Method for preparing high permeability nanofiltration membrane by adjusting interlayer spacing of intermediate layer

Abstract

The application discloses a method for preparing a high-permeability nanofiltration membrane by adjusting the layer spacing of an intermediate layer, and belongs to the technical field of membrane separation materials. Polyethylene oxide is mixed with a water dispersion of molybdenum disulfide nanosheets to obtain a polyethylene oxide intercalated molybdenum disulfide composite dispersion; the composite dispersion is deposited on the surface of a polyethersulfone ultrafiltration support membrane by vacuum-assisted suction filtration to form an intermediate layer, and then sequentially contacted with a water-phase piperazine solution and an organic-phase trimesoyl chloride solution, and an interfacial polymerization and thermal curing are performed to form a polyamide selective separation layer. The layer spacing of the intermediate layer can be adjusted by adjusting the mass ratio of polyethylene oxide to molybdenum disulfide nanosheets, the mass transfer behavior of piperazine is improved, a polyamide layer with a small thickness and obvious wrinkle structure is obtained, the water permeability of the nanofiltration membrane is improved while the salt rejection rate is maintained, and the nanofiltration membrane can be used for nanofiltration separation of salt-containing water.

Description

Technical Field

[0001] This invention relates to the field of membrane separation materials technology, and specifically to a method for preparing a high-permeability nanofiltration membrane by controlling the interlayer spacing of the intermediate layer. Background Technology

[0002] Nanofiltration is a pressure-driven membrane separation technology that falls between ultrafiltration and reverse osmosis. It offers advantages such as lower operating pressure, higher separation efficiency, lower energy consumption, and ease of continuous operation, and has been applied in drinking water purification, industrial wastewater treatment, water softening, salt separation, and material concentration. Thin-film composite nanofiltration membranes typically consist of a porous support membrane and a polyamide selective separation layer. The polyamide selective separation layer is generally formed by interfacial polymerization of aqueous amine monomers and organic acyl chloride monomers. Its thickness, degree of cross-linking, surface morphology, and effective mass transfer area directly affect the membrane's water permeability and solute retention performance.

[0003] In traditional interfacial polymerization, aqueous amine monomers are first adsorbed and stored on the surface and within the pores of a porous support membrane, and then diffuse towards the organic phase and react with acyl chloride monomers. However, the surface roughness, pore size distribution, and hydrophilicity of the porous support membrane are difficult to control precisely, easily leading to uneven adsorption and diffusion rates of amine monomers. This results in problems such as excessively rapid local growth, uneven thickness, or insufficient effective mass transfer area in the polyamide layer. The resulting polyamide layer is usually thick and predominantly nodular, with a long water molecule transport path, making it difficult to simultaneously achieve good permeability and selectivity in nanofiltration membranes.

[0004] To regulate the interfacial polymerization process, existing technologies propose placing an intermediate layer between the porous support membrane and the polyamide selective separation layer. This intermediate layer improves the surface morphology and hydrophilicity of the support membrane and acts as an adsorbent, storage, and slow-release agent for the aqueous amine monomers, thereby regulating their diffusion behavior towards the organic phase and controlling the formation rate and microstructure of the polyamide layer. Two-dimensional nanomaterials such as graphene oxide, molybdenum disulfide, transition metal carbides, or nitrides possess layered structures, high specific surface areas, and excellent film-forming capabilities, enabling the formation of a two-dimensional intermediate layer on the support membrane surface.

[0005] Molybdenum disulfide nanosheets possess good chemical stability and a layered structure, allowing for the formation of water molecule and solute transport channels between their layers. However, uncontrolled molybdenum disulfide nanosheets tend to densely stack during deposition, resulting in a small interlayer spacing with limited adjustment range. This not only increases the resistance to water molecule transport but also restricts the adsorption, diffusion, and release of aqueous amine monomers within the interlayer, hindering the full realization of its regulatory effect on interfacial polymerization. Furthermore, uneven deposition of two-dimensional nanosheets leads to inconsistencies in the thickness and coverage of the interlayer, thereby affecting the uniformity of the polyamide selective separation layer and the membrane's separation performance.

[0006] Therefore, how to adjust the interlayer spacing of molybdenum disulfide nanosheets in a simple and controllable way, and uniformly deposit them on the surface of a porous support membrane to form a continuous intermediate layer, so as to improve the transport behavior of water molecules and amine monomers, control the thickness and surface morphology of the polyamide selective separation layer, and improve the water permeability of nanofiltration membranes while maintaining a high salt rejection rate, remains a technical problem to be solved in this field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for preparing high-permeability nanofiltration membranes by controlling the interlayer spacing of the intermediate layers.

[0008] A method for preparing a high-permeability nanofiltration membrane by controlling the interlayer spacing of the intermediate layer includes the following steps: S1. Mix polyethylene oxide with molybdenum disulfide nanosheet aqueous dispersion to obtain polyethylene oxide intercalated molybdenum disulfide composite dispersion. S2. Vacuum-assisted filtration is used to deposit the poly(ethylene oxide) intercalated molybdenum disulfide composite dispersion onto the surface of a polyethersulfone ultrafiltration support membrane to form a poly(ethylene oxide) intercalated molybdenum disulfide intermediate layer. S3. The polyethersulfone ultrafiltration support membrane loaded with the polyoxyethylene intercalated molybdenum disulfide intermediate layer is sequentially contacted with a piperazine aqueous phase solution and a pyromellitic trimethylol chloride organic phase solution to allow the piperazine and pyromellitic trimethylol chloride to undergo an interfacial polymerization reaction. After thermal curing, a polyamide selective separation layer is formed on the surface of the polyoxyethylene intercalated molybdenum disulfide intermediate layer to obtain a nanofiltration membrane.

