Cd (II) coordination polymer as well as preparation method and application thereof

Abstract

The invention provides a Cd (II) coordination polymer, the chemical expression of the polymer is {[Cd2 (bptc) (dpb) 1.5 (H2O)]. (H2O). 0.5 (dpb)} n, H4bptc is a 2, 3, 3 ', 4'-biphenyl tetracarboxylic acid organic ligand, dpb is a 1, 4-bis (pyridine-4-yl) benzene (dpb) nitrogen-containing ligand, the crystal of the complex belongs to a triclinic system, the space group is Pi, the cell parameters are as follows: # imgabs0 # c = 13.3406 (3), alpha = 110.165 (1) degrees, beta = 107.476 (1) degrees, gamma = 97.459 (1) degrees, and a coordinated water molecule is a coordinated water molecule. The asymmetric unit consists of two Cd < 2 + > ions (Cd1 and Cd2) which are independent in crystallography, one deprotonated bptc4-ligand, three dpb ligands (dpbI, dpbII and dpbIII; the occupancy rate of dpbI is 1, and the occupancy rate of dpbII and dpbIII is 0.5), one coordination water molecule (O9) and one crystal lattice water (O10). The Cd (II) coordination polymer provided by the invention can be used for specific detection of nitrofuran antibiotics in irrigation water.

Description

Technical Field

[0001] The invention belongs to the technical field of transition metal complex materials, and specifically relates to a Cd(II) coordination polymer and a preparation method and application thereof. Background Art

[0002] With the advancement of science and technology and the development of society, environmental problems are becoming increasingly severe. Among them, the excessive use of antibiotics has made antibiotic pollution in water bodies more serious, posing a serious threat to human health and the ecological environment. Therefore, efficient and accurate detection of antibiotic content in water bodies is of great significance to curbing the continued spread of pollution and protecting people's life, health and safety. However, most of the current detection methods have the disadvantages of old equipment, cumbersome procedures, poor timeliness, etc., which cannot meet people's current detection requirements. For example, immunoassay has the significant advantages of simple operation and low cost, but poor selectivity and sensitivity, and relatively long sensing time; chromatographic combination technology mainly uses mass spectrometry and chromatographic sensing technology combined with other complex procedures. Although mature, it requires large and expensive instruments and requires professional operation. Therefore, it is of great significance to develop cheap, efficient and fast detection methods.

[0003] The Xihe River is one of the main irrigation water sources for Xinyang City. It is dispatched and managed through the Nanwan Reservoir to provide irrigation water for farmland in the irrigation area. The Nanwan Reservoir is located on the Xihe River, a tributary of the Huaihe River, 6 kilometers southwest of Xinyang City. It is a large-scale water conservancy project built in the early days of the founding of the People's Republic of China to control the Huaihe River and develop water conservancy. The main functions of the reservoir include comprehensive utilization such as flood control, irrigation, power generation, aquaculture, urban water supply and tourism development. In the dry season, the Xinyang City Water Conservancy Department will scientifically dispatch water sources to ensure the irrigation needs of farmland. Therefore, it is particularly important to detect and confirm whether the furazolidone (NFZ) and nitrofurantoin (NFT) in the river exceed the standard. Summary of the invention

[0004] Under this background, the present invention provides a Cd(II) coordination polymer and a preparation method and application thereof.

[0005] In order to overcome at least one of the above disadvantages of the prior art, on the one hand, the present invention provides a Cd(II) coordination polymer, the chemical expression of which is,

[0006] {[Cd2(bptc)(dpb) 1.5 (H2O)]·(H2O)·0.5(dpb)} n , wherein H4bptc is a 2,3,3′,4′-biphenyltetracarboxylic acid organic ligand, dpb is a 1,4-di(pyridin-4-yl)benzene (dpb) nitrogen-containing ligand,

[0007] The crystal of the complex belongs to the triclinic system, the space group is Pī, and the unit cell parameters are c=13.3406(3), α=110.165(1)°, β=107.476(1)°, γ=97.459(1)°, and its asymmetric unit consists of two crystallographically independent Cd 2+ ions (Cd1, Cd2), 1 deprotonated bptc 4- ligand, 3 dpb ligands (dpb I, dpb II, dpb III; occupancy: dpb I is 1, dpb II and dpb III are 0.5), 1 coordinated water molecule (O9) and 1 lattice water (O10).

