A boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane and a preparation method thereof

Abstract

The application discloses a boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane and a preparation method thereof. The method comprises the following steps: adding tri-aldehyde-based phloroglucinol into n-octanoic acid, and then adding the obtained solution into a diamino benzene sulfonic acid solution; after reaction for 3-5 days, the solution is dialyzed with deionized water and centrifuged in sequence to obtain a COF nanosheet dispersion liquid; the COF nanosheet dispersion liquid, a boron nitride nanosheet dispersion liquid and an aramid nanofiber suspension liquid are uniformly mixed, and the mass ratio of the COF nanosheet dispersion liquid to the boron nitride nanosheet dispersion liquid is equal to the mass ratio of the aramid nanofiber suspension liquid to the boron nitride nanosheet dispersion liquid to obtain a composite dispersion liquid; and the composite dispersion liquid is assembled on a mechanical support layer by vacuum filtration to obtain the boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane. The boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane has high permeability and selectivity, and is easy to realize industrial application.

Description

Technical Field

[0001] This invention belongs to the field of nanofiltration membrane preparation, specifically a boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane and its preparation method. Background Technology

[0002] With the rapid development of industry and agriculture, the serious waste and pollution of water resources, and the rapid deterioration of ecosystems, the shortage of usable freshwater resources worldwide is becoming increasingly serious. Utilizing membrane separation technology is of great significance for achieving seawater desalination and wastewater reuse to alleviate the freshwater resource crisis.

[0003] Nanofiltration membranes are a new type of pressure-driven separation membrane material that falls between ultrafiltration and reverse osmosis membranes. They have low operating pressure and high permeability, with a pore size of about 1 nm, and can be used to retain most organic molecules and a range of polyvalent salts.

[0004] Nanofiltration membranes typically consist of a thick mechanical support layer and a thin separation layer. Boron nitride nanosheets (BNNS) have attracted widespread attention as a separation layer material for nanofiltration membranes due to their strong chemical stability, sub-nanometer-scale interlayer capillary channels, and high surface charge density, which are beneficial for mass transport. However, the separation layer formed by BNNS is brittle and has poor adhesion to the mechanical support layer, making it unable to withstand high pressures during separation and prone to rupture, leading to a decrease in the selectivity of the nanofiltration membrane. Furthermore, the separation layer formed by BNNS has fewer water molecule transport channels, typically exhibiting lower permeability. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane and its preparation method. The operation is simple, the raw material cost is low, and the resulting composite nanofiltration membrane has strong permeability and selectivity, making it easy to achieve industrial application.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing a boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane includes the following steps:

[0008] S1, add trialdehyde phloroglucinol to octanoic acid at a ratio of (10-30) mg: (20-40) mL, dissolve it, and then drop it onto the diaminobenzenesulfonic acid solution. After reacting for 3-5 days, dialyze with deionized water and centrifuge to obtain a COF nanosheet dispersion with a concentration of 0.1-0.5 mg / mL.

[0009] S2, mix a COF nanosheet dispersion (0.1–0.5 mg / mL), a boron nitride nanosheet dispersion (0.1–0.5 mg / mL), and an aramid nanofiber suspension (0.01–0.02 mg / mL) evenly, wherein the mass ratio of the COF nanosheet dispersion to the boron nitride nanosheet dispersion is ≤ The mass ratio of aramid nanofiber suspension to boron nitride nanosheet dispersion is ≤ A composite dispersion was obtained;

[0010] S3, using a microfiltration membrane as a mechanical support layer, the composite dispersion is assembled on the mechanical support layer by vacuum filtration, forming a separation layer on the mechanical support layer, and then dried to obtain a boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane.

[0011] Preferably, in step S1, 15–40 mg of diaminobenzenesulfonic acid is added to 20–40 mL of deionized water and sonicated for 10–30 min to obtain a diaminobenzenesulfonic acid solution.

[0012] Furthermore, S1 adds trialdehyde phloroglucinol to octanoic acid, sonicates for 10–30 min, and then adds it dropwise over the diaminobenzenesulfonic acid solution.