[0009] In step S1, the mass ratio of polyethylene oxide to molybdenum disulfide nanosheets is (0.01-1):1, and the mixing time of the aqueous dispersion of polyethylene oxide and molybdenum disulfide nanosheets is 8-16 h.

[0010] The weight-average molecular weight of the polyethylene oxide is 20,000-500,000 Da.

[0011] In step S1, the molybdenum disulfide nanosheet aqueous dispersion is prepared by the following method: The molybdenum disulfide nanosheet suspension was centrifuged, the supernatant was discarded, the resulting precipitate was resuspended in deionized water and ultrasonically dispersed to obtain the molybdenum disulfide nanosheet aqueous dispersion. The concentration of molybdenum disulfide nanosheets in the aqueous dispersion is 0.01-10 g / L.

[0012] In step S2, the molecular weight cutoff of the polyethersulfone ultrafiltration support membrane is 20,000-250,000 Da; after vacuum-assisted filtration, the polyethersulfone ultrafiltration support membrane loaded with the polyethylene oxide intercalated molybdenum disulfide interlayer is dried.

[0013] In step S3: the concentration of piperazine in the piperazine aqueous solution is 5-12 g / L, and the contact time between the polyethersulfone ultrafiltration support membrane loaded with the polyethylene oxide intercalated molybdenum disulfide interlayer and the piperazine aqueous solution is 0.5-5 min; The concentration of trimesoyl chloride in the organic phase solution is 0.01-5 g / L, and the interfacial polymerization reaction time is 0.5-5 min. The thermosetting temperature is 50-70℃, and the thermosetting time is 3-10 min.

[0014] The polyethersulfone ultrafiltration support membrane has a molecular weight cutoff of 20,000 Da; the concentration of molybdenum disulfide nanosheets in the aqueous dispersion of molybdenum disulfide nanosheets is 0.02 g / L; and the weight-average molecular weight of the polyethylene oxide is 100,000 Da. The concentration of piperazine in the aqueous phase solution is 10 g / L, and the polyethersulfone ultrafiltration support membrane with the intermediate layer is in contact with the aqueous phase solution of piperazine for 2 min. The organic phase solution of pyromellitic chloride is a hexane solution of pyromellitic chloride, wherein the concentration of pyromellitic chloride is 1.5 g / L, and the interfacial polymerization reaction time is 1 min; The thermosetting temperature is 60°C, and the thermosetting time is 5 min.

[0015] A polyoxyethylene intercalated molybdenum disulfide interlayer nanofiltration membrane: comprising a polyethersulfone ultrafiltration support membrane, a polyoxyethylene intercalated molybdenum disulfide interlayer, and a polyamide selective separation layer arranged sequentially; The polyoxyethylene intercalated molybdenum disulfide intermediate layer is formed by inserting polyoxyethylene between the layers of molybdenum disulfide nanosheets; The polyamide selective separation layer is formed by interfacial polymerization of piperazine and pyromellitic trimethylol chloride.

[0016] The interlayer spacing of the molybdenum disulfide nanosheets in the poly(ethylene oxide) intercalated molybdenum disulfide intermediate layer is 11.5-15.8 Å.

[0017] Application of a polyethylene oxide intercalated molybdenum disulfide interlayer nanofiltration membrane in saline nanofiltration separation, wherein the saline contains at least one of Na2SO4, MgSO4, MgCl2 and NaCl.

[0018] Due to the adoption of the above technical solutions, the beneficial effects of the present invention include: (1) This invention uses polyethylene oxide to intercalate molybdenum disulfide nanosheets. By adjusting the mass ratio of polyethylene oxide to molybdenum disulfide nanosheets, the stacking state and interlayer spacing of the molybdenum disulfide nanosheets are changed. When the mass ratio increases from 0 to 1.0 g / g, the interlayer spacing of molybdenum disulfide increases from 11.0 Å to 15.8 Å, realizing the controllable adjustment of the interlayer spacing of the intermediate layers, and the operation is simple.

[0019] (2) The polyoxyethylene intercalated molybdenum disulfide intermediate layer can improve the surface state of the polyethersulfone ultrafiltration support membrane and regulate the adsorption, diffusion and release behavior of piperazine during the interfacial polymerization process, so that the polyamide selective separation layer formed has a more obvious wrinkled structure and a smaller thickness, thereby increasing the effective mass transfer area and shortening the water molecule transport path.

