Modification of flexible part in Cu2+ interdigitated framework for CH4/CO2 separation

Article abstract of DOI:10.1039/c0cc01294g

The structural flexibility of Cu²⁺ interdigitated layer type framework was controlled and the compound represented clear separation property of CH₄/CO₂ at range of 0-1.0 MPa and recovery of adsorbed CO₂ above 0.

Full text of DOI:10.1039/c0cc01294g

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2+
Modification of flexible part in Cu interdigitated framework
for CH /CO separationw
4
2
a
b
b
c
Yasutaka Inubushi, Satoshi Horike,* Tomohiro Fukushima, George Akiyama,
bcd
cd
Ryotaro Matsuda and Susumu Kitagawa*
Received 8th May 2010, Accepted 8th October 2010
DOI: 10.1039/c0cc01294g
2
+
The structural flexibility of Cu
interdigitated layer type
frameworks accompanied by guest sorption processes and it
8
is often sensitive to the specific guest molecule.
,10–12
framework was controlled and the compound represented clear
separation property of CH /CO at range of 0–1.0 MPa and
Extended frameworks constructed from two-dimensional
(2D) layers have been widely studied because they can
accommodate various guest molecules in the interlayer
4
2
recovery of adsorbed CO above 0.1 MPa.
2
1
3,14
Development of materials and technology for selective
spaces.
Likewise, 2D PCPs are significant motifs for
adsorption of CO
2
gas from CH
4
/CO
2
mixture has been a
selective gas adsorption because we can tune the flexibility of
the layer–layer interaction and intrinsic flexibility of the
significant challenge in the area of natural-gas processing.
Regarding the porous materials for selective CO2 capture
1
5,16
coordination bond.
has encouraged us to optimize the gas separation performance,
especially the capture of CO gas from CH /CO mixture at
Rational design of a PCP framework
from CH /CO2 mixture, we could employ either kinetic or
4
1
equilibrium-based separation. Activated carbon or zeolites
2
4
2
have been mainly studied as equilibrium-based adsorbents and
the main drawbacks are either low selectivity or regenerability.
For a porous material design, we have to control gas sorption
isotherms and some points are required. First, desorption
ambient condition. Herein we demonstrate a modification of
flexibility in a 2D PCP framework by ligand design and
control the adsorption isotherms of CO
for the optimization of gas separation property.
Previously we reported a flexible 2D PCP; [Cu(dhbc)
and CH to give idea
2
4
pressure of CO
it should not be lower than 0.1 MPa, otherwise we need a
vacuum to regenerate the CO . Second, the separation ability
2
is related to the energy of CO
2
recovery and
2
bpy]ꢀ
H
O
(1*H
O), where Hdhbc = 2,5-dihydroxybenzoic
0
2
2
acid and bpy = 4,4 -bipyridyl, which represents various
2
1
7,18
should be observed in a wide range of pressure (B1.0 MPa)
for various types of pressure-swing processes. Especially the
‘‘gate-opening’’ type gas adsorption profiles.
adsorptions at 298 K were reported and to carefully investigate
the adsorption behavior at below 0.1 MPa, the CO and CH
adsorption isotherms of 1 at 273 K were measured as shown in
Fig. 1c. It starts to adsorb CO at P = 0.04 MPa and CH at
0.65 MPa. Many flexible PCPs including 1 adsorb CO below
0.1 MPa and CH below 1.0 MPa and the compounds are not
satisfactory for CH /CO separation with a low energetic
Several gas
materials are required not to adsorb CH at all in the pressure
4
2
4
range mentioned above.
Porous coordination polymers (PCPs) or metal–organic
framework (MOFs) constructed from metal cations and
organic linkers are a new class of microporous materials that
show promise for gas separation applications because of their
2
4
2
4
4
2
2
–7
structural versatility. Especially the PCPs whose structures
have a flexible nature are attractive due to their potential
cycle. To elucidate the structural contribution for the gas
adsorption profiles, we characterized the crystal structure of
guest-free 1. Careful degas treatment of a single crystal of
8
,9
applications in gas separation with unique mechanisms.
They represent a reversible transformation of open/close
1*H
Although the coordination environment around the Cu
ion is not different compared with 1*H O, the benzene rings
2
O gave the closed structure of 1 (Fig. 1a and b).
2
+
2
a
Synthesis Research Laboratory, Kurashiki Research Center,
of the dhbc ligand largely tilt because of the bending of
coordination bonds (Cu–O) in carboxylate and hydroxy
groups. Two dhbc ligands have trans-type fashion around
Kuraray Co. Ltd., 2045-1, Sakazu, Kurashiki, Okayama 710-0801,
Japan
Department of Synthetic Chemistry and Biological Chemistry,
b
2
+
the Cu
ion, whereas they have cis-type fashion in the
Graduate School of Engineering, Kyoto University, Katsura,
Nishikyo-ku, Kyoto 615-8510, Japan
Kitagawa Integrated Pores Project,
original phase (1*H O). The local reorientation affects the
2
c
stacking of 2D layers and the networks are densely packed
19
resulting in the guest accessible void volume of 2.1%. This
Exploratory Research for Advanced Technology (ERATO), Japan
Science and Technology Agency (JST), Kyoto Research Park,
Bldg#3, Chudoji, Awata-cho, Shimogyo-ku, Kyoto 600-8815, Japan
2
means the structural transformation is ‘‘porous’’ (1*H O)
to ‘‘nonporous’’ (1) and it causes the gate-opening type
12,20
adsorption behavior for various gasses.
d
Institute for Integrated Cell-Material Sciences (iCeMS),
Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan.
E-mail: kitagawa@icems.kyoto-u.ac.jp; Fax: +81-75-383-2732;
Tel: +81-75-383-2733
1
has high flexibility in the part of the dhbc because of the
w Electronic supplementary information (ESI) available: Synthesis,
elemental analysis, TGA curve, XRPD patterns with LeBail fitting,
coordination bond with hydroxy group and the size of ligand
and it promoted the overall transformation. The structural
transformation had a low activation energy and afforded the
favorable adsorptions of CO and CH at low pressure at 273 K.
H
2
O adsorption/desorption isotherms, simultaneous measurements of
CO adsorption and XRPD measurement. CCDC reference numbers
76333 (1) and 776334 (2*Acetone). For ESI and crystallographic
2
7
2
4
data in CIF or other electronic format see DOI: 10.1039/c0cc01294g
To shift the gate-opening pressure of CO above 0.1 MPa and
2
This journal is c The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 9229–9231 9229

