A hydroxylated microporous crystalline material with ultra-low humidity water adsorption performance and a method of making the same

Abstract

The application discloses a kind of hydroxylated microporous crystalline materials with ultra-low humidity water adsorption performance and preparation method thereof, the microporous crystalline material has three-dimensional periodic network structure, general structure formula is M6O4 (OH) 4L6, wherein M=Zr or Hf, L is linear type bicarboxylic acid organic ligand BDC-(OH) modified with one or more hydroxyl X (X=1-4);The three-dimensional periodic network structure includes tetrahedral pore cage of diameter and octahedral pore cage of diameter, the hydroxylation of crystalline material is realized by modifying different number of hydroxyl groups on BDC ligand, and the modified channel structure is densely covered with-OH hydrophilic group, so as to be able to capture trace water vapor from extremely low humidity air as adsorbent material;The hydroxylated microporous crystalline material has good hydrophilicity, and has larger pore volume than zeolite, so it can realize higher water adsorption capacity under extremely low humidity, and has superior application potential in trace water capture field.

Description

Technical Field

[0001] This invention belongs to the field of energy and water adsorption, specifically relating to a hydroxylated microporous crystal material with ultra-low humidity water adsorption performance and its preparation method. This material can be used as a water vapor adsorption material for the adsorption of trace water vapor under extremely low humidity conditions. Background Technology

[0002] With continuous economic development, the demand for freshwater is constantly increasing. Currently, two-thirds of the world's population faces water pressure, and by 2025, freshwater scarcity will become a severe problem faced by countries worldwide, especially for arid inland regions that are already extremely short of water resources. Atmospheric water is ubiquitous, breaking the spatial and temporal limitations inherent in conventional freshwater resources. Even in extremely arid regions, the atmosphere typically contains abundant water vapor (10%-20% relative humidity), thus atmospheric water is considered a rich and recyclable freshwater resource in arid regions. Conventional atmospheric water collection technologies, such as fogging and condensation methods, cannot be applied to arid regions with high temperatures and low humidity. Under these circumstances, adsorption-based atmospheric water collection technology using porous materials has attracted widespread attention due to its high feasibility in solving the problem of freshwater scarcity in arid regions. Adsorption-based atmospheric water harvesting technology utilizes the vapor pressure difference between the surface of a dry water adsorbent and the ambient air as the driving force for moisture absorption. It can spontaneously absorb water vapor from the surrounding low-humidity air. The saturated adsorbent can be desorbed and regenerated by inputting external heat, thereby obtaining a clean freshwater source. However, adsorption-based atmospheric water harvesting technology is heavily dependent on the water adsorbent used. Developing adsorbent materials with excellent low-pressure water adsorption performance is key to further promoting the development of atmospheric water harvesting technology in arid regions.

[0003] Metal-organic frameworks (MOFs) are a class of solid crystalline porous materials formed by the self-assembly of metal ion clusters and organic ligands. Due to their higher specific surface area and pore volume compared to traditional porous materials, as well as their excellent structural tunability and designability, MOFs have been developed as high-performance adsorbents in recent years. However, the reported stability of MOFs is poor, making it difficult to meet practical production needs, and satisfactory water absorption capacity is difficult to achieve in extremely low humidity environments (below 15% relative humidity). Therefore, to promote the practical application of atmospheric water harvesting technology based on adsorbents in arid regions, it is urgent to develop MOF materials with high stability and high ultra-low humidity trace water vapor capture capabilities. Summary of the Invention

[0004] To address the technical challenges in the aforementioned background technology, this invention provides a hydroxylated microporous crystal material with ultra-low humidity water adsorption performance and its preparation method. This hydroxylated microporous crystal material exhibits excellent acid, alkali, and water stability as well as high trace water vapor adsorption capacity, effectively promoting the further development of adsorption-based atmospheric water collection technology in arid regions based on porous materials.

[0005] The present invention adopts the following technical solution:

[0006] A hydroxylated microporous crystalline material with ultra-low humidity water adsorption properties has the general structural formula M6O4(OH)4L6, where M = Zr or Hf, and L is a linear dicarboxylic acid organic ligand BDC-(OH) modified with one or more hydroxyl groups. X (X = 1-4); the microporous crystalline material has a three-dimensional periodic network structure, the three-dimensional periodic network structure including diameters... tetrahedral perforated cage and diameter Octahedral perforated cage.

[0007] Furthermore, the successful application of the hydroxyl functionalization strategy in this material results in the dense distribution of hydrophilic groups -OH within the pore structure, enabling it to act as an adsorbent material to capture trace amounts of water vapor in the air of extremely arid regions under extremely low humidity conditions.

