Preparation method and application of fluoroalkylated MIL-101 (Cr) material for enhancing adsorption of short-chain perfluorinated compound

Abstract

The invention discloses a preparation method and application of a fluoroalkylated MIL-101 (Cr) material for enhanced adsorption of short-chain perfluorinated compounds, relates to the technical field of metal organic framework (MOF) materials, and aims to solve the problem that the conventional MOF material has insufficient adsorption performance on short-chain PFASs. According to the MIL-101 (Cr)-TF structure, a pair of trifluoromethyl is connected to each benzene ring of original MIL-101 (Cr) in a para-position mode, and the average pore size of the MIL-101 (Cr)-TF structure is three times or above that of an MIL-101 (Cr) material; the removal rates of the MIL-101 (Cr)-TF on PFBA and PFHxA belonging to short-chain PFAS in the simulated wastewater are not lower than 94% and 99% respectively, and the total removal rate of PFOA, PFOS, PFBA, PFHxA and 6: 2 FTS is not lower than 96%; the preparation method comprises the following steps: taking 2, 5-bis (trifluoromethyl) terephthalic acid as an organic ligand, and preparing with chromium nitrate nonahydrate through a hydrothermal method; the preparation method disclosed by the invention is simple and relatively low in cost, and the prepared MIL-101 (Cr)-TF has excellent adsorption performance on short-chain PFASs and is not easily influenced by environmental factors.

Description

Technical Field

[0001] The present invention relates to the technical field of metal organic framework (MOF) materials, and in particular to a preparation method of a fluoroalkylated MIL-101 (Cr) material for enhanced adsorption of short-chain perfluorinated compounds and an application thereof. Background Art

[0002] Perfluorinated surfactants (PFASs) are a class of synthetic chemicals with excellent properties such as chemical stability, heat resistance, hydrophobicity, oleophobicity, and surface activity. They are widely used in industrial production and consumer products, including fluoroplastics, foam fire extinguishing, metal electroplating, textile processing, semiconductors, and other fields. However, in recent years, PFASs have been increasingly found to present environmental hazards such as persistence, bioaccumulation, and long-range migration, and can cause health threats such as reproductive toxicity, hepatotoxicity, developmental toxicity, and even cancer (Caron-Beaudoin et al., 2019; Chang et al., 2022). They have been included in the Ministry of Ecology and Environment's "List of New Pollutants Under Key Control (2023 Edition)." The development of efficient pollution removal materials has become an urgent need to protect public health and ecological security. Metal-organic frameworks (MOFs) are a new class of hybrid crystalline porous materials with unsaturated metal sites, ultra-large specific surface area (SSA), and high porosity. These properties make MOFs ideal for adsorbing PFASs. Furthermore, MOFs can be endowed with specific functionalities by tailoring their composition, structure, and properties. At present, research on improving the adsorption performance of PFASs by functionalized MOF materials is an important development direction for the efficient control of new pollutants.

[0003] The invention patent application, entitled "A Porous Material Adsorbent, Preparation Method, and Application thereof," with publication number CN113385144A, discloses a method for preparing a porous adsorbent material modified with ethylenediaminetetraacetic acid (EDTA) (MOF-808), characterized by a simple process and significant adsorption performance. By loading functional carboxyl groups onto MOF-808, the method improves the material's adsorption capacity for PFASs in water. The process steps are simple and controllable. However, the PFASs used in the specification for adsorption performance testing are perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), both of which are long-chain PFASs. Existing functionalized MOFs materials, similar to those described in the patent, exhibit good adsorption performance for long-chain PFASs, but their adsorption performance for short-chain PFASs remains to be improved (Li et al., 2023). Long-chain PFASs are subject to national regulatory control due to their severe environmental hazards. To meet market demand, short-chain PFASs are being widely used as alternatives, inevitably releasing them into the environment. Compared to their long-chain counterparts, short-chain PFASs have smaller molecular weights and greater mobility, making them less susceptible to adsorption and more easily transported to groundwater, surface water, and soil pore water, where they are absorbed and accumulated by humans, aquatic animals, and plants (Evich et al., 2022). Studies have found that short-chain PFASs exhibit similar toxicological effects to their long-chain counterparts, harming reproductive, neurological, and metabolic systems, as well as the growth and development of fetuses and young children. The health risks and ecological threats they pose are becoming increasingly prominent (Sunderland et al., 2018).

[0004] In summary, compared with long-chain PFASs, short-chain PFASs are more difficult to remove and their pollution and toxicity hazards affect a wider range. Therefore, a method for preparing a fluoroalkylated MIL-101(Cr) material with enhanced adsorption of short-chain perfluorinated compounds and its application are urgently needed to solve this problem. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method and application of a fluoroalkylated MIL-101(Cr) material for enhanced adsorption of short-chain perfluorinated compounds, so as to solve the problem of insufficient adsorption performance of existing MOF materials for short-chain PFASs.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a fluoroalkylated MIL-101(Cr) material for enhanced adsorption of short-chain perfluorinated compounds, specifically MIL-101(Cr)-TF, whose structure is a pair of trifluoromethyl groups connected to the para position on each benzene ring of MIL-101(Cr).

