Hierarchically porous covalent organic frameworks assembled in ionic liquids for highly effective catalysis of C-C coupling reactions

Article abstract of DOI:10.1039/d0gc00223b

Although significant progress has been made in the synthesis of covalent organic frameworks (COFs) in recent years, the construction of hierarchical pores in such materials remains a great challenge. Herein, we report a facile synthesis of hierarchically porous COFs (HP-COFs) under mild conditions in ionic liquids 1-alkyl-3-methylimidazolium tetrafluoroborates ([C_nmim][BF₄], n = 4, 6, 10). It has been found that apart from the inherent micropores, a large mesoporous structure has been produced in the COFs in which the size of pores can be simply tuned by adjusting the alkyl chain length of the ionic liquids. These mesopores have been confirmed by N₂ sorption and electron microscopy techniques. Importantly, this approach is applicable for the preparation of various HP-COFs, such as imine and hydrazone based COFs, which are quite difficult to acquire through traditional methods. In addition, these HP-COFs show highly effective catalytic performance for C-C bond formation, especially for large size molecule based C-C coupling reactions in comparison with uni-pore COFs.

Full text of DOI:10.1039/d0gc00223b

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DOI: 10.1039/D0GC00223B
ARTICLE
Hierarchically Porous Covalent Organic Frameworks Assembled in
Ionic Liquids for Highly Effective Catalysis of C-C Coupling
Reactions
Received 00th January 20xx,
Accepted 00th January 20xx
Jikuan Qiu,aƚ Huiyong Wang,aƚ Yuling Zhao,a* Pengxin Guan,a Zhiyong Li,a Hucheng Zhang,a
DOI: 10.1039/x0xx00000x
Hongshuai Gao,b Suojiang Zhang,b and Jianji Wang a*
Although significant progress has been made in the synthesis of covalent organic frameworks (COFs) in recent years, the
construction of hierarchical pore in such materials remains a great challenge. Herein, we report a facile synthesis of
hierarchically porous COFs (HP-COFs) under mild conditions in ionic liquids 1-alkyl-3-methylimidazolium tetrafluoroborates
([Cnmim][BF4], n = 4, 6, 10). It is found that apart from the inherent micropore, large mesoporous structure has been
produced in the COFs in which the size of pores can be simply tuned by adjusting alkyl chain length of the ionic liquids.
These mesopores have been confirmed by N2 sorption and electron microscopy techniques. Importantly, this approach is
applicable for the preparation of various HP-COFs, such as imine and hydrazone based COFs, which are quite difficult to
acquire through traditional methods. In addition, these HP-COFs show highly effective catalytic performance for C-C bond
formation, especially for large size molecules based C-C coupling reactions in comparison with uni-pore COFs.
Introduction
construction of diverse HP-COFs. Recently, template-assisted
(defect formation) strategy has been reported for the
Covalent organic frameworks (COFs) are a novel class of
porous crystalline polymers constructed from organic building
blocks through reversible covalent bonds.1,2 Due to their
tunable composition, structure and porosity, COFs have shown
potential application in many fields, such as molecules storage
preparation of HP-COFs,37-38 where polystyrene spheres (as
hard template) and in situ gas phase foaming techniques are
used to enable the formation of tunable macroporous
structures. Compared to the purely uni-pore COFs, the
resulting HP-COF materials exhibit significantly improved mass
diffusion properties. However, this method requires additional
experimental procedures to remove the templates. Therefore,
it is highly desirable to develop a simple and facile strategy for
the fabrication of HP-COFs.
and separation,3-10 catalysis,
drug delivery,
proton
11-18
19
conduction,20,21 energy storage,22 and sensors.23-25 In recent
years, the construction of hierarchically porous COFs (HP-
COFs) has attracted great interest owing to their peculiar
features of high porosity and interconnected different types of
pore sizes.26-29 In contrast to uni-pore COFs with homogeneous
pore environments, the HP-COFs with structural heterogeneity
have exhibited important prospects in a range of applications
including semiconductor device, storage and transportation of
different guests, and among others.30-35 However, report on
such materials is rather rare because of the inherent
challenges in design and syntheses of the building blocks.36
Meanwhile, the harsh reaction conditions (for example, high
temperature up to 120 oC), complex operations, and long
reaction time (up to days) also create hurdles in the
Ionic liquids (ILs), as a novel class of multi-functional liquid
materials, have attracted considerable attention due to their
unique properties.39, 40 Besides using as solvents, ILs have been
widely applied in catalysis,41, 42 medicine,43 mineral extraction,
electrochemistry44 and material chemistry.45-50 In 2018, Fang
and co-workers51 reported the pioneering work on the
preparation of 3D COFs by using ILs as solvent and catalyst.
