English

• 0.   Introduction

  With the rapid development of human industry, some chemical pollutants such as nitroaromatic hydrocarbons, toxic metal ions, and pesticide residues infiltrate the natural environment, threatening human health^[1-3]. For example, 2, 4, 6-trinitrophenol (TNP) has a wide range of applications as an important chemical raw material in pharmaceuticals, explosives, paper, textiles, etc^[4-6]. However, TNP and its transformed products (such as picric acid) have been identified as highly toxic to biota and can cause chronic diseases such as syphilis and cancer^[7-9]. Among many metal ions, in addition to heavy metal ions, some transition metal ions that exceed the allowable range (such as Fe³⁺) are also considered to be toxic water pollutants^{[10, 13]}. Fluazinam (FLU) is a common pesticide that can penetrate directly into soil and surface water and seriously affects human health^[14-18]. Therefore, it is necessary to find a rapid and sensitive method to detect TNP, Fe³⁺, and FLU.

  At present, the existing detection methods include ion chromatography^[19], high-performance liquid chromatography^[20], inductively coupled plasma atomic emission spectrometry^[21], and other instrumental analysis methods for the detection of pollutants, but they generally have disadvantages such as low sensitivity and difficult operation. In contrast, fluorescence detection is more intuitive, simple to use, and can quickly detect trace amounts of environmental pollutants^[22-24].

  Coordination polymers (CPs) refer to a class of crystalline hybrid materials composed of metal ions (or clusters) and organic ligands. Owing to the distinctive structure of CPs, they have been widely applied in catalysis^[25], chemical detection^[26], drug transportation^[27], and fluorescence sensing^[28].

  The nature of CPs is easily affected by various factors, for example, the choice of metal ions and pH, temperature, ligands, etc. Transition metal ions with a d¹⁰ electronic structure are stable, and the synthesized complexes usually have good luminescence properties. The advantage of polycarboxylic acids as ligands is that they can be completely or partially deprotonated, which is not only as potential coordination sites, but also as hydrogen bond donors and acceptors, and constructing supramolecular network structures through the deprotonation of carboxyl groups. Based on the above characteristics, we selected 2-hydroxyterephthalic acid (H₂L) as the primary ligand and 1, 4-bis(imidazol- 1-ylmethyl) benzene (1, 4-bib) as the auxiliary ligand (Fig. 1), A novel CP1 [Cd₄(L)₄(1, 4-bib)₄]·2DMA (DMA=N, N-dimethylacetamide) was synthesized under hydrothermal conditions. The structure and stability of CP1 were characterized by powder X‑ray diffraction (PXRD), elemental analysis, single‑crystal X‑ray diffraction, and thermogravimetric analysis (TGA). Moreover, CP1 has good fluorescence properties and can detect TNP, Fe³⁺, and FLU efficiently and sensitively. The mechanism of fluorescence recognition has also been explored in detail. More importantly, we modified a portable test paper with carboxymethyl cellulose, which greatly facilitated the detection of FLU.

  Figure 1

  

  Figure 1.  Structure of (a) H₂L and (b)1, 4-bib

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  1.   Experimental

  1.1   Reagents and instruments

  All reagents were commercially available analytical reagents. Single crystal X-ray data were collected by a Bruker Smart APEX-Ⅱ CCD diffractometer with Cu Kα radiation. Infrared spectra were recorded with a Shimadzu FTIR-8400s spectrophotometer for KBr particles in a range of 4 000-400 cm^-1. TGA was performed on a TA TAG550 nitrogen atmosphere analyzer in a temperature range of 30-800 ℃ with a ramp rate of 20 ℃·min^-1. PXRD data were recorded with a Bruker D8 Advance instrument at 40 kV and 30 mA using Cu Kα radiation (λ=0.154 18 nm) at a scanning rate of 2 (°)·min^-1 from 5° to 50°. Fluorescence spectral analysis was performed using a Hitachi F-7100 fluorescence spectrophotometer.

