Water treatment membrane with pH response and switchable membrane aperture and preparation method thereof

Abstract

The invention discloses a water treatment membrane with pH response and switchable membrane aperture and a preparation method thereof. The preparation method comprises the following steps: firstly, mixing and stirring polyvinylpyrrolidone, N-methyl pyrrolidone, polyacrylonitrile powder and polysulfone particles, defoaming, and carrying out phase conversion to obtain an ultrafiltration membrane; hydrolyzing the ultrafiltration membrane, and drying to obtain a polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane; the polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane is sequentially subjected to primary PEI aqueous solution soaking, drying, low-temperature plasma treatment, secondary PEI aqueous solution soaking and drying, and the water treatment membrane is obtained. The retention rate of the water treatment membrane to bovine serum albumin reaches up to 94%, the separation performance is excellent, meanwhile, the water treatment membrane has excellent pH response sensitivity and can be reused, the pore size of the membrane can be changed through movement of polymer side chains under different pH values, and the performance of the membrane can be recovered through acid washing and alkali washing after the membrane is blocked, so that the reusability is achieved. In addition, the preparation method has the characteristics of rapidness, high efficiency and environmental protection, and is easy to realize large-scale popularization and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and in particular relates to a water treatment membrane with a pH-responsive switchable membrane pore size and a preparation method thereof. Background Art

[0002] In the field of membrane separation technology, water treatment membranes are one of the most commonly used methods for industrial water resource treatment. Among them, pH-responsive water treatment membranes are a special type of membrane material that can change their surface properties, such as pore size, surface charge state, and surface hydrophilicity, in response to changes in solution pH. This ability to adapt its properties with changes in solution pH makes these membranes not only reusable but also selectively permeable. For example, as the pH of a solution increases or decreases, the pore size of some membranes may decrease or increase, potentially increasing or decreasing the membrane's ability to retain pollutants. In certain specific circumstances, an increase or decrease in solution pH may trigger a change in the charge on the membrane surface, protonating or deprotonating surface functional groups, thereby affecting the membrane's hydrophilicity and potentially allowing the selective passage of certain charged particles, thereby reducing membrane fouling. With continued research and technological innovation, water treatment membranes with pH-responsive, switchable pore sizes will have even broader application prospects in environmental protection and resource recovery.

[0003] The key factor in polymer membrane pH responsiveness is the presence of numerous pH-sensitive groups (weak electrolyte groups) on the polymer backbone, such as carboxyl, amino, sulfonic, and phosphoric acid groups. When the pH of a solution changes, these groups are protonated or deprotonated, altering the electrostatic repulsion between groups within the polymer chain, ultimately causing the polymer chain to contract or extend, expanding or shrinking the pore size on the membrane surface. For example, when the pH of a solution decreases, the carboxyl groups on the polymer chain become protonated, reducing the electrostatic repulsion between groups within the polymer chain and ultimately causing the polymer chain to contract. Common membrane materials such as polysulfone (PSF), polyethersulfone (PES), and polyvinylidene fluoride (PVDF) are hydrophobic. By blending pH-responsive polymers into the membrane to render it hydrophilic, the membrane's hydrophilicity can be improved. The pore size can also be adjusted by controlling the pH of the solution, thereby enhancing the membrane's separation capability and anti-fouling properties. For example, Chinese patent CN 114768548A discloses a pH-responsive blended modified ultrafiltration membrane and its preparation method. The method first prepares a composite ultrafiltration membrane by blending polysulfone and acrylonitrile powder, and then places the composite ultrafiltration membrane in an alkaline solution of a certain concentration for hydrolysis modification to make the membrane pH-responsive. However, the anti-pollution ability of the blended modified ultrafiltration membrane is not strong and its service life is limited. Chinese patent CN117815911A discloses an amphiphilic ultrafiltration membrane and its preparation method and application. The method first treats the base membrane with low-temperature plasma and then grafts silane on the membrane surface to obtain a polysiloxane-base membrane and treats its end with amino. Then, the base membrane is placed in a glutamic acid solution for grafting reaction, and finally an amphiphilic ultrafiltration membrane is obtained. The surface of this base membrane also has a certain pH responsiveness.