And the as-synthesized materials showed high potential in the
gas separation. However, in this new space, the synthesis of
HP- COFs by using ILs has never been reported up to date.
Herein, for the first time, we have developed a simple, and
environmental benign strategy for the synthesis of HP-COFs
under mild conditions in ILs [Cnmim][BF4] (n = 4, 6, 10) without
the need of additional template (Figure 1a). It is shown that
the as-synthesized HP-COFs exhibit high crystalline networks
and good stability. In addition to the dominant mirocpores in
the original structure, large mesopores have been produced in
the COF, and the porosity properties can be facilely tuned by
alkyl chain length of the ILs. This new strategy can be used not
a. Collaborative Innovation Center of Henan Province for Green Manufacturing of
Fine Chemicals, Key Laboratory of Green Chemical Media and Reactions, Ministry
of Education, School of Chemistry and Chemical Engineering, Henan Normal
University, Xinxiang, Henan 453007 (P. R. China). Email: jwang@htu.cn,
ylzhao@htu.cn
b. Beijing Key Laboratory of Ionic Liquids Clean Process, Institute of Process
Engineering, Chinese Academy of Sciences, Beijing 100190 (P. R. China).
† These authors contributed equally.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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DOI: 10.1039/D0GC00223B
Figure 1 (a) Schematic representation for the synthesis of HP-TpAzo; (b) PXRD patterns of HP-TpAzo and TpAzo. Inset: Space-
filling packing diagram of TpAzo COF; (c) N2 sorption isotherms of HP-TpAzo and TpAzo at 77 K; (d) DFT pore size distribution of
HP-TpAzo and TpAzo; (e-g) HRTEM images of HP-TpAzo, the inset in (e) shows the corresponding SAED patterns, and the inset in
(f) is a magnified view. In (b, c, d), the blue color stands for HP-TpAzo, while the green color stands for TpAzo.
only for imine-linked structures but also for hydrazone-linked yield. The highly crystalline HP-TpAzo was obtained only within
COFs, suggesting the potential universality for the synthesis of 12 hours, which was 60 hours shorter than that from
HP-COFs. Furthermore, these HP-COFs have shown solvothermal method. High crystalline HP-COFs were also
significantly enhanced catalytic activity for large size molecules synthesized in [C6mim][BF4] and [C10mim][BF4] by the similar
based C-C coupling reactions, which greatly extends the procedures. In order to study the role of the ILs in the
application of COF materials in catalytic reactions.
synthesis of HP-COFs, attempt was made to prepare the COF in
neat organic solvent (such as DMSO) with and without
[C4mim][BF4] at room temperature (Figure S1). It was clearly
noted that a high crystalline network was obtained in DMSO in
the presence of catalytic amounts of [C4mim][BF4] (12 mol%
based on Tp), but only an amorphous polymer network was
formed in neat organic solvent. These results indicate that the
IL was an efficient catalyst in the formation of COF.
Importantly, these ILs could be reused at least three cycles
without significant decrease in the catalytic activity (Figure S2).
