Naturally occurring gallic acid derived multifunctional porous polymers for highly efficient CO2 conversion and I2 capture

Article abstract of DOI:10.1039/c8gc02685h

Assembly of naturally occurring building blocks into functional materials is of great importance. Herein, we utilized plant-derived polyphenols as building blocks to prepare porous organic polymers (POPs) with multifunctional sites, and a typical POP (denoted as GA-azo-POP) could be achieved from gallic acid through an azo-coupling strategy. As a superior support, GA-azo-POP supported Ag nanoparticles could efficiently catalyze the carboxylative cyclization of propargyl alcohols with CO₂ with a very low usage of Ag (0.14 mol%). Meanwhile, the GA-azo-POP showed a high capacity for I₂ adsorption (up to 287 mg g^-1), which was higher than that of the reported solid materials at a similar I₂ concentration. More interestingly, after adsorbing I₂, the GA-azo-POP could efficiently catalyze the formation of cyclic carbonates from CO₂. The excellent performance of the GA-azo-POP resulted from the co-existence of aromatic, azo, and phenolic OH functional groups and its porous structure.

Full text of DOI:10.1039/c8gc02685h

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Naturally occurring gallic acid derived multifunctional porous
polymer for highly efficient CO2 conversion and I2 capture
Chao Xie,a,b Jinliang Song,*a Haoran Wu,a,b Yue Hu,a,b Huizhen Liu,a,b Youdi Yang,a,b Zhanrong
Zhang,a Bingfeng Chena and Buxing Han*a,b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Assembly of naturally occurring building blocks into functional materials is of great importance. Herein, we utilized plant-
derived polyphenols as the building blocks to prepare porous organic polymer (POP) with multifunctional sites, and a
typical POP (denoted as GA-azo-POP) could be achieved from gallic acid through an azo-coupling strategy. As a superior
support, GA-azo-POP supported Ag nanoparticles could efficiently catalyze the carboxylative cyclization of propargyl
alcohols with CO2 with a very low usage of Ag (0.14 mol%). Meanwhile, GA-azo-POP showed a high capacity for I2
adsorption (up to 287 mg/g), which was higher than that of reported solid materials under the similar I2 concentration.
More interesting, after adsorbing I2, GA-azo-POP could efficiently catalyze the formation of cyclic carbonates from CO2. The
excellent performance of GA-azo-POP resulted from the co-existence of aromatic, azo, and phenolic OH functional groups
and its porous structure.
www.rsc.org/
integrated by employing different functional monomers,
resulting in the wide applications of POPs in various areas.18-23
In this respect, azo-bridged POP (azo-POP) is one of the most
Introduction
promising POPs. As
a general route, azo-POPs can be
With the depletion of fossil resources, increasing attention has
been paid to efficient utilization of naturally occurring or
biomass-derived compounds.1-7 In this regard, assembly of
naturally occurring compounds for functional materials has
been recognized as a highly attractive strategy.8-11 Among
various natural compounds, polyphenols, widely existing in
plant tissues, have gained many applications in pharmaceutical
and food industries.12,13 Especially, functional coating and
capsule materials have been successful synthesized on the
basis of metal chelation feature of these polyphenols.14-17
However, making full use of these polyphenols to prepare
functional materials is still in its early stage. Novel routes for
designing functional materials by using polyphenols in plants
are highly desired.
synthesized by azo-coupling between aromatic diazonium salts
and phenols.24 The azo-POPs obtained through this route
contain azo and phenolic -OH groups simultaneously, resulting
in potential applications especially in catalysis and adsorption.
Of interest to us is that the phenols used for the synthesis of
azo-POPs can be replaced by the renewable polyphenols in
plants, which could decrease the reliance of fossil-based
chemicals. More importantly, the structural diversity of
polyphenols in plants (Scheme S1) provides a range of
possibilities for preparing various POPs with different
properties.
Herein, we described for the first time the synthesis of a
biomass-based POP (denoted as GA-azo-POP hereafter) using a
renewable polyphenol, gallic acid, which can be obtained from
tannic acid (a specific form of tannin from Chinese gall) via
hydrolysis,25-27 as the building block through a simple azo-
coupling reaction. Due to the co-existence of azo, aromatic and
phenolic -OH groups, the obtained GA-azo-POP could be used
as a multifunctional material to support Ag nanoparticles for
Porous organic polymers (POPs) have received
considerable interest due to their distinctive properties. A
salient feature of POPs is that multiple functionalities can be
a.Beijing National Laboratory for Molecular Science, CAS Key Laboratory of Colloid
and Interface and Thermodynamics, CAS Research/Education Center for efficient CO2 fixation, and also as an efficient solid adsorbent
Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of
for I2 capture with a very high capacity of 287 mg/g. Moreover,
Sciences, Beijing 100190, China. E-mails: songjl@iccas.ac.cn, hanbx@iccas.ac.cn
b.School of Chemistry and Chemical Engineering, University of Chinese Academy of
Sciences, Beijing 100049, China.
