A method for preparing a porous membrane for separating polycyclic aromatic hydrocarbons from wastewater and the porous membrane itself.

Abstract

This invention discloses a method for preparing a porous membrane for separating polycyclic aromatic hydrocarbons (PAHs) from wastewater, and the porous membrane itself. The preparation method includes: firstly, grafting 1-vinyl-3-butylimidazolium tetrafluoroborate onto polyvinylidene fluoride (PVDF) substrate by electron beam irradiation to obtain a graft copolymer; then, preparing a PVDF-g-IL porous membrane using an immersion precipitation phase inversion method; finally, replacing the tetrafluoroborate anions in the PVDF-g-IL porous membrane with sulfobutyl-β-cyclodextrin anions using anion exchange technology to obtain a PVDF-g-IL-SBE-β-CD porous membrane. This invention also provides the PVDF-g-IL porous membrane and the PVDF-g-IL-SBE-β-CD porous membrane prepared by the above method. The porous membrane prepared by this invention exhibits excellent separation and removal performance for PAHs in wastewater, and the preparation process is simple and low-cost, showing broad application prospects.

Description

Technical Field

[0001] This invention pertains to membrane separation methods, specifically a method for preparing a PVDF-g-IL-SBE-β-CD porous membrane for separating wastewater containing polycyclic aromatic hydrocarbons, and the porous membrane itself. Background Technology

[0002] Emulsified wastewater, due to its stable oil-water mixture and the presence of numerous recalcitrant pollutants, presents significant challenges to traditional physical, chemical, and biological treatment methods, making efficient separation and thorough purification difficult. Therefore, developing efficient, energy-saving, and environmentally friendly emulsified wastewater treatment technologies has become a research hotspot in the field of environmental remediation. Compared to traditional methods, membrane separation has attracted considerable attention due to its excellent separation performance and advantages such as ease of operation, high efficiency, energy saving, and environmental friendliness.

[0003] β-Cyclodextrin is a special organic compound with a hydrophilic outer layer and a hydrophobic inner cavity structure. Studies have shown that its unique cavity structure can efficiently remove polycyclic aromatic hydrocarbons (PAHs) through host-guest inclusion interactions. Furthermore, β-Cyclodextrin possesses a certain degree of hydrophilicity due to its outer hydroxyl groups, making it a promising green treatment approach for removing PAHs from emulsion wastewater and exploring synergistic multi-technology treatment methods. Current technologies for modifying separation membranes with β-Cyclodextrin primarily involve physical blending or surface coating, which suffers from drawbacks such as easy cyclodextrin detachment and unstable membrane performance. While ionic liquid grafting modification can improve membrane hydrophilicity and antifouling properties, its host-guest recognition and inclusion capabilities for PAHs are limited. Therefore, developing a porous membrane preparation method that can stably immobilize cyclodextrin and synergistically utilize the dual functions of ionic liquids and cyclodextrin has significant technological value. Summary of the Invention

[0004] Purpose of the invention: To address the problems of low separation efficiency, poor antifouling performance, and complex preparation processes of existing membrane materials for separating polycyclic aromatic hydrocarbons (PAHs) in wastewater, this invention provides a method for preparing a porous membrane for separating PAHs in wastewater and the porous membrane itself. This method involves grafting ionic liquids with electron beam irradiation and introducing sulfobutyl-β-cyclodextrin through anion exchange to obtain a porous membrane that combines high separation efficiency, good hydrophilicity, and excellent antifouling performance.

[0005] Technical solution: The method for preparing the porous membrane for separating polycyclic aromatic hydrocarbons in wastewater involves first grafting 1-vinyl-3-butylimidazolium tetrafluoroborate onto polyvinylidene fluoride substrate by electron beam irradiation to obtain a graft copolymer; then preparing a PVDF-g-IL porous membrane by immersion precipitation phase inversion method using the graft copolymer; finally, replacing the tetrafluoroborate anions in the PVDF-g-IL porous membrane with sulfobutyl-β-cyclodextrin anions using anion exchange technology to obtain a PVDF-g-IL-SBE-β-CD porous membrane.

