Defective MOF (Metal Organic Framework) material with high water absorption capacity and adsorption rate as well as preparation method and application thereof

Abstract

The invention relates to the technical field of adsorption type materials for extracting water from air, in particular to a defective MOF material with high water absorption capacity and adsorption rate and a preparation method and application thereof.The preparation method of the defective MOF material comprises the following steps that organic carboxylic acid ligands, metal salt and a base catalyst are taken and added into deionized water, ultrasonic mixing is conducted to be uniform, standing reaction is conducted for 10-12 h at the temperature of 95-105 DEG C, and the defective MOF material is obtained. Centrifuging the obtained reaction liquid, collecting a solid product, and drying; and mixing the solid product with an alkali etching agent, standing for 16-20 hours, cleaning with deionized water, centrifuging, carrying out ultrasonic treatment, and drying to obtain the defective MOF material. The inorganic base is adopted as an etching agent, ligand deletion structure defects are formed in MOFs through induction, raw materials are cheap, and the synthesis method is simple. The obtained defective MOFs has a hierarchical pore structure, reduces the mass transfer resistance of water molecules, not only improves the adsorption kinetics of the water molecules, but also improves the adsorption capacity of the water molecules, and can realize rapid adsorption and capture of the water molecules in the air.

Description

Technical Field

[0001] The present invention relates to the technical field of adsorptive air water harvesting materials, and particularly to defective MOF materials with both high water absorption capacity and adsorption rate, and a preparation method and application thereof. Background Art

[0002] The adsorptive air water harvesting technology is not restricted by time and space and is universal globally, and can even be applied in arid environments. The application principle of the adsorptive air water harvesting technology is to enrich water vapor in the surrounding environment in the adsorbent, and then control the temperature and pressure to release the water vapor from the adsorbent, and finally the released water vapor is condensed and collected. Conventional nanoporous material adsorbents (such as silica gel, zeolite, and molecular sieve, etc.) applied in the field of air water harvesting, although their costs are low, these materials usually have problems of low water absorption capacity or high regeneration temperature, thus limiting their large-scale application.

[0003] Metal-Organic Frameworks (MOFs) are a class of crystalline porous materials with a periodic network structure formed by metal ions or metal clusters and organic ligands connected to each other through coordination bonds. MOFs have advantages such as regular pore structures, high specific surface areas, high porosities, and highly adjustable structures, making their water absorption capacity and regeneration temperature improved compared with traditional nanoporous materials, and are expected to become ideal adsorbent materials in the application of air water harvesting technology.

[0004] By changing the pore size, specific surface area, and functional groups, the hydrophilic density of the microenvironment inside the pores can be adjusted, thereby regulating the water adsorption performance of MOF materials. Motkuri et al. from the University of Washington in the United States explored the water adsorption behavior based on the Ni-MOF-74 series of materials using the isoreticular expansion strategy (J. Am. Chem. Soc., 2017, 139, 31, 10601-10604). Ni-MOF-74-TPP has the largest extended framework and exhibits 0.90 g g at 60% RH. -1High water adsorption capacity. Qian Guodong et al. from Zhejiang University comprehensively studied the effects of pore size, specific surface area, and pore hydrophilicity / hydrophobicity on water adsorption performance based on UiO series MOF materials (J. Mater. Chem. A, 2023, 11, 1246 - 1255). By changing the length of the organic linker or introducing hydrophilic / hydrophobic groups, 13 isoreticular MOFs were selectively synthesized. Introducing hydrophilic groups into UiO-66 can improve the water adsorption capacity and promote water adsorption kinetics. Yaghi et al. from the University of California, Berkeley, USA, combined experimental and theoretical simulation methods to synthesize MOF-303 by attaching a single vinyl group to the 3,5-pyrazoledicarboxylic acid linker, increasing its pore volume and still being able to collect water in arid environments (ACS Cent. Sci., 2023, 9, 3, 551–557).

