A rare (3,12)-connected zirconium metal-organic framework with efficient iodine adsorption capacity and pH sensing

Article abstract of DOI:10.1039/c9ta03126j

We report here a stable rare zirconium metal-organic framework (MOF) exhibiting a sky topology, Zr₆(μ₃-O)₄(μ₃-OH)₄(ITTC)₄ (UPC-158) (where H₃ITTC = 4,4′,4′′-(1H-imidazole-2,4,5-t

Full text of DOI:10.1039/c9ta03126j

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PAPER
Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
MoS nanocages as a lithium ion battery anode material
2
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DOI: 10.1039/C9TA03126J
A rare (3,12)-connected zirconium metal-organic framework with
efficient iodine adsorption capacity and pH sensing
Bingbing Guo,a,† Fugang Li,a,† Chiming Wang,c,† Liangliang Zhang, * Daofeng Sun *
b,
a,
We synthesized a rare (3,12)-connected zirconium metal-organic framework with sky
topology showing efficient iodine adsorption and pH sensing capacity

J Po lue ran sael od fo Mn aot te rai ad l js u Cs ht emm ai rs gt ri yn sA
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DOI: 10.1039/C9TA03126J
Journal Name
ARTICLE
A rare (3,12)-connected zirconium metal-organic framework with
efficient iodine adsorption capacity and pH sensing
Received 00th January 20xx,
Accepted 00th January 20xx
Bingbing Guo,a,† Fugang Li,a,† Chiming Wang, Liangliang Zhang, * Daofeng Sun *
c,†
b,
a,
DOI: 10.1039/x0xx00000x
ABSTRACT：We report here a stable rare zirconium metal-organic framework (MOF) exhibiting sky topology
Zr
6
(µ
3
-O)
4
(µ
3
-OH)
4
(ITTC)
(µ -O)
4
(UPC-158) (where
3
H ITTC = 4,4',4''-(1H-imidazole-2,4,5-triyl)tribenzoic acid)
www.rsc.org/
established by Zr
6
3
4
(µ -OH) (-COO)12 clusters and 4,4',4''-(1H-imidazole-2,4,5-triyl)tribenzoic acid with
3
4
abundant π-electron as an ideal material for removing iodine vapor-a major radioactive fission waste. The
iodine adsorption effect of the acid-treated UPC-158-HX series has a substantial improvement compared
-1
-1
with the parental UPC-158 (1.77 g·g ), and the iodine vapor uptake of 2.92 g·g at 343.15 K for UPC-158-HCl
has reached the maximum value among the reported MOF materials. In addition, the protonation and
deprotonation of imidazole nitrogen alter the symmetry of internal structures, resulting in a strong
fluorescence enhancement of the material in the pH range from 10~11, making it a potentially precise pH
meter. This work not only provides insights into the discovery of unprecedented structures and topologies
through the rational choice of organic linkers via experimental and simulation method but also pave the way
to understand the structure related functional applications. It also opens up a window for the design and
construction of highly complicate porous and stable structures for sophisticated applications.
According to the soft and hard acid-base theory,18, 19 the MOFs
based on carboxylates linkers and with high oxidation state metal
ions or clusters have shown high chemical stability than those that
Introduction
As an emerging class of crystalline porous materials, metal-organic
frameworks (MOFs) constructed from inorganic metal ions or
clusters and organic linkers via coordination bonds have attracted
considerable interest in the past decades.1, 2 On account of their
structural and functional tunability, high surface area as well as
suitable pore size, MOFs have shown great promise in multifarious
fields, such as gas storage and separation,3,
heterogeneous catalysis,8, 9 and biochemical systems.10-13 So far,
more and more MOFs with high tunability of surface chemistry
environments and pore textural properties have been synthesized
for targeted applications. However, the stability of MOFs, especially
under harsh conditions, has become an important obstacle,
hindering their further applications and the rational design and
synthesis of highly stable MOFs remain a challenge.14-17
constructed from low oxidation transition element / earth element
metal and carboxylates linkers. Thus, chemists devoted their efforts
3
+
3+
3+
3+
4+
to MOFs with high-valence metals (Fe , Al , Cr , Re , Zr ), such
as MIL-101 series,20 UiO-66,21 PCN series,22, 23 MOF-525-54524 and
their stabilities were improved significantly. Among them, due to its
extremely high valence state, the tetravalent zirconium MOF was
easier forming into strong metal coordination bonds with carboxylic
acid ligands, enabling its remarkable stability, offering Zr-MOF an
advantage in practical applications.
