A highly stable MOF material forming method based on alginate gel and its air water extraction application

Abstract

The present invention provides a molding method of a highly stable metal-organic framework material based on alginate gel and its air water extraction application. The highly stable MOF material uses high-valent metal ions as metal nodes and carboxylic acid organic ligands as connectors to form a three-dimensional network structure with permanent voids. This type of material can be used as an adsorbent to adsorb water molecules from the air. The present invention mixes the MOF material and alginate-polyethylene glycol solution and drips the mixture into a divalent cation solidifying liquid to form a spherical gel loaded with the MOF material in situ. Using the spherical gel as a template, ultra-low temperature freeze-drying is performed to obtain MOF material molded particles with an internal network structure. The molding method of the present invention can mold and process a large number of MOF materials in a short time, and the obtained molded particles have uniform morphology, controllable particle size and high wear resistance, while retaining the adsorption performance of the original powder material to the greatest extent, greatly promoting the progress of industrial application of MOF materials.

Description

Technical Field

[0001] The present invention relates to the technical fields of adsorption material forming technology and environment and energy, and in particular to a forming processing method of a highly stable metal-organic framework material (MOFs) and its air water absorption application. Background Art

[0002] Adsorption-based air water extraction technology can capture freshwater resources from the air in arid regions, potentially providing a new approach to ensuring a stable freshwater supply in water-scarce areas. The core of this technology lies in the design and preparation of high-performance water-absorbing materials. Metal-organic frameworks (MOFs) are composed of organic ligands and metal clusters connected by coordination bonds. They offer advantages such as high specific surface area, adjustable pore structure, and ease of functionalization. MOF materials primarily capture water molecules from the air through interactions between functional sites and water molecules. This interaction is weaker than chemical adsorption, resulting in a lower heat of adsorption, enabling low-temperature regeneration of the adsorbent material and reducing energy consumption. Furthermore, through rational pore structure design, a rich set of active sites can be constructed within the MOF material framework, enabling the simultaneous adsorption of water molecules at multiple adsorption sites, ultimately achieving a high adsorption capacity. These high adsorption capacity, rapid adsorption / desorption kinetics, and low regeneration energy consumption make MOF materials promising for the application of air water extraction in arid regions.

[0003] Currently, MOF materials have achieved some research results in the field of water adsorption. However, these studies are mostly limited to the structural design and regulation of the MOF materials themselves. The prepared MOFs are essentially powder materials. In practical applications, there are problems such as powder leakage, accumulation, and agglomeration. In addition, they are difficult to load, transport, and recycle, which seriously limits the practical application methods and scenarios of the materials and devices. To promote the industrial application of MOF materials in the field of air water extraction, it is necessary to develop a molding process suitable for MOF adsorption materials.

[0004] Traditional molding methods include tableting, injection molding, and binder granulation. These molding methods all involve pressurizing the powdered material. For example, the granulation method requires mixing the binder and MOF material, extruding strips, then cutting into pellets, and finally rolling granulation. This process of applying external pressure will, on the one hand, cause a certain degree of damage to the MOF material framework, reducing the water absorption capacity of the molded body. On the other hand, it will increase the density of the molded body, reduce the porosity of the molded body, hinder the transport of water molecules within the particles, and severely reduce the adsorption / desorption rate of the molded body. In addition, traditional molding methods often use organic binders. These binders are generally linear polymers. They fix the adsorbent material, maintain the morphology of the molded body, and improve the mechanical strength of the molded body through the sufficient entanglement between the binder molecular chains. On the one hand, this linear polymer binder will block the pores of the adsorbent material, reducing the material's adsorption performance. On the other hand, it will entangle with each other and cover the pore surface of the adsorbent material, preventing water molecules from entering the pores of the adsorbent material. Summary of the Invention

[0005] The purpose of the present invention is to address the deficiencies of the prior art and provide a method for forming a highly stable metal-organic framework material (MOFs) based on alginate gel. The forming method provided by the present invention uses alginate as a cross-linking agent. As a green and harmless food additive, the introduction of alginate can avoid pollution of water bodies during air water extraction. This method first uniformly loads the MOF material on the alginate spherical gel, uses the alginate gel as a template, and obtains MOF molded particles by ultra-low temperature freeze-drying. The molded particles obtained by this method have a good and uniform morphology, the size of the particles can be controlled, the wear resistance of the particles is excellent, and most importantly, the interior of the molded particles is a porous network structure, which can retain the water absorption properties of the powdered raw materials to the greatest extent. This technology has greatly promoted the progress of the industrial application of MOF water-absorbing materials.