[0020] (3) The present invention can improve the water permeability of nanofiltration membrane while maintaining salt rejection performance; and can still maintain good divalent sulfate rejection performance, which helps to alleviate the trade-off between permeability and selectivity of nanofiltration membrane. Attached Figure Description

[0021] Figure 1 For PES, PES-MoS2 and PES-P Y XRD patterns and interlayer spacing of / M; Figure 2 for TFC-PES (ab), TFC-MoS2 (cd), TFC-P 0.02 / M(ef),TFC-P 0.1 / M(gh) and TFC-P 0.45 / M(ij) SEM images of the surface and cross-section of the membrane; Figure 3 For TFC-PES, TFC-MoS2 and TFC-P Y / M water permeability coefficient diagram; Figure 4 For TFC-PES, TFC-MoS2 and TFC-P Y / M Salt rejection rate diagram. Detailed Implementation

[0022] The present invention will be further described below with reference to preparation examples and embodiments, so that those skilled in the art can understand and implement the present invention. However, the following preparation examples and embodiments are not intended to limit the scope of protection of the present invention.

[0023] Example 1: Preparation and Interlayer Spacing Control of Polyethylene Oxide Intercalated Molybdenum Disulfide Composite Material A thin-layer molybdenum disulfide nanosheet suspension (purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., catalog number 100928, item number XF135, concentration 1 mg / mL, hereinafter the same) was transferred to a 10 mL centrifuge tube and centrifuged at 8000 r / min for 10 min. The supernatant was discarded to obtain a precipitate, thereby removing LiOH and small-diameter nanosheets. The obtained precipitate was resuspended in deionized water and ultrasonically dispersed to prepare an aqueous dispersion of molybdenum disulfide nanosheets with a concentration of 0.02 g / L.

[0024] Polyethylene oxide (PEO) with a weight-average molecular weight of 100,000 Da was added to an aqueous dispersion of molybdenum disulfide nanosheets, with mass ratios of PEO to molybdenum disulfide nanosheets of 0, 0.01, 0.02, 0.03, 0.04, 0.1, 0.45, and 1.0 g / g, respectively. The mixture was stirred at room temperature for 12 h to obtain PEO / molybdenum disulfide composite dispersions with different degrees of intercalation. The material obtained when the mass ratio was 0 was the unintercalated molybdenum disulfide material.

[0025] Polyethylene oxide / molybdenum disulfide composite dispersions with different mass ratios were transferred to 250 mL volumetric flasks and diluted to volume with deionized water. 30 mL of each dispersion was then taken and filtered under vacuum onto the surface of a polyethersulfone (PES) ultrafiltration membrane (molecular weight cutoff of 200,000 Da). After filtration, the membrane was dried at 25 °C for 30 min to obtain the intermediate layer membrane for X-ray diffraction testing.

[0026] The interlayer spacing of molybdenum disulfide nanosheets is defined as the distance between adjacent nanosheet crystal planes, calculated according to Bragg's law based on the position of the (002) crystal plane diffraction peak in the X-ray diffraction pattern: 2d·sinθ=nλ In the formula, d is the interlayer spacing; θ is the incident angle; n is the diffraction order, taken as n=1; λ is the X-ray wavelength, taken as λ=1.54 Å.

[0027] A polyethersulfone film and a polyethersulfone film loaded with an unintercalated molybdenum disulfide interlayer were used as controls. X-ray diffraction patterns and calculated interlayer spacings are shown below. Figure 1 As shown, when the mass ratio of polyethylene oxide to molybdenum disulfide nanosheets was 0, 0.01, 0.04, 0.1, 0.45, and 1.0 g / g, the corresponding interlayer spacings were 11.0, 11.5, 14.4, 15.1, 15.7, and 15.8 Å, respectively. The results indicate that polyethylene oxide can penetrate between the molybdenum disulfide nanosheets, and the interlayer spacing can be adjusted by changing its mass ratio.

[0028] Example 2: Preparation of nanofiltration membrane Composite dispersions of polyethylene oxide and molybdenum disulfide nanosheets prepared in Example 1 at mass ratios of 0.02, 0.1, and 0.45 g / g were selected respectively. Following the method described in Example 1, 30 mL of each composite dispersion was vacuum-assisted filtered onto the surface of a polyethersulfone ultrafiltration membrane with a molecular weight cutoff of 20,000 Da. After filtration, the membrane was dried at 25 °C for 30 min and then stored in deionized water for later use.

[0029] A polyethersulfone ultrafiltration membrane with a poly(ethylene oxide) intercalated molybdenum disulfide interlayer was fixed onto a polytetrafluoroethylene (PTFE) frame. 5 mL of a 10 g / L piperazine (PIP) aqueous solution was added to the membrane surface, ensuring complete coverage. The membrane was allowed to stand for 2 min. The remaining piperazine solution was removed by vacuum filtration. Then, a 1.5 g / L trimesoyl chloride (TMC) / n-hexane organic solution was added, and the reaction was allowed to proceed for 1 min. After the reaction, the PTFE frame was tilted approximately 45°, and the organic solution on the membrane surface was poured off. Residual liquid at the membrane edge was removed using a pipette. The membrane surface was then rinsed twice with n-hexane for 30 s each time to remove the organic solution. The membrane was then transferred to a 60 °C oven for heat curing for 5 min to obtain the nanofiltration membrane. The resulting membranes were designated TFC-P. 0.02 / M、TFC-P 0.1 / M and TFC-P 0.45 / M, and stored in deionized water.