[0005] Based on the above research status at home and abroad, the practical application of adsorption-based air water harvesting technology is still limited by the water adsorption capacity and adsorption / desorption kinetics of adsorbent materials. Although certain achievements have been obtained in this field of research, MOF adsorbent materials still face problems such as excellent single-sided performance in adsorption capacity or adsorption kinetics and large mass transfer resistance of water molecules. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide defective MOF materials with both high water absorption capacity and adsorption rate, as well as their preparation methods and applications, to at least solve the problems of excellent single-sided performance in adsorption capacity or adsorption kinetics and large mass transfer resistance of water molecules existing in existing MOF adsorbent materials for adsorption-based air water harvesting.

[0007] The present invention solves the above technical problems through the following technical means:

[0008] The first aspect of the embodiment of the present invention provides a preparation method of defective MOF materials with both high water absorption capacity and adsorption rate, including the following steps:

[0009] Take an organic carboxylic acid ligand, a metal salt, and a base catalyst and add them to deionized water, mix evenly by ultrasonic wave, and react statically at 95 - 105 °C for 10 - 12 h to obtain a reaction solution. Centrifuge to collect the solid product and dry it;

[0010] Mix the solid product and an alkali etching agent, let it stand for 16 - 20 h, then wash with deionized water, centrifuge, perform ultrasonic treatment, and dry to obtain defective MOF materials.

[0011] Combined with the first aspect, in some embodiments, the molar ratio of the organic carboxylic acid ligand, the metal salt, and the base catalyst is 2:1 - 4:2 - 6.

[0012] In combination with the first aspect, in some embodiments, the organic carboxylic acid ligand is selected from any one of fumaric acid, terephthalic acid, and trimesic acid.

[0013] In combination with the first aspect, in some embodiments, the metal salt is selected from any one of aluminum trichloride hexahydrate, aluminum nitrate nonahydrate, and zirconium tetrachloride.

[0014] In combination with the first aspect, in some embodiments, the base catalyst is sodium hydroxide or potassium hydroxide.

[0015] In combination with the first aspect, in some embodiments, the base etchant is an aqueous solution of an inorganic base with an inorganic base etchant concentration of 0.1 - 0.5 mol / L.

[0016] In combination with the first aspect, in some embodiments, the inorganic base etchant is selected from any one of sodium bicarbonate, sodium carbonate, and sodium acetate.

[0017] The second aspect of the embodiments of the present invention provides a defective MOF material with both high water absorption capacity and adsorption rate, which is prepared by the preparation method described in the first aspect.

[0018] The third aspect of the embodiments of the present invention provides the application of the defective MOF material described in the second aspect in an adsorptive air water harvesting material.

[0019] The present invention uses an inorganic base as an etchant to induce the formation of ligand - deficient structural defects inside MOFs. The raw materials are cheap and the synthesis method is simple. The defective MOFs material prepared by the preparation method of the present invention has a hierarchical pore structure, which reduces the mass transfer resistance of water molecules, not only improving the water molecule adsorption kinetics but also the water molecule adsorption capacity. Under the conditions of 25 °C and 30% relative humidity, within a specific adsorption time of 120 min, the water adsorption capacity and adsorption rate of the synthesized defective Al - Fum material are 1.05 and 1.52 times that of the original Al - Fum material respectively, demonstrating the application potential of defective MOF materials with high water adsorption capacity and high adsorption rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic flow chart of the preparation method of the defective MOF material in Examples 1 - 15;

[0021] Figure 2 is a characterization atlas of Al - Fum synthesized in Comparative Example 1. Among them, a is the X - ray diffraction pattern of Al - Fum synthesized in Comparative Example 1, b is the N2 adsorption - desorption isotherm curve of Al - Fum synthesized in Comparative Example 1, and c is the pore size distribution map of Al - Fum synthesized in Comparative Example 1;