[0006] The present invention utilizes the ionic crosslinking properties between alginate and divalent cations to form an alginate-divalent cation-polyethylene glycol spherical gel in situ in an aqueous solution, and evenly loads the MOF material onto the network within the gel. Subsequently, using the alginate spherical gel as a template, ultra-low temperature freeze-drying is employed to remove moisture from the gel while maintaining the network structure, resulting in low-density, high-porosity MOF material shaped particles with a porous network structure within. This molding method avoids the problems of adsorption material pore blockage and pore surface coverage associated with traditional organic binders. It also avoids the extrusion, compression, and granulation processes inherent in traditional molding methods, thereby increasing the porosity of the molded particles.

[0007] The molding method provided by this invention effectively controls the particle size of the molding material, prevents clogging of the adsorption material pores, reduces the density of the molding material, and increases its porosity, thereby maximizing the water absorption properties of the powdered material. Furthermore, the introduction of polyethylene glycol not only improves the dispersibility of the powdered material but also entangles it with the alginate molecular chains, imparting excellent wear resistance to the molded material, ensuring long-term use. This significantly advances the industrial application of MOF water-absorbing materials.

[0008] The present invention is implemented by the following technical solutions:

[0009] A method for forming highly stable metal-organic frameworks (MOFs), wherein the highly stable MOF material uses high-valent metal ions as metal nodes and carboxylic acid organic ligands as connectors to form a three-dimensional network structure with permanent voids; the highly stable MOF material has good water stability and can exist stably in aqueous solution; the forming method comprises mixing the MOF material and alginate slurry, dripping the mixture into a divalent cation solidifying liquid to prepare a spherical gel, and then using the spherical gel as a template to obtain MOF molded particles through ultra-low temperature freeze-drying. The forming method uses the alginate gel as a template and obtains molded particles with an internal network structure through ultra-low temperature freeze-drying. The forming process does not involve steps such as extrusion, compression, and granulation, which can reduce the density of the molded body and increase the porosity of the molded body; the molded body obtained by the forming method has good wear resistance and can retain the adsorption properties of the original powder material to the greatest extent.

[0010] In the above technical solution, further, the high-valent metal ions include Al 3+ Cr 3+ 、Fe 3+ 、Ti 4+ and Zr 4+ The carboxylic acid organic ligands include fumaric acid, terephthalic acid, isophthalic acid, trimesic acid, aminoterephthalic acid, 2,5-pyrazinedicarboxylic acid, 2,5-pyridinedicarboxylic acid, 3,5-pyridinedicarboxylic acid, 2,4-pyrroledicarboxylic acid, 1H-pyrrole-2,5-dicarboxylic acid and 3,5-pyrazoledicarboxylic acid.

[0011] An in-situ forming method for MOF materials specifically comprises the following steps:

[0012] 1) Grinding the MOF material and sieving it through a sieve with a mesh size of 80 to 100 to obtain an initial fine powder;

[0013] 2) adding alginate and polyethylene glycol to deionized water and stirring for 24 hours to obtain a clear alginate-polyethylene glycol mixed solution; the alginate has an M / G ratio of 0.5 to 1.5; the alginate comprises sodium alginate and potassium alginate; the alginate has a viscosity range of 150 to 200 mPa·s; the polyethylene glycol has a molecular weight of 1000 to 1500; and the mass ratio of the alginate, polyethylene glycol, and deionized water is (0.015 to 0.025):(0.003 to 0.006):1;

[0014] 3) adding 1 mol / L HCl aqueous solution to the alginate-polyethylene glycol mixed solution to adjust the pH to 5-7, thereby regulating the viscosity of the alginate-polyethylene glycol mixed solution;

