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REVIEW
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The current status of hydrogen storage in metal–organic
frameworks—updated†
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Published on 15 June 2011 on http://pubs.rsc.org | doi:10.1039/C1EE01240A
Julian Sculley, Daqiang Yuan* and Hong-Cai Zhou*
Received 28th February 2011, Accepted 10th May 2011
DOI: 10.1039/c1ee01240a
Hydrogen storage in metal–organic frameworks (MOFs), or porous coordination polymers, has been
extensively investigated in the last two years and this review is to serve as an up to date account of the
recent progress. The effects of MOF sample preparation and activation, functionalization (including
post-synthetic), catenation, unsaturated metal sites, metal doping and spillover have been discussed
using recent examples. In addition to a condensed reference table of all recently reported MOFs for
hydrogen storage, future directions are discussed based on promising new materials and reported
computational analyses.
1. Introduction
The current status of hydrogen storage in metal–organic frameworks (MOFs),1 the predecessor to this review, was published
two years ago. Since then slightly more than 130 new MOFs
related to hydrogen storage have appeared in the chemical
literature. This revisited review builds directly on the framework
of the first one and is intended to stand on its own merits for
readers already familiar with the field but to be used in tandem
with the first one by those with a less detailed background. In this
review, we will focus on the most recent two years of progress in
hydrogen storage in MOFs.
The issues of energy sourcing, including fossil fuel use, climate
change, and sustainable energy generation have prompted the
search for alternative clean energy carriers to supplement the
current fuel supplies. Among various alternatives, hydrogen
stands at the forefront due to its clean combustion and high
Department of Chemistry, Texas A&M University, College Station, Texas,
77842, USA. E-mail: dyuan@mail.chem.tamu.eu; zhou@mail.chem.tamu.
edu; Fax: +1 979 845-1595; Tel: +1 979 845-4034
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c1ee01240a
gravimetric energy density. Safe and effective hydrogen storage is
widely recognized as a critical enabling technology for
a ‘Hydrogen Economy’ in the 21st century. In the last decades, the
research of hydrogen storage has witnessed explosive development and rapid progress. Scientists are looking for novel candidate materials which can hold sufficient hydrogen in terms of
gravimetric and volumetric densities. The promising candidate
methods include chemical storage (metal hydrides, complex
metal hydrides, synthesized hydrocarbons, ammonia, amine
borane complexes, formic acid, imidazolium ionic liquids,
phosphonium borate, and carbonite substances), and physical
storage (cryo-compressed, carbon nanotubes, activated carbon,
glass capillary arrays, glass microspheres, keratine, clathrate
hydrates, porous polymers, doped polymers, covalent organic
frameworks (COFs), and MOFs).2 The emergence of a large
number of relevant reviews reflects that the field of hydrogen
storage materials research is a center of interest.2–8 However,
considering all key factors including high gravimetric and volumetric hydrogen density, thermodynamics, and fast charge/
release kinetics, except for cryogenic liquid-hydrogen storage, no
other technology can meet the US Department of Energy (DOE)
hydrogen storage targets set in 2003. In April 2009, the DOE set
Broader context
Hydrogen has the potential to be the primary vector of energy. This clean fuel has attracted so much attention because of its high
energy density, but also because of the technological difficulties involved with storing and releasing it. Metal–organic frameworks
(MOFs) have provided enticing solutions to both of these problems because of the physisorptive nature of the interaction. The
record-breaking storage capacities, particularly in the last two years, and quick release kinetics have helped to keep MOFs as a frontrunner in the hydrogen storage field. Advances in bridging the gaps between physi- and chemisorptive materials, such as metal
hydrides, have also provided dramatic boosts in hydrogen uptake capacities. Although many challenges still exist in this field, the
advances in the last two years have been catalyzed by novel approaches and record breaking materials, providing researchers with an
even more exciting future.
This journal is ª The Royal Society of Chemistry 2011
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the new targets for on-board hydrogen storage systems: 0.045 kg
kg1 for system gravimetric capacity and 0.028 kg L1 for system
volumetric capacity by the year 2010, and 0.055 kg kg1 and
0.040 kg L1 by 2015 (Table 1).9 It is important to note that the
units for the revised DOE gravimetric targets are in units of mass/
mass instead of previous wt%. The unit of wt% is equal to (mass
of adsorbed H2)/(mass of adsorbed H2 + mass of host), however,
it has unfortunately been frequently misused by neglecting the
second term in the denominator, which leads to complications in
comparing hydrogen uptake capacities of different materials.
Therefore, it is highly necessary and important that the revised
DOE targets’ units of kg kg1 and kg L1 be used for gravimetric
capacity and volumetric capacity, respectively, when reporting
hydrogen uptakes in porous materials. Due to the inconsistency
of units and low frequency of reporting volumetric data, we have
chosen to compare the MOFs on a gravimetric basis, as this
fulfills the purpose of comparing one material to another.
2. MOFs as physisorbent materials for hydrogen
storage
With the merits of high crystallinity, purity, high porosity and
controllable
structural
characteristics,
metal–organic
Julian Sculley was born in Birkenfeld, Germany in 1987. He
received his BS (2009) from
Virginia Military Institute.
After that he joined Professor
Hong-Cai Zhou’s group as
a graduate student at Texas
A&M University. His research
interests include carbon capture
related gas separation and postsynthetic modification of porous
frameworks to increase sorbent
interactions.
Julian Sculley
Daqiang Yuan was born in
Anhui, China in 1976. He
received his BS (1999) and MS
(2002) from Beijing Normal
University, and his PhD (2005)
in Physical Chemistry from
Fujian Institute of Research on
the Structure of Matter, Chinese
Academy of Sciences under the
supervision of Professor Maochun Hong. Since then, he has
been working as a Research
Assistant in Prof. Maochun
Daqiang Yuan
Hong’s group. He joined
Professor Hong-Cai Zhou’s
group as a Postdoctoral Associate (2007 until now). His research interests include the rational
design and synthesis of metal–organic frameworks and their
application in gas storage.
Energy Environ. Sci.
frameworks have proven to be a very promising candidate in the
field of hydrogen storage.10–19 In 2003, Yaghi and coworkers
reported the first MOF-based hydrogen storage result.20 Since
then, MOFs have attracted worldwide attention in the area of
hydrogen energy, particularly for hydrogen storage.1,21–29 The
over 1300 hits when searching ‘‘metal–organic framework’’ and
‘‘hydrogen storage’’ on ISI Web of Knowledge and the significant
contributions to this number in the last two years shows that the
area is receiving a concentrated interest from the scientific
community to instigate MOFs as the means to deliver hydrogen
to the world (Fig. 1). Table 2 is an up-to-date summary of the
new MOF materials that have been investigated for hydrogen
adsorption.
It should be pointed out that the decisive effect of the material
density on the volumetric hydrogen capacity of MOFs must be
addressed. There are two criteria for the sorbent’s hydrogen
storage capacity in DOE targets for on-board hydrogen storage
systems: gravimetric capacity and volumetric capacity. Usually,
the gravimetric capacity of MOFs may accurately and directly be
extracted from experimental measurements. However, in most
literature, the amount of hydrogen adsorbed has been recalculated converting gravimetric data to volumetric units using the
crystal density of MOFs. It is obvious that this will give exaggerated volumetric hydrogen storage values because the crystal
density does not include the inter-particle space.30 For example,
the tap density (i.e. filling and vibrating a container with a known
sample weight and measuring the volume) for MOF-5 is 0.3 g
cm3 which is within the typical values for a MOF powder
(0.2–0.4 g cm3) and is significantly lower than the crystal
density. MOF-5 presents a hydrogen uptake of 15 g L1 using the
tap density, which is almost half of the calculated value of 30 g
L1 (using the crystal density). The density increases in the
following sequence: tap density < packing density < crystal
density < true density (must be measured using a helium
pycnometer). The type of the density used should be specified,
giving details about the experimental procedure used to measure
it. The use of the tap density of MOFs or its packing density
(same as tap density except inducing a pressure of 415 kg cm2) is
strongly recommended for converting gravimetric to volumetric
data, because they both take particle volume, internal pore
volume and inter-particle space volume into account.
Hong-Cai Zhou
Hong-Cai ‘‘Joe’’ Zhou obtained
his PhD in 2000 from Texas
A&M University under the
supervision of F. A. Cotton.
After a postdoctoral stint at
Harvard University with R. H.
Holm, he joined the faculty of
Miami University, Oxford in
2002. Since the fall of 2008, he
has been a Professor of Chemistry at Texas A&M University.
His research interest focuses on
hydrogen/methane storage and
gas separation that are relevant
to clean energy technologies.
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Table 1 Revised DOE targets for on-board hydrogen storage systems
Storage parameter
Units
2010
2015
Ultimate
System gravimetric capacity net useful
energy/max system mass
System volumetric capacity net useful
energy/max system volume
Min/max delivery temperature
Cycle life (1/4 tank to full)
Max delivery pressure from storage system
System fill time (for 5 kg H2)
Fuel purity (H2 from storage)
kg H2 per kg system
0.045
0.055
0.075
kg H2 per L system
0.028
0.040
0.070
C
Cycles
Atm (abs)
min (Kg H2 per min)
% H2
40/85
1000
100
4.2 min (1.2 kg min1)
99.99 (dry basis)
40/85
1500
100
3.3 min (1.5 kg min1)
40/85
1500
100
2.5 min (2.0 kg min1)
Table 2 is to serve as a quick reference to all of the materials
synthesized in the last two years; an in depth look at selected
materials is presented in the following sections. Of particular
note, in terms of a quick glance at recent advances in the field is
MOF-210 (Zn4O(bte)4/3(bpdc)) which currently holds the records
for highest BET and Langmuir surface areas with 6240 and
10 400 m2 g1 respectively. Although NU-100 (PCN-610; Cu3
(ttei)) falls slightly short of the BET surface area record (6143 m2
g1), it surpasses all previously synthesized materials with an
excess hydrogen storage capacity of 9.05 wt% at 56 bar. MOFs
with high unsaturated sites have also shown promise, particularly
regarding the heats of adsorption at low coverage. With the
unsaturated CoII sites of SNU-15, Suh and coworkers have achieved the highest adsorption enthalpy with 15.1 kJ mol1.
As it can already be deduced from this introduction, there is
a need for standardized terminology, nomenclature and methods
of calculation within this rather new interdisciplinary research
field. An attempt to fix this problem, largely because of the extent
of this rapidly growing field and the interest of the chemical
industry, an IUPAC project final report regarding some of these
issues will be published in 2011.115 The authors would further like
to advise researchers to adhere to guidelines and standards of
calculating weight percent, BET surface area heats of adsorption
etc. as this will aid when comparing new materials.
3. Factors influencing hydrogen uptake
The control over the construction of MOFs, compared with that
of other hydrogen storage materials, grants a quasi-infinite
Fig. 1 Publications with topics ‘‘metal–organic framework’’ and
‘‘hydrogen storage’’(source: ISI Web of Knowledge in Feb 2011).
This journal is ª The Royal Society of Chemistry 2011
number of possibilities in terms of material design. The ability to
tune ligands in terms of functional groups or post-synthetic
modification, as well as the variety of metal clusters has provided
a myriad of materials as the field has matured. Some of the
methods used to improve the hydrogen uptake capacities of
MOFs in the last two years are discussed below.
3.1.
Sample preparation and activation
In hydrogen uptake studies in MOFs, sample activation has been
recognized as a key to obtain repeatable and reliable data. In
traditional MOF sample pre-treatment procedures, samples were
soaked in low boiling point solvents (such as CH2Cl2, CHCl3,
MeOH, EtOH, etc.) to exchange and remove high boiling point
solvents (such as DMF, DMA, DMSO, etc.) which typically
occupy pores and channels of as-synthesized MOFs. The lower
boiling point guest solvent is evacuated under vacuum or by mild
heating. The limitations to this strategy have become clear in
some MOFs with very high porosity, where pore performance is
reduced because the surface tension will drive the pores to
collapse. Recently, two new techniques, supercritical drying and
freeze drying, were shown to drastically improve pore performance as well as provide a route to previously inaccessible
materials.116,117
In the supercritical activation, the solvent (providing that it is
miscible with liquid CO2) is replaced by supercritical carbon
dioxide (sc-CO2) under mild conditions (temperature and pressure above 31 C and 73 atm) and removed from the porous
material by depressurization without crossing the liquid–gas
phase boundary. This mild activation eliminates the discontinuity in density when a liquid crosses into the gas phase, thus
eliminating deleterious effects such as surface tension which can
lead to pore blockage and strain that causes framework collapse.