4
sensing,5-7
In the process of designing stable zirconium MOFs, 2-, 3-, 4-
connected ligands are mostly used, and 4-connected linker could
take two configuration modes: square or tet-; the cluster shows 4-c,
6
-, 8-, 10-, 12- connected, and highly symmetrical 12-c cluster has
multiple transformation configurations such as cuo, ico hpr, tte.17, 25
Types of linkers or SBUs (secondary building units) depend on the
connections. Therefore, combined flexibility of cluster and linker
makes topology prediction a great challenge for MOFs.26
a. School of Materials Science and Engineering, College of Science, China University
of Petroleum (East China), Qingdao, Shandong 266580, China, E-mail:
dfsun@upc.edu.cn
Xi'an Institute of Flexible Electronics(IFE), Northwestern Polytechnical
b.
Among all the reported Zr-MOFs, compared to 2- and 4-
connected linkers, only few 3-connected linkers have been used to
University(NPU), Xi'an 710072, China, Email: iamllzhang@nwpu.edu.cn
Beijing Key Laboratory for Science and Application of Functional Molecular and
c.
Crystalline Materials, Department of Chemistry, University of Science and
Technology Beijing, Beijing 100083, China.
build Zr-MOFs.
H
3
TATB (H
3
TATB
=
4,4',4''-(1,3,5-triazine-2,4,6-
5'-(4-carboxyphenyl)-
1,1':3',1''-terphenyl]-4,4''-dicarboxylate)28 usually exhibit coplanar
†
These authors contributed equally.
triyl)tribenzoic acid),27 H3BTB (H BTB
=
3
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
[
with D3h symmetry to construct (3, 6)-c Zr-MOF with D3d symmetry
J. Name., 2013, 00, 1-3 | 1
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J Po lue ran sael od fo Mn aot te rai ad l js u Cs ht emm ai rs gt ri yn sA
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Journal Name
of Zr
group into the meta-position of H
benzene ring to form a D3h-symmetric H
carboxyphenyl)-2ʹ,4ʹ,6ʹ-trimeth-yl-[1,1ʹ:3ʹ,1ʹʹ-terphenyl]-4,4ʹʹ-
dicarboxylic acid).29 As the symmetry of the ligand decreases, the thermogravimetric analyzer at a rate of 10 K·min under nitrogen
6
cluster. Recently, Li and co-authors introduced three methyl diffractometer equipped with a Cu sealed tube (λ = 1.5V4ie1w7A8rtiÅcle) Oatnl4in0e
BTB to rotate the carboxyl-linked kV and 40 mA. Nuclear magnetic resonanDcOeI: 1(0N.1M03R9)/Cd9aTtAa03w12e6reJ
CTTA (H CTTA = 5ʹ-(4- collected on a Mercury 400 NMR spectrometer. Thermogravimetric
analysis (TGA) data were obtained on Mettler Toledo
3
3
3
a
–1
–1
Zr
6
cluster occupies a higher D4h symmetry mode, thus constructing atmosphere (100 mL·min ). N
2
adsorption-desorption isotherms
a (3,8)-connected Zr-MOF. More connections of the Zr
6
cluster were measured using a Micrometritics ASAP 2020 system at 77 K.
contribute to higher stability of the Zr-MOFs. Mohamed Eddaoudi The UV-vis absorption spectra were recorded on a Shimadzu UV-
pointed out the combination of cuo-12-connected MBBs (molecular 2450 spectrophotometer. SEM and TEM images were collected via a
building blocks) with either linear (2-connected) or square (3- scanning electron microscope (Philips XL30 FEG SEM) and
connected) MBBs leads to the formation of fcu or ftw net, transmission electron microscope (JEOL JEM-2100TEM). X-ray
respectively, and that no structure can be formed when it combined photoelectron spectroscopy (XPS) was carried out with a Thermo
with a 3-connected unit. Apparently, it is not compatible to 12- ESCALAB 250 surface analysis system.
connected Zr
recently, Yaghi reported the only (3,12)-connected sky net, named
6
cluster combined with triangular ligands.30 Very
Synthesis of compounds.
