Forward osmosis membrane and its manufacturing method

Abstract

A forward osmosis membrane and a method for manufacturing the same are provided. The forward osmosis membrane has a sequentially laminated membrane structure, which includes a hydrophilic support grid and a hydrophilic polymer film layer. The support grid is a non-woven fabric or polyester screen modified with antibacterial nanoparticles, particularly a mixture of nano-Ag and nano-TiO2.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to Chinese Patent Application No. 202111053419.X, filed on September 9, 2021, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to the technical field of polymeric separation membranes and their manufacturing methods, and more particularly to antibacterial forward osmosis membranes and their manufacturing methods. [Background technology]

[0003] The forward osmosis (FO) process is a process in which water is automatically diffused from the low osmotic pressure raw water side to the high osmotic pressure draw liquid side through a selectively permeable membrane, driven by the osmotic pressure difference between the draw liquid and the feed liquid. This process does not require external force or energy.

[0004] Unlike pressure-driven membrane separation processes such as ultrafiltration, nanofiltration, and reverse osmosis, forward osmosis can be operated at low or no pressure, resulting in low operating energy consumption. Low-pressure operation is characterized by the absence of pressure-induced cake formation and low membrane fouling.

[0005] If there is a sufficient osmotic pressure difference, high water recovery rates that cannot be achieved by conventional separation membranes can be achieved.

[0006] Due to its characteristics of low energy consumption, low membrane fouling, and high rejection, forward osmosis has developed rapidly in recent years as a new membrane separation technology, attracting attention from researchers both at home and abroad. It is used in fields such as food, medicine, and energy, and is particularly expected to be applied in many fields such as seawater desalination, drinking water treatment, and wastewater treatment.

[0007] An ideal forward osmosis membrane should simultaneously possess good hydrophilicity, high permeation flux, high salt rejection, low internal concentration difference, durability, and good antibacterial properties. These are also the research directions that have attracted attention in this field in recent years. For example, Chinese Patent Application No. CN201811285404.4 discloses a graphene-added forward osmosis membrane without a support grid, which uses graphene to increase membrane strength, improve water permeation flux, and reduce internal concentration difference polarization while reducing membrane thickness. Chinese Patent Application No. CN201410065806.9 discloses the addition of chitin nanocrystalline particles to cellulose triacetate to reduce internal concentration difference polarization, improve hydrophilicity, and reduce internal concentration difference polarization. The technical solutions disclosed or described in these two patent technologies have antibacterial properties, but they both involve adding graphene material or chitin nanocrystals to the active layer of the forward osmosis membrane to provide a cellulose triacetate membrane layer of the forward osmosis membrane that has been modified. These solutions mainly address performance issues such as improving water permeation flux and reducing the polarization of internal concentration differences, and the antibacterial effect is not very high.

[0008] In recent years, with the advancement of forward osmosis technology, forward osmosis membranes have become more adaptable to more complex water qualities. However, conventional technologies and products, such as the forward osmosis membranes disclosed in the above-mentioned patent documents and patented technologies, lack antibacterial efficiency and are therefore unable to meet the long-term effective use of forward osmosis membranes in complex and eutrophic water qualities. During long-term use, eutrophic raw water is prone to large amounts of bacteria growing in the raw water, which can easily contaminate and clog the membrane, affecting its performance. Currently, there is an urgent need to provide comprehensive and high-performance forward osmosis membranes, which is an important factor in improving forward osmosis efficiency. Summary of the Invention

[0009] An object of the present invention is to provide a forward osmosis membrane that can improve the performance of the forward osmosis membrane by inhibiting bacterial growth and improving the antibacterial effect.

[0010] Another object of the present invention is to provide a method for manufacturing a forward osmosis membrane that can improve the performance of the forward osmosis membrane by inhibiting bacterial growth and improving the antibacterial effect.

[0011] In order to achieve the above object, the present invention employs the following technical means. The present invention relates to a forward osmosis membrane. The forward osmosis membrane provided by the present invention has a membrane structure that is sequentially laminated. The laminate includes a hydrophilic support grid and a hydrophilic polymer film layer. The support grid is a nonwoven fabric or polyester screen modified with antimicrobial nanoparticles.

