A method for preparing a low-humidity water-absorbing aluminum-based MOF material monocrystal based on carboxylate hydrolysis

Abstract

The application provides a method for preparing a low-humidity water-absorbing aluminum-based MOF material single crystal based on carboxylate hydrolysis. The aluminum-based MOF single crystal material has a crystal size greater than 20 microns. Compared with the powder material, the aluminum-based MOF single crystal material has a more complete crystal morphology, higher crystallinity, fewer defects and a larger crystal size, thereby having higher stability, higher water absorption and faster water absorption rate. The single crystal can be used as an adsorbent to absorb a large number of water molecules from air under low humidity conditions (< 30% RH). The single crystal preparation method is based on the hydrolysis reaction of carboxylate organic ligands. By adjusting the pH value of the reaction solution, the hydrolysis rate of the carboxylate and the coordination reaction process can be accurately controlled, the reaction rate is reduced, the crystal growth time is prolonged, the internal structure defects of the product are reduced, the crystallinity of the material is improved, the high-crystallinity large-size single crystal is obtained, and finally the good stability and high water absorption performance under low humidity are realized. The application provides a new way for performance regulation of water-absorbing MOF materials.

Description

Technical Field

[0001] This invention relates to the single crystal growth of microporous crystal materials, crystal size control, and corresponding improvement of low humidity water absorption performance. Specifically, it relates to a method for preparing low humidity water-absorbing aluminum-based MOF material single crystals based on carboxylic acid ester hydrolysis. Compared with powder materials, the aluminum-based MOF single crystal material has significantly improved stability and water absorption performance under low humidity, and can be used for air water absorption in low humidity environments (<30%RH). Background Technology

[0002] It is estimated that approximately 2.2 billion people worldwide face water shortages, with the majority living in arid inland regions where traditional water extraction methods are ineffective. Therefore, a new freshwater replenishment method is urgently needed. The atmosphere contains abundant water resources, accounting for about 10% of usable freshwater resources. Obtaining freshwater from the atmosphere through atmospheric water extraction is virtually inexhaustible and an effective way to ensure a continuous and stable freshwater supply. Atmospheric water extraction methods include fogging, air cooling and condensation, and adsorption-based methods. The first two methods require high air humidity (>50% RH) and are energy inefficient. Adsorption-based methods, however, utilize adsorbent materials to capture water molecules from the air. Once the material is nearly saturated, it is heated to produce high-humidity water vapor, which is then condensed to obtain freshwater. This method has low energy consumption and a wide applicable humidity range, making it an effective way to solve the problem of continuous freshwater supply in arid regions.

[0003] The core of adsorption-based air hydration technology is the absorbent material. Traditional absorbent materials have various drawbacks. For example, hygroscopic salts deliquesce after absorbing water, easily leading to loss and equipment corrosion; commercial molecular sieve materials have excessively strong forces on water molecules, resulting in desorption difficulties (>300℃); and commercial silica gel has poor water absorption performance, with insufficient water absorption at low humidity levels. Therefore, there is an urgent need to develop a new type of high-performance absorbent material to achieve air hydration in arid regions.

[0004] Novel porous metal-organic frameworks (MOFs) hold promise as high-performance absorbent materials due to their excellent porosity, structural tunability, and ease of functionalization. Among them, aluminum-based MOFs have attracted significant attention in the field of low-humidity air absorption due to the advantages of inexpensive and environmentally friendly aluminum sources, easy scalability of the synthesis process, and diverse pore structures. However, currently reported aluminum-based MOFs use carboxylic acid ligands. During the reaction, these ligands readily deprotonate to generate coordinateable carboxylic acid oxygen, which rapidly forms Al-O coordination bonds with aluminum clusters in the reaction solvent. The rapid formation of Al-O bonds results in extremely fast formation rates for aluminum-based MOFs. During the reaction, a large number of fine grains are generated in a short time. These grains agglomerate, hindering further MOF crystal growth, resulting in products that are mostly small (nanoscale) powder materials. The agglomeration of these powder particles blocks part of the pore surface, significantly reducing the specific surface area of ​​the material. Furthermore, due to the excessively rapid reaction rate, some organic ligands cannot fully coordinate with the aluminum clusters before material formation, resulting in numerous defects in the material structure. This reduces the hydrophilicity of the material's pores, thereby decreasing its low-humidity water absorption capacity. Therefore, aluminum-based MOF powder materials obtained by traditional synthesis methods based on carboxylic acid ligands exhibit significant shortcomings in terms of stability and low-humidity water absorption performance. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing low-humidity water-absorbing aluminum-based MOF material single crystals based on carboxylic acid ester hydrolysis. This method effectively improves the stability and water absorption performance of the material under low humidity. The aluminum-based MOF single crystals prepared by this method possess complete crystal morphology, large crystal size, and good crystallinity. Compared to powder materials, this well-crystallized single crystal material exhibits higher chemical stability, thermal stability, and water stability, and demonstrates higher water absorption and a faster water absorption rate under low humidity, providing a new strategy for developing high-performance water-absorbing MOF materials for low humidity.