[0022] Figure 3It is the atlas of defect MOFs prepared in Examples 1-5. Among them, a is the X-ray diffraction pattern of the defect MOFs prepared in Examples 1-5, b is the N2 adsorption-desorption isotherm curve of the defect MOFs prepared in Examples 1-5, c is the pore size distribution map of the defect MOFs prepared in Examples 1-5, and d is the thermogravimetric diagram of the defect MOFs prepared in Examples 1-5 and the Al-Fum product synthesized in Comparative Example 1;

[0023] Figure 4 It is the atlas of defect MOFs prepared in Examples 3, 8 and 13. Among them, a is the X-ray diffraction pattern of the defect MOFs prepared in Examples 3, 8, 13, b is the N2 adsorption-desorption isotherm curve of the defect MOFs prepared in Examples 3, 8, 13, c is the pore size distribution map of the defect MOFs prepared in Examples 3, 8, 13, and d is the thermogravimetric diagram of the defect MOFs prepared in Examples 3, 8, 13 and the Al-Fum product synthesized in Comparative Example 1;

[0024] Figure 5 It is the dynamic water adsorption-desorption curve of the defect MOFs prepared in Examples 1, 3 and 5 and Al-Fum synthesized in Comparative Example 1;

[0025] Figure 6 It is the dynamic water adsorption-desorption curve of the defect MOFs prepared in Examples 3, 8 and 13 and Al-Fum synthesized in Comparative Example 1;

[0026] Figure 7 It is the dynamic water adsorption-desorption curve of Al-Fum in Example 1;

[0027] Figure 8 It is the dynamic water adsorption curve of the defect MOFs prepared in Examples 1, 2, 3 and Al-Fum in Example 1 under the conditions of 298K and 30% RH;

[0028] Figure 9 It is the dynamic water adsorption curve of the defect MOFs prepared in Examples 3, 8, 13 and Al-Fum in Example 1 under the conditions of 298K and 30% RH. Detailed implementation manners

[0029] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the scope of protection of the present application.

[0030] In the embodiments of the present application, words such as "exemplary" or "for example" are used to represent examples, illustrations or explanations. Any embodiment or design solution described as "exemplary" or "for example" in the embodiments of the present application should not be construed as being more preferred or having more advantages than other embodiments or design solutions. Rather, the use of words such as "exemplary" or "for example" is intended to present relevant concepts in a specific manner.

[0031] Aiming at the problems existing in the MOF adsorbent material for adsorptive air water intake, such as excellent single - sided performance of adsorption capacity or adsorption kinetics and large mass transfer resistance of water molecules, the present invention provides a preparation method of defective MOF materials with mild conditions, green and simple, so as to improve the adsorption capacity and adsorption kinetics of the MOF adsorbent material. Please refer to Figure 1 The preparation method of the defective MOF material with both high water absorption capacity and adsorption rate of the present invention includes the following steps: taking an organic carboxylic acid ligand, a metal salt and an alkali catalyst, adding them into deionized water, mixing evenly by ultrasonic wave, standing and reacting at 95 - 105 °C for 10 - 12 h to obtain a reaction solution, centrifuging to collect the solid product, and drying; mixing the solid product and an alkali etching agent, standing for 16 - 20 h, washing with deionized water, centrifuging, ultrasonic treating, and drying to obtain the defective MOF material.

[0032] Among them, the molar ratio of the organic carboxylic acid ligand, the metal salt and the alkali catalyst is 2:1 - 4:2 - 6; the organic carboxylic acid ligand is selected from any one of fumaric acid, terephthalic acid and trimesic acid; the metal salt is selected from any one of aluminum trichloride hexahydrate, aluminum nitrate nonahydrate, zirconium tetrachloride; the alkali catalyst is sodium hydroxide or potassium hydroxide; the alkali etching agent is an inorganic alkali aqueous solution with an inorganic alkali etching agent concentration of 0.1 - 0.5 mol / L; the inorganic alkali etching agent is selected from any one of sodium bicarbonate, sodium carbonate, sodium acetate.

[0033] In order to better understand the above - mentioned technical solution, the above - mentioned technical solution will be described in detail below in conjunction with the specification drawings and specific embodiments.

