Monovalent / divalent ion separated block structure polymer composite nanofiltration membrane and preparation method thereof

Abstract

The invention belongs to the technical field of separation membrane preparation, and particularly relates to a monovalent / divalent ion separated block structure polymer composite nanofiltration membrane and a preparation method thereof, and the preparation method comprises the following steps: (1) preparation of a PSF-b-PEG base membrane; (2) surface modification: performing interface polymerization for the first time; and (3) surface modification: carrying out secondary interfacial polymerization. The prepared composite nanofiltration membrane has the advantages of excellent monovalent and multivalent ion selectivity, high flux, good hydrophilic pollution resistance, low cost and the like, and has wide application prospects in practical application related to complex component treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of separation membrane preparation, and particularly relates to a block-structured polymer composite nanofiltration membrane for monovalent / divalent ion separation and a preparation method thereof. Specifically, it is a preparation of a composite nanofiltration membrane based on an amphiphilic block-structured polymer matrix and surface interfacial polymerization thereon to load a hydrophilic zwitterionic copolymer to achieve long-term and efficient separation of monovalent / divalent ions independent of charge. Background Art

[0002] Nanofiltration membranes (NF membranes) have been widely used in the fields of water purification, wastewater reuse, and seawater desalination due to their excellent selective permeability and low operating pressure. Especially in ion separation, NF membranes can effectively remove monovalent and multivalent ions in water under low energy consumption conditions. Traditional reverse osmosis membranes (RO membranes) can efficiently remove dissolved salts in water, but due to their high operating pressure and large energy consumption, their wide application in some fields is limited. In contrast, when separating monovalent ions (such as sodium ions, chloride ions) from multivalent ions (such as calcium ions, magnesium ions, cobalt ions, lead ions, etc.), NF membranes can provide better selectivity and have a lower operating pressure, thus showing a more extensive application prospect in water treatment, drinking water purification, industrial wastewater treatment, and selective separation and efficient enrichment of heavy metal ions. However, existing NF membranes usually can only achieve the separation of different valence ions with the same charge, and they have poor anti-fouling performance and high production costs. Therefore, there is an urgent need to develop a new type of general composite nanofiltration membrane that can achieve efficient and long-term separation of monovalent and multivalent ions independent of charge at a relatively low cost, so as to meet the huge demand in practical applications. Summary of the Invention

[0003] To solve the above-mentioned technical problems existing in the existing nanofiltration membranes, the present invention proposes a composite nanofiltration membrane based on an amphiphilic block structure polymer matrix, which realizes the efficient separation of monovalent and multivalent ions independent of charge by loading a hydrophilic zwitterionic copolymer through surface interfacial polymerization. Specifically, an amphiphilic block structure polymer is selected, and a non-woven fabric is used as the substrate. By precisely controlling various parameters in the preparation process, a substrate membrane with high flux, excellent hydrophilicity and anti-fouling properties is formed. Subsequently, it is modified by secondary interfacial polymerization (IP): the first IP modification loads a ultrathin and dense polyamide (PA) layer on the membrane surface, and the pore size distribution of the membrane layer is finely regulated by adjusting the reaction parameters, so as to significantly reduce the transfer of divalent ions through the steric effect and ensure excellent permeation selectivity between monovalent and divalent ions; the second IP modification loads a hydrophilic zwitterionic copolymer on the membrane surface. This copolymer locally exhibits charged characteristics but is nearly neutral as a whole, significantly reducing the dependence on the charge sign of ion repulsion or attraction during salt transport, thus realizing the universal separation of monovalent / divalent ions independent of charge. The prepared composite nanofiltration membrane can effectively achieve the selective separation of monovalent and divalent cations and anions when treating water with complex components, showing significant performance advantages and broad practical application prospects. The specific technical solutions are as follows:

[0004] (1) Preparation of PSF-b-PEG substrate membrane

[0005] A casting solution is prepared by mixing PSF-b-PEG, DMAc and THF in a certain proportion, stirred at a certain temperature, and then placed in a dryer at room temperature for defoaming to obtain a homogeneous and transparent casting solution. The environmental temperature and humidity are strictly controlled during the preparation process. The casting solution is evenly poured onto the non-woven fabric, and a stainless steel scraper is used to scrape it into a film and placed in the air for a period of time. Then, the scraped film is put into a deionized water coagulation bath for phase inversion to form a film, and the film piece is taken out after a period of time.