[0007] Preferably, the average pore size of the MIL-101(Cr)-TF material is more than three times that of MIL-101(Cr), and the static contact angle of the MIL-101(Cr)-TF material is more than 40% higher than that of MIL-101(Cr).

[0008] Preferably, the removal rates of the above-mentioned MIL-101(Cr)-TF material for PFBA and PFHxA, which are short-chain perfluorinated compounds in simulated wastewater, are not less than 94% and 99%, respectively, and the total removal rate of the five PFASs is not less than 96%; the simulated wastewater contains five PFASs, PFOA, PFOS, PFBA, PFHxA and 6:2 FTS, each with a concentration of 100 μg / L, and the dosage of the MIL-101(Cr)-TF material is 100 mg / L.

[0009] Another technical solution provided by the present invention is a method for preparing the above-mentioned fluoroalkylated MIL-101(Cr) material, comprising using 2,5-ditrifluoromethylterephthalic acid as an organic ligand and chromium nitrate nonahydrate to prepare MIL-101(Cr)-TF by a hydrothermal method, and using an organic solvent to purify the material.

[0010] Preferably, the preparation method comprises the following specific steps: adding 2,5-ditrifluoromethylterephthalic acid and Cr(NO3)3·9H2O to ultrapure water and stirring evenly, ultrasonically dispersing the resulting suspension at room temperature, then heating to 220°C in a Teflon-lined autoclave and keeping warm until the reaction is complete; after cooling to room temperature, centrifuging and collecting the precipitate; washing with an organic solvent under high temperature and high pressure conditions to remove unreacted materials, and vacuum drying to obtain MIL-101(Cr)-TF.

[0011] Preferably, in the above preparation method, the molar ratio of 2,5-ditrifluoromethylterephthalic acid to Cr(NO3)3·9H2O is (0.9~1.1):(1~1.5); the heating rate is 5°C / min, and the insulation time until the reaction is complete is 16~24 h; the centrifugation is centrifugation at 4000 r / min for 10~20 min; the washing includes washing with N,N-dimethylformamide in an autoclave at 80~120°C for 3~5 times, each for 6~12 h, and then washing with ethanol in an autoclave at 80~120°C for 3~5 times, each for 6~12 h; and the drying is drying in a vacuum oven at 65~75°C for 6~12 h.

[0012] The present invention provides another technical solution: the above-mentioned fluoroalkylated MIL-101(Cr) material, or the fluoroalkylated MIL-101(Cr) material obtained by the above-mentioned preparation method is MIL-101(Cr)-TF, which is used to remove PFASs in water.

[0013] Preferably, the above-mentioned MIL-101(Cr)-TF is used to remove short-chain PFASs in water.

[0014] Preferably, according to the adsorption isotherm model, the saturated adsorption capacity of MIL-101(Cr) for PFBA is 0.59 mmol / g, and the saturated adsorption capacity of MIL-101(Cr)-TF for PFBA is several times that of MIL-101(Cr), reaching 2.95 mmol / g.

[0015] Preferably, MIL-101(Cr)-TF is used to treat water bodies under conditions that inhibit the adsorption of PFASs, and the inhibitory conditions include alkaline environment and dissolved organic matter DOM.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The fluoroalkylated MIL-101(Cr) material for enhanced adsorption of short-chain perfluorinated compounds has good adsorption performance for PFASs, especially short-chain PFASs, thanks to its relatively large average pore size and the hydrophobic effect and fluorine-fluorine effect brought by a large number of trifluoromethyl groups on the benzene ring. In addition, the adsorption performance is relatively less affected by environmental factors such as pH value, DOM concentration, and sulfate concentration.

[0018] 2. The preparation method of the fluoroalkylated MIL-101(Cr) material for enhanced adsorption of short-chain perfluorinated compounds is simple and low-cost. It only requires the hydrothermal reaction of 2,5-ditrifluoromethylterephthalic acid and Cr(NO3)3·9H2O, followed by centrifugation, washing, and drying. Controlling the preparation conditions is sufficient, which is conducive to large-scale production.

