Zinc-based metal organic framework Zn-MOF material as well as preparation method and application thereof

Abstract

The invention discloses a zinc-based metal organic framework (Zn-MOF) material and a preparation method and application thereof, and belongs to the technical field of adsorption materials, the zinc-based metal organic framework (Zn-MOF) material has a three-dimensional structure, can be used for adsorbing iodine molecules without activation, and has high adsorption capacity for the iodine molecules in iodine steam; the material is still excellent in adsorption performance under certain humidity and different temperatures, excellent in cycle performance and firm in adsorption. The Zn-MOF material provided by the invention is simple in synthesis process and short in time consumption, and can be synthesized only in 4-5 days.

Description

Technical Field

[0001] The present invention belongs to the technical field of adsorption materials, and particularly relates to a zinc-based metal-organic framework Zn-MOF material, a preparation method thereof, and an application thereof. Background Art

[0002] With the growth of the global population and the rapid development of the world economy, the overall global demand for energy shows an upward trend. At the same time, the decline in the availability of fossil fuels has prompted the world to seek efficient, stable, and low-emission energy. Compared with traditional energy sources, nuclear energy has become an attractive alternative energy source. However, radioactive waste and spent fuel generated by nuclear power plants are a potential environmental problem. 129 I is a radioactive iodine isotope and is considered to be one of the main radionuclides causing environmental pollution, with a half-life of about 15.7 million years. Another iodine isotope 131 I has a shorter radioactive half-life of 8.02 days. However, long-term human exposure to radioactive iodine may lead to thyroid diseases, cancer, and other diseases. Therefore, more and more scholars are committed to studying effective methods for capturing radioactive iodine in exhaust gases. Using porous adsorbents to adsorb and retain iodine is a promising method, but traditional porous materials such as activated carbon and zeolite have low adsorption capacity and few active adsorption sites. Therefore, new porous adsorption materials need to be developed for iodine adsorption.

[0003] Metal-organic frameworks are porous materials that have developed rapidly and been studied extensively at present. They are formed by the coordination assembly of metal ions and organic ligands. By reasonably selecting metal ions and organic ligands, the structure and properties of porous materials can be regulated, thereby obtaining porous materials with specific properties. Due to their high specific surface area, adjustable structural characteristics, and excellent stability, they exhibit better adsorption performance than traditional porous materials. Among the MOF materials reported currently, most show good reversible adsorption performance for iodine molecules, but their adsorption capacity is low and the adsorption is not firm enough, and it is possible to release the adsorbed iodine, polluting the environment and being unfavorable for the preservation of adsorbed iodine molecules within a certain period of time. For example, "Functionalized Metal-Containing Azo Organic Frameworks for Efficient Iodine Capture with Double Bonds and Amide Groups" (DOI: 10.1021 / acs.cgd.4c00261) discloses the synthesis of a MOF material, namely [Zn3(ABTC), from Zn(NO3)2·6H2O and 4-pyridinecarboxaldehyde isonicotinoyl hydrazone, 2,2′,5,5′-azobenzenetetracarboxylic acid ligands 1.5(4-Hpich)(H2O)3]·10H2O, and its preparation method is as follows: Zn(NO3)2·6H2O (0.015 g, 0.05 mmol), Hpcih (4-pyridinecarboxaldehyde isonicotinoyl hydrazone) (0.076 g, 0.04 mmol) and H4ABTC (2,2′,5,5′-azobenzenetetracarboxylic acid) (0.0072 g, 0.02 mmol) are sealed in a 10 mL reagent bottle together with DMA (2 mL), H2O (1 mL) and five drops of HNO3 (1 mol L -1 ) mixture, heated at 80 °C for 96 hours. When the mixture cools to room temperature, yellow block crystals are obtained. The synthesis process is relatively complex, and its maximum capacity for adsorbing gaseous iodine at 75 °C is only 2.02 g / g. Its iodine adsorption capacity needs to be improved. In addition, different humidity and temperature conditions will affect the adsorption effect of the relevant adsorbent, seriously affecting the application of MOF materials in iodine adsorption. Summary of the Invention

[0004] Aiming at the problems of low iodine adsorption capacity, weak adsorption, and insufficient influence of humidity and temperature of existing porous MOF materials, the present invention provides a zinc-based metal-organic framework Zn-MOF material, its preparation method and application. This material has a high adsorption capacity and strong adsorption, and at the same time, the influence of temperature and humidity is small.