[0012] In another preferred embodiment of the present invention, the antibacterial nanoparticles are a mixture of nano Ag and nano TiO2. The mass ratio of the two is 1:1 to 1:5. The average particle size of the nano Ag is 20 nm, and the average particle size of the nano TiO2 is 5-10 nm. Preferably, the mass ratio of the nano Ag to nano TiO2 is 1:2, more preferably, 0.2 wt.% of nano Ag and 0.4 wt.% of nano TiO2, and this more preferred ratio is the mass ratio relative to the modified suspension.

[0013] In another preferred embodiment of the present invention, the support grid has a thickness of 30 μm-80 μm and a pore size of 100-200 mesh. The forward osmosis membrane has a thickness of 30 μm-100 μm. Preferably, the support grid has a thickness of 30 μm, 50 μm, or 70 μm and a pore size of 100 mesh, 120 mesh, or 150 mesh. Preferably, the forward osmosis membrane has a thickness of 30 μm, 50 μm, 70 μm, or 100 μm.

[0014] In another preferred embodiment of the present invention, a support grid modified with antibacterial nanoparticles is manufactured by ultrasonically dispersing 0.1-0.5 wt.% nano Ag and 0.2-1 wt.% nano TiO in a 2-8 wt.% aqueous polyvinyl alcohol solution to prepare a modified suspension. A polyester screen is then immersed in the suspension and allowed to dry. Preferably, the nano Ag content is 0.2 wt.%, the nano TiO content is 0.4 wt.%, and the aqueous polyvinyl alcohol content is 4 wt.%.

[0015] In another preferred embodiment of the present invention, the hydrophilic polymer material is at least one of polyacrylonitrile, polyacrylate, polymethyl methacrylate, cellulose acetate, cellulose triacetate, polyvinyl alcohol, polyethylene oxide, and polyvinyl acetate.

[0016] In accordance with another object of the present invention, the present invention also relates to a method for producing a forward osmosis membrane, said method comprising the steps of: (a) manufacturing an antimicrobially modified support grid, the support grid being a hydrophilic nonwoven fabric or polyester screen; (b) preparing a casting solution: mixing a hydrophilic polymer in an aqueous solvent system to prepare a casting solution; (c) pouring the casting solution prepared in step (b) onto a glass plate covered with the antibacterial modified support grid prepared in step (a) to obtain an initial forward osmosis membrane having a specific thickness; (d) treating the outer layer of the initial forward osmosis membrane to remove the solvent and form a dense skin layer on the outer layer of the initial forward osmosis membrane to obtain a second initial forward osmosis membrane; (e) forming a phase separation membrane or an interface membrane on the second initial forward osmosis membrane to obtain the forward osmosis membrane; Includes.

[0017] The antibacterial modified support grid is a polyester screen modified with nano Ag and nano TiO2, and is prepared by the following method: nano Ag and nano TiO2 are placed in an aqueous polyvinyl alcohol solution to form a suspension, and a polyester screen is immersed in the suspension, dried, and stored until use.

[0018] The suspension is obtained by ultrasonically dispersing 0.1-0.5 wt.% nano Ag and 0.2-1 wt.% nano TiO2 in a 2-8 wt.% polyvinyl alcohol aqueous solution. Preferably, the nano Ag mass percentage is 0.2 wt.%, the nano TiO2 mass percentage is 1 wt.%, and the polyvinyl alcohol mass percentage is 4 wt.%. Preferably, the nano Ag mass percentage is 0.2 wt.%, and the nano TiO2 mass percentage is 0.4 wt.%.

[0019] The support grid has a thickness of 30 μm-80 μm and a pore size of 100-200 mesh. The forward osmosis membrane has a thickness of 30 μm-100 μm. Preferably, the support grid has a thickness of 30 μm, 50 μm, or 70 μm and a pore size of 100 mesh, 120 mesh, or 150 mesh. Preferably, the forward osmosis membrane has a thickness of 30 μm, 50 μm, 70 μm, or 100 μm.