  1.2   Synthesis of CP1

  Cd(NO₃)₂·4H₂O (0.1 mmol, 0.030 8 g), H₂L (0.05 mmol, 0.011 3 g), 1, 4-bib (0.05 mmol, 0.011 9 g), H₂O (2 mL), and DMA (2 mL) were sealed in a 10 mL glass bottle, and then it is placed in an electric heating blast drying oven. The reactants reacted at 95 ℃ for 3 d. Then the mixture was cooled to room temperature at a rate of 5 ℃·h^-1 and filtered. The filter cake was washed well with ethyl alcohol and H₂O, and dried to give light yellow crystals. Yield 61.3% (based on H₂L). Anal. Calcd. for C₉₆H₉₀Cd₄N₁₈O₂₂(%): C 50.18, H 3.94, N 10.98; Found(%): C 50.17, H 3.84, N 10.99. IR (KBr, cm^-1): 3 124(m), 2 947(w), 2 397(w), 2 306(w), 1 558(s), 1 408(s), 1 238(m), 1 097(m), 1 022(w), 941(w), 831(m), 754(m), 648(w), 594(w), 5451(w).

  1.3   X-ray crystallography

  The crystals of CP1 with regular shapes, transparent colors, and appropriate sizes were selected and placed in a single crystal diffractometer. Single crystal X-ray diffraction data were collected on a Bruker Smart APEX Ⅱ CCD diffractometer equipped with graphite monochromated Mo Kα radiation (λ=0.071 073 nm) at room temperature. The diffraction intensity data were corrected using the SADABS program by semi‑ empirical absorption. The structure was solved by direct methods. All non-hydrogen atoms and anisotropy parameters were refined using the full-matrix least-squares on F ² method by the SHELXL-2014/2016 program. The detailed crystallographic data are listed in Table 1, and the selected bond lengths and angles are listed in Table 2.

  Table 1

  

  Table 1.  Crystallographic data of CP1

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  Parameter	CP1		Parameter	CP1
  Empirical formula	C96H90Cd4N18O22		Dc/(g·cm-3)	1.668
  Formula weight	2 297.45		F(000)	2 320
  Temperature/K	296.15(10)		2θ range for data collection/(°)	3.304-62.03
  Crystal system	Orthorhombic		Reflection collected	36 536
  Space group	Pna21		Independent reflection	11 497 (Rint=0.023 2, Rσ=0.016 2)
  a/nm	2.081 88(5)		Data, restraint, number of parameters	11 497, 2 533, 871
  b/nm	1.529 61(3)		Goodness-of-fit on F 2	1.049
  c/nm	1.436 80(3)		Final R indexes [I≥2σ(I)]a, b	R1=0.077 6, wR2=0.219 0
  Volume/nm3	4.575 44(18)		Final R indexes (all data)	R1=0.084 2, wR2=0.226 62
  Z	2
  a R1=∑(|Fo|-|Fc|)/∑|Fo|; b wR2={∑[w(|Fo|2-|Fc|2)2]/∑(w|Fo|2)}1/2.

  Table 2

  

