Hypercrosslinked porous polycarbazoles from carbazolyl-bearing aldehydes or ketones

Article abstract of DOI:10.1016/j.polymer.2018.03.062

Hypercrosslinked polymers have drawn increasing interest due to their porous structure, large specific surface area, and excellent chemical and thermal stability. Using the carbonyl bearing carbazole monomers Cz-22～27, a series of hypercrosslinked porous polycarbazoles CPOP-22～27 have been synthesized through oxidative coupling polymerization and Friedel–Crafts reaction in one-step promoted by FeCl₃. The Brunauer–Emmett–Teller specific surface areas of CPOP-22～27 are between 440 and 760 m² g^?1. Their dominant pore sizes vary from 0.99 to 1.06 nm, which indicating that the polymers are predominantly microporous. This work provides a new method to synthesis of hypercrosslinked porous polycarbazoles from carbonyl functionalized carbazoles. It is also found that parts of aldehyde groups can not react through the Friedel–Crafts alkylation when increasing the number of carbazole groups. The residual aldehyde groups in the polymer can even react with Tollens’ reagent solution to form Ag nanoparticles composite.

Full text of DOI:10.1016/j.polymer.2018.03.062

Polymer 143 (2018) 87e95
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Hypercrosslinked porous polycarbazoles from carbazolyl-bearing
aldehydes or ketones
a
,
b
b
b
b
,
***
, Wei-Hua Luo a
, **
Rong-Rong Zhang , Qing Yin , Hai-Peng Liang , Qi Chen
Bao-Hang Han
a
,
b, *
Department of Chemical Engineering and Technology, Central South University of Forestry and Technology, Changsha, 410004, China
CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and
b
Technology, Beijing, 100190, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 December 2017
Received in revised form
Hypercrosslinked polymers have drawn increasing interest due to their porous structure, large specific
surface area, and excellent chemical and thermal stability. Using the carbonyl bearing carbazole
monomers Cz-22~27, a series of hypercrosslinked porous polycarbazoles CPOP-22~27 have been syn-
thesized through oxidative coupling polymerization and FriedeleCrafts reaction in one-step promoted by
18 March 2018
Accepted 27 March 2018
Available online 29 March 2018
FeCl
3
. The BrunauereEmmetteTeller specific surface areas of CPOP-22~27 are between 440 and
2
ꢀ1
760 m g . Their dominant pore sizes vary from 0.99 to 1.06 nm, which indicating that the polymers are
predominantly microporous. This work provides a new method to synthesis of hypercrosslinked porous
polycarbazoles from carbonyl functionalized carbazoles. It is also found that parts of aldehyde groups can
not react through the FriedeleCrafts alkylation when increasing the number of carbazole groups. The
residual aldehyde groups in the polymer can even react with Tollens' reagent solution to form Ag
nanoparticles composite.
Keywords:
Carbazole
Carbonyl group
Friedelecrafts reaction
Oxidative coupling polymerization
Hypercrosslinked polymers
Porosity
© 2018 Elsevier Ltd. All rights reserved.
1. Introduction
flexibility.
3
FeCl -catalyzed oxidative coupling polymerization is a cost-
Hypercrosslinked polymers (HCPs) [1e3] have been reported in
earlier time and known as one category of porous organic polymers
POPs) [4,5]. These porous polymers with high surface area and
good chemo/thermal stability have shown wide applications as
effective approach to prepare porous polycarbazoles firstly re-
ported by our group [24,25]. Through this simple and convenient
method, we and other groups have developed a series of porous
conjugated polycarbazoles [26,27], which show potential use in
selective gas storage [24], organic photocatalysis [28,29], hetero-
(
catalyst supports [6e9], gas storage materials [10e13], separation
[
14], and purification matrix [15,16]. HCPs are usually prepared
3
geneous transformation [30], and catalyst encapsulation [31]. FeCl ,
with low cost methods and cheap raw materials. Up to now, Lewis
acid catalyzing FriedeleCrafts alkylation is one of the most used
template-free methods to prepare HCPs with high Bru-
nauereEmmetteTeller (BET) specific surface area [17e20]. Using
suitable monomers and linkers, different types of hypercrosslinked
porous polymers can be synthesized. In some cases, monomer and
linker can be designed as a single monomer [21e23]. Therefore,
synthesis of HCPs with this method exhibits high efficiency and
as an oxidant and Lewis acid, can be the catalyst for both oxidative
coupling polymerization and FriedeleCrafts reaction [32e34].
