PVDF nanofiltration membrane constructed based on microwave-enhanced bridging interfacial polymerization and preparation method and application of PVDF nanofiltration membrane

Abstract

The invention provides a PVDF (Polyvinylidene Fluoride) nanofiltration membrane constructed on the basis of microwave-enhanced bridging interfacial polymerization as well as a preparation method and application of the PVDF nanofiltration membrane. The method comprises the following steps: reacting PVDF powder with an organic alkali to prepare a modified film-forming solution, blade-coating the modified film-forming solution on a non-woven fabric supporting layer, placing the non-woven fabric supporting layer in an ethanol-water or methanol-water coagulating bath, and preparing a PVDF supporting film by virtue of assistance of an ice template; weighing the functionalized nano material and an amino silane coupling agent, performing ultrasonic dispersion, and adding a catalyst for reaction to obtain dispersion liquid; immersing a PVDF support membrane into the dispersion liquid to obtain a modified membrane; immersing the modified membrane into an aqueous solution containing an amine monomer and an organic solution containing an acyl chloride monomer, and carrying out microwave radiation. The interface reaction rate and selectivity are enhanced through the microwave excitation effect, and meanwhile, the hydrophilicity and reaction activity of the PVDF base membrane are cooperatively regulated and controlled, so that the separation efficiency and the anti-pollution capacity of the membrane are remarkably improved. The obtained PVDF nanofiltration membrane has high flux, high selectivity and excellent structural stability, and is suitable for efficient purification and resource recovery application in a complex water system.

Description

Technical Field

[0001] The present invention relates to the field of nanofiltration membrane technology, and specifically to a PVDF nanofiltration membrane constructed based on microwave-enhanced bridging interfacial polymerization, and a preparation method and application thereof, which belongs to the research scope of construction and application of high-performance separation membrane materials. Background Art

[0002] In recent years, as global water pollution has become increasingly severe, traditional water treatment technologies have gradually exposed numerous problems, such as low efficiency, insufficient selectivity, and poor pollution resistance. Nanofiltration membranes, as highly efficient, energy-saving, and precise screening separation materials, have shown great potential for application in environmental protection, resource recovery, and biomedicine. In particular, nanofiltration membranes have become a hot research area due to their unique selective separation mechanism and low energy consumption in removing small organic pollutants, multivalent salt ions, and trace antibiotic residues.

[0003] Polyvinylidene fluoride (PVDF), as a nanofiltration membrane support layer material, is widely used in the membrane separation field due to its excellent film-forming properties, outstanding mechanical strength, and good chemical stability. However, the significant hydrophobicity and surface chemical inertness of traditional PVDF materials lead to poor interfacial adhesion between the membrane surface and the polyamide (PA) layer and structural instability. Under long-term operation conditions, the polyamide separation layer often falls off or the interface structure relaxes, seriously restricting the stable operation and separation effect of the nanofiltration membrane.

[0004] To address this challenge, current studies have attempted to introduce functionalized two-dimensional nanomaterials such as graphene oxide (GO) as an interfacial bridging layer to improve the hydrophilicity and interfacial activity of the PVDF membrane surface. However, GO materials in existing technologies generally have serious stacking and aggregation problems, and the physical adsorption between them and the PVDF substrate is mostly weak interaction, and the interfacial layer is very likely to peel off and fail during long-term operation. In addition, the reaction rate of traditional interfacial polymerization processes is difficult to accurately control, and the polyamide layer usually has problems such as uneven thickness, obvious micropore defects, and loose interfacial structure, resulting in insufficient selective retention performance of the membrane and poor treatment effect on complex water quality systems (such as antibiotic wastewater, dye wastewater, and high salt and organic coexistence systems).

[0005] Furthermore, existing membrane separation materials face long-term challenges in treating complex water systems, including surface contamination accumulation and interfacial structural stability. Currently, there is a lack of systematic solutions that simultaneously achieve interfacial structural stability, efficient reactions, and anti-fouling self-maintenance capabilities. In particular, achieving an efficient, precise, and stable interfacial synergy mechanism in the construction of functional interfacial structures using PVDF as a substrate has become a bottleneck in achieving technological breakthroughs in this field.