[0008] In the above scheme, the preparation method of the material is as follows: soluble metallic zirconium / hafnium salt, BDC-(OH)X (X=1-4), reaction solvent and regulator are mixed in a certain proportion and ultrasonically treated, followed by hydrothermal reaction. After synthesis, the homogeneous crystal material, namely the hydroxylated microporous crystal material, can be obtained by filtration, washing and drying.

[0009] Furthermore, the soluble metallic zirconium / hafnium salt is Zr. 4+ / Hf 4+ One or more of the following: chloride, nitrate, acetate, carbonate, sulfate, or perchlorate;

[0010] The reaction solvent is one or more of N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, deionized water, ethanol, methanol, and acetonitrile;

[0011] The amount of the soluble zirconium / hafnium salt and the organic ligand BDC-(OH) X The amount of substance and the volume ratio of reaction solvent to regulator are: 1 mmol: 0.5-3 mmol: 2-15 mL: 0.2-3 mL;

[0012] The regulator is one or more of hydrochloric acid, nitric acid, sulfuric acid, acetic acid, formic acid, trifluoroacetic acid, and hydrofluoric acid;

[0013] The ultrasonic temperature is 25-50℃, and the ultrasonic time is 10-60 min;

[0014] The hydrothermal reaction temperature is 80-150℃, and the reaction time is 6-72h;

[0015] The drying process requires the use of a solvent exchange method to exchange the homogeneous crystal material obtained after filtration and washing with one of methanol, ethanol, or acetone multiple times, with an interval of at least 3 hours between each exchange. Then, it is vacuum activated for 12 hours at room temperature and 60-120°C respectively to obtain a hydroxylated microporous crystal material with ultra-low humidity water adsorption properties.

[0016] All reagents and materials involved were purchased directly from the market and can be used without further purification. The beneficial effects of this invention are:

[0017] (1) This invention provides a hydroxylated microporous crystal material with ultra-low humidity water adsorption performance and its preparation method. The microporous crystal material is a zirconium-based / hafnium-based metal-organic framework material with two sizes of pore cages, tetrahedral and octahedral. The overall framework structure exhibits excellent acid, alkali and water stability, effectively solving the problem of poor stability in the current development of MOF materials, and has the potential for industrial application.

[0018] (2) This invention provides a hydroxyl functionalization strategy. By modifying BDC ligands with hydrophilic hydroxyl sites, on the one hand, the introduced hydroxyl sites reduce the pore size to a certain extent, thereby enhancing the pore confinement effect of the pore structure on water molecules. On the other hand, the hydroxyl sites can serve as adsorption sites for water molecules, effectively capturing water molecules through hydrogen bonding interactions. The enhanced pore confinement effect combined with the high density of hydrophilic hydroxyl sites in the pores results in the hydroxylated microporous crystal material provided by this invention exhibiting excellent hydrophilicity and achieving high low-pressure water adsorption capacity under extremely low air humidity. Guided by the hydroxyl functionalization strategy, the synthesized zirconium-based / hafnium-based microporous metal-organic framework materials achieved high hydrophilicity and low-pressure water adsorption capacity. The highest water adsorption capacity of this series of materials at 298K and 15% relative humidity is 280 cm³. 3 g -1 It exhibits good adsorption capacity for trace water vapor.

[0019] The hydroxylated zirconium-based / hafnium-based microporous metal-organic framework material designed and synthesized in this invention exhibits excellent acid, alkali, and water stability and high low-pressure water adsorption capacity, successfully overcoming the problems of poor stability and low low-pressure water adsorption capacity of existing MOFs. This provides a new perspective for the adsorption-based air water collection of metal-organic framework materials in extremely arid regions and greatly promotes the practical application of metal-organic framework materials in this field. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the organic ligands involved in the present invention.

[0021] Figure 2 The image shows the PXRD pattern of the material in Example 1.

[0022] Figure 3 The image shows the 77K nitrogen isotherm full adsorption curve of the material in Example 1.

[0023] Figure 4 The image shows the isothermal water adsorption curve of the material in Example 1.

[0024] Figure 5 This is a schematic diagram of the crystal structure of the material in Example 2.

[0025] Figure 6 The image shows the PXRD pattern of the material in Example 2.

[0026] Figure 7 The image shows the isothermal water adsorption curve of the material in Example 2. Detailed Implementation

[0027] The following examples will further illustrate the content of the present invention. However, 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 effort are still within the scope of protection of the present invention.