[0008] The second aspect of the present invention provides a method for preparing a Cd(II) coordination polymer, the method comprising the following steps: (1) dissolving cadmium acetate dihydrate, 2,3,3′,4′-biphenyltetracarboxylic acid and 1,4-di(pyridin-4-yl)benzene in deionized water and stirring, and then adjusting the pH value with a NaOH aqueous solution;

[0009] (2) transferring the product from the previous step into a reaction kettle and heating it for reaction;

[0010] (3) After the reaction is completed, the reaction system is cooled and filtered to obtain {[Cd2(bptc)(dpb) 1.5 (H2O)]·(H2O)·0.5(dpb)} n , abbreviated as XYNU-1.

[0011] Furthermore, according to the method for preparing a Cd(II) coordination polymer according to claim 2, it is characterized in that the molar ratio of cadmium acetate dihydrate to 2,3,3′,4′-biphenyltetracarboxylic acid in step (1) is 1:1.

[0012] Furthermore, in the step (1), the molar ratio of cadmium acetate dihydrate to 1,4-di(pyridin-4-yl)benzene is 2:3.

[0013] Furthermore, the concentration of the NaOH aqueous solution in step (1) is 0.1M.

[0014] Furthermore, in step (1), the pH value is adjusted to 8.

[0015] Furthermore, in step (2), the material of the reaction kettle is polytetrafluoroethylene, the reaction conditions are 110-120° C., and the reaction time is 2-4 days.

[0016] Furthermore, in the step (3), the cooling temperature is room temperature, and after filtering, the product is washed with distilled water, and the obtained XYNU-1 is white block crystals.

[0017] A third aspect of the present invention provides a use of a Cd(II) coordination polymer for specific detection of nitrofuran antibiotics in irrigation water systems.

[0018] The beneficial effects of the present invention are:

[0019] The present invention selects Cd 2+ As the metal center, the aromatic polycarboxylic acid ligand 2,3,3′,4′-biphenyltetracarboxylic acid (H4bptc) with flexible coordination mode and the nitrogen-containing ligand 1,4-di(pyridin-4-yl)benzene (dpb) were selected for self-assembly under hydrothermal conditions to successfully prepare {{[Cd2(bptc)(dpb) 1.5 (H2O)]·(H2O)·0.5(dpb)} n (XYNU-1). Studies have shown that XYNU-1 is very stable in water systems and can be used to specifically identify nitrofuran antibiotics NFT and NFZ in river water, showing the characteristics of high sensitivity, low detection limit, good selectivity, and strong anti-interference ability. Further studies have shown that the XYNU-1 prepared by the present invention can be used as a fluorescent detection material to monitor nitrofuran antibiotic pollutants in river water. It has the advantages of low cost, easy operation, fast response, high sensitivity, and low detection limit. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0021] Figure 1 The structural diagrams of H4bptc organic ligand and dpb nitrogen-containing ligand;

[0022] Figure 2 Various structural diagrams of XYNU-1;

[0023] Figure 3 is the PXRD pattern of XYNU-1;

[0024] Figure 4 is the FT-IR spectrum of XYNU-1;

[0025] Figure 5 This is a graph showing the selective detection of XYNU-1 against nitrofuran antibiotics NFT and NFZ;

[0026] Figure 6 The exponential relationship between I0 / I and (a) NFT and (b) NFZ concentration at high concentrations.

[0027] Figure 7 (a) PXRD spectrum and (b) FTIR spectrum of XYNU-1 recovered from the sensing experiment.

[0028] Figure 8 The excited state decay curves of XYNU-1 suspension at different (a) NFT and (b) NFZ concentrations.

