Carbohydrate based hyper-crosslinked organic polymers with -OH functional groups for CO2 separation

Article abstract of DOI:10.1039/c5ta03213j

Recently, microporous organic polymers, especially those hyper-crosslinked from functionalized aromatic monomers, have been shown to be effective for CO₂ capture and storage with considerable capacity and selectivity. Herein, a class of novel m

Full text of DOI:10.1039/c5ta03213j

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Carbohydrate based hypercross-linked organic polymers with –OH
functional group for CO separaꢀon†
2
Received 00th January 20xx,
Accepted 00th January 20xx
#a, b
#c
b
c
c
Haiying Li,
Bo Meng, Shannon M. Mahurin, Songhai Chai, Kimberly M. Nelson, David C.
c
*a
*b, c
Baker, Honglai Liu and Sheng Dai
DOI: 10.1039/x0xx00000x
Recently, microporous organic polymers, especially those hypercross-linked from functionalized aromatic monomers, have
shown to be effective for CO capture and storage with considerable capacity and selectivity. Herein, a class of novel
www.rsc.org/
2
microporous hypercross-linked polymers (HCPs), based on green and renewable carbohydrates, was synthesized by
Friedel−Craꢀs alkylaꢁon for carbon capture and storage by hydrogen bonding and dipole−quadrupole interacꢁon. These
2
-1
carbohydrate polymers, which have BET surface areas around 800 m g , can absorb considerable amount of CO
CO /N selectivity up to 42 at 273 K, and 96 under 100 kPa in the mixed gases (0.15 mol CO , 0.85 mol N ). Furthermore,
we experimentally and computationally studied the structures of carbohydrate backbones and determined several
features that govern their CO absorption ability, which sheds light on understanding the structure/function relationship
for designing better CO separation materials.
2
with the
2
2
2
2
2
2
cause additional environmental issues. Therefore, the
synthesis of cost-effective and environmentally friendly MOPs
remains an important challenge.
Introduction
Anthropogenic CO
2
is one of the primary atmospheric
To address this challenge, we designed and synthesized a
greenhouse gases with a significant contribution to global
climate change and long-term negative effects on the
1
environment. Consequently, the ability to capture and store
series of novel hypercross-linked carbohydrate MOPs for CO
2
capture and storage. Carbohydrates are ubiquitous in nature
and play many varied and essential roles in a wide range of
8
processes in living systems. Their wide availability and
CO from combustion exhausts and other sources is critical for
2
2
3
managing future climate risks. Over the years, much effort
has been devoted to the design and fabrication of functional
properties such as renewable and sustainable character,
9
tunable polarity, mechanical properties, and biodegradability,
10
materials for CO capture. One promising approach has been
2
4
the design and synthesis of microporous organic polymers
along with their affinities
with lectins, lipids and
carbohydrates, have led to significant development in the
synthesis of carbohydrate-based materials in various
(MOPs) which has attracted considerable attention because of
their high permanent microporosity and physicochemical
5
stability. Recently, the application of Friedel–Crafts alkylation
1
applications such as reaction catalysis, drug discovery and
1
1
2
13
delivery and virus detection. The six-membered pyranose
ring structure is the most representative monosaccharide
structure, generally with a large number of attached hydroxyl
groups. This implies a weak nucleophilicity and the potential to
of aromatic CO -philic moiety monomers was demonstrated
2
6
via the “knitting” of MOPs. The networks are derived from the
high cross-linking of the polymer monomers whose inefficient
packing of rigid and contorted components leads to an open
7
microporous structure. While the realization of this strategy is
physisorptively bind CO
by means of a dipole−quadrupole
2
1
4
6
significant, the vast majority of porous hypercross-linked
interaction as well as the formation of hydrogen bonds.
Moreover, each sugar could work as a “functional group base
station” with its hydroxyl groups either flexibly and
regioselectively retained or substituted with alternate polar
polymers (HCPs) described to date are composed of aromatic-
based skeletons derived from non-renewable petrochemical
feedstock that do not readily degrade, which could potentially
1
5
2
functional groups, which are critical in selective CO capture.
