Preparation method and application of a high-throughput boron nitride nanofiltration membrane with a sandwich structure

Abstract

The present invention discloses a preparation method and application of a high-throughput boron nitride nanofiltration membrane with a sandwich structure. The preparation method includes the following steps: functionalizing h-BN with PDA to prepare an h-BN / PDA modified material; preparing HMSN using ZIF-8 as a self-sacrificing template; and layer-by-layer assembling h-BN / PDA and HMSN on a CA membrane with PEI as an adhesive to fabricate a high-throughput boron nitride nanofiltration membrane with a "sandwich" structure having a high rejection rate and antifouling properties. The invention can solve the problem that in the separation process of nanofiltration membranes, it is necessary to sacrifice the permeation flux and antifouling ability to obtain a high rejection rate. The preparation process of the high-throughput boron nitride nanofiltration membrane with a sandwich structure is simple, the conditions are mild, no pollutants are generated, the application range is wide, and it is easy to carry out industrial production and market promotion.

Description

Technical Field

[0001] The invention relates to the technical field of nanofiltration membrane separation, and in particular to a preparation method and application of a high-flux boron nitride nanofiltration membrane with a sandwich structure. Background Art

[0002] Nanofiltration (NF) membrane separation technology is widely used in the removal of pollutants such as dyes, heavy metals, drugs, and soluble organic molecules, and has been proven to be a very effective water purification technology. Nanofiltration membrane separation technology has shown great advantages in the field of wastewater treatment due to its advantages such as high separation efficiency, low energy consumption, no phase change, and no secondary pollution. However, there are still some unavoidable problems in the actual production application of nanofiltration membranes, such as the inability to achieve high flux, high retention rate, and high anti-fouling properties, which greatly reduces the wastewater treatment efficiency of nanofiltration membranes. Therefore, it is necessary to modify the nanofiltration membrane to improve its performance in actual production applications. Summary of the invention

[0003] In view of the above-mentioned shortcomings, the present invention provides a preparation method and application of a high-flux boron nitride nanofiltration membrane with a sandwich structure to solve the problem that the nanofiltration membrane cannot maintain high levels of three properties: retention rate, permeation flux and anti-fouling property.

[0004] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0005] A preparation method and application of a high-flux boron nitride nanofiltration membrane with a sandwich structure, characterized in that it comprises the following steps:

[0006] S1: Preparation of h-BN / PDA modified material: Take hexagonal boron nitride nanosheet (h-BN) powder, prepare a uniform hexagonal boron nitride dispersion with a concentration of 1 g / L, add tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl) to make its concentration in the dispersion 1.6 g / L, adjust the pH to 8.5, add dopamine (DA) to make its concentration in the dispersion 2 g / L, stir magnetically for 16 h, centrifuge the product, wash it with pure water, and dry it at 60°C to obtain h-BN / PDA;

[0007] S2: Preparation of ZIF-8 self-sacrificial template material: 5.6 g of 2-methylimidazole was dissolved in 50 mL of methanol, and 2.5 g of zinc nitrate hexahydrate (Zn(NO3)·6H2O) was dissolved in 50 mL of methanol. The two solutions were evenly mixed, magnetically stirred for 1 h, and allowed to stand for 24 h. The product was centrifuged and washed with methanol several times, and then dried to obtain ZIF-8.

[0008] S3: Preparation of HMSN with hollow mesoporous structure: Prepare 540 mL of water and ethanol mixed solution (5:4), add 2.5 g of 2-methylimidazole and 1.6 g of hexadecyltrimethylammonium bromide (CTAB), stir for 30 min to make it fully mixed, slowly add 5 mL of tetraethyl orthosilicate (TEOS), stir vigorously for 2 h, centrifuge the product, wash the product with methanol several times, and dry it to obtain ZIF-8@mSiO 2 , the product was placed in 0.1 M hydrochloric acid (HCl), stirred for 30 min, the ZIF-8 template was etched, the product was washed with deionized water several times, and after drying, a hollow mesoporous HMSN with ZIF-8 as the template was obtained;

[0009] S4: Preparation of a high-throughput boron nitride nanofiltration membrane with a sandwich structure: Weigh h-BN / PDA and disperse it in pure water. Ultrasonicate for 1 hour to obtain a 0.01 g / L h-BN / PDA uniform dispersion. Add PEI to the h-BN / PDA dispersion to a concentration of 0.2 g / L and stir for 10 minutes. Then prepare a 0.06 g / L HMSN uniform dispersion, add PEI to a concentration of 0.1 g / L and stir for 10 minutes. The HMSN / PEI uniform dispersion and the h-BN / PDA / PEI uniform dispersion are filtered to the surface of the bottom membrane through a vacuum filtration device at a pressure of 0.09 Mbar to obtain a high-throughput boron nitride nanofiltration membrane with a sandwich structure.

