A method for preparing a bipolar membrane with identical anion / cation exchange layer backbone

Abstract

This invention relates to the field of membrane preparation technology and discloses a method for preparing a bipolar membrane with the same main chain for both anion and cation exchange layers. Using sulfonated polyarylene ether sulfone as the cation exchange layer and Br-3C-IM imidazole salt-functionalized polyarylene ether sulfone as the anion exchange layer improves the compatibility between the anion and cation layers, thereby enhancing the mechanical and chemical stability of the bipolar membrane. Using a bifunctionalized MOF as the intermediate interface layer, the –SO3H and –NH2 groups in the MOF interact with the anion and cation layers to form intramolecular hydrogen bonds, resulting in strong adhesion between the anion and cation layers and the intermediate interface layer, which helps prevent bipolar membrane delamination. Furthermore, the bifunctionalized MOF contains two catalytic sites acting as inorganic metal ions and organic ligands, promoting the water dissociation rate through a protonation-deprotonation mechanism.

Description

Technical Field

[0001] This invention belongs to the field of membrane preparation technology, and in particular relates to a method for preparing a bipolar membrane with the same main chain for anion / cation exchange layers. Background Technology

[0002] Bipolar membranes are a novel type of ion exchange membrane, composed of three parts: an anion exchange layer (AEL), a cation exchange layer (CEL), and an intermediate interface layer (IL). Under the influence of a DC electric field, water molecules decompose into H+ in the intermediate interface layer. + and OH – Then H + It moves through the cation exchange layer towards the negative electrode, while OH... — It moves through the anion exchange layer towards the positive electrode, and finally produces OH- at the cation exchange layer. — H is obtained at the anion exchange layer + 。 Unlike traditional water dissociation, bipolar membrane water dissociation generates acids and bases during electrodialysis without producing byproducts such as hydrogen and oxygen, significantly reducing energy consumption and greatly expanding the potential of this process in new industrial applications.

[0003] Bipolar membrane technology and its applications have played a unique role in optimizing existing industrial processes and creating new industrial engineering, providing technical support for solving problems in environmental, chemical, biological, and marine chemical industries. In recent years, research and development around bipolar membranes has gradually become a highly regarded branch of the membrane field. For example, bipolar membrane electrodialysis technology can be applied to various fields such as acid and alkali manufacturing, seawater desalination, and industrial wastewater treatment. Due to its advantages such as low energy consumption, high resource recovery rate, and low initial cost, it has revolutionized traditional industrial technologies and will play an increasingly important role in environmental sustainability.

[0004] However, existing bipolar membranes suffer from defects such as poor stability and compatibility between the cathode and cation layers, easy detachment, poor mechanical properties, and high membrane resistance, which limit the widespread application of bipolar membrane technology. Summary of the Invention

[0005] To address the aforementioned technical problems in the existing technology, this invention provides a method for preparing a bipolar membrane with the same main chain for both anion and cation exchange layers, employing the following technical solution:

[0006] A method for preparing a bipolar membrane with identical anion / cation exchange layer backbones includes the following steps:

[0007] (1) Weigh a certain amount of N-methylimidazolium and 1,3-dibromopropane and mix them with a certain amount of acetone. Under nitrogen protection, add the former dropwise to the latter. Stir for 12-48 hours at 20-60℃. After cooling to room temperature, wash several times with ethyl acetate and anhydrous diethyl ether. After washing, the solution is rotary evaporated to obtain a pale yellow viscous solution, which is Br-3C-IM imidazolium salt. Its chemical structure is shown in formula (Ⅰ).

