A hydrophilic nanosheet, its preparation, and ultrafiltration membrane based thereon, as well as its preparation method and application

Abstract

A hydrophilic nanosheet, its preparation and an ultrafiltration membrane based thereon, and its preparation method and application. The present invention belongs to the field of ultrafiltration membrane materials. The present invention aims to provide a hydrophilic nanosheet and its preparation method. Aromatic polyamine monomers with specific functional groups react rapidly with aromatic polyphenol monomers and diazonium salts at the interface of water-organic solution, and a rich microphase water-oil interface is obtained by stirring, thereby increasing the interfacial area of ​​the reaction and realizing the large-scale preparation of two-dimensional nanosheets. In addition, the application of the above-mentioned hydrophilic nanosheet in ultrafiltration membrane is also provided, wherein the prepared nanosheet is doped into the casting liquid as an additive to prepare the ultrafiltration membrane, and the nanosheet is further cross-linked with the polymer membrane matrix using Lewis acid. The introduction of covalent bonds increases the interaction force between the nanosheet filler and the polymer chain, and the nanosheet is not eluted during its use. The prepared membrane has a high porosity and excellent hydrophilicity, anti-fouling performance and permeability.

Description

Technical Field

[0001] The invention belongs to the field of ultrafiltration membrane materials, and in particular relates to a hydrophilic nanosheet, its preparation, an ultrafiltration membrane based on the hydrophilic nanosheet, and a preparation method and application thereof. Background Art

[0002] Ultrafiltration technology utilizes the principle of pore size screening to separate materials. Under pressure, the selective permeability of ultrafiltration membranes is used to separate, concentrate, and purify certain substances in a solution. This separation process offers advantages such as low operating costs and high separation efficiency. Poly(arylethersulfone) is widely used in the field of ultrafiltration membrane materials due to its excellent oxidative stability and mechanical strength. However, its relatively hydrophobic nature results in low ultrafiltration membrane flux and poor anti-fouling properties, which presents challenges in practical application. To ensure that poly(arylethersulfone) membranes meet the required performance requirements, they require hydrophilic modification.

[0003] At present, the hydrophilic modification method for polyarylethersulfone membrane materials is usually to add hydrophilic additives such as polyvinylpyrrolidone and polyethylene glycol to the casting solution, and prepare ultrafiltration membranes by phase inversion method. However, during storage and use, the above-mentioned water-soluble additives are very easy to be lost, which reduces the filtration performance, anti-fouling performance and long-term stability of the ultrafiltration membrane. In response to these problems, researchers at home and abroad are committed to studying the modification method of ultrafiltration membranes and have made some progress in recent years. For example, by forming a hydrophilic functional layer on the hydrophobic polyethersulfone surface, the polyethersulfone ultrafiltration membrane is hydrophilically modified. The hydrophilicity and permeation flux of the modified ultrafiltration membrane are increased, and the retention rate is improved. The surface modification method can improve the hydrophilicity of the membrane surface, but the membrane interior is prone to contamination during use.

[0004] Mixed-matrix membranes (MMMs) are composed of polymers and organic / inorganic fillers incorporated into the polymer matrix. By combining the processing versatility of polymer membrane materials with the high separation efficiency of organic / inorganic fillers, they overcome the interdependent constraints between permeability and selectivity during ultrafiltration membrane operation, achieving comprehensive improvement of the membrane's performance. Porous materials, such as zeolites, carbon nanotubes, graphene oxide, two-dimensional sheet materials, and metal-organic frameworks (MOFs), are widely used in the field of MMMs due to their high surface area and highly porous structure. However, the introduction of fillers in a blended form can lead to the easy dissolution of the porous nanomaterials, significantly reducing the long-term stability of the MMM. Therefore, the development of a membrane material that combines excellent hydrophilicity, antifouling properties, permeability, and long-term stability is crucial. Summary of the Invention

[0005] In order to overcome the defects of the above-mentioned prior art, the present invention provides a hydrophilic nanosheet, its preparation, and an ultrafiltration membrane based on the hydrophilic nanosheet, as well as its preparation method and application.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] One of the purposes of the present invention is to provide a method for preparing a hydrophilic nanosheet, wherein the method for preparing the hydrophilic nanosheet is carried out according to the following steps:

[0008] S1: Add aromatic amine monomers to water, then add inorganic acid, mechanically stir until completely dissolved, and place in an environment of 0-10°C to obtain an aromatic amine solution;

[0009] S2: Add sodium nitrite aqueous solution dropwise to the aromatic amine solution, stir at 0-10°C for 10-30 min, then add inorganic base solution and adjust the pH value to 1-10 to obtain a diazonium salt solution;

[0010] S3: Add the organic solution of aromatic polyphenols dropwise to the diazonium salt solution, vigorously stir at 0-10°C for 0.05-48 h at a stirring speed of 100-8000 rpm, and filter to obtain ultrathin nanosheets;

[0011] S4: Dispersing the ultrathin nanosheets in a solvent, adding a hydrophilizing agent, and reacting at a certain temperature to obtain hydrophilic nanosheets.