[0004] While numerous methods for preparing water treatment membranes with pH-responsive, switchable pore sizes have been reported, most are limited to basement membrane or surface modification. Basement membrane modification complicates the preparation process, requiring the use of toxic and hazardous chemical reagents to aid the reaction, leading to high production costs and difficulties in achieving large-scale production. Surface modification and functionalization of membranes only impart pH responsiveness on the surface of the water treatment membrane. Coating the surface with modifying substances results in an unstable bond between the modified layer and the membrane substrate, leading to instability in long-term membrane use. Furthermore, surface modification makes it difficult to achieve pH responsiveness throughout the membrane. Summary of the Invention

[0005] In view of the problems existing in the background technology, the purpose of the present invention is to provide a water treatment membrane with a pH-responsive switchable pore size and a preparation method thereof. This method solves the problem that the pH responsiveness of traditional water treatment membranes only exists on the surface of the water treatment membrane and it is difficult to form pH responsiveness throughout the membrane body. At the same time, the filtration accuracy and recycling performance of the obtained water treatment membrane are greatly improved.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A first aspect of the present invention provides a method for preparing a water treatment membrane having a pH-responsive switchable membrane pore size, comprising the following steps: S1, mixing polyvinyl pyrrolidone, N-methyl pyrrolidone, polyacrylonitrile powder and polysulfone particles, and then performing vacuum degassing and phase conversion to obtain an ultrafiltration membrane; S2, placing the obtained ultrafiltration membrane in an alkaline solution for hydrolysis, and then drying to obtain a polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane; S3. The obtained polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane is immersed in a first PEI (polyethyleneimine) aqueous solution, dried, and treated with low-temperature plasma, and then immersed in a second PEI (polyethyleneimine) aqueous solution and dried to obtain a water treatment membrane with a pH-responsive switchable membrane pore size.

[0007] Preferably, in step S1, the thickness of the ultrafiltration membrane is 200-250 μm.

[0008] Preferably, in step S1, the mixing temperature is 80-90°C and the mixing time is 10-15h; The vacuum degassing temperature is 25-35° C., and the degassing time is 6-10 hours.

[0009] Preferably, in step S2, the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution, and the hydrolysis time is 50-70 minutes.

[0010] Preferably, in step S3, the low-temperature plasma treatment conditions are: power of 40-100 W, air gas flow rate of 2.5-15 ml / min, and treatment time of 10-90 s.

[0011] Preferably, the mass concentration of the first PEI aqueous solution is 0.5-1.5%, and the immersion time in the first PEI aqueous solution is 10-18 hours; the mass concentration of the second PEI aqueous solution is 0.5-1.5%, and the immersion time in the second PEI aqueous solution is 10-18 hours.

[0012] Preferably, the mass ratio of the polyvinyl pyrrolidone, N-methyl pyrrolidone, polyacrylonitrile powder and polysulfone particles is 8-24:100-231:3-9:12-36.

[0013] A second aspect of the present invention provides a water treatment membrane having a pH-responsive switchable membrane pore size obtained by the above-mentioned preparation method.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. The water treatment membrane with a pH-responsive switchable membrane pore size prepared by the present invention has an excellent high retention rate (the retention rate for bovine serum albumin is as high as 94%), indicating that it has excellent separation performance and can effectively retain large molecular substances, and is suitable for separation processes with high separation requirements.

[0015] 2. The preparation method of the present invention is fast, efficient, and environmentally friendly. When grafting PEI using low-temperature plasma treatment technology, the power of the plasma generator is less than 100W and it only takes tens of seconds to complete. In addition, the grafting monomer used is soluble in water, which can reduce the use of organic solvents and is easy to achieve large-scale promotion and application.

[0016] 3. The water treatment membrane prepared by the present invention has high pH response sensitivity and is reusable. The movement of polymer side chains at different pH values can change the size of the membrane pores. After the membrane is clogged, the performance of the membrane can be restored by acid washing and alkaline washing to achieve reusability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The SEM images of the water treatment membrane surfaces prepared in Example 2 and Comparative Example 1 are shown; Figure 2 Graph showing the comparative results of bovine serum albumin rejection rates of the water treatment membranes prepared in Examples 1-6 and Comparative Examples 1-2; Figure 3 The water flux results of the water treatment membranes prepared in Example 2 and Comparative Example 1 at different pH values are shown; Figure 4 Graph showing the reversible water flux results of the water treatment membranes prepared in Example 2 and Comparative Example 1 in NaOH (pH=12) and HCl (pH=1) aqueous solutions. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below with reference to the embodiments so that those skilled in the art can implement the invention with reference to the description.

