A structure-reversible interconversion type metal framework adsorptive material, a preparation method and application thereof

Abstract

The application discloses a structure reversible interconversion type metal framework adsorbing material and a preparation method and application thereof, and belongs to the technical field of adsorbing materials, and comprises the following steps: dissolving anhydrous calcium chloride and 2, 5-pyrazine dicarboxylic acid in a mixed solvent, then adding concentrated nitric acid to perform a heating reaction, continuously activating the obtained solid product at 50-420 DEG C for 24 hours to realize structure conversion, and obtaining the structure reversible interconversion type metal framework adsorbing material. The reversible interconversion type metal framework provided by the application provides a new strategy for the research and development of multifunctional MOFs materials, so that the material can adjust the pore characteristics and three-dimensional space structure according to temperature change, and significantly influences the macroscopic adsorbing performance. The preparation process provided by the application is simple, and provides a new strategy for cadmium ion sewage treatment.

Description

Technical Field

[0001] This invention belongs to the field of adsorption material technology, and particularly relates to a reversibly mutated metal framework adsorption material, its preparation method and application. Background Technology

[0002] Metal-organic frameworks (MOFs) are a novel type of crystalline porous material formed by metal ions and organic ligands. Due to their inherent characteristics such as directional structural design and abundant porosity, they have wide applications in ion adsorption, gas storage and separation, catalysis, drug delivery, and sensing. Among these MOFs, those capable of controllable transformations of their microstructure in response to external environmental stimuli have attracted considerable attention due to their unique macroscopic properties.

[0003] With the acceleration of industrialization, environmental pollution problems are becoming increasingly serious, especially the pollution from heavy metal ions such as cadmium. These ions not only damage ecosystems but also seriously threaten human health. Currently, adsorption has become an economical and efficient strategy for treating cadmium-containing wastewater, and MOF materials, as excellent adsorbents with tunable structures, have been widely studied. However, there are still many practical problems to be solved in the application of MOF materials for cadmium ion adsorption.

[0004] Therefore, how to obtain a MOF material with good adsorption capacity for cadmium ions, and whether the structure can be recycled, is currently a key focus of those skilled in the art. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a reversibly interchangeable metal framework adsorbent material, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing a reversibly tautomer metal framework adsorbent material includes the following steps:

[0008] Anhydrous calcium chloride and 2,5-pyrazine dicarboxylic acid were dissolved in a mixed solvent, and then concentrated nitric acid was added for heating to generate a one-dimensional MOF material (Ca-MOFs-1D). The resulting solid product was then activated at 50-420℃ for 24 hours, during which the coordination of calcium changed, and the one-dimensional MOF structure transformed into a three-dimensional MOF material (Ca-MOFs-3D) in the solid phase, thus obtaining the reversible interconversion metal framework adsorbent material.

[0009] Beneficial effects: The principle of reversibility: As the activation temperature increases, the reduction of coordinated water molecules triggers the recombination of the coordination structure, causing the material structure to transform from one-dimensional to three-dimensional. Reversibility can be achieved through a solvothermal method: the material is redissolved in a mixed solvent, and with the original composition remaining unchanged, the recoordination of water molecules allows the material to recover its original structure.

[0010] Preferably, the molar ratio of anhydrous calcium chloride to 2,5-pyrazine dicarboxylic acid is 1:1.

[0011] Beneficial effect: The structure formed under this ratio is a one-dimensional structure.

[0012] Preferably, the mixed solvent is obtained by mixing N,N-dimethylacetamide (DMA) and water at a volume ratio of 2:1.

[0013] Beneficial effect: The one-dimensional material exhibits the best crystallization state under this solvent ratio.

[0014] Preferably, the volume ratio of concentrated nitric acid to the mixed solvent is 100 μL: 6 mL.

[0015] Beneficial effects: The addition of an appropriate amount of concentrated nitric acid helps the reaction to proceed and promotes the formation of coordination structures.

[0016] Preferably, the heating reaction is carried out at a temperature of 80°C for 48 hours.

[0017] Beneficial effects: The reaction temperature and reaction time allow the one-dimensional material to reach its optimal crystallization state.

[0018] Preferably, the activation temperature is 50°C, 60°C, 70°C, 80°C, 100°C, 140°C, 180°C, 220°C, 320°C, or 420°C.

[0019] Beneficial effects: By exploring a series of activation temperatures, the optimal structural transformation conditions can be determined, thereby optimizing the pore structure of the material, improving its adsorption performance, and ensuring that the material achieves the best results in the application of cadmium adsorption.

[0020] Preferably, the structural restoration of the reversible and reversible metal framework adsorbent material includes the following steps:

[0021] The reversible and tautomer metal framework adsorbent material is dissolved in a mixed solvent, and then concentrated nitric acid is added for heating reaction. After the reaction is completed, the structure of the reversible and tautomer metal framework adsorbent material is restored.

[0022] Beneficial effect: The reversible and reversible metal framework adsorbent material can be restored from a three-dimensional structure to a one-dimensional structure by a solvothermal method, which proves the structural reversibility of the material.

[0023] A method for preparing a reversibly tautomer metal framework adsorbent material.

[0024] Beneficial effects: The material can be reversibly transformed between one-dimensional and three-dimensional structures. This characteristic allows the material to adjust its porosity and three-dimensional spatial structure according to temperature changes, thereby significantly affecting its macroscopic adsorption performance.

[0025] Application of a reversibly tautomer metal framework adsorbent in the adsorption of cadmium ions in water.

[0026] Preferably, the adsorption temperature is 35°C.

[0027] Beneficial effect: The adsorption effect is optimal at this adsorption temperature.

[0028] Compared with the prior art, the present invention has the following advantages and technical effects:

[0029] This invention achieves a transformation of a metal framework material from a one-dimensional to a three-dimensional structure through precise control of the activation temperature. This structural change significantly optimizes the material's porosity, thereby increasing its adsorption capacity for cadmium ions. The unique structural transformation characteristics of the metal framework material provided by this invention offer a new strategy for the structural research of MOFs (Metal-Oxide-Foil) materials, enabling the material to adjust its porosity according to temperature changes and significantly improving its macroscopic adsorption performance. Furthermore, this invention allows for the recyclability of the material's structure through structural restoration. Finally, the preparation process provided by this invention is simple, offering a new strategy for cadmium ion wastewater treatment. Attached Figure Description

[0030] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0031] Figure 1 This is a flowchart illustrating the preparation process of the reversible and tamperotropic metal framework adsorbent material in this invention.

[0032] Figure 2 SEM image of the material prepared in Example 2 with an activation temperature of 60°C;

[0033] Figure 3 SEM image of the material prepared in Example 3 with an activation temperature of 70°C;

[0034] Figure 4 SEM image of the material prepared in Example 4 with an activation temperature of 80°C;

[0035] Figure 5 The structure diagram of Ca-MOFs-1D is shown.

[0036] Figure 6 The diagram shows the 3D structure of Ca-MOFs.

[0037] Figure 7 The PXRD diagrams are of the reversible and interchangeable metal frame materials obtained in Examples 1-5 and 7.

[0038] Figure 8 This is a graph showing the adsorption capacity of cadmium ions by the reversible tautomer metal framework materials obtained in Examples 1-10. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] This invention provides a method for preparing a reversibly tautomer metal framework adsorbent material, comprising the following steps:

[0042] Anhydrous calcium chloride and 2,5-pyrazine dicarboxylic acid were dissolved in a mixed solvent, and then concentrated nitric acid was added for heating to generate a one-dimensional MOF material (Ca-MOFs-1D). The resulting solid product was then activated at 50-420℃ for 24 hours, during which the coordination of calcium changed, and the one-dimensional MOF structure transformed into a three-dimensional MOF material (Ca-MOFs-3D) in the solid phase, thus obtaining the reversible interconversion metal framework adsorbent material.

[0043] In a preferred embodiment, the molar ratio of anhydrous calcium chloride to 2,5-pyrazine dicarboxylic acid is 1:1.

[0044] In a preferred embodiment, the mixed solvent is obtained by mixing N,N-dimethylacetamide and water at a volume ratio of 2:1.

[0045] In a preferred embodiment, the volume ratio of concentrated nitric acid to the mixed solvent is 100 μL: 6 mL.

[0046] In a preferred embodiment, the heating reaction is carried out at a temperature of 80°C for 48 hours.

[0047] In a preferred embodiment, the activation temperature is 50℃, 60℃, 70℃, 80℃, 100℃, 140℃, 180℃, 220℃, 320℃, or 420℃. When the activation temperature is between 80℃ and 220℃, the prepared metal framework adsorbent material exhibits a relatively large adsorption capacity for heavy metal ions. Therefore, in a preferred embodiment, considering both improved adsorption efficiency and energy saving, the optimal activation temperature is 80℃.

[0048] In a preferred embodiment, the structural restoration of the reversible and reversible metal framework adsorbent material includes the following steps:

[0049] The reversible and tautomer metal framework adsorbent material is dissolved in a mixed solvent, and then concentrated nitric acid is added for heating reaction. After the reaction is completed, the structure of the reversible and tautomer metal framework adsorbent material is restored.

[0050] This invention also provides a method for preparing a reversibly tautomer metal framework adsorbent material.

[0051] This invention also provides an application of a reversibly interchangeable metal framework adsorbent material in the adsorption of cadmium ions in water.

[0052] In a preferred embodiment, the adsorption temperature is 35°C.

[0053] In a preferred embodiment, the specific steps include:

[0054] The reversible and tautomer metal framework adsorbent was placed in a solution containing cadmium ions and adsorbed by shaking in a constant-temperature water bath at a temperature of 35°C.

[0055] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.

[0056] Unless otherwise specified, room temperature or normal temperature in the embodiments of the present invention refers to 25±3℃.

[0057] The concentration of concentrated nitric acid used in the following examples is 14.4-15.2 mol / L.

[0058] Example 1

[0059] A method for preparing a reversibly tautomer metal framework adsorbent material, such as Figure 1 As shown, it includes the following steps:

[0060] (1) Add DMA (4 mL) and H2O (2 mL) to a 10 mL sample vial, and sonicate to mix thoroughly. Then weigh 2,5-pyrazine dicarboxylic acid (16.8 mg, 0.1 mmol) and anhydrous calcium chloride (11.0 mg, 0.1 mmol) and add them to the sample vial. Add concentrated nitric acid (100 μL) dropwise, seal the vial, and sonicate until uniformly dispersed. Then place the sample vial in an 80 °C oven for 48 h. After cooling to room temperature, filter the product and wash it with DMA and anhydrous ethanol. The obtained product is denoted as Ca-MOFs-1D, and its structural diagram is shown below. Figure 5 As shown, it was then placed in an oven at 50°C for 24 hours to activate it, thereby achieving a structural transformation and obtaining a white powdery metal framework adsorbent material, denoted as Ca-MOF-50.

[0061] (2) Structure restoration: Take 20 mg of the structurally transformed material and add it to a mixed solvent of DMA (4 mL) and H2O (2 mL). Add concentrated nitric acid (100 μL), seal the container, and sonicate until completely dissolved. Then place the sample vial in an 80°C oven and heat for 48 h. After cooling to room temperature, filter the product and wash it with DMA and anhydrous ethanol to achieve structure restoration.

[0062] Example 2

[0063] A method for preparing a reversibly tautomer metal framework adsorbent material is characterized by the fact that, unlike Example 1, the activation temperature in step (1) is 60°C. All other process steps and parameters are the same as in Example 1. The metal framework adsorbent material obtained in step (1) is designated as Ca-MOF-60.

[0064] Example 3

[0065] A method for preparing a reversibly tautomer metal framework adsorbent material is characterized by the fact that, unlike Example 1, the activation temperature in step (1) is 70°C. All other process steps and parameters are the same as in Example 1. The metal framework adsorbent material obtained in step (1) is designated as Ca-MOF-70.

[0066] Example 4

[0067] A method for preparing a reversibly tautomer metal framework adsorbent material is characterized by the fact that, unlike Example 1, the activation temperature in step (1) is 80°C. All other process steps and parameters are the same as in Example 1. The metal framework adsorbent material obtained in step (1) is designated as Ca-MOF-80.

[0068] Example 5

[0069] A method for preparing a reversibly tautomer metal framework adsorbent material is characterized by the fact that, unlike Example 1, the activation temperature in step (1) is 100°C. All other process steps and parameters are the same as in Example 1. The metal framework adsorbent material obtained in step (1) is denoted as Ca-MOF-100.

[0070] Example 6

[0071] A method for preparing a reversibly tautomer metal framework adsorbent material is characterized by the fact that, unlike Example 1, the activation temperature in step (1) is 140°C. All other process steps and parameters are the same as in Example 1. The metal framework adsorbent material obtained in step (1) is designated as Ca-MOF-140.

[0072] Example 7

[0073] A method for preparing a reversibly tautomer metal framework adsorbent material is characterized by the fact that, unlike Example 1, the activation temperature in step (1) is 180°C. All other process steps and parameters are the same as in Example 1. The metal framework adsorbent material obtained in step (1) is denoted as Ca-MOF-180.

[0074] Example 8

[0075] A method for preparing a reversibly tautomer metal framework adsorbent material is characterized by the fact that, unlike Example 1, the activation temperature in step (1) is 220°C. All other process steps and parameters are the same as in Example 1. The metal framework adsorbent material obtained in step (1) is designated as Ca-MOF-220.

[0076] Example 9

[0077] A method for preparing a reversibly tautomer metal framework adsorbent material is characterized by the fact that, unlike Example 1, the activation temperature in step (1) is 320°C. All other process steps and parameters are the same as in Example 1. The metal framework adsorbent material obtained in step (1) is designated as Ca-MOF-320.

[0078] Example 10

[0079] A method for preparing a reversibly tautomer metal framework adsorbent material is characterized by the fact that, unlike Example 1, the activation temperature in step (1) is 420°C. All other process steps and parameters are the same as in Example 1. The metal framework adsorbent material obtained in step (1) is designated as Ca-MOF-420.

[0080] Characterization tests:

[0081] The reversible and interconvertible metal framework adsorbents obtained in Examples 1-10 were characterized.

[0082] 1. SEM Analysis

[0083] The metal framework adsorbents obtained in Examples 2-4 were characterized by SEM, and the results are as follows: Figure 2-4 As shown, it can be observed that the material maintains its complete crystal morphology at an activation temperature of 60℃. With the activation temperature gradually increasing, slight cracks appear on the crystal surface when the temperature reaches 70℃. Further increasing the activation temperature to 80℃, the crystal fracture becomes more pronounced, the surface becomes rougher, and the porosity increases, indicating that the internal structure of the material has changed, which may affect its adsorption capacity.

[0084] 2. Powder X-ray diffraction analysis

[0085] The metal framework adsorbents obtained in Examples 1-5 and 7 were characterized by powder X-ray diffraction, and the results are as follows: Figure 7 As shown, the diffraction pattern changes with increasing activation temperature, indicating that the structure of the adsorbent material gradually transforms. At an activation temperature of 80℃, its microstructure changes, and subsequent single-crystal structure data confirms that the material completely transforms from a one-dimensional to a three-dimensional structure.

[0086] 3. Crystal parameter analysis

[0087] Crystallographic analysis was performed on the Ca-MOFs-1D metal framework adsorbent obtained in step (1) of Example 1 and the Ca-MOFs-3D whose structure was transformed at 80℃ in Example 4. The crystallographic data are shown in Tables 1 and 2. Ca-MOFs-1D crystallizes in a monoclinic system with space group C2 / c, and its asymmetric unit contains a Ca 2+ It contains one deprotonated organic ligand and four water molecules. One of these is Ca... 2+ Ca coordinates with the nitrogen and carbonyl oxygen on the two pyrazine rings to form five-membered rings, and this process is repeated to form a one-dimensional chain structure similar to the "Heisenberg spin chain model" in the longitudinal direction. 2+ The remaining coordination sites are laterally allocated to the oxygen in the four water molecules, and laterally maintain a certain spacing in the one-dimensional chain structure (e.g., Figure 5 (As shown). When the temperature rises, due to Ca... 2+ With the number of coordination water cells reduced to one, the crystal (Ca-MOFs-3D) transforms from monoclinic to triclinic (space group P-1). Correspondingly, Ca 2+ The coordination centers move closer together, forming an alternating structure of four-membered and five-membered rings. The chains are connected by organic ligands to construct a three-dimensional structure, forming certain cavities and channels (such as...). Figure 6 (As shown).

[0088] Table 1

[0089]

[0090]

[0091] Table 2

[0092]

[0093]

[0094] As can be seen from Tables 1 and 2, the crystallographic data of the metal framework adsorbent material changed after activation, indicating that its crystal structure underwent a transformation.

[0095] Application Example 1

[0096] The reversible tautomer metal framework adsorbent materials obtained in Examples 1-10 are applied to the adsorption of cadmium ions, including the following steps:

[0097] 25 mg of the adsorbent was added to an aqueous solution with a cadmium ion concentration of 500 mg / L. The solution was incubated at 35°C with shaking for 12 hours. The supernatant was collected and filtered through a 0.22 μm microporous membrane. The concentration of cadmium ions in the filtrate was measured, and the adsorption capacity was calculated. The adsorption capacity is as follows: Figure 8 As shown, the adsorption effect of the prepared adsorbent material on cadmium ions improves with increasing activation temperature, reaching its maximum and stabilizing after 80℃. However, when the activation temperature is further increased from 220℃, the adsorption capacity of the prepared adsorbent material for cadmium ions gradually decreases. Considering both adsorption efficiency and economic factors, an activation temperature of 80℃ is optimal.

[0098] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a reversibly tautomer metal framework adsorbent material, characterized in that, Includes the following steps: Anhydrous calcium chloride and 2,5-pyrazine dicarboxylic acid were dissolved in a mixed solvent, and then concentrated nitric acid was added for heating reaction. The resulting solid product was further activated at 50-420 °C for 24 h to achieve structural transformation, thus obtaining the reversible tautomer metal framework adsorbent material. The structural restoration of the reversible and reversible metallic framework adsorbent material includes the following steps: The reversible and tautomer metal framework adsorbent material is dissolved in a mixed solvent, then concentrated nitric acid is added and heated to react. After the reaction is completed, the structure of the reversible and tautomer metal framework adsorbent material is restored. The mixed solvent is obtained by mixing N,N-dimethylacetamide and water at a volume ratio of 2:

1.

2. The method for preparing a reversibly alternating metal framework adsorbent material according to claim 1, characterized in that, The molar ratio of anhydrous calcium chloride to 2,5-pyrazine dicarboxylic acid is 1:

1.

3. The method for preparing a reversibly alternating metal framework adsorbent material according to claim 1, characterized in that, The volume ratio of concentrated nitric acid to the mixed solvent is 100 μL: 6 mL.

4. The method for preparing a reversibly alternating metal framework adsorbent material according to claim 1, characterized in that, The heating reaction was carried out at a temperature of 80 °C for 48 h.

5. The method for preparing a reversibly tautomer metal framework adsorbent material according to claim 1, characterized in that, The activation temperature is 50 ℃, 60 ℃, 70 ℃, 80 ℃, 100 ℃, 140 ℃, 180 ℃, 220 ℃, 320 ℃ or 420 ℃.

6. The reversible tautomer metal framework adsorbent material prepared by the method for preparing a reversible tautomer metal framework adsorbent material according to any one of claims 1-5.

7. The application of the reversible and tautomer metal framework adsorbent material as described in claim 6 in the adsorption of cadmium ions in water.

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