[0006] The present invention adopts the following technical solution:

[0007] A method for growing single crystals of low-humidity, water-absorbing aluminum-based MOF materials prepared by carboxylic acid ester hydrolysis, wherein the aluminum-based MOF material has a three-dimensional network structure with the general formula [Al(OH)(XCOO)2]. nX is a five- or six-membered heterocyclic ring; the single crystal of the aluminum-based MOF material has a crystal size greater than 20 micrometers, exhibiting higher stability and better water absorption performance under low humidity compared to powder materials. It can be used as an adsorbent to adsorb large amounts of water molecules from the air in low humidity environments (<30%RH). This method reduces the contact between reactants by using a layered two-phase solvent, controls the hydrolysis rate of the carboxylic acid ester ligand by adjusting the pH value of the reaction solvent, and further controls the coordination reaction process between the organic ligand and the aluminum cluster by controlling the hydrolysis rate of the carboxylic acid ester organic ligand. This reduces the reaction rate, prolongs the crystal growth time, reduces internal structural defects in the product, improves the crystallinity of the material, and obtains highly crystalline large-size single crystals, ultimately achieving good stability and high water absorption performance under low humidity.

[0008] In the above technical solution, the organic ligand used for the single crystal growth of the MOF material is a carboxylic acid ester ligand, including dimethyl pyridine-3,5-dicarboxylate (CAS: 4591-55-3), dimethyl furan-2,5-dicarboxylate (CAS: 4282-32-0), 1H-pyrrole-2,5-dicarboxylate (CAS: 1757-29-5), dimethyl 3,5-pyrazol dicarboxylate (CAS: 4077-76-3), and dimethyl 2,5-thiophene dicarboxylate (CAS: 4282-34-2).

[0009] Furthermore, the specific steps of the method for preparing low-humidity water-absorbing aluminum-based MOF material single crystals based on carboxylic acid ester hydrolysis are as follows:

[0010] 1) Add the carboxylic acid ester organic ligand to an organic solvent that is insoluble in water and stir at room temperature (e.g., for 10 minutes) until a clear solution A is obtained; add the inorganic salt of aluminum to an alkaline aqueous solution to obtain solution B; slowly add solution A to solution B to obtain a two-phase solution with layers, and then let it stand in an oven for a certain time. After the reaction is completed, slowly cool down and filter to obtain single crystal particles, and wash them successively with deionized water and anhydrous methanol / ethanol.

[0011] 2) Vacuum drying at room temperature for 4-8 hours, followed by vacuum drying at 373-423 K for 6-12 hours, yields a low-humidity water-absorbing aluminum-based MOF single crystal material. This single crystal material can act as an adsorbent to adsorb large amounts of water molecules from low-humidity (<30%RH) air. The purpose of the two vacuum drying processes is to activate the material.

[0012] Further, the water-insoluble organic solvent is tetrahydrofuran, ethyl acetate, and dichloromethane, etc.; the concentration of the carboxylic acid ester organic ligand in solution A is 0.1–0.3 mol / L; the inorganic salt of aluminum is aluminum chloride hexahydrate, aluminum sulfate octadecahydrate, or aluminum nitrate nonahydrate; the molar ratio of the inorganic salt of aluminum to the carboxylic acid ester organic ligand is 1:(1–2); the pH value of the alkaline aqueous solution is 7–10; the volume ratio of solution B to solution A is (1–2):1; and the slow cooling rate is 5–20 °C / h.

[0013] Furthermore, the reaction process can be controlled by adjusting the pH of the alkaline aqueous solution. The lower the pH value, the longer the reaction time and the larger the crystal product size. The reaction time in the oven is specifically: the reaction time range is 12 to 72 hours; the oven temperature is 80 to 120°C.