[0019] It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified.

[0020] The present invention provides a method for preparing a water treatment membrane having a pH-responsive switchable membrane pore size, comprising the following steps: S1, mixing polyvinyl pyrrolidone, N-methyl pyrrolidone, polyacrylonitrile powder and polysulfone particles, and then performing vacuum degassing and phase conversion to obtain an ultrafiltration membrane; S2, placing the obtained ultrafiltration membrane in an alkaline solution for hydrolysis, and then drying to obtain a polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane; in this step, some nitrile groups in the polyacrylonitrile in the obtained ultrafiltration membrane will be hydrolyzed into carboxylic acid groups under alkaline conditions; S3. The obtained polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane is immersed in a first PEI (polyethyleneimine) aqueous solution, dried, and treated with low-temperature plasma. In this step, the purpose of immersing in the first PEI aqueous solution is to prevent the plasma from damaging the membrane surface during subsequent plasma treatment, that is, to buffer and protect the membrane surface. After the low-temperature plasma treatment, hydrophilic groups such as amino groups and carboxyl groups will be generated on the membrane surface, and these groups will be activated. Then, the membrane is placed in a second PEI (polyethyleneimine) aqueous solution and dried to obtain a water treatment membrane with a pH-responsive switchable membrane pore size. In this step, the membrane is immersed in the second PEI aqueous solution, and the amino groups in the PEI will undergo a condensation reaction with the carboxyl groups on the membrane surface, thereby achieving a large amount of PEI grafting on the membrane surface. Example 1 (1) 16 g of polyvinyl pyrrolidone, 154 g of N-methyl pyrrolidone, 6 g of polyacrylonitrile powder and 24 g of polysulfone particles were placed in a reactor and stirred at 85 °C for 12 h. The mixture was then placed in a vacuum drying oven and vacuum degassed at 35 °C for 8 h. The degassed casting liquid was then phase-converted into a membrane. After standing in deionized water for 48 h, the ultrafiltration membrane was placed in a 2% sodium hydroxide solution for hydrolysis for 50 min. After the hydrolysis, the ultrafiltration membrane was washed and placed in a vacuum drying oven and vacuum-dried at 35 °C for 24 h to obtain a polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane with a thickness of 200 μm.

[0021] (2) The polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane was immersed in a first PEI aqueous solution with a mass fraction of 1.5% for 12 h, and then the immersed membrane was placed in a vacuum drying oven and vacuum dried at 35 °C for 12 h; (3) The membrane soaked in PEI and dried was placed in a low-temperature plasma generator with a power of 40 W and an air gas flow rate of 2.5 ml / min. Air was used as the gas source and low-temperature plasma treatment was performed for 10 seconds. The membrane was then placed in a second PEI aqueous solution with a mass fraction of 0.5% and soaked for 12 hours. The soaked ultrafiltration membrane was then placed in a vacuum drying oven and vacuum dried at 35°C for 12 hours to obtain a water treatment membrane with a pH-responsive switchable membrane pore size.

[0022] Example 2 (1) 16 g of polyvinyl pyrrolidone, 154 g of N-methyl pyrrolidone, 6 g of polyacrylonitrile powder and 24 g of polysulfone particles were placed in a reactor and stirred at 85 °C for 12 h. Then, the mixture was placed in a vacuum drying oven and vacuum degassed at 35 °C for 8 h. The degassed casting liquid was then phase-converted into a membrane. After standing in deionized water for 48 h, the ultrafiltration membrane was placed in a 2% sodium hydroxide solution for hydrolysis for 60 min. After the hydrolysis, the ultrafiltration membrane was washed and placed in a vacuum drying oven and vacuum-dried at 35 °C for 24 h to obtain a polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane with a thickness of 220 μm.

