Supramolecular action exfoliation method of a MOF material

Abstract

The application discloses a supramolecular interaction exfoliation method of MOF material, and belongs to the technical field of functional materials. The method firstly introduces a macrocyclic molecule into a linear ligand molecule through supramolecular interaction to form a pseudorotaxane ligand, and expands the interlayer structure through a large number of hydrogen bonds and other weak interactions; the pseudorotaxane ligand is used for coordination assembly with metal nodes to synthesize MOF material, and then ion exchange intercalation is used for exfoliation treatment to prepare two-dimensional MOF nanosheet material. The supramolecular interaction and ion exchange are combined to exfoliate the MOF material into two-dimensional MOF nanosheets, the exfoliation effect is good, the operation steps are simple, the two-dimensional MOF nanosheets obtained are generally good in morphology, the material is high in integrity, and is not easy to be restacked.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, specifically relating to a supramolecular interaction exfoliation method for MOF materials. Background Technology

[0002] Actinide coordination polymers are essentially infinite extensions in a certain dimension, with regularly repeating structures. They are generally insoluble in common solvents and are an important research subject in actinide solid-state chemistry. In supramolecular chemistry, the introduction of supramolecular ligands with mechanically interlocked structures into the study of organometallic coordination polymers has revealed that these molecularly interlocked quasi-rotaxanes have significant application value in molecular devices and molecular switches. Supramolecular quasi-rotaxane ligands possess unique dynamic molecular effects. Introducing quasi-rotaxane ligands into the study of metal coordination polymers allows for the regulation of molecular structure and increases the toughness of materials, resulting in a novel class of organometallic coordination polymers—organometallic coordination polyrotaxanes (MORFs). In MOF material research, two-dimensional planar MOF nanosheets possess a wide lateral dimension, flexible and designable pores, and extremely high porosity. These materials have enormous application value in many fields, such as catalysis, electrochemistry, gas separation, and detection and identification.

[0003] The preparation of MOF nanosheet materials can be divided into two methods: "top-down" and "bottom-up". The "top-down" method refers to the process of exfoliating the MOF material after synthesizing it with a two-dimensional structure. Methods include ultrasonic exfoliation, mechanical exfoliation, and chemical exfoliation. The "bottom-up" preparation mode refers to the direct synthesis of two-dimensional nanosheet materials using metal nodes and organic ligands. However, current methods for preparing nanosheet materials suffer from problems such as re-stacking and long preparation cycles. Therefore, there is a need in this field for an efficient and non-reversible exfoliation method. Summary of the Invention

[0004] To address the problems of easy re-stacking, high destructiveness, and complex preparation of two-dimensional MOF nanosheets prepared by ultrasonic exfoliation, mechanical exfoliation, and chemical exfoliation, this invention provides a method for exfoliating MOF materials. By combining supramolecular interactions with ion exchange, MOF materials are exfoliated into two-dimensional MOF nanosheets. This method has good exfoliation effect, simple operation steps, and generally good morphology and high material integrity of the obtained two-dimensional MOF nanosheets.

[0005] This invention provides a method for exfoliating MOF materials, characterized in that macrocyclic molecules are introduced onto linear ligand molecules through supramolecular interactions and coordinated with MOF metal nodes; then, exfoliation is performed through large-size ion exchange intercalation to obtain nanoscale two-dimensional MOF nanosheet materials.

[0006] Furthermore, the specific steps include:

[0007] Step 1: The macrocyclic molecule with a hollow cavity inside and the linear ligand with coordinating groups at both ends are mixed and then subjected to hydrothermal reaction to assemble the quasi-rotaxane ligand;

[0008] Step 2: Add an aqueous solution of MOF metal precursor and an alkaline solution to the quasi-rotaxane ligand, and continue the hydrothermal reaction to obtain a two-dimensional coordinated polyrotaxane MOF material;

[0009] Step 3: Select large-sized anions to perform ion exchange with the coordinating anions in the aqueous solution of the MOF metal precursor to obtain two-dimensional MOF nanosheet materials.

[0010] Further, in step 1, the molar ratio of macrocyclic molecule to linear ligand is 1:(0.5~1.5); the hydrothermal reaction temperature is 140~170℃, and the hydrothermal time is 42~50h.

[0011] Furthermore, the linear ligand is 4,4'-bis(4-carboxyphenyl)diphenylamine; the macrocyclic molecule is cucurbita[7]urea.

[0012] Furthermore, the MOF metal precursor aqueous solution is an aqueous solution of uranyl nitrate.

[0013] Further, in step 2, the molar ratio of the MOF metal precursor aqueous solution to the macrocyclic molecule is (1~2):1; the alkaline solution is sodium hydroxide.

[0014] Furthermore, in step 2, the hydrothermal reaction temperature is 140~170℃, and the hydrothermal time is 42~50h.

[0015] Furthermore, in step 3, the organometallic coordination polyrotaxane is washed and dried and then placed in an aqueous solution containing anions, wherein the equivalent diameter of the anions is greater than 3.5 Å.

[0016] Further, in step 3, the mass-to-volume ratio of the organometallic coordination polyrotaxane to the anionic solution is 1 mg: (2~3) mL; the concentration of the anionic solution is 40~60 mg / L.

[0017] Furthermore, in step 3, the ion exchange time is 10-50 hours; the ion exchange environment is a neutral condition.

[0018] The beneficial effects of this invention are as follows:

[0019] The method of this invention combines supramolecular interactions with ion exchange to exfoliate MOF materials into two-dimensional MOF nanosheets. During ion exchange, large-sized anions are used to help disrupt the weak intermolecular interactions between coordination layers. The synergistic effect of supramolecular interactions and ion exchange overcomes the shortcomings of traditional methods (such as ultrasonic exfoliation) such as low yield, uneven sheet formation, easy structural damage, and easy stacking. This invention achieves a method for optimizing the preparation of MOF nanosheet materials through supramolecular chemistry. Attached Figure Description

[0020] Figure 1 Two-dimensional MOF materials prepared by the method of this invention;

[0021] Figure 2 The material ReO4 in Embodiment 1 of the present invention - Ion exchange kinetics curves.

[0022] Figure 3 The figures show the results of the embodiments and comparative examples of the present invention under different pH conditions; wherein figure (a) shows NO3. - Adsorption amount, Figure (b) shows the uranium leaching amount;

[0023] Figure 4 The figures show the morphology of two-dimensional MOF materials under different pH conditions in the embodiments and comparative examples of the present invention; wherein Figure (a) is pH=5.87, Figure (b) is pH=3, Figure (c) is pH=5, Figure (d) is pH=7, Figure (e) is pH=7, and Figure (f) is pH=9. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings. The embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0025] This invention discloses a delamination method for MOF materials. First, macrocyclic molecules are introduced onto linear ligand molecules through supramolecular interactions and then coordinated and assembled with metal nodes. This allows the two-dimensional MOF layer to be opened up by a large number of weak interactions such as hydrogen bonds between molecules. Then, the delamination process is carried out by ion exchange intercalation to prepare two-dimensional MOF nanosheet materials with a thickness of nanoscale.

[0026] In some embodiments, the linear ligand and macrocyclic molecule should meet the following requirements: the macrocyclic molecule has a hollow cavity inside, and the linear ligand is a ligand with coordinating groups at both ends; the linear ligand is required to be able to perform supramolecular assembly with the macrocyclic molecule and have the ability to coordinate with metal nodes; the molar ratio of the linear ligand to the macrocyclic molecule meets the supramolecular assembly requirements; and the temperature, solvent and other conditions of the supramolecular quasi-rotaxane assembly process should meet the assembly requirements of the linear ligand and the macrocyclic molecule.

[0027] In some embodiments, the metal ion in the MOF material is specifically a uranyl ion. The metal ion should meet the requirement of forming a coordination bond with the quasi-rotaxane ligand, and also meet the coordination assembly requirements with the quasi-rotaxane ligand. The coordination of the metal ion with the quasi-rotaxane ligand is adjusted by adjusting the pH.

[0028] In some embodiments, the specific steps of ion exchange include: washing and drying the synthesized organometallic coordinated polyrotaxane and then placing it in a container containing ReO4. - In aqueous solutions of anions, the equivalent diameter of the anions must be greater than 3.5 Å.

[0029] In some embodiments, the ion exchange treatment time is sufficient to fully exchange the guest ions in the MOF material, and the pH of the solution system meets the ion exchange requirements and ensures the stability of the MOF material.

[0030] Example 1

[0031] Cucurbita[7]urea (CB[7]) (0.0582 g, 0.05 mmol) and 4,4'-bis(4-carboxyphenyl)diphenylamine ((H2bcbp)Cl2) ligand (0.0235 g, 0.05 mmol) were weighed and placed in a 20 mL polytetrafluoroethylene reactor. Then, 2 mL of deionized water was added to the reactor and mixed. The reactor was sealed and placed in an oven. After hydrothermal reaction at 150 °C for 48 hours, the reactor was cooled to room temperature. A pale yellow solution was obtained in the reactor. Uranyl nitrate aqueous solution (100 μL 5 mol / L, 0.05 mmol) was added to the hydrothermal reactor of the previous step, and 150 μL 1 mol / L NaOH solution was added to the reactor. After hydrothermal reaction at 150 °C for 48 hours, yellow blocky crystals were obtained. This crystal is the MOF material in which macrocyclic molecules are introduced onto linear ligand molecules through supramolecular interactions.

[0032] Choose larger anions and NO3 in the pores - Ion exchange, using larger anions to penetrate the pores, helps to increase the spacing between different coordination layers, thereby disrupting the weak intermolecular interactions between the coordination layers and promoting the delamination process. ReO4 is used. - NO3 in the exchange channel - First, weigh 60 mg of yellow crystalline solids and add them to 120 mL of 50 ppm ReO4. - In the solution, the pH is adjusted to 7 to carry out ion exchange.

[0033] like Figure 2 As shown in the kinetic curve of ion exchange, the maximum ion exchange adsorption capacity is observed at an exchange time of 12 h.

[0034] Comparative Example 1

[0035] The difference between this comparative example and Example 1 is that ReO4 is used. - NO3 in the exchange channel - First, weigh 60 mg of yellow crystalline solids and add them to 120 mL of 50 ppm ReO4. - In the solution, the pH is adjusted to 3 to carry out ion exchange.

[0036] All other conditions and parameters are the same as in Example 1.

[0037] Comparative Example 2

[0038] The difference between this comparative example and Example 1 is that ReO4 is used. - NO3 in the exchange channel - First, weigh 60 mg of yellow crystalline solids and add them to 120 mL of 50 ppm ReO4. - In the solution, the pH is adjusted to 5 to carry out ion exchange.

[0039] All other conditions and parameters are the same as in Example 1.

[0040] Comparative Example 3

[0041] The difference between this comparative example and Example 1 is that ReO4 is used. - NO3 in the exchange channel - First, weigh 60 mg of yellow crystalline solids and add them to 120 mL of 50 ppm ReO4. - In the solution, the pH was adjusted to 5.87 to carry out ion exchange.

[0042] All other conditions and parameters are the same as in Example 1.

[0043] Comparative Example 4

[0044] The difference between this comparative example and Example 1 is that ReO4 is used. - NO3 in the exchange channel - First, weigh 60 mg of yellow crystalline solids and add them to 120 mL of 50 ppm ReO4. - In the solution, the pH is adjusted to 9 to carry out ion exchange.

[0045] All other conditions and parameters are the same as in Example 1.

[0046] like Figure 3 and Figure 4 As shown, during ion exchange, NO3- is present when the solution pH is acidic or alkaline. -The adsorption amount of uranium was significantly less, while the leaching amount of uranium was greater. When the pH was adjusted to pH=7, the ion exchange effect was the best, and the leaching amount of U was the least. This indicates that the molecular structure of MOF is destroyed under acidic atmosphere, making it difficult to ensure its stable existence. Furthermore, the morphology after exfoliation is obviously irregular, which also confirms the damage to its molecular structure.

[0047] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A method for exfoliating MOF materials, characterized in that, Macrocyclic molecules are introduced onto linear ligand molecules via supramolecular interactions and then coordinated and assembled with MOF metal nodes. Nanoscale two-dimensional MOF nanosheets are obtained by exfoliation through large-size ion exchange intercalation.

2. The method for peeling MOF materials according to claim 1, characterized in that, Specifically, the following steps are included: Step 1: The macrocyclic molecule with a hollow cavity inside and the linear ligand with coordinating groups at both ends are mixed and then subjected to hydrothermal reaction to assemble the quasi-rotaxane ligand; Step 2: Add an aqueous solution of MOF metal precursor and an alkaline solution to the quasi-rotaxane ligand, and continue the hydrothermal reaction to obtain a two-dimensional coordinated polyrotaxane MOF material; Step 3: Select large-sized anions to perform ion exchange with the coordinating anions in the aqueous solution of the MOF metal precursor to obtain two-dimensional MOF nanosheet materials.

3. The method for peeling MOF materials according to claim 1, characterized in that, In step 1, the molar ratio of macrocyclic molecules to linear ligands is 1:(0.5~1.5); the hydrothermal reaction temperature is 140~170℃, and the hydrothermal time is 42~50h.

4. The delamination method for MOF materials according to claim 2, characterized in that, The linear ligand is 4,4'-bis(4-carboxyphenyl)diphenylamine; the macrocyclic molecule is cucurbita[7]urea.

5. The delamination method for MOF materials according to claim 4, characterized in that, The MOF metal precursor aqueous solution is an aqueous solution of uranyl nitrate.

6. The method for peeling MOF materials according to claim 2, characterized in that, In step 2, the molar ratio of the MOF metal precursor aqueous solution to the macrocyclic molecule is (1~2):1; the alkaline solution is sodium hydroxide.

7. The method for peeling MOF materials according to claim 2, characterized in that, In step 2, the hydrothermal reaction temperature is 140~170℃, and the hydrothermal time is 42~50h.

8. The method for peeling MOF materials according to claim 2, characterized in that, In step 3, the organometallic coordination polyrotaxane is washed and dried and then placed in an aqueous solution containing anions with an equivalent diameter greater than 3.5 Å.

9. The method for peeling MOF materials according to claim 2, characterized in that, In step 3, the mass-to-volume ratio of the organometallic coordination polyrotaxane to the anionic solution is 1 mg: (2~3) mL; the concentration of the anionic solution is 40~60 mg / L.

10. The method for peeling MOF materials according to claim 2, characterized in that, In step 3, the ion exchange time is 10-50 hours; the ion exchange environment is a neutral condition.

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