Preparation method and application of a double-layer COF composite membrane

Abstract

The application discloses a preparation method and application of a double-layer COF composite membrane and belongs to the technical field of gas separation membranes. The double-layer COF composite membrane is prepared by the following steps: taking a porous polymer membrane as a support layer, depositing macroporous TpBD-2SO3H nanosheets on the surface of the base membrane through vacuum suction filtration, and interfacially polymerizing a microporous ACOF-1 layer. The application induces ACOF-1 to be generated on the surface of the TpBD-2SO3H nanosheets through electrostatic interaction between the TpBD-2SO3H nanosheets and amine monomers, and a dense and defect-free composite membrane is obtained, which exhibits excellent H2 / CO2 separation performance. The method is ingeniously designed, and the double-layer COF composite membrane prepared by the method has important application potential in the field of H2 separation.

Description

[0001] Technical Field: This invention relates to a method for preparing a double-layer COF composite membrane and its application, belonging to the field of gas separation membranes.

[0002] Background Technology: The development of sustainable energy is a global priority, and hydrogen (H2) energy systems are considered an ideal solution for achieving a sustainable future. However, the production of H2 through processes such as hydrocarbon reforming or fossil fuel gasification often generates large amounts of carbon dioxide. Therefore, the efficient purification and separation of H2 from H2 / CO2 mixtures is crucial. Currently, industrial H2 / CO2 separation mainly relies on pressure swing adsorption (PSA) and cryogenic separation technologies. The former is limited by high energy consumption for adsorbent regeneration and low cycle efficiency, while the latter faces bottlenecks such as harsh cryogenic operating conditions and huge equipment investment. In contrast, membrane separation technology, as a low-energy-consumption, simple-to-operate, and environmentally friendly technology, has been widely used in complex gas separation processes.

[0003] Covalent organic frameworks (COFs) are ideal for constructing high-performance gas separation membranes due to their designable pore sizes, high specific surface areas, and excellent stability. However, the inherent pore size of COFs is typically 0.8–5 nm, much larger than the kinetic diameters of H2 (0.289 nm) and CO2 (0.33 nm), making it difficult to achieve effective H2 / CO2 separation with a single COF layer. Researchers have tried to reduce the pore size by introducing ionic liquids into the COF channels, but this significantly reduces the gas permeation flux. Alternatively, the "masking effect" of polymers on COFs can be used to reduce the pore size, but the membrane stability is poor under high pressure or humid environments. Therefore, this greatly limits the application of COFs in gas separation. This invention proposes a bilayer COF strategy. Large-pore TpBD-2SO3H nanosheets are filtered onto an HPAN layer. The electrostatic interaction between -SO3H and hydrazine hydrate induces the directional polymerization of small-pore ACOF-1 at the interface, forming a dense, defect-free selective layer. The two types of COFs are stacked alternately, effectively reducing the sieve pore size. Simultaneously, hydrazine hydrate, permeating into the TpBD-2SO3H layer, reacts with the aldehyde monomer to generate ACOF-1, filling the defects between the TpBD-2SO3H nanosheets in situ. This invention achieves optimized membrane structure integrity and exhibits ultra-high H2 flux in H2 / CO2 separation.

[0004] Summary of the Invention: This invention provides a method for preparing a bilayer COF composite membrane. This method is ingeniously designed and can effectively separate H2. The specific technical solution of this invention is as follows:

[0005] (1) Hydrolysis of PAN base film

[0006] The PAN base film was hydrolyzed by immersing it in a 1 M NaOH aqueous solution and then thoroughly rinsed with deionized water until the water became neutral, resulting in the hydrolyzed PAN base film HPAN.

[0007] (2) Preparation of TpBD-2SO3H nanosheets

[0008] A certain mass of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde and 2,2'-benzidine disulfonic acid were weighed and dissolved separately in 5 mL of dimethyl sulfoxide. The two solutions were dissolved separately by sonication, and finally, they were mixed and placed in a 120 ℃ forced-air oven for a certain period of time. The obtained TpBD-2SO3H nanosheets were dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cutoff of 3500 to remove residual unreacted monomers or oligomers.

