A Versatile Microporous Zinc(II) Metal-Organic Framework for Selective Gas Adsorption, Cooperative Catalysis, and Luminescent Sensing

Article abstract of DOI:10.1021/acs.inorgchem.8b00938

A versatile microporous zinc(II) MOF (1) with plentiful Lewis basic sites and open metal sites synchronously has been synthesized successfully. The resultant microporous material displays excellent selectivity adsorption for small gases. The IAST selectivity values for CO₂/CH₄, C₂H₆/CH₄, CO₂/N₂, and C₃H₈/CH₄ are 7, 21, 38, and 125 at 101 kPa and 298 K, respectively. 1 exhibits remarkably heterogeneous catalytic performance for acid-base one-pot reactions. Furthermore, 1 exhibits recyclable selective detectability for TNP. The results illustrate that 1 is a versatile material for selective gas adsorption, cooperative catalysis, and luminescent sensing.

Full text of DOI:10.1021/acs.inorgchem.8b00938

Article
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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
A Versatile Microporous Zinc(II) Metal−Organic Framework for
Selective Gas Adsorption, Cooperative Catalysis, and Luminescent
Sensing
Hongming He,*,† De-Yu Zhang,† Feng Guo,§ and Fuxing Sun*,‡
†Key Laboratory of Inorganic−Organic Hybrid Functional Material Chemistry of the Ministry of Education, College of Chemistry,
Tianjin Normal University, Tianjin 300387, People’s Republic of China
‡State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012,
People’s Republic of China
§School of Chemistry and Chemical Engineering, Yangtze Normal University, Chongqing 408100, People’s Republic of China
S
* Supporting Information
ABSTRACT: A versatile microporous zinc(II) MOF (1) with plentiful Lewis
basic sites and open metal sites synchronously has been synthesized
successfully. The resultant microporous material displays excellent selectivity
adsorption for small gases. The IAST selectivity values for CO2/CH4, C2H6/
CH4, CO2/N2, and C3H8/CH4 are 7, 21, 38, and 125 at 101 kPa and 298 K,
respectively. 1 exhibits remarkably heterogeneous catalytic performance for
acid−base one-pot reactions. Furthermore, 1 exhibits recyclable selective
detectability for TNP. The results illustrate that 1 is a versatile material for
selective gas adsorption, cooperative catalysis, and luminescent sensing.
problems all over the world. Currently, a potential method to
efficiently detect NACs for homeland security and environ-
mental protection vis ia luminescent materials. Hence, it is a
crucial challenge to develop and explore multifunctional porous
materials for the above goals.
INTRODUCTION
■
The primary component of greenhouse gas is carbon dioxide
(CO2) in the atmosphere. CO2 has attracted a great deal of
research interest from chemists and materials scientists recently,
as it raises a number of energy crises and environmental
concerns in daily life.1 Thus far, gas adsorption separation
technology is the most effective method of dealing with CO2.2
Natural gas, as a major fossil fuel, can be considered to be a
preferable alternative energy fuel, and it contains abundant
methane (CH4) and varying amounts of C2H6 and C3H8.
Notably, CH4 is not only a prevalent and clean fuel but also an
available C1 source in industry for multiple C1 and C2
chemicals.3 A great deal of effort has been focused on exploring
novel porous materials to store CO2 and purify CH4 from
natural gas. Currently, a gradually increasing interest has been
focused on the development of heterogeneous catalysis for one-
pot and sequential reactions, which is mainly ascribed to their
high efficiency, energy efficiency, and reduction of waste.4
Significantly, considerable attention has been given to acid−
base one-pot catalysis reactions, which have been widely used in
common organic synthesis. Due to the acid−base neutralization
reaction between the acid and base sites, it is a remarkable
challenge to prepare efficiently site isolating acid−base one-pot
heterogeneous catalysts. Meanwhile, nitroaromatic compounds
(NACs) are the most common explosives and contaminants
and are broadly used in the military, agriculture, and industry. It
is found that NACs trigger a series of environmental and safety
Metal−organic frameworks (namely MOFs)5 have attracted
tremendous interest in the past 12 years due to their diverse
architectures and applications in heterogeneous catalysis,6 gas
sorption,7 sensing,8 enzyme immobilization,9 and optical
apparatus.10 Because of the relationship between structures
and characteristics in MOFs, MOFs are able to be designed and
tuned through rationalization of bridging linkers and metal
units. Therefore, we speculate that if the frameworks possess
both Lewis basic sites (LBSs) and unsaturated open metal sites
(OMSs) and have luminescent properties, they can form
multifunctional materials for gas separation, catalysis for acid−
base sequential reactions, and luminescent sensing for NACs.
