Water-Stable Zirconium-Based Metal–Organic Framework Material with High-Surface Area and Gas-Storage Capacities

Article abstract of DOI:10.1002/chem.201402895

We designed, synthesized, and characterized a new Zr-based metal–organic framework material, NU-1100, with a pore volume of 1.53 ccg^?1and Brunauer–Emmett–Teller (BET) surface area of 4020 m²g^?1; to our knowledge, currently the highest published for Zr-based MOFs. CH₄/CO₂/H₂adsorption isotherms were obtained over a broad range of pressures and temperatures and are in excellent agreement with the computational predictions. The total hydrogen adsorption at 65 bar and 77 K is 0.092 g g^?1, which corresponds to 43 g L^?1. The volumetric and gravimetric methane-storage capacities at 65 bar and 298 K are approximately 180 v_STP/v and 0.27 g g^?1, respectively.

Full text of DOI:10.1002/chem.201402895

DOI: 10.1002/chem.201402895
Communication
&
Surface Chemistry
Water-Stable Zirconium-Based Metal–Organic Framework Material
with High-Surface Area and Gas-Storage Capacities
Oleksii V. Gutov,[a] Wojciech Bury,[a, b] Diego A. Gomez-Gualdron,[c] Vaiva Krungleviciute,[d, e]
David Fairen-Jimenez,[f] Joseph E. Mondloch,[a] Amy A. Sarjeant,[a] Salih S. Al-Juaid,[g]
Randall Q. Snurr,*[c] Joseph T. Hupp,*[a] Taner Yildirim,*[d, e] and Omar K. Farha*[a, g]
board applications include thermal, chemical, and mechanical
Abstract: We designed, synthesized, and characterized
a new Zr-based metal–organic framework material, NU-
1100, with a pore volume of 1.53 ccgÀ1 and Brunauer–
Emmett–Teller (BET) surface area of 4020 m2gÀ1; to our
knowledge, currently the highest published for Zr-based
MOFs. CH4/CO2/H2 adsorption isotherms were obtained
over a broad range of pressures and temperatures and are
in excellent agreement with the computational predic-
tions. The total hydrogen adsorption at 65 bar and 77 K is
0.092 ggÀ1, which corresponds to 43 gLÀ1. The volumetric
and gravimetric methane-storage capacities at 65 bar and
298 K are approximately 180 vSTP/v and 0.27 ggÀ1, respec-
tively.
stability (required for damage-free pelletization of the adsorb-
ent; pelletization lowers back pressure during tank filling,
thereby facilitating more rapid filling).
Over the last decade, significant progress has been made to-
wards building new classes of MOFs with desired material
characteristics. To a significant degree, MOFs can now be con-
sidered as programmable.[9] This circumstance has been
achieved by tailoring the pore geometry and volume, surface
area, and density of MOFs by the incorporation of different
linkers and metal centers. Control over these parameters is cru-
cial for constructing materials with high-capacity gas uptake,
as well as stability. However, most known MOFs are not suffi-
ciently stable to allow their application for gas storage in the
presence of water.[10] To overcome this problem, we targeted
Zr-based MOFs. These materials are known to possess high
chemical and mechanical stability due strong ionic bonding
between Zr4+ and carboxylate oxygen atoms.[11–15] However, Zr
MOFs have been much less extensively investigated for hydro-
gen or methane storage than have many other MOF families.
Recent studies have demonstrated the feasibility of tuning
the porosity of Zr-based MOFs by selective linker removal,[16,17]
control over the framework topology, or ligand modifica-
tions.[18] These studies suggest that appropriate design of Zr
MOFs can lead to materials with high surface area, a feature of
exceptional importance for hydrogen storage at low tempera-
tures.[6] Reticular synthesis, a methodology based on systemat-
ic extension of organic linkers between inorganic nodes, is the
first choice approach for constructing MOFs with higher sur-
Well-defined metal–organic frameworks (MOFs) featuring mo-
lecular-scale pores and high internal-surface areas constitute
a growing and remarkable chemically diverse class of materials
of potential utility in a wide range of applications including
catalysis,[1,2] gas separation,[3,4] sensing,[5] and storage.[6,7,8] In
particular, MOFs have attracted much interest for on-board hy-
drogen or methane storage in vehicles. Both methane and hy-
drogen are promising candidates as replacements for gasoline
(petrol). However, their compact storage in molecular form, es-
pecially in the case of hydrogen, remains a great challenge.