[0029] Fig. 9 The UV-visible absorption spectra of different antibiotics and the excitation / emission spectra of XYNU-1;

[0030] Fig.10 Energy transfer quenching mechanism for NFT / NFZ: a possible pathway to PET. DETAILED DESCRIPTION

[0031] It should be mentioned before discussing the exemplary embodiments in more detail that some exemplary embodiments are described as processes or methods depicted as flow charts. Although the flow charts describe the operations as sequential processes, many of the operations therein can be implemented in parallel, concurrently or simultaneously. In addition, the order of the operations can be rearranged. The process can be terminated when its operation is completed, but can also have additional steps not included in the accompanying drawings. The process can correspond to a method, function, procedure, subroutine, subprogram, etc.

[0032] It should be understood that, although the terms "first", "second", etc. may be used herein to describe various units, these units should not be limited by these terms. These terms are used only to distinguish one unit from another unit. For example, without departing from the scope of the exemplary embodiments, the first unit may be referred to as the second unit, and similarly the second unit may be referred to as the first unit. The term "and / or" used herein includes any and all combinations of one or more of the listed associated items.

[0033] The present invention provides a Cd(II) coordination polymer, wherein the chemical expression of the coordination polymer is:

[0034] {[Cd2(bptc)(dpb) 1.5 (H2O)]·(H2O)·0.5(dpb)} n , wherein bptc is a 2,3,3′,4′-biphenyltetracarboxylic acid organic ligand, dpb is a 1,4-di(pyridin-4-yl)benzene (dpb) nitrogen-containing ligand,

[0035] The crystal of the complex belongs to the triclinic system, the space group is Pī, and the unit cell parameters are c=13.3406(3), α=110.165(1)°, β=107.476(1)°, γ=97.459(1)°, and its asymmetric unit consists of two crystallographically independent Cd 2+ions (Cd1, Cd2), 1 deprotonated bptc 4- ligand, 3 dpb ligands (dpb I, dpb II, dpb III; occupancy: dpb I is 1, dpb II and dpb III are 0.5), 1 coordinated water molecule (O9) and 1 lattice water (O10).

[0036] Provided is a method for preparing a Cd(II) coordination polymer, the method comprising the following steps: (1) dissolving cadmium acetate dihydrate, 2,3,3′,4′-biphenyltetracarboxylic acid and 1,4-di(pyridin-4-yl)benzene in deionized water, stirring, and adjusting the pH value with a NaOH aqueous solution;

[0037] (2) transferring the product from the previous step into a reaction kettle and heating it for reaction;

[0038] (3) After the reaction is completed, the reaction system is cooled and filtered to obtain {[Cd2(bptc)(dpb) 1.5 (H2O)]·(H2O)·0.5(dpb)} n , abbreviated as XYNU-1.

[0039] The chemical reagents used in the present invention are all analytically pure and can be used directly. The structural diagrams of H4bptc and dpb ligands are shown in Figure 1 As shown. By using Cu-Kα rays ( ) PXRD patterns were prepared on a Smartlab9 X-ray powder diffractometer. Fourier transform infrared (FT-IR) spectra were collected on a ThermoFisher spectrometer. Ultraviolet visible (UV-vis) spectra were collected on a Lambda950 spectrometer. Elemental analysis (C, H, and N) characterization was performed on a PerkinElmer 2400LS II elemental analyzer. The thermal stability under air atmosphere was studied using a synchronous thermal analyzer (TA Q600) with a heating rate of 10 °C min -1 The fluorescence spectra at room temperature were collected on a FLS1000 fluorescence / phosphorescence spectrophotometer (xenon lamp). The Gaussian 09 program was used to optimize the configuration, and the B3LYP functional with a 6-31G (d, p) basis set was used for structural optimization and calculation of the frontier molecular orbital energy levels of the relevant molecules. The following is an explanation of the specific feed ratio and reaction conditions.