[0006] Furthermore, the method includes the following steps: (1) Polyvinylidene fluoride and 1-vinyl-3-butylimidazolium tetrafluoroborate were added to dimethylformamide solvent and dissolved to obtain a homogeneous solution A; (2) Pour solution A into a mold and dry it in an air-circulating oven; (3) The dried product is transferred to a vacuum oven for further drying to obtain a precursor film; (4) The product dried in the previous step was subjected to electron beam vacuum irradiation at room temperature; (5) The irradiated sample is extracted to remove unreacted substances and obtain product B; (6) Dissolve product B in dimethylformamide solvent and heat to dissolve to obtain a uniform casting solution; (7) After cooling, the casting solution is coated onto the substrate and immersed in the coagulation bath to form a porous membrane; (8) Rinse and soak the porous membrane with deionized water; (9) The rinsed porous membrane was freeze-dried to obtain product C; (10) After placing product C in an aqueous solution containing sodium sulfobutyl-β-cyclodextrin and letting it stand, remove it and rinse it with deionized water; (11) After repeating step (10) several times, the membrane is freeze-dried to obtain the target product PVDF-g-IL-SBE-β-CD porous membrane.

[0007] Furthermore, electron beam vacuum irradiation was performed at room temperature using a dose of 50 kGy.

[0008] Furthermore, the amount of 1-vinyl-3-butylimidazolium tetrafluoroborate [VBIM][BF4] is 6%-15% of the mass of polyvinylidene fluoride (PVDF).

[0009] Furthermore, the amount of 1-vinyl-3-butylimidazolium tetrafluoroborate [VBIM][BF4] is 6%, 10% or 15% of the mass of polyvinylidene fluoride (PVDF).

[0010] Furthermore, the polycyclic aromatic hydrocarbon is phenanthrene, anthracene, or naphthalene.

[0011] A PVDF-g-IL porous membrane is composed of polyvinylidene fluoride body and 1-vinyl-3-butylimidazolium tetrafluoroborate grafted thereon by electron beam irradiation.

[0012] A PVDF-g-IL-SBE-β-CD porous membrane is obtained by anion exchange of the PVDF-g-IL porous membrane, and its surface contains sulfobutyl-β-cyclodextrin anions.

[0013] The main innovation of this invention lies in the following: First, an ionic liquid cation (1-vinyl-3-butylimidazolium cation) is covalently grafted onto the PVDF molecular chain by electron beam irradiation to form a stable polymer backbone. Then, ion exchange technology is used to introduce sulfobutyl-β-cyclodextrin anions, which have specific inclusion capabilities for polycyclic aromatic hydrocarbons (PAHs), into the membrane material through electrostatic interactions. This method cleverly combines the stability of covalent bonds with the designability of non-covalent bonds (ionic bonds), avoiding the physical loss of cyclodextrin and endowing the membrane material with the dual function of 'adsorption-separation' of PAHs. Compared with existing technologies, in the porous membrane prepared by this invention, the imidazole cation and cyclodextrin anion work synergistically. The former improves the hydrophilicity and antifouling properties of the membrane, while the latter provides host-guest recognition sites for PAHs, thereby achieving efficient and stable removal of PAHs.

[0014] Compared with the prior art, the present invention has the following beneficial effects: Excellent and stable separation performance: The sulfobutyl-β-cyclodextrin immobilized by ionic bonds is not easily lost, and the removal rate of polycyclic aromatic hydrocarbons such as naphthalene, phenanthrene, and anthracene can reach more than 95% (up to 98.9% in the examples), and still maintains a removal rate of more than 80% after recycling.

[0015] Significantly improved permeate flux: The introduction of sulfobutyl-β-cyclodextrin anions provided numerous hydrogen bonding sites, synergistically enhancing the hydrophilicity of the membrane surface with imidazole cations (contact angle decreased from 77.9° to 62.1°), with a maximum pure water flux reaching 750.9 L·m -2 ·h -1 It improves efficiency by 2-3 times compared to non-exchange membranes.

[0016] The preparation process is both innovative and practical: it employs electron beam irradiation grafting, resulting in uniform and readily accessible reactions; the anion exchange process is mild and efficient. The entire process does not involve complex organic synthesis, keeping costs under control and making it suitable for large-scale production.

