A method for preparing a dual-functionalized flexible metal-organic framework material for ammonia storage

Abstract

The present invention discloses a method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage, the preparation method comprising the following steps: taking aluminum nitrate, a first ligand, and a second ligand, sequentially placing them in pure water and mixing them to obtain a mixture, subjecting the mixture to a hydrothermal reaction to obtain solid I; dissolving solid I in an organic solvent, subjecting the mixture to a solvothermal reaction to obtain solid II; collecting solid II by centrifugation to obtain centrifuge I, washing centrifuge I alternately with N,N-dimethylformamide and anhydrous ethanol, filtering the centrifuge after washing, and then drying and activating the centrifuge in a vacuum drying oven to obtain the final product (OH)2@NH2-Al(BDC). The present invention introduces amino and hydroxyl functional groups through ligands to increase the ammonia adsorption sites of the material, thereby obtaining a bifunctionalized flexible metal-organic framework material for ammonia storage with a stable structure, large adsorption capacity, and easy regeneration, which can be widely used in the field of ammonia storage.

Description

Technical Field

[0001] The present invention belongs to the technical field of ammonia storage, and in particular relates to a method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage. Background Art

[0002] In recent years, ammonia storage technology using solid adsorption has gained great favor. It not only has a wide operating temperature range, but can also be used as an energy storage carrier. However, in the studies reported so far, most of them use rigid metal-organic framework materials and single-functional group modified metal-organic framework materials for NH3 adsorption applications. There are shortcomings such as structural destruction and low adsorption capacity during NH3 adsorption.

[0003] Metal-organic frameworks (MOFs) are porous crystalline materials with periodic lattices formed by the self-assembly of inorganic metal ions or metal atom clusters and organic ligands. They are a type of coordination polymer. Due to their large specific surface area, low crystal density, designable and tunable structure and properties, and diverse variety, they hold great promise for application in adsorption and storage. MOFs, in particular, possess a flexible structure that maintains its structure during adsorption and desorption, overcoming the corrosive effects of NH₃, facilitating material desorption and recycling. However, due to the high chemical activity of NH₃, MOFs remain in short supply for NH₃ adsorption research.

[0004] In summary, in the field of NH3 adsorption and storage, there is an urgent need to find bifunctionalized flexible metal-organic framework materials with stable structure, large adsorption capacity and easy regeneration. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage. The present invention can not only achieve efficient adsorption and storage of NH3, but also has good regeneration performance and can effectively desorb NH3 to achieve subsequent ammonia cracking and hydrogen production applications.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage, characterized by comprising the following steps:

[0007] Step 1: aluminum nitrate, a first ligand, and a second ligand are sequentially placed in pure water and mixed to obtain a mixture, and the mixture is subjected to a hydrothermal reaction. The specific operation of the hydrothermal reaction is as follows: the mixture is placed in a reaction kettle, and the reaction kettle is placed in a reaction vessel for reaction. After the reaction is completed, the reaction kettle is cooled to room temperature to obtain a solid I having an amino functional group and a hydroxyl functional group;

[0008] Step 2: performing a solvothermal reaction on the solid I obtained in step 1. The specific operation of the solvothermal reaction is as follows: dissolving the solid I in an organic solvent, mixing uniformly to obtain a mixed solution, placing the mixed solution in the reactor, and then placing the reactor in the reaction vessel to react. After the reaction is completed, the reactor is cooled to room temperature to obtain solid II.

[0009] Step 3: Centrifuge the solid II obtained in step 2 to obtain a centrifuge I, wash the centrifuge I alternately with N,N-dimethylformamide and anhydrous ethanol, and filter the centrifuge I after washing to obtain a filtered centrifuge I. Then, dry the filtered centrifuge I in a vacuum drying oven to obtain the final product (OH)2@NH2-Al(BDC), which is a dual-functionalized flexible metal-organic framework material for ammonia storage.

[0010] The above-mentioned method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage is characterized in that in step 1, the first ligand is a coordination compound having an amino functional group; and the second ligand is a coordination compound having a hydroxyl functional group.