[0006] Therefore, there is an urgent need to develop a new PVDF nanofiltration membrane construction method that combines efficient interfacial polymerization reaction mechanism, high interfacial structure stability and anti-pollution self-maintenance function. Summary of the Invention

[0007] The present invention aims to address the technical bottlenecks of existing PVDF-based nanofiltration membranes, such as insufficient interfacial activity, poor hydrophilicity, low stability of the polyamide separation layer, and limited anti-pollution performance, and proposes a new high-performance PVDF nanofiltration membrane preparation method that utilizes the synergistic coupling of aminosilane and functional nanomaterials combined with microwave-enhanced interfacial polymerization.

[0008] Based on the above technical problems, the present invention innovatively proposes a novel membrane-forming method that utilizes the synergistic coupling of aminosilanes and functionalized nanomaterials, combined with microwave radiation to precisely control interfacial polymerization reactions. This method synergistically enhances interfacial reaction activity by combining aminosilanes and nanomaterials, while simultaneously utilizing the precise microwave heating effect to significantly improve the activity of interfacial reaction sites and the density and uniformity of the polyamide layer, thereby producing a high-performance PVDF nanofiltration membrane with high interfacial bonding strength, strong selective retention, and significantly improved anti-fouling properties.

[0009] The technical solution of the present invention is achieved as follows:

[0010] A method for preparing a PVDF nanofiltration membrane based on microwave-enhanced bridged interfacial polymerization comprises the following steps:

[0011] (1) reacting polyvinylidene fluoride powder with an organic base solution, wherein the organic base is a bicyclic guanidine compound, to achieve precise induction and activation of active sites on the surface of PVDF to form modified PVDF; then adding the solution to an organic solvent and stirring to obtain a modified film-forming solution;

[0012] (2) coating the modified membrane-forming solution of step (1) on a non-woven fabric support layer and placing it in an ethanol-water or methanol-water mixed coagulation bath, and preparing a PVDF support membrane with a directional microporous structure by an ice template-assisted non-solvent-induced phase inversion method;

[0013] (3) weighing the functionalized nanomaterial and the aminosilane coupling agent, ultrasonically dispersing them in a solvent, adding a catalyst to react, and obtaining a composite dispersion;

[0014] (4) immersing the PVDF support membrane of step (2) in the composite dispersion of step (3), drying, and obtaining a modified membrane, and treating the PVDF support membrane in the dispersion to construct an intermediary coupling interface layer;

[0015] (5) The modified membrane obtained in step (4) is first immersed in an aqueous solution containing amine monomers, and then immersed in an organic solution of acyl chloride monomers for interfacial contact. The bridging interfacial polymerization reaction is precisely enhanced by microwave radiation, and a dense and uniform polyamide separation layer is generated in situ on the surface of the intermediate interface layer, thereby finally obtaining a multifunctional PVDF nanofiltration membrane with high selectivity, high stability and anti-pollution ability.

[0016] The present invention modifies PVDF powder with an organic base to prepare a uniform film-forming solution, introduces functionalized nanomaterials with groups such as carboxyl, hydroxyl or epoxy groups on its surface, and performs interfacial coupling with aminosilane coupling agents to construct a bridged intermediate interface structure; then, interfacial polymerization of amine / acyl chloride monomers is carried out on the membrane surface, and rapid and dense film formation is achieved under the action of microwave radiation to form a polyamide separation layer with a negative charge and stable structure. The present invention enhances the interfacial reaction rate and selectivity through microwave excitation, while synergistically regulating the hydrophilicity and reactivity of the PVDF-based membrane, significantly improving the separation efficiency and anti-pollution ability of the membrane. The resulting PVDF nanofiltration membrane has high flux, high selectivity and excellent structural stability, and is suitable for high-efficiency purification and resource recovery applications in complex water systems.