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
after adsorbing I2, the GA-azo-POP could also be used as an
efficient catalyst for cycloaddition of CO2 to epoxides with no
additional cocatalyst.
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and 13C NMR (Data in supporting information).
Experimental
Synthesis of GA-azo-POP
Reusability of Ag/GA-azo-POP
The synthesis of GA-azo-POP was carried out in two steps.
Firstly, 1,3-bis(4-aminophenoxy)benzene (6 mmol) was loaded
in a 500 mL flat-bottomed flask charged with 200 mL of
deionized water and 3 mL of concentrated hydrochloric acid.
After stirring under ice-water bath for 15 min, the mixture was
added with 30 mL of aqueous solution of sodium nitrite (12
mmol) and stirred for 25 min to make amino groups be
completely converted to diazonium salts. Subsequently, the
mixture was neutralized with saturated solution of Na2CO3, and
then 30 mL of aqueous solution of galic acid (5 mmol) and
Na2CO3 (20 mmol) was added into the mixture dropwisely in an
ice-bath. After 12 h, solid sample was separated from the
reaction solution by filtration and washed by the solvents
several times in the order: water, methanol, THF, methanol,
water and then Soxhlet extracted with methanol overnight to
remove any unreacted monomers. Followed by freeze drying,
the polymer sample was obtained in a high yield of 82%.
Elemental analysis data: C 67.11%, H 4.09%, and N 5.49%.
Other azo-POPs were prepared as the same way by the
reaction of other polyphenols with different arylamines.
To examine the reusability of Ag/GA-azo-POP, the catalyst was
recovered by centrifugation and washed with ethyl ether (5 ×
10 mL). After drying under vacuum at 80 oC for 12 h, the
recovered catalyst was reused for the next cycle.
Typical procedures for the synthesis of cyclic carbonates from
various epoxides and CO2
In a typical experiment, desired epoxide (10 mmol) and 50 mg
I2/GA-azo-POP were charged into a stainless reactor with a
Teflon tube (22 ml inner volume) equipped with a magnetic
stirrer. After sealing, CO2 was charged into the reactor until the
desired pressure was reached. Then, the reactor was put into a
constant temperature air bath at desired temperature, and the
stirrer was started. After a certain reaction time, the reactor
was placed into ice water and CO2 was released slowly passing
through a cold trap containing ethanol to absorb the trace
amounts of reactant and product entrained by CO2. After
depressurization, ethanol in the cold trap and internal standard
n-butanol were added into the reactor. The reaction mixture
was then analyzed quantitatively by GC (Agilent 6820)
equipped with a flame-ionized detector.
Synthesis of Ag/GA-azo-POP
500 mg GA-azo-POP was dispersed in 100 ml deionized water
under continuous stirring firstly, and then 10 mg silver nitrate
was dissolved in 10 ml deionized water. The aqueous solution
of silver nitrate was added into the mixture slowly with intense
stirring. The mixture was stirred for another 5 hours. The Ag
nanoparticles could be uniformly dispersed on the GA-azo-POP
due to the reduction effect of the phenolic -OH groups. The Ag
loaded GA-azo-POP was then collected by filtration, washed by
Results and discussion
Synthesis and characterization of GA-azo-POP
The GA-azo-POP was synthesized through a catalyst-free diazo-
coupling reaction between biomass-derived gallic acid and 1,3-
bis(4-aminophenoxy)benzene
under
alkaline
aqueous
conditions (Scheme 1), and detail information was described in
the Experimental Section. Fourier transform infrared (FT-IR)
spectroscopy (Fig. S1) showed two bands around 1200 and
1400 cm-1, which were the characteristic symmetric and
asymmetric vibrations of the azo group,24,28 suggesting the
formation of -N=N- functionality in the as-prepared GA-azo-
POP.29 The solid UV-vis adsorption of GA-azo-POP showed
strong optical adsorption from 200 to 800 nm (Fig. S2), further
verifying the formation of -N=N- functionality.24,30 N2
adsorption-desorption isotherm showed that the GA-azo-POP
was a porous material with a broad mesopore-size distribution
as determined by the Barrett-Joyner-Halenda (BJH) method
(Fig. 1A), which showed the same tendency with some POP
materials,24 and the mesopores probably originated from the
hydrogen bonding interaction between the gallic acid and
water, and water acted as a soft template. Meanwhile,
Brunauer-Emmett-Teller (BET) surface area and pore volume
were 143 m2/g and 0.61 cm3/g, respectively, and the relative
low surface area may be caused by the geometry structure of
the gallic acid and the 1,3-bis(4-aminophenoxy)benzene.24 XRD
pattern indicated that the GA-azo-POP had low crystallinity (Fig.