[0023] (2) The polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane was immersed in a first PEI aqueous solution with a mass fraction of 1% for 12 h, and then the immersed membrane was placed in a vacuum drying oven and vacuum dried at 35 °C for 12 h; (3) The membrane soaked in PEI and dried was placed in a low-temperature plasma generator with a power of 60 W and a low-temperature plasma air gas flow rate of 5 ml / min. Air was used as the gas source for plasma treatment for 30 seconds. After that, it was placed in a second PEI aqueous solution with a mass fraction of 1% and soaked for 12 hours. Finally, the soaked ultrafiltration membrane was placed in a vacuum drying oven and vacuum dried at 35°C for 12 hours to obtain a water treatment membrane with a pH-responsive switchable membrane pore size.

[0024] Example 3 (1) 16 g of polyvinyl pyrrolidone, 154 g of N-methyl pyrrolidone, 6 g of polyacrylonitrile powder and 24 g of polysulfone particles were placed in a reactor and stirred at 85 °C for 12 h. The mixture was then placed in a vacuum drying oven and vacuum degassed at 35 °C for 8 h. The degassed casting liquid was then phase-converted into a membrane. After standing in deionized water for 48 h, the ultrafiltration membrane was placed in a 2% sodium hydroxide solution for hydrolysis for 70 min. After the hydrolysis, the ultrafiltration membrane was washed and placed in a vacuum drying oven and vacuum-dried at 35 °C for 24 h to obtain a polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane with a thickness of 230 μm.

[0025] (2) Soak the polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane in a first PEI aqueous solution with a mass fraction of 0.5% for 12 hours, then place the soaked membrane in a vacuum drying oven and vacuum dry it at 35°C for 12 hours; (3) The membrane soaked in PEI and dried was placed in a low-temperature plasma generator with a power of 80 W and a low-temperature plasma air gas flow rate of 10 ml / min. Air was used as the gas source for plasma treatment for 60 seconds. The membrane was then placed in a second PEI aqueous solution with a mass fraction of 1.5% and soaked for 12 hours. Finally, the soaked ultrafiltration membrane was placed in a vacuum drying oven and vacuum dried at 35°C for 12 hours to obtain a water treatment membrane with a pH-responsive switchable membrane pore size.

[0026] Example 4 (1) 16 g of polyvinyl pyrrolidone, 154 g of N-methyl pyrrolidone, 6 g of polyacrylonitrile powder and 24 g of polysulfone particles were placed in a reactor and stirred at 85 °C for 12 h. The mixture was then placed in a vacuum drying oven and vacuum degassed at 35 °C for 8 h. The degassed casting liquid was then phase-converted into a membrane. After standing in deionized water for 48 h, the ultrafiltration membrane was placed in a 2% alkaline solution for hydrolysis. After the hydrolysis, the ultrafiltration membrane was washed and placed in a vacuum drying oven and vacuum-dried at 35 °C for 24 h to obtain a polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane with a thickness of 250 μm.

[0027] (2) The polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane was immersed in a first PEI aqueous solution with a mass fraction of 1.5% for 12 h, and then the immersed membrane was placed in a vacuum drying oven and vacuum dried at 35 °C for 12 h; (3) The membrane soaked in PEI and dried was placed in a low-temperature plasma generator with a power of 100 W and a low-temperature plasma air gas flow rate of 15 ml / min. Air was used as the gas source for plasma treatment for 90 seconds. The membrane was then placed in a second PEI aqueous solution with a mass fraction of 1.5% and soaked for 12 hours. Finally, the soaked ultrafiltration membrane was placed in a vacuum drying oven and vacuum dried at 35°C for 12 hours to obtain a water treatment membrane with a pH-responsive switchable membrane pore size.

[0028] Example 5 (1) 8 g of polyvinyl pyrrolidone, 77 g of N-methyl pyrrolidone, 3 g of polyacrylonitrile powder and 12 g of polysulfone particles were placed in a reactor and stirred at 85 °C for 12 h. Then, the mixture was placed in a vacuum drying oven and vacuum degassed at 35 °C for 8 h. The degassed casting liquid was then phase-converted into a membrane. After standing in deionized water for 48 h, the ultrafiltration membrane was placed in a 2% sodium hydroxide solution for hydrolysis for 60 min. After the hydrolysis, the ultrafiltration membrane was washed and placed in a vacuum drying oven and vacuum-dried at 35 °C for 24 h to obtain a polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane with a thickness of 220 μm.