[0011] The above-mentioned method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage is characterized in that the first ligand is 2-aminoterephthalic acid and the second ligand is 2,5-dihydroxyterephthalic acid.

[0012] The above-mentioned method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage is characterized in that the molar ratio of the aluminum nitrate and the first ligand in step 1 is 2:3-3:2, and the molar ratio of the first ligand to the second ligand is 1:2-2:1.

[0013] The above-mentioned method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage is characterized in that the organic solvent in step 2 is N,N-dimethylformamide.

[0014] Compared with the prior art, the present invention has the following advantages and effects:

[0015] 1. The bifunctionalized flexible metal-organic framework material for ammonia storage prepared by the present invention adopts a hydrothermal followed by solvent thermal synthesis method, which can have a higher product yield compared with direct hydrothermal or solvent thermal synthesis methods.

[0016] 2. Compared with the existing single-functional metal-organic framework materials, the dual-functionalized flexible metal-organic framework material for ammonia storage prepared by the present invention introduces amino functional groups and hydroxyl functional groups into the material skeleton. The synergistic effect produced by the dual functional groups can better modify the material, increase the ammonia adsorption sites in the material, improve the chemical adsorption effect of the material, and have a better NH3 storage effect.

[0017] 3. The (OH)2@NH2-Al(BDC) material synthesized by the present invention is easy to desorb NH3: Figure 3 It can be seen that the material prepared in the present invention has weak acid sites, and vacuum thermal desorption at 150° C. can achieve effective desorption of ammonia.

[0018] 4. The (OH)2@NH2-Al(BDC) synthesized by the present invention uses flexible MOFs as raw materials, so (OH)2@NH2-Al(BDC) has a flexible structure, which makes the structure of (OH)2@NH2-Al(BDC) reversible before and after ammonia adsorption. After 5 cycles of adsorption and desorption, it still maintains an adsorption effect of 90% of the original adsorption amount, and has good regeneration ability.

[0019] The present invention is further described in detail below with reference to the accompanying drawings and examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 XRD spectra of (OH)2@NH2-Al(BDC) prepared in Example 1 and Al-BDC prepared in Comparative Example 1;

[0021] Figure 2 FT-IR spectra of (OH)2@NH2-Al(BDC) prepared in Example 1 and Al-BDC prepared in Comparative Example 1;

[0022] Figure 3 This is the NH3-TPD spectrum of (OH)2@NH2-Al(BDC) prepared in Example 1. DETAILED DESCRIPTION

[0023] The present invention is further described below with reference to Examples 1 to 6, but the present invention is not limited to the following Examples.

[0024] Example 1

[0025] A method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage comprises the following steps:

[0026] Step 1: 1.14 g of aluminum nitrate, 0.65 g of 2-aminoterephthalic acid, and 0.35 g of 2,5-dihydroxyterephthalic acid were placed in 45 ml of pure water and mixed. The mixture was then transferred to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave. The autoclave was then placed in an oven at 180° C. for hydrothermal reaction for 5 h. After the reaction was completed, it was cooled to room temperature to obtain solid I having amino and hydroxyl functional groups.

[0027] Step 2: dissolving the solid I obtained in step 1 in 45 ml of N,N-dimethylformamide, stirring magnetically for 1 hour, transferring the solution to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave, and then placing the autoclave in an oven at 180°C for solvothermal reaction for 20 hours. After the reaction, cooling to room temperature to obtain solid II;

[0028] Step 3: The solid II obtained in step 2 is collected by centrifugation and washed alternately with N,N-dimethylformamide and anhydrous ethanol, filtered, dried in a vacuum drying oven, and activated to obtain (OH)2@NH2-Al(BDC);

[0029] The yield of (OH)2@NH2-Al(BDC) obtained in this example is 73.8%.

[0030] Example 2

[0031] A method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage comprises the following steps:

[0032] Step 1: 0.66 g of aluminum nitrate, 0.57 g of 2-aminoterephthalic acid, and 0.62 g of 2,5-dihydroxyterephthalic acid were placed in 45 ml of pure water and mixed. The mixture was then transferred to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave. The autoclave was then placed in a 210° C. oven for hydrothermal reaction for 4 hours. After the reaction was completed, it was cooled to room temperature to obtain solid I having amino and hydroxyl functional groups.

