Application of metal organic framework material MOF-818 in PFAS adsorption

Abstract

The invention relates to the technical field of fluorine-containing organic compound PFAS adsorption, in particular to application of a metal organic framework material MOF-818 in PFAS adsorption. MOF-818 is composed of two clusters of [M6 (mu3-O) 4 (mu3-OH) 4 (OH) 6 (mu-PyC) 6 (H2O) 6] and [Cu3 (mu3-O) (mu-PyC) 3 (H2O) 3] according to a molar ratio of 1: 2, M is Zr or Hf, PyC is 1H-pyrazole-4-formic acid, and each of the two clusters contains a plurality of coordination sites capable of further coordination. Efficient and rapid adsorption of PFAS is achieved through a large number of coordinatable sites and mesoporous structures in the material, the known highest saturated adsorption capacity is achieved, rapid adsorption kinetics is achieved, and saturated adsorption can be achieved within 5 minutes; and effective removal of the ultra-low concentration PFAS is realized. The material can be desorbed under an acidic condition after adsorbing PFAS, so that the material can obtain efficient adsorption capacity again, and the material has recyclability. In addition, the metal organic framework material has excellent structural stability under the conditions of strong base, strong acid, high temperature and the like, and has extremely high tolerance to a complex water body environment.

Description

Technical Field

[0001] This invention relates to the field of fluorine-containing organic compound adsorption technology, specifically to the application of a metal-organic framework material MOF-818 in PFAS adsorption. Background Technology

[0002] Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a class of synthetically produced fluorinated organic compounds widely used in industrial production and consumer products (such as fire-fighting foam, non-stick coatings, and waterproof textiles). Due to the extremely high chemical stability of the CF bonds in PFAS molecules, they are difficult to degrade naturally in the environment and are known as "permanent chemicals." Studies have shown that PFAS can accumulate in organisms through drinking water and the food chain, and are closely associated with health risks such as cancer, immune system suppression, and endocrine disruption. Currently, the U.S. Environmental Protection Agency (EPA) has set the recommended safe drinking water levels for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) at 0.004 ppt and 0.02 ppt, respectively, highlighting their toxic risks at extremely low concentrations.

[0003] Currently, the main technologies for removing PFAS from water bodies include adsorption, ion exchange, membrane separation, and advanced oxidation, but all of them have significant technical bottlenecks.

[0004] Activated carbon adsorption: Traditional activated carbon (AC) is widely used due to its large specific surface area and low cost. However, its adsorption efficiency for short-chain PFAS (such as PFBA and PFBS) is low (<30%), and its adsorption capacity is significantly affected by the competitive effect of natural organic matter (NOM) in water. In addition, activated carbon regeneration requires high-temperature treatment (>800℃), resulting in high energy consumption and the risk of secondary pollution.

[0005] Ion exchange resins: Anion exchange resins (such as IRA67) exhibit high selectivity for long-chain PFAS, but their synthesis cost is high (approximately $50-100 / kg), and their exchange capacity drops sharply in high-salinity or complex matrix water bodies. Experiments show that when the sulfate concentration in water exceeds 50 mg / L, the adsorption efficiency of the resin for PFOS decreases by more than 40%.

[0006] Nanomaterial adsorption: Although nanomaterials such as graphene oxide (GO) exhibit high adsorption capacity, they are difficult to apply on a large scale due to problems such as complex preparation process, poor material stability (e.g., GO is prone to agglomeration and deactivation) and potential environmental toxicity.

[0007] Membrane separation technology: Reverse osmosis (RO) and nanofiltration (NF) membranes can effectively retain PFAS (retention rate >90%), but the high-concentration concentrate produced still requires subsequent treatment, and the flux decline caused by membrane fouling increases operating costs by 30%-50%.

[0008] Advanced oxidation / reduction methods: Techniques such as UV-activated persulfate and ultrasonic degradation can destroy the PFAS structure through free radical reactions, but their degradation efficiency for perfluorocarboxylic acids is insufficient (<60%), and they may generate more toxic short-chain byproducts.

[0009] Existing technologies include the adsorption of PFAS using organic nanomaterials with covalent organic frameworks (COFs), as reported in CN120365635A and CN118978658A. However, these materials have high raw material costs, require stringent preparation conditions, have low yields, and lack structural stability.

