A Stable Amino-Functionalized Interpenetrated Metal-Organic Framework Exhibiting Gas Selectivity and Pore-Size-Dependent Catalytic Performance

Article abstract of DOI:10.1021/acs.inorgchem.7b02148

An amino-functionalized doubly interpenetrated microporous zinc metal-organic framework (UPC-30) has been solvothermally synthesized. UPC-30 can be stable at 190 °C and confirmed by powder X-ray diffraction. Gas adsorption measurements indicate that UPC-3

Full text of DOI:10.1021/acs.inorgchem.7b02148

Communication
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Cite This: Inorg. Chem. XXXX, XXX, XXX-XXX
A Stable Amino-Functionalized Interpenetrated Metal−Organic
Framework Exhibiting Gas Selectivity and Pore-Size-Dependent
Catalytic Performance
Weidong Fan,† Yutong Wang,† Zhenyu Xiao,† Liangliang Zhang,† Yaqiong Gong,*,‡ Fangna Dai,†
Rongming Wang,† and Daofeng Sun*,†
†College of Science, China University of Petroleum (East China), Qingdao, Shandong 266580, People’s Republic of China
‡Chemical Engineering and Enviroment Institute, North University of China, Taiyuan 030051, People’s Republic of China
S
* Supporting Information
based on the C−C coupling reaction. Conventionally, these
ABSTRACT: An amino-functionalized doubly interpene-
trated microporous zinc metal−organic framework (UPC-
30) has been solvothermally synthesized. UPC-30 can be
stable at 190 °C and confirmed by powder X-ray
diffraction. Gas adsorption measurements indicate that
UPC-30 exhibits high H2 adsorption heat and CO2/CH4
reactions are catalyzed by homogeneous catalysts. However, it is
difficult to recycle the catalysts because of the low stability and
high recovery cost. Therefore, it is highly desirable to develop
heterogeneous catalysts with high stability and good recyclability.
In this Communication, we present a new amino-functional
3D zinc-based MOF, [Zn3(OH)(ATTCA)2(H2O)]·C2H6NH2·
4DMF·H2O (denoted as UPC-30), where H3ATTCA = 2-
amino[1,1:3,1-terphenyl]-4,4,5-tricarboxylic acid. UPC-30 ex-
hibits a doubly interpenetrated microporous framework with 1D
rhombic channels. It is interesting that the material demonstrates
high CO2/CH4 separation efficiency and pore-size-dependent
catalytic properties for Knoevenagel condensation reactions.
+
separation efficiency. After the exchange of Me2NH2 by
Li+ in the channels, the H2 adsorption heat increased by
19.7%. Because of the existence of −NH2 groups in the
channels, UPC-30 can effectively catalyze Knoevenagel
condensation reactions with high yield and pore-size-
dependent selectivity.
Additionally, through the exchange of Me2NH2 by Li+ in the
+
channels, the H2 adsorption heat of UPC-30 increased by 19.7%.
Colorless block crystals of UPC-30 were obtained by a
solvothermal reaction of H3ATTCA and Zn(NO3)2·6H2O in
N,N-dimethylformamide (DMF)/ethanol/water (5:2:1, v/v/v)
at 100 °C for 2 days. UPC-30 was characterized by single-crystal
X-ray diffraction, thermogravimetric analysis (TGA), and
elemental analysis. Single-crystal X-ray diffraction analysis
revealed that UPC-30 crystallizes in the monoclinic system
with a space group P21/c. The asymmetrical unit contains two
deprotonated ATTCA3− ligands, three zinc ions, a coordinated
water molecule, a μ3-hydroxyl, a protonated dimethylamine
molecule, an uncoordinated water molecule, and four DMF
solvent molecules. Three zinc ions possess two different
coordination environments: Zn1 and Zn2 are coordinated by a
μ3-oxygen atom and three oxygen atoms from three different
TTCA3− ligands, and the average Zn−O distance is 1.966 Å; Zn3
is coordinated by a coordinated water molecule, a μ3-oxygen
atom, and four oxygen atoms from four different ATTCA3−
ligands, with an average Zn−O distance of 2.108 Å. Three zinc
ions are connected through four carboxyl oxygen atoms and one
μ3-oxygen atom to form a trinuclear [Zn3(OH)(COO)4]
secondary building unit (Figure 1a). Structurally speaking,
UPC-30 presents a 3D network constructed by the [Zn3(OH)-
(COO)4] units and the tricarboxylate ligand with 1D rhombic
s a useful functional material for the separation of small gas
Amolecules, microporous metal−organic frameworks
(MOFs), which can be easily assembled from metal ions/
clusters and organic linkers, have attracted wide research
interest.1−4 For their easily adjustable pore size and functional
pore surface, the microporous MOF can achieve efficient
separation of small molecules by maximizing their size-selective
sieving effects and enhancing their specific affinity. Actually, on
the basis of postsynthesis ion exchange5,6 and amino
modification, various microporous MOFs show high perform-
ance for H2 storage and CO2/CH4 separation.7,8
Porous MOF-based functional materials for efficient adsorp-
tion and separation of CO2 have some specific characteristics and
requirements:9−11 (i) excellent thermal stability; (ii) accessible
channels; (iii) naked nitrogen-containing heterocycles (iv)
uncoordinated functional groups (e.g., −NH2 or −OH groups);
(v) open-metal sites.12,13 A number of MOFs with these
characteristics, such as UTSA-48,14 NOTT-101,15 MFM-130,16
and UPC-21,17 displayed a high CO2/CH4 separation perform-
ance. Furthermore, some other MOFs with multifold inter-
penetrated frameworks18 also exhibited good CO2/CH4
separation efficiency. However, these types of interpenetrated
MOFs for CO2/CH4 separation are rare19 because the
interpenetration will reduce the porosity in the framework.