[0012] It is further defined that the aromatic amine monomer in S1 is 2,2'-benzidine disulfonic acid, 2,5-diaminobenzenesulfonic acid, 2,5-diaminobenzene-1,4-disulfonic acid, 2,5-diaminobenzoic acid, 2,5-diaminoterephthalic acid, 4,4-aminobiphenyl-2,2-dicarboxylic acid or 2,4,6-tris(4-aminophenyl)-1,3,5-triazine.

[0013] It is further defined that the inorganic acid in S1 is concentrated hydrochloric acid, concentrated sulfuric acid, concentrated nitric acid or tetrafluoroboric acid.

[0014] It is further defined that the concentration of the aromatic amine in the aromatic amine solution in S1 is 0.01-50 wt %, and the concentration of the inorganic acid is 0.01-20 vol %.

[0015] It is further defined that the molar ratio of sodium nitrite in S2 to the amino group in the aromatic amine is (0.5~5):1.

[0016] It is further defined that the concentration of the sodium nitrite aqueous solution in S2 is 0.1~10 w / v%.

[0017] It is further defined that the aromatic polyphenol in S3 is hydroquinone, resorcinol, catechol, pyrogallol, 1,2,4,5-tetrahydroxybenzene, biphenol, 2,5-bisdimethylaminohydroquinone, 3-dimethylaminomethyl-4-(2-dimethylaminomethyl)-4-hydroxyphenylphenol or 4,4'-dihydroxy-1,1'-biphenyl-2-carboxylic acid.

[0018] It is further defined that the molar ratio of the aromatic polyphenols in S3 to the amino groups in the aromatic amines in S1 is (0.2~5):1.

[0019] It is further defined that the concentration of the organic solution of aromatic polyphenols in S3 is 0.1-20 w / v%.

[0020] It is further defined that the solvent in S4 is water, ethanol, methanol, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, diphenyl sulfone or sulfolane.

[0021] It is further defined that the mass ratio of ultrathin nanosheets to solvent in S4 is (0.01~20):100.

[0022] It is further defined that the mass ratio of ultrathin nanosheets to solvent in S4 is (1~9):100.

[0023] It is further defined that the hydrophilizing agent in S4 includes sulfuric acid, hydrochloric acid, acetic acid, and phosphoric acid.

[0024] It is further defined that the reaction in S4 is carried out at 30-120°C for 0.2-36 h.

[0025] Further limit the reaction time to 1~24 h.

[0026] A second object of the present invention is to provide a hydrophilic nanosheet prepared according to the above method, wherein the thickness of the hydrophilic nanosheet is 2 to 10 nm.

[0027] A third object of the present invention is to provide a method for preparing an ultrafiltration membrane, wherein the method for preparing the ultrafiltration membrane is carried out according to the following steps:

[0028] Step 1: Dispersing the hydrophilic nanosheets and the polymer matrix in an organic solvent to obtain a nanosheet dispersion and a polymer solution, respectively, and then mixing the two to obtain a casting solution;

[0029] Step 2: filtering and degassing the casting solution to form a flat asymmetric membrane or a hollow fiber asymmetric membrane, which is then immersed in a coagulation bath for solidification to obtain an ultrafiltration membrane precursor;

[0030] Step 3: Immerse the ultrafiltration membrane precursor in a Lewis acid solution and perform cross-linking at a certain temperature. After washing, blow dry with nitrogen to obtain an ultrafiltration membrane.

[0031] It is further defined that in step 1, the polymer matrix is ​​polysulfone, polyethersulfone, polyvinylidene fluoride, polypropylene, polyvinyl chloride or polyacrylonitrile.

[0032] It is further defined that the organic solvent in step 1 is N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, diphenyl sulfone or sulfolane.

[0033] Further limiting, in step 1, the concentration of the nano-dispersion liquid is 0.01-20 wt %, and the concentration of the polymer solution is 2-50 wt %. Further limiting, in step 1, the concentration of the nano-dispersion liquid is 1-9 wt %, and the concentration of the polymer solution is 10-20 wt %.

[0034] It is further defined that the mass ratio of the hydrophilic nanosheets to the polymer matrix in the casting solution in step 1 is (0.0005~5):1.

[0035] It is further defined that the casting solution in step 1 also includes one or more of a polymer additive, an organic small molecule additive, and an inorganic salt.

[0036] To further define, the polymer additive includes but is not limited to polyethylene glycol, polyethylene glycol methyl ether, and polyvinyl pyrrolidone.

[0037] It is further defined that the organic small molecule additives include but are not limited to ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, acetone, tetrahydrofuran, and dioxane.

[0038] To further define, inorganic salts include but are not limited to LiCl and LiNO3.

[0039] It is further defined that when forming the flat asymmetric membrane in step 2, a aging process is also included after degassing.

[0040] It is further specified that the aging is carried out at a constant temperature of 28-45°C for 6-14 hours.

[0041] Furthermore, the aging is carried out at a constant temperature of 40°C for 12 h.

[0042] It is further defined that the coagulation bath in step 2 includes but is not limited to water, alcohol, organic solvent aqueous solution or acid, alkali, or salt aqueous solution.

[0043] It is further defined that the Lewis acid solution in step 3 includes but is not limited to phosphoric acid, polyphosphoric acid, sulfuric acid, aluminum trichloride, sulfur trioxide, and ferric bromide.