[0006]

[0007] (2) Preparation of PES-b-PEG substrate membrane

[0008] A casting solution is prepared by mixing PES-b-PEG, DMF, acetone and anhydrous LiCl in a certain proportion, heated and stirred for several hours, and a homogeneous casting solution is obtained after complete dissolution. Then, it is placed in a dryer at room temperature for sufficient defoaming for a period of time. The environmental temperature and humidity are controlled. The casting solution is evenly poured onto the non-woven fabric, and a stainless steel scraper is used to scrape it into a film and placed in the air for a period of time. Then, the scraped film is put into a deionized water coagulation bath for phase inversion to form a film, and the film piece is taken out after a period of time.

[0009]

[0010] (3) Surface modification: The first interfacial polymerization

[0011] Immerse the two prepared base membranes separately into the aqueous solution containing PIP for a period of time to allow PIP molecules to be absorbed and dispersed into the inner surface of the base membrane. Then, remove the excess solution with flowing air, and then immerse it into the n - hexane solution of TMC. After curing by heating, the obtained PA membrane is obtained.

[0012]

[0013] (4) Surface modification: The second interfacial polymerization

[0014] After immersing in the n - hexane solution of TMC in the previous step of modification, immerse it into the amphiphilic copolymer MPC - co - AEMA solution for a period of time and remove the excess solution. Through the reaction of the amino group of MPC - co - AEMA with the acyl chloride in the PA layer, after curing by heating, the second - modified PA / MPC membrane is obtained.

[0015]

[0016] Preferably, the mass ratio of the casting solution in step (1) is PSF - b - PEG:DMAc:THF = 20:60:20.

[0017] Preferably, the reaction temperature in step (1) is 40 - 80 °C, the reaction time is 6 - 24 h, and more preferably 60 °C, 6 h.

[0018] Preferably, the static defoaming time in step (1) is 6 - 24 h, and more preferably 12 h.

[0019] Preferably, the ambient temperature and humidity in step (1) are 18 - 25 °C and 20 - 50 RH%, and more preferably 25 °C, 40 RH%.

[0020] Preferably, the air - bath time in step (1) is 0 - 60 s, and more preferably 50 s.

[0021] Preferably, the gap of the doctor blade in step (1) is 100 - 200 μm, and more preferably 150 μm.

[0022] Preferably, the temperature of the deionized water coagulation bath in step (1) is 15 - 25 °C, and more preferably 25 °C.

[0023] Preferably, the phase - inversion time in step (1) is 5 - 10 min, and more preferably 8 min.

[0024] Preferably, the mass ratio of the casting solution in step (2) is PES-b-PEG particles: DMF: acetone: anhydrous LiCl = 20:60:15:5.

[0025] Preferably, the reaction temperature in step (2) is 40 - 80 °C, and the reaction time is 4 - 12 h, more preferably 40 °C and 4 h.

[0026] Preferably, the static defoaming time in step (2) is 6 - 24 h, more preferably 12 h.

[0027] Preferably, the ambient temperature and humidity in step (2) are 18 - 25 °C and 20 - 50 RH%, more preferably 25 °C and 30 RH%.

[0028] Preferably, the air bath time in step (2) is 0 - 60 s, more preferably 30 s.

[0029] Preferably, the gap of the doctor blade in step (2) is 100 - 200 μm, more preferably 150 μm.

[0030] Preferably, the temperature of the deionized water coagulation bath in step (2) is 15 - 25 °C, more preferably 25 °C.

[0031] Preferably, the phase inversion time in step (2) is 5 - 10 min, more preferably 8 min.

[0032] Preferably, the PIP concentration in step (3) is 0.2 - 2 wt.%, and the soaking time is 1 - 10 min, more preferably 0.5 wt.% and 5 min.

[0033] Preferably, the TMC concentration in step (3) is 0.1 - 1 wt.%, and the soaking time is 5 - 10 min, more preferably 0.1 wt.% and 10 min.

[0034] Preferably, the curing temperature in step (3) is 60 - 80 °C, and the time is 3 - 5 min, more preferably 70 °C and 3 min.

