 (ABC),  =  = 90o and
 = 120o, which give (100) facet at 2 = 2.5o. The PXRD
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Gas Sorption Studies. The successful incorporation of
triazine and benz-bis(imidazole) functionalized pore sites
in TBICOF and its stability based on TGA and PXRD
were the keys to exploring its potential gas sorption
studies. Thus, its sorption studies at different temperatures
(N2 at 77 K; CO2, N2, CH4 at 263, 273, 298 and 313 K) have
been performed. A mixture of type I and type IV reversible
isotherm was observed for N2 at 77 K. The Brunnauer-
Emmet-Teller (BET) and Langmuir surface areas were
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Figure 3. (a) FESEM image focussing on micro-flower areas in TBICOF. (b) STEM image of TBICOF. (c) TEM image of TBICOF
depicting of microflower. (d, e, f) HRTEM images of TBICOF. (g) 2D AFM image of TBICOF revealing its porous spherical nature. (h)
3D AFM height profile ruminating the uniform nature. (i) Height profile.
found to be 1424 m2g-1 and 1702 m2g-1, respectively
(Figure 4a and S20). The Non-Local Density Functional
Theory (NLDFT) was utilised to compute the pore size
distribution of TBICOF and was found to be ~0.8-4.5 nm
(with the highest peak at 2.5 nm compared to the same from
simulated at 2.9 nm), which is attributed to mixture of
micro or macro porous nature32 (Figure 4b and S21). This
broad pore size is due to the presence of flexible TFPC
linker in TBICOF (Figure 4b, inset). The chemical
stability was not only checked by WAX pattern and
FESEM but also followed by N2 sorption isotherm (Figure
4a). N2 sorption isotherms indicate that the porosity was
perfectly maintained in the presence of acid and base.
Additionally, it was observed that the BET surface area and
pore diameter were almost remain constant.
The CO2 sorption curves exhibit fully reversible
isotherms at 313 K, 298 K, 283 K, 273 K and 263 K. The
CO2 uptake at 313, 298 K, 283 K, 273 K and 263 K was
23.96, 39.04, 54.07, 68.89, and 84.5 cm3g-1 (STP, 4.6, 7.48,
10.62, 13.53 and 16.59 wt%), respectively (Figure 5a).
Interestingly, this uptake of CO2 is higher or comparable
with triazine and benz-bis(imidazole) based COFs and
other well-known MOFs or POPs such as COF-1, COF-5,
COF-6, COF-8, COF-10, COF-102-103, TpPa-series,
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Figure 4. Gas adsorption-desorption curves for TBICOF: (a)
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N2 at 77 K. (b) Pore-size distribution; (inset) simulated pore-
size of TBICOF including van der Waal radii.
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TpBD-series, DhaTpH, ACOF, azoCOP-1-3, PECONF-1,
TBILP-1, ZIF-100, Cd-ATAIA, Co-MOF and IISERP-
MOF20 (see Table S4 for the full list).15-22,33-44 It is
noteworthy to observe the high uptakes of CO2 at 0.5 bar
(2.54 mmolg-1 at 263 K, 2.01 mmolg-1 at 273 K, 1.61
mmolg-1 at 283 K, 1.01 mmolg-1 at 298 K and 0.632
mmolg-1 at 313 K), which is the partial pressure of CO2 in
landfill gas mixture. This steep uptake of CO2 at low-
pressure region indicates strong dipole-quadrupole
interactions of CO2 molecules with N and O centers present
in the triazine and benz-bis(imidazole) moieties of
TBICOF. These uptakes are pretty less due to higher pore
size of TBICOF compared to BILPs organic
polymers.20-22 Surprisingly, when the temperature was
lowered to 195 K, a drastic improvement of high CO2
uptake (377.14 cm3g-1 or 73.4 wt% at 1 bar) was obtained,
confirming its high affinity towards the framework (Figure
5b). The CH4 sorption curves exhibit fully reversible
isotherms with an uptake of 7.59, 13.7, 23.37, and 29.09
cm3g-1 (STP, 0.54, 0.98, 1.67 and 2.08 wt%) at 313, 298,
273 and 263 K, respectively (Figure 5c, Table S4). On the
other hand, the uptake of N2 is lower (5.74 cm3g-1, STP, at
263 K; 4.31 cm3g-1, STP, at 273 K and 2.04 cm3g-1, STP, at
298 K) (Figure S22). The quantitative binding affinity was
evaluated from coverage-dependent adsorption enthalpies
of CO2, CH4 and N2 gas molecules in TBICOF calculated
from their adsorption isotherm at 263, 273 and 298 K by
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Figure 5. (a) CO2 sorption at 313, 298, 283, 273 and 263 K. (b) CO2 sorption at 195 K. (c) CH4 sorption at 313, 298, 273 and 263 K. (d)
Recycling efficiency of TBICOF for CO2 capture.
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Figure 6. Selectivity of CO2 over N2 and CH4 for TBICOF at 313, 298, 273 and 263 K: (Column 1) uptake of CO2, N2 and CH4; (Column
2) change of adsorption selectivity with increasing CO2 mol% from 5 to 30 % at interval of 5% mixture of CO2/N2; (Column 3) change of
adsorption selectivity with increasing CO2 mol% from 10 to 50% at interval of 10% in a binary CO2/CH4.
using Clausius-Clapeyron equation and their fitting by
virial45 method (Figures S23-S28, Table S5). These two
methods showed excellent agreement with each other. The
isosteric heat of adsorption (Qst) at zero loading are 42.8,
21.3 and 16.2 kJmol-1 for CO2, CH4 and N2, respectively,
which further confirms a decrease of binding affinity in the
order of CO2 > CH4 > N2. The Qst for CO2 of TBICOF at
zero coverage (42.8 kJmol-1) reflect the very strong
interactions between CO2 and triazine and benz-
bis(imidazole) functionalized pore walls of TBICOF
(Figure S24). Moreover, its Qst value is exceptionally
higher than other functionalized MOFs, COFs and POPs
listed in Table S7.14,15,16 On the other hand, the higher Qst
value for CH4 than that of N2 indicates the stronger
adsorbate-absorbent interaction of CH4 compared to N2.