[0020] The hydrophilic polymer material is at least one of polyacrylonitrile, polyacrylate, polymethyl methacrylate, cellulose acetate, cellulose triacetate, polyvinyl alcohol, polyethylene oxide, and polyvinyl acetate. The solvent system includes a mixture of 1,4-dioxane, acetone, methanol, and lactic acid. The mass percentage of the hydrophilic polymer is 8-15 wt.%, the mass percentage of 1,4-dioxane is 30-60 wt.%, the mass percentage of acetone is 5-20 wt.%, the mass percentage of methanol is 5-10 wt.%, and the mass percentage of lactic acid is 6-8 wt.%.

[0021] The method further includes the following steps: (b-1) The casting liquid obtained in step (b) is degassed. In step (c), the casting liquid degassed in step (b-1) is further poured onto a glass plate on which an antibacterial-modified hydrophilic support grid is laid, and an initial forward osmosis membrane having a specific thickness is produced using a film applicator. In the outer layer treatment and solvent removal step (d), the resulting initial forward osmosis membrane is left standing in air to volatilize the solvent and form a dense skin layer on the outer layer. In the step (e), the second initial forward osmosis membrane is immersed in deionized water to cause gelation and phase separation to occur, thereby forming a membrane. (f) The forward osmosis membrane obtained in step (e) is immersed in deionized water to remove residual organic solvents. (g) Remove the forward osmosis membrane, rinse with deionized water, and store in a solution of sodium metabisulfite until use.

[0022] The hydrophilic support grid is a polyester screen, which is pre-washed before use. During the pre-washing step, the polyester screen is immersed in 10% sodium hydroxide and 2% hydrochloric acid for 1 hour to remove impurities adsorbed on the surface, then rinsed with deionized water, dried, and stored. The initial forward osmosis membrane fabricated using a film applicator has a thickness of 30 μm-100 μm.

[0023] In step (b) of the preparation method, the mixture is stirred at 30-50°C for 12-48 hours to achieve uniform mixing, preferably at 40°C for 24 hours. The degassing method involves leaving the mixture to stand for 12-36 hours to fully degas, or ultrasonically assisted degassing, preferably for 24 hours. The air-standing condition involves leaving the mixture to stand for 30-90 seconds at a temperature of 25°C or below and a humidity of 90% or above to form a dense skin layer, preferably at 25°C and 90% humidity for 60 seconds. In step (f) of the preparation method, the membrane is heat-treated in a 40-50°C water bath for 5-20 minutes before immersing in deionized water, and then immersed in deionized water to remove residual organic solvents. The immersion time is 12-36 hours, preferably 24 hours. In step (g) of the preparation method, the concentration of sodium metabisulfite is 0.5-2%, preferably 1%.

[0024] In the forward osmosis membrane and its manufacturing method provided by the present invention, the support grid layer of the membrane is completely covered with antibacterial nanoparticles, particularly a mixture of nano Ag and nano TiO2, thereby providing effective, long-lasting, and comprehensive antibacterial effects without reducing the strength, water permeation flux, or salt rejection rate of the forward osmosis membrane. In the present invention, the support grid of the forward osmosis membrane is antibacterially modified with antibacterial nanoparticles, particularly a mixture of nano Ag and nano TiO2, thereby inhibiting bacterial growth on the forward osmosis membrane, improving forward osmosis performance, and improving the safety of the entire purification and filtration system. The antibacterial forward osmosis membrane of the present invention can be used to purify and purify complex water sources, especially those prone to bacterial growth due to eutrophication. Furthermore, the safety of nanosilver has been commercially recognized, and it is widely used in baby products such as tableware and baby bottles. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a flowchart of a manufacturing process for a forward osmosis membrane of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] In order to further explain the technical means and effects for achieving the objectives of the present invention, the forward osmosis membrane and its manufacturing method of the present invention, as well as its specific embodiments, structure, manufacturing method, features and functions, will be described below with reference to the drawings and preferred examples. The present invention will be further described herein with reference to the following examples, which are merely for the purpose of illustrating the present invention and are not intended to limit the present invention.