1B), and the broad peak at 2θ=~20o suggested that the GA-azo-
POP was a layer material to some extent, and the interlayer
distance was 4.43Å calculated by the Bragg equation.
Furthermore, SEM and TEM images also demonstrated that the
GA-azo-POP was porous (Fig. 1C, D and Fig. S3), which agreed
o
deionized water several times and dried under vacuum (60 C,
24 h).
Typical procedures for the synthesis of α-alkylidene cyclic
carbonates from propargyl alcohols and CO2
In a typical experiment, propargyl alcohols (1 mmol), DBU (1
mmol), 20 mg Ag/GA-azo-POP and THF (2 mL) were charged
into a stainless reactor with a Teflon tube (22 ml inner volume)
equipped with a magnetic stirrer. After sealing, CO2 was
charged into the reactor until the desired pressure was
reached. Then, the reactor was put into
a constant
temperature air bath at room temperature, and the stirrer was
started. After a certain reaction time, the reactor was placed
into ice water and CO2 was released slowly passing through a
cold trap containing the corresponding solvent to absorb the
trace amounts of reactant and product entrained by CO2. After
depressurization, the solvent in the cold trap and the internal
standard 1,3,5-trioxane were added into the reactor. The
reaction mixture was analyzed quantitatively by Bruker Avance
III HD 400 MHz NMR spectrometer. To obtain the isolated
yields of some typical α-alkylidene cyclic carbonates, the
reaction mixture was concentrated and purified by column
chromatography (silica gel with petroleum ether/EtOAc = 20:1).
Meanwhile, the pure product was characterized by 1H NMR
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with the results from N2 sorption and XRD measurements. Notably, other azo-POPs could also be successful synthesized
Additionally, the generated GA-azo-POP was found to be from the reaction of gallic acid with 4,4’-diamonodiphenyl
insoluble in water or common organic solvents (DMF, THF, sulfone, or the reaction of tannic acid (another common
DMSO, Fig. S4), indicating its highly stable and interwoven polyphenols in plants, Scheme S1) with 4,4’-diamonodiphenyl
structure. The thermogravimetry analysis further confirmed sulfone or 1,3-bis(4-aminophenoxy)benzene (Fig. S6),
the stability of GA-azo-POP (Fig. S5). The prepared GA-azo-POP indicating that this method was highly flexible and applicable
may have wide-ranging applications in different fields due to to prepare a variety of azo-POPs by simply adjusting the
the existence of multifunctional groups and its stable property. biomass-derived polyphenols and arylamines.
ONa
ONa
OH
OH
O
Na2CO3
NaOOC
HOOC
H2O, 0-5 o
C
N
O
O
ONa
OH
Gallic acid
N
HO
HO
HO
N N
COOH
N N
Para-substitution
+
Na2CO3
O
O
NH2
O
O
N2
1. HCl
2. NaNO2
N
H2O, 0-5 o
C
N
+
NH2
N2
O
GA-azo-POP
1,3-Bis(4-aminophenoxy)benzene
Scheme 1. Synthetic process of GA-azo-POP through diazo-coupling reaction between gallic acid and 1,3-bis(4-aminophenoxy)benzene.