Also, the Qst of CH4 is comparable and higher than other
MOF, COF and POP based systems (Table S7).15-22,33-43
Recyclability and Efficiency of CO2 Capture. To
utilize for practical application in gas uptake and
separation, the compatibility and recyclability of material
are urgent. For this purpose, TBICOF was implicated as
an adsorbent for CO2 uptake cycles at 298, 273 and 263 K
up to 1 bar pressure. Remarkably, TBICOF almost
reclaimed its CO2 uptake capability up to three consecutive
cycles and also even after all gas or vapor sorption (Figure
5d and S29). To perform the sorption measurement, the
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o
material was degassed at 120 C for 24 h under high
vacuum. Also it provided very similar result after gas (N2,
CO2, CH4) and vapor (Bz, Cy and water) sorption.
and POP based systems such as CTFs (CO2/N2: 31.2/273 K),33
TBILP-1 (CO2/N2: 62/298 K, CO2/CH4: 9/298 K),22 and Azo-
COP-1-3 (CO2/N2: 96-130.6/298 K, CO2/N2: 63.7-109.6/273 K
and CO2/N2: 27.4-44/263 K)34. Literature survey on both
CO2/N2 and CO2/CH4 selectivity at different pressure,
temperature, concentration is tabulated in Table S7. These
selectivity and gas uptakes are tremendous by a porous
TBICOF with remarkable physical and chemical stability
making these materials very promising for CO2 separation from
flue gas as well as landfill gas mixture and also for future use in
gas storage.
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CO2/N2 and CO2/CH4 Selectivity by IAST Method.
Motivated from the aforementioned results, we further
investigated the potential of TBICOF for gas separation.
To emulate the separation behaviour of TBICOF under a
more genuine world setting, binary mixture selectivity at
four different temperatures (313, 298, 273 and 263 K) were
enumerated by employing the IAST method developed by
Myers and Prausnitz.46 The binary mixture of CO2/N2
(15:85, flue gas composition) and CO2/CH4 (50:50, landfill
gas composition) with the pressure range up to 100 kPa
were used for calculation. The dual-site Langmuir-
Freundlich (DSLF) isotherm model has been applied for
the fitting the unary isotherms of CO2, N2 and CH4 at 263,
273, 298 and 313 K with very good R2 value (Figures S30-
S41). Using this fitting, the saturation capacities (qm),
affinity coefficients (b) and deviation from an ideal
homogeneous surface (n) for different gases such as CO2,
N2 and CH4 at 313, 298, 273 and 263 K were obtained
(Table S6). The calculated adsorption selectivity of
TBICOF is 26.6, 27.38, 38.9 and 40.8 (zero coverage) and
44.03, 40.3, 46.7 and 37.3 (higher pressure, 1 atm) at 313,
298, 273 and 263 K for CO2/N2 (15:85), respectively
(Figure 6). On the other hand, the CO2/CH4 (50:50)
selectivity of TBICOF is 7.74, 8.78, 9.73 and 10.9 (zero
coverage) and 5.96, 7.72, 11 and 9.5 (higher pressure (1
atm)) at 313, 298, 273 and 263 K, respectively. It was
observed that the selectivity increased slightly from 0 to 12
kPa pressure and decreased up to 35 kPa pressure, followed
by a sharp increase at higher pressure at 298 K for CO2/N2
(Figure 6). There is an increase in selectivity with increase
in pressure at 313, 273 and 263 K for CO2/N2. On the other
hand, there is a sharp decrease in selectivity at lower
pressure followed by increase in selectivity at higher
pressure at 313, 298, 273 and 263 K for CO2/CH4 (50:50),
respectively. This result demonstrates that the adsorption
selectivity of CO2/N2 is better than that of CO2/CH4.
We also tested and demonstrated the selectivity by increasing
the molar ratio of CO2 from 5 to 30% with the increment of 5
mol% for a mixture of CO2/N2 and 10 to 50% with increment
of 10 mol% for a mixture of CO2/CH4. The calculated result
shows that the predicted selectivity for TBICOF was increasing
with an increase in CO2 mole fraction. It was observed that the
selectivity increased from 41.13 to 46.09, 33 to 47.7, 32.5 to
78.8 and 28.8 to 55.6 with the increased molar ratio of CO2 from
5 to 30% for a mixture of CO2/N2 at 313, 298, 273 and 263 K,
respectively. Also, the selectivity increased from 5.36 to 5.96,
7.3 to 7.8, 10.2 to 11 and 7.9 to 9.5 with increased molar ratio
of CO2 from 10 to 50% for a mixture of CO2/CH4 at 313, 298,
273 and 263 K, respectively. Such an enhancement of CO2 in
both the cases at all temperatures is remarkable (Figure 6). All
these selectivity values are significantly higher and comparable
with many well- known MOF based systems such as PCN-88
(CO2/N2: 18/298 K, CO2/CH4: 5/296 K),36 PCN-61 (CO2/N2:
15/298 K),37 ZIF-100 (CO2/N2: 25/298 K and CO2/CH4: 5.9/298
K),40 Cd-ATAIA (CO2/N2: 54.08/298 K and CO2/N2: 46.98/273
K),42 NOTT-202 (CO2/N2: 26.7/273 K and CO2/CH4: 4.3/293
K, CO2/CH4: 2.9/273 K),43 Co-MOF (CO2/CH4: 16.9/313 K)44
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Quantum Computational Studies. To understand the high
CO2 capture selectivity compared to N2 and CH4, quantum
computational studies based on DFT47 using the Gaussian 09
program and GCMC48 molecular simulation using Material
studio program were carried out. For DFT analysis, crucial
benz-bis(imidazole) repeating unit of TBICOF in the presence
of CO2, N2 and CH4 were optimized using B3LYP/6-31G+(d,p)
basis set (Figures 7a-c and S42-S44). It has been observed that
the binding affinity of benz-bis(imidazole) is more towards CO2
in comparison to N2 and CH4. In particular, the binding energy
was calculated for CO2 (BE = -3.6 (N-H…O) or -3.1 (N…C=O)
kcal/mol), N2 (BE = -1.88 kcal/mol) and CH4 (BE = -2.08
kcal/mol) which revealed that CO2 is more stabilized than N2
and CH4. TBICOF adsorbent consisting of (2 x 2 x 1) unit cells