[0009] (3) Preparation of TpBD-2SO3H / HPAN membrane

[0010] A certain volume of TpBD-2SO3H nanosheets was dispersed in 70 mL of deionized water and sonicated to ensure that the nanosheets were uniformly dispersed in the deionized water. The TpBD-2SO3H nanosheet solution was then vacuum filtered onto the surface of HPAN to obtain a TpBD-2SO3H / HPAN membrane.

[0011] (4) Preparation of ACOF-1-TpBD-2SO3H / HPAN membrane

[0012] (4.1) Preparation of precursor solution

[0013] Hydrazine hydrate was dissolved in deionized water and sonicated to ensure that the amine monomer was uniformly dispersed in the deionized water, resulting in an aqueous solution with a certain mass-volume fraction. 1,3,5-trialdehydebenzene was dissolved in benzene and a certain volume of glacial acetic acid was added. The solution was then sonicated to ensure that the aldehyde monomer was uniformly dispersed in the benzene, resulting in an oil solution with a certain mass-volume fraction.

[0014] (4.2) Interface aggregation

[0015] (4.2.1) Pour the aqueous solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane, keep the aqueous solution on the membrane surface for a certain time, pour out the aqueous solution and air dry the membrane at room temperature to prevent defects from forming on the membrane surface. (4.2.2) Pour the oil phase solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane treated in step (4.2.1), react for a certain time, then pour out the excess oil phase solution, wash several times with benzene to remove unreacted monomers, and obtain the TpBD-2SO3H / HPAN membrane.

[0016] (4.3) Heat treatment

[0017] The TpBD-2SO3H / HPAN membrane prepared in step (4.2) was heat-treated at 60 °C for 5 min to enhance the bonding force between the composite membrane and the HPAN base membrane.

[0018] The hydrolysis described in step (1) above is hydrolysis at 50 °C for 1 h.

[0019] The measured amounts of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde and 2,2'-benzidine disulfonic acid mentioned in step (2) above are 4.2 mg and 10.3 mg, respectively.

[0020] The reaction time described in step (2) above is 15 days.

[0021] The TpBD-2SO3H nanosheets of a certain volume mentioned in step (3) above are 0.2~1.5 mL, preferably 1 mL.

[0022] The aqueous phase solution with a certain mass volume fraction mentioned in step (4.1) above is 0.5% (w / v), and the oil phase solution with a certain mass volume fraction is 0.2% (w / v).

[0023] The certain volume of glacial acetic acid mentioned in step (4.1) above is 15 μL.

[0024] The time to maintain the position as described in step (4.2.1) above is 20 minutes.

[0025] The reaction time described in step (4.2.2) above is 0.2 to 2 hours, preferably 1 hour.

[0026] The method of this invention involves depositing TpBD-2SO3H nanosheets on a porous substrate, followed by coating with a layer of ACOF-1 via interfacial polymerization to obtain a bilayer COF composite film. Compared with existing technologies, this invention has the following advantages:

[0027] (1) This method utilizes the electrostatic interaction between TpBD-2SO3H and hydrazine hydrate to enhance the stability of the composite membrane;

[0028] (2) By using two types of COF to stack alternately, the sieve aperture is effectively reduced, and the prepared composite membrane can effectively separate H2 / CO2 and realize rapid H2 transport. Attached Figure Description

[0029] Figure 1 These are the preparation flowcharts for Examples 1-5.

[0030] Figure 2This is a scanning electron microscope image of the surface of the ACOF-1-TpBD-2SO3H / HPAN film prepared in Example 2.

[0031] Figure 3 This is an elemental distribution diagram of the ACOF-1-TpBD-2SO3H / HPAN membrane prepared in Example 2.

[0032] Figure 3 This is a cross-sectional scanning electron microscope image of the ACOF-1-TpBD-2SO3H / HPAN membrane prepared in Example 2.

[0033] Detailed Implementation: The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific examples.

[0034] Example 1

[0035] (1) Hydrolysis of PAN base film

[0036] The PAN base film was immersed in a 1 M NaOH aqueous solution at 50 °C for 1 h for hydrolysis, and then thoroughly rinsed with deionized water until the water became neutral, resulting in the hydrolyzed PAN base film HPAN.