[0033] Step 2: dissolving the solid I obtained in step 1 in 45 ml of N,N-dimethylformamide, stirring magnetically for 1 hour, transferring the solution to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave, and then placing the autoclave in a 210°C oven for solvothermal reaction for 16 hours. After the reaction, cooling to room temperature to obtain solid II;

[0034] Step 3: The solid II obtained in step 2 is collected by centrifugation and washed alternately with N,N-dimethylformamide and anhydrous ethanol, filtered, dried in a vacuum drying oven, and activated to obtain (OH)2@NH2-Al(BDC);

[0035] The yield of (OH)2@NH2-Al(BDC) obtained in this example is 64.3%.

[0036] Example 3

[0037] A method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage comprises the following steps:

[0038] Step 1: 0.16 g of aluminum nitrate, 0.21 g of 2-aminoterephthalic acid, and 0.47 g of 2,5-dihydroxyterephthalic acid were placed in 45 ml of pure water and mixed. The mixture was then transferred to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave. The autoclave was then placed in a 150° C. oven for hydrothermal reaction for 6 h. After the reaction was completed, it was cooled to room temperature to obtain solid I having amino and hydroxyl functional groups.

[0039] Step 2: dissolving the solid I obtained in step 1 in 45 ml of N,N-dimethylformamide, stirring magnetically for 1 hour, transferring the mixture to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave, and then placing the autoclave in a 150°C oven for solvothermal reaction for 24 hours. After the reaction, cooling the mixture to room temperature to obtain solid II;

[0040] Step 3: The solid II obtained in step 2 is collected by centrifugation and washed alternately with N,N-dimethylformamide and anhydrous ethanol, filtered, dried in a vacuum drying oven, and activated to obtain (OH)2@NH2-Al(BDC);

[0041] The yield of (OH)2@NH2-Al(BDC) obtained in this example is 63.1%.

[0042] Example 4

[0043] A method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage comprises the following steps:

[0044] Step 1: 1.28 g of aluminum nitrate, 0.72 g of 2-aminoterephthalic acid, and 0.79 g of 2,5-dihydroxyterephthalic acid were placed in 45 ml of pure water and mixed. The mixture was then transferred to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave. The autoclave was then placed in an oven at 180° C. for hydrothermal reaction for 5 h. After the reaction was completed, it was cooled to room temperature to obtain solid I having amino and hydroxyl functional groups.

[0045] Step 2: dissolving the solid I obtained in step 1 in 45 ml of N,N-dimethylformamide, stirring magnetically for 1 hour, transferring the mixture to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave, and then placing the autoclave in an oven at 180°C for solvothermal reaction for 20 hours. After the reaction, cooling the mixture to room temperature to obtain solid II;

[0046] Step 3: The solid II obtained in step 2 is collected by centrifugation and washed alternately with N,N-dimethylformamide and anhydrous ethanol, filtered, dried in a vacuum drying oven, and activated to obtain (OH)2@NH2-Al(BDC);

[0047] The yield of (OH)2@NH2-Al(BDC) obtained in this example is 65.6%.

[0048] Example 5

[0049] A method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage comprises the following steps:

[0050] Step 1: 0.92 g of aluminum nitrate, 0.52 g of 2-aminoterephthalic acid, and 1.13 g of 2,5-dihydroxyterephthalic acid were placed in 45 ml of pure water and mixed. The mixture was then transferred to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave. The autoclave was then placed in a 210° C. oven for hydrothermal reaction for 6 h. After the reaction was completed, it was cooled to room temperature to obtain solid I having amino and hydroxyl functional groups.