Moreover, the pristine TpAzo was also prepared for
comparison by following the procedures of traditional
solvothermal synthesis.21
Results and discussion
Synthesis of the HP-COFs
21
In the synthesis of HP-COFs, the well established TpAzo COF
was firstly synthesized in [C4mim][BF4] as a representative
example. To this end, mixture of 1,3,5-triformyl
a
phloroglucinol (Tp) and 4,4'-azobenzenediamine (Azo) was
suspended in the IL, and the system was stirred at 50 oC. After
the reaction was finished, the produced precipitate was
isolated by filtration and then activated using Soxhlet
extraction in methanol to afford red crystalline HP-TpAzo in 92%
2 | J. Name., 2012, 00, 1-3
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Fourier transform infrared (FTIR) spectrum of HP-TpAzo was the additional mesopores may be assigned to tVhieew sAtrtriculecOtunlrinael
fond to exhibit an intense −C=C stretching at 1568 cm−1 and a defects of the COFs. 38
DOI: 10.1039/D0GC00223B
−C−N stretching at 1284 cm−1, indicating the formation of keto-
The morphological feature of the as-synthesized HP-COF
form structure (Figure S3). It was also noted that there were was characterized by using electron microscopy techniques
still strong characteristic absorption peaks of –C=O stretching although it is very difficult for such materials. Images of field
(at 1634 cm−1) of Tp and N−H stretching (at 3200−3475 cm−1) emission scanning electron microscopy (FESEM) exhibited a
of Azo in the hierarchically porous COF. However, the flakiness-like morphology with large domain size from 200 nm
characteristic N−H stretching of primary amines and the C=O to 2.5 μm (Figure S7). The clearly contiguous straight channels
stretching in Tp almost completely disappeared in TpAzo with a spacing of ~5 nm was evidenced in high resolution
prepared by solvothermal approach. They could be attributed transmission electron microscopy (HRTEM) (Figure 1e-f), which
to the amino groups and terminal aldehyde at the edges of HP- was close to the mesopore distribution derived from N2
TpAzo.13 Solid-state 13C CP/MAS NMR spectroscopy was used sorption analysis (Figure 1d). Selected-area electron diffraction
to confirm the keto-form structure, which exhibited the patterns revealed the high crystallinity of the material (Figure
characteristic signals at 141 and 185 ppm, corresponding to 1e, inset). Moreover, the HP-TpAzo composed of parallel
the chemical shift of the newly formed C−N and C=O bonds of crystal planes with the lattice spacing of 3.1Å (Figure 1g) was
HP-TpAzo, respectively (Figure S4).
observed. This was very close to the (100) diffraction plane as
seen in the profile, indicating highly ordered alignment of the
HP-COF synthesized in the IL.
Structural characteristics of the HP-COFs
To test the crystallinity of the HP-TpAzo, powder X-ray
diffraction (PXRD) analysis was performed for HP-TpAzo and
TpAzo. The HP-COF was found to have an intense peak at 2θ =
3.1°, corresponding to (100) plane reflection, and sharp
diffraction peaks with (110) and (210) planes at 5.3 and 7.3o
(Figure 1b, blue line). The observed pattern is very similar to
that of the pristine TpAzo, which confirms the formation of
ordered 2D crystalline structure of TpAzo. Similar results were
also reported in recent reports on the fabrication of HP-COF by
template-induced defect-formation strategy37-38 and in a
number of literatures related to the preparation of
hierarchical-pore metal organic frameworks (MOFs).52,53
Chemical stability of the HP-COF was investigated by soaking
HP-TpAzo in different solvents such as THF, EtOH, aqueous 3 M
NaOH, and 3 M HCl at room temperature for 3 days. We found
that the framework was very stable under these conditions,
and the PXRD peak intensity remained intact (Figure S5).
Moreover, similar with the pristine TpAzo, thermal gravimetric
analysis (TGA) demonstrates that HP-TpAzo was stable up to
350 °C under N2 atmosphere (Figure S6).
The porosity parameters of HP-TpAzo and TpAzo were
evaluated by N2 absorption isotherm measurements at 77 K.
As shown in Figure 1c (green line), the TpAzo exhibits a typical
type I sorption curve with a steep increase at low relative
pressure, which indicates a character of microporous materials.
The microporosity of TpAzo was further confirmed by the
corresponding pore size distribution (Figure 1d, inset). In the
case of HP-TpAzo, the isotherm also displays a type I sorption
curve but with a pronounced hysteresis loop, which is the
typical mesoporous character and indicates that additional
mesoporosity was successfully introduced (Figure 1c, blue line).