[0037] (2) Preparation of TpBD-2SO3H nanosheets

[0038] 4.2 mg of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde and 10.3 mg of 2,2'-benzidine disulfonic acid were weighed and dissolved separately in 5 mL of dimethyl sulfoxide. The two solutions were dissolved separately by sonication, and then mixed together and placed in a 120 °C oven for 15 days. The resulting TpBD-2SO3H nanosheets were dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cutoff of 3500 to remove residual unreacted monomers or oligomers.

[0039] (3) Preparation of TpBD-2SO3H / HPAN membrane

[0040] 0.2 mL of TpBD-2SO3H nanosheets were dispersed in 70 mL of deionized water and sonicated to ensure that the nanosheets were uniformly dispersed in the deionized water. The TpBD-2SO3H nanosheet solution was then vacuum filtered onto the surface of HPAN to obtain a TpBD-2SO3H / HPAN membrane.

[0041] (4) Preparation of ACOF-1-TpBD-2SO3H / HPAN membrane

[0042] (4.1) Preparation of precursor solution

[0043] Measure 25 μL of hydrazine hydrate and dissolve it in 5 mL of deionized water, then sonicate the solution to ensure that the amine monomer is uniformly dispersed in the deionized water, resulting in an aqueous solution with a mass-volume fraction of 0.5% (w / v). Weigh 10 mg of 1,3,5-trialdehydebenzene and dissolve it in 5 mL of benzene, then add 15 μL of glacial acetic acid and sonicate the solution to ensure that the aldehyde monomer is uniformly dispersed in the benzene, resulting in an oil solution with a mass-volume fraction of 0.2% (w / v).

[0044] (4.2) Interface aggregation

[0045] (4.2.1) Pour the aqueous solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane, keep the aqueous solution on the membrane surface for 20 min, pour out the aqueous solution and let the membrane air dry at room temperature to prevent defects from forming on the membrane surface.

[0046] (4.2.2) Pour the oil phase solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane after treatment in step (4.2.1), react for 1 h, then pour out the excess oil phase solution, wash with benzene several times to remove unreacted monomers, and obtain the TpBD-2SO3H / HPAN membrane.

[0047] (4.3) Heat treatment

[0048] The TpBD-2SO3H / HPAN membrane prepared in step (4.2) was heat-treated at 60 °C for 5 min to enhance the bonding force between the composite membrane and the HPAN base membrane. Gas permeation experiments were conducted on the membrane prepared in this embodiment to test its H2 and CO2 separation performance. The transmembrane pressure difference was controlled at 1.0 bar, the permeate side pressure was maintained at atmospheric pressure, and the test temperature was room temperature. The test results showed that the H2 flux was 1287.8 GPU, the CO2 flux was 561.9 GPU, and the H2 and CO2 separation selectivity was 2.3.

[0049] Example 2

[0050] (1) Hydrolysis of PAN base film

[0051] The PAN base film was immersed in a 1 M NaOH aqueous solution at 50 °C for 1 h for hydrolysis, and then thoroughly rinsed with deionized water until the water became neutral, resulting in the hydrolyzed PAN base film HPAN.

[0052] (2) Preparation of TpBD-2SO3H nanosheets

[0053] 4.2 mg of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde and 10.3 mg of 2,2'-benzidine disulfonic acid were weighed and dissolved separately in 5 mL of dimethyl sulfoxide. The two solutions were dissolved separately by sonication, and then mixed together and placed in a 120 °C oven for 15 days. The resulting TpBD-2SO3H nanosheets were dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cutoff of 3500 to remove residual unreacted monomers or oligomers.

[0054] (3) Preparation of TpBD-2SO3H / HPAN membrane

[0055] 1 mL of TpBD-2SO3H nanosheets was dispersed in 70 mL of deionized water and sonicated to ensure that the nanosheets were uniformly dispersed in the deionized water. The TpBD-2SO3H nanosheet solution was then vacuum filtered onto the surface of HPAN to obtain a TpBD-2SO3H / HPAN membrane.

