Precisely embedding active sites into a mesoporous Zr-framework through linker installation for high-efficiency photocatalysis

Article abstract of DOI:10.1021/jacs.0c05758

The pore engineering of microporous metal-organic frameworks (MOFs) has been extensively investigated in the past two decades, and an expansive library of functional groups has been introduced into various frameworks. However, the reliable procurement of MOFs possessing both a targeted pore size and preferred functionality together is less common. This is especially important since the applicability of many elaborately designed materials is often restricted by the small pore sizes of microporous frameworks. Herein, we designed and synthesized a mesoporous MOF based on Zr6 clusters and tetratopic carboxylate ligands, termed PCN-808. The accessible coordinatively unsaturated metal sites as well as the intrinsic flexibility of the framework make PCN-808 a prime scaffold for postsynthetic modification via linker installation. A linear ruthenium-based metalloligand was successfully and precisely installed into the walls of open channels in PCN-808 while maintaining the mesoporosity of the framework. The photocatalytic activity of the obtained material, PCN-808-BDBR, was examined in the aza-Henry reaction and demonstrated high conversion yields after six catalytic cycles. Furthermore, thanks to the mesoporous nature of the framework, PCN-808-BDBR also exhibits exceptional yields for the photocatalytic oxidation of dihydroartemisinic acid to artemisinin.

Full text of DOI:10.1021/jacs.0c05758

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Article
Precisely Embedding Active Sites into a Mesoporous Zr-Framework
through Linker Installation for High-efficiency Photocatalysis
Jiandong Pang, Zhengyi Di, Jun-Sheng Qin, Shuai Yuan, Christina T. Lollar, Jialuo
Li, Peng Zhang, Mingyan Wu, Daqiang Yuan, Maochun Hong, and Hong-Cai Zhou
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.0c05758 • Publication Date (Web): 08 Aug 2020
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Precisely Embedding Active Sites into a Mesoporous Zr-Framework
through Linker Installation for High-efficiency Photocatalysis
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†
‡,¶
§
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Jiandong Pang, Zhengyi Di, Jun-Sheng Qin, Shuai Yuan, Christina T. Lollar, Jialuo Li, Peng
†
,‡,¶
‡,¶
‡,¶
,†
Zhang, Mingyan Wu,* Daqiang Yuan, Maochun Hong, and Hong-Cai Zhou*
†Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255, United States
‡State Key Laboratory of Structure Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese
Academy of Sciences, Fuzhou, Fujian 350002, China
§State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, International Center
of Future Science, Jilin University, Changchun 130012, China
¶University of Chinese Academy of Sciences, Beijing 100049, China
Supporting Information Placeholder
ABSTRACT: The pore engineering of microporous metal-organic frameworks (MOFs) has been extensively investigated in
the past two decades and an expansive library of functional groups have been introduced into various frameworks. However,
the reliable procurement of MOFs possessing both a targeted pore size and preferred functionality together is less common.
This is especially important since the applicability of many elaborately designed materials is often restricted by the small
6
pore sizes of microporous frameworks. Herein, we designed and synthesized a mesoporous MOF based on Zr clusters and
tetratopic carboxylate ligands, termed PCN-808. The accessible coordinatively unsaturated metal sites as well as the
intrinsic flexibility of the framework make PCN-808 a prime scaffold for post-synthetic modification via linker installation.
A linear ruthenium-based metalloligand was successfully and precisely installed into the walls of open channels in PCN-
8
08 while maintaining the mesoporosity of the framework. The photocatalytic activity of the obtained material, PCN-808-
BDBR, was examined in the aza-Henry reaction and demonstrated high conversion yields after 6 catalytic cycles.
Furthermore, thanks to the mesoporous nature of the framework, PCN-808-BDBR also exhibits exceptional yields for the
photocatalytic oxidation of dihydroartemisinic acid to artemisinin.
placement of functional groups in one-pot synthesized
MTV-MOFs is a huge challenge. Crystallographic disorder
INTRODUCTION
Precise pore environment adjustments in porous
materials have been one of the most important topics in
materials science because of the significant influence they
have on the resulting applicability of the material.
Thanks to their regular and highly tunable pore
architectures, the class of porous materials known as
can be relieved in the cases of MUF-series MOFs reported
by Telfer and co-workers, in which three kinds of linkers
with different symmetries are compartmentalized in a
1
-3
20-23
predetermined array.