[0005] One of the technical solutions provided by the present invention:

[0006] A zinc-based metal-organic framework Zn-MOF material, whose chemical general formula is [Zn2(C 12 H 10 N2)3(NO2)3(H2O)2]H2O·NO3, where C 12 H 12 N2 is a ligand structure; the structural formula of the ligand structure is:

[0007] In each asymmetric unit of the main framework of its crystal structure, each Zn 2+ (1) / Zn 2+ (2) coordinates with three nitrite ions and three Zn 2+ (2) / Zn 2+ (2) to form a zigzag two-dimensional plane; the zigzag two-dimensional plane forms a three-dimensional porous framework under the connection of the ligand structure.

[0008] Preferably, the asymmetric unit includes two zinc atoms, three ligands, four nitrite ions and two coordinated water molecules; the three-dimensional porous framework also includes uncoordinated nitrate ions and water molecules.

[0009] Preferably, the crystal of the zinc-based metal-organic framework Zn-MOF material belongs to the orthorhombic system;

[0010] Its unit cell parameters are: α = 90°, β = 90°, γ = 90°.

[0011] The second technical solution provided by the present invention:

[0012] A preparation method of the above-mentioned zinc-based metal-organic framework Zn-MOF material, comprising the following steps: mixing 1,2-bis(4-pyridyl)ethylene and zinc nitrate hexahydrate; adding a mixed solution of N,N'-dimethylformamide and water to the obtained mixture to obtain a suspension, ultrasonically dispersing and then carrying out a heating reaction, cooling, filtering, and washing to obtain the zinc-based metal-organic framework Zn-MOF material.

[0013] Preferably, the molar ratio of the zinc nitrate hexahydrate to 1,2-bis(4-pyridyl)ethylene is 2:(3 - 5).

[0014] When the ratio of Zn(NO3)2·6H2O to 1,2-bis(4-pyridyl) is less than 2:5, the excessive ligand may occupy the coordination sites of Zn 2+ , resulting in multi-ligand binding or the formation of unstable intermediates (such as monodentate coordination), and the excess ligand forms amorphous polymers or competitive by-products (such as ligand aggregates), reducing the product purity; when the ratio is greater than 2:3, the coordination number of Zn 2+ is not fully satisfied, resulting in structural defects or low-dimensional networks (such as chain-like rather than framework structures).

[0015] Preferably, the volume ratio of the N,N'-dimethylformamide to water is 2:3.

[0016] Preferably, the time of ultrasonic dispersion is 3 - 5 min.

[0017] Preferably, the temperature of the heating reaction is 80 °C and the time is 4 days.

[0018] The third technical solution provided by the present invention:

[0019] An application of the above-mentioned zinc-based metal-organic framework Zn-MOF material in iodine adsorption.

[0020] Preferably, during the adsorption process, iodine molecules are in the vapor.

[0021] Compared with the prior art, the present invention has the following advantages and technical effects:

[0022] The present invention provides a zinc-based metal-organic framework Zn-MOF material. This material has a three-dimensional structure, can be used for the adsorption of iodine molecules without activation, and has a high adsorption capacity for iodine molecules in iodine vapor. Under certain humidity and different temperatures, the adsorption performance of this material is still excellent, and it also has excellent cycling performance and strong adsorption. The Zn-MOF material provided by the present invention has a simple synthesis process and short time consumption, and can be synthesized in only 4 to 5 days. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 Schematic diagram of the serrated two-dimensional plane of the zinc-based metal-organic framework Zn-MOF material prepared in Example 1;