[0044] It is further defined that in step 3, crosslinking is performed at 25-200° C. for 1-48 h.

[0045] Furthermore, in step 3, crosslinking is performed at 100-180° C. for 5-12 h.

[0046] A fourth object of the present invention is to provide an ultrafiltration membrane prepared according to the above method, wherein the hydrophilic nanosheets and the polymer matrix in the ultrafiltration membrane are bonded by covalent bonds.

[0047] A fifth object of the present invention is to provide an application of an ultrafiltration membrane prepared according to the above method in treating wastewater containing BSA protein.

[0048] Compared with the prior art, the present invention has the following significant effects:

[0049] (1) The present invention aims to provide a hydrophilic nanosheet and a method for preparing the same. Aromatic polyamine monomers with specific functional groups react rapidly with aromatic polyphenol monomers and diazonium salts at the interface of a water-organic solution. A rich microphase water-oil interface is obtained by stirring, increasing the interfacial area for the reaction and enabling the mass production of two-dimensional nanosheets. Furthermore, by adjusting the monomer structures of aromatic amines and aromatic polyphenols, hydrophilic nanosheet materials with different pore structures and specific surface areas can be prepared.

[0050] (2) The present invention also provides the use of the above-mentioned hydrophilic nanosheets in ultrafiltration membranes. The prepared nanosheets are doped as additives into a casting solution to prepare an ultrafiltration membrane. The nanosheets are further cross-linked with a polymer membrane matrix using a Lewis acid. The introduction of covalent bonds increases the interaction between the nanosheet filler and the polymer chain, preventing the nanosheets from being eluted during use. In addition, since the addition of the nanosheets accelerates the phase separation rate, the prepared membrane has a high porosity and excellent hydrophilicity, anti-fouling properties, and permeability. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Schematic diagram of the hydrophilic nanosheet structure prepared by the method of Example 1;

[0052] Figure 2 This is the nitrogen adsorption-desorption curve of the hydrophilic nanosheets prepared by the method of Example 1 at 77 K;

[0053] Figure 3 Atomic force microscope images of the hydrophilic nanosheets prepared by the method of Example 1 and the thickness diagram of the nanosheets; (a) - atomic force, (b) - thickness;

[0054] Figure 4 Schematic diagram of the hydrophilic nanosheet structure prepared by the method of Example 2;

[0055] Figure 5 This is the infrared spectrum of the hydrophilic nanosheets prepared by the method of Example 2;

[0056] Figure 6 This is a physical picture of the hydrophilic nanosheet powder prepared by the method of Example 2;

[0057] Figure 7 This is the nitrogen adsorption-desorption curve of the hydrophilic nanosheets prepared by the method of Example 2 at 77 K;

[0058] Figure 8Atomic force microscope images of the hydrophilic nanosheets prepared by the method of Example 2 and the thickness diagram of the nanosheets; (a) - atomic force, (b) - thickness;

[0059] Figure 9 Schematic diagram of cross-linking between the nanosheets prepared in Example 2 and the polyethersulfone membrane matrix;

[0060] Figure 10 IR spectra of the ultrafiltration membrane before and after cross-linking in Example 2;

[0061] Figure 11 This is a physical picture of the ultrafiltration membrane prepared by the method of Example 2;

[0062] Figure 12 Schematic diagram of the hydrophilic nanosheet structure prepared by the method of Example 3;

[0063] Figure 13 Atomic force microscope images of the hydrophilic nanosheets prepared by the method of Example 3 and thickness diagram of the nanosheets; (a) - atomic force, (b) - thickness;

[0064] Figure 14 This is a physical picture of the ultrafiltration membrane prepared by the method of Example 3;

[0065] Figure 15 Graph showing changes in pure water flux of different membrane materials for Examples 1-5 and Comparative Examples 1-5. DETAILED DESCRIPTION

[0066] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0067] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used are conventional in the art and can be obtained commercially by those skilled in the art unless otherwise specified.

[0068] As used in the following examples, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0069] When amount, concentration or other value or parameter are represented with the range of scope, preferred range or a series of upper preferred value and lower preferred value limit, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, and no matter whether this scope is disclosed separately.For example, when disclosing scope "1 to 5", described scope should be interpreted as including scope "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc.When numerical range is described in this article, unless otherwise stated, otherwise this scope is intended to include its end value and all integers and fractions within the scope.In this application specification and claims, range limitation can be combined and / or interchanged, and if these ranges are not otherwise stated, include all subranges contained therein.

[0070] The indefinite articles "a" and "an" before the elements or components of the present invention do not limit the quantity requirement (i.e. the number of times they appear). Therefore, "a" or "an" should be interpreted as including one or at least one, and elements or components in the singular also include plural forms, unless the quantity clearly refers to only the singular form.

