Meso/microporous carbons from conjugated hyper-crosslinked polymers based on tetraphenylethene for high-performance co2 capture and supercapacitor

Article abstract of DOI:10.3390/molecules26030738

In this study, we successfully synthesized two types of meso/microporous carbon materials through the carbonization and potassium hydroxide (KOH) activation for two different kinds of hyper-crosslinked polymers of TPE-CPOP1 and TPE-CPOP2, which were synthesized by using Friedel–Crafts reaction of tetraphenylethene (TPE) monomer with or without cyanuric chloride in the presence of AlCl₃ as a catalyst. The resultant porous carbon materials exhibited the high specific area (up to 1100 m² g^?1 ), total pore volume, good thermal stability, and amorphous character based on thermogravimetric (TGA), N₂ adsoprtion/desorption, and powder X-ray diffraction (PXRD) analyses. The as-prepared TPE-CPOP1 after thermal treatment at 800^?C (TPE-CPOP1-800) displayed excellent CO₂ uptake performance (1.74 mmol g^?1 at 298 K and 3.19 mmol g^?1 at 273 K). Furthermore, this material possesses a high specific capacitance of 453 F g^?1 at 5 mV s^?1 comparable to others porous carbon materials with excellent columbic efficiencies for 10,000 cycle at 20 A g^?1 .

Full text of DOI:10.3390/molecules26030738

molecules
Article
Meso/Microporous Carbons from Conjugated
Hyper-Crosslinked Polymers Based on Tetraphenylethene for
High-Performance CO2 Capture and Supercapacitor
Mohamed Gamal Mohamed 1,2 , Mahmoud M. M. Ahmed 1,3, Wei-Ting Du 1 and Shiao-Wei Kuo 1,4,
*
1
Department of Materials and Optoelectronic Science, Center of Crystal Research, National Sun Yat-sen
University, Kaohsiung 804, Taiwan; mgamal.eldin34@gmail.com (M.G.M.);
mahmoud.ahmed@mail.ntust.edu.tw (M.M.M.A.); justguita@gmail.com (W.-T.D.)
Chemistry Department, Faculty of Science, Assiut University, Assiut 71516, Egypt
Chemistry Department, Chung Yuan Christian University, Taoyuan 320, Taiwan
Department of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung 807, Taiwan
Correspondence: kuosw@faculty.nsysu.edu.tw
2
3
4
*
Abstract: In this study, we successfully synthesized two types of meso/microporous carbon materials
through the carbonization and potassium hydroxide (KOH) activation for two different kinds of
hyper-crosslinked polymers of TPE-CPOP1 and TPE-CPOP2, which were synthesized by using
Friedel–Crafts reaction of tetraphenylethene (TPE) monomer with or without cyanuric chloride in the
presence of AlCl3 as a catalyst. The resultant porous carbon materials exhibited the high specific area
(up to 1100 m2 g−1), total pore volume, good thermal stability, and amorphous character based on
thermogravimetric (TGA), N2 adsoprtion/desorption, and powder X-ray diffraction (PXRD) analyses.
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
◦
The as-prepared TPE-CPOP1 after thermal treatment at 800 C (TPE-CPOP1-800) displayed excellent
Citation: Mohamed, M.G.;
Ahmed, M.M.M.; Du, W.-T.;
Kuo, S.-W. Meso/Microporous
Carbons from Conjugated
CO2 uptake performance (1.74 mmol g−1 at 298 K and−31.19 mmol g−1 at 273 K). Furthermore, this
−1
material possesses a high specific capacitance of 453 F g at 5 mV s comparable to others porous
−1
carbon materials with excellent columbic efficiencies for 10,000 cycle at 20 A g
.
Hyper-Crosslinked Polymers
Based on Tetraphenylethene for
High-Performance CO2 Capture
and Supercapacitor. Molecules 2021,
26, 738. https://doi.org/10.3390/
molecules26030738
Keywords: Friedel–Craftsreaction; porouspolymers; triazinecovalentframework; CO2 capture; supercapacitor
1. Introduction
The developing new storage technologies and other energy resources with high spe-
cific power and energy storage capability such as supercapacitors and batteries have
Academic Editor: Guanglin Xia
Received: 12 January 2021
Accepted: 28 January 2021
Published: 31 January 2021
become an important topic in both the academic and industry areas [
fossil fuels by designing devices like supercapacitors and batteries can reduce and prevent
global warming, inadequate environment, and polluted atmosphere [ ]. Ultra-capacitors
1]. The replacing of
2–7
or electric double layer capacitors (also called supercapacitors) are energy storage devices
that possess long cycle life, low maintenance, low internal resistance, light weight, deliv-
ering high energy and high efficiency, high power, flexible packaging, light weight and
maintenance, and a wide range of temperature compared with other energy devices such
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published maps and institutional affil-
iations.
as batteries [
pacitors can be divided into electrical double layer capacitor (EDLC), hybrid capacitor,
and finally pseudocapacitor [16 27]. Hyper-crosslinked polymers (HCPs) [28 33], covalent
organic frameworks (COF) [34 40], conjugated microporous polymers (CMPs) [41 45], and
polymers of intrinsic microporosity (PIMs) are considered as types of microporous organic
polymers (MOPs) [46 49]. As mentioned above, HCPs are considered as a kind of porous
8–15]. Based on the supercapacitors mechanism for energy storage, superca-
–
–
–
–
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© 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
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4.0/).
–
material that can be easily synthesized through the Friedel–Crafts alkylation reaction of
rigid aromatic monomers with an external crosslinker such as formaldehyde dimethyl
acetal, 1,3,5-trichlorotriazine, and 1,4-bis(chloromethyl)benzene [50
other microporous material such as activated carbon, HCPs can be synthesized by low-cost
monomers, catalysts, and suitable reaction conditions [53 54]. In addition, HCPs materials
–52]. Compared with
,
Molecules 2021, 26, 738. https://doi.org/10.3390/molecules26030738
https://www.mdpi.com/journal/molecules