[0029] (2) The polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane was immersed in a first PEI aqueous solution with a mass fraction of 1% for 12 h, and then the immersed membrane was placed in a vacuum drying oven and vacuum dried at 35 °C for 12 h; (3) The membrane soaked in PEI and dried was placed in a low-temperature plasma generator with a power of 60 W and a low-temperature plasma air gas flow rate of 5 ml / min. Air was used as the gas source for plasma treatment for 30 seconds. After that, it was placed in a second PEI aqueous solution with a mass fraction of 1% and soaked for 12 hours. Finally, the soaked ultrafiltration membrane was placed in a vacuum drying oven and vacuum dried at 35°C for 12 hours to obtain a water treatment membrane with a pH-responsive switchable membrane pore size.

[0030] Example 6 (1) 24 g of polyvinyl pyrrolidone, 231 g of N-methyl pyrrolidone, 9 g of polyacrylonitrile powder and 36 g of polysulfone particles were placed in a reactor and stirred at 85 °C for 12 h. Then, the mixture was placed in a vacuum drying oven and vacuum degassed at 35 °C for 8 h. The degassed casting liquid was then phase-converted into a membrane. After standing in deionized water for 48 h, the ultrafiltration membrane was placed in a 2% sodium hydroxide solution for hydrolysis for 60 min. After the hydrolysis, the ultrafiltration membrane was washed and placed in a vacuum drying oven and vacuum-dried at 35 °C for 24 h to obtain a polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane with a thickness of 220 μm.

[0031] (2) The polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane was immersed in a first PEI aqueous solution with a mass fraction of 1% for 12 h, and then the immersed membrane was placed in a vacuum drying oven and vacuum dried at 35 °C for 12 h; (3) The membrane soaked in PEI and dried was placed in a low-temperature plasma generator with a power of 60 W and a low-temperature plasma air gas flow rate of 5 ml / min. Air was used as the gas source for plasma treatment for 30 seconds. After that, it was placed in a second PEI aqueous solution with a mass fraction of 1% and soaked for 12 hours. Finally, the soaked ultrafiltration membrane was placed in a vacuum drying oven and vacuum dried at 35°C for 12 hours to obtain a water treatment membrane with a pH-responsive switchable membrane pore size.

[0032] Comparative Example 1 (1) 16 g of polyvinyl pyrrolidone, 154 g of N-methyl pyrrolidone, 6 g of polyacrylonitrile powder and 24 g of polysulfone particles were placed in a reactor and stirred at 85 °C for 12 h. Then, the mixture was placed in a vacuum drying oven and vacuum degassed at 35 °C for 8 h. The degassed casting liquid was then phase-converted into a membrane. After standing in deionized water for 48 h, the ultrafiltration membrane was placed in a 2% sodium hydroxide solution for hydrolysis for 60 min. After the hydrolysis, the ultrafiltration membrane was washed and placed in a vacuum drying oven and vacuum-dried at 35 °C for 24 h to obtain a polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane with a thickness of 220 μm.

[0033] (2) The polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane was immersed in a first PEI aqueous solution with a mass fraction of 1% for 12 h, and then the immersed membrane was placed in a vacuum drying oven and vacuum dried at 35 °C for 12 h; (3) The membrane soaked in PEI and dried was placed in a second PEI aqueous solution with a mass fraction of 1% and soaked for 12 hours. Finally, the soaked ultrafiltration membrane was placed in a vacuum drying oven and vacuum dried at 35°C for 12 hours to obtain a water treatment membrane.

[0034] Comparative Example 2 (1) 16 g of polyvinyl pyrrolidone, 154 g of N-methyl pyrrolidone, 6 g of polyacrylonitrile powder and 24 g of polysulfone particles were placed in a reactor and stirred at 85 °C for 12 h. Then, the mixture was placed in a vacuum drying oven and vacuum degassed at 35 °C for 8 h. The degassed casting liquid was then phase-converted into a membrane. After standing in deionized water for 48 h, the ultrafiltration membrane was placed in a 2% sodium hydroxide solution for hydrolysis for 60 min. After the hydrolysis, the ultrafiltration membrane was washed and placed in a vacuum drying oven and vacuum-dried at 35 °C for 24 h to obtain a polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane with a thickness of 220 μm.

