Triazine Based MOFs with Abundant N Sites for Selective Nitrobenzene Detection

Article abstract of DOI:10.1002/zaac.202100089

High sensitivity and selectivity detection of nitrobenzene based on luminescence technology requires high density of functional sites. Due to the abundant functional N sites and good solubility in solvents, triazine derivative ligands are potential to construct frameworks as luminescence detection agent. Herein, a Pt₃O₄ topology Zn-MOF (FJU-120) based on 2-amino-4,6-bis(4-pyridine)-1,3,5-triazine(DAPT) and 1,3,5-Tris-(p-carboxyphenyl)benzene (H₃BTB) as dual-ligands was synthesized for selective detection of nitrobenzene. FJU-120 crystallizes in the cubic system and Pm (Formula presented.) n space group with a=27.5191(9), b=27.5191(9), c=27.5191(9) ?, β=90°, V=20840(2) ?³, Z=90, Mr=448.72, Dc=0.429 g/cm³, F(000)=2736. FJU-120 shows selective fluorescence quenching behavior with nitrobenzene existing, and the corresponding (Formula presented.) constant is 1124.65 L mol^?1. This work reports a new potential crystalline porous material for toxic organic molecular fluorescence detection.

Full text of DOI:10.1002/zaac.202100089

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.202100089
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Triazine Based MOFs with Abundant N Sites for Selective
Nitrobenzene Detection
Jingan Chen,[a] Ting Chen,[a] Shengchang Xiang,[a, b] Jindan Zhang,*[a] and
Zhangjing Zhang*[a, b]
High sensitivity and selectivity detection of nitrobenzene based
on luminescence technology requires high density of functional
sites. Due to the abundant functional N sites and good
solubility in solvents, triazine derivative ligands are potential to
construct frameworks as luminescence detection agent. Herein,
a Pt3O4 topology Zn-MOF (FJU-120) based on 2-amino-4,6-bis(4-
pyridine)-1,3,5-triazine(DAPT) and 1,3,5-Tris-(p-carboxyphenyl)
benzene (H3BTB) as dual-ligands was synthesized for selective
detection of nitrobenzene. FJU-120 crystallizes in the cubic
system and Pm3n space group with a=27.5191(9), b=
�
3
°
27.5191(9), c=27.5191(9) Å, β=90 , V=20840(2) Å , Z=90,
Mr=448.72, Dc=0.429 g/cm3, F(000)=2736. FJU-120 shows
selective fluorescence quenching behavior with nitrobenzene
existing, and the corresponding KSV constant is 1124.65 LmolÀ 1.
This work reports a new potential crystalline porous material for
toxic organic molecular fluorescence detection.
Introduction
derivative ligands in crystalline porous materials is far from
enough, Only Chand et al[10] used 2,4-diamino-6-(4-pyridine)-1,3,5-
triazine ligands and a series of dicarboxylic acid ligands to
synthesize the crystalline state of cadmium according to different
conditions. The material is used for the adsorption of CO2 and
cationic dyes. And many interesting crystalline porous materials
have yet to be synthesized and explored,[11–13] especially in the
field of luminescent detection.
Nitrobenzene (NB) is one of the most important intermediates in
organic synthesis industry, such as dyes, perfumes, explosives etc.
However, nitrobenzene is extremely toxic to the human body, and
excessive nitrobenzene would cause methemoglobinemia.[1]
Therefore, the design and synthesis of high-sensitivity fluorescent
probes are of great significance for the detection of toxic
nitrobenzene emitted by factories.[2] Among various detection
methods, luminescence detection technology has the advantage
of simple operation, intuition, high sensitivity, and selectivity. To
reach these requirements, luminescent metal organic framework
(LMOFs) is regarded as potential detection materials due to its
structure-designable and function-controllable nature.[3–5] However,
great efforts are still required on the detection of the NB, because
it is difficult to reduce the limit of detection (LD) and the usage
amount of luminescent materials owing to the low density site of
many LMOFs.
