Preparation method and application of double-layer COF composite film

Abstract

The invention discloses a preparation method and application of a double-layer COF composite membrane, and belongs to the technical field of gas separation membranes. The preparation method comprises the following steps: by taking a porous polymer membrane as a supporting layer, depositing a macroporous TpBD-2SO3H nanosheet on the surface of a base membrane in a vacuum filtration manner, and polymerizing a small-pore ACOF-1 layer on the interface, thereby preparing the double-layer COF composite membrane with staggered pore diameters. According to the method disclosed by the invention, ACOF-1 is induced to be generated on the surface of the TpBD-2SO3H nanosheet through electrostatic interaction between the TpBD-2SO3H nanosheet and the amine monomer, so that the compact and defect-free composite membrane is obtained, and excellent H2 / CO2 separation performance is shown. The method is ingenious in design, and the prepared double-layer COF composite membrane has important application potential in the field of H2 separation.

Description

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

[0002] Background Art: The development of sustainable energy is an urgent global task, and the hydrogen (H2) energy system is 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 a large amount of carbon dioxide. Therefore, it is crucial to efficiently purify and separate H2 from H2 / CO2 mixtures. Currently, the separation of H2 / CO2 in industry mainly relies on pressure swing adsorption and cryogenic separation technologies. The former is limited by the high energy consumption of adsorbent regeneration and low cycle efficiency, while the latter faces the bottlenecks of harsh low-temperature operating conditions and huge equipment investment. In contrast, membrane separation technology, as a low-energy consumption, easy-to-operate, and environmentally friendly technology, has been widely applied in complex gas separation processes.

[0003] Covalent organic framework (COFs) materials have become an ideal choice for constructing high-performance gas separation membranes due to their designable pore sizes, high specific surface areas, and excellent stability. However, the inherent pore sizes of COFs are usually in the range of 0.8 - 5 nm, which are much larger than the kinetic diameters of H2 (0.289 nm) and CO2 (0.33 nm). It is difficult for a single COF layer to effectively separate H2 / CO2. Researchers have introduced ionic liquids into the COF pores to reduce the pore size, but this greatly reduces the gas permeation flux. Or they use the "shielding effect" of polymers on COFs to reduce the pore size, but the membrane has poor stability when working under high pressure or humid environments. Therefore, this greatly limits the application of COFs in gas separation.

[0004] Therefore, the present invention proposes a double-layer COF strategy. The large-pore TpBD-2SO3H nanosheets are vacuum filtered onto HPAN, and the electrostatic interaction between -SO3H and hydrazine hydrate is used to induce the interfacial polymerization of small-pore ACOF-1 to form a dense and defect-free selective layer. The two COFs are stacked in an interleaved manner, effectively reducing the sieving pore size. At the same time, the hydrazine hydrate that penetrates into the TpBD-2SO3H layer reacts with the aldehyde monomer to generate ACOF-1, in-situ filling the defects between the TpBD-2SO3H nanosheets. The present invention realizes the optimization of the integrity of the membrane layer structure and exhibits an ultra-high H2 flux in H2 / CO2 separation.

[0005] Summary of the Invention: The present invention provides a preparation method of a double-layer COF composite membrane, which is ingeniously designed and can effectively separate H2.

[0006] The technical solution of the present invention is as follows:

[0007] (1) Hydrolyze the PAN-based membrane

[0008] The PAN-based membrane was immersed in 1 M aqueous NaOH solution for hydrolysis, and the membrane was thoroughly rinsed with deionized water until the water became neutral, obtaining the hydrolyzed PAN-based membrane HPAN.

[0009] (2) Preparation of TpBD-2SO3H nanosheets

[0010] Weighed a certain mass of 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde and 2,2'-biphenyldisulfonic acid and dissolved them in 5 mL of dimethyl sulfoxide respectively. The two solutions were sonicated for dissolution, and finally the two were mixed and placed in a forced-air oven at 120 °C for reaction 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 cut-off of 3500 to remove residual unreacted monomers or oligomers.