[0019] 3. The fluoroalkylated MIL-101(Cr) material with enhanced adsorption of short-chain perfluorinated compounds can be used to remove PFASs from water, especially short-chain PFASs. It has a high saturated adsorption capacity, is less affected by environmental factors, and can be adapted to a wide range of application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 XRD patterns of MIL-101(Cr) and MIL-101(Cr)-TF prepared in Example 1;

[0021] Figure 2 SEM images of MIL-101(Cr) and MIL-101(Cr)-TF prepared in Example 1;

[0022] Figure 3 FTIR spectra of MIL-101(Cr) and MIL-101(Cr)-TF prepared in Example 1;

[0023] Figure 4 a is the static contact angle of MIL-101(Cr) obtained in Example 1,

[0024] Figure 4 b is the static contact angle of MIL-101(Cr)-TF prepared in Example 1;

[0025] Figure 5 The pore size distribution of MIL-101(Cr) and MIL-101(Cr)-TF prepared in Example 1;

[0026] Figure 6 The pore size distribution changes of MIL-101(Cr)-TF prepared in Example 1 before and after adsorption of PFOA and PFBA;

[0027] Figure 7 The adsorption isotherms of short-chain PFBA and long-chain PFOA on MIL-101(Cr) and MIL-101(Cr)-TF prepared in Example 1 are shown;

[0028] Figure 8 The removal rates of each PFASs and ∑PFASs in simulated contaminated water by MIL-101(Cr) and MIL-101(Cr)-TF prepared in Example 1;

[0029] Figure 9 、 10 Figure 9 shows the effect of pH on the adsorption capacity of the material, and Figure 10 shows the effect of pH on the relative adsorption capacity of the material. The relative adsorption capacity is calculated as (q e / q e_max ) * 100%, q e_max is the maximum adsorption observed for the two materials within the tested pH range;

[0030] Figure 11 、 12 Figure 11 shows the adsorption changes of short-chain PFBA and long-chain PFOA on MIL-101(Cr) and MIL-101(Cr)-TF prepared in Example 1 under different DOM concentrations; Figure 12 shows the effect of different DOM concentrations on the adsorption capacity of the materials. Figure 12 It shows the effect of different DOM concentrations on the relative adsorption capacity of the material. The relative adsorption capacity is calculated as (q e / q e_max ) *100%,q e_max is the maximum adsorption observed for the two MOF materials within the tested DOM concentration range; DETAILED DESCRIPTION

[0031] The perfluorinated compounds mentioned in the present invention are abbreviated as PFASs.

[0032] The present invention mainly provides a fluoroalkylated MIL-101(Cr) material for enhanced adsorption of short-chain PFASs, specifically MIL-101(Cr)-TF, whose structure is a pair of trifluoromethyl groups connected to each benzene ring of the MIL-101(Cr) organic ligand at the para position, and its structure can be expressed as , where MIL-101(Cr) has two pairs of vacant para positions on the benzene ring, and the trifluoromethyl group can be located at any para position.

[0033] The MIL-101(Cr)-TF material in the present invention has excellent adsorption performance for PFASs. Compared with other functionalized skeleton materials, its adsorption performance for short-chain PFASs is more outstanding. This is due to the fact that the average pore diameter of the MIL-101(Cr)-TF material of the present invention is more than 3 times the average pore diameter of the MIL-101(Cr) material, and its large number of mesoporous structures are conducive to the rapid filling of short-chain PFBA; it is also due to the large number of trifluoromethyl groups on the benzene ring of the organic ligand of the MIL-101(Cr)-TF material of the present invention, which helps to form hydrophobic effects and fluorine-fluorine effects with PFASs. The static contact angle of the MIL-101(Cr)-TF material is increased by more than 40% compared with MIL-101(Cr), further enhancing the adsorption performance of PFASs.

[0034] To obtain the above-mentioned MIL-101(Cr)-TF material, the following method is required: 2,5-bis(trifluoromethyl)terephthalic acid is used as an organic ligand to prepare MIL-101(Cr)-TF through a hydrothermal method with chromium nitrate nonahydrate. The purity of both raw materials should be greater than 98%. More specifically, 2,5-bis(trifluoromethyl)terephthalic acid and Cr(NO3)3·9H2O are added to ultrapure water and stirred evenly. The resulting suspension is ultrasonically dispersed at room temperature and then heated to 220°C in a Teflon-lined autoclave. ℃, and keep warm until the reaction is complete; after cooling to room temperature, centrifuge and collect the precipitate; after washing with an organic solvent to remove unreacted materials under high temperature and high pressure conditions, vacuum drying is performed to obtain MIL-101(Cr)-TF; in a preferred embodiment, the molar ratio of 2,5-ditrifluoromethylterephthalic acid to Cr(NO3)3·9H2O is (0.9~1.1):(1~1.5); the time for keeping warm until the reaction is complete is 16~24 h; washing includes washing with N,N-dimethylformamide in an autoclave at 80~120 ℃ for 3~5 times, each time for 6~12 h, and then washing with ethanol in an autoclave at 80~120 ℃ for 3~5 times, each time for 6~12 h; drying is drying in a vacuum oven at 65~75 ℃ for 6~12 h.