The mesoporosity property could be verified using the pore
size distribution of HP-TpAzo shown in Figure 1d. Compared to
the dominant micropore in the original structure, the large
hysteresis loop in N2 sorption isotherm made the pore size
range to extend to 13 nm with another peak at ~5 nm. Notably,
the HP-COFs assembled in the ILs have large mesopores and
maintain the original microporosity at the same time. Here,
Figure 2 (a) N2 sorption isotherms and (b) DFT pore size
distribution of HP-TpAzo prepared in [C10mim][BF4]; (c) HRTEM
images of HP-TpAzo; (d) a magnified view of the (c).
To clarify the influence of alkyl chain length of the ILs, the ILs
with different alkyl chain lengths were used in the synthesis of
HP-COFs. It was found that similar PXRD patterns were also
observed for the HP-COFs synthesized in [C6mim][BF4] and
[C10mim][BF4]. As shown in Figure S8, these HP-COFs exhibited
weak crystallite structure compared with that derived from
[C4mim][BF4]. Unfortunately, an amorphous polymer network
was obtained in [C12mim][BF4] (Figure S9) possibly resulted
from the high viscosity of this IL. Figure 2a-b and Figure S10-11
showed the representative N2 sorption isotherms and pore
size distribution of the resultant HP-TpAzo prepared in
[C10mim][BF4] and [C6mim][BF4], respectively. It was clear that
the N2 sorption isotherm also gave a pronounced hysteresis
loop for HP-TpAzo synthesized in these two ILs, revealing the
typical mesoporous character (Figure 2a and Figure S10). More
interestingly, the pore diameter could be tuned via altering the
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alkyl chain length of the lLs. Especially, when carbon atom the formation of HP-COFs. Furthermore, as shown in Figure 2c-
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number in the alkyl chain of the ILs was increased to 10, the 2d, the as-obtained HP-TpAzo was an iDnOteI:r1c0o.1n0n3e9c/Dte0dGCp0o0r2o2u3Bs
pore size range of HP-TpAzo was extended to 25 nm (Figure structure with the irregular mesoporous, and the mesopore
2b). It was also noted that with the increase of alkyl chain size within 5 to 20 nm was conserved, which was consistent
length, the ratio of the micropore to the total porosity with the mesopore size distribution obtained from N2 sorption
decreased, but that of the mesoporosity increased. This result analysis.
clearly showed that microstructure of the ILs was crucial for
Figure 3 (a) General synthesis of HP-COFs from different linkers; (b) The corresponding experimental (black), Pawley-refined
(red), and predicted (blue) PXRD patterns of HP-TpPa, HP-TpPa(CH3)2, HP-TpBD and HP-COF-HNU1. The plots for the difference
between experimental Pawley-refined patterns are presented in green. Inset: Space-filling packing models of the respective COFs.
(c) DFT pore size distribution for HP-TpPa(CH3)2, HP-TpPa, HP-TpBD, and HP-HNU1.
In addition, in order to examine whether the additional morphology of the HP-COF also confirms that there is almost
mesopores were derived from amorphous porous polymers, no amorphous porous polymer in our HP-COF materials. This
amorphous polymer with no apparent crystallinity was result suggests that the additional mesopores were derived
prepared through the condensation of Tp and Azo in from the hierarchically crystalline COF (Figure S13).