Very recently, Stoddart and coworkers reported γ-
cyclodextrin-based metal-organic framework (MOF) materials
2
for CO capture and demonstrated the formation of a
carbonate with orientated primary hydroxyl groups on the C-6
1
4,16
17
position
of each glucose unit on γ-cyclodextrin.
Herein, we report the polymerization of various benzylated
carbohydrates with/without a free hydroxyl group at the C-6
position in the monosaccharide form using formaldehyde
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a Varian VNMRS 500 MHz or a Varian VNMRS 600 instrument.
Chemical shifts are reported in δ-units (ppm) relative to the
1
13
3
residual H CDCl at δ 7.26 ppm and C at δ 77.16 ppm. Mass
spectrometric analysis was performed on a QSTAR Elite
quadrupole time-of-flight (QTOF) mass spectrometer with an
ESI source. Compounds Glc-3 and Ara-1 were purchased from
Sigma−Aldrich and compound Gal-1 was purchased from Santa
S1
S2
S2
Cruz Biotechnology. Compounds Glc-1 , Glc-2 , and Gal-2
are synthesized on the base of literature procedures.
General polymerization of benzylated carbohydrates
Typically, to a solution of the monomer and FDA in anhydrous
1,2-dichlorehane, a slurry of FeCl in DCE was slowly added
3
under nitrogen atmosphere. The mixture was then heated to
4
5 °C for 5 h and 80 °C for 19 h. The resulting brown
precipitate was collected and washed with methanol and
water until the filtrate became colorless and further purified
by Soxhlet Extraction with methanol for 24 h. The polymer was
dried under vacuum for 24 h at 60 °C. For different monomers,
Scheme 1. Structures of featured benzylated carbohydrate monomers and
representative polymerization by Friedel–Crafts alkylation.
the ratio of external cross-linker FDA and catalysis FeCl was
3
dimethyl acetal (FDA) in a Friedel–Crafts alkylation hypercross- adjusted because of the diverse numbers of benzyl rings as
linking process. We initially prepared and synthesized a series illustrated in Table S1.
of benzylated carbohydrate monomers including glucosides Computational details
(
Glc), galactosides (Gal) and an arabinoside (Ara), which
Quantum chemistry calculations were performed based on
DFT method by G09 program. Since the calculation processes
are expensive and time-consuming, basic monomers with
simplified structures were applied in the assessment of each
type of hyper cross-linked polymers (Figure S6). The
geometries of all the monomer and monomer–gas pairs were
fully optimized with M062x/6-311g(d, p) method, which is one
of the most popular DFT methods in the study of
intermolecular interactions. Frequency calculations at the
same level were also performed to make sure all optimized
structures could represent the actual minimum potential
energy. Moreover, all the interaction calculations were
corrected with the basis set superposition error (BSSE) by Boys
and Bernardi’s procedure. In the initial analysis of
featured several typical carbohydrate skeletons (Scheme 1).
These carbohydrate monomers were prepared in a hierarchical
1
8
fashion: Glc-1 and Gal-1 were directly benzylated from
methyl α- -glucopyranoside and methyl α-D-
D
galactopyranoside, respectively, without any free hydroxyl
group; Glc-2, Gal-2 and Glc-3 were selectively benzylated, with
either one primary (Glc-2 and Gal-2) or secondary hydroxyl
group (Glc-3) left free. Ara-1 was only benzylated on the
anomeric position with most of its hydroxyl groups left free.
