Cadmium (II)-based metal organic framework crystalline material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of fluorescent active substance development, and particularly relates to a cadmium (II)-based metal organic framework crystalline material as well as a preparation method and application thereof. The molecular formula of the cadmium (II)-based metal organic framework crystalline material is {[Cd3 (Br-BDC) 3 (BMIP) 2]. 2H2O} n, cadmium (II) ions serve as connecting nodes, BMIP and H2 (Br-BDC) ligands serve as bridging ligands to be in mutual bridging to form a three-dimensional space structure, Cd-O secondary structural units are contained in the structure, three Cd atoms form a trinuclear Cd-O cluster structure through the Cd-O secondary structural units, and the Cd (II)-based metal organic framework crystalline material has the structural formula shown in the description. The Cd1 atom and the Cd1 # atom are in mirror symmetry. The divalent cadmium ion fluorescence sensing material can be prepared by adopting a one-pot solvothermal reaction; the preparation method has the advantages of simple process, convenience in operation, high yield, good reproducibility and the like; the cadmium (II) fluorescent sensing material disclosed by the invention is relatively high in fluorescence emission spectrum intensity and can be applied to the fields of molecular fluorescent probes, metal ion detection and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of fluorescent active material development, and in particular to a cadmium (II)-based metal organic framework crystalline material and a preparation method and application thereof. Background Technology

[0002] In recent years, environmental pollution remains a global challenge. For example, water pollution, industrial wastewater, domestic sewage and agricultural non-point source pollution have caused water pollution problems to remain serious. Some rivers, lakes and offshore waters have been polluted to varying degrees, affecting aquatic ecosystems and human health. Industrial wastewater: A large amount of wastewater containing pollutants such as heavy metals and organic matter generated during industrial production is directly discharged into water bodies without effective treatment, causing serious pollution to surface water and groundwater. Agricultural pollution: The excessive use of fertilizers and pesticides, as well as the discharge of livestock and poultry breeding waste, leads to a large amount of nutrients such as nitrogen and phosphorus entering the water body, causing eutrophication of the water body. Domestic sewage: With the acceleration of urbanization, the discharge of domestic sewage continues to increase. Pollutants such as organic matter and detergents have a great impact on the water environment. Atmospheric deposition: Sometimes chemicals released from chimneys enter the atmosphere and then fall back to the earth in the form of rainwater, entering the ocean, rivers and lakes, which can also cause water pollution.

[0003] In addition, there is soil pollution, where pollutants such as heavy metals, pesticide residues and plastic particles accumulate in the soil, posing a threat to crop growth and human health.

[0004] Currently, there are different means of detecting environmental pollutants. High-performance gas-liquid chromatography, mass spectrometry, Raman spectroscopy and other detection methods mainly rely on expensive instruments. These analytical techniques have certain disadvantages, such as the need for well-trained professionals, high costs and complex equipment. MOFs as fluorescent sensing materials have been widely favored by scientific researchers due to their advantages such as simple operation, high selectivity and fast detection speed. There are three factors that cause MOFs to emit light: the conjugation effect produced by organic ligands, the central metal ions and the d 10 MOFs formed by metals with valence electrons will cause them to emit light. Because MOFs materials have the characteristics of high specific surface area and pore structure, they show high adsorption capacity and better selectivity. Therefore, they are excellent in the adsorption of heavy metal ions and the detection of organic pollutants and pesticides. MOFs for Fe 3+ 、Cd 2+ 、Cr 3+ 、Ag + 、K + 、Mn 2 + 、Al 3+It has a detection function. Therefore, by detecting the fluorescence changes before and after contact with organic pollutants, heavy metal ions and pesticides, it can be used to qualitatively or even quantitatively detect excessive organic pollutants, heavy metal ions and pesticides in the environment. SUMMARY OF THE INVENTION

[0005] The technical problem to be solved by the present invention is to provide a cadmium (II)-based metal organic framework crystalline material and its preparation method and application in view of the deficiencies of the above-mentioned prior art. The molecular formula of the cadmium (II)-based metal organic framework crystalline material is {[Cd 3 (Br-BDC) 3 (BMIP) 2 ]·2H 2 O} n , with cadmium (II) ions as connecting nodes, BMIP and H 2 (Br-BDC) ligands are used as bridging ligands to bridge each other to form a three-dimensional structure. They are prepared by one-pot solvent thermal preparation and can be used in fluorescent sensors to detect ionic pollutants. They can also be used to detect Al 3+ fluorescent probe.