Sorption or cryosorption in nanoporous materials is a promising
way to lower the pressure required for storage of a given deliv-
erable quantity of gas. Further practical requirements for on-
[a] Dr. O. V. Gutov,+ Dr. W. Bury,+ Dr. J. E. Mondloch, Dr. A. A. Sarjeant,
Prof. Dr. J. T. Hupp, Prof. Dr. O. K. Farha
E-mail: taner@seas.upenn.edu
[e] Dr. V. Krungleviciute, Prof. Dr. T. Yildirim
Department of Chemistry and International Institute for Nanotechnology
Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (USA)
E-mail: j-hupp@northwestern.edu
Department of Materials Science and Engineering
University of Pennsylvania, Philadelphia, PA 19104 (USA)
[f] Dr. D. Fairen-Jimenez
o-farha@northwestern.edu
[b] Dr. W. Bury+
Department of Chemical Engineering and Biotechnology
University of Cambridge, Pembroke Street, Cambridge CB2 3RA (UK)
Department of Chemistry, Warsaw University of Technology
Noakowskiego 3, 00-664 Warsaw (Poland)
[g] S. S. Al-Juaid, Prof. Dr. O. K. Farha
Department of Chemistry, Faculty of Science
[c] Dr. D. A. Gomez-Gualdron, Prof. Dr. R. Q. Snurr
Department of Chemical & Biological Engineering
Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (USA)
E-mail: snurr@northwestern.edu
King Abdulaziz University, Jeddah (Saudi Arabia)
[+] These authors contributed equally to this work.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201402895.
[d] Dr. V. Krungleviciute, Prof. Dr. T. Yildirim
NIST Center for Neutron Research
National Institute of Standards and Technology
Gaithersburg, MD 20899 (USA)
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face areas and pore volumes than the prototypical structure in
a MOF series. We sought to utilize this approach to design
a new high surface area Zr MOF based on the ftw (4,12-con-
nected net) topology.[19]
Such an arrangement helps to compensate the small deviation
of the linker periphery from a perfect square geometry
(length-to-height ratios of the ligand carbon core are 0.96 and
0.97 in the crystal structures of L4H and NU-1100, respectively).
The measured PXRD pattern of the NU-1100 sample is in ex-
cellent agreement with the simulated pattern from single-crys-
tal-structure data, confirming the single-phase nature of the
bulk sample (Figure 2a). Thermal gravimetric analysis (TGA) of
the “as synthesized” material showed 60% weight loss, corre-
sponding to an equivalent accessibility by solvent molecules
(Figure S5.3 in the Supporting Information). These initial results
demonstrated the highly porous nature of the studied materi-
al. A TGA measurement of the NU-1100 sample activated at
1208C revealed stability up to 5008C (Figure S5.3 in the Sup-
porting Information). A small weight loss was observed above
approximately 2008C for both “as synthesized” and desolvated
Herein, we designed and synthesized a highly porous Zr
12+
MOF, NU-1100, based on Zr6O4(OH)4
clusters and a pyrene-
based tetratopic ligand 4-[2-[3,6,8-tris[2-(4-carboxyphenyl)-
ethynyl]-pyren-1-yl]ethynyl]-benzoic acid (L4H).
Two major design considerations in selecting the linker
were: 1) the ligand should exhibit planar geometry to make
the connectivity motif required for the ftw topology possible;
and 2) the relative dimensions of the linker should be such
that the four carboxylates define a rectangle that closely ap-
proximates a square, thereby enable the formation of cube-like
boxes upon coordination to nodes. With this in mind, we de-
signed ligand L4H and computationally tested the possibility of
its incorporation (as L4À) into the ftw topology. The initial
model of the NU-1100 structure was optimized by applying
a procedure based on molecular energy minimizations de-
scribed previously.[7] The resulting model demonstrated that
L4À can form a MOF with the desired topology without serious
distortion of bond lengths and angles (Figure S3.1 in
the Supporting Information).
samples, corresponding to the elimination of water molecules
12+
from Zr6O4(OH)4
nodes.[16]
Computationally, NU-1100 was predicted to have a large
surface area and pore volume with high capacities for sorption
of N2, H2, CH4, and CO2. To validate these predictions, we have
The ligand L4H was synthesized in four steps, in-
cluding Sonogashira coupling reactions, followed by
saponification of the resulting tetraester (Figure 1a,
for synthetic details, see the Supporting Information).
The structure of L4H was confirmed by single-crystal
X-ray diffraction studies, which revealed the planar
geometry of the molecules resulting in dense pack-
ing in the crystal structure (Figure S4.1 in the Sup-
porting Information), which is commonly observed
for conjugated systems.[20,21] Solvothermal reaction of
L4H, ZrOCl2·8H2O and benzoic acid (used as a modula-
tor) in N,N’-dimethylformamide (DMF) at 1208C gave
a material with a powder X-ray diffraction (PXRD) pat-
tern similar to that simulated for our preliminary
computational model (Figure S3.2 in the Supporting
Information), indicating the formation of a structure
with the targeted ftw topology. Single crystals of NU-
1100 were obtained, and the structure was analyzed
by means of single-crystal X-ray diffraction studies.
