Cationic modified montmorillonite as well as preparation method and application method thereof in defluorination

Abstract

The invention discloses cation modified montmorillonite, a preparation method thereof and an application method of the cation modified montmorillonite in defluorination. Belongs to the technical field of modified montmorillonite. The cation modified montmorillonite is cetyl trimethyl ammonium bromide and / or octadecyl trimethyl ammonium bromide modified montmorillonite; the application method comprises the following steps: adding the cation modified montmorillonite into a solution of perfluoro and polyfluoroalkyl substances (PFAS), adjusting the pH value of the mixed solution to 11-13, and carrying out a hydrothermal reaction at 100-220 DEG C. According to the invention, PFAS can be efficiently mineralized through the montmorillonite modified by cations under mild reaction conditions.

Description

Technical Field

[0001] This invention relates to the technical field of modified montmorillonite, and particularly to a cationic modified montmorillonite and its preparation and application in defluorination. Background Technology

[0002] Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are ubiquitous in the environment, wildlife, and humans, attracting significant global attention. Due to the high bond energy of the CF bond, the destruction of PFAS is extremely challenging, and the complete mineralization of PFAS into inorganic fluorides is also difficult to achieve.

[0003] Montmorillonite is one of the main constituent minerals of bentonite. It is a 2:1 type layered clay mineral. Based on the type of exchangeable cations, it can be divided into four types: sodium-based, calcium-based, magnesium-based, and aluminum (hydrogen)-based. Among them, sodium-based... + The most common is sodium-montmorillonite. Due to its negatively charged surface, montmorillonite exhibits significant hydrophilicity, resulting in poor adsorption of weakly polar and non-polar organic pollutants, which limits its application range to some extent. In existing technologies, to improve its adsorption capacity, it is often modified by replacing the exchangeable cations or structural water between the montmorillonite layers with organic functional groups or organic matter, thereby enhancing its adsorption performance for hydrophobic organic pollutants.

[0004] However, the modified montmorillonite obtained through existing modification methods can only perform certain adsorption-based defluorination of perfluorinated compounds, and cannot truly achieve the mineralization of perfluorinated compounds, that is, convert them from organic fluorides into inorganic fluoride ions. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a novel cationic modified montmorillonite and its preparation and application in defluorination. The application method enables the efficient mineralization of perfluoroalkyl substances and polyfluoroalkyl substances (PFAS) by montmorillonite modified with cationic surfactants such as hexadecyltrimethylammonium bromide and / or octadecyltrimethylammonium bromide under mild reaction conditions.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing cationic modified montmorillonite includes: dissolving sodium-montmorillonite in hot water, then adding a cationic surfactant for mixing and impregnation, washing and drying the impregnated sodium-montmorillonite to obtain the cationic modified montmorillonite; wherein the cationic surfactant is selected from hexadecyltrimethylammonium bromide and / or octadecyltrimethylammonium bromide.

[0008] According to some preferred embodiments of the present invention, the temperature of the hot water is 60-80°C.

[0009] According to some preferred embodiments of the present invention, the mixing and impregnation time is 1-3 hours.

[0010] According to some preferred embodiments of the present invention, the drying temperature is 50-70°C.

[0011] According to some preferred embodiments of the present invention, the mass ratio of the sodium-montmorillonite to the cationic surfactant is 10:3-10:8.

[0012] The present invention further provides cationic modified montmorillonite prepared according to the above preparation method.

[0013] XRD characterization analysis showed that, compared with sodium-montmorillonite, the interlayer spacing of cationic modified montmorillonite increased, for example, from 1.27 nm to 3.47 nm. The introduction of cationic surfactants led to charge reversal, that is, the montmorillonite surface was converted into a positively charged state.

[0014] The present invention further provides a method for applying the obtained cationic modified montmorillonite in defluorination, which includes applying the cationic modified montmorillonite to the mineralization of perfluoroalkyl and / or polyfluoroalkyl substances, i.e., PFAS.

[0015] According to some preferred embodiments of the present invention, the application method includes:

[0016] The cationic modified montmorillonite was added to a PFAS solution and mixed in a sealed container to obtain a mixture.

[0017] The pH of the mixture was adjusted to 11-13 to obtain the mixed system;

[0018] The mixture was subjected to a hydrothermal reaction at 100-220℃ for 2-8 hours to obtain a defluorinated liquid.