[0035] Preferably, the MPC-co-AEMA concentration in step (4) is 0.1 - 1 wt.%, and the soaking time is 3 - 10 min, more preferably 0.8 wt.% and 10 min.

[0036] Preferably, the curing temperature in step (4) is 50 - 80 °C, and the time is 5 - 15 min, more preferably 70 °C and 10 min.

[0037] The composite nanofiltration membrane prepared by the present invention has advantages such as excellent monovalent and multivalent ion selectivity, high flux, good hydrophilicity and antifouling property, and low cost, and has broad application prospects in practical applications involving the treatment of complex components.

[0038] Compared with the prior art, the advantages of the present invention are as follows:

[0039] 1. The prepared composite nanofiltration membrane substrate has the characteristics of uniform pore size and high porosity, ensuring that the filtered substances are of the same size, avoiding the mixing of particles of different sizes, improving the filtration effect and high selectivity, and thus providing a good interface basis for the further preparation of composite nanofiltration membrane by interfacial polymerization modification.

[0040] 2. The prepared composite nanofiltration membrane is loaded with hydrophilic zwitterionic copolymer through surface interfacial polymerization, and can achieve the separation of monovalent / divalent ions independent of charge. Different from traditional nanofiltration membranes that can only separate different valence ions with the same charge, it can effectively separate monovalent and divalent ions of different valence states, such as Li + / Mg 2+ 、Cl - / SO4 2- , significantly improving the universality and application breadth of the membrane.

[0041] 3. Through secondary interfacial polymerization modification, an ultra-thin and dense PA layer and a hydrophilic zwitterionic copolymer layer are loaded on the surface of the ultrafiltration substrate membrane, which not only optimizes the pore size distribution of the membrane, but also effectively enhances the hydrophilicity and antifouling property of the membrane. This design significantly reduces the membrane fouling rate while improving the selectivity, extends the service life of the membrane, and reduces the maintenance cost.

[0042] 4. The amphiphilic block copolymer matrix and hydrophilic zwitterionic copolymer used are relatively inexpensive, and the preparation process is relatively simple, which can effectively reduce the production cost of the membrane. At the same time, the durability and high efficiency of the membrane can reduce the later replacement and maintenance costs, and have high economic benefits. Specific Embodiments

[0043] To further illustrate the technical solution of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific embodiments, but it should be understood that these descriptions are only to further illustrate the features and advantages of the present invention, rather than a limitation on the claims of the present invention.

[0044] Example 1

[0045] Prepare a casting solution by mixing PSF-b-PEG particles, DMAc, and THF at a mass ratio of PSF-b-PEG:DMAc:THF = 20:60:20. Stir and react at 40 °C for 6 h, then place it in a dryer at room temperature for 12 h for degassing to obtain a uniform casting solution. During the preparation process, strictly control the environmental temperature and humidity at 25 °C and 40RH%. Pour the casting solution evenly onto the non-woven fabric, control the gap of the doctor blade at 150 μm, scrape it into a film, and place it in the air for 30 s. Then put the scraped film into a 15 °C deionized water coagulation bath for phase inversion film formation, and take out the film after 5 min. Subsequently, immerse the prepared bottom film in a 0.5 wt.% PIP aqueous solution for 5 min. After removing the excess solution with flowing air, immerse it in a 0.1 wt.% TMC n-hexane solution for 10 min for the first IP on its surface. Immerse it in a 0.8 wt.% amphiphilic copolymer MPC-co-AEMA solution for 10 min and remove the excess solution for the second surface IP. After curing at 70 °C for 5 min, the finished film is obtained.

[0046] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. The specific test method can be found in the reference document "Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes".

[0047] Example 2

[0048] Prepare a casting solution by mixing PSF-b-PEG particles, DMAc, and THF at a mass ratio of PSF-b-PEG:DMAc:THF = 20:60:20. Stir and react at 60 °C for 6 h, then place it in a dryer at room temperature for 12 h for degassing to obtain a uniform casting solution. During the preparation process, strictly control the environmental temperature and humidity at 25 °C and 40RH%. Pour the casting solution evenly onto the non-woven fabric, control the gap of the doctor blade at 150 μm, scrape it into a film, and place it in the air for 30 s. Then put the scraped film into a 25 °C deionized water coagulation bath for phase inversion film formation, and take out the film after 8 min. Subsequently, immerse the prepared bottom film in a 0.2 wt.% PIP aqueous solution for 5 min. After removing the excess solution with flowing air, immerse it in a 0.5 wt.% TMC n-hexane solution for 10 min for the first IP on its surface. Immerse it in a 0.5 wt.% amphiphilic copolymer MPC-co-AEMA solution for 10 min and remove the excess solution for the second surface IP. After curing at 70 °C for 5 min, the finished film is obtained.