  Table 2.  Selected bond distances (nm) and bond angles (°) for CP1

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  Cd1—O2#1	0.232 2(9)	Cd1—O4#2	0.235 6(10)	Cd1—O5#2	0.257 0(9)
  Cd1—O7#1	0.239 9(12)	Cd1—N4	0.210 4(17)	Cd1—N5	0.212 6(14)
  Cd2—O1	0.242 2(11)	Cd2—O6	0.230 4(9)	Cd2—N1	0.213 9(16)
  Cd2—O9#3	0.242 2(9)	Cd2—O10#3	0.256 7(9)	Cd2—N8A#4	0.197(4)
  O2#1—Cd1—O4#2	139.7(4)	O2#1—Cd1—O5#2	85.1(3)	O2#1—Cd1—O7#1	127.1(3)
  O4#2—Cd1—O5#2	54.7(3)	O4#2—Cd1—O7#1	93.1(3)	O7#1—Cd1—O5#2	147.8(3)
  N4—Cd1—O2#1	92.6(6)	N4—Cd1—O4#2	87.9(6)	N4—Cd1—O5#2	92.9(5)
  N4—Cd1—O7#1	85.3(66)	N4—Cd1—N5	168.1(6)	N4—Cd1—O5A	173.9(7)
  N5—Cd1—O2#1	75.8(6)	N5—Cd1—O4#2	99.2(8)	N5—Cd1—O5#1	83.6(6)
  N5—Cd2—O7#1	103.7(6)	O1—Cd2—O9#3	92.3(3)	O1—Cd2—O10#3	146.9(3)
  N1—Cd2—O1	98.0(5)	N1—Cd2—O6	92.6(6)	N1—Cd2—O9#3	86.6(5)
  N1—Cd2—O10#3	87.8(5)	O6—Cd2—O1	126.1(3)	O6—Cd2—O9#3	141.2(4)
  O6—Cd2—O10#3	85.8(3)	N8A#4—Cd2—O1	72(8)	N8A#4—Cd2—O6	102(8)
  N8A#4—Cd2—N1	165(8)
  Symmetry codes: #1: x, y, 1+z; #2:1/2+x, 3/2-y, 1+z; #3: -1/2+x, 1/2-y, z; #4: 1-x, 1-y, -3/2+z.

  CCDC: 2338048

  1.4   Fluorescence sensing experiment

  Detailed procedures of fluorescence experiments can be found in the Supporting information.

  2.   Results and discussion

  2.1   Structural description of CP1

  Crystallographic analysis shows that CP1 crystallizes in the orthorhombic system with the space group of Pna2₁. The asymmetric unit of CP1 contains four independent Cd²⁺ ions, four H₂L ligands, four 1, 4-bib ligands, and two lattice DMA molecules.

  Cd1 is coordinated with five oxygen atoms (O1#1, O2#1, O4#2, O5#2, O7#1) from three L^2- ligands and two N atoms (N5, N4) from two 1, 4-bib ligands to form a pentagonal bipyramidal configuration. O1#1, O2#1, O4#2, O5#2, and O7#1 are located on the plane, and N4 and N5 are located on the cone top. Cd2 coordinates with five oxygen atoms (O1, O6, O7, O9#3, O10#3) from three L^2- ligands and two N atoms (N1, N8A#4) atom from the 1, 4-bib ligand to form a pentagonal bipyramidal configuration, where O1, O6, O7, O9#3, and O10#3 are located on the plane and N4, N5 are located on the cone top (Fig. 2a). In Fig. 2a, the 1, 4-bib ligand is disordered, so some disordered atoms are removed for ease of reading. The Cd—O bond lengths are in a range of 0.232 2(9)-0.257 0(9) nm and Cd—N bond lengths are in a range of 0.197 0(4)-0.213 9(16) nm, which is consistent with the reported value^[29-32]. In CP1, L^2- is completely deprotonated and shows a μ₃- к²∶к²∶к¹ high-coordination pattern (Fig. 2b).

  Figure 2

  

  Figure 2.  (a) Coordination environment diagram of CP1 (Ellipsoidal probability: 30%); (b) Coordination pattern diagram (Ellipsoidal probability: 30%); (c) 2D structure parallel to the ab-plane; (d) 2D structure parallel to the ac-plane;(e) 3D bipartite interpolation; (f) 3D network of topology pcu

  Symmetry codes: #1: x, y, 1+z; #2: 1/2+x, 3/2-y, 1+z; #3:-1/2+x, 1/2-y, z; #4: 1-x, 1-y, -3/2+z; #5:-1/2+x, 3/2-y, -1+z;#6: x, y, -1+z; #7: x, 1+y, z; #8: x, 1+y, -1+z; #9: -1/2+x, 3/2-y, 1+z.

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  Remarkably, the Cd²⁺ are connected into a 2D network structure parallel to the ab-plane via the L^2- ligand (Fig. 2c) and expanded into a porous 3D network structure in the c-axis direction via the 1, 4-bib ligand (Fig. 2d). Two identical networks interpenetrate each other, forming a double parallel interpenetrating network (Fig. 2e). As shown in Fig. 2d, the 1, 4-bib ligand headed by N5 linked by Cd1 is completely disordered and does not participate in the composition of the 3D structure, so it is removed from the figure. From the perspective of topological analysis, with Cd1 and Cd2 as one node, L^2- and 1, 4-bib as connectomes, the entire 3D structure can be simplified into a single-node pcu topology, and the topological symbol is {4¹²·6³} (Fig. 2f).