[0019] The above application method of the present invention can enrich PFAS on the surface and interlayer of cationic modified montmorillonite, and then completely mineralize it using a hydrothermal reaction. The defluorination rate is significantly improved compared with the direct adsorption of cationic modified montmorillonite or the direct hydrothermal degradation of PFAS. Moreover, the inventors unexpectedly discovered that in the above application method of the present invention, PFAS is not only adsorbed and hydrothermally degraded, but also reacts with cationic modified montmorillonite, causing the fluorocarbon bond in PFAS to break, and the organic PFAS can be fully converted into inorganic fluoride ions.

[0020] Meanwhile, the inventors unexpectedly discovered that the pH value of the mixed system without pH adjustment, i.e. its background pH value, is around 8.4. When the pH is adjusted to be greater than 8.4-10, the defluorination rate will decrease to a certain extent, while further adjusting the pH to above 11 will significantly improve the defluorination rate.

[0021] According to some preferred embodiments of the present invention, the sealed mixing time is 3-5 hours.

[0022] According to some preferred embodiments of the present invention, the application method includes: adjusting the pH of the mixed solution to 12.5.

[0023] The inventors unexpectedly discovered that this pH value could achieve a better defluorination rate.

[0024] According to some preferred embodiments of the present invention, the application method includes: subjecting the mixed system to a hydrothermal reaction at 200°C for 6 hours.

[0025] The inventors unexpectedly discovered that the hydrothermal reaction temperature and time could achieve a better defluorination rate and lower energy consumption.

[0026] According to some preferred embodiments of the present invention, in the cationic modified montmorillonite, the molar ratio of the cationic surfactant to the cation exchange capacity of sodium-montmorillonite is 1.55.

[0027] The inventors unexpectedly discovered that this raw material could achieve a better defluorination rate.

[0028] According to some preferred embodiments of the present invention, the PFAS includes long-chain PFAS such as perfluorooctanoic acid and short-chain PFAS such as trifluoroacetic acid.

[0029] The beneficial effects of this invention include:

[0030] The cationic modified montmorillonite obtained by this invention has a good defluorination effect;

[0031] Compared with traditional high-temperature hydrothermal treatment methods, the defluorination application method of the present invention has mild reaction conditions, low energy consumption, and is environmentally friendly, and has higher defluorination effect and faster defluorination speed; compared with traditional adsorption methods, the defluorination application method of the present invention does not require high-cost post-treatment and has higher defluorination rate and faster defluorination speed.

[0032] In the defluorination application method of the present invention, PFAS can be adsorbed and enriched and then react chemically with cationic modified montmorillonite, resulting in the breaking of its fluorine-carbon bonds and achieving complete mineralization of PFAS.

[0033] Compared with traditional liquid-liquid homogeneous defluorination methods, the defluorination application method of the present invention can realize the synergistic effect of the mineral-alkali-PFAS heterogeneous system, which is more compatible with the complex scenario in the real environment where PFAS is often adsorbed on soil / sediment (solid phase), and has stronger practical applicability.

[0034] The defluorination application method of the present invention has good defluorination effect on both long-chain PFAS (such as perfluorooctanoic acid) and short-chain PFAS (such as trifluoroacetic acid). Attached Figure Description

[0035] Figure 1 The image shows a comparison of X-ray diffraction patterns of Na-Mt, Na-Mt@CTAB, Na-Mt@CTAB after PFOA adsorption, and the sample after adsorption and hydrothermal reaction in Example 1.

[0036] Figure 2 This is a comparison chart of the defluorination effects of different defluorination treatments on PFOA in Example 1.

[0037] Figure 3 This is a comparison chart of the defluorination effects of different defluorination treatments on PFOA in Example 2.

[0038] Figure 4 The image shows the effect of the defluorination treatment on trifluoroacetic acid in Example 3.

[0039] Figure 5 This is a comparison chart of the defluorination effects of different defluorination treatments on PFOA in Example 4.

[0040] Figure 6 This is a comparison chart of the defluorination effects of different defluorination treatments on PFOA in Example 5.

[0041] Figure 7 This is a comparison chart of the defluorination effects of different Na-Mt@CTAB on PFOA in Example 6.

[0042] Figure 8 The graph shows a comparison of the defluorination effects of different defluorination treatments on PFOA in Comparative Examples 1-3.

