Nanofiltration membrane containing organic composite material interlayer and preparation method thereof

Abstract

The application provides a nanofiltration membrane containing a molecular sieve organic composite material intermediate layer and a preparation method thereof, and belongs to the field of membrane separation technology. The nanofiltration membrane comprises a base film, an intermediate layer and a polyamide separation layer which are sequentially fixed in a polymethyl methacrylate frame. A dispersion solution of molecular sieve and an aqueous solution of an amino-containing organic polymer material are uniformly mixed, stirred and ultrasonically treated to obtain a dispersion liquid. The dispersion liquid is suction filtered to obtain the intermediate layer. The intermediate layer is fixed in the polymethyl methacrylate frame with the side of the dispersion liquid facing upwards, the surface of the intermediate layer is covered with an aqueous solution of a polyamine, and then the surface of the intermediate layer is covered with an organic solution of a polyacyl chloride, and the intermediate layer is cleaned and heat treated to obtain the nanofiltration membrane containing the polyamide separation layer. The nanofiltration membrane is placed in deionized water for use. The preparation process is simple, the desalination performance is excellent, and the nanofiltration membrane has a wide application prospect in salt-containing wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a method for preparing a nanofiltration membrane containing a molecular sieve organic composite material interlayer. Background Technology

[0002] The ever-increasing population and rapid industrialization have led to a surge in demand for freshwater. Solving the global water shortage requires sustainable water management methods, such as seawater desalination, brackish water treatment, and wastewater treatment. Currently, reverse osmosis (RO) and nanofiltration (NF) are playing an increasingly important role in efficient water treatment. Among these, the most widely used water treatment membranes are nanofiltration and reverse osmosis membranes with thin-film composite (TFC) structures. Traditional TFC membranes consist of a porous substrate and a polyamide separation layer (PA). The polyamide separation layer (PA) is typically formed by the polymerization of an aqueous polyamine monomer (piperazine (PIP) or m-phenylenediamine (MPD)) and an organic polyacrylamide chloride monomer (trimethylammonium chloride (TMC)) at the interface between the two phases. The high reactivity and diffusion rate of these two monomers make precise control of the IP process to regulate the membrane structure extremely challenging.

[0003] Over the past decade, advancements in nanoscience have led to the widespread development of TFC membranes incorporating nanomaterials. Hock et al. first introduced porous zeolite nanoparticles into the polyamide separation layer of a reverse osmosis membrane and proposed the concept of thin-film nanocomposite membranes (TFN) (J.Membr.Sci.,2007,294:1-7). Other researchers have added nanomaterials to substrates to prepare thin-film composite membranes (TFCn) with nanocomposite substrates. In recent years, constructing an intermediate layer between the separation layer and the substrate has opened up new dimensions and directions for optimizing the structure and performance of TFC membranes. In 2015, Livingston et al. controlled the IP reaction rate by introducing a nano-cadmium hydroxide intermediate layer on the substrate surface, achieving a water flux two orders of magnitude higher than that of commercial membranes (Science,2015,348(624):1347-1351). Subsequently, a series of other nanomaterials, such as nanoparticles (zeolites, TiO2, metal nanoparticles, etc.), 1D (carbon nanotubes, metal nanowires, etc.), and 2D (GO, MOF, COF, etc.), have been applied to the interlayer material of TFNi membranes. However, compatibility issues make it difficult to obtain a homogeneous interlayer structure, resulting in a singular improvement in the permeability of the composite membrane with minimal selectivity enhancement. For example, Chinese invention patent CN 107081078 A discloses a new method for preparing a nanostructured composite ultrafiltration membrane, using an air-jet impregnation pore-opening method, which simultaneously creates pores in the coating layer, enabling rapid and effective control of the thickness and uniformity of the functional barrier layer on the surface of the composite membrane. However, it does not disclose how to improve the structural stability and selectivity of the interlayer. For example, Chinese invention patent CN111992039B discloses a method for preparing nanofiltration membranes by constructing a ZIF-8 interlayer. This method uses a water / oil interface synthesis method to prepare a ZIF-8 interlayer on a substrate, resulting in a uniform structure, small thickness, and low agglomeration. The nanofiltration membrane prepared based on this interlayer exhibits high flux and effective retention capacity for divalent anions and dyes. However, the in-situ generation of the microporous material interlayer on the substrate surface limits the scale-up preparation of the nanofiltration composite membrane. Chinese invention patent CN109126463B discloses a method for preparing a high-flux nanofiltration membrane containing a microporous interlayer. This technical solution involves covering the membrane surface with a microporous material dispersion and then performing interfacial polymerization. The microporous materials include ZIF-67, ZIF-8, UIO-66, SNW-1, graphene oxide, columnar aromatics, hydroquinone, cyclodextrin, cucurbita, and mesoporous phenolic resins, etc. The preparation process of these intermediate layer materials is complex, requiring a large number of additives, polymers, and organic reagents in the preparation of the microporous material dispersion. Furthermore, the microporous materials suffer from insufficient stability and high cost, limiting their industrial scale-up. In addition, these intermediate layer materials do not form a homogeneous and continuous structure, and the compatibility between the intermediate layer and the polyamide layer is poor. Their main advantage is improving the water permeability of the composite membrane, while their effect on improving selectivity is minimal.