[0071] The endpoints of the ranges and any values ​​disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0072] Example 1:

[0073] The preparation method of the ultrafiltration membrane of this embodiment is carried out according to the following steps:

[0074] The first step is to prepare hydrophilic nanosheets:

[0075] S1: Add 2,4,6-tris(4-aminophenyl)-1,3,5-triazine to water, then add 37 wt% concentrated hydrochloric acid, stir mechanically for 12 min to completely dissolve it, and place it in an environment of 1°C to obtain an aromatic amine solution with a 2,4,6-tris(4-aminophenyl)-1,3,5-triazine concentration of 15 wt% and a concentrated hydrochloric acid concentration of 6 vol%;

[0076] S2: Add 50 mL of a 3 w / v% sodium nitrite aqueous solution dropwise to 50 mL of the aromatic amine solution obtained in S1, stir at 5°C for 30 min, then add a 0.9 w / v% cesium carbonate solution and adjust the pH to 12 to obtain a diazonium salt solution;

[0077] S3: 100 mL of 0.55 mol / L 4,4'-dihydroxy-1,1'-biphenyl-2-carboxylic acid / ethyl propionate solution was added dropwise to 100 mL of the diazonium salt solution. The mixture was vigorously stirred at 7°C for 180 h at a stirring speed of 900 rpm. After filtering, the crude product was washed with dichloromethane to obtain ultrathin nanosheets.

[0078] S4: Disperse 1 g of ultrathin nanosheets in 100 g of water, add 100 mL of 37 wt% concentrated hydrochloric acid, and react at 25 °C for 24 h to obtain hydrophilic nanosheets.

[0079] Figure 1 Schematic diagram of the obtained hydrophilic nanosheet structure;

[0080] Figure 2 The nitrogen adsorption-desorption curve of the obtained hydrophilic nanosheets at 77 K is shown in Figure 2. The BET specific surface area calculated by DFT method is 196.33 m 2 / g, and the pore size is mainly distributed at 1.915 nm.

[0081] Figure 3 The atomic force microscope image of the obtained hydrophilic nanosheets and the thickness map of the nanosheets indicate that the prepared nanosheets have a scale of hundreds of nanometers and a thickness of 2.5 nm.

[0082] Step 2: Preparation of ultrafiltration membrane:

[0083] Step 1: Ultrasonic dispersion of the hydrophilic nanosheets in N,N-dimethylacetamide to obtain a 0.5 wt% nanosheet dispersion; ultrasonic dispersion of polyethersulfone in N,N-dimethylacetamide to obtain a 20 wt% polyethersulfone solution; 10 mL of the nanosheet dispersion and 90 mL of the polyethersulfone solution were mixed to obtain a casting solution (mass ratio of hydrophilic nanosheets to polyethersulfone was 0.0028:1);

[0084] Step 2: After filtering and degassing the casting solution and aging it at 40°C for 24 h, the membrane was scraped on a clean glass plate with a scraper with a blade gap of 150 μm, and then immersed in deionized water for solidification to obtain an ultrafiltration membrane precursor;

[0085] Step 3: The ultrafiltration membrane precursor was immersed in a polyphosphoric acid solution and cross-linked at 160° C. for 12 h. After the reaction, the ultrafiltration membrane was washed three times with deionized water and dried with nitrogen to obtain an ultrafiltration membrane.

[0086] Example 2:

[0087] The preparation method of the ultrafiltration membrane of this embodiment is carried out according to the following steps:

[0088] The first step is to prepare hydrophilic nanosheets:

[0089] S1: Add 2,2'-benzidine disulfonic acid to water, then add 68 wt% concentrated nitric acid, stir mechanically for 15 min to completely dissolve it, and place it in an environment at 3°C ​​to obtain an aromatic amine solution with a 2,2'-benzidine disulfonic acid concentration of 5 wt% and a concentrated nitric acid concentration of 2 vol%;

[0090] S2: Add 30 mL of 0.35 w / v% sodium nitrite aqueous solution dropwise to 50 mL of the aromatic amine solution obtained in S1, stir at 5°C for 18 min, then add 3 w / v% sodium hydroxide solution and adjust the pH to 7 to obtain a diazonium salt solution;

[0091] S3: 100 mL of 0.008 mol / L pyrogallol / toluene solution was added dropwise to 100 mL of diazonium salt solution. The mixture was vigorously stirred at 8°C for 96 h at a stirring speed of 1600 rpm. The crude product was filtered and washed with methanol to obtain ultrathin nanosheets.

[0092] S4: Disperse 1 g of ultrathin nanosheets in 100 mL of water, add 20 mL of 5 mol / L hydrochloric acid, and react at 25°C for 24 h to obtain hydrophilic nanosheets.

[0093] Figure 4 Schematic diagram of the obtained hydrophilic nanosheet structure;

[0094] Figure 5 is the infrared spectrum of the obtained hydrophilic nanosheets;

[0095] Figure 6 This is a physical picture of the obtained hydrophilic nanosheet powder;

[0096] Figure 7 The nitrogen adsorption-desorption curve of the obtained hydrophilic nanosheets at 77 K is shown in Figure 2. The BET specific surface area calculated by DFT method is 187.23 m 2 / g.

[0097] Figure 8 The atomic force microscope image of the obtained hydrophilic nanosheet and the thickness map of the nanosheet indicate that the prepared nanosheet has nanoscale dimensions and a thickness of 1.4 nm.