[0013] Preferably, the reaction described in S1 is carried out at 20–40°C.

[0014] Preferably, in step S2, boron nitride nanosheets are added to deionized water and then ultrasonically dispersed for 10-20 minutes to obtain the boron nitride nanosheet dispersion.

[0015] Preferably, the aramid nanofiber suspension described in S2 is obtained by the following process:

[0016] Aramid fibers, potassium hydroxide, and dimethyl sulfoxide were mixed evenly at a ratio of 1g:1.5g:500mL, and then stirred continuously for 7–14 days to obtain a deprotonated ANF dispersion. Then, 1mL of the deprotonated ANF dispersion was protonated with 100–200mL of deionized water to obtain the aramid nanofiber suspension.

[0017] Preferably, in step S2, the COF nanosheet dispersion, boron nitride nanosheet dispersion and aramid nanofiber suspension are first mixed, then ultrasonically dispersed at 300-800W for 10-20 min, and then stirred for 6-18 h to obtain a composite dispersion.

[0018] Preferably, the microfiltration membrane described in S3 is made of polytetrafluoroethylene.

[0019] Preferably, the drying process described in S3 is carried out at room temperature for 6 to 18 hours.

[0020] A boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane obtained by the preparation method of boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane described in any one of the above claims.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] This invention discloses a method for preparing a boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane. By using boron nitride nanosheets (BNNS) as the matrix to provide abundant two-dimensional fluid channels, and alumina nanofibers (ANF) as the film-forming and binding phase to enhance the membrane's stability, the method utilizes a two-dimensional organic polymer (COF) material. COF effectively addresses the compatibility issue between ANF and BNNS, and its oriented sub-nanometer pore structure and two-dimensional nanochannel structure provide abundant water channels, resulting in a high-flux and highly selective nanofiltration membrane. This invention addresses the technical problem of poor selectivity and mechanical fragility in inorganic BNNS (i.e., pure BNNS) separation layers, leading to poor stability. It introduces highly film-forming one-dimensional ANF nanosheets and porous COF nanosheets with high crystallinity and tunable pore size into two-dimensional BNNS to construct a ternary composite nanofiltration membrane. The different dimensions and structures of the nanomaterials play the aforementioned roles, endowing the nanofiltration membrane with abundant water channels while ensuring excellent selectivity, thus achieving a synergistic improvement in separation flux and efficiency. Attached Figure Description

[0023] Figure 1 This is a planar SEM image of the BNNS nanofiltration membrane described in the comparative example of the present invention at 10 μm.

[0024] Figure 2 This is a planar SEM image of the BNNS / COF / ANF composite nanofiltration membrane obtained in Example 1 of the present invention at 10 μm.

[0025] Figure 3 This is a cross-sectional view of the BNNS / COF / ANF composite nanofiltration membrane obtained in Example 1 of the present invention at 2 μm.

[0026] Figure 4 The ultraviolet absorption spectra of the filtrate and the feed liquid after separation by the BNNS / COF / ANF composite nanofiltration membrane obtained in Example 1 of this invention are shown.

[0027] Figure 5 The images shown are, in order, a 4 ppm methylene blue solution (feed solution) and the filtrate obtained after separation by the BNNS / COF / ANF composite nanofiltration membrane obtained in Example 1 of this invention. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0029] This invention provides a method for preparing a boron nitride nanosheet (BNNS) / covalent organic framework (COF) / aramid nanofiber (ANF) composite nanofiltration membrane, the specific steps of which are as follows:

[0030] Step (1): Add BNNS to deionized water and then sonicate for 10-20 minutes to obtain a colorless and transparent BNNS / water dispersion with a concentration of 0.1-0.5 mg / mL for later use.

[0031] Step (2): Add 15-40 mg of diaminobenzenesulfonic acid to 20-40 mL of deionized water, sonicate for 10-30 min to form a diaminobenzenesulfonic acid solution, and pour it into the bottom of a beaker.