[0051] Step 2: dissolving the solid I obtained in step 1 in 45 ml of N,N-dimethylformamide, stirring magnetically for 1 hour, transferring the solution to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave, and then placing the autoclave in a 150°C oven for solvothermal reaction for 20 hours. After the reaction, cooling to room temperature to obtain solid II;

[0052] Step 3: The solid II obtained in step 2 is collected by centrifugation and washed alternately with N,N-dimethylformamide and anhydrous ethanol, filtered, dried in a vacuum drying oven, and activated to obtain (OH)2@NH2-Al(BDC);

[0053] The yield of (OH)2@NH2-Al(BDC) obtained in this example is 62.2%.

[0054] Example 6

[0055] A method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage comprises the following steps:

[0056] Step 1: 1.01 g of aluminum nitrate, 0.86 g of 2-aminoterephthalic acid, and 0.47 g of 2,5-dihydroxyterephthalic acid were placed in 45 ml of pure water and mixed. The mixture was then transferred to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave. The autoclave was then placed in a 150° C. oven for hydrothermal reaction for 4 h. After the reaction was completed, it was cooled to room temperature to obtain solid I having amino and hydroxyl functional groups.

[0057] Step 2: dissolving the solid I obtained in step 1 in 45 ml of N,N-dimethylformamide, stirring magnetically for 1 hour, transferring the solution to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave, and then placing the autoclave in a 150°C oven for solvothermal reaction for 16 hours. After the reaction, cooling to room temperature to obtain solid II;

[0058] Step 3: The solid II obtained in step 2 is collected by centrifugation and washed alternately with N,N-dimethylformamide and anhydrous ethanol, filtered, dried in a vacuum drying oven, and activated to obtain (OH)2@NH2-Al(BDC);

[0059] The yield of (OH)2@NH2-Al(BDC) obtained in this example is 64.2%.

[0060] Comparative Example 1

[0061] This comparative example is compared with the preparation method of Example 1, except that only the ligand is changed, and the amino and hydroxyl functional groups are not introduced. The other conditions remain unchanged, and the steps are as follows:

[0062] Step 1: 1.14 g of aluminum nitrate and 0.65 g of terephthalic acid were sequentially placed in 45 ml of pure water and mixed. The mixture was then transferred to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave and placed in a 180° C. oven for hydrothermal reaction for 5 h. After the reaction, the mixture was cooled to room temperature to obtain solid I.

[0063] Step 2: The solid I obtained in step 1 was collected by centrifugation and dissolved in 45 ml of N,N-dimethylformamide. After magnetic stirring for 1 hour, the mixture was transferred to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave and placed in an oven at 180°C for solvothermal reaction for 20 hours. After the reaction, it was cooled to room temperature to obtain solid II.

[0064] Step 3: Collect the obtained solid II by centrifugation and wash it alternately with N,N-dimethylformamide and anhydrous ethanol. After vacuum filtration, dry it in a vacuum drying oven and activate it to obtain the final product Al-BDC.

[0065] The yield of Al-BDC obtained in this comparative example was 50.2%.

[0066] Comparative Example 2

[0067] Compared with Example 2, this comparative example only changed the ligand, and did not introduce amino and hydroxyl functional groups. The other conditions remained unchanged. The steps are as follows:

[0068] Step 1: 0.66g aluminum nitrate and 0.57g terephthalic acid were placed in 45ml pure water and mixed, and then the mixture was transferred to a 100ml polytetrafluoroethylene-lined stainless steel autoclave and placed in a 210℃ oven for hydrothermal reaction. 4 h, after the reaction is completed, cool to room temperature to obtain solid Ⅰ;

[0069] Step 2: The solid I obtained in step 1 was collected by centrifugation and dissolved in 45 ml of N,N-dimethylformamide. After magnetic stirring for 1 hour, the mixture was transferred to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave and placed in a 210°C oven for solvothermal reaction for 16 hours. After the reaction, it was cooled to room temperature to obtain solid II.

[0070] Step 3: Collect the obtained solid II by centrifugation and wash it alternately with N,N-dimethylformamide and anhydrous ethanol. After vacuum filtration, dry it in a vacuum drying oven and activate it to obtain the final product Al-BDC.

[0071] The yield of Al-BDC obtained in this comparative example was 56.4%.