Hupp and coworkers successfully maximized gas-accessible
specific surface area (SSA) of four MOFs by using a supercritical
drying procedure. IRMOF-16 for example, showed a 400%
increase compared to the solvent-exchanged sample.118 Other
examples of enhanced H2 uptake capacities in MOFs have been
presented by Hupp’s record holding NU-100 with a capacity of
9.05 wt% at 77 K and Yaghi’s MOF-210 with a capacity of
7.92 wt%.80,94
The second technique, freeze drying, works by similar principles. By sublimating a solvent, such as benzene, it is possible to
avoid the liquid phase and the corresponding destructive effects
of surface tension. Lin and coworkers showed that freeze drying
tripled the Langmuir surface area over the conventional solvent
exchange method of activation; this was accompanied by an
Energy Environ. Sci.
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Table 2 Surface area, porosity, and hydrogen adsorption data for selected MOFs
Maximum H2 uptake per wt%d/g L1
SA/m2 g1
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Material
Be(bdc)
Be12(OH)12(btb)4
Cd(tpom)(SH)2
Cd2(tzc)2
Cd5(tz)9(NO3)3
CeZn1.5(oda)3
Co(1,4-bdp)
Co(dpt24)2
Co(Hbtc)(4,40 -bipy)
Co(imdc)(1,2-pda)
Co(mdpt24)2
Co(tpom)(SH)2
Co2(bdc)2(dabco)
Co4(H2O)4(mtb)2
Co4(ip)4(dabco)
CPM-5,[(CH3)2NH2]In9O2(btc)8
CPM-6, (CH3NH2)In9O2(btc)8
Cu(3,40 -bpdc)
Cu(3,40 -bpdc)
Cu(bpe)0.5(2,6-ndc)
Cu(diyb)
Cu(ttpm)2 0.7CuCl2
Cu(tzip)
Cu2(abtc)
Cu2(abtc)(dmf)2
Cu2(bdi)
Cu2(becb)
(R)-Cu3(dbtb)(H2dbtb)
Cu2(mtb)
Cu2(mtbdt)
Cu2(mtbet)
Cu2(mttc)
Cu2(pmtb)
Cu2(tcpom)
Cu3(4,40 -bipy)1.5(2,6-ndc)3
Cu3(btei)
Cu4(bbnip)
Cu4(denip)
Cu4(dhnip)
Cu4(R-dbtb)(S-dbtb)
(DMA+)In(Himdc)2
DMOF-1–NH2, Zn2(abdc)2(dabco)
DMOF-1–NH2–AMPh,
Zn2(abdc)0.74(babdc)1.26(dabco)
DUT-4, Al(OH)(2,6-ndc)
DUT-5, Al(OH)(bpdc)
DUT-6, Zn4O(2,6-ndc)(btb)4/3
DUT-9, Ni5O2(btb)2
Fe(tpom)S0.54(SH)1.46
Fe3[(Fe4Cl)3(btt)8
Ga6(btc)8
IRMOF-3, Zn4O(abdc)3
IRMOF-3–AM5, Zn4O
(abdc)0.42(habdc)2.58
IRMOF-3–AMPh-a, Zn4O
(abdc)2.04(babdc)0.96
IRMOF-3–AMPh-b, Zn4O
(abdc)1.68(babdc)1.32
IRMOF-3–AMPh-c, Zn4O
(abdc)0.9(babdc)2.1
IRMOF-3-URPh, Zn4O
(abdc)1.77(pubdc)1.23
JUC-62, Cu2(abtc)
K3(NO3)3In4(tzdc)4(1,2-dach)4
KHo(ox)2
Li(int)
LiIn(Himdc)2
MCF-19, Ni3(OH)(pba)3(2,6-ndc)1.5
Energy Environ. Sci.
Pore
volume/
cm3 g
H2 uptake at
77 Ka per 1
atm per wt%
4100
4400
764
339
338
1.44
1.24
1.6
1.03
0.55
0.75
2670
683
0.93
BET/
Langmiur
3500
4030
575
230
310
784
1382
767
1600
1802
580
596
541
435
2506
810
2357
1840
1560
262
555
1020
2718
382
3730
1605
2149
2285
0.134
0.82
0.165
0.97
0.258
3111
2020
2018
1725
272
641
1127
4485
507
113
4180
1841
2486
2650
2106
0.34
1.113
0.151
0.11
0.64
0.86
0.92
1369
913
1308
1306
1996
2335
617
2010
204.9
2639
1239
813
0.68
0.81
2.02
2.18
236.2
0.50c, 80 bar
2.29
1.8
2.5
2.1
0.8
0.95
2.08
1.69
1.66
1.29
2.3
0.47
1.51
1.21
11.9
5.5
5.3
5.7
62
62
63
64
33
65
66
61
61
9.2
8.8
6.0
15.1
6–7
2.26 (22.0), 10 bar
1.64 (12.2), 10 bar
0.96 (13.2), 15 bar
0.57
2.8
1.86
2.87
1.83
1.64
2.12
0.8
1.42
1.0
1.1
1.73
1.6
1.22
8.0
5.6
7.0
0.86, 34 bar
0.41
1.58
2.27
0.74
1.4–1.5
1.24
1.88
3.98 (36), 17 bar
3.4 (31.0), 20 bar
4.5
8.6
8.4
7.2
11.60
6.53
6.9
8.9
0.88 (13.4), 15 bar
5.0 (29.8), 30 bar
3.7
9.2
4.1 (30.0), 20 bar
5.22 (40.1), 50 bar
2.1 (16.6), 30 bar
3.3 (21.6), 40 bar
5.64 (23.1), 50 bar
5.85 (29.0), 40 bar
3.7 (30.6), 12 bar
1.1c, 100 bar
Ref.
31
32
33
34
35
36
37
38
39
40
38
33
41
42
43
44
44
45
45
46
47
48
49
50
50
51
52
53
54
55
55
54
56
57
46
58
59
59
59
53
60
61
61
11.4
13.5
2.05 (16.1), 60 bar
3.5c, 20 bar
0.18
DHads/
kJ mol1
5.5
0.67
0.22
338
579
2745
1063
298 K
5.0 (22.1), 24 bar
6.0 (27.0), 20 bar
1.34, 34 bar
3.1 (22.9), 30 bar
0.54
0.67
499
1015
2300
356
2722
733
931
77 K
2267
1.73
5.3
61
2052
1.73
5.7
61
1657
1.68
6.0
61
1940
1.54
5.7
61
395
4.71 (38.4), 40 bar
0.95c, 20 bar
0.70 (15.2), 16 bar
0.76 (7.9), 6.4 bar
0.19
324
190
2316
2667
0.95
0.91
1.56
0.35c, 80 bar
9.21
9.9
9.1
67
40
68
69
60
70
This journal is ª The Royal Society of Chemistry 2011
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Table 2 (Contd. )
Maximum H2 uptake per wt%d/g L1
SA/m2 g1
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Material
MFU-4l, Zn5Cl4(btdd)
Mg(tcpbda)
Mg3(bpt)2
MgIn2(Himdc)4
g-Mg3(O2CH)6
MIL-68(Ga), Ga(OH)(bdc)
MIL-68(In), In(OH)(bdc)
Mn(tpom)(SH)2
Mn2(bpybc)(ox)2
Mn3(4,40 -bipy)3Cr(CN)6
Mn4(bpdc)4
MOC-2, In8(Himdc)12
MOF-200, Zn4O(bbc)2
MOF-205, Zn4O(btb)4/3(2,6-ndc)
MOF-210, Zn4O(bte)4/3(bpdc)
Ni(cyclam)2(mtb)
Ni(Hbtc)(4,40 -bipy)
NOTT-100, Cu2(bptc)
NOTT-101, Cu2(tptc)
NOTT-102, Cu2(qptc)
NOTT-103, Cu2(ndip)
NOTT-105, Cu2(ftptc)
NOTT-106, Cu2(mtptc)
NOTT-107, Cu2(tmtptc)
NOTT-109, Cu2(tftptc)
NOTT-110, Cu2(phdip)
NOTT-111, Cu2(dhdip)
NOTT-112, Cu2(bbtei)
NOTT-116, Cu3(ptei)
PCN-12, Cu2(mdip)
PCN-120 , Cu2(mdip)
PCN-12-Si, Cu2(dmsdip)
PCN-14, Cu2(adip)
PCN-16, Cu2(ebdc)
PCN-160 , Cu2(ebdc)
PCN-19, Ni3O(adc)32(C4H10NO+)
PCN-20, Cu3(ttca)2
PCN-46, Cu2(bdi)
PCN-61, Cu3(btei)
PCN-610, NU-100, Cu3(ttei)
PCN-66, Cu3(ntei)
PCN-68, Cu3(ptei)
PCN-9(Co), Co4O(tatb)8/3
PCN-9(Fe), Fe4O(tatb)8/3
PCN-9(Mn), Mn4O(tatb)8/3
Sm(bdc)1.5(e-urea)
SNU-6, Cu2(bpndc)2(4,40 -bpy)
UMCM-150(N)1, Cu3(cpip)2
UMCM-150(N)2, Cu3(cpmip)2
UMCM-150, Cu3(bhtc)2
UMCM-152, Cu2(cptt)
UMCM-153, Cu2(cptt)
UMCM-1–NH2, Zn4(btb)4/3(abdc)
UMCM-1–NH2–AMPh, Zn4(btb)4/
3(abdc)0.24(babdc)0.76
UMCM-2, Zn4O(t2dc)(btb)4/3
UoC-10 , (H3O)Zn7(OH)3(bpdc)2
Zn(1,3-bdp)
Zn(1,4-bdp)
Zn(5-at)2
Zn(bpe)(tfbdc)3
Zn(miai)
Zn2(abtc)(dmf)2
Zn2(bpdc)2(bpee)
Zn2(bpndc)2(4,40 -bipy)
Zn2(btbz)
Zn2(cnc)2(dpt)
BET/
Langmiur
2750
714
795
837
120
1117
746
622
1410
1139
816
Pore
volume/
cm3 g
1.26
0.368
H2 uptake at
77 Ka per 1
atm per wt%
5200
820
1710
355.3
512
802
328
824
1420
10 400
6170
10 400
154
2425
1962
2800
2200
823
4200
2800
3500
4600
6033
1355
848
1057
262
2910
0.46
0.44
0.23 (1.7), 5 bar
1.37
0.71
0.72 (9.2), 45 bar
0.535
3.59
2.16
3.60
0.055
0.81
0.680
0.886
1.138
1.142
0.898
0.798
0.767
0.705
1.22
1.19
1.69
2.17
0.94
0.73
0.93
1.06
0.84
0.38
1.59
1.102
1.36
2.82
1.63
2.13
0.51
0.33
0.41
1.05
1.0
2.32
0.203
0.34
This journal is ª The Royal Society of Chemistry 2011
0.171
0.366
0.404
0.19
11.5
0.77
2.17
0.7
2.52c
2.46c
2.19c
2.56c
2.46c
2.24c
2.21c
2.28c
2.64c
2.56c
1.9
2.3
3.05
2.40
2.6
2.7
2.6
1.7
0.95
2.1
1.95
2.25
1.79
1.87
1.53
1.06
1.26
0.66
1.68
2.2
2.1
2.1
6.5
6.89 (16.4), 50 bar
6.54 (26.7), 45 bar
7.92 (21.2), 50 bar
1.25 (12.3), 40 bar
3.42 (27.6), 60 bar
3.86c, 20 bar
6.19c, 60 bar
6.72c, 60 bar
7.22c, 60 bar
5.12c, 20 bar
4.31c, 20 bar
4.27c, 20 bar
3.98c, 20 bar
5.43 (46.8), 55 bar
5.47 (45.4), 48 bar
7.07 (35.6), 35 bar
6.4 (27.8), 27 bar
4.42 (36.6), 50 bar
5.1 (38.8), 45 bar
2.9 (22.8), 45 bar
1.67 (15.93), 48 bar
6.2 (29.1), 50 bar
5.31 (34.7), 32 bar
5.87 (35.0), 33 bar
9.05 (27.8), 56 bar
6.25 (29.6), 45 bar
6.82 (28), 50 bar
4.87 (15.4), 70 bar
5.0 (32.8), 22 bar
4.9 (32.1), 22 bar
5.0 (32.8), 22 bar
5.7 (34.3), 25 bar
5.9 (36.7), 29 bar
1.35
1.54
483
1034
1370
342
5.0
9.5
7.5
9.0
b
2.46 (23.9), 40 bar
1.98 (20.0), 40 bar
3850
3730
6060
649
1161
2320
433.8
DHads/
kJ mol1
298 K
4.0 (23.3), 20 bar
1.08
1.3
0.91
1.0
353
4530
4460
6240
141
1590
1640
2316
2942
2929
2387
1855
1822
1718
2960
2930
3800
4664
1943
1577
2430
1753
2273
1760
723
3525
2500
3000
6143
4000
5109
1064
682
836
186
2590
3020
2980
2910
3480
3370
3917
3770
77 K
1.28
0.87
1.6
1.6
1.6
1.04
1.5
2.07
0.38
0.24
2.2
1.28
7.0
6.31
5.32
5.70
5.41
5.77
6.34
6.70
5.68
6.21
5.64
6.7
8.6
0.66 (3.74), 90 bar
0.78 (3.50), 90 bar
1.00 (4.10), 90 bar
7.20
6.36
6.1
6.22
6.09
10.1
6.4
8.7
7.74
7.8
7.8
7.8
4.6
5.2
6.4 (27.4), 46 bar
2.1 (24.0), 10 bar
4.7 (35.3), 40 bar
6.4
6.8
6.6
6.9
6.2
3.70 (37.8), 50 bar
1.82 (23.0), 70 bar
3.63 (40.2), 90 bar
7.24
8–10
8.1
7.85
Ref.