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single crystals of [Cu(H
2
dhbpc)
2
bpy]ꢀ2Acetone (2*Acetone)
and the crystal structure is shown in Fig. 2a and 2b. The
framework has a similar motif with 1*H O and the dhbpc
2
replace the positions of dhbc to form an interdigitated
+
framework. The coordination environment around the Cu
2
center is octahedrally coordinated to dhbpc and bpy, and the
2
+
dihedral angle of benzene rings in dhbpc is 34.01. The Cu
and dhbpc and bpy form 2D layers and each layer is stacked
with interdigitated fashion containing two acetone molecules
as guests. The void volume of the framework of 2*Acetone is
2
2
0% and it is comparable to the 1*H O. We have not
determined the crystal structure of degassed 2 because of the
large transformation confirmed by powder X-ray measurement
but clearly it showed reversible transformation via guest
accommodation and release. We refined the cell parameters
of guest-free 2 from XRD pattern by LeBail fitting and the
refined values are different from that of 2*Acetone which
indicates the large structural transformation. We could expect
higher activation energy from close to open phase than 1 if 2
2
+
has a similar reorientation around the Cu
atoms with 1
because of the size of the dhbpc ligand. Thermogravimetric
analysis of guest-free 2 supported a thermal stability of the
framework until 500 K.
2
represented a different type of gas adsorption profile from
. For CO2 adsorption at 273 K, the 2 represented double
stepwise adsorption (Fig. 2c). Initial gas uptake was at
1
0
.04 MPa and first uptake occurred to reach saturation
1
Fig. 1 Representations of crystal structure transformation of 1 and
ꢁ
2+
(34 mL
g
). The plateau appears in the range of
1
*H
stacking motif with/without guest molecules. Guests are omitted.
c) Adsorption and desorption isotherms of CO (open and closed
circles) and CH (open and closed triangles) for 1 at 273 K.
2
O (a) environment around the Cu
ions and (b) 2D layer
0
.20–0.55 MPa and moved to next uptake to the second
ꢁ
1
(
2
saturation point (115 mLg ). To obtain structural information,
we studied simultaneous measurements of CO adsorption and
4
2
powder X-ray diffraction at 195 K to investigate the structural
information via adsorption at each plateau. The XRD pattern
at P = 3.9 kPa was slightly different from degassed 2 indicating
the presence of metastable phase of structure. As the pressure
increased, the second step occurred and was attributed by the
transformation to reach the stable structure which was similar
avoid CH adsorption in the pressure range of zero to 1 MPa,
4
we prepared an interdigitated framework by employing
0
4
,4 -dihydroxybiphenyl-3-carboxylic acid (H
2
dhbpc) as a
3
dhbpc can be regarded as an elongated
2
ligand. The H
1
version of the dhbc ligand in 1 and the enlargement of the
ligand could promote a lower flexibility in the 2D layers
because of an increase of activation energy for structural
1
5
with 2*Acetone. From the measurement, we could pursue
the stepwise transformations of structure of 2. The bulkiness
of dhbpc ligand would not permit to give perfect nonporous
stacking of layer structure like 1 and it resulted in the initial
3
transformation. The H dhbpc was synthesized according to
2
the literature method. Slow diffusion of Cu(NO
1
3
)
2
ꢀ3H
2
O and
H
3
dhbpc with bpy in acetone and water solution formed green
2
microporosity. In desorption process, the adsorbed CO at the
2+
Fig. 2 Representation of crystal structures of 2 (a) around the Cu ion and (b) 2D layer stacking. Guests are omitted. (c) Adsorption and
desorption isotherms of CO (open and closed circles) and CH (open and closed triangles) for 2 at 273 K.
2
4
9
230 Chem. Commun., 2010, 46, 9229–9231
This journal is c The Royal Society of Chemistry 2010