Therefore, we have designed and synthesized vinyl or hydrox-
ymethyl bearing carbazole derivatives to prepare hypercrosslinked
porous polycarbazoles through FriedeleCrafts reaction and oxida-
tive coupling polymerization in one-step using FeCl
[22].
3
as catalyst
As we know, aldehyde and ketone are also the suitable sub-
strates for the FriedeleCrafts alkylation [32]. In order to develop
new hypercrosslinked porous polycarbazoles and explore facile
synthetic methods, herein, a series of carbazole-based hyper-
crosslinked porous polymers have been synthesized via
FriedeleCrafts reaction and oxidative coupling polymerization in
*
Corresponding author.
*
*
* Corresponding author.
** Corresponding author.
E-mail addresses: chenq@nanoctr.cn (Q. Chen), lwh6803@163.com (W.-H. Luo),
hanbh@nanoctr.cn (B.-H. Han).
3
one-step catalyzed by FeCl from carbazolyl-bearing aldehydes or
https://doi.org/10.1016/j.polymer.2018.03.062
0
032-3861/© 2018 Elsevier Ltd. All rights reserved.

88
R.-R. Zhang et al. / Polymer 143 (2018) 87e95
ketones under refluxing conditions or room temperature. Mono-
mers with different structures were designed to tune the porosities
of the obtained porous materials. Moreover, as to the porous
polymer prepared from aldehyde derivatives, Ag nanoparticles can
be loaded into the material by the chemical reduction in situ of the
Tollens' reagent [35e37]. We think it is a facile approach to prepare
HCPs supported metal nanoparticle composite materials.
2.4. Synthesis of Cz-24
To a two-neck flask were added 4-(9H-9-Carbazole)phenyl-
boronic
acid
(1.52 g,
5.3 mmol),
4-bromo-2,6-
difluorobenzylaldehyde (0.77 g, 3.5 mmol), THF (20.0 mL), and
aqueous potassium carbonate solution (12.5 mL, 2.0 M). The
mixture was degassed by the freezeepumpethaw cycle two times.
3 2 2
Pd(PPh ) Cl (280.4 mg, 0.4 mmol) was added and degassed by
freezeepumpethaw once again. Then the bright yellow solution
was slowly heated to 80 C under nitrogen atmosphere and kept for
2
. Experimental section
ꢁ
4
8 h and then extracted with DCM and water. The organic layers
2.1. Materials
were combined and dried with anhydrous Na SO . Finally, the
2
4
crude product was concentrated under reduced pressure and
Carbazole (98.0 wt%, Adamas), 1,4-dibromobenzene (98.0 wt%,
further purified by silica gel column chromatography (PE/DCM ¼ 1/
Adamas), 4-acetylphenylboronic acid (97 þ wt%, Adamas), 4-
bromo-2,6-difluorobenzylaldehyde (98 þ wt%, Adamas), 1-(4-
bromo-2,6-difluorophenyl)ethenone (97.0 wt%, Innochem), 4-
fluoroacetophenone (98.0 wt%, Innochem), 4-fluorobenzaldehyde
1
4
e1/2) to furnish the desired product Cz-24 (1.25 g, 93.0%). H NMR
(
400 MHz, CDCl
3
)
d
10.43 (s, 1H), 8.19 (d, J ¼ 7.7 Hz, 2H), 7.85 (d,
J ¼ 8.5 Hz, 2H), 7.75 (d, J ¼ 8.5 Hz, 2H), 7.48 (dt, J ¼ 8.1, 7.5 Hz, 4H),
1
3
7
1
1
[
.38e7.32 (m, 4H). C NMR (100 MHz, CDCl
48.6, 140.5, 139.3, 136.1, 128.6, 127.6, 126.2, 123.7, 120.4, 112.8,
10.7, 109.7. MS (EI-TOF) m/z: calculated for C25 NO: 383.11
M]; found: 383 [M].