Carboxylative cyclization of CO2 and propargyl alcohols over groups (Fig. 2A).43,44 There were two peaks at 368.47 and
Ag/GA-azo-POP 374.47 eV in X-ray photoelectron spectroscopy (XPS) spectrum
The carboxylative cyclization of propargyl alcohols with CO2 is of Ag in Ag/GA-azo-POP, which corresponded to the spin states
an attractive reaction for CO2 transformation to synthesize α- of Ag, Ag 3d5/2 and Ag 3d3/2, respectively, confirming the
alkylidene cyclic carbonates, which are versatile intermediates formation of Ag0 in the Ag/GA-azo-POP.30,38 Meanwhile, The
in organic synthesis.31,32 Although some homogeneous area ratio of the two spin states (Ag 3d5/2/Ag 3d3/2) was about
catalysts showed relative activity for the cyclization of 3:2, which was consistent with the theoretical value.45 The
propargyl alcohols with CO2,33-36 heterogeneous catalysts are average diameter of these Ag particles centered around 1 nm
more attractive in separation and recyclability. So far, only (Fig. 2A) with a Ag content of 0.74 wt% determined by ICP-AES.
several heterogeneous catalysts have been developed for this
important transformation, and these catalytic systems
generally suffered from low efficiency, high CO2 pressure, or
high loading of transition metals (up to 10 mol%).37,38
Therefore, it is highly desired to design efficient heterogeneous
catalysts for the reaction between CO2 and propargyl alcohols.
It has been reported that metal nanoparticles supported on
porous materials show good activity on CO2 fixation
reactions.39,40 Considering the advantage of the supported
metal nanoparticles and the properties of the synthesized GA-
azo-POP, i.e., the CO2-philic property of azo groups and the
stabilization ability of phenolic -OH groups on metal
nanoparticles,41,42 the prepared GA-azo-POP showed great
potential to be used as a multifunctional porous material to
design supported catalysts for the above-mentioned CO2
transformation. Herein, we prepared GA-azo-POP supported
Ag nanoparticles (denoted as Ag/GA-azo-POP) for the reaction
of propargyl alcohols with CO2 by treating GA-azo-POP in the
aqueous solution of silver nitrate (detail process shown in
Supporting Information). The Ag nanoparticles could be highly
dispersed on the GA-azo-POP owing to the reduction role and
the stabilization effect on Ag particles of the phenolic -OH
Fig. 1. Characterization of the obtained GA-azo-POP. A) N2 adsorption-
desorption isotherm (The inset is the mesopore-size distribution), B)
Powder XRD pattern, C) Scanning electron microscopy (SEM) image,
and D) Transmission electron microscopy (TEM) image.
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Table 1. Carboxylative cyclization of 2-methyl-3-butyn-2-ol with CO2.a
O
O
O
OH +
CO2
Entry
Catalyst
Base
Time/h
Yield
(%)b
<1
<1
98
2
TOF
(h-1)c
--
1
2
Ag/GA-azo-POP
--
--
7
7
DBU
DBU
--
Fig. 2. A) TEM image for Ag/GA-azo-POP. The insert is the Ag particle
size distribution. B) XPS spectrum of metallic Ag0 in Ag/GA-azo-POP.
3
Ag/GA-azo-POP
Ag/GA-azo-POP
Ag/GA-azo-POP
Ag/GA-azo-POP
Ag/GA-azo-POP
GA-azo-POP
Ag/GA-azo-POP
Ag/GA-azo-POP
DMAM-PS-CuI
PS-NHC-Ag
7
100
--
4
Cs2CO3
DABCO
DMAP
NMP
DBU
DBU
DBU
--
7
The cyclization of 2-methyl-3-butyn-2-ol with CO2 was first
investigated as a model reaction to examine the catalytic
activity of the prepared Ag/GA-azo-POP (Table 1) at room
5
7
0
--
6
7
2
--
temperature with
a CO2 pressure of 1 MPa. Control
7
7
0
--
experiments indicated that nearly no product was detected in
the presence of DBU or Ag/GA-azo-POP alone (Table 1, entries
1 and 2), indicating the synergistic effect of DBU and Ag/GA-
azo-POP for the reaction. Among various bases (Table 1,
entries 3-7), DBU showed the best performance (Table 1, entry
3) with a yield of 98% resulting from its stronger basicity. In the
reaction cycle, DBU played the key role on the activation of the
propargyl alcohol,38,46,47 which was beneficial for the insertion
of CO2 to generate a carbonate intermediate (Scheme S2), an
important step for the synthesis of α-alkylidene cyclic
carbonates. Meanwhile, GA-azo-POP/DBU showed very low
activity (Table 1, entry 8), suggesting the catalytic effect of Ag
nanoparticles. Furthermore, kinetic experiments indicated that
the reaction could be completed in 7 h (Fig. S7) in the presence
of very low Ag usage (0.14 mol%) at room temperature. A high
TOF value of 400 could be achieved in 0.5 h (Table 1, entry 9),
and the TOF value (372) was comparable with a prolonging
reaction time of 1 h (Table 1, entry 10), indicating the higher
reaction rate in the initial stage. Additionally, Ag/GA-azo-POP
showed higher activity than the reported heterogeneous
8
7
<1
28
52
99
96
91
85
59
94
--
9
0.5
1
400
371
0.52
1
10
11d
12e
13f
14g
15h
16i
24
24
10
5
--
AgNPs/SMR
DBU
DBU
DBU
DBU
0.91
1.7
30
47
AgOAc
AgOAc
1
AgOAc/Azobenzene
1
aReaction conditions: substrate, 1 mmol; catalyst, 20 mg; base, 1 mmol; THF,
2 mL; CO2 pressure, 1 MPa; r.t. bThe yields were determined by 1H NMR
(CDCl3, 400 MHz) using 1,3,5-trioxacyclohexane as an internal standard.