Nonetheless, it is immediately
apparent that multiple structures of MOFs can be obtained
as impure phases. In addition, the range of chemical
functionality within the linkers used in one-pot synthesis
is rather limited because the linkers cannot contain
functional groups that are thermally labile under the high
temperature solvothermal conditions common for MOF
metal-organic
frameworks
(MOFs),
or
porous
coordination networks (PCNs), can be used as intriguing
platforms to develop strategies of precise regulation in the
pore environments of crystalline solid-state porous
4-7
materials. In order to modify the pore interiors of MOFs,
syntheses. To
a certain degree, a wider range of
introduction of functionalized linkers or groups via one-
pot synthesis methods and post-synthetic framework
decorations are two generally used strategies.
the most illustrious examples of the one-pot synthesis
strategy are the MTV-MOFs developed by Yaghi’s group,
which have multivariate functionalities assembled from
functionalities can be introduced into MOFs under
relatively mild conditions via post-synthetic modification
methods. Notwithstanding, the reaction conditions for
post-synthetic functionalization of MOFs (including both
inorganic and organic transformations) are very hard to
control and rely upon the premise that no degradation or
collapse of the framework occurs. Furthermore,
comprehensive characterization of crystalline powders
resulting from post-synthetic methods urgently requires
8
-18
Among
1
9
linkers
hosting
different
functional
groups.
Unfortunately, the distribution of the incorporated
functional groups in MTV-MOFs are disorganized and
therefore difficult to characterized using traditional
techniques like X-ray diffraction. In general, the precise
9
additional developments.
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Figure 1. Construction of the topologically equivalent PCN-608 and PCN-808. (a) The rectangular, planar, 4-connected, tetratopic
ligand in PCN-608. (b) The 8-connected Zr
tetratopic ligand in PCN-808. (d) Crystal structure of PCN-608 viewed along the c axis. (e) The csq net topology of the mesoporous
MOFs, PCN-608 and PCN-808. (f) Crystal structure of PCN-608 viewed along the c axis. R = OH, NH or OMe, R = H or CF3.
6
cluster in PCN-608 and PCN-808. (c) The expanded rectangular, planar, 4-connected,
1
2
2
1
Color scheme: black, C; red, O; light blue, Zr; yellow, substituents R on the ligands.
Fortunately, our group has developed an alternative
method, linker installation, for introducing and precisely
placing functional groups into MOFs under mild
microporous MOF, UiO-67.30-34 As has been mentioned
above, the Ru loading amount is usually lower than
expected by incorporation of BDBR via one-pot mixed
linker synthesis. The characterization of the resulting
material remains difficult because of the high level of
disorder in mixed linker MOFs as well as the breakage of
single crystallinity in the MOFs. What’s more, the doping
of the photocatalytic active site may block the pores of
microporous MOFs, which may be harmful to applicability.
Therefore, we tried to synthesize a mesoporous MOF with
BDBR incorporated through linker installation. Under the
guidance of crystal engineering and reticular chemistry, a
2
4
conditions.
synthesized
Zr (OH)
We have judiciously designed and
series of Zr-MOFs with 8-connected
a
2
5
6
O
4
8
(H
2
O)
4
clusters as platforms.
Linear
dicarboxylate linkers with distinct lengths and functional
groups can be sequentially installed into the platform by
-
replacement of the terminal OH /H
2
O ligands on the Zr
6
clusters. Consequently, tailoring of the pore environment
2
6-28
in these MOFs was successfully implemented.
Furthermore, this new strategy can be expanded to
mesoporous MOFs, defined as containing pores with
diameters between 2 and 50 nm according to the IUPAC
notation, which should be more useful for practical
applications of the functional groups incorporated. In our
previous work it was shown that anionic mesoporous
Zr-based
mesoporous
MOF
(termed
PCN-808,
topologically equal to PCN-608) was designed and
synthesized (Figure 1). The ditopic linear ligand BPDC and
BDBR can be installed and precisely placed into the new
mesoporous MOF, which can be characterized
demonstratively through single crystal X-ray diffraction.
More importantly, the mesoporosity of the MOF as well as
the photocatalytic activity of BDBR survive linker
installation.