[0049] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. The specific test method can be found in the reference document "Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes".

[0050] Example 3

[0051] PSF-b-PEG particles, DMAc and THF were configured into a casting solution at a mass ratio of PSF-b-PEG:DMAc:THF = 20:60:20, stirred and reacted at 60 °C for 12 h, and then placed in a dryer at room temperature for 12 h for degassing to obtain a uniform casting solution. The preparation process strictly controlled the environmental temperature and humidity at 25 °C and 40RH%, the casting solution was evenly poured on the non-woven fabric, the gap of the doctor blade was controlled at 150 μm and it was scraped into a film and placed in the air for 60 s, and then the scraped film was put into a 15 °C deionized water coagulation bath for phase inversion to form a film, and the film was taken out after 10 min. Subsequently, the prepared bottom film was immersed in a 0.2 wt.% PIP aqueous solution for 5 min, and after removing the excess solution with flowing air, it was immersed in a 0.5 wt.% TMC n-hexane solution for 10 min for the first IP on its surface. It was immersed in a 0.5 wt.% amphiphilic copolymer MPC-co-AEMA solution for 10 min and the excess solution was removed for the second surface IP, and the finished film was obtained after curing at 70 °C for 5 min.

[0052] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. The specific test method can be found in the reference document "Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes".

[0053] Example 4

[0054] Prepare a casting solution by mixing PSF-b-PEG particles, DMAc, and THF at a mass ratio of PSF-b-PEG:DMAc:THF = 20:60:20. Stir and react at 80 °C for 6 h, then place it in a dryer at room temperature for 12 h to remove air bubbles, so as to obtain a homogeneous casting solution. During the preparation process, strictly control the environmental temperature and humidity at 25 °C and 40RH%. Pour the casting solution evenly onto the non-woven fabric, control the gap of the doctor blade at 150 μm, scrape it into a film and place it in the air for 10 s, then put the scraped film into a 15 °C deionized water coagulation bath for phase inversion to form a film, and take out the film after 5 min. Subsequently, immerse the prepared bottom film in a 0.2 wt.% PIP aqueous solution for 5 min. After removing the excess solution with flowing air, immerse it in a 0.1 wt.% TMC n-hexane solution for 10 min to perform the first IP on its surface. Immerse it in a 0.1 wt.% amphiphilic copolymer MPC-co-AEMA solution for 10 min and remove the excess solution to perform the second surface IP. After curing at 60 °C for 5 min, the finished film is obtained.

[0055] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. The specific test method can be found in the reference document "Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes".

[0056] Example 5

[0057] Prepare a casting solution by mixing PSF-b-PEG particles, DMAc, and THF at a mass ratio of PSF-b-PEG:DMAc:THF = 20:60:20. Stir and react at 80 °C for 24 h, then place it in a dryer at room temperature for 12 h to remove air bubbles, so as to obtain a homogeneous casting solution. During the preparation process, strictly control the environmental temperature and humidity at 25 °C and 40RH%. Pour the casting solution evenly onto the non-woven fabric, control the gap of the doctor blade at 150 μm, scrape it into a film and place it in the air for 60 s, then put the scraped film into a 25 °C deionized water coagulation bath for phase inversion to form a film, and take out the film after 8 min. Subsequently, immerse the prepared bottom film in a 2 wt.% PIP aqueous solution for 5 min. After removing the excess solution with flowing air, immerse it in a 1 wt.% TMC n-hexane solution for 10 min to perform the first IP on its surface. Immerse it in a 1 wt.% amphiphilic copolymer MPC-co-AEMA solution for 10 min and remove the excess solution to perform the second surface IP. After curing at 80 °C for 15 min, the finished film is obtained.

[0058] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. The specific test method can be found in the reference document "Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes".