[0015] 4) adding the sieved MOF material powder to the mixed solution and stirring uniformly to obtain a mixed slurry; the MOF material is used in an amount of 100 to 200 mg per milliliter of alginate-polyethylene glycol mixed solution; the stirring rate is 500 to 800 r / min; and the stirring time is 12 to 48 hours;

[0016] 5) adding a divalent metal salt to deionized water to prepare a solidifying solution; the divalent metal salt includes calcium chloride, calcium nitrate, copper chloride, and zinc chloride; and the concentration of divalent cations in the solidifying solution is 0.05 to 0.1 mol / L;

[0017] 6) using a peristaltic pump to slowly drip the mixed slurry into the curing liquid, and the slurry droplets are instantly cured to obtain spherical gel; the inner diameter of the peristaltic pump silicone tube is 0.5 to 5 mm; the speed of the peristaltic pump is 50 to 150 r / min;

[0018] 7) Allow the spherical gel to stand in the curing solution for 12 to 24 hours. After the gel is fully cured, soak it in deionized water for 12 to 24 hours to wash away excess divalent metal ions.

[0019] 8) After filtering the spherical gel, air-dry it at room temperature to remove moisture from the surface of the gel, and then rapidly freeze it with liquid nitrogen, and then freeze-dry it with a freeze dryer to obtain MOF material shaped particles; the freeze-drying temperature is -85°C, and the freeze-drying time is 48 hours.

[0020] 9) The formed particles are vacuum dried at room temperature for 3 to 8 hours, and then dried at 373 to 423 K for 3 to 8 hours to complete activation, thereby obtaining a particle material that can be used for air water extraction.

[0021] The MOF material shaped particles prepared by the above method can be adjusted in size from 1 to 6 mm by using peristaltic pump pipes with different inner diameters. The shaped particles have excellent wear resistance. According to the wear test of GB / T10505.2 method, the mass loss of the particles is less than 2% after 100,000 rotations in the drum. The shaped particles have a low density of less than 0.5 g / cm 3 The water adsorption performance of the molded particles is less than 2% of that of the original powder; the molded particles have good adsorption / desorption kinetics.

[0022] The inventive principle of the present invention is:

[0023] The present invention prefers highly stable MOF materials as molding raw materials. According to Lewis acid-base theory, high-valent metal cations belong to strong acids, and carboxylic acid organic ligands belong to strong bases. Strong acid and strong base can form a strong coordination bond to ensure a stable connection between the two. Based on this theory, the present invention selects Al 3+ Cr 3+ 、Fe 3+ 、Ti 4+ and Zr 4+ The MOF material prepared by using high-valent metals as metal nodes and carboxylic acid organic ligands as connectors has good water stability and can exist stably in aqueous solution for a long time, providing a material basis for in situ forming in aqueous solution.

[0024] The molding method provided by the present invention utilizes the ionic crosslinking characteristics of alginate, and the raw material slurry is added dropwise to the solidification solution. The crosslinking effect of the alginate in the raw material slurry and the divalent cations in the solidification solution is utilized to automatically convert the slurry into a spherical gel at the moment of entering the solidification solution. Subsequently, the method of ultra-low temperature freeze drying is used to remove the moisture in the gel while maintaining the internal network structure of the spherical gel to obtain the final molded particles. There is no pressurization process in the whole process, which avoids the damage to the MOF material framework and maintains the adsorption performance of the powder raw material to the greatest extent. In addition, the inside of the molded particles is a porous network structure with a lower density and a higher porosity, which can ensure the rapid transmission of water molecules within the particles and greatly improve the adsorption / desorption rate of the material.

[0025] Alginate is a byproduct of the extraction of iodine and mannitol from brown algae such as kelp or sargassum. Its molecules are composed of β-D-mannuronic acid (M monomer) and α-L-guluronic acid (G monomer) linked by a (1→4) bond. Due to differences in the types of raw materials extracted, the content of M and G monomers in the produced alginate molecules varies, resulting in differences in their physicochemical properties. Alginate molecules have numerous carboxyl and hydroxyl groups, and carry a high negative charge after dissolution. When alginate and divalent cations meet, they cross-link through electrostatic interactions in a very short time, forming a stable network structure, ultimately resulting in a three-dimensional gel network.