[0035] Example 1:

[0036] 20 mmol of 2,5-bis(trifluoromethyl)terephthalic acid (purity >98%) and 20 mmol of Cr(NO₃)₃·9H₂O (purity >98%) were added to 100 mL of ultrapure water and stirred for 60 min. The resulting suspension was sonicated at room temperature for 30 min and then heated to 220°C in a 200 mL Teflon-lined autoclave at a heating rate of 5°C / min and held for 20 h. After cooling to room temperature, the crude product was collected by centrifugation at 4000 rpm for 15 min. The centrifugal precipitate was washed in an autoclave at 100°C with N,N-dimethylformamide three times for 12 h each, and then with ethanol three times for 12 h each in an autoclave at 100°C to remove excess unreacted terephthalic acid. The resulting material was dried in a vacuum oven at 70°C for 12 h to obtain MIL-101(Cr)-TF.

[0037] In addition, terephthalic acid (purity>98%) was used instead of 2,5-ditrifluoromethylterephthalic acid (purity>98%), and other conditions were the same as the above preparation process to prepare MIL-101(Cr).

[0038] Depend on Figure 1 It can be seen that compared with MIL-101(Cr), some typical peaks of MIL-101(Cr)-TF disappear or the diffraction peaks are not obvious; Figure 2 The results show that MIL-101(Cr)-TF mainly exists in a regular crystal structure, but also has some irregular long columnar structures. The size of MIL-101(Cr)-TF is much smaller than that of the original MIL-101(Cr), indicating that the fluoroalkyl ligand is not conducive to the growth of the MIL-101(Cr)-TF grain size, restricting the structural topology of the material. Figure 3 It shows that after fluoroalkyl functionalization, MIL-101(Cr)-TF has the highest peaks at 1309 and 1275 cm -1 A new CF bond vibration peak appeared at , indicating that the fluoroalkyl functional group can exist stably in the fluorine-functionalized material. Figure 1 、 2 , 3 confirmed the relevant characteristic functional groups, and the analysis showed that MIL-101(Cr)-TF is a new type of functionalized MOF material.

[0039] Figure 4The static contact angle of MIL-101(Cr) is about 18.5°, while the static contact angle of MIL-101(Cr)-TF increases to about 30.8°, which is an increase of more than 40%, indicating that the hydrophobicity of the material is greatly increased after fluoroalkylation; in addition, the surface energy of MIL-101(Cr) on the water surface is 69.9 mN / m, while the surface energy of MIL-101(Cr)-TF on the water surface is reduced to 66.6 mN / m, that is, the interaction force with water is reduced, which further shows that the hydrophobicity of MIL-101(Cr)-TF material increases, which helps to improve the adsorption performance of PFASs, but it still needs to be verified by adsorption experimental results.

[0040] Figure 5 Figure 2 is the pore size distribution diagram of MIL-101(Cr) and MIL-101(Cr)-TF. The average pore size of MIL-101(Cr) is 2.47 nm, while the average pore size of MIL-101(Cr)-TF increases to 10.9 nm. It can be seen from the figure that MIL-101(Cr)-TF has a large number of mesoporous structures. In this regard, the present invention has conducted more preparation experiments under the above-mentioned preferred conditions (specifically, the molar ratio of 2,5-ditrifluoromethylterephthalic acid to Cr(NO3)3·9H2O is (0.9~1.1):(1~1.5); the time for insulation until the reaction is complete is 16~24 h; washing includes washing with N,N-dimethylformamide in an autoclave at 80~120°C for 3~5 times, each time for 6~12 h, and then washing with ethanol in an autoclave at 80~120°C for 3~5 times, each time for 6~12 h; drying includes drying in a vacuum oven at 65~75°C for 6~12 h). The average pore diameter of the prepared MIL-101(Cr)-TF is more than 3 times that of MIL-101(Cr), generally 3~5 times. In order to verify whether the pore diameter is related to the preparation method, the present invention has conducted more data consultation, theoretical analysis and experiments, and the experimental results are as follows;

[0041] Comparative Example 1:

[0042] The method of Example 8 in the invention patent application with publication number CN117205903A was adopted, specifically: 2-(trifluoromethyl)terephthalic acid (2.34 g) and hydrofluoric acid (0.4 mL) were added to a container containing 40 mL of deionized water and stirred for 10 minutes, and then chromium nitrate hydrate (4.00 g) was added to the container and stirred for 20 minutes; the mixture was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and heated at 433K (i.e., 160°C) for 12 hours; the resulting mixture was filtered out, and the resulting solid was refluxed in hot water (353K, i.e., 80°C, 300 mL) and hot ethanol (343K, i.e., 70°C, 300 mL) to remove unreacted reactants; finally, the green solid was dried at 393K (i.e., 120°C) overnight to obtain MIL-101(Cr)-CF3 as comparative material 1; tests found that the pore size of the prepared material was mainly concentrated in the range of 1.5~4.0 nm, which is the same as that recorded in the invention patent application. Its average pore diameter is similar to that of MIL-101 (Cr) material, which is about 3 nm.