Recently, 1,3,5-triazine functional groups have been imported
successfully into MOFs and can serve as efficient LBSs for
many applications.11 In view of the aforementioned discussion
of the documented studies, we selected a semirigid organic
ligand with abundant N-rich functional groups, 2,4-bis(3,5-
dicarboxyphenylamino)-6-ol triazine (H4BDPO).11d Under
solvothermal conditions, the organic ligand can coordinate
Received: April 11, 2018
© XXXX American Chemical Society
A
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with ZnII to form a rare three-dimensional (3D) ZnII paddle-
wheel-based microporous MOF with the formula
[Zn24(BDPO)12(DMF)12]·6DMF·52H2O (1; DMF = N,N-
dimethylformamide). Thanks to ZnII having a closed-shell d10
electron configurations without any luminescence quenching
effects, 1 has luminescent properties as for the free organic
ligand H4BDPO. As we expected, the obtained MOF illustrated
remarkably selective adsorption (CO2 over N2 and CH4 and
CH4 over C2H6 and C3H8), had excellent performance as a
heterogeneous catalyst for acid−base sequential reactions, and
exhibited highly selective sensing for TNP (as shown in
Scheme 1).
atoms were directly located and anisotropically refined. Due to the fact
that the solvent molecules were highly disordered, the SQUEEZE
method of PLATON was used to delete them.14 The solvents could be
determined from TGA and elemental analysis results. The crystallo-
graphic results are given in Table 1, and selected bond angles and
lengths are summarized in Table S2.
Table 1. Crystallographic Data for 1
empirical formula
formula wt
cryst syst
C282H338O178N78Zn24
9222
cubic
space group
a = b = c (Å)
α = β = γ (deg)
V (Å3)
Im3m
̅
27.9409(14)
90.00
Scheme 1. Versatile Microporous MOF for Gas Adsorption,
Cooperative Catalysis, and Luminescent Detection
21813.3(19)
24
Z
ρcalcd (g cm−3
)
1.109
μ (mm−1
)
1.361
Nref
2014
F(000)
R(int)
7248.0
0.0345
goodness of fit on F2
R1, wR2 (I > 2σ(I))
R1, wR2 (all data)
1.087
0.0879, 0.2583
0.0895, 0.2610
RESULTS AND DISCUSSION
Structure Description. 2,4-Bis(3,5-dicarboxyphenylami-
no)-6-ol triazine (H4BDPO) and Zn(NO3)2·6H2O were both
dissolved in DMF and H2O at 120 °C for 3 days, generating
colorless block-shaped crystals. The single-crystal data illus-
■
trated that 1 belongs to the cubic space group Im3m space
̅
group (Figure S1 in the Supporting Information). Figure 1
EXPERIMENTAL SECTION
■
Materials and Methods. Chemicals and reagents were purchased
commercially and used without any purification. Room-temperature
powder X-ray diffraction (PXRD) data were collected on a D-Max
2550 diffractometer with Cu Kα radiation at 40 kV and 200 mA with
the 2θ values from 4 to 40°. Thermogravimetric analyses (TGA) were
carried out with a TGA Q500 analyzer under an N2 flow to 800 °C. A
Vario MICRO elemental analyzer was used to obtain elemental
analyses of C, H, and N. Fourier-transform infrared spectra (FT-IR)
were directly recorded on a nano-FTIR instrument from 4000 to 400
cm−1. All gas measurements were measured with a Micrometrics ASAP
2020 apparatus. UV−vis absorption spectra were obtained with a
Mapada V-1200 spectrophotometer. All luminescence data were
obtained on a Cary Eclipse fluorescence spectrophotometer at room
temperature. The gas chromatographic results were directly obtained
with an Agilent 6890 instrument.