[0010] In recent years, metal-organic frameworks (MOFs) have gained attention due to their ultra-high specific surface area (>1000 m²). 2 With their tunable pore size and rich surface chemical properties, MOF materials are considered potential breakthrough materials in the field of PFAS adsorption. However, existing MOF materials still face core bottlenecks in practical applications, such as low selectivity, poor water stability, and difficulty in regeneration.

[0011] MOFs form periodic porous structures through coordination bonds between metal nodes and organic ligands. Their adsorption performance can be directionally optimized by controlling the metal centers, ligand functional groups, and pore size. Current research on MOFs for PFAS adsorption mainly focuses on the following categories:

[0012] MOFs containing Zr clusters, such as UiO-66, MOF-808, and PCN-999, use Zr6O4(OH)4 as the basic building unit. These building units are then linked together by carboxylic acid ligands to form a three-dimensional porous framework structure. On the inner surface of the pores, there are numerous unsaturated metal sites (Zr6O4(OH)4). 4+ ) and hydroxyl (-OH) groups are exposed within the pores, through Zr 4+ The site forms a strong coordination with the sulfonic acid / carboxylic acid group of PFAS, and the hydrogen bonds between the hydroxyl group and the polar group, as well as the hydrophobic channels and the van der Waals forces of the perfluorinated chain, synergistically promote adsorption.

[0013] Cu-containing MOFs, such as NH2-CuBTC and F-Cu-NH2BDC, contain Cu 2+High coordination saturation, few unsaturated metal sites on the surface, and weak polarity are common problems. Treatments such as introducing amino groups, fluorine functionalization, and composite with carbon materials are typically employed to adjust their adsorption capacity, enabling them to better adapt to PFAS molecule adsorption. (Functionalized MOFs: Adsorption is enhanced by introducing functional groups such as amine (-NH2) and sulfonic acid (-SO3H) through post-modification. For example, NH2-MIL-53(Al) increases the adsorption capacity of PFBA to 85 mg / g (3 times higher than unmodified materials), but the modification process requires toxic solvents, and the functional groups are easily detached during repeated use.)

[0014] CN117487185A reports the application of a zinc-based diimidazole mixed-ligand metal-organic framework (MOF) material in the adsorption of perfluoroalkyl acids (PFAS). This patent involves adding two different imidazole organic ligands to a reaction solvent containing a regulator, ultrasonically dispersing them until the solution is clear; then adding a divalent zinc salt and stirring the mixture at room temperature for 8–72 hours; the reaction product is then washed sequentially with deionized water and ethanol, centrifuged, solvent-displaced, and vacuum-dried to obtain the zinc-based diimidazole mixed-ligand MOF material. This patent utilizes imidazole derivative ligands to generate multiple interactions with negatively charged perfluoroalkyl carboxylic acids, primarily electrostatic interactions, supplemented by hydrogen bonding, hollow body interactions, and hydrophobic interactions, thus achieving highly efficient adsorption of these compounds. By controlling the types and ratios of the two organic ligands, the zinc-based diimidazole mixed-ligand MOF material allows for finer structural and performance control of the MOF adsorbent, improving the structure-activity relationship with perfluoroalkyl carboxylic acids, further enhancing their interaction forces, and significantly improving the treatment capacity for these pollutants. A zinc-based biimidazole mixed-ligand metal-organic framework (MOF) material was prepared by coordination polymerization of two different imidazole ligands with zinc salt. This material exhibits advantages such as greater structural stability, higher specific surface area, and superior adsorption performance. It demonstrates excellent adsorption and removal efficiency for persistent perfluorinated compounds and possesses certain recyclability. Furthermore, by controlling the types and ratios of the two organic ligands, more precise structural and performance regulation of the MOF adsorbent can be achieved.

[0015] CN113842889A reports the microwave synthesis of a metal-organic framework material DUT-5(Al) and its application in PFAS adsorption. DUT-5(Al) is prepared by the following method: biphenyl dicarboxylic acid is dissolved in N,N-dimethylformamide, and then Al(NO3)3·9H2O is added and stirred until homogeneous. The mixture is then subjected to a microwave reaction. During the reaction, the temperature is increased to 120-140℃ at a rate of 10-20℃ / min, and the reaction is continued for 1-2 hours. After the reaction, the reaction solution is cooled, centrifuged, and the precipitate is collected, washed, and dried to obtain the metal-organic framework material DUT-5(Al). It exhibits good removal rates for PFOS and PFOA.