[0027] Figure 1 is a flow chart of the manufacturing process of the forward osmosis membrane of the present invention. The specific process is as follows: 1. Preparation of antibacterial support grid: The support grid is a hydrophilic nonwoven fabric or polyester screen. In the present invention, a polyester screen modified with nano Ag and nano TiO2 is preferably prepared. Nano Ag and nano TiO2 are placed in a polyvinyl alcohol aqueous solution and ultrasonically dispersed to prepare a suspension. The support grid is immersed in this suspension, then air-dried and stored until use. 2. Preparation of the casting liquid: The hydrophilic polymer material and the organic solvent are mixed uniformly. In the present invention, the hydrophilic polymer material is added to the aqueous organic solvent mixture and stirred at 30-50°C for 12-48 hours to obtain a uniform casting liquid. More preferably, in the present invention, cellulose triacetate is added to a mixture of 1,4-dioxane, acetone, methanol, and lactic acid and stirred at 40°C for 24 hours to obtain a uniform casting liquid. 3. Defoaming: The casting liquid obtained in step 2 is left to stand for 12-36 hours to be thoroughly defoamed, or ultrasonic defoaming is used as an aid. In the present invention, more preferably, the casting liquid is left to stand for 24 hours to be thoroughly defoamed. 4. Preparation of initial forward osmosis membrane: The completely degassed casting liquid is poured onto a glass plate on which the prepared antibacterial support grid is laid, and an initial forward osmosis membrane with a specific thickness is prepared using a film applicator. 5. Film formation: The film obtained in step 4 is left to stand in air at a predetermined temperature and humidity for several seconds to form a dense skin layer, and then immersed in deionized water to gel and undergo phase separation to form a film. In the present invention, the film is preferably left to stand in air at a temperature of 25°C or less and a humidity of 90% or more for 30 to 90 seconds. 6. Optimization treatment: The membrane obtained in step 5 is placed in a water bath at 40-50°C for 5-20 minutes for heat treatment, and then immersed in deionized water for 24 hours to remove residual organic solvents, resulting in a further optimized forward osmosis membrane. 7. Storage until use: Remove the forward osmosis membrane, rinse with deionized water, and then place in a 0.5-2% sodium metabisulfite solution, preferably a 1% sodium metabisulfite solution, and store until use. Decide whether to store until use as needed.

[0028] The method for producing the forward osmosis membrane provided by the present invention will be further described below. Preparation of nano Ag / TiO2 modified polyester screen: Add nano Ag at a mass percentage of 0.1-0.5 wt.% and nano TiO2 at a mass percentage of 0.2-1 wt.% to a polyvinyl alcohol aqueous solution at a mass percentage of 2-8 wt.%, and disperse ultrasonically to prepare a suspension. Immerse a polyester screen in this suspension, then air dry it and store it until use. Casting liquid preparation: Cellulose triacetate is added at a mass percentage of 8-15 wt.% to a mixture of acetone mass percentage of 5-20 wt.%, methanol mass percentage of 5-10 wt.%, lactic acid mass percentage of 6-8 wt.%, and the remainder 1,4-dioxane, and stirred at a temperature of 40°C for 24 hours to obtain a uniform casting liquid. The resulting casting liquid is allowed to stand for 24 hours and thoroughly degassed, or ultrasonic degassing is performed to assist. The completely degassed casting solution is poured onto a glass plate covered with the modified polyester screen, and a film applicator is used to produce an initial forward osmosis membrane of 30-100 μm. The membrane obtained in the previous step is left in air for 60-90 seconds at 25°C and 90% humidity to form a dense skin layer, and then immersed in deionized water to gel and undergo phase separation to form the membrane. The thickness of the modified polyester screen is 30-80 μm, preferably 30, 50, or 70 μm.

[0029] The forward osmosis membrane obtained by gel phase separation membrane formation was heat-treated in a water bath at 40-50°C for 5-15 minutes, and then immersed in deionized water for 24 hours to remove residual organic solvents.

[0030] The antibacterial forward osmosis membrane of the present invention has a membrane permeation flux of 8-13 L / (m) by using 0.5 mol / L sodium chloride and 0.01 mol / L magnesium sulfate as the draw and feed liquids, respectively. 2 *h), the magnesium sulfate inhibition rate is higher than 97%, the antibacterial rate is higher than 90%, and the antibacterial rate in the antibacterial durability test is higher than 90%.