for CO2, N2 and CH4 was utilised to perform GCMC simulation
at 298 K up to 10 bar (Figures S45a-d). It is noteworthy to
observe that the probability distribution of CO2 is very high as
depicted by the increase in probability density (illustrated in red
color) from 1 bar to 10 bar pressure (blue to red depicting high
probability). Based on the loading vs pressure plot it is more
clear that the CO2 uptake and selectivity is exclusively high
compared to that of N2 and CH4 (Figure S45e). This is in
accordance with the obtain experimental results. In addition to
that, the very strong interaction of TBICOF with CO2 was also
established via GCMC simulation by evaluating the binding
energy of CO2 (-35.6 kJ/mol), N2 (-8 kJ/mol) and CH4 (-8.7
kJ/mol) (Figure S45f). This result was well correlated with the
isosteric heat of adsorption (Qst) which was obtained from
thermodynamic of adsorption process (vide supra). From fixed
pressure metropolis GCMC method, the number of CO2
molecules for (2 x 2 x 1) unit cells were calculated to be 9 (3
CO2 molecules per unit cell) in a pore which is well
corroborated with the experimental result (2.95 CO2) (Figures
7d and S46). It was observed that there was strong adsorbate-
adsorbent and adsorbate-adsorbate interactions. The
intermolecular distance between CO2 and TBICOF was
validated with the DFT calculation (d = 2.27 Å (GCMC)/2.3 Å
(DFT) (N-H…O)) or 3.31 Å (GCMC)/3.1 Å (DFT (N…C=O) Å
and the bond angle of CO2 is reduced to 174.9o. A very close
intermolecular distance between CO2 and BILPs (2.72-2.89 Å
using M06/6-311+G* level) and similar angle deformation of
CO2 were reported in the literature.49 It is also observed that
there is an interaction of CO2 with the phenyl ring of the central
benz-bis(imidazole) and the phenyl ring attached to the triazine
moiety and thus the overall system becomes highly polar. In the
channel, three CO2 molecules arrange themselves in a triangle,
where the + carbon atom of one CO2 interacts with - oxygen
atom of another CO2 molecule (Figure 7e). This electrostatic
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Figure 7. DFT optimization at B3LYP/6-31G+(d,p) level of benz-bis(imidazole) repeating unit of TBICOF with CO2 (a), N2 (b) and CH4
(c). GCMC molecular simulation: (d) CO2 position in TBICOF. (e) Interaction and distance between CO2 and TBICOF. (f) CH4 position
in TBICOF. (g) GCMC simulation of CO2/CH4 (50:50) mixture at 298 K, (h) their binding energies and (i) loading amount in mixed gas
phase (simulated and experimental).
interaction between CO2 molecules and the framework
attributes to the dipole-quadrupole interaction.49 Furthermore, it
was observed that the number of CH4 molecules is 0.67 per unit
cell which is also similar to the experimental result (0.72 per
unit cell) (Figure 7f). Moreover, GCMC simulation was
accomplished for mix gas CO2/CH4 (50:50) at 298 K up to 1 bar
(Figure 7g). The very high selectivity, BE and loading were
observed for CO2 over CH4 (Figure 7h). The mix gas loading
was well validated with GCMC (simulated) and IAST
(experimental) results (Figure 7i). Similarly, GCMC simulation
was also utilized for mixed gases CO2/CH4 and CO2/N2 (50:50)
at 313 K and the high selectivity of CO2 was observed over N2
and CH4 (Figure S47).
Chemical Fixation of CO2 Under Ambient Conditions.
The inherent CO2-adsorbing property and embedded Lewis
basic N and O sites in the framework indicate that TBICOF
should act as the favorable heterogeneous catalyst for CO2
related reactions. One of the chemical reactions for CO2
conversion involves epoxides, which upon reaction with CO2
lead to the formation of cyclic carbonates. These cycloaddition
products have been intensively scrutinized due to vast
applications in pharmaceutical and electrochemical
industries.50-52 In this regard, catalytic performance of TBICOF
(in presence of tetra-n-butylamonium bromide (TBAB) under
CO2 balloon pressure at room temperature for 24 h) in the
cycloaddition of CO2 with various aromatic and nonaromatic
epoxides to produce various cyclic carbonates were explored.
However, very limited COFs have been explored for
heterogeneous chemical fixation of CO2.53,54
The obtained TBICOF was commenced as a heterogeneous
catalyst for CO2 cycloaddition without any prior treatment.
Initial optimization conditions were carried out for the
cycloaddition of CO2 with epichlorohydrin under various
catalyst concentration and time. As shown in Table S8,
TBICOF shows the efficient catalytic activity for the model
reaction with yields 70-95% at room temperature and ambient
condition in presence of the co-catalyst TBAB (0.1-0.5 mol%)
and CO2 balloon pressure for 24 h. Moreover, the cycloaddition
reaction was carried out in the presence of only catalyst, and no
product was obtained for the model reaction (entry 7, Table S8).
However, only 28% product was obtained from the
cycloaddition of CO2 in the presence of TBAB (0.5 mol %) only
(entry 8, Table S8). These results depicted that the
cycloaddition of CO2 with epichlorohydrin can be obtained in
high yield by synergistic utilization of TBICOF and co-catalyst
TBAB under ambient condition.54-62
After optimization, the substrate scope was explored for the
cycloaddition reaction flourished above (0.1 mol% of
TBICOF, 0.5 mol% TBAB and CO2 balloon at ambient
condition). For the first time, we developed the effect of
halobenzene for the cycloaddition reaction of CO2. The
cycloaddition reaction of 2-(4-bromophenyl)oxirane with CO2
provided better yield compared to other 3- or 4-chloro
substituted epoxide and styrene epoxide (Table1, entry 4).