71
72
73
60
74
75
75
33
76
77
78
79
80
80
80
81
39
82
82
82
82
82
82
82
82
83
83
84
85
86
86
87
88
89
89
90
91
92
93
94
93
93
95
95
95
96
97
98
98
98
99
99
61
61
100
101
102
102
103
104
105
50
106
107
108
109
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Table 2 (Contd. )
Maximum H2 uptake per wt%d/g L1
SA/m2 g1
Material
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Zn2Ca(BTC)2
Zn4(ip)4(dabco)
Zn4(mip)4(dabco)
Zn4O(cbab)3
Zn4O(cbab)3
Zn4O(fma)3
Zn5(trza)6(tfbdc)2
Zn5Cl4(bbta)3
BET/
Langmiur
730
1609
1533
548
549
1120
1075
2420
2178
Pore
volume/
cm3 g
H2 uptake at
77 Ka per 1
atm per wt%
0.47
0.86
0.79
2.2
1.4–1.5
1.4–1.5
77 K
298 K
6–7
6–7
1.9 (9.7), 20 bar
1.6 (8.6), 20 bar
4.94 (42.2), 39 bar
1618
0.42
DHads/
kJ mol1
0.32 (2.6), 40 bar
0.4
1.62
4.2
8
Ref.
110
43
43
111
111
112
113
114
a
wt% ¼ 100 (weight of adsorbed H2)/(weight of MOF material + weight of adsorbed H2). b 308 K. c Absolute hydrogen uptake. d Calculated using
crystal density; 1,2-pda ¼ 1,2-propanediamine; 1,2-dach ¼ 1,2-diaminocyclohexane; 1,3-bdp ¼ 1,3-benzenedi(4-pyrazol-1-ide); 1,4-bdp ¼ 1,4-benzenedi
(4-pyrazol-1-ide); 2,6-ndc ¼ 2,6-naphthalenedicarboxylate; 2,7-ndc ¼ 2,7-naphthalenedicarboxylate; 3,40 -bpdc ¼ 3,40 -biphenyldicarboxylate; 4,40 -bipy
¼ 4,40 -bipyridine; 5-at ¼ 5-aminotetrazol-1-ide; abdc ¼ 2-aminobenzene-1,4-dicarboxylate; abtc ¼ azobenzene-3,30 ,5,50 -tetracarboxylate; adc ¼
anthracene-9,10-dicarboxylate; adip ¼ 5,50 -(9,10-anthracenediyl)di-isophthalate; babdc ¼ 2-benzamidoterephthalate; bbc ¼ 4,40 ,400 -(benzene-1,3,5triyl-tris(benzene-4,1-diyl))tribenzoate; bbnip ¼ 5,50 ,500 ,5000 -(2,20 -bis(benzoyloxy)-[1,10 -binaphthalene]-4,40 ,6,60 -tetrayl)tetraisophthalate; bbta ¼ benzo
[1,2-d:4,5-d0 ]bis([1,2,3]triazole)-1,5-diide; bbtei ¼ 5,50 ,500 -(benzene-1,3,5-triyltris(benzene-4,1-diyl))triisophthalate; bceb ¼ 5,50 -(1,3-phenylenebis
(ethyne-2,1-diyl))diisophthalate; bdc ¼ 1,4-benzenedicarboxylate; bhtc ¼ biphenyl-3,40 ,5-tricarboxylate; bpdc ¼ 4,40 -biphenyldicarboxylate; bpe ¼
1,2-bis(4-pyridyl)ethane; bpee ¼ 1,2-di(pyridin-4-yl)ethane; bpndc ¼ benzophenone-4,40 -dicarboxylate; bpt ¼ biphenyl-3,40 ,5-tricarboxylate; bptc ¼
3,30 ,5,50 -biphenyltetracarboxylate; bpybc ¼ 4,40 -([4,40 -bipyridine]-1,10 -diium-1,10 -diylbis(methylene))dibenzoate; btb ¼ benzene-1,3,5-tribenzoate;
btbz ¼ 4,40 ,400 ,4000 -benzene-1,2,4,5-tetrayltetrabenzoate; btc ¼ 1,3,5-benzenetricarboxylate; btdd ¼ bis(1,2,3-triazolo-[4,5-b],[40 ,50 -i])dibenzo[1,4]
dioxin; bte ¼ 4,40 ,400 -(Benzene-1,3,5-triyltris(ethyne-2,1-diyl))tribenzoate; btei ¼ 5,50 ,500 -(benzene-1,3,5-triyltris(ethyne-2,1-diyl))triisophthalate; btt ¼
1,3,5-benzenetristetrazolate; cbat ¼ 4-(4-carboxylatobenzamido)benzoate; cnc ¼ 4-carboxycinnamic; cpip ¼ 5-(5-carboxylatopyridin-2-yl)
isophthalate; cpmip ¼ 5-(5-carboxylatopyrimidin-2-yl)isophthalate; cptt ¼ 50 -(4-carboxylatophenyl)-[1,10 :30 ,100 -terphenyl]-3,400 ,5-tricarboxylate;
cyclam ¼ 1,4,8,11-tetraazacyclotetradecane; dabco ¼ 1,4-diazabicyclo[2.2.2]octane; dbi ¼ 5,50 -(buta-1,3-diyne-1,4-diyl)diisophthalate; dbtb ¼ 2,20 diethoxy-1,10 -binaphthyl-4,40 6,60 -tetrabenzoate; denip ¼ 5,50 ,500 ,5000 -(2,20 -diethoxy-[1,10 -binaphthalene]-4,40 ,6,60 -tetrayl)tetraisophthalate; dhdip ¼
5,50 -(9,10-dihydrophenanthrene-2,7-diyl)diisophthalate; dhnip ¼ 5,50 ,500 ,5000 -(2,20 -dihydroxy-[1,10 -binaphthalene]-4,40 ,6,60 -tetrayl)tetraisophthalate;
diyb ¼ 4,40 -(1,4-phenylene)bis(imidazol-1-ide); dmsdip ¼ 5,50 -(dimethylsilanediyl)diisophthalate; dpt ¼ 3,6-di-4-pyridyl-1,2,4,5-tetrazine; dpt24 ¼ 3(2-pyridyl)-5-(4-pyridyl)-1,2,4-triazolate; ebdc ¼ 5,50 -(1,2-ethynediyl)bis(1,3-benzenedicarboxylate); e-urea ¼ 2-imidazolidinone; fma ¼ fumarate;
ftptc ¼ 20 ,50 -difluoro-[1,10 :40 ,100 -terphenyl]-3,300 ,5,500 -tetracarboxylate; habdc ¼ 2-hexanamidoterephthalate; Himdc ¼ 1H-imidazole-4,5dicarboxylate; Himdc ¼ 4,5-imidazoledicarboxylate; ip ¼ isophthalate; int ¼ isonicotinate; mdip ¼ 5,50 -methylene-di-isophthalate; mdpt24 ¼ 3-(3methyl-2-pyridyl)-5-(4-pyridyl)-1,2,4-triazolate; miai ¼ 2-methylimidazolate-4-amide-5-imidate; mip ¼ 5-methylisophthalate; mtb ¼ methane
tetrabenzoate; mtbdt ¼ 3,30 ,300 ,3000 -(methanetetrayltetrakis(benzene-4,1-diyl))tetraacrylate; mtbet ¼ 4,40 ,400 ,4000 -((methanetetrayltetrakis(benzene-4,1diyl))tetrakis(ethyne-2,1-diyl))tetrabenzoate; mtptc ¼ 20 ,50 -dimethyl-[1,10 :40 ,100 -terphenyl]-3,300 ,5,500 -tetracarboxylate; mttc ¼ 400 ,400000 ,400000000 ,400000000000 methanetetrayltetrakis(([1,10 :40 ,100 -terphenyl]-4-carboxylate)); ndip ¼ 5,50 -(naphthalene-2,6-diyl)diisophthalate; ntei ¼ 5,50 ,500 -((nitrilotris(benzene4,1-diyl))tris(ethyne-2,1-diyl))triisophthalate; oda ¼ 2,20 -oxydiacetate; ox ¼ oxalate; pba ¼ 4-(pyridin-4-yl)benzoate; phdip ¼ 5,50 -(phenanthrene-2,7diyl)diisophthalate; pmtb ¼ diphenylmethane-3,30 ,5,50 -tetrakis(3,5-bisbenzoate); ptei ¼ 5,50 -((50 -(4-((3,5-dicarboxylatophenyl)ethynyl)phenyl)[1,10 :30 ,100 -terphenyl]-4,400 -diyl)bis(ethyne-2,1-diyl))diisophthalate; pubdc ¼ 2-(3-phenylureido)terephthalate; qptc ¼ quaterphenyl-3,3000 ,5,5000 tetracarboxylate; tatb ¼ 4,40 ,400 -s-triazine-2,4,6-triyltribenzoate; tcpbda ¼ N,N,N0 ,N0 -tetrakis(4-carboxyphenyl)-biphenyl-4,40 -diamine; tcpom ¼
tetrakis[4-(carboxyphenyl)oxamethyl]methane; tfbdc ¼ tetrafluoroterephthalate; tftptc ¼ 20 ,30 ,50 ,60 -tetrafluoro-[1,10 :40 ,100 -terphenyl]-3,300 ,5,500 tetracarboxylate; tmtptc ¼ 20 ,30 ,50 ,60 -tetramethyl-[1,10 :40 ,100 -terphenyl]-3,300 ,5,500 -tetracarboxylate; tpdc ¼ [1,10 :40 ,100 -terphenyl]-3,300 -dicarboxylate;
tpom ¼ tetrakis-(4-pyridyloxymethyl)methane; tptc ¼ terphenyl-3,300 ,5,500 -tetracarboxylate; trza ¼ 1,2,4-triazolate; ttca ¼ triphenylene-2,6,10tricarboxylate; ttei ¼ 5,50 ,500 –(((benzene-1,3,5-triyltris(ethyne-2,1-diyl))tris(benzene-4,1-diyl))tris(ethyne-2,1-diyl))triisophthalate; tz ¼ tetrazolate; tzc
¼ tetrazolate-5-carboxylate; tzdc ¼ 4,5-dicarboxylato-1,2,3-triazol-1-ide; tzip ¼ 5-(1H-tetrazol-1-yl)isophthalate.(refer to ESI† for more details).
increase in H2 uptake from 0.78 wt% to 1.42 wt% at 1 bar
and 77 K.54,55
3.2.
Surface area and pore volume
There has been some discussion about the correlation between
hydrogen uptake and various physical attributes of MOFs.
Hydrogen uptake seems to be proportional to heat of adsorption
at low pressures, surface area at moderate pressures and free
volume at high pressures. Various attempts to determine strong
correlations between these physical attributes and hydrogen
uptake at low and high temperatures over a range of pressures
have been made.25,119,120 Fig. 2 plots the roughly linear relationship between BET surface area or pore volume and the 77 K
saturation hydrogen uptake data for selected MOFs.
An empirical expression (eqn. (1)) can evaluate the contributions from BET surface area (SBET) and the pore volume (V) to
the limiting hydrogen sorption capacity of the MOF.25
Energy Environ. Sci.
N ¼ a SBET + b V
(1)
where N is the absorption of hydrogen, wt%; a is the mass of
hydrogen sorbed on 1 m2 of surface, g 100; SBET is BET
surface area, m2 g1; b is the density of hydrogen in the micropores, g cm3 100; V is the pore volume, cm3 g1. The coefficients a and b were determined by the simplex method by
P
P
minimizing the function R2 ¼ (Nexpt Ncalc)2/ (Nexpt)2. The
best fit for MOFs is obtained with a ¼ 2.1 103 (0.1 103)
(% H2), b ¼ 0.1 (0.02) (% H2) g cm3 (R2 ¼ 8.9 103).