3
) d 184.2, 164.9, 162.3,
(
(
(
98.0
wt%,
Alfa), 1-(4-bromo-2,6-difluorophenyl)ethenone
97.0 wt%, Ark), 3,5-dibromobenzaldehyde (98.0 wt%, Ark), dis
triphenylphosphine)palladium (II) dichloride (99.9 wt%, Acros),
15 2
H F
Iron (III) chloride anhydrous (98.0 wt%, Adamas), and silver nitrate
98.9 wt%, Alfa) were purchased from the corresponding com-
panies. Ammonia, potassium carbonate (99.0 wt%), 1,10-
(
þ
2.5. Synthesis of Cz-25
phenanthroline (98 wt%), copper iodide (99.9 wt%), potassium
tert-butoxide (98.0 wt%), and tetrakis (triphenylphosphine) palla-
dium (0) (99.9 wt%) were ordered from Aladdin Industrial Corpo-
ration, Shanghai. N, N-Dimethylformamide (DMF), petroleum ether
The monomer Cz-25 was synthesized in the yield of 74.1%
following the similar procedure of the monomer Cz-22 using 4-
1
fluoroacetophenone as reagent. H NMR (400 MHz, CDCl
3
) d 8.24
(
PE), dichloromethane (DCM), methanol, 1,2-dichloroethane (DCE),
and tetrahydrofuran (THF) are of analytically pure and were ob-
tained from Beijing Chemical Reagents Company. Ultrapure water
(
7
d, J ¼ 8.5 Hz, 2H), 8.18 (d, J ¼ 7.7 Hz, 1H), 7.74 (d, J ¼ 8.6 Hz, 1H),
13
.53e7.44 (m, 2H), 7.38e7.33 (m, 1H), 2.73 (s, 2H). C NMR
(
100 MHz, CDCl 197.0, 142.2, 140.2, 135.5, 130.1, 126.5, 126.2,
3
) d
(
18 MU cm) was produced by a Millipore-ELIX water purification
123.8, 120.6, 120.5, 109.8, 26.7. MS (EI-TOF) m/z: calculated for
system. All the other chemical reagents and solvents were
commercially available. 4-(9H-9-Carbazolyl)phenylboronic acid,
and 9-(4-bromophenyl)-9H-carbazole were synthesized according
to the reported procedure [26]. Cz-22 was prepared following the
reported procedure [30]. Carbon dioxide (99.5%), methane
20
C H15NO: 285.12 [M]; found: 285 [M].
2.6. Synthesis of Cz-26
(
99.999%), and nitrogen (99.999%) were purchased from Haike
The monomer Cz-26 was synthesized in the yield of 82.0%
Yuanchang Gas Company.
following the similar procedure of the monomer Cz-24 using 4-
1
bromo-2,6-difluorobenzylaldehyde as reagent. H NMR (400 MHz,
2
.2. Structural characterization and instrumental analysis
CDCl
3
)
d
8.19 (d, J ¼ 7.7 Hz, 2H), 7.83 (d, J ¼ 8.5 Hz, 2H), 7.73 (d,
J ¼ 8.5 Hz, 2H), 7.47 (ddd, J ¼ 9.8, 9.3, 4.5 Hz, 4H), 7.35 (dd, J ¼ 11.4,
The detail information was shown in the Supporting
13
4
1
1
.8 Hz, 4H), 2.70 (s, 3H). C NMR (100 MHz, CDCl
59.5, 145.4, 140.6, 138.8, 136.6, 128.5, 127.5, 126.1, 123.6, 120.4,
10.8,110.5,109.7, 32.6. MS (EI-TOF) m/z: calculated for C26 NO:
3
) d 194.3, 162.0,
Information.
17 2
H F
2.3. Synthesis of Cz-23
397.13 [M]; found: 397 [M].
To a two-neck flask were added 9-(4-bromophenyl)-9H-carba-
zole (0.58 g, 1.8 mmol), 4-acetylphenylboronic acid (0.42 g,
2.7. Synthesis of Cz-27
2
2
.8 mmol), and aqueous potassium carbonate solution (8.0 mL,
.0 M) in THF (10.0 mL). The mixture was degassed by the freeze-
To a two-neck flask were added carbazole (1.93 g, 11.5 mmol),
3,5-dibromobenzaldehyde (1.33 g, 5.1 mmol), DMF (20.0 mL), po-
tassium carbonate (2.88 g, 20.9 mmol), 1,10-phenanthroline (0.23 g,
1.2 mmol), and copper iodide (2.02 g, 10.6 mmol). The solution was
kept stirring under nitrogen atmosphere for 10 min at room tem-
3 4
epumpethaw cycle two times. Pd(PPh ) (104.01 mg, 0.09 mmol)
was added and degassed by freezeepumpethaw once again. The
white solution was slowly heated to 80 C with nitrogen protection
and kept for 48 h and then extracted with DCM and water. The
ꢁ
ꢁ
organic layers were combined and dried with anhydrous Na
2
SO
4
.