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application (Table S9).27,65,66 For further detailed study, the
Furthermore, in case of sterically hindered epoxide
substrate like butyl glycidyl ether, the yield decreased to
72% under the same condition (Table 1, entry 9). This
occurrence may be due to limited diffusion of large substrate
into the 1D pore channels of TBICOF.55-62 In the endeavor, the
cycloaddition reaction of CO2 with cyclohexene oxide gave
70% yield with TON of 700 (Table 1, entry 10). To the best of
our knowledge, these TON are comparable with other
previously reported MOF based catalyst under similar
condition.55-62
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key separation of Bz/Cy was enumerated by IAST
calculation. The unary isotherm of Bz and Cy was fitted
with R2 = 0.991 and 0.996, respectively, by employing
DSLF isotherm model (Figure S49-S50). The adsorption
selectivity (Sads) for an equimolar Bz/Cy mixture by
TBICOF was analyzed by the IAST method to obtain a
value of >44 at 298 K (Figure 9b).
Catalytic Cycloaddition of CO2 with Epoxide to Produce
Cyclic Carbonates
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O
TBICOF catalyst/
In order to examine the stability and durability of
TBICOF, the catalyst was isolated after the reaction by
centrifugation, filtration and washed with acetone and
dried in vacuum. To determine the reusability of TBICOF
during the catalytic process, epichlorohydrin has been
taken as an example to produce 4-(chloromethyl)-1,3-
dioxolan-2-one. It was recycled in five consecutive
experiments and its catalytic activity was monitored. There
is no significant change in the original catalytic activity of
TBICOF (Figure 8a) with yield preserved up to > 90%.
The recovered framework was characterized by the WAX
and FESEM images (Figures 8b,c).
Based on the current results and previous reports on
related systems52,53,63,64, a possible mechanism for the
TBICOF catalyzed cycloaddition reaction of CO2 with
epoxides is proposed in Figure 8d. In addition to
understanding the interaction of epoxide with TBICOF,
GCMC simulation was performed between TBICOF and
propylene oxide (PO). It is observed that there is a strong
H-bonding interaction between C-O of PO and N-H of
TBICOF layers (N-H…O = 2.14-3.6 Å) (Figure S48).
Based on the above results, the C-O bond of the epoxide
ring is activated by the N-H group of benz-bis(imidazole)
ring on the pore wall of the COF via H-bonding.
Concomitantly, the less sterically hindered carbon atom of
the epoxide is attacked by the Br- of TBAB to form the
intermediate (I). This step is followed by the opening of
the epoxide to form an oxyanion which is stabilized by the
benz-bis(imidazole) N group on the adjacent layer (II).
Next, the oxyanion intermediate undergoes a nucleophilic
addition to the CO2 molecule to form an alkylcarbonate
anion (III). Finally, the ring closure of the intermediate III
followed by removal of Br- produces the cyclic carbonate
and rejuvenates the COF for further cycles. Therefore,
TBICOF is an excellent candidate as a heterogeneous
catalyst marked by its high activity and recyclability for
chemical fixation via CO2.
TBAB
Room temperature
24 h
O
CO2
O
O
+
R
R
Table 1. Substrate scope for cycloaddition of CO2 reaction
catalysed by TBICOFa
Conversionb
Entry
R
Product
TONc
(%)
O
O
O
1
54
540
O
O
O
2
3
67
70
671
703
Cl
Cl
O
O
O
Cl
Br
Cl
O
O
O
4
5
86
64
862
638
Br
O
O
O
O
O
O
O
O
6
7
H3C
98
95
981
952
O
O
Cl
Cl
O
O
O
8
9
82
72
70
819
724
700
H3C
O
O
O
O
H3C
O
O
H3C
O
O
O
10
O
aReaction conditions: 0.1 mol% of TBICOF, TBAB (0.5 mmol),
epoxide (1.5 mmol), CO2 (balloon pressure), solvent-free at 26-28 ◦C
for 24 h. bCalculated using 1H NMR spectroscopy. cNumber of moles
of product per mole of the catalyst.
The high sorption and selectivity of benzene over
cyclohexane was observed due to the strong - interaction
between -electron deficient triazine ring and benz-
bis(imidazole) moieties and the -electron rich benzene. To
further understand the good selectivity of Bz over Cy, GCMC
molecular simulation was performed on TBICOF (Figure 9c).
Interestingly, it was observed that the uptake of Bz is very high
and negligible uptake for Cy with a very high BE of Bz (-47
kJ/mol) compared to Cy (Figure 9c-e). From the fixed pressure
metropolis GCMC method, the number and position of Bz
molecules for a (1 x 1 x 1) unit cells of TBICOF were observed
(Figure S51). Water sorption is very much important for many
Vapor Sorption: Separation of Benzene Over
Cyclohexane. To establish the selective sorption
behaviour of Bz/Cy by TBICOF, the vapor sorption
experiment of Bz and Cy was measured at 298 K (Figure
9). It is observed that the uptake amount of Bz (STP, 641.9
cm3g-1 at p/p0 ~ 1 was significantly higher than that of Cy
(186.2 cm3g-1, at p/p0 ~ 1) (Figure 9a). Both Bz and Cy
show type IV sorption isotherm with very large hysteresis
in case of Bz compared to Cy indicating strong interaction
with the host. TBICOF adsorption for Bz and Cy are
surprisingly higher than those reported for COFs and
MOFs, suggesting it is a suitable candidate for industrial
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Figure 8. (a) Catalytic recyclability of TBICOF for CO2 cycloaddition reaction with epichlorohydrin. (Yield: violet color and selectivity:
brown color). (b) PXRD profiles of TBICOF before and after five runs of chemical fixation. (c) FESEM images of TBICOF before and
after five runs of chemical fixation. (d) Plausible mechanism for CO2 cycloaddition reaction catalysed by TBICOF.
wall to permit potential small gas/vapor storage and separation.