Synthesis of [Zn24(BDPO)12(DMF)12]·6DMF·52H2O (1). Zn-
(NO3)2·6H2O (0.030 g, 0.0001 mol) and H4BDPO (0.020 g,
0.000044 mol) were both dissolved in DMF (5 mL), H2O (0.75
mL), and HNO3 aqueous solution (2 M, 0.2 mL) and placed into a 18
mL autoclave and heated at 120 °C for 3 days. Crystals were formed
and washed with fresh DMF. The yield was 76% based on H4BDPO.
Anal. Calcd for C282H338O178N78Zn24: C, 36.89; H, 3.72; N, 11.98.
Found: C, 36.70; H, 3.67; N, 11.84. Representational FT-IR data (KBr
pellet, cm−1): 3339 (br), 2931 (s), 2867 (s), 1661 (s), 1595 (s), 1556
(s), 1531 (s), 1375 (s), 1254 (s), 1085 (s), 896 (s), 806 (s), 775 (s),
734 (s), 667 (s), 639 (s), 585 (s), 489 (s).
Single-Crystal X-ray Crystallography. Room-temperature sin-
gle-crystal X-ray diffraction measurements for 1 were collected on
APEXII Quazar CCD instrument with Cu Kα radiation. The beam
absorption effects were corrected using the SADABS program.12 The
final structure of 1 was solved successfully by direct methods and
refined on F2 values by the SHELXTL program.13 Non-hydrogen
Figure 1. Illustration for the construction of 1.
shows that the H4BDPO ligand contains two terminal
isophthalate moieties, which can be assembled with ZnII
paddle-wheel motifs to fabricate the typical MOP-1 structure.
Fascinatingly, one axial site of the paddle-wheel motif
coordinates to a nitrogen atom from the ligand to increase
the net connectivity to 5. 1 has three different microporous
cages in the overall structure. The terminal isophthalate
moieties can be assembled with classical paddle-wheel motifs
to form the typical MOP-1 about 14.9 Å. The medium-sized
cages (12.1 Å) are built from eight units and four linkers. Other
small cages (8.9 Å) are formed by six units and six linkers.
B
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These different cages are further connected by bridging ligands
to generate a 3D structure with multiple pore systems. The
resultant 3D network was symbolized as a rare 5-node uninodal
topology with the point symbol [46·64] (Figure S2 in the
Supporting Information).15 The free volume of 1 was calculated
to be about 49.1% after elimination of solvent molecules by the
PLATON/VOID method.14b
12.7 Å were found by the DFT method, which agrees with the
single crystal results (Figure 2, insert).
The activated crystals were further measured for some other
small gases. The low-pressure uptake for H2 is reversible, and
the maximum adsorption amounts are about 1.76 wt % (198
cm3 g−1) and 1.23 wt % (138 cm3 g−1) at 77 and 87 K under 1
atm, respectively (Figure S8 in the Supporting Information),
which are higher than those of PCN-6′ (1.37 wt %)16 and
HKUST-1 (1.44 wt %)17 at 77 K. The isosteric heat (Qst) at
zero coverage (6.57 kJ mol−1) was obtained from H2 adsorption
isotherms at 77 and 87 K by the virial equation (Figure S10 in
the Supporting Information). Furthermore, the adsorption
amount of O2 at 77 K is about 408 cm3 g−1 (Figure S9 in the
Supporting Information), which is similar to that of other high-
BET MOFs.18 The maximum uptakes of CO2 were about 109
cm3 g−1 (273 K) and 79 cm3 g−1 (298 K) under 1 atm (Figure
3a), which are higher than those of SUN-50 (106 cm3 g−1)19
PXRD, FT-IR, and Thermal Analysis. The PXRD data of 1
at room temperature illustrated that the obtained crystalline
materials are pure (Figure S3 in the Supporting Information).