[0010] Furthermore, in step S1, the mass ratio of hexagonal boron nitride to dopamine is in the range of 1:1.4-2;

[0011] Further, the base for adjusting the pH in step S1 includes one or more of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, and sodium bicarbonate, the pH range is 8-9, and the magnetic stirring time after adding DA is 10-20h;

[0012] Furthermore, in step S2, the mass ratio of 2-methylimidazole to zinc nitrate hexahydrate is in the range of 2:2.5, the standing time of the product is in the range of 16-26 hours, and the organic solvent used for washing the product includes one of methanol, ethanol, and a methanol-ethanol mixture;

[0013] Furthermore, in step S3, the volume ratio of water to ethanol when preparing the mixed solution of water and ethanol is in the range of 6:5-4:3, and the organic solvent used for washing the product includes one of methanol, ethanol, and a mixed solution of methanol and ethanol;

[0014] Further, in step S3, the mass ratio of 2-methylimidazole to hexadecyltrimethylammonium bromide is in the range of 1:1.3-1.8, the stirring time of the product is in the range of 25-35 min, and the volume ratio of ethyl orthosilicate to the mixture of water and methanol is in the range of 1:0.008-0.012;

[0015] Further, the acid used to etch the ZIF-8 template in step S3 includes one or more of hydrochloric acid, sulfuric acid, nitric acid, persulfate, and perchloric acid; the molar concentration of the acid is in the range of 0.05-0.15M;

[0016] Further, in step S4, the mass concentration range of the h-BN / PDA uniform dispersion is 0.008-0.012 g / L, the mass ratio range of h-BN / PDA to PEI is 1:0.04-0.06, and the stirring time range is 1-20 min; the mass concentration range of the HMSN is 0.04-0.08 g / L, the mass ratio range of HMSN to PEI is 1:0.4-0.8, and the stirring time range is 1-20 min;

[0017] Furthermore, the base membrane selected in step S4 includes one or more of CA membrane, polyvinylidene fluoride membrane, nylon membrane, polyacrylonitrile membrane, polyethersulfone membrane, and polysulfone membrane. The order of filtration is HMSN / PEI uniform dispersion liquid first, and h-BN / PDA / PEI uniform dispersion liquid later, and the pressure range selected during filtration is 0.07-0.1Mbar;

[0018] The present invention provides a preparation method and application of a high-flux boron nitride nanofiltration membrane with a sandwich structure. The h-BN / PDA obtained by functionalizing h-BN with polydopamine (PDA) is assembled layer by layer with HMSN on a CA membrane under the action of PEI to prepare a high-flux boron nitride nanofiltration membrane with a "sandwich" structure having the characteristics of high retention rate and easy synthesis. PDA is rich in hydrophilic hydroxyl and amine free radicals, which improves the hydrophilicity of h-BN and helps h-BN / PDA to achieve the function of an "anti-fouling layer". HMSN synthesized with ZIF-8 as a self-sacrificing template is used as a "support layer" of the composite membrane to increase the specific surface area, permeation flux and retention rate of the membrane. PEI is used as a cross-linking agent to not only improve the hydrophilicity of the membrane, but also enhance the stability of the membrane. The invention can solve the problem of sacrificing permeation flux and anti-fouling ability to obtain a high retention rate in the nanofiltration membrane separation process.

[0019] Beneficial effects:

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The high-throughput boron nitride nanofiltration membrane with a sandwich structure can effectively intercept small molecular pollutants through the size screening effect and can be used in the treatment process of wastewater containing dye pollutants.

[0022] (2) The structure of the high-flux boron nitride nanofiltration membrane with a sandwich structure is divided into three parts: an anti-fouling layer, a support layer, and a base membrane. It is cross-linked with PEI, has a strong and stable structure, and can operate stably in large-volume wastewater treatment processes.

[0023] (3) The high-throughput boron nitride nanofiltration membrane with a sandwich structure has a large permeability flux, a high retention rate, and excellent anti-fouling performance.