[0016] The literature "Exceptionally High Perfluorooctanoic Acid Uptake in Water by a Zirconium-Based Metal–Organic Framework through Synergistic Chemical and Physical Adsorption" (J.Am.Chem.Soc.2024,146,14,9811-9818.https: / / doi.org / 10.1021 / jacs.3c14487) reports the ultra-high adsorption performance of a zirconium-based metal-organic framework PCN-999 for perfluorooctanoic acid in water. However, PCN-999 involves complex ligand synthesis, which is costly and difficult to industrialize.

[0017] While there are numerous reports on the adsorption of PFAS by MOFs in existing technologies, the following bottlenecks remain: The contradiction between pore size and mass transfer efficiency: Small-pore MOFs (<1 nm) improve selectivity but lead to slow adsorption kinetics (equilibrium time > 24 h), making it difficult to meet the throughput requirements of practical water treatment; Irreversible loss due to functionalization modifications: Surface-modified groups (such as quaternary ammonium groups) gradually fail during regeneration due to chemical corrosion or pyrolysis, resulting in a significant reduction in material lifespan; Trade-off between cost and performance: High-stability MOFs (such as PCN-222) require expensive ligands (porphyrin derivatives), resulting in high synthesis costs far exceeding the threshold for engineering applications. Furthermore, while many existing technologies report on the adsorption of PFAS by MOFs, most studies focus on adsorption capacity, with few reports on the adsorption effect of ultra-low concentration PFAS. The inventors also experimented with a large number of existing MOFs and found that while many have high PFAS adsorption capacities, the adsorption process is slow, and the adsorption effect on ultra-low concentration PFAS is poor. Summary of the Invention

[0018] To address the shortcomings of existing MOFs (Metallic Optical Facility) technologies in achieving a comprehensive performance that balances high adsorption capacity, high selectivity, rapid adsorption efficiency, long service life, and excellent removal efficiency for ultra-low concentrations of PFAS, and the complex preparation processes and high manufacturing costs of some MOFs hindering industrialization, this invention provides a MOF-818 for PFAS adsorption. MOF-818 achieves rapid and efficient PFAS adsorption through its coordinating sites and mesoporous structure, exhibiting high efficiency in removing even ultra-low concentrations of PFAS. Furthermore, MOF-818 also demonstrates high selectivity, high adsorption capacity, excellent stability and recyclability, and superior removal efficiency for ultra-low concentrations of PFAS.

[0019] MOF-818 is a metal-organic framework material based on trinuclear copper clusters (Cu3 clusters). In its structure, copper sites are linked by organic ligands to form redox-active catalytic centers. This structure endows it with activity similar to natural catechol oxidases, enabling it to catalyze the oxidation of phenolic compounds. The Zr clusters in MOF-818 are not independent structural units but participate in the framework construction as auxiliary metals alongside the trinuclear Cu clusters. Zr exists in mononuclear or oligomeric forms, while the core SBUs are trinuclear Cu clusters connected by μ3-oxygen bridges, forming catalytic nodes with enzyme-mimicking activity. The pores of MOF-818 are predominantly composed of pyrazole rings (nonpolar), with fewer exposed polar sites such as hydroxyl groups, lacking sites capable of forming strong coordination or hydrogen bonding with the polar groups of PFAS molecules. Therefore, MOF-818 is applied in biomedical fields, such as wound healing, treatment of femoral head necrosis, and immunoassay; as well as in chemical catalysis and UV-protective materials for silk fabrics. There are currently no reports on the use of MOF-818 for perfluoroalkyl and polyfluoroalkyl substances (PFAS). MOF-818 possesses advantages such as simple and low-cost preparation process, mesoporous pore size, high specific surface area, high stability, and abundant coordination sites, making it a potential adsorbent for PFAS. This invention provides the following technical solution:

[0020] The application of a metal-organic framework material MOF-818 in PFAS adsorption, wherein MOF-818 is composed of two clusters, [M6(μ3-O)4(μ3-OH)4(OH)6(μ-PyC)6(H2O)6] and [Cu3(μ3-O)(μ-PyC)3(H2O)3], in a molar ratio of 1:2, where M is Zr and / or Hf, and PyC is 1H-pyrazole-4-carboxylic acid; wherein the PFAS is at least one of perfluoroalkyl and polyfluoroalkyl substances.