[0004] To overcome the above challenges, this invention introduces a highly coupled molecular sieve organic composite material interlayer. The coupled molecular sieve organic composite material compensates for the shortcomings of single materials: the nano-molecular sieve has strong hydrophilicity, uniform pores, and excellent mechanical stability. The hydrophilicity modulates the properties of the substrate and controls the desorption and diffusion rates of amine monomers. The high porosity enhances the amine storage capacity of the substrate and improves the selectivity of the interlayer. In addition, the organic material coupled with the molecular sieve is rich in positively charged amino groups, which shields the negative charge of the nano-molecular sieve, changes the charge type of the interlayer, enhances the electrostatic interaction between the interlayer and the substrate and separation layer, reduces the interfacial incompatibility of the interlayer, and improves the structural stability of the composite membrane. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the technical problem to be solved by the present invention is how to improve the structural stability and selectivity of the intermediate layer.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a nanofiltration membrane containing a molecular sieve organic composite material intermediate layer, comprising a base membrane, an intermediate layer and a polyamide separation layer sequentially fixed in a polymethyl methacrylate framework, wherein the intermediate layer is made of a molecular sieve / polymer composite material.

[0007] The thickness of the intermediate layer is 50-500 nm, and the thickness of the polyamide separation layer is 20-150 nm.

[0008] A method for preparing a nanofiltration membrane containing a molecular sieve organic composite material interlayer includes the following steps:

[0009] S1. The molecular sieve dispersion solution and the aqueous solution of the amino-containing organic polymer are uniformly mixed, stirred, and sonicated to obtain a dispersion.

[0010] S2. Filter the dispersion to obtain a bottom film with an intermediate layer;

[0011] S3. With the side of the intermediate layer with the dispersion deposited facing upwards, fix it in a polymethyl methacrylate frame, cover the surface of the intermediate layer with an aqueous solution of polyamine, let it stand, and remove visible droplets from the surface; then cover the surface of the intermediate layer with an organic solution of polyacrylamide chloride, let it stand, clean the surface of the intermediate layer membrane, and perform heat treatment to obtain a nanofiltration membrane containing a polyamide separation layer, and place it in deionized water for later use.

[0012] The molecular sieve can be any one of EMT type molecular sieve, SOD type molecular sieve, or FAU type molecular sieve.

[0013] The molecular sieve has a crystal size in the nanometer range.

[0014] The amino-containing organic polymeric material is any one of polydopamine, polyethyleneimine, polyaniline, and ethylenediamine.