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feature easy functionalization, good chemical and thermal properties, microporous nature,
and large surface areas [50–54]. Nowadays, the preparation of porous carbon materials
has attracted much attention due to their interesting properties such as excellent electrical
conductivity, high surface areas and high pore volumes, and good chemical, thermal, and
mechanical stabilities [55–59]. Therefore, porous carbonaceous materials have been applied
in many real-life applications, for example catalysis, gas separation, gas capture, energy
storage in supercapacitors and batteries, fuel cells, water treatment and purification, and
electromagnetic interface shielding [60–64]. As reported, the preparation of porous carbona-
ceous materials with high surface area and excellent porosity nature can be achieved by
chemical activation for many polymers’ precursors, for example conjugated microporous
polymers (CMPs), metal-organic frameworks (MOFs), HCPs, and porous aromatic frame-
works (PAFs) [62–64]. Herein, we successfully prepared porous carbon materials derived
from KOH activation at 800 ◦C of TPE-CPOP1 and TPE-CPOP2 as hypercross-linked poly-
mers, which were prepared by the Friedel–Crafts polymerization of tetraphenylethene with
or without cyanuric chloride as an external crosslinker in the presence of AlCl3 as a cata-
lyst. The TGA, XPS, Raman, BET, and PXRD measurements were used to understand and
determine their thermal stability, chemical compositions, surface areas, and crystallinity
properties. Furthermore, the electrochemical and CO2 uptake analyses for TPE-CPOP1
and TPE-CPOP2 after thermal treatment at 800 ◦C were done to investigate their potential
application in energy storage and gas capture.
2. Results
2.1. Synthesis and Character of TPE-CPOP1 and TPE-CPOP2
Scheme 1 shows the synthetic route for the preparation of hyper-crosslinked poly-
mers and microporous carbon materials from TPE as a building monomer. Firstly, the
TPE monomer was synthesized through the reaction of benzophenone with zinc and ti-
tanium tetrachloride (TiCl4) in the presence of THF at 80 ◦C to give TPE as a white solid.
Secondly, TPE-CPOP1 and TPE-CPOP2 were prepared through a simple Friedel–Crafts
reaction of TPE monomer with or without cyanuric chloride in the presence of anhydrous 1,
2-dichloroethane as solvent and AlCl3 as a catalyst (Scheme 1a–d). Finally, TPE-CPOP1-800
and TPE-CPOP2-800 were prepared through the carbonization and KOH activation process
for their corresponding polymers as presented in Scheme 1e.
(c)
AlCl3/DCM
60 o
C
(a)
(b)
O
TPE-CPOP1
Zn/THF
TiCl4
(d)
N
Cl
N
N
Cl
N
N
N
N
N
N
N
N
N
N
N
Cl
AlCl3/DCM/ 60 o
C
N
TPE-CPOP2
(e)
O
O
O
O
O
O
KOH Activation
800 oC, N2
HO
OH
Micro/Mesoporous Carbon Materials
Scheme 1. Preparation of (
b) tetraphenylethene (TPE), (c) TPE-CPOP1 (conjugated porous organic
polymer), (d) TPE-CPOP2, and (e) microporous carbon materials from benzophenone (a).