cTurnover number (TON) = mol of product per mole of Ag; TOF = TON h-1.
dData from Ref. 30. eData from Ref. 34. fData from Ref. 31. gData from Ref. 35.
h2 mol% Ag. i2 mol% Ag, 10 mol% azobenzene.
To verify the adaptability of Ag/GA-azo-POP, other
propargyl alcohols with typical structures were also examined
(Table 2). Ag/GA-azo-POP could also efficiently catalyze the
cyclization of CO2 with all the used terminal propargylic
alcohols with both alkyl (Table 2, entries 1-5) and aryl
substitutes (Table 2, entry 6) at the propargylic position,
further proving the high catalytic activity of Ag/GA-azo-POP.
Moreover, the as-prepared Ag/GA-azo-POP showed no obvious
decrease in activity for the cyclization of CO2 with 2-methyl-3-
butyn-2-ol after 5 cycles (Fig. S8), and TEM image of the
recovered Ag/GA-azo-POP showed no aggregation after five
times reuse (Fig. S9), indicating that Ag/GA-azo-POP had good
recyclability and stability. Additionally, the heterogeneous
nature of Ag/GA-azo-POP for cyclization of 2-methyl-3-butyn-
2-ol with CO2 was evaluated by removing it after the reaction
was performed for 2 h, and then the reaction continued to be
carried out for another 7 h. No further reaction occurred (Fig.
S7), indicating the heterogeneous nature of the Ag/GA-azo-POP.
Meanwhile, no Ag was detected in the reaction solutions by
ICP-AES method, verifying the negligible leaching of Ag. The
results above indicated that the obtained GA-azo-POP could be
catalysts,
including
(dimethylamino)-methyl-polystyrene-
supported CuI (Table 1, entry 11),37 polystyrene-supported
NHC-Ag complexes (Table 1, entry 12),48 and some supported
Ag nanoparticles (Table 1, entry 13).38 More importantly, the
catalytic activity of Ag/GA-azo-POP was higher than some
reported homogeneous Ag salts (Table 1, entry 14) under
similar conditions.49 These results indicated that Ag/GA-azo-
POP was
a superior heterogeneous catalyst for the
carboxylative cyclization of propargyl alcohols with CO2.
Control experiments were performed over AgOAc with
azobenzene as an additive to explore the reasons of the high
performance of Ag/GA-azo-POP. It was clearly that the
azobenzene could improve the activity of AgOAc (Table 1,
entries 15 and 16), indicating the key role of azo groups in
Ag/GA-azo-POP owing to the CO2-philic property of the azo
groups. Therefore, the high catalytic activity of Ag/GA-azo-POP
may result from the porous structure with highly dispersed Ag
nanoparticles as well as the promotion effect of azo groups.
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used as a superior material for CO2 fixation.
was reached (Fig. 3A). The I2 capture capacity of GA-azo-POP
calculated based on UV-vis spectroscopy (Fig. S10) could be
Table 2. Cyclization of various propargyl alcohols with CO2 over Ag/GA- reached up to 287 mg/g, which was higher than that of the
azo-POP.a
reported solid adsorbents (Table S1) under similar I2
concentration. XPS spectrum of the GA-azo-POP after soaking
in I2 cyclohexane solution indicated that the I2 adsorbed by GA-
Time
(h)
Yield
(%)b
Entry
Substrate
Product
-
azo-POP existed in the form of I2 and I3 (Fig. 3B).50 This
O
examination suggested that the adsorbed I2 on the GA-azo-POP
could be readily transformed into various polyiodide states,
-
especially I3 , which was generated by the formation of charge-
>99
(94)c
1
2
O
O
8
OH
OH
transfer complexes (Scheme S3) between the absorbed I2 and
the azo groups (good electron donors) on the GA-azo-POP via
charge-transfer interaction.28,51-53 The change of I2 valence
state suggested the chemisorption taking place together with
the physical absorption, such as the hydrogen-halogen bond
between I2 and phenolic -OH,50,52,53 and thus a high amount of
I2 uptake (up to 287 mg/g) was achieved.