The incorporation of polar Lewis basic nitrogen-rich benz-
bis(imidazole) functional group paved a way for significant
CO2 sorption. The highly selective separation of CO2 over N2
and CH4 by TBICOF shows its potential toward flue gas and
landfill gas separation under the relevant conditions. The high
Qst value of CO2 attributes to the strong quadruple moment of
CO2 and its interaction with the nitrogen-rich centers embedded
in the pore wall. DFT and GCMC molecular simulations
matched well with the experimental results. The development
of thermo- and chemo-stable porous COFs embedded with
multiple functional sites to procreate a synergistic effect and
amplify their interactions with CO2 can be a new path forward
for practical applications with regard to CO2 separation.
Importantly, TBICOF behave not only selective to sorption and
separation of CO2, also it acts as a promising metal-free
organocatalyst for chemical fixation of CO2 with epoxide under
solvent free ambient conditions. The remarkable efficiency
from this result shed light on the affinity of CO2 towards the
framework. The high sorption and selectivity of Bz over Cy was
attributed to the strong - interaction with the -electron
deficient triazine ring and benz-bis(imidazole) moieties and the
-electron rich benzene, which was further proved by GCMC
molecular simulation. Utilizing this approach, the separation of
Bz/Cy is an advanced key from the energy-economy standpoint
of industrial separation. This high selectivity and gas/vapor
uptake by TBICOF among other porous COFs is remarkable.
Finally due to its remarkable chemical and physical stability, it
serves as a class of promising materials for future use in
environmental clean-up and industrial gas/vapor storage.
applications and the pore size hold an important role in
sorption.67,68 TBICOF shows limited water uptake at lower
pressure, indicating the affinity of water towards
hydrophobic organic COF surface is low (Figure S52). At
higher vapor pressure (P/P0 = 0.7), the uptake started and
reached a maximum of 310 cm3g-1, indicating pore filling
at higher pressure due to large pore size. Moreover, the
water sorption exhibits a type IV sorption isotherm
accompanied with a large desorption hysteresis due to its
strong interaction with TBICOF at higher pressure. This
high water uptake capacity at higher pressure anticipates a
good correlation with respect to porosity and this result is
well correlated with PIZOF-2 reported by Yaghi et al.68
The number and position of H2O molecules for a (2 x 2 x
1) unit cells of TBICOF has been shown through GCMC
simulation and its corresponding binding energy also
calculated as 17.6 kcal/mol (Figure S53).
CONCLUSION
In summary,
a new functional triazine based benz-
bis(imidazole) bridged nitrogen-rich COF, TBICOF, was
synthesized under solvothermal conditions and fully
characterized by various analytical techniques. The surface
properties were characterized by FESEM, HRTEM and AFM
analyses. TBICOF possesses hexagonal 2D honeycomb layers
with an AA stacking for high thermal and chemo stability. It has
high surface area, large pore volume and heteroatom in the pore
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EXPERIMENTAL SECTION
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Materials and methods have been described in SI.
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ASSOCIATED CONTENT
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Supporting Information. The Supporting Information is
available free of charge on the ACS Publication website at
DOI:10.1021/
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Synthesis and characterization details of TBICOF, gas sorption
study, Qst and selectivity, comparable table, DFT and GCMC
simulation, catalysis, Bz/Cy sorption, water sorption.
AUTHOR INFORMATION
Corresponding Author
*E-mail: sanjaymandal@iisermohali.ac.in
Notes
The authors declare no competing financial interests.
ACKNOWLEDGEMENTS
This work was funded by IISER Mohali. P. D. is thankful to
MHRD, India for a research fellowship. Authors acknowledge
the use of departmental and central (NMR, X-ray, SAX, AFM
and FESEM) facilities at IISER Mohali and HRTEM analysis
by NIPER Mohali.
REFERENCES
(1) Chu, S. Carbon Capture and Sequestration. Science 2009, 325,
1599.
(2) Sumida, K.; Rogow, D. L.; Mason, J. A.; McDonald, T. M.; Bloch,
E. D. Herm, Z. R. Bae, T. H.; Long, J. R. Carbon Dioxide Capture in
Metal–Organic Frameworks. Chem. Rev. 2012, 112, 724-781.
(3) National Research Council, National Academy of Engineering,
National Academy of Sciences, Division on Engineering and Physical
Sciences, Committee on America's Energy Future. America’s Energy
Future: Technology and Transformation, National Academies Press:
Washington, DC, 2009. https://doi.org/10.17226/12091.
(4) Habib, M. A.; Nemitallah M.; Ben-Mansour, R. Recent
Development in Oxy-Combustion Technology and Its Applications to
Gas Turbine Combustors and ITM Reactors. Energy Fuels 2013, 27, 2-
19.
(5) Lin, L.-C.; Berger, A. H.; Martin, R. L.; Kim, J.; Swisher, J. A.;
Jariwala, K.; Rycroft, C. H.; Bhown, A. S.; Deem, M. W.; Haranczyk,
M.; Smit, B. In Silico Screening of Carbon-Capture Materials. Nat.
Mater. 2012, 11, 633–641.
(6) Haszeldine, R. S. Carbon Capture and Storage: How Green Can
Black Be? Science 2009, 325, 1647-1652.
(7) D’Alessandro, D. M.; Smit, B.; Long, J. R. Carbon Dioxide
Capture: Prospects for New Materials. Angew. Chem. Int. Ed. 2010, 49,
6058-6082.
(8) Yoshida, M.; Ihara, M. Novel Methodologies for the Synthesis of
Cyclic Carbonates. Chem.Eur. J. 2004, 10, 2886-2893.
(9) Zhang, S. S. A Review on Electrolyte Additives for Lithium-Ion
Batteries. J. Power Sources 2006, 162, 1379-1394.
(10) Datta, S. J.; Khumnoon, C.; Lee, Z. H.; Moon, W. K.;
Docao, S.; Nguyen,T. H.; Hwang, I. C.; Moon, D.; Oleynikov, P.;
Terasaki, O.; Yoon, K. B. CO2 Capture from Humid Flue Gases
and Humid Atmosphere Using a Microporous Coppersilicate.
Science 2015, 350, 302.
(11) Diercks, C. S.; Liu, Y.; Cordova, K. E.; Yaghi, O. M. The
Role of Reticular Chemistry in the Design of CO2 Reduction
Catalysts. Nat. Materials 2018, 17, 301-307.ꢀ
Figure 9. Sorption and separation of Bz over Cy by TBICOF: (a)
Adsorption-desorption isotherms of Bz (red) and Cy (blue) at 298
K, (b) Uptake capacity of an equimolar Bz (cyan)/Cy (purple)
mixture and selectivity (blue) of Bz over Cy calculated by IAST.