[0015] In S2, a porous membrane is used for filtration. The porous membrane is any one of polyethersulfone microfiltration membrane, polysulfone microfiltration membrane, polyvinylidene fluoride microfiltration membrane, nylon microfiltration membrane, polyethylene microfiltration membrane, polyacrylonitrile microfiltration membrane, and polyimide microfiltration membrane.

[0016] The polyamine is any one of piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, m-phenylenediamine, and p-phenylenediamine, and the polyacrylamide is any one of trimesoyl chloride, phthaloyl chloride, and terephthaloyl chloride.

[0017] The concentration of the aqueous solution of the polyamine is 0.5–3 wt%.

[0018] The concentration of the organic solution of the polyacrylamide chloride is 0.05–2 wt%.

[0019] The beneficial effects of this invention are as follows: the highly hydrophilic, highly porosimetric, and highly stable nano-molecular sieves alter the surface properties of the substrate, enhance the storage capacity of amine monomers on the substrate, slow down the desorption and diffusion rate of amines, and facilitate the reduction of the polyamide layer thickness; while the polymeric material coupled with the molecular sieve has abundant positive charges that shield the negative charges of the molecular sieve, enhance the charge interaction between the intermediate layer and the substrate and the polyamide separation layer, and improve the structural stability of the intermediate layer. Attached Figure Description

[0020] Figure 1 The image shown is a SEM image of the surface of a traditional nanofiltration membrane.

[0021] Figure 2 The image shown is a SEM image of the nanofiltration membrane surface in Embodiment 1 of the present invention;

[0022] Figure 3 The image shown is a SEM image of the nanofiltration membrane surface in Embodiment 4 of the present invention. Detailed Implementation

[0023] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0024] The most crucial concept of this invention lies in coupling nano-molecular sieves and amino-containing polymeric materials, preparing an intermediate layer by simple filtration or deposition on the surface of a bottom membrane, and obtaining an ultra-thin polyamide separation layer through interfacial polymerization to improve desalination performance.

[0025] Please refer to Figures 1 to 3As shown, the nanofiltration membrane of the present invention, which contains a molecular sieve organic composite material intermediate layer, comprises a base membrane, an intermediate layer and a polyamide separation layer sequentially fixed in a polymethyl methacrylate framework, wherein the intermediate layer is made of a molecular sieve / polymer composite material.

[0026] A method for preparing a nanofiltration membrane containing a molecular sieve organic composite material interlayer includes the following steps:

[0027] S1. The molecular sieve dispersion solution and the aqueous solution of the amino-containing organic polymer are uniformly mixed, stirred, and sonicated to obtain a dispersion.

[0028] S2. Filter the dispersion to obtain the intermediate layer;

[0029] S3. With the side of the intermediate layer with the dispersion deposited facing upwards, fix it in a polymethyl methacrylate frame, cover the surface of the intermediate layer with an aqueous solution of polyamine, and let it stand; then cover the surface of the intermediate layer with an organic solution of polyacrylamide chloride, let it stand, clean the surface of the intermediate layer membrane and perform heat treatment to obtain a nanofiltration membrane containing a polyamide separation layer, and place it in deionized water for later use.

[0030] As described above, the beneficial effects of this invention are as follows: The nano-molecular sieve possesses high porosity, high hydrophilicity, and high mechanical stability, enabling it to regulate the interfacial polymerization process and enhance the structural stability of the nanofiltration membrane. The negatively charged nano-molecular sieve is highly coupled with the positively charged polymer material, compensating for the deficiencies of a single material. The hydroxyl groups on the sieve surface and the organic polymer mix to form hydrogen bonds and other interactions, which is beneficial for improving the stability of the intermediate layer structure. The high porosity, strong hydrophilicity, and high stability of the nano-molecular sieve, as the main body of the intermediate layer, alter the properties of the substrate. Its abundant pores and strong hydrophilicity can increase the storage capacity of polyamine monomers on the substrate and slow down the desorption and diffusion rates of amine monomers, regulating the interfacial polymerization process. Furthermore, the hydrophilic sieve provides a preferential flow path for water molecules, contributing to improved selectivity. In addition, the organic material highly coupled with the sieve is rich in positively charged amino groups, shielding the negative charge of the nano-molecular sieve, enhancing the electrostatic interaction between the intermediate layer and the substrate and polyamide separation layer, and improving the structural stability of the nanofiltration membrane.