  2.2   PXRD pattern and thermal stability of CP 1

  The structure of CP1 was verified by PXRD measurements. As shown in Fig.S1 (Supporting information), the PXRD pattern of synthesized CP1 was in good agreement with the simulation results, indicating that the phase is pure and the crystallinity is high.

  The thermal stability of CP1 was characterized by TGA. As shown in Fig.S2, CP1 was stable before 300 ℃, and the weight loss between 300 and 750 ℃ was 76.08%, corresponding to the decomposition of L^2- and 1, 4-bib ligand (Calcd. 75.87%). The residual material is presumed to be CdO (Obsd. 23.92%, Calcd. 24.13%).

  2.3   Photoluminescence properties and fluorescence sensing of CP1

  Since d¹⁰ metal CPs generally have outstanding luminescence properties, luminescence properties of CP1, H₅L, and 1, 4-bib were tested. As shown in Fig. 3, the H₂L ligand had an obvious emission peak at 430 nm when excited at 376 nm, and the 1, 4-bib ligand had a fluorescence emission peak at 502 nm when excited at 408 nm. CP1 had an emission peak at 441 nm under 340 nm excitation, The emission peak of the complex has a certain redshift compared to the ligand, which may be due to the n-π* or π-π* transition of the H₂L ligand^[33]. CP1 showed stronger fluorescence emission than the ligand. It may be attributed to the ligand forming complexes with the metal, effectively increasing the rigidity of the ligand and reducing the energy loss from non-radiative decay^[34].

  Figure 3

  

  Figure 3.  Fluorescence emission spectra of CP1 and the ligands

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  2.3.1   Fluorescence sensing experiment of CP1 for nitro explosive

  Given the structural characteristics and good luminescence properties of CP1, we used CP1 as a probe to sense a series of nitro explosives, including 2, 4, 6- trinitrophenol (TNP), 4-nitrobenzene (4-NP), 2, 4, 6- trinitrophenylhydrazine (TRI), 4‑dinitrophenylhydrazine (DNP), 2-nitroaniline (2-NA), 4-nitrophenylhydrazine (4-NPH), nitrobenzene (NB), 2-nitrophenol (2-NP), 2-nitrotoluene (2-NT), 4-nitrobenzoic acid (4-NBA), and 3-nitroaniline (3-NA). The structural formulas of 11 nitro-explosives are shown in Table S1. As shown in Fig. 4a, after adding nitro explosive, the fluorescence intensity of CP1 was quenched to different degrees. Notably, TNP showed strong quenching behavior. The experiment of anti-interference was further carried out, as shown in Fig. 4b, the fluorescence of CP1 was still quenched to a large extent after TNP and other nitro explosives were added at the same time, indicating that CP1 has a good selectivity for TNP. Moreover, under the condition of the Yanhe River, the obvious fluorescence quenching effect was still observed when TNP was added (Fig.S3). Then, concentration titration experiments were carried out and it was observed that the fluorescence emission intensity was quenched with the increase of TNP concentration (Fig. 4c). The Stern-Volmer (S-V) equation: I₀/I=1+ K_SVc_TNP^[35] was used to evaluate the fluorescence quenching effect of TNP on CP1, where I₀ and I respectively represent the fluorescence intensity of CP1 without and after the addition of TNP, K_SV is the quenching constant, and c_TNP is the concentration of TNP. We found that the concentration of TNP and I₀/I show a linear relationship in a range of 0-0.39 μmol·L^-1, K_SV was calculated by linear equation (1.16×10⁵ L·mol^-1), and the limit of detection (LOD) was 0.051 μmol·L^-1 (at 3σ level) (Fig. 4d). The LOD of CP1 for TNP was better than that reported in the literature (Table S3). The above results indicate that CP1 can be used as a fluorescent probe for the detection of TNP.