[0040] Example 1

[0041] (1) Cadmium acetate dihydrate (0.02 mmol, 5.3 mg), 2,3,3′,4′-biphenyltetracarboxylic acid (0.02 mmol, 5.9 mg) and 1,4-di(pyridin-4-yl)benzene (0.03 mmol, 4.6 mg) were dissolved in deionized water and stirred for 1.5 h, and then the pH was adjusted to 8 with 0.1 M NaOH aqueous solution;

[0042] (2) The product from the previous step was transferred into a 20 mL polytetrafluoroethylene reaction kettle and heated at 120° C. for 3 days for reaction;

[0043] (3) After the reaction is completed, the reaction system is cooled to room temperature, filtered, and washed with distilled water to obtain white block crystals {[Cd2(bptc)(dpb) 1.5 (H2O)]·(H2O)·0.5(dpb)} n , referred to as XYNU-1, with a yield of 62.5%.

[0044] C 48 H 34 N4O 10 Cd2: Theoretical value C: 54.77%; H: 3.23%; N: 5.33%; Experimental value C: 54.74%; H: 3.28%; N: 5.30%. FTIR (cm -1 ): 3372w, 3071w, 1603s, 1538s, 1485m, 1394s, 1324s, 1226m, 1140w, 1067m, 1010w, 853m, 809s, 772m, 710m, 574w, 489m.

[0045] The following is the relevant characterization and property test of the Cd(II) coordination polymer XYNU-1 provided by the present invention. X-ray single crystal diffraction data

[0046] The diffractometer was a Bruker D8 Venture (IUS3.0) with a graphite monochromated Mo-Kα radiation source ( ), Cu-CP single crystal X-ray diffraction data were collected at 296K, and the structure was analyzed and refined by SHELXT-2014 / 7 program with Olex2 program package as the interface. Hydrogen atoms and non-hydrogen atoms were refined and assigned using isotropic and anisotropic methods, respectively. Table 1 shows the specific parameters of the crystal structure data and the final refinement results.

[0047] Table 1 Crystallographic data of compound XYNU-1.

[0048]

[0049]

[0050] Structural Description

[0051] Figure 2 (a) Asymmetric unit of compound XYNU-1; (b) Cd center and bptc 4- The ligand forms a two-dimensional layer structure extending along the bc plane; (c) bptc observed along the c axis 4- -Cd two-dimensional layer structure; (d) 3D structure; (e) topological structure (Symmetry codes: A: x-1, y, z-2; B: x, y, z-1; C: -x+2, -y, -z+3; D: x, y, z+1; E: -x+2, -y+1, -z+2; F: x+1, y, z+2; G: -x+1, -y, -z+2; H: -x+1, -y, -z+1).

[0052] X-ray single crystal analysis results show that XYNU-1 belongs to the Pī space group of the triclinic system. Figure 2 As shown in a, the asymmetric unit consists of two crystallographically independent Cd 2+ ions (Cd1, Cd2), 1 deprotonated bptc 4- The Cd1 center is composed of three dpb ligands (dpb I, dpb II, dpb III; occupancy: dpb I is 1, dpb II and dpb III are 0.5), one coordinated water molecule (O9) and one lattice water (O10). Each Cd1 center adopts an octahedral coordination mode. Its equatorial plane is composed of three different bpt c4- The four carboxyl oxygen atoms (O4D, O5C, O6, O7) of the ligand are occupied, and the axial position is occupied by two pyridine nitrogen atoms (N1, N3F) from two different dpb molecules. Cd2 is hexacoordinated and is occupied by three different bptc 4- The four carboxyl oxygen atoms (O1E, O2E, O3, O7B) of the molecule are coordinated by a pyridinic nitrogen atom (N2) from dpb and a coordinated water molecule (O9). The Cd-O / N bond length is , O / N-Cd-O / N bond angle is 55.26(4)—177.04(2)°. Each bptc4-ligand molecule simultaneously connects 6 Cd 2+ Ion, coordination mode is μ6:

[0053] like Figure 2 As shown in b, two Cd in central symmetric positions 2+ Ions are bptc 4- The ligands are connected to form a binuclear cluster unit Cd2(COO)4, and the distance between Cd1···Cd1 is Adjacent quad-core clusters are connected to each other through bptc 4- The ligands are further connected to form a two-dimensional layer that extends infinitely along the bc axis ( Figure 2 b). This two-dimensional layer is supported by μ2-dpb I / dpb II ligands, ultimately forming a three-dimensional framework structure of XYNU-1 ( Figure 2 d). The π…π stacking interaction between the benzene rings and pyridine rings of adjacent two-dimensional layers in the three-dimensional network (av.: ) further enhances the stability of the entire three-dimensional framework. The 1D channel of the system is calculated by PLATON. The solvent-fillable volume after removing the guest molecules (lattice water and dpb III molecules) is , accounting for the total unit cell volume From a topological perspective, the three-dimensional structure can be simplified into a 3-node network with 4, 5, 6 connections, and the topological symbol is {4 3 6 3}{4 3 6 6 ·8}{4 6 6 7 8 2}( Figure 2 e).

[0054] X-ray powder diffraction

[0055] In order to verify that the complex is a single pure phase, the synthesized XYNU-1 was subjected to X-ray powder diffraction (PXRD) test. Figure 3 As shown in Figure 2, the PXRD diffraction peaks of XYNU-1 are consistent with the diffraction peaks simulated by the single crystal structure. This result shows that the obtained sample is pure phase and can be used for further performance testing.

[0056] Infrared spectroscopy

[0057] The present invention also characterizes the infrared spectrum (FT-IR) spectrum of XYNU-1. Figure 4 As shown, XYNU-1 is at 3134-3597cm -1 The strong OH vibration at 710 cm-1 comes from the coordinated water molecules and lattice water molecules in the complex structure. -1 The vibration peak at 1602 cm -1 and 1394cm -1 The strong absorption peaks at 93 cm and 10 cm respectively correspond to the asymmetric and symmetric stretching vibrations of the carboxyl group -C=O. Compared with the free H4bptc ligand, the two characteristic absorption peaks show -1 / 52cm -1The blue / red shifts indicate that the carboxyl groups on the H4bptc ligand molecules are completely deprotonated and bind to Cd 2+ The metal center undergoes coordination. In addition, the characteristic peak of the CN bond in the dpb ligand (1592cm -1 ) in the XYNU-1 complex is blue-shifted to 1539 cm -1 This further illustrates that the pyridine nitrogen atom in dpb and Cd 2+ The center is also coordinated, which is consistent with the results of single crystal X-ray diffraction analysis.

[0058] Stability of XYNU-1

[0059] The stability of coordination polymer materials largely determines whether they can be applied in real life and scientific research production. Therefore, the present invention first tested the water stability of the synthesized sample. Considering the complexity of the actual water sample, the present invention detected the PXRD pattern of the XYNU-1 sample immersed in aqueous solutions with different pH values ​​for 48 hours, and found that the PXRD pattern of XYNU-1 in a solution with a pH of 2 to 12 was basically the same as that of the original sample, and the positions of all diffraction peaks were almost the same as those of the original sample ( Figure 5 ), indicating that the material synthesized by the present invention can maintain structural integrity in aqueous solution over a wide pH range. In addition to testing chemical stability, the thermal stability of the coordination polymer is also important. -1 The thermal stability of the coordination polymer was tested in the range of 25 to 800 °C at a heating rate. Figure 6 As shown, the framework of the complex can be stable to about 340°C. The excellent water stability and thermal stability provide important prerequisites for the application of the material in fluorescent sensing in water phase.