[0011] (3) Preparation of TpBD-2SO3H / HPAN membrane

[0012] Measured a certain volume of TpBD-2SO3H nanosheets and dispersed them in 70 mL of deionized water, and ultrasonicated to ensure that the nanosheets were uniformly dispersed in deionized water. The TpBD-2SO3H nanosheet solution was vacuum filtered onto the surface of HPAN to obtain the TpBD-2SO3H / HPAN membrane;

[0013] (4) Preparation of ACOF-1-TpBD-2SO3H / HPAN membrane (4.1) Preparation of precursor solution

[0014] Measured hydrazine hydrate and dissolved it in deionized water, and ultrasonicated to ensure that the amine monomer was uniformly dispersed in deionized water, obtaining an aqueous solution with a certain mass-volume fraction. Weighed 1,3,5-triformylbenzene and dissolved it in benzene, and added a certain volume of glacial acetic acid, and ultrasonicated to ensure that the aldehyde monomer was uniformly dispersed in benzene, obtaining an oil-phase solution with a certain mass-volume fraction.

[0015] (4.2) Interfacial polymerization

[0016] (4.2.1) Poured the aqueous solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane, allowed the aqueous solution to remain on the membrane surface for a certain time, poured out the aqueous solution and air-dried the membrane at room temperature to prevent defects on the membrane surface.

[0017] (4.2.2) Poured the oil-phase solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane treated in step (4.2.1), reacted for a certain time, then poured out the excess oil-phase solution, and washed several times with benzene to remove unreacted monomers, obtaining the TpBD-2SO3H / HPAN membrane.

[0018] (4.3) Heat treatment

[0019] The TpBD-2SO3H / HPAN membrane prepared in step (4.2) was heat-treated at 60 °C for 5 min to enhance the binding force between the composite membrane and the HPAN base membrane.

[0020] The hydrolysis described in the above step (1) was hydrolysis at 50 °C for 1 h.

[0021] The certain masses of 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde and 2,2'-biphenyldiamine disulfonic acid described in the above step (2) were 4.2 mg and 10.3 mg respectively.

[0022] The certain reaction time described in the above step (2) was 15 days.

[0023] The certain volume of TpBD-2SO3H nanosheets described in the above step (3) was 0.2 - 1.5 mL, preferably 1 mL.

[0024] The aqueous solution with a certain mass-volume fraction described in the above step (4.1) was 0.5 w / v%, and the concentration of the oil-phase solution with a certain mass-volume fraction was 0.2 w / v%.

[0025] The certain volume of glacial acetic acid described in the above step (4.1) was 15 μL.

[0026] The certain holding time described in the above step (4.2.1) was 20 min.

[0027] The certain reaction time described in the above step (4.2.2) was 0.2 - 2 h, preferably 1 h.

[0028] The method of the present invention deposits TpBD-2SO3H nanosheets on a porous substrate, and then covers a layer of ACOF-1 by interfacial polymerization to obtain a bilayer COF composite membrane. Compared with the prior art, the present invention has the following advantages:

[0029] (1) This method utilizes the electrostatic interaction between TpBD-2SO3H and hydrazine hydrate to enhance the stability of the composite membrane;

[0030] (2) By using the staggered stacking of two COFs, the sieving pore size is effectively reduced, and the prepared composite membrane can effectively separate H2 / CO2 and achieve rapid H2 transmission.

[0031] Description of the drawings: Figure 1 It is the preparation flow chart of Examples 1 - 5.

[0032] Figure 2 It is the surface scanning electron micrograph of the ACOF-1-TpBD-2SO3H / HPAN membrane prepared in Example 2.

[0033] Figure 3It is the elemental distribution map of the ACOF-1-TpBD-2SO3H / HPAN membrane prepared in Example 2.

[0034] Figure 3 It is the cross-sectional scanning electron micrograph of the ACOF-1-TpBD-2SO3H / HPAN membrane prepared in Example 2.