[0014] Compared with powder products obtained by traditional methods, the single crystal products prepared by the method of this invention have significantly improved stability, water absorption under low humidity, and water absorption rate.

[0015] The inventive principle of this invention is as follows:

[0016] This invention is the first to select carboxylic acid ester organic ligands, utilizing the fundamental principle that carboxylic acid ester ligands must first hydrolyze to form carboxylic acid ligands before coordinating with metallic aluminum clusters to generate Al-MOF materials. The carboxylic acid ester hydrolysis rate is slow and can be precisely controlled by the solution pH, significantly slowing down the MOF material formation rate—a rate-determining step in material formation. By controlling the solution pH, the hydrolysis rate and coordination reaction process can be precisely controlled, resulting in well-dispersed, large-size single-crystal products and significantly reducing structural defects in the material. This effectively improves the stability and low-humidity water absorption performance of aluminum-based MOF materials, providing a new strategy for enhancing and controlling the water absorption performance of water-absorbing MOF materials.

[0017] This invention utilizes two immiscible solvents to dissolve the organic ligand and metal salt separately, followed by slow mixing of the two solutions to obtain a two-phase reaction solution with stratification. This controls the reaction process at the interface between the two solutions, significantly slowing down the reaction rate. Furthermore, unlike traditional synthetic methods that use carboxylic acid-based organic ligands, this invention specifically selects carboxylic acid ester-based organic ligands for the reaction, thus splitting the original one-step reaction process into three steps: The first step is the hydrolysis of the carboxylic acid ester, which continuously generates carboxylic acid organic ligands; the second step is crystal nucleation. Due to the small number of organic ligands initially obtained from hydrolysis, the number of MOF crystal nuclei generated by coordination with aluminum ions is small and uniformly dispersed at the interface between the two solutions, without mutual interference; the third step is grain growth. As the carboxylic acid ester continues to hydrolyze, organic ligands are continuously generated. These newly generated organic ligands migrate to the solution interface as raw materials for grain growth, promoting the continuous growth of MOF grains.

[0018] Throughout the reaction, the hydrolysis rate of the carboxylic acid ester ligands can be controlled by adjusting the pH of the reaction solvent; the closer the pH is to 7, the slower the hydrolysis rate. Furthermore, by controlling the hydrolysis rate of the carboxylic acid ester ligands, the coordination reaction process between the organic ligands and metal clusters can be controlled, reducing the crystal growth rate, prolonging the ligand growth time, and minimizing product defects, ultimately yielding a large-sized single-crystal material with good crystallinity. Good crystallinity improves the material's stability and increases its lifespan; fewer defects enhance the hydrophilicity of the MOF channels, thereby increasing the material's water absorption under low humidity conditions; and uniformly dispersed large-sized single-crystal particles help improve the mass transfer efficiency between particles, thus increasing the material's water absorption rate.

[0019] The beneficial effects of this invention are as follows:

[0020] (1) This invention provides a new approach to regulating the performance of water-absorbing MOF materials. By increasing the crystallinity of the material, the stability of the material is increased; by reducing the internal defects of the material, the water absorption of the material under low humidity is increased; and by increasing the crystal size and dispersion of the material, the dynamic performance of the material is improved. This provides a new perspective for the development of high-performance water-absorbing MOF materials.

[0021] (2) This invention provides a method for preparing low-humidity water-absorbing aluminum-based MOF material single crystals based on the hydrolysis of carboxylic acid esters. This method can control the hydrolysis rate of carboxylic acid ester ligands by adjusting the pH value of the reaction solvent, thereby controlling the coordination reaction process, solving the problem of excessively fast reaction in traditional synthesis methods, obtaining large-size and highly crystalline aluminum-based MOF material single crystals, and improving the stability and water absorption performance of the material under low humidity.

[0022] (3) The present invention successfully prepared a single crystal of aluminum-based MOF material with low humidity water absorption. The single crystal material has good stability and high water absorption performance under low humidity, which is higher than that of the materials reported so far. It breaks through the performance bottleneck of existing materials and promotes the progress of MOF material application in low humidity water absorption. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the material in Example 1;

[0024] Figure 2 The XRD curve of the material in Example 1;

[0025] Figure 3 The images shown are scanning electron microscope (SEM) and optical microscope (OEM) images of the materials in Example 1.