[0025] Figure 2 Schematic diagram of the crystal structure of the zinc-based metal-organic framework Zn-MOF material prepared in Example 1;

[0026] Figure 3 Powder XRD and its simulation diagram of the zinc-based metal-organic framework Zn-MOF material prepared in Example 1;

[0027] Figure 4 Thermogravimetric diagram of the zinc-based metal-organic framework Zn-MOF material prepared in Example 1;

[0028] Figure 5 Relationship diagram of the adsorption amount and time of the zinc-based metal-organic framework Zn-MOF material prepared in Example 1 for adsorbing iodine molecules in iodine vapor at 75°C;

[0029] Figure 6 Pseudo-second-order kinetic fitting diagram of the zinc-based metal-organic framework Zn-MOF material prepared in Example 1 for adsorbing iodine molecules in iodine vapor at 75°C;

[0030] Figure 7 Relationship diagram of the adsorption amount and time of the zinc-based metal-organic framework Zn-MOF material prepared in Example 1 for adsorbing iodine molecules in iodine vapor at 75°C and 17% RH;

[0031] Figure 8 Adsorption amount of the zinc-based metal-organic framework Zn-MOF material prepared in Example 1 for adsorbing iodine molecules in iodine vapor at different temperatures for 48 h;

[0032] Figure 9Graph showing the relationship between the weight of iodine molecules adsorbed by the zinc-based metal-organic framework Zn-MOF material prepared in Example 1 and time within three days after adsorbing iodine molecules in iodine vapor at 75°C;

[0033] Figure 10 Adsorption cycling performance of the zinc-based metal-organic framework Zn-MOF material prepared in Example 1 for iodine vapor at 75°C. Detailed implementation manners

[0034] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation embodiments of the present invention.

[0035] It should be understood that the terms described in the present invention are only for describing particular implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the range.

[0036] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0037] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the present invention specification, which are obvious to those skilled in the art. Other implementation manners obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and embodiments are only exemplary.

[0038] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0039] The room temperature in the present invention refers to 25 ± 2°C.

[0040] Example 1 Preparation method of a zinc-based metal-organic framework Zn MOF material

[0041] At room temperature, Zn(NO3)2·6H2O (0.1 mmol, 29.75 mg) and 1,2-bis(4-pyridyl) (0.25 mmol, 36.44 mg) were mixed to obtain a mixture. 5 mL of a water / DMF mixture (volume ratio of water to DMF is 3:2) was added to the mixture, and it was sonicated for 5 min, sealed, and stored in an oven at 80 °C for 4 days. After taking it out, it was slowly cooled at room temperature, and the transparent white needle-like crystals were obtained by filtration. They were washed thoroughly three times with DMF and ethanol respectively, and then dried in a fume hood to obtain the zinc-based metal-organic framework Zn-MOF material.

[0042] Example 2

[0043] Same as Example 1, except that zinc nitrate hexahydrate and 1,2-bis(4-pyridyl) were replaced in an equimolar ratio of 2:3.

[0044] Structure characterization test

[0045] (1) Single crystal X-ray diffraction determination

[0046] From the Zn-MOF synthesized in Example 1, crystals suitable for single crystal determination in size were selected by microscope. X-ray diffraction data were collected at 193 K on a Bruker APEX-II CCD single crystal diffractometer (Ga-Kα, graphite monochromator). The crystal structure was solved by the direct method, and the structure analysis and refinement were both completed by the SHELXTL-2016 program package. All non-hydrogen atoms were refined anisotropically by full-matrix least squares with F2. The hydrogen atom coordinates of the organic ligand were obtained by theoretical hydrogenation. The solvent molecules in the pores were removed using the PLATON / SQUEEZE program. The main crystallographic data are shown in Table 1.