[0035] Specific implementation manner: The technical solution of the present invention will be further elaborated in detail below with reference to the accompanying drawings and specific examples.

[0036] Example 1

[0037] (1) Hydrolysis of PAN-based membrane

[0038] The PAN-based membrane was immersed in 1M NaOH aqueous solution and hydrolyzed at 50 °C for 1 h, and the base membrane was thoroughly rinsed with deionized water until the water became neutral to obtain the hydrolyzed PAN-based membrane HPAN.

[0039] (2) Preparation of TpBD-2SO3H nanosheets

[0040] Weighed 4.2 mg of 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde and 10.3 mg of 2,2'-biphenyldiamine disulfonic acid and dissolved them in 5 mL of dimethyl sulfoxide respectively. The two solutions were ultrasonically dissolved, and finally the two were mixed and placed in a blast drying oven at 120 °C for 15 days. The obtained TpBD-2SO3H nanosheets were dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cut-off of 3500 to remove residual unreacted monomers or oligomers.

[0041] (3) Preparation of TpBD-2SO3H / HPAN membrane

[0042] Measured 0.2 mL of TpBD-2SO3H nanosheets and dispersed them in 70 mL of deionized water, and ultrasonically treated to ensure that the nanosheets were evenly dispersed in deionized water. The TpBD-2SO3H nanosheet solution was vacuum filtered on the surface of HPAN to obtain the TpBD-2SO3H / HPAN membrane;

[0043] (4) Preparation of ACOF-1-TpBD-2SO3H / HPAN membrane (4.1) Preparation of precursor solution

[0044] Measured 25 μL of hydrazine hydrate and dissolved it in 5 mL of deionized water, and ultrasonically treated to ensure that the amine monomer was evenly dispersed in deionized water to obtain an aqueous solution with a mass-volume fraction of 0.5 w / v%. Weighed 10 mg of 1,3,5-triformylbenzene and dissolved it in 5 mL of benzene, and added 15 μL of glacial acetic acid, and ultrasonically treated to ensure that the aldehyde monomer was evenly dispersed in benzene to obtain an oil phase solution with a mass-volume fraction of 0.2 w / v%.

[0045] (4.2) Interfacial polymerization

[0046] (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 air-dry the membrane at room temperature to prevent defects on the membrane surface.

[0047] (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 1 h, then pour out the excess oil-phase solution, and wash it several times with benzene to remove the unreacted monomers, obtaining the TpBD-2SO3H / HPAN membrane.

[0048] (4.3) Heat treatment

[0049] Heat-treat the TpBD-2SO3H / HPAN membrane prepared in step (4.2) at 60 °C for 5 min to enhance the bonding force between the composite membrane and the HPAN base membrane.

[0050] Conduct gas permeation experiment tests on the membrane prepared in this example, and test the separation performance for H2 and CO2. The transmembrane pressure difference is controlled at 1.0 bar, the pressure on the permeate side is kept at atmospheric pressure, and the test temperature is room temperature. The test results show that the flux of H2 is 1287.8 GPU, the flux of CO2 is 561.9 GPU, and the separation selectivity of H2 and CO2 is 2.3.

[0051] Example 2

[0052] (1) Hydrolyze the PAN base membrane

[0053] Immerse the PAN base membrane in 1 M aqueous NaOH solution and hydrolyze it at 50 °C for 1 h, and thoroughly rinse the base membrane with deionized water until the water becomes neutral, obtaining the hydrolyzed PAN base membrane HPAN.

[0054] (2) Preparation of TpBD-2SO3H nanosheets

[0055] Weigh 4.2 mg of 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde and 10.3 mg of 2,2'-biphenyldiamine disulfonic acid and dissolve them in 5 mL of dimethyl sulfoxide respectively. Ultrasonically dissolve the two solutions, and finally mix them and place them in a forced-air oven at 120 °C for reaction for 15 days. The obtained TpBD-2SO3H nanosheets are dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cut-off of 3500 to remove the residual unreacted monomers or oligomers.