[0026] Figure 4 The 77 K nitrogen adsorption curve of the material in Example 1;

[0027] Figure 5 XRD for the chemical stability of the material in Example 1;

[0028] Figure 6 XRD pattern for the thermal stability of the material in Example 1;

[0029] Figure 7 The water adsorption curve at 25°C for the material in Example 1;

[0030] Figure 8 The water adsorption-desorption kinetics curves for the material in Example 1 are shown below.

[0031] Figure 9 The XRD curves of the material in Comparative Example 1;

[0032] Figure 10 The images show scanning electron microscope (SEM) and optical microscope (OEM) images of the material in Comparative Example 1.

[0033] Figure 11 The nitrogen adsorption curve at 77 K for the material in Comparative Example 1;

[0034] Figure 12 The water adsorption curves at 25℃ for the material in Comparative Example 1 are shown.

[0035] Figure 13 The water adsorption-desorption kinetics curves for the material in Comparative Example 1 are shown.

[0036] Figure 14 This is a schematic diagram of the structure of the material in Example 2;

[0037] Figure 15 The XRD curves of the materials in Example 2;

[0038] Figure 16 The image shows an optical micrograph of the material in Example 2.

[0039] Figure 17 The water adsorption curve at 25°C for the material in Example 2;

[0040] Figure 18 The XRD curves of the material in Comparative Example 2;

[0041] Figure 19 The optical microscope image of the material in Comparative Example 2;

[0042] Figure 20 The adsorption curve of the material in Comparative Example 2 is the water adsorption curve at 25℃. Detailed Implementation

[0043] The following examples will further illustrate the content of this invention, but these examples do not limit the scope of protection of this invention. Various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of this invention are still within the scope of protection of this invention.

[0044] Example 1

[0045] 1 mmol of dimethyl 1H-pyrrole-2,5-dicarboxylic acid (Dimethyl-H2PyDC, CAS: 1757-29-5) was dissolved in 4 mL of tetrahydrofuran solution to obtain a clear solution A. 1 mmol of aluminum chloride hexahydrate was added to 5 mL of alkaline aqueous solution (pH = 10), and the mixture was sonicated for 20 minutes to obtain solution B. Solution A was slowly added to solution B, resulting in a layered reaction solution with solution A on top and solution B on the bottom. The reaction solution was sealed and heated in an oven at 100 °C for 12 h. The oven was then cooled to room temperature at a rate of 5 °C / h. The reaction solution was filtered to obtain Al-PyDC single crystals, which were washed successively with deionized water and anhydrous methanol, and then vacuum dried at room temperature for 4 h and then vacuum dried at 393 K for 6 h to obtain activated Al-PyDC single crystal material.

[0046] A schematic diagram of the structure of the obtained single crystal material is shown below. Figure 1 XRD characterization data can be found in Figure 2 .like Figure 3 Scanning electron microscope (SEM) images and optical microscope (OEM) images of Al-PyDC single crystals, from Figure 3 It can be seen that Al-PyDC single crystals have good crystal morphology, large crystal size (> 20 μm) and good dispersibility.

[0047] like Figure 4 The figure shows the nitrogen adsorption curve of Al-PyDC single crystal at 77 K. The saturated nitrogen adsorption capacity of Al-PyDC single crystal is 319 cm⁻¹. 3 / g, the calculated specific surface area of ​​BET is 1210 m² 2 / g.

[0048] like Figure 5 The chemical and water stability of Al-PyDC single crystals are shown. The material remains stable for extended periods in solutions with pH=1, pH=12, and boiling water. Figure 6 The figure shows the thermal stability of Al-PyDC single crystals; the material remains structurally stable even at 350℃.

[0049] like Figure 7 The figure shows the water adsorption curve of Al-PyDC single crystal at 25℃. Al-PyDC exhibits good water absorption performance, with a water absorption of 0.43 g / g at 20%RH and 0.45 g / g at 30%RH.

[0050] like Figure 8 The results of the kinetic performance test of Al-PyDC single crystals were obtained by adsorption at 25℃ and 20%RH until saturation. The saturated samples were then desorbed at 65℃, and the change in sample mass over time was recorded during the test.

[0051] Comparative Example 1

[0052] This case serves as a comparison with Example 1, using a conventional method to synthesize the material from Example 1. 1 mmol of 1H-pyrrole-2,5-dicarboxylic acid (H₂PyDC) and 2 mmol of sodium hydroxide were dissolved in 5 mL of water. The solution was sonicated for 20 minutes to obtain a clear solution. A 1 mol / L aqueous solution of aluminum chloride was added dropwise to the solution at 50 μL / min using a peristaltic pump at 25°C with stirring for 30 minutes. The temperature was then increased to 120°C at a rate of 0.5°C per minute and refluxed with stirring for 12 hours. The resulting solid was filtered and washed repeatedly with water and methanol to obtain purified Al-PyDC powder.