[0031] The present invention will be further described below with reference to specific examples.

[0032] Example 1 1. Polyester screens with a thickness of 30 μm and a pore size of 100 mesh were immersed in 2% hydrochloric acid and 10% sodium hydroxide for 1 hour to remove impurities adsorbed on the surface, then rinsed with deionized water, dried, and stored until use. 2. Preparation of nano-Ag and nano-TiO2 modified polyester screen: Nano-Ag (0.2 wt.%), nano-TiO2 (0.4 wt.%), and polyvinyl alcohol (4 wt.%) aqueous solution were added and ultrasonically dispersed to prepare a suspension. Polyester screen was immersed in this suspension, then air-dried and stored until use. 3. Cellulose triacetate was added at a mass percentage of 13 wt.% to a mixture of 1,4-dioxane (54 wt.%), acetone (19 wt.%), methanol (8 wt.%), and lactic acid (6 wt.%), and stirred at 40°C for 24 hours to prepare a uniform casting liquid. 4. The cast liquid obtained in step 3 was allowed to stand for 24 hours and then thoroughly degassed or assisted by ultrasonic degassing. 5. The completely degassed casting liquid was poured onto a glass plate on which the prepared modified polyester screen having a thickness of 30 μm was laid, and an initial forward osmosis membrane having a thickness of 50 μm was prepared using a film applicator. 6. The membrane obtained in step 5 was left to stand in air at 25°C and 90% humidity for 30 seconds to form a dense skin layer. It was then immersed in deionized water, which caused it to gel and phase-separate to form a membrane. 7. The membrane obtained in step 6 was heat-treated in a water bath at 50°C for 15 minutes, and then immersed in deionized water for 24 hours to remove residual organic solvents.

[0033] Membrane performance The forward osmosis membrane produced in the above steps has a thickness of 50 μm. When 0.5 mol / L sodium chloride and 0.01 mol / L magnesium sulfate are used as the draw and feed liquids, respectively, the membrane permeation flux is 12.5 L / (m 2 *h), the magnesium sulfate blocking rate was 97.8%, and the antibacterial rate was 95%. In the antibacterial durability test, the antibacterial rate was 93%. Specific performance tests are shown in Table 1.

[0034] Example 2 1. Polyester screens with a thickness of 50 μm and a pore size of 100 mesh were immersed in 2% hydrochloric acid and 10% sodium hydroxide for 1 hour to remove impurities adsorbed on the surface, then rinsed with deionized water, dried, and stored until use. 2. Preparation of nano-Ag and nano-TiO2 modified polyester screen: Nano-Ag (0.2 wt.%), nano-TiO2 (0.4 wt.%), and polyvinyl alcohol (4 wt.%) aqueous solution were added and ultrasonically dispersed to prepare a suspension. Polyester screen was immersed in this suspension, then air-dried and stored until use. 3. Cellulose triacetate was added at a mass percentage of 13 wt.% to a mixture of 1,4-dioxane (54 wt.%), acetone (19 wt.%), methanol (8 wt.%), and lactic acid (6 wt.%), and stirred at 40°C for 24 hours to prepare a uniform casting liquid. 4. The resulting casting liquid was allowed to stand for 24 hours and then thoroughly degassed or assisted by ultrasonic degassing. 5. The completely degassed casting liquid was poured onto a glass plate on which the prepared modified polyester screen having a thickness of 50 μm was laid, and an initial forward osmosis membrane having a thickness of 70 μm was prepared using a film applicator. 6. The membrane obtained in step 5 was left to stand in air at 25°C and 90% humidity for 60 seconds to form a dense skin layer. It was then immersed in deionized water, which caused it to gel and phase-separate to form a membrane. 7. The membrane obtained in step 6 was heat-treated in a water bath at 45°C for 20 minutes, and then immersed in deionized water for 24 hours to remove residual organic solvents.

[0035] Membrane performance The forward osmosis membrane produced in the above steps has a thickness of 70 μm. When 0.5 mol / L sodium chloride and 0.01 mol / L magnesium sulfate are used as the draw and feed liquids, respectively, the membrane permeation flux is 11.0 L / (m 2 *h), the magnesium sulfate blocking rate was 98.1%, and the antibacterial rate was 94%. In the antibacterial durability test, the antibacterial rate was 92%. Specific performance tests are shown in Table 1.

