Ferroelectric Cu-Asp MOF material and preparation method thereof

Abstract

The invention discloses a ferroelectric Cu-Asp MOF material. The crystal structure formula of the material is [Cu (Asp) (H2O)] infinity, cu < 2 + > in the asymmetric unit is in a hexa-coordinate irregular octahedral configuration, the crystal structure is a two-dimensional layered structure formed by assembling a one-dimensional chain structure under the action of Van der Waals force, then the two-dimensional layer is further stacked to form a three-dimensional blocky structure, the crystal of the material is rod-shaped, and the length is 50-1000 [mu] m; the preparation method comprises the following steps: step 1, preparing an anhydrous copper chloride solution and an L / D-Asp solution; 2, adding the L / D-Asp solution in the step 1 into an anhydrous copper chloride solution to obtain a mixed solution; step 3, dropwise adding a NaOH solution into the mixed solution to obtain a mixed solution with an acidic pH value; continuously reacting the mixed solution with acidic pH, and pouring out the supernate to obtain a blue rod-like single crystal; the Cu-Asp MOF prepared by the preparation method disclosed by the invention has the characteristics of high purity, high crystallinity and clear rodlike morphology; meanwhile, the method has the advantages of being easy to operate and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of MOF material preparation technology, and in particular to a ferroelectric Cu-Asp MOF material and its preparation method. Background Technology

[0002] Metal-organic frameworks (MOFs) are a class of organic-inorganic hybrid materials formed by the self-assembly of metal ions and organic ligands. They have advantages such as large specific surface area and tunable pore size. Most of them are polycrystalline powder materials and are widely used in gas adsorption, catalysis and other fields.

[0003] Currently, traditional methods for synthesizing MOFs have limitations: solution methods are difficult to control crystal growth, easily resulting in small sizes or irregular morphologies; solid-state reactions consume a lot of energy and produce poor crystal uniformity; although solvothermal methods can obtain high-quality single crystals, the reaction time is long.

[0004] Furthermore, most MOFs only possess adsorption or catalytic properties and lack ferroelectricity. Ferroelectric materials, due to their spontaneous polarization characteristics, are crucial in fields such as memory and sensors; however, traditional inorganic ferroelectric materials suffer from toxicity and processing difficulties. Ferroelectric MOFs, as organic-inorganic hybrid materials, induce ferroelectricity by selecting amino acids with polar groups as ligands, but current research still faces bottlenecks such as the difficulty in achieving ferroelectricity and the challenges in preparing large-size single crystals, limiting their applications.

[0005] Chinese patent application CN112301375A discloses a sulfur-modified Cu-based MOF material, its preparation method, and its application in electrocatalytic CO2 reduction reactions. The material is composed of sulfur and a Cu-based MOF, wherein the Cu-based MOF material is HKUST-1, and the Cu-based MOF material has an octahedral structure with a size of 10–100 micrometers. This material is prepared by preparing a Cu-based MOF precursor, preparing a sulfur-containing precursor solution, and using a wet chemical reaction method to dope sulfur into the Cu-based MOF material. Applied to the electrocatalytic CO2 reduction reaction system, compared with existing Cu-based materials, this invention requires only a trace amount of sulfur-modified Cu-based MOF material to significantly improve the selectivity of ethylene production in the electrocatalytic CO2 reduction reaction. Furthermore, the method is simple to synthesize, low in cost, has a short reaction cycle, and high reproducibility, making it very important in the field of clean energy. However, its small crystal size affects its lifespan.

[0006] Chinese patent application CN118955922A discloses a copper-based MOF material, its preparation method, and its applications. The method includes the following steps: adding an organic ligand solution to a metal salt solution, adding tetrafluoroboric acid, mixing thoroughly, and reacting to obtain the copper-based MOF material; the organic ligands include camphoric acid, aminopyrazine, and triethylenediamine; the metal salt is a copper salt. This invention's copper-based MOF material can be synthesized under normal pressure conditions, with simple synthesis steps, low raw material costs, and a scalable preparation method, which is beneficial for practical industrial applications. The obtained material can be used to sieve dibranched hexane isomers (22DMB) in a one-step process, and can be applied to hexane isomer separation, serving as a gasoline additive to increase the octane number of gasoline, thereby improving fuel quality. However, the solvent used is an organic solvent, which may pollute the environment. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the present invention aims to provide a ferroelectric Cu-Asp MOF material and its preparation method. Using anhydrous copper chloride, L / D aspartic acid (L / D-Asp), and sodium hydroxide as raw materials, and H2O as solvent, the ferroelectric Cu-Asp MOF material is prepared via a one-step hydrothermal method. The Cu-Asp MOF prepared by this method exhibits high purity, high crystallinity, and a clear rod-like morphology. Furthermore, this method is simple to operate and environmentally friendly, solving the technical problem of being unable to synthesize large-size ferroelectric MOF single crystals in a short time.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A ferroelectric Cu-Asp MOF material with the crystal structure [Cu(Asp)(H2O)] ∞ The space group is C2, and each asymmetric element consists of a Cu. 2+ The ion consists of two deprotonated Asp ligands and two coordinated water molecules.