[0056] (3) Preparation of TpBD-2SO3H / HPAN membrane

[0057] Measure 1 mL of TpBD-2SO3H nanosheets and disperse them in 70 mL of deionized water, and then perform ultrasonic treatment to ensure that the nanosheets are evenly dispersed in the deionized water. Vacuum filter the TpBD-2SO3H nanosheet solution onto the surface of HPAN to obtain the TpBD-2SO3H / HPAN membrane;

[0058] (4) Preparation of ACOF-1-TpBD-2SO3H / HPAN membrane (4.1) Preparation of precursor solution

[0059] Measure 25 μL of hydrazine hydrate and dissolve it in 5 mL of deionized water, and then perform ultrasonic treatment to ensure that the amine monomer is evenly dispersed in the deionized water to obtain an aqueous solution with a mass-volume fraction of 0.5 w / v%. Weigh 10 mg of 1,3,5-triformylbenzene and dissolve it in 5 mL of benzene, and add 15 μL of glacial acetic acid, and then perform ultrasonic treatment to ensure that the aldehyde monomer is evenly dispersed in the benzene to obtain an oil-phase solution with a mass-volume fraction of 0.2 w / v%.

[0060] (4.2) Interfacial polymerization

[0061] (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 air-dry the membrane at room temperature to prevent defects on the membrane surface.

[0062] (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 1 h, then pour out the excess oil-phase solution, and wash it several times with benzene to remove the unreacted monomers to obtain the TpBD-2SO3H / HPAN membrane.

[0063] (4.3) Heat treatment

[0064] Heat-treat the TpBD-2SO3H / HPAN membrane prepared in step (4.2) at 60 °C for 5 min to enhance the binding force between the composite membrane and the HPAN base membrane.

[0065] Perform gas permeation experiment tests on the membrane prepared in this example, and test the separation performance of H2 and CO2. The transmembrane pressure difference is controlled at 1.0 bar, the pressure on the permeate side is kept at atmospheric pressure, and the test temperature is room temperature. The test results show that the flux of H2 is 1773.1 GPU, the flux of CO2 is 264.3 GPU, and the separation selectivity of H2 and CO2 is 6.7.

[0066] Example 3

[0067] (1) Hydrolyze the PAN base membrane

[0068] The PAN-based membrane was immersed in a 1 M aqueous NaOH solution and hydrolyzed at 50 °C for 1 h, and the membrane was thoroughly rinsed with deionized water until the water became neutral, obtaining the hydrolyzed PAN-based membrane HPAN.

[0069] (2) Preparation of TpBD-2SO3H nanosheets

[0070] Weigh 4.2 mg of 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde and 10.3 mg of 2,2'-biphenyldiamine disulfonic acid and dissolve them in 5 mL of dimethyl sulfoxide respectively. Ultrasonically dissolve the two solutions, and finally mix them and place them in a blast drying oven at 120 °C for 15 days. The obtained TpBD-2SO3H nanosheets were dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cut-off of 3500 to remove residual unreacted monomers or oligomers.

[0071] (3) Preparation of TpBD-2SO3H / HPAN membrane

[0072] Measure 1.5 mL of TpBD-2SO3H nanosheets and disperse them in 70 mL of deionized water, and ultrasonically treat to ensure that the nanosheets are uniformly dispersed in deionized water. Vacuum filter the TpBD-2SO3H nanosheet solution onto the surface of HPAN to obtain the TpBD-2SO3H / HPAN membrane;

[0073] (4) Preparation of ACOF-1-TpBD-2SO3H / HPAN membrane (4.1) Preparation of precursor solution

[0074] Measure 25 μL of hydrazine hydrate and dissolve it in 5 mL of deionized water, and ultrasonically treat to ensure that the amine monomer is uniformly dispersed in deionized water, obtaining an aqueous solution with a mass-volume fraction of 0.5 w / v%. Weigh 10 mg of 1,3,5-triformylbenzene and dissolve it in 5 mL of benzene, and add 15 μL of glacial acetic acid, and ultrasonically treat to ensure that the aldehyde monomer is uniformly dispersed in benzene, obtaining an oil-phase solution with a mass-volume fraction of 0.2 w / v%.