[0043] Still using this method, the 2-(trifluoromethyl)terephthalic acid in the raw material was replaced with the 2,5-bis(trifluoromethyl)terephthalic acid of the present invention (maintaining the molar ratio, i.e., 3.02 g). The obtained material was used as comparative material 2. The average pore diameter was slightly increased to about 5 nm, which was still much lower than the average pore diameter of MIL-101(Cr)-TF of the present invention (7.7-12.6 nm).

[0044] Comparative Example 1 essentially confirms that the larger average pore diameter of the present invention's MIL-101(Cr)-TF is primarily a result of the combined effects of raw material selection and preparation method. The large average pore diameter and mesoporous structure of MIL-101(Cr)-TF facilitate rapid and dense packing of PFASs (particularly short-chain PFASs), improving adsorption performance. However, microscopic characterization is still required for further verification. Therefore, the present inventors further tested the pore structure of MIL-101(Cr)-TF before and after adsorption of PFBA and PFOA to verify the pore filling mechanism during the adsorption process, which is further illustrated in the following examples.

[0045] Example 2:

[0046] Two 0.5 mg portions of MIL-101(Cr)-TF were weighed using an electronic balance and added to 40 mL centrifuge tubes. Then, 20 mL of 0.48 mmol / L solutions of different PFASs (PFBA and PFOA) were added. The tubes were placed in a rotary shaking incubator at 200 rpm and equilibrated at room temperature (25.0 ± 1.0°C) for 2 h. The pH of the MIL-101(Cr)-TF suspension was adjusted to 5 ± 0.1 using 0.1–1 mol / L HCl and NaOH. The tubes were then placed in the incubator at 200 rpm for 12 h and then centrifuged at 12,000 rpm for 2 min. The precipitates were collected and freeze-dried to obtain the PFAS-adsorbed MOFs. These were labeled PFBA@MIL-101(Cr)-TF and PFOA@MIL-101(Cr)-TF, respectively, according to the PFASs added. BET pore size analysis was performed on MIL-101(Cr)-TF, PFBA@MIL-101(Cr)-TF, and PFOA@MIL-101(Cr)-TF to further confirm the occupancy of MIL-101(Cr)-TF pores by PFASs of different chain lengths during adsorption. Figure 6 As shown, compared with long-chain PFOA, short-chain PFBA occupies more mesopores in MIL-101(Cr)-TF. This significant difference may significantly enhance the adsorption performance of short-chain PFBA, but further adsorption experiments are needed to verify this. To clarify its effect on the adsorption capacity of PFASs of different chain lengths, the following examples are used to further explore this effect.

[0047] Example 3:

[0048] 0.5 mg of MOF (MIL-101(Cr)-TF, MIL-101(Cr)) powder was weighed using a 100,000 micrometer balance and added to 40 mL round-bottom polypropylene centrifuge tubes containing 2 mmol / L NaH2PO4 as background ion. Adsorption isotherms of two PFASs (short-chain PFBA and long-chain PFOA) of varying chain lengths were measured for MIL-101(Cr) and MIL-101(Cr)-TF at various concentrations. The centrifuge tubes were placed in a rotary shaking incubator at 200 rpm and equilibrated at room temperature (25.0 ± 1.0°C) for 2 h. The specified amounts of PFBA and PFOA standard solutions were then added to the tubes to achieve adsorption isotherm concentrations ranging from 0 to 1 mmol / L. The pH of the MOF suspension was adjusted to 5 ± 0.1 using 0.1 to 1 mol / L HCl and NaOH. The centrifuge tube was placed in a constant temperature incubator and shaken at 200 rpm for 12 hours to allow adsorption equilibrium to be achieved. After 12 hours, 1.5 mL of the suspension was removed from the tube and placed in a 1.5 mL centrifuge tube. The tube was centrifuged at 12,000 rpm for 2 minutes. 1 mL of the supernatant was then transferred to a sealed brown vial and stored at 4°C. PFAS concentrations were analyzed using liquid chromatography-mass spectrometry (LC-MS). The experiment was repeated.

[0049] In this example, the Freundlich and Langmuir models were selected to fit the adsorption isotherms. The Freundlich model assumes that the adsorption process occurs on a non-uniform surface and adsorption can occur in multiple molecular layers, while the Langmuir model assumes that the adsorption process occurs on a uniform surface and each active site can only adsorb one molecule, which is also called the monolayer adsorption model. The adsorption isotherms of PFASs with different chain lengths on MIL-101(Cr)-TF and MIL-101(Cr) are shown in Figure 2. Figure 7 As shown in the table below, the specific adsorption isotherm model parameters of the two materials for PFASs with different chain lengths are shown:

[0050] Table 1 Adsorption isotherm model parameters of the two materials for PFASs with different chain lengths

[0051]