[0053] XRD characterization data of Al-PyDC powder are shown in [reference needed]. Figure 9 Scanning electron microscope (SEM) and light microscope (Light Microscope) images of the powder samples are as follows: Figure 10 ,from Figure 10 As can be seen, powder materials prepared by traditional synthesis methods have uneven particle morphology, small particle size (2~4 μm), and severe particle packing.

[0054] The Al-PyDC powder obtained in the above steps was subjected to multiple solvent exchange reactions in anhydrous methanol, with each exchange occurring at least 3 hours apart. Then, under a vacuum of 3 μmHg, the powder was successively placed at room temperature for 12 hours and at 393 K for 12 hours. The nitrogen adsorption curve of the Al-PyDC powder at 77 K was subsequently measured, as shown below. Figure 11As shown, the saturated nitrogen adsorption capacity of Al-PyDC powder is 295 cm⁻¹. 3 / g, the calculated specific surface area of ​​BET is 1129 m². 2 / g.

[0055] like Figure 12 The figure shows the water adsorption curve of Al-PyDC powder at 25℃. Compared with single crystal materials, the water absorption performance of Al-PyDC powder is significantly reduced, with a water absorption of 0.39 g / g at 20%RH and 0.41 g / g at 30%RH.

[0056] like Figure 13 The results of the kinetic performance tests of Al-PyDC powder are shown in 2. 5℃ The adsorption was carried out under 20% RH conditions until saturation, and then the saturated sample was desorbed at 65℃. The change in sample mass over time was recorded during the test. It can be seen that the water absorption rate of the powder material is significantly lower than that of the single crystal material.

[0057] Example 2

[0058] 1 mmol of dimethyl furan-2,5-dicarboxylic acid (Dimethyl-H2FDC, CAS: 4282-32-0) was dissolved in 5 mL of tetrahydrofuran solution to obtain clear solution A. 0.5 mmol of aluminum sulfate nonahydrate was added to 5 mL of alkaline aqueous solution (pH = 8), and the mixture was sonicated for 20 minutes to obtain solution B. Solution A was slowly added to solution B, resulting in a layered reaction solution with solution A on top and solution B on the bottom. The reaction solution was sealed and heated in a 90°C oven for 72 h. The oven was then cooled to room temperature at a rate of 10°C / h. The reaction solution was filtered to obtain Al-FDC single crystals, which were washed successively with deionized water and anhydrous methanol, and then vacuum dried successively at room temperature for 4 h and at 393 K for 6 h to obtain activated Al-FDC single crystals.

[0059] See the schematic diagram of the material structure. Figure 14 XRD characterization data can be found in Figure 15 .like Figure 16 The image shown is an optical micrograph of an Al-FDC single crystal sample. Al-FDC single crystals have good crystal morphology, large crystal size (> 50 μm) and good dispersibility.

[0060] like Figure 17 The image shows the water adsorption curves of Al-FDC single crystals at 25℃. Al-FDC exhibits good water absorption performance, with a water absorption of 0.39 g / g at 20%RH and 0.41 g / g at 30%RH.

[0061] Furthermore, the water absorption rate of Al-FDC single crystals was tested, and the material could reach saturation in 90 minutes at 20% RH.

[0062] Comparative Example 2

[0063] This case serves as a comparison with Example 2, using a conventional method to synthesize the material from Example 2. 1 mmol of furan-2,5-dicarboxylic acid (H₂FDC) and 2 mmol of sodium hydroxide were dissolved in 6 mL of water and sonicated for 20 minutes. Then, a 1 mol / L aqueous solution of aluminum chloride was added dropwise to the solution at 25°C using a peristaltic pump at a rate of 50 μL / min, with stirring for 20 minutes. Subsequently, the temperature was increased to 100°C at a rate of 1°C per minute and refluxed with stirring for 12 hours. The resulting solid was filtered and washed repeatedly with water and methanol to obtain purified Al-FDC powder.