[0017] Strong antifouling ability: The hydration layer formed on the membrane surface can effectively block oil droplet contamination, and the flux recovery rate is high, demonstrating good reusability. Attached Figure Description

[0018] Figure 1 Microstructure of PVDF-g-IL-SBE-β-CD porous membranes, Figures a and b; Figures c and d; Figures e and f show the surface microstructure of the membranes before and after replacement with M6, M10, and M15, respectively; Figure 2Surface chemical composition of PVDF-g-IL and PVDF-g-IL-SBE-β-CD porous membranes, XPS full spectrum of a = M0, c = M15-SBE-β-CD and C1s core energy spectrum of b = M0, d = M15-SBE-β-CD; Figure 3 Hydrophilicity of PVDF-g-IL-SBE-β-CD porous membranes, and static water contact angles of M0, M6, M10, M15, and M15-SBE-β-CD membranes; Figure 4 SBE-β-CD - Pure water flux of porous membrane before and after replacement; Figure 5 Flux recovery rate (FRR) and irreversible flux loss rate (Rir) of the membrane before and after SBE-β-CD replacement; Figure 6 Emulsion wastewater flux and rejection rate of PVDF-g-IL and PVDF-g-IL-SBE-β-CD porous membranes; Figure 7 M15-SBE-β-CD's performance in removing emulsions containing low molecular weight polycyclic aromatic hydrocarbons; Figure 8 Cyclic antifouling performance of M15-SBE-β-CD; Figure 9 Mechanism of emulsion wastewater separation. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be further described below.

[0020] Example 1: 10 g of polyvinylidene fluoride (PVDF) was added to 25 g of dimethylformamide (DMF) solvent and dissolved at 60°C for at least 2 hours to obtain a homogeneous solution. The homogeneous PVDF solution was then cast into glass dishes and placed in an air-circulating oven at 60°C. After 24 hours, the PVDF was transferred to a vacuum oven at 60°C and dried for 24 hours to obtain the final PVDF. The PVDF was then vacuum dried and irradiated with an electron beam at a dose of 50 kGy at room temperature for 48 hours. The irradiated sample was placed in a Soxhlet extraction apparatus and extracted with methanol for at least 60 hours to remove ungrafted ionic liquids, and then stored under vacuum.

[0021] 1 g of PVDF was dissolved in 5 g of DMF solvent and heated at 60°C until a homogeneous casting solution was obtained. After the casting solution cooled to room temperature, it was coated onto a glass substrate using a 50 μm four-sided coater. Subsequently, the glass plate coated with the casting solution was immersed in a coagulation bath (deionized water) to form a PVDF-g porous membrane, denoted as M0. After membrane preparation, M0 was rinsed with deionized water and soaked for 24 hours, with the water changed every 2 hours to remove excess DMF. Finally, it was freeze-dried to remove moisture, thereby obtaining the desired porous membrane. All the phase inversion membrane preparation processes described above were carried out at room temperature.

[0022] Place M0 in a solution containing 0.1 mol / L -1 The membrane was placed in an aqueous solution of sodium sulfobutyl β-cyclodextrin (SBE-β-CD) and allowed to stand for 20 minutes before being removed. It was then rinsed with deionized water for 10 minutes. This process was repeated 5-6 times, and the membrane was then freeze-dried for later use. The final membrane was designated as MO-SBE-β-CD.

[0023] Example 2: 10 g of polyvinylidene fluoride (PVDF) and 6 wt% of 1-vinyl-3-butylimidazolium tetrafluoroborate ([VBIM][BF4]) were added to 25 g of dimethylformamide (DMF) solvent and dissolved at 60°C for at least 2 hours to obtain a homogeneous solution. The homogeneous PVDF / IL solution was then cast into glass dishes and placed in an air-circulating oven at 60°C. After 24 hours, the PVDF / IL blend was transferred to a vacuum oven at 60°C and dried for 24 hours. PVDF / IL-6 was finally obtained. The PVDF / IL-6 blend was vacuum dried and irradiated with an electron beam at a dose of 50 kGy at room temperature for 48 hours. After irradiation, the sample was placed in a Soxhlet extraction apparatus and extracted with methanol for at least 60 hours to remove ungrafted ionic liquids and then stored under vacuum.

[0024] 1 g of PVDF / IL-6 was dissolved in 5 g of DMF solvent and heated at 60°C until a homogeneous casting solution was obtained. After the casting solution cooled to room temperature, it was coated onto a glass substrate using a 50 μm four-sided coater. Subsequently, the glass plate coated with the casting solution was immersed in a coagulation bath (deionized water) to form a PVDF-g-IL-6 porous membrane, denoted as M6. After membrane preparation, M6 was rinsed with deionized water and soaked for 24 hours, with the water changed every 2 hours to remove excess DMF. Finally, it was freeze-dried to remove moisture, thereby obtaining the desired porous membrane. All the phase inversion membrane preparation processes described above were carried out at room temperature.