[0024] (4) The preparation process of high-throughput boron nitride nanofiltration membrane with sandwich structure is simple, the conditions are mild, no pollutants are produced, the application range is wide, and it is easy to carry out industrial production and market promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a surface scanning electron microscope image of cellulose acetate membrane;

[0026] Figure 2 Surface scanning electron microscopy image of CA@HMSN film;

[0027] Figure 3 This is a surface scanning electron microscope image of a boron nitride nanofiltration membrane;

[0028] Figure 4 This is a cross-sectional scanning electron microscope image of a boron nitride nanofiltration membrane;

[0029] Figure 5 This is the EDS spectrum of boron nitride nanofiltration membrane; DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution 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 used to limit the present invention.

[0031] Test method:

[0032] The test method of high-throughput boron nitride nanofiltration membrane with sandwich structure uses a membrane permeation selectivity test system to test the membrane's permeation flux, retention rate and flux recovery rate. The test system consists of a circulating water vacuum pump, a filtration device, and a pressure and flow detection device. The effective membrane area is 12.57cm 2 , the test pressure is 0.09Mbar, the test environment temperature is 25±0.5℃. The concentration of the dye solution used in the test process is 20ppm.

[0033] The calculation formula of permeation flux is J = V / (A·t·P), where J(L·m 2 ·h -1 bar -1 ) is the permeation flux of the membrane, V(L) is the volume of the solution, A(m 2 ) is the effective filtration area of ​​the membrane, t(h) is the filtration time, and P(bar) is the filtration pressure.

[0034] The calculation formula of interception rate is: R = (1-C p / C f )*100%, where R(%) is the retention rate of the membrane, C p (mg / L) and C f (mg / L) are the concentrations of the dye solution before and after separation, respectively.

[0035] The calculation formula of flux recovery rate is: FRR = (J 2 / J 1 )*100, where FRR (%) is the flux recovery rate, J 1 (L·m 2 ·h -1 bar -1 ), J 2 (L·m 2 ·h -1 bar -1 ) are the permeate fluxes before and after membrane cleaning, respectively.

[0036] Embodiment 1:

[0037] Weigh h-BN / PDA and disperse it in pure water. Ultrasonicate for 1 hour to obtain 0.01g / L h-BN / PDA uniform dispersion. Add PEI to the h-BN / PDA dispersion to make the concentration of PEI 0.2g / L and stir for 10 minutes. Then prepare 0.06g / L HMSN uniform dispersion, add PEI to make the concentration of PEI 0.1g / L and stir for 10 minutes. 20mL of HMSN / PEI uniform dispersion and 125mL of h-BN / PDA / PEI uniform dispersion were filtered onto the surface of CA membrane by vacuum filtration device at a pressure of 0.09Mbar to obtain a high-flux boron nitride nanofiltration membrane with a sandwich structure.

[0038] The Congo red flux of the prepared high-flux boron nitride nanofiltration membrane with a sandwich structure was tested to be 2934.6 L·m 2 ·h -1 bar -1 , the retention rate is 99.9%.

[0039] Embodiment 2:

[0040] Weigh h-BN / PDA and disperse it in pure water. Ultrasonicate for 1 hour to obtain 0.01g / L h-BN / PDA uniform dispersion. Add PEI to the h-BN / PDA dispersion to make the concentration of PEI 0.2g / L and stir for 10 minutes. Then prepare 0.06g / L HMSN uniform dispersion, add PEI to make the concentration of PEI 0.1g / L and stir for 10 minutes. 20mL of HMSN / PEI uniform dispersion and 100mL of h-BN / PDA / PEI uniform dispersion were filtered onto the surface of CA membrane by vacuum filtration device at a pressure of 0.09Mbar to obtain a high-flux boron nitride nanofiltration membrane with a sandwich structure.

[0041] The Congo red flux of the prepared high-flux boron nitride nanofiltration membrane with a sandwich structure was tested to be 2952.6 L·m 2 ·h -1 bar -1 , the retention rate is 99.3%.

[0042] Embodiment 3:

[0043] Weigh h-BN / PDA and disperse it in pure water. Ultrasonicate for 1 hour to obtain 0.01g / L h-BN / PDA uniform dispersion. Add PEI to the h-BN / PDA dispersion to make the concentration of PEI 0.2g / L and stir for 10 minutes. Then prepare 0.06g / L HMSN uniform dispersion, add PEI to make the concentration of PEI 0.1g / L and stir for 10 minutes. 20mL of HMSN / PEI uniform dispersion and 75mL of h-BN / PDA / PEI uniform dispersion were filtered onto the surface of CA membrane by vacuum filtration device at a pressure of 0.09Mbar to obtain a high-flux boron nitride nanofiltration membrane with a sandwich structure.