[0008]

[0009] (2) Weigh a certain amount of 4,4'-difluorodiphenyl sulfone monomer, 2,2'-bis(3-amino4-hydroxyphenyl)hexafluoropropane and hexafluorobisphenol A monomer, dissolve them in a high-boiling-point polar aprotic solvent, use potassium carbonate as a salting agent and toluene as a dehydrating agent, and react at 100-180℃ for 3-24h under nitrogen protection. After the reaction is completed, separate and dry to obtain a random copolymer of amino-containing polyarylene ether sulfone in the main chain with a molecular weight of 30,000-60,000. In formula (II), x and y represent the molar percentages of the two chains as x% and y%, respectively, and x+y=100; where x=1-100 and y=1-100; the molar ratio of 2,2'-bis(3-amino4-hydroxyphenyl)hexafluoropropane to hexafluorobisphenol A monomer is 0-80%:100-20%, and its chemical structure is shown in formula (II).

[0010]

[0011] (3) Weigh a certain amount of Br-3C-IM imidazole salt obtained in step (1) and amino-containing polyarylene sulfone obtained in step (2), dissolve them in DMF respectively, add the former dropwise to the latter under nitrogen protection, stir for 12-24 h at 20-90℃, cool to room temperature, precipitate in isopropanol, and obtain imidazole-functionalized polyarylene sulfone by washing and vacuum drying, the chemical structure of which is shown in formula (III).

[0012]

[0013] (4) Weigh a certain amount of 1,3-propanesulfonic acid lactone and the amino-containing polyarylene sulfone obtained in step (2), dissolve them in DMF, add the former dropwise to the latter under nitrogen protection, stir for 24 h at 80 °C, cool to room temperature, precipitate in isopropanol, and obtain sulfonated polyarylene sulfone by washing and vacuum drying. Its chemical structure is shown in formula (Ⅳ).

[0014]

[0015] (5) Weigh a certain amount of terephthalic acid and Cr(NO3)·9H2O and place them in a high pressure vessel containing a polytetrafluoroethylene container. Add a certain amount of 5M HF aqueous solution and heat in an oven to carry out a hydrothermal reaction. After the reaction, the solution is ultrasonicated and washed several times to obtain a green solid. Dry the green solid in a vacuum drying oven at 70℃ for 7h to obtain MIL-101(Cr), whose chemical structure is shown in formula (V).

[0016]

[0017] (6) Weigh a certain amount of ClSO3H and MIL-101(Cr) obtained in step (5) and mix them with a certain amount of CH2Cl2. Add the former dropwise to the latter and stir for several hours. After the reaction, the solution is sonicated, washed and dried several times to obtain MIL-101(Cr)-SO3H, whose chemical structure is shown in formula (VI).

[0018]

[0019] (7) Weigh a certain amount of 2-aminoterephthalic acid and Cr(NO3)·9H2O and place them in a high pressure vessel containing a polytetrafluoroethylene container. Add a certain amount of NaOH aqueous solution and heat in an oven at 150°C for 8 hours. After the reaction, the solution is ultrasonicated and washed several times to obtain a green solid. Dry the green solid in a vacuum drying oven for several hours to obtain MIL-101(Cr)-NH2, whose chemical structure is shown in formula (VII).

[0020]

[0021] (8) Weigh a certain amount of 1,3-propanesulfonic acid lactone, MIL-101(Cr)-NH2 obtained in step (7) and a certain amount of CHCl3, mix them, heat and stir for several hours, and after the reaction, the solution is sonicated, washed and dried several times to obtain bifunctionalized MIL-101(Cr), whose chemical structure is shown in formula (VIII).

[0022]

[0023] (9) Weigh a certain amount of imidazole-functionalized polyarylene sulfone obtained in step (3) and sulfonated polyarylene sulfone obtained in step (4) and dissolve them in an organic solvent to obtain AEL and CEL casting solutions. Cast the AEL casting solution onto a clean glass plate and irradiate it under an IR lamp. After the solvent is completely evaporated, AEL is obtained. Then, 5 mL of a 5% (w / v) MIL-101(Cr)-SO3H / MIL-101(Cr)-NH2 / bifunctionalized MIL-101(Cr) solution is cast onto AEL and AEL-IL is obtained under an IR lamp. Finally, the CEL casting solution is further cast onto AEL-IL and irradiated under an IR lamp. After the solvent evaporates, the bipolar film on the glass plate is peeled off and further dried in a vacuum drying oven. After the solvent is completely removed, BPM-S / BPM-N / BPM-B is obtained.