MOF-1004, which contributes to the twist of longer linkers (H
,4',4''-[benzene-1,3,5-triyltris(ethyne-2,1-diyl)]tribenzoate)
more flexible and longer than the previously reported backbone.31
However, associated with the flexible long linkers, there is an
unknown phase formed in MOF-1004 produces, impeding the
further characterization and applications.
3
BTE =
with
3
Synthesis of ligand: The synthesis of H ITTC (4,4',4''-(1H-imidazole-
4
2
,4,5-triyl)tribenzoic acid) is based on the method of the previous
literatures.32 (See supporting information Section 1 for details)
Synthesis of ligand single crystal (UPC-157): 5.0 mg H
dissolved in 2.0 mL mixed solution of methanol and acetonitrile
1:1), and heated at 75 °C for two days to precipitate a single crystal
3
ITTC was
(
Inspired by the above researches, saturated Zr clusters can be
achieved under high stability multi-linkage number, and we
of the ligand.
assembled (3,12)-c Zr-MOF with
a tricarboxylic acid ligand
4 3
Synthesis of UPC-158: 0.024 g of ZrCl and 0.010 g H ITTC were
containing modifiable active sites (N, S et al) and strong conjugate
electron, interacting with a guest molecule or facilitating post-
modification, to achieve such stable MOFs. Herein, we reported a
simple and economical reaction where the methyl p-
formylbenzoate was the main reaction material to form the new
dissolved in 3.0 ml DMF solution with 1.1 mol/L benzoic acid. Then,
the solution was heated in a vacuum oven at 120 °C for 48 h under
constant pressure. After cooling, triangular prism-shaped crystals
were obtained. The sample was purified with fresh DMF three time
to remove the benzoic acid and unreacted raw material, then
methanol solution (95%) was used three times to make sure that
the occluded DMF molecules were totally exchanged. After drying,
UPC-158 was obtained under vacuum at 100 °C for 10 h.
imidazole-tricarboxylate linker
3 3
H ITTC (H ITTC = 4,4',4''-(1H-
imidazole-2,4,5-triyl)tribenzoic acid) (Scheme S1), in which
imidazole ring acts as an equatorial plane, and the three benzene
rings connected thereto deviate from the same side of the
equatorial plane by 5.741, 41.887, 41.888 degrees, respectively (Fig.
S4). The angles of the benzene rings in the ligands are slightly
twisted to 8.926, 15.183, 15.183 degrees, respectively (Fig. S5),
Preparation of UPC-158-HX(X = F, Cl, Br, I): The fresh crystals of
UPC-158 were washed with DMF several times, then, soaked with
HX aqueous solution (pH = 3) for two days, during which the solvent
was removed and replenished two times. After that, the solvent
was decanted, soaking in methanol for two days and changed the
fresh methanol three times a day. After drying, UPC-158-HX was
obtained under vacuum at 100 °C for 10 h.
combined with Zr
6
clusters to generate a high-symmetry MOF (UPC-
1
58) that enables a robust porous framework owing to the strong
affinity between Zr(IV) and carboxylate-O.18 UPC-158 exhibits a
fluorescence-pH dependent relationship after varying degrees of
protonation, which makes it a potentially precise pH meter.
Moreover, UPC-158-HX exhibits different iodine adsorption
capacity after treatment with different halogen acids.
Results and discussion
Structure description
Experimental Section
Colorless triangular prism-shaped of UPC-158 was obtained via
Materials and Methods.
4 3
solvothermal reactions of ZrCl with H ITTC ligand in DMF at 120 °C
for 72 h by using benzoic acid as a modulator. Single-crystal X-ray
diffraction reveals that UPC-158 crystallizes in the cubic crystal
system with Pmퟑn space group and is composed of the cuo-12-
All the reagents and solvents were used as received from
commercial suppliers without further purification. Single crystal
data were collected by X-ray diffractometer with a Cu sealed tube (λ
connected Zr
ITTC linker to form the 3-D network. As shown in Fig. 1, Zr
O) (μ -OH) (-COO)12 cluster in UPC-158 adopts O symmetry and
6
(μ
3
-O)
4
(μ
3
-OH)
4
(-COO)12 clusters connected by tritopic
=
1.5406) at 40 kV and 40 mA. Powder X-ray diffraction (PXRD) was
H
3
6
(μ
3
-
carried out on a BRUKER D8-Focus Bragg-Brentano X-ray powder
4
3
4
h
2
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each edge of the Zr
6
cube is linked by one carboxylate from a ITTC3- Thermal and chemical stability analysis.