[0044] The Congo red flux of the prepared high-flux boron nitride nanofiltration membrane with a sandwich structure was tested to be 3008.2 L·m 2 ·h -1 bar -1 , the retention rate was 95.2%.

[0045] Embodiment 4:

[0046] Weigh h-BN / PDA and disperse it in pure water. Ultrasonicate for 1 hour to obtain 0.01g / L h-BN / PDA uniform dispersion. Add PEI to the h-BN / PDA dispersion to make the concentration of PEI 0.2g / L and stir for 10 minutes. Then prepare 0.06g / L HMSN uniform dispersion, add PEI to make the concentration of PEI 0.1g / L and stir for 10 minutes. 10mL of HMSN / PEI uniform dispersion and 125mL of h-BN / PDA / PEI uniform dispersion were filtered onto the surface of CA membrane by vacuum filtration device at a pressure of 0.09Mbar to obtain a high-flux boron nitride nanofiltration membrane with a sandwich structure.

[0047] The Congo red flux of the prepared high-flux boron nitride nanofiltration membrane with a sandwich structure was tested to be 2346.9 L·m 2 ·h -1 bar -1 , the interception rate was 98.7%.

[0048] Embodiment 5:

[0049] Weigh h-BN / PDA and disperse it in pure water. Ultrasonicate for 1 hour to obtain 0.01g / L h-BN / PDA uniform dispersion. Add PEI to the h-BN / PDA dispersion to make the concentration of PEI 0.2g / L and stir for 10 minutes. Then prepare 0.06g / L HMSN uniform dispersion, add PEI to make the concentration of PEI 0.1g / L and stir for 10 minutes. 30mL of HMSN / PEI uniform dispersion and 125mL of h-BN / PDA / PEI uniform dispersion were filtered onto the surface of CA membrane by vacuum filtration device at a pressure of 0.09Mbar to obtain a high-flux boron nitride nanofiltration membrane with a sandwich structure.

[0050] The Congo red flux of the prepared high-flux boron nitride nanofiltration membrane with a sandwich structure was tested to be 1809.1 L·m 2 ·h -1 bar -1 , the retention rate is 99.9%.

[0051] Embodiment 6:

[0052] Weigh h-BN / PDA and disperse it in pure water. Ultrasonicate for 1 hour to obtain 0.01g / L h-BN / PDA uniform dispersion. Add PEI to the h-BN / PDA dispersion to make the concentration of PEI 0.2g / L and stir for 10min. Then prepare 0.06g / L HMSN uniform dispersion, add PEI to make the concentration of PEI 0.1g / L and stir for 10min. 20mL of HMSN / PEI uniform dispersion and 125mL of h-BN / PDA / PEI uniform dispersion were filtered to the surface of CA membrane through a vacuum filtration device at a pressure of 0.09Mbar to obtain a high-flux boron nitride nanofiltration membrane with a sandwich structure. 20mL of Congo red simulated dye wastewater (20ppm) was used as a circulation unit and circulated 10 times. Between two separation cycles, the residual dye surface of the membrane was rinsed with ethanol and pure water, and 20mL of pure water was filtered.

[0053] The test showed that the Congo red flux of the high-flux boron nitride nanofiltration membrane with sandwich structure was 1960.7 L·m during the tenth separation cycle. 2 ·h -1 bar -1 , the retention rate was 90.2% and the flux recovery rate was 94.8%.

[0054] Comparative Example 1:

[0055] A 0.06 g / L HMSN uniform dispersion was prepared, PEI was added to make the PEI concentration 0.1 g / L, and stirred for 10 min. 20 mL of the HMSN / PEI uniform dispersion was filtered through a vacuum filtration device at a pressure of 0.09 Mbar onto the surface of the CA membrane to obtain a CA@HMSN membrane.

[0056] The Congo red flux of the prepared CA@HMSN membrane was tested to be 3050.1 L·m 2 ·h -1 bar -1 , the retention rate is 89.9%.

[0057] Comparative Example 2:

[0058] Weigh h-BN / PDA and disperse it in pure water. Ultrasonicate for 1 h to obtain 0.01 g / L h-BN / PDA uniform dispersion. Add PEI to the h-BN / PDA dispersion to make the PEI concentration 0.2 g / L and stir for 10 min. Filter 125 mL of the h-BN / PDA / PEI uniform dispersion onto the surface of the CA membrane through a vacuum filtration device at a pressure of 0.09 Mbar to obtain a CA@h-BN / PDA membrane.