[0047] Table 1

[0048]

[0049] a R1 = Σ||F o |-|F c || / |F o |, b wR2 = [Σw(F o 2 -F c 2 ) 2 / Σw(F o 2 ) 2 1 / 2 ,where w = 1 / [σ 2 (F o 2 ​)+(aP)2+bP].P=(F o 2 +2F c 2 ) / 3;

[0050] *The refined result is based on the data obtained by squeeze processing.

[0051] Single crystal X-ray diffraction results show that the asymmetric unit of the zinc-based metal-organic framework Zn-MOF material prepared by the present invention contains two zinc atoms, three ligands, four nitrite ions, and two coordinated water molecules. In the structure, each Zn 2+ (1) / Zn 2+ (2) forms a zigzag two-dimensional plane by coordinating with three nitrite ions and three Zn 2+ (2) / Zn 2+ (2), and the above two-dimensional plane forms a three-dimensional porous framework under the connection of C 12 H 10 N2 ligands.

[0052] Figure 1 Schematic diagram of the zigzag two-dimensional plane of the zinc-based metal-organic framework Zn-MOF material prepared in Example 1.

[0053] Figure 2 Schematic diagram of the crystal structure of the zinc-based metal-organic framework Zn MOF material prepared in Example 1.

[0054] (2) Powder X-ray diffraction measurement

[0055] Figure 3 Powder XRD and its simulation diagram of the zinc-based metal-organic framework Zn-MOF material prepared in Example 1. By comparing with the simulated spectrum obtained by single crystal X-ray, it can be seen that the product synthesized by the present invention has a relatively high phase purity.

[0056] (3) Thermogravimetric analysis

[0057] Figure 4 Thermogravimetric diagram of the zinc-based metal-organic framework Zn-MOF material prepared in Example 1. It can be analyzed from Figure 4 that the weight loss observed between 70 °C and 140 °C can be attributed to the volatilization of DMF solvent molecules and free water molecules in the substance, resulting in an overall weight reduction of about 8% compared to the initial weight. At a high temperature of about 210 °C, the mass of this Zn-MOF material rapidly decreases until the decomposition process ends, proving that the zinc-based metal-organic framework Zn-MOF material prepared by the present invention has good thermal stability below 210 °C.

[0058] Performance test experiment 1: Adsorption experiment of iodine in iodine vapor

[0059] Two small glass containers (10 mL) containing 50 mg of the zinc-based metal-organic framework Zn-MOF materials prepared in Example 1 and Example 2 were respectively placed in two larger glass bottles (250 mL) containing an excess of iodine (500 mg), and it was ensured that there was no physical contact between the Zn-MOF materials and iodine. The entire device was placed in an incubator and maintained at 75 °C. The weight change of the iodine-loaded samples with time was recorded at different time intervals (0.5, 1, 2, 3, 4, 6, 9, 12, 24, 48, 72, 96, and 120 h), as Figure 5 shown, the maximum iodine adsorption capacity of the zinc-based metal-organic framework Zn-MOF material prepared in Example 1 was 4.49 g / g, and its adsorption kinetic data was as Figure 6 shown, with a good linear relationship, conforming to the pseudo-second-order kinetic equation (R 2 = 99). Under the same conditions, the maximum iodine adsorption capacity of the zinc-based metal-organic framework Zn-MOF material prepared in Example 2 was 4.21 g / g.

[0060] Performance Test Experiment 2 Adsorption experiment of iodine molecules in iodine vapor at 17% RH

[0061] Based on Performance Test Experiment 1, an adsorption experiment was conducted on the zinc-based metal-organic framework Zn-MOF material prepared in Example 1. An additional 50 mL of saturated calcium chloride (CaCl2) solution was added to the larger glass bottle (250 mL) to maintain a constant relative humidity (RH, 17%, 75 °C). The adsorption situation was as Figure 7 shown. In the presence of water vapor, the adsorption capacity still reached 3.71 g / g.