[0024] Furthermore, the reaction temperature in step (1) is 40°C and the reaction time is 24h; the molar ratio of N-methylimidazole to 1,3-dibromopropane is 1:3.

[0025] Furthermore, in step (2), the preferred molar ratio of 2,2'-bis(3-amino-4-hydroxyphenyl)hexafluoropropane to hexafluorobisphenol A is 70%:30%, i.e., x:y = 70%:30%; the high-boiling-point polar aprotic solvent is N-methylpyrrolidone, and the polycondensation reaction conditions are 155°C for 4 hours, then increased to 165°C for 3 hours.

[0026] Furthermore, the reaction conditions for step (3) are 80°C and stirring for 24 hours.

[0027] Furthermore, the vacuum drying temperature in step (4) is 110°C.

[0028] Furthermore, the hydrothermal reaction conditions described in step (5) are 220°C for 8 hours.

[0029] Furthermore, the reaction conditions described in step (6) are 0°C for 1 hour and the vacuum drying conditions are 60°C for 24 hours.

[0030] Furthermore, in step (7), the molar ratio of 2-aminoterephthalic acid and Cr(NO3)·9H2O is 1:1, and the drying conditions are 100℃ for 12h.

[0031] Furthermore, the heating temperature in step (8) is 45°C and the heating time is 3 hours.

[0032] Furthermore, the organic solvent in step (9) is N-methylpyrrolidone; the mass-volume concentration of polyarylene ether sulfone in the AEL and CEL casting solutions is 5%; the vacuum drying temperature is 70°C and the vacuum drying time is 24h.

[0033] The bipolar membrane with identical anion / cation exchange layer backbone prepared by this invention has advantages such as good mechanical stability, chemical stability, good water molecule permeability, high water dissociation rate, and low membrane resistance. In particular, it has broad application prospects in the field of bipolar membrane electrodialysis.

[0034] Compared with the prior art, the advantages of this invention are:

[0035] (1) Sulfonated polyarylene ether sulfone is used as the cation exchange layer and Br-3C-IM imidazole salt functionalized polyarylene ether sulfone is used as the anion exchange layer. The anion and cation layers use the same polymer backbone, which is beneficial to improve the compatibility between the anion and cation layers, thereby improving the mechanical and chemical stability of the prepared bipolar membrane.

[0036] (2) Using bifunctional MOF as the intermediate interface layer, the –SO3H and –NH2 groups in MOF interact with the anion and cation layers to form intramolecular hydrogen bonds, resulting in strong adhesion between the anion and cation layers and the intermediate interface layer, which is beneficial to prevent the delamination of the bipolar film.

[0037] (3) Using bifunctional MOF as the intermediate interface layer, there are two catalytic sites in MOF that serve as inorganic metal ions and organic ligands, which promote the water dissociation rate through the protonation-deprotonation mechanism. Detailed Implementation

[0038] To further illustrate the technical solution of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the claims of the present invention.

[0039] Example 1:

[0040] (1) Synthesis of Br-3C-IM imidazole salt:

[0041] Measure 11.16 mL (0.14 mol) of N-methylimidazole and 58.98 mL (0.42 mol) of 1,3-dibromopropane and mix them with 60 mL and 240 mL of acetone, respectively. Under nitrogen protection, the former is then added dropwise to the latter. The mixture is stirred at 40 °C for 24 h. After cooling to room temperature, the mixture is washed several times with ethyl acetate and anhydrous diethyl ether. The washed solution is then rotary evaporated to obtain a pale yellow viscous solution, which is the desired Br-3C-IM imidazole salt.