[0021] Furthermore, the PFAS is selected from at least one of perfluorobutyric acid, perfluorovalerate, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluorobutane sulfonic acid, perfluorohexane sulfonic acid, perfluorooctane sulfonic acid, perfluoroalkyl ether sulfonate, and hexafluoropropylene oxide trimer.

[0022] MOF-818 can be prepared using the method described in the literature “Mesoporous Cages in Chemically Robust MOFs Created by a Large Number of Vertices with Reduced Connectivity”, J. Am. Chem. Soc. 2019, 141, 488-496. The parameters and structure of MOF-818 are described in that literature.

[0023] Further, the MOF-818 is prepared by a method including the following steps: Zr source (or Hf source), Cu source and 1H-pyrazole-4-carboxylic acid are added to an organic solvent, mixed evenly under ultrasonic conditions, trifluoroacetic acid is added, heated to 80-110℃ and kept at that temperature for 4-24 hours, cooled and centrifuged, the obtained solid product is soaked in an organic solvent for 1-5 days, during which solvent exchange is performed with fresh organic solvent, and dried to obtain MOF-818 powder.

[0024] The molar ratio of Zr source (or Hf source), Cu source and 1H-pyrazole-4-carboxylic acid is 1:3.5-4.5:2-3, preferably 1:3.7-4.0:2-2.3.

[0025] Furthermore, the Zr source is selected from ZrCl4, ZrOCl2 or their hydrates, the Hf source is selected from HfCl4, HfOCl2 or their hydrates, the Cu source is selected from copper nitrate or its hydrate, and the organic solvent is selected from at least one of DMF, DMSO, DMA, DEF, and acetonitrile.

[0026] The present invention also provides a method for removing PFAS from water, comprising the following steps: immersing a metal-organic framework material MOF-818 in water containing PFAS for adsorption, and centrifuging to separate the PFAS-adsorbed MOF-818 after adsorption.

[0027] After MOF-818 is added to water containing PFAS, a mixing process is performed to ensure uniform mixing, which includes at least one of stirring, shaking, and ultrasonication.

[0028] Furthermore, the water containing PFAS can be groundwater, surface water, tap water, domestic sewage, industrial wastewater, agricultural wastewater, or medical wastewater. Due to its extremely high stability and excellent selectivity, MOF-818 can effectively adsorb PFAS in water over a wide range of pH and temperature conditions.

[0029] Furthermore, the concentration of PFAS in the water is 0.01-5000 ppm, preferably 0.1-3000 ppm, and the amount of MOF-818 added is calculated based on the water volume and the PFAS content in the water.

[0030] Furthermore, the concentration of PFAS in the water is 10-1000 ppb, preferably 100-1000 ppb. For extremely low concentrations of PFAS (10-1000 ppb), existing MOFs are ineffective at adsorption and removal. The inventors discovered that MOF-818 not only has a high adsorption capacity for PFAS, but also exhibits excellent adsorption and removal effects even for extremely low concentrations of PFAS such as 10-1000 ppb.

[0031] Furthermore, the method for removing PFAS from water also includes a step of desorbing the PFAS-adsorbed MOF-818 and reusing it as an adsorbent.

[0032] Furthermore, the desorption involves treating the MOF-818 adsorbed with PFAS with a regeneration solution, which is an acidic solution with a pH of 1-5. The acid is selected from inorganic or organic acids. The inorganic acid is selected from hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. The organic acid is selected from formic acid, acetic acid, p-toluenesulfonic acid, and trifluoroacetic acid.

[0033] This invention reveals that MOF-818 exhibits excellent comprehensive adsorption performance for perfluoroalkyl and polyfluoroalkyl substances (PFAS) in water, possessing high adsorption capacity, rapid adsorption rate, high selectivity, and stability. It can effectively adsorb and remove PFAS from water within a wide pH and temperature range. The MOF-818 provided by this invention is also suitable for adsorbing PFAS in water with ultra-low PFAS concentrations, effectively adsorbing and removing trace amounts of PFAS (250 ppb). After adsorption treatment, water containing 250 ppb of PFOA had only 15 ppb of PFOA remaining, while other MOFs with high adsorption capacity (such as PCN999) still left more than 100 ppb of PFOA residue after adsorption treatment. Attached Figure Description

[0034] Figure 1 XRD pattern of MOF-818(Zr).