[0030] Example 3: Preparation of nanofiltration membrane The thin-layer molybdenum disulfide nanosheet suspension was transferred to a 10 mL centrifuge tube and centrifuged at 8000 r / min for 10 min. The supernatant was discarded to obtain a precipitate, thus removing LiOH and small-diameter nanosheets. The precipitate was resuspended in deionized water and ultrasonically dispersed to prepare an aqueous dispersion of molybdenum disulfide nanosheets with a concentration of 0.01 g / L.

[0031] 60 mL of the aforementioned molybdenum disulfide nanosheet aqueous dispersion, containing 0.60 mg of molybdenum disulfide nanosheets, was measured. 60 μL of a 0.1 g / L aqueous solution of polyethylene oxide with a weight-average molecular weight of 20,000 Da was added to the molybdenum disulfide nanosheet aqueous dispersion, resulting in an polyethylene oxide addition of 0.006 mg and a polyethylene oxide to molybdenum disulfide nanosheet mass ratio of 0.01:1. The mixture was stirred at room temperature for 8 h to obtain a polyethylene oxide-intercalated molybdenum disulfide composite dispersion.

[0032] The obtained composite dispersion was filtered under vacuum-assisted conditions onto the surface of a polyethersulfone ultrafiltration support membrane with a molecular weight cutoff of 20,000 Da, allowing polyethylene oxide-intercalated molybdenum disulfide nanosheets to deposit on the surface of the polyethersulfone ultrafiltration support membrane, forming a polyethylene oxide-intercalated molybdenum disulfide interlayer. After filtration, the resulting membrane was dried at 20°C for 60 min and then stored in deionized water for later use.

[0033] A polyethersulfone ultrafiltration support membrane with a polyoxyethylene intercalated molybdenum disulfide interlayer was fixed on a polytetrafluoroethylene frame. 5 mL of a 5 g / L piperazine aqueous solution was added to the membrane surface to completely cover it, and the membrane was allowed to stand for 5 min. The residual piperazine aqueous solution on the membrane surface was then removed by vacuum filtration.

[0034] A 0.5 g / L solution of trimesoyl chloride / n-hexane was added to the membrane surface, and interfacial polymerization was carried out for 5 min. After the reaction, the organic phase solution was removed, and the membrane surface was cleaned with n-hexane. The resulting membrane was transferred to a 50°C oven for heat curing for 10 min, allowing piperazine and trimesoyl chloride to interfacially polymerize to form a polyamide selective separation layer, resulting in a polyoxyethylene intercalated molybdenum disulfide interlayer nanofiltration membrane, which was then stored in deionized water.

[0035] Example 4: Preparation of nanofiltration membrane The thin-layer molybdenum disulfide nanosheet suspension was transferred to a 10 mL centrifuge tube and centrifuged at 8000 r / min for 10 min. The supernatant was discarded to obtain a precipitate, thus removing LiOH and small-diameter nanosheets. The precipitate was resuspended in deionized water and ultrasonically dispersed to prepare an aqueous dispersion of molybdenum disulfide nanosheets with a concentration of 0.1 g / L.

[0036] 6 mL of the aforementioned molybdenum disulfide nanosheet aqueous dispersion, containing 0.60 mg of molybdenum disulfide nanosheets, was measured. 0.60 mL of a 1 g / L polyethylene oxide aqueous solution with a weight-average molecular weight of 500,000 Da was added to the molybdenum disulfide nanosheet aqueous dispersion, resulting in a polyethylene oxide addition amount of 0.60 mg and a polyethylene oxide to molybdenum disulfide nanosheet mass ratio of 1:1. The mixture was stirred at room temperature for 16 h, and then deionized water was added to adjust the volume of the resulting composite dispersion to 30 mL, yielding a polyethylene oxide-intercalated molybdenum disulfide composite dispersion.

[0037] The obtained poly(ethylene oxide) intercalated molybdenum disulfide composite dispersion (30 mL) was filtered under vacuum-assisted filtration onto the surface of a polyethersulfone ultrafiltration support membrane with a molecular weight cutoff of 250,000 Da. This allowed poly(ethylene oxide) intercalated molybdenum disulfide nanosheets to deposit on the surface of the polyethersulfone ultrafiltration support membrane, forming a poly(ethylene oxide) intercalated molybdenum disulfide intermediate layer. After filtration, the resulting membrane was dried at 30 °C for 20 min and then stored in deionized water for later use.

[0038] A polyethersulfone ultrafiltration membrane with a polyoxyethylene intercalated molybdenum disulfide interlayer was fixed onto a polytetrafluoroethylene frame. 5 mL of a 12 g / L piperazine aqueous solution was added to the membrane surface to completely cover it, and the membrane was allowed to stand for 0.5 min. The residual piperazine aqueous solution on the membrane surface was then removed by vacuum filtration.

[0039] A 3 g / L solution of trimesoyl chloride / n-hexane was added to the membrane surface, and interfacial polymerization was carried out for 0.5 min. After the reaction, the organic phase solution was removed, and the membrane surface was cleaned with n-hexane. The resulting membrane was transferred to a 70°C oven for heat curing for 3 min, allowing piperazine and trimesoyl chloride to interfacially polymerize to form a polyamide selective separation layer, resulting in a polyoxyethylene intercalated molybdenum disulfide interlayer nanofiltration membrane, which was then stored in deionized water.