[0006] The present invention provides a cadmium (II)-based metal organic framework crystalline material, the molecular formula of the cadmium (II)-based metal organic framework crystalline material is {[Cd 3 (Br-BDC) 3 (BMIP) 2 ]·2H 2 O} n , the cadmium (II)-based metal organic framework crystalline material uses cadmium (II) ions as connecting nodes, 1,3-bis(dimethylimidazolyl)propane and 2,5-dibromoterephthalic acid ligands as bridging ligands to bridge each other to form a three-dimensional spatial structure; the structure contains Cd-O secondary structural units, and three Cd atoms form a trinuclear Cd-O cluster structure through the Cd-O secondary structural units, and the Cd1 atom and the Cd1# atom are mirror-symmetric.

[0007] The present invention provides a method for preparing the above-mentioned cadmium (II)-based metal organic framework crystalline material, comprising the following steps: S1, adding cadmium salt, 1,3-bis(dimethylimidazolylpropane) and 2,5-dibromoterephthalic acid into solvent DMA to obtain a mixture, adding glacial acetic acid to the mixture to adjust the pH value of the mixture to 4.5-6.5, and then performing a solvent thermal reaction in a closed environment to obtain a reaction product; S2. Allow the reaction product prepared in S1 to cool naturally and crystallize, wash and filter under reduced pressure to obtain colorless needle-shaped crystals, and dry to obtain cadmium (II)-based metal organic framework crystalline material.

[0008] ​​​​​​​​According to the preparation method provided by the present invention, the molar volume ratio of the cadmium salt, 1,3-bis(dimethylimidazolyl)propane, 2,5-dibromoterephthalic acid and DMA in S1 is (0.5-1.5) mmol: (0.05-0.15) mmol: (0.1-0.5) mmol: (2-10) mL, the amount of glacial acetic acid used is 50 µL, the concentration of glacial acetic acid is 17 mol / L, the temperature of the solvent thermal reaction is 90 °C, and the time of the solvent thermal reaction is (36-72) h.

[0009] According to the preparation method provided by the present invention, the molar volume ratio of the cadmium salt, 1,3-bis(dimethylimidazolylpentane), 2,5-dibromoterephthalic acid and DMA in S1 is 1.5 mmol:0.05mmol:0.5mmol:4mL, the amount of glacial acetic acid used is 50 µL, the temperature of the solvent thermal reaction is 90 °C, and the time of the solvent thermal reaction is 48 h.

[0010] According to the preparation method provided by the present invention, the drying temperature in S2 is 60°C, and the drying time is 2 to 4 hours.

[0011] The present invention also provides an application of the above-mentioned cadmium (II)-based metal organic framework crystalline material, which can be used in fluorescent sensors to detect ion pollutants and can also be used as a detector of Al 3+ fluorescent probe.

[0012] Compared with the prior art, the present invention has the following advantages: The present invention can prepare cadmium (II)-based metal organic framework crystalline materials {[Cd 3 (Br-BDC) 3 (BMIP) 2 ]·2H 2 O} n , n is a positive integer. The preparation method has the advantages of simple process, convenient operation, high yield, good reproducibility, etc. The fluorescence emission spectrum of the cadmium (II)-based metal organic framework crystalline material is strong and can be applied to the fields of molecular fluorescence enhancement or quenching effect, metal ion detection, etc. The detection method of cadmium (II)-based metal organic framework crystalline material has the advantages of simple operation, low cost, high selectivity, and fast detection speed. Brief Description of the Figures