[C4mim][BF4] at 25oC for 0.5h (Figure S12-a). Then, the
To investigate the universality of this synthetic strategy,
comparative experiments between amorphous polymer and several other amine linkers (benzene-1,4-diamine (Pa), 2,5-
crystalline COF were performed. The results of solid-state 13C dimethylbenzene-1,4-diamine (Pa(CH3)2) benzidine (BD), and a
cross-polarization magic angle spinning (CP/MAS) nuclear new hydrazone-linked COF were used to fabricate the
magnetic resonance (NMR) spectroscopy suggest the corresponding HP-COFs, and these HP-COFs were named as
anticipated covalent bonding of HP-COF at atomic level, HP-TpPa, HP-TpPa(CH3)2, HP-TpBD and (HP-COF-HNU1),
indicating that there is no amorphous porous polymer in our respectively (Figure 3a). As expected, all the samples exhibited
COF materials (Figure S12-b). Moreover, the distribution high crystalline structure as characterized by PXRD (see Figure
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3b and Figures S14-17). Notably, mesopores of these HP-COFs
ARTICLE
In addition, 1H and 13C NMR spectra of the HP-TpAzo
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DOI: 10.1039/D0GC00223B
were created in the ILs as evidenced by the N2 sorption synthesized in [C4mim][BF4] were measured by solid-state CP/
isotherms and pore-distribution studies (Figures S18-21 and MAS NMR technique. It was found that the HP-COF exhibited
Figure 3c). However, owing to the low degree of mesoporosity the peaks similar to those in aqueous [C4mim][BF4], although
in some of the as-synthezied HP-COFs, the hysteresis loops in they were relatively weak and broad (Figure 4b and 4c). It was
N2 sorption isotherms were not obvious. The BET surface area noteworthy that chemical shifts of the IL in 1H MAS NMR
and pore size distribution of these HP-COFs were given in shifted from down field to up field compared with that in
Table S1. In addition, TEM images exhibited the pronounced liquid. This phenomenon could be attributed to the formation
mesoporous structures for each of these HP-COFs, indicating of hydrogen bond between the IL and N-H group of the porous
the versatility of this synthesis approach (Figure S22-24).
crystalline polymers.41 This result suggests that the IL was
indeed incorporated into the pore channels of HP-COF during
crystallization.54 Because of the microscopic heterogeneity in
Possible formation mechanism
In order to have insight in the formation of hierarchically the ILs, the domains with different scales might be involved in
porous structure of COFs, molecular dynamics simulations of the formation process of the HP-COFs, which led to a steric
[Cnmim][BF4] (n = 4, 6, 10) were performed to explore hindrance and then partly impedes the assembly in the
microstructures of the ILs. As shown in Figure 4a, self- direction of ordered architectures.55 When the IL was removed
aggregation structures were found in these ILs and the after the process, mesopore size was created. This indicates
nonpolar domains (green parts) became larger with increasing that the IL acted as a soft template in the synthesis process of
alkyl chain length of the cations. To quantify the nano- COFs. Similar template effect had been observed, but not
segregation between polar and nonpolar domains, radial using ILs, by Zhou et al.56 in the synthesis of hierarchically
distribution function g(r) of the anion around terminal tail of porous MOFs.
the cations was calculated (Figure S25). It was found that in
these systems, the value of radial distribution function was 14 Catalytic activity of the HP-COFs
Å, 15 Å, and 20 Å, respectively, in the case of g(r) ≈ 1. This Taking into account the advantages of both micropores and
result indicates that aggregate size of the ILs became larger mesopores for the as-synthesized HP-COFs, we envision that
with the increase of alkyl chain length, which matches well the HP-COFs should enhance diffusion rate of molecules and
with the trend of pore size of COFs synthesized in the ionic show excellent catalytic performance in C-C coupling reaction
liquids with different alkyl chain lengths.
reactions. As a proof-of-concept study, we compared the
catalytic performance of HP-COF and its parent uni-pore COF
in Knoevenagel condensation reaction. It is known that each
crystalline macrocycle in the framework consists of 12 N-H
groups, and these functional groups show stronger basicity.
This was combined by the advantages of both micro- and
meso-pores to facilitate the mass transport, thereby leading to
effective contact of the reactants with the basic sites.
Therefore, β-ketoenamine based HP-COFs might efficient
catalyze the base-catalyzed reaction such as Knoevenagel
condensation reaction.
Here, HP-TpPa(CH3)2 was used, as an example, to
investigate the catalysis on the reaction between 4-
biphenylcarboxaldehyde and malononitrile. As seen from
Figure 5 and Table S1, the size of product (7.6×18.7 Å2) was
smaller than the window of HP-TpPa(CH3)2, but larger than the
pore size of the uni-pore TpPa(CH3)2 (13 Å). The limited pore
size of TpPa(CH3)2 restricted diffusion of the reactants and
product, and also prevented the reactants molecules from
accessing the active sites in COF channels. Therefore, HP-
TpPa(CH3)2 exhibited superior catalytic performance than
TpPa(CH3)2.
