Enhancing proton conductivity in a metal-organic framework at: T > 80 °c by an anchoring strategy

Article abstract of DOI:10.1039/c7ta10148a

A new Zr(iv)-based metal-organic framework, termed VNU-23 [Zr₆O₈(H₂O)₈(H₂SNDC)₄], where H₂SNDC^2- = 4,8-disulfonaphthalene-2,6-dicarboxylate, was synthesized. Subsequently, detailed structural analysis revealed that VNU-23 adopted the bcu topology with a structure characterized by densely packed sulfonic acid groups lining 6 ? channels. With this structural feature, an anchoring strategy was employed to dock the proton transfer agent, histamine, into the void space of VNU-23 to enhance the proton conductivity. Remarkably, the proton conductivity of this material reached 1.79 × 10^-2 S cm^-1 at 95 °C and 85% relative humidity without any appreciable loss of performance for at least 120 h.

Full text of DOI:10.1039/c7ta10148a

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ISSN 2050-7488
PAPER
Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
MoS2 nanocages as a lithium ion battery anode material
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Enhancing Proton Conductivity in a Metal-Organic Framework at T
> 80 °C by Anchoring Strategy
My V. Nguyen,a,b Tien H. N. Lo,a Loc C. Luu,c Hue T. T. Nguyena and Thach N. Tu*a,c
Received 00th January 20xx,
Accepted 00th January 20xx
A
new Zr(IV)-based metal-organic framework, termed VNU-23 [Zr6O8(H2O)8(H2SNDC)4; where H2SNDC2-
= 4,8-
DOI: 10.1039/x0xx00000x
disulfonaphthalene-2,6-dicarboxylate, was synthesized. Subsequently, detailed structural analysis revealed that VNU-23
adopted the bcu topology with the structure highlighted by densely packed sulfonic acid groups lining 6 Å channels. With
this structural feature, anchoring strategy has been carried out to dock the proton transfer agent, histamine into the void
space of VNU-23 to enhance the proton conductivity. Remarkably, the proton conductivity of this material reached 1.79 ×
10-2 S cm-1 at 95 °C and 85% relative humidity without any appreciated loss of performance for at least 120 h.
www.rsc.org/
transfer agents within the pores,7t10 functionalizing
coordinatively unsaturated metal sites,11,12 tuning the acidity of
the pore channels through incorporating specific functional
1. Introduction
Proton exchange membrane fuel cells (PEMFC) have emerged
as the new and sustainable energy technologies with the
potential application in the mobile engine.1 Among the
assembled components, development of novel electrolyte
materials, which are capable of working under realistic and
practical working conditions has become intensive focus.
Traditional electrolyte materials based on perfluorosulfonic
acid (PFSA) polymers (i.e. fully hydrated Nafion), are capable of
reaching proton conductivities of 1 × 10-1 S cm-1 at 80 °C,
however, required relative humidity (RH) that is greater than
98%.2 This, indeed, with the minor temperature fluctuation,
possibly results a flooding at the cathode, leading to a loss in
fuel cell performance.3 Furthermore, high operating
temperatures, which minimize CO poisoning at Pt-based
catalysts and increase efficiency, lead to decreased
conductivities as a result of dehydration of the electrolyte
materials.4 Therefore, it raised the demand to design and
synthesize new electrolyte materials that maintain high proton
conductivity at the working condition under elevated
temperatures and low relative humidity.5
groups,13,14 controlling and modifying defect sites15 and among
others.16t20 Typically, the proton conduction value of MOFs
have reached the magnitude of 10-2 S cm-1 at high relative
humidity (RH > 90%) and low temperature (T < 80 °C).21,22 On
the other hand, only a few MOFs exhibited this high level proton
conductivity at higher temperature and lower relative humidity,
which lesson CO poisoning at Pt-based catalysts.16,23 Moreover,
it lacks of a strategy toward the design and synthesis of MOFs,
which conduct proton over the magnitude of 10-2 S cm-1,
especially , at T C 100 °C and RH < 90%.21,22
Doping of proton transfer agents in MOFs has been adopted
among viable approaches, to design composites that can
conduct proton under anhydrous condition, however the value
typically reached the order of magnitude of 10-3 S cm-1,24t29 and
those with higher conductivity are exceptionally rare.30
Moreover, there is the fact that these agents released from
MOFs at this condition (with temperatures up to 130 °C).7 With
this in mind, we believed that the successful introduction of the
dense Brønsted acid moieties inside the pore of MOFs, which
are connected by the optimum proton conduction pathway
constructed from the stable proton transfer agents, is vital to
design composites that can reach high level proton conductivity
~• E íì-2 S cm-1) at high temperature (T C 100 °C). Additionally,
it is also needed to emphasize the proper choice of proton
transfer agent, which need satisfy both factors: i) Stability
without releasing from host framework at high temperature; ii)
high polarity to attract water from the surrounding
environment to promote the formation of the optimum proton
conduction pathway.8,9
Metal-organic frameworks (MOFs) are a class of materials,
which possess the modular nature of design and synthesis, in
which the material backbone [e.g. inorganic and organic
secondary building units (SBUs)] can be tailored to satisfy
particular applications.6 Recently, MOFs have been used for
proton conduction, for which, several notified strategies have
been employed, for example, the incorporation of proton
a.Center for Innovative Materials and Architectures (INOMAR), Vietnam National
University-Ho Chi Minh (VNU-HCM), Ho Chi Minh City 721337, Vietnam.