[0017] Preferably, in step (1), the organic base is selected from one or more of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD).

[0018] Preferably, in step (1), the mass volume ratio of the PVDF powder to the organic alkali solution is 1:4-6 in g / ml.

[0019] Preferably, in step (1), the concentration of the organic base solution is 15%-25% wt.

[0020] Preferably, in step (1), the reaction temperature is 50-70° C. and the reaction time is 1-3 h.

[0021] Preferably, in step (1), the organic solvent is selected from any one of N,N-dimethylacetamide and N-methylpyrrolidone, or a combination of two or more thereof.

[0022] Preferably, in step (1), the mass volume ratio of the PVDF powder to the organic solvent is 1:4-6 in g / ml.

[0023] Preferably, in step (1), the stirring temperature is 55-65° C. and the stirring time is 3-5 h.

[0024] Preferably, in step (2), the volume ratio of ethanol to water in the ethanol-water is 1:3-5, and the volume ratio of methanol to water in the methanol-water is 1:3-5.

[0025] Preferably, in step (3), the functionalized nanomaterial is selected from any one or a combination of two or more of carboxylated graphene oxide, hydroxylated graphene, amino MXene, modified carbon nanotubes, and functionalized silica.

[0026] Preferably, in step (3), the aminosilane coupling agent is an organosilicon coupling agent containing an amino group and a trialkoxysilyl group, selected from any one or a combination of two or more of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-ethylaminopropyltrimethoxysilane or their derivatives.

[0027] Preferably, in step (3), the solvent is selected from any one or a combination of two or more of anhydrous ethanol, methanol, isopropanol, and ethylene glycol.

[0028] Preferably, in step (3), the catalyst is glacial acetic acid.

[0029] Preferably, in step (3), the mass ratio of the functionalized nanomaterial to the aminosilane coupling agent is 1:0.5-2.

[0030] Preferably, in step (3), the material-liquid ratio of the functionalized nanomaterial to the solvent is 1:90-110 g / mL.

[0031] Preferably, in step (3), the mass volume ratio of the functionalized nanomaterial to the catalyst is 1:3-6 in g / ml.

[0032] Preferably, in step (3), the ultrasonic dispersion time is 20-40 min.

[0033] Preferably, in step (3), the reaction temperature is 30-70° C. and the reaction time is 10-60 minutes.

[0034] Preferably, in step (4), the PVDF support membrane is immersed in the composite dispersion for 20-40 minutes; the drying temperature is 55-65° C., and the drying time is 10-15 hours.

[0035] Preferably, in step (5), the amine-containing monomer is selected from any one or a combination of two or more of piperazine, polyethyleneimine or their derivatives.

[0036] Preferably, in step (5), the acyl chloride monomer is selected from any one of isophthaloyl chloride and terephthaloyl chloride, or a combination of two or more thereof.

[0037] Preferably, in step (5), the concentration of the aqueous solution containing amine monomers is 0.15%-0.25% wt.

[0038] Preferably, in step (5), the concentration of the acyl chloride monomer organic solution is 0.05%-0.15% wt.

[0039] Preferably, in step (5), the time for immersing in the aqueous solution containing amine monomers and the organic solution containing acyl chloride monomers is 1-3 minutes.

[0040] Preferably, in step (5), the power of the microwave is 30-100 W, and the irradiation time is 10-60 seconds.

[0041] A PVDF nanofiltration membrane constructed based on microwave-enhanced bridging interfacial polymerization is prepared by the preparation method of the PVDF nanofiltration membrane described in any one of the present inventions. The membrane structure of the PVDF nanofiltration membrane includes a modified PVDF support layer, a bridging intermediate coupling layer and a polyamide separation layer in sequence. The polyamide separation layer has a thickness of 10-100 nm and a membrane surface zeta potential of -30 to -50 mV.