On the basis of the empirical expression, the limiting hydrogen
sorption capacity for a new MOF can be predicted knowing only
the SBET and V parameters. D€
uren and coworkers developed
a simple method to calculate the accessible surface area of
MOFs.119,121 The accessible surface area is a geometric method to
determine the surface area of a MOF and it compares very well
with the BET surface area determined for good quality samples.
At the same time, the pore volume can be easily obtained using
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Fig. 2 Maximum hydrogen storage capacity versus BET surface area or pore volume of selected MOFs. The solid line shows the empirical linear fitting
results, where H2 wt% ¼ 3.0(4) + 8.1(9) 104 SBET. (1: SNU-6; 2: Be(bdc); 3: UMCM-150; 4: PCN-16; 5: PCN-46; 6: NOTT-110; 7: NOTT-111; 8:
PCN-61; 9: Be12(OH)12(btb)4; 10: PCN-20; 11: PCN-66; 12: NOTT-116; 13: UMCM-2; 14: MOF-205; 15: PCN-68, 16: MOF-200; 17: MOF-210; 18:
NU-100.)
PLATON software (calc void probe [1.8]).122 These data can thus
provide an easy route to screen samples and calculate hydrogen
sorption information about a synthesized MOF sample.
To date there have been a multitude of examples regarding the
effects of pore size and geometry of a framework on the surface
area and uptake capacity of a MOF.1,22,25,27,28 One method to
attempt to draw significant conclusions is by designing MOFs
with the same topology and varying only, for example, the
organic ligand, thus eliminating some variables (unsaturated
metal sites etc.) and focusing on differences in surface area and
pore volume in relation to hydrogen uptake. A prominent
example in terms of a systematic investigation into the effects of
these properties on the hydrogen uptake has been conducted on
copper containing NbO-type MOFs (Fig. 3a).50,51,67,82,92 Schr€
oder
and coworkers have synthesized the series of NOTT frameworks
(100 to 110), which are constructed from tetracarboxylate
ligands with dicopper paddlewheel SBUs to yield a framework
with two types of channels.82 The diameter of one of these
channels is primarily controlled by the length of the linker. By
extending the ligand length and thereby increasing the window
in NOTT-100 to 15.96 A
in NOTT-102 (Cu–Cu
size from 7.60 A
distance) they observed an increase in BET surface area from
1640 m2 g1 to 2942 m2 g1. The augmentation of pore size and
surface area resulted in a slight decrease in H2 uptake at low
pressures (2.59 wt% to 2.24 wt%) but a dramatic increase at 20
bar from 4.02 to 6.07 wt% in NOTT-102 (total uptake of 7.20 wt
% at 60 bar). The introduction of functional groups has also shed
some insight into the interaction potentials of H2 and the pore
surface, marked by slight enhancements at low coverage.82 Zhou
and coworkers constructed an NbO-type MOF via the in situ
generation of a polyyne-coupled di-isophthalate that shows
similar uptake at 60 bar (7.16 wt%) despite a slight reduction in
pore size and surface area; this can possibly be attributed to the
higher DHads of 7.2 kJ mol1.92 Other recent examples of NbOtype MOFs include the azobenzene linker used by Qiu and
coworkers resulting an uptake of only 4.71 wt% at 40 bar.67 Suh
and coworkers have recently published three NbO-type frameworks.50 The hydrogen uptakes of the copper–MOF with and
without unsaturated metal centers are 2.87 and 1.83 wt% (1 bar),
respectively, which correlates well with the zero-coverage
enthalpies of 11.60 and 6.53 kJ mol1. The isostructural zincpaddlewheel MOF was only observed with coordinated solvent
molecules and showed an uptake of 2.07 wt% and DHads of
7.24 kJ mol1.50
Increased ligand length has yielded MOFs with higher pore
volumes and surface areas, as well as a stepwise increase in H2
uptake at high pressure. The larger pore diameter has, however
had adverse effects on the uptake at low pressures as well as the
heat of adsorption at low coverage. The comparison between an
a- and b-phase of the NbO-type structure, conducted by Zhou
and coworkers, revealed that the b-phase (larger open channels)
showed a reduction in Langmuir surface area of 600 m2 g1 and
a corresponding drop in H2 uptake from 2.6 wt% to 1.7 wt% at
low pressures and 5.1 wt% to 2.9 wt% at high pressures.89
A strategy to augment the physical attributes of MOFs, using
mixed ligand systems for the synthesis of new frameworks, has
been employed by Matzger and coworkers.100 The resulting
UMCM-2 was constructed from a linear dicarboxylate,
Fig. 3 Connectivity of nbo, umt and rht(3,24)-coordinated nets.
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a trigonal planar ligand, and the familiar Zn4O cluster (Fig. 3b).
The reported BET surface area of 5200 m2 g1 was the highest
reported until recent literature from Yaghi and coworkers,80 but
the hydrogen data did not surpass that of MOF-177 at 6.9 wt%
(77 K and 46 bar).123,124 Using the same multi-ligand approach,
Kaskel and coworkers constructed a MOF with a H2 uptake
capacity of 5.64 wt% at 77 K and 50 bar.63
Yaghi and coworkers have constructed ultrahigh porosity
MOFs using a blend of methods (ligand extension, mixed
ligands, sc-CO2 drying).80 Extended tritopic ligands were used to
synthesize MOFs that are isoreticular to MOF-177 and mixed
ligand systems to synthesize MOFs that have a similar topology
to UMCM-2. MOF-210 has a BET surface area of 6240 m2 g1
and a hydrogen uptake of 86 mg g1 at 55 bar.
An approach to introduce multiple functional groups into the
same framework and determine the effects on a series of isostructural MOFs was the multivariate (MTV) functionality
approach used by Yaghi and colleagues.125 By introducing
multiple functional groups into the struts of the archetypal
MOF-5 framework, enhancements in H2 uptake of MTV-MOF5-AHI by a maximum of 84% over MOF-5 were observed.
Another synthetic route towards ultrahigh surface area
MOFs is to use a polyhedron based hierarchical assembly
(Fig. 3c).43,58,84,85,93,94 The MOFs with rht (3,24)-coordinated nets
are composed of hexatopic ligands (three isophthalate moieties
radiate from a central trigonal node) that form cuboctahedral
cages with copper paddlewheels which are connected to each other
through dendritic trigonal ligands.93 The idea behind this design is
that the 3,24 net cannot interpenetrate and the size of the cuboctahedral cages is essentially fixed, thus making the framework
stable. PCN-68, the largest MOF for which experimental data
could be obtained, in a series by Zhou and coworkers has
a hydrogen uptake capacity of 73.2 mg g1 at 50 bar (10.1 mg g1 at
298 K and 90 bar). Schr€
oder and coworkers have used the same
approach to construct NOTT-112 and NOTT-116 (same structure as PCN-68),84 the latter of which has an uptake capacity of
68.4 mg g1.85 Farha et al. reported the successful activation of
PCN-610 (designated as NU-100 in their paper) by sc-CO2
drying.94 NU-100 has a BET surface area of 6143 m2 g1 and holds
the hydrogen storage record with 99.5 mg g1 excess (at 77 K and
56 bar) and 164 mg g1 total uptake (70 bar).
Chun and coworkers reported an isoreticular series of MOFs,
using a similar polyhedron based building approach, made up of
isophthalate ligands and ZnII/CoII-paddlewheel SBUs which
were connected via DABCO linkers.43 The cobalt–MOF had
a slightly higher surface area (2722 vs. 2420 m2 g1).
3.3.
Interpenetration (catenation)
Catenation results in a reduction in pore volume when two
identical frameworks interpenetrate with each other. Constructing both catenated and non-catenated frameworks has
been used as a method to study the effects of pore size and
surface area.
A recent simulations study by Snurr and coworkers has shown
that catenation may be beneficial at low loadings because of the
reduced pore size and higher number of metal sites per unit
volume, both of which lead to higher heats of adsorption.126 At
high pressures however, the non-catenated structures have higher
Energy Environ. Sci.
uptake capacities due to the available free volume; these findings
are consistent with previously reported data.119 Liu et al. also
showed that interpenetration reduces hydrogen diffusivity, which
is directly related to free volume, by a factor of 2 to 3 at room
temperature.127
Investigations into the isomer pair of PCN-6 and PCN-60 have
been continued by analyzing the H2 interactions with the framework using inelastic neutron scattering (INS). The results showed
that the Cu paddlewheels are the first loading sites and have
comparable interaction energies in both isomers, however, at high
pressures, where the H2 primarily adsorbs around the linkers, the
catenated isomer (PCN-6) has significantly stronger interaction
energies explaining the significant uptake at high pressures of
PCN-6 (6.7 wt% excess uptake at 77 K and 50 bar).128 A recent
example of a two-fold interpenetrating framework, exhibiting
high H2 storage, is that of PMOF-3 synthesized by Lah and
coworkers. Although the hydrogen storage capacities are not
ground-breaking (3.4 wt% at 77 K and 20 bar), the thermal and
hydrothermal stability of this MOF which retains its crystallinity
after refluxing in water overnight, provides some evidence for the
advantages of interpenetration in new materials.52
Matzger and coworkers have explored the method of using
desymmetrized ligands to suppress interpenetration with the goal
of increased pore volumes in mind. UMCM-152 and -153 are
polymorphic frameworks, constructed from the same ligand and
metal SBU, showing similar surface areas and gas uptake
including high pressure H2 adsorption of 5.7 and 5.8 wt% (at 77
K) respectively.99 Other methods of eliminating catenation are
using temperature, concentration, bulky ligands and nets that
cannot interpenetrate.52,53,109,129–132
3.4.
Ligand structure and functionalization
Another example of using rational ligand design to modify
a structure is the expansion of the NbO-type series of frameworks designated NOTT-1xx.82 The two most recent additions,
NOTT-110 and NOTT-111 built upon the quaterphenyl3,30 ,5,50 -tetracarboxylate ligand of NOTT-102 (6.07 wt% at 77 K
and 20 bar) by introducing ligand curvature. The BET surface
areas and pore volumes showed only a moderate increase from
NOTT-102, but the low pressure H2 uptake capacities were
about 18% higher and the total uptake at 77 K and 20 bar
increased to 6.59 and 6.48 wt% for NOTT-110 and -111,
respectively. Expanding upon the work of HKUST-1 and
PCN-60 which use the familiar copper paddlewheel SBU and
trigonal planar ligands, Zhou and coworkers have recently
synthesized the twisted boracite structure designated PCN-20.91
The highly conjugated triphenylene-2,6,10-tricarboxylate ligand
was designed to provide more adsorption sites for hydrogen and
the intermediate pore size compared to the afore mentioned
structures was designed to maximize the surface interactions. The
resulting framework has a remarkable low pressure uptake
capacity of 2.1 wt% and a high pressure excess uptake of 6.2 wt%
(77 K), which is higher than that of the model systems. This
MOF clearly illustrates the importance of rational ligand design
in the synthesis of new structures that can push the limits.
The synthesis of zeolite-like MOFs with both a free amino
group and a free tetrazole nitrogen has only recently been
accomplished by Banerjee and coworkers.103 ZIFs with one
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Fig. 4 Scheme of postsynthetic modification.
functionality have previously been reported, however incorporation of both is difficult because the two free functional groups
compete for similar metal coordination environments. The
resulting MOF has shown significantly higher hydrogen uptake
than other members of the ZIF series at 1.6 wt% (77 K and 1 bar)
despite the comparatively low surface area.
Although postsynthetic modification of MOFs encompasses
everything from the removal of coordinated solvent molecules to
create unsaturated metal sites, to ion exchange, to doping with
metal nanoparticles, this section will focus on modification
through covalent bonds (Fig. 4). Cohen and coworkers have
modified three different MOFs containing free amino groups,
IRMOF-3, UMCM-1–NH2, and DMOF-1–NH2.61 Each
framework is built up from 2-amino-1,4-benzenedicarboxylate,
which can be modified to form amides and urea products
through a condensation between the free amino group and alkyl
anhydrides or isocyanates, respectively. The modified MOFs of
the parent IRMOF-3 showed higher heats of adsorption across
the entire coverage range and an increase from 1.51 wt% to 1.73
wt% in IRMOF-3-AMPh; this increase can also be quantified as
nearly 1.6 additional H2 molecules per formula unit. They
observed similarly enhanced uptakes in the modified MOFs
denoted UMCM-1-AMPh and DMOF-1-AMPh. The conclusion was drawn that aromatic substituents enhanced the
hydrogen uptake even at higher pressures compared to the
unmodified MOFs because of the additional binding site.