[0013] ​​​​In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0014] Figure 1 is a single molecule image of a cadmium (II) based metal organic framework crystalline material; Figure 2 It is a three-dimensional porous framework structure of cadmium (II)-based metal organic framework crystalline material; Figure 3 Topological structure view of cadmium (II)-based metal organic framework crystalline materials; Figure 4 IR graph of cadmium (II) based metal organic framework crystalline material; Figure 5 is the XRD pattern of cadmium (II) based metal organic framework crystalline material; Figure 6 is the fluorescence spectrum of cadmium (II) based metal organic framework crystalline material; Figure 7 The fluorescence emission intensity diagram of cadmium (II)-based metal organic framework crystalline materials dispersed in 7 organic solvents; Figure 8 For coordination polymers to Al 3+ Schematic diagram of specificity of ion detection; Figure 9 The relationship between the fluorescence spectrum of cadmium (II) based metal organic framework crystalline materials in ethanol solvent and the change of metal ion concentration; Figure 10 Cd(II)-based metal organic framework crystalline material with Al 3+ Solution concentration fluorescence intensity change and fitting diagram. Specific implementation method

[0015] Example 1

[0016] This embodiment provides a method for preparing a cadmium (II)-based metal organic framework crystalline material, and the specific steps are as follows: S1. 1.5 mmol of cadmium nitrate hexahydrate, 0.05 mmol of 1,3-bis(dimethylimidazolylpropane) (BMIP) and 0.5 mmol of 2,5-dibromoterephthalic acid (H 2(Br-BDC) was dissolved in 4 mL of N, N'-dimethylacetamide (DMA) to obtain a mixture, 50 µL of 17 mol / L glacial acetic acid was added to adjust the pH value of the mixture to 5.5, which was weakly acidic. The mixture was placed in a glass scintillation vial and subjected to solvothermal reaction at 90 °C for 48 h to obtain the reaction product; The structural formula of the above BMIP is shown in the following formula (I):

[0017] Formula (I); The above H 2 The structural formula of (Br-BDC) is shown in the following formula (II):

[0018] Formula (Ⅱ); The structural formula of the above DMA is shown in the following formula (III):

[0019] Formula (III); S2. The reaction product is cooled and crystallized naturally, and the crystals are washed with deionized water. The crystals are filtered under reduced pressure to obtain colorless needle-shaped crystals, which are placed in an oven at 60°C for 3 h to obtain a cadmium (II)-based metal organic framework crystalline material.

[0020] The main preparation method provided in this embodiment is intended to overcome the problems of low yield, very low repeatability and excessive influence of reaction conditions in the existing preparation methods of cadmium (II)-based metal organic framework crystalline materials.

[0021] Example 2 This embodiment provides a method for preparing a cadmium (II)-based metal organic framework crystalline material, and the specific steps are as follows: S1. Dissolve 0.5 mmol of cadmium chloride, 0.1 mmol of 1,3-bis(dimethylimidazolylpropane) and 0.3 mmol of 2,5-dibromoterephthalic acid in 2 mL of N,N'-dimethylacetamide to obtain a mixture, add 50 µL of 17 mol / L glacial acetic acid to adjust the pH value of the mixture to 4.5, which is weakly acidic, place the mixture in a glass scintillation vial, and perform a solvothermal reaction at 90 °C for 36 h to obtain a reaction product; S2. The reaction product is cooled and crystallized naturally, and the crystals are washed with deionized water. The crystals are filtered under reduced pressure to obtain colorless needle-shaped crystals, which are placed in an oven at 60°C for 2 h to obtain a cadmium (II)-based metal organic framework crystalline material.

[0022] Example 3 ​This embodiment provides a method for preparing a cadmium (II)-based metal organic framework crystalline material, and the specific steps are as follows: S1. Dissolve 1.0 mmol of cadmium acetate, 0.15 mmol of 1,3-bis(dimethylimidazolylpropane) and 0.1 mmol of 2,5-dibromoterephthalic acid in 10 mL of N,N'-dimethylacetamide to obtain a mixture, add 50 µL of 17 mol / L glacial acetic acid to adjust the pH value of the mixture to 6.5, which is weakly acidic, place the mixture in a glass scintillation vial, and perform a solvothermal reaction at 90°C for 72 h to obtain a reaction product; S2. The reaction product is cooled and crystallized naturally, and the crystals are washed with deionized water. The crystals are filtered under reduced pressure to obtain colorless needle-shaped crystals, which are placed in an oven at 60°C for 4 h to obtain a cadmium (II)-based metal organic framework crystalline material.