Herein,
a
bisymmetric zinc-based LMOFs [Zn6(BTB)4
(DAPT)3]·38DMF·108H2O (FJU-120) with cluster node {Zn2(COO)4}
was synthesized for fluorescence sensing. two organic ligands (
2,4-diamino-6-(4-pyridine)-1,3,5-triazine (DAPT) and tridentate
1,3,5-tri(p-carboxyl Phenyl) benzene (H3BTB)) were coordinated
with metal zinc ions was successfully synthesized by hydrothermal
method. Due to the quenching effect, the material has good
selectivity and sensitivity to nitrobenzene. Therefore, FJU-120 can
be used as a potential material for the detection of nitrobenzene.
In consequent, from the fluorescence experiment of FJU-120 at
different nitrobenzene concentrations, combined with the Stern-
Volmer equation, the quenching constant KSV is calculated, which
is 1124.65 LmolÀ 1.
Triazine derivatives with abundant nitrogen atoms, which can
be used as functional sites, are widely used as ligand for MOFs
with enriched the functional site.[6,7] Among those, the bifunctional
triazine derivative ligands are not only rich in functional N sites,
but also have good solubility in solvents.[8,9] Therefore, frameworks
based triazine derivative ligand would be potential as luminescent Results and discussion
materials. However, at present, the study of bifunctional triazine
Crystal structures
[a] J. Chen, T. Chen, S. Xiang, J. Zhang, Z. Zhang
FJU-120 is synthesized with Zn(NO3)2 ·6H2O, 2-amino-4,6-bis(4-
College of Chemistry and Materials Science, Fujian Provincial Key
Laboratory of Polymer Materials, Fujian Normal University, 32
Shangsan Road, Fuzhou 350007, China
pyridine)-1,3,5-triazine (DAPT) and 1,3,5-Tris-(p-carboxyphenyl)
benzene (H3BTB), as first and second ligands. SCXRD reveals that
�
E-mail: zhangjindan@fjnu.edu.cn
FJU-120 crystallizes in the cubic system and Pm3n space group.
zzhang@fjnu.edu.cn
[b] S. Xiang, Z. Zhang
The molecular formula is [Zn6(BTB)4 (DAPT)3]·38DMF·108H2O. As
shown in Figure 1, the structure contains a crystallographically
independent zinc atom connected to four carboxyl oxygens from
the BTB ligand and one pyridine nitrogen or triazine nitrogen from
the DAPT ligand, two symmetrical zinc forms a paddle wheel-
shaped dinuclear zinc carboxylate (paddle wheel) cluster node
State Key Laboratory of Structural Chemistry, Fujian Institute of
Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou, Fujian 350002, PR China
Supporting information for this article is available on the WWW
under https://doi.org/10.1002/zaac.202100089
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Figure 1. Crystal structure of FJU-120. (a) coordination mode; (b) three-dimensional framework; (c) simplified nodes; (d) Pt3O4 topology.
{Zn2(COO)4}. The {Zn2(COO)4} cluster nodes in FJU-120 are further
Thermogravimetric analysis (TGA) curves are presented in
Figure S3. It can be seen from the figure that the first weight
extended by three-linked BTB ligands, which are connected to
form a framework with a (3,4)-linked Pt3O4 topology. The frame-
work is further bridged by the pyridine nitrogen atom or triazine
nitrogen atom on the linear DAPT ligand to form an extended
Pt3O4 topology. The structure of FJU-120 is the same as that of FJI-
1 reported by Hong et al,[14] except that the bridged ligand used is
different. The 2,4-diamino-6-(4-pyridine)-1,3,5-triazine ligand is
consistent with the 4,4-bipyridine ligand, and both inhibit the
interspersion of the framework. The porosity of FJU-120 calculated
by PLATON is 78.5%.
°
°
loss interval of FJU-120 is between 30 C and 200 C, which is
the loss of solvent molecules within the framework. After
°
200 C, the frame begins to degrade.
Combined with SCXRD, elemental analysis (experimental
part in supporting information) and TGA results, the molecular
formula of FJU-120 can be determined as[Zn6(BTB)4
(DAPT)3]·38DMF·108H2O.
