A stable pyrazole-based metal-organic framework material, a preparation method thereof and application thereof in PFAS degradation

Abstract

The application discloses a kind of stable pyrazole-based metal organic framework materials and preparation method and application in PFAS degradation thereof.The preparation method of the application is first with 1,2,4,5-tetrabromobenzene and 4-boronic acid pinacol ester-1-tetrahydropyran-pyrazole as raw material under specific and suitable conditions Synthesis four connection pyrazolyl ligand H4TPB, then with Zn metal under specific and suitable conditions Preparation of stable pyrazole-based metal organic framework material Zn-TPB-MOF.The material structure is novel, excellent in property, with higher stability, simultaneously with excellent PFAS degradation performance.In addition, the synthesis and preparation method of the application is simple, and the cost is lower.

Description

Technical Field

[0001] This invention belongs to the field of metal-organic framework materials, specifically relating to a stable pyrazole-based metal-organic framework material, its preparation method, and its application in PFAS degradation. Background Technology

[0002] Perfluorinated and polyfluoroalkyl substances (PFAS) persist in the environment due to their extremely high carbon-fluorine bond energy (approximately 485 kJ / mol), exhibiting bioaccumulation and toxicity, and are closely associated with various health risks. Efficiently removing and degrading PFAS in water has become a key challenge in the environmental field. Existing treatment technologies each have their limitations: physical adsorption (such as activated carbon) only transfers pollutants without achieving true degradation; advanced oxidation requires harsh conditions (high temperature, high pressure, or strong oxidants), resulting in high energy consumption and the potential for toxic byproducts; membrane separation is limited by membrane fouling and high costs. A single technology cannot simultaneously achieve efficient enrichment and mineralization of PFAS.

[0003] Metal-organic frameworks (MOFs) hold great promise for adsorption and catalysis due to their high specific surface area and tunable pore structure. However, traditional carboxylic acid-based MOFs (such as MIL-101 and UiO-66) typically exhibit poor stability in aqueous solutions, particularly under alkaline conditions, as their metal-carboxylic acid coordination bonds are prone to hydrolysis and breakage. Furthermore, most MOFs show low selectivity for PFAS adsorption and lack catalytic degradation activity, hindering in-situ integrated adsorption-degradation treatment. Pyrazol-based ligands, due to the strong coordination ability of nitrogen atoms, construct pyrazol-based metal-organic frameworks (Pz-MOFs) with excellent stability. However, the high stability of Pz-MOFs often results in low crystallinity, posing a significant challenge for in-depth structural analysis requiring high-quality single crystals. Therefore, achieving a comprehensive solution for PFAS degradation and obtaining stable single-crystal Pz-MOFs is challenging. Moreover, systematic research on the use of Pz-MOFs for PFAS removal is still in its early stages, with few reports on highly efficient catalytic degradation performance. Perfluorooctanoic acid (PFOA) is the most typical and widely studied representative compound in the PFAS family. Previous literature has reported a form that, under heating conditions (120°C), exhibits... o C) PFOA is efficiently degraded in a mixed solution of alkaline dimethyl sulfoxide (DMSO) and water (Trang, Li et al. 2022). Therefore, it is necessary to develop a novel pyrazolium-based metal-organic framework with high alkalinity and catalytic degradation activity for PFAS, and to realize its mineralization technology for low-temperature degradation of PFAS in complex aquatic environments. This has significant scientific and application value. Summary of the Invention

[0004] This invention provides a stable pyrazole-based metal-organic framework material, its preparation method, and its application in PFAS degradation. This metal-organic framework material has a novel structure, excellent properties, high stability, and efficient PFAS degradation performance.

[0005] The specific technical solution is as follows: A stable pyrazole-based metal-organic framework material, Zn-TPB-MOF, is formed by the coordination linking of an organic ligand (H4TPB) with Zn.

[0006] The organic ligand has the following chemical structure: .