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The spectral analyses of TPE monomer were in agreement with our reported results
(Figures S1 and S2). The chemical molecular structure of TPE-CPOP1 and TPE-CPOP2 was
carefully confirmed by using FTIR and the solid state 13C NMR spectra analyses. Figure 1
presents the FTIR profile of TPE monomer, TPE-CPOP1 and TPE-CPOP2, respectively,
recorded at room temperature. The characteristics absorption bands appeared at 3022
and 1599 cm−1 corresponding to the stretching C–H aromatic groups and C=C bonds as
displayed in FTIR spectrum of TPE (Figure 1a). Meanwhile, the FTIR spectra (Figure 1b,c
)
of both TPE-CPOP1 and TPE-CPOP2 showed absorption bands at ca. 3447, 3022 and
1595 cm−1, which are attributed to the presence of a hydroxyl group from adsorbed water
by these porous materials, the stretching C–H aromatic groups and C=C bonds, respectively.
CH aromatic
3022 cm-1
C=C, 1595 cm-1
(a)
OH, 3447 cm-1
CH aromatic
3018 cm-1
C=C, 1612 cm-1
(b)
(c)
OH, 3437 cm-1
C=C, 1616 cm-1
CH aromatic
3012 cm-1
N
N
N
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
Figure 1. FTIR spectra of (a) TPE, (b) TPE-CPOP1, and (c) TPE-CPOP2.
The chemical structure of TPE-CPOP1 and TPE-CPOP2 was further analyzed by solid-
state 13C NMR measurements (Figure 2). The appearance peaks in the range 145.80–136.51 ppm
in TPE-CPOP1 (Figure 2a) and 147–137 ppm in TPE-CPOP2 (Figure 2b), respectively; cor-
responded to the aromatic carbon nuclei. In addition, the peaks about 171 ppm in the
TPE-CPOP2 could be assigned to the C=N in triazine units (Figure 2b).
Based on FTIR and solid-state NMR analyses showed the successful incorporation of
the triazine ring into the TPE-CPOP2 framework. The thermal stability of porous materials
is important for the real-life application. Thus, the thermal stability of TPE-CPOP1 and TPE-
CPOP2, TPE-CPOP1-800, and TPE-CPOP2-800 were determined by thermogravimetric
analysis (TGA) (Figure 3, Table 1). The values of degradation temperatures when the
weight loss of the sample reached 5% (Td5), 10% (Td10), and char yield for TPE-CPOP1 and
◦
◦
TPE-CPOP2 were 412, 519 C, and 69% and 284, 365 C, and 67%, respectively. Meanwhile,
after carbonization and KOH activation at 800 ◦C for 8 h, the degradation temperatures
◦
(Td5 and Td10) and char yield were 365, 464 C, and 70%, respectively, for TPE-CPOP1-
800 and 375, 500, and 72%, respectively, for TPE-CPOP2-800. According to TGA results,
our materials featured good thermal stability comparable with other porous materials.
As displayed in Figure S4, the XPS survey spectra showed signals at 284 eV and 530 eV
representing the carbon atoms of the aromatic rings and oxygen atoms in both TPE-CPOP1
and TPE-CPOP2. In addition, the XPS profile of TPE-CPOP2 displayed signal at 400 eV
representing the nitrogen atoms in the triazine units.

Molecules 2021, 26, 738
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(a)
Aromatic
Aromatic
*
*
*
(b)
N
N
N
N
N
N
N
N
N
N
N
N
N
N
*
N
180
160
140
120
100
80
60
Chemical Shift (ppm)
Figure 2. Solid state 13CNMR spectra (
a) TPE-CPOP1 and (b) TPE-CPOP2. where * is the side band
of solid-state NMR.
100
80
60
40
20
0
(a) TPE-CPOP1
(b) TPE-CPOP2
(c) TPE-CPOP1-800
(d) TPE-CPOP2-800
100
200
300
400
500
600
700
Temperature (oC)
Figure 3. TGA diagram of (
a
) TPE-CPOP1 and (
b) TPE-CPOP2, (c) TPE-CPOP1-800, and (d) TPE-
CPOP2-800.
All the as-synthesized materials in this study appeared a broad peak ca. 12.45◦ and all
these porous materials are not crystalline polymers as illustrated in PXRD pattern (Figure 4).

Molecules 2021, 26, 738
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Table 1. Thermal stability and porosity properties of TPE, TPE-CPOP1, TPE-CPOP2, TPE-CPOP1-800,
and TPE-CPOP2-800.
Sample
Td5 (◦C)
412
Td10 (◦C)
519
Char Yield (wt%)
Surface Area (m2 /g)
Pore Size (nm)
1.49, 1.82
2.57
TPE-CPOP1
69
67
70
72
489
146
TPE-CPOP2
248
365
TPE-CPOP1-800
TPE-CPOP2-800
356
464
1177
1165
1.04, 2.99
1.02, 2.29
375
500
(a)
(b)
(c)
(d)
10
20
30
40
50
2 Theta
Figure 4. PXRD pattern of (a) TPE-CPOP1 and (b) TPE-CPOP2, (c) TPE-CPOP1-800, and (d) TPE-
CPOP2-800.
2.2. Porosity
The porosity properties like Brunauer–Emmett–Teller (BET) surface areas, total pore
volume, and pore size diameter of TPE-CPOP1 and TPE-CPOP2 before carbonization and
KOH activation process were characterized by N2 adsorption/desorption measurements at
77 K and 1 bar, as presented in Figure 5. Both the N2 adsorption isotherms of TPE-CPOP-1
and TPE-CPOP2 showed increase the N2 capture at low- and high-pressure P/P0 values
indicating that both two materials curves could be classified as type I according to IUPAC
classification (Figure 5a). In addition, the N2 adsorption isotherms of TPE-CPOP1 and
TPE-CPOP2 at high-pressure values possesses a hysteresis loop, which indicates that the
obtained polymer framework contains a mesoporous and microporous structure. Further-
more, the hysteresis loop for both materials does not close, which could be attributed to
the flexibility network structure and the swelling of the frameworks during gas adsoprtion
by elastic deformations [52]. The BET surface areas of TPE-CPOP1 and TPE-CPOP2 were
found to be 489 an−d1146 m2 g−1, respectively, and their pore volumes were found to be
0.269 and 0.1 cm3 g at P/P0 = 0.996, respectively. In addition, the pore size diameter was
estimated by the nonlocal density functional theory (NLDFT) and the results showed that
the pore size diameter was 1.49 and 1.82 nm, respectively, for TPE-CPOP1 and 2.57 nm for
TPE-CPOP2 (Figure 5b).

Molecules 2021, 26, 738
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(a)
(b)
250
200
150
100
50
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
TPE-CPOP1 (adsorption)
TPE-CPOP1 (desorption)
TPE-CPOP2 (adsorption)
TPE-CPOP2 (desorption)
TPE-CPOP1
TPE-CPOP2
0
0.0
0.2
0.4
0.6
0.8
1.0
1
2
3
4
5
6
7
8
Relative Pressure (P/P0)
Pore Diameter (nm)
Figure 5. (a) N2 adsorption desorption pattern (filled cycles: adsorption; empty cycles: desorption)
and (b) pore size diameter of TPE-CPOP1 and TPE-CPOP2.
As shown in Table 1, the BET surface area of TPE-CPOP2 lower than that of TPE-
CPOP1, presumably because of the low attachment of triazine units into TPE moiety
during the Friedel–Crafts reaction [65,66]. Figure 6 shows the N2 adsorption/desorption
and pore size distribution of TPE-CPOP1-800 and TPE-CPOP2-800 to investigate their
porous nature. As shown in Figure 6, both TPE-CPOP1-800 and TPE-CPOP2-800 exhibited
a rapid N2 capture ability at low pressure and continued to increase for N2 adsorption
at high-pressure regions, which indicated the presence of micropores and mesopores in
the materials. Based on the IUPAC classification, the adsorption/desorption isotherm
of TPE-CPOP1-800 and TPE-CPOP2-800 possesses type I and type IV. The values of BET
surface area, total pore volume, and pore size diameter were 1177 m2 g−1, 0.48 cm3 g−1
and 1.04–2.99 nm, respectively, for TPE-CPOP1-800 and 1165 m2 g−1, 0.62 cm3 g−1, and
1.02–2.29 nm, respectively, for TPE-CPOP2-800. In addition, the lack of difference in surface
area between TPE-CPOP1-800 and TPE-CPOP2-800 due to the KOH acts as an activation
agent for TPE-CPOP1 and TPE-CPOP2 to produce carbon materials and enhance their
porosity properties such as specific surface area, pore size, and total pore volume [67].
The surface morphologies of TPE-CPOP1-800 and TPE-CPOP2-800 showed ultra-
,
micropours and these materials are amorphous based on TEM images as shown in Figure S5
.
The presence of the carbon and oxygen atoms in the surface of TPE-CPOP1-800 and TPE-
CPOP2-800 was confirmed by XPS analysis (Figure 7). As displayed in Figure 7, the XPS
survey spectra for both these materials possesses signals at 284 eV and 530 eV repre-
senting the carbon atoms of the aromatic rings and oxygen atoms in the microporous
carbon materials.