[0025] Place M6 in a solution containing 0.1 mol / L -1 The membrane was placed in an aqueous solution of sodium sulfobutyl β-cyclodextrin (SBE-β-CD) and allowed to stand for 20 minutes before being removed. It was then rinsed with deionized water for 10 minutes. This process was repeated 5-6 times, and the membrane was then freeze-dried for later use. The final membrane was designated M6-SBE-β-CD.

[0026] Example 3: 10 g of polyvinylidene fluoride (PVDF) and 10 wt% of 1-vinyl-3-butylimidazolium tetrafluoroborate ([VBIM][BF4]) were added to 25 g of dimethylformamide (DMF) solvent and dissolved at 60°C for at least 2 hours to obtain a homogeneous solution. The homogeneous PVDF / IL solution was then cast into glass dishes and placed in an air-circulating oven at 60°C. After 24 hours, the PVDF / IL blend was transferred to a vacuum oven at 60°C and dried for 24 hours. PVDF / IL-10 was finally obtained. The PVDF / IL-10 blend was vacuum dried and irradiated with an electron beam at a dose of 50 kGy at room temperature for 48 hours. After irradiation, the sample was placed in a Soxhlet extraction apparatus and extracted with methanol for at least 60 hours to remove ungrafted ionic liquids and then stored under vacuum.

[0027] 1 g of PVDF / IL-10 was dissolved in 5 g of DMF solvent and heated at 60°C until a homogeneous casting solution was obtained. After the casting solution cooled to room temperature, it was coated onto a glass substrate using a 50 μm four-sided coater. Subsequently, the glass plate coated with the casting solution was immersed in a coagulation bath (deionized water) to form a PVDF-g-IL-10 porous membrane, denoted as M10. After membrane preparation, M10 was rinsed with deionized water and soaked for 24 hours, with the water changed every 2 hours to remove excess DMF. Finally, it was freeze-dried to remove moisture, thereby obtaining the desired porous membrane. All the phase inversion membrane preparation processes described above were carried out at room temperature.

[0028] Place M10 in a solution containing 0.1 mol / L -1 The membrane was placed in an aqueous solution of sodium sulfobutyl β-cyclodextrin (SBE-β-CD) and allowed to stand for 20 minutes before being removed. It was then rinsed with deionized water for 10 minutes. This process was repeated 5-6 times, and the membrane was then freeze-dried for later use. The final membrane was designated M10-SBE-β-CD.

[0029] Example 4: 10 g of polyvinylidene fluoride (PVDF) and 15 wt% of 1-vinyl-3-butylimidazolium tetrafluoroborate ([VBIM][BF4]) were added to 25 g of dimethylformamide (DMF) solvent and dissolved at 60°C for at least 2 hours to obtain a homogeneous solution. The homogeneous PVDF / IL solution was then cast into glass dishes and placed in an air-circulating oven at 60°C. After 24 hours, the PVDF / IL blend was transferred to a vacuum oven at 60°C and dried for 24 hours. PVDF / IL-15 was finally obtained. The PVDF / IL-15 blend was vacuum dried and irradiated with an electron beam at a dose of 50 kGy at room temperature for 48 hours. After irradiation, the sample was placed in a Soxhlet extraction apparatus and extracted with methanol for at least 60 hours to remove ungrafted ionic liquids and then stored under vacuum.

[0030] 1 g of PVDF / IL-15 was dissolved in 5 g of DMF solvent and heated at 60°C until a homogeneous casting solution was obtained. After the casting solution cooled to room temperature, it was coated onto a glass substrate using a 50 μm four-sided coater. Subsequently, the glass plate coated with the casting solution was immersed in a coagulation bath (deionized water) to form a PVDF-g-IL-15 porous membrane, denoted as M15. After membrane preparation, M15 was rinsed with deionized water and soaked for 24 hours, with the water changed every 2 hours to remove excess DMF. Finally, it was freeze-dried to remove moisture, thereby obtaining the desired porous membrane. All the phase inversion membrane preparation processes described above were carried out at room temperature.