[0032] Step (3): Dissolve 10-30 mg of trialdehyde phloroglucinol in 20-40 mL of octanoic acid, sonicate for 10-30 min, add the resulting solution dropwise above the solution of diaminobenzenesulfonic acid, and react at 20-40 °C for 3-5 days using interfacial polymerization. After dialysis with deionized water and centrifugation, a clear red COF nanosheet / aqueous dispersion with a concentration of 0.1-0.5 mg / mL is obtained.

[0033] In step (4), aramid fiber, potassium hydroxide, and dimethyl sulfoxide are mixed evenly in a reactor at a ratio of 1g:1.5g:500mL. The mixture is then stirred continuously at room temperature for 7–14 days to obtain a deprotonated ANF dispersion. 1mL of the ANF dispersion is then protonated with 100–200mL of deionized water (i.e., simply add deionized water and stir until homogeneous) to obtain an ANF / water suspension with a concentration of 0.01–0.02 mg / mL.

[0034] Step (5): Mix the BNNS / aqueous dispersion, COF nanosheet / aqueous dispersion, and ANF / aqueous suspension obtained in steps (1), (3), and (4), respectively, wherein the mass ratio of COF nanosheet / aqueous dispersion to BNNS / aqueous dispersion is ≤ The mass ratio of ANF / aqueous suspension to BNNS / aqueous dispersion ≤ Then, it was ultrasonically dispersed at 300-800W for 10-20 minutes, and then placed on a magnetic stirrer and stirred for 6-18 hours to obtain a BNNS / COF / ANF composite dispersion.

[0035] Step (6): Using polytetrafluoroethylene microfiltration membrane as mechanical support layer, the dispersion obtained in step (5) is assembled on the mechanical support layer by vacuum filtration, forming a separation layer on the mechanical support layer. After drying at room temperature for 6 to 18 hours, the BNNS / COF / ANF composite nanofiltration membrane is obtained.

[0036] Example 1

[0037] Step (1): Add BNNS to deionized water and sonicate for 10 min to obtain a colorless and transparent BNNS / water dispersion with a concentration of 0.1 mg / mL for later use.

[0038] Step (2): Add 25 mg of diaminobenzenesulfonic acid to 30 mL of deionized water, sonicate for 20 min, and pour it into the bottom of a beaker.

[0039] In step (3), 25 mg of trialdehyde phloroglucinol was dissolved in 30 mL of octanoic acid and sonicated for 20 min. The solution was then added dropwise above the solution in step (2). After reacting at 30 °C for 4 days using interfacial polymerization, a clear red COF nanosheet / aqueous dispersion with a concentration of 0.3 mg / mL was obtained by dialysis and centrifugation.

[0040] In step (4), 1g of aramid fiber, 1.5g of potassium hydroxide and 500mL of dimethyl sulfoxide are mixed evenly in a reactor and stirred continuously at room temperature for 7 days to obtain a deprotonated ANF dispersion. Then, 1mL of the ANF dispersion is protonated with 200mL of deionized water to obtain an ANF / water suspension with a concentration of 0.01mg / mL.

[0041] Step (5): The BNNS / water dispersion, COF nanosheet / water dispersion and ANF / water suspension obtained in steps (1), (3) and (4) respectively (mass ratio 78:14:8) are mixed and ultrasonically dispersed at 700W for 15 min. The mixture is then placed on a magnetic stirrer and stirred for 12 h to obtain the BNNS / COF / ANF composite dispersion.

[0042] Step (6): Using polytetrafluoroethylene microfiltration membrane as mechanical support layer, the dispersion obtained in step (5) is assembled into a separation layer on the mechanical support layer by vacuum filtration. After drying at room temperature for 12 hours, the BNNS / COF / ANF composite nanofiltration membrane is obtained.

[0043] Comparative Example

[0044] Step (1): Add BNNS to deionized water and sonicate for 10 min to obtain a colorless and transparent BNNS / water dispersion with a concentration of 0.1 mg / mL for later use.

[0045] Step (2): Using polytetrafluoroethylene microfiltration membrane as mechanical support layer, the BNNS / water dispersion obtained in step (1) is assembled into a separation layer on the mechanical support layer by vacuum filtration. After drying at room temperature for 12 hours, a BNNS nanofiltration membrane is obtained.