[0056] (4) Preparation of ACOF-1-TpBD-2SO3H / HPAN membrane

[0057] (4.1) Preparation of precursor solution

[0058] Measure 25 μL of hydrazine hydrate and dissolve it in 5 mL of deionized water, then sonicate the solution to ensure that the amine monomer is uniformly dispersed in the deionized water, resulting in an aqueous solution with a mass-volume fraction of 0.5% (w / v). Weigh 10 mg of 1,3,5-trialdehydebenzene and dissolve it in 5 mL of benzene, then add 15 μL of glacial acetic acid and sonicate the solution to ensure that the aldehyde monomer is uniformly dispersed in the benzene, resulting in an oil solution with a mass-volume fraction of 0.2% (w / v).

[0059] (4.2) Interface aggregation

[0060] (4.2.1) Pour the aqueous solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane, keep the aqueous solution on the membrane surface for 20 min, pour out the aqueous solution and let the membrane air dry at room temperature to prevent defects from forming on the membrane surface.

[0061] (4.2.2) Pour the oil phase solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane after treatment in step (4.2.1), react for 1 h, then pour out the excess oil phase solution, wash with benzene several times to remove unreacted monomers, and obtain the TpBD-2SO3H / HPAN membrane.

[0062] (4.3) Heat treatment

[0063] The TpBD-2SO3H / HPAN membrane prepared in step (4.2) was heat-treated at 60 °C for 5 min to enhance the bonding force between the composite membrane and the HPAN base membrane. Gas permeation experiments were conducted on the membrane prepared in this embodiment to test its H2 and CO2 separation performance. The transmembrane pressure difference was controlled at 1.0 bar, the permeate side pressure was maintained at atmospheric pressure, and the test temperature was room temperature. The test results showed that the H2 flux was 1773.1 GPU, the CO2 flux was 264.3 GPU, and the H2 and CO2 separation selectivity was 6.7.

[0064] Example 3

[0065] (1) Hydrolysis of PAN base film

[0066] The PAN base film was immersed in a 1 M NaOH aqueous solution at 50 °C for 1 h for hydrolysis, and then the base film was thoroughly rinsed with deionized water until the water became neutral, resulting in the hydrolyzed PAN base film HPAN.

[0067] (2) Preparation of TpBD-2SO3H nanosheets

[0068] 4.2 mg of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde and 10.3 mg of 2,2'-benzidine disulfonic acid were weighed and dissolved separately in 5 mL of dimethyl sulfoxide. The two solutions were dissolved separately by sonication, and then mixed together and placed in a 120 °C oven for 15 days. The resulting TpBD-2SO3H nanosheets were dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cutoff of 3500 to remove residual unreacted monomers or oligomers.

[0069] (3) Preparation of TpBD-2SO3H / HPAN membrane

[0070] 1.5 mL of TpBD-2SO3H nanosheets were dispersed in 70 mL of deionized water and sonicated to ensure that the nanosheets were uniformly dispersed in the deionized water. The TpBD-2SO3H nanosheet solution was vacuum filtered onto the surface of HPAN to obtain a TpBD-2SO3H / HPAN membrane.

[0071] (4) Preparation of ACOF-1-TpBD-2SO3H / HPAN membrane

[0072] (4.1) Preparation of precursor solution

[0073] Measure 25 μL of hydrazine hydrate and dissolve it in 5 mL of deionized water, then sonicate the solution to ensure that the amine monomer is uniformly dispersed in the deionized water, resulting in an aqueous solution with a mass-volume fraction of 0.5% (w / v). Weigh 10 mg of 1,3,5-trialdehydebenzene and dissolve it in 5 mL of benzene, then add 15 μL of glacial acetic acid and sonicate the solution to ensure that the aldehyde monomer is uniformly dispersed in the benzene, resulting in an oil solution with a mass-volume fraction of 0.2% (w / v).

[0074] (4.2) Interface aggregation

[0075] (4.2.1) Pour the aqueous solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane, keep the aqueous solution on the membrane surface for 20 min, pour out the aqueous solution and let the membrane air dry at room temperature to prevent defects from forming on the membrane surface.

[0076] (4.2.2) Pour the oil phase solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane after treatment in step (4.2.1), react for 1 h, then pour out the excess oil phase solution, wash with benzene several times to remove unreacted monomers, and obtain the TpBD-2SO3H / HPAN membrane.