Hupp and coworkers postsynthetically modified the Zn nodes of
a MOF by fully activating the MOF (removing all of the coordinated DMF species) and coordinating a series of functionalized
pyridine ligands.108 The fully activated sample showed the highest
surface area and hydrogen sorption, but providing a general route
to modify the metal nodes could be useful in the future.
3.5.
Unsaturated metal sites
It has been shown that coordinatively unsaturated metal sites
show high hydrogen binding affinities and are in many cases the
first loading sites.21 Solvent or guest molecules can in some cases
be removed from the metal centers of MOFs without causing any
structural collapse. The series of MOFs CPO-27-M (also referred
This journal is ª The Royal Society of Chemistry 2011
to as MOF-74-M; where M ¼ Ni2+, Co2+, Mg2+, Zn2+) has been
investigated.133–137 CPO-27-Ni shows an initial adsorption
enthalpy of 13.5 kJ mol1, among the highest reported, by
monitoring the H–H stretching frequencies using VTIR.137 Zhou
et al. expanded on this work by adding the isostructural Mn2+
framework testing H2 storage at 77 K and calculating adsorption
enthalpies for the series.133 They reported a trend of increasing
binding energies of Zn < Mn < Mg < Co < Ni, which is closely
correlated with the cationic radius of the exposed metal site.133
Dietzel and coworkers confirmed these results although reporting slightly higher values across the series and expanded on the
work with INS measurements.136
A series of isostructural MOFs, denoted PCN-9 (Co/Mn/Fe),
characterized by entatic metal centers, has been studied by Zhou
and coworkers.95 In this work, the hydrogen uptake (1.53, 1.26
and 1.06 wt% for Co, Mn and Fe) capacities correlate well with
the surface areas (1064, 836 and 682 m2 g1 for Co, Mn and Fe),
and the enthalpies of adsorption for PCN-9(Co), PCN-9(Mn),
and PCN-9(Fe) are 10.1, 8.7 and 6.4 kJ mol1 respectively; the
slight deviation from the Irving–Williams sequence is possibly
attributed to partial oxidation of Fe2+ to Fe3+.
The nickel containing MOF, synthesized by Kaskel and
coworkers, was activated by the sc-CO2 drying method.64 The
activated sample showed high pore volume (1.75 cm3 g1) and
hydrogen uptake (1.33 wt% at 1 bar and 4.99 wt% at 45 bar) at 77
K. Upon additional heating the coordinated solvent molecules
were removed and the nickel sites were exposed, resulting in an
increased pore volume of 2.18 cm3 g1 and an excess hydrogen
uptake of 1.66 wt% at 1 bar and 5.85 wt% at 40 bar thus highlighting the importance of complete activation. One MOF with
great potential, for which the activation conditions have not yet
been optimized, is the most recent addition to the series of BTT
containing MOFs.65 Fe–BTT shows moderate hydrogen loading
of 4.1 wt% (35 g L1) at 77 K and 95 bar but a high zero-coverage
isosteric heat of adsorption of 11.9 kJ mol1. Compared to Cu–
BTT, the zero-coverage DHads is higher in Fe–BTT but the
partial methanol retention results in Cu–BTT having a higher
heat of adsorption at coverage above 0.4 wt% and a higher total
uptake of 5.7 wt% at 90 bar.
Other MOFs with exposed metal sites have also been reported,
such as the zeolite-like MOC-2, which shows high stability and
hydrogen uptake at 77 K and 1 bar (2.17 wt%) with an initial
heats of adsorption of only 6.5 kJ mol1, although partially
exposed indium sites are present.79 [Mn3(bipy)3][Cr(CN)6]2 has
a high heat of adsorption (11.5 kJ mol1) and volumetric
hydrogen uptake at 77 K of 81 cm3 g1, due to a combination of
coordinately unsaturated Mn2+ sites as well as free and coordinated cyanide groups.77 SNU-15, synthesized by Suh and
coworkers, yields low H2 loading (0.74 wt% at 77 K/1 atm) but
a remarkable adsorption enthalpy of 15.1 kJ mol1, which has
been ascribed to the exposed metal site on every Co2+ in the
framework.42 The exposed Zn metal sites of the fully desolvated
Zn2Ca(btc)2 show a hydrogen uptake of 2.2 wt% at 77 K per
1 bar.110
3.6.
Chemical doping
Chemical doping for MOFs has received a considerable amount
of attention in the last two years because calculations have shown
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that post-synthetic modification of MOFs with atomic or
cationic lithium can provide a route to surpass the DOE
targets.138–144
Froudakis and coworkers have computationally explored the
effects of lithium doping on various MOFs, including IRMOF14.145 The simulations show that the single Li(0) per organic
linker case can lead to a storage capacity that is 7.5 times larger
than the undoped IRMOF-14. This work was expanded by
substituting cationic Li+ in the form of a lithium alkoxide functional group on the ligands of IRMOF-8 and -14 instead of
atomic lithium. The modified IRMOF-8 showed a gravimetric
uptake of 4.5 wt % at 295 K and 100 bar and 10 wt% at 77 K and
100 bar.146 Further work on this type of modification was
computationally explored by attaching a sulfonate group,
a potential hydrogen adsorption site, to the pyrene ligand of
IRMOF-14. The negatively charged SO31 group was charged
balanced with Li+ cations, resulting in a further increase in
binding energies.147 The trend for the hydrogen capacities is in all
cases (gravimetric and volumetric at 77 K and 300 K) undoped<
SO31< SO31Li+ except in the high pressure gravimetric realm at
77 K where pore volume remains the dominant factor.
Hartman and coworkers recently synthesized a MIL-53(Al)
analogue containing a free hydroxyl group that was postsynthetically modified to the lithium alkoxide functionalized
MOF.139 The physical measurements of hydroxyl-MIL-53(Al)
are in close agreement with the previously reported data of the
unmodified framework, however, the lithium doped counterpart
showed a significant increase in hydrogen uptake capacity from
0.50 to 1.7 wt% at 77 K, and doubled heats of adsorption at low
coverage (5.8 vs. 11.6 kJ mol1).
The diol containing strut of a MOF recently synthesized by
Hupp and coworkers was post-synthetically modified using
lithium t-butoxide and Mg(OMe)2.142 Samples with high (2.62
Li+/Zn2; 2.02 Mg2+/Zn2) and low loading (0.20 Li+/Zn2; 0.86
Mg2+/Zn2) of lithium and magnesium were prepared and
compared to the parent diol MOF. In both low loading cases
framework integrity, confirmed by slight increases in surface
area, was retained; in the lithiation case an increase in H2 uptake
of 0.09 wt%, corresponding to an additional two H2/Li+, was
observed. Another study of lithium and magnesium doping in
MOFs was conducted by Eddaoudi and coworkers on
a carboxylic acid functionalized zeolite-like MOF. They determined that a large contribution to the enhancement of heats of
adsorption in cation-doped frameworks is the presence of an
electrostatic field in the cavity.60
Schr€
oder and coworkers conducted ion exchange experiments
on a MOF containing Me2NH2+cations, which were replaced with
smaller Li+ cations. The doped-MOF showed a 22% increase in
hydrogen uptake at 20 bar, which correlates well with the increase
in BET surface area resulting from the smaller Li+ cations.140 A
further examination of the cation exchange effects was conducted
on an indium MOF in which piperazine cations were exchanged
for Li+. The exchange induced modulation was observed as
a threefold increase in BET surface area and an enthalpy increase
of 1.1 kJ mol1. The conclusion was drawn that the bulky piperazine cation acts as a kinetic hydrogen trap, which is why the
hysteretic sorption behavior disappears upon cation exchange.144
An alternate strategy employed by the Hupp group is that of
chemically reducing a MOF and doping it with alkali metal
Energy Environ. Sci.
Fig. 5 Chemical reduction of MOF using metal naphthalenide in THF
(M ¼ Li, Na, K).
cations (Li+, Na+, K+) (Fig. 5).141 Although the average DHads
values were highest for the Li+ doped case (5.96 kJ mol1), the
highest uptake (1.54 wt%) was the result of the K+0.06/ligand
doping, despite the greater contribution to the molecular weight
of the framework. This prompted further investigation which
showed that increased doping merely resulted in an overall
reduction of adsorbed H2 and heats of adsorption. A later study
used an analogous framework which revealed similar results:
doping increased the hydrogen uptake by up to 43% in the Na+
doped case (1.60 wt%) compared to the undoped case (1.12 wt%)
and in line with the previous study, increasing the metal content
from 0.05 Li+ per Zn to 0.35 resulted in a reduction from 1.46 to
0.54 wt%.143
3.7.
Spillover
It has been suggested that hydrogen spillover will play a much
larger role in terms of hydrogen storage at ambient temperatures
(vs. 77 K), which is the preferred temperature realm for practically applications.148–155 Hydrogen spillover is generally defined
as the diffusion of dissociated hydrogen from a metal surface to
the support surface. Although there is still some ambiguity on the
exact mechanism involved, several computational and experimental studies have shed light onto the phenomenon and
provided guidance on how to improve current materials and thus
achieve the DOE targets of room temperature storage.148 The
review by Wang and Yang149 provides tremendous insights into
the physical properties of hydrogen spillover as well as a detailed
investigation into some of the related MOF literature; this
section is to serve as an update in this area.
Hydrogen spillover in MOFs can be achieved by doping
MOFs with metal nanoparticles. The intra-framework generation of palladium nanoparticles (PdNPs) to enhance hydrogen
storage was explored by Suh and coworkers who incorporated
a redox-active ligand into SNU-3.138 The MOF resulting from
the ligand catalyzed reduction of Pd(NO3)2 to nanoparticles of
about 3.0 nm, designated 3 wt% PdNPs@[SNU-3]0.54+(NO3)0.54,
was charge balanced by the retention of nitrate ions in the
framework. The PdNP doped MOF showed an increased
hydrogen capacity at 77 K of 1.48 wt% compared to the 1.03 wt%
of the pristine material, despite the decreased surface area and
added weight. An analysis of the low-coverage heats of adsorption of Pd-doped SNU-3 compared to the pristine material as
well as a comparison to the uptake of materials with similar
surface areas revealed that a spillover mechanism must be at play
in the surprisingly large uptake of 0.30 wt% at 298 K and 95 bar.
One of the most pronounced examples of hydrogen spillover in
MOFs is that of MIL-100(Al) embedded with PdNPs that are
approximately 2.0 nm in size.156 The PdNPs are generated in the
MOF framework, resulting in a low size distribution or the
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particles, and induce a significant loss in BET surface area, total
pore volume, and hydrogen uptake at 77 K in the modified MOF.
The nearly twofold increase in hydrogen uptake at 298 K to 0.39
wt% has been partially attributed to b-hydride formation at low
pressures and a spillover mechanism at pressures above 4.5 kPa.
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3.8.
Adsorption mechanism
The adsorption mechanism in MOFs is usually physisorption,
where H2 molecules interact weakly with the framework through
dispersion forces (<10 kJ). This has the advantage that the
uptake is fully reversible and usually requires little energy.
Chabal and coworkers have conducted the first room
temperature infrared (IR) study of MOFs for hydrogen
storage.157 This work elucidates the location of the adsorbed
hydrogen molecules at 300 K over a range of pressures in a series
of MOFs with similar structures. The conclusions were drawn
that in the presence of saturated metal centers, the identity of the
metal center does not play a role in hydrogen adsorption, as the
shifts correlate with the organic linkers. In the presence of small
1-D pores, the metal center influences the hydrogen because of
a change in pore size rather than a direct metal–H2 interaction.
Similar results were observed in a computational investigation of
MOF-5.158 The strongest interaction energies were found to be
when the H2 molecule is orthogonally oriented to the phenyl
linker (3.5 kJ mol1) and that the adsorption capacity is most
strongly related to the nanoporosity rather than any electrostatic
interactions that are produced by host–guest interactions. This
was experimentally probed by FitzGerald et al. using diffuse
reflectance infrared spectroscopy.159 The range of binding energies (2.5 to 4 kJ mol1) was estimated from the induced redshifts
in the vibrational mode frequencies and matched the calculated
values fairly well.
MOFs with unsaturated metal sites have also been explored.
Brown and coworkers concluded from their INS data of
HKUST-1 that the major contribution to the overall binding
comes from classical Coulomb interactions between H2 and the
copper paddlewheel as evidenced by short H2–copper
distances.160 As FitzGerald et al. showed by isotope studies using
HD and D2 in MOF-74, the concentration-dependent frequency
shifts provide evidence that the interactions between adsorbed
molecules on neighboring sites are non-negligible.135 Further
investigation into MOF-74(Mg) using H2 sorption data coupled
with IR and INS by Long and colleagues provided further insight
into the binding sites of molecular hydrogen.161
4. Future developments
4.1.