[0036] Example 3 1. Polyester screens with a thickness of 50 μm and a pore size of 100 mesh were immersed in 2% hydrochloric acid and 10% sodium hydroxide for 1 hour to remove impurities adsorbed on the surface, then rinsed with deionized water, dried, and stored until use. 2. Preparation of nano-Ag and nano-TiO2 modified polyester screen: Nano-Ag (0.2 wt.%), nano-TiO2 (0.4 wt.%), and polyvinyl alcohol (4 wt.%) aqueous solution were added and ultrasonically dispersed to prepare a suspension. Polyester screen was immersed in this suspension, then air-dried and stored until use. 3. Cellulose triacetate was added at a mass percentage of 10 wt.% to a mixture of 1,4-dioxane (57 wt.%), acetone (19 wt.%), methanol (8 wt.%), and lactic acid (6 wt.%), and the mixture was stirred at 40°C for 24 hours to prepare a uniform casting liquid. 4. The resulting casting liquid was allowed to stand for 24 hours and then thoroughly degassed or assisted by ultrasonic degassing. 5. The completely degassed casting liquid was poured onto a glass plate on which the prepared modified polyester screen having a thickness of 50 μm was laid, and an initial forward osmosis membrane having a thickness of 100 μm was prepared using a film applicator. 6. The membrane obtained in step 5 was left to stand in air at 25°C and 90% humidity for 80 seconds to form a dense skin layer. It was then immersed in deionized water, which caused it to gel and phase-separate to form a membrane. 7. The membrane obtained in step 6 was heat-treated in a water bath at 40°C for 15 minutes, and then immersed in deionized water for 24 hours to remove residual organic solvents.

[0037] Membrane performance The forward osmosis membrane produced in the above steps has a thickness of 100 μm. When 0.5 mol / L sodium chloride and 0.01 mol / L magnesium sulfate are used as the draw and feed liquids, respectively, the membrane permeation flux is 10.5 L / (m 2 *h), the magnesium sulfate blocking rate was 98.2%, and the antibacterial rate was 95%. In the antibacterial durability test, the antibacterial rate was 93%. Specific performance tests are shown in Table 1.

[0038] Table 1: Performance evaluation of membranes using 0.5 mol / L sodium chloride and 0.01 mol / L magnesium sulfate as draw and feed liquids, respectively.

[0039] [Table 1]

[0040] As can be seen from Table 1, the forward osmosis membrane of the present invention equipped with an antibacterial support grid has high antibacterial properties. After immersion in eutrophic raw water for 10 days and subsequent testing after simple rinsing, the antibacterial properties were still maintained at over 90%, and the membrane's permeation flux and salt rejection were not affected. Because conventional forward osmosis membranes made of cellulose triacetate and forward osmosis membranes of conventional products do not have antibacterial properties, the membrane performance deteriorated significantly with increasing immersion time due to the growth of organisms.

[0041] In the examples of the present invention, the concentrations of sodium hydroxide, hydrochloric acid and sodium metabisulfite are calculated by mass ratio.

[0042] In the forward osmosis membrane and manufacturing method thereof provided by the present invention, the invented forward osmosis membrane is a forward osmosis membrane with an antibacterial modified support grid, which can inhibit bacterial growth under environmental conditions of eutrophic raw water, improve the permeability of the forward osmosis membrane, enable the forward osmosis membrane to be used effectively for a long period of time, extend the service life of the forward osmosis membrane system, and reduce the operating costs.

[0043] While the invention has been described herein with reference to specific embodiments, it will be apparent that various modifications and changes can be made thereto without departing from the spirit and scope of the invention. Accordingly, the present specification and drawings are to be regarded as illustrative rather than restrictive.

Claims

1. A forward osmosis membrane, The forward osmosis membrane has a sequentially laminated membrane structure, which includes a hydrophilic support grid and a hydrophilic polymer film layer. The support grid is a nonwoven fabric or polyester screen modified with antibacterial nanoparticles. The support grid is modified with antibacterial nanoparticles by the following method: nano Ