Z.-Q. Liu et al.
Molecular Catalysis 504 (2021) 111437
92.18 m2 gꢀ 1 and 0.0995 cm3 gꢀ 1, respectively (Table 1, entry 2), when
alkene-modified Fe3O4 nanoparticles were embedded in the polymers.
In addition, P(2DVB-[4-VP][ClO4]) in present of Fe3O4 nanoparticles
shows a typical type-IV isotherm with a hysteresis loop of type H2 in the
relative pressure (P/P0) range of 0.47 to 0.90, revealing the existence of
mesopores in the resulting sample. These results illustrate that the added
alkene-modified Fe3O4 nanoparticles is performed to favor the meso-
porous construction in MPILs. The reason for the formation of MPILs
with abundant and well-ordered mesopores may ascribe to the vital role
of alkene-modified Fe3O4 as a structural reinforcer to stabilize meso-
porous framework.
Table 1
Textural parameters of P(xDVB-[4-VP][ClO4]). a
N e
Ionic
b
c
d
Entry
Samples
SBET
DAV
Vtotal
(m2 gꢀ 1
)
(nm)
(cm3 gꢀ 1
)
(%)
moieties f
(mmol gꢀ 1
)
1
P(2DVB-[4-
12.86
3.95
0.0463
2.5
2.01
VP][ClO4])
g
2
3
P(2DVB-[4-
VP][ClO4])
P(2DVB-[4-
92.18
87.96
4.59
3.88
0.0995
0.0852
1.8
1.6
1.74
1.56
VP][ClO4])
h
It is well known that the porogenic solvent during the synthesis of
various porous polymers has a profound impact on their specific pore
construction. Hence, the popular porogenic solvents, such as MeOH,
EtOH, and MeCN were used for preparing MPILs. Interestingly, the
sample of P(2DVB-[4-VP][ClO4]) synthesized in MeOH displays a
favourable SBET of 92.18 m2 gꢀ 1, large Vtotal of 0.0995 cm3 gꢀ 1, and
sufficient IL content of 1.74 mmol gꢀ 1 (Table 1, entry 2). As displayed in
Fig. 2C, P(2DVB-[4-VP][ClO4]) synthesized in MeOH shows a typical
type-IV isotherm with a hysteresis loop of type H2, revealing the exis-
tence of mesopores in the prepared sample. In addition, the corre-
sponding pore-diameter distribution curves is also showed in Fig. 2D. P
(2DVB-[4-VP][ClO4]) was also acquired using EtOH (SBET of
4
5
6
P(2DVB-[4-
83.28
67.47
74.37
3.43
4.16
4.41
0.0811
0.0967
0.0931
1.5
4.3
3.5
1.43
2.68
2.39
VP][ClO4])
i
P(0.5DVB-
[4-VP]
[ClO4])
P(0.8DVB-
[4-VP]
[ClO4])
7
8
9
P(DVB-[4-
VP][ClO4])
P(4DVB-[4-
VP][ClO4])
P(2DVB-[4-
82.06
86.16
91.09
4.55
3.82
4.49
0.0957
0.0895
0.0988
3.2
0.9
1.7
2.31
1.18
1.71
87.96 m2 gꢀ 1 and Vtotal of 0.0852 cm3 gꢀ 1
) and MeCN (SBET of
VP][ClO4])
83.28 m2 gꢀ 1 and Vtotal of 0.0811 cm3 gꢀ 1) as porogenic solvents.
Nevertheless, the content of ionic moieties is slightly decreased (1.56
and 1.43 mmol gꢀ 1, Table 1 entries 3 and 4, respectively) compared
with the porogenic solvent of MeOH. Hence, MeOH is selected as the
appropriate porogenic solvent for further investigation.
j
a
Polymerization reaction conducted in CH3OH unless otherwise specified.
b
Brunauer–Emmett–Teller (BET) surface area calculated over the relative
pressure range of.0.05ꢀ 0.20.
c
Average pore size.
d
Total pore volume.
The ratio of IL monomer and cross-linker has a profound effect on the
composition of MPILs and their porous structures. As demonstrated in
Fig. 2E, the different molar ratio of [4-VP][ClO4] and DVB was further
optimized to prepared MPILs with appropriate [4-VP][ClO4] content
and well-defined mesopores. Herein, the sample of MPILs synthesized
with various molar ratios (x) of DVB to [4-VP][ClO4] was named as P
(xDVB-[4-VP][ClO4]). P(0.5DVB-[4-VP][ClO4]) with a low DVB-to-IL
ratio exhibits a typical type-IV isotherm, indicating the existence of
mesopores in the sample. When the molar ratio of DVB-to-IL increases
from 0.5:1 to 2:1, MPILs also display the typical type-IV isotherm.
