Cd (II) coordination polymer, preparation method and application thereof

Abstract

The application provides a Cd(II) coordination polymer, the chemical expression of the polymer is {[Cd2(bptc)(dpb) 1.5 (H2O)]·(H2O)·0.5(dpb)} n , wherein H4bptc is 2,3,3',4'-biphenyl tetracarboxylic acid organic ligand, dpb is 1,4-di(pyridin-4-yl)benzene (dpb) nitrogen-containing ligand, the crystal of the complex belongs to a triclinic system, the space group is Pī, the cell parameters are c=13.3406(3), α=110.165(1)°, β=107.476(1)°, γ=97.459(1)°, and the asymmetric unit is composed of 2 crystallographically independent Cd 2+ ions (Cd1, Cd2), 1 deprotonated bptc 4‑ ligand, 3 dpb ligands (dpbI, dpbII, dpbIII; occupancy: dpbI is 1, and dpbII and dpbIII are 0.5), 1 coordinated water molecule (O9) and 1 lattice water (O10). The Cd(II) coordination polymer provided by the application can be used for specific detection of nitrofuran antibiotics in irrigated water bodies.

Description

TECHNICAL FIELD

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

[0002] With the progress of science and technology and the development of society, environmental problems are increasingly serious. Excessive use of antibiotics has made antibiotic pollution in water bodies more serious, which has caused serious threats to human health and ecological environment. Therefore, efficient and accurate detection of the content of antibiotics in water bodies has important significance for curbing the continuous spread of pollution and protecting the safety of people's life and health. However, the current detection methods mostly have the shortcomings of old equipment, complicated procedures, poor timeliness, etc., and cannot meet the current detection requirements of people. For example, the immunoassay method has the significant advantages of simple operation and low cost, but has poor selectivity and sensitivity and relatively long sensing time; the chromatography combination technology mainly adopts sensing technology of mass spectrometry and chromatography combined with other complex procedures, which is mature, but needs large and expensive instruments and professional operation. Therefore, it is of great significance to develop a cheap, efficient and fast detection method.

[0003] The He River is one of the main irrigation water sources in Xinyang City, and is dispatched and managed through the Nanwan Reservoir to provide irrigation water for farmland. The Nanwan Reservoir is located on the He River, a tributary of the Huaihe River, 6 kilometers southwest of Xinyang City, and is a large-scale water conservancy project built in the early years 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 flood control, irrigation, power generation, breeding, urban water supply and tourism development, and comprehensive utilization. In the dry season, the water conservancy department of Xinyang City will scientifically dispatch water sources to ensure the irrigation needs of farmland, so it is particularly important to detect and confirm whether furazolidone (NFZ) and nitrofurantoin (NFT) in the river exceed the standard. SUMMARY

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

[0005] In order to overcome at least one of the above-mentioned shortcomings of the prior art, on the one hand, the application provides a Cd(II) coordination polymer, and the chemical formula of the coordination polymer is,

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

[0007] The crystal of the complex belongs to triclinic system, space group Pī, and the cell parameters are a = 9. 0000(3), b = 9. 0000(3), c = 13. 3406(3), α = 110. 165(1) °, β = 107. 476(1) °, γ = 97. 459(1) °, and the asymmetric unit is composed of 2 crystallographically independent Cd c = 13. 3406(3), α = 110. 165(1) °, β = 107. 476(1) °, γ = 97. 459(1) °, and the asymmetric unit is composed of 2 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, and 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 application provides a preparation method of a Cd (II) coordination polymer, which comprises the following steps: (1) dissolving cadmium acetate dihydrate, 2,3,3',4'-biphenyl-tetracarboxylic acid and 1,4-bis (pyridine-4-yl) benzene in deionized water, stirring, and adjusting the pH value with an aqueous NaOH solution;

[0009] (2) transferring the product of the above step into a reaction kettle, and then heating and reacting;

[0010] (3) after the reaction is completed, cooling the reaction system of the above step, and filtering to finally obtain {[Cd2(bptc)(dpb 1.5 (H2O)]·(H2O)·0.5(dpb)} n , which is referred to as XYNU-1.