[0034] Example 1

[0035] The preparation method of the defective MOF material in this example is as follows:

[0036] Weigh 3.45 mmol of fumaric acid (Fum) powder, 3.45 mmol of aluminum chloride hexahydrate, and 5.16 mmol of potassium hydroxide in a hydrothermal autoclave, and then add 60 mL of deionized water. Ultrasonically treat the mixture for 5 minutes, then let it stand and react in an oven at 100 °C for 12 hours to produce a white precipitate. After cooling to room temperature, centrifuge to collect the white powder, wash it 5 times with deionized water and ethanol respectively, and then dry it in an oven at 80 °C for 6 hours to obtain a white powder (denoted as Al-Fum). Add 100 mg of the obtained Al-Fum and 5 mL of a sodium carbonate aqueous solution with a concentration of 0.1 mol L -1 into a plastic centrifuge tube, and let it stand for 16 hours. Remove the supernatant, add deionized water to the obtained mixture, centrifuge at 9000 rpm for 2 minutes, then ultrasonically treat for 5 minutes, remove the supernatant, add deionized water and centrifuge again. Repeat the process of adding deionized water and centrifuging until the supernatant is removed 5 times. Finally, dry the sample in an oven at 80 °C for 6 hours to obtain a defective MOF material in the form of a white powder, denoted as D-Al-Fum-16h-0.1.

[0037] Example 2

[0038] The difference between this example and Example 1 is only that the concentration of the sodium carbonate aqueous solution in Example 1 is set to 0.2 mol L -1 , and the obtained product is denoted as D-Al-Fum-16h-0.2.

[0039] Example 3

[0040] The difference between this example and Example 1 is only that the concentration of the sodium carbonate aqueous solution in Example 1 is set to 0.3 mol L -1 , and the obtained product is denoted as D-Al-Fum-16h-0.3.

[0041] Example 4

[0042] The difference between this example and Example 1 is only that the concentration of the sodium carbonate aqueous solution in Example 1 is set to 0.4 mol L -1 , and the obtained product is denoted as D-Al-Fum-16h-0.4.

[0043] Example 5

[0044] The difference between this example and Example 1 is only that the concentration of the sodium carbonate aqueous solution in Example 1 is set to 0.5 mol L -1 , and the obtained product is denoted as D-Al-Fum-16h-0.5.

[0045] Example 6

[0046] The difference between this example and Example 1 is only that the standing time after mixing the alkali etching agent in Example 1 is set to 18 hours. The obtained product is denoted as D-Al-Fum-18h-0.1.

[0047] Example 7

[0048] The difference between this example and Example 1 is only that the concentration of the sodium carbonate aqueous solution in Example 1 is set to 0.2 mol / L -1 , and the standing time after mixing the alkali etching agent is set to 18 hours. The obtained product is denoted as D-Al-Fum-18h-0.2.

[0049] Example 8

[0050] The difference between this example and Example 1 is only that the concentration of the sodium carbonate aqueous solution in Example 1 is set to 0.3 mol / L -1 , and the standing time after mixing the alkali etching agent is set to 18 hours. The obtained product is denoted as D-Al-Fum-18h-0.3.

[0051] Example 9

[0052] The difference between this example and Example 1 is only that the concentration of the sodium carbonate aqueous solution in Example 1 is set to 0.4 mol / L -1 , and the standing time after mixing the alkali etching agent is set to 18 hours. The obtained product is denoted as D-Al-Fum-18h-0.4.

[0053] Example 10

[0054] The difference between this example and Example 1 is only that the concentration of the sodium carbonate aqueous solution in Example 1 is set to 0.5 mol / L -1 , and the standing time after mixing the alkali etching agent is set to 18 hours. The obtained product is denoted as D-Al-Fum-18h-0.5.

[0055] Example 11

[0056] The difference between this example and Example 1 is only that the standing time after mixing the alkali etching agent in Example 1 is set to 20 hours. The obtained product is denoted as D-Al-Fum-20h-0.1.