[0075] (4.2) Interfacial polymerization

[0076] (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 air-dry the membrane at room temperature to prevent defects on the membrane surface.

[0077] (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 1 h, then pour out the excess oil-phase solution, and wash it several times with benzene to remove unreacted monomers, obtaining the TpBD-2SO3H / HPAN membrane.

[0078] (4.3) Heat treatment

[0079] The TpBD-2SO3H / HPAN film prepared in step (4.2) was heat-treated at 60 °C for 5 min to enhance the binding force between the composite film and the HPAN base film.

[0080] The film prepared in this example was tested by gas permeation experiment, and the separation performance of H2 and CO2 was tested. The transmembrane pressure difference was controlled at 1.0 bar, the pressure on the permeate side was maintained at atmospheric pressure, and the test temperature was room temperature. The test results showed that the flux of H2 was 979.7 GPU, the flux of CO2 was 165.9 GPU, and the separation selectivity of H2 and CO2 was 5.9.

[0081] Example 4

[0082] (1) Hydrolysis of PAN base film

[0083] The PAN base film was immersed in 1 M aqueous NaOH solution and hydrolyzed at 50 °C for 1 h, and the base film was thoroughly rinsed with deionized water until the water became neutral to obtain the hydrolyzed PAN base film HPAN.

[0084] (2) Preparation of TpBD-2SO3H nanosheets

[0085] Weighed 4.2 mg of 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde and 10.3 mg of 2,2'-biphenyldiaminedisulfonic acid were respectively dissolved in 5 mL of dimethyl sulfoxide. The two solutions were ultrasonically dissolved, and finally the two were mixed and placed in a blast oven at 120 °C for 15 days. The obtained TpBD-2SO3H nanosheets were dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cut-off of 3500 to remove residual unreacted monomers or oligomers.

[0086] (3) Preparation of TpBD-2SO3H / HPAN film

[0087] Measured 1 mL of TpBD-2SO3H nanosheets were dispersed in 70 mL of deionized water and ultrasonically treated to ensure that the nanosheets were uniformly dispersed in deionized water. The TpBD-2SO3H nanosheet solution was vacuum filtered on the surface of HPAN to obtain the TpBD-2SO3H / HPAN film;

[0088] (4) Preparation of ACOF-1-TpBD-2SO3H / HPAN film (4.1) Preparation of precursor solution

[0089] Measure 25 μL of hydrazine hydrate and dissolve it in 5 mL of deionized water, and then perform ultrasonic treatment to ensure that the amine monomer is uniformly dispersed in the deionized water, obtaining an aqueous solution with a mass-volume fraction of 0.5 w / v%. Weigh 10 mg of 1,3,5-triformylbenzene and dissolve it in 5 mL of benzene, add 15 μL of glacial acetic acid, and perform ultrasonic treatment to ensure that the aldehyde monomer is uniformly dispersed in the benzene, obtaining an oil-phase solution with a mass-volume fraction of 0.2 w / v%.

[0090] (4.2) Interfacial polymerization

[0091] (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 air-dry the membrane at room temperature to prevent defects on the membrane surface.

[0092] (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 0.2 h, then pour out the excess oil-phase solution, and wash it several times with benzene to remove the unreacted monomers, obtaining the TpBD-2SO3H / HPAN membrane.

[0093] (4.3) Heat treatment

[0094] Heat-treat the TpBD-2SO3H / HPAN membrane prepared in step (4.2) at 60 °C for 5 min to enhance the binding force between the composite membrane and the HPAN base membrane.

[0095] Perform gas permeation experiment tests on the membrane prepared in this example, and test the separation performance of H2 and CO2. The transmembrane pressure difference is controlled at 1.0 bar, the pressure on the permeate side is maintained at atmospheric pressure, and the test temperature is room temperature. The test results show that the flux of H2 is 2027.5 GPU, the flux of CO2 is 654.0 GPU, and the separation selectivity of H2 and CO2 is 3.1.