[0042] (2) Synthesis of amino-containing polyarylether sulfones:

[0043] 10.16 g (40.00 mmol) of 4,4'-difluorodiphenyl sulfone monomer, 10.26 g (28.00 mmol) of 2,2'-bis(3-amino-4-hydroxyphenyl)hexafluoropropane monomer, and 4.03 g (12.00 mmol) of hexafluorobisphenol A were weighed into a 500 mL round-bottom flask equipped with a water separator. 120 mL of NMP was added, along with 10.12 g of K2CO3 as a salt-forming agent and 80 mL of toluene as a dehydrating agent. Under nitrogen protection, the mixture was reacted at 155 °C for 4 h, followed by a reaction at 165 °C for 3 h. After the solution cooled to room temperature, it was poured into 400 mL of ethanol and flocculated under high-speed stirring to obtain a precipitate. After separation by suction filtration, a brown solid was obtained, which was repeatedly washed with ethanol and water, and then dried under vacuum at 80 °C for 24 h to obtain 10.18 g of amino-containing polyarylene ether sulfone with a molecular weight of 56,000.

[0044] (3) Synthesis of functionalized polyarylether sulfone:

[0045] Weigh 1.14 g of Br-3C-IM imidazole salt and 4.00 g of amino-containing polyarylene ether sulfone, dissolve them separately in 40 mL of DMF, and under nitrogen protection, add the former dropwise to the latter. Stir at 80 °C for 24 h, cool to room temperature, precipitate in isopropanol, and obtain imidazole-functionalized polyarylene ether sulfone by washing and vacuum drying at 110 °C for 12 h.

[0046] Weigh 1.13 g of 1,3-propanesulfonic acid lactone and 4.00 g of amino-containing polyarylene ether sulfone, dissolve them separately in 40 mL of DMF, and under nitrogen protection, add the former dropwise to the latter. Stir at 80 °C for 24 h, cool to room temperature, precipitate in isopropanol, wash and vacuum dry at 110 °C for 12 h to obtain sulfonated polyarylene ether sulfone.

[0047] (4) Preparation of anion exchange membranes:

[0048] Weigh 0.70 g of imidazole-functionalized polyarylether sulfone and dissolve it in 15 mL of NMP. Cast the solution onto a clean glass plate and irradiate it under an IR lamp. After the solvent has completely evaporated, peel off the film from the glass plate and dry it under vacuum at 70 °C for 24 h to completely remove the solvent and obtain AEM.

[0049] (5) Membrane performance:

[0050] The thickness, ion exchange capacity, water absorption rate, swelling rate, acid and alkali stability, and transmembrane voltage (current density 600 A·m) of the prepared membrane were experimentally tested using national standard methods. –2The electrodialysis performance and burst strength were measured. The sheet resistance and migration number of the membrane were tested using a self-made device. The results are shown in Table 1. (For specific test methods, please refer to the literature reports: Journal of Membrane Science 577(2019)153–164; Journal of Materials Chemistry A 9(2021)5485–5496).

[0051] Example 2:

[0052] (1) Synthesis of Br-3C-IM imidazole salt: The same preparation process as in Example 1 was used.

[0053] (2) Synthesis of amino-containing polyarylether sulfone: The same preparation process as in Example 1 was used.

[0054] (3) Synthesis of functionalized polyarylether sulfone: The same preparation process as in Example 1 was used.

[0055] (4) Preparation of cation exchange membranes:

[0056] The same preparation process as in Example 1 was used, except that 0.70 g of sulfonated polyarylether sulfone was weighed and dissolved in 15 mL of NMP, the casting solution was poured onto a clean glass plate, irradiated under an IR lamp, and after the solvent was completely evaporated, the film on the glass plate was peeled off and vacuum dried at 70 °C for 24 h to completely remove the solvent, thus obtaining CEM.