[0057] Example 12

[0058] The difference between this example and Example 1 is only that the concentration of the sodium carbonate aqueous solution in Example 1 is set to 0.2 mol / L -1 , and the standing time after mixing the alkali etching agent is set to 20 hours. The obtained product is denoted as D-Al-Fum-20h-0.2.

[0059] Example 13

[0060] The difference between this example and Example 1 is only that the concentration of the sodium carbonate aqueous solution in Example 1 is set to 0.3 mol / L -1 , and the standing time after mixing the alkali etching agent is set to 20 hours. The obtained product is denoted as D-Al-Fum-20h-0.3.

[0061] Example 14

[0062] The difference between this example and Example 1 is only that the concentration of the sodium carbonate aqueous solution in Example 1 is set to 0.4 mol / L -1 , and the standing time after mixing the alkali etching agent is set to 20 hours. The obtained product is denoted as D-Al-Fum-20h-0.4.

[0063] Example 15

[0064] The difference between this example and Example 1 is only that the concentration of the sodium carbonate aqueous solution in Example 1 is set to 0.5 mol / L -1 , and the standing time after mixing the alkali etching agent is set to 20 hours. The obtained product is denoted as D-Al-Fum-20h-0.5.

[0065] Example 16

[0066] The preparation method of the defective MOF material in this example is as follows:

[0067] Weigh 2 mmol of terephthalic acid, 4 mmol of zirconium tetrachloride, and 6 mmol of sodium hydroxide in a hydrothermal autoclave, and then add 60 mL of deionized water. Ultrasonically treat the mixture for 10 minutes, and then let it stand and react in an oven at 95 °C for 11 hours to produce a precipitate. After cooling to room temperature, centrifuge to collect the precipitate, wash it 5 times with deionized water and ethanol respectively, and then dry it in an oven at 85 °C for 6 hours to obtain a solid intermediate. Add 100 mg of the solid intermediate and 5 mL of a sodium bicarbonate aqueous solution with a concentration of 0.1 mol / L -1 to a plastic centrifuge tube, and let it stand for 16 hours. Remove the supernatant, add deionized water to the obtained mixture, centrifuge at 9000 rpm for 2 minutes, then ultrasonically treat for 5 minutes, remove the supernatant, add deionized water and centrifuge again, and repeat the process of adding deionized water and centrifuging until the supernatant is removed 5 times. Finally, dry the sample in an oven at 80 °C for 6 hours to obtain the defective MOF material.

[0068] Example 17

[0069] The preparation method of the defective MOF material in this example is as follows:

[0070] Weigh 2 mmol of terephthalic acid, 1 mmol of zirconium tetrachloride and 2 mmol of sodium hydroxide in a hydrothermal reactor, and then add 60 mL of deionized water. Ultrasonically treat the mixture for 8 minutes, and then leave it to react in an oven at 105 °C for 10 hours to produce a precipitate. After cooling to room temperature, centrifuge to collect the precipitate, wash it 5 times with deionized water and ethanol respectively, and then dry it in an oven at 85 °C for 6 hours to obtain a solid intermediate. Add 100 mg of the solid intermediate and 5 mL of an aqueous sodium acetate solution with a concentration of 0.2 molL -1 in a plastic centrifuge tube, and leave it standing for 16 hours. Remove the supernatant, add deionized water to the obtained mixture, centrifuge at 9000 rpm for 2 minutes, then ultrasonically treat for 5 minutes, remove the supernatant, add deionized water and centrifuge again. Repeat the process of adding deionized water and centrifuging until the supernatant is removed 5 times. Finally, dry the sample in an oven at 80 °C for 6 hours to obtain a defective MOF material.