[0040] Comparative Example 1: Preparation of TFC-PES nanofiltration membrane without intermediate layer A polyethersulfone ultrafiltration support membrane with a molecular weight cutoff of 20,000 Da was selected and fixed onto a polytetrafluoroethylene frame. 5 mL of a 10 g / L piperazine aqueous solution was added to the surface of the polyethersulfone ultrafiltration support membrane to completely cover the membrane surface, and the membrane was allowed to stand for 2 min. The residual piperazine aqueous solution on the membrane surface was then removed by vacuum filtration.

[0041] Subsequently, a 1.5 g / L solution of trimesoyl chloride / n-hexane was added to the membrane surface, and interfacial polymerization was carried out for 1 min. After the reaction, the organic phase solution was removed, and the membrane surface was cleaned with n-hexane. The resulting membrane was transferred to a 60°C oven for heat curing for 5 min to obtain a nanofiltration membrane without an intermediate layer, denoted as TFC-PES, and stored in deionized water for later use.

[0042] The only difference between this comparative example and Example 2 is that: the polyethersulfone ultrafiltration support membrane is used directly as the interfacial polymerization substrate, and the polyethylene oxide intercalated molybdenum disulfide intermediate layer is not set on the surface of the polyethersulfone ultrafiltration support membrane; the other interfacial polymerization and thermosetting conditions are the same as those in Example 2.

[0043] Comparative Example 2: Preparation of TFC-MoS2 nanofiltration membrane without intercalated molybdenum disulfide interlayer The thin-layer molybdenum disulfide nanosheet suspension was transferred to a centrifuge tube and centrifuged at 8000 r / min for 10 min. The supernatant was discarded to remove LiOH and small-diameter molybdenum disulfide nanosheets from the suspension. The resulting precipitate was resuspended in deionized water and ultrasonically dispersed to prepare an aqueous dispersion with a molybdenum disulfide nanosheet concentration of 0.02 g / L. No polyethylene oxide was added to this aqueous dispersion.

[0044] The molybdenum disulfide nanosheet aqueous dispersion was transferred to a 250 mL volumetric flask and diluted to volume with deionized water. 30 mL of the molybdenum disulfide nanosheet aqueous dispersion was then filtered under vacuum until it reached the surface of a polyethersulfone ultrafiltration membrane with a molecular weight cutoff of 20,000 Da, allowing the molybdenum disulfide nanosheets to deposit and form an unintercalated molybdenum disulfide interlayer. After filtration, the membrane was dried at 25°C for 30 min and then stored in deionized water for later use.

[0045] A polyethersulfone ultrafiltration support membrane loaded with an unintercalated molybdenum disulfide interlayer was fixed on a polytetrafluoroethylene frame. 5 mL of a 10 g / L piperazine aqueous solution was added to the membrane surface to completely cover the membrane surface. The membrane was left to stand for 2 min. The residual piperazine aqueous solution on the membrane surface was removed by vacuum filtration.

[0046] Subsequently, a 1.5 g / L solution of trimesoyl chloride / n-hexane was added to the membrane surface, and interfacial polymerization was carried out for 1 min. After the reaction, the organic phase solution was removed, and the membrane surface was cleaned with n-hexane. The resulting membrane was transferred to a 60°C oven for heat curing for 5 min to obtain an unintercalated molybdenum disulfide interlayer nanofiltration membrane, designated TFC-MoS2, which was stored in deionized water for later use.

[0047] The only difference between this comparative example and Example 2 is that: no polyethylene oxide is added when preparing the molybdenum disulfide interlayer, and the resulting interlayer is an unintercalated molybdenum disulfide interlayer; the other interlayer deposition, interfacial polymerization and thermosetting conditions are the same as in Example 2.

[0048] Comparative Example 3: Nanofiltration membrane without sufficient intercalation treatment The thin-layer molybdenum disulfide nanosheet suspension was transferred to a 10 mL centrifuge tube, centrifuged at 8000 r / min for 10 min, the supernatant was discarded, the resulting precipitate was resuspended in deionized water and ultrasonically dispersed to prepare an aqueous dispersion of molybdenum disulfide nanosheets with a concentration of 0.02 g / L.

[0049] Polyethylene oxide with a weight-average molecular weight of 100,000 Da was added to an aqueous dispersion of molybdenum disulfide nanosheets, resulting in a mass ratio of polyethylene oxide to molybdenum disulfide nanosheets of 0.1:1. After adding polyethylene oxide, the mixture was stirred for only 5 min without undergoing a 12-hour intercalation treatment, immediately yielding a mixed dispersion of polyethylene oxide and molybdenum disulfide.

[0050] Take 30 mL of the mixed dispersion and filter it under vacuum to the surface of a polyethersulfone ultrafiltration support membrane with a molecular weight cutoff of 20,000 Da. After filtration, dry it at 25°C for 30 min.