[0060] Fluorescence sensing test method

[0061] The collected water samples of the Xihe River were centrifuged at a speed of 5000r / min for 3 minutes to precipitate impurities, and the supernatant was taken. For water system fluorescence sensing, 2 mg of ground XYNU-1 sample was dispersed in 2 ml of Xihe River water, ultrasonicated for 0.5h and aged for 3 days to obtain a uniform suspension. The suspension was transferred to a 12.5mm×12.5mm×45mm four-light-transmitting cuvette to collect its luminescence spectrum. For the fluorescence titration test, under the same other conditions, different volumes of 1mM NFT / NFZ were added to the blank suspension with a pipette, and the luminescence spectrum after each addition was recorded. In the competitive experiment, equimolar amounts of potential interferents (erythromycin (ERM), roxithromycin (RXM), chloramphenicol (CAP), gentamicin sulfate (GMS), penicillin potassium (PCL), kanamycin sulfate (KMS), azithromycin (AZM), ampicillin (APL), ornidazole (ONZ)) tobramycin (TOB), azithromycin (AZI), kanamycin sulfate (KMS), penicillin potassium (PCL), erythromycin (ERM), amoxicillin (AMX), tetracycline (THI), fluorometholone (FF), roxithromycin (RXM), ampicillin (APL), streptomycin sulfate (SMS) and gentamicin sulfate (GMS), NFT and NFZ were added to the blank samples to test the specificity of the probe. In addition, a series of three-step anti-interference experiments were performed on XYNU-1 to determine its anti-interference ability. First, the emission intensity of the blank sample of the probe itself was collected, and then the interfering substances were introduced into the CP suspension respectively, and the fluorescence spectrum was measured. Finally, an equal amount of substrate (NFT / NFZ) was added to the CP suspension containing the interfering analyte to test its emission intensity. All emission spectra were tested under the same conditions: the excitation wavelength was 275 nm (excitation slit = 5 nm, emission slit = 5 nm), and the emission spectrum collection range was 300-530 nm.

[0062] Chemical sensing

[0063] Selective detection of nitrofuran antibiotics NFT and NFZ

[0064] Fluorescence detection has the advantages of being less time-consuming, convenient and fast. The coordination polymer Cd-CP synthesized in this experiment can be used as a fluorescent probe. Figure 5 (a) Fluorescence intensity of XYNU-1 dissolved in different antibiotic solutions; (b) Fluorescence intensity of XYNU-1 in the case of NFZ / NFT+different antibiotics; (c) Effect of different concentrations of NFT on the emission spectrum of XYNU-1; (d) Effect of different concentrations of NFZ on the emission spectrum of XYNU-1; (e) SV diagram of NFT at low concentration; (f) SV diagram of NFZ at low concentration.

[0065] First, the selectivity of XYNU-1 for commonly used antibiotics, such as Figure 5 As shown in (a), 0.2 mM of 14 different types of antibiotics were added to the suspension of XYNU-1 in the water of the Xihe River. The fluorescence intensity of the XYNU-1 suspension after adding antibiotics was detected. It was found that only when nitrofuran antibiotics were added, the XYNU-1 suspension showed an obvious fluorescence quenching effect (NFZ was 94.8%, NFT was 95.6%), and other types of antibiotics had no obvious quenching effect. The preliminary conclusion is that the luminescence intensity of XYNU-1 in the water system of the Xihe River is highly correlated with the type of antibiotics, and it has high selectivity for nitrofuran antibiotics, and can selectively identify nitrofuran antibiotics NFT and NFZ in the water of the Xihe River through the fluorescence quenching effect.

[0066] Sensitivity test

[0067] To further study the quantitative relationship between the content of nitrofuran antibiotics and the fluorescence signal intensity of the XYNU-1 suspension, 1 mM NFZ or NFT was added dropwise to the XYNU-1 suspension, and fluorescence titration experiments were performed by slowly increasing the concentrations of NFZ and NFT. Figure 5 As shown in (c) and (d), the fluorescence intensity of the XYNU-1 suspension decreases with the increase of NFZ / NFT concentration. When the molar concentration of NFZ / NFT is 0.25mM / 0.21mM, the quenching efficiency of XYNU-1 reaches 97.8% and 97.3%, respectively. This shows that XYNU-1 has high sensitivity for detecting NFZ / NFT. At low concentrations, the quenching efficiency (I0 / I) shows a good linear relationship with the NFZ / NFT concentration. In the concentration range of 0-50μM / 0-40μM, using the SV formula I0 / I=1+K SV [Analyte] is accurately simulated, such as Figure 5 As shown in (e) and (f), for NFZ, K SV =2.29×10 4 M -1 , R 2 =0.9905, for NFT, K SV =2.44×10 4 M -1 , R 2 =0.9928. The calculation formula of the detection limit (LOD) is: LOD = 3σ / Ksv (σ represents the standard deviation of 10 tests of the blank solution, K SVThe slope of the fitted linear curve is shown in Figure 2. The detection limit of NFT is 2.21 nM and that of NFZ is 2.36 nM, which are lower than those of most reported CP materials. However, when the content of nitrofuran antibiotics in the solution is high, the quenching efficiency (I0 / I) is no longer linearly related to the NFZ / NFT concentration, but exponentially related ( Figure 6 ).