[0042] The preparation method of the present invention has mild conditions and is applicable to conventional membrane preparation processes such as coating, impregnation, and interfacial polymerization, and has strong process adaptability and amplification potential. The PVDF nanofiltration membrane prepared by the present invention has the characteristics of stable structure, dense separation layer, good surface hydrophilicity, and negative charge, and is suitable for selective separation of various complex water systems. The present invention also provides the application of the PVDF nanofiltration membrane in water treatment, including but not limited to deep purification and desalination in the fields of antibiotic wastewater, dye wastewater, and salt-containing organic polluted water, and is particularly suitable for nanofiltration fields with high requirements for high flux, high retention rate and anti-pollution performance.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) The present invention significantly improves the interfacial reaction efficiency and active site density by synergistically combining aminosilane with functional nanomaterials and supplemented by microwave-enhanced bridging interfacial polymerization, thereby constructing a dense and stable polyamide separation layer;

[0045] (2) The present invention achieves precise control of the crystalline structure of the PVDF support layer, obtains excellent piezoelectric response performance and hydrophilic interfacial activity, and improves the precise interception capability of small molecule pollutants and salts;

[0046] (3) The surface negative charge of the nanofiltration membrane of the present invention is evenly distributed, and the anti-organic pollution performance is outstanding. It also has the self-cleaning property of rapid recovery and is suitable for the efficient purification of dye wastewater, antibiotic wastewater, and high-salt organic pollution wastewater;

[0047] (4) The whole preparation process of the application is clear, mild in conditions, easy to scale up, and has strong industrial amplification potential and practical application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 Figure 1 is a scanning electron microscope image of a PVDF nanofiltration membrane based on the synergistic coupling of aminosilane and functionalized nanomaterials according to an embodiment of the application. DETAILED DESCRIPTION

[0049] Unless otherwise specified, the experimental methods used in the embodiments of the application are conventional methods.

[0050] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the application can be obtained from commercial channels.

[0051] PVDF: polyvinylidene fluoride

[0052] Example 1

[0053] (1) PVDF powder and 20wt% 1,8-diazabicyclo[5.4.0]undec-7-ene aqueous solution were added to a reaction vessel at a mass-volume ratio g / ml of 1:5, and reacted at a temperature of 60℃ for 2h to obtain modified PVDF; the modified PVDF was added to N,N-dimethylacetamide (DMAC), and the mass-volume g / ml of PVDF powder and DMAC was 15:75, and the modified membrane-forming solution was prepared by magnetic stirring at 60℃ for 4h.

[0054] (2) The modified membrane-forming solution of step (1) was coated on a non-woven fabric support layer by blade coating, and then placed in an ethanol-water coagulation bath, wherein the volume ratio of ethanol to water was 1:4, and a PVDF support membrane was prepared by ice template assisted phase inversion.

[0055] (3) 1.0g of carboxylated graphene oxide (cGO) and 1.0g of 3-aminopropyltriethoxysilane (APTES) were added to 100ml of anhydrous ethanol and ultrasonically dispersed for 30min, 5ml of glacial acetic acid was added, and the mixture was reacted at 50℃ for 2h to obtain a composite solution.

[0056] (4) The PVDF support membrane of step (2) was immersed in the composite solution of step (3) for 30min, and dried at 60℃ for 12h to obtain a modified membrane.

[0057] (5) The modified membrane of step (4) was first immersed in a 0.2wt% piperazine (PIP) aqueous solution for 2min, and then immersed in a 0.1wt% terephthaloyl chloride (TMC) n-hexane solution for 2min, and a 50W microwave-assisted interfacial polymerization reaction was performed for 30s, the membrane was washed and dried in an oven at 50℃ for 10min to obtain a NF-1 nanofiltration membrane.

[0058] Example 2

[0059] (1) The same PVDF film forming steps as in Example 1 were used to prepare a PVDF support membrane.

[0060] (2) Weigh 1.0 g of carboxylated graphene oxide (cGO) and 2.0 g of 3-aminopropyltriethoxysilane (APTES), add them to 100 mL of anhydrous ethanol, and ultrasonically disperse them for 30 min. Then, react them at 50 °C for 2 h in the presence of 5 mL of glacial acetic acid to obtain a composite solution.