[0010] Cu in the asymmetric unit 2+ It exhibits an irregular octahedral configuration with six coordinations.

[0011] The crystal structure is first assembled from a one-dimensional chain structure to form a two-dimensional layered structure by means of van der Waals forces, and then the two-dimensional layers are further stacked to form a three-dimensional block structure.

[0012] The material has a rod-shaped crystal with a length of 50–1000 μm.

[0013] A method for preparing ferroelectric Cu-Asp MOF materials includes the following steps:

[0014] Step 1: Dissolve anhydrous copper chloride in ultrapure water to obtain anhydrous copper chloride solution; dissolve L / D-Asp in boiling water to obtain L / D-Asp solution;

[0015] Step 2: Add the L / D-Asp solution from Step 1 dropwise to the anhydrous copper chloride solution from Step 1 and stir to obtain a mixed solution;

[0016] Step 3: Add NaOH solution dropwise to the mixed solution obtained in Step 2 and stir until homogeneous to obtain a mixed solution with an acidic pH. Continue to maintain the mixed solution with an acidic pH at a reaction temperature of 85℃~105℃ for 24~48h. After the reaction is complete, discard the supernatant to obtain blue rod-shaped single crystals.

[0017] The molar volume ratio of anhydrous copper chloride to ultrapure water in step 1 is (1-2) mmol: (2-5) mL, and the molar volume ratio of L / D-Asp to boiling water is (2-4) mmol: (15-25) mL.

[0018] In step 2, the volume ratio of the mixed solution is anhydrous copper chloride solution: L / D-Asp solution = (2-5): (15-25).

[0019] In step 3, 0.04 g to 0.08 g of NaOH is dissolved in 10 to 20 mL of deionized water, and the pH of the mixed solution is 2 to 3. The obtained blue MOF single crystal is washed 2 to 3 times with anhydrous ethanol and dried at a temperature of 25 to 60 °C for 12 to 24 hours to obtain dried blue single crystal.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) Step 1 of this invention adopts a simple hydrothermal method, which can achieve the dissolution of anhydrous copper chloride and L / D-Asp under mild conditions. The solvent used is non-toxic and pollution-free, which overcomes the disadvantages of commonly used organic solvents in traditional synthesis processes, which are volatile, highly toxic and easily cause environmental hazards. In addition, the prepared single crystal has biocompatibility, which solves the problem that some existing materials are limited in their application in the biomedical field due to biotoxicity.

[0022] (2) In step 2 of the present invention, the L / D-Asp solution is added dropwise to anhydrous copper chloride solution and stirred. The reaction process can be controlled by controlling the mixing rate of the reactants to grow large-size 2D MOF single crystals. Compared with some existing preparation methods that are prone to poor crystallinity and small MOF size, the ferroelectric Cu-Asp MOF material prepared by the present invention has the characteristics of high purity, high crystallinity and size up to 1 mm.

[0023] (3) In step 3 of this invention, the pH of the mixed solution is adjusted by adding NaOH solution dropwise, and then the reaction is carried out at 85℃~105℃ for 24~48h. The structure and properties of the single crystal can be induced by controlling the pH value and temperature. The prepared ferroelectric Cu-Asp MOF material has a chiral structure, a high decomposition temperature, as well as ferroelectricity and piezoelectricity.