Molecules 2021, 26, 738
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(a)
(b)
0.4
0.3
0.2
0.1
0.0
TPE-CPOP1-800
TPE-CPOP2-800
TPE-CPOP1-800 (adsorption)
TPE-CPOP1-800 (desorption)
TPE-CPOP2-800 (adsorption)
TPE-CPOP2-800 (desorption)
440
400
360
320
280
240
0.0
0.2
0.4
0.6
0.8
1.0
1
2
3
4
5
6
7
8
Relative Pressure (P/P0)
Pore Diameter (nm)
Figure 6. (a) N2 adsorption desorption pattern (filled cycles: adsorption; empty cycles: desorption)
and (b) pore size diameter of TPE-CPOP1-800 and TPE-CPOP2-800.
(a)
(b)
C1S
O1S
C1S
O1S
200
300
400
500
600 200
300
400
500
600
Binding Energy (eV)
Figure 7. XPS profile of (a) TPE-CPOP1-800 and (b) TPE-CPOP2-800.

Molecules 2021, 26, 738
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The Raman spectra (Figure 8) showed that TPE-CPOP1-800 exhibits a definite car-
bonized structure with two identical bands of D and G, which correspond to sp3 and
sp2 carbons, respectively [68
–70]. The D and G band positions were found at 1325.0 and
1580.9 cm−1, respectively. In addition, the ID/IG ratio was found to be 1.5, which clearly
describes that sp3 carbons are higher than sp2 carbons due to the structural functionaliza-
tion. This indicated that the activation process did not destroy the chemical structure. In
addition, upon activating TPE-CPOP2-800 the band position was shifted. In detail, D band
−1
was found at 1308.4 cm and G band was at 1577.2 cm−1, which indicated a change in the
Fermi energy level caused by the Lewis acid reaction [71,72]. In addition, the ID/IG ratio
reached 1.9 indicating further sp3 hybridizations was found upon the activation process
possibly due to further functionalization occurred during the heating procedure. These
results clearly indicated that the KOH activation did not destroy the graphitic structure
and maintained the sp2 and sp3 hybridizations [11,73].
(a) TPE-CPOP1-800
1308 cm-1
(b) TPE-CPOP2-800
1577 cm-1
ID/IG: 2.1
(a)
(b)
1325 cm-1
1581 cm-1
ID/IG: 1.1
1000
1200
1400
1600
1800
Raman Shift (cm-1)
Figure 8. Raman profile of (a) TPE-CPOP1-800 and (b) TPE-CPOP2-800.
2.3. CO2 Uptake
Based on BET results, our new materials TPE-CPOP1, TPE-CPOP2, and their resulting
microporous carbon materials (TPE-CPOP1-800 and TPE-CPOP2-800), after carbonization
and KOH activation process, feature high surface areas, large pore. volumes, and meso
and microporous structures. Therefore, we expected that all these materials could be
applied as candidates for gas capture and energy storage. The CO2 uptake performance
of TPE-CPOP1, TPE-CPOP2, TPE-CPOP1-800, and TPE-CPOP2-800 were determined
by CO2 isotherm measurements at 298 and 273 K, respectively (Figures 9 and 10). The
results revealed that the values of the CO2 adsorption capacity were found to be 0.89 and
1.15 mmol g−1 at 298 K for TPE-CPOP1 and TPE-CPOP2, respectively (Figure 9a). On the
contrary, the adsoprtion capacity of CO2 at 273 K reached 0.99 and 1.26 mmol g−1 for
TPE-CPOP1 and TPE-CPOP2, respectively (Figure 9b). We supposed the TPE-CPOP2 had
higher and excellent CO2 uptake performance compared to TPE-CPOP1 due to the presence
of triazine units in the TPE-CPOP2 framework, which facilitate the dipole–quadrupole
interactions with the CO2 molecules. As previously reported, the improvement of CO2
uptake performance of porous polymers can be achieved by carbonization and KOH
activation process at elevated temperatures [74]. Thus, we did the calcination and KOH