[0011] Further, the preparation method of the Cd (II) coordination polymer is characterized in that the molar ratio of cadmium acetate dihydrate to 2,3,3',4'-biphenyl-tetracarboxylic acid in the step (1) is 1:1.

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

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

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

[0015] Further, the material of the reaction kettle in the step (2) is polytetrafluoroethylene, the reaction condition is 110-120 ℃, and the time is 2-4 days.

[0016] Further, the cooling temperature in the step (3) is room temperature, and the obtained XYNU-1 is a white block crystal after being washed with distilled water after filtration.

[0017] The third aspect of the present application provides a use of a Cd(II) coordination polymer for specific detection of nitrofuran antibiotics in an irrigation water system.

[0018] The present application has the following advantages:

[0019] The present application selects Cd 2+ As a metal center, aromatic polycarboxylic acid ligand 2,3,3',4'-biphenyl tetracarboxylic acid (H4bptc) and nitrogen-containing ligand 1,4-bis (pyridine-4-yl) benzene (dpb) with flexible coordination mode are selected to self-assemble under hydrothermal conditions, and a Cd(II) coordination polymer {{[Cd2(bptc)(dpb) 1.5 (H2O)]·(H2O)·0.5(dpb)} n (XYNU-1) is prepared. Research shows that XYNU-1 is very stable in a water system, can be used for specific recognition of nitrofuran antibiotics NFT and NFZ in river water, and has the characteristics of high sensitivity, low detection limit, good selectivity, and strong anti-interference ability. Further research shows that the XYNU-1 prepared by the present application can be used as a fluorescent detection material to monitor nitrofuran antibiotic pollutants in river water. The present application has the advantages of low cost, convenient operation, fast response, high sensitivity, and low detection limit. BRIEF DESCRIPTION OF DRAWINGS

[0020] The present application will be further described below in combination with the drawings and examples.

[0021] Figure 1 is a structural diagram of H4bptc organic ligand and dpb nitrogen-containing ligand;

[0022] Figure 2 is a variety of structural diagrams of XYNU-1;

[0023] Figure 3 is a PXRD spectrum of XYNU-1;

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

[0025] Figure 5 is a selective detection diagram of XYNU-1 on nitrofuran antibiotics NFT and NFZ;

[0026] Figure 6 is an exponential relationship diagram of I0 / I and (a) NFT; (b) NFZ concentration under high concentration;

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

[0028] Figure 8Figure for the excited state decay curves of XYNU-1 suspension at different (a) NFT; (b) NFZ concentrations;

[0029] Figure 9 Figure for the UV-Vis absorption spectra of different antibiotics and the excitation / emission spectra of XYNU-1;

[0030] Figure 10 Figure for the energy transfer quenching mechanism of NFT / NFZ: one possible path PET. DETAILED DESCRIPTION

[0031] Before any examples embodiments are described in further detail, it should be noted that some example embodiments are described as processes depicted as flow diagrams. Although the processes are described in a particular sequential order, many of the processes can be performed concurrently, in parallel, or simultaneously. In addition, the order of the processes can be re-arranged. The processes can be terminated when their operations are completed, but the processes can also end in response to events that are external to the processes. The processes can correspond to methods, functions, procedures, subroutines, subprograms, etc.

[0032] It should be understood that, although terms such as "first" and "second" can be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the scope of the example embodiments. The term "and / or" as used herein encompasses any and all combinations of one or more of the associated associated items.

[0033] The present application provides a Cd(II) coordination polymer, the chemical formula of which is,

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

[0035] The crystal of the complex belongs to triclinic system, space group Pī, and the cell parameters are a = 9. 1 1 1 1 (3), b = 9. 1 1 1 1 (3), c = 13.3406(3), α = 1 10.165(1 )°, β = 107.476(1 )°, γ = 97.459(1 )°, and the asymmetric unit is composed of 2 crystallographically independent Cd ions (Cd1, Cd2), 1 deprotonated bptc c = 13.3406(3), α = 1 10.165(1 )°, β = 107.476(1 )°, γ = 97.459(1 )°, and the asymmetric unit is composed of 2 crystallographically independent Cd ions (Cd1, Cd2), 1 deprotonated bptc 2+ ligand (bptc), 1 dpb ligand (dpb), 1 water molecule (H2O), and 0.5 dpb molecule (dpb).4- It consists of a ligand, 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 molecule (O10).