On the other hand, the functional MOF materials with highly
ordered pores also show great potential for catalytic
applications.20 For instance, PCN-124 can catalyze the
Knoevenagel condensation reactions, which was considered to
be an efficient way to obtain valuable intermediate chemicals
+
channels (Figure 1b). The Me2NH2 cations, derived from in situ
decomposition of DMF molecules, are located within the
accessible voids, resulting in charge equilibrium.21 From a
Received: August 26, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b02148
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Communication
Figure 1. (a) Coordination environment of Zn2+ ions and coordination
modes of ATTCA3−. (b) 2-fold interpenetrating framework along the b
axis. (c) 3,6-connected “sit” net.
Figure 3. (a and b) N2 sorption isotherms and pore-size distribution for
UPC-30 (red) and Li-UPC-30 (black) at 77 K. (c) H2 sorption
isotherms for UPC-30 (red and black) and Li-UPC-30 (blue and green).
(d) Adsorption heat (Qst) of H2 for UPC-30 (red) and Li-UPC-30
(black).
topological point of view, the ATTCA3− ligands can be simplified
into three-connected nodes and [Zn3(OH)(COO)4] units into
six-connected nodes. Therefore, a classical “sit” architecture with
a topological point symbol of {4.62}2{42.610.83} was obtained
(Figure 1c).
heat is 8.6 kJ·mol−1 at zero coverage and decreases slowly with
increasing H2 loading, calculated by the Clausius−Clapeyron
equation (Figure 3d). These values are higher than those of
famous MOF materials, such as NOTT-122 (6.0 kJ·mol−1),12
MOF-5 (5.2 kJ·mol−1),22b and HKUST-1 (6.6 kJ·mol−1).22c
The thermal stability of UPC-30 was studied by variable-
temperature powder X-ray diffraction (PXRD; Figure 2). The
After the exchange of Me2NH2 by Li+ (see the SI), the surface
+
areas of BET and Langmuir of the resultant Li-UPC-30
decreased slightly to 278 and 321 m2·g−1, and the pore size
was slightly reduced by 0.05 nm (Figure 3b) based on the steric
effects.23,24 The adsorption amount of H2 increased by 14.8%
(for 97.4 cm3·g−1, 0.89 wt %) and 21.6% (for 77.3 cm3·g−1, 0.69
wt %) at 77 and 87 K, respectively (Figure 3c), and the
adsorption heat of H2 increased by 19.7% (for 10.3 kJ·mol−1;
Figure 3d). These observations are consistent with many reports
that Li+ can increase the adsorption amount and Qst values for H2,
which is based on the strengthened intermolecular interactions
between H2 and Li+ in the host framework.25 In addition, narrow
pores can also increase the Qst value of H2, which provides more
overlap potential energy fields.5
The CO2, CH4, C2H6, C2H4, C2H2, C3H8, and C3H6
adsorption isotherms for UPC-30 exhibit I-type behavior, with
adsorption amounts of 41.5, 14.1, 22.7, 24.5, 30.9, 18.0, and 21.2
cm3·g−1, respectively, at 273 K (Figure 4a). The relatively higher
CO2 uptake capacity for UPC-30 prompted us to further
investigate the ability to separate CO2 from other gases by the
ideal adsorbed solution theory model26 with 50:50 and 10:90
binary gas mixtures, respectively. The adsorption selectivities for
Figure 2. PXRD patterns of UPC-30 at different conditions.
PXRD pattern of the samples heated at different temperatures
showed similar diffraction peaks until temperatures up to 190 °C,
indicating that the framework of UPC-30 was stable below 190
°C, which is consistent with the results observed from TGA.
Despite the 2-fold interpenetration, UPC-30 was still porous
with a free volume of 45.9%, which was calculated by PLATON
after removal of the guest solvent molecule. To elucidate the
permanent porosity and pore properties of UPC-30, gas-uptake
experiments were performed with desolvated samples (see the
Supporting Information, SI). N2-uptake (77 K) measurements
gave typical I-type isotherms for a microporous solid with an
adsorption of 86.2 cm3·g−1 (Figure 3a,b). The surface areas of
Brunauer−Emmett−Teller (BET) and Langmuir calculated
from the N2 adsorption isotherm were 284 and 330 m2·g−1,
respectively. The H2 adsorption experiments were carried out at
77 and 87 K with an adsorption capacity of 84.8 and 63.6 cm3·g−1
(0.76 and 0.57 wt %; Figure 3c). The moderate H2 absorption of
UPC-30 is comparable to those of PCN-131 (0.84 wt %) and
PCN-19 (0.95 wt %) at 77 K.22a In addition, the H2 adsorption
Figure 4. (a) CO2, CH4, C2H6, C2H4, C2H2, C3H8, and C3H6 sorption
isotherms at 273 K for UPC-30. (b) CO2/CH4, CO2/C3H8, CO2/C3H6,
CO2/C2H6, CO2/C2H4, and CO2/C2H2 selectivities at 273 K (50:50
and 10:90, v/v).