[0007] The method for preparing the organic ligand includes the following: (1) 1,2,4,5-Tetrabromobenzene, 4-boronic acid pinacol ester-1-tetrahydropyran-pyrazole, Pd SPhos Gen III, K3PO4, 1,4-dioxane and H2O were added to a reaction vessel, a condenser was connected, and the mixture was degassed by bubbling nitrogen. The reaction was stirred at 95-105 °C for 1-3 days. After cooling to room temperature, the solvent was removed under reduced pressure, and the crude solid was purified by column chromatography to obtain a white solid, namely compound 1:

[0008] (2) Dissolve compound 1 in an ethanol solution, add 11-13 mol / L concentrated hydrochloric acid solution, stir the mixture overnight at room temperature, and filter to obtain a solid, i.e., the organic ligand:

[0009] In step (1): the molar ratio of 1,2,4,5-tetrabromobenzene and 4-boronic acid pinacol ester-1-tetrahydropyran-pyrazole is 1:6; In step (1), the amount of Pd SPhos Gen III added is 5% to 10% of the amount of 1,2,4,5-tetrabromobenzene; In step (1), the volume ratio of the solvent dioxane to water is 4:1; In step (1), the eluent used in column chromatography is dichloromethane and methanol in a volume ratio of 1:40. The preparation method of the stable pyrazole-based metal-organic framework material as described above includes the following steps: The organic ligand and zinc nitrate hexahydrate were added to a mixed solution of N,N-dimethylformamide, ammonia and trifluoroacetic acid for a solvothermal reaction to obtain the stable pyrazole-based metal-organic framework material Zn-TPB-MOF.

[0010] The mass ratio of zinc nitrate hexahydrate to the organic ligand is not less than 2:1; The volume ratio of N,N-dimethylformamide, ammonia, and trifluoroacetic acid in the mixed solution is 80:10:3, and the ammonia is ammonia with a mass fraction of 25-28%. The ratio of the organic ligand to the N,N-dimethylformamide is 2 mg : 1 mL; The solvothermal reaction is carried out at a temperature of 110-130℃ for a duration of 48-72 h. After the solvothermal reaction is completed, the process includes a post-treatment step of solvent exchange with N,N-dimethylformamide, followed by washing and drying with acetone, to finally obtain a stable pyrazole-based metal-organic framework material. This invention also provides the application of the metal-organic framework material Zn-TPB-MOF in the degradation of PFAS, preferably in the degradation of PFOA. This invention first designs and synthesizes a novel tetra-linked pyrazole ligand, and then synthesizes the highly stable metal-organic framework material Zn-TPB-MOF under specific and suitable conditions. After activation, it is used to degrade PFOA under alkaline conditions. The activation treatment involves vacuum drying the metal-organic framework material at 110-130 °C and then... o The degradation rate reached 70% after 36 hours at C, and 90% after 1 hour. o The degradation rate reached 97% after 44 hours at C.

[0011] Compared with the prior art, the beneficial effects of this invention are as follows: 1. This invention creatively synthesizes a novel four-linked pyrazolyl organic ligand, H4TPB.

[0012] 2. The preparation method of the tetra-linked pyrazolyl organic ligand provided by the present invention is simple to operate, has a high yield, and is low in cost.

[0013] 3. The preparation method of the metal-organic framework material provided by the present invention is simple and suitable for large-scale synthesis.

[0014] 4. The metal-organic framework material provided by this invention has a high PFOA degradation rate, low degradation temperature and mild conditions, and has high practical application value.

[0015] 5. The metal-organic framework material provided by this invention has a stable structure and is convenient for long-term use. Attached Figure Description

[0016] Figure 1This is a schematic diagram of the a-side of the metal-organic framework material Zn-TPB formed by the coordination linking of the organic ligands of the present invention with Zn metal. The light blue tetrahedrons represent zinc ions, the gray atoms represent carbon atoms, and the blue atoms represent nitrogen atoms. Figure 2 This is a schematic diagram of the b-side of the metal-organic framework material Zn-TPB formed by the coordination linking of the organic ligands of the present invention with Zn metal. Figure 3 This is a comparison of the experimental and simulated PXRD patterns of Zn-TPB-MOF in the metal-organic framework material in Example 2. Figure 4 This is a graph showing the nitrogen adsorption-desorption curves of the metal-organic framework material in Example 2 at different activation temperatures; Figure 5 The image shows a single-crystal micrograph of the metal-organic framework material in Example 2. Figure 6 Quantitative analysis of PFOA degradation reaction in the control group without Zn-TPB-MOF metal-organic framework at 80℃. 19 F NMR spectrum; Figure 7 To quantify the degradation reaction of PFOA at 80℃ under the condition of adding metal-organic framework material Zn-TPB-MOF. 19 F NMR spectrum; Figure 8 To quantify the degradation reaction of PFOA at 90℃ under the condition of adding metal-organic framework material Zn-TPB-MOF. 19 F NMR spectrum. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0018] The organic ligand used in this invention is H4TPB, which is synthesized under specific and suitable conditions from 1,2,4,5-tetrabromobenzene and 4-borate pinacol ester-1-tetrahydropyran-pyrazole as raw materials. Stable pyrazole-based metal-organic framework materials can be prepared by combining this organic ligand with Zn metal under specific and suitable conditions, and can be applied to low-temperature PFOA degradation.