[0059] The Congo red flux of the prepared CA@h-BN / PDA membrane was tested to be 2001.3 L·m2 ·h -1 bar -1 , the retention rate was 96.9%.

[0060] Comparative Example 3:

[0061] Prepare 0.06g / L HMSN uniform dispersion, add PEI to make the concentration of PEI 0.1g / L, and stir for 10min. Then filter 20mL of HMSN / PEI uniform dispersion to the surface of CA membrane through vacuum filtration device at a pressure of 0.09Mbar to obtain CA@HMSN membrane. Take 20mL Congo red simulated dye wastewater (20ppm) as a circulation unit, and cycle 10 times. Between two separation cycles, rinse the residual dye surface of the membrane with ethanol and pure water, and filter 20mL of pure water.

[0062] The Congo red flux of the prepared CA@h-BN / PDA membrane was tested to be 663.6 L·m 2 ·h -1 bar -1 , the retention rate was 61.2% and the flux recovery rate was 76.7%.

[0063] from Figure 1 It can be seen that the CA membrane is porous and the pore size distribution is uneven. Figure 2 It can be seen that after HMSN is loaded onto the CA membrane, HMSN is evenly dispersed on the CA membrane, and the original large and irregular pores of the CA membrane are optimized to form a separation channel with a smaller diameter, thereby improving the separation effect in the dye separation process. Figure 3 It can be seen that after the CA@HMSN membrane is successfully loaded with h-BN / PDA, the h-BN / PDA sheets are stacked into a multi-layer loose structure. This unique structure provides excellent separation flux while ensuring a high removal rate. Figure 4 It can be seen that the cross-section of the high-flux boron nitride nanofiltration membrane with a sandwich structure is clearly divided into three parts, namely the anti-fouling layer formed by the upper h-BN / PDA, the supporting layer formed by the middle HMSN and the bottom CA membrane as the base layer, which is a typical "sandwich" structure. Figure 5 It can be seen that the five elements B, C, N, O, and Si are evenly distributed in the high-flux boron nitride nanofiltration membrane with a sandwich structure, which provides a basis for the various components of the high-flux boron nitride nanofiltration membrane with a sandwich structure to play a role.

[0064] Therefore, the present invention adopts the above-mentioned structure to prepare a method and application of a high-flux boron nitride nanofiltration membrane with a sandwich structure. The prepared boron nitride nanofiltration membrane has a sandwich structure, which enables the composite membrane to obtain a large flux and a high retention rate while improving the anti-fouling ability, and has great potential in the field of wastewater treatment in the future.

[0065] The above description is not intended to impose any form of limitation on the present invention. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a high-throughput boron nitride nanofiltration membrane with a sandwich structure, It is characterized in that The following steps are involved: S1: Preparation of h-BN / PDA modified material: Take hexagonal boron nitride nanosheets h-BN powder, prepare a uniform hexagonal boron nitride dispersion with a concentration of 1 g / L, add tris-hydroxymethylaminomethane hydrochloride Tris-HCl to make its concentration in the dispersion 1.6 g / L, adjust the pH to 8.5, add dopamine DA to make its concentration in the dispersion 2 g / L, stir magnetically for 16 hours, centrifuge the product, wash it with pure water, and dry it at 60°C to obtain h-BN / PDA; S2: Preparation of ZIF-8 self-sacrificial template material: Dissolve 5.6 g of 2-methylimidazole in 50 mL of methanol. At the same time, dissolve 2.5 g of zinc nitrate hexahydrate Zn(NO 3 )·6H 2 O in 50 mL of methanol. Mix the above two solutions evenly, stir magnetically for 1 h, and let stand for 24 h. Centrifuge the product, wash it several times with methanol, and dry it to obtain ZIF-8; S3: Preparation of HMSN with a hollow mesoporous structure: Prepare a 540 mL water and ethanol mixed solution at a ratio of 5:4, add ZIF-8, 2.5 g of 2-methylimidazole, and 1.6 g of cetyltrimethylammonium bromide (CTAB), stir for 30 min to mix well, slowly add 5 mL of tetraethyl orthosilicate (TEOS), stir vigorously for 2 h, centrifuge the product, wash the product with methanol several times, and dry to obtain ZIF-8@mSiO 2 , put the product into 0.1 M hydrochloric acid (HCl), stir for 30 min, etch the ZIF-8 template, wash the product with deionized water several times, and dry to obtain HMSN with a hollow mesoporous structure templated by ZIF-8; S4: Preparation of a high-throughput boron nitride nanofiltration membrane with a sandwich structure: Weigh h-BN / PDA and disperse it in pure water. Ultrasonicate for 1 hour to obtain a 0.01 g / L h-BN / PDA uniform dispersion. Add PEI to the h-BN / PDA dispersion to a concentration of 0.2 g / L and stir for 10 minutes. Then prepare a 0.06 g / L HMSN uniform dispersion, add PEI to a concentration of 0.1 g / L and stir for 10 minutes. The HMSN / PEI uniform dispersion and the h-BN / PDA / PEI uniform dispersion are filtered to the surface of the bottom membrane through a vacuum filtration device at a pressure of 0.09 Mbar to obtain a high-throughput boron nitride nanofiltration membrane with a sandwich structure.