[0057] (5) Membrane performance:

[0058] The thickness, ion exchange capacity, water absorption rate, swelling rate, acid and alkali stability, and transmembrane voltage (current density 600 A·m) of the prepared membrane were experimentally tested using national standard methods. –2 The electrodialysis performance and burst strength were measured. The sheet resistance and migration number of the membrane were tested using a self-made device. The results are shown in Table 1. (For specific test methods, please refer to the literature reports: Journal of Membrane Science 577(2019)153–164; Journal of Materials Chemistry A 9(2021)5485–5496).

[0059] Example 3:

[0060] (1) Synthesis of Br-3C-IM imidazole salt: The same preparation process as in Example 1 was used.

[0061] (2) Synthesis of amino-containing polyarylether sulfone: The same preparation process as in Example 1 was used.

[0062] (3) Synthesis of functionalized polyarylether sulfone: The same preparation process as in Example 1 was used.

[0063] (4) Preparation of bipolar films:

[0064] 0.70 g of imidazole-functionalized polyarylene ether sulfone and sulfonated polyarylene ether sulfone were weighed and dissolved in 15 mL of NMP to obtain AEL and CEL casting solutions. The AEL casting solution was cast onto a clean glass plate and irradiated under an IR lamp. After the solvent was completely evaporated, AEL was obtained. Then, the CEL casting solution was further cast onto AEL and irradiated under an IR lamp. After the solvent evaporated, the bipolar film on the glass plate was peeled off and vacuum dried at 70 °C for 24 h. After the solvent was completely removed, BPM-1 was obtained.

[0065] (5) Membrane performance:

[0066] The thickness, ion exchange capacity, water absorption rate, swelling rate, acid and alkali stability, and transmembrane voltage (current density 600 A·m) of the prepared membrane were experimentally tested using national standard methods. –2 The electrodialysis performance and burst strength were measured. The sheet resistance and migration number of the membrane were tested using a self-made device. The results are shown in Table 1. (For specific test methods, please refer to the literature reports: Journal of Membrane Science 577(2019)153–164; Journal of Materials Chemistry A 9(2021)5485–5496).

[0067] Example 4:

[0068] (1) Synthesis of Br-3C-IM imidazole salt: The same preparation process as in Example 1 was used.

[0069] (2) Synthesis of amino-containing polyarylether sulfone: The same preparation process as in Example 1 was used.

[0070] (3) Synthesis of functionalized polyarylether sulfone: The same preparation process as in Example 1 was used.

[0071] (4) Synthesis of MIL-101(Cr)-SO3H:

[0072] Weigh 0.50 g (3.00 mmol) of terephthalic acid and 1.20 g (3.00 mmol) of Cr(NO3)·9H2O and place them in an autoclave containing a polytetrafluoroethylene container. Add 15 mL of 5M HF aqueous solution and heat in an oven at 220 °C for 8 h for hydrothermal reaction. After the reaction, the solution is sonicated and washed several times to obtain a green solid. Dry the green solid in a vacuum drying oven at 70 °C for 7 h to obtain MIL-101(Cr).

[0073] Weigh 0.3 mL ClSO3H and 0.50 g MIL-101(Cr) powder and mix them with 15 mL CH2Cl2. Add the former dropwise to the latter and stir at 0 °C for 1 h. After the reaction, the solution is sonicated several times, washed, and vacuum dried at 60 °C for 24 h to obtain MIL-101(Cr)-SO3H.

[0074] (5) Preparation of bipolar films:

[0075] 0.70 g of imidazole-functionalized polyarylene ether sulfone and sulfonated polyarylene ether sulfone were weighed and dissolved in 15 mL of NMP to obtain AEL and CEL casting solutions. The AEL casting solution was cast onto a clean glass plate and irradiated under an IR lamp. After the solvent was completely evaporated, AEL was obtained. Then, 5 mL of 5% (w / v) MIL-101(Cr)-SO3H solution was cast onto AEL and AEL-IL was obtained under an IR lamp. Finally, the CEL casting solution was further cast onto AEL-IL and irradiated under an IR lamp. After the solvent evaporated, the bipolar film on the glass plate was peeled off and vacuum dried at 70 °C for 24 h. After the solvent was completely removed, BPM-S was obtained.