MOFs formed by installation of negatively charged linear
2+
linkers can be used to encapsulate cationic [Ru(bpy)
3
]
29
catalysts by exploiting electrostatic interactions. The
resulting hybrid material showed high photocatalytic
activity and moderate reusability. However, the strength of
electrostatic interactions is still too weak to efficiently
immobilize the cations, especially in ionizable solvents
such as water or in the presence of ionic substrates.
Therefore, a more optimized method is desired.
RESULTS AND DISCUSSION
MOF Synthesis and Structural Description. The
longer rectangular tetratopic carboxylate ligand H
4
TPTB-
H
(H TPTB 5',5'''-bis(4-carboxylatophenyl)-4''',6'-
4
=
For more effective immobilization of Ru-containing
functional groups, installation of a Ru-containing linker
should prove to be a better method. A linear linker,
dimethoxy-[1,1':3',1'':4'',1''':3''',1''''-quinquephenyl]-4,4''''-
dicarboxylate) was synthesized similarly to the shorter
H
4
TPCB with pre-elongation of the biphenol (Scheme S1).
H
2
BDBR (H
dicarboxy-2,2’-bipyridine-)ruthenium(II)] dichloride), has
previously been successfully doped into a H BPDC
BPDC biphenyl-4,4’-dicarboxylate)-based
2
BDBR
=
[bis(2,2’-bipyridine,N1,N1’)(5,5’-
Additionally, H TPTB was obtained when trifluoromethyl
4
groups were introduced to the central phenyl ring,
increasing the solubility of the ligand (Scheme S2).
Solvothermal reaction of H TPTB and ZrCl in the presence
4 4
2
(
H
2
=
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of benzoic acid afforded the hexagonal columnar
become 10-connected nodes in PCN-808-BPDC and PCN-
808-BDBR after linker installation (Figure S8).
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framework complex PCN-808. It should be noted that
single crystals suitable for X-ray diffraction can only be
obtained when the trifluoromethyl-decorated ligand,
4
-
TPTB , is employed. Therefore, structural characterization
and further linker installation was carried out with the
trifluoromethyl-functionalized PCN-808 as representative.
Single crystal X-ray diffraction experiments at 100 K show
that PCN-808 crystallizes in the hexagonal space group
P
6
/mmm, which is the same as the PCN-608 series. Each
Zr cluster in PCN-808 connects to eight fully
deprotonated TPTB fragments and each TPTB fragment
links to four Zr clusters conversely. The central phenyl
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ring is approximately perpendicular to the other two
lateral phenyl rings in the inner terphenyl part of the TPTB
ligand (two sets of disordered phenyl rings were observed
o
with a dihedral angle of 61.63 in reference to the lateral
phenyl rings in the single crystal structure). However, the
two lateral phenyl rings are inclined to be coplanar and
overall the TPTB ligand adopts the C2v symmetry necessary
3
5-36
to form a csq net framework (Figure S7).
Within the
structure, two kinds of one dimensional open channels
were formed, i.e. one hexagonal channel with radius of
approximately 3.3 nm and one triangular channel with
dimensions of approximately 1.2 nm.
Tuning the Structure of MOFs by Linker Installation.
As shown in Figure 2, the distance between two
neighboring Zr
about 8.2 Å, while the distance between two neighboring
Zr clusters along the c axis in PCN-808 is about 11.7 Å due
6
clusters along the c axis in PCN-608 is
6
to the elongation of the TPTB ligand. The lengths of linear
linkers BDC and BPDC are about 6.9 Å and 11.2 Å
respectively, which are all slightly shorter than the open
pockets in the mesoporous MOFs. As has been confirmed
in our previous research, linker installation of BDC has
been successfully implemented into PCN-608 thanks to
the inherent flexibility of the framework. The distance
Figure 2. Crystal structures of (a) PCN-608, (b) PCN-608-
BDC, (c) PCN-808, (d) PCN-808-BPDC, and (e) PCN-808-
BDBR. (f) Perspective view of PCN-808-BDBR along the c axis.
Color scheme: black, C; red, O; light blue, Zr; dark blue, N;
pink, Ru; yellow, substituents R on the ligands (R = OH, NH
1 1 2
or OMe). Trifluoromethyl groups on TPTB ligands omitted for
clarity.