  Figure 4

  

  Figure 4.  (a) Fluorescence intensity of CP1 in the presence of 11 nitro-explosives; (b) Fluorescence spectra of CP1 in the presence of other (except TNP) nitro explosives and TNP; (c) Fluorescence spectra of CP1 (0.3 mg·mL^-1, 1 mL) upon the gradual addition of TNP solution (10 mmol·L^-1); (d) Plot of I₀/I-1 vs c_TNP for CP1 detecting TNP; (e) Time-dependent fluorescence intensity for CP1 detecting TNP; (f) Cyclic stability of TNP detection by CP1

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  In practical applications, response time and the reused ability are critical. We observed that after adding TNP, the fluorescence of CP1 was quenched within 10 s and remained stable within 190 s (Fig. 4e). Then, to verify its cyclic stability, cyclic experiments were carried out. CP1 was soaked in TNP for a few minutes, washed with deionized water, and centrifugally filtered. It was found that CP1 could be reused five times (Fig. 4f). Therefore, CP1 is a correspondingly fast and recyclable fluorescent sensor for detecting TNP.

  2.3.2   Fluorescence sensing experiments of CP1 on metal ions

  In addition, a series of metal ions in the water system were detected. As shown in Fig. 5a, the fluorescence was maximally quenched when Fe³⁺ was added to the CP1 system. In the subsequent anti-interference experiments, the fluorescence of CP1 was still quenched to a large extent after Fe³⁺ and other metal ions were added at the same time (Fig. 5b). Moreover, under the condition of the Yanhe River, the obvious fluorescence quenching effect was still observed when Fe³⁺ was added (Fig.S3). The results show that CP1 has good selectivity to Fe³⁺. A concentration titration experiment was carried out to explore the relationship between the concentration of Fe³⁺ and the fluorescence intensity of CP1. As shown in Fig. 5c, the fluorescence emission intensity of CP1 decreased with the increase in Fe³⁺ concentration. The K_SV and LOD were calculated by using the SV equation. As shown in Fig. 5d, the concentration of Fe³⁺ and I₀/I showed a good linear relationship in the concentration range of 0-0.39 μmol·L^-1. The K_SV value of CP1 for Fe³⁺ was calculated to be 1.16×10⁴ L·mol^-1, and the LOD was 0.65 μmol·L^-1 (at 3σ level). Further, we investigated the response time and recyclability of CP1. When Fe³⁺ was added to CP1 suspension, the fluorescence was quenched within 10 s and remained stable within 190 s (Fig. 5e). In the cycling experiment, CP1 was soaked in a solution of Fe³⁺ for a few minutes, washed with deionized water, and centrifugally filtered. CP1 could be reused five times (Fig. 5f). The above results show that CP1 can selectively detect Fe³⁺ with fast response time and can be reused.

  Figure 5

  

  Figure 5.  (a) Fluorescence intensity of CP1 in the presence of 21 metal ions; (b) Fluorescence spectra of CP1 in the presence of other (except Fe³⁺) metal ions and Fe³⁺; (c) Fluorescence spectra of CP1 (0.3 mg·mL^-1, 1 mL) upon the gradual addition of Fe³⁺ solution (5 mmol·L^-1); (d) Plot of I₀/I-1 vs c_Fe³⁺ for CP1 detecting Fe³⁺; (e) Time-dependent fluorescence intensity for CP1 detecting Fe³⁺; (f) Cyclic stability of Fe³⁺ detection by CP1

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  2.3.3   Fluorescence sensing experiment of CP1 on pesticides