[0076] (6) Membrane performance:

[0077] The thickness, ion exchange capacity, water absorption rate, swelling rate, acid and alkali stability, and transmembrane voltage (current density 600 A·m) of the prepared membrane were experimentally tested using national standard methods. –2 The electrodialysis performance and burst strength were measured. The sheet resistance and migration number of the membrane were tested using a self-made device. The results are shown in Table 1. (For specific test methods, please refer to the literature reports: Journal of Membrane Science 577(2019)153–164; Journal of Materials Chemistry A 9(2021)5485–5496).

[0078] Example 5:

[0079] (1) Synthesis of Br-3C-IM imidazole salt: The same preparation process as in Example 1 was used.

[0080] (2) Synthesis of amino-containing polyarylether sulfone: The same preparation process as in Example 1 was used.

[0081] (3) Synthesis of functionalized polyarylether sulfone: The same preparation process as in Example 1 was used.

[0082] (4) Synthesis of MIL-101(Cr)-NH2:

[0083] Weigh 0.54 g (3.00 mmol) of 2-aminoterephthalic acid and 1.20 g (3.00 mmol) of Cr(NO3)·9H2O and place them in a high-pressure reactor containing a polytetrafluoroethylene container. Add 20 mL of 3.5% NaOH aqueous solution and heat in an oven at 150 °C for 8 h. After the reaction, the solution is sonicated and washed several times to obtain a green solid. Dry the green solid in a vacuum oven at 100 °C for 12 h to obtain MIL-101(Cr)-NH2.

[0084] (5) Preparation of bipolar membrane: The same preparation process as in Example 4 was used, except that 5 mL of MIL-101(Cr)-NH2 with a mass-volume concentration of 5% was cast on the AEL to obtain BPM-N.

[0085] (6) Membrane performance:

[0086] The thickness, ion exchange capacity, water absorption rate, swelling rate, acid and alkali stability, and transmembrane voltage (current density 600 A·m) of the prepared membrane were experimentally tested using national standard methods. –2 The electrodialysis performance and burst strength were measured. The sheet resistance and migration number of the membrane were tested using a self-made device. The results are shown in Table 1. (For specific test methods, please refer to the literature reports: Journal of Membrane Science 577(2019)153–164; Journal of Materials Chemistry A 9(2021)5485–5496).

[0087] Example 6:

[0088] (1) Synthesis of Br-3C-IM imidazole salt: The same preparation process as in Example 1 was used.

[0089] (2) Synthesis of amino-containing polyarylether sulfone: The same preparation process as in Example 1 was used.

[0090] (3) Synthesis of functionalized polyarylether sulfone: The same preparation process as in Example 1 was used.

[0091] (4) Synthesis of bifunctionalized MIL-101(Cr):

[0092] Weigh 115 μL of 1,3-propanesulfonic acid lactone, 500 mg of MIL-101(Cr)-NH2 and 25 mL of CHCl3 and mix them. Stir at 45 °C for 3 h. After the reaction, the solution is sonicated several times, washed and dried under vacuum at 60 °C for 24 h to obtain bifunctionalized MIL-101(Cr).

[0093] (5) Preparation of bipolar membrane: The same preparation process as in Example 4 was used, except that 5 mL of bifunctionalized MIL-101(Cr) with a mass-volume concentration of 5% was cast on the AEL to obtain BPM-B.

[0094] (6) Membrane performance:

[0095] The thickness, ion exchange capacity, water absorption rate, swelling rate, acid and alkali stability, and transmembrane voltage (current density 600 A·m) of the prepared membrane were experimentally tested using national standard methods. –2 The electrodialysis performance and burst strength were measured. The sheet resistance and migration number of the membrane were tested using a self-made device. The results are shown in Table 1. (For specific test methods, please refer to the literature reports: Journal of Membrane Science 577(2019)153–164; Journal of Materials Chemistry A 9(2021)5485–5496).