Email: tnthach@inomar.edu.vn
b.University of Science, VNU-HCM, Ho Chi Minh City 721337, Vietnam.
c. Bach Khoa University, VNU-HCM, Ho Chi Minh City 721337, Vietnam.
•Electronic Supplementary Information (ESI) available: Full synthesis and
characterization, crystallographic data, and additional proton conductivity
measurement details. See DOI: 10.1039/x0xx00000x
With all of this taken into account, we introduced the
synthesis and characterizations of a new Zr-based MOF, termed
VNU-23, constructed from Brønsted acid-rich 4,8-
disulfonaphthalene-2,6-dicarboxylic acid linker (H4SNDC) and
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Fig. 1 The backbone structure of VNU-23 is constructed from 8-connected, cubic Zr6O8(H2O)8(COO)8 clusters (a) linked together by linear, ditopic H2SNDC2- linkers (b) to form
a structure adopting the bcu topology (c, view from the [001] plane). The architecture of VNU-23, Zr6O8(H2O)8(H2SNDC)4, is depicted (d). Atom colors: Zr, blue polyhedra; C,
black; O, red; S, yellow. All H atoms are omitted for clarity.
Zr6O8(H2O)8(COO-)8 cluster. Analysis resulted that this material deionized water, filtered, and precipitated by 50 mL of
formulated as [Zr6O8(H2O)8(H2SNDC)4], with a structure that concentrated HCl (37 wt%). This precipitated product was then
adopts the bcu topology, highlighted by 6 Å channels along Oz filtered and washed with excess amounts (100 mL) of
axis. As a result, VNU-23 featured with the dense Brønsted acid concentrated HCl and dried under vacuum at 150 °C to obtain
1
functionalities lining the 6 Å channels. Following this, the pure H4SNDC linker in 70% yield (1.2 g, 3.2 mmol). H-NMR
immobilized strategy using VNU-23 as the platform for (DMSO-d6U ñìì IÌ•W w A õXñõ ~•U îI• ꢀvꢁ ôXðõ ~•U îI• (see
anchoring histamine molecules has been performed to Electronic Supporting Information, Fig. S1•). FT-IR: 3105 (m);
synthesize His8.2´VNU-23. Indeed, histamine is chosen as the 2648 (w); 2547 (w); 1691 (s); 1604 (m); 1485 (w); 1425 (s); 1374
proton transfer agent with an anticipation to be stable under (m); 1325 (w); 1286 (s); 1238 (s); 1189 (s); 1145 (s); 1109 (s);
protonated form, which virtually prevent this agent from 1019 (s); 914 (s); 804 (s); 768 (s); 734 (s); 653 (m); 634 (m).
releasing, and the high polarity of this agent can also attract and Synthesis of pristine VNU-23. A mixture of H4SNDC (0.033 g,
hold water from the surrounding environment to promote the 0.088 mmol) and ZrOCl2·8H2O (0.026 g, 0.081 mmol) was
formation of the optimum proton conduction pathway. As dissolved in DMF (4 mL), following by adding of formic acid (1
expected, His8.2´VNU-23 exhibited maximum conductivity of mL). The mixture was heated at 120 °C for 72 h, to obtain the
1.79 × 10-2 S cm-1 under 85% RH and 95 °C, with proton colourless microcrystals, which were exchanged with DMF for 3
conductivity maintained without any appreciable loss for at days (3 × 5 mL). Subsequently, this material was exchanged with
least 120 hours.
CH2Cl2 (3 × 5 mL), dried and activated under vacuum (10-3 Torr)
at room temperature to yield pristine VNU-23 sample (80%
yield based on Zr4+). EA (activated sample): Calcd. for
Zr6C64H141.9O78.93S8N8 = [Zr6O8(H2O)8(SNDC)4]·(DMA)8·22.93H2O
(DMA = dimethyamonium): C, 24.83; H, 4.59; N, 3.62; and S,
8.27%. Found: C, 25.25; H, 4.01; N, 3.27; and S, 7.7%. FT-IR: 3098
(w); 2808 (w); 1652 (s); 1582 (s); 1466 (m); 1416 (s); 1363 (s);
1227 (m); 1178 (s); 1115 (m); 1067 (w); 1035 (s); 925(w); 812
(m); 786 (s); 762 (s); 656 (s); 612 (s).
2. Experimental Section
Synthesis of 4,8-disulfonaphthalene-2,6-dicarboxylic acid
(H4SNDC) linker. A mixture of H2NDC (1 g, 4.63 mmol) and 5 ml
of oleum (SO3 in H2SO4, 50 wt%) was added to a 50 mL flask
bottle and continuously stirred at 150 °C for 1 day. Then, fresh
oleum (3 mL) was introduced and stirred at 170 °C for 2 days.
Finally, fresh oleum (2 mL) was added and stirred at 190 °C for
1 day. Subsequently, the reaction was cooled to room
temperature and the product was dissolved in 100 mL of
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Fig. 2 Anchor of histamine onto the internal surface of VNU-23: (a) Plausible mechanism for anchoring of histamine; (b) powder X-ray diffraction analysis of as-synthesized pristine
VNU-23 (red) and activated His8.2´VNU-23 (blue) in comparison with the pattern simulated from the single crystal structure of VNU-23 (black); (c) Fourier transform-infrared
spectroscopy analysis of histamine (Black), VNU-23 (red), and His8.2´VNU-23 (blue); (d) the deposited position of histamine in VNU-23; (e) the distance between histamine, sulfonic
acid groups and the coordination water molecules. Atom colours: C, black; O, red; N, green; S, yellow; VNU-23 backbone, light blue. Four disordered positions of sulfonate groups,
which are not at the centre of the five disordered positions, were omitted for clarity.
9.32; and S, 6.93%. Found: C, 28.70; H, 3.96; N, 9.68; and S,
Synthesis of VNU-23. Pristine VNU-23 was exchanged with 6.43%. FT-IR: 3127 (m); 1607 (m); 1573 (s); 1466 (w); 1408 (s);
MeOH/H2O solution of H2SO4 for 2 days (0.3 M H2SO4, 1358 (s); 1222 (m); 1178 (s); 1107 (m); 1034 (s); 936 (w); 811
v
MeOH/vH O = 4/1 mL mL-1, 5 × 5 mL). Thereafter, this sample was (m); 785 (s); 766 (s); 654 (s); and 612 (s).
2
centrifuged, washed with copious amount of MeOH/H2O (5 × 5
mL; vMeOH/vH O = 4/1 mL mL-1) until the decanted liquor reached
2
3. Results and discussion
pH = 5. Subsequently, this material was washed with MeOH (5
× 5 mL), dried and activated under dynamic vacuum (10-3 Torr)
Synthesis and Characterization of VNU-23. Pristine VNU-23
was solvothermally synthesized at 120 °C from ZrOCl2.8H2O salt
and H4SNDC linker in N,N-dimethylformamide (DMF) with the
use of formic acid as modulator. This reaction led to the
formation of colorless needle crystals. X-ray diffraction analysis
of single crystal showed that VNU-23 crystalized in the
tetragonal space group, I4/m (No.87), with unit cell parameters,
a = b = 17.75 and c = 22.48 Å. The architecture of VNU-23 is built
from 8-connected Zr6O8(H2O)8(-CO2)8 clusters, which are
bridged by SNDC4- linkers (Fig. 1a,b). This, indeed, realizes a
three-dimensional structure with bcu topology (Fig. 1c,d).31
Accordingly, this structure is highlighted with 6 Å pore channels
lining along Oz axis, which are densely decorated with sulfonate
groups (Fig. 1c, d).
1
at room temperature to acquire VNU-23. H-NMR (Digested
VNU-23, DMSO-d6U ñìì IÌ•W w A õXñõ ~•U îI• ꢀvꢁ ôXðõ ~•U îI• (see
Electronic Supporting Information, Fig. S12•). EA (activated
sample):
Calcd.
For
Zr6C49.96H95.88O81S8N0.98
=
[Zr6O8(H2O)8(H2SNDC)3(HSNDC)]·(DMA)0.98·25H2O: C, 21.30; H,
3.44; N, 0.49; and S, 9.10%. Found: C, 21.31; H, 3.08; N, 1.00;
and S, 9.45%. FT-IR: 1696 (w); 1607 (m); 1557 (m); 1495 (w);
1414(s); 1364 (m); 1173 (s); 1070 (w); 1035(s); 923 (w); 846 (w);
809 (m); 784 (m); 764 (s); 656 (w); and 610 (m).
Synthesis of His8.2´VNU-23. 120 mg of VNU-23 was added to
10 mL of MeOH solution of histamine (His, 0.5 M). The mixture
was shaken at 45 °C for 3 days, cooled to room temperature,
then centrifuged and washed with mixture of MeOH and CH2Cl2
(3 × 2 mL; vMeOH/vCH2Cl2 = 1/19 mL mL-1) to remove histamine
within the intercrystalline regions. Thereafter, the sample was
activated overnight under dynamic vacuum (10-3 Torr) at room
The bulk phase purity of as-synthesized pristine VNU-23 was
further confirmed by powder X-ray diffraction (PXRD) analysis,
in which, the coincidence between the experimental and
simulated pattern have been recognized (Fig. 2b). Following
this, as-synthesized pristine VNU-23 was exchanged with DMF
temperature to obtain His8.2´VNU-23. EA (activated sample):
Zr6C89H165.4N24.6O81.8S8
Calcd. for
=
[Zr6O8(H2O)8(H2SNDC)4]·8.2His·25.8H2O: C, 28.91; H, 4.48; N,
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and MeOH, respectively, and activated to obtain dried pristine analysis. From the resulting spectra, the protonated
VNU-23, for which the structure maintenance was proven by histamine/H4SNDC ratio of 1.98 was calculated, this
PXRD. Elemental microanalysis (EA) was further performed on corresponded to 7.92 histamine molecules loaded per formula
pristine VNU-23, this resulted the chemical formula of unit of VNU-23 (Fig. S13•). This value was further confirmed by
{[Zr6O8(H2O)8(H2SNDC)4]·(DMA)8}·22.93H2O (Calcd: C, 24.83; H, EA analysis, in which, the chemical formulas were determined
4.59; N, 3.62; and S, 8.27%. Found: C, 25.25; H, 4.01; N, 3.27; to be [Zr6O8(H2O)8(SNDC)4]·8.2His·25.8H2O (Calcd: C, 28.91; H,
and S, 7.7%). Due to the presence of dimethyamonium (DMA) 4.48; N, 9.32; and S, 6.93%. Found: C, 28.70; H, 3.96; N, 9.68;
ions, that interacted with sulfonate moieties, pristine VNU-23 and S, 6.43%). All two quantitative measurements were
was exchanged with H2SO4 (0.3 M) and washed with excess consistent in determining the loading of x = 8.2 histamine
amount of solvents until the eluent reached pH = 5, to remove molecules, respectively.
these guest molecules. Subsequently, this sample was activated
To gain deeper insight into the anchoring mechanism of
under vacuum and digested in DMSO-d6 for 1H-NMR analysis, histamine onto the internal surface of VNU-23, the single crystal
for which, the result indicated the absence of DMA signal in X-ray diffraction was carried out for His8.2´VNU-23. Accordingly,
digested sample (See electronic supporting information, Fig the deposition of histamine inside VNU-23 has been identified, in
S12•). We further carried out thermogravimetric analysis (TGA) which, the relatively close distance (2.7 < d < 3.2 Å) between N atoms
on VNU-23 under airflow (20% O2, 80% N2), in which, the of histamine with sulfonate groups and the coordination water
framework demonstrated the thermal stability up to 450 °C (Fig. molecules of Zr6O8(H2O)8(-CO2)8 clusters was observed (Fig. 2d, e).
S7•). Fourier transform infrared (FT-IR) spectroscopy analysis This confirmed the formation of the hydrogen bonds between the
was measured, which clearly demonstrated the presence of protonated histamine and the docking centers in VNU-23
.
coordinated carboxylate with the characteristic band of Furthermore, it noticed that the low site occupation of
carbonyl group (C=O) appears at 1607 cm-1. The presence of histamine inside VNU-23 (15%) was found by single crystal X-ray
sulfonic group was also confirmed by two peaks at 1173 and diffraction method. Indeed, this was deduced to the naturally
1193 cm-1 (Fig. S6•). Additionally, it noticed that VNU-23 lost the large size of the single crystal, which, with the dense occupation
long range structural order after activating, however, the of histamine near the surface, prevented other histamine
crystallinity was fully recovered upon solvating in water (Fig. molecules from diffusing deeper inside into the crystal. In
S3•).
addition, we specifically emphasized that the presence of
Loading of histamine within VNU-23. VNU-23 was subjected to several large single crystals were uncommon and this could only
the anchoring process with histamine. In detail, the sample was be collected on the wall of reaction vials and the microcrystal
soaked in MeOH solution of histamine (3 days, 5 mL, 0.5 M), product of VNU-23 was found to be common.
filtered and washed with excess amount of organic solvents (3 Proton Conductivity Properties. Prior to carrying out proton
× 2 mL; vMeOH/vCH2Cl2 = 1/19 mL mL-1) to remove absorbed conductivity measurements of His8.2´VNU-23, water sorption
histamine within intercrystalline regions, then activated under experiments were performed at 25 °C. Accordingly, the water
dynamic vacuum to obtain the dried product, termed uptake of His8.2´VNU-23 was found to be 191, 248, 339 cm3 g-1 at
Hisx´
unit of VNU-23) (Fig. 2a).
VNU-23 (x = amount of immobilized histamine per formula P/P0 = 0.7, 0.8, 0.85, respectively. Additionally, we found that water
was condensed upon P/P0 = 0.87, thus P/P0 = 0.85 was chosen as cut
Recalling the fact that VNU-23 lost the structural order upon off point for proton conductivity measurements in order to
activating, we deduced that if histamine was successfully loaded minimize the effect of condensed water during the
in the pore of VNU-23, the structure would maintain its measurement (Fig. S16•).
structural order upon activation, thus PXRD analysis have been
Accounting from the high water uptake of His8.2´VNU-23 and
carried out as an initial assessment for whether histamine was the structural features with the dense array of sulfonate moieties
loaded into the pore of VNU-23. Accordingly, PXRD pattern that conjugated with protonated histamine, we wished to
revealed that Hisx´VNU-23 remained its crystalline after evaluate the proton conductivity of this composite. As a result,
activation, thus proven the existence of anchoring histamine the systematic investigations of ac impedance spectroscopy
within the pore of VNU-23 (Fig. 2b). Additionally, the systematic measurements of pelletized His8.2´VNU-23 under varying
investigations of FT-IR spectroscopy have been carried out, in relative humidity (RH; 50-85%) at an elevated temperature of
which, the spectra displayed unique peaks, centered at 3127 95 °C have been carried. The resulting Nyquist plots
cm-1 which were present in the control histamine spectrum, but demonstrated
a strong dependence on the RH, with
absent in the spectrum for VNU-23. These were assigned to the conductivity values increasing from 1.3 × 10-6 S cm-1 under 50%
vN-H stretching modes of terminal amine groups (Figure S6•). On RH and 95 °C to 1.79 × 10-2 S cm-1 under 85% RH and 95 °C (Fig.
the other hand, the absence of an absorption band centered at 3). Additionally, the ac impedance spectroscopy measurements
1650 cm-1 (assigned to the N-H bending in the ring of histamine have been carried on pristine VNU-23 and VNU-23, which
molecules) in Hisx
histamine on the surface or within the intercrystalline regions 1.1 × 10-5 S cm-1 under 90% RH and 70 °C (note the higher RH are
(Fig. 2c and S6•).
needed). It is noted that this value is at least 102 times lower
Subsequently, the amount of histamine in VNU-23 have been than the conductivity value of His8.2´VNU-23 under 85% RH and
quantitatively determined by 1H-NMR and EA. First, Hisx VNU- 70 °C (1.2 × 10-2 S cm-1), thus the importance of immobilzed
23 was digested in acidic DMSO-d6 in order to carry out 1H-NMR histamine inside VNU-23 has been confirmed. Additionally,
´
VNU-23 samples confirmed the absence of respectively resulted the conductivity value of 1.54 × 10-4 and
´
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despite the fact that sulfonic acid group can donate H+ to the
conduction pathways more favorably than protonated
histamine, His8.2´VNU-23 exhibited higher proton conductivity than
VNU-23. Indeed, this phenomenon can be deduced to high
polarity of protonated histamine molecules that drived fully
hydration of entired pore and grain boundary of MOFs particles
and this had been observed before.8 Furthermore, we note that
the proton conductivity of His8.2´VNU-23 under 85% RH and
95 °C exceeds the values at 85% RH for several of the highest
performing MOF materials reported t conditions (Table 1).
Fig. 4 Temperature-dependent proton conductivity measurements (60 t 95 °C) of
His8.2´VNU-23 under 85% RH. From the Arrhenius plot, an activation energy of 0.27 eV
was calculated, indicating the proton conduction occurs via Grotthuss mechanism. Inset:
Time-dependent proton conductivity at 85% RH and 95 °C demonstrating that
His8.2´VNU-23 maintains high proton conductivity, without loss in performance, for at
least 120 h.
To gain insight into the proton-conduction mechanism,
temperature-dependent proton conductivities of His8.2´VNU-23
were measured. Initially, His8.2´VNU-23 was allowed to balance for
at least 15 hours under 85% RH and 95 °C, then the temperature
was gradually decreased from 95 °C to 30 °C. At 95 °C, the
Fig. 3 Dependence of proton conductivity in His8.2´VNU-23 as a function of relative
humidity at 95 °C, inset: Nyquist plot of His8.2´VNU-23 under 85% RH and 95 °C.
maximum conductivity value was 1.65 × 10-2 S cm>1
. As
temperature decreased, we observed a jump in conductivity
from 60 °C to 50 °C, then the conductivity reached the minimum
value of 3.4 × 10>5 S cm>1 at 30 °C (Fig. S28•). Indeed, this jump of
conductivity could be attributed to the re-arrangement of
protonated histamine inside His8.2´VNU-23, which is similar with
those observed for CsHSO4.37 Additionally, this phenomenon
have been previously observed for MOFs and similar materials,
Table 1. Proton conductivity values of His8.2´VNU-23 in comparison
with high-performing water-mediated proton conducting MOFs.
Material
• l { ꢂu-1
Conditions
Ref
1.79 × 10-2
95 °C, 85% RH
This work
His8.2´VNU-23
32
33
14
Fe-CAT-5
7.94 × 10-3
2.51 × 10-3
7.50 × 10-3
3.40 × 10-3
1.25 × 10-4
3.16× 10-8
5.62 × 10-3
7.58 × 10-3
6.93 × 10-3
1.44 × 10-3
25 °C, 85% RH
60 °C, 98% RH
70 °C, 85% RH
30 °C, 97% RH
30 °C, 85% RH
30 °C, 85% RH
65 °C, 95% RH
42 °C, 99% RH
65 °C, 95% RH
120 °C
such
as
[Zn(HPO4)(H2PO4)2](ImH2)2,24
[Zn3(H2PO4)6(H2O)3](Hbim),25
t-PCMOF2(Tz)0.45 and t-
PCMOF-5
PCMOF2(Tz)0.6.27 Subsequently, the temperature-dependent
proton conductivities were then cycled in the temperature
ranges from 60-95 °C, which provided strong evidence for the
stability of His8.2´VNU-23 under these measurement conditions.
Arrhenius fitting of this data resulted the activation energy of
0.27 eV, indicated that the proton conduction in His8.2´VNU-23
occurs through a Grotthuss mechanism (Fig. 4).
PCMOF10
UiO-66-SO3H
UiO-66-(CO2H)2
UiO-66
34
35
36
15
28
SA@Zr6O4(OH)L4·xH2O
MOF-808
Finally, the working capacity of His8.2´VNU-23 was
investigated as the function of time. Remarkably, it noticed that
pelletized His8.2´VNU-23 maintained its high proton conductivity
(1.52 × 10-2 S cm-1) for at least 120 hours, without any significant loss
in performance (Fig. 4, inset). Additionally, the stability and structural
maintenance of His8.2´VNU-23 after concluding the time-dependent
proton conductivity investigations were confirmed by PXRD and FT-
IR analysis, in which a high degree of correspondence was observed
for His8.2´VNU-23 samples before and after time-dependent
Zr6O4(OH)6(BDC)5
HIm´UiO-67
SA = Sulfoacetate; L = 2-sulfoterephthalate; BDC = Terephthalate;
HIm = Imidazole.
investigation (Section S15••
.
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ARTICLE
Journal Name
22 A. L. Li, Q. Gao, J. Xu, X. H. Bu, Coord. Chem. Rev., 2017, 344
54.
,
4. Conclusion
23 V. G. Ponomareva, K. A. Kovalenko, A. P. Chupakhin, D. N.
Dybtsev, E. S. Shutova, V. P. Fedin, J. Am. Chem. Soc., 2012,
134, 15640.
24 S. Horike, D. Umeyama, M. Inukai, T. Itakura, S. Kitagawa, J.
Am. Chem. Soc., 2012, 134, 7612.
25 D. Umeyama, S. Horike, M. Inukai, S. Kitagawa, J. Am. Chem.
Soc., 2013, 135, 11345.
26 S. Bureekaew, S. Horike, M. Higuchi, M. Mizuno, T. Kawamura,
In summary, we have succeeded to synthesize and characterize a
new Zr-based MOF, termed VNU-23. Through structural analysis,
VNU-23 was found to adopt the bcu architecture, highlighted by
Brønsted acid lining along 6 Å channels. Following this, an anchoring
strategy has been carried out to dope histamine into the void space
of VNU-23 to form His8.2´VNU-23. As a result of this structural
feature, His8.2´VNU-23 exhibited high proton conductivity (1.79 ×
10-2 S cm-1) at the practical conditions of 85% RH and 95 °C with the
proton conductivity retained without any loss for at least 120 h.
D. Tanaka, N. Yanai, S. Kitagawa, Nat. Mater., 2009,
27 J. A. Hurd, R. Vaidhyanathan, V. Thangadurai, C. I. Ratcliffe, I.
8, 831.
L. Moudrakovski, G. K. H. Shimizu, Nat. Chem., 2009,
28 S. Liu, Z. Yue, Y. Liu, Dalt. Trans., 2015, 44, 12976.
1, 705.
29 T. Homburg, C. Hartwig, H. Reinsch, M. Wark, N. Stock, Dalt.
Trans, 2016, 45, 15041.
30 S. Horike, W. Chen, T. Itakura, M. Inukai, D. Umeyama, H.
Asakura, S. Kitagawa, Chem. Commun., 2014, 50, 10241.
31 V. Bon, I. Senkovska, M. S. Weiss, S. Kaskel, CrystEngComm,
2013, 15, 9572.
32 N. T. T. Nguyen, H. Furukawa, F. Gándara, C. A. Trickett, H. M.
Jeong, K. E. Cordova, O. M. Yaghi, J. Am. Chem. Soc., 2015,
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33 J. M. Taylor, K. W. Dawson, G. K. H. Shimizu, J. Am. Chem. Soc.,
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Acknowledgements
We thank Prof. Felipe Gándara at ICMM for single crystal
analysis, Ms. Huong D. T. Nguyen for performing the elemental
microanalysis measurements. This work was supported by the
U.S. Office of Naval Research Global: Naval International
Cooperative Opportunities in Science and Technology Program
(No. N62909-16-1-2146).
34 F. Yang, H. Huang, X. Wang, F. Li, Y. Gong, C. Zhong, J. R. Li,
Cryst. Growth Des., 2015, 15, 5827.
35 J. M. Taylor, T. Komatsu, S. Dekura, K. Otsubo, M. Takata, H.
Kitagawa, J. Am. Chem. Soc., 2015, 137, 11498.
36 H. B. Luo, M. Wang, S. X. Liu, C. Xue, Z. F. Tian, Y. Zou, X. M.
Ren, Inorg. Chem., 2017, 56, 4169.
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6 | J. Name., 2012, 00, 1-3
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