[0068] Anti-interference test

[0069] For practical applications, intelligent fluorescence sensors not only need high sensitivity and high selectivity, but also need to have strong anti-interference ability. Further anti-interference experiments show that Figure 5 As shown in (b), the fluorescence intensity of XYNU-1 can still be significantly quenched by NFZ / NFT even in the presence of equivalent amounts of other potential interfering antibiotics TOB, AZI, KMS, PCL, ERM, AMX, THI, FF, RXM, APL, SMS and GMS. This experimental result shows that the coordination polymer XYNU-1 can be used for the specific detection of nitrofuran antibiotics in aqueous systems and exhibits excellent anti-interference ability.

[0070] Fluorescence recognition mechanism study

[0071] Understanding the principle of fluorescence quenching not only helps to reveal the sensing mechanism, but also provides a theoretical basis for designing and synthesizing smarter sensor materials. Based on this, the present invention systematically explores the possible mechanism of XYNU-1's specific recognition of NFT / NFZ. First, the structural integrity of the coordination polymer is confirmed by testing the PXRD spectrum after NFT / NFZ treatment ( Figure 7 a) As can be seen from the figure, the framework structure of XYNU-1 remains intact during the detection process. Therefore, fluorescence quenching caused by structural damage can be preliminarily ruled out. In addition, the present invention also tests the FT-IR spectrum of XYNU-1 after NFT / NFZ treatment. Figure 7 As shown in b, the infrared spectrum of the XYNU-1 sample after treatment with the analyte did not change significantly, which also ruled out the possibility of forming a ground state complex.

[0072] According to the literature, there are many reasons that can cause the quenching of the luminescence intensity of fluorescent chromophores, including fluorescence resonance energy transfer (FRET), internal filter effect (IFE), etc. The above mechanisms can be divided into two categories: dynamic quenching and static quenching. These two quenching mechanisms can be distinguished by the fluorescence lifetime of the fluorescent sensor before and after analyte treatment. If the fluorescence lifetime before and after analyte treatment remains constant, the quenching system is static, and if they have different fluorescence lifetimes, they are dynamic in nature. Figure 8a-8b shows that the fluorescence decay curves of CP suspensions with different NFT / NFZ contents do not completely overlap with those of CP without analyte treatment, which proves the possibility of a dynamic quenching mechanism.

[0073] By collecting UV-Vis spectra of all antibiotics, the present invention analyzed the possibility of FRET and IFE. Fig. 9 As shown in the figure, only the UV-visible spectrum of NFT / NFZ overlaps with the excitation spectrum of XYNU-1 suspension, which indicates that IFE is also one of the main reasons for the fluorescence quenching of XYNU-1 caused by NFT / NFZ. After the addition of NFT / NFZ, part of the excitation light may be absorbed by NFT / NFZ, which ultimately reduces the fluorescence signal output of the sensor. In addition, Fig. 9 The partial overlap between the UV-visible absorption of NFT / NFZ and the emission spectrum of XYNU-1 suspension also demonstrated the contribution of FRET to fluorescence quenching. Fig.10 It can be seen that NFT (-2.85 eV) / NFZ (-2.62 eV) has a lower LUMO (lowest unoccupied molecular orbital) energy level than the H4bptc ligand (-1.90 eV). Under photoexcitation, the excited electrons jump from the HOMO (highest occupied molecular orbital) of the H4bptc ligand to its LUMO state, and then transfer to the LUMO state of NFT / NFZ instead of returning to its ground state, resulting in fluorescence quenching. In summary, the detection mechanism of NFT / NFZ by Cu-CP should be attributed to the synergistic effect of dynamic IFE, FRET and PET processes.