perature and then 120 C for 24 h. Ice water (50.0 mL) was poured
The crude product was concentrated under reduced pressure and
to quench the reaction. The gray green crude product was filtrated,
further purified by silica gel column chromatography (PE/DCM ¼ 1/
washed with water and dried. The resulting solid was obtained by
1
6
e1/3) to produce the desired compound (0.38 g, 60.3%). H NMR
further purification via silica gel column chromatography (PE/
1
(
400 MHz, CDCl
3
)
d
10.13 (s, 1H), 8.19 (d, J ¼ 7.7 Hz, 2H), 8.05 (d,
DCM ¼ 2/1) to give Cz-27 (1.31 g, 59.0%). H NMR (400 MHz, CDCl
3
)
J ¼ 8.1 Hz, 2H), 7.90 (t, J ¼ 7.1 Hz, 4H), 7.73 (d, J ¼ 8.3 Hz, 2H), 7.49
d
10.22 (s, 1H), 8.23 (s, 2H), 8.17 (d, J ¼ 7.7 Hz, 3H), 8.12 (s, 1H), 7.54
13
13
(
dd, J ¼ 16.8, 7.6 Hz, 4H), 7.34 (t, J ¼ 7.3 Hz, 2H). C NMR (100 MHz,
CDCl 191.0, 145.3, 139.8, 137.8, 137.3, 134.6, 129.6, 128.0, 126.8,
26.6, 125.2, 122.7, 119.6, 119.4, 108.9. MS (EI-TOF) m/z: calculated
for C25 17NO: 347.13 [M]; found: 347 [M].
(d, J ¼ 8.0 Hz, 4H), 7.47 (t, J ¼ 7.3 Hz, 4H), 7.35 (t, J ¼ 7.0 Hz, 4H).
C
3
)
d
3
NMR (100 MHz, CDCl ) d 191.1, 141.3, 140.9, 140.2, 131.2, 127.1, 126.8,
1
124.6, 121.6, 121.3, 110.1. MS (MALDI-TOF) m/z: calculated for
31 20 2
C H N O: 436.16 [M]; found: 436.3 [M].
H

R.-R. Zhang et al. / Polymer 143 (2018) 87e95
89
2
.8. Synthesis of CPOP-22e27
added dropwise to a mixture of silver nitrate (0.20 g, 1.12 mmol)
and deionized water (10.0 mL) to form a yellow precipitate. The
fresh Tollens' reagent can be obtained after the dissolving of the
yellow precipitation. CPOP-27 (0.25 g, 0.57 mmol) was then added
to the freshly prepared Tollens' reagent solution immediately. The
Polymers CPOP-22~27 can be synthesized from the corre-
3
sponding monomers Cz-22~27 via FeCl -promoted reaction indi-
vidually. The detail procedure of preparing CPOP-22 from
monomer Cz-22 is given as follows. Under nitrogen atmosphere,
Cz-22 (0.09 g, 0.33 mmol) was dissolved in anhydrous DCE
ꢁ
mixture was kept stirring at 45 C for 24 h out of the light. A yellow
solid of 0.26 g was obtained after filtrating, washing with ethanol
ꢁ
(
10.0 mL). The mixture was added dropwise through a constant-
and water, and drying in vacuum oven at 45 C for 24 h.