Fluorescent property
FT-IR, PXRD and thermogravimetric analysis (TGA)
Fluorescence performance of FJU-120, metal organic frames
containing d10 metal centers usually have photoluminescence
properties and can be used as luminescent materials. Therefore,
we tested the solid-state luminescence spectra of FJU-120, ligand
DAPT and ligand H3BTB at room temperature. As shown in
Figure 2(a), when the excitation wavelength is 348 nm, the
emission wavelengths of FJU-120, ligand DAPT and ligand H3BTB
mainly appear at 441 nm, 440 nm, and 435 nm. The strong
emission peaks in the ligand DAPT and ligand H3BTB are attributed
to the n!π* or π!π* charge transfer inside the ligand.
Considering that the divalent metal zinc ion is not prone to redox
reactions, the photoluminescence behavior of FJU-120 is neither
metal-ligand charge transfer (MLCT) nor ligand-metal charge
transfer (LMCT).[15] Since the emission spectrum of FJU-120 is close
FT-IR curve of FJU-120 is shown in Figure S1, the asymmetric
and symmetrical vibration absorption peaks of the carboxyl
group in the H3BTB ligand are located at 1593 cmÀ 1 and
1389 cmÀ 1, the double absorption peaks of moderate intensity
at 3336 cmÀ 1 and 3310 cmÀ 1 are the characteristic absorption
peaks of the amino group on the DAPT ligand.
Power X-ray diffraction (PXRD) pattern of FJU-120 is shown
in Figure S2, And compared the simulated and synthesized
PXRD patterns. The PXRD pattern of synthesized samples
matches the simulated curves well, implying the complete
structure and high purity of the synthesized samples.
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Figure 2. (a) Solid-state fluorescence emission spectra of DAPT, H3BTB ligands and FJU-120. The emission spectra were collected with an
excitation wavelength of 348 nm; (b) Fluorescence spectra of FJU-120 in various pure organic solvents (excited at 348 nm).
to the emission spectrum of ligand DAPT and ligand H3BTB, the
photoluminescence behavior of FJU-120 may come from the
charge transfer of the ligand within the framework, that is n!π*
or π!π*. The small peak around 350 nm in DAPT curve relates to
the excitation light, which was not completely filtered by the filter.
Small molecules play an important role in chemical and
biological systems. Therefore, it is necessary to study the
recognition and sensing of small molecules. At present, more and
more scientists have participated in it. After experiments, we
found that FJU-120 has photoluminescence behavior. In order to
further study its luminescence behavior in small molecule solvents,
the following experiments were carried out. We first add the fully
ground FJU-120 to the organic solvent, make it immersed and
completely dispersed, and then test the fluorescence spectrum of
FJU-120. We use N,N-dimethylformamide (DMF), N,N-dimeth-
ylacetamide (DMA), 1,4-dioxane, ethyl acetate (EAC), dichloro-
methane (CH2Cl2), nitrobenzene (NB), acetone, acetonitrile (CH3CN)
and methanol (CH3OH) solvents were tested. The emission spectra
of FJU-120 in solvent are all tested under the same conditions. The
experimental results show that the fluorescence intensity of FJU-
120 is different in different organic solvents (Figure 2(b)). It can be
seen from the figure that nitrobenzene exhibits a more significant
fluorescence quenching behavior on the sample, while for other
solvents, the effect on the fluorescence intensity of the sample is
relatively smaller.
FJU-120 can be used as a simple sensor to detect nitro-
benzene molecules. In FJU-120’s fluorescence sensing experi-
ment on a series of small organic molecules, only nitrobenzene
exhibited highly selective fluorescence quenching behavior, so
FJU-120 can sense nitrobenzene molecules. In order to further
evaluate the quenching effect of nitrobenzene on FJU-120 in
DMF solution, we tested the fluorescence spectra of samples at
various nitrobenzene (NB) concentrations. As shown in Fig-
ure 3(a), as the concentration of nitrobenzene increased from
0 mM to 2.93 mM, FJU-120 showed significant fluorescence
quenching. The quenching percentage (QP) was calculated by
the equation,[16,17] (QP)=(I0À I)/I0 ×100%, in which I0 and I are
the fluorescence intensity of the suspensions without and with
the addition of NB, respectively. When the concentration of NB
in the suspensions is up to 2.93 mM, the QP values are 77.59%.