[0072] Comparative Example 3

[0073] Compared with Example 1, this comparative example only carried out the hydrothermal reaction, and the other conditions remained unchanged. The steps are as follows:

[0074] Step 1: 1.14 g of aluminum nitrate, 0.65 g of 2-aminoterephthalic acid, and 0.35 g of 2,5-dihydroxyterephthalic acid were placed in 45 ml of pure water and mixed. The mixture was then transferred to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave. The autoclave was then placed in an oven at 180° C. for hydrothermal reaction for 5 h. After the reaction was completed, it was cooled to room temperature to obtain solid I having amino and hydroxyl functional groups.

[0075] Step 2: The solid I having amino and hydroxyl functional groups obtained in step 1 is collected by centrifugation and washed alternately with N,N-dimethylformamide and anhydrous ethanol, filtered, dried in a vacuum drying oven, and activated to obtain (OH)2@NH2-Al(BDC);

[0076] The yield of (OH)2@NH2-Al(BDC) obtained in this comparative example was 24.2%.

[0077] The yield of (OH)2@NH2-Al(BDC) prepared by only hydrothermal reaction in this comparative example is much lower than the yield of (OH)2@NH2-Al(BDC) prepared by the preparation method of hydrothermal reaction followed by solvent thermal reaction in Example 1. This shows that the preparation method of hydrothermal reaction followed by solvent thermal reaction can obtain a higher product yield.

[0078] Comparative Example 4

[0079] Compared with Example 3, this comparative example only carried out the solvent thermal reaction, and the other conditions remained unchanged. The steps are as follows:

[0080] Step 1: 0.16 g of aluminum nitrate, 0.21 g of 2-aminoterephthalic acid, and 0.47 g of 2,5-dihydroxyterephthalic acid were placed in 45 ml of N,N-dimethylformamide, and magnetically stirred for 1 hour, and then transferred to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave. The autoclave was then placed in a 150°C oven for a solvothermal reaction for 24 hours. After the reaction, it was cooled to room temperature to obtain a solvothermal solid.

[0081] Step 2: The solvent hot solid obtained in step 1 is collected by centrifugation and washed alternately with N,N-dimethylformamide and anhydrous ethanol, filtered, dried in a vacuum drying oven, and activated to obtain (OH)2@NH2-Al(BDC);

[0082] The yield of (OH)2@NH2-Al(BDC) obtained in this comparative example was 28.4%.

[0083] The yield of (OH)2@NH2-Al(BDC) prepared by only solvent thermal reaction in this comparative example is much lower than the yield of (OH)2@NH2-Al(BDC) prepared by the preparation method of first hydrothermal and then solvent thermal in Example 3. This shows that the preparation method of first hydrothermal and then solvent thermal can obtain a higher product yield.

[0084] 1. Comparison of saturated adsorption capacity test

[0085] The materials prepared in Examples 1-6 and Comparative Examples 1-2 were tested for ammonia adsorption performance. The specific steps were as follows: 0.15 g of adsorption material was weighed and placed in a U-shaped quartz adsorption tube of the adsorption evaluation system, and the adsorption column was placed in a constant temperature heating oil bath. The reaction temperature was maintained at 25°C, and the air flow rate was controlled at 50 ml·min. -1 The ammonia adsorption performance of the materials of each embodiment and comparative example was tested under normal pressure with an ammonia concentration of 1%. -1 The tail gas was absorbed by dilute sulfuric acid and the ammonia concentration in the tail gas was detected by spectrophotometry to calculate the saturated adsorption capacity of each material. The results are shown in Table 1.

[0086] Table 1

[0087]

[0088] It can be seen from Table 1 that the bifunctional modified flexible metal-organic framework material (OH)2@NH2-Al(BDC) prepared according to Examples 1-6 has better ammonia adsorption effect than the unmodified flexible metal-organic framework material Al-BDC in Comparative Examples 1-2, among which the ammonia adsorption effect of Example 1 is better, equivalent to 2.45 times that of Comparative Example 2.