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

[0037] (2) Transfer the product from the previous step into the reaction vessel and then heat it to react;

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

[0039] All chemical reagents used in this invention are analytical grade and can be used directly. The structural diagrams of H4bptc and dpb ligands are shown below. Figure 1 As shown. By utilizing Cu-Kα rays PXRD patterns were obtained using a Smartlab9 X-ray powder diffractometer. Fourier transform infrared (FT-IR) spectra were collected using a Thermo Fisher spectrometer. Ultraviolet-visible (UV-vis) spectra were collected using a Lambda 950 spectrometer. Elemental analysis (C, H, and N) characterization was performed using a PerkinElmer 2400LS II elemental analyzer. Thermal stability under air atmosphere was studied using a simultaneous thermal analyzer (TA Q600) at a heating rate of 10 °C / min. -1 Fluorescence spectra at room temperature were collected using an FLS1000 fluorescence / phosphorescence spectrophotometer (xenon lamp). The Gaussian 09 program was used for configuration optimization, with structural optimization performed using a B3LYP functional with a 6-31G(d,p) basis set, and frontier molecular orbital energy levels of the relevant molecules calculated. The specific feed ratios and reaction conditions are described below.

[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-bis(pyridin-4-yl)benzene (0.03 mmol, 4.6 mg) were dissolved in deionized water and stirred for 1.5 h. The pH was then adjusted to 8 with 0.1 M NaOH aqueous solution.

[0042] (2) The product of the above step was transferred into a polytetrafluoroethylene reactor with a volume of 20 mL, heated at 120℃ for 3 days to react;

[0043] (3) After the reaction was completed, the reaction system of the above step was cooled to room temperature, filtered, washed with distilled water, and finally white block crystals {[Cd2(bptc)(dpb) 1.5 (H2O)]·(H2O)·0.5(dpb)} were obtained. n , abbreviated 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 Cd(II) coordination polymer XYNU-1 provided by the present application is characterized and tested for properties as follows. X-ray single crystal diffraction data

[0046] Cu-CP single crystal X-ray diffraction data was collected on a Bruker D8 Venture diffractometer (IUS3.0) using a graphite monochromatic Mo-Kα radiation source Cu-CP single crystal X-ray diffraction data was collected on a Bruker D8 Venture diffractometer (IUS3.0) using a graphite monochromatic Mo-Kα radiation source

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

[0048]

[0049]

[0050] Structure description

[0051] Figure 2 (a) Asymmetric unit of compound XYNU-1; (b) Cd center and bptc 4-(c) A two-dimensional layered structure view of ligands extending along the bc plane; bptc viewed 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 confirm that XYNU-1 belongs to the Pī space group of the triclinic system. For example... Figure 2 As shown in a, its asymmetric unit consists of two crystallographically independent Cd atoms. 2+ Ions (Cd1, Cd2), 1 deprotonated bptc 4- The molecule consists of ligands, three dpb ligands (dpb I, dpb II, dpb III; occupancy: dpb I = 1, dpb II and dpb III = 0.5), one coordinated water molecule (O9), and one lattice water molecule (O10). Each Cd1 center employs an octahedral coordination mode. Its equatorial plane is composed of ligands from three different bpt molecule groups. c4- The four carboxyl oxygen atoms (O4D, O5C, O6, O7) of the ligand are occupied, while the axial positions are occupied by two pyridine nitrogen atoms (N1, N3F) from two different dpb molecules. Cd2 is six-coordinated, with each atom occupied by a different bptc. 4- The molecule's four carboxyl oxygen atoms (O1E, O2E, O3, O7B) are coordinated with a pyridine nitrogen atom (N2) from dpb and a coordinated water molecule (O9). The Cd-O / N bond length is... The O / N-Cd-O / N bond angle is 55.26(4)–177.04(2)°. Each bptc4-ligand molecule simultaneously bonds to 6 Cd atoms. 2+ Ion, coordination mode μ6:

[0053] like Figure 2 As shown in b, two Cd are in a centrally symmetrical position. 2+ Ions are bptc 4- Ligand linkages form a binuclear cluster unit Cd2(COO)4, with Cd1···Cd1 distances being... Adjacent quad-core clusters are interconnected via bptc 4- The ligands further connect 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 the three-dimensional framework structure of XYNU-1. Figure 2d). π…π stacking interactions between benzene rings and pyridine rings in adjacent two-dimensional layers of this three-dimensional network. This further enhances the stability of the entire three-dimensional framework. Approximately [value missing] was observed in the c-axis direction. The 1D channel, calculated by PLATON, has a solvent-fillable volume of [volume missing] after removing guest molecules (lattice water and dpb III molecules]. Percentage of total unit cell volume 23.5%. From a topological perspective, this three-dimensional structure can be simplified to a 3-node network with 4, 5, and 6 connections, with the topological notation {4...}. 3 ·6 3}{4 3 ·6 6 ·8}{4 6 ·6 7 ·8 2}( Figure 2 e).

[0054] X-ray powder diffraction

[0055] To verify that the complex is a single pure phase, X-ray powder diffraction (PXRD) was performed on the synthesized XYNU-1. Figure 3 As shown, the PXRD diffraction peaks of XYNU-1 agree well with the diffraction peaks simulated from the single-crystal structure. This result indicates that the obtained sample is a pure phase and can be used for further performance testing.

[0056] Infrared spectroscopy

[0057] The present invention also characterized the Fourier Transmission-Infrared (FT-IR) spectrum of XYNU-1. For example... Figure 4 As shown, XYNU-1 is located at 3134-3597 cm⁻¹. -1 The strong OH vibration at 710 cm⁻¹ originates from coordinated water molecules and lattice water molecules in the complex structure. -1 The vibrational peak at 1602 cm⁻¹ is attributed to the stretching vibration of the CH bond in the benzene ring of the organic ligand. -1 and 1394cm -1 The strong absorption peaks at these locations correspond to the asymmetric and symmetric stretching vibrations of the carboxyl group —C=O, respectively. Compared to the free H4bptc ligand, the characteristic absorption peaks at these two locations exhibit a 93 cm⁻¹ pattern. -1 / 52cm -1 The blue / red shift indicates that the carboxyl group on the H4bptc ligand molecule in the complex is completely deprotonated and reacts with Cd. 2+ Coordination occurred at the metal center. Furthermore, the characteristic peak of the CN bond in the dpb ligand (1592 cm⁻¹) was observed. -1 In the XYNU-1 complex, the blue shift was observed to 1539 cm⁻¹. -1, further illustrating that the pyridine nitrogen atom in dpb in the complex coordinates with Cd 2+ The center also coordinates, which is consistent with the result of single crystal X-ray diffraction analysis.

[0058] Stability of XYNU-1

[0059] The stability of the coordination polymer material determines whether it can be applied to practical life and scientific research production to a great extent. Therefore, the water stability of the synthesized sample is first tested. Considering the complexity of the actual water sample, the PXRD pattern of the XYNU-1 sample immersed in an aqueous solution with different pH values for 48 h is detected, and it is found that the PXRD pattern of XYNU-1 in a solution with pH of 2-12 is basically the same as that of the original sample, and the positions of all diffraction peaks are almost consistent with those of the original sample diffraction peaks, indicating that the material synthesized in the application can still maintain the structure integrity in the aqueous solution with a wider pH range. In addition to testing the chemical stability, the thermal stability of the coordination polymer is also important, and the thermal stability performance of the coordination polymer in the range of 25-800 DEG C is tested at a rate of 10 DEG C·min -1 The skeleton of the complex can be stable to about 340 DEG C. The excellent water stability and thermal stability provide an important prerequisite for the application of the material in the fluorescence sensing in the aqueous phase.