GCMC molecular simulation: (c) Probability distribution plot of
Bz on TBICOF at 10 bar. (d) Loading of Bz and Cy per unit cell of
TBICOF. (e) BE of Bz.
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(12) Furukawa, H.; Yaghi, O. M. Storage of Hydrogen, Methane, and
of Imine-Linked Covalent Organic Frameworks Catalyzed by Metal
Triflates. J. Am. Chem. Soc. 2017, 139, 4999−5002.
(32) Ding, S. Y.; Gao, J.; Wang, Q.; Zhang, Y.; Song, W. G.; Su, C.Y.;
Wang, W. Construction of Covalent Organic Framework for Catalysis:
Pd/COF-LZU1 in Suzuki–Miyaura Coupling Reaction. J. Am. Chem.
Soc. 2011, 133, 19816-19822.
(33) Kuhn, P.; Antonietti, M.; Thomas, A. Porous, Covalent
Triazine‐Based Frameworks Prepared by Ionothermal Synthesis.
Angew. Chem. Int. Ed. 2008, 47, 3450-3453.
Carbon Dioxide in Highly Porous Covalent Organic Frameworks for
Clean Energy Applications. J. Am. Chem. Soc. 2009, 131, 8875-8883.
(13) Zhao, Y.; Yao, K. X.; Teng, B.; Zhang, T.; Han, Y. A
Perfluorinated Covalent Triazine-Based Framework for Highly Selective
and Water–Tolerant CO2 Capture. Energy Environ. Sci. 2013, 6, 3684-
3692.
1
2
3
4
5
6
(14) Zeng, Y.; Zou, R.; Zhao, Y. Covalent Organic Frameworks for
CO2 Capture. Adv. Mater. 2016, 28, 2855–2873.
7
8
9
(15) Tilford, R. W.; Mugavero, S. J.; Pellechia, P. J.; Lavigne, J. J.
Tailoring Microporosity in Covalent Organic Frameworks. Adv. Mater.
2008, 20, 2741-2746.
(16) Chandra, S.; Kandambeth, S.; Biswal, B. P.; Lukose, B.; Kunjir,
S. M.; Chaudhary, M.; Babarao, R.; Heine, T.; Banerjee, R.
Mechanochemical Synthesis of Chemically Stable Isoreticular
Covalent Organic Frameworks. J. Am. Chem. Soc. 2013, 135,
17853−17861.
(17) Kandambeth, S.; Mallick, A.; Lukose, B.; Mane, M. V.; Heine,
T.; Banerjee, R. Construction of Crystalline 2D Covalent Organic
Frameworks with Remarkable Chemical (Acid/Base) Stability via a
Combined Reversible and Irreversible Route. J. Am. Chem. Soc. 2012,
134, 19524−19527.
(18) Li, Z.; Feng, X.; Zou, Y.; Zhang, Y.; Xia, H.; Liu, X.; Mua, Y.
A 2D Azine-Linked Covalent Organic Framework for Gas Storage
Applications. Chem. Commun. 2014, 50, 13825-13828.
(19) Gao, Q.; Li, X.; Ning, G.-H.; Xu, H.-S.; Liu, C.; Tian, B.; Tang,
W.; Loh, K. P. Covalent Organic Framework with Frustrated Bonding
Network for Enhanced Carbon Dioxide Storage. Chem. Mater. 2018,
30, 1762−1768.
(20) Rabbani, M. G.; El-Kaderi, H. M. Synthesis and Characterization
of Porous Benzimidazole-Linked Polymers and Their Performance in
Small Gas Storage and Selective Uptake. Chem. Mater. 2012, 24,
1511−1517.
(21) Sekizkardes, A. K.; Altarawneh, S.; Kahveci, Z.; İ slamoglu, T.;
El-Kaderi, H. M. Highly Selective CO2 Capture by Triazine-Based
Benzimidazole-Linked Polymers. Macromolecules 2014, 47,
8328−8334.
(22) Rabbani, M. G.; El-Kaderi, H. M. Template-Free Synthesis of a
Highly Porous Benzimidazole-Linked Polymer for CO2 Capture and
H2 Storage. Chem. Mater. 2011, 23, 1650–1653.
(23) Waller, P. J.; AlFaraj, Y. S.; Diercks, C. S.; Jarenwattananon, N.
N.; Yaghi, O. M. Conversion of Imine to Oxazole and Thiazole
Linkages in Covalent Organic Frameworks. J. Am. Chem. Soc. 2018,
140, 9099−9103.
(34) Patel, H. A.; Je, S. H.; Park, J.; Chen, D. P.; Jung, Y.; Yavuz, C.
T.; Coskun, A. Unprecedented High-Temperature CO2 Selectivity in
N2-phobic Nanoporous Covalent Organic Polymers. Nat. Commun.
2013, 4, 1357.
(35) Ben, T.; Pei, C.; Zhang, D.; Xu, J.; Deng, F.; Jinga, X.; Qiu, S.
Gas Storage in Porous Aromatic Frameworks (PAFs). Energy Environ.
Sci. 2011, 4, 3991–3999.
(36) Li, J.-R.; Yu, J.; Lu, W.; Sun, L.-B.; Sculley, J.; Balbuena, P. B.;
Zhou, H.-C. Porous Materials with Pre-Designed Single-Molecule
Traps for CO₂ Selective Adsorption. Nat. Commun. 2013, 4, 1538.
(37) Zheng, B.; Bai, J.; Duan, J.; Wojtas, L.; Zaworotko, M. J.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Enhanced CO2 Binding Affinity of
a
High-Uptake rht-Type
Metal−Organic Framework Decorated with Acylamide Groups. J. Am.
Chem. Soc. 2011, 133, 748-751.