Molecules 2021, 26, 738
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◦
activation process for TPE-CPOP1 and TPE-CPOP2 at 800 C for 8 h under a N2 atmosphere
to produce microporous carbon materials with high specific BET surface areas and pore
size diameters. Interestingly, the values of CO2 uptake were 1.74 and 1.72 mmol g−1
at 298 K for TPE-CPOP1-800 and TPE-CPOP2-800, respectively (Figure 10a). At 273 K,
the CO2 adsorption capacity reached 3.19 and 2.93 mmol g−1 for the TPE-CPOP1-800
and TPE-CPOP2-800, respectively (Figure 10b). We revealed that both TPE-CPOP1-800
and TPE-CPOP2-800 showed higher CO2 adsorption capacity that than that of the Th850
(
2.4 mmol at 298 K) [74], which can be attributed to their high specific surface areas (up to
1100 m2 g−1) and total pore volume (up to 0.48 cm3 g−1).
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
TPE-CPOP1
TPE-CPOP2
TPE-CPOP1
TPE-CPOP2
1.26
0.99
25 oC
0 oC
1.15
0.89
0.0
0.2
0.4
0.6
0.8
1.0 0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/P0)
◦
◦
Figure 9. CO2 uptake of TPE-CPOP1 and TPE-CPOP2 at 25 C (a) and 0 C (b).
(a)
(b)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
TPE-CPOP1-800
TPE-CPOP2-800
TPE-CPOP1-800
TPE-CPOP2-800
3.19
2.93
25 oC
0 oC
1.74
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/P0)
◦
◦
Figure 10. CO2 uptake of TPE-CPOP1-800 and TPE-CPOP2-800 at 25 C (a) and 0 C (b).

Molecules 2021, 26, 738
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2.4. Electrochemical Performance
The electrochemical characteristics of the TPE-CPOP1-800 and TPE-CPOP2-800 were
investigated using cyclic voltammetry (CV), charge/discharge (CD) and cycling stability.
The CV was tested over the potential range between –1.0 and 0.0 V at various scan rates
of 5 mV/s up to 200 mV/s (Figure 11a). The CV shape of the TPE-CPOP1-800 and TPE-
CPOP2-800 showed a perfect electric double layer behavior all over the potential range and
at all investigated scan rates. It is important to notice the difference between the two cases of
KOH activation; as it can be clearly seen in (Figure 11b), since the TPE-CPOP1-800 showed
an almost double area of the CV loop at all investigated scan rates compared to TPE-CPOP2-
800. This is clear evidence of the importance of a synergistic effect upon the activation
processes in enhancing the electrochemical performances without defecting the main EDLC
of the carbon structure [73,75]. The activation process provided an efficient increase in the
surface area of the obtained porous carbon materials. The main difference between both
porous carbon materials is the existence of the triazine moiety in the TPE-CPOP2 that is ex-
pected to have a strong steric hindrance that reduced the effect of KOH activation reaction to
reach the inner carbon structure. Therefore, the obtained surface area of TPE-CPOP2 upon
KOH activation was less than TPE-CPOP1-800. Moreover, upon plotting the capacitance
versus scan rates, the achieved capacitance value for the TPE-CPOP1-800 reached 453 F g−1
,
−1
which was 200 F g for TPE-CPOP2-800 at the same scan rate of 5 mV/s
(Figure 11c). It is
believed that the well-designed porous structure in TPE-CPOP1-800 was yielded by the
efficient electron transfer between KOH and TPE-CPOP1 that could promote the surface
area of the porous carbon structure and provide better electron transfer efficiencies lead-
ing to an outstanding EDLC performance than other reported porous carbons including
e.g., porous carbons derived from poly(caprolactone–b–ethylene oxide–b–caprolactone
)
triblock copolymer that reached a capacitance of 90 F g−1 at 5 mV s−1
[
76]. In addition,
both TPE-CPOP1-800 and TPE-CPOP2-800 exhibit dual pore features. However, TPE-
CPOP1-800 has higher pore size (2.99 nm) than that of TPE-CPOP2-800 (2.29 nm) and this
is leading to the rapid transfer of electrolyte ions at the interface between the electrolyte
and the electrode [11
reported results of porous carbon derived from natural resources of jackfruit seed and
sorghum biomass-derived porous carbons, which achieved 292.2 F g−1 and 240 F g−1
respectively, at 5 mV s−1
79 80]. Activation of Lapsi seed yielded porous carbon with
high surface area of 1316.7 m2 g−1 with a capacitance of 317.5 F g−1 at 5 mV s−1
81]. It is
,77,78]. In addition, this capacitance value is still higher than other
,
[
,
[
interesting to compare the effect of different Lewis acids e.g., FeCl3 in graphite intercalated
compounds when reacted with dodcecyl amine and heated at higher temperatures of
900 ◦C and 2000 ◦C without activation to accomplish a surface area of 17 and 53 m2 g−1
and a capacitance of 42 and 90 F g−1, respectively [82
,83]. Therefore, it is important to note
the effect of KOH as activating agent here to provide such an enormous enhancement in
the obtained surface area and electrochemical capacitance performances that would have
been impossible without KOH activation. As presented in Table S1, The TPE-CPOP1-800
displayed the highest capacitance values compared with other porous carbon materials.
In addition, the charge/discharge behavior was investigated at a wider potential range of
( 1.0 to 1.0 V) to obtain a clear overview of the full potential range. The charge/discharge
−
showed a symmetric behavior with no obvious IR drop at all investigated current densi-
ties. This indicated that there were no obvious defects in the structure after the activation
process occurred [84]. Moreover, similar to the CV results, the charge/discharge behavior
was compared for both TPE-CPOP1-800 and TPE-CPOP2-800 after the activation process,
it was found that the activation process for TPE-CPOP1-800 yielded a double efficiency
compared to the activated TPE-CPOP2-800 carbons at all investigated current densities
(Figure 11d,e). These results also confirmed the CV results that triazine moiety has de-
creased the efficiencies of the KOH activation process in the electrochemical performance.
Moreover, the columbic efficiencies were also compared for both conditions. It was found
that the TPE-CPOP1-800 showed efficient stability of 96% as average stability upon cycling
for 10,000 cycles at 20 A g−1, however the TPE-CPOP2-800 conditions only showed 93%