[0098] Step 2: Preparation of ultrafiltration membrane:

[0099] Step 1: Ultrasonic dispersion of the hydrophilic nanosheets in N,N-dimethylacetamide to obtain a 0.5 wt% nanosheet dispersion; ultrasonic dispersion of polyethersulfone in N,N-dimethylacetamide to obtain a 20 wt% polyethersulfone solution; 10 mL of the nanosheet dispersion and 90 mL of the polyethersulfone solution were mixed to obtain a casting solution (mass ratio of hydrophilic nanosheets to polyethersulfone was 0.0028:1);

[0100] Step 2: After filtering and degassing the casting solution and aging it at 40°C for 24 h, the membrane was scraped on a clean glass plate with a scraper with a blade gap of 150 μm, and then immersed in deionized water for solidification to obtain an ultrafiltration membrane precursor;

[0101] Step 3: The ultrafiltration membrane precursor was immersed in a polyphosphoric acid solution and cross-linked at 160° C. for 12 h. After the reaction, the ultrafiltration membrane was washed three times with deionized water and dried with nitrogen to obtain an ultrafiltration membrane.

[0102] Figure 9 Schematic diagram of the cross-linking of nanosheets and polyethersulfone membrane matrix.

[0103] Figure 10 The infrared spectra of the prepared ultrafiltration membrane before and after cross-linking.

[0104] Figure 11 This is a physical picture of the prepared ultrafiltration membrane. As shown in the figure, no obvious unevenness or nanosheet agglomeration was found on the surface of the blend matrix membrane, indicating that the interface compatibility between the nanosheets and polyethersulfone is good and the properties of the membrane are uniform.

[0105] Example 3:

[0106] The preparation method of the ultrafiltration membrane of this embodiment is carried out according to the following steps:

[0107] The first step is to prepare hydrophilic nanosheets:

[0108] S1: Add 4,4-aminobiphenyl-2,2-dicarboxylic acid to water, then add 68 wt% concentrated nitric acid, stir mechanically for 15 minutes to completely dissolve it, and place it in an environment at 3°C ​​to obtain an aromatic amine solution with a 4,4-aminobiphenyl-2,2-dicarboxylic acid concentration of 5 wt% and a concentrated nitric acid concentration of 2 vol%;

[0109] S2: Add 30 mL of 0.35 w / v% sodium nitrite aqueous solution dropwise to 50 mL of the aromatic amine solution obtained in S1, stir at 5°C for 18 min, then add 3 w / v% sodium hydroxide solution and adjust the pH to 7 to obtain a diazonium salt solution;

[0110] S3: 100 mL of 0.008 mol / L pyrogallol / toluene solution was added dropwise to 100 mL of diazonium salt solution. The mixture was vigorously stirred at 8°C for 96 h at a stirring speed of 1600 rpm. The crude product was filtered and washed with methanol to obtain ultrathin nanosheets.

[0111] S4: Disperse 1 g of ultrathin nanosheets in 1 L of water, add 20 mL of 5 mol / L hydrochloric acid, and react at 25 °C for 24 h to obtain hydrophilic nanosheets.

[0112] Figure 12 Schematic diagram of the obtained hydrophilic nanosheet structure;

[0113] Figure 13 The atomic force microscope image of the obtained hydrophilic nanosheet and the thickness map of the nanosheet indicate that the prepared nanosheet has nanoscale dimensions and a thickness of 2.8 nm.

[0114] Figure 14 This is a physical picture of the obtained hydrophilic nanosheet powder;

[0115] Step 2: Preparation of ultrafiltration membrane:

[0116] Step 1: Ultrasonic dispersion of the hydrophilic nanosheets in N,N-dimethylacetamide to obtain a 0.5 wt% nanosheet dispersion; ultrasonic dispersion of polyethersulfone in N,N-dimethylacetamide to obtain a 20 wt% polyethersulfone solution; 10 mL of the nanosheet dispersion and 90 mL of the polyethersulfone solution were mixed to obtain a casting solution (mass ratio of hydrophilic nanosheets to polyethersulfone was 0.0028:1);

[0117] Step 2: After filtering and degassing the casting solution and aging it at 40°C for 24 h, the membrane was scraped on a clean glass plate with a scraper with a blade gap of 150 μm, and then immersed in deionized water for solidification to obtain an ultrafiltration membrane precursor;

[0118] Step 3: The ultrafiltration membrane precursor was immersed in a polyphosphoric acid solution and cross-linked at 160° C. for 12 h. After the reaction, the ultrafiltration membrane was washed three times with deionized water and dried with nitrogen to obtain an ultrafiltration membrane.

[0119] Example 4:

[0120] The preparation method of the ultrafiltration membrane of this embodiment is carried out according to the following steps:

[0121] The first step is to prepare hydrophilic nanosheets:

[0122] S1: Add 4,4-aminobiphenyl-2,2-dicarboxylic acid to water, then add 68 wt% concentrated nitric acid, stir mechanically for 15 minutes to completely dissolve it, and place it in an environment at 3°C ​​to obtain an aromatic amine solution with a 4,4-aminobiphenyl-2,2-dicarboxylic acid concentration of 5 wt% and a concentrated nitric acid concentration of 2 vol%;

[0123] S2: Add 30 mL of 0.35 w / v% sodium nitrite aqueous solution dropwise to 50 mL of the aromatic amine solution obtained in S1, stir at 5°C for 18 min, then add 3 w / v% sodium hydroxide solution and adjust the pH to 7 to obtain a diazonium salt solution;

[0124] S3: 100 mL of 0.008 mol / L pyrogallol / toluene solution was added dropwise to 100 mL of diazonium salt solution. The mixture was vigorously stirred at 8°C for 96 h at a stirring speed of 1600 rpm. The crude product was filtered and washed with methanol to obtain ultrathin nanosheets.