pressure drop funnel to the solution of anhydrous ferric chloride
(
1.30 g, 8.25 mmol) in anhydrous DCE (20.0 mL). The mixture was
ꢁ
kept stirring for 48 h at 80 C, and then methanol (50.0 mL) was
added to quench the polymerization. The crude polymer was
filtered and washed with methanol, water, and THF. The as-
prepared polymer CPOP-22 was further purified with boiling
methanol for 24 h and then with THF for another 24 h in a Soxhlet
2
2
.10. Catalytic reduction of 4-nitrophenol (4-NP) by AgNPs/CPOP-
7 composite
In order to measure the catalytic activity of AgNPs/CPOP-27
composite, the reduction of 4-NP was performed in quartz cuvette
ꢁ
extractor and dried in a vacuum oven at 110 C overnight (99% in
(
(
(
1 cm of optical path, volume 4 mL), and the sodium borohydride
NaBH ) was used as a reductant. In the experiment, 4-NP
1.44 mM, 0.10 mL) was added to the quartz cuvette followed by
solution
6.87 mM, 2.80 mL). AgNPs/CPOP-27 composite (1.0 mg/mL,
yield). Following the similar procedure, polymers CPOP-23 and
CPOP-24 were obtained with yields 89% and 96%, respectively.
CPOP-25 (yield 98%) and CPOP-26 (yield 96%) were obtained from
the monomers Cz-25 and Cz-26 at room temperature polymeriza-
tion, respectively. For CPOP-27, it was obtained from the monomer
Cz-27 at room temperature in DCM with yield of 82%.
4
treated with the freshly prepared aqueous NaBH
(
0
mixed solution mentioned above. The reducing progress is moni-
tored and recorded by UVevis spectra with the absorbance ranging
from 244 to 600 nm and defined time intervals at room tempera-
ture. (The catalytic reduction reaction should be carried out within
a few minutes after the solution was prepared so as to minimize the
4
.10 mL) dispersed well in deionized water was dropped to the
2.9. Preparation of AgNPs/CPOP-27 composite
Procedure for preparation of AgNPs/CPOP-27 composite was
according to the improved method [38]. Dilute ammonia (0.5%) was
4
decomposition of NaBH .)
Scheme 1. Preparation of the monomers Cz-22~27.

90
R.-R. Zhang et al. / Polymer 143 (2018) 87e95
Scheme 2. Preparation of the hypercrosslinked polycarbazoles CPOP-22~27.

R.-R. Zhang et al. / Polymer 143 (2018) 87e95
91
Fig. 1. 13C CP/MAS NMR spectra of CPOP-22, CPOP-26, and CPOP-27.
3. Results and discussion
A series of carbazolyl-bearing aldehydes or ketones Cz-22~26
Scheme 1) were synthesized as monomers by classical N-arylation
and Suzuki coupling reaction, respectively. All the monomers were
(
1
13
well characterized with H NMR, C NMR, and MS. It has been
reported that the number of carbazolyl group in the monomer plays
important roles in permanent porosity of porous polycarbazoles via
3
FeCl -promoted oxidative coupling reaction [26,39]. Furthermore,
we also prepared the monomer Cz-27 to investigate effects on the
chemical structure and porosity of the corresponding hyper-
crosslinked polycarbazole. For these monomers, carbazole moieties
can either be linked each other by FeCl
coupling reaction, or coupled with aldehyde or ketone groups by
FeCl -catalyzed FriedeleCrafts alkylation. Therefore, the corre-
3
-promoted oxidative
3
sponding hypercrosslinked polycarbazoles CPOP-22~27 (shown in
Scheme 2) were synthesized through FriedeleCrafts reaction/
oxidative coupling polymerization in one-step using FeCl
alytic reagent.
3
as cat-
All the hypercrosslinked polycarbazoles are characterized by 13
C
CP/MAS NMR. The spectra of CPOP-22, CPOP-26, and CPOP-27
were illustrated as representative examples (see Fig. 1). For CPOP-
22, the main resonance signals are located at about 139, 124, 110,
and 53 ppm. Generally, the signal peak at 139 ppm corresponds to
the phenyl carbons linking with nitrogen atom. High intensity peak
of 124 ppm is attributed to the signal peak of other substituted
phenyl carbons. The unsubstituted phenyl carbons are located at
110 ppm. These three signal peaks are derived from the poly-
carbazole networks consistent with previous reports [26,27]. The
tertiary methylene carbons linked with phenyl and carbazole are
located at 53 ppm. For CPOP-26, besides the main resonance sig-
nals mentioned above, the peak at 159 ppm is belonged to the
phenyl carbons bonding with fluorine atom. The peak of methyl
13
carbon was located at 32 ppm. The C CP/MAS NMR spectra for the
other obtained polymers are shown in Fig. S1 (Supporting Infor-
mation), which appear with similar resonance intensity to CPOP-22
and CPOP-26. From all the spectra, we can see a new broad peak at
Fig. 2. (a) Nitrogen adsorptionedesorption isotherms of CPOP-22~27 measured at
7 K, the adsorption and desorption branches are labeled with solid and open symbols,
respectively. (For clarity, the isotherms of CPOP-23~27 were shifted vertically by 105,
7
53 ppm ascribed to the tertiary carbon methylene carbons linked
3
ꢀ1
with phenyl and carbazole. Meanwhile, the carbon signals of
295, 215, 60, and 75 cm g , respectively.) (b) The PSD profiles of CPOP-22~27
calculated by NLDFT.