Balancing between surface area and pore size
There appears to be a linear relationship between the BET
specific surface area and the hydrogen uptake at 77 K and high
pressures. This has been reported in previous papers and in
a recent study by Poirier and Dailly the trends were again
apparent.162 There are some classes of MOFs that do not follow
this rule of thumb: flexible MOFs often have different capacities
at a low and high pressure; MOFs with unsaturated metal sites
have higher uptakes at low pressure due to increased interaction
energies at low loadings; and MOFs with pores in the mesoporous range suffer from lower adsorption capacities. One
This journal is ª The Royal Society of Chemistry 2011
method for increasing the gravimetric hydrogen sorption in
MOFs is to substitute metals for lighter metals that can build the
same SBUs. Substituting beryllium163 for zinc in the familiar
Zn4O cluster that is characteristic of the IRMOF series has been
a goal for a number of years because it could enhance the
gravimetric hydrogen storage capacity by about 50%. Experimental difficulties, due largely to the smaller ionic radius of
beryllium, have made this a difficult task, but Matzger and
colleagues have successfully synthesized Be4O(BDC)6 (Be–MOF5).31 The BET surface area is 3500 m2 g1, which is comparable to
that of MOF-5, and the hydrogen uptake at 77 K per 24 bar is 5.0
wt%. Another Be–MOF, synthesized by Sumida et al., uses the
trigonal1,3,5-benzenetribenzoate ligand to construct a MOF
with SBET of 4030 m2 g1 and excess hydrogen uptake of 6.0 wt%
at 77 K and 20 bar (gravimetric and volumetric totals are 9.2 wt%
and 43 g L1 at 100 bar); the capacity at 298 K is among the
highest reported (2.3 wt% and 11 g L1).32
4.2.
Enhancing interaction between hydrogen and framework
Strengthening the adsorbent–adsorbate interactions is a task that
must be accomplished to meet the DOE targets; one possible item
of concern in this arena is potentially increasing the interaction
energy so much as to negatively affect the desorption behavior.
Understanding how strong these interactions must be and which
combination of methods is best to achieve this is being investigated computationally and experimentally. Bae and Snurr have
examined the effects of heat of adsorption on the overall and the
deliverable (1.5–120 bar) capacity. Their calculations showed
that the storage capacity increased linearly as DHads was elevated
as long as there was no reduction in free volume. The deliverable
capacity also closely correlated with DHads, however, the relationship was not linear and it was determined that the average
DHads over the entire pressure range would optimally lie between
18.5 and 22 kJ mol1.164 One approach to achieve these values
without using exposed metal sites is to constrain pore size as per
example in the partially fluorinated MOF synthesized by Cheetham and coworkers.113 The framework shows a high DHads (8 kJ
mol1) for a material with purely physisorptive adsorption,
however, the gravimetric sorption capacity is not good because
the free volume is so small.
Fr€
oba and coworkers discussed various methods of calculating
hydrogen capacities of MOFs and determined that depending on
the temperature, different models are more appropriate and
match the experimental data better.165 However, most of the
deviations were related to the presence of unsaturated metal sites,
which indicate that the strong binding of hydrogen at these sites
cannot be modeled in the framework of a potential material that
considers only van der Waals interactions, and that the inclusion
of charge–quadrupole interactions is not sufficient to overcome
this deficiency.
4.3.
Optimizing sorption isotherms
A stimuli-dependent pore opening/closing process is usually
characterized by large hysteresis and is usually the result of
structural phase transitions.13 It appears that the flexible cobalt–
pyrazolyl MOF undergoes a pore opening mechanism that is
temperature-, pressure- and gas-dependent.37 The five step
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adsorption of N2 is unique in microporous materials and the
temperature dependent hysteresis of H2 can provide some
insights into what properties of a MOF are necessary to generate
a change in the sorption isotherm (Fig. 6). Stepwise adsorption
has been linked to multilayer adsorption, multiple interactions
that differ in energy, and structural transitions. The hysteretic
adsorption of H2 at 77 K is clearly seen as virtually no gas is
adsorbed until 20 bar after which the uptake shoots to
a maximum of 3.1 wt% at 30 bar; desorption does not occur until
about 15 bar. Such a pronounced loop is typical of much
stronger adsorbent–adsorbate interactions such as those found in
chemisorptions processes. This type of pronounced hysteresis
could be useful as one could imagine filling up a portable tank
and then lowering the pressure until it is slightly higher than the
desorption pressure, thus reducing the risks of a highly pressurized portable unit; the disadvantages here could come from
a poor fuel release rate. SNU-9, reported by Park and Suh, shows
a two-step adsorption isotherm for H2 with a plateau from about
15 to 20 bar (1.32 wt%) followed by a sharp increase and
a maximum excess sorption of 3.63 wt% at 90 bar.107 Framework
flexibility is further confirmed by a hysteresis loop.
4.4.
Fig. 6 Isotherms for the excess uptake of H2 within Co(BDP), showing
temperature-dependent hysteresis loops at 65, 77, and 87 K. Filled and
open symbols represent adsorption and desorption curves, respectively.
Other novel approaches
Thornton and coworkers have investigated the effects of
impregnating MOFs with fullerenes (C60) and Mg10C60
analogues.166 The trend of heats of adsorption for pure IRMOF8, C60@IRMOF-8 and Mg10C60@IRMOF-8 is an increase from
5 to 9 to 10.5 kJ mol1. The trend is the same for low pressure
hydrogen uptake until about 8 bar when surface area begins to
dominate and at 13 bar the empty MOF shows higher adsorption
because of the larger free volume. Dybtsev et al. included
a [Mo6Br8F6]2 cluster into MIL-101(Cr) and observed an initial
heat of adsorption of 13.5 kJ mol1 compared to the 9 of the
empty MOF, however at high pressures the uptake was lower.167
Using carboranes as the linkers in MOFs has shown some
promise for hydrogen storage.168–170 The systematic substitution
of first row transition metals into the carborane cluster reveals
that scandium and titanium are the best candidates as they have
high binding energies, bind up to 10 H2 molecules, and are light
weight which will be beneficial at high pressure and room
temperature adsorption.168 Leoni and coworkers have developed
lithium–boron imidazolates, that are isostructural to the ZIF
family of frameworks.171 They determined that the fau-type net
adsorbed the most amount of hydrogen at 7.8 wt%.
Liberation of H2 from metal hydrides has been studied and is
one option to deliver usable hydrogen to fuel cells, provided of
course that this process is reversible and can undergo multiple
regeneration cycles.7,8 NaAlH4 is one material that has shown
promise, however the large particle size distribution of bulk
samples means that the desorption occurs rapidly and at high
temperatures (250 C). Allendorf and coworkers have infused
HKUST-1 with 4 wt% NaAlH4 and because of the uniform
particle size (formed in the rigid framework) and favorable
chemical environment the sample was able to desorb 80% of the
total H2 at 155 C.172 Li and coworkers efficiently generated
hydrogen gas from ammonia borane (AB), NH3BH3, solutions
by placing them in contact with a nickel–MOF. It is worth noting
here that regeneration of MOF–host lattices is currently difficult
Energy Environ. Sci.
Fig. 7 Confinement of AB within the pores of MOF.
partly because the decomposition products remain challenging to
remove from the MOF.173 The gas was released linearly over time
at several concentrations of AB in methanol. They reasoned that
the accessible nickel sites remained separated even after reduction and only aggregated to tiny, highly reactive metal clusters.
This work was expanded by infusing neat AB (19.3 wt%
hydrogen content) into a MOF with unsaturated yttrium sites.174
The AB released 8.0 wt% (based on neat AB) hydrogen in only 10
minutes at the DOE suggested temperature limit of 85 C or the
full amount (13 wt%) at 95 C in three hours. The AB incorporated within the MOF-74(Mg) shows clean and dramatically
improved H2 release properties when compared to pristine AB.175
The MOF-74(Mg) system can accommodate a large mass fraction, up to approximately 26 wt %, of nanoconfined AB. Such
a combined strategy of entrapping materials such as AB could be
a fruitful future direction for MOF research (Fig. 7).
5. Conclusions
Despite some promising achievements in terms of hydrogen
storage in MOFs, the weak interaction between dihydrogen and
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the framework still appears to be a hurdle that must be overcome
to reach the DOE targets. It is possible that with a strong enough
initial heat of adsorption and large enough surface area and pore
volume, MOFs will be able to reach the DOE set targets for room
temperature adsorption. Another possible solution could be
making use of a combination of strategies, such as incorporating
complex metal hydrides. To reach these goals synthetic chemists
must work in collaboration with computational experts to
develop new strategies and materials and work in a feedback
loop with engineers to determine which materials function best in
harsh real-world conditions.
References
1 D. Zhao, D. Q. Yuan and H. C. Zhou, Energy Environ. Sci., 2008, 1,
222.
2 U. Eberle, M. Felderhoff and F. Schuth, Angew. Chem., Int. Ed.,
2009, 48, 6608.
3 P. Chen and M. Zhu, Mater. Today, 2008, 11, 36.
4 K. L. Lim, H. Kazemian, Z. Yaakob and W. R. W. Daud, Chem.
Eng. Technol., 2010, 33, 213.
5 E. Reguera, Int. J. Hydrogen Energy, 2009, 34, 9163.
6 U. Sahaym and M. G. Norton, J. Mater. Sci., 2008, 43, 5395.
7 F. Schuth, Eur. Phys. J. Spec. Top., 2009, 176, 155.
8 J. Yang, A. Sudik, C. Wolverton and D. J. Siegel, Chem. Soc. Rev.,
2010, 39, 656.
9 http://www1.eere.energy.gov/hydrogenandfuelcells/mypp/pdfs/storage.
pdf.
10 A. Carne, C. Carbonell, I. Imaz and D. Maspoch, Chem. Soc. Rev.,
2011, 40, 291.
11 A. U. Czaja, N. Trukhan and U. Muller, Chem. Soc. Rev., 2009, 38,
1284.
12 G. Ferey, Struct. Bonding, 2009, 132, 87.
13 S. Horike, S. Shimomura and S. Kitagawa, Nat. Chem., 2009, 1, 695.
14 R. J. Kuppler, D. J. Timmons, Q. R. Fang, J. R. Li, T. A. Makal,
M. D. Young, D. Q. Yuan, D. Zhao, W. J. Zhuang and
H. C. Zhou, Coord. Chem. Rev., 2009, 253, 3042.
15 S. T. Meek, J. A. Greathouse and M. D. Allendorf, Adv. Mater.,
2011, 23, 249.
16 O. M. Yaghi and Q. W. Li, MRS Bull., 2009, 34, 682.
17 S. Q. Ma, Pure Appl. Chem., 2009, 81, 2235.
18 S. Q. Ma and L. Meng, Pure Appl. Chem., 2011, 83, 167.
19 S. Q. Ma and H. C. Zhou, Chem. Commun., 2010, 46, 44.
20 N. L. Rosi, J. Eckert, M. Eddaoudi, D. T. Vodak, J. Kim,
M. O’Keeffe and O. M. Yaghi, Science, 2003, 300, 1127.
21 M. Dinca and J. R. Long, Angew. Chem., Int. Ed., 2008, 47, 6766.
22 M. Hirscher, B. Panella and B. Schmitz, Microporous Mesoporous
Mater., 2010, 129, 335.
23 Y. H. Hu and L. Zhang, Adv. Mater., 2010, 22, E117.
24 S. V. Kolotilov and V. V. Pavlishchuk, Theor. Exp. Chem., 2009, 45,
277.
25 S. V. Kolotilov and V. V. Pavlishchuk, Theor. Exp. Chem., 2009, 45,
75.
26 L. J. Murray, M. Dinca and J. R. Long, Chem. Soc. Rev., 2009, 38,
1294.
27 K. M. Thomas, Dalton Trans., 2009, 1487.
28 B. Xiao and Q. C. Yuan, Particuology, 2009, 7, 129.
29 S. S. Han, J. L. Mendoza-Cortes and W. A. Goddard, Chem. Soc.
Rev., 2009, 38, 1460.
30 J. Juan-Juan, J. P. Marco-Lozar, F. Suarez-Garcia, D. CazorlaAmoros and A. Linares-Solano, Carbon, 2010, 48, 2906.
31 W. W. Porter, A. Wong-Foy, A. Dailly and A. J. Matzger, J. Mater.
Chem., 2009, 19, 6489.