[0043] Figure 9 This is a comparison chart showing the defluorination effects of different defluorination treatments on PFOA in Comparative Example 4.

[0044] Figure 10 This is a comparison chart showing the defluorination effects of different defluorination treatments on PFOA in Comparative Example 5. Detailed Implementation

[0045] The technical solutions of the present invention will be further described below with reference to the embodiments and accompanying drawings. The embodiments described below are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0046] In the following examples, fluoride ion concentration was measured using a fluoride ion electrode (Orion Dual StarpH / ISE dual-channel benchtop measuring instrument), and the defluorination rate was obtained according to the following calculation formula:

[0047] Defluorination rate = (C F -V 液 ) / C0V0P F ×100%

[0048] Among them, C F V represents the measured concentration of fluoride ions in the solution (mg / L). 液 Where C0 is the initial concentration of the perfluorooctanoic acid (PFOA) solution (mg / L), V0 is the initial volume of the PFOA solution (mL), and P is the volume of the solution. F This represents the percentage of fluorine atoms in the molecular weight of perfluorooctanoic acid (PFOA).

[0049] Example 1

[0050] Hexadecyltrimethylammonium bromide (CTAB) modified montmorillonite Na-Mt@CTAB was prepared by the following method:

[0051] Dissolve 10g of sodium-montmorillonite (Na-Mt) in 100ml of water at 70℃ and stir at 650r / min for 1h. Then add 6g of cetyltrimethylammonium bromide (CTAB) and continue stirring at 650r / min for 2h. Wash with 1L of ultrapure water and then centrifuge at 8000rpm for 5min. Dry the product in a 60℃ oven for 24h to obtain the Na-Mt@CTAB solid sample (1.55CEC-Mt@CTAB).

[0052] The obtained Na-Mt@CTAB solid sample was subjected to defluorination, including the following steps:

[0053] (1) Add 20 mL of perfluorooctanoic acid (PFOA) solution with a concentration of 20 mg / L to a 50 mL reactor, then add 1 g of Na-Mt@CTAB, stir in a sealed container for 4 h, and then adjust the pH to 12.5 with sodium hydroxide (NaOH) to obtain a mixed system;

[0054] (2) The mixed system was subjected to hydrothermal reaction at 220℃, 200℃, 180℃, 160℃ and 120℃ for 6 hours respectively to obtain defluorination liquid.

[0055] Furthermore, the fluoride ion content in the defluorination solution was determined by the following method: ultrapure water was added to the defluorination solution and ultrasonic treatment was performed at 100 Hz for 15 min, followed by centrifugation at 10000 rpm for 5 min. The supernatant obtained by centrifugation was taken out and filtered through a 0.22 μm polyethersulfone filter membrane to obtain the analytical solution. The analytical solution was diluted to 20 ml with ultrapure water and the fluoride ion concentration was determined by a fluoride ion electrode.

[0056] X-ray diffraction characterization was performed on Na-Mt@CTAB (Mt@CTAB shown in the figure) prepared in Example 1, the sample after direct adsorption of perfluorooctanoic acid (adsorption method: Na-Mt@CTAB and perfluorooctanoic acid solution were stirred at 650 r / min for 4 h at room temperature) (A-Mt@CTAB), and the samples after adsorbing perfluorooctanoic acid through the above defluorination application and undergoing hydrothermal reaction at 200℃ (H-Mt@CTAB and H-12.5-Mt@CTAB, both of which were samples after hydrothermal reaction at 200℃). The results are shown in the appendix. Figure 1 As shown, unmodified sodium-montmorillonite (Na-Mt) is used as a reference.

[0057] from Figure 1 It can be seen that Na-Mt has characteristic diffraction peaks belonging to sodium montmorillonite with the (001) crystal plane; after CTAB modification, the peak of the (001) crystal plane shifts to the left, and the interlayer spacing of the (001) crystal plane increases, indicating that CATB... + Ions enter the Mt interlayer; while the (001) crystal plane of the sample after direct adsorption of perfluorooctanoic acid solution continues to increase, indicating that perfluorooctanoic acid has entered the Na-Mt@CTAB interlayer; and after adsorption and hydrothermal reaction, the interlayer spacing of the (001) crystal plane decreases, indicating that perfluorooctanoic acid has been degraded.