  In addition, the fluorescence sensing ability of CP1 to a series of pesticides including emamectin benzoate (EMB), triazolone (TDI), prochloraz (PRO), pyrimethanil (PTH), 2, 4-epigenin lactone (2, 4-EPI), pyraclostrobin (PST), imazalil (IMA), zhongshengmycin (MYC), and FLU was also studied. The structural formula is shown in Table S2. The fluorescence intensities of CP1 were quenched at different degrees when adding pesticides (Fig. 6a). Notably, FLU showed a strong quenching behavior. Then the anti-interference experiment was carried out to test the selectivity of CP1 to FLU (Fig. 6b). The fluorescence of CP1 was still quenched to a large extent after FLU and other pesticides were added at the same time. Moreover, under the condition of the Yanhe River, the obvious fluorescence quenching effect was still observed when TNP was added (Fig.S3). It is proved that CP1 has good anti-interference ability. In addition, the concentration titration experiment was carried out. As shown in Fig. 6c, the fluorescence emission peak of CP1 gradually decreased with the increase of FLU concentration. Using the SV equation, the K_SV and LOD were calculated. The concentration of FLU and I₀/I showed a good linear relationship in the concentration range of 0-69.5 μmol·L^-1 (Fig. 6d). The K_SV value of CP1 to FLU is 3.83×10⁴ L·mol^-1, and the LOD is 0.14 μmol·L^-1 (at 3σ level). These results indicate that CP1 can be used as a fluorescent probe for detecting FLU. As shown in Fig. 6e, fluorescence quenching occurred within 10 s and remained stable within 190 s. Then, to verify the recyclability of CP1, a cycle experiment was carried out. CP1 was soaked in FLU solution for a few minutes, washed with deionized water, and centrifuged for recovery. CP1 could be reused at least five times, and the initial fluorescence intensity was only slightly reduced (Fig. 6f), proving that CP1 was a reusable fluorescence sensor for FLU.

  Figure 6

  

  Figure 6.  (a) Fluorescence intensity of CP1 in the presence of 9 pesticides; (b) Fluorescence spectra of CP1 in the presence of other (except FLU) pesticides and FLU; (c) Fluorescence spectra of CP1 (0.3 mg·mL^-1, 1 mL) upon the gradual addition of FLU solution (10 mmol·L^-1); (d) Plots of I₀/I-1 vs c_FLU for CP1 detecting FLU; (e) Time-dependent fluorescence intensity for CP1 detecting FLU; (f) Cyclic stability of FLU detection by CP1

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  2.3.4   Fluorescence quenching mechanism

  According to literature reports, the causes of fluorescence quenching mainly include: (Ⅰ) crystal skeleton collapse, (Ⅱ) energy competitive absorption mechanisms, (Ⅲ) exchange of central metal ions, (Ⅳ) energy resonance transfer mechanisms, and 􀃰 photoinduced electron transfer^[36-39]. To verify the mechanism of fluorescence quenching, we conducted a series of experiments. First, CP1 was immersed in TNP, Fe³⁺, and FLU solutions respectively, and the PXRD patterns and IR spectra were determined after 3 d. The position of the PXRD peak of CP1 after immersion was consistent with the simulated peak (Fig. 7), and there was no obvious change in IR spectra (Fig.S4), which proves that the fluorescence quenching is not caused by skeleton collapse. To further explain the influence of TNP, Fe³⁺, and FLU on the fluorescence quenching of CP1, the UV-Vis absorption spectra were tested. As can be seen in Fig. 8, the fluorescence excitation spectrum of CP1 had a large overlap with the absorption spectra of TNP, Fe³⁺, and FLU. This indicates that during CP1 excitation, the detected molecules (TNP, Fe³⁺, and FLU) competitively absorb the excitation wavelength of light, resulting in the fluorescence quenching of CP1, which belongs to the energy competition absorption mechanism^[40].

  Figure 7

  

  Figure 7.  PXRD patterns of CP1 and CP1 after soaking in TNP, Fe³⁺, and FLU solutions for 3 d

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  Figure 8

  

  Figure 8.  Excitation spectra of CP1 with the UV-Vis absorption spectra of (a) TNP, (b) Fe³⁺, and (c) FLU

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  2.4   Application of CP1 in actual samples

  CIE coordinates are the most intuitive to see the change in fluorescence color. We corresponded the fluorescence color of the titration experiments to the CIE coordinates (Fig.S5) and found that the fluorescence color had different degrees of change with the increase of the concentration of the detection substances. Among them, the fluorescence color change of FLU was more obvious, so we prepared a portable test paper by using the method described in the literature (Supporting information for detailed procedures)^[41]. Different concentrations of FLU solution were dropped onto portable paper and images were taken with a camera under 365 nm ultraviolet light. As shown in Fig. 9, the portable test strips prepared could not only selectively detect FLU, but also showed different colors under different concentrations of FLU.