[0031] The modified organic nanofiltration membrane prepared by the method of the present invention containing a molecular sieve organic composite material intermediate layer can be widely used in various fields such as environment, food, medicine, and chemical industry.

[0032] Furthermore, the thickness of the intermediate layer is 50–500 nm, and the thickness of the polyamide separation layer is 20–150 nm.

[0033] As can be seen from the above description, the multifunctional molecular sieve organic composite intermediate layer has good compatibility with the polyamide separation layer and the substrate, provides physical support for the polyamide separation layer, improves the antifouling properties of the nanofiltration membrane, provides additional lateral channels for the flow of water molecules within the nanofiltration membrane, and helps to improve the membrane permeability; the molecular sieve organic composite intermediate layer inhibits the reaction of polyamide spheres to the substrate during interfacial polymerization, and suppresses the generation of bubbles in interfacial polymerization.

[0034] Furthermore, the nano-molecular sieve is any one of EMT-type molecular sieve, SOD-type molecular sieve, and FAU-type molecular sieve; even further, the synthesis method is a template-free synthesis method.

[0035] As can be seen from the above description, the molecular sieves synthesized using the template-free method do not require calcination or cold drying, thus avoiding the aggregation of nano-molecular sieves.

[0036] Furthermore, the crystal size of the molecular sieve is in the nanometer range, preferably 10-100 nm.

[0037] As can be seen from the above description, the crystal size of molecular sieves within the above range can be orderly and uniformly dispersed on the surface of the bottom membrane. Molecular sieves with larger crystal sizes are difficult to construct an orderly intermediate layer by means of filtration or deposition.

[0038] Furthermore, the amino-containing organic polymeric material is any one of polydopamine, polyethyleneimine, polyaniline, and ethylenediamine.

[0039] As can be seen from the above description, the selected organic polymer materials are all positively charged materials with amino groups, which improves the stability of the intermediate layer.

[0040] Furthermore, in S2, a porous base membrane is used for filtration. The porous base membrane is any one of polyethersulfone microfiltration membrane, polysulfone microfiltration membrane, polyvinylidene fluoride microfiltration membrane, nylon microfiltration membrane, polyethylene microfiltration membrane, polyacrylonitrile microfiltration membrane, and polyimide microfiltration membrane.

[0041] As can be seen from the above description, constructing a continuous and dense intermediate layer on the surface of the bottom membrane by vacuum filtration improves the properties of the bottom membrane. The uniform pores of the intermediate layer provide preferential flow channels for water molecules to pass through the membrane, significantly improving the water permeability of the nanofiltration membrane.

[0042] Further, the polyamine is any one of piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, m-phenylenediamine, and p-phenylenediamine, and the polyacrylamide chloride is any one of trimesoyl chloride, phthaloyl chloride, and terephthaloyl chloride; even further, the organic solvent of the organic solution of the polyacrylamide chloride is any one of n-hexane, cyclohexane, n-heptane, and toluene.

[0043] Furthermore, the concentration of the aqueous solution of the polyamine is 0.5–3 wt%.

[0044] Furthermore, the concentration of the organic solution of the polyacrylamide chloride is 0.05–2 wt%.

[0045] As can be seen from the above description, the aqueous solution on the surface of the intermediate membrane is removed by using an aqueous solution of polyamine, and the organic phase solution after the reaction is removed by using an organic solution of polyacrylamide chloride.