[0035] Figure 2XPS spectra of MOF-818(Zr).

[0036] Figure 3 The adsorption capacity of MOF-818(Zr) for different concentrations of PFOA is given.

[0037] Figure 4 The adsorption kinetics of PFOA by MOF-818(Zr) are shown.

[0038] Figure 5 The nitrogen adsorption-desorption curves of MOF-818(Zr) before and after PFOA adsorption are shown.

[0039] Figure 6 The thermogravimetric curves of MOF-818(Zr) before and after PFOA adsorption are shown.

[0040] Figure 7 The adsorption capacity of MOF-818(Zr) for PFOA in the presence of other components is denoted as PFOA.

[0041] Figure 8 The cyclic adsorption capacity of MOF-818(Zr) for PFOA is given.

[0042] Figure 9 This is a comparison of the adsorption capacity of PFOA for reported MOF systems. Detailed Implementation

[0043] The present invention will now be described in detail with reference to the embodiments.

[0044] Example 1

[0045] This embodiment provides a method for preparing MOF-818(Zr), the steps of which are as follows:

[0046] S1. Dissolve 212.5 mg ZrOCl2·8H2O (0.66 mmol), 620.0 mg Cu(NO3)2·3H2O (2.56 mmol), and 162.5 mg 1H-pyrazole-4-carboxylic acid (1.45 mmol) in 50 mL of DMF in sequence. Obtain a homogeneous mixed solution under ultrasonic treatment. Then add 600 μL of trifluoroacetic acid (7.83 mmol) to the mixed solution, heat at 100 °C for 10 h, cool to room temperature, centrifuge at 10000 rpm for 10 min, and collect the product.

[0047] S2. Soak the product obtained in step S1 in DMF for 3 days, during which time fresh DMF is used to perform solvent exchange 5 times a day. Then soak it in acetone for 4 days, 5 times a day. Finally, vacuum dry the sample at room temperature to obtain MOF-818(Zr) powder.

[0048] S3. Perform powder X-ray diffraction (XRD) on the obtained MOF-818(Zr). Figure 1 ) and X-ray photoelectron spectroscopy (XPS) Figure 2 Its structure.

[0049] XRD and XPS analysis showed that the main peak positions of its XRD were consistent with the single-crystal simulated structure, indicating that its crystal structure met expectations and its crystallinity was very high; its XPS contained elements such as carbon, nitrogen, oxygen, copper, and zirconium, which were consistent with the expected elemental composition.

[0050] The organic framework material MOF-818(Zr) prepared in Example 1 exhibits excellent structural stability under conditions of strong bases and acids (pH = 2-12) and high temperatures (room temperature to 250°C).

[0051] Example 2

[0052] This embodiment provides a test for the adsorption capacity of MOF-818(Zr) for PFOA, and the steps are as follows:

[0053] S21. Prepare PFOA aqueous solutions with concentrations of 100, 300, 500, 700, 900, 1200, 2000, and 3000 ppm in sequence. Take 2 mL of each solution, add 2 mg of MOF-818 (Zr) powder, mix, and rotate on a rotary mixer for 2 hours.

[0054] S22. Centrifuge the mixed dispersion from step S21, collect the supernatant, add an internal standard, and perform nuclear magnetic resonance spectroscopy analysis on the residual amount of PFOA in the supernatant to calculate the concentration dependence of MOF-818(Zr) on PFOA adsorption. Figure 3 As shown.

[0055] It can be seen that MOF-818(Zr) can completely remove PFOA when the PFOA concentration is below 900 ppm; its saturated adsorption capacity reaches 1.20 g / g; and its concentration gradient adsorption conforms to the Langmuir adsorption process.

[0056] Example 3

[0057] This embodiment provides a kinetic test of MOF-818(Zr) adsorption on PFOA, and the steps are as follows:

[0058] S31. Prepare a PFOA aqueous solution with a concentration of 2000ppm. Take 2mL and place it in multiple sample tubes. Add 2mg of MOF-818(Zr) powder to each sample tube. Mix and then rotate on a rotary mixer for different times.