[0035] (2) The polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane was placed in a low-temperature plasma generator, the power was set to 100 W, the low-temperature plasma air gas flow rate was 15 ml / min, and air was used as the gas source. The plasma treatment was carried out for 90 seconds, and then the membrane was placed in a second PEI aqueous solution with a mass fraction of 1.5% and soaked for 12 hours. Finally, the soaked ultrafiltration membrane was placed in a vacuum drying oven and vacuum dried at 35°C for 12 hours to obtain a water treatment membrane.

[0036] Water treatment membrane surface structure characterization and performance testing 1. SEM characterization of water treatment membrane Depend on Figure 1 It can be seen that the water treatment membrane prepared in Example 2 is rougher than the membrane prepared in Comparative Example 1, and has a small number of obvious membrane pores, but the number is relatively small. At the same time, the marks left by high-energy active particles bombarding the defects on the membrane surface can be clearly seen.

[0037] 2. Retention rate test Retention rate is an important indicator for evaluating the separation performance of water treatment membranes. At 0.1MPa - 0.2MPa, a 1 g / L bovine serum albumin solution was retained using an ultrafiltration cup. The absorbance of the prepared solution and filtrate was measured using a UV-visible spectrophotometer. Based on the relationship between absorbance and concentration, the retention rate of bovine serum albumin by the water treatment membrane was calculated using the following formula:

[0038] Where R is the retention rate (%),C p represents the BSA mass concentration in the filtrate (g / L); C f Indicates the mass concentration of BSA in the feed solution (g / L). Use a UV spectrophotometer to measure the absorbance of BSA in the solution, and then calculate the mass concentration of BSA and the standard curve of UV absorbance. C p and C f The rejection rate R is calculated by the value of . The rejection rate of bovine serum albumin for the water treatment membranes prepared in Examples 1-6 and Comparative Examples 1-2 is shown in Figure 2 .

[0039] from Figure 2 From the results, it can be seen that the retention rate of the water treatment membrane prepared in Example 2 reaches 94%. This is because a large amount of PEI is grafted onto the surface of the water treatment membrane. PEI will adsorb bovine serum albumin and aggregate on the membrane surface, thereby blocking more bovine serum albumin from passing through the membrane. In Comparative Example 1, no plasma treatment was performed. Even if it was immersed in the second PEI solution, PEI could not be grafted onto the membrane surface, resulting in poor hydrophilicity. At the same time, there was no adsorption effect of PEI, so the retention rate of the obtained water treatment membrane was much lower than that of Example 2; in Comparative Example 2, the membrane was not immersed in the first PEI solution before plasma treatment. Due to the lack of buffering protection on the membrane surface, the pores on the membrane surface increased and enlarged under the action of plasma etching, so the retention rate of the obtained water treatment membrane was much lower than that of Example 2. The above results show that the water treatment membrane prepared by the present invention has excellent separation performance, can efficiently intercept macromolecular substances, and is suitable for separation processes with higher separation requirements.

[0040] 3. pH response test Cut the water treatment membrane into the appropriate size and place it at the bottom of the ultrafiltration cup. Then add deionized water to the cup until it reaches 2 / 3 of the cup. Under normal pressure, adjust the pressure valve so that the pressure in the ultrafiltration cup is 0.1 MPa. Pre-press for more than 60 minutes to stabilize the membrane flux.

[0041] HCl and NaOH were used to prepare solutions of different pH values, and the pH value of the solution was accurately adjusted using a pH meter. The pure water in the ultrafiltration cup was replaced with the solution of the corresponding pH value, and the pressure in the ultrafiltration cup was adjusted to 0.2 MPa for flux testing. After the test, the membrane was removed and rinsed with pure water, and the above experiment was repeated. The water flux calculation formula of the water treatment membrane is as follows:

[0042] in, is the water flux (L·m –2 ·h –1 ),V is the volume of liquid flowing out of the ultrafiltration cup during the measurement time (L), A is the effective filtration area of the water treatment membrane, and t is the measurement time (h).