[0046] like Figure 1 As can be seen, the inorganic BNNS separation layer is brittle and has many cracks on its surface.

[0047] like Figure 2 As can be seen, the surface of the BNNS / COF / ANF composite nanofiltration membrane is smooth and free of cracks.

[0048] like Figure 3 As can be seen, the thickness of the separation layer of the BNNS / COF / ANF composite nanofiltration membrane is approximately 150 nm.

[0049] like Figure 4 As can be seen, the absorbance of the 4 ppm methylene blue solution (feed solution) at 664 nm is 0.97, while the absorbance of the filtrate separated by the BNNS / COF / ANF composite nanofiltration membrane obtained in Example 1 of this invention is 0.0039 at 664 nm, and its separation efficiency can reach over 99%. Furthermore, the BNNS / COF / ANF composite nanofiltration membrane also exhibits a high absorbance of 194 L·m⁻¹. -2 ·h -1 ·bar -1 The permeation flux.

[0050] like Figure 5 As can be seen, the 4ppm methylene blue solution (feed liquid) presents a clear blue state, while the filtrate separated by the BNNS / COF / ANF composite nanofiltration membrane obtained in Example 1 of this invention presents a colorless and transparent state.

[0051] Example 2

[0052] Step (1): Add BNNS to deionized water and sonicate for 15 min to obtain a colorless and transparent BNNS / water dispersion with a concentration of 0.3 mg / mL for later use.

[0053] Step (2): Add 15 mg of diaminobenzenesulfonic acid to 20 mL of deionized water, sonicate for 10 min, and pour it into the bottom of a beaker.

[0054] In step (3), 10 mg of trialdehyde phloroglucinol was dissolved in 20 mL of octanoic acid and sonicated for 10 min. The solution was then added dropwise above the solution from step (2). After reacting at 20 °C for 5 days using interfacial polymerization, a clear red COF nanosheet / aqueous dispersion was obtained by dialysis and centrifugation.

[0055] In step (4), 1g of aramid fiber, 1.5g of potassium hydroxide and 500mL of dimethyl sulfoxide are mixed evenly in a reactor and stirred continuously at room temperature for 10 days to obtain a deprotonated ANF dispersion. Then, 1mL of the ANF dispersion is protonated with 100mL of deionized water to obtain an ANF / water suspension with a concentration of 0.02mg / mL.

[0056] Step (5): The BNNS / water dispersion, COF nanosheet / water dispersion and ANF / water suspension obtained in steps (1), (3) and (4) respectively (mass ratio of 73:18:9) are mixed and ultrasonically dispersed at 300W power for 20 min. Then, the mixture is placed on a magnetic stirrer and stirred for 6 h to obtain the BNNS / COF / ANF composite dispersion.

[0057] Step (6): Using polytetrafluoroethylene microfiltration membrane as mechanical support layer, the dispersion obtained in step (5) is assembled into a separation layer on the mechanical support layer by vacuum filtration. After drying at room temperature for 6 hours, the BNNS / COF / ANF composite nanofiltration membrane is obtained.

[0058] Example 3

[0059] Step (1): Add BNNS to deionized water and sonicate for 20 min to obtain a colorless and transparent BNNS / water dispersion with a concentration of 0.5 mg / mL for later use.

[0060] Step (2): Add 40 mg of diaminobenzenesulfonic acid to 40 mL of deionized water, sonicate for 30 min, and pour it into the bottom of a beaker.

[0061] In step (3), 30 mg of trialdehyde phloroglucinol was dissolved in 40 mL of octanoic acid and sonicated for 30 min. The solution was then added dropwise above the solution from step (2). After reacting at 40 °C for 3 days using interfacial polymerization, a clear red COF nanosheet / aqueous dispersion was obtained by dialysis and centrifugation.

[0062] In step (4), 1g of aramid fiber, 1.5g of potassium hydroxide and 500mL of dimethyl sulfoxide are mixed evenly in a reactor and stirred continuously at room temperature for 14 days to obtain a deprotonated ANF dispersion. Then, 1mL of the ANF dispersion is protonated with 150mL of deionized water to obtain an ANF / water suspension with a concentration of 0.013mg / mL.