[0031] Place M15 in a solution containing 0.1 mol / L -1 The membrane was placed in an aqueous solution of sodium sulfobutyl β-cyclodextrin (SBE-β-CD) and allowed to stand for 20 minutes before being removed. It was then rinsed with deionized water for 10 minutes. This process was repeated 5-6 times, and the membrane was then freeze-dried for later use. The final membrane was designated M15-SBE-β-CD.

[0032] Figure 1 Microstructure of PVDF-g-IL-SBE-β-CD porous membrane The differences in the microstructure of the membrane surface before and after anion replacement were characterized and analyzed using scanning electron microscopy (SEM). Figures ab, cd, and ef show the microstructure of the membrane surface before and after replacement of M6, M10, and M15, respectively. No significant changes or defects were observed on the membrane surface, indicating that anion replacement has almost no effect on the microstructure of the membrane surface.

[0033] 2. Surface chemical composition of PVDF-g-IL and PVDF-g-IL-SBE-β-CD porous membranes X-ray photoelectron spectroscopy (XPS) was used to analyze the surface elements of the composite film to detect changes in elemental composition and distribution before and after modification.

[0034] Pure PVDF membranes contain C1s (286.3 eV), F1s (687.3 eV), and O1s (532.1 eV). The primary emission peak was observed. Since the electron beam irradiation process was not carried out under complete vacuum conditions, oxygen in the air reacted with PVDF, resulting in the appearance of the O1s (532.1 eV) peak. For the M15-SBE-β-CD film, the XPS spectrum showed the addition of N1s and S2p peaks. This demonstrates that the ionic liquid [VBIm][BF4] was successfully grafted onto PVDF and that the sulfobutyl-β-cyclodextrin (SBE-β-CD) anion successfully replaced the original tetrafluoroborate ion.

[0035] XPS was used to perform peak fitting of the C1s peaks of M0 and M15-SBE-β-CD. Figure d reveals five carbon-containing functional groups: 290.3 eV (CF), 284.8 eV (CC), 287.5 eV [(COC), SBE-β-CD], 286.7 eV [(CO), SBE-β-CD], and 284.4 eV [(CH), IL]. The C1s fitting plot of M15 shows that the CO peak area is the largest, and a COC peak is also present, indicating successful substitution of the SBE-β-CD anion. Furthermore, subsequent EDS analysis showed that M15-SBE- The presence of sulfur (S) on the β-CD membrane surface further confirms the successful introduction of the SBE-β-CD anion.

[0036] 3. Hydrophilicity of PVDF-g-IL-SBE-β-CD porous membranes To investigate the effect of SBE-β-CD on emulsion separation performance, the difference in hydrophilicity between M15 and M15-SBE-β-CD was analyzed and tested, such as... Figure 3 As shown in the figure, comparing the contact angles of M6, M10, and M15 reveals that the change in contact angle is not significant with increasing grafting ratio. However, when BF4ˉ is replaced with SBE-β-CD- using an aqueous solution of sodium sulfobutyl-β-cyclodextrin, the membrane contact angle decreases from 77.9° to 62.1° (M15-SBE-β-CD), significantly enhancing the membrane's hydrophilicity. This indicates that SBE-β-CD- has a significant effect on improving hydrophilicity.

[0037] 4. Pure water flux of PVDF-g-IL-SBE-β-CD porous membrane Figure 4 It is the pure water flux of the porous membrane before and after SBE-β-CD replacement.

[0038] Figure 5 It is the flux recovery rate of the porous membrane before and after SBE-β-CD replacement.

[0039] It was found that replacing the BF4- anion in the ionic liquid with SBE-β-CD- significantly improved the water flux of the membrane, increasing it by 2-3 times compared to membranes without anion exchange. Specifically, the water flux reached 17.6 Lm⁻² h⁻¹ for M6-SBE-β-CD, 192.2 Lm⁻² h⁻¹ for M10-SBE-β-CD, and 750.9 Lm⁻² h⁻¹ for M15-SBE-β-CD, showing a significant improvement over pure PVDF membranes. This significant improvement is closely related to the enhanced hydrophilicity of the anion exchange membrane, which has been verified by static water contact angle testing. The introduction of SBE-β-CD- provides more hydrogen bond formation sites for water molecules, further enhancing the membrane's water flux performance. This result indicates that the introduction of SBE-β-CD- has a positive promoting effect on the membrane's hydrophilicity and permeability. The introduction of SBE-β-CD further improves the water flux of the porous membrane; however, the difference in flux recovery rate between PVDF-g-IL-SBE-β-CD and PVDF-g-IL is not significant.