[0074] The above is only an embodiment of the present invention. The common sense such as the known specific structure and characteristics in the scheme is not described in detail here. The ordinary technicians in the relevant field know all the common technical knowledge in the technical field of the invention before the application date or priority date, can know all the existing technologies in the field, and have the ability to apply the conventional experimental means before that date. The ordinary technicians in the relevant field can improve and implement this scheme in combination with their own abilities under the enlightenment given by this application. Some typical known structures or known methods should not become obstacles for ordinary technicians in the relevant field to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which should also be regarded as the scope of protection of the present invention, which will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A Cd(II) coordination polymer, characterized in that: The chemical expression of the coordination polymer is: {[Cd2(bptc)(dpb) 1.5 (H2O)]·(H2O)·0.5(dpb)} n , wherein H4bptc is a 2,3,3′,4′-biphenyltetracarboxylic acid organic ligand, dpb is a 1,4-di(pyridin-4-yl)benzene (dpb) nitrogen-containing ligand, The crystal of the complex belongs to the triclinic system, the space group is Pī, and the unit cell parameters are c=13.3406(3), α=110.165(1)°, β=107.476(1)°, γ=97.459(1)°, and its asymmetric unit consists of two crystallographically independent Cd 2+ ions (Cd1, Cd2), 1 deprotonated bptc 4- ligand, 3 dpb ligands (dpb I, dpb II, dpb III; occupancy: dpb I is 1, dpb II and dpb III are 0.5), 1 coordinated water molecule (O9) and 1 lattice water (O10).

2. A method for preparing a Cd(II) coordination polymer as claimed in claim 1, characterized in that: The method comprises the following steps: (1) dissolving cadmium acetate dihydrate, 2,3,3′,4′-biphenyltetracarboxylic acid and 1,4-di(pyridin-4-yl)benzene in deionized water and stirring, and adjusting the pH value with a NaOH aqueous solution; (2) transferring the product from the previous step into a reaction kettle and heating it for reaction; (3) After the reaction is completed, the reaction system is cooled and filtered to obtain {[Cd2(bptc)(dpb) 1.5 (H2O)]·(H2O)·0.5(dpb)} n , abbreviated as XYNU-1.

3. The method for preparing a Cd(II) coordination polymer according to claim 2, characterized in that: In the step (1), the molar ratio of cadmium acetate dihydrate to 2,3,3′,4′-biphenyltetracarboxylic acid is 1:

1.

4. The method for preparing a Cd(II) coordination polymer according to claim 2, characterized in that: In the step (1), the molar ratio of cadmium acetate dihydrate to 1,4-di(pyridin-4-yl)benzene is 2:

3.

5. The method for preparing a Cd(II) coordination polymer according to claim 2, characterized in that: The concentration of the NaOH aqueous solution in step (1) is 0.1M.

6. The method for preparing a Cd(II) coordination polymer according to claim 2, characterized in that: In the step (1), the pH value is adjusted to 8.

7. The method for preparing a Cd(II) coordination polymer according to claim 2, characterized in that: The material of the reaction kettle in step (2) is polytetrafluoroethylene, the reaction conditions are 110-120° C., and the reaction time is 2-4 days.

8. The method for preparing a Cd(II) coordination polymer according to claim 2, characterized in that: The cooling temperature in the step (3) is room temperature, and the product is filtered and washed with distilled water to obtain XYNU-1 in the form of white block crystals.

9. Use of the Cd(II) coordination polymer as claimed in claim 1, characterized in that: Used for the specific detection of nitrofuran antibiotics in irrigation water systems.

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