  Figure 9

  

  Figure 9.  (a) Images of portable test papers with different pesticides; (b) Images of portable test papers with different concentrations of FLU (From left to right, CP1 was not loaded, CP1 was loaded and the FLU concentrations were 0, 5, 10, 20, 50 μmol·L^-1, respectively.)

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  3.   Conclusions

  In this work, a cadmium-based coordination polymer [Cd₄(L)₄(1, 4-bib)₄]·2DMA (CP1) with pcu topological structure was synthesized successfully, and its structure and stability were verified by single-crystal X-ray diffraction, elemental analysis, TGA, PXRD, infrared, and other method. The result shows that CP1 has good fluorescence properties. The nitro explosives, metal ions, and pesticide sensing experiments revealed that CP1 shows high sensitivity to TNP, Fe³⁺, and FLU, with LOD of 0.051, 0.65, and 0.14 μmol·L^-1 (FLU), respectively. More importantly, we found that the fluorescence color of the FLU titration experiment had a great change. A portable test paper was prepared that can not only selectively detect FLU, but also showed different fluorescence colors under different concentrations of FLU, which greatly facilitates the detection of FLU.

  Supporting information is available at http://www.wjhxxb.cn

  
  
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• 

  Figure 1  Structure of (a) H₂L and (b)1, 4-bib

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  Figure 2  (a) Coordination environment diagram of CP1 (Ellipsoidal probability: 30%); (b) Coordination pattern diagram (Ellipsoidal probability: 30%); (c) 2D structure parallel to the ab-plane; (d) 2D structure parallel to the ac-plane;(e) 3D bipartite interpolation; (f) 3D network of topology pcu

  Symmetry codes: #1: x, y, 1+z; #2: 1/2+x, 3/2-y, 1+z; #3:-1/2+x, 1/2-y, z; #4: 1-x, 1-y, -3/2+z; #5:-1/2+x, 3/2-y, -1+z;#6: x, y, -1+z; #7: x, 1+y, z; #8: x, 1+y, -1+z; #9: -1/2+x, 3/2-y, 1+z.

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  Figure 3  Fluorescence emission spectra of CP1 and the ligands

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  Figure 4  (a) Fluorescence intensity of CP1 in the presence of 11 nitro-explosives; (b) Fluorescence spectra of CP1 in the presence of other (except TNP) nitro explosives and TNP; (c) Fluorescence spectra of CP1 (0.3 mg·mL^-1, 1 mL) upon the gradual addition of TNP solution (10 mmol·L^-1); (d) Plot of I₀/I-1 vs c_TNP for CP1 detecting TNP; (e) Time-dependent fluorescence intensity for CP1 detecting TNP; (f) Cyclic stability of TNP detection by CP1

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  Figure 5  (a) Fluorescence intensity of CP1 in the presence of 21 metal ions; (b) Fluorescence spectra of CP1 in the presence of other (except Fe³⁺) metal ions and Fe³⁺; (c) Fluorescence spectra of CP1 (0.3 mg·mL^-1, 1 mL) upon the gradual addition of Fe³⁺ solution (5 mmol·L^-1); (d) Plot of I₀/I-1 vs c_Fe³⁺ for CP1 detecting Fe³⁺; (e) Time-dependent fluorescence intensity for CP1 detecting Fe³⁺; (f) Cyclic stability of Fe³⁺ detection by CP1

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  Figure 6  (a) Fluorescence intensity of CP1 in the presence of 9 pesticides; (b) Fluorescence spectra of CP1 in the presence of other (except FLU) pesticides and FLU; (c) Fluorescence spectra of CP1 (0.3 mg·mL^-1, 1 mL) upon the gradual addition of FLU solution (10 mmol·L^-1); (d) Plots of I₀/I-1 vs c_FLU for CP1 detecting FLU; (e) Time-dependent fluorescence intensity for CP1 detecting FLU; (f) Cyclic stability of FLU detection by CP1