[0028] Example 1

[0029] 1 mmol ZrOCl2·8H2O and 1 mmol BDC-(OH)2 were dissolved in 10 mL N,N-dimethylformamide and 4 mL formic acid, and the mixture was sonicated for 30 minutes until a homogeneous turbid solution was obtained. The reaction vessel was then placed in an oven at 120 °C and reacted for 24 h. The resulting solid was washed with N,N-dimethylformamide and ethanol, and dried in air to obtain the microporous metal-organic framework material Zr-BDC-(OH)2.

[0030] The organic ligands used in Zr-BDC-(OH)2 and other similar organic ligands used in this invention are described in [reference needed]. Figure 1 .

[0031] PXRD characterization data can be found in... Figure 2 ,Depend on Figure 2 It can be seen that the material has good crystallinity and phase purity.

[0032] To test the specific surface area of ​​Zr-BDC-(OH)2, a nitrogen isotherm adsorption test was performed at 77 K. The test results are shown below. Figure 3The BET specific surface area of ​​Zr-BDC-(OH)2 is 1065 m². 2 g -1 .

[0033] To test the water adsorption performance of Zr-BDC-(OH)2, isothermal water adsorption curves were determined. 30 mg of the adsorbent, after complete solvent exchange and activation, was used to determine the isothermal water adsorption curve at an adsorption temperature of 25 °C. The isothermal water adsorption curves are shown below. Figure 4 As shown in the figure, Zr-BDC-(OH)2 exhibits good hydrophilicity, with a sharp increase in adsorption occurring before 20% RH (relative humidity). At 15% RH, the adsorption can reach 280 cm⁻¹. 3 g -1 It has a good water adsorption capacity.

[0034] Example 2

[0035] 1.2 mmol ZrCl4 and 1.5 mmol BDC-OH were dissolved in 15 mL N,N-dimethylformamide and 1 mL hydrochloric acid, and the mixture was sonicated for 30 minutes until a homogeneous turbid solution was obtained. The reaction vessel was then placed in an oven at 80 °C and reacted for 24 h. The resulting solid was washed with N,N-dimethylformamide and ethanol and dried in air to obtain the microporous metal-organic framework material Zr-BDC-OH.

[0036] A schematic diagram of the microcrystalline structure of Zr-BDC-OH is shown below. Figure 5 As can be seen from the figure, the three-dimensional crystal structure of this material is densely covered with hydrophilic -OH functional groups (circled in the figure).

[0037] The PXRD characterization data of Zr-BDC-OH are shown in [reference needed]. Figure 6 The good crystallinity of Zr-BDC-OH can be seen from the figure.

[0038] To test the water adsorption performance of Zr-BDC-OH, isothermal water adsorption curves were determined. 30 mg of the adsorbent, after complete solvent exchange and activation, was used to determine the isothermal water adsorption curve at an adsorption temperature of 25 °C. The isothermal water adsorption curves are shown below. Figure 7 As shown in the figure, Zr-BDC-OH also exhibits good hydrophilicity.

[0039] It can be seen that the microporous crystal material prepared by this invention has two sizes of pore cages: tetrahedral and octahedral, with diameters of [missing information]. tetrahedral perforated cage and diameter The octahedral porous cage, with the introduction of hydroxyl sites into its structure, reduces the cage size to a certain extent. This enhances the pore confinement effect of the pore structure on water molecules, while the hydroxyl sites also serve as adsorption sites for water molecules, effectively capturing them through hydrogen bonding. The enhanced pore confinement effect, combined with the high density of hydrophilic hydroxyl sites in the pores, results in the hydroxylated microporous crystal material provided by this invention exhibiting excellent hydrophilicity. Furthermore, this material has a larger pore volume than zeolite, achieving high low-pressure water adsorption capacity even at extremely low air humidity. In addition, the material exhibits excellent acid, alkali, and water stability, which is beneficial for its widespread application in the field of trace water capture.

Claims

1. A method for preparing a hydroxylated microporous crystalline material with ultra-low humidity water adsorption properties, characterized in that, 1 mmol ZrOCl2·8H2O and 1 mmol BDC-(OH)2 were dissolved in 10 mL N,N-dimethylformamide and 4 mL formic acid. The mixture was sonicated for 30 minutes to obtain a homogeneous turbid liquid. The solution was then placed in an oven at 120 °C and reacted for 24 h. The resulting solid was washed with N,N-dimethylformamide and ethanol and dried in air to obtain the microporous metal-organic framework material Zr-BDC-(OH)2, which is the hydroxylated microporous crystal material with ultra-low humidity water adsorption performance.

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