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ligand and each triangular face is bridged by (μ
group, which is similar to that of UiO series,21 PCN-221,33 PCN-228-
30,34 PCN-56,35 and MOF-525.24 Surprisingly, the symmetry of
3
-O) and (μ
3
-OH)
DOI: 10.1039/C9TA03126J
To explore the thermal stability of UPC-158, TGA curves were
measured, indicating that UPC-158 is stable up to about 500 °C (Fig.
S7). PXRD patterns of UPC-158 at different temperatures were
performed to further demonstrate thermal stability. As shown in Fig.
2a, UPC-158 maintains its crystallinity after heating at 450 °C for 1 h
2
H
3
ITTC ligand is reduced to the lowest C symmetry to connect
three Zr clusters, which is different from the D3h symmetry in MOF-
s
6
08,36 PCN-777,27 BTU-12-1328 and C
in Zr-BTB.29 This symmetry
reduction contributes to the triangular ligand symmetrically
compatible with the Zr (μ -O) (μ -OH) (-COO)12 clusters. Moreover,
8
1
2
in N . Apart from the high thermal stability, UPC-158 also possesses
excellent chemical stability. UPC-158 was separated into solutions
with different pH (0.5, 1, 2, 7, 10, 11 and 12) for 24 hours, PXRD
results prove that UPC-158 remains intact between pH = 0-11.
Surprisingly, UPC-158 can maintain unchanged in 3 M HCl aqueous
solutions (Fig. S8).
6
3
4
3
4
there exist two kinds of cages in the sizes of around 12.69 and 20.00
Å in UPC-158, respectively. As we predicted, the combination of the
unique linker and the Zr clusters results in a sky topology in the
6
2
0
24 22
3
Reticular Chemistry Structure Resource with {4 6 8 }{4 }
topology.
4
Thus, the chemical stability of UPC-158 towards halogen acid is
investigated by immersing them into different aqueous solutions of
halogen acid (pH = 3) for two days. The resultant PXRD patterns are
very consistent with the simulated ones, demonstrating that UPC-
1
58 can survive in halogen acids (Fig. 2b). The excellent thermal and
chemical stability are attributed to the saturated multi-coordination
number and strong coordination capacity between Zr and
carboxylate group based on Hard-Soft-Acid-Base theory. Other
reasons may arise from deprotonation of imidazole group of H ITTC
6
3
ligand involved in the UPC-158 framework. When the pH is acidic, -
+
N group in imidazole will obtain an H , forming protonation format.
In comparison, when the pH is basic, -NH group in imidazole will
+
lose an H , forming deprotonation format (Fig. 2c).
Fig. 1 Crystal structure of UPC-158: (a) 3-connected organic ligand; (b) cuo 12-
connected Zr cluster; (c) simplified 3-connected linker; (d) 12-connected node; (e) 3D
6
network; (f) sky topology; (g)(f) big cage in UPC-158; (h)(j) small cage in UPC-158.
DFT calculation on ligand energy barrier
The density functional theory (DFT) calculations were used to
interpret the successful formation of (3,12)-connected sky net in
UPC-158 at the level of M06-2X-D3/6-311+G(2d,2p) in the SMD
solvent mode using Gaussian 09 D.01.37 To simplify the calculations,
Fig. 2 (a) PXRD of UPC-158 treated through Different temperature (30~480 °C). (b)
PXRD of UPC-158 treated with different halogen acid solutions at pH = 3. (c)
the effect of Zr
crystal structure of H
6
clusters on energy barrier was ruled out and the Protonation and deprotonation processes of porphyrin involved in UPC-158 framework
2
in experimental acidic and basic media (pH = 0-11). (d) N adsorption isotherms for
3
ITTC linker was also performed as a reference.
UPC-158 and UPC-158-HX (X = F, Cl, Br, I).