[0058] The concentrations of fluoride ions in the analytical solution at different hydrothermal reaction temperatures measured in Example 1 were statistically analyzed, and the results are shown in the appendix. Figure 2 As shown, the defluorination rate corresponding to a hydrothermal reaction temperature of 120℃ is 18.03%, indicating that there are relatively few carbon-fluorine bond breaks in PFOA. The defluorination rate increases to 39.34% at 160℃, 72.64% at 180℃, and 81.58% at 200℃. Further increasing the temperature to 220℃, the defluorination rate is 84.47%. It can be seen that when the temperature is increased from 200℃ to 220℃, the defluorination rate only increases by less than 3 percentage points. The increase in defluorination rate due to the increase in temperature is not significant compared with the additional energy consumption / cost. Considering the balance between defluorination efficiency and energy consumption, 200℃ is the better hydrothermal reaction temperature.

[0059] Example 2

[0060] Octadecyltrimethylammonium bromide (STAB) modified montmorillonite Na-Mt@STAB was prepared by the following method:

[0061] Dissolve 10g of sodium-montmorillonite (Na-Mt) in 100ml of water at 70℃ and stir at 650r / min for 1h. Then add 6g of octadecyltrimethylammonium bromide (STAB) and continue stirring at 650r / min for 2h. Wash with 1L of ultrapure water and then centrifuge at 8000rpm for 5min. Dry the product in a 60℃ oven for 24h to obtain the Na-Mt@STAB solid sample.

[0062] The obtained Na-Mt@STAB solid sample was subjected to defluorination, including the following steps:

[0063] (1) Add 20 mL of perfluorooctanoic acid (PFOA) solution with a concentration of 20 mg / L to a 50 mL reactor, then add 1 g of Na-Mt@STAB, stir in a sealed container for 4 h, and then adjust the pH to 12.5 with sodium hydroxide (NaOH) to obtain a mixed system;

[0064] (4) The mixed system was subjected to hydrothermal reaction at 220℃, 200℃, 180℃, 160℃ and 120℃ for 6 hours respectively to obtain defluorination liquid.

[0065] Furthermore, the analytical solution was prepared using the same method as in Example 1, and its fluoride ion concentration was determined. The statistical results are shown in the attached figure. Figure 3 As shown in the figure, the defluorination rate corresponding to the hydrothermal reaction temperature of 120℃ is 17.22%, indicating that there are relatively few carbon-fluorine bond breaks in PFOA. The defluorination rate increases to 45.51% at 160℃, 51.12% at 180℃, and 79.16% at 200℃. Further increasing the temperature to 220℃, the defluorination rate reaches 81.75%, indicating that Na-Mt modified with octadecyltrimethylammonium bromide (STAB) also has a good defluorination effect.

[0066] Example 3

[0067] The Na-Mt@CTAB solid sample was defluorinated in accordance with the method of Example 1, except that the defluorination solution was a solution of short-chain PFAS trifluoroacetic acid, that is, 20 mL of trifluoroacetic acid (TFA) solution with a concentration of 20 mg / L was added to a 50 mL reaction vessel, and the mixture was subjected to hydrothermal reaction at 200 °C for 6 h to obtain a defluorinated solution.

[0068] The analytical solution was prepared and its fluoride ion concentration was determined using the same method as in Example 1. The statistical results are shown in the appendix. Figure 4 As shown.

[0069] Example 4

[0070] The Na-Mt@CTAB solid sample was defluorinated according to the method in Example 1, except that the pH was adjusted to 12, 12.5 and 13 respectively, and the mixed system was subjected to hydrothermal reaction at 200°C for 6 hours to obtain the defluorinated solution.

[0071] The analytical solution was prepared and its fluoride ion concentration was determined using the same method as in Example 1. The statistical results are shown in the appendix. Figure 5 As shown.

[0072] It can be seen that as pH increases, the defluorination rate first increases and then decreases. Specifically, the defluorination rate is 47.92% at pH 12, 81.58% at pH 12.5, and 55.07% at pH 13. Therefore, pH = 12.5 is the optimal pH value.

[0073] Example 5

[0074] The Na-Mt@CTAB solid sample was defluorinated according to the method in Example 1, except that the mixed system was subjected to hydrothermal reaction at 200°C for 4h, 6h and 8h respectively to obtain the defluorinated liquid.