As shown in Figure S4 in the Supporting Information, TGA
curves of 1 under an N2 flow showed a slow weight loss of
24.47% from room temperature to 310 °C due to the solvent
molecules in 1 (calculated 24.40%). The main skeleton
framework started to decompose with an increase in temper-
ature from 400 °C. The as-synthesized crystals were exchanged
solvent molecules with MeOH for 3 days and CH2Cl2 for 3
days, respectively. Then samples were evacuated at 100 °C ofr
about 10 h to obtain the activated samples for small gas
adsorptions. The activated sample’s PXRD pattern showed that
the pristine structure was retained well after the activation
process (Figure S3 in the Supporting Information). Figure S5
in the Supporting Information shows that the characteristic
peak (1704 cm−1) of −COOH only appeared in the free
H4BDPO ligand, confirming that all of the carboxyl groups
were fully deprotonated in 1. In addition, the typical peak
(1645 cm−1) of CO of DMF molecules disappeared in the
activated sample. The results showed that all DMF molecules
were removed thoroughly, which was in agreement with the
TGA results (Figure S4 in the Supporting Information). In
addition, 1 displays excellent stability in different organic
solvents and high heat stability still at 300 °C in air (Figures S6
and S7 in the Supporting Information).
Gas Sorption Properties. N2 gas sorption measurements
(77 K) of the activated sample were carried out to verify the
permanent pore character. As indicated in Figure 2, N2 sorption
isotherms featured a type I isotherm characteristic of the low-
pressure region. The Brunauer−Emmett−Teller surface area
and Langmuir surface area are 1021 and 1154 m2 g−1,
respectively. To acquire an in-depth insight into the pore
structure, the pore width distributions of about 7.3, 10.9, and
Figure 3. Gas sorption isotherms of CO2 (a), N2 (b), CH4 (c), C2H6
(d), and C3H8 (e) at 273 and 298 K, respectively, and (f) the
corresponding Qst values of these small gases.
and ZIF-20 (69.8 cm3 g−1)20 at 273 K under 1 atm. The
adsorption enthalpy of CO2 is 24.81 kJ mol−1 at 0 loading
(Figure 3f and Figure S11 in the Supporting Information). As
illustrated in Figure 3b,c, the adsorption and desorption
isotherms of N2 and CH4 were obtained at 273 and 298 K.
The maximum N2 uptakes at 1 atm are 10 and 6 cm3 g−1 and
those of CH4 are 35 and 25 cm3 g−1, respectively. The Qst
values of N2 and CH4 are 16.98 and 13.81 kJ mol−1 at zero
loading, respectively (Figure 3f and Figures S12 and S13 in the
Supporting Information). To study CO2 separation ability, the
IAST method was used to predict the theoretical binary gas
mixture separation ability from the experimental single-
component adsorption data. In addition, the dual-site
Langmuir−Frendlich equations can fit the corresponding
experimental results (Figure 4a). The predicted results were
Figure 2. N2 sorption isotherms at 77 K. Inset: the pore size
distribution via the DFT method and the corresponding microporous
framework in 1.
C
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dehyde by an acid-catalyzed process. The following reaction is
Knoevenagel condensation by a base-catalyzed process. In a
typical experiment, a mixture of dimethoxymethylbenzene
(0.001 mol), malononitrile (0.0012 mmol), toluene (4 mL),
and 1 (0.1 g) was placed in a glass reactor (20 mL) and stirred
at 90 °C for 3 h. A GC equipped with a DB-5HT column was
used to monitor the product yield. The reaction results are
summarized in Table 2. 1 was an effectively cooperative catalyst
a
Table 2. Catalytic Reaction Using Various Catalysts
conversn of
yield of
f
yield of
f
f
entry
catalyst
1 (%)
2 (%)
3 (%)
1
2
3
4
1
≥99
91
7
trace
83
≥99
8
HY zeolite
MgO
2
5
HY zeolite +
83
52
31
b
MgO
c
5
6
7
8
HCl
≥99
trace
trace
trace
97
2
d
TEA
trace
trace
trace
trace
trace
trace
Figure 4. Gas adsorption isotherms of CO2, N2, CH4, C2H6, and C3H8
with DSLF fits (a, c) and binary gas adsorption selectivity by the IAST
method (b, d).
e
HCl + TEA
no catalyst
a
Conditions unless specified otherwise: dimethoxymethylbenzene
(0.001 mol), malononitrile (0.0012 mol), toleune (4 mL), catalyst
b
evaluated from landfill binary gas mixtures (50/50, m/m) at
298 K (Figure 4b). The predicted selectivity values for CO2/
CH4 and CO2/N2 are 7 and 38 under 101 kPa, respectively.