[0046] The nanofiltration membrane containing a molecular sieve organic composite material interlayer of the present invention is suitable for applications such as brackish water treatment, high-salinity industrial wastewater treatment, and seawater desalination. Specific embodiments are described below:

[0047] Please refer to Figures 1 to 3 As shown, Embodiment 1 of the present invention is as follows:

[0048] (1) Preparation of the intermediate layer: 100 mg of polyethyleneimine (PEI) was dissolved in 100 g of deionized water, stirred for 6 h, and sonicated in an ice-water bath for 2 h to obtain a homogeneous PEI aqueous solution; 1 g of EMT-type nano-molecular sieve was dissolved in 100 g of deionized water, sonicated in an ice-water bath for 1 h, and then the molecular sieve aqueous solution was centrifuged at 5000 rpm for 15 min, and 50 g of the centrifuged supernatant was recorded as the molecular sieve dispersion; 1 g of PEI aqueous solution and 1 g of molecular sieve dispersion were mixed and diluted with deionized water to 15 g, stirred for 1 h, and sonicated in an ice-water bath for 1 g to obtain a nano-molecular sieve organic composite material dispersion. The polysulfone ultrafiltration membrane was fixed in a vacuum filtration device and wetted with water. Under a vacuum filtration pressure of 0.02 MPa, the molecular sieve organic composite material was deposited on the surface of the substrate by vacuum filtration to obtain the molecular sieve organic composite material intermediate layer.

[0049] (2) Preparation of polyamide separation layer: The molecular sieve organic composite intermediate layer membrane was fixed in a polymethyl methacrylate frame. 5 mL of 1.0 wt% PIP aqueous solution was taken and covered on the membrane surface. After soaking for 3 min, the aqueous solution on the membrane surface was removed by roller. Then, 5 mL of 0.1 wt% TMC n-hexane solution was poured on the membrane surface and allowed to stand for 30 s. The surface organic solution was poured off, and the membrane was cleaned with n-hexane and then heat-treated (60 °C, 2 min) to obtain a nanofiltration membrane containing a molecular sieve organic composite intermediate layer.

[0050] The materials and reagents used in the preparation were sourced as follows: nylon microfiltration membranes and polyvinylidene fluoride microfiltration membranes were purchased from Haiyan Yibo Filter Material Factory; polysulfone ultrafiltration membranes were purchased from Beijing OriginWater Technology Co., Ltd.; polyethersulfone ultrafiltration membranes were purchased from Guizhou Wharton Technology Co., Ltd.; various nano-molecular sieves were prepared in the laboratory; dopamine hydrochloride, polyethyleneimine (Mw=1800), piperazine, tris(hydroxymethyl)aminomethane, and anhydrous ethanol were purchased from Aladdin Reagent (Shanghai) Co., Ltd.; trimesoyl chloride was purchased from Sigma-Aldrich; cyclohexane, n-hexane, and n-heptane were purchased from Tianjin Fuyu Fine Chemical Co., Ltd.; sodium sulfate (Na2SO4), magnesium sulfate (MgSO4), magnesium chloride (MgCl2), and sodium chloride (NaCl) were purchased from Sinopharm Group Chemical Reagent Co., Ltd. (The same applies below).

[0051] Example 2:

[0052] (1) Preparation of the intermediate layer: 100 mg of polyethyleneimine was dissolved in 100 g of deionized water, stirred for 6 h, and sonicated in an ice-water bath for 2 h to obtain a homogeneous PEI aqueous solution; 1 g of SOD-type nano-molecular sieve was dissolved in 100 g of deionized water, sonicated in an ice-water bath for 1 h, and then the molecular sieve aqueous solution was centrifuged at 10000 rpm for 20 min, and 50 g of the centrifuged supernatant was recorded as the molecular sieve dispersion; 1 g of PES aqueous solution and 0.5 g of molecular sieve dispersion were mixed and diluted with deionized water to 15 g, stirred for 1 h, and sonicated in an ice-water bath for 1 g to obtain a nano-molecular sieve organic composite material dispersion. The nylon microfiltration membrane was fixed in a vacuum filtration device and wetted with water. Under a vacuum filtration pressure of 0.02 MPa, the molecular sieve organic composite material was deposited on the surface of the substrate by vacuum filtration to obtain the molecular sieve organic composite material intermediate layer.