[0026] During experimental exploration, the team discovered that the properties of alginate gels are influenced by the M / G ratio of the alginate raw material, the concentration of the alginate slurry, and the pH of the slurry. By manipulating these parameters, the present invention controls the porosity of the gel network, achieving a well-formed spherical gel while maintaining a high porosity.

[0027] The present invention adds a certain amount of polyethylene glycol during the slurry preparation process. By selecting an appropriate polyethylene glycol molecular weight, the slurry has good dispersibility, allowing the MOF material to be evenly distributed within the slurry, ensuring uniform material properties after molding. Furthermore, the polyethylene glycol molecular chains will entangle to a certain extent with the alginate molecular chains, thereby improving the wear resistance of the molded particles.

[0028] The molding process of the present invention does not involve an external pressurization step. The moment the mixed slurry is dripped into the curing agent, the alginate in the outer layer of the slurry will cross-link with the divalent cations to form a gel shell, while maintaining a spherical morphology under the action of surface tension. As the static curing time increases, the interior of the slurry gradually gels, and eventually the entire slurry droplet is converted into a solid gel network. The entire ionic cross-linking process is automatically completed in the curing liquid, and there is no pressurized shaping step. Therefore, there are a large number of pores inside the gel, which is beneficial to increase the porosity of the final molded particles, thereby increasing the adsorption / desorption rate of the molded particles.

[0029] The present invention regulates the curing speed by controlling the concentration of divalent cations. If the curing speed is too slow, the gel network will have an irregular morphology and may even become dispersed in the curing liquid. If the curing speed is too fast, the spherical gel will shrink significantly, reducing the porosity of the formed particles. Therefore, precise control of the divalent cation concentration is necessary.

[0030] Ultimately, the present invention uses ultra-low temperature freeze-drying to remove moisture from the spherical gel. The gel is first frozen with liquid nitrogen to preserve its macroscopic appearance. Ultra-low temperature freeze-drying is then used to remove the water from the gel, effectively preserving the network structure within the spherical gel. The resulting MOF particles exhibit a porous network structure with a uniform morphology, low density, high porosity, and excellent wear resistance, maximizing the adsorption properties of the original powder.

[0031] The beneficial effects of the present invention are:

[0032] (1) The molding method of the present invention can effectively control the particle size of the product and can be produced continuously on a large scale. By adjusting the inner diameter of the peristaltic pump silicone tube used for dripping the slurry, the size of the slurry droplets can be effectively controlled, and then the size of the spherical gel after solidification can be controlled, and finally the size of the molded particles can be regulated. There are many sizes of peristaltic pump silicone tubes on the market, so the size of the molded samples can be easily controlled to meet the size requirements of particles in different application scenarios. Compared with the traditional molding method that requires customized molds of different sizes to control the size of the molded particles, the method of the present invention can easily achieve precise control of the size of the molded particles. In addition, this method can realize the molding of samples from milligrams to kilograms without the use of complex equipment, and is extremely practical.

[0033] (2) The raw material powder of the molding method of the present invention is evenly dispersed, the molding process is continuous, and the morphology, size, mechanical properties and water absorption properties of the final molded sample are uniform.

[0034] (3) The present invention uses alginate ion crosslinking agent to avoid the use of traditional organic binders. Since the alginate crosslinking agent contains a large number of six-membered rings, it can avoid the problem of adsorption material pore blockage existing in traditional molding methods. In addition, the electrostatic repulsion between adjacent chains inhibits the full entanglement between alginate molecules, further avoiding coverage of the pore surface of the adsorption material, and maintaining the adsorption performance of the original powder material to the greatest extent.

[0035] (4) The molding process of the present invention uses a spherical alginate gel network as a template, and there is no step of applying external pressure. Therefore, the framework structure of the MOF can be maintained to the greatest extent, and the resulting molded particles have a low density and high porosity. The porous network structure inside the molded particles is conducive to the rapid transmission of water molecules, greatly improving the adsorption / desorption rate of the molded particles. As a green and harmless food additive, the introduction of alginate can avoid water pollution during the air water extraction process.