Thus, DFT calculations were carried out on the ligands with
different configurations. One is free state in UPC-157 and the other
is in UPC-158. As depicted by DFT calculations, the energy barrier
△G) between two states is 28.73 kcal/mol, which can be easily
overcome. Thus, it is suggested that the rational choice of organic
To assess the porosities of UPC-158 and UPC-158-HX (X = F, Cl, Br,
I), we investigated N sorption experiments at 77 K (Fig.2d). UPC-
58 and UPC-158-HX exhibit a type-I isotherm of N sorption with
uptakes of ~600 cm /g at 1 bar, implying the existence of
micropores in UPC-158. Indeed, the pore size distribution shows the
presence of two pore sizes of 12 Å and 20 Å. The resulting 3D UPC-
2
(
1
N
2
3
2
linkers is the key factor to construct rare (3,12)-connected sky net.
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1
58 exhibits high specific surface area. The experimental symmetry of ligands changes from C
s
to C
s
. In comparison, when the
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Brunauer−Emmett−Teller surface areas of UPC-158, UPC-158-HF, pH is higher than 10, the fluorescence inteDnOsiIt:y10o.1f03U9P/CC-91T5A803r1i2s6eJs
2
-1
UPC-158-HCl, UPC-158-HBr and UPC-158-HI are 2170.16 m ·g , gradually in line with the increment of pH and reaches up to the
2
-1
2
-1
2
-1
2
-1
2
136.72 m ·g , 2289.13 m ·g , 2151.35 m ·g , 1953.55 m ·g , maximum when the pH is 11.08. It is noted that an obvious blue
respectively, and their porosities are 0.928591, 0.956570, 0.992850, shift of 13 nm (pH > 9.7) of emission maxima was detected (Fig. 3b).
3
0
.931357, 0.853214 cm /g, in good agreement with the results The fluorescence enhancement and blue-shift in pH (9.7-11.2)
calculated using the non-disordered structure. Therefore, the high solution arise from deprotonation of N-H group of imidazole and
porosity of UPC-158 can be used to carry out the adsorption and the symmetry of ligands changes to chiral symmetric structure
encapsulation experiment of difficult-to-capture guest molecules.
again. After that, the fluorescence decrease gradually accompanied
by the partially destroy of UPC-158. Significantly, the correlation
relationship between fluorescence intensity and pH values can be
divided into three pieces: When pH varies from 0-1.04, a simple
linear relationship with slope is 0.08489. And when the pH is in the
range of 1.04-10.2, the fluorescence intensity keeps constant.
However, when the pH is between 10.2-11.08, another linear
relationship appears with slope is 1.07825.
To further analyze the changes in fluorescence intensity, the
fluorescence lifetime and quantum yield tests were recorded. As
depicted in Fig. 3c, in pH < 9 solution, their fluorescence lifetime are
maintained at approximately 2.7 ns, When the pH is between 10
and 11, the fluorescence lifetime is extended to 3.13 ns. At the
same time, the quantum yield is correspondingly increased from 5%
to 30%, which is consistent with the fluorescent mutation region
(
Fig. 3d). The excellent pH sensing properties make UPC-158 be a
Fig. 3 (a) Blue points showed the normalized fluorescence intensity at ~448 nm in
different pH solution; (b) Normalized to show blue shift (pH > 9.7) of the fluorescence
emission wavelength; (c) Fluorescence lifetime of UPC-158 in different pH solutions; (d)
The quantum yield of UPC-158 in different pH solutions.
potentially precise pH meter, especially in the range of pH = 10~11.
pH sensing analysis
Fluorescent pH sensors have certain advantages in electrode and
current wide range of environmental analysis, bioanalytical
chemistry for medical diagnostics, etc.35 However, only a few MOFs
as pH-dependent fluorescence sensors have been reported (Table
S2). The excellent chemical stability towards acid and base has
propelled us to use UPC-158 as a potential pH detector. UPC-158
shows strong fluorescence emission of H
room temperature with λex = 350 nm, owing to π -π transition
3
ITTC ligand at 448 nm at
*
between intraligands (Fig. S9). The coordination with Zr
with linkers did not affect the fluorescence emission, and there is
no electron and long range energy transfer processes between Zr
and linkers. Furthermore, the pH dependent fluorescence
6
clusters
6
Fig. 4. XPS high-resolution spectra of the F 1s region (a); Cl 2p region; (b) Br 3d region;
properties of UPC-158 were investigated by exposing UPC-158 to (c) and I 3d region (d).
aqueous solution with different pH values. Interestingly, the Adsorption and release of iodine.
fluorescence intensity of UPC-158 is in close association with pH
Due to the ultra-high energy density and low carbon emissions of
nuclear power, it has become an important and widely used energy
source.38 The radionuclides 129I and 131I are nuclear waste streams
changes of the dispersed solutions (pH range from 0 to 12.2) (Fig.
a, S10, 11). Altogether, UPC-158 exhibits weak fluorescence in
3
acidic solution while strong fluorescence in basic solution with the
highest intensity in pH = 11.08. When the pH < 1.04, which is
characteristic of protonation of the imidazole ring, the increasing
pH causes a slight increase of the fluorescence emission intensity.