[0071] Comparative Example 1

[0072] Synthesize Al-Fum:

[0073] Weigh 3.45 mmol of fumaric acid (Fum) powder, 3.45 mmol of aluminum chloride hexahydrate and 5.16 mmol of potassium hydroxide in a 100 mL hydrothermal reactor, and then add 60 mL of deionized water. Ultrasonically treat the mixture for 5 minutes, and then leave it to react in an oven at 100 °C for 12 hours to produce a white precipitate. After cooling to room temperature, centrifuge to collect the white powder, wash it 5 times with deionized water and ethanol respectively. Then, dry the obtained white powder sample in an oven at 80 °C for 6 hours to obtain white powder Al-Fum.

[0074] Use the final products prepared in Examples 1-15 and Comparative Example 1 as samples for the following performance tests:

[0075] (1) By analyzing the X-ray diffraction pattern, test the phase, unit cell parameters, interplanar spacing, grain size and other information of the above products. (2) Perform N2 adsorption and desorption tests at 77 K. By analyzing the N2 adsorption and desorption isotherm curve, information such as the BET specific surface area, pore size and pore volume of the material can be obtained. (3) The thermogravimetric analysis curve was recorded on a Netzsch STA449F5 instrument, and the test atmosphere and flow rate are as follows: the nitrogen flow rate is 50 mL min -1 , and the oxygen flow rate is 20 mL min -1 ; the test heating rate is 5 °C / min -1; The test temperature range is: 30 - 800 °C. Before the test, the synthesized MOFs were activated in a vacuum oven at 120 °C for 12 h. Through thermogravimetric analysis, information such as the number of defective ligands of the above products was tested. (4) The dynamic water vapor adsorption and desorption isotherm curves were obtained by testing with a BETTER intelligent gravimetric analyzer (model: BSD-DVS) at 25 °C and 30% relative humidity. Before the test, the synthesized MOFs were activated in a vacuum oven at 120 °C for 12 h. By analyzing the water vapor adsorption and desorption isotherm curves, information such as the adsorption rate and adsorption capacity of the material for water can be obtained. Please refer to the above test results Figure 2-6 。

[0076] The specific surface area, average pore diameter, and pore volume information of the defective MOFs materials prepared in Examples 1 - 15 are shown in Table 1.

[0077] Table 1

[0078]

[0079]

[0080] Figure 2 is the characterization atlas of Al-Fum synthesized in Comparative Example 1. Among them, a is the X-ray diffraction pattern of Al-Fum synthesized in Comparative Example 1, b is the N2 adsorption-desorption isotherm curve of Al-Fum synthesized in Comparative Example 1, and c is the pore size distribution map of Al-Fum synthesized in Comparative Example 1. Figure 2 The data shows that the XRD results obtained from the experimental tests of the initially synthesized Al-Fum of the present invention are basically consistent with the simulation results, and the crystallinity is good. It can be known from the N2 adsorption-desorption test that the specific surface area of the initial Al-Fum is 1198 m 2 g -1 , and the pore diameter is 0.9 nm.

[0081] By characterizing and testing the defective Al-Fum synthesized in Examples 1 - 5, the influence of the etching agent concentration on the degree of defect was explored. Figure 3 is the characterization atlas of the defective MOFs prepared in Examples 1 - 5. Among them, a is the X-ray diffraction pattern of the defective MOFs prepared in Examples 1 - 5, b is the N2 adsorption-desorption isotherm curve of the defective MOFs prepared in Examples 1 - 5, c is the pore size distribution map of the defective MOFs prepared in Examples 1 - 5, and d is the thermogravimetric diagram of the defective MOFs prepared in Examples 1 - 5 and the Al-Fum product synthesized in Comparative Example 1. As Figure 3As shown, when the etching time (16 h) is kept constant, the degree of defects in Al-Fum increases with the increase in the concentration of the alkaline etchant (from 0.1 to 0.5 mol / L). Specifically, with the increase in the etchant concentration, the crystallinity of defective Al-Fum gradually weakens, but the structural integrity of the original Al-Fum is still retained. The specific surface area of defective Al-Fum also gradually decreases with the increase in the etchant concentration, from the initial 1198 m 2 g -1 and finally becomes 597 m 2 g -1 . The pore size distribution analysis of defective Al-Fum shows that with the increase in the etchant concentration, the proportion of micropores in the sample decreases, and mesopores appear in the range of 5 - 15 nm. The thermogravimetric curve shows that defective Al-Fum exhibits two different mass loss stages between 150 - 300 °C and 350 - 500 °C, corresponding to the weight loss of hydroxyl groups of defective Al clusters and the decomposition of the framework structure respectively. The weight loss degree of defective Al-Fum also increases with the increase in the etchant concentration, which also indicates the increase in the degree of defects. In summary, the concentration of the alkaline etchant is the key factor affecting the degree of defects in MOF materials.