[0024] In summary, compared with existing technologies, this invention can achieve the dissolution of anhydrous copper chloride and L / D-Asp under mild conditions, and the solvent used is non-toxic and pollution-free. Ferroelectric Cu-Asp MOF materials are prepared by a one-step hydrothermal method. The Cu-Asp MOF prepared by this method has the characteristics of high purity, high crystallinity and clear rod-shaped morphology. At the same time, this method has the advantages of simple operation and environmental friendliness, and can solve the technical problem that large-size ferroelectric MOF single crystals cannot be synthesized in a short time. Attached Figure Description

[0025] Figure 1 These are optical micrographs and physical images of the single crystal of the ferroelectric Cu-Asp MOF material prepared in Example 1 of the present invention; wherein, (a) is an optical micrograph of the single crystal of the ferroelectric Cu-Asp MOF material, and (b) is a physical image of the single crystal of the ferroelectric Cu-Asp MOF material.

[0026] Figure 2 This is a schematic diagram of the structure of the ferroelectric Cu-Asp MOF material prepared in Example 1 of the present invention, wherein, Figure 1 In the middle (a), Cu 2+ Central coordination environment diagram, Figure 1 (b) shows the nucleus structure of Cu(II) centers. Figure 1 (c) is a two-dimensional layered diagram of Cu-Asp MOF.

[0027] Figure 3 The X-ray diffraction patterns are those of the ferroelectric Cu-Asp MOF materials prepared in Examples 1 and 2 of this invention.

[0028] Figure 4 Fourier transform infrared spectra of the ferroelectric Cu-Asp MOF materials prepared in Examples 1 and 2 of this invention.

[0029] Figure 5 Thermogravimetric analysis curve of the ferroelectric Cu-Asp MOF material prepared in Example 1 of this invention.

[0030] Figure 6 The second-order octave spectrum of the ferroelectric Cu-Asp MOF material prepared in Example 1 of this invention.

[0031] Figure 7The polarization and angle-dependent SHG intensity distribution diagrams of the ferroelectric Cu-Asp MOF material prepared in Example 1 of this invention are shown.

[0032] Figure 8 The PE hysteresis loop is the ferroelectric Cu-Asp MOF material prepared in Example 1 of this invention.

[0033] Figure 9 The graph shows the amplitude of the ferroelectric Cu-Asp MOF material prepared in Example 1 of this invention as a function of different AC voltages. Detailed Implementation

[0034] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. 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 should fall within the scope of protection of the present invention.

[0035] The present invention will now be described in further detail with reference to the accompanying drawings:

[0036] A method for preparing ferroelectric Cu-Asp MOF materials includes the following steps:

[0037] Step 1: Dissolve anhydrous copper chloride in ultrapure water to obtain anhydrous copper chloride solution; dissolve L / D-Asp in boiling water to obtain L / D-Asp solution;

[0038] Step 2: Add the L / D-Asp solution from Step 1 dropwise to the anhydrous copper chloride solution from Step 1 and stir to obtain a mixed solution;

[0039] Step 3: Add NaOH solution dropwise to the mixed solution obtained in Step 2 and stir until homogeneous to obtain a mixed solution with an acidic pH. Continue to maintain the mixed solution with an acidic pH at a reaction temperature of 85℃~105℃ for 24~48h. After the reaction is complete, discard the supernatant to obtain blue rod-shaped single crystals.

[0040] Furthermore, the crystal structure of the ferroelectric Cu-Asp MOF material is [Cu(Asp)(H2O)]. ∞ It has a space group of C2, belongs to the monoclinic crystal system, and each asymmetric unit contains a Cu. 2+ The ion, two deprotonated Asp ligands, and two coordinated water molecules. Cu in the asymmetric unit. 2+It exhibits a six-coordinate irregular octahedral configuration, with its coordination environment consisting of two ligands and a water molecule as the solvent: one ligand participates in coordination through an amino nitrogen atom and a carboxyl oxygen atom at one end, while the other ligand provides two carboxyl oxygen atoms; the remaining two coordination sites are occupied by oxygen atoms from two coordinated water molecules. This coordination mode, through ligand bridging, allows Cu to... 2+ It extends in space to form a two-dimensional chain-like structure.

[0041] Example 1

[0042] A method for preparing ferroelectric Cu-Asp MOF materials includes the following steps:

[0043] Step 1: Dissolve 1 mmol of anhydrous copper chloride in 2 mL of ultrapure water to obtain anhydrous copper chloride solution; dissolve 2 mmol of L-Asp in 15 mL of boiling water to obtain L-Asp solution.

[0044] Step 2: Add the L-Asp solution dropwise to the anhydrous copper chloride solution and stir to obtain a mixed solution;

[0045] Step 3: Dissolve 0.04g NaOH in 10mL of deionized water, add it dropwise to the above mixed solution and stir well to obtain an acidic mixed solution with a pH of 2.5. Maintain the reaction temperature at 85℃ for 48h. After the reaction is completed, discard the supernatant to obtain blue rod-shaped single crystals.

[0046] The crystal structure of the ferroelectric Cu-Asp MOF material in this embodiment is [Cu(L-Asp)(H2O)]. ∞ .

[0047] This single crystal possesses high crystallinity, good thermal stability, and also exhibits excellent properties such as piezoelectricity and ferroelectricity.

[0048] like Figure 1 As shown, 2D Cu-Asp MOF materials were synthesized using the above hydrothermal method. They appear as blue rods with a glossy surface and a size of 0.2–1 mm.

[0049] As shown in Table 1, the crystal structure of this material was determined by X-ray single-crystal diffraction, and its crystallographic parameters were obtained. The results show that the single crystal belongs to the monoclinic crystal system, space group C2, and its cell parameters are as follows:

[0050]

[0051]

[0052] The crystallographic parameters of Cu-L-Asp are shown in Table 2. The determined bond lengths of Cu-O, Cu-N, CO, OO, and NO are as follows:

[0053]

[0054]

[0055] Table 2. Spacing of Selected Atoms in Cu-L-Asp

[0056] like Figure 2 As shown, the structural unit of this single crystal consists of one Cu ion, two Asp molecules, and two water molecules; Cu 2+ It is a six-coordinate irregular octahedron, connected to three oxygen atoms and one nitrogen atom from two ligands, as well as two oxygen atoms from H2O involved in coordination. N and O004 come from the nitrogen atom on the amino group and the oxygen atom on the carboxyl group at one end of the ligand, O003 and O005 come from the two oxygen atoms on the carboxyl group of the other ligand, and O006 and O007 come from the oxygen atoms in the solvent water. Each Cu ion is connected by ligands to form a two-dimensional chain structure.

[0057] Depend on Figure 3 As shown, the crystallinity of the synthesized Cu-Asp was verified by X-ray diffraction, and the standard XRD pattern of Cu-Asp was simulated using the CIF file of the obtained single crystal with Mercury software. By comparison, it can be seen that the diffraction peaks of the synthesized Cu-L-Asp and Cu-D-Asp are basically consistent with the diffraction peaks obtained by simulation, which proves that Cu-L-Asp and Cu-D-Asp have good purity and their structures are the same.

[0058] Depend on Figure 4 As shown, to further characterize the structure of Cu-Asp, infrared spectroscopy was used for analysis. The structures of Cu-L-Asp and Cu-D-Asp were analyzed in the range of 1000–1720 cm⁻¹. -1 The characteristic peaks appearing within this range originate from the stretching vibration absorption of the C=O, CO, and CN bonds in the carboxyl and amino groups of the ligand L-Asp, while the peaks in the 3100–3500 cm⁻¹ range are due to the absorption of these vibrations. -1 The vibrational absorption peaks within the range are formed by the stretching vibration of the NH bond in the amino group. Their vibrational peaks are the same, indicating that Cu-L-Asp and Cu-D-Asp have the same structure.

[0059] Depend on Figure 5 As shown, the thermogravimetric analysis of Cu-L-Asp was conducted in an Ar atmosphere. The weight loss of Cu-L-Asp in the temperature range of 30℃ to 170℃ was approximately 45%, which is attributed to the interaction with Cu. 2+The decomposition of coordinated H2O, which gradually transforms into an amorphous state above 300℃, indicates that Cu-L-Asp has high thermal stability.

[0060] Depend on Figure 6 As shown, under 1550nm laser excitation, Cu-L-Asp produces a strong power-dependent SHG spectrum at a wavelength of 775nm, and the signal intensity is positively correlated with the laser power.

[0061] Depend on Figure 7 As shown, polarization-resolved SHG signal measurements revealed a characteristic double pattern, indicating that the MOF structure has non-centrosymmetry.

[0062] Depend on Figure 8 As shown, Figure 8 The hysteresis loop of Cu-Asp MOF is shown, with saturation polarization of approximately 0.47 μC / cm. 2 The remanent polarization is approximately 0.03 μC / cm. 2 The coercive field is approximately 1.97 kV / cm, indicating that the material exhibits ferroelectric properties.

[0063] Depend on Figure 9 As shown, the piezoelectric constant was verified using PFM testing. To eliminate the influence of the sample surface potential on the test, the surface potential of the test sample was first characterized using KPFM, and an opposite voltage was applied during the test to neutralize its own charge. A voltage of 1–5 V was applied to the crystal, and the measured piezoelectric constant value was 9.72 pm / V.

[0064] Example 2

[0065] A method for preparing ferroelectric Cu-Asp MOF materials includes the following steps:

[0066] Step 1: Dissolve 1 mmol of anhydrous copper chloride in 2 mL of ultrapure water to obtain anhydrous copper chloride solution; dissolve 2 mmol of D-Asp in 15 mL of boiling water to obtain D-Asp solution.

[0067] Step 2: Add the D-Asp solution dropwise to the anhydrous copper chloride solution and stir to obtain a mixed solution;

[0068] Step 3: Dissolve 0.04g NaOH in 10mL of deionized water, add it dropwise to the above mixed solution and stir well to obtain an acidic mixed solution with pH 2.5. Maintain the reaction temperature at 85℃ for 48h. After the reaction is completed, discard the supernatant to obtain blue rod-shaped single crystals.

[0069] The crystal structure of the ferroelectric Cu-Asp MOF material in this embodiment is [Cu(D-Asp)(H2O)]∞.

[0070] This single crystal possesses high crystallinity, good thermal stability, and also exhibits excellent properties such as piezoelectricity and ferroelectricity.

[0071] Example 3

[0072] A method for preparing ferroelectric Cu-Asp MOF materials includes the following steps:

[0073] Step 1: Dissolve 1.5 mmol of anhydrous copper chloride in 3.5 mL of ultrapure water to obtain anhydrous copper chloride solution; dissolve 3 mmol of L-Asp in 20 mL of boiling water to obtain L-Asp solution;

[0074] Step 2: Add the L-Asp solution dropwise to the anhydrous copper chloride solution and stir to obtain a mixed solution;

[0075] Step 3: Dissolve 0.06g NaOH in 15mL of deionized water, add it dropwise to the above mixed solution and stir well to obtain an acidic mixed solution with a pH of 2.5. Maintain the reaction temperature at 95℃ for 24h. After the reaction is completed, discard the supernatant to obtain blue rod-shaped single crystals.

[0076] The crystal structure of the ferroelectric Cu-Asp MOF material in this embodiment is [Cu(L-Asp)(H2O)]. ∞ .

[0077] This single crystal possesses high crystallinity, good thermal stability, and also exhibits excellent properties such as piezoelectricity and ferroelectricity.

[0078] Example 4

[0079] A method for preparing ferroelectric Cu-Asp MOF materials includes the following steps:

[0080] Step 1: Dissolve 1.5 mmol of anhydrous copper chloride in 3.5 mL of ultrapure water to obtain anhydrous copper chloride solution; dissolve 3 mmol of D-Asp in 20 mL of boiling water to obtain D-Asp solution;

[0081] Step 2: Add the D-Asp solution dropwise to the anhydrous copper chloride solution and stir to obtain a mixed solution;

[0082] Step 3: Dissolve 0.06g NaOH in 15mL of deionized water, add it dropwise to the above mixed solution and stir well to obtain an acidic mixed solution with a pH of 2.5. Maintain the reaction temperature at 95℃ for 24h. After the reaction is completed, discard the supernatant to obtain blue rod-shaped single crystals.

[0083] The crystal structure of the ferroelectric Cu-Asp MOF material in this embodiment is [Cu(D-Asp)(H2O)]. ∞ .

[0084] This single crystal possesses high crystallinity, good thermal stability, and also exhibits excellent properties such as piezoelectricity and ferroelectricity.

[0085] Example 5

[0086] A method for preparing ferroelectric Cu-Asp MOF materials includes the following steps:

[0087] Step 1: Dissolve 2 mmol of anhydrous copper chloride in 5 mL of ultrapure water to obtain anhydrous copper chloride solution; dissolve 4 mmol of L-Asp in 25 mL of boiling water to obtain L-Asp solution.

[0088] Step 2: Add the L-Asp solution dropwise to the anhydrous copper chloride solution and stir to obtain a mixed solution;

[0089] Step 3: Dissolve 0.08g NaOH in 20mL of deionized water, add it dropwise to the above mixed solution and stir well to obtain an acidic mixed solution with pH 2.5. Maintain the reaction temperature at 105℃ for 24h. After the reaction is completed, discard the supernatant to obtain blue rod-shaped single crystals.

[0090] The crystal structure of the ferroelectric Cu-Asp MOF material in this embodiment is [Cu(L-Asp)(H2O)]. ∞ .

[0091] This single crystal possesses high crystallinity, good thermal stability, and also exhibits excellent properties such as piezoelectricity and ferroelectricity.

[0092] Example 6

[0093] A method for preparing ferroelectric Cu-Asp MOF materials includes the following steps:

[0094] Step 1: Dissolve 2 mmol of anhydrous copper chloride in 5 mL of ultrapure water to obtain anhydrous copper chloride solution; dissolve 4 mmol of D-Asp in 25 mL of boiling water to obtain D-Asp solution.

[0095] Step 2: Add the D-Asp solution dropwise to the anhydrous copper chloride solution and stir to obtain a mixed solution;

[0096] Step 3: Dissolve 0.08g NaOH in 20mL of deionized water, add it dropwise to the above mixed solution and stir well to obtain an acidic mixed solution with pH 2.5. Maintain the reaction temperature at 105℃ for 24h. After the reaction is completed, discard the supernatant to obtain blue rod-shaped single crystals.

[0097] The crystal structure of the ferroelectric Cu-Asp MOF material in this embodiment is [Cu(D-Asp)(H2O)]. ∞ .

[0098] This single crystal possesses high crystallinity, good thermal stability, and also exhibits excellent properties such as piezoelectricity and ferroelectricity.

[0099] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A ferroelectric Cu-Asp MOF material, characterized in that, The crystal structure of this material is [Cu(Asp)(H2O)]. ∞ The space group is C2, and each asymmetric element consists of a Cu. 2+ The ion consists of two deprotonated Asp ligands and two coordinated water molecules.

2. The ferroelectric Cu-Asp MOF material according to claim 1, characterized in that, Cu in the asymmetric unit 2+ It exhibits an irregular octahedral configuration with six coordinations.

3. The ferroelectric Cu-Asp MOF material according to claim 1, characterized in that, The crystal structure is first assembled from a one-dimensional chain structure to form a two-dimensional layered structure by means of van der Waals forces, and then the two-dimensional layers are further stacked to form a three-dimensional block structure.

4. The ferroelectric Cu-Asp MOF material according to claim 1, characterized in that, The material has a rod-shaped crystal with a length of 50–1000 μm.

5. A method for preparing a ferroelectric Cu-Asp MOF material, characterized in that, Includes the following steps: Step 1: Dissolve anhydrous copper chloride in ultrapure water to obtain anhydrous copper chloride solution; L / D-Asp is dissolved in boiling water to obtain an L / D-Asp solution; Step 2: Add the L / D-Asp solution from Step 1 dropwise to the anhydrous copper chloride solution from Step 1 and stir to obtain a mixed solution; Step 3: Add NaOH solution dropwise to the mixed solution obtained in Step 2 and stir until homogeneous to obtain a mixed solution with an acidic pH. Continue to maintain the mixed solution with an acidic pH at a reaction temperature of 85℃~105℃ for 24~48h. After the reaction is complete, discard the supernatant to obtain blue rod-shaped single crystals.

6. The method for preparing a ferroelectric Cu-Asp MOF material according to claim 5, characterized in that, The molar volume ratio of anhydrous copper chloride to ultrapure water in step 1 is (1-2) mmol: (2-5) mL, and the molar volume ratio of L / D-Asp to boiling water is (2-4) mmol: (15-25) mL.

7. The method for preparing a ferroelectric Cu-Asp MOF material according to claim 5, characterized in that, In step 2, the volume ratio of the mixed solution is anhydrous copper chloride solution: L / D-Asp solution = (2-5): (15-25).

8. The method for preparing a ferroelectric Cu-Asp MOF material according to claim 5, characterized in that, In step 3, 0.04 g to 0.08 g of NaOH is dissolved in 10 to 20 mL of deionized water, and the pH of the mixed solution is 2 to 3. The obtained blue MOF single crystal is washed 2 to 3 times with anhydrous ethanol and dried at a temperature of 25 to 60 °C for 12 to 24 hours to obtain dried blue single crystal.

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