[0061] (3) The PVDF support membrane prepared in step (1) was treated in the composite solution prepared in step (2) for 30 min and vacuum dried at 60° C. for 12 h to obtain a modified membrane.

[0062] (4) The modified membrane prepared in step (3) was immersed in a 0.2 wt% piperazine aqueous solution for 2 min, and then immersed in a 0.1 wt% isophthaloyl chloride n-hexane solution for 2 min. The interfacial polymerization reaction was enhanced by a 50 W microwave-assisted method for 40 s. The membrane was rinsed and dried in an oven at 50 °C for 10 min to obtain an NF-2 nanofiltration membrane.

[0063] Example 3

[0064] (1) PVDF powder and 20 wt% 1,8-diazabicyclo[5.4.0]undec-7-ene aqueous solution were added to a reaction vessel at a mass volume ratio of 1:5 g / ml, and reacted at 60°C for 2 h to obtain modified PVDF; and the modified PVDF was added to N,N-dimethylacetamide (DMAC) at a mass volume ratio of PVDF powder to DMAC of 15:75 g / ml, and magnetically stirred at 60°C for 4 h to prepare a modified film-forming solution.

[0065] (2) After the membrane solution in step (1) is scraped off, it is solidified in methanol-water under the guidance of an ice template, wherein the volume ratio of methanol to water is 1:4, to obtain a PVDF support membrane with a microporous structure.

[0066] (3) Weigh 1.0 g of carboxylated MXene and 1.0 g of APTES, add them to 100 mL of anhydrous ethanol, ultrasonicate for 30 min, and react at 50 °C for 2 h to obtain a MXene–APTES composite solution.

[0067] (4) The PVDF support membrane prepared in step (2) was treated in the MXene–APTES composite solution prepared in step (3) for 30 min and dried at 60° C. for 12 h to obtain a modified membrane.

[0068] (5) The modified membrane prepared in step (4) was first immersed in a 0.2 wt% piperazine (PIP) aqueous solution for 2 min, and then immersed in a 0.1 wt% isophthaloyl chloride (TMC) n-hexane solution for 2 min. A 60 W microwave was used to assist in enhancing the interfacial polymerization reaction for 40 s. Under the assistance of microwave radiation, the intermediate interface activation and the formation of the polyamide layer were completed. The membrane was rinsed and dried in an oven at 50 ° C for 10 minutes to finally obtain the NF-3 nanofiltration membrane.

[0069] Comparative Example 1

[0070] Comparative Example 1 differs from Example 1 in that no functionalized nanomaterial (carboxylated graphene oxide) is added. Step (3): 1.0 g of 3-aminopropyltriethoxysilane (APTES) is weighed and added to 100 mL of anhydrous ethanol, followed by ultrasonic dispersion for 30 minutes. After adding 5 mL of glacial acetic acid, the mixture is reacted at 50° C. for 2 hours to obtain a composite solution. The remaining raw materials and preparation method are the same as those in Example 1.

[0071] Comparative Example 2

[0072] Comparative Example 2 differs primarily from Example 1 in that no catalyst (glacial acetic acid) is added. Step (3) includes weighing 1.0 g of carboxylated graphene oxide (cGO) and 1.0 g of 3-aminopropyltriethoxysilane (APTES), adding them to 100 mL of anhydrous ethanol, ultrasonically dispersing them for 30 minutes, and reacting them at 50°C for 2 hours to obtain a composite solution. The remaining raw materials and preparation method are the same as those of Example 1.

[0073] Comparative Example 3

[0074] Comparative Example 3 differs primarily from Example 1 in that APTES is not added. Step (3): 1.0 g of carboxylated graphene oxide (cGO) was weighed and added to 100 mL of anhydrous ethanol, followed by ultrasonic dispersion for 30 min. 5 mL of glacial acetic acid was then added and reacted at 50°C for 2 h to obtain a composite solution. The remaining raw materials and preparation method were the same as those in Example 1.