[0096] Example 5

[0097] (1) Hydrolyze the PAN base membrane

[0098] Immerse the PAN base membrane in 1 M aqueous NaOH solution and hydrolyze it at 50 °C for 1 h, and thoroughly rinse the base membrane with deionized water until the water becomes neutral, obtaining the hydrolyzed PAN base membrane HPAN.

[0099] (2) Preparation of TpBD-2SO3H nanosheets

[0100] Weigh 4.2 mg of 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde and 10.3 mg of 2,2'-benzidine disulfonic acid and dissolve them separately in 5 mL of dimethyl sulfoxide. Ultrasonically dissolve the two solutions, and finally mix them and place them in a forced-air oven at 120 °C for 15 days. The obtained TpBD-2SO3H nanosheets are dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cut-off of 3500 to remove residual unreacted monomers or oligomers.

[0101] (3) Preparation of TpBD-2SO3H / HPAN membrane

[0102] Measure 1 mL of the TpBD-2SO3H nanosheet dispersion and disperse it in 70 mL of deionized water, and ultrasonically treat it to ensure that the nanosheets are evenly dispersed in deionized water. Vacuum filter the TpBD-2SO3H nanosheet solution onto the surface of HPAN to obtain the TpBD-2SO3H / HPAN membrane;

[0103] (4) Preparation of ACOF-1-TpBD-2SO3H / HPAN membrane (4.1) Preparation of precursor solution

[0104] Measure 25 μL of hydrazine hydrate and dissolve it in 5 mL of deionized water, and ultrasonically treat it to ensure that the amine monomer is evenly dispersed in deionized water to obtain an aqueous solution with a mass-volume fraction of 0.5 w / v%. Weigh 10 mg of 1,3,5-triformylbenzene and dissolve it in 5 mL of benzene, and add 15 μL of glacial acetic acid, and ultrasonically treat it to ensure that the aldehyde monomer is evenly dispersed in benzene to obtain an oil-phase solution with a mass-volume fraction of 0.2 w / v%.

[0105] (4.2) Interfacial polymerization

[0106] (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 air-dry the membrane at room temperature to prevent defects on the membrane surface.

[0107] (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 2 h, then pour out the excess oil-phase solution, and wash it several times with benzene to remove unreacted monomers to obtain the TpBD-2SO3H / HPAN membrane.

[0108] (4.3) Heat treatment

[0109] Heat-treat the TpBD-2SO3H / HPAN membrane prepared in step (4.2) at 60 °C for 5 min to enhance the binding force between the composite membrane and the HPAN base membrane.

[0110] The membrane prepared in this example was tested for gas permeation experiments, and the separation performance for H2 and CO2 was tested. The transmembrane pressure difference was controlled at 1.0 bar, the pressure on the permeate side was maintained at atmospheric pressure, and the test temperature was room temperature. The test results showed that the flux of H2 was 1262.8 GPU, the flux of CO2 was 227.6 GPU, and the separation selectivity of H2 and CO2 was 5.5.

[0111] Comparative Example 1

[0112] (1) Hydrolyzed PAN-based membrane

[0113] The PAN-based membrane was immersed in 1 M aqueous NaOH solution and hydrolyzed at 50 °C for 1 h, and the base membrane was thoroughly rinsed with deionized water until the water became neutral to obtain the hydrolyzed PAN-based membrane HPAN.

[0114] (2) Preparation of TpBD-2SO3H nanosheets

[0115] Weigh 4.2 mg of 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde and 10.3 mg of 2,2'-biphenyldiamine disulfonic acid and dissolve them in 5 mL of dimethyl sulfoxide respectively. The two solutions were ultrasonically dissolved, and finally the two were mixed and placed in a blast oven at 120 °C for 15 days. The obtained TpBD-2SO3H nanosheets were dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cut-off of 3500 to remove residual unreacted monomers or oligomers.