[0036] (5) The method of the present invention adds polyethylene glycol to the slurry and utilizes the entanglement of polyethylene glycol and alginate molecular chains to improve the wear resistance of the formed particles, making them meet the requirements of industrial applications and greatly promoting the practical application progress of MOF water-absorbing materials.

[0037] (6) The molding method provided by the present invention can be used to mold large quantities of MOF materials in a short period of time. The obtained molded particles have uniform morphology, controllable particle size and high wear resistance, while retaining the adsorption properties of the original powder material to the greatest extent, greatly promoting the progress of the industrial application of MOF materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the structure of the powder raw material in Example 1.

[0039] Figure 2 This is the PXRD of the powdered raw material in Example 1.

[0040] Figure 3 77K nitrogen isotherm adsorption curve of the powder raw material in Example 1.

[0041] Figure 4 This is the macroscopic morphology of the powder raw material in Example 1.

[0042] Figure 5 This is the in-situ molding flow chart in Example 1.

[0043] Figure 6 This is a picture of molded particles of different sizes in Example 1.

[0044] Figure 7 This is the abrasion tester diagram in Example 1.

[0045] Figure 8 77K nitrogen isotherm adsorption curve of the molded particles in Example 1.

[0046] Figure 9 This is the room temperature water adsorption curve of the molded particles in Example 1.

[0047] Figure 10 This is a structural diagram of the powder raw material in Example 2.

[0048] Figure 11 This is the PXRD of the powder raw material in Example 2.

[0049] Figure 12 This is the room temperature water adsorption curve of the molded particles in Example 2.

[0050] Figure 13 This is a structural diagram of the powder raw material in Example 3.

[0051] Figure 14This is the PXRD of the powder raw material in Example 3.

[0052] Figure 15 This is the room temperature water adsorption curve of the molded particles in Example 3. DETAILED DESCRIPTION

[0053] The contents of the present invention will be further illustrated below with reference to examples, but these examples do not limit the scope of protection of the present invention. Based on the technical solution of the present invention, various modifications or variations that can be made by those skilled in the art without creative work are still within the scope of protection of the present invention.

[0054] Example 1

[0055] Aluminum-based MOF material Al-PyDC was selected as the raw material for molding processing (ligand is 1H-pyrrole-2,5-dicarboxylic acid). The synthesis method of Al-PyDC is as follows: 5 mol 1H-pyrrole-2,5-dicarboxylic acid and 15 mol sodium hydroxide were dissolved in 20L water, stirred at 100°C for 1h until the solution was completely clear, and then 5 mol aluminum chloride hexahydrate was added. Then reflux and stirring were continued for 12 hours. The solid obtained by the reaction was filtered and washed with water and ethanol several times to obtain 1kg of purified metal-organic framework material Al-PyDC, and then Al-PyDC was ground and sieved through a sieve to obtain Al-PyDC powder; the mesh size of the sieve was 80-100 mesh. The structure of Al-PyDC can be seen in Figure 1 , powder X-ray diffraction pattern is shown in Figure 2 , 77K nitrogen adsorption data see Figure 3 , macroscopic appearance Figure 4 .

[0056] The molding method is as follows: weigh 75g of sodium alginate (M / G=1 / 2, viscosity 200mPa·S) and place it in a bucket filled with 5L of deionized water, add 30g of polyethylene glycol (molecular weight 1000), add 1mol / L hydrochloric acid aqueous solution to adjust the pH value to 6.5, and stir for 24 hours to obtain a uniform liquid; add 750g of Al-PyDC powder and continue stirring for 24 hours to obtain a uniform slurry; dissolve 80g of anhydrous calcium chloride in 10L of deionized water to prepare a solidifying liquid. Use a peristaltic pump to drip the slurry into the solidifying liquid, let it stand and solidify for 24 hours, then soak it in deionized water for 12 hours, filter out the gel particles and dry them. After freezing with liquid nitrogen, freeze-dry at -85°C for 48 hours to obtain molded particles. The molding process is as follows Figure 5 shown.