6
between two neighboring Zr clusters along the c axis in
PCN-608-BDC is about 7.3 Å after BDC is installed.
Considering PCN-608 and PCN-808 have the same
topology, BPDC and its derivatives are expected to be
installable into PCN-808. To prove our hypothesis, linear
ligand BPDC and the geometrically equivalent BDBR with
a bulky functional group were installed into PCN-808 via
single-crystal to single-crystal transformations. The open
pockets along the c axis in PCN-808 could be filled with
either BPDC or BDBR by incubating crystals in DMF
solutions of the appropriate linker, further connecting
In PCN-808-BPDC, the installed linker BPDC can be
easily located without disorder. However, the BDBR linker
is split into two sets due to the steric effects from the
2 2
Ru(bpy) group. Both Ru(bpy) parts of the installed ligand
point into the hexagonal channels, which may be a benefit
in applications like catalysis (Figure 2f). It should be noted
that the splitting of BDBR linker in PCN-808-BDBR is
different from that of MTV-MOFs. The location of the
BDBR linker in PCN-808-BDBR is predesigned and
precisely arranged rather than chaotically mixed into solid
solutions.
neighboring Zr
6
clusters through replacement of terminal
-
2
OH /H O ligands. After installation, the c axis contracts
Porosity Analysis and Composition Determination.
N adsorption isotherms for PCN-808, PCN-808-BPDC and
2
PCN-808-DBDR were recorded under 77 K and 1 atm to test
the porosity of the frameworks before and after linker
installation. As shown in Figure 3a, typical type IV sorption
from 19.633 Å in PCN-808 to 19.208 Å in PCN-808-BPDC
and 19.202 Å in PCN-808-BDBR, thanks to the intrinsic
flexibility of PCN-808. Accordingly, the distance between
two neighboring Zr
BPDC and PCN-808-BDBR are also reduced from 11.7 Å to
1.3 Å and 11.4 Å, respectively, which is similar to that of the
PCN-608 series (Figure 2). Also similar to that in the PCN-
08 series, the 8-connected Zr clusters in PCN-808
6
clusters along the c axis in PCN-808-
isotherms were obtained for all three MOFs with N
2
1
adsorption decreasing after linker installation, indicative
of the mesoporosity of these materials. The Brunauer–
6
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Figure 3. (a) N
2
sorption isotherms of PCN-808 and its derivatives under 77 K and 1 atm. (b) Powder X-ray diffraction (PXRD)
o
patterns of PCN-808 and its derivatives. Note, peaks around 5 move slightly after linker installation.
Emmett–Teller (BET) apparent surface areas for PCN-808,
PCN-808-BPDC, and PCN-808-BDBR calculated from the
higher than what is obtained from one-pot synthesis of
UiO-67-Ru (~ 3 wt%) and similar to that of the post-
2
-1
2
-1
2
32, 37
N
2
1
adsorption data are 2384 m g , 2441 m g , and 1894 m
synthetically produced UiO-67-Ru (~ 15 wt%).
It should
-
g , respectively. The pore size distribution of PCN-808 and
its derivatives were also analyzed by NLDFT methods
be noted that the maximum theoretical value of BDBR
linker contents in ideal PCN-808-BDBR and UiO-67-Ru are
~ 22 wt% and ~ 68 wt%, respectively. In other words, the
completion of the controllable introduction of BDBR into
the frameworks for PCN-808 is much higher than those of
UiO-67.
2
based on the N sorption data, showing two main pores in
PCN-808 series MOFs (i.e. micropores of approximately 1.2
nm and mesopores of approximately 2.5 – 3 nm, Figure S9).
Additionally, powder X-ray diffraction patterns of
activated samples and H NMR spectra of digested samples
1
Photocatalysis of the multicomponent MOF.