[0040] 5. Experiments on emulsion wastewater filtration using PVDF-g-IL and PVDF-g-IL-SBE-β-CD porous membranes The figure shows the flux and rejection rates of different membranes for emulsion wastewater. The flux of M0 is 0, while the PVDF-g-IL porous membrane grafted with the ionic liquid [VBIm][BF4] shows a significant increase in flux: M6 at 1.1 Lm⁻² h⁻¹, M10 at 15.4 Lm⁻² h⁻¹, and M15 reaching 86.6 Lm⁻² h⁻¹. The emulsion flux of the SBE-β-CD-substituted PVDF-g-IL-SBE-β-CD porous membrane continues to increase: M6-SBE-β-CD at 17.5 Lm⁻² h⁻¹, M10-SBE-β-CD at 77.4 Lm⁻² h⁻¹, and M15-SBE-β-CD reaching 296.2 Lm⁻² h⁻¹. The introduction of SBE-β-CD not only improves the hydrophilicity of the membrane, but also provides more sites for water molecules to form hydrogen bonds with the membrane, thereby significantly improving demulsification efficiency and emulsion flux.

[0041] 6. Polycyclic aromatic hydrocarbon removal performance The removal performance of porous membranes for polycyclic aromatic hydrocarbons was characterized by high performance liquid chromatography (HPLC). The PVDF-g-IL porous membrane improved the naphthalene rejection rate from 43.3% to 89.7%.

[0042] With the introduction of ionic liquids, the flux significantly increased from 1.1 Lm⁻² h⁻¹ to 86.6 Lm⁻² h⁻¹, indicating that the introduction of ionic liquids simultaneously improved the membrane's permeation performance and retention efficiency. The modified membrane after replacing BF₄⁻ with SBE-β-CD further enhanced the removal rate of PAHs. Compared with M6 and M6-SBE-β-CD membranes, the naphthalene removal rate increased from 43.3% to 90.06%.

[0043] Through synergistic effects with imidazole cations, the naphthalene removal rate was significantly improved, reaching 90.06%. From M6-SBE-β-CD to M15-SBE-β-CD, the naphthalene removal rate further increased, from 90.06% to 98.9%, indicating that increasing the grafting amount has a positive promoting effect on the removal of polycyclic aromatic hydrocarbons (PAHs) like naphthalene. Compared to the water flux of pure PVDF membranes, which approaches 0, the M15-SBE-β-CD membrane has a flux as high as 750 Lm⁻² h⁻¹, close to 300 Lm⁻² h⁻¹, and achieves a naphthalene removal rate of 98.9%, with an oil rejection rate as high as 99%.

[0044] To characterize the removal capacity of the M15-SBE-β-CD porous membrane for different polycyclic aromatic hydrocarbons (PAHs), phenanthrene and anthracene were selected for comparative experiments with naphthalene. As shown in the figure, the emulsion flux for all three PAHs was above 200 Lm⁻² h⁻¹ and the removal rate was greater than 95%. These results indicate that the MX-SBE-β-CD membrane has excellent removal capacity for low molecular weight PAHs.

[0045] 7. Antifouling properties of PVDF-g-IL-SBE-β-CD porous membranes The resistance to PAH fouling of the PVDF-g-IL-SBE-β-CD porous membrane was characterized using cyclic experiments. The figure shows the naphthalene removal rate under M15-SBE-β-CD cyclic experiments. After the first two cycles, the naphthalene removal rate did not show a significant decrease, and after three cycles, the naphthalene removal rate remained above 80%. These results indicate that the PVDF-g-IL-SBE-β-CD porous membrane possesses excellent resistance to PAH fouling.