[0075] The analytical solution was prepared and its fluoride ion concentration was determined using the same method as in Example 1. The statistical results are shown in the appendix. Figure 6 As shown.

[0076] It can be seen that as the hydrothermal reaction time increases, the defluorination rate first increases and then decreases. Specifically, when the hydrothermal reaction time is 4 hours, the defluorination rate is 67.07%; when the hydrothermal reaction time is 6 hours, the defluorination rate is 81.58%; and when the hydrothermal reaction time is 8 hours, the defluorination rate is 77.97%. Therefore, the optimal hydrothermal reaction time is 6 hours.

[0077] Example 6

[0078] Na-Mt@CTAB solid samples were prepared according to Example 1, the only difference being that the amount of hexadecyltrimethylammonium bromide (CTAB) added was 6 and 7.72 g, respectively, resulting in two Na-Mt@CTAB solid samples with molar ratios of CTAB and CEC (cation exchange capacity, 106 mmol / 100 g) of 1.55 and 2, respectively.

[0079] The two Na-Mt@CTAB solid samples were subjected to the same defluorination application as in Example 1, except that the mixed system was subjected to a hydrothermal reaction at 200°C for 6 hours to obtain a defluorinated liquid.

[0080] The analytical solution was prepared and its fluoride ion concentration was determined using the same method as in Example 1. The statistical results are shown in the appendix. Figure 7 As shown.

[0081] It can be seen that the defluorination rate of 1.55CEC-Mt@CTAB is 81.58%, while that of 2CEC-Mt@CTAB is 70.72%. This indicates that the defluorination rate of 1.55CEC-Mt@CTAB is better than that of 2CEC-Mt@CTAB (70.72%). This may be because 1.55CEC-Mt@CTAB is closer to a monolayer, with quaternary ammonium salt molecules evenly distributed on the mineral surface in a flat manner, forming a dense hydrophobic layer that can improve the adsorption of PFAS pollutants. However, if the amount of CTAB is further increased to 2CEC, CTAB may form a bilayer or micelle structure, resulting in site shielding. The outer CTAB layer covers the inner active site, reducing the chance of contact with PFAS.

[0082] Comparative Example 1

[0083] Unmodified sodium-montmorillonite is applied for defluorination as follows:

[0084] Add 20 mL of 20 mg / L perfluorooctanoic acid (PFOA) solution to a 50 mL reactor, then add 1 g of unmodified Na-Mt, and stir in a sealed container for 4 h to obtain a defluorinated solution.

[0085] Comparative Example 2

[0086] Na-Mt@CTAB adsorption defluorination treatment is performed through the following process:

[0087] 20 mL of perfluorooctanoic acid (PFOA) solution with a concentration of 20 mg / L was added to a 50 mL reactor, followed by 1 g of Na-Mt@CTAB solid sample prepared in Example 1. The mixture was stirred in a sealed container for 4 h to obtain a defluorinated solution.

[0088] Comparative Example 3

[0089] Unmodified sodium-montmorillonite is applied for defluorination as follows:

[0090] Add 20 mL of 20 mg / L perfluorooctanoic acid (PFOA) solution to a 50 mL reactor, then add 1 g of unmodified Na-Mt, and stir in a sealed container for 4 h to obtain a mixed system.

[0091] The mixture was subjected to a hydrothermal reaction at 200°C for 6 hours to obtain a defluorinated liquid.

[0092] Comparative Example 4

[0093] Hydrothermal defluorination of perfluorooctanoic acid (PFOA) is performed through the following process:

[0094] Add 20 mL of a 20 mg / L perfluorooctanoic acid (PFOA) solution to a 50 mL reactor. Perform hydrothermal reactions at 200 °C for 6 h, with and without pH adjustment, and with pH set to 12.5, respectively, to obtain a defluorinated solution.

[0095] Comparative Example 5

[0096] CATB hydrothermal defluorination is performed through the following process:

[0097] Add 20 mL of 20 mg / L perfluorooctanoic acid (PFOA) solution to a 50 mL reactor, then add 1 g of CATB, and stir in a sealed container for 4 h to obtain a mixed system.

[0098] The mixture was subjected to a hydrothermal reaction at 200°C for 6 hours, with and without pH adjustment of the mixture, and with pH adjusted to 12.5, respectively, to obtain a defluorination solution.