O
>99(93)c
O
O
12
O
OH
O
O
>99(95)c
3
12
O
O
OH
O
O
O
>99(94)c
4
12
Fig. 3. A) Time-dependent UV-vis absorption spectra of I2 uptake. The
insert was the related I2 concentration calculated by UV-vis absorbance
at 525 nm. Adsorption conditions: GA-azo-POP, 10 mg; cyclohexane
solution of I2 (2.07 mg/mL), 1.5 mL; room temperature. B) XPS
spectrum of I2 adsorbed on GA-azo-POP.
OH
O
O
96(92)c
5
6
12
36
5
5
Cycloaddition of CO2 with epoxides over I2/GA-azo-POP
Generally, efficient utilization of the captured I2 is an
interesting topic. As well-known, I- and phenolic -OH could
promote the cycloaddition of CO2 with epoxides to produce
cyclic carbonates,54,55 which is a very important reaction for
CO2 fixation.56-60 On the basis of the above analysis, there were
OH
92(87)c
O
O
-
aReaction conditions: substrate, 1 mmol; Ag/GA-azo-POP, 20 mg; DBU, 1
mmol; THF, 2 mL; CO2 pressure, 1 MPa; r.t. bThe yields were determined by
1H NMR (CDCl3, 400 MHz) using 1,3,5-trioxacyclohexane as an internal
standard. cValues in parentheses were isolated yields.
many I3 ions formed from I2 adsorbed on GA-azo-POP and
plenty of phenolic -OH existed in GA-azo-POP. Therefore, this
provided the possibility that I2 adsorbed on GA-azo-POP
(denoted as I2/GA-azo-POP) could catalyze the cycloaddition of
CO2 with epoxides. Herein, we attempted to apply I2/GA-azo-
POP as
a metal-free heterogeneous catalyst for this
I2 capture by GA-azo-POP
transformation (Table 3). To our delight, various epoxides could
be converted with CO2 into cyclic carbonates with high yields,
suggesting I2/GA-azo-POP was suitable for cycloaddition of
various epoxides with CO2 into cyclic carbonates, and this was
a new application for the adsorbed I2. In addition, the GA-azo-
POP without adsorbing I2 could not catalyze the cycloaddition,
indicating the catalytic role of the adsorbed I2 species. In the
catalytic cycle, the epoxide was firstly activated by the
hydrogen bonding formed between the oxygen atom in the
epoxy ring and the phenolic -OH on GA-azo-POP, and then the
Except for the utilization of GA-azo-POP in CO2 fixation,
considering that GA-azo-POP possesses plenty of aromatic, azo,
and phenolic -OH groups, we attempted to use the GA-azo-POP
as a solid adsorbent for radiological I2 capture, which is an
unavoidable environmental issue associated with nuclear
energy. The I2 capture ability of GA-azo-POP was examined in
the cyclohexane solution of I2 (2.07 mg/ml) at room
temperature, and UV-vis spectroscopy was used to monitor the
I2 capture process by GA-azo-POP (Fig. 3A). The I2 adsorption
capacity of GA-azo-POP increased quickly during the first 24 h,
and then the adsorption rate decreased until the equilibrium
-
Ix anion generated from the absorbed I2 attacked the less
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hindered carbon atom of the activated ring, followed by ring cocatalyst. We believe that more functional porous polymers
opening reaction step. Subsequently, CO2 was reacted with the could be prepared using naturally occurring polyphenols for
opened epoxy ring to form an alkylcarbonate anion, which was different applications.
stablilized via the hydrogen bonding. Finally, the intramolecular
cyclic step was happened to generate the corresponding cyclic
Conflicts of interest
carbonates (Scheme S3).
There are no conflicts to declare.
Table 3. Cycloaddition of various epoxides with CO2 over I2/GA-azo-
POP.a
Yield
Acknowledgements
Entry
Epoxide
Product
(%)b
This work was supported by the National Key Research
and Development Program of China (2018YFB0605801),
National Natural Science Foundation of China (21673249),
Youth Innovation Promotion Association of CAS (2017043),
and Key Research Program of Frontier Sciences of CAS
(QYZDY-SSW-SLH013).
O
O
1
97
O
O
O
O
2
3
4
94
96
97
O
O
Notes and references
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