92
R.-R. Zhang et al. / Polymer 143 (2018) 87e95
Table 1
Porosity properties and gas uptake capacities of polymers.
a
BET (m2
ꢀ1
micro (m2
b
ꢀ1
total (cm3
c
ꢀ1
d
uptakee (wt%)
CH
4
uptakee (wt%)
Polymers
S
g
)
S
g
)
V
g
)
D
pore (nm)
CO
2
CPOP-22
CPOP-23
CPOP-24
CPOP-25
CPOP-26
CPOP-27
440
760
750
755
530
674
313
552
575
545
464
408
0.24
0.45
0.62
0.42
0.31
0.29
1.06
0.99
1.02
0.99
1.06
1.04
6.91
9.78
9.13
9.76
9.34
6.96
1.07
1.44
1.33
1.23
1.52
1.18
a
Specific surface area calculated from the nitrogen adsorption isotherm using the BET method.
b
c
Micropore surface area calculated from the adsorption branch of the nitrogen adsorptionedesorption isotherm using the t-plot method.
Total pore volume at P/P
0
¼ 0.99.
d
e
Date calculated from nitrogen adsorption isotherms with the NLDFT method.
Date were obtained at 1.0 bar and 273 K.
ꢀ
1
monomer aldehyde or ketone group (190e180 ppm) almost dis-
appeared except for CPOP-27. These results prove that the
FriedeleCrafts reaction with aldehyde or ketone group takes place
definitely. Furthermore, the competition consists in the
FriedeleCrafts alkylation of aldehyde groups and oxidative
coupling reaction of carbazole group. For CPOP-27, we can see that
the peak belonging to the aldehyde carbon is also located clearly at
signals at about 1700 cm of monomer aldehyde or ketone group
become weaker after polymerization. The result can also prove that
the aldehyde or ketone group participate the FriedeleCrafts reac-
tion during the polymerization. The thermal stabilities of all the
ꢁ
polymers are characterized by TGA via heating the sample to 800 C
at a heating rate of 10 C min under nitrogen atmosphere (Fig. S3,
Supporting Information). TGA plot shows that there still have about
ꢁ
ꢀ1
ꢁ
191 ppm after polymerization, indicating that a part of aldehyde
70% mass residues even when the temperature rises to 800 C
groups have not reacted through FriedeleCrafts alkylation due to
competition of more carbazole groups in the oxidative coupling
reaction.
(calculation based on the weight of materials after removing
ꢁ
adsorbed water at temperature above 100 C) and the decomposi-
ꢁ
tion temperature of the polymers is about 400e500 C, indicating
Based on the comparison of FTIR spectra from monomers and
polymers (Fig. S2, Supporting Information), we can find the strong
the good thermal stability of obtained polymers.
A series of polymers were synthesized from monomers with
Scheme 3. Preparation of AgNPs/CPOP-27 composite.

R.-R. Zhang et al. / Polymer 143 (2018) 87e95
93
Fig. 3. TEM images of AgNPs/CPOP-27 composite in different reaction time: (a) 12 h; (b) 24 h; (c) 48 h; (d) the corresponding EDX of AgNPs/CPOP-27 composite.
various structures to not only establish the methodology but also
tune the porosity such as BET specific surface area, PSD, and pore
volume. For porous organic polymers with irregular pore struc-
tures, porosity tuning is mainly affected by the monomer structure
and preparative method [40,41]. To investigate the porosity of the
polymers CPOP-22~27, the nitrogen adsorptionedesorption testing
was conducted. As shown in Fig. 2a, the materials display the for-
mation of the model I combined with II sorption isotherms ac-
cording to the IUPAC classification [42]. A sharp increase at the
filtered and washed with plenty of water to remove the soluble
impurities. To explore the formation and related morphology of
AgNPs/CPOP-27 composite, TEM images of AgNPs/CPOP-27 com-
posite in different reaction time are shown in Fig. 3 (aed). We can
see the AgNPs gradually grows and the related particle sizes
become apparently larger from 2 to 10 nm (8 h) to 5e20 nm (24 h)
with the reaction time. The corresponding EDX technique suggests
that AgNPs are embedded in the CPOP-27 successfully (Fig. 3d).