[0053] (2) Preparation of polyamide separation layer: The molecular sieve organic composite intermediate membrane was fixed in a polymethyl methacrylate frame. 5 mL of 1.0 wt% PIP aqueous solution was taken and covered on the membrane surface. After soaking for 2 min, the aqueous solution on the membrane surface was removed by roller (no droplets were visible to the naked eye). Then, 5 mL of 0.1 wt% TMC n-hexane solution was poured on the membrane surface and allowed to stand for 30 s. The surface organic solution was poured off, and the membrane was cleaned with n-hexane and then heat-treated (60 °C, 2 min) to obtain a nanofiltration membrane containing a molecular sieve organic composite intermediate layer.

[0054] Example 3:

[0055] (1) Preparation of the intermediate layer: Take 25g of EMT molecular sieve aqueous solution with a concentration of 20mg / g, add 25g of deionized water and 50g of methanol, stir for 30min to mix evenly, then add 50mg of dopamine hydrochloride and 10mL of 0.1mol / L Tris mild aqueous solution (pH=8.5) in sequence, stir at room temperature for 5h to obtain PD / EMT solution, then wash the product twice with methanol and once with water, dilute the product to 100g of water and centrifuge, centrifuge the diluted solution at 5000rpm for 15min, and record the supernatant as PD / EMT aqueous solution. Take 1g of PD / EMT aqueous solution and dilute to 15g, sonicate in an ice-water bath for 1h to obtain a dispersion of nano-molecular sieve organic composite material, fix the nylon microfiltration membrane in a vacuum filtration device, wet with water, and deposit the nano-molecular sieve organic composite material on the surface of the nylon microfiltration membrane under a vacuum filtration pressure of 0.01MPa to obtain the intermediate layer of nano-molecular sieve organic composite material.

[0056] (2) Preparation of polyamide separation layer: The obtained molecular sieve organic composite intermediate layer membrane was fixed in a polymethyl methacrylate frame. 5 mL of 1.0 wt% PIP aqueous solution was taken to cover the membrane surface and immersed for 2 min. The aqueous phase solution on the membrane surface was then removed. Subsequently, 5 mL of 0.1 wt% TMC n-hexane solution was poured on the membrane surface and allowed to stand for 20 s. The surface organic solution was then poured off and the membrane was washed with n-hexane and then heat-treated (60 °C, 2 min) to obtain a nanofiltration membrane containing a molecular sieve organic composite intermediate layer.

[0057] Example 4:

[0058] (1) Preparation of intermediate layer: Take 40g of laboratory-made sulfonated polyaniline, add 1g of EMT molecular sieve, stir at room temperature for 12h, and sonicate in ice water bath for 1h to obtain aniline-modified EMT molecular sieve. Centrifuge and wash the modified molecular sieve 5 times, dissolve the obtained filter cake in 100g of water, sonicate in ice water bath for 1h, centrifuge the solution (5000rpm, 20min), and take the supernatant after centrifugation as aniline-modified EMT dispersion; fix the polysulfone ultrafiltration membrane in the vacuum filtration device and wet it with water, cover the membrane surface with 5g of aniline-modified EMT dispersion, and deposit for 12h to obtain intermediate layer modified polysulfone ultrafiltration membrane. Transfer the obtained membrane to deionized water and soak for 12h to obtain molecular sieve organic polymer material intermediate layer.

[0059] (2) Preparation of polyamide separation layer: The molecular sieve organic composite intermediate membrane was fixed in a polymethyl methacrylate frame. 5 mL of 1.0 wt% PIP aqueous solution was taken and covered on the membrane surface. After soaking for 3 min, the aqueous solution on the membrane surface was removed by roller (no droplets were visible to the naked eye). Then, 5 mL of 0.1 wt% TMC n-hexane solution was poured on the membrane surface and allowed to stand for 30 s. The surface organic solution was poured off and washed with n-hexane. The membrane was then transferred to a 60-degree oven for 2 min to obtain a nanofiltration membrane containing a molecular sieve organic composite intermediate layer.