[0064] XRD characterization data of Al-FDC powder are shown in [reference needed]. Figure 18 .like Figure 19 Light micrographs of powder samples, from Figure 19 As can be seen, powder materials prepared by traditional synthesis methods have uneven particle morphology, small particle size (1~3 μm), and severe particle packing.

[0065] like Figure 20 The figure shows the room temperature water absorption curve of Al-FDC powder material. The water absorption performance of the powder material is significantly lower than that of the single crystal material in Example 2.

[0066] Furthermore, the water absorption rate of the Al-FDC powder material was tested. The material reached saturation in 130 minutes at 20% RH, and the water absorption rate was significantly slower than that of the single crystal material.

Claims

1. A method for preparing low-humidity, water-absorbing aluminum-based MOF material single crystals based on carboxylic acid ester hydrolysis, characterized in that, The aluminum-based MOF material has a three-dimensional network structure with the general formula [Al(OH)(XCOO)2]. n X is a five- or six-membered heterocyclic ring; the single crystal of the low-humidity water-absorbing aluminum-based MOF material has a crystal size greater than 20 micrometers and can be used as an adsorbent to adsorb water molecules from the air in a low-humidity environment of <30%RH; the method is as follows: the organic ligand and the metal salt are dissolved in two immiscible solvents respectively, and then the two solutions are slowly mixed to obtain a two-phase reaction solution with layers, thereby controlling the reaction process at the interface between the two solutions and slowing down the reaction rate; the organic ligand is a carboxylic acid ester organic ligand, and the hydrolysis rate of the carboxylic acid ester organic ligand is controlled by adjusting the pH value of the solution, and further the coordination reaction process between the organic ligand and the aluminum metal cluster is controlled by the hydrolysis rate of the carboxylic acid ester organic ligand, thereby reducing the reaction rate, prolonging the crystal growth time, and finally obtaining a large-size single crystal of low-humidity water-absorbing aluminum-based MOF material; wherein, the lower the pH value of the solution, the longer the reaction time and the larger the crystal product size.

2. The method for preparing low-humidity, water-absorbing aluminum-based MOF material single crystals based on carboxylic acid ester hydrolysis according to claim 1, characterized in that, The carboxylic acid ester organic ligands include dimethyl pyridine-3,5-dicarboxylate (CAS: 4591-55-3); dimethyl furan-2,5-dicarboxylate (CAS: 4282-32-0); dimethyl 1H-pyrrole-2,5-dicarboxylate (CAS: 1757-29-5); dimethyl 3,5-pyrazolidinedicarboxylate (CAS: 4077-76-3); and dimethyl 2,5-thiophene dicarboxylate (CAS: 4282-34-2).

3. A method for preparing low-humidity, water-absorbing aluminum-based MOF material single crystals based on carboxylic acid ester hydrolysis as described in claim 1 or 2, characterized in that, The steps are as follows: 1) Add the carboxylic acid ester organic ligand to an organic solvent that is insoluble in water and stir at room temperature until a clear solution A is obtained; add the inorganic salt of aluminum to an alkaline aqueous solution to obtain solution B; slowly add solution A to solution B to obtain a two-phase solution with layers, and then react in an oven for a certain time. After the reaction is completed, slowly cool down and filter to obtain single crystal particles, which are then washed with deionized water and anhydrous methanol / ethanol in sequence. 2) Vacuum dry at room temperature for 4-8 hours, then vacuum dry at 373-423K for 6-12 hours to obtain low-humidity water-absorbing aluminum-based MOF single crystal material.

4. The method for preparing low-humidity, water-absorbing aluminum-based MOF material single crystals based on carboxylic acid ester hydrolysis according to claim 3, characterized in that, The water-insoluble organic solvents include tetrahydrofuran, ethyl acetate, and dichloromethane; the concentration of the carboxylic acid ester organic ligand in solution A is 0.1–0.3 mol / L; the inorganic salt of aluminum is aluminum chloride hexahydrate, aluminum sulfate octadechydrate, or aluminum nitrate nonahydrate; the molar ratio of the inorganic salt of aluminum to the carboxylic acid ester organic ligand is 1:(1–2); the pH value of the alkaline aqueous solution is 7–10; the volume ratio of solution B to solution A is (1–2):1; and the slow cooling rate is 5–20 °C / h.

5. The method for preparing low-humidity, water-absorbing aluminum-based MOF material single crystals based on carboxylic acid ester hydrolysis according to claim 3, characterized in that, The reaction time in the oven is specifically 12-72 h; the oven temperature is 80-120℃.

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