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  Figure 7  PXRD patterns of CP1 and CP1 after soaking in TNP, Fe³⁺, and FLU solutions for 3 d

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  Figure 8  Excitation spectra of CP1 with the UV-Vis absorption spectra of (a) TNP, (b) Fe³⁺, and (c) FLU

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  Figure 9  (a) Images of portable test papers with different pesticides; (b) Images of portable test papers with different concentrations of FLU (From left to right, CP1 was not loaded, CP1 was loaded and the FLU concentrations were 0, 5, 10, 20, 50 μmol·L^-1, respectively.)

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  Table 1.  Crystallographic data of CP1

  Parameter	CP1		Parameter	CP1
  Empirical formula	C96H90Cd4N18O22		Dc/(g·cm-3)	1.668
  Formula weight	2 297.45		F(000)	2 320
  Temperature/K	296.15(10)		2θ range for data collection/(°)	3.304-62.03
  Crystal system	Orthorhombic		Reflection collected	36 536
  Space group	Pna21		Independent reflection	11 497 (Rint=0.023 2, Rσ=0.016 2)
  a/nm	2.081 88(5)		Data, restraint, number of parameters	11 497, 2 533, 871
  b/nm	1.529 61(3)		Goodness-of-fit on F 2	1.049
  c/nm	1.436 80(3)		Final R indexes [I≥2σ(I)]a, b	R1=0.077 6, wR2=0.219 0
  Volume/nm3	4.575 44(18)		Final R indexes (all data)	R1=0.084 2, wR2=0.226 62
  Z	2
  a R1=∑(|Fo|-|Fc|)/∑|Fo|; b wR2={∑[w(|Fo|2-|Fc|2)2]/∑(w|Fo|2)}1/2.

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  Table 2.  Selected bond distances (nm) and bond angles (°) for CP1

  Cd1—O2#1	0.232 2(9)	Cd1—O4#2	0.235 6(10)	Cd1—O5#2	0.257 0(9)
  Cd1—O7#1	0.239 9(12)	Cd1—N4	0.210 4(17)	Cd1—N5	0.212 6(14)
  Cd2—O1	0.242 2(11)	Cd2—O6	0.230 4(9)	Cd2—N1	0.213 9(16)
  Cd2—O9#3	0.242 2(9)	Cd2—O10#3	0.256 7(9)	Cd2—N8A#4	0.197(4)
  O2#1—Cd1—O4#2	139.7(4)	O2#1—Cd1—O5#2	85.1(3)	O2#1—Cd1—O7#1	127.1(3)
  O4#2—Cd1—O5#2	54.7(3)	O4#2—Cd1—O7#1	93.1(3)	O7#1—Cd1—O5#2	147.8(3)
  N4—Cd1—O2#1	92.6(6)	N4—Cd1—O4#2	87.9(6)	N4—Cd1—O5#2	92.9(5)
  N4—Cd1—O7#1	85.3(66)	N4—Cd1—N5	168.1(6)	N4—Cd1—O5A	173.9(7)
  N5—Cd1—O2#1	75.8(6)	N5—Cd1—O4#2	99.2(8)	N5—Cd1—O5#1	83.6(6)
  N5—Cd2—O7#1	103.7(6)	O1—Cd2—O9#3	92.3(3)	O1—Cd2—O10#3	146.9(3)
  N1—Cd2—O1	98.0(5)	N1—Cd2—O6	92.6(6)	N1—Cd2—O9#3	86.6(5)
  N1—Cd2—O10#3	87.8(5)	O6—Cd2—O1	126.1(3)	O6—Cd2—O9#3	141.2(4)
  O6—Cd2—O10#3	85.8(3)	N8A#4—Cd2—O1	72(8)	N8A#4—Cd2—O6	102(8)
  N8A#4—Cd2—N1	165(8)
  Symmetry codes: #1: x, y, 1+z; #2:1/2+x, 3/2-y, 1+z; #3: -1/2+x, 1/2-y, z; #4: 1-x, 1-y, -3/2+z.

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