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ꢁ
1
second step (total 81 mL g ) was released at P = 0.4 MPa
which was higher than 0.1 MPa and that of 1. It is desirable for
remarkable change in the gas adsorption properties, which is
relevant for appropriate gas separation condition with low
energy consumption process.
the regeneration of CO from adsorbed phase.
2
The stepwise adsorption behavior was also observed in
The authors would like to acknowledge Dr. Keiko Miura
and Dr. Keiichi Osaka of SPring-8 for performing the powder
X-ray measurement in beam line BL19B2 in SPring-8. This
work was supported by the New Energy and Industrial
Technology Development Organization (NEDO), Japan.
H O adsorption at 298 K. Although 1 represented single
2
gate-opening type adsorption at 2.2 kPa, 2 gave gradual
uptake until P = 2.2 kPa and a second jump was observed.
Both compounds had large hysteresis in desorption curves
which was indicative of stabilization of water molecule
in the pores. The final adsorption amount of CO
2
for 2 was
Notes and references
1
.5 times larger than that of 1 and comparable to the other
2
1
R. T. Yang, Gas Separation by Adsorption Processes, Imperial
College Press, London, 1997.
2–24
adsorbents.
The low flexibility in 2 also affected an
. The 2 provided negligible amount of uptake
isotherm of CH
4
2 S. Kitagawa, R. Kitaura and S. Noro, Angew. Chem., Int. Ed.,
004, 43, 2334–2375.
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for CH even at pressure of 1.0 MPa at 273 K. Although 1
4
3
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Sci. U. S. A., 2008, 105, 11623–11627.
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ꢁ
1
,
gradually adsorbed CH4 until P = 0.65 MPa (10 mLg
ꢁ1
Fig. 1c) and showed abrupt uptake to reach 58 mL g at
ꢁ
1
G. V. Baron and J. F. M. Denayer, J. Am. Chem. Soc., 2008,
130, 7110–7118.
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0
.95 MPa, 2 adsorbed only 4 mL g at 1.0 MPa, resulting in
the better selectivity on CH /CO . The low flexiblity of 2 for
is unique for creation of repulsive property against the
molecule at wide pressure range. It provides another idea
/CO separation with other metal–
organic frameworks having rigid porous scaffold and preferable
4
2
5
CH
CH
4
4
1477–1504.
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B. Chen, S. Xian and G. Qian, Acc. Chem. Res., 2010, 43,
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4
2
1
8
2
5–27
binding character for CO
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from CH /CO mixture gas and executed the co-adsorption
2
gas.
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575–1581.
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over CH
4
9
4
2
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´
rey,
mixture gas (CH : CO = 1 : 1(vol)) for 2 under the condition
4
2
1
1
´
of total pressure 0.1 MPa and 273 K then waited three hours
for the equilibrium co-adsorption process and detected the
adsorbed gas species by gas chromatography. Although the
6
ꢁ
1
6
total adsorbed amount of gas was low (17 mL g ) because of
the low total pressure in this measurement, we hardly observed
1
1
1
the trace of CH
4
which indicated that all the adsorbed gas was
from
CO , and we observed clear separation property for CO
2
2
15 A. Kondo, H. Noguchi, L. Carlucci, D. M. Proserpio, G. Ciani,
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2
007, 129, 12362–12363.
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1
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2
4
2
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1
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2
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2
releases adsorbed CO
2
2
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of coordination bonds in the layer and the approach is feasible
only if we employ the 2D porous coordination layer.
2
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2
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This journal is c The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 9229–9231 9231