[0060] Comparative Example 1:

[0061] The only difference between Comparative Example 1 and Example 1 is that the dispersion (i.e., a dispersion solution without molecular sieves) was prepared by using an aqueous solution of a single amino-containing organic polymer material, and a nanofiltration membrane containing an intermediate layer was finally obtained.

[0062] (1) Preparation of the intermediate layer: 100 mg of polyethyleneimine (PEI) was dissolved in 100 g of deionized water, stirred for 6 h, and sonicated in an ice-water bath for 2 h to obtain a homogeneous PEI aqueous solution; 1 g of PEI aqueous solution was taken and diluted with deionized water to 15 g, stirred for 1 h, and sonicated in an ice-water bath for 1 g to obtain a polyethyleneimine (PEI) dispersion. The polysulfone ultrafiltration membrane was fixed in a vacuum filtration device and wetted with water. Under a vacuum filtration pressure of 0.02 MPa, polyethyleneimine (PEI) was deposited on the surface of the substrate by vacuum filtration to obtain the intermediate layer of the molecular sieve organic composite material.

[0063] (2) Preparation of polyamide separation layer: The polyethyleneimine (PEI) interlayer membrane was fixed in a polymethyl methacrylate frame. 5 mL of 1.0 wt% PIP aqueous solution was taken and covered on the membrane surface. After soaking for 3 min, the aqueous phase solution on the membrane surface was removed by roller. Then, 5 mL of 0.1 wt% TMC n-hexane solution was poured on the membrane surface and allowed to stand for 30 s. The surface organic solution was poured off, and the membrane was cleaned with n-hexane and then heat-treated (60 °C, 2 min) to obtain a nanofiltration membrane containing a polyethyleneimine (PEI) interlayer.

[0064] Comparative Example 2:

[0065] The only difference between Comparative Example 2 and Example 1 is that a dispersion (i.e., an aqueous solution without amino-containing organic polymer materials) was prepared using a single EMT molecular sieve dispersion solution, and a nanofiltration membrane with an intermediate layer was finally obtained.

[0066] (1) Preparation of intermediate layer: 1g of EMT type nano molecular sieve was dissolved in 100g of deionized water and sonicated in an ice water bath for 1h. Then the molecular sieve aqueous solution was centrifuged at 5000rpm for 15min. 50g of the centrifugation supernatant was taken as molecular sieve dispersion. The polysulfone ultrafiltration membrane was fixed in the vacuum filtration device and wetted with water. Under a vacuum filtration pressure of 0.02Mpa, the molecular sieve dispersion was deposited on the surface of the substrate by vacuum filtration to obtain a single molecular sieve intermediate layer.

[0067] (2) Preparation of polyamide separation layer: The molecular sieve intermediate layer membrane was fixed in a polymethyl methacrylate frame. 5 mL of 1.0 wt% PIP aqueous solution was taken and covered on the membrane surface. After soaking for 3 min, the aqueous phase solution on the membrane surface was removed by roller. Then, 5 mL of 0.1 wt% TMC n-hexane solution was poured on the membrane surface and allowed to stand for 30 s. The surface organic solution was poured off, and the membrane was cleaned with n-hexane and then heat-treated (60 °C, 2 min) to obtain a nanofiltration membrane containing a single molecular sieve intermediate layer.

[0068] The nanofiltration membranes containing molecular sieve organic composite intermediate layers prepared in Example 1 and Comparative Examples 1-2 were subjected to a separation test with 1000 μg / g sodium sulfate (1 MPa), and the average value was taken. The results are shown in Table 1.

[0069] Table 1

[0070] Serial Number <![CDATA[Flux (L m -2 h -1 bar -1 )]]> Selectivity (%) Example 1 14.85 97.38 Comparative Example 1 5.75 89.84 Comparative Example 2 15.75 52.84

[0071] It can be seen that the method for preparing nanofiltration membranes containing molecular sieve organic composite material intermediate layers provided by the present invention has both good flux and selectivity.