32 K. Sumida, M. R. Hill, S. Horike, A. Dailly and J. R. Long, J. Am.
Chem. Soc., 2009, 131, 15120.
33 J. Zhang, Y. S. Xue, L. L. Liang, S. B. Ren, Y. Z. Li, H. B. Du and
X. Z. You, Inorg. Chem., 2010, 49, 7685.
34 D.-C. Zhong, W.-X. Zhang, F.-L. Cao, L. Jiang and T.-B. Lu, Chem.
Commun., 2011, 47, 1204.
35 D. C. Zhong, J. B. Lin, W. G. Lu, L. Jiang and T. B. Lu, Inorg.
Chem., 2009, 48, 8656.
This journal is ª The Royal Society of Chemistry 2011
36 Y. Wang, M. Fang, Y. Li, J. Liang, W. Shi, J. Chen and P. Cheng,
Int. J. Hydrogen Energy, 2010, 35, 8166.
37 H. J. Choi, M. Dinca and J. R. Long, J. Am. Chem. Soc., 2008, 130,
7848.
38 J. B. Lin, J. P. Zhang and X. M. Chen, J. Am. Chem. Soc., 2010, 132,
6654.
39 Y. Q. Li, L. Xie, Y. Liu, R. Yang and X. G. Li, Inorg. Chem., 2008,
47, 10372.
40 S. Wang, T. Zhao, G. Li, L. Wojtas, Q. Huo, M. Eddaoudi and
Y. Liu, J. Am. Chem. Soc., 2010, 132, 18038.
41 H. Wang, J. Getzschmann, I. Senkovska and S. Kaskel, Microporous
Mesoporous Mater., 2008, 116, 653.
42 Y. E. Cheon and M. P. Suh, Chem. Commun., 2009, 2296.
43 H. Chun, H. J. Jung and J. W. Seo, Inorg. Chem., 2009, 48, 2043.
44 S.-T. Zheng, J. T. Bu, Y. Li, T. Wu, F. Zuo, P. Feng and X. Bu, J.
Am. Chem. Soc., 2010, 132, 17062.
45 L. Feng, Z. X. Chen, T. B. Liao, P. Li, Y. Jia, X. F. Liu, Y. T. Yang
and Y. M. Zhou, Cryst. Growth Des., 2009, 9, 1505.
46 P. Kanoo, R. Matsuda, M. Higuchi, S. Kitagawa and T. K. Maji,
Chem. Mater., 2009, 21, 5860.
47 S.-S. Chen, M. Chen, S. Takamizawa, M.-S. Chen, Z. Su and
W.-Y. Sun, Chem. Commun., 2011, 47, 752.
48 M. Dinca, A. Dailly and J. R. Long, Chem.–Eur. J., 2008, 14, 10280.
49 S.-M. Zhang, Z. Chang, T.-L. Hu and X.-H. Bu, Inorg. Chem., 2010,
49, 11581.
50 Y. G. Lee, H. R. Moon, Y. E. Cheon and M. P. Suh, Angew. Chem.,
Int. Ed., 2008, 47, 7741.
51 B. Zheng, Z. Q. Liang, G. H. Li, Q. S. Huo and Y. L. Liu, Cryst.
Growth Des., 2010, 10, 3405.
52 X. F. Liu, M. Park, S. Hong, M. Oh, J. W. Yoon, J. S. Chang and
M. S. Lah, Inorg. Chem., 2009, 48, 11507.
53 L. Q. Ma and W. B. Lin, Angew. Chem., Int. Ed., 2009, 48, 3637.
54 L. Q. Ma, A. Jin, Z. G. Xie and W. B. Lin, Angew. Chem., Int. Ed.,
2009, 48, 9905.
55 D. Liu, Z. Xie, L. Ma and W. Lin, Inorg. Chem., 2010, 49, 9107.
56 W. J. Zhuang, S. Q. Ma, X. S. Wang, D. Q. Yuan, J. R. Li, D. Zhao
and H. C. Zhou, Chem. Commun., 2010, 46, 5223.
57 L. L. Liang, J. Zhang, S. B. Ren, G. W. Ge, Y. Z. Li, H. B. Du and
X. Z. You, CrystEngComm, 2010, 12, 2008.
58 S. Hong, M. Oh, M. Park, J. W. Yoon, J. S. Chang and M. S. Lah,
Chem. Commun., 2009, 5397.
59 L. Q. Ma, D. J. Mihalcik and W. B. Lin, J. Am. Chem. Soc., 2009,
131, 4610.
60 F. Nouar, J. Eckert, J. F. Eubank, P. Forster and M. Eddaoudi, J.
Am. Chem. Soc., 2009, 131, 2864.
61 Z. Q. Wang, K. K. Tanabe and S. M. Cohen, Chem.–Eur. J., 2010,
16, 212.
62 I. Senkovska, F. Hoffmann, M. Fr€
oba, J. Getzschmann,
W. B€
ohlmann and S. Kaskel, Microporous Mesoporous Mater.,
2009, 122, 93.
63 N. Klein, I. Senkovska, K. Gedrich, U. Stoeck, A. Henschel,
U. Mueller and S. Kaskel, Angew. Chem., Int. Ed., 2009, 48, 9954.
64 K. Gedrich, I. Senkovska, N. Klein, U. Stoeck, A. Henschel,
M. R. Lohe, I. A. Baburin, U. Mueller and S. Kaskel, Angew.
Chem., Int. Ed., 2010, 49, 8489.
65 K. Sumida, S. Horike, S. S. Kaye, Z. R. Herm, W. L. Queen,
C. M. Brown, F. Grandjean, G. J. Long, A. Dailly and
J. R. Long, Chem. Sci., 2010, 1, 184.
66 D. Banerjee, S. J. Kim, H. Wu, W. Xu, L. A. Borkowski, J. Li and
J. B. Parise, Inorg. Chem., 2011, 50, 208.
67 M. Xue, G. S. Zhu, Y. X. Li, X. J. Zhao, Z. Jin, E. Kang and
S. L. Qiu, Cryst. Growth Des., 2008, 8, 2478.
68 S. Mohapatra, K. P. S. S. Hembram, U. Waghmare and T. K. Maji,
Chem. Mater., 2009, 21, 5406.
69 B. F. Abrahams, M. J. Grannas, T. A. Hudson and R. Robson,
Angew. Chem., Int. Ed., 2010, 49, 1087.
70 Y. B. Zhang, W. X. Zhang, F. Y. Feng, J. P. Zhang and X. M. Chen,
Angew. Chem., Int. Ed., 2009, 48, 5287.
71 D. Denysenko, M. Grzywa, M. Tonigold, B. Streppel, I. Krkljus,
M. Hirscher, E. Mugnaioli, U. Kolb, J. Hanss and D. Volkmer,
Chem.–Eur. J., 2011, 17, 1837.
72 Y. E. Cheon, J. Park and M. P. Suh, Chem. Commun., 2009,
5436.
73 Z. Y. Guo, G. H. Li, L. Zhou, S. Q. Su, Y. Q. Lei, S. Dang and
H. J. Zhang, Inorg. Chem., 2009, 48, 8069.
Energy Environ. Sci.
Downloaded by Texas A & M University on 06 July 2011
Published on 15 June 2011 on http://pubs.rsc.org | doi:10.1039/C1EE01240A
View Online
74 A. Mallick, S. Saha, P. Pachfule, S. Roy and R. Banerjee, Inorg.
Chem., 2011, 1392.
75 C. Volkringer, M. Meddouri, T. Loiseau, N. Guillou, J. Marrot,
G. Ferey, M. Haouas, F. Taulelle, N. Audebrand and
M. Latroche, Inorg. Chem., 2008, 47, 11892.
76 Q. X. Yao, L. Pan, X. H. Jin, J. Li, Z. F. Ju and J. Zhang, Chem.–
Eur. J., 2009, 15, 11890.
77 A. Hazra, P. Kanoo and T. K. Maji, Chem. Commun., 2011, 47, 538.
78 R. Q. Zhong, R. Q. Zou, M. Du, T. Yamada, G. Maruta, S. Takeda,
J. Li and Q. Xu, CrystEngComm, 2010, 12, 677.
79 D. F. Sava, V. C. Kravtsov, J. Eckert, J. F. Eubank, F. Nouar and
M. Eddaoudi, J. Am. Chem. Soc., 2009, 131, 10394.
80 H. Furukawa, N. Ko, Y. B. Go, N. Aratani, S. B. Choi, E. Choi,
A. O. Yazaydin, R. Q. Snurr, M. O’Keeffe, J. Kim and
O. M. Yaghi, Science, 2010, 329, 424.
81 Y. E. Cheon and M. P. Suh, Chem.–Eur. J., 2008, 14, 3961.
82 X. Lin, I. Telepeni, A. J. Blake, A. Dailly, C. M. Brown,
J. M. Simmons, M. Zoppi, G. S. Walker, K. M. Thomas,
T. J. Mays, P. Hubberstey, N. R. Champness and M. Schr€
oder, J.
Am. Chem. Soc., 2009, 131, 2159.
83 S. H. Yang, X. Lin, A. Dailly, A. J. Blake, P. Hubberstey,
N. R. Champness and M. Schr€
oder, Chem.–Eur. J., 2009, 15, 4829.
84 Y. Yan, X. Lin, S. H. Yang, A. J. Blake, A. Dailly,
N. R. Champness, P. Hubberstey and M. Schr€
oder, Chem.
Commun., 2009, 1025.
85 Y. Yan, I. Telepeni, S. H. Yang, X. Lin, W. Kockelmann, A. Dailly,
A. J. Blake, W. Lewis, G. S. Walker, D. R. Allan, S. A. Barnett,
N. R. Champness and M. Schr€
oder, J. Am. Chem. Soc., 2010, 132, 4092.
86 X. S. Wang, S. Q. Ma, P. M. Forster, D. Q. Yuan, J. Eckert,
J. J. Lopez, B. J. Murphy, J. B. Parise and H. C. Zhou, Angew.
Chem., Int. Ed., 2008, 47, 7263.
87 S. E. Wenzel, M. Fischer, F. Hoffmann and M. Fr€
oba, Inorg. Chem.,
2009, 48, 6559.
88 S. Q. Ma, J. M. Simmons, D. F. Sun, D. Q. Yuan and H. C. Zhou,
Inorg. Chem., 2009, 48, 5263.
89 D. F. Sun, S. Q. Ma, J. M. Simmons, J. R. Li, D. Q. Yuan and
H. C. Zhou, Chem. Commun., 2010, 46, 1329.
90 S. Q. Ma, J. M. Simmons, D. Q. Yuan, J. R. Li, W. Weng, D. J. Liu
and H. C. Zhou, Chem. Commun., 2009, 4049.
91 X. S. Wang, S. Q. Ma, D. Q. Yuan, J. W. Yoon, Y. K. Hwang,
J. S. Chang, X. P. Wang, M. R. Jorgensen, Y. S. Chen and
H. C. Zhou, Inorg. Chem., 2009, 48, 7519.
92 D. Zhao, D. Q. Yuan, A. Yakovenko and H. C. Zhou, Chem.
Commun., 2010, 46, 4196.
93 D. Q. Yuan, D. Zhao, D. F. Sun and H. C. Zhou, Angew. Chem., Int.
Ed., 2010, 49, 5357.
€ ur Yazaydın, I. Eryazici, C. D. Malliakas,
94 O. K. Farha, A. Ozg€
B. G. Hauser, M. G. Kanatzidis, S. T. Nguyen, R. Q. Snurr and
J. T. Hupp, Nat. Chem., 2010, 2, 944.
95 S. Q. Ma, D. Q. Yuan, J. S. Chang and H. C. Zhou, Inorg. Chem.,
2009, 48, 5398.
96 J. Zhang, T. Wu, S. M. Chen, P. Y. Feng and X. H. Bu, Angew.
Chem., Int. Ed., 2009, 48, 3486.
97 H. J. Park and M. P. Suh, Chem.–Eur. J., 2008, 14, 8812.
98 T.-H. Park, K. A. Cychosz, A. G. Wong-Foy, A. Dailly and
A. J. Matzger, Chem. Commun., 2011, 47, 1452.
99 J. K. Schnobrich, O. Lebel, K. A. Cychosz, A. Dailly, A. G. WongFoy and A. J. Matzger, J. Am. Chem. Soc., 2010, 132, 13941.
100 K. Koh, A. G. Wong-Foy and A. J. Matzger, J. Am. Chem. Soc.,
2009, 131, 4184.
101 E. Neofotistou, C. D. Malliakas and P. N. Trikalitis, Chem.–Eur. J.,
2009, 15, 4523.