[0096]

[0097] Table 1.

Claims

1. A method for preparing a bipolar membrane with identical anion / cation exchange layer backbones, comprising the following steps: (1) Weigh a certain amount of N-methylimidazolium and 1,3-dibromopropane and mix them with a certain amount of acetone. Under nitrogen protection, add the former dropwise to the latter. Stir for 12-48 h at 20-60℃. After cooling to room temperature, wash several times with ethyl acetate and anhydrous diethyl ether. After washing, the solution is rotary evaporated to obtain a pale yellow viscous solution, which is Br-3C-IM imidazolium salt. Its chemical structure is shown in formula (I). （Ⅰ） (2) Weigh a certain amount of 4,4'-difluorodiphenyl sulfone monomer, 2,2'-bis(3-amino4-hydroxyphenyl)hexafluoropropane and hexafluorobisphenol A monomer, dissolve them in a high-boiling-point polar aprotic solvent, use potassium carbonate as a salting agent and toluene as a dehydrating agent, and react at 100-180℃ for 3-24 h under nitrogen protection. After the reaction is completed, separate and dry to obtain a random copolymer of amino-containing polyarylene ether sulfone in the main chain with a molecular weight of 30,000-60,000. In formula (II), x and y represent the molar percentages of the two chains as x% and y%, respectively, and x+y=100; where x=1-100 and y=1-100; where the molar ratio of 2,2'-bis(3-amino4-hydroxyphenyl)hexafluoropropane to hexafluorobisphenol A monomer is 0-80%:100-20%, and its chemical structure is shown in formula (II). （Ⅱ） (3) Weigh a certain amount of Br-3C-IM imidazole salt obtained in step (1) and amino-containing polyarylene sulfone obtained in step (2), dissolve them in DMF respectively, add the former dropwise to the latter under nitrogen protection, stir for 12-24 h at 20-90℃, cool to room temperature, precipitate in isopropanol, and obtain imidazole-functionalized polyarylene sulfone by washing and vacuum drying, the chemical structure of which is shown in formula (III); （Ⅲ） (4) Weigh a certain amount of 1,3-propanesulfonic acid lactone and amino-containing polyarylene sulfone obtained in step (2), dissolve them in DMF, add the former dropwise to the latter under nitrogen protection, stir for 24 h at 80°C, cool to room temperature, precipitate in isopropanol, and obtain sulfonated polyarylene sulfone by washing and vacuum drying. Its chemical structure is shown in formula (Ⅳ). （Ⅳ） (5) Weigh a certain amount of terephthalic acid and Cr(NO3)·9H2O and place them in a high pressure vessel containing a polytetrafluoroethylene container. Add a certain amount of 5 M HF aqueous solution and heat in an oven to carry out a hydrothermal reaction. After the reaction, the solution is ultrasonicated and washed several times to obtain a green solid. Dry the green solid in a vacuum drying oven at 70℃ for 7 h to obtain MIL-101(Cr), whose chemical structure is shown in formula (V). （Ⅴ） (6) Weigh a certain amount of ClSO3H and MIL-101(Cr) obtained in step (5) and mix them with a certain amount of CH2Cl2. Add the former dropwise to the latter and stir for several hours. After the reaction, the solution is sonicated, washed and dried several times to obtain MIL-101(Cr)-SO3H, whose chemical structure is shown in formula (VI). （Ⅵ） (7) Weigh a certain amount of 2-aminoterephthalic acid and Cr(NO3)·9H2O and place them in a high pressure vessel containing a polytetrafluoroethylene container. Add a certain amount of NaOH aqueous solution and heat in an oven at 150°C for 8 h. After the reaction, the solution is ultrasonicated and washed several times to obtain a green solid. Dry the green solid in a vacuum drying oven for several hours to obtain MIL-101(Cr)-NH2, whose chemical structure is shown in formula (VII). （Ⅶ） (8) Weigh a certain amount of 1,3-propanesulfonic acid lactone, MIL-101(Cr)-NH2 obtained in step (7) and a certain amount of CHCl3, mix them, heat and stir for several hours, and after the reaction, the solution is sonicated, washed and dried several times to obtain bifunctionalized MIL-101(Cr), whose chemical structure is shown in formula (VIII). （Ⅷ） (9) Weigh a certain amount of imidazole-functionalized polyarylene sulfone obtained in step (3) and sulfonated polyarylene sulfone obtained in step (4) and dissolve them in an organic solvent to obtain AEL and CEL casting solutions. Cast the AEL casting solution onto a clean glass plate and irradiate it under an IR lamp. After the solvent is completely evaporated, AEL is obtained. Then, 5 mL of 5% (w / v) MIL-101(Cr)-SO3H or MIL-101(Cr)-NH2 or bifunctionalized MIL-101(Cr) solution is cast onto AEL and AEL-IL is obtained under an IR lamp. Finally, CEL casting solution is further cast onto AEL-IL and irradiated under an IR lamp. After the solvent evaporates, the bipolar film on the glass plate is peeled off and further dried in a vacuum drying oven. After the solvent is completely removed, BPM-S / BPM-N / BPM-B is obtained.