were measured to confirm the phase purity and
compositions of the multicomponent MOFs. The PXRD
patterns after linker installation are slightly different from
those of PCN-808 due to the contraction of the c axis. The
experimental patterns are consistent with the simulated
ones, revealing the phase purity of the MOFs both before
and after linker installation (Figure 3b). The linker ratio of
TPTB:BPDC in PCN-808-BPDC is about 1:1 according to the
Considering the high porosity of the framework and
2
+
precisely placed [Ru(bpy)
3
]
sites pointing to the
good photocatalyst
mesopores, PCN-808-BDBR is
a
candidate. The one-dimensional open mesopores are
suitable for the diffusion of the substrates and the chelated
coordination of the BDBR linker is beneficial to the
recyclability of the photocatalyst, preventing leakage of the
precious metal. A 450 nm LED lamp was selected as the
light source for the photocatalytic reactions according to
the DR-UV-Vis spectra of PCN-808-BDBR (Figure S 11). In
order to investigate the photocatalytic activity of PCN-808-
BDBR, the aza-Henry reaction was selected as a model
reaction under visible light. As shown in Table 1, the
conversion yields of three substrates with different
substituents catalyzed by PCN-808-BDBR are similar to
1
H NMR spectra, which is much higher than is calculated
based on single crystal data because some of the linear
linkers may coordinate to the Zr cluster with only one
6
carboxylate, leaving the other end dangling(Figure S2 and
Table S1). Attempts to remove the excess BPDC linkers
encapsulated into the mesopores by heating the as-
o
synthesized PCN-808-BPDC sample in DMF at 85 C for 24
2+
hrs and 48 hrs failed. As shown in Figure S4 and S5, the
linker ratios of TPTB:BPDC are almost unchanged after
treatment, indicating that the excess BPDC linker is hard
to remove by washing. However, the linker ratio of
TPTB:BDBR in PCN-808-BDBR is about 8:3 according to
those of the free [Ru(bpy)
3
]
cations, indicating that the
Ru-immobilized mesoporous MOF is a highly effective
photocatalyst. Pristine PCN-808 shows photocatalytic
activity for the aza-Henry reactions with conversion yields
of 18 % to 33 % which is similar to that of the background
reaction in the absence of the photocatalyst reported by
1
the H NMR spectra and the Zr:Ru ratio (Zr:Ru = 8:1) from
3
2
eds mapping, which is a little lower than is calculated from
single crystal data and should be ascribed to the steric
hindrance of the bulky Ru(bpy) group (Figure S3 & S12 and
2
Table S1). Although the amount of installed BDBR is
slightly lower than the theoretical value, PCN-808-BDBR
contains about 17 wt% of BDBR linker which is much
Lin and co-workers. In order to ascertain the influence of
the temperature rise under irradiation, wavelength
dependence of the aza-Henry reaction rate on PCN-808-
BDBR was also conducted using an 808 nm LED lamp
instead of the 450 nm LED lamp with a conversion yield of
28 %, indicating the importance of the photocatalytic
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conditions rather than thermal catalysis on PCN-808-
1
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BDBR. In addition, the PCN-808-BDBR catalyst could be
recycled with the substrate conversion retaining a value of
93
% after six cycles (Figure S10). Although the
photocatalytic activity of PCN-808-BDBR is similar to that
2+
3
of free [Ru(bpy) ] , the embedding of the active sites into
the frameworks enables facile recycling of this expensive
compound.
conversion (%) / yield (%)a
Table 1. Aza-Henry reactions catalyzed by PCN-808-
BDBR
catalyst
3 2
Ru(bpy) Cl
run 1
run 2
run 3
N.A.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
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3
3
3
3
3
3
3
4
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4
4
4
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5
5
5
5
5
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>99 / 47 N.A.
PCN-808
<5 / <5
30 / <5
92 / 42
N.A.
N.A.
N.A.
UiO-67-Ru
N.A.
PCN-808-BDBR
a
88 / 51
90 / 49
1
Conversion yields were determined by H NMR of the
crude product.
photocatalyst / conversion (%)b
substratea Ru(bpy)
PCN-808
PCN-808-BDBR
3
Cl
2
CONCLUSIONS
1
1
a
99
27
33
18
>99
94
In conclusion, a csq topology mesoporous Zr-MOF,
PCN-808, was designedly synthesized through elongation
of the tetratopic ligand. The size suitable coordinatively
unsaturated pockets as well as the inherent flexibility of
the framework play important roles to allow for successful
linker installation. A Ru-containing linear linker in
addition to a geometrically equivalent linker, BPDC, have
been successfully installed into the open pockets of PCN-
b
>99
>99
1c
99
a
For the substrate and the product, 1a, 2a, R = H; 1b, 2b, R =
b
Br; 1c, 2c, R = OCH
by H NMR of the crude product.