[0059] S32. Centrifuge the mixed dispersion from step S31, collect the supernatant, add an internal standard, and perform nuclear magnetic resonance spectroscopy analysis on the residual amount of PFOA in the supernatant to calculate the kinetic process of PFOA adsorption by MOF-818(Zr). Figure 4 As shown.

[0060] It can be seen that MOF-818(Zr) has ultrafast adsorption kinetics for PFOA, and saturation adsorption can be achieved within 5 minutes.

[0061] Example 4

[0062] This embodiment provides a test of the changes in pore structure of MOF-818(Zr) before and after PFOA adsorption, and the steps are as follows:

[0063] The MOF-818(Zr) prepared in Example 1 and the MOF-818(Zr) adsorbed with PFOA in a 2000 ppm PFOA aqueous solution in Example 2 were subjected to nitrogen adsorption-desorption experiments to obtain the corresponding pore size distribution and specific surface area information, such as... Figure 5 As shown.

[0064] It can be seen that the BET specific surface area of ​​MOF-818(Zr) before adsorption reaches 1108 m². 2 / g, its average pore size by BJH method is 2.8nm, which is close to the theoretical value; the BET specific surface area of ​​PFOA@MOF-818 after adsorption is only 20m². 2 / g, its pore size distribution is very wide and not significant.

[0065] Example 5

[0066] This embodiment provides a thermogravimetric behavior test of MOF-818(Zr) before and after PFOA adsorption, and the steps are as follows:

[0067] The MOF-818(Zr) prepared in Example 1 and the MOF-818(Zr) adsorbed with PFOA in a 2000 ppm PFOA aqueous solution in Example 2 were heated at a rate of 10 °C / min under nitrogen atmosphere, and the corresponding thermogravimetric curves were obtained, as shown below. Figure 6 As shown.

[0068] It can be seen that MOF-818(Zr) before adsorption exhibits high thermal stability below 200℃, with a weight loss of approximately 50% around 300℃; while PFOA@MOF-818 after adsorption shows a weight loss of more than 80% around 300℃. This weight loss behavior is consistent with the saturated adsorption capacity of PFOA for MOF-818(Zr) of 1.20 g / g.

[0069] Example 6

[0070] This embodiment provides a test of the anti-interference ability of MOF-818(Zr) for PFOA adsorption, and the steps are as follows:

[0071] S61. Prepare five sets of sample solutions by adding 2 mg of common water components such as ferric chloride, aluminum chloride, potassium chloride, sodium sulfate, and acetic acid to 2 mL of PFOA aqueous solution with a concentration of 2000 ppm, and then adding 2 mg of MOF-818 (Zr) powder. After mixing, rotate the mixture on a rotary mixer for 2 hours.

[0072] S62. Centrifuge the mixed dispersion from step S61, collect the supernatant, add an internal standard, and perform nuclear magnetic resonance spectroscopy to analyze the residual amount of PFOA in the supernatant, thereby calculating the selectivity of MOF-818(Zr) for PFOA adsorption. Figure 7 As shown in the figure, MOF-818(Zr) exhibits good anti-interference properties in the adsorption of PFOA.

[0073] Example 7

[0074] This embodiment provides a test of the cyclic adsorption performance of MOF-818(Zr) for PFOA, and the steps are as follows:

[0075] S71. MOF-818(Zr) adsorbed with PFOA was placed in hydrochloric acid solution with pH=2, rotated on a rotary mixer for 24 hours, centrifuged, the supernatant was removed, and the resulting solid was dried to obtain MOF-818(Zr) without PFOA.

[0076] S72. The MOF-818(Zr) from step S71 was placed in a 2000ppm PFOA aqueous solution and rotated for 2 hours. After centrifugation and removal of the supernatant, its cyclic adsorption performance was tested by nuclear magnetic resonance spectroscopy.

[0077] Repeating S71 and S72 yielded the cyclic adsorption performance of MOF-818(Zr) for PFOA, such as... Figure 8 As shown in the figure, after 5 cycles, MOF-818(Zr) still has an adsorption capacity of 1.19 g / g for PFOA.