[0082] The defective Al-Fum synthesized in Examples 3, 8, and 13 was characterized and tested to explore the effect of etching time on the degree of defects. Figure 4 Figure 214 shows the characterization atlas of defective MOFs prepared in Examples 3, 8, and 13. Among them, a is the X-ray diffraction pattern of defective MOFs prepared in Examples 3, 8, and 13, b is the N2 adsorption-desorption isotherm curve of defective MOFs prepared in Examples 3, 8, and 13, c is the pore size distribution map of defective MOFs prepared in Examples 3, 8, and 13, and d is the thermogravimetric diagram of defective MOFs prepared in Examples 3, 8, and 13 and the Al-Fum product synthesized in Comparative Example 1. As Figure 4 shown, when the etchant concentration (0.3 mol / L -1 ) is kept constant, the degree of defects in Al-Fum increases with the increase in the etching time (from 16 to 20 h). Specifically, with the increase in the etching time, the crystallinity of defective Al-Fum gradually weakens, but the structural integrity of the original Al-Fum is also retained. The specific surface area of defective Al-Fum also gradually decreases with the increase in the etching time, from the initial 1198 m 2 g -1 and finally becomes 599 m 2 g -1The pore size distribution analysis of defective Al-Fum showed that with the increase of etching time, the proportion of micropores in the sample decreased, and mesopores appeared in the range of 5-15 nm. The thermogravimetric curve indicated that the weight loss degree of defective Al-Fum also increased with the increase of etching time, which also demonstrated the increase of defect degree. In summary, the etching time is another key factor affecting the defect degree of MOF materials.

[0083] The dynamic water adsorption-desorption tests were carried out on the defective MOFs of Examples 1, 3 and 5 and Comparative Example 1 to explore the influence of etching agent concentration on water adsorption performance. As Figure 5 shown, at a relatively low relative humidity (P / P0 = 0.3), defective Al-Fum exhibited strong water absorption performance (adsorption rate and adsorption capacity), and its dynamic water adsorption performance showed a trend of first increasing and then decreasing with the increase of etching agent concentration. The adsorption capacity of the sample with the best water absorption performance reached 300.8 mg / g, which was 1.05 times that of Comparative Example 1.

[0084] The dynamic water adsorption-desorption tests were carried out on the defective MOFs of Examples 3, 8 and 13 and Comparative Example 1 to explore the influence of etching time on water adsorption performance. As Figure 6 shown, at a relatively low relative humidity (P / P0 = 0.3), defective Al-Fum exhibited strong water absorption performance (adsorption rate and adsorption capacity), and its dynamic water adsorption performance also showed a trend of first increasing and then decreasing with the increase of etching time, which was similar to the Figure 5 results shown. The adsorption capacity of the sample with the best water absorption performance reached 313.8 mg / g, which was 1.1 times that of Comparative Example 1, demonstrating the application potential of the defective MOFs of the present invention in the field of air water intake.

[0085] The above two exploration experiments showed that the defect degree is a key index affecting water adsorption performance. MOFs with an appropriate defect degree have a hierarchical pore structure, which reduces the mass transfer resistance of water molecules, not only improving the water molecule adsorption kinetics but also the adsorption capacity of water molecules. However, with the increase of the defect degree, due to the collapse of some micropore channels in the MOF structure, the water absorption performance will be affected, and the rapid adsorption and capture of water molecules in the air can be realized. Therefore, the defective MOFs prepared in the present invention can be applied to adsorption air water intake.