2. A method for preparing a high-flux boron nitride nanofiltration membrane with a sandwich structure as claimed in claim 1, It is characterized in that In the step S1, the mass ratio of hexagonal boron nitride to dopamine is in the range of 1:1.4-2.

3. A method for preparing a high-flux boron nitride nanofiltration membrane with a sandwich structure as claimed in claim 1, It is characterized in that The alkali used to adjust the pH in step S1 includes one or more of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, and sodium bicarbonate. The pH range is 8-9, and the magnetic stirring time after adding DA is 10-20 hours.

4. A method for preparing a high-flux boron nitride nanofiltration membrane with a sandwich structure as claimed in claim 1, It is characterized in that In step S2, the mass ratio of 2-methylimidazole to zinc nitrate hexahydrate is in the range of 2:2.5, the standing time of the product is in the range of 16-26 hours, and the organic solvent used for washing the product includes one of methanol, ethanol, and a methanol-ethanol mixture.

5. A method for preparing a high-flux boron nitride nanofiltration membrane with a sandwich structure as claimed in claim 1, It is characterized in that In the step S3, the volume ratio of water to ethanol when preparing the water-ethanol mixed solution is in the range of 6:5-4:3, and the organic solvent used for washing the product includes one of methanol, ethanol, and a methanol-ethanol mixed solution.

6. A method for preparing a high-flux boron nitride nanofiltration membrane with a sandwich structure as claimed in claim 1, It is characterized in that In step S3, the mass ratio range of 2-methylimidazole to cetyltrimethylammonium bromide is 1:1.3 - 1.8, the stirring time range of the product is 25 - 35 min, and the volume ratio range of tetraethyl orthosilicate to the water-methanol mixture is 1:0.008 - 0.

012.

7. A method for preparing a high-flux boron nitride nanofiltration membrane with a sandwich structure as described in claim 1, characterized in that, the acid used for etching the ZIF-8 template in step S3 includes one or more of hydrochloric acid, sulfuric acid, nitric acid, and perchloric acid; the molar concentration range of the acid is 0.05 - 0.15 M.

8. A method for preparing a high-flux boron nitride nanofiltration membrane with a sandwich structure as described in claim 1, characterized in that, in step S4, the mass concentration range of the prepared h-BN / PDA homogeneous dispersion is 0.008 - 0.012 g / L, the mass ratio range of h-BN / PDA to PEI is 1:0.04 - 0.06, and its stirring time range is 1 - 20 min; the mass concentration range of the prepared HMSN is 0.04 - 0.08 g / L, the mass ratio range of HMSN to PEI is 1:0.4 - 0.8, and its stirring time range is 1 - 20 min.

9. A method for preparing a high-flux boron nitride nanofiltration membrane with a sandwich structure as described in claim 1, characterized in that, the bottom membrane selected in step S4 includes one or more of a CA membrane, a polyvinylidene fluoride membrane, a nylon membrane, a polyacrylonitrile membrane, a polyethersulfone membrane, and a polysulfone membrane; the suction filtration order is that the HMSN / PEI homogeneous dispersion is first and the h-BN / PDA / PEI homogeneous dispersion is second, and the selected pressure range during suction filtration is 0.07 - 0.1 Mbar.

10. A high-flux boron nitride nanofiltration membrane with a sandwich structure prepared by using the method for preparing a high-flux boron nitride nanofiltration membrane with a sandwich structure according to any one of claims 1 - 9.

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