[0099] The defluorination solutions of Comparative Examples 1-5 were prepared into analytical solutions and their fluoride ion concentrations were determined using the same method as in Example 1. The statistical results for Comparative Examples 1-3 are shown in the attached figure. Figure 8 As shown (ND indicates a defluorination rate of 0), the statistical results of Comparative Example 4 are attached. Figure 9 As shown in the attached figure, the statistical results for Comparative Example 5 are as follows. Figure 10 As shown.

[0100] pass Figure 8 It can be seen that the defluorination rate of pure sodium-montmorillonite (Na-Mt) adsorbing PFOA solution (Comparative Example 1) and the direct adsorption of PFOA solution by modified Na-Mt@CTAB (Comparative Example 2) is 0. The defluorination rate of pure sodium-montmorillonite (Na-Mt) adsorbing PFOA solution and undergoing hydrothermal reaction at 200℃ for 6 hours (Comparative Example 3) is only 1.48%. This indicates that the adsorption of pure Na-Mt and modified Na-Mt@CTAB, as well as the adsorption of Na-Mt followed by hydrothermal treatment, cannot significantly achieve the cleavage of carbon-fluorine bonds in PFOA.

[0101] pass Figure 9 It can be seen that when PFOA solution is directly hydrothermally degraded without pH adjustment, the defluorination rate is 0. When the pH is adjusted to 12.5, the defluorination rate is only 3.17%, indicating that the defluorination rate of PFOA by direct hydrothermal degradation is very low regardless of whether the pH value is adjusted.

[0102] pass Figure 10 It can be seen that when PFOA is adsorbed and degraded using the surfactant CTAB without pH adjustment, the defluorination rate is 3.45%. When the pH is adjusted to 12.5, the defluorination rate is only 16.58%, indicating that the surfactant CTAB cannot achieve efficient defluorination regardless of whether it is under strong alkaline conditions.

[0103] It should be noted that the above descriptions are merely preferred embodiments of the present invention and should not limit the scope of protection of the technical solutions of the present invention. Any modifications made to the technical solutions described in the foregoing embodiments, or equivalent substitutions of technical features, by those skilled in the art within the spirit and principles of the present invention, should be included within the scope of protection of the present invention.

Claims

1. A method for preparing cationic modified montmorillonite, characterized in that, It includes: Sodium-montmorillonite is dissolved in hot water, and then a cationic surfactant is added for mixing and impregnation. The impregnated sodium-montmorillonite is washed and dried to obtain the cationic modified montmorillonite. The cationic surfactant is selected from hexadecyltrimethylammonium bromide and / or octadecyltrimethylammonium bromide.

2. The preparation method according to claim 1, characterized in that, in, The temperature of the hot water is 60-80℃; and / or the mixing and impregnation time is 1-3 hours; and / or the drying temperature is 50-70℃.

3. The preparation method according to claim 1, characterized in that, The mass ratio of sodium-montmorillonite to the cationic surfactant is 10:3-10:

8.

4. The cationic modified montmorillonite prepared by the preparation method according to any one of claims 1-3.

5. The method of applying the cationic modified montmorillonite according to claim 4 in defluorination, comprising applying the cationic modified montmorillonite to the mineralization of perfluoroalkyl and / or polyfluoroalkyl substances, i.e., PFAS.

6. The application method according to claim 5, characterized in that, It includes: The cationic modified montmorillonite was added to a PFAS solution and mixed in a sealed container to obtain a mixture. The pH of the mixture was adjusted to 11-13 to obtain the mixed system; The mixture was subjected to a hydrothermal reaction at 100-220℃ for 2-8 hours to obtain a defluorinated liquid.

7. The application method according to claim 6, characterized in that, in, The sealed mixing time is 3-5 hours.

8. The application method according to claim 6, characterized in that, It includes: Adjust the pH of the mixed solution to 12.5; And / or, subject the mixture to a hydrothermal reaction at 200°C for 6 hours.

9. The application method according to claim 6, characterized in that, In the cationic modified montmorillonite, the molar ratio of the cationic surfactant to the cation exchange capacity of sodium-montmorillonite is 1.

55.

10. The application method according to claim 6, characterized in that, The PFAS includes long-chain PFAS and short-chain PFAS.

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