[0075] Performance Testing

[0076] (1) Pure water flux test: The membrane samples obtained in Examples 1-3 and Comparative Examples 1-3 were cut into discs with a diameter of 47 mm and installed on a plate with an effective filtration area of ​​28.3 cm 2 In the nanofiltration device, the test pressure is 0.5 MPa and the temperature is 25°C. Deionized water is used as the feed solution. After the operation is stable, the permeation volume within 1 hour is measured and the pure water flux (L·m -2 ·h -1 The results show that the flux of the example membrane is significantly higher than that of the comparative example membrane, indicating that the interfacial cooperative structure has a promoting effect on the transport of water molecules.

[0077] (2) NaCl Rejection Test: A 1 g / L NaCl solution was used as the feed, and the apparatus conditions were consistent with those used in the flux test. The salt concentration of the permeate was measured by conductivity, and the retention rate was then calculated. The test results showed that the example membranes maintained good ion screening capabilities, with NaCl retention rates generally superior to those of the comparative example membranes, indicating that the intermediary functional layer of the present invention helps improve the selective separation performance of the membrane.

[0078] (3) Anti-pollution Performance Test: Using a 1 g / L bovine serum albumin (BSA) solution as the contamination source, the anti-pollution performance of Example 1 and Comparative Example 2 was tested. The test steps were as follows: measuring the initial pure water flux (J0), measuring the post-contamination flux (J1) after filtering the BSA solution for 1 hour, and then measuring the recovery flux (J2) after rinsing with pure water for 30 minutes. The flux recovery rate (FRR) was calculated as (J2 / J0) × 100%. The results showed that the membrane of Example 1 had a higher flux recovery rate and better anti-pollution ability than the membrane of Comparative Example.

[0079] (4) Test results

[0080]

[0081] The above results show that, compared with three representative commercially available nanofiltration membranes, the PVDF synergistic interfacial nanofiltration membranes prepared in Examples 1-3 of the present invention still exhibit excellent comprehensive performance at an operating pressure of 0.5 MPa. Among them, Example 1 achieved a NaCl rejection rate of over 61% and a pure water flux of 15.8 L·m without sacrificing flux. -2 ·h-1, FRR is as high as 92%, showing the synergistic advantages of high flux, high selectivity and excellent anti-pollution ability. The results of comparative examples 1-3 further show that when the membrane material does not introduce functionalized nanomaterials or is not stabilized by aminosilane coupling agents, the membrane structure lacks effective coupling, resulting in a significant decrease in water flux and retention performance, indicating that the intermediate layer design and interface regulation play a key role in improving membrane performance. In summary, it can be seen that the synergistic interface construction method provided by the present invention can effectively regulate the structural and functional matching relationship of PVDF nanofiltration membranes, giving it comprehensive advantages such as low pressure and high efficiency, pollution resistance, and controllable screening, and has good engineering application prospects.

Claims

1. A method for preparing a PVDF nanofiltration membrane based on microwave-enhanced bridging interfacial polymerization, characterized in that: The following steps are involved: (1) reacting polyvinylidene fluoride powder with an organic base solution, wherein the organic base is a bicyclic guanidine compound, and then adding the organic solvent and stirring to obtain a modified film-forming solution; (2) coating the modified membrane-forming solution of step (1) on a non-woven fabric support layer and placing it in an ethanol-water or methanol-water coagulation bath, and preparing a PVDF support membrane with the assistance of an ice template; (3) weighing the functionalized nanomaterial and the aminosilane coupling agent, ultrasonically dispersing them in a solvent, adding a catalyst to react, and obtaining a composite dispersion; (4) immersing the PVDF support membrane from step (2) into the composite dispersion from step (3), and drying to obtain a modified membrane; (5) The modified membrane of step (4) is first immersed in an aqueous solution containing amine monomers, and then immersed in an organic solution of acyl chloride monomers, and microwave irradiation is used to obtain the target PVDF nanofiltration membrane.