2. A method for the preparation of a bipolar membrane with identical backbone of the anion / cation exchange layers according to claim 1, characterized in that: The reaction temperature in step (1) is 40℃ and the reaction time is 24 h; the molar ratio of N-methylimidazole to 1,3-dibromopropane is 1:

3.

3. A method for preparing a bipolar membrane having the same backbone of anion- and cation-exchange layers according to claim 1, characterized by: In step (2), the molar ratio of 2,2'-bis(3-amino-4-hydroxyphenyl)hexafluoropropane to hexafluorobisphenol A is 70%:30%, i.e., x:y = 70%:30%; the high-boiling-point polar aprotic solvent is N-methylpyrrolidone, and the polycondensation reaction conditions are 155°C for 4 h, then increased to 165°C for 3 h.

4. A method for preparing a bipolar membrane having the same backbone of anion- and cation-exchange layers according to claim 1, characterized by: The reaction conditions for step (3) are 80°C and stirring for 24 h.

5. A method for preparing a bipolar membrane having the same backbone of anion- and cation-exchange layers according to claim 1, characterized by: The vacuum drying temperature in step (4) is 110°C.

6. The method for preparing a bipolar membrane with identical anion / cation exchange layer backbones according to claim 1, characterized in that: The hydrothermal reaction conditions described in step (5) are 220℃ for 8 hours.

7. The method for preparing a bipolar membrane with identical anion / cation exchange layer backbones according to claim 1, characterized in that: The reaction conditions described in step (6) are 0°C for 1 h and vacuum drying conditions are 60°C for 24 h.

8. The method for preparing a bipolar membrane with identical anion / cation exchange layer backbones according to claim 1, characterized in that: In step (7), the molar ratio of 2-aminoterephthalic acid and Cr(NO3)·9H2O is 1:1, and the drying conditions are 100℃ for 12 h.

9. The method for preparing a bipolar membrane with identical anion / cation exchange layer backbones according to claim 1, characterized in that: The heating temperature in step (8) is 45°C and the heating time is 3 hours.

10. The method for preparing a bipolar membrane with identical anion / cation exchange layer backbones according to claim 1, characterized in that: The organic solvent in step (9) is N-methylpyrrolidone; the mass volume concentration of polyarylene sulfone in the AEL and CEL casting solutions is 5%; the vacuum drying temperature is 70℃ and the vacuum drying time is 24 h.

Images