[0052] According to the adsorption isotherm model, the saturated adsorption capacity of MIL-101(Cr) for short-chain PFBA was 0.59 mmol / g, while that of MIL-101(Cr)-TF increased to 2.95 mmol / g, a fourfold increase. The saturated adsorption capacity of MIL-101(Cr) for long-chain PFOA was 1.50 mmol / g, while that of MIL-101(Cr)-TF was 1.58 mmol / g, a slight improvement. The significant improvement in the adsorption performance of MIL-101(Cr)-TF for short-chain PFBA is likely due to the material's larger pore size and the large number of trifluoromethyl groups on its organic ligands. The larger mesoporous structure facilitates the rapid and dense filling of short-chain PFBAs, which can then be further adsorbed and captured through hydrophobic interactions and fluorine-fluorine interactions. Although MIL-101(Cr)-TF has fewer microporous structures, which is not conducive to the microporous locking of long-chain PFOA, the large number of trifluoromethyl groups on the organic ligands can compensate for the adsorption capacity of long-chain PFOA through hydrophobic interaction and fluorine-fluorine interaction. Therefore, the adsorption capacity of PFOA on MIL-101(Cr)-TF is also improved. In summary, the MIL-101(Cr)-TF of the present invention significantly improves the adsorption performance of short-chain PFASs, and the adsorption performance of long-chain PFASs is also slightly improved. In actual environments

[0053] In actual environments, there is often co-contamination by multiple PFASs of different chain lengths. To further verify the co-removal capability of MIL-101(Cr)-TF in the present invention for multiple PFASs, the following examples were carried out.

[0054] Example 4:

[0055] A simulated contaminated water body was prepared, which contained four traditional PFASs with different chain lengths (PFBA, PFHxA, PFOA, PFOS) and a new PFASs (6:2 FTS). The concentration of each PFASs was 100 μg / L (representing the level of severely polluted industrial wastewater), of which PFBA and PFHxA are short-chain PFASs, and PFOA, PFOS and 6:2 FTS are long-chain PFASs. The two materials MIL-101(Cr) and MIL-101(Cr)-TF prepared in Example 1 were respectively subjected to adsorption tests using this simulated contaminated water. An electronic balance was used to accurately weigh 2 mg of MOFs (MIL-101(Cr)-TF, MIL-101(Cr)) powder into 40 mL brown glass centrifuge tubes. 20 mL of the simulated wastewater solution prepared above was then added to separate centrifuge tubes. The tubes were then placed in a rotary shaking incubator at 200 rpm and equilibrated at room temperature (25.0 ± 1.0°C) for 12 hours, sufficient to achieve adsorption equilibrium. Subsequently, 1.5 mL of the suspension was centrifuged at 12,000 rpm for 2 minutes. 1 mL of the supernatant was then transferred to a sealed brown sampling bottle and stored in a refrigerator at 4°C. The concentrations of various PFASs were analyzed by LC-MS. Replicate experiments were performed.

[0056] See Figure 8 , although the total removal rate of MIL-101(Cr)-TF for the five PFASs was 96.6%, which was higher than the total removal rate of MIL-101(Cr) for the five PFASs (92.0%); although MIL-101(Cr)-TF had a The removal rate of MIL-101(Cr)-TF for short-chain PFBA and PFHxA was comparable to that of MIL-101(Cr) (the removal rates of both materials for long-chain PFASs were 94-98.8%), but the removal rates of MIL-101(Cr)-TF for short-chain PFBA and PFHxA were as high as 94.6% and 99.8%, respectively, which were significantly higher than the removal rates of MIL-101(Cr) for short-chain PFBA and PFHxA (the removal rates of MIL-101(Cr) for PFBA and PFOA were 77.1% and 98.8%, respectively). The present invention also tested more MIL-101(Cr)-TF material samples prepared under the parameters of the above-mentioned different preferred embodiments, and the removal rates of PFBA and PFHxA in simulated contaminated water were not less than 94% and 99%, respectively, and the total removal rate of the five PFASs was not less than 96%. Obviously, the MIL-101(Cr)-TF of the present invention can be used to remove a variety of PFASs in water, especially its excellent adsorption and removal performance for short-chain PFASs.

[0057] Because the adsorption behavior of traditional MOF materials for PFASs primarily involves polar interactions such as electrostatics, hydrogen bonding, and coordination, their adsorption performance is susceptible to adverse effects from environmental factors such as alkaline pH and negatively charged dissolved organic matter (DOM). The numerous trifluoromethyl groups on the organic ligands of MIL-101(Cr)-TF enhance hydrophobic interactions and fluorine-fluorine interactions with PFASs. The larger pore size and mesoporous structure of MIL-101(Cr)-TF also facilitate rapid loading of PFASs, particularly short-chain PFASs. These unique mechanisms, primarily weak / non-polar, mitigate the inhibitory effects of environmental factors such as alkaline pH and DOM on PFAS adsorption. The following examples further tested the adsorption capacity of PFASs of varying chain lengths on MIL-101(Cr)-TF in response to changes in pH and DOM concentration.