[0125] S4: Disperse 1 g of ultrathin nanosheets in 1 L of water, add 20 mL of 5 mol / L hydrochloric acid, and react at 25 °C for 24 h to obtain hydrophilic nanosheets.

[0126] Step 2: Preparation of ultrafiltration membrane:

[0127] Step 1: Ultrasonic dispersion of the hydrophilic nanosheets in N,N-dimethylacetamide to obtain a 1 wt% nanosheet dispersion. Ultrasonic dispersion of polyethersulfone in N,N-dimethylacetamide to obtain an 18 wt% polyethersulfone solution. Mix 10 mL of the nanosheet dispersion with 90 mL of the polyethersulfone solution to obtain a casting solution (mass ratio of hydrophilic nanosheets to polyethersulfone is 0.0056:1).

[0128] Step 2: After filtering and degassing the casting solution and aging it at 40°C for 24 h, the membrane was scraped on a clean glass plate with a scraper with a blade gap of 150 μm, and then immersed in deionized water for solidification to obtain an ultrafiltration membrane precursor;

[0129] Step 3: The ultrafiltration membrane precursor was immersed in a polyphosphoric acid solution and cross-linked at 160° C. for 12 h. After the reaction, the ultrafiltration membrane was washed three times with deionized water and dried with nitrogen to obtain an ultrafiltration membrane.

[0130] Example 5:

[0131] The preparation method of the ultrafiltration membrane of this embodiment is carried out according to the following steps:

[0132] The first step is to prepare hydrophilic nanosheets:

[0133] S1: Add 4,4-aminobiphenyl-2,2-dicarboxylic acid to water, then add 68 wt% concentrated nitric acid, stir mechanically for 15 minutes to completely dissolve it, and place it in an environment at 3°C ​​to obtain an aromatic amine solution with a 4,4-aminobiphenyl-2,2-dicarboxylic acid concentration of 5 wt% and a concentrated nitric acid concentration of 2 vol%;

[0134] S2: Add 30 mL of 0.35 w / v% sodium nitrite aqueous solution dropwise to 50 mL of the aromatic amine solution obtained in S1, stir at 5°C for 18 min, then add 3 w / v% sodium hydroxide solution and adjust the pH to 7 to obtain a diazonium salt solution;

[0135] S3: 100 mL of 0.008 mol / L pyrogallol / toluene solution was added dropwise to 100 mL of diazonium salt solution. The mixture was vigorously stirred at 8°C for 96 h at a stirring speed of 1600 rpm. The crude product was filtered and washed with methanol to obtain ultrathin nanosheets.

[0136] S4: Disperse 1 g of ultrathin nanosheets in 1 L of water, add 20 mL of 5 mol / L hydrochloric acid, and react at 25°C for 24 h to obtain hydrophilic nanosheets.

[0137] Step 2: Preparation of ultrafiltration membrane:

[0138] Step 1: Ultrasonic dispersion of the hydrophilic nanosheets in N,N-dimethylacetamide to obtain a 1 wt% nanosheet dispersion. Ultrasonic dispersion of polyethersulfone in N,N-dimethylacetamide to obtain an 18 wt% polyethersulfone solution. Mix 10 mL of the nanosheet dispersion with 90 mL of the polyethersulfone solution to obtain a casting solution (mass ratio of hydrophilic nanosheets to polyethersulfone is 0.0112:1).

[0139] Step 2: After filtering and degassing the casting solution and aging it at 40°C for 24 h, the membrane was scraped on a clean glass plate with a scraper with a blade gap of 150 μm, and then immersed in deionized water for solidification to obtain an ultrafiltration membrane precursor;

[0140] Step 3: The ultrafiltration membrane precursor was immersed in a polyphosphoric acid solution and cross-linked at 160° C. for 12 h. After the reaction, the ultrafiltration membrane was washed three times with deionized water and dried with nitrogen to obtain an ultrafiltration membrane.

[0141] Comparative Example 1: This comparative example differs from Example 1 in that step 3 in the second step is omitted. Other steps and parameters are the same as those in Example 1.

[0142] Comparative Example 2: This comparative example differs from Example 2 in that step 3 in the second step is omitted. Other steps and parameters are the same as those in Example 2.

[0143] Comparative Example 3: This comparative example differs from Example 3 in that step 3 in the second step is omitted. Other steps and parameters are the same as those in Example 3.