Molecules 2021, 26, 738
11 of 16
of the average stability at the same current densities (Figure 11e,f). These results are sup-
porting the previous results found from both CV and charge/discharge behavior. It also
showed the efficient stabilities of both TPE-derived carbons after long cycles capacities
and higher current densities. The calculated energy density vs. scan rates showed efficient
energy densities values for TPE-CPOP1-800 at all scan rates as displayed in Figure S6. The
energy density achieved 63 Wh Kg−1 at 5 mV s−1, which is mainly due to the efficient
electrical double layer capacitor (EDLC) capacitive performance within the wide potential
window. This value is considered much higher than other related graphene composites that
achieved a maximum energy density of 46 Wh Kg−1 at 5 mV s−1 without activation [82
,85].
Therefore, it is believed that the KOH activation has a unique characteristic to enrich the
carbon materials with excellent electrochemical properties for high capacitive and high
energy densities performances. We believe that this method will open the door for further
investigations of activation procedures for various carbon-derived polymers for efficient
energy storage applications.
Figure 11.
) CV performance of TPE-CPOP1-800 at various scan rates (5~200 mV s−1). (
of TPE-CPOP1-800 and TPE-CPOP2-800 at various scan rates. ( ) Galvanic charge/discharge (GCD)
) Columbic efficiencies of
(a) Comparison of CV performance between TPE-CPOP1-800 and TPE-CPOP2-800 at 50 mV/s.
(b
c) Capacitance performance
d
performance of TPE-CPOP1-800. (e) GCD performance of TPE-CPOP2-800. (f
TPE-CPOP1-800 and TPE-CPOP2-800 at 20 A g−1 for 10,000 cycles. The inset figure represents the first
−1
and last few cycles of GCD behavior at 20 A g
.