[0058] Example 5:

[0059] 0.5 mg of each MOF material (MIL-101(Cr) or MIL-101(Cr)-TF) was weighed using an electronic balance and added to a 40 mL centrifuge tube. Then, 20 mL of a 0.48 mmol / L solution of PFASs of varying chain lengths (short-chain PFBA and long-chain PFOA) was added, along with a 2 mmol / L NaH2PO4 buffer as a background solution. The tubes were then placed in a rotary shaking incubator at 200 rpm and equilibrated at room temperature (25.0 ± 1.0°C) for 2 h. The pH of the MOF suspension was adjusted to 4, 5, 6, 7, 8, 9, and 10 using 0.1–1 mol / L HCl and NaOH to determine the effect of pH variation on the adsorption performance of different PFASs. After 12 hours, 1.5 mL of the suspension was removed and placed in a 1.5 mL centrifuge tube. The tube was centrifuged at 12,000 rpm for 2 minutes. 1 mL of the supernatant was then transferred to a sealed brown injection bottle and stored in a refrigerator at 4°C. PFAS concentrations were analyzed by LC-MS. The experiment was repeated.

[0060] See Figure 9 、 10Under different pH conditions (4-10), the adsorption capacity of MIL-101(Cr)-TF for PFBA and PFOA was higher than that of MIL-101(Cr); it is worth mentioning that under different pH conditions (4-10), the adsorption capacity of MIL-101(Cr)-TF for short-chain PFBA was 3-6 times that of MIL-101(Cr); as the pH value increased from 4 to 10, the adsorption capacity of MIL-101(Cr)-TF and MIL-101(Cr) for PFBA decreased by 39% and 66.2%, respectively, and the adsorption capacity of MIL-101(Cr)-TF and MIL-101(Cr) for PFOA decreased by 57.4% and 72.9%, respectively. It can be seen from this that as the environmental pH increases, the decrease in the adsorption capacity of PFASs of different chain lengths by MIL-101(Cr)-TF is smaller than that of MIL-101(Cr). This is mainly due to the unique pore filling, fluorine-fluorine interaction, and hydrophobic effect of MIL-101(Cr)-TF, which partially offsets the negative impact of the reduction in polar interactions such as electrostatic attraction, hydrogen bonding, and coordination under high pH conditions on the adsorption capacity of PFASs. It also further shows that the MIL-101(Cr)-TF of the present invention alleviates the inhibitory effect of increased pH on the adsorption capacity of PFASs, thereby improving the applicability of the material.

[0061] Example 6:

[0062] A 100 mg / L DOM stock solution was prepared and diluted with various PFAS solutions to obtain DOM concentrations of 2, 5, 10, 20, and 50 mg / L, respectively. Each PFAS concentration was 0.48 mmol / L. 0.5 mg of each MOF powder (MIL-101(Cr) and MIL-101(Cr)-TF) was accurately weighed using an electronic balance and added to a 40 mL centrifuge tube. 20 mL of each of the prepared PFAS solutions was then added. The pH of the MOF suspension was adjusted to 5 ± 0.1 using 0.1–1 mol / L HCl and NaOH. The centrifuge tube was shaken in an incubator at 200 rpm for 12 hours to achieve adsorption equilibrium. After 12 hours, 1.5 mL of the suspension was removed and placed in a 1.5 mL centrifuge tube. The tube was centrifuged at 12,000 rpm for 2 minutes. 1 mL of the supernatant was then transferred to a sealed brown injection bottle and stored in a refrigerator at 4°C. PFAS concentrations were analyzed by LC-MS. The experiment was repeated.

[0063] See Figure 11 、 12At various DOM concentrations (0–50 mg / L), MIL-101(Cr)-TF exhibited higher adsorption capacities for short-chain PFBAs than MIL-101(Cr). As DOM concentration increased from 0 to 50 mg / L, the adsorption capacities of PFBA by MIL-101(Cr)-TF and MIL-101(Cr) decreased by 64.4% and 81.2%, respectively, while the adsorption capacities of PFOA by MIL-101(Cr)-TF and MIL-101(Cr) decreased by 45.6% and 79.4%, respectively. This indicates that the decrease in the adsorption capacity of PFASs of varying chain lengths by MIL-101(Cr)-TF was smaller than that by MIL-101(Cr) with increasing DOM concentration, primarily due to DOM clogging the micropores of MIL-101(Cr), while having less effect on the larger pores of MIL-101(Cr)-TF. In addition, although the negative charge of DOM can lead to a decrease in polar interactions such as electrostatic attraction, hydrogen bonding, and coordination, which is not conducive to the adsorption behavior of PFASs, the unique pore filling, fluorine-fluorine interaction, and hydrophobic effect of MIL-101(Cr)-TF can partially offset this negative effect, playing the role of stabilizing the adsorption capacity of PFASs. It also further shows that the MIL-101(Cr)-TF of the present invention alleviates the inhibitory effect of increased DOM concentration on the adsorption capacity of PFASs, thereby improving the applicability of the material.