[0144] Comparative Example 4:

[0145] The preparation method of the pure polyethersulfone ultrafiltration membrane of this comparative example is carried out according to the following steps:

[0146] Step 1: Prepare a casting solution of 18 wt% polyethersulfone / 10 wt% PEG400 / N,N-dimethylacetamide;

[0147] Step 2: Degas the casting solution at 25°C for 1 hour, then place it in a constant temperature chamber at 40°C for 12 hours, then use a scraper to scrape the film on a clean glass plate with a blade gap of 150 μm. Immediately place the glass plate in deionized water for curing, and then transfer it to deionized water for immersion to remove residual solvent to obtain a pure polyethersulfone flat ultrafiltration membrane.

[0148] Comparative Example 5

[0149] The preparation method of the ultrafiltration membrane of this embodiment is carried out according to the following steps:

[0150] Step 1: Preparation of nanosheets:

[0151] S1: Add 4,4'-dihydroxybiphenyl to water, then add 68 wt% concentrated nitric acid, stir mechanically for 15 min to completely dissolve it, and place it in an environment at 3°C ​​to obtain an aromatic amine solution with a 4,4'-dihydroxybiphenyl concentration of 5 wt% and a concentrated nitric acid concentration of 2 vol%;

[0152] S2: Add 30 mL of 0.35 w / v% sodium nitrite aqueous solution dropwise to 50 mL of the aromatic amine solution obtained in S1, stir at 5°C for 18 min, then add 3 w / v% sodium hydroxide solution and adjust the pH to 7 to obtain a diazonium salt solution;

[0153] S3: 100 mL of 0.008 mol / L pyrogallol / toluene solution was added dropwise to 100 mL of diazonium salt solution. The mixture was vigorously stirred at 8°C for 96 h at a stirring speed of 1600 rpm. The crude product was filtered and washed with methanol to obtain ultrathin nanosheets.

[0154] S4: Disperse 1 g of ultrathin nanosheets in 1 L of water, add 20 mL of 5 mol / L hydrochloric acid, and react at 25°C for 24 h to obtain hydrophilic nanosheets.

[0155] Step 2: Preparation of ultrafiltration membrane:

[0156] Step 1: Ultrasonic dispersion of the hydrophilic nanosheets in N,N-dimethylacetamide to obtain a 0.5 wt% nanosheet dispersion; ultrasonic dispersion of polyethersulfone in N,N-dimethylacetamide to obtain a 20 wt% polyethersulfone solution; 10 mL of the nanosheet dispersion and 90 mL of the polyethersulfone solution were mixed to obtain a casting solution (mass ratio of hydrophilic nanosheets to polyethersulfone was 0.0056:1);

[0157] Step 2: After filtering, degassing, and aging the casting solution at 40 °C for 24 h, use a scraper to scrape the membrane on a clean glass plate with a blade gap of 150 μm, and then immerse it in deionized water to solidify to obtain an ultrafiltration membrane.

[0158] (1) The water contact angles of the ultrafiltration membranes prepared in Examples 1-5 and Comparative Examples 1-5 were tested. The results are shown in Table 1.

[0159] (II) The ultrafiltration membranes prepared in Examples 1-5 and Comparative Examples 1-5 were tested for their rejection rates of 1 g / L BSA protein solution. The results are shown in Table 1.

[0160] (III) The ultrafiltration membranes prepared in Examples 1-5 and Comparative Examples 1-5 were continuously tested for pure water flux at 0.1 MPa for 24 h, and the changes in pure water flux were recorded every 1 h. Figure 15 And Table 1.

[0161] (IV) To test the solubility of the nanosheets, the ultrafiltration membranes prepared in Examples 1-5 and Comparative Examples 1-5 were tested using pure water at 0.1 MPa for 1 h. The absorbance of the outflowing liquid was monitored by UV-visible spectrophotometry, and the concentration of the nanosheets in the solution was calculated. The dissolution rate results are shown in Table 1.

[0162] Table 1 Hydrophilicity, permeability and flux stability of different ultrafiltration membranes

[0163]

[0164] In summary, the performance of polyethersulfone ultrafiltration membranes doped with hydrophilic nanosheets is significantly improved. As shown in Table 1, the water contact angle of the doped membranes decreases significantly, decreasing with increasing doping levels. This is due to the migration of the hydrophilic nanosheets to the membrane surface during phase inversion, increasing the hydrophilicity of the membrane surface. The permeability of the hydrophilic-doped membranes is significantly improved, as the addition of the nanosheets increases the phase separation rate, thereby increasing the membrane porosity and thus the water flux. Furthermore, the hydrophilic nanosheets are fixed in the membrane matrix through a Lewis acid-catalyzed cross-linking reaction, which stabilizes the membrane performance during use and significantly improves the membrane's flux stability. Therefore, hydrophilic nanosheets are ideal fillers for preparing ultrafiltration membranes with anti-fouling and high permeability.