[0051] Interfacial polymerization was performed according to the method in Example 2: 5 mL of a 10 g / L piperazine aqueous solution was added to the membrane surface, and the membrane was allowed to stand for 2 min. The residual aqueous solution was removed by vacuum filtration. A 1.5 g / L pyromellitic chloride / n-hexane organic solution was added, and the membrane was reacted for 1 min. The organic solution was poured out by tilting the membrane, and the membrane surface was washed with n-hexane. The membrane was then heat-cured at 60°C for 5 min to obtain a nanofiltration membrane that had not undergone sufficient intercalation treatment.

[0052] Comparative Example 4: Polyvinylpyrrolidone-modified molybdenum disulfide interlayer nanofiltration membrane The thin-layer molybdenum disulfide nanosheet suspension was centrifuged at 8000 r / min for 10 min, the supernatant was discarded, the resulting precipitate was resuspended in deionized water and ultrasonically dispersed to prepare an aqueous dispersion of molybdenum disulfide nanosheets with a concentration of 0.02 g / L.

[0053] In Example 2, the polyethylene oxide was replaced with an equal mass of polyvinylpyrrolidone with a weight-average molecular weight of 100,000 Da. The mass ratio of polyvinylpyrrolidone to molybdenum disulfide nanosheets was 0.1:1. The mixture was stirred at room temperature for 12 h to obtain a polyvinylpyrrolidone / molybdenum disulfide composite dispersion.

[0054] Take 30 mL of the composite dispersion and filter it under vacuum-assisted conditions until it reaches the surface of a polyethersulfone ultrafiltration support membrane with a molecular weight cutoff of 20,000 Da. After filtration, dry it at 25°C for 30 min. The remaining interfacial polymerization, hexane cleaning, and thermosetting operations are the same as in Example 2 to obtain a polyvinylpyrrolidone modified molybdenum disulfide interlayer nanofiltration membrane.

[0055] Comparative Example 5: Nanofiltration membrane with insufficient polyethylene oxide dosage Nanofiltration membranes were prepared according to the method of Example 2, with the only difference being: Polyethylene oxide with a weight-average molecular weight of 100,000 Da was added to an aqueous dispersion of molybdenum disulfide nanosheets with a concentration of 0.02 g / L, so that the mass ratio of polyethylene oxide to molybdenum disulfide nanosheets was 0.005:1. The mixture was stirred at room temperature for 12 h to obtain a polyethylene oxide / molybdenum disulfide composite dispersion with a low amount of polyethylene oxide.

[0056] Take 30 mL of the composite dispersion and vacuum-assisted filter it to the surface of a polyethersulfone ultrafiltration support membrane with a molecular weight cutoff of 20,000 Da. Dry it at 25°C for 30 min. The remaining interfacial polymerization and thermosetting operations are the same as in Example 2 to obtain a nanofiltration membrane with too low a polyoxyethylene content.

[0057] Comparative Example 6: Nanofiltration membrane with excessive polyethylene oxide content Nanofiltration membranes were prepared according to the method of Example 2, with the only difference being: Polyethylene oxide with a weight-average molecular weight of 100,000 Da was added to an aqueous dispersion of molybdenum disulfide nanosheets with a concentration of 0.02 g / L, so that the mass ratio of polyethylene oxide to molybdenum disulfide nanosheets was 1.5:1. The mixture was stirred at room temperature for 12 h to obtain a polyethylene oxide / molybdenum disulfide composite dispersion with a high amount of polyethylene oxide.

[0058] Take 30 mL of the composite dispersion and vacuum-assisted filter it to the surface of a polyethersulfone ultrafiltration support membrane with a molecular weight cutoff of 20,000 Da. Dry it at 25°C for 30 min. The remaining interfacial polymerization and thermosetting operations are the same as in Example 2, and a nanofiltration membrane with excessive polyethylene oxide content is obtained.

[0059] Comparative Example 7: Non-vacuum assisted deposition of intermediate nanofiltration membrane A polyethylene oxide intercalated molybdenum disulfide composite dispersion with a PEO / MoS2 mass ratio of 0.1:1 was prepared according to the method in Example 2.

[0060] Take 30 mL of the composite dispersion and concentrate it to 1 mL under reduced pressure. Place a polyethersulfone ultrafiltration support membrane with a molecular weight cutoff of 20000 Da horizontally, and uniformly drop the concentrated composite dispersion onto the surface of the polyethersulfone ultrafiltration support membrane, ensuring that the total amount of molybdenum disulfide nanosheets used is the same as in Example 2. After the drop addition is complete, allow it to stand and dry at 25°C until there is no obvious liquid on the surface, and then continue drying at 25°C for 30 min to form a drop-coated polyethylene oxide intercalated molybdenum disulfide intermediate layer.

[0061] The remaining piperazine aqueous phase treatment, pyromellitic trimethylol chloride interfacial polymerization, n-hexane cleaning and thermal curing operations were the same as in Example 2, resulting in an intermediate layer nanofiltration membrane prepared by non-vacuum assisted deposition.

[0062] Test Example 1: Membrane Morphology Characterization Scanning electron microscopy was used to study TFC-PES, TFC-MoS2, and TFC-P. 0.02 / M、TFC-P 0.1 / M and TFC-P 0.45 The surface and cross-sectional morphology of the / M film were characterized, and the results are as follows: Figure 2 As shown.