When the pH is acidic, -N group in imidazole will obtain an H+,
forming protonation format, destroying the π system of imidazole
and thus resulting in significant fluorescence quenching, and the
generated by nuclear power. The colored guest iodine molecules
can be encapsulated by suitable multi-stage channels in MOFs. The
active site "N" and the strong conjugated π-electrons of the ligands
provide possibilities to interact strongly with guest molecules.
Moreover, UPC-158 crystals with large specific surface areas and
porous channels also make UPC-158 performing high guest
molecule-capturing. Although previous reports have focused on
4
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how to design porous materials with high capacity, ultra high UPC-158-HX show that the materials were stable afVteierwtAhrteicleioOdnilninee
stability, and easy reusability, few studies have explored the ability adsorption (Fig. S24). This sorption was kinDeOtiI:c10fa.1s0t3e9r/Cth9aTnA0o31th26eJr
to affect iodine adsorption differently modified materials.
observed in most porous iodine MOFs,39-45 some CMP 46-48 and
traditional activated carbon adsorbent (Table S3).49, 50 XPS was
implemented to further verify the morphology of iodine in UPC-158
series (Fig. S25). Peak splitting originates from the 3d3/2 and 3d5/2
orbitals of iodine, which correspond to the binding energy peaks at
In view of the fact that neutral UPC-158 can be protonated in the
acidic environment, it is bound to change the electrical properties
of the skeleton. To investigate the effects on the iodine adsorption
capacity of protonated UPC-158, we compared the effects of
protonated cation skeleton of UPC-158-HX (F, Cl, Br, I) on the ability
to adsorb iodine. The characterization results of XPS (Fig. 4) and
EDS-mapping (Fig. S13~18) proved the entry of halogen elements.
Therefore, based on the above characteristics, and iodine
adsorption experiments were carried out.
6
30.6 and 619.2 eV, respectively. The peaks at ~630.2 and ~618.8
eV of UPC-158 series are attributed to covalently bound to iodine.
3 2
Fig. 6. The electronic static potential of neutral and acid state H ITTC and I molecule,
and their corresponding adsorption energies to I molecule.
2
DFT calculation on Iodine adsorption
To clarify the different absorption ability between the neutral and
halogenated and protonated state, density function theory (DFT)
calculations were carried out on the basis of M06-2X-D3/6-
3
11G(d,p)/SDDALL//6-311G+(2d,2p)/SDDALL using Gaussian 09
D.01 software package.37 The electrostatic potential (ESP)
populations of neutral, protonated and halogenated state of MOF-
unit together with I
shown in Table 1: the binding energy of H
2
molecule are calculated and the results are
ITTC-HX to the iodine
3
Fig. 5. (a) Time-dependent iodine vapor capture capacities of UPC-158 and UPC-158-HX molecule is HCl > HBr > HI > HF > netural. The H ITTC is overall
3
(
X=F, Cl, Br, I); The colour change of UPC-158 (a)sample and single crystal during iodine
neutral among the molecule. After protonation, the entire
imidazole molecule is positively charged. On the other hand, the
entirety of the iodine molecule exhibits a weaker electronegativity,
except that the two sides exhibit a strong positive charge. As a
consequence, the iodine molecule can not only interact with
positive charges, but also generate mutual electrostatic forces with
halogen ions. The calculation results show that both iodine
adsorption for 3h, respectively; (c) Color transformation from dark red to colorless of a
single crystal of UPC-158.
In this work, the stable 127I was substitute to radioactive 129I and
131I, because these isotopic iodine elements possess nearly identical
chemical behaviour. When the activated UPC-158 series were
exposed to iodine vapor environment of 343.15 K and 1 bar, its
colour changes from colorless to red until the final black throughout
molecules and neutral and protonated/halogenated H
electrostatically adsorbed. For the purpose of further measuring the
adsorption capacity of the iodine molecule and the H ITTC in both
3
ITTC can be
(
Fig. 5a, 5b). The weight of the corresponding iodine-loaded
adsorbent also gradually increases in the surrounding environment.