This regioselective benzylation protocol allows for facile
hypercross-linking
polymerization
with an external cross-linker and easy expansion
of their functionality by incorporating one or several hydroxyl
groups that would facilitate their CO absorption ability.
by
Friedel–Crafts
1
9, 6b
alkylation
2
CO −carbohydrate pair systems’ geometries, both hydrogen
2
bonding and dipole−quadrupole interactions were considered
as initial structures (Figure S7). The binding energy between
carbohydrate and gases was calculated by the following
formula:
Experimental and computational section
General carbohydrate monomer synthesis
ΔE ꢀ ꢁꢂꢃꢄꢅ ꢆ ꢇꢈꢉꢈꢇꢊꢋꢌ ꢆ ꢁꢂꢃꢄꢅꢌ ꢆ ꢁꢂꢇꢈꢉꢈꢇꢊꢋꢌ
ꢍ ꢁꢂꢎꢏꢏꢁꢌ
See supporting information for experimental and
All chemicals were purchased as reagent grade and used
without further purification, unless otherwise noted. Reagent
(
2 2
grade dichloromethane (CH Cl ), tetrahydrofuran (THF),
computational details.)
methanol (MeOH) and N, N-dimethylformamide (DMF) were
obtained from the Pure-Solv (Innovation Technologies) solvent
system that uses alumina columns, except for DMF, which was
dried over a column of 5Å molecular sieves. Pyridine was
Results and discussion
distilled over CaH
under anhydrous conditions unless otherwise noted. Reactions confirmed by FTIR and the structures were verified by solid-
prior to use. All reactions were performed The backbones of successfully synthesized HCPs were
2
1
3
were monitored by thin-layer chromatography (TLC) on silica state C NMR cross-polarization magic angle spinning nuclear
gel precoated aluminum plates. Zones were detected by UV magnetic resonance spectroscopy (CP-MAS NMR), (Figure S1).
irradiation using a 254 nm lamp and/or by heat/charring with The CP-MAS NMR gave resonance signals at 130, 60−70, and
p-anisaldehyde–sulfuric acid development reagent. Column 40−50 ppm. The peak at 60−70 ppm corresponds to the
1
chromatography was performed on silica gel (40−63 μm). H carbohydrate backbone in the polymer while the remaining
1
and C NMR spectra were recorded at room temperature with peaks can be attributed to aromatic carbons and linkers,
3
2
| J. Name., 2012, 00, 1-3
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2
respectively. In addition, the broad X-ray powder diffraction CO . However, Gal-2 possesses the highest BET surface area,
(
XRD) spectra confirmed that all of the HCPs were amorphous
see Figure S2). Analysis of thermal stability was carried out by
(
thermal gravimetric analysis (TGA) on the amorphous HCPs
Figure S3). Notably, even though carbohydrate monomers are
(
not regarded as highly stable at high temperature, these
carbohydrate HCPs show excellent thermal stability
4
e
comparable to custom HCPs , retaining more than 60−70 % of
their mass even at 800 °C.
The porosity was investigated by nitrogen adsorption analysis
at 77 K. As shown in Figure 1, the fully reversible isotherms of
most HCPs represent type I isotherms with steep nitrogen
uptake at low pressure and limited micropore distribution,
except for Gal-2, which shows a type II isotherm indicating
nitrogen condensation in the mesopore/macropores of Gal-2.
This is not uncommon in hydroxyl-containing porous
6
a
polymers. Clearly, the six-membered pyranose ring structure
is rigid enough to form microporous polymers with high BET
surface area and narrow pore range, which is similar to
previously reported HCPs (Table 1), in line with the pore size
distribution and TEM images of representative carbohydrate-
4
e
based HCPs (Figure 1). The Ara-1 polymer exhibits the lowest
2
BET surface area (470 m g ) and smallest pore volume (0.30
-1
3
-1
cm g ), because there is only one aromatic ring for
hypercross-linking in each unit. Although Gal-2 shows the
highest BET surface area, it has the smallest micropore
percentage but wide micro and meso-pore distributions. We
attribute this to a steric effect since the C−O bond on C-4 of
the galactoside epimer is axial, and all the benzyl groups on C-
2
yet exhibits a CO adsorption capacity similar to Glc-2 because
Figure 1. a) Nitrogen adsorption (solid symbols)−desorpꢁon (open symbols)
2
, C-3 and C-4 are oriented in different directions, which lead
to less intensive hypercross-linking. However, it is still notable isotherms at 77 K of samples. b) pore sizes distribution of six samples. c) TEM
that the slight change of benzylated degree in the
carbohydrate monomer has a negligible impact on the surface
area, especially on the micropore surface area/volume (Table
S1). In order to investigate the stability of HCP’s pores in
moisture and acidic conditions, all samples were soaked in
water at pH=5 at 80°C for 48 hours and dried overnight at
Table 1. Characteristics and gas adsorption properties of carbohydrate HCPs.