[0023] Comparative Example 1 This comparative example provides a method for adjusting the pH by performing a solvent thermal reaction compared to Example 1, and the specific steps are as follows: (1) 1.5 mmol of cadmium nitrate hexahydrate, 0.05 mmol of BMIP and 0.016 g of 2,5-dibromoterephthalic acid were dissolved in 4 mL of solvent DMA to obtain a mixture, and the mixture was subjected to solvothermal reaction at 90°C in a glass scintillation vial for 48 hours; (2) The reactants were cooled naturally to obtain a clear and transparent solution. The reason for the lack of crystallization was that the pH of the reaction system did not match.

[0024] Example 4 This example characterizes the cadmium (II)-based metal organic framework crystalline material prepared in Example 1: (1) Crystal structure determination of cadmium (II) based metal organic framework crystalline materials Select the appropriate size of 0.15×0.13×0.11 mm under the microscope 3 The single crystal of was subjected to X-ray diffraction experiments at room temperature. The diffraction data were collected on a Bruker P4 CCD single crystal diffractometer and monochromated with a graphite monochromator. Mo-Kα ray (λ = 0.71073 Å), with φ-ω Scanning method to collect diffraction points.

[0025] In addition, the SADABS program was used to perform absorption correction and factor correction on Lp. The SHELX-97 program was used to perform full matrix least squares correction based on all non-hydrogen atoms and their anisotropic thermal parameters. Detailed crystal measurement data are shown in Table 1, and important bond length and bond angle data are shown in Table 2.

[0026] ​​Table 1 Main crystallographic data of cadmium (II)-based metal organic framework crystalline materials

[0027] Table 2 Important bond lengths (Å) and bond angles (°) of cadmium (II)-based metal organic framework crystalline materials

[0028] In Table 1, a, b and c represent the edge lengths of the crystal in the directions of the three crystal axes, α, β and γ represent the angles between a and b, a and c, and b and c respectively; Z is the number of molecules contained in the unit cell; the diffraction index range of the limiting factor is (h, k, l); F (000) is the number of electrons in the unit cell; Final R indices [ I 2σ( I )] is the residual factor R value for the observable diffraction point; R is the non-weighted consistency factor; R 1 and wR 2 All are weight consistency factors; In the first row of Table 2, Cd(1) refers to Cd atom 1 in the cadmium (II)-based metal organic framework crystalline material single crystal, O(3) refers to O atom 3 in the cadmium (II)-based metal organic framework crystalline material single crystal, and Cd(1)-O(3) represents the bond length between Cd atom 1 and O atom 3, which is 2.342±5, with 5 being the standard deviation; O(3)-Cd(1)-O(6) represents the bond angle between O atom 3, Cd atom 1 and O atom 6, and its bond angle is 84.74±18; Single molecules of cadmium (II)-based metal organic framework crystalline materials such as Figure 1 As shown, the three-dimensional porous framework structure is shown in Figure 2 , the topology structure view is as follows Figure 3 As shown, the cadmium (II)-based metal organic framework crystalline material contains three Cd (II) ions, two BMIP ligands, and three deprotonated Br-BDC 2- ligands and two crystal water molecules. Among them, the Cd1 ion and the Cd1# ion are mirror-symmetrical and have the same coordination mode. The Cd1 center is connected to the Br-BDC 2- The three O atoms of the ligands form a distorted trigonal bipyramidal coordination model. The coordination mode of Cd2 is different from that of Cd1. The six coordinated O atoms in Cd2 come from the chelation coordination of the carboxyl and carbonyl groups of the two ligands, forming an octahedral coordination model. The above three Cd(II) ions are catalyzed by BDC 2- The bridging connection of the carboxyl oxygen of the ligand forms a trinuclear Cd-O cluster secondary structural unit, and through BDC​​​2- Ligand bridging formed a two-dimensional double-layer structure, on this basis, BMIP ligands were further bridged to form a three-dimensional skeleton.

[0029] (2) IR spectral characterization of cadmium (II) based metal organic framework crystalline materials Figure 4 is the IR spectrum of cadmium (II) based metal organic framework crystalline material. The sample infrared spectrum data collection is 500~4000 cm -1 , using KBr tablets. By Figure 5 It can be seen that the crystalline material of cadmium (II)-based metal organic framework has a peak at 3445cm -1 shows a strong and broad absorption peak, which is the stretching vibration peak of the OH group, 1608 cm -1 represents the asymmetric and symmetric stretching vibrations of the carbonyl group.

[0030] The molecular formula of this material is {[Cd 3 (Br-BDC) 3 (BMIP) 2 ]·2H 2 O} n , n is a positive integer, denoted as {[Cd 3 (Br-BDC) 3 (BMIP) 2 ]·2H 2 O} n。

[0031] (3) Phase purity characterization of cadmium (II)-based metal organic framework crystalline materials Using Bruker / D8Advance X-ray diffractometer, the powder XRD characterization results of cadmium (II)-based metal organic framework crystalline materials showed that it has reliable phase purity, which provides a guarantee for its use as a fluorescent probe to detect excessive organic pollutants, pesticides, and heavy metal ions emitted in the environment, such as Figure 5 As shown.

[0032] (4) Solid-state fluorescence characterization of cadmium (II)-based metal-organic framework crystalline materials Using Edinburgh instruments / FLS 1000 fluorescence spectrometer, the solid fluorescence performance of cadmium (II) based metal organic framework crystalline material was tested. The cadmium (II) based metal organic framework crystalline material has a strong fluorescence emission peak at 450nm with an excitation wavelength of 385nm, such as Figure 6 As shown.

[0033] Effect Example 1 ​​​​​​​​2.0 mg of the crystalline powder of the cadmium (II)-based metal organic framework crystalline material prepared in Example 1 was weighed and placed in 7 4 mL organic solvents respectively after being fully ground. After being ultrasonicated for half an hour and allowed to stand for one hour, the supernatant was taken and placed in a cuvette. At an excitation wavelength of 255 nm, the crystalline powder was measured in N,N'-diethylformamide (DEA), N,N'-diethylformamide (DEF), ethanol (EtOH), acetonitrile (ACN), water (H 2 O), N,N'-dimethylacetamide (DMA), N,N'-dimethylformamide (DMF), fluorescence emission intensity in suspensions as solvents, such as Figure 7 As shown.

[0034] By Figure 7 It can be seen that the fluorescence intensity of the cadmium (II)-based metal organic framework fluorescent sensing material is the strongest in ethanol solvent.

[0035] Effect Example 2 Take 2 mg of the crystalline powder of the cadmium (II)-based metal organic framework crystalline material prepared in Example 1 and place it in 4 mL of ethanol solvent. After ultrasonication for half an hour and standing for one hour, take 3 mL of the supernatant and place it in a cuvette. At an excitation wavelength of 255 nm, 15 different aqueous solutions of metal cations are sequentially added to the supernatant of the cadmium (II)-based metal organic framework crystalline material to measure their corresponding fluorescence response effects, as shown in Figure 8 As shown.

[0036] By Figure 8 It can be seen that coordination polymers have a great influence on Al 3+ It has a significant fluorescence quenching effect.

[0037] Effect Example 3 In order to further study the preparation of {[Cd 3 (Br-BDC) 3 (BMIP) 2 ]·2H 2 O} n To Al 3+ The sensitivity and selectivity of ion detection were further studied by quantitative titration experiments on Al 3+ Ion detection capabilities, such as Figure 9 As shown, it can be clearly found that {[Cd 3 (Br-BDC) 3 (BMIP) 2 ]·2H 2 O} n The fluorescence intensity of increases with the Al 3+ The ion concentration gradually increased and showed a trend of gradually weakening. When 30 μL Al 3+ ​​​​​​​​After ions, the fluorescence intensity is about one-fifth of the original.

[0038] Based on the above experimental data, the supernatant of ethanol of cadmium (II)-based metal organic framework crystalline material was further analyzed. I / I 0 Value( I Represents the fluorescence intensity of cadmium (II)-based metal organic framework crystalline materials in ethanol solvent after adding organic solvent; I 0 represents the fluorescence intensity of cadmium (II) based metal organic framework crystalline material in ethanol solvent when no organic solvent is added) and metal ion Al 3+ The linear regression equation of the ion aqueous solution was further calculated based on 3σ / slope (σ is the standard deviation of the fluorescence emission intensity of 11 groups of blank experiments, and the slope value is obtained from the linear calibration curve of fluorescence intensity and target ion concentration) {[Cd 3 (Br-BDC) 3 (BMIP) 2 ]·2H 2 O} n To Al 3+ The detection limit (LOD) of is 1.86643×10 -6 mol / L.

[0039] According to Figure 10 It can be seen that {[Cd 3 (Br-BDC) 3 (BMIP) 2 ]·2H 2 O} n The fluorescence emission spectrum intensity of increases with the Al 3+ The concentration increases and shows a sharp downward trend. When Al 3+ The concentration of reached 300 μmol·L -1 , the fluorescence intensity of the coordination polymer no longer decreases and gradually becomes flat. {[Cd 3 (Br-BDC) 3 (BMIP) 2 ]·2H 2 O} n The fluorescence intensity of and Al 3+ The concentration of showed a good linear relationship (R 2 =0.99341), it can be explained that {[Cd 3 (Br-BDC) 3 (BMIP) 2 ]·2H 2 O} n Can sensitively detect Al in aqueous solution 3+ ions. According to the prepared coordination polymer {[Cd 3 ​​​​​​​​​​​​​​​​​​​(Br-BDC) 3 (BMIP) 2 ·2H 2 O} n For Al 3+ there is an obvious fluorescence quenching effect, so {[Cd 3 (Br-BDC) 3 (BMIP) 2 ·2H 2 O} n can be used as a new type of fluorescence probe for detecting Al 3+ .

[0040] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent variations made to the above embodiments based on the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A cadmium (II)-based metal organic framework crystalline material, characterized in that: The molecular formula of the cadmium (II)-based metal organic framework crystalline material is {[Cd3(Br-BDC)3(BMIP)2]·2H2O} n The cadmium (II)-based metal organic framework crystalline material uses cadmium (II) ions as connecting nodes, and 1,3-bis(dimethylimidazolylpropane) and 2,5-dibromoterephthalic acid ligands as bridging ligands to bridge each other to form a three-dimensional spatial structure; the structure contains Cd-O secondary structural units, and three Cd atoms form a trinuclear Cd-O cluster structure through the Cd-O secondary structural units, and the Cd1 atom and the Cd1# atom are mirror-symmetric.

2. A method for preparing a cadmium (II)-based metal organic framework crystalline material as claimed in claim 1, characterized in that: The following steps are involved: S1, adding cadmium salt, 1,3-bis(dimethylimidazolylpropane) and 2,5-dibromoterephthalic acid into solvent DMA to obtain a mixture, adding glacial acetic acid into the mixture to adjust the pH value of the mixture to 4.5-6.5, and then performing a solvent thermal reaction in a closed environment to obtain a reaction product; S2. Allow the reaction product prepared in S1 to cool naturally and crystallize, wash it, and then filter it under reduced pressure to obtain colorless needle-shaped crystals, which are then dried to obtain a cadmium (II)-based metal organic framework crystalline material.

3. The preparation method according to claim 2, characterized in that: The cadmium salt described in S1 is any one of cadmium chloride, cadmium nitrate and cadmium acetate.

4. The preparation method according to claim 2, characterized in that: The molar volume ratio of the cadmium salt, 1,3-bis(dimethylimidazolylpropane), 2,5-dibromoterephthalic acid and DMA in S1 is (0.5-1.5) mmol: (0.05-0.15) mmol: (0.1-0.5) mmol: (2-10) mL, the amount of glacial acetic acid used is 50 µL, the concentration of glacial acetic acid is 17 mol / L, the temperature of the solvothermal reaction is 90 °C, and the time of the solvothermal reaction is (36-72) h.

5. The preparation method according to claim 2, characterized in that: The drying temperature in S2 is 60° C., and the drying time is 2 to 4 h.

6. An application of the cadmium (II)-based metal organic framework crystalline material as claimed in claim 1, characterized in that: The cadmium (II)-based metal organic framework crystalline material can be used in fluorescent sensors to detect ionic pollutants, and can also be used as a detector for Al 3+ of fluorescent probes.

Images