[0043] 4. pH reversibility test Refer to Test Method 3. The pH of the solution was adjusted to pH = 1, and the pressure in the ultrafiltration cup was adjusted to 0.2 MPa for flux testing. After the test, the membrane was removed and rinsed with pure water. The pH of the solution was then adjusted to pH = 12, and the above experiment was repeated. The water flux of the water treatment membrane was calculated using the formula in Test Method 2.

[0044] The water flux results of the water treatment membranes prepared in Example 2 and Comparative Example 1 at different pH values are shown in Figure 3 The reversible water flux results of the water treatment membranes prepared in Example 2 and Comparative Example 1 in NaOH (pH = 12) and HCl (pH = 1) aqueous solutions are shown in Figure 4 .

[0045] Depend on Figure 3 and Figure 4 As a result, the water treatment membrane prepared in Example 2 has pH responsiveness and reversibility. A large amount of PEI containing hydrophilic terminal amino groups is grafted onto the membrane surface. Under alkaline conditions, the amino groups in PEI are deprotonated to shrink the molecular chains, reducing the membrane pore size. However, the membrane has a large number of membrane pores under the action of plasma etching, thereby increasing the water flux of the membrane. Under acidic conditions, the amino groups contained in the PEI molecular chains on the membrane surface accept protons and are positively charged. Under the action of electrostatic repulsion, the distance between the polymer chains increases, the membrane pore size increases, and the water flux of the membrane is increased. The water treatment membrane provided by the present invention has excellent pH response sensitivity and is reusable. The movement of the polymer side chains under different pH values can change the size of the membrane pore size. After the membrane is blocked, the performance of the membrane can be restored by acid washing and alkali washing to achieve reusability.

[0046] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a water treatment membrane having a pH-responsive switchable membrane pore size, characterized in that: The following steps are involved: S1, mixing polyvinyl pyrrolidone, N-methyl pyrrolidone, polyacrylonitrile powder and polysulfone particles, and then performing vacuum degassing and phase conversion to obtain an ultrafiltration membrane; S2, placing the obtained ultrafiltration membrane in an alkaline solution for hydrolysis, and then drying to obtain a polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane; S3. Soaking the obtained polysulfone / polyacrylonitrile hydrolysis ultrafiltration membrane in a first PEI aqueous solution, drying, and treating with low-temperature plasma, soaking in a second PEI aqueous solution, and drying to obtain a water treatment membrane.

2. The method for preparing a water treatment membrane having a pH-responsive switchable membrane pore size according to claim 1, characterized in that: In step S1, the thickness of the ultrafiltration membrane is 200-250 μm. m .

3. The method for preparing a water treatment membrane having a pH-responsive switchable membrane pore size according to claim 1, characterized in that: In step S1, the mixing temperature is 80-90° C., and the mixing time is 10-15 hours; the vacuum degassing temperature is 25-35° C., and the degassing time is 6-10 hours.

4. The method for preparing a water treatment membrane having a pH-responsive switchable membrane pore size according to claim 1, characterized in that: In step S2, the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution, and the hydrolysis time is 50-70 minutes.

5. The method for preparing a water treatment membrane having a pH-responsive switchable membrane pore size according to claim 1, characterized in that: In step S3, the low-temperature plasma treatment conditions are: power of 40-100 W, air gas flow rate of 2.5-15 ml / min, and treatment time of 10-90 s.

6. The method for preparing a water treatment membrane having a pH-responsive switchable membrane pore size according to claim 1, characterized in that: The mass concentration of the first PEI aqueous solution is 0.5-1.5%, and the immersion time in the first PEI aqueous solution is 10-18 hours; the mass concentration of the second PEI aqueous solution is 0.5-1.5%, and the immersion time in the second PEI aqueous solution is 10-18 hours.

7. The method for preparing a water treatment membrane having a pH-responsive switchable membrane pore size according to claim 1, characterized in that: The mass ratio of the polyvinyl pyrrolidone, N-methyl pyrrolidone, polyacrylonitrile powder and polysulfone particles is 8-24:100-231:3-9:12-36.

8. A water treatment membrane having a pH-responsive switchable membrane pore size, prepared by the preparation method according to any one of claims 1 to 7.

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