[0165] The foregoing are merely preferred embodiments of the present invention. These embodiments are all different implementations based on the overall concept of the present invention. The scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a hydrophilic nanosheet, characterized in that: Follow these steps: S1: adding an aromatic amine monomer to water, then adding an inorganic acid, mechanically stirring until completely dissolved, and placing in an environment of 0-10° C. to obtain an aromatic amine solution; the aromatic amine monomer is 2,2'-benzidinedisulfonic acid, 2,5-diaminobenzenesulfonic acid, 2,5-diaminobenzene-1,4-disulfonic acid, 2,5-diaminobenzoic acid, 2,5-diaminoterephthalic acid, 4,4-aminobiphenyl-2,2-dicarboxylic acid, or 2,4,6-tris(4-aminophenyl)-1,3,5-triazine; the inorganic acid is concentrated hydrochloric acid, concentrated sulfuric acid, concentrated nitric acid, or tetrafluoroboric acid; the concentration of the aromatic amine in the aromatic amine solution is 0.01-50 wt %, and the concentration of the inorganic acid is 0.01-20 vol %; S2: Add sodium nitrite aqueous solution dropwise to the aromatic amine solution, stir at 0-10°C for 10-30 min, then add inorganic base solution and adjust the pH value to 1-10 to obtain a diazonium salt solution; the molar ratio of sodium nitrite to amino group in the aromatic amine is (0.5-5):1, and the concentration of the sodium nitrite aqueous solution is 0.1-10 w / v; S3: adding an organic solution of aromatic polyphenols dropwise to a diazonium salt solution, vigorously stirring at 0-10°C for 0.05-48h at a stirring speed of 100-8000 rpm, and filtering to obtain ultrathin nanosheets; the aromatic polyphenols are hydroquinone, resorcinol, catechol, pyrogallol, 1,2,4,5-tetrahydroxybenzene, biphenol, 2,5-bis(dimethylamino)hydroquinone, 3-dimethylaminomethyl-4-(2-dimethylaminomethyl)-4-hydroxyphenylphenol or 4,4'-dihydroxy-1,1'-biphenyl-2-carboxylic acid; the molar ratio of the aromatic polyphenols to the amino group in the aromatic amine in S1 is (0.2-5):1, and the concentration of the organic solution of the aromatic polyphenols is 0.1-20 w / v; S4: Disperse the ultrathin nanosheets in a solvent, add a hydrophilizing agent, and react at 30-120°C for 0.2-36 h to obtain hydrophilic nanosheets. The solvent is water, ethanol, methanol, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, diphenyl sulfone, or cyclopentane. The mass ratio of the ultrathin nanosheets to the solvent is (0.01-20):

100. The hydrophilizing agent includes sulfuric acid, hydrochloric acid, acetic acid, and phosphoric acid.

2. The method according to claim 1, characterized in that The mass ratio of ultrathin nanosheets to solvent in S4 is (1~9):100, and the reaction in S4 is 1~24 h.

3. The hydrophilic nanosheet prepared by the method according to any one of claims 1 to 2, characterized in that: Its thickness is 2~10nm.

4. A method for preparing an ultrafiltration membrane, characterized in that: Follow these steps: Step 1: Dispersing the hydrophilic nanosheets and the polymer matrix according to claim 3 in an organic solvent to obtain a nanosheet dispersion and a polymer solution, and then mixing the two to obtain a casting solution; Step 2: filtering and degassing the casting solution to form a flat asymmetric membrane or a hollow fiber asymmetric membrane, which is then immersed in a coagulation bath for solidification to obtain an ultrafiltration membrane precursor; Step 3: Immerse the ultrafiltration membrane precursor in a Lewis acid solution and perform cross-linking at a certain temperature. After washing, blow dry with nitrogen to obtain an ultrafiltration membrane.

5. The method according to claim 4, characterized in that In step 1, the polymer matrix is ​​polysulfone, polyethersulfone, polyvinylidene fluoride, polypropylene, polyvinyl chloride or polyacrylonitrile, the organic solvent is N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, diphenyl sulfone or cyclopentane, the concentration of the nanodispersion liquid is 0.01~20 wt%, the concentration of the polymer solution is 2~50 wt%, the mass ratio of the hydrophilic nanosheets and the polymer matrix in the casting solution is (0.0005~5):1, and the casting solution also includes one or more of a polymer additive, an organic small molecule additive, and an inorganic salt. When forming the flat asymmetric membrane in step 2, an aging process is further included after degassing, specifically, aging at a constant temperature of 28~45°C for 6~14 h, the coagulation bath includes water, alcohol, organic solvent aqueous solution or acid, alkali, salt aqueous solution, the Lewis acid solution in step 3 includes phosphoric acid, polyphosphoric acid, sulfuric acid, aluminum chloride, sulfur trioxide, and ferric bromide, and the crosslinking in step 3 is carried out at 25-200° C. for 1-48 h.

6. The method according to claim 5, characterized in that In step 1, the concentration of hydrophilic nanosheets in the casting solution is 1~9 wt%, the concentration of the polymer is 10~20 wt%, the polymer additives include polyethylene glycol, polyethylene glycol methyl ether, polyvinyl pyrrolidone, the organic small molecule additives include ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, acetone, tetrahydrofuran, dioxane, and the inorganic salts include LiCl and LiNO3. The aging is performed at a constant temperature of 40°C for 12 hours, and in step 3, the crosslinking is performed at 100~180°C for 5-12 hours.

7. The ultrafiltration membrane prepared by the method according to any one of claims 4 to 6, characterized in that The hydrophilic nanosheets are bonded to the polymer matrix through covalent bonds.

8. Use of the ultrafiltration membrane prepared by the method according to any one of claims 4 to 6 in treating wastewater containing BSA protein.

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