[0078] Example 8

[0079] This embodiment provides an adsorption test of MOF-818(Zr) for ultra-low concentrations of PFOA, and the steps are as follows:

[0080] S81. Prepare 2 mL of PFOA aqueous solution with a concentration of 250 ppb, add 2 mg of MOF-818 (Zr) powder, mix and rotate on a rotary mixer for 2 hours.

[0081] S82. Centrifuge the mixed dispersion from step S81, take the supernatant, and analyze the residual amount of PFOA in the supernatant by HPLC-MS to calculate the adsorption effect of MOF-818(Zr) on ultra-low PFOA. The residual amount of PFOA in the supernatant is about 15 ppb, which meets the EU requirements for ultra-low concentration of PFAS.

[0082] Example 9

[0083] This embodiment provides a method for preparing MOF-818(Hf), the steps of which are as follows:

[0084] S91. Dissolve 270.0 mg HfOCl2·8H2O, 620.0 mg Cu(NO3)2·3H2O and 162.5 mg H2PyC in 50 mL DMF in sequence. Obtain a homogeneous mixed solution under ultrasonic treatment. Then add 600 μL TFA to the mixed solution, heat at 100 °C for 10 h, cool to room temperature, centrifuge at 10000 rpm for 10 min, and collect the product.

[0085] S92. The product obtained in S91 was soaked in DMF for 3 days, with solvent exchange performed 5 times a day using fresh DMF. Then it was soaked in acetone for 4 days, 5 times a day. Finally, the sample was vacuum dried at room temperature to obtain MOF-818(Hf) powder.

[0086] Example 10

[0087] This embodiment provides a test for the adsorption capacity of MOF-818(Hf) for PFOA, and the steps are as follows:

[0088] S101. Prepare 2 mL of PFOA aqueous solution with a concentration of 2000 ppm, add 2 mg of MOF-818(Hf) powder, mix and rotate on a rotary mixer for 2 hours.

[0089] S102. Centrifuge the mixed dispersion from step S101, take the supernatant, add an internal standard, and perform nuclear magnetic resonance spectroscopy to analyze the residual amount of PFOA in the supernatant, thereby calculating the saturated adsorption capacity of MOF-818(Hf) for PFOA, which is approximately 1.15 g / g.

[0090] S103. Prepare 2 mL of PFOA aqueous solution with a concentration of 250 ppb, add 2 mg of MOF-818(Hf) powder, mix and rotate on a rotary mixer for 2 hours.

[0091] S104. Centrifuge the mixed dispersion from step S81, take the supernatant, and analyze the residual amount of PFOA in the supernatant by HPLC-MS to calculate the adsorption effect of MOF-818(Hf) on ultra-low PFOA. The residual amount of PFOA in the supernatant is about 18 ppb, which meets the EU requirements for ultra-low concentration of PFAS.

[0092] Comparative Example 1

[0093] This comparative example provides a metal-organic framework material, PCN-999, containing only zirconium clusters with empty coordination sites, and tests its adsorption capacity for PFOA. The steps are as follows:

[0094] SD11. Prepare a 2000ppm PFOA aqueous solution. Take 2mL of the solution, add 2mg of PCN-999 powder, mix, and then rotate on a rotary mixer for 2 hours.

[0095] SD12 and SD11 were centrifuged, and the supernatant was collected. An internal standard was added, and nuclear magnetic resonance spectroscopy was performed to analyze the residual amount of PFOA in the supernatant. The saturated adsorption capacity of PCN-999 for PFOA was then calculated, and the value was approximately 1.08 g / g. This result is consistent with the results in the paper "Exceptionally High Perfluorooctanoic Acid Uptake in Water by a Zirconium-Based Metal–Organic Framework through Synergistic Chemical and Physical Adsorption".

[0096] The adsorption test procedure for PCN-999 on ultra-low concentrations of PFOA is as follows:

[0097] SD1. Prepare 2 mL of PFOA aqueous solution with a concentration of 250 ppb, add 2 mg of PCN-999 powder, mix and rotate on a rotary mixer for 2 hours.

[0098] SD22. The mixed dispersion from step SD21 was centrifuged, and the supernatant was collected. The residual amount of PFOA in the supernatant was analyzed by HPLC-MS to calculate the adsorption effect of PCN-999 on ultra-low PFOA. The residual amount of PFOA in the supernatant was 105 ppb. It is evident that although PCN-999 has a high adsorption capacity for PFOA, its effect on ultra-low concentrations of PFOA is poor, far inferior to MOF-818 of this application. Such technical performance is unpredictable for those skilled in the art.