[0059] Example 6

[0060] PES-b-PEG particles, DMF, acetone and anhydrous LiCl were configured into a casting solution at a mass ratio of PES-b-PEG:DMF:acetone:anhydrous LiCl = 20:60:15:5, stirred and reacted at 40 °C for 12 h, and then placed in a dryer at room temperature for 12 h for degassing to obtain a homogeneous casting solution. The preparation process strictly controlled the environmental temperature and humidity at 25 °C and 40RH%, the casting solution was evenly poured on the non-woven fabric, the gap of the doctor blade was controlled at 150 μm and it was scraped into a film and placed in the air for 30 s, and then the scraped film was put into a 25 °C deionized water coagulation bath for phase inversion to form a film, and the film was taken out after 8 min. Subsequently, the prepared bottom film was immersed in a 0.5 wt.% PIP aqueous solution for 5 min, and after removing the excess solution with flowing air, it was immersed in a 0.1 wt.% TMC n-hexane solution for 10 min to perform the first IP on its surface. It was immersed in an 0.8 wt.% amphiphilic copolymer MPC-co-AEMA solution for 10 min and the excess solution was removed to perform the second surface IP, and the finished film was obtained after curing at 70 °C for 10 min.

[0061] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. The specific test method can be found in the reference document "Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes".

[0062] Example 7

[0063] A casting solution was prepared by mixing PES-b-PEG particles, DMF, acetone and anhydrous LiCl in a mass ratio of PES-b-PEG:DMF:acetone:anhydrous LiCl = 20:60:15:5. The mixture was stirred at 40 °C for 24 h and then degassed in a desiccator at room temperature for 12 h to obtain a homogeneous casting solution. During the preparation process, the environmental temperature and humidity were strictly controlled at 25 °C and 40RH%. The casting solution was evenly poured onto the non-woven fabric, and the film was formed by scraping with a doctor blade with a gap of 150 μm and left in the air for 60 s. Then, the scraped film was placed in a 15 °C deionized water coagulation bath for phase inversion to form a film, and the film was taken out after 7 min. Subsequently, the prepared bottom film was immersed in a 0.5 wt.% PIP aqueous solution for 5 min. After removing the excess solution with flowing air, it was immersed in a 0.1 wt.% TMC hexane solution for 10 min for the first surface IP. It was immersed in a 0.5 wt.% amphiphilic copolymer MPC-co-AEMA solution for 10 min and the excess solution was removed for the second surface IP. After curing at 70 °C for 8 min, the finished film was obtained.

[0064] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. The specific test method can be found in the reference document "Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes".

[0065] Example 8

[0066] A casting solution was prepared by mixing PES-b-PEG particles, DMF, acetone and anhydrous LiCl in a mass ratio of PES-b-PEG:DMF:acetone:anhydrous LiCl = 20:60:15:5. The mixture was stirred at 60 °C for 6 h and then degassed in a desiccator at room temperature for 12 h to obtain a homogeneous casting solution. During the preparation process, the environmental temperature and humidity were strictly controlled at 25 °C and 40RH%. The casting solution was evenly poured onto the non-woven fabric, and the film was formed by scraping with a doctor blade with a gap of 150 μm and left in the air for 30 s. Then, the scraped film was placed in a 15 °C deionized water coagulation bath for phase inversion to form a film, and the film was taken out after 5 min. Subsequently, the prepared bottom film was immersed in a 0.5 wt.% PIP aqueous solution for 5 min. After removing the excess solution with flowing air, it was immersed in a 0.1 wt.% TMC hexane solution for 10 min for the first surface IP. It was immersed in a 0.8 wt.% amphiphilic copolymer MPC-co-AEMA solution for 10 min and the excess solution was removed for the second surface IP. After curing at 70 °C for 5 min, the finished film was obtained.

[0067] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. The specific test method can be found in the reference document "Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes".