The results are distinctly better than those for many previously
reported porous MOFs.21
(100 mg), 90 °C, 3 h. HY zeolite (50 mg) and MgO (50 mg) were
c
d
both used as catalysts. 0.0001 mol of HCl as a catalyst. 0.0001 mol of
e
triethylamine (TEA) as a catalyst. HCl (0.05 mmol) and TEA (0.05
mmol) were both used as catalysts. The yields were determined by
f
GC with diphenyl as an internal standard.
Furthermore, C2H6 and C3H8 adsorption capacities were
both studied at 273 and 298 K (Figure 3d,e). The maximum
adsorbed uptakes of C2H6 are 80 and 72 cm3 g−1 and of C3H8
are 112 and 86 cm3 g−1, respectively. The Qst values at zero
coverage are 29.60 and 54.37 kJ mol−1 for C2H6 and C3H8 via
the virial method (Figure 3f and Figures S14 and S15 in the
Supporting Information). The dual-site Langmuir−Frendlich
(DSLF) equation was applied to match the adsorption data in
Figure 4c. The predicted results for C2H6/CH4 and C3H8/CH4
could be calculated from a feed landfill gas (50/50, m/m) at
room temperature under 1 atm (Figure 4d). The C2H6/CH4
adsorption selectivity is about 21, higher than those for
numerous porous MOFs, including Mg-MOF-74 (11.5),
NOTT-101 (12), and FIR-7a (14.6).22 The C3H8/CH4
selectivity value is about 125, which is higher than those for
UTSA-35a23 and JLU-Liu18.24 The results illustrated that 1 can
be considered to be a promising material not only for
separation and storage of CO2 but also for purification of
CH4 from natural gas, mainly due to the abundant OMSs and
LBSs in 1.
for this reaction with a yield of ≥99% after 3 h (Table 2, entry
1). Some control experiments were performed under similar
conditions. The traditional HY zeolite (SiO2/Al2O3 = 30) was
employed as the acid catalyst for the first reaction (Table 2,
entry 2). MgO solid was used as a basic catalyst, which gave
almost no products (Table 2, entry 3). When HY zeolite and
MgO were both applied as catalysts, the conversion was
significantly lower than that of 1 (Table 2, entry 4). In contrast,
homogeneous catalysts were used for this reaction. HCl, as an
acid catalyst, only effectively catalyzed the first step (Table 2,
entry 5). Triethylamine (TEA) was applied as a basic catalyst,
which generated almost no products even after 3 h (Table 2,
entry 6). As we know, it is easy to neutralize acid and base
catalysts in homogeneous systems. When a mixture of HCl and
TEA was used as catalyst, the reaction hardly proceeded (Table
2, entry 7). In the absence of catalysts, the reaction also hardly
occurred (Table 2, entry 8). The results illustrate that 1 is a
bifunctional acid−base catalyst. In addition, ZnII ions cannot be
detected in the reaction solution using inductively coupled
plasma analysis, further confirming the heterogeneous nature of
1. 1 is easily separated by filtration and can be reused at least
for five cycles with similar activity effects (Figure S16a in the
Supporting Information). The frameworks of reused samples
were confirmed by the PXRD patterns (Figure S16b in the
Supporting Information).