[0060] Fluorescence sensing test method

[0061] The collected Lihe River water samples were centrifuged at a speed of 5000 r / min for 3 min to precipitate impurities, and the supernatant was taken. For water system fluorescence sensing, 2 mg of ground XYNU-1 sample was dispersed into 2 ml of Lihe River water, ultrasonicated for 0.5 h, and aged for 3 days to obtain a uniform suspension. The suspension was transferred to a 12.5 mm x 12.5 mm x 45 mm four-transmittance cuvette to collect its luminescence spectrum. For fluorescence titration test, under the same conditions, different volumes of 1 mM NFT / NFZ were added to the blank suspension using a pipette, and the luminescence spectrum after each addition was recorded. In the competitive experiment, equal molar 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), thiamphenicol (THI), flurothiamphenicol (FF), roxithromycin (RXM), ampicillin (APL), streptomycin sulfate (SMS) and gentamicin sulfate (GMS), NFT and NFZ were added to the blank sample to test the specificity of the probe. In addition, a series of three-step anti-interference experiments were carried out on XYNU-1 to determine its anti-interference ability. First, the emission intensity of the probe itself blank sample was collected, then the interference substances were introduced into the CP suspension respectively, and the fluorescence spectrum was measured. Finally, equal amounts of substrate (NFT / NFZ) were added to the CP suspension containing the interference analyte, and the emission intensity was tested. All emission spectrum test conditions were the same: excitation wavelength was 275 nm (excitation slit = 5 nm, emission slit = 5 nm), and 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 time-consuming, convenient and fast, etc. The coordination polymer Cd-CP synthesized in this experiment can be used as a fluorescence probe. Figure 5 (a) Fluorescence intensity of XYNU-1 dissolved in different antibiotic solutions; (b) XYNU-1 fluorescence intensity in the presence 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) S-V plot of NFT at low concentration; (f) S-V plot of NFZ at low concentration.

[0065] Firstly, the selectivity of XYNU-1 to common antibiotics was studied, such as Figure 5 (a), 0.2 mM of 14 different types of antibiotics were added into the suspension of XYNU-1 in He River water, respectively, and the fluorescence intensity of the suspension of XYNU-1 after adding the antibiotics was detected. It was found that only after adding nitrofuran antibiotics, the suspension of XYNU-1 could show obvious fluorescence quenching effect (NFZ was 94.8%, NFT was 95.6%), and other types of antibiotics had no obvious quenching effect. It can be preliminarily concluded that the luminescence intensity of XYNU-1 in He River water system is highly related to the type of antibiotic, and has high selectivity to nitrofuran antibiotics, which can be used to selectively recognize nitrofuran antibiotics NFT and NFZ in He River water through fluorescence quenching effect.

[0066] Sensitivity test

[0067] Further study on the quantitative relationship between the content of nitrofuran antibiotics and the fluorescence signal intensity of the suspension of XYNU-1, 1 mM of NFZ or NFT was added dropwise into the suspension of XYNU-1, and fluorescence titration experiment was carried out by slowly increasing the concentration of NFZ and NFT. As shown in Figure 5 (c) and (d), the fluorescence intensity of the suspension of XYNU-1 continuously decreased with the increase of the concentration of NFZ / NFT, and when the molar concentration of NFZ / NFT was 0.25 mM / 0.21 mM, the quenching efficiency of XYNU-1 reached 97.8% and 97.3%, respectively. This indicates that XYNU-1 has high sensitivity for detecting NFZ / NFT. At low concentration, the quenching efficiency (I0 / I) has a good linear relationship with the concentration of NFZ / NFT, and in the concentration range of 0-50 μM / 0-40 μM, the S-V formula I0 / I = 1+K SV [analyte] was accurately simulated, as shown in Figure 5 (e) and (f), for NFZ, K SV = 2.29 x 10 4 M -1 , R 2 = 0.9905, for NFT, K SV = 2.44 x 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 SVBy calculation, the present application obtains the detection limit of NFT as 2.21 nM and the detection limit of NFZ as 2.36 nM, which is lower than most of the reported CP materials. However, when the content of nitrofuran antibiotics in the solution is high, the quenching efficiency (I0 / I) and the concentration of NFZ / NFT will not be linearly related, but exponentially related. Figure 6

[0068] Anti-interference test

[0069] For practical application, the intelligent fluorescent sensor not only needs high sensitivity and high selectivity, but also needs strong anti-interference ability. Further anti-interference experiments show that, Figure 5 (b) shows that the fluorescence intensity of XYNU-1 can be obviously 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, which shows that the coordination polymer XYNU-1 can be used for specific detection of nitrofuran antibiotics in water systems and exhibits excellent anti-interference ability.