[0057] After testing, the density of the original powder before molding is 0.83g / cm 3 The density of the particles after molding is 0.42g / cm 3, which is much lower than the traditional molding method. Then, different sizes of peristaltic pump silicone tubes (0.8mm, 1.2mm and 1.6mm) were replaced to obtain molding particles of different sizes ( Figure 6 The wear resistance of the particles was then tested using a molecular sieve abrasion tester ( Figure 7 ), the test method refers to GB / T10505.2. According to the test, the mass loss of the formed particles after 1,000 rotations in the drum is less than 0.1%, and the mass loss after 100,000 rotations is about 1.2%.

[0058] The molded particles were vacuum dried at room temperature for 3 h, and then vacuum dried at 373 K for 3 h to complete the activation. The activated samples were subjected to nitrogen adsorption test at 77 K ( Figure 8 ), water adsorption test at room temperature ( Figure 9 ). From the test results, it can be seen that compared with the original powder material before molding, the specific surface area and water adsorption performance of the particles after molding are basically not lost.

[0059] Example 2

[0060] The chromium-based MOF material MIL-101 was selected as the raw material for molding processing (the ligand is terephthalic acid). The synthesis method of MIL-101 is as follows: 8g of chromium nitrate nine hydrate, 3.3g of terephthalic acid and 15mL of acetic acid (36wt%) were added to 100mL of deionized water and heated at 473K for 8h. After filtering, it was washed with deionized water, DMF and ethanol in turn, and vacuum dried to obtain a pure phase crystalline material, which was then ground and sieved through a sieve to obtain MIL-101 powder; the mesh size of the sieve was 80 to 100 meshes. The structure of MIL-101 is shown in Figure 10 , powder X-ray diffraction pattern is shown in Figure 11 .

[0061] The molding method is as follows: Weigh 0.25g of sodium alginate (M / G = 1 / 2, viscosity 200mPa·s) and place it in a bottle containing 20mL of deionized water. Add 0.1g of polyethylene glycol (molecular weight 1500), add 1mol / L hydrochloric acid aqueous solution to adjust the pH to 6, and stir for 24 hours to obtain a homogeneous liquid. Add 2.5g of MIL-101 powder and continue stirring for 24 hours to obtain a homogeneous slurry. Dissolve 0.4g of anhydrous calcium nitrate in 40mL of deionized water to prepare a curing liquid. Use a peristaltic pump to drop the slurry into the curing liquid. After standing and curing for 24 hours, soak it in deionized water for 12 hours, filter out the gel particles, and dry them. After freezing with liquid nitrogen, freeze-dry at -85°C for 48 hours to obtain the molded particles.

[0062] The molded particles were vacuum dried at room temperature for 6 h, and then vacuum dried at 423 K for 6 h to complete the activation. The water adsorption curve of the activated molded particles was tested, as shown in Figure 2. Figure 12As shown, the adsorption performance of the formed particles is almost the same as that of the original powder material.

[0063] Example 3

[0064] The zirconium-based MOF material MOF-801 was selected as the raw material for molding processing (the ligand is fumaric acid). The synthesis method of MOF-801 is as follows: 16g of zirconium oxychloride octahydrate and 5.8g of fumaric acid were added to a mixed solution of 200mL DMF and 70mL of formic acid, and heated at 400K for 12h. After filtration, it was washed with deionized water, DMF and ethanol in turn, and vacuum dried to obtain a pure phase crystalline material, which was then ground and sieved through a sieve to obtain MOF-801 powder; the mesh size of the sieve was 80-100 mesh. The structure of MOF-801 is shown in Figure 13 , powder X-ray diffraction pattern is shown in Figure 14 .

[0065] The molding method is as follows: 0.25g of sodium alginate (M / G = 1 / 2, viscosity 200mPa·s) is weighed and placed in a bottle containing 20mL of deionized water. 0.08g of polyethylene glycol solution (molecular weight 1500) is added. The pH value is adjusted to 6 by adding 1mol / L hydrochloric acid aqueous solution, and the mixture is stirred for 24 hours to obtain a homogeneous liquid. 0.25g of MOF-801 powder is added and stirred for another 24 hours to obtain a homogeneous slurry. 0.3g of anhydrous calcium chloride is dissolved in 40mL of deionized water to prepare a curing solution. The slurry is dripped into the curing solution using a peristaltic pump. After curing for 24 hours, the mixture is soaked in deionized water for 12 hours. The gel particles are filtered and air-dried. After freezing with liquid nitrogen, the particles are freeze-dried at -85°C for 48 hours to obtain the formed particles.