[0116] (3) Preparation of TpBD-2SO3H / HPAN membrane

[0117] Measure 1 mL of TpBD-2SO3H nanosheets and disperse them in 70 mL of deionized water, and ultrasonically treat to ensure that the nanosheets are evenly dispersed in deionized water. The TpBD-2SO3H nanosheet solution was vacuum filtered on the surface of HPAN to obtain the TpBD-2SO3H / HPAN membrane;

[0118] The membrane prepared in this comparative example was tested for gas permeation experiments, and the separation performance for H2 and CO2 was tested. The transmembrane pressure difference was controlled at 1.0 bar, the pressure on the permeate side was maintained at atmospheric pressure, and the test temperature was room temperature. The test results showed that the flux of H2 was 2363.5 GPU, the flux of CO2 was 1243.9 GPU, and the separation selectivity of H2 and CO2 was 1.9.

[0119] Figure 1 It is the preparation flow chart of Examples 1-5. TpBD-2SO3H nanosheets were deposited on the HPAN base membrane by a vacuum self-assembly strategy, and then a layer of ACOF-1 was interfacially polymerized to obtain a bilayer COF composite membrane.

[0120] Figure 2It is the surface scanning electron microscopy image of the ACOF-1-TpBD-2SO3H / HPAN membrane prepared in Example 2. From Figure 2 it can be seen that the membrane surface is dense and defect-free.

[0121] Figure 3 It is the element distribution map of the ACOF-1-TpBD-2SO3H / HPAN membrane prepared in Example 2. From Figure 2 it can be seen that the S element is evenly distributed on the membrane surface, proving that the TpBD-2SO3H nanosheets are evenly deposited on the HPAN base membrane.

[0122] Figure 4 It is the cross-sectional scanning electron microscopy image of the ACOF-1-TpBD-2SO3H / HPAN membrane prepared in Example 2. From Figure 4 it can be seen that the double-layer COF selective layer is relatively thin, with a thickness of only about 143 nm.

Claims

1. A method for preparing a double-layer COF composite film, characterized in that: The following steps are involved: (1) Hydrolyzed PAN-based membrane The PAN-based membrane was immersed in a 1M NaOH aqueous solution for hydrolysis, and the membrane was thoroughly rinsed with deionized water until the water became neutral, thereby obtaining a hydrolyzed PAN-based membrane HPAN; (2) Preparation of TpBD-2SO3H nanosheets 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde and 2,2'-benzidine disulfonic acid were weighed and dissolved in 5 mL of dimethyl sulfoxide, and the two solutions were ultrasonically dissolved. Finally, the two solutions 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 TpBD-2SO3H nanosheets were dispersed in 70 mL of deionized water and ultrasonically treated, and the TpBD-2SO3H nanosheet solution was vacuum filtered on the surface of HPAN to obtain a TpBD-2SO3H / HPAN membrane; (4) Preparation of ACOF-1-TpBD-2SO3H / HPAN membrane (4.1) Preparation of precursor solution Amount of hydrazine hydrate is dissolved in deionized water and ultrasonically dissolved to obtain an aqueous phase solution; 1,3,5-trialdehyde benzene is weighed and dissolved in benzene and ultrasonically dissolved, and 15 μL of glacial acetic acid is added to obtain an oil phase solution; (4.2) Interface 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 air-dry the membrane at room temperature; (4.2.2) pouring the oil phase solution prepared in step (4.1) onto the surface of the TpBD-2SO3H / HPAN membrane treated in step (4.2.1), reacting for a certain period of time, then pouring out the excess oil phase solution, washing with benzene several times, and obtaining a TpBD-2SO3H / HPAN membrane; (4.3) Heat treatment The TpBD-2SO3H / HPAN membrane prepared in step (4.2) was heat treated at 60°C for 5 min.

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

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

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

5. The method according to claim 1, characterized in that: The volume of the TpBD-2SO3H nanosheets described in step (3) is 0.2 to 1.5 mL, preferably 1 mL.

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

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

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

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