[0064] The above Examples 5 to 6 show that MIL-101(Cr)-TF has certain advantages when used to treat water bodies under conditions that inhibit the adsorption of PFASs.

[0065] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection defined by the claims.

[0066] Any matters not described in detail in the present invention are well-known technologies to those skilled in the art.

Claims

1. A fluoroalkylated MIL-101(Cr) material for enhanced adsorption of short-chain perfluorinated compounds, characterized by: The fluoroalkylated MIL-101(Cr) material is MIL-101(Cr)-TF, and its structure is that a pair of trifluoromethyl groups are connected to the para position of each benzene ring of MIL-101(Cr).

2. The fluoroalkylated MIL-101(Cr) material for enhanced adsorption of short-chain perfluorinated compounds according to claim 1, characterized in that: The average pore size of the MIL-101(Cr)-TF material is more than three times that of MIL-101(Cr), and the static contact angle of the MIL-101(Cr)-TF material is increased by more than 40% compared with MIL-101(Cr).

3. The fluoroalkylated MIL-101(Cr) material for enhanced adsorption of short-chain perfluorinated compounds according to claim 1 or 2, characterized in that: The MIL-101(Cr)-TF material has a removal rate of no less than 94% and 99% respectively for PFBA and PFHxA, which are short-chain perfluorinated compounds in simulated wastewater, and a total removal rate of no less than 96% for the five PFASs; the simulated wastewater contains five PFASs, namely PFOA, PFOS, PFBA, PFHxA and 6:2 FTS, with each concentration of 100 μg / L, and the dosage of the MIL-101(Cr)-TF material is 100 mg / L.

4. The method for preparing the fluoroalkylated MIL-101(Cr) material for enhanced adsorption of short-chain perfluorinated compounds according to any one of claims 1 to 3, characterized in that: The method includes using 2,5-ditrifluoromethylterephthalic acid as an organic ligand and chromium nitrate nonahydrate to prepare MIL-101(Cr)-TF through a hydrothermal method, and using an organic solvent to purify the material.

5. The method for preparing a fluoroalkylated MIL-101(Cr) material for enhanced adsorption of short-chain perfluorinated compounds according to claim 4, characterized in that: The method comprises the following specific steps: adding 2,5-ditrifluoromethylterephthalic acid and Cr(NO3)3·9H2O into ultrapure water and stirring uniformly, ultrasonically dispersing the resulting suspension at room temperature, then heating it to 220°C in a Teflon-lined autoclave and keeping the temperature until the reaction is complete; after cooling it to room temperature, collecting the precipitate by centrifugation; washing with an organic solvent to remove unreacted materials under high temperature and high pressure conditions, and vacuum drying the mixture to obtain MIL-101(Cr)-TF.

6. The method for preparing a fluoroalkylated MIL-101(Cr) material for enhanced adsorption of short-chain perfluorinated compounds according to claim 5, characterized in that: The molar ratio of the 2,5-ditrifluoromethylterephthalic acid to Cr(NO3)3·9H2O is (0.9~1.1):(1~1.5); the heating rate is 5°C / min, and the insulation time until the reaction is complete is 16~24 hours; the centrifugation is performed at a speed of 4000 r / min for 10~20 minutes; the washing includes washing with N,N-dimethylformamide in an autoclave at 80~120°C for 3~5 times, each for 6~12 hours, and then washing with ethanol in an autoclave at 80~120°C for 3~5 times, each for 6~12 hours; and the drying is performed in a vacuum oven at 65~75°C for 6~12 hours.

7. The fluoroalkylated MIL-101(Cr) material according to any one of claims 1 to 3, or the fluoroalkylated MIL-101(Cr) material obtained by the preparation method according to any one of claims 4 to 6, characterized in that: The fluoroalkylated MIL-101(Cr) material is MIL-101(Cr)-TF, which is used to remove perfluorinated compounds PFASs in water.

8. The use according to claim 7, characterized in that: The MIL-101(Cr)-TF is used to remove short-chain PFASs from water.

9. The use according to claim 7, characterized in that: According to the adsorption isotherm model, the saturated adsorption capacity of MIL-101(Cr) for PFBA is 0.59 mmol / g, and the saturated adsorption capacity of MIL-101(Cr)-TF for PFBA is several times that of MIL-101(Cr), reaching 2.95 mmol / g.

10. The use according to any one of claims 7 to 9, characterized in that: The MIL-101(Cr)-TF is used to treat water bodies under conditions that inhibit the adsorption of PFASs, and the inhibitory conditions include alkaline environment and dissolved organic matter DOM.

Images