[0089] 2. Ammonia cycle adsorption and desorption test

[0090] The bifunctionalized flexible metal-organic framework (OH)2@NH2-Al(BDC) prepared in Example 1 was subjected to cyclic ammonia adsorption and desorption testing to investigate the material's regeneration performance. After saturated adsorption, the material was desorbed by vacuum thermal desorption before the ammonia adsorption test was repeated. The adsorption results after five cycles of this cycle are shown in Table 2.

[0091] Table 2

[0092] Adsorption times 1 2 3 4 5 <![CDATA[Adsorption capacity mg·g -1 > 174.27 169.33 164.68 161.75 162.09

[0093] Table 2 shows that although the ammonia adsorption capacity of the bifunctionalized (OH)2@NH2-Al(BDC) material decreased after five cycles of adsorption and desorption, the adsorption capacity remained above 90% of the original capacity, demonstrating excellent ammonia adsorption performance. This indicates that the material exhibits no structural damage after multiple cycles of ammonia adsorption and desorption, demonstrating good reusability.

[0094] like Figure 1 As shown, the material curves of (OH)2@NH2-Al(BDC) synthesized in Example 1 and the material curves of Al-BDC synthesized in Comparative Example 1 are compared with the simulation curves in the spectrum. It can be seen that the main characteristic peaks of the materials synthesized in Example 1 and Comparative Material 1 correspond well to the simulation curves, indicating that the synthesized materials have high crystallinity and the material synthesis is successful.

[0095] like Figure 2 As shown, from the FT-IR spectra of (OH)2@NH2-Al(BDC) synthesized in Example 1 and the unmodified metal organic framework material Al-BDC synthesized in Comparative Example 1, it can be seen that the bifunctionalized flexible metal organic framework material (OH)2@NH2-Al(BDC) prepared in Example 1 has richer functional groups such as hydroxyl, amino, and carboxyl groups, and has more ammonia adsorption sites.

[0096] like Figure 3 As shown, from the NH3-TPD diagram of the bifunctionalized flexible metal-organic framework material (OH)2@NH2-Al(BDC) synthesized in Example 1, it can be seen that the (OH)2@NH2-Al(BDC) material has weakly acidic sites and ammonia desorption can be achieved at 150°C.

[0097] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural transformation made to the above embodiment based on the technical essence of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage, characterized in that: The following steps are involved: Step 1: aluminum nitrate, a first ligand, and a second ligand are sequentially placed in pure water and mixed to obtain a mixture, and the mixture is subjected to a hydrothermal reaction. The specific operation of the hydrothermal reaction is as follows: the mixture is placed in a reaction kettle, and the reaction kettle is placed in a reaction vessel for reaction. After the reaction is completed, the reaction kettle is cooled to room temperature to obtain a solid I having an amino functional group and a hydroxyl functional group; The first ligand is 2-aminoterephthalic acid, and the second ligand is 2,5-dihydroxyterephthalic acid; Step 2: performing a solvothermal reaction on the solid I obtained in step 1. The specific operation of the solvothermal reaction is as follows: dissolving the solid I in an organic solvent, mixing uniformly to obtain a mixed solution, placing the mixed solution in the reactor, and then placing the reactor in the reaction vessel to react. After the reaction is completed, the reactor is cooled to room temperature to obtain solid II. Step 3: Centrifuge the solid II obtained in step 2 to obtain a centrifuge I, wash the centrifuge I alternately with N,N-dimethylformamide and anhydrous ethanol, and filter the centrifuge I after washing to obtain a filtered centrifuge I. Then, dry the filtered centrifuge I in a vacuum drying oven to obtain the final product (OH)2@NH2-Al(BDC), which is a dual-functionalized flexible metal-organic framework material for ammonia storage.

2. The method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage according to claim 1, wherein: In step 1, the molar ratio of the aluminum nitrate to the first ligand is 2:3-3:2, and the molar ratio of the first ligand to the second ligand is 1:2-2:

1.

3. The method for preparing a bifunctionalized flexible metal-organic framework material for ammonia storage according to claim 1, characterized in that: The organic solvent in step 2 is N,N-dimethylformamide.

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