[0086] Figure 7 is the dynamic water adsorption-desorption curve of Al-Fum in Example 1, which was obtained by testing Al-Fum in Example 1 as a sample with a BETTER intelligent gravimetric analyzer (model: BSD-DVS) at 25 °C and 30% relative humidity. Figure 8Dynamic water adsorption curves of the defective MOFs prepared in Examples 1, 2, and 3 and Al-Fum in Example 1 under the conditions of 298K and 30% RH. Figure 9 Dynamic water adsorption curves of the defective MOFs prepared in Examples 3, 8, and 13 and Al-Fum in Example 1 under the conditions of 298K and 30% RH. In 120 min, the water adsorption capacity of D-Al-Fum-18h-0.5 was divided by the time to represent the adsorption rate of D-Al-Fum-18h-0.5. Similarly, the water adsorption capacity of Al-Fum was divided by the time to represent the adsorption rate of Al-Fum. Thus, the water adsorption capacity and adsorption rate of the synthesized defective Al-Fum materials within a specific adsorption time of 120 min were 1.05 and 1.52 times that of the original Al-Fum material, respectively, demonstrating the application potential of defective MOF materials with high water adsorption capacity and high adsorption rate.

[0087] The present invention has developed a means for synthesizing defective MOF materials with mild conditions, greenness, and simplicity to improve the water adsorption capacity and adsorption kinetics of MOF adsorbent materials. The present invention induces the formation of ligand-deficient structural defects inside MOFs through a simple post-synthesis modification method. This synthesis scheme has wide applicability and can be extended to the synthesis of various types of defective MOFs, including Al-Fum, MOF-801, MOF-808, etc.

[0088] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention. The technologies, shapes, and structures not described in detail in the present invention are all well-known technologies.

Claims

1. A method for preparing a defective MOF material having both high water absorption capacity and adsorption rate, characterized in that: The following steps are involved: Add the organic carboxylic acid ligand, metal salt and alkali catalyst into deionized water, mix by ultrasonic, and react at 95-105° C. for 10-12 hours. Centrifuge the reaction solution to collect the solid product and dry it. The solid product and the alkaline etchant are mixed, left to stand for 16 to 20 hours, washed with deionized water, centrifuged, ultrasonically treated, and dried to obtain a defective MOF material.

2. The method for preparing the defective MOF material having both high water absorption capacity and adsorption rate according to claim 1, characterized in that: The molar ratio of the organic carboxylic acid ligand, the metal salt and the base catalyst is 2:1-4:2-6.

3. The method for preparing the defective MOF material having both high water absorption capacity and adsorption rate according to claim 1 or 2, characterized in that: The organic carboxylic acid ligand is selected from any one of fumaric acid, terephthalic acid and trimesic acid.

4. The method for preparing the defective MOF material having both high water absorption capacity and adsorption rate according to claim 1 or 2, characterized in that: The metal salt is selected from any one of aluminum trichloride hexahydrate, aluminum nitrate nonahydrate, and zirconium tetrachloride.

5. The method for preparing the defective MOF material having both high water absorption capacity and adsorption rate according to claim 1 or 2, characterized in that: The alkaline catalyst is sodium hydroxide or potassium hydroxide.

6. The method for preparing the defective MOF material having both high water absorption capacity and adsorption rate according to claim 1, characterized in that: The alkali etchant is an inorganic alkali aqueous solution with an inorganic alkali etchant concentration of 0.1 to 0.5 mol / L.

7. The method for preparing the defective MOF material having both high water absorption capacity and adsorption rate according to claim 6, characterized in that: The inorganic alkaline etchant is selected from any one of sodium bicarbonate, sodium carbonate and sodium acetate.

8. A defective MOF material having high water absorption capacity and adsorption rate, prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the defective MOF material according to claim 8 in an adsorption-type air water extraction material.

Images