[0077] (4.3) Heat treatment

[0078] The TpBD-2SO3H / HPAN membrane prepared in step (4.2) was heat-treated at 60 °C for 5 min to enhance the bonding force between the composite membrane and the HPAN base membrane. Gas permeation experiments were conducted on the membrane prepared in this embodiment to test its H2 and CO2 separation performance. The transmembrane pressure difference was controlled at 1.0 bar, the permeate side pressure was maintained at atmospheric pressure, and the test temperature was room temperature. The test results showed that the H2 flux was 979.7 GPU, the CO2 flux was 165.9 GPU, and the H2 and CO2 separation selectivity was 5.9.

[0079] Example 4

[0080] (1) Hydrolysis of PAN base film

[0081] The PAN base film was immersed in a 1 M NaOH aqueous solution at 50 °C for 1 h for hydrolysis, and then thoroughly rinsed with deionized water until the water became neutral, resulting in the hydrolyzed PAN base film HPAN.

[0082] (2) Preparation of TpBD-2SO3H nanosheets

[0083] 4.2 mg of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde and 10.3 mg of 2,2'-benzidine disulfonic acid were weighed and dissolved separately in 5 mL of dimethyl sulfoxide. The two solutions were dissolved separately by sonication, and then mixed together and placed in a 120 °C oven for 15 days. The resulting TpBD-2SO3H nanosheets were dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cutoff of 3500 to remove residual unreacted monomers or oligomers.

[0084] (3) Preparation of TpBD-2SO3H / HPAN membrane

[0085] 1 mL of TpBD-2SO3H nanosheets was dispersed in 70 mL of deionized water and sonicated to ensure that the nanosheets were uniformly dispersed in the deionized water. The TpBD-2SO3H nanosheet solution was then vacuum filtered onto the surface of HPAN to obtain a TpBD-2SO3H / HPAN membrane.

[0086] (4) Preparation of ACOF-1-TpBD-2SO3H / HPAN membrane

[0087] (4.1) Preparation of precursor solution

[0088] Measure 25 μL of hydrazine hydrate and dissolve it in 5 mL of deionized water, then sonicate the solution to ensure that the amine monomer is uniformly dispersed in the deionized water, resulting in an aqueous solution with a mass-volume fraction of 0.5% (w / v). Weigh 10 mg of 1,3,5-trialdehydebenzene and dissolve it in 5 mL of benzene, then add 15 μL of glacial acetic acid and sonicate the solution to ensure that the aldehyde monomer is uniformly dispersed in the benzene, resulting in an oil solution with a mass-volume fraction of 0.2% (w / v).

[0089] (4.2) Interface aggregation

[0090] (4.2.1) Pour the aqueous solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane, keep the aqueous solution on the membrane surface for 20 min, pour out the aqueous solution and let the membrane air dry at room temperature to prevent defects from forming on the membrane surface.

[0091] (4.2.2) Pour the oil phase solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane after treatment in step (4.2.1), react for 0.2 h, then pour out the excess oil phase solution, wash with benzene several times to remove unreacted monomers, and obtain the TpBD-2SO3H / HPAN membrane.

[0092] (4.3) Heat treatment

[0093] The TpBD-2SO3H / HPAN membrane prepared in step (4.2) was heat-treated at 60 °C for 5 min to enhance the bonding force between the composite membrane and the HPAN base membrane. Gas permeation experiments were conducted on the membrane prepared in this embodiment to test its H2 and CO2 separation performance. The transmembrane pressure difference was controlled at 1.0 bar, the permeate side pressure was maintained at atmospheric pressure, and the test temperature was room temperature. The test results showed that the H2 flux was 2027.5 GPU, the CO2 flux was 654.0 GPU, and the H2 and CO2 separation selectivity was 3.1.

[0094] Example 5

[0095] (1) Hydrolysis of PAN base film

[0096] The PAN base film was immersed in a 1 M NaOH aqueous solution at 50 °C for 1 h for hydrolysis, and then the base film was thoroughly rinsed with deionized water until the water became neutral, resulting in the hydrolyzed PAN base film HPAN.