[c]
Polyme
r
Surface Surface
CO
2
uptake
CO
2
/N
2
Qst/
[a]
[b]
3
-1
area
area
cm (STP)/g
selectivity
kJ mol
-1
(S
BET)/
(S )/
L
2
(mmol g )
2
-1
-1
m g
m g
8
0°C. The BET surface areas of all these samples remain over
7%, which makes it possible for industrial application (Table
273 K
298 K
(initial
slope, 273
K/298 K)
25/18
8
S2).
Because of the high BET surface areas of the carbohydrate
Glc-1
Glc-2
Glc-3
Gal-1
Gal-2
Ara-1
735
816
829
858
1090
470
970
1080
1096
1136
1466
623
51.3
29.9
(1.34)
31.8
27.9
26.4
25.8
26.3
24.6
28.8
(2.30)
polymers and the presence of -OH groups, we examined the
53.0
39/18
41/27
33/21
42/34
--/26
CO adsorption properties of the polymers up to 1 bar at 273 K
2
(2.36)
(1.42)
33.0
and 298 K (Figure 2/S4, Table 1). At approximately 1 bar, most
54.0
2
carbohydrate HCPs exhibit a CO adsorption capacity greater
(2.43)
(1.45)
35.0
-1
-1
than 10.1 wt% (2.30 mmol g ) and 5.89 wt% (1.34 mmol g ) at
73 K and 298 K, respectively, with perfectly reversible
unsaturated isotherms. Compared with the hypercross-linked
60.3
2
(2.70)
(1.57)
30.9
52.6
4
e
polymer of benzyl alcohol (8.46 wt%), which also has an, the
alcohol hydroxyl group in the monomer carbohydrate HCPs
(2.35)
37.8
(1.38)
21.9
show higher CO
surface area. The BET surface area, particularly the micropore
surface area, plays a significant role in determining the CO
uptake of the carbohydrate polymers, similar to other types of
2
adsorption ability with almost identical BET
(1.69)
(0.98)
[
a] Surface area calculated from nitrogen adsorption isotherms at 77 K by BET
2
equation. [b] Surface area calculated from nitrogen adsorption isotherms at 77 K
by the Langmuir equation. [c] Measured at a pressure of 1 bar.
3
a
MOPs reported in previous work. For example, Ara-1 has the
lowest BET surface area and adsorbs the smallest amount of
images of Glc-1. d) TEM images of Gal-1.
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2
2
of its limited micropore surface area. Moreover, Glc-1, Glc-2 standard counterpoise method of Boys and Bernardi. As
and Glc-3 adsorb a similar amount of CO because of their shown in Figure 3, the hydroxyl groups on C-6 in Glc-2 and Gal-
2
comparable micropore surface areas. As for fully benzylated 2 preferentially form intramolecular hydrogen bonds and
carbohydrate polymers, the change of configuration from
2
glucose to galactose slightly enhances the CO adsorption
capacity (Glc-1 10.10 wt% vs. Gal-1 11.90 wt%), in agreement
with the galactose-based HCPs of higher BET surface area.
Meanwhile, the heats of adsorption for all carbohydrate HCPs
-1
were calculated to be 25−28 kJ mol , which is below the
-1
energy of chemisorptive processes (>44 kJ mol ), indicating
strong physisorption and facile CO release.