In order to evaluate the quenching effect, the Stern-Volmer
equation[18] is used to calculate the quenching constant, and
the corresponding equation is as follows:
Figure 3. (a) The fluorescence spectrum of FJU-120 at different concentrations of nitrobenzene (NB) solutions in DMF; (b) Stern-Volmer plot,
excited at 348 nm and monitored at 425 nm.
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Aknowledgements
I0
I
¼ KSVbMc þ 1
This work was supported by the National Natural Science
Foundation of China (21805039, 21975044 and 21971038), the
Fujian Provincial Department of Science and Technology
(2018J07001 and 2019H6012), and Education Department of
Fujian province (JT180090).
Among them, I0 and I are the fluorescence intensity detected
before and after adding nitrobenzene, bMc is the molar concen-
tration of nitrobenzene, and KSV is the quenching constant. At low
concentrations, the linear relationship between I0=I and bMc can
be obtained, and the value of KSV can be obtained. As shown in
Figure 3(b), the calculated KSV is 1124.65 MÀ 1, which is comparable
to or better than that of the previously reported well-designed
compounds, such as Ln-MOFs 2(1323 MÀ 1),[12] {[Cd2(L)(DMA)]·[H2N-
(Me)2]}n(2700 MÀ 1),[19] [Tb(L1)(H2O)2]·guest and [Tb(L2)(H2O)2]·guest
(589.5, 445.6 MÀ 1),[20] more MOFs-based fluorescent sensing materi-
als are shown in Table S4. On the basis of the KSV values and the
standard deviations for five repeated luminescence measurements
of the blank solutions, the detection limits (LD=3σ/KSV)[21] of the
FJU-120 are calculated (Table S5). According to 3σ/KSV the
detection limit is 5.6×10À 2 M, which demonstrated the high
sensitivity of the sensor toward NB. Currently, the detection limits
does not reach the current industrial tolerant level (10À 4 M) of NB.
However, the framework based on triazine derivatives is potential
for abundant N sites and the structure designability, and thus,
more works are needed to reduce detection limit in the future.
Keywords: Metal-organic frameworks · Triazine derivatives ·
Fluorescence sensing
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Conclusion
In short, we successfully synthesized a three-dimensional metal
organic framework material (FJU-120) by hydrothermal method
using dual-ligand (2-amino-4,6-bis(4-pyridine)-1,3,5-triazine and
1,3,5-Tris-(p-carboxyphenyl)benzene) and metal zinc ions. FJU-120
has photoluminescence properties, and its photoluminescence
behavior may come from the n!π* or π!π* charge transfer of
the ligand in the framework. The photoluminescence behavior of
FJU-120 in different organic solvents shows that the fluorescence
intensity of the sample depends on the solvent used, and
nitrobenzene exhibits obvious fluorescence quenching behavior
for the sample. Because FJU-120 has
a highly selective
fluorescence quenching effect on nitrobenzene, it can be used as
a simple sensor to detect nitrobenzene molecules. Finally, from
the fluorescence experiment of FJU-120 at different nitrobenzene
concentrations, combined with the Stern-Volmer equation, the
quenching constant KSV is calculated, which is 1124.65 LmolÀ 1.
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Supplementary materials
CCDC 2069008 contains the supplementary crystallographic
data for this paper. Additional FT-IR, PXRD and thermogravi-
metric analysis (TGA), Crystallographic Data.
Manuscript received: March 14, 2021
Revised manuscript received: April 8, 2021
Accepted manuscript online: April 11, 2021
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ARTICLE
J. Chen, T. Chen, S. Xiang, J. Zhang*,
Z. Zhang*
1 – 5
Triazine Based MOFs with
Abundant N Sites for Selective Ni-
trobenzene Detection