[0097] (2) Preparation of TpBD-2SO3H nanosheets

[0098] 4.2 mg of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde and 10.3 mg of 2,2'-benzidine disulfonic acid were weighed and dissolved separately in 5 mL of dimethyl sulfoxide. The two solutions were dissolved separately by sonication, and then mixed together and placed in a 120 °C oven for 15 days. The resulting TpBD-2SO3H nanosheets were dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cutoff of 3500 to remove residual unreacted monomers or oligomers.

[0099] (3) Preparation of TpBD-2SO3H / HPAN membrane

[0100] 1 mL of TpBD-2SO3H nanosheets was dispersed in 70 mL of deionized water and sonicated to ensure that the nanosheets were uniformly dispersed in the deionized water. The TpBD-2SO3H nanosheet solution was then vacuum filtered onto the surface of HPAN to obtain a TpBD-2SO3H / HPAN membrane.

[0101] (4) Preparation of ACOF-1-TpBD-2SO3H / HPAN membrane

[0102] (4.1) Preparation of precursor solution

[0103] Measure 25 μL of hydrazine hydrate and dissolve it in 5 mL of deionized water, then sonicate the solution to ensure that the amine monomer is uniformly dispersed in the deionized water, resulting in an aqueous solution with a mass-volume fraction of 0.5% (w / v). Weigh 10 mg of 1,3,5-trialdehydebenzene and dissolve it in 5 mL of benzene, then add 15 μL of glacial acetic acid and sonicate the solution to ensure that the aldehyde monomer is uniformly dispersed in the benzene, resulting in an oil solution with a mass-volume fraction of 0.2% (w / v).

[0104] (4.2) Interface aggregation

[0105] (4.2.1) Pour the aqueous solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane, keep the aqueous solution on the membrane surface for 20 min, pour out the aqueous solution and let the membrane air dry at room temperature to prevent defects from forming on the membrane surface.

[0106] (4.2.2) Pour the oil phase solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane after treatment in step (4.2.1), react for 2 h, then pour out the excess oil phase solution, wash with benzene several times to remove unreacted monomers, and obtain the TpBD-2SO3H / HPAN membrane.

[0107] (4.3) Heat treatment

[0108] The TpBD-2SO3H / HPAN membrane prepared in step (4.2) was heat-treated at 60 °C for 5 min to enhance the bonding force between the composite membrane and the HPAN base membrane. Gas permeation experiments were conducted on the membrane prepared in this embodiment to test its H2 and CO2 separation performance. The transmembrane pressure difference was controlled at 1.0 bar, the permeate side pressure was maintained at atmospheric pressure, and the test temperature was room temperature. The test results showed that the H2 flux was 1262.8 GPU, the CO2 flux was 227.6 GPU, and the H2 and CO2 separation selectivity was 5.5.

[0109] Comparative Example 1

[0110] (1) Hydrolysis of PAN base film

[0111] The PAN base film was immersed in a 1 M NaOH aqueous solution at 50 °C for 1 h for hydrolysis, and then thoroughly rinsed with deionized water until the water became neutral, resulting in the hydrolyzed PAN base film HPAN.

[0112] (2) Preparation of TpBD-2SO3H nanosheets

[0113] 4.2 mg of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde and 10.3 mg of 2,2'-benzidine disulfonic acid were weighed and dissolved separately in 5 mL of dimethyl sulfoxide. The two solutions were dissolved separately by sonication, and then mixed together and placed in a 120 °C oven for 15 days. The resulting TpBD-2SO3H nanosheets were dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cutoff of 3500 to remove residual unreacted monomers or oligomers.

[0114] (3) Preparation of TpBD-2SO3H / HPAN membrane

[0115] 1 mL of TpBD-2SO3H nanosheets was dispersed in 70 mL of deionized water and sonicated to ensure uniform dispersion. The TpBD-2SO3H nanosheet solution was then vacuum filtered onto an HPAN surface to obtain a TpBD-2SO3H / HPAN membrane. Gas permeation experiments were conducted on the membrane prepared in this comparative example to test its H2 and CO2 separation performance. The transmembrane pressure difference was controlled at 1.0 bar, the permeate side pressure was maintained at atmospheric pressure, and the test temperature was room temperature. The test results showed that the H2 flux was 2363.5 GPU, the CO2 flux was 1243.9 GPU, and the H2 and CO2 separation selectivity was 1.9.