To further investigate the advantages of the HP-COFs,
palladium (Pd) nanoparticles immobilized on HP-TpAzo (HP-
TpAzo@Pd) was prepared, with Pd loading of 5.2 wt% as
confirmed by inductively coupled plasma (ICP) analysis, to
catalyze the Suzuki-Miyaura coupling reactions of
phenylboronic acid and various aryl bromides. As shown in
Figure S26, the binding energy (BE) of Pd3d5/2 in HP-TpAzo@Pd
was 337.8 eV, indicating that the Pd was present in +2 species
Figure 4 Computational and NMR analysis for the role of the
ILs in the synthesis of HP-COF. (a) Snapshot of microstructure
in [Cnmim][BF4] (n = 4, 6, 10), red parts stand for polar domain
composed from imidazolium headgroups and anion, green
parts stand for nonpolar domains composed from alkyl chains
1
of cations in the ILs; (b) H NMR and (c) 13C NMR spectra of
[C4mim][BF4] in the solid HP-TpAzo (1) and in aqueous solution
(2).
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13. Then, the reaction was performed in xylene at 100 C, the
We carried out a control experiment to confirm that the
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DOI: 10.1039/D0GC00223B
1
conversion efficiency was detected by H NMR spectroscopy, reaction was indeed catalyzed by HP-COF@Pd instead of free
and the results were shown in Figure 6. It was noted that for Pd nanoparticles. For this purpose, the mixture of HP-
the small sized substrate A (6.69×6.94 Å2), both HP-TpAzo@Pd TpAzo@Pd, xylene and K2CO3 was heated and stirred for 7 h at
and TpAzo@Pd showed similar conversion rate (99% and 94%, 100 oC in the absence of reactants. Then, the catalyst was
respectively). When the molecule size of substrate was isolated from the hot mixture, and the filtrate was used to
increased (substrate B, 10.7×16.2 Å2), significant influence of catalyze the reaction of p-methylbromobenzene and
the reactants size on the reaction was observed, where HP- phenylboronic acid. It was found that no conversion could be
TpAzo@Pd and TpAzo@Pd gave the yield of 98% and 53%, observed in this case, indicating that almost no Pd content was
respectively. Furthermore, the superiority of HP-COFs became leached out into the filtrate. This result suggests that Pd(II)
more apparent for the larger sized substrate C (13.6×13.6 Å2). species is strongly coordinated within HP-COF under the
The reaction also proceeds well with high yield (94%) by HP- applied reaction conditions, and that the Suzuki-Miyaura
TpAzo@Pd, but very low yield (12%) was observed by reaction is indeed catalyzed by HP-COF@Pd 13. Moreover, the
TpAzo@Pd under the same conditions. These results indicate catalyst could be simply recovered by centrifugal separation,
that the hierarchically porous COFs are very beneficial to the and then reused for at least five times without obvious loss of
transport of large sized substrates/products.
catalytic activity (Figure S27).
As another alternative, we studied the catalytic performance
of HP-COFs in other C-C bond formation reactions. To this end,
HP-TpAzo@Ag (see Supporting Information for synthetic
details) was employed as catalyst for the carboxylation of CO2
with terminal alkynes, which represents one of the most
promising methods for the fixation of CO257. This catalyst had
an Ag loading of 1.1 wt% as confirmed by ICP analysis, and the
Ag existed as a metallic state on the HP-TpAzo@Ag (Figure
S28). As seen in Table S2, HP-TpAzo@Ag also showed high
activity for catalyzing these reactions under similar reaction
conditions compared with its parent uni-pore COF.
Conclusions
Here, we developed, for the first time, a novel, environmental
benign and template-free strategy for the synthesis of HP-
COFs in ILs. The as-synthesized HP-COFs exhibited high
crystalline networks, good stability, and hierarchical pores. The
synthetic conditions were environmentally friendly, and the
HP-COFs could be quickly produced within 12h under mild
conditions. More importantly, the porosity properties of HP-
COFs could be easily adjusted by changing alkyl chain length of
the ionic liquid. Compared with the uni-pore COFs synthesized
by solvothermal approach, these HP-COFs exhibited
significantly improved catalytic activity for C-C bond formation,
especially for the large sized molecules based C-C coupling
reactions. We believe that the strategy reported here may
open a new and simple pathway for the synthesis of new HP-
COFs for various applications. The conclusions section should
come in this section at the end of the article, before the
acknowledgements.