(38) Xiang, S.; He, Y.; Zhang, Z.; Wu, H.; Zhou, W.; Krishna, R.;
Chen, B. Microporous Metal-Organic Framework with Potential for
Carbon Dioxide Capture at Ambient Conditions. Nat. Commun. 2012,
3, 954-963.
(39) Li, B.; Zhang, Z.; Li, Y.; Yao, K.; Zhu, Y.; Deng, Z.; Yang, F.;
Zhou, X.; Li, G.; Wu, H.; Nijem, N.; Chabal, Y. J.; Lai, Z.; Han, Y.;
Shi, Z.; Feng, S.; Li, J. Enhanced Binding Affinity, Remarkable
Selectivity, and High Capacity of CO2 by Dual Functionalization of a
rht-type Metal-Organic Framework. Angew. Chem. Int. Ed. 2012, 51,
1412–1415.
(40) Phan, A.; Doonan, C. J.; Uribe-Romo, F. J.; Knobler, C. B.;
O’Keeffe, M.; Yaghi, O. M. Synthesis, Structure, and Carbon Dioxide
Capture Properties of Zeolitic Imidazolate Frameworks. Acc. Chem.
Res. 2010, 43, 58-67.
(41) Nandi, S.; Maity, R.; Chakraborty, D.; Ballav, H.;
Vaidhyanathan, R. Preferential Adsorption of CO2 in an
Ultramicroporous MOF with Cavities Lined by Basic Groups and
Open-Metal Sites. Inorg. Chem. 2018, 57, 5267–5272.
(42) Das, P.; Mandal. S. K. Strategic Design and Functionalization
of an Amine-Decorated Luminescent Metal Organic Framework
for Selective Gas/Vapor Sorption and Nanomolar Sensing of
2,4,6-Trinitrophenol in Water. ACS Appl. Mater. Interfaces 2018,
10, 25360−25371.
(43) Yang, S.; Lin, X.; Lewis, W.; Suyetin, M.; Bichoutskaia, E.;
Parker, J. E.; Tang, C. C.; Allan, D. R.; Rizkallah, P. J.; Hubberstey,
P.; Champness, N. R.; Thomas, K. M.; Blake, A. J.; Schröder, M. A.
Partially Interpenetrated Metal-Organic Framework for Selective
Hysteretic Sorption of Carbon Dioxide. Nat. Mater. 2012, 11,
710−716.
(44) Wang, H.-H.; Hou, L.; Li, Y.-Z.; Jiang, C.-Y.; Wang, Y.-Y.; Zhu,
Z. Porous MOF with Highly Efficient Selectivity and Chemical
Conversion for CO2. ACS Appl. Mater. Interfaces 2017, 9,
17969−17976.
(45) Ansn, A.; Jagiello, J.; Parra, J. B.; Sanjun, M. L.; Benito, A. M.;
Maser, W. K.; Martnez, M. T. Porosity, Surface Area, Surface Energy,
and Hydrogen Adsorption in Nanostructured Carbons. J. Phys. Chem.
B 2004, 108, 15820-15826.
(24) Wei, P.-F.; Qi, M.-Z.; Wang, Z.-P.; Ding, S.-Y.; Yu, W.; Liu,
Q.; Wang, L.-K.; Wang, H.-Z.; An, W.-K.; Wang, W. Benzoxazole-
Linked Ultrastable Covalent Organic Frameworks for Photocatalysis.
J. Am. Chem. Soc. 2018, 140, 4623−4631.
(25) Bao, Z.; Chang, G.; Xing, H.; Krishna, Ren, R.; Q.; Chen, B.
Potential of Microporous Metal–Organic Frameworks for Separation
of Hydrocarbon Mixtures. Energy Environ. Sci. 2016, 9, 3612−3641.
(26) Ward, M. D. Photo-Induced Electron and Energy Transfer in
Non-Covalently Bonded Supramolecular Assemblies. Chem. Soc. Rev.
1997, 26, 365-375.
(27) Das, P.; Mandal, S. K. A Dual-Functionalized, Luminescent and
Highly Crystalline Covalent Organic Framework: Molecular Decoding
Strategies for VOCs and Ultrafast TNP Sensing. J. Mater. Chem. A
2018, 6, 16246–16256.
(28) Khalafi-Nezhad, A.; Panahi, F. Ruthenium-Catalyzed Synthesis
of Benzoxazoles Using Acceptorless Dehydrogenative Coupling
Reaction of Primary Alcohols with 2-Aminophenol under
Heterogeneous Conditions. ACS Catal. 2014, 4, 1686-1692.
(29) Uribe-Romo, F. J.; Doonan, C. J.; Furukawa, H.; Oisaki, K.;
Yaghi, O. M. Crystalline Covalent Organic Frameworks with
Hydrazone Linkages. J. Am. Chem. Soc. 2011, 133, 11478-11481.
(30) Ding, S. Y.; Dong, M.; Wang, Y. W.; Chen, Y. T.; Wang, H. Z.;
Su, C. Y.; Wang, W. Thioether-Based Fluorescent Covalent Organic
Framework for Selective Detection and Facile Removal of
Mercury(II). J. Am. Chem. Soc. 2016, 138, 3031−3037.
(31) Matsumoto, M.; Dasari, R. R.; Ji, W.; Feriante, C. H.; Parker, T.
C.; Marder, S. R.; Dichtel, W. R. Rapid, Low Temperature Formation
(46) Myers, A. L.; Prausnitz, J. M. Thermodynamics of Mixed-Gas
Adsorption. AIChE J. 1965, 11, 121-127.
(47) Frisch, M. J. et al. Gaussian 09; Gaussian, Inc: Wallingford, CT,
2013.
(48) Yeganegi, S.; Gholami, M.; Sokhanvaran, V. Molecular
Simulations of Adsorption and Separation of Acetylene and Methane
and their Binary Mixture on MOF-5, HKUST-1 and MOF-505 Metal–
Organic Frameworks. Molecular Simulation 2017, 43, 260–266.
(49) Altarawneh, S.; Behera, S.; Jena, P.; El-Kaderi H. M. New
ACS Paragon Plus Environment

Chemistry of Materials
Page 14 of 15
Insights into Carbon dioxide Interactions with Benzimidazole-linked
Polymers. Chem. Commun. 2014, 50, 3571-3574.
