DOI: 10.1002/cplu.201600121
Full Papers
Modulation of Gas Sorption Properties through Cation
Exchange within an Anionic Metal–Organic Framework
Yong-Liang Huang, Long Jiang, and Tong-Bu Lu*[a]
A
novel 3D anionic metal–organic framework (MOF) of
both before and after Li+ exchange show highly selective ad-
sorption for CO2 over CH4 and N2 gases, and the Li+-ex-
changed MOF exhibits enhanced CO2, CH4, and H2 storage
properties.
(Me2NH2)4[Ni8(PTCA)4(m3-OH)4(H2O)4](DMF)5(H2O)13 (H4PTCA=
pyrene-1,3,6,8-tetracarboxylic acid) has been synthesized, in
which Me2NH2 can be exchanged by Li+ ions. The results of
+
gas sorption measurements indicate that the desolvated MOFs
Introduction
Metal–organic frameworks (MOFs) are multifunctional materials
that have attracted much attention in the past two decades,
owing to their intriguing structural diversities and potential ap-
plications, such as gas separation and storage,[1] ionic/molecu-
lar recognition,[2] heterogeneous catalysis,[3] luminescence
tuning,[4] energy storage devices.[5] In particular, their adjusta-
ble pore sizes and controllable pore surface properties make
them good adsorbents in clean energy applications, such as
hydrogen and methane storage, and CO2 capture.[6] To date,
a large number of MOFs have been constructed by using tran-
sition-metal and lanthanide ions as framework nodes and aro-
matic carboxylic ligands as framework linkers, as discussed in
several reviews.[7]
has been reported to exhibit nearly double the hydrogen
uptake capacity of undoped MOF.[9]
Herein, we report a 3D anionic MOF, (Me2NH2)4[Ni8(PTCA)4(m3-
OH)4(H2O)4](DMF)5(H2O)13 (1), which was constructed by the co-
ordination of nickel(II) with a tetracarboxylate ligand, H4PTCA
(H4PTCA=pyrene-1,3,6,8-tetracarboxylic acid). Based on
+
a cation-exchange strategy, in which Me2NH2 in 1 was ex-
changed by Li+, the desolvated Li-exchanged MOF shows an
enhanced CO2, CH4, and H2 uptake capability, relative to the
original MOF.
Results and Discussion
As we know, CO2 emission is currently a tremendous threat
in global warming and carbon capture and storage (CCS)[8] and
the development of renewable and clean energy sources have
been regarded as effective approaches to solve this problem.
Hydrogen and methane are considered as clean and efficient
energy sources. However, the design and construction of mate-
rials that can effectively store hydrogen and methane remain
a great challenge. MOFs have shown great potential for gas
storage, but most MOF materials still display relatively low H2
and CH4 uptakes. Therefore, the development of more efficient
approaches to enhance H2 and CH4 adsorption is critically im-
portant. Previous investigations have proved that the storage
capacity of gases is strongly dependent upon the interactions
between the gases and the functional groups within the
frameworks of the MOFs. For example, lithium-doped MIL-53
Structure of 1
Compound 1 crystallizes in the monoclinic space group P21/n.
As illustrated in Figure 1a, the asymmetric unit of 1 contains
four crystallographically independent NiII cations, two PTCA4À
anions, two m3-OH groups, and two coordinated water mole-
cules. Four nickel atoms exhibit two different coordination ge-
ometries, in which Ni1 and Ni4 are six-coordinated by three
carboxylate oxygen atoms from the PTCA ligands, two m3-OH
groups, and one water molecule to form a distorted octahedral
geometry; Ni2 and Ni3 are also six-coordinated with a distorted
octahedral geometry through five carboxylate oxygen atoms
from the PTCA ligands and one m3-OH group. Four NiII ions are
bridged by two m3-OH to form a planar tetranuclear cluster
Ni4(m3-OH)2 as a secondary building unit (SBU). The Ni4(m3-OH)2
SBUs are bridged by PTCA4À linkers to generate a novel 3D
anionic MOF of 1, with 1D channels packed parallel along the
ab plane (Figure 1b). It is interesting to note that the adjacent
1D parallel channels within the ab plane are perpendicularly
packed along the c axis in an AB/AB fashion (Figure 1b). The
sizes of the channels are 9.7ꢀ11.0 ꢁ (centroid–centroid distan-
ces between two opposite PTCA ligands within one channel),
[a] Y.-L. Huang, Dr. L. Jiang, Prof. T.-B. Lu
MOE Key Laboratory of Bioinorganic and Synthetic Chemistry
School of Chemistry and Chemical Engineering
Sun Yat-Sen University, Guangzhou 510275 (P. R. China)
Supporting information for this article can be found under http://
+
and are filled by Me2NH2 cations decomposed from N,N-dime-
thylformamide (DMF), and disordered DMF and H2O molecules.
The calculated porosity and voids per unit cell volume deter-
This article is part of a Special Issue on “Coordination Polymers/MOFs”. A
link to the issue will appear here once it is compiled.
ChemPlusChem 2016, 81, 1 – 7
1
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&
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