[0019] Example 1: Synthetic method of organic ligand H4TPB:

[0020] (1) 1,2,4,5-Tetrabromobenzene (0.786 g, 2.00 mmol), 4-boronic acid pinacol ester-1-tetrahydropyran-pyrazole (3.338 g, 12.00 mmol), Pd SPhos Gen III (78.0 mg, 0.1 mmol), K3PO4 (3.31 g, 24 mmol), 1,4-dioxane (80 mL), and H2O (20 mL) were added to a 250 mL round-bottom flask. A condenser was connected to the flask, and the mixture was degassed by bubbling nitrogen for 30 minutes. The reaction was carried out at 95°C. o Stirred at C for 2 days. After cooling to room temperature, remove the solvent under reduced pressure. Purify the crude solid by column chromatography using dichloromethane / methanol (1:40) as eluent to obtain a white solid, compound 1. (2) Compound 1 (0.9 g, 1.3 mmol) was dissolved in ethanol solution (30 mL). 12 mol / L concentrated hydrochloric acid solution (5 mL) was added, and the mixture was stirred overnight at room temperature. The organic ligand was obtained by filtration.

[0021] Example 2: Synthesis methods of metal-organic frameworks (MOFs): Zinc nitrate hexahydrate (16 mg) and the organic ligand (8 mg) were dissolved in a mixture of 4 mL DMF, 0.5 mL ammonia (28% by mass), and 0.15 mL trifluoroacetic acid, and the solution was placed in a 15 mL vial. The mixture was then sonicated for 3 minutes. The resulting mixture was sealed and heated to 120 °C and maintained for 48 hours. A white powder was obtained. The white powder was harvested and exchanged with DMF 6 times over three days, followed by washing with acetone 6 times over three days. After washing with acetone and drying, the metal-organic framework material Zn-TPB-MOF was obtained.

[0022] Example 3: Degradation experiment of Zn-TPB-MOF on PFOA at 80℃, perfluorooctanoic acid (PFOA) degradation experiment method:

[0023] Zn-TPB-MOF used in the PFOA degradation experiment was activated by vacuum drying at 120℃ for 24 h before use. PFOA (20 mg), Zn-TPB-MOF (10 mg), and sodium hydroxide (30 mg) were dissolved in a mixture of 4 mL deuterated dimethyl sulfoxide and 75 μL water, and the solution was placed in a 15 mL vial. The mixture was then sonicated for 10 minutes. The resulting mixture was sealed and heated to 80℃ and maintained for 36 h, during which 600 μL samples were taken periodically for analysis. 19F NMR) Test results are as follows Figure 7 As shown, after adding Zn-TPB-MOF, the degradation rate of PFOA reached 70% after 36 hours at 80℃.

[0024] Example 4: Degradation experiment of Zn-TPB-MOF on PFOA at 90℃: Except for adjusting the reaction temperature to 90℃ and maintaining it for 44 hours, the amounts of other reactants, solvent system, ultrasonic treatment method, and sealing method were all adjusted. 19 The F NMR testing methods are the same as in Example 3.

[0025] Test results are as follows Figure 8 As shown, after adding Zn-TPB-MOF, the degradation rate of PFOA reached 97% at 90℃ for 44 h. This result indicates that increasing the reaction temperature can further promote the degradation of PFOA.

[0026] Comparative example: PFOA degradation control experiment without Zn-TPB-MOF: PFOA (20 mg) and sodium hydroxide (30 mg) were added to a mixed solution of 4 mL deuterated dimethyl sulfoxide and 75 μL water, and then placed in a 15 mL vial. The mixture was then sonicated for 10 minutes. The resulting mixture was sealed and heated to 80 °C for 24 h, during which 600 μL samples were taken periodically for analysis. 19 F NMR.