[0070] Research on fluorescence recognition mechanism

[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 more intelligent sensor materials. Based on this, the present application systematically explores the possible mechanism of specific recognition of NFT / NFZ by XYNU-1. First, the PXRD pattern of XYNU-1 after being treated by NFT / NFZ is tested to confirm the structural integrity of the coordination polymer Figure 7 a). As can be seen from the figure, the framework structure of XYNU-1 remains intact during the detection process. Therefore, it can be initially ruled out that the fluorescence quenching is caused by structural damage. In addition, the present application also tests the FT-IR pattern of XYNU-1 after being treated by NFT / NFZ. As shown in Figure 7 b, the infrared spectrum of the XYNU-1 sample after being treated by the analyte has no obvious change, which also rules out the possibility of forming a ground-state complex.

[0072] According to the literature, there are many reasons that can cause the fluorescence quenching of the fluorescent chromophore, including fluorescence resonance energy transfer (FRET), internal filter effect (IFE) and the like. The above mechanisms can be divided into dynamic quenching and static quenching. These two kinds of quenching mechanisms can be distinguished by the fluorescence lifetime of the fluorescent sensor before and after being treated by the analyte. If the fluorescence lifetime before and after being treated by the analyte remains constant, the quenching system is static, and if they have different fluorescence lifetimes, it is dynamic in nature. Figure 8 ​As shown in a-8b, 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 the UV-Vis spectra of all antibiotics, this invention analyzed the possibilities of FRET and IFE. Figure 9 As shown, only the UV-Vis spectrum of NFT / NFZ overlaps with the excitation spectrum of the XYNU-1 suspension, indicating 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, some of the excitation light may be absorbed by NFT / NFZ, ultimately reducing the fluorescence signal output of the sensor. Furthermore, Figure 9 The partial overlap between the UV-Vis absorption of NFT / NFZ and the emission spectrum of the XYNU-1 suspension also demonstrates the contribution of FRET to fluorescence quenching. Figure 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, leading to fluorescence quenching. In summary, the detection mechanism of Cu-CP for NFT / NFZ should be attributed to the synergistic effect of dynamic IFE, FRET, and PET processes.

[0074] The above descriptions are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, based on the guidance provided in this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described 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 for the coordination polymer is: {[Cd2(bptc)(dpb)} 1.5 (H2O)]·(H2O)·0.5(dpb)} n H4bptc is the organic ligand of 2,3,3′,4′-biphenyltetracarboxylic acid, and dpb is the nitrogen-containing ligand of 1,4-bis(pyridin-4-yl)benzene. The coordination polymer crystal belongs to the triclinic crystal system, with space group Pī and unit cell parameters of [missing information]. c = 13.3406(3), α = 110.165(1)°, β = 107.476(1)°, γ = 97.459(1)°, its asymmetric unit consists of two crystallographically independent Cd 2+ Ions, 1 deprotonated bptc 4- The ligand consists of three dpb ligands, namely dpb I, dpb II, and dpb III; the occupancy rate is 1 for dpb I, 0.5 for dpb II and dpb III, and is composed of one coordinated water molecule O9 and one lattice water O10.

2. A method for preparing the Cd(II) coordination polymer as described in claim 1, characterized in that: The method includes the following steps: (1) Cadmium acetate dihydrate, 2,3,3′,4′-biphenyltetracarboxylic acid and 1,4-bis(pyridin-4-yl)benzene were dissolved in deionized water and stirred. The pH value was then adjusted with NaOH aqueous solution. (2) Transfer the product from the previous step into the reaction vessel and then heat it to react; (3) After the reaction is complete, the reaction system is cooled and filtered to obtain {[Cd2(bptc)(dpb)}. 1.5 (H2O)]·(H2O)·0.5(dpb)} n It is abbreviated as XYNU-1.

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

1.

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

3.

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

7. The method for preparing the Cd(II) coordination polymer according to claim 2, characterized in that: In step (2), the reactor is made of polytetrafluoroethylene, and the reaction conditions are 110-120℃ for 2-4 days.

8. The method for preparing the Cd(II) coordination polymer according to claim 2, characterized in that: In step (3), the cooling temperature is room temperature, and after filtration, the product is washed with distilled water. The resulting XYNU-1 is a white blocky crystal.

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

Images