adsorption experiments were also carried out to calculate
the CO /N selectivity of these polymers. The selectivity was
2
N
2
2
2
calculated in two ways. First, we used the slope of the CO and
2
N isotherms at low pressure (i.e., in the Henry’s law region)
2
and calculated the ratio. Second, we determined the mixed gas
selectivity based on the single gas isotherms using the ideal
adsorbed solution theory at 0.15 mol CO , 0.85 mol N and
2
2
different pressures (see Supporting Information and Figures
S5-6, Table S3 for details). The selectivity of these polymers
ranges from 24 to 42 at 273 K, from 18 to 34 at 298 K (Table 1)
and rose to 96 in the mixed gas calculation at 100 kPa,
comparable with those benzene-based hypercross-linked
polymers, and even better than some hydroxyl group
functionalized HCPs such as 1-naphthol (16) and 1,1-bi-2-
6
a
Figure 2. CO
2
adsorption (solid symbols)−desorpꢁon isotherms (open symbols) of
naphthol (26) under the same conditions (Table S4). samples up to 1.01bar at 273 K (a) and 298 K (b).
Compared with the fully benzylated carbohydrate network, the Figure 3. Optimized simplified carbohydrate monomer-gas dimer structures
obtained from quantum chemistry calculations. In this figure, HB represents
polymers with free hydroxyl groups achieve higher CO /N
hydrogen bonding and D-Q stands for dipole-quadrupole interactions.
2
2
selectivity (Glc-1 vs. Glc-2/3 and Gal-1 vs. Gal-2). Interestingly,
the secondary hydroxyl groups on C-1 of Glc-3 show stronger interact with CO2 by dipole–quadrupole interactions. In
affinity with CO than those primary hydroxyl groups on C-6 of contrast, in Glc-3 and Ara-1, both hydrogen bonds and dipole–
2
Glc-2 under either 298 K or mixed gas system. Moreover, the quadrupole interactions occur between the carbohydrate
selectivity can be clearly enhanced by changing the monomer monomers and CO . This can explain why the secondary
2
structure from glucose to galactose. To be more specific, for hydroxyl groups in Glc-3 can boost CO /N selectivity when
2
2
benzylated carbohydrate polymers with/without hydroxyl compared with the primary hydroxyl groups in Glc-2, especially
groups on C-6, the selectivity of the galactose-based HCPs is under higher pressure in mixed gases or at higher
higher than the glucose-based HCPs (Glc-1 vs. Gal-1, Glc-2 vs. temperature. Specifically, to achieve the most stable
Gal-2), especially in the mixed gas simulations.
The fact that galactose-based polymers exhibit better CO2 form relatively weaker dipole–quadrupole interactions with
configuration, the primary hydroxyl groups in Glc-2 can only
-1
capture performance than glucose-based polymers with a CO (-21 kJ mol ). In contrast, stronger hydrogen bonding
2
-1
comparable framework indicates that the carbohydrate between the –OH groups and CO (-34 kJ mol ) enhances the
2
structure does affect both the CO adsorption capacity and the carbon capture performance of Glc-3. In addition, Gal-2 has a
2
-1
CO /N selectivity of the HCPs. In order to further explore the stronger affinity with CO than Glc-2 (-29 kJ mol vs. -21 kJ
2
2
2
-1
nature of the interactions between the carbohydrate polymers mol ), in line with the higher CO /N selectivity of Gal-2
2
2
and gases, the effects of the –OH moieties in the framework obtained experimentally. Generally, the CO /N selectivity is
2
2
on their affinity with CO
2 2
2 2
and N was studied by quantum determined by both the CO -philic and N -phobic properties of
2
0
chemistry calculations with the M062x/6-311g(d, p) method
chemical functional groups in MOPs. For the –OH groups on C-
using G09 program. It has been widely accepted that non- 2, 3, 4 of Ara-1, both their hydrogen bonding and dipole–
covalent interactions play a key role in CO physisorption of quadrupole interactions with CO2 are moderate, but their
MOPs. In this case, both hydrogen bonding and interactions with N are extremely low (approximately -3 kJ
2
1
2
2
-1
dipole−quadrupole interactions between the –OH group of mol ). These N -phobic hydroxyl groups also serve to enhance
2
simplified carbohydrate monomers and gas molecules were the CO /N selectivity of Ara-1 compared to Glc-2.