[0063] Step (5): The BNNS / water dispersion, COF nanosheet / water dispersion and ANF / water suspension obtained in steps (1), (3) and (4) respectively (mass ratio 91:6:3) are mixed and ultrasonically dispersed at 800W for 10 min. The mixture is then placed on a magnetic stirrer and stirred for 18 h to obtain the BNNS / COF / ANF composite dispersion.

[0064] Step (6): Using polytetrafluoroethylene microfiltration membrane as mechanical support layer, the dispersion obtained in step (5) is assembled into a separation layer on the mechanical support layer by vacuum filtration. After drying at room temperature for 18 hours, the BNNS / COF / ANF composite nanofiltration membrane is obtained.

Claims

1. A method for preparing a boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane, characterized in that, Includes the following steps: S1, add trialdehyde phloroglucinol to octanoic acid at a ratio of (10-30) mg: (20-40) mL, dissolve it, and then drop it onto the diaminobenzenesulfonic acid solution. After reacting for 3-5 days, dialyze with deionized water and centrifuge to obtain a COF nanosheet dispersion with a concentration of 0.1-0.5 mg / mL. S2, mix COF nanosheet dispersion (0.1–0.5 mg / mL), boron nitride nanosheet dispersion (0.1–0.5 mg / mL), and aramid nanofiber suspension (0.01–0.02 mg / mL) evenly, wherein the mass ratio of COF nanosheet dispersion to boron nitride nanosheet dispersion is... Mass ratio of aramid nanofiber suspension to boron nitride nanosheet dispersion A composite dispersion was obtained; S3, using a microfiltration membrane as a mechanical support layer, the composite dispersion is assembled on the mechanical support layer by vacuum filtration, forming a separation layer on the mechanical support layer, and then dried to obtain a boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane.

2. The method for preparing the boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane according to claim 1, characterized in that, S1. Add 15-40 mg of diaminobenzenesulfonic acid to 20-40 mL of deionized water and sonicate for 10-30 min to obtain a diaminobenzenesulfonic acid solution.

3. The method for preparing the boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane according to claim 2, characterized in that, S1 involves adding trialdehyde phloroglucinol to octanoic acid, sonicating for 10–30 minutes, and then adding it dropwise over a solution of diaminobenzenesulfonic acid.

4. The method for preparing the boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane according to claim 1, characterized in that, The reaction described in S1 is carried out at 20–40 °C.

5. The method for preparing the boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane according to claim 1, characterized in that, S2. Add boron nitride nanosheets to deionized water and then ultrasonically disperse for 10-20 minutes to obtain the boron nitride nanosheet dispersion.

6. The method for preparing the boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane according to claim 1, characterized in that, The aramid nanofiber suspension described in S2 is obtained through the following process: Aramid fibers, potassium hydroxide, and dimethyl sulfoxide were mixed evenly at a ratio of 1g:1.5g:500mL, and then stirred continuously for 7–14 days to obtain a deprotonated ANF dispersion. Then, 1mL of the deprotonated ANF dispersion was protonated with 100–200mL of deionized water to obtain the aramid nanofiber suspension.

7. The method for preparing the boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane according to claim 1, characterized in that, S2 First, the COF nanosheet dispersion, boron nitride nanosheet dispersion and aramid nanofiber suspension are mixed, then ultrasonically dispersed at 300-800W for 10-20 min, and then stirred for 6-18 h to obtain a composite dispersion.

8. The method for preparing the boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane according to claim 1, characterized in that, The microfiltration membrane described in S3 is made of polytetrafluoroethylene.

9. The method for preparing the boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane according to claim 1, characterized in that, The drying process described in S3 is carried out at room temperature for 6–18 hours.

10. A boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane obtained by the preparation method of the boron nitride nanosheet / covalent organic framework / aramid nanofiber composite nanofiltration membrane according to any one of claims 1 to 9.

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