However, both SBET values and DAV values of MPILs increase from 67.47
to 92.18 m2 gꢀ 1 and from 4.16 to 4.59 nm, respectively, with increment
of the molar ratio of DVB-to-IL (Table 1, entry 2 and entries 5–7).
Meanwhile, the IL content and matching N content drop from 2.68 to
1.74 mmol gꢀ 1 and from 4.3 % to 1.85, respectively. The molar ratio of
DVB-to-IL increases to 4:1, while SBET value, Vtotal value, and IL content
of P(4DVB-[4-VP][ClO4]) slightly lower than that of P(2DVB-[4-VP]
[ClO4]) (Table 1, entry 8). Thus, P(2DVB-[4-VP][ClO4]) with large SBET
value and well-defined mesoporous structures shows significant poten-
tial application in catalysis.
e
f
Determined by elemental analysis.
Calculated from N content.
g
Polymerization reaction in absence of Fe3O4 nanoparticles.
h
With ethanol as the polymerization solvent.
i
j
With acetonitrile as the polymerization solvent.
After 10th recycling.
Barrett–Joyner–Halenda model. FT-IR spectra were collected by using a
Bruker 66 V FT-IR spectrometer. SEM images were performed on JEOL
6335 F field emission scanning electron microscope. TEM images were
performed on a JEM-2100 F electron microscope. Elemental analysis
was performed on a Perkin-Elmer series II CHNS analyzer 2400. Powder
XRD patterns of the samples were collected using an X-ray diffractom-
eter (MiniFlex 600, produced by Rjgaku company). TGA was carried out
with a NETZSCH STA 409 PC instrument. VSM was carried out with a
Dyna Cool PPMS. NMR spectra were acquired in a 500 MHz Bruker NMR
spectrometer.
3. Results and discussion
Fig. 3 displays the SEM images of mesoporous P(2DVB-[4-VP]
[ClO4]). It can be seen that mesoporous P(2DVB-[4-VP][ClO4]) is uni-
formly distributed with dimensional homogeneity and the size distri-
butions is relatively concentrated at diameters of approximately 25 nm.
Most gaps among the nanoparticles are larger than 10 nm, confirming
that the mesoporous copolymer of P(2DVB-[4-VP][ClO4]) with pore
diameter of approximately 4.59 nm is not obtained by simple and
physical stacking of bulky materials. In addition, mesoporous P(2DVB-
[4-VP][ClO4]) surfaces are unfairly rough as it conforms to the typical
copolymer characteristics with rough surface. This further indicates that
[4-VP][ClO4] is successful grafted to Fe3O4 nanoparticle surfaces.
TEM images were used to obtain direct information about the sample
morphology and its structure. Fig. 4 shows the TEM images of meso-
porous P(2DVB-[4-VP][ClO4]), and the results display that the meso-
porous P(2DVB-[4-VP][ClO4]) diameters are almost uniform
(approximately 25 nm) and is consistent with previous SEM results. The
sample comprises a body with Fe3O4 nanoparticles core, and the nano-
3.1. Catalyst characterization
It is generally believed that the well-defined porosity and abundant
functionalized sites in MPILs are considered essential in a variety of
applications, especially in catalysis. Nevertheless, the traditional poly-
merization processes are very challenging for the resulting copolymer
with abundant IL moieties besides well-defined mesoporous structures.
Consequently, the research interest is to find the appropriate materials
for preparing MPILs with an ordered mesoporous structures and abun-
dant active sites. Initially, P(2DVB-[4-VP][ClO4]) was prepared by using
IL monomer of [4-VP][ClO4] and crosslinker of DVB, and the resulting
copolymer shows a significantly lower SBET value of 12.86 m2 gꢀ 1 and
V
total value of 0.0463 cm3 gꢀ 1 (Table 1, entry 1) and nonporous struc-
ture, and this result is further confirmed by a typical type-II isotherm
and pore-diameter distribution curves (Fig. 1A). Surprisingly, the SBET
value and Vtotal value of P(2DVB-[4-VP][ClO4]) significantly increase to
4