[0068] Example 9

[0069] PES-b-PEG particles, DMF, acetone and anhydrous LiCl were used to prepare a casting solution at a mass ratio of PES-b-PEG:DMF:acetone:anhydrous LiCl = 20:60:15:5. The mixture was stirred and reacted at 60 °C for 12 h, and then degassed in a dryer at room temperature for 12 h to obtain a homogeneous casting solution. During the preparation process, the environmental temperature and humidity were strictly controlled at 25 °C and 40RH%. The casting solution was evenly poured onto the non-woven fabric, and the gap of the doctor blade was controlled at 150 μm to scrape it into a film and placed in the air for 60 s. Then the scraped film was put into a 25 °C deionized water coagulation bath for phase inversion to form a film, and the film was taken out after 8 min. Subsequently, the prepared bottom film was immersed in a 0.2 wt.% PIP aqueous solution for 5 min. After removing the excess solution with flowing air, it was immersed in a 0.5 wt.% TMC n-hexane solution for 10 min for the first IP on its surface. It was immersed in a 0.5 wt.% amphiphilic copolymer MPC-co-AEMA solution for 10 min and the excess solution was removed for the second surface IP. After curing at 70 °C for 15 min, the finished film was obtained.

[0070] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. The specific test method can be found in the reference document "Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes".

[0071] Example 10

[0072] A casting solution was prepared by mixing PES-b-PEG particles, DMF, acetone, and anhydrous LiCl in a mass ratio of PES-b-PEG:DMF:acetone:anhydrous LiCl = 20:60:15:5. The mixture was stirred at 80 °C for 6 h and then degassed in a desiccator at room temperature for 12 h to obtain a homogeneous casting solution. During the preparation process, the environmental temperature and humidity were strictly controlled at 25 °C and 40% RH. The casting solution was evenly poured onto the non-woven fabric, and a film was formed by scraping with a doctor blade with a gap of 150 μm and left in the air for 10 s. Then, the scraped film was placed in a 15 °C deionized water coagulation bath for phase inversion to form a film, and the film was taken out after 5 min. Subsequently, the prepared bottom film was immersed in a 0.2 wt.% PIP aqueous solution for 5 min. After removing the excess solution with flowing air, it was immersed in a 0.1 wt.% TMC hexane solution for 10 min for the first surface IP. It was then immersed in a 0.1 wt.% amphiphilic copolymer MPC-co-AEMA solution for 10 min and the excess solution was removed for the second surface IP. After curing at 60 °C for 5 min, the finished film was obtained.

[0073] Performance testing: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. The specific test method can be found in the reference document "Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes".

[0074] Example 11

[0075] A casting solution was prepared by mixing PES-b-PEG particles, DMF, acetone, and anhydrous LiCl in a mass ratio of PES-b-PEG:DMF:acetone:anhydrous LiCl = 20:60:15:5. The mixture was stirred at 80 °C for 24 h and then degassed in a desiccator at room temperature for 12 h to obtain a homogeneous casting solution. During the preparation process, the environmental temperature and humidity were strictly controlled at 25 °C and 40% RH. The casting solution was evenly poured onto the non-woven fabric, and a film was formed by scraping with a doctor blade with a gap of 150 μm and left in the air for 60 s. Then, the scraped film was placed in a 25 °C deionized water coagulation bath for phase inversion to form a film, and the film was taken out after 10 min. Subsequently, the prepared bottom film was immersed in a 2 wt.% PIP aqueous solution for 5 min. After removing the excess solution with flowing air, it was immersed in a 1 wt.% TMC hexane solution for 10 min for the first surface IP. It was then immersed in a 1 wt.% amphiphilic copolymer MPC-co-AEMA solution for 10 min and the excess solution was removed for the second surface IP. After curing at 80 °C for 15 min, the finished film was obtained.

[0076] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. The specific test method can be found in the reference document "Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes".

[0077]

[0078]

[0079] Table 1 Parameter table of the preparation method.

[0080]

[0081]

[0082] Table 2 Test result table.

Claims

1. A method for preparing a block structure polymer composite nanofiltration membrane for monovalent / divalent ion separation, comprising the following steps: (1) Preparation of PSF-b-PEG based membrane; (2) Surface modification: first interfacial polymerization The base film prepared in step (1) is immersed in an aqueous solution containing PIP for a period of time so that the PIP molecules are absorbed and dispersed on the inner surface of the base film. Then, the excess solution is removed by flowing air. Then, the base film is immersed in a n-hexane solution of TMC. After heating and curing, a PA film is obtained. The structure is shown in formula (III): (3) Surface modification: second interfacial polymerization The PA membrane prepared in step (2) is immersed in the amphiphilic copolymer MPC-co-AEMA solution for a period of time and the excess solution is removed. The amino groups of MPC-co-AEMA react with the acyl chloride in the PA layer, and then the PA / MPC membrane is obtained after heating and curing. The structure is shown in formula (IV):