The sample was found to have Im-3 space group
with an ftw topology;[19] to our knowledge, this rep-
resents the first example of isoreticular extension of
the ftw topology. The structure of NU-1100 consists
12+
of 12 connected Zr6O4(OH)4
nodes linked by
planar tetratopic molecules of L4À to form two types
of pores (Figure 1b and c). Ligand orientation is dif-
ferent in adjacent, rectilinear and nearly cubic, boxes,
with two possible combinations of the box faces that
finally form a “supercube” (Figure 1c and d). Alternat-
ing orientations of the linker molecule in the crystal
structure demonstrated a way for a twofold symmet-
rical ligand to be incorporated into a topology that,
in principle, requires fourfold symmetrical ligands, re-
Figure 1. a) Scheme for L4H synthesis. b),c) Structural elements and crystal packing of
NU-1100 (Zr atoms are shown as purple spheres, O atoms as yellow spheres, and carbon
skeleton as gray sticks. Dark pink and light blue spheres occupy two major pore types in
the crystal. d) Schematic representation of NU-1100 supramolecular structure as a super-
sulting in a highly symmetric cubic space group. position of two different cubes (red and blue).
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benchmark MOFs, such as NU-100 and MOF-177, are
based on copper paddlewheels or Zn4O clusters,
which are not as stable as the Zr-based NU-1100. Hy-
drogen uptake drops rapidly with increasing temper-
ature. Nevertheless, NU-1100 showed a non-negligi-
ble total uptake of 0.012 ggÀ1 at 298 K and 65 bar.
Additionally, NU-1100 exhibited significant CO2
uptake at high pressures. The maximum CO2 uptake
at 220 K is 37.3 mmolgÀ1, which gives a pore volume
of 1.42 ccgÀ1 (7% lower than that derived from nitro-
gen and methane). The CO2 uptake at room tempera-
ture and 30 bar is approximately 26.2 mmolgÀ1, cor-
responding to 70% of the total pore volume.
Figure 2. a) PXRD patterns of NU-1100 after different treatments in comparison to the
simulated pattern. b) N2 adsorption isotherms of activated NU-1100 at 77 K before and
after immersion in water.
Methane-adsorption isotherms of NU-1100 are
shown in Figure 3. We obtained a maximum uptake
of approximately 404 vSTP/v (38.6 mmolgÀ1) at 125 K.
thermally activated a sample of NU-1100 and studied its po-
rosity by collecting nitrogen isotherms at 77 K, which were ob-
tained independently at Northwestern University (NU) and the
National Institute of Standards and Technology (NIST; for de-
tails, see the in the Supporting Information and Figure S5.4).
Temperature-dependent high-pressure adsorption measure-
ments were performed at NIST by using a computer-controlled
Sievert apparatus, the details of which have been published
elsewhere.[22] The experimental isotherms and resulting BET
surface areas obtained at NU (Figure S5.7 in the Supporting In-
formation) and NIST are very similar: 4020 m2gÀ1 and
4060 m2gÀ1, respectively. These numbers are also in good
agreement with the calculated value of 4333 m2gÀ1
(Figure S5.8 in the Supporting Information) and represent, to
our knowledge, the highest reported to date for Zr-based
MOFs. The pore volume of NU-1100, derived from the ob-
tained N2 isotherm, is 1.53 ccgÀ1, which is lower than the cal-
culated value of 1.67 ccgÀ1 (78.1% porosity) by PLATON.[23] The
pore-size distributions extracted from simulated and experi-
mental isotherms by using the DFT method (Figure S5.6 in the
Supporting Information) are in good agreement and showed
the two pore types observed in the NU-1100 crystal structure
(Figure 1c).
This value effectively corresponds to the upper limit for the
amount of gas that can be adsorbed under very high external
pressures at ambient temperature. The observed maximum
CH4 uptake gave a pore volume of 1.54 ccgÀ1 (assuming liquid
methane density at 125 K), which is in excellent agreement
Besides its high thermal stability, NU-1100 showed excellent
stability against water, retaining its crystallinity and full porosi-
ty following soaking in liquid water for 24 h (Figure 2).