[0027] Test results are as follows Figure 6 As shown, without the addition of Zn-TPB-MOF, the degradation rate of PFOA at 80℃ was 9.3%. This result indicates that it is difficult to achieve efficient degradation of PFOA under the same temperature conditions using only an alkaline reaction system composed of sodium hydroxide, deuterated dimethyl sulfoxide, and water.

[0028] The structural schematic diagram of the metal-organic framework material Zn-TPB-MOF prepared in Example 2 is shown below. Figure 1 , 2 As shown, Figure 3 The PXRD pattern of Zn-TPB-MOF shows that it has high crystallinity. Figure 4 The nitrogen adsorption curves of Zn-TPB-MOF at different activation temperatures are shown. Figure 5 It is a single crystal of Zn-TPB-MOF, and it can be seen that it has a regular shape.

[0029] Depend on Figure 6 and Figure 7It can be seen that in the comparative example without Zn-TPB-MOF, the degradation rate of PFOA after 24 hours at 80℃ was only 9.3%; while with the addition of Zn-TPB-MOF, the degradation rate of PFOA after 24 hours at 80℃ was 35%, and the degradation rate reached 70% after 36 hours at 80℃. Figure 8 The results show that at 90℃, the degradation rate of PFOA was 79% after 24 hours, 84% after 36 hours, and reached 97% after 44 hours. These results indicate that Zn-TPB-MOF can significantly promote the degradation of PFOA at lower temperatures and can serve as a metal-organic framework material to promote the low-temperature degradation of PFOA.

[0030] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A stable pyrazole-based metal-organic framework material, characterized in that, It is a Zn-TPB-MOF, which is formed by the coordination linking of the organic ligand H4TPB with Zn; The organic ligand H4TPB has the following chemical structure: 。 2. The method for preparing the stable pyrazole-based metal-organic framework material according to claim 1, characterized in that, Including the following steps: S1, the organic ligand and zinc nitrate hexahydrate are added to a mixed solution of N,N-dimethylformamide, ammonia and trifluoroacetic acid for a solvothermal reaction to obtain the stable pyrazole-based metal-organic framework material.

3. The preparation method according to claim 2, characterized in that, The method for preparing the organic ligand includes: (1) 1,2,4,5-Tetrabromobenzene, 4-boronic acid pinacol ester-1-tetrahydropyran-pyrazole, Pd SPhos Gen III, K3PO4, 1,4-dioxane and H2O were added to a reaction vessel, a condenser was connected, and the mixture was degassed by bubbling nitrogen. The reaction was stirred at 95-105℃ for 1-3 days. After cooling to room temperature, the solvent was removed under reduced pressure, and the crude solid was purified by column chromatography to obtain a white solid, namely compound 1: ； (2) Dissolve compound 1 in an ethanol solution, add 11-13 mol / L concentrated hydrochloric acid solution, stir the mixture overnight at room temperature, and filter to obtain a solid, i.e., the organic ligand: 。 4. The preparation method according to claim 3, characterized in that, In step (1): The molar ratio of 1,2,4,5-tetrabromobenzene and 4-boronic acid pinacol ester-1-tetrahydropyran-pyrazole is 1:6; The amount of Pd SPhos Gen III added is 5% to 10% of the molar amount of 1,2,4,5-tetrabromobenzene; The volume ratio of the solvent dioxane to water is 4:

1.

5. The preparation method according to claim 3, characterized in that, The eluent used in column chromatography was dichloromethane and methanol in a volume ratio of 1:

40.

6. The preparation method according to claim 2, characterized in that, In step S1: The mass ratio of zinc nitrate hexahydrate to the organic ligand is not less than 2:1; The volume ratio of N,N-dimethylformamide, ammonia, and trifluoroacetic acid in the mixed solution is 80:10:3, and the ammonia is ammonia with a mass fraction of 25-28%. The ratio of the organic ligand to the N,N-dimethylformamide is 2 mg : 1 mL.

7. The preparation method according to claim 2, characterized in that, The solvothermal reaction is carried out at a temperature of 110-130℃ for a time of 48-72 h.

8. The preparation method according to claim 2, characterized in that, After the solvothermal reaction is completed, the process includes a post-treatment step of solvent exchange with N,N-dimethylformamide, followed by washing and drying with acetone, ultimately yielding a stable pyrazole-based metal-organic framework material.

9. The application of the stable pyrazole-based metal-organic framework material according to claim 1 in PFAS degradation.

10. The application according to claim 9, characterized in that, The metal-organic framework material is first activated by vacuum drying at 110-130℃.

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