2. The method for preparing the block structure polymer composite nanofiltration membrane for monovalent ion / divalent ion separation according to claim 1, characterized in that: Step (1) is as follows: PSF-b-PEG, DMAc and THF are prepared into a casting solution in a certain ratio, stirred and reacted at a certain temperature, and then placed in a desiccator at room temperature for degassing to obtain a homogeneous and transparent casting solution; the ambient temperature and humidity are controlled, the casting solution is evenly poured on a non-woven fabric, and a stainless steel scraper is used to scrape it until it forms a film and placed in the air for a period of time, and then the scraped film is placed in a deionized water coagulation bath for phase conversion into a film, and the film is taken out after a period of time, and the structure is shown in formula (I):

3. The method for preparing the block structure polymer composite nanofiltration membrane for monovalent ion / divalent ion separation according to claim 1, characterized in that: Step (1) is as follows: PES-b-PEG, DMF, acetone and anhydrous LiCl are prepared into a casting solution in a certain proportion, heated and stirred to react, and a uniform casting solution is obtained after full dissolution, and then placed in a desiccator at room temperature for full degassing for a period of time; the ambient temperature and humidity are controlled, the casting solution is evenly poured on a non-woven fabric, and a stainless steel scraper is used to scrape it until it forms a film and placed in the air for a period of time, and then the scraped film is placed in a deionized water coagulation bath for phase conversion into a film, and the film is taken out after a period of time, and the structure is shown in formula (II):

4. The method for preparing the block structure polymer composite nanofiltration membrane for monovalent ion / divalent ion separation according to claim 2, characterized in that: The mass ratio of the casting solution in step (1) is PSF-b-PEG:DMAc:THF=20:60:

20.

5. The method for preparing the block structure polymer composite nanofiltration membrane for monovalent ion / divalent ion separation according to claim 3, characterized in that: The mass ratio of the casting solution in step (2) is PES-b-PEG particles: DMF: acetone: anhydrous LiCl = 20:60:15:

5.

6. The method for preparing the block structure polymer composite nanofiltration membrane for monovalent ion / divalent ion separation according to claim 2 or 3, characterized in that: The reaction temperature of step (1) is 40-80°C, the reaction time is 6-24h, more preferably 60°C, 6h; the standing degassing time is 6-24h, more preferably 12h; the ambient temperature and humidity are 18-25°C, 20-50RH%, respectively, more preferably 25°C, 40RH%.

7. The method for preparing the block structure polymer composite nanofiltration membrane for monovalent ion / divalent ion separation according to claim 2 or 3, characterized in that: In step (1), the air bath time is 0 to 60 s, more preferably 50 s; the scraping knife gap is 100 to 200 μm, more preferably 150 μm; the deionized water coagulation bath temperature is 15 to 25° C., more preferably 25° C.; the phase inversion time is 5 to 10 min, more preferably 8 min.

8. The method for preparing the block structure polymer composite nanofiltration membrane for monovalent ion / divalent ion separation according to claim 1, characterized in that: The concentration of the aqueous solution containing PIP in step (3) is 0.2-2wt.%, and the soaking time is 1-10 min, more preferably 0.5wt.%, 5 min, the concentration of TMC is 0.1-1wt.%, and the soaking time is 5-10 min, more preferably 0.1wt.%, 10 min; the curing temperature is 60-80°C, the time is 3-5 min, more preferably 70°C, 3 min.

9. The method for preparing the block structure polymer composite nanofiltration membrane for monovalent ion / divalent ion separation according to claim 1, characterized in that: In step (4), the MPC-co-AEMA concentration is 0.1-1wt.%, the immersion time is 3-10 min, and more preferably 0.8wt.%, 10 min; the curing temperature is 50-80°C, the time is 5-15 min, and more preferably 70°C, 10 min.

10. A block structure polymer composite nanofiltration membrane for monovalent / divalent ion separation, characterized in that: The preparation is prepared by the preparation method according to any one of claims 1 to 9.

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