[0063] The TFC-PES membrane surface mainly exhibits a nodular morphology of the polyamide layer, with a polyamide layer thickness of 82.3 ± 3.6 nm. After introducing an unintercalated molybdenum disulfide interlayer, micro-wrinkles appear on the TFC-MoS2 membrane surface, and the polyamide layer thickness decreases to 71.3 ± 5.3 nm. TFC-P 0.02 / M、TFC-P 0.1 / M and TFC-P 0.45 The wrinkled structure on the / M membrane surface further increases, corresponding to polyamide layer thicknesses of 71.1±2.9 nm, 52.3±4.9 nm, and 63.7±2.0 nm, respectively. Among them, TFC-P 0.1 The / M membrane exhibits a more pronounced wrinkled morphology and the smallest polyamide layer thickness, indicating that a suitable interlayer spacing is beneficial for regulating piperazine monomer mass transfer and polyamide layer growth.

[0064] Test Example 2: Separation Performance Test The water permeability and salt rejection performance of the prepared nanofiltration membrane were evaluated using a laboratory-scale cross-flow filtration apparatus. The test temperature was 25 ± 0.5 ℃. A 25 mm × 25 mm membrane sheet was installed in the test cell and first compacted with deionized water at a pressure of 4.0 bar for 2 h to stabilize the water permeability. Subsequently, tests were conducted using aqueous solutions of Na₂SO₄, MgSO₄, MgCl₂, and NaCl at concentrations of 1 g / L, respectively, at an operating pressure of 4.0 bar and a cross-flow velocity of 20 cm / s.

[0065] The water permeability coefficient J and the salt rejection rate R are calculated according to the following formulas: J=V / (Δt×A×P) R=(1-C p / C f )×100% In the formula, V is the volume of permeate during the test time Δt, in L; Δt is the test time, in h; and A is the effective area of ​​the membrane, in m². 2 P represents operating pressure, in bar; C p and C f These are the salt concentrations of the permeate and feed solution, respectively. The salt concentrations were measured using a conductivity meter.

[0066] The water permeability coefficients of each membrane are as follows Figure 3 As shown. When the mass ratio of polyethylene oxide to molybdenum disulfide nanosheets is 0.1 g / g, TFC-P 0.1 The water permeability coefficient of the / M membrane was further increased to 12.01 ± 0.51 L·m. -2 ·h -1 ·bar -1These figures are 2.14 times and 1.68 times that of TFC-PES membrane and TFC-MoS2 membrane, respectively.

[0067] Salt rejection rates of each membrane are as follows: Figure 4 As shown, TFC-PES, TFC-MoS2, and nanofiltration membranes with different polyethylene oxide intercalated molybdenum disulfide interlayers all exhibited retention rates of over 98% for Na2SO4 and MgSO4. The retention rates of MgCl2 and NaCl changed accordingly with variations in the mass ratio of polyethylene oxide to molybdenum disulfide nanosheets, but remained consistent for SO4-containing membranes. 2- The divalent salts maintained a high rejection rate. These results indicate that by adjusting the interlayer spacing of the intermediate layers, the water permeability of the nanofiltration membrane can be significantly improved while maintaining the divalent salt rejection performance.

[0068] Table 1 Water permeability coefficients of each membrane

[0069] A comparison of the water permeability performance of the examples and comparative examples shows that the improvement in the water permeability coefficient of the nanofiltration membrane of the present invention is not solely due to the addition of hydrophilic materials to the surface of the polyethersulfone ultrafiltration support membrane, but rather the result of the synergistic effects of polyethylene oxide intercalation, molybdenum disulfide interlayer spacing control, vacuum-assisted deposition, and interfacial polymerization. Comparative Example 1, without an interlayer, allowed piperazine to directly enter the polyethersulfone membrane pores and diffuse unevenly, resulting in a thick polyamide layer with a predominantly nodular structure, leading to a longer water transport path and thus the lowest water permeability coefficient. Comparative Example 2 used an unintercalated molybdenum disulfide interlayer, resulting in a smaller interlayer spacing and denser layer stacking, which significantly hindered the transport of water molecules and piperazine monomers, limiting the improvement effect. In Comparative Example 3, the mixing time between polyethylene oxide and molybdenum disulfide was too short, preventing the polyethylene oxide from fully penetrating between the layers and forming a simple physical mixture structure, making it difficult to effectively regulate the adsorption and diffusion of piperazine. Comparative Example 4 used polyvinylpyrrolidone (PVP) instead of polyethylene oxide (PEO). However, PPVP's steric hindrance from its side groups was significant, easily covering the molybdenum disulfide surface or occupying interlayer channels, preventing the formation of a uniform and controllable intercalation structure. In Comparative Example 5, the amount of PPVP was too low, resulting in insufficient interlayer spacing and a weak improvement in the mass transfer of water and piperazine by the intermediate layer. In Comparative Example 6, the amount of PPVP was too high, leading to excessive polymer accumulation on the sheet surface and within the channels, causing localized blockage and increasing the mass transfer resistance of the intermediate layer. Comparative Example 7 used a drop-coating method to construct the intermediate layer, which easily resulted in the coffee ring effect, nanosheet agglomeration, and uneven thickness, leading to uneven polyamide layer growth. These findings indicate that only under suitable PPVP dosage, sufficient intercalation, and uniform vacuum-assisted deposition conditions can a molybdenum disulfide intermediate layer with appropriate interlayer spacing and uniform coverage be formed, thereby obtaining a thinner, more wrinkled, and more effective mass transfer area polyamide selective separation layer, achieving a significant improvement in water permeability.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. However, any modifications, alterations, and variations made by those skilled in the art without departing from the scope of the present invention based on the disclosed technical content are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a high-permeability nanofiltration membrane by controlling the interlayer spacing of the intermediate layer, characterized in that, Includes the following steps: S1. Mix polyethylene oxide with molybdenum disulfide nanosheet aqueous dispersion to obtain polyethylene oxide intercalated molybdenum disulfide composite dispersion. S2. Vacuum-assisted filtration is used to deposit the poly(ethylene oxide) intercalated molybdenum disulfide composite dispersion onto the surface of a polyethersulfone ultrafiltration support membrane to form a poly(ethylene oxide) intercalated molybdenum disulfide intermediate layer. S3. The polyethersulfone ultrafiltration support membrane loaded with the polyoxyethylene intercalated molybdenum disulfide intermediate layer is sequentially contacted with a piperazine aqueous phase solution and a pyromellitic trimethylol chloride organic phase solution to allow the piperazine and pyromellitic trimethylol chloride to undergo an interfacial polymerization reaction. After thermal curing, a polyamide selective separation layer is formed on the surface of the polyoxyethylene intercalated molybdenum disulfide intermediate layer to obtain a nanofiltration membrane.