[0046] 8. Mechanism of Emulsion Wastewater Separation The figure illustrates the mechanism of emulsion separation. The PVDF porous membrane grafted with IL plays a crucial role in the separation of oil-in-water emulsions due to its hydrophilic surface groups. Water molecules form a water film at the interface between the hydrophilic groups of the membrane and the emulsion through hydrogen bonds. This water film not only promotes emulsion demulsification but also blocks soybean oil from entering the membrane pores. Simultaneously, the blocked small oil droplets gradually aggregate into larger droplets, thereby improving the membrane's antifouling performance. According to experimental data from M6, the naphthalene removal rate was 43.3%. Although naphthalene is more lipid-soluble than water-soluble, the concentration of naphthalene in the emulsion is low (1 mg L⁻¹), and the solubility of naphthalene in water can reach 20 mg L⁻¹. Therefore, the water film cannot completely block naphthalene from passing through the PVDF membrane, which explains the relatively low naphthalene removal rate in M6.

[0047] Combined Examples 1-4 and Figure 1-6 The results show that the ungrafted PVDF membrane (M0) and its anion exchange membrane (M0-SBE-β-CD) exhibit extremely low flux and polycyclic aromatic hydrocarbon (PAH) removal rates for emulsion wastewater. However, the series of membranes (M6 / 10 / 15-SBE-β-CD) grafted with ionic liquid via electron beam irradiation followed by anion exchange with SBE-β-CD show a significant improvement in both emulsion flux and PAH removal rate. This fully demonstrates that both the "ionic liquid covalent grafting" and "cyclodextrin anion exchange" steps are indispensable, and their synergistic effect is what achieves the outstanding technical effect of this invention.

[0048] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the present invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in the present invention without departing from the scope of the present invention shall be deemed to have remained within the protection scope of the present invention.

Claims

1. A method for preparing a porous membrane for separating polycyclic aromatic hydrocarbons from wastewater, characterized in that, First, 1-vinyl-3-butylimidazolium tetrafluoroborate was grafted onto polyvinylidene fluoride by electron beam irradiation to obtain a graft copolymer. Then, the graft copolymer was used to prepare a PVDF-g-IL porous membrane by immersion precipitation phase inversion. Finally, the tetrafluoroborate anions in the PVDF-g-IL porous membrane were replaced with sulfobutyl-β-cyclodextrin anions using anion exchange technology to obtain a PVDF-g-IL-SBE-β-CD porous membrane.

2. The method according to claim 1, characterized in that, Includes the following steps: (1) Polyvinylidene fluoride and 1-vinyl-3-butylimidazolium tetrafluoroborate were added to dimethylformamide solvent and dissolved to obtain a homogeneous solution A; (2) Pour solution A into a mold and dry it in an air-circulating oven; (3) The dried product is transferred to a vacuum oven for further drying to obtain a precursor film; (4) The product dried in the previous step was subjected to electron beam vacuum irradiation at room temperature; (5) The irradiated sample is extracted to remove unreacted substances and obtain product B; (6) Dissolve product B in dimethylformamide solvent and heat to dissolve to obtain a uniform casting solution; (7) After cooling, the casting solution is coated onto the substrate and immersed in the coagulation bath to form a porous membrane; (8) Rinse and soak the porous membrane with deionized water; (9) The rinsed porous membrane was freeze-dried to obtain product C; (10) After placing product C in an aqueous solution containing sodium sulfobutyl-β-cyclodextrin and letting it stand, remove it and rinse it with deionized water; (11) After repeating step (10) several times, the membrane is freeze-dried to obtain the target product PVDF-g-IL-SBE-β-CD porous membrane.

3. The method according to claim 2, characterized in that, Electron beam vacuum irradiation was performed at room temperature using a dose of 50 kGy.

4. The method according to claim 2, characterized in that, The amount of 1-vinyl-3-butylimidazolium tetrafluoroborate [VBIM][BF4] is 6%-15% of the mass of polyvinylidene fluoride (PVDF).

5. The method according to claim 4, characterized in that, The amount of 1-vinyl-3-butylimidazolium tetrafluoroborate [VBIM][BF4] is 6%, 10% or 15% of the mass of polyvinylidene fluoride (PVDF).

6. The method according to claim 2, characterized in that, The polycyclic aromatic hydrocarbon is phenanthrene, anthracene, or naphthalene.

7. A PVDF-g-IL porous membrane, characterized in that, It consists of polyvinylidene fluoride body and 1-vinyl-3-butylimidazolium tetrafluoroborate grafted onto it by electron beam irradiation.

8. A PVDF-g-IL-SBE-β-CD porous membrane, characterized in that, The PVDF-g-IL porous membrane described in claim 7 is obtained by anion exchange, and its surface contains sulfobutyl-β-cyclodextrin anions.

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