102 H. J. Choi, M. Dinca, A. Dailly and J. R. Long, Energy Environ. Sci.,
2010, 3, 117.
103 T. Panda, P. Pachfule, Y. Chen, J. Jiang and R. Banerjee, Chem.
Commun., 2011, 47, 2011.
104 Z. Hulvey, D. A. Sava, J. Eckert and A. K. Cheetham, Inorg. Chem.,
2011, 52, 403.
105 F. Debatin, A. Thomas, A. Kelling, N. Hedin, Z. Bacsik,
I. Senkovska, S. Kaskel, M. Junginger, H. Muller, U. Schilde,
C. Jager, A. Friedrich and H. J. Holdt, Angew. Chem., Int. Ed.,
2010, 49, 1258.
106 A. J. Lan, K. H. Li, H. H. Wu, L. Z. Kong, N. Nijem, D. H. Olson,
T. J. Emge, Y. J. Chabal, D. C. Langreth, M. C. Hong and J. Li,
Inorg. Chem., 2009, 48, 7165.
Energy Environ. Sci.
107 H. J. Park and M. P. Suh, Chem. Commun., 2010, 46, 610.
108 O. K. Farha, K. L. Mulfort and J. T. Hupp, Inorg. Chem., 2008, 47,
10223.
109 M. Xue, S. Q. Ma, Z. Jin, R. M. Schaffino, G. S. Zhu,
E. B. Lobkovsky, S. L. Qiu and B. L. Chen, Inorg. Chem., 2008,
47, 6825.
110 R. Zou, R. Zhong, S. Han, H. Xu, A. K. Burrell, N. Henson,
J. L. Cape, D. D. Hickmott, T. V. Timofeeva, T. E. Larson and
Y. Zhao, J. Am. Chem. Soc., 2010, 132, 17996.
111 J. Duan, J. Bai, B. Zheng, Y. Li and W. Ren, Chem. Commun., 2011,
47, 2556.
112 M. Xue, Y. Liu, R. M. Schaffino, S. C. Xiang, X. J. Zhao, G. S. Zhu,
S. L. Qiu and B. L. Chen, Inorg. Chem., 2009, 48, 4649.
113 Z. Hulvey, E. H. L. Falcao, J. Eckert and A. K. Cheetham, J. Mater.
Chem., 2009, 19, 4307.
114 S. Biswas, M. Grzywa, H. P. Nayek, S. Dehnen, I. Senkovska,
S. Kaskel and D. Volkmer, Dalton Trans., 2009, 6487.
115 http://www.iupac.org/web/ins/2009-012-2-200.
116 Z. H. Xiang, D. P. Cao, X. H. Shao, W. C. Wang, J. W. Zhang and
W. Z. Wu, Chem. Eng. Sci., 2010, 65, 3140.
117 A. I. Cooper and M. J. Rosseinsky, Nat. Chem., 2009, 1, 26.
118 A. P. Nelson, O. K. Farha, K. L. Mulfort and J. T. Hupp, J. Am.
Chem. Soc., 2009, 131, 458.
119 H. Frost, T. D€
uren and R. Q. Snurr, J. Phys. Chem. B, 2006, 110,
9565.
120 J. K. Schnobrich, K. Koh, K. N. Sura and A. J. Matzger, Langmuir,
2010, 26, 5808.
121 T. D€
uren, F. Millange, G. Ferey, K. S. Walton and R. Q. Snurr, J.
Phys. Chem. C, 2007, 111, 15350.
122 A. L. Spek, PLATON, A Multipurpose Crystallographic Tool,
Utrecht University, 2010.
123 H. K. Chae, D. Y. Siberio-Perez, J. Kim, Y. Go, M. Eddaoudi,
A. J. Matzger, M. O’Keeffe and O. M. Yaghi, Nature, 2004, 427, 523.
124 H. Furukawa, M. A. Miller and O. M. Yaghi, J. Mater. Chem., 2007,
17, 3197.
125 H. Deng, C. J. Doonan, H. Furukawa, R. B. Ferreira, J. Towne,
C. B. Knobler, B. Wang and O. M. Yaghi, Science, 2010, 327, 846.
126 P. Ryan, L. J. Broadbelt and R. Q. Snurr, Chem. Commun., 2008,
4132.
127 B. Liu, Q. Y. Yang, C. Y. Xue, C. L. Zhong and B. Smit, Phys.
Chem. Chem. Phys., 2008, 10, 3244.
128 S. Q. Ma, J. Eckert, P. M. Forster, J. W. Yoon, Y. K. Hwang,
J. S. Chang, C. D. Collier, J. B. Parise and H. C. Zhou, J. Am.
Chem. Soc., 2008, 130, 15896.
129 H. He, D. Yuan, H. Ma, D. Sun, G. Zhang and H.-C. Zhou, Inorg.
Chem., 2010, 49, 7605.
130 O. K. Farha, C. D. Malliakas, M. G. Kanatzidis and J. T. Hupp, J.
Am. Chem. Soc., 2009, 132, 950.
131 O. Shekhah, H. Wang, M. Paradinas, C. Ocal, B. Schupbach,
A. Terfort, D. Zacher, R. A. Fischer and C. Woll, Nat. Mater.,
2009, 8, 481.
132 J. Zhang, L. Wojtas, R. W. Larsen, M. Eddaoudi and
M. J. Zaworotko, J. Am. Chem. Soc., 2009, 131, 17040.
133 W. Zhou, H. Wu and T. Yildirim, J. Am. Chem. Soc., 2008, 130,
15268.
134 N. Nijem, J.-F. o. Veyan, L. Kong, H. Wu, Y. Zhao, J. Li,
D. C. Langreth and Y. J. Chabal, J. Am. Chem. Soc., 2010, 132, 14834.
135 S. A. FitzGerald, J. Hopkins, B. Burkholder, M. Friedman and
J. L. C. Rowsell, Phys. Rev. B: Condens. Matter Mater. Phys.,
2010, 81, 104305.
136 P. D. C. Dietzel, P. A. Georgiev, J. Eckert, R. Blom, T. Strassle and
T. Unruh, Chem. Commun., 2010, 46, 4962.
137 J. G. Vitillo, L. Regli, S. Chavan, G. Ricchiardi, G. Spoto,
P. D. C. Dietzel, S. Bordiga and A. Zecchina, J. Am. Chem. Soc.,
2008, 130, 8386.
138 Y. E. Cheon and M. P. Suh, Angew. Chem., Int. Ed., 2009, 48, 2899.
139 D. Himsl, D. Wallacher and M. Hartmann, Angew. Chem., Int. Ed.,
2009, 48, 4639.
140 S. Yang, X. Lin, A. J. Blake, K. M. Thomas, P. Hubberstey,
N. R. Champness and M. Schr€
oder, Chem. Commun., 2008, 6108.
141 K. L. Mulfort and J. T. Hupp, Inorg. Chem., 2008, 47, 7936.
142 K. L. Mulfort, O. K. Farha, C. L. Stern, A. A. Sarjeant and
J. T. Hupp, J. Am. Chem. Soc., 2009, 131, 3866.
143 K. L. Mulfort, T. M. Wilson, M. R. Wasielewski and J. T. Hupp,
Langmuir, 2009, 25, 503.
This journal is ª The Royal Society of Chemistry 2011
Downloaded by Texas A & M University on 06 July 2011
Published on 15 June 2011 on http://pubs.rsc.org | doi:10.1039/C1EE01240A
View Online
144 S. H. Yang, X. Lin, A. J. Blake, G. S. Walker, P. Hubberstey,
N. R. Champness and M. Schr€
oder, Nat. Chem., 2009, 1, 487.
145 A. Mavrandonakis, E. Tylianakis, A. K. Stubos and
G. E. Froudakis, J. Phys. Chem. C, 2008, 112, 7290.
146 E. Klontzas, A. Mavrandonakis, E. Tylianakis and G. E. Froudakis,
Nano Lett., 2008, 8, 1572.
147 A. Mavrandonakis, E. Klontzas, E. Tylianakis and G. E. Froudakis,
J. Am. Chem. Soc., 2009, 131, 13410.
148 H. S. Cheng, L. Chen, A. C. Cooper, X. W. Sha and G. P. Pez,
Energy Environ. Sci., 2008, 1, 338.
149 L. F. Wang and R. T. Yang, Energy Environ. Sci., 2008, 1, 268.
150 M. Suri, M. Dornfeld and E. Ganz, J. Chem. Phys., 2009, 131, 174703.
151 B. D. Adams, C. K. Ostrom, S. Chen and A. Chen, J. Phys. Chem. C,
2010, 114, 19875.
152 C. S. Tsao, M. S. Yu, C. Y. Wang, P. Y. Liao, H. L. Chen,
U. S. Jeng, Y. R. Tzeng, T. Y. Chung and H. C. Wut, J. Am.
Chem. Soc., 2009, 131, 1404.
153 N. P. Stadie, J. J. Purewal, C. C. Ahn and B. Fultz, Langmuir, 2010,
26, 15481.
154 N. R. Stuckert, L. F. Wang and R. T. Yang, Langmuir, 2010, 26, 11963.
155 R. Campesi, F. Cuevas, M. Latroche and M. Hirscher, Phys. Chem.
Chem. Phys., 2010, 12, 10457.
156 C. Zlotea, R. Campesi, F. Cuevas, E. Leroy, P. Dibandjo,
C. Volkringer, T. Loiseau, G. Ferey and M. Latroche, J. Am.
Chem. Soc., 2010, 132, 2991.
157 N. Nijem, J. F. Veyan, L. Z. Kong, K. H. Li, S. Pramanik,
Y. G. Zhao, J. Li, D. Langreth and Y. J. Chabal, J. Am. Chem.
Soc., 2010, 132, 1654.
158 A. Kuc, T. Heine, G. Seifert and H. A. Duarte, Chem.–Eur. J., 2008,
14, 6597.
159 S. A. FitzGerald, K. Allen, P. Landerman, J. Hopkins, J. Matters,
R. Myers and J. L. C. Rowsell, Phys. Rev. B: Condens. Matter
Mater. Phys., 2008, 77, 224301.
This journal is ª The Royal Society of Chemistry 2011
160 C. M. Brown, Y. Liu, T. Yildirim, V. K. Peterson and C. J. Kepert,
Nanotechnology, 2009, 20, 204025.
161 K. Sumida, C. M. Brown, Z. R. Herm, S. Chavan, S. Bordiga and
J. R. Long, Chem. Commun., 2011, 47, 1157.
162 E. Poirier and A. Dailly, Langmuir, 2009, 25, 12169.
163 I. Series, Beryllium: Environmental Health Criteria 106, World
Health Orgnization, Geneva, 1990.
164 Y. S. Bae and R. Q. Snurr, Microporous Mesoporous Mater., 2010,
132, 300.
165 M. Fischer, F. Hoffmann and M. Fr€
oba, ChemPhysChem, 2009, 10,
2647.
166 A. W. Thornton, K. M. Nairn, J. M. Hill, A. J. Hill and M. R. Hill,
J. Am. Chem. Soc., 2009, 131, 10662.
167 D. Dybtsev, C. Serre, B. Schmitz, B. Panella, M. Hirscher,
M. Latroche, P. L. Llewellyn, S. Cordier, Y. Molard, M. Haouas,
F. Taulelle and G. Ferey, Langmuir, 2010, 26, 11283.
168 A. K. Singh, A. Sadrzadeh and B. I. Yakobson, J. Am. Chem. Soc.,
2010, 132, 14126.
169 O. K. Farha, A. M. Spokoyny, K. L. Mulfort, S. Galli, J. T. Hupp
and C. A. Mirkin, Small, 2009, 5, 1727.
170 T. K. A. Hoang and D. M. Antonelli, Adv. Mater., 2009, 21,
1787.
171 I. A. Baburin, B. Assfour, G. Seifert and S. Leoni, Dalton Trans.,
2011, 40, 3796.
172 R. K. Bhakta, J. L. Herberg, B. Jacobs, A. Highley, R. Behrens,
N. W. Ockwig, J. A. Greathouse and M. D. Allendorf, J. Am.
Chem. Soc., 2009, 131, 13198.
173 Y. Q. Li, L. Xie, Y. Li, J. Zheng and X. G. Li, Chem.–Eur. J., 2009,
15, 8951.
174 Z. Y. Li, G. S. Zhu, G. Q. Lu, S. L. Qiu and X. D. Yao, J. Am. Chem.
Soc., 2010, 132, 1490.
175 S. Gadipelli, J. Ford, W. Zhou, H. Wu, T. J. Udovic and T. Yildirim,
Chem.–Eur. J., 2011, 22, 6043.
Energy Environ. Sci.