2. The method according to claim 1, characterized in that, In step S1, the mass ratio of polyethylene oxide to molybdenum disulfide nanosheets is (0.01-1):1, and the mixing time of the aqueous dispersion of polyethylene oxide and molybdenum disulfide nanosheets is 8-16 h.

3. The method according to claim 2, characterized in that, The weight-average molecular weight of the polyethylene oxide is 20,000-500,000 Da.

4. The method according to any one of claims 1-3, characterized in that, In step S1, the molybdenum disulfide nanosheet aqueous dispersion is prepared by the following method: The molybdenum disulfide nanosheet suspension was centrifuged, the supernatant was discarded, the resulting precipitate was resuspended in deionized water and ultrasonically dispersed to obtain the molybdenum disulfide nanosheet aqueous dispersion. The concentration of molybdenum disulfide nanosheets in the aqueous dispersion is 0.01-10 g / L.

5. The method according to any one of claims 1-3, characterized in that, In step S2, the molecular weight cutoff of the polyethersulfone ultrafiltration support membrane is 20,000-250,000 Da; after vacuum-assisted filtration, the polyethersulfone ultrafiltration support membrane loaded with the polyethylene oxide intercalated molybdenum disulfide interlayer is dried.

6. The method according to claim 1, characterized in that, In step S3: the concentration of piperazine in the piperazine aqueous solution is 5-12 g / L, and the contact time between the polyethersulfone ultrafiltration support membrane loaded with the polyethylene oxide intercalated molybdenum disulfide interlayer and the piperazine aqueous solution is 0.5-5 min; The concentration of trimesoyl chloride in the organic phase solution is 0.01-5 g / L, and the interfacial polymerization reaction time is 0.5-5 min. The thermosetting temperature is 50-70℃, and the thermosetting time is 3-10 min.

7. The method according to claim 6, characterized in that, The polyethersulfone ultrafiltration support membrane has a molecular weight cutoff of 20,000 Da; the concentration of molybdenum disulfide nanosheets in the aqueous dispersion of molybdenum disulfide nanosheets is 0.02 g / L; and the weight-average molecular weight of the polyethylene oxide is 100,000 Da. The concentration of piperazine in the aqueous phase solution is 10 g / L, and the polyethersulfone ultrafiltration support membrane with the intermediate layer is in contact with the aqueous phase solution of piperazine for 2 min. The organic phase solution of pyromellitic chloride is a hexane solution of pyromellitic chloride, wherein the concentration of pyromellitic chloride is 1.5 g / L, and the interfacial polymerization reaction time is 1 min; The thermosetting temperature is 60°C, and the thermosetting time is 5 min.

8. A polyoxyethylene intercalated molybdenum disulfide interlayer nanofiltration membrane, characterized in that, It includes a polyethersulfone ultrafiltration support membrane, a polyethylene oxide intercalated molybdenum disulfide intermediate layer, and a polyamide selective separation layer arranged sequentially. The polyoxyethylene intercalated molybdenum disulfide intermediate layer is formed by inserting polyoxyethylene between the layers of molybdenum disulfide nanosheets; The polyamide selective separation layer is formed by interfacial polymerization of piperazine and pyromellitic trimethylol chloride.

9. The polyoxyethylene intercalated molybdenum disulfide interlayer nanofiltration membrane according to claim 8, characterized in that, The interlayer spacing of the molybdenum disulfide nanosheets in the poly(ethylene oxide) intercalated molybdenum disulfide intermediate layer is 11.5-15.8 Å.

10. The application of the polyethylene oxide intercalated molybdenum disulfide interlayer nanofiltration membrane according to claim 8 or 9 in saline nanofiltration separation, characterized in that, The saline solution contains at least one of Na2SO4, MgSO4, MgCl2, and NaCl.

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