2
2
considered as typical initial structures for optimization (Figures
S7-8). All interaction energies were estimated as the difference
between the total energy of the monomer−gas complex and
the sum of the total energy of the minimum geometry of the
monomer and gas molecule, and then rectified with the
Conclusions
In summary, we have designed and synthesized a series of
novel carbohydrate-based microporous organic polymers by
4
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hypercross-linking
various
hydroxyl-functionalized 12 (a) S S. Shivatare, S-H. Chang, T-I. Tsai, C-T. Ren, H-Y.
Chuang, L. Hsu, C-W. Lin, S-T. Li, C-Y. Wu, C-H. Wong, J. Am.
carbohydrate monomers with the cross-linker FDA. We have
also explored and demonstrated that several factors, including
quantity and reactivity of hydroxyl groups and the structure of
Chem. Soc., 2013, 135, 15382; (b) L. Li, Y. Xu, I. Milligan, L. Fu,
E. A. Franckowiak, W. Du, Angew. Chem. Int. Ed., 2013, 52
3699.
,
1
the carbohydrate monomers all contribute to the CO
2
13 J. Wei, L. Zheng, X. Lv, Y. Bi, W. Chen, W. Zhang, Y. Shi, L.
Zhao, X. Sun, F. Wang, S. Cheng, J. Yan, W. Liu, X. Jiang, G. F.
Gao, X. Li, ACS Nano, 2014, 5, 4600.
adsorption. In general, these carbohydrate-based polymers
show robust microporous structures, good thermal stability,
1
4 J. J. Gassensmith, H. Furukawa, R. A. Smaldone, R. S. Forgan,
Y. Y. Botros, O. M. Yaghi, J. F. Stoddart, J. Am. Chem. Soc.,
high surface area, respectable CO
2
uptake and competitive
. Moreover, the green
adsorption selectivity for CO over N
2
2
2
011, 133, 15312.
chemistry nature of these carbohydrate-based polymers 15 A. Thomas, Angew. Chem. Int. Ed., 2010, 49, 8328.
makes them amenable to solve environmental issues like CO
2
16 They proposed it based on the well-established principle that
reactivity of primary hydroxyl groups is higher than
secondary hydroxyl groups.
absorption, and we hope these promising microporous
polymers will find broad applications in carbon capture.
1
7 (a) R. A. Smaldone, R. S. Forgan, H. Furukawa, J. J.
Gassensmith, A. M. Z. Slawin, O. M. Yaghi, J. F Stoddart,
Angew. Chem. Int. Ed., 2010, 49, 8630; (b) R. S. Forgan, R. A.
Smaldone, J. J. Gassensmith, H. Furukawa, D. B. Cordes, Q. Li,
C. E. Wilmer, Y. Y. Botros, R. Q. Snurr, A. M. Z. Slawin, J. F.
Stoddart, J. Am. Chem. Soc., 2012, 134, 406; (c) D. Wu, J. J.
Gassensmith, D. Gouvea, S. Ushakov, J. F. Stoddart, A.
Navrotsky, J. Am. Chem. Soc., 2013, 135, 6790; (d) J. J.
Gassensmith, J. Y. Kim, J. M. Holcroft, O. K. Farha, J. F.
Stoddart, J. T. Hupp, N. C. Jeong, J. Am. Chem. Soc., 2014,
Acknowledgements
HYL and HLL thank the National Basic Research Program of
China (2013CB733501), the National Natural Science
Foundation of China (No. 91334203), the 111 Project of China
(No. B08021) and the Fundamental Research Funds for the
Central Universities of China. This work was also supported by
the U.S. Department of Energy, Office of Science, Basic Energy
Sciences, Chemical Sciences, Geosciences, and Biosciences
Division.
1
36, 8277.
1
8 (a) G. J. L. Bernardes, E. J. Grayson, S. Thompson, J. M.
Chalker, J. C. Errey, F. E. Oualid, T. D. W. Claridge, B. G. Davis,
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K-Y. Lin, H-W. Liu, J. Am. Chem. Soc., 2012, 134, 17432.
9 B. Li, R. Gong, W. Wang, X. Huang, W. Zhang, H. Li, C. Hu, B.
Tan, Macromolecules, 2011, 44, 2410.
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2
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