[0072] In summary, the nanofiltration membrane with a molecular sieve organic composite material interlayer provided by this invention enhances the storage capacity of polyamine monomers on the bottom membrane by introducing a highly hydrophilic molecular sieve organic composite material interlayer, and reduces the desorption and diffusion rates of polyamine monomers on the bottom membrane, which is beneficial for forming an ultrathin, highly cross-linked polyamide separation layer. The organic layer in the molecular sieve organic composite material interlayer, which is highly coupled with the molecular sieve, can shield the negative charge of the molecular sieve, enhance the electrostatic interaction between the interlayer, the polyamide separation layer, and the bottom membrane, and reduce the interfacial incompatibility between the interlayer, the bottom membrane, and the polyamide separation layer. The highly coupled molecular sieve organic composite material interlayer improves the properties of the bottom membrane, and the uniform channels of the interlayer provide preferential flow channels for water molecules to pass through the membrane, significantly improving the water permeability of the nanofiltration membrane.

[0073] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention's specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a nanofiltration membrane containing a molecular sieve organic composite material interlayer, characterized in that, Includes the following steps: S1. The molecular sieve dispersion solution and the aqueous solution of the amino-containing organic polymer are uniformly mixed, stirred, and sonicated to obtain a dispersion. S2. Filter the dispersion to obtain a bottom film with an intermediate layer; S3. With the side of the intermediate layer with the dispersion deposited facing upwards, fix it in a polymethyl methacrylate frame, cover the surface of the intermediate layer with an aqueous solution of polyamine, and let it stand; then cover the surface of the intermediate layer with an organic solution of polyacrylamide chloride, let it stand, clean the surface of the intermediate layer membrane and perform heat treatment to obtain a nanofiltration membrane containing a polyamide separation layer, and place it in deionized water for later use. The molecular sieve is any one of EMT type molecular sieve, SOD type molecular sieve, and FAU type molecular sieve; The amino-containing organic polymeric material is any one of polydopamine, polyethyleneimine, and polyaniline.

2. The method for preparing a nanofiltration membrane containing a molecular sieve organic composite material interlayer according to claim 1, characterized in that, The molecular sieve has a crystal size in the nanometer range.

3. The method for preparing a nanofiltration membrane containing a molecular sieve organic composite material interlayer according to claim 1, characterized in that, In S2, a porous base membrane is used for filtration. The porous base membrane is any one of polyethersulfone microfiltration membrane, polysulfone microfiltration membrane, polyvinylidene fluoride microfiltration membrane, nylon microfiltration membrane, polyethylene microfiltration membrane, polyacrylonitrile microfiltration membrane, and polyimide microfiltration membrane.

4. The method for preparing a nanofiltration membrane containing a molecular sieve organic composite material interlayer according to claim 1, characterized in that, The polyamine is any one of piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, m-phenylenediamine, and p-phenylenediamine, and the polyacrylamide is any one of pyromellitic methyl chloride, phthaloyl chloride, and terephthaloyl chloride.

5. The method for preparing a nanofiltration membrane containing a molecular sieve organic composite material interlayer according to claim 1, characterized in that, The concentration of the aqueous solution of the polyamine is 0.5~3wt%.

6. The method for preparing a nanofiltration membrane containing a molecular sieve organic composite material interlayer according to claim 1, characterized in that, The concentration of the organic solution of the polyacrylamide chloride is 0.05~2wt%.

7. The nanofiltration membrane containing a molecular sieve organic composite material interlayer prepared by the preparation method according to any one of claims 1 to 6, characterized in that, It comprises a base film, an intermediate layer and a polyamide separation layer sequentially fixed in a polymethyl methacrylate framework, wherein the intermediate layer is made of a molecular sieve / polymer composite material.

8. The nanofiltration membrane containing a molecular sieve organic composite material interlayer according to claim 7, characterized in that, The thickness of the intermediate layer is 50~500 nm, and the thickness of the polyamide separation layer is 20~150 nm.

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