[0066] The molded particles were vacuum dried at room temperature for 6 h, and then vacuum dried at 393 K for 6 h to complete the activation. The water adsorption curve of the activated molded particles was tested, as shown in Figure 2. Figure 15 As shown in the figure, the adsorption performance of the formed particles is almost the same as that of the original powder material.

Claims

1. A method for forming a highly stable MOF material based on alginate gel, characterized in that: The highly stable MOF material uses high-valent metal ions as metal nodes and carboxylic acid organic ligands as connectors to form a three-dimensional network structure with permanent voids. The highly stable MOF material has good water stability and can exist stably in aqueous solution. The molding method comprises: mixing the MOF material and alginate slurry, dripping the mixture into a divalent cation curing liquid to prepare a spherical gel, and then using the spherical gel as a template to obtain MOF molded particles through ultra-low temperature freeze drying. The specific steps are as follows: 1) Grinding the MOF material and sieving it through a sieve with a mesh size of 80 to 100 to obtain an initial fine powder; 2) adding alginate and polyethylene glycol to deionized water and stirring until a clear alginate-polyethylene glycol mixed solution is obtained; the alginate has an M / G ratio of 0.5 to 1.5; the alginate comprises sodium alginate and potassium alginate; the alginate has a viscosity range of 150 to 200 mPa·s; the polyethylene glycol has a molecular weight of 1000 to 1500; and the mass ratio of the alginate, polyethylene glycol, and deionized water is (0.015 to 0.025):(0.003 to 0.006):1; 3) Add 1 mol / L HCl aqueous solution to the alginate-polyethylene glycol mixed solution to adjust the pH of the mixed solution to 5-7; 4) Add the sieved MOF material initial fine powder to the alginate-polyethylene glycol mixed solution and stir evenly to obtain a mixed slurry; the stirring rate is 500-800 r / min; the stirring time is 12-48 h; 5) adding a divalent metal salt to deionized water to prepare a curing solution; the divalent metal salt is calcium chloride, calcium nitrate, copper chloride, or zinc chloride; and the concentration of divalent cations in the curing solution is 0.05 to 0.1 mol / L; 6) Use a peristaltic pump to slowly drip the mixed slurry into the curing liquid. The slurry droplets instantly solidify to obtain spherical gels. The inner diameter of the peristaltic pump silicone tube is 0.5-5 mm. The peristaltic pump speed is 50-150 r / min. 7) Allow the spherical gel to stand in the curing solution for 12 to 24 hours. After the gel is fully cured, soak it in deionized water for 12 to 24 hours to wash away excess divalent metal ions. 8) After filtering the spherical gel, air-dry it at room temperature to remove moisture from the gel surface, then quickly freeze it with liquid nitrogen and freeze-dry it in a freeze dryer to obtain MOF material particles; the freeze-drying temperature is -85°C and the freeze-drying time is 48 hours; 9) The formed particles are vacuum dried at room temperature for 3 to 8 hours, and then dried at 373 to 423 K for 3 to 8 hours to complete activation, thereby obtaining a particle material that can be used for air water extraction.

2. The method for forming a highly stable MOF material based on alginate gel according to claim 1, characterized in that: The high-valent metal ions include Al 3+ Cr 3+ 、Fe 3+ 、Ti 4+ and Zr 4+ The carboxylic acid organic ligands include fumaric acid, terephthalic acid, isophthalic acid, trimesic acid, aminoterephthalic acid, 2,5-pyrazinedicarboxylic acid, 2,5-pyridinedicarboxylic acid, 3,5-pyridinedicarboxylic acid, 2,4-pyrroledicarboxylic acid, 1H-pyrrole-2,5-dicarboxylic acid and 3,5-pyrazoledicarboxylic acid.

3. The method for forming a highly stable MOF material based on alginate gel according to claim 1, characterized in that: The size of the MOF material shaped particles is 1 to 6 mm; the shaped particles have extremely high wear resistance.

4. The highly stable MOF material prepared by the method according to any one of claims 1 to 3, characterized in that: Acts as an adsorbent to absorb water molecules in the air.

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