Molecules 2021, 26, 738
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3. Materials and Methods
3.1. General Information
Benzophenone (99%), potassium carbonate (K2CO3, 99.9%), titanium tetrachloride
(TiCl4, 99.9%), zinc (Zn, 98%), and 1,2-dichloroethane (DCE, 99.8%) were ordered from Alfa
Aesar. Anhydrous magnesium sulfate (MgSO4, 99.5%), ethylacetate (EA), tetrahydrofuran
(THF), acetone, methanol (CH3OH), and dichloromethane (DCM) were purchased from
Showa (Tokyo, Japan).
3.2. Synthesis
TPE: Tetraphenylethene (TPE) monomer was successfully synthesized according to
our previous report [47,
50]. FTIR (KBr, cm−1, Figure S1): 3047 (aromatic C–H stretching),
1
1602 (C=C stretching). H-NMR (500 MHz, δ, ppm, CDCl3, Figure S2): 7.05–7.15 (m, 20H).
13C-NMR (125 MHz, δ, ppm, CDCl3, Figure S3): 140.7; 141.0; 131.3; 127.7; 126.4.
TPE-CPOP1: A solution tetraphenylethene (0.50 g, 1.51 mmol),) and AlCl3 (0.20 g,
1.51 mmol) in dry 1,2-dichloroethane (20 mL). The mixture was stirred at room temperature
for 0.5 h and then refluxed at 60 ◦C for 24 h. After cooling to 25 ◦C, the brown solid was
filtered and washed three times with chloroform, dichloromethane, methanol, THF, and
acetone to remove the unreacted TPE and AlCl3 and dried under vacuum at 60 ◦C to give
TPE-CPOP1 as a brown powder (0.45 g, 90%).
TPE-CPOP2: A solution of tetraphenylethene (0.50 g, 1.51 mmol), cyanuric chloride
(0.37 g, 2 mmol), and AlCl3 (0.20 g, 1.51 mmol) in dry 1,2-dichloroethane (20 mL) was
stirred at room temperature for 0.5 h and then heated at 60 ◦C for 24 h. After cooling at
room temperature, the solid was filtered and washed three times with THF, methanol,
chloroform, and acetone to remove the unreacted monomer and AlCl3 and dried under
vacuum at 60 ◦C to obtain chloroform, dichloromethane, methanol, THF, and acetone to
◦
remove the unreacted TPE and AlCl3 and dried under vacuum at 60 C to get TPE-CPOP2
as brown solid (0.4 g, 80%).
Preparation of TPE-CPOP1-800 and TPE-CPOP2-800: 0.4 g of TPE-CPOP1 or TPE-
CPOP2 and 0.4 g of KOH were mixed in 3 mL of water and the mixture was stirred for
5 h at room temperature. After that, the water solution was removed from the mixt◦ure at
120 ◦C for 24 h. Then, the dried sample powder was calcinated in the furnace at 800 C for
8 h under a N2 atmosphere (a heating rate of 5 ◦C min−1). After cooling to RT, the black
solid was washed with 2 N HCl, water, THF, methanol, and acetone, respectively, to give
TPE-CPOP1-800 (0.25 g, 63%) and TPE-CPOP2-800 (0.27 g, 68%).
4. Conclusions
In summary, two kinds of HCPs (TPE-CPOP1 and TPE-CPOP2) were successfully pre-
pared through the simple and friendly Friedel Crafts polymerization of tetraphenylethene
−
with or without cyanuric chloride in the presence of AlCl3 as a catalyst. Their chemical
structures were confirmed by FTIR and NMR analyses. Interestingly, the obtained TPE-
CPOP1-800 porous materials after the carbonization and KOH activation displayed good
thermal stability, high surface area, excellent CO2 adsorption capacity (1.74 mmol g−1 at
298 K and 3.19 mmol g−1 at 273 K), a high specific capacitance of 453 F g−1 at 5 mV s−1
and efficient stability of 96% as average stability upon cycling for 10,000 cycles.
,
Supplementary Materials: The following are available online, Figure S1. FT-IR spectrum of TPE.
1
Figure S2. H NMR spectrum of TPE. Figure S3. 13C NMR spectrum of TPE. Figure S4. XPS profile
of (a) TPE-CPOP1and (b) TPE-CPOP2. Figure S5. TEM images of (a) TPE-CPOP1-800 and (b) TPE-
CPOP2-800. Figure S6. Energy density vs. scan rate for TPE-COP1-800 and TPE-COP2-800. Table S1.
comparison list of other activated carbon materials.
Author Contributions: M.G.M. and M.M.M.A. conceptualized and designed the experiment route,
performed all of the experiment work, participated in the discussion of results, and wrote the paper.
W.-T.D. helped to design the reaction. S.-W.K. supervised the work and discussed the result. All
authors have read and agreed to the published version of the manuscript.

Molecules 2021, 26, 738
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Funding: This study was supported financially by the Ministry of Science and Technology, Taiwan,
under contracts MOST 106-2221-E-110- 067-MY3, 108-2638-E-002-003-MY2, and 108-2221-E-110-014-MY3.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: The data presented in this study are available in the article and
supplementary material.
Acknowledgments: The authors thank to the staff at National Sun Yat-sen University for assistance
with TEM (ID: EM022600) experiments.
Conflicts of Interest: The authors declare no conflict of interest.
Sample Availability: Samples of the compounds are not available from the authors.
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