3
.
Conversion yields were determined
1
It should be noted that the BDBR has been successfully
incorporated into microporous UiO-67 and the resulting
material (UiO-67-Ru) shows high catalytic activities for
8
08. In the resulting mesoporous PCN-808-BDBR, the
2+
32
[Ru(bpy)
3
]
functional groups are precisely placed
aza-Henry reactions. However, the small pore size of
pointing to the mesopores. Photocatalytic performance of
PCN-808-BDBR was examined by aza-Henry reaction with
high conversion yields and stability. Furthermore, the
mesoporous nature of PCN-808-BDBR makes it suitable for
the photocatalytic reactions of large substituents. Our
research sheds light on application-oriented, controllable
regulations of pore environments in mesoporous MOFs.
UiO-67-Ru limits its utility to the photocatalysis of
reactions involving large substituents. Compared to UiO-
67-Ru, PCN-808-BDBR may be suitable for the
photocatalytic reactions of large substituents due to its
mesoporous nature. Therefore, PCN-808-BDBR was
investigated as a photocatalyst for the photocatalytic
oxidation of dihydroartemisinic acid to artemisinin. As
shown in Table 2, the conversion and yields of artemisinin
catalyzed by PCN-808-BDBR are similar to those of the free
ASSOCIATED CONTENT
2+
Supporting Information.
[
Ru(bpy)
3
]
cations and are much higher than those of
The Supporting Information is available free of charge via the
PCN-808 and UiO-67-Ru. As expected, large substituents
such as dihydroartemisinic can easily diffuse into the
mesopores of PCN-808-BDBR where the active sites in the
microporous UiO-67-Ru would be inaccessible for such
substituents. PXRD patterns were also measured after
catalytic tests on PCN-808-BDBR to check the stability of
the photocatalyst. The patterns are consistent with the as-
synthesized ones, suggesting high stability of the material
Internet
at
http://pubs.acs.org.
Text, tables, and figures giving experimental procedures for
the syntheses of the ligands, PXRD, N
2
adsorption isotherms,
1
H NMR spectra, and other additional information (PDF)
X-ray crystallographic details of PCN-608 and derivatives
(
CIF)
X-ray crystallographic details of PCN-808 and derivatives
CIF)
(
Figure 3b).
(
Table 2.
Photocatalytic
oxidation
of
dihydroartemisinic acid to artemisinin by PCN-808-
BDBR
AUTHOR INFORMATION
Corresponding Author
*wumy@fjirsm.ac.cn
*zhou@chem.tamu.edu
Notes
The authors declare no competing financial interest.
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enhancement of gas adsorption in multivariate metal-organic
framework-177. J. Am. Chem. Soc. 2015, 137, 2641-2650.
13) Zhao, X.; Bu, X.; Zhai, Q. G.; Tran, H.; Feng, P., Pore space
partition by symmetry-matching regulated ligand insertion and
dramatic tuning on carbon dioxide uptake. J. Am. Chem. Soc. 2015,
ACKNOWLEDGMENT
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The gas sorption studies were supported by the Center for Gas
Separations, an Energy Frontier Research Center funded by
the U.S. Department of Energy, Office of Science, Office of
Basic Energy Sciences (DE-SC0001015). Structural analyses
were supported by the Robert A. Welch Foundation through
a Welch Endowed Chair to H.-C. Z (A-0030). This material is
based upon work supported by the National Science
Foundation Graduate Research Fellowship under Grant No.
DGE: 1252521. The authors also acknowledge the financial
support of the U.S. Department of Energy Office of Fossil
(
1
37, 1396-1399.
14) Jiang, J.; Furukawa, H.; Zhang, Y. B.; Yaghi, O. M., High
(
Methane Storage Working Capacity in Metal-Organic
Frameworks with Acrylate Links. J. Am. Chem. Soc. 2016, 138,
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P., Multivariable Modular Design of Pore Space Partition. J. Am.
Chem. Soc. 2016, 138, 15102-15105.
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National
Energy
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DEFE0026472) and National Science Foundation Small
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financial supports of the Key Research Program of Frontier
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SLH019 and QYZDY-SSW-SLH025), National Nature Science
Foundation of China (21771177, 21390392 and 21371169), Youth
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