2. The method for preparing a PVDF nanofiltration membrane based on microwave-enhanced bridging interfacial polymerization according to claim 1, characterized in that: In step (1), the organic base is selected from one or more of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD); the mass volume ratio of the PVDF powder to the organic base solution is 1:4-6 in g / ml, and the concentration of the organic base solution is 15%-25%wt; the organic solvent is selected from any one of N,N-dimethylacetamide and N-methylpyrrolidone, or a combination of two or more thereof; the mass volume ratio of the PVDF powder to the organic solvent is 1:4-6 in g / ml.

3. The method for preparing a PVDF nanofiltration membrane based on microwave-enhanced bridging interfacial polymerization according to claim 1 or 2, characterized in that: In step (1), the reaction temperature is 50-70°C, and the reaction time is 1-3 hours; the stirring temperature is 55-65°C, and the stirring time is 3-5 hours.

4. The method for preparing a PVDF nanofiltration membrane based on microwave-enhanced bridging interfacial polymerization according to claim 1, wherein: In step (2), the volume ratio of ethanol to water in the ethanol-water is 1:3-5, and the volume ratio of methanol to water in the methanol-water is 1:3-5.

5. The method for preparing a PVDF nanofiltration membrane based on microwave-enhanced bridging interfacial polymerization according to claim 1, wherein: In step (3), the functionalized nanomaterial is selected from any one or a combination of two or more of carboxylated graphene oxide, hydroxylated graphene, amino MXene, modified carbon nanotubes, and functionalized silica; The aminosilane coupling agent is selected from any one or a combination of two or more of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-ethylaminopropyltrimethoxysilane or their derivatives; The solvent is selected from any one or a combination of two or more of ethanol, methanol, isopropanol, and ethylene glycol; the catalyst is glacial acetic acid; The mass ratio of the functionalized nanomaterial to the aminosilane coupling agent is 1:0.5-2; the solid-liquid ratio of the functionalized nanomaterial to the solvent is 1:90-110 g / mL; the mass-volume ratio of the functionalized nanomaterial to the catalyst is 3-6 g / ml; The ultrasonic dispersion time is 20-40 minutes; the reaction temperature is 30-70° C., and the time is 10-60 minutes.

6. The method for preparing a PVDF nanofiltration membrane based on microwave-enhanced bridged interfacial polymerization according to claim 1, wherein: In step (4), the PVDF support membrane is immersed in the composite dispersion for 20-40 minutes; the drying temperature is 55-65° C., and the drying time is 10-15 hours.

7. The method for preparing a PVDF nanofiltration membrane based on microwave-enhanced bridged interfacial polymerization according to claim 1, characterized in that: Step (5), the amine-containing monomer is selected from any one or a combination of two or more of piperazine, polyethyleneimine or their derivatives, and the acyl chloride monomer is selected from any one or a combination of two or more of isophthaloyl chloride and terephthaloyl chloride; The concentration of the aqueous solution containing amine monomers is 0.15%-0.25% wt; the concentration of the organic solution containing acyl chloride monomers is 0.05%-0.15% wt; The time of immersing in the aqueous solution containing amine monomers and the organic solution containing acyl chloride monomers is 1-3 minutes respectively; The power of the microwave is 30-100W, and the irradiation time is 10-60 seconds.

8. A PVDF nanofiltration membrane constructed based on microwave-enhanced bridging interfacial polymerization, characterized in that: The PVDF nanofiltration membrane is prepared by the preparation method of any one of claims 1 to 7, wherein the membrane structure of the PVDF nanofiltration membrane includes a modified PVDF support layer, a bridging intermediate coupling layer and a polyamide separation layer in sequence, the polyamide separation layer has a thickness of 10-100 nm, and the membrane surface zeta potential is -30 to -50 mV.

9. Application of the PVDF nanofiltration membrane constructed based on microwave-enhanced bridging interfacial polymerization as claimed in claim 8 in the field of water treatment.

10. The use according to claim 9, characterized in that The PVDF nanofiltration membrane is used for removing pollutants and purifying water quality in antibiotic wastewater, dye wastewater or salt-containing organic polluted water.

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