[0062] Performance Test Experiment 3 Adsorption experiment of iodine molecules in iodine vapor

[0063] Based on Performance Test Experiment 1, an adsorption experiment was conducted on the zinc-based metal-organic framework Zn-MOF material prepared in Example 1. The iodine adsorption at different temperatures (55, 65, 75, 85, and 95 °C) was compared after exposure to iodine vapor for 48 h. The adsorption situation was as Figure 8 shown. The iodine adsorption improved with a moderate increase in temperature. When the temperature was too high, the adsorption capacity decreased, but the performance was less affected, and it had a wide applicable temperature range.

[0064] Performance Test Experiment 4 Iodine retention rate experiment in three days after iodine adsorption

[0065] Based on Performance Test Experiment 1, an adsorption experiment was conducted on the zinc-based metal-organic framework Zn-MOF material prepared in Example 1. After iodine adsorption, it was kept at ambient temperature for three days, and the vial containing the sample was weighed every day to check the weight fluctuation. The retention situation was as Figure 9As shown, after 96 hours, only about 3.7% of iodine was found to be lost from the material.

[0066] Performance Test Experiment 5 Regenerability Evaluation Experiment

[0067] Based on Performance Test Experiment 1, an adsorption test was conducted on the zinc-based metal-organic framework Zn-MOF material prepared in Example 1. The vial containing the zinc-based metal-organic framework Zn-MOF material was placed in an oil bath at 100 °C and heated for 2 h to release iodine, and then Performance Test Experiment 1 was repeated. The above process was repeated five times to obtain five iodine adsorption cycles. As Figure 10 shown, even after five adsorption-desorption cycles, the zinc-based metal-organic framework Zn-MOF material still maintained 85% of its iodine adsorption capacity at 75 °C, indicating its high reusability.

[0068] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A zinc-based metal-organic framework Zn-MOF material, characterized in that, Its chemical general formula is [Zn2(C 12 H 10 N2)3(NO2)3(H2O)2]H2O·NO3, where C 12 H 12 N2 is the ligand structure; In each asymmetric unit of the main framework of its crystal structure, each Zn 2+ (1) / Zn 2+ (2) coordinates with three Zn 2+ (2) / Zn 2+ (2) through three nitrite ions to form a zigzag two-dimensional plane; the zigzag two-dimensional plane forms a three-dimensional porous framework under the connection of the ligand structure.

2. The zinc-based metal-organic framework Zn-MOF material according to claim 1, wherein The asymmetric unit includes two zinc atoms, three ligands, four nitrite ions and two coordinated water molecules; the three-dimensional porous framework also includes uncoordinated nitrate ions and water molecules.

3. The zinc-based metal-organic framework Zn-MOF material according to claim 1, wherein The crystal of the zinc-based metal-organic framework Zn-MOF material belongs to the orthorhombic system; Its unit cell parameters are as follows: α = 90°, β = 90°, γ = 90°.

4. A method for preparing the zinc-based metal-organic framework Zn-MOF material according to any one of claims 1-3, characterized in that, It includes the following steps: mixing 1,2-bis(4-pyridyl)ethylene and zinc nitrate hexahydrate; adding a mixed solution of N,N'-dimethylformamide and water to the obtained mixture to obtain a suspension, ultrasonically dispersing and then carrying out a heating reaction, cooling, filtering, washing to obtain the zinc-based metal-organic framework Zn-MOF material.

5. The preparation method according to claim 4, wherein The molar ratio of the zinc nitrate hexahydrate to 1,2-bis(4-pyridyl)ethylene is 2∶(3-5).

6. The preparation method according to claim 4, characterized in that, The volume ratio of the N,N'-dimethylformamide to water is 2∶3.

7. The preparation method according to claim 4, characterized in that, The time for ultrasonic dispersion is 3-5 min.

8. The preparation method according to claim 4, wherein, The temperature of the heating reaction is 80 °C and the time is 4 days.

9. Use of the zinc-based metal-organic framework Zn-MOF material according to any one of claims 1-3 in iodine adsorption.

10. The application according to claim 9, wherein During the adsorption process, iodine molecules are in the vapor.

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