[0116] Figure 1 The flowcharts for Examples 1-5 are shown. TpBD-2SO3H nanosheets were deposited on an HPAN substrate using a vacuum self-assembly strategy, followed by interfacial polymerization of an ACOF-1 layer to obtain a bilayer COF composite film.

[0117] Figure 2 This is a scanning electron microscope (SEM) image of the surface of the ACOF-1-TpBD-2SO3H / HPAN film prepared in Example 2. From... Figure 2 It can be seen that the membrane surface is dense and without defects.

[0118] Figure 3 This is the elemental distribution diagram of the ACOF-1-TpBD-2SO3H / HPAN membrane prepared in Example 2. From... Figure 2 It can be seen that the S element is uniformly distributed on the membrane surface, proving that the TpBD-2SO3H nanosheets are uniformly deposited on the HPAN base film.

[0119] Figure 4 This is a cross-sectional scanning electron microscope (SEM) image of the ACOF-1-TpBD-2SO3H / HPAN membrane prepared in Example 2. From... Figure 4 It can be seen that the selective layer of the bilayer COF is relatively thin, with a thickness of only about 143 nm.

Claims

1. A method for preparing a bilayer COF composite membrane, characterized in that, Includes the following steps: (1) Hydrolyze the PAN base film. Immerse the PAN base film in a 1 M NaOH aqueous solution for hydrolysis, and rinse the base film thoroughly with deionized water until the water becomes neutral to obtain the hydrolyzed PAN base film HPAN. (2) Preparation of TpBD-2SO3H nanosheets: 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde and 2,2'-benzidine disulfonic acid were weighed and dissolved in 5 mL of dimethyl sulfoxide. The two solutions were dissolved by sonication. Finally, the two were mixed and reacted at 120 °C for a certain time. The obtained TpBD-2SO3H nanosheets were dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cutoff of 3500. (3) Preparation of TpBD-2SO3H / HPAN membrane: The TpBD-2SO3H nanosheets obtained in step (2) were dispersed in 70 mL of deionized water and ultrasonically treated. The TpBD-2SO3H nanosheet solution was vacuum filtered onto the HPAN surface to obtain the TpBD-2SO3H / HPAN membrane. (4) Preparation of ACOF-1-TpBD-2SO3H / HPAN membrane, (4.1) Preparation of precursor solution: Dissolve hydrazine hydrate in deionized water and sonicate to obtain aqueous solution; dissolve 1,3,5-trialdehydebenzene in benzene and sonicate, and add 15 μL of glacial acetic acid to obtain oil solution. (4.2) Interfacial polymerization, (4.2.1) Pour the aqueous solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane, keep the aqueous solution on the membrane surface for 20 min, then pour out the aqueous solution and let the membrane air dry at room temperature; (4.2.2) Pour the oil phase solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane after treatment in step (4.2.1), react for a certain time, then pour out the excess oil phase solution, wash with benzene several times to obtain the ACOF-1-TpBD-2SO3H / HPAN membrane; (4.3) Heat treatment: The ACOF-1-TpBD-2SO3H / HPAN membrane prepared in step (4.2) is heat treated at 60 °C for 5 min.

2. The preparation method according to claim 1, characterized in that: The hydrolysis conditions in step (1) are 50 °C for 1 h.

3. The preparation method according to claim 1, characterized in that: In step (2), the masses of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde and 2,2'-benzidine disulfonic acid were 4.2 mg and 10.3 mg, respectively.

4. The preparation method according to claim 1, characterized in that: The reaction time at 120 ℃ in step (2) is 15 days.

5. The preparation method according to claim 1, characterized in that: In step (3), measure 0.2-1.5 mL of the TpBD-2SO3H nanosheets prepared in step (2).

6. The preparation method according to claim 1, characterized in that: In step (4.1), the concentration of the aqueous phase solution is 0.5% (w / v) and the concentration of the oil phase solution is 0.2% (w / v).

7. The preparation method according to claim 1, characterized in that: The reaction time in step (4.2.2) is 0.2~2 h.

8. A double-layer COF composite membrane, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7 and used for H2 / CO2 separation.

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