(50) Sakakura, T.; Kohno, K. The
Organic Carbonates from Carbon Dioxide. Chem. Commun. 2009, 0,
1312-1330.
(51) North, M.; Pasquale, R.; Young, C. Synthesis of Cyclic
Carbonates from Epoxides and CO2. Green Chem. 2010, 12, 1514-
1539.
(52) Dai, W.; Luo, S.; Yin, S.; Au, C. The Direct Transformation of
Carbon Dioxide to Organic Carbonates Over Heterogeneous Catalysts.
Appl. Catal. A 2009, 366, 2-12.
(53) Sun, Q.; Aguila, B.; Perman, J.; Nguyen, N.; Ma, S. Flexibility
Matters: Cooperative Active Sites in Covalent Organic Framework and
Threaded Ionic Polymer. J. Am. Chem. Soc. 2016, 138, 15790-15796.
(54) Zhi, Y.; Shao, P.; Feng, X.; Xia, H.; Zhang, Y.; Shi, Z.; Mu, Y.;
Liu, X. Covalent Organic Frameworks: Efficient, Metal-Free,
Heterogeneous Organocatalysts for Chemical Fixation of CO2 Under
Mild Conditions. J. Mater. Chem. A 2018, 6, 374–382.
(55) Miralda, C. M.; Macias, E. E.; Zhu, M.; Ratnasamy, P.; Carreon,
M. A. Zeolitic Imidazole Framework-8 Catalysts in the Conversion of
CO2 to Chloropropene Carbonate. ACS Catal. 2012, 2, 180-183.
(56) Xie, Y.; Wang, T.; Liu, X.; Zou, K.; Deng, W. Capture and
Topology Metal-Organic Framework for Chemical Fixation of CO2
Under Ambient Conditions. Angew. Chem. Int. Ed. 2014, 53, 2615-
2619.
1
2
3
4
5
6
7
8
Synthesis
of
(61) Beyzavi, M. H.; Klet, R. C.; Tussupbayev, S.; Borycz, J.;
Vermeulen, N. A.; Cramer, C. J.; Stoddart, J. F.; Hupp, J. T. Farha, O.
K. A Hafnium-Based Metal–Organic Framework as an Efficient and
Multifunctional Catalyst for Facile CO2 Fixation and Regioselective
and Enantioretentive Epoxide Activation. J. Am. Chem. Soc. 2014, 136,
15861-15864.
(62) Li, P.; Wang, X.; Liu, J.; Lim, J.; Zou, R.; Zhao, Y. A Triazole-
Containing Metal–Organic Framework as a Highly Effective and
Substrate Size-Dependent Catalyst for CO2 Conversion. J. Am. Chem.
Soc. 2016, 138, 2142-2145.
(63) Wang, J.; Zhang, Y. Boronic Acids as Hydrogen Bond Donor
Catalysts for Efficient Conversion of CO2 into Organic Carbonate in
Water. ACS Catal. 2016, 6, 4871-4876.
(64) Whiteoak, C. J.; Nova, A.; Maseras, F.; Kleij, A. W. Merging
Sustainability with Organocatalysis in the Formation of Organic
Carbonates by Using CO2 as a Feedstock. ChemSusChem 2012, 5,
2032-2038.
(65) Karmakar, A.; Samanta, P.; Desai, A. V.; Ghosh. S. K. Guest-
Responsive Metal–Organic Frameworks as Scaffolds for Separation
and Sensing Applications. Acc. Chem. Res. 2017, 50, 2457−2469.
(66) Karmakar, A.; Kumar, A.; Chaudhari, A. K.; Samanta, P.; Desai,
A. V.; Krishna, R.; Ghosh, S. K. Bimodal Functionality in a Porous
Covalent Triazine Framework by Rational Integration of an
Electron‐Rich and ‐Deficient Pore Surface. Chem. Eur. J. 2016, 22,
4931−4937.
(67) Golubovic, M. N.; Hettiarachchi, H. D. M.; Worek, W. M.
Sorption properties for different types of molecular sieve and their
influence on optimum dehumidification performance of desiccant
wheels. Int. J. Heat Mass Transfer 2006, 49, 2802-2809.
(68) Furukawa, H.; Gandara, F.; Zhang, Y.-B.; Jiang, J.; Queen, W.
L.; Hudson, M. R.; Yaghi, O. M. Water Adsorption in Porous Metal–
Organic Frameworks and Related Materials. J. Am. Chem. Soc. 2014,
136, 4369−4381.
9
10
11
12
13
14
15
16
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19
20
21
22
23
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47
48
49
50
51
52
53
54
55
56
57
58
59
60
Conversion of CO2 at Ambient Conditions by
a Conjugated
Microporous Polymer. Nat. Commun. 2013, 4, 1960.
(57) Li, C.; Wang, W.; Li, Y.; Wang, Y.; Jiang, M.; Ding, Y.
Phosphonium Salt and ZnX2–PPh3 Integrated Hierarchical Pops:
Tailorable Synthesis and Highly Efficient Cooperative Catalysis in
CO2 Utilization. J. Mater. Chem. A 2016, 4, 16017-16027.
(58) Wang, S.; Song, K.; Zhang, C.; Shu, Y.; Li, T.; Tan, B. A Novel
Metalporphyrin-Based Microporous Organic Polymer with High
CO2 Uptake and Efficient Chemical Conversion of CO2 Under
Ambient Conditions. J. Mater. Chem. A 2017, 5, 1509-1515.
(59) Yuan, F.; Li, J.; Namuangruk, S.; Kungwan, N.; Guo, J.; Wang,
C. Microporous, Self-Segregated, Graphenal Polymer Nanosheets
Prepared by Dehydrogenative Condensation of Aza-PAHs Building
Blocks in the Solid State. Chem. Mater. 2017, 29, 3971-3979.
(60) Gao, W.; Chen, Y.; Niu, Y.; Williams, K.; Cash, L.; Perez, P. J.;
Wojtas, L.; Cai, J.; Chen, Y.; Ma, S. Crystal Engineering of an Nbo
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