[0099] In summary, the purpose of this invention is to provide a porous material for adsorbing PFAS, which achieves rapid and efficient adsorption of PFAS through the coordinating sites and mesoporous structure of MOF-818, and also has a high efficiency in removing PFAS even at ultra-low concentrations; and has selectivity, stability and recyclability.

Claims

1. The application of a metal-organic framework material MOF-818 in PFAS adsorption, characterized in that, The MOF-818 is composed of two clusters, [M6(μ3-O)4(μ3-OH)4(OH)6(μ-PyC)6(H2O)6] and [Cu3(μ3-O)(μ-PyC)3(H2O)3], in a molar ratio of 1:2, where M is Zr and / or Hf, and PyC is 1H-pyrazole-4-carboxylic acid; the PFAS is selected from at least one of perfluoroalkyl and polyfluoroalkyl substances.

2. The application according to claim 1, characterized in that, The PFAS is selected from at least one of perfluorobutyric acid, perfluorovalerate, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluorobutane sulfonic acid, perfluorohexane sulfonic acid, perfluorooctane sulfonic acid, perfluoroalkyl ether sulfonate, and hexafluoropropylene oxide trimer.

3. The application according to claim 1, characterized in that, The MOF-818 is prepared by the following steps: Zr source (or Hf source), Cu source and 1H-pyrazole-4-carboxylic acid are added to an organic solvent, mixed evenly under ultrasonic conditions, trifluoroacetic acid is added, heated to 80-110℃ and kept at that temperature for 4-24 hours, cooled and centrifuged, the obtained solid product is soaked in an organic solvent for 1-5 days, during which time it is solvent exchanged with fresh organic solvent, and dried to obtain MOF-818 powder.

4. The application according to claim 3, characterized in that, The molar ratio of Zr source (or Hf source), Cu source and 1H-pyrazole-4-carboxylic acid is 1:3.5-4.5:2-3, preferably 1:3.7-4.0:2-2.

3.

5. The application according to claim 3, characterized in that, The Zr source is selected from ZrCl4, ZrOCl2 or their hydrates, the Hf source is selected from HfCl4, HfOCl2 or their hydrates, the Cu source is selected from copper nitrate or its hydrates, and the organic solvent is selected from at least one of DMF, DMSO, DMA, DEF, and acetonitrile.

6. A method for removing PFAS from water, comprising the following steps: The metal-organic framework material MOF-818 was added to water containing PFAS, mixed evenly, and then adsorbed. After adsorption, the MOF-818 containing adsorbed PFAS was separated by centrifugation. The MOF-818 is composed of two clusters, [M6(μ3-O)4(μ3-OH)4(OH)6(μ-PyC)6(H2O)6] and [Cu3(μ3-O)(μ-PyC)3(H2O)3], in a molar ratio of 1:

2. M is Zr and / or Hf, and PyC is 1H-pyrazole-4-carboxylic acid. The PFAS is selected from at least one of perfluoroalkyl and polyfluoroalkyl substances.

7. The method according to claim 6, characterized in that, The mixing process involves at least one of stirring, shaking, and ultrasonication.

8. The method according to claim 6, characterized in that, The water containing PFAS is groundwater, surface water, tap water, domestic sewage, industrial wastewater, agricultural wastewater, or medical wastewater; further, the concentration of PFAS in the water is 0.01-5000 ppm, preferably 0.1-3000 ppm, and the amount of MOF-818 added is calculated based on the water volume and the PFAS content in the water.

9. The method according to claim 6, characterized in that, The method for removing PFAS from water also includes the step of desorbing MOF-818 that adsorbs PFAS and recycling it as an adsorbent.

10. The method according to claim 9, characterized in that, The desorption process involves treating the MOF-818 adsorbed with PFAS with a regeneration solution. The regeneration solution is an acidic solution with a pH of 1-5, and the acid is selected from inorganic or organic acids. The inorganic acid is selected from hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid; the organic acid is selected from formic acid, acetic acid, p-toluenesulfonic acid, and trifluoroacetic acid.

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