TGA data in Fig. S6 (Supporting Information) also indicate the actual
loading capacity of AgNPs is about 2.0 wt % via heating the sample
0
relative pressure (P/P ) under 0.05 indicates permanent micropo-
ꢁ
ꢁ
ꢀ1
rous nature of the obtained polymers. The other sharp increase at
high relative strain above 0.90 can indicate the macroporous
property. Hysteresis can be observed apparently in the entire scope
of the relative strain. The BET specific surface areas of CPOP-22~27
to 800 C at a heating rate of 10 C min under air atmosphere.
The BET specific surface area of the AgNPs/CPOP-27 composite
is not obviously changed with compared to CPOP-27. Both of CPOP-
27
and
AgNPs/CPOP-27
display
similar
nitrogen
calculated from 0.01 to 0.10 (P/P
0
) are ranged from 440 to
adsorptionedesorption isotherm and PSD profile. The as-
synthesized AgNPs/CPOP-27 composite shows microporous fea-
tures and its dominant PSD are mainly located around 0.53, 0.73,
and 1.26 nm based on NLDFT method shown in Fig. 4. The AgNPs
encapsulated in the porous polymer can be utilized as catalyst for
the catalytic transformation in the pharmaceuticals and agro-
chemical [43]. The AgNPs loaded on the polymer show good cata-
lytic activity in reduction, which can be used for the conversion of
nitro compound precursors or intermediates to the corresponding
amino or amine compounds. The catalytic activity of AgNPs/CPOP-
27 composite was examined by the reduction of 4-NP to 4-
aminophenol (4-AP) at room temperature with slightly excess
2
ꢀ1
760 m g . From the adsorption branch of the isotherms, the PSD
profiles of the polymers can be obtained using the NLDFT approach.
As shown in Fig. 2b, the primary pore sizes of CPOP-22~27 vary
from 0.99 to 1.06 nm.
The absorbing ability of CPOP-22~27 for methane and carbon
dioxide were measured at 273 K. Figs. S4 (Supporting Information),
and S5 (Supporting Information) show the methane and carbon
dioxide adsorption isotherms. The carbon dioxide capture capac-
ities range from 6.91 to 9.78 wt% and the methane capture capac-
ities vary from 1.07 to 1.52 wt%, which indicate that the uptake
performance of all the obtained materials are at a moderate level.
The key porosity parameters of CPOP-22~27 are listed in Table 1,
including the BET specific surface area, micropore surface area, pore
volume, dominant pore size, and gas uptake performance.
CPOP-27 containing aldehyde groups even can be used as the
supporting matrices for loading AgNPs via further redox reaction
with Tollens' reagent (Scheme 3). CPOP-27 was added to the freshly
4
NaBH as reducing reagent [44]. We can easily distinguish the
process of catalytic reaction by the color change of solution from
yellow to colorless gradually. Both the reactant and product can be
monitored by UVevis spectroscopy without any detectable
byproduct. Fig. S7a (Supporting Information) depicts the time-
varying catalytic reaction performance of 4-NP with the existence
of AgNPs/CPOP-27. The absorption peak of 4-nitrophenolate ions at
400 nm decreased gradually accompanied by the rising up of 4-AP
ꢁ
prepared Tollens' reagent solution at 45 C and the mixture was
stirred for 24 h under dark condition, the desired product was

94
R.-R. Zhang et al. / Polymer 143 (2018) 87e95
composite, which is a facile method to prepare HCP/AgNPs com-
posite for catalytic reduction.
Acknowledgements
The financial support of the National Science Foundation of
China Grants (21574031 and 21574032) and the Sino-German
Center for Research Promotion (Grant GZ1286) is acknowledged.
Appendix A. Supplementary data
Supplementary data related to this article can be found at
https://doi.org/10.1016/j.polymer.2018.03.062.
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