Catalysis Properties. Only a few MOFs were applied to a
tandem one-pot acid−base deacetalization−Knoevenagel con-
densation with high yields.25 Thanks to its large amount of
OMSs and LBSs, 1 can be used as a bifunctional catalyst for a
tandem one-pot acid−base deacetalization−Knoevenagel con-
densation (Scheme 2). The first reaction process is the
deacetalization of dimethoxymethylbenzene to obtain benzal-
Furthermore, the luminescent spectra of the H4BDPO ligand
and ground sample were both obtained. Figure 5a shows that
the free ligand exhibits an emission at 382 nm under excitation
at 337 nm. In comparison, the resultant sample shows an
emission at 422 nm (λex 292 nm) (Figure 5b), indicating the
luminescence of 1 from H4BDPO. To discuss the detectability
of NACs, the emission peak of ground powders in DMF with
600 ppm of analytes was checked under 292 nm, considering
that the crystal samples were insoluble and had highly
Scheme 2. Illustration of the Deacetalization−Knoevenagel
Condensation
D
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efficiency was confirmed by the Stern−Volmer equation: I0/I =
1 + KSV[Q]. I0 is the original luminescence intensity, I is the
luminescence intensity after addition of analytes as quencher,
[Q] denotes the molar concentration, and KSV can be
determined as the Stern−Volmer constant. When I0/I vs [Q]
is almost linear, KSV can be confirmed. The Stern−Volmer plots
were almost linear at low concentrations (Figure S18 in the
Supporting Information), but the plots significantly deviated
from linear at higher concentrations (Figure S19 in the
Supporting Information). This may be due to autoadsorption.24
The KSV values are 9.1 × 102 M−1 for NB, 1.0 × 103 M−1 for
1,3-DNB, 1.2 × 103 M−1 for 2,4-DNT, and 1.6 × 104 M−1 for
TNP, respectively. Notably, the resulting sample is an efficient
sensor for TNP (Table S3 in the Supporting Information).26
Thanks to the three nitro groups, 1 exhibited the most sensitive
detection effect for TNP. With increasing −NO2, effective
charge transfer can take place from electron rich 1 to more
electron deficient analytes, leading to more efficient lumines-
cence quenching.27 In addition, the UV−vis spectrum
illustrated that the emission band of 1 has a coverage with
the adsorption spectrum in DMF (Figure S20 in the
Supporting Information). In fact, 1 is easily recollected from
the dispersed mixture and washed with DMF. The detectability
of 1 was very well retained even after five cycles (Figure S21a in
the Supporting Information). The stability of the recollected
crystals can be demonstrated by their PXRD patterns (Figure
S21b in the Supporting Information).
Figure 5. Excitation and emission spectra of H4BDPO (a) and 1 (b).
(c) Luminescence intensity of 1 with different analytes (600 ppm) in
DMF. (d) Emission spectra of 1 (0.1 mg mL−1) by adding NB in
DMF.
luminescence intensity in DMF (Figure 5c). Notably, 1 exhibits
significant luminescent quenching behavior in nitrobenzene
(NB). The emissive response of 1 can be measured by adding
NB of various concentrations (Figure 5d). The luminescence
intensity sharply decreased to 44% at 1 × 10−3 M and 97% at 1
× 10−2 M, respectively (Figure S17a in the Supporting
Information). The luminescence quenching may be mainly
due to electron transfer from 1 to the electron-deficient NB.8d,e
The quenching behavior is mainly in connection with the
electron-withdrawing −NO2 group. Hence, a series of NACs
were used to explore the luminescence detectability of 1,
including 1,3-dinitrobenzene (1,3-DNB), 2,4-dinitrotoluene
(2,4-DNT) and 2,4,6-trinitrophenol (TNP). The alteration of
luminescence can be measured at 292 nm by adding analytes
(Figure 6a−c), and it can be almost quenched completely
(Figure S17a in the Supporting Information). The quenching
CONCLUSION
■
In summary, a microporous MOF (1) was synthesized
successfully, which exhibits excellent luminescence properties
and possesses many OMSs and LBSs. The resultant material
displays high adsorption selectivity for CO2 over CH4 and N2
and for CH4 over C2H6 and C3H8. It also exhibits remarkably
heterogeneous catalytic performance with high yields. Fur-
thermore, the resultant sample can detect NACs via
luminescence quenching effects. The results display that 1 is
a multifunctional porous material for gas separation, cascade
catalysis, and luminescence sensing.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b00938.
FT-IR, TGA, gas sorption, PXRD, UV−vis spectra, and
luminescent spectra (PDF)
Accession Codes
CCDC 1829961 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_
request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
*E-mail for H.H.: hehongminghz@163.com.
*E-mail for F.S.: fxsun@jlu.edu.cn.
■
Figure 6. Emission spectra of 1 after addition of 1,3-DNB (a), 2,4-
DNT (b), and TNP (c) in DMF, respectively. (d) Relationships
between luminescent intensities of 1 and the corresponding
concentrations of NB, 1,3-DNB, 2,4-DNT, and TNP, respectively.
ORCID
Hongming He: 0000-0001-5535-8825
E
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We appreciate the financial support from the Tianjin Science
and Technology Fund Project for High Education
(2017KJ127), Doctoral Program Foundation of Tianjin Normal
University (043135202-XB1702), and the NSFC (Grant No.
21501064).
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