B
DOI: 10.1021/acs.inorgchem.7b02148
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Inorganic Chemistry
Communication
CO2/CH4 are approximately 9.2 (50:50) and 10.3 (10:90) at 273
K. However, the selectivity for CO2 over C3H8, C3H6, C2H6,
C2H4, or C2H2 is significantly poorer (<2 at both 50:50 and 10:90
at 273 K; Figure 4b). Although it is common to selectively
capture CO2 from MOF materials,27−30 UPC-30 exhibits
application potential in the selective adsorption of CO2 because
of its high selectivity and thermal stability.
For the Lewis basic −NH2 group present in the channel, UPC-
30 was used to catalyze the Knoevenagel condensation
reaction.31 As a demonstration, because of possible clathration
within the MOF channel, the aromatic aldehyde was selected as
the substrate. The catalytic results of different substrates are
summarized in Table 1. As a control experiment, the reaction was
completely stopped after the removal of UPC-30, and this was
supported by gas chromatography (GC)−mass spectrometry
(Figure S5).
condensation reactions. A further study on the synthesis of other
porous MOF materials with this ligand is underway in our
laboratory.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b02148.
Synthesis and activation of UPC-30, crystal data, TGA
curves, IR pattern, room-temperature emission spectra,
CO2, CH4, C2H6, C2H4, C2H2, C3H8, and C3H6 sorption
isotherms and CO2/CH4, CO2/C3H8, CO2/C3H6, CO2/
C2H6, CO2/C2H4, and CO2/C2H2 selectivities at 273 K
for Li-UPC-30, evidence of the heterogeneous nature of
catalysis in the Knoevenagel reaction of benzaldehyde, and
GC spectrum (PDF)
Table 1. Knoevenagel Reactions Catalyzed by UPC-30
Accession Codes
CCDC 1543307 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_
request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: +44 1223 336033.
a
b
entry
R
t (h)
yield (%)
1
2
3
4
5
6
7
8
9
Ph
5
5
5
5
5
5
5
5
5
94.1
74.4
71.4
21.5
18.9
18.4
16.6
5.1
4-NO2Ph
4-MePh
4-C(CH3)3Ph
1-naphthyl
4-FPh
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: gyq@nuc.edu.cn.
*E-mail: dfsun@upc.edu.cn.
4-PhOPh
4-MeOPh
4-PhPh
0
ORCID
a
Reaction conditions: activated sample UPC-30 (10 wt %),
malononitrile (1.0 mmol, 0.066 g), an aldehyde (1.0 mmol), CH2Cl2
(3 mL), room temperature. GC yield.
Yutong Wang: 0000-0001-8943-1832
Daofeng Sun: 0000-0003-3184-1841
b
Notes
The authors declare no competing financial interest.
UPC-30 can be recovered from the reaction system by
centrifugation and reused three cycles without significant loss of
activity. The PXRD pattern of the recovered catalyst was found
to be unchanged after three cycles (Figure 2), indicating its
excellent chemical stability. A pore-size-dependent catalytic
capacity was observed for UPC-30. The yield for Knoevenagel
condensation of benzaldehyde and malononitrile can reach
94.1% after 5 h at room temperature. It should be noted that
these values are lower than those for PCN-124 (99%)32a and Cz-
MOF (99%)32b but still comparable to that of PCP-1 (96%)32c
and higher than that of 1Cu′ (90%),32d making these MOFs
qualified considerable candidates for C−C coupling reaction. As
a comparison, the yield decreased with an increase in the bulk of
the substituent on the aldehyde substrate. When a bulky
aldehyde of 1,1′-biphenyl-4-carbaldehyde was selected as the
substrate, the reaction does not proceed (Table 1).
In conclusion, using tricarboxylic acid H3ATTCA as the
ligand, a doubly interpenetrated microporous zinc MOF (UPC-
30) was synthesized, which incorporates pendent −NH2 groups.
In UPC-30, the [Zn3O(COO)4] subunits are linked by the
tricarboxylic acid ligand to form a microporous framework
possessing a 1D channel. After the exchange of Me2NH2+ by Li+
in the channels, the H2 adsorption heat increased by 19.7%.
UPC-30 exhibit selective adsorption of CO2 over CH4 at 273 K,
providing some benefit for the major challenges of gas separation.
In addition, the presence of Lewis basic −NH2 groups allows
UPC-30 to act as a catalyst for size-selective Knoevenagel
ACKNOWLEDGMENTS
■
We are grateful for financial support from the Taishan Scholar
Foundation (Grant ts201511019) and the National Natural
Science Foundation of China (Grants 21371179 and 21571187).
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