Figure
5 Time dependent conversion in Knoevenagel
condensation reaction between 4-biphenylcarboxaldehyde
and malononitrile catalyzed by HP-TpPa(CH3)2 and TpPa(CH3)2,
respectively.
Experimental
Materials
Figure 6 Conversion in C-C bond formation reaction between
phenylboronic acid and aryl bromides catalyzed by HP-
TpAzo@Pd and TpAzo@Pd, respectively.
Diamines such as p-phenylenediamine (Pa), 2,5-dimethyl-1,4-
benzenediamine (Pa(CH3)2), 4,4'-diaminoazobenzene (Azo),
benzidine (BD) were purchased from J&K Scientific Company
Limited (Beijing, China). The ILs [C4mim][BF4], [C6mim][BF4],
[C10mim][BF4] and [C12mim][BF4] were purchased from LICP,
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1
CAS, China. 1,3,5-Triformyl phloroglucinol (TP) and 2,5- were applied. Solid-state H MAS NMR spectra wVeierweArreticcleoOrdnleinde
DOI: 10.1039/D0GC00223B
diethoxyter- ephthalohydra-zide (EPH) were synthesized on an Agilent 600 DD2 spectrometer at resonance frequency
according to the procedures reported in literature.58 Pa(OAc)2 of 599.72 MHz. The powder samples were placed in a pencil-
and other reagents were acquired from Inno-chem Company type zirconia rotor of 4.0 mm o.d. The spectra were obtained
Limited (Beijing, China) and used without further purification.
at a spinning speed of 8 kHz with a recycle delay of 5 s. The
adamantane was used as the reference of 1H chemical shift. N2
adsorption and desorption isotherms were determined at 77 K
on ASIQM0002200-7 system, and the nonlocal density
functional theory (NLDFT) model was used to study the pore
size distributions. FSEM images were observed by a Hitachi
SU8010 microscope, and HRTEM images were acquired on a
JEOL-2010 transmission electron microscope. XPS data were
obtained with an ESCALab220i-Xi Thermo Scientific electron
spectrometer. The binding energies were referenced to the
C1s line at 284.8 eV from adventitious carbon.
Synthetic Procedures of HP-COFs in the ILs
For the synthesis of HP-TpAzo, 0.1125 mmol of p-Azoaniline
was dissolved in 200 ul of IL under vigorous stirring. Then,
0.075 mmol (15.7 mg) of 1,3,5-triformylphloroglucinol was
introduced into the mixture, and the reaction was proceeded
for 12 hours at 50 oC. After the reaction was finished, the
mixture was soaked in ethanol, and the precipitate was
isolated by filtration. The IL could be recovered from the
filtrate by removing ethanol under reduced pressure, and the
recovery percent of the IL was 96.3, 90.8, 83.3% respectively
after three cycles. Then, the precipitate was washed with THF
and DMF three times to remove small amount of polymer
molecules. At the end, the collected powder was activated
using Soxhlet extraction in methanol for three times and then
dried at 110 °C for 36 h to give a red powder with up to 90-92%
isolated yield (92% in [C4mim][BF4], 92% in [C6mim][BF4], and
90% in [C10mim][BF4].
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (No.U1704251, 21733011, 21773058), the
National Key Research and Development Program of China
(2017YFA0403 101), and the 111 project (No.D17007).
Synthetic Procedures of TpAzo in DMSO Using IL as Catalyst
at Room Temperature
For the synthesis of TpAzo, 0.1125 mmol of p-Azoaniline, 0.075
mmol (15.7 mg) of 1,3,5-triformylphloroglucinol, and 12 mol%
of [C4mim][BF4] (based on Tp) were added into 2 mL of DMSO.
o
Then the reaction was carried out at 25 C for 12 hours under
Notes and references
vigorous stirring. After the reaction was finished, the
precipitate was isolated by filtration and washed with THF and
DMF three times. Finally, the collected powder was activated
using Soxhlet extraction in methanol for 3 hours and then
dried at 110 °C for 36 h to give a red powder with up to 90%
isolated yield.
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