Figure 3 shows CH4, CO2, and H2 adsorption isotherms over
a wide range of pressures and temperatures. Low-temperature
adsorption-isotherm data are indispensable, because they pro-
vide information on the maximum gas-storage capacity of the
material. The excess H2 isotherm at 77 K (Figure S6.1 in the
Supporting Information) showed a shallow maximum uptake
of 0.062 ggÀ1 near 45 bar and a slight decrease to 0.06 ggÀ1 at
65 bar. Consistent with this nearly flat excess isotherm, the
total isotherm does not saturate with increasing pressure,
reaching a very high value of 0.092 ggÀ1 at 65 bar (the highest
pressure examined). The corresponding volumetric uptake is
43 gLÀ1, among the highest values reported to date for H2
storage (i.e., 35 gLÀ1 for PCN-68,[24] 36 gLÀ1 for MOF-200,[8]
41 gLÀ1 for MOF-210,[8] 47 gLÀ1 for NU-100,[7] and 49 gLÀ1 for
NU-111[25] and MOF-177[26]). It is important to note that these
Figure 3. Total gravimetric gas-uptake isotherms for NU-1100 at various
temperatures. The lines with filled circles are experimental data, whereas the
solid lines are simulated isotherms by using the Dreiding force field.
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with the nitrogen pore volume. This suggests that methane is
able to access most of the pores in NU-1100 that are accessi-
ble to nitrogen at 77 K. The material has high volumetric and
gravimetric methane-storage capacities at 65 bar and 298 K of
approximately 180 vSTP/v and 0.27 ggÀ1, respectively. Ultimately,
the deliverable methane capacity determines the driving range
of a natural-gas vehicle (NGV). In this case, it is important for
a porous material to have low capacity in the approximately
5 bar range, and high capacity in the 60–70 bar range. The ad-
sorption isotherm of NU-1100 has a relatively shallow gradient
at low pressure; taking 5 bar as the specific lower-pressure
limit and 65 bar as the upper limit, the volumetric deliverable
capacity of NU-1100 is 156 vSTP/v at 298 K. This value is lower
than that of HKUST-1 (190 vSTP/v) and similar to other promis-
ing methane storage MOFs, such as UTSA-20 (170 vSTP/v) and
PCN-14 (157 vSTP/v).[22] However, the advantages that NU-1100
can offer are: 1) high gravimetric deliverable capacity
(0.24 ggÀ1), which is higher than in the abovementioned
MOFs: 56% higher than in HKUST-1 (0.154 ggÀ1), 75% higher
than in PCN-14 (0.136 ggÀ1), and 78% higher than in UTSA-20
(0.134 ggÀ1); 2) high thermal stability; and 3) high water stabili-
ty compared to the abovementioned MOFs. Simulated iso-
therms for CH4, CO2, and H2 are in good agreement with the
experimental data (Figure 3); however, there is a systematic
overprediction of adsorption at all temperatures.[27]
tion measurements, NU-1100 demonstrated high stability
against water. The total volumetric hydrogen adsorption at
65 bar and 77 K is 43 gLÀ1 (0.092 ggÀ1), which places it among
the best performing MOFs for hydrogen storage at low tem-
peratures. The methane volumetric deliverable capacity of NU-
1100 between 65 and 5 bar is approximately 160 vSTP/v, which
is comparable to those of the most promising methane-stor-
age materials, but its gravimetric deliverable capacity
(0.24 ggÀ1) is significantly higher. These results, together with
the possibilities to tune the porosity by ligand extension, es-
tablish NU-1100 as a promising platform to further improve
gas-sorption capacities in a highly stable MOF structure.
Acknowledgements
O.K.F., J.T.H., and R.Q.S. thank DOE ARPA-E and the Stanford
Global Climate and Energy Project for support of work relevant
to methane and CO2, respectively. T.Y. acknowledges support
by the U.S. Department of Energy through BES Grant No. DE-
FG02-08ER46522. W.B. acknowledges support from the Foun-
dation for Polish Science through the “Kolumb” Program. D.F.J.
acknowledges the Royal Society (UK) for a University Research
Fellowship. This material is based on work supported by the
National Science Foundation (grant CHE-1048773).
Importantly, we have tested the cycling stability of NU-1100.
Upon multiple cycles of methane adsorption/desorption,
which are shown in Figure S6.7 in the Supporting Information,
NU-1100 showed no evidence for sample degradation (as was
evident from the straight line fit with zero slope (green-dashed
line)). The variation of the total adsorption at 65 bar is less
than Æ2%, which is within the experimental error of our
measurements.
Keywords: gas storage
frameworks · methane · zirconium
·
hydrogen
·
metal–organic
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Received: April 1, 2014
Published online on August 14, 2014
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