The results show the introduction of different halogens F ,Cl , Br
3
-
-
-
states, we also calculated the binding energy of the two molecules
in the two states. As presented in Fig. 6, the physical adsorption
between I molecule and H ITTC are favourable in both states.
2 3
-
and I did make the iodine adsorption of UPC-158 increase, from the
original 178% to 219%, 292%, 275% and 259%, respectively (Fig. 5c),
in line with the TGA results (Fig. S19-23). It is worth noting that the
iodine adsorption capacity of the crystal after protonatied by HCl is
significantly improved to 292%, which was the highest among MOFs,
and the equilibrium uptake for UPC-158 series were reached quickly
within 4 h, and no further changes in the iodine loading amounts
were observed after 20 h, indicating that the iodine uptake in the
system was basically saturated. In addition, we can clearly see the
iodine particles adsorbed in UPC-158-HF by high-power
transmission electron microscopy (Fig. S18). The XRD results of
Undoubtedly, the adsorption of iodine molecules with protonated
imidazole ligands is stronger than that of neutral imidazole ligands,
which is consistent with the experimental observations. The
introduction of protonation and halogenation increases the force of
the iodine molecular guest and the skeleton to varying degrees,
thereby increasing the adsorption of iodine (The role of iodine and
ITTC in different states can be found in detail in supporting
information Section 6).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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Page 7 of 8
J Po lue ran sael od fo Mn aot te rai ad l js u Cs ht emm ai rs gt ri yn sA
ARTICLE
Journal Name
Table 1. The combination energy between H
state.
3
ITTC and I
2
in neutral and acid deprotonation of nitrogen atom in the imidazole grVoieuwpA, rtUicPleCO-n1l5in8e
exhibits pH-dependent fluorescence with theDOfluI:o1r0e.1s0c3e9n/cCe9TinAt0e3n1s2i6tJy
increasing rapidly at pH = 9.7~11.2, which provides the basis for
Processing
conditions
Combination
Energy
Amount of iodine
adsorption
MOF as an accurate pH meter. Moreover, after treatment with
different halogen acids, iodine absorption capacities of UPC-158-HX
are greatly improved, and the iodine absorption capacity of UPC-
(kcal/mol)
-1
(
g·g )
Neutral
HF
HCl
HBr
HI
-1.52
-4.95
-19.40
-11.47
-9.22
1.78
2.19
2.92
2.75
2.59
1
58-HCl can reach up to 292%, which is the highest record among
MOFs. These results on the structure–property relationships have
the potential to guide future experimental syntheses of functional
MOF materials with novel structures. Meanwhile, this research is of
great significance to new functional porous material designs for pH
sensing and iodine loading.
The single crystal X-ray diffraction on the iodine-loaded crystals
of UPC-158-HX@I can give the bigger crystal cell compared with
2
the as-synthesized one; however, due to the weak diffraction of the
crystal, the resolution of the structure was poor, and the single
Conflicts of interest
There are no conflicts to declare
crystal XRD data of iodine-loaded crystals of UPC-158-HX@I
not obtained. Neverthless, the XRD pattern of UPC-158 before and
after adsorption of I confirmed its crystalline status.
2
was
2
Acknowledgements
In order to verify the recyclability of UPC-158, we implemented
the iodine release experiments. The iodine-loaded sorbents UPC- This work was supported by the National Natural Science
58-HX@I were placed in dry methanol and the color of the Foundation of China (NSFC 21875285, 21571187 and
solution slowly turned red to uniform (Fig. S26). After several times 21701187), Taishan Scholar Foundation (ts201511019), and
of washing, the solution turns to colorless and no longer changes. Shandong Provincial Natural Science Foundation
The crystal color of UPC-158-HX@I
changes back to the near-white (ZR2017BB038)
1
2
2
state, It is worth noting that the color of UPC-158 crystals without
acid treatment is dark yellow (Fig. 27), indicating that part of the
iodine molecules cannot be released. XRD curves of UPC-158 series
after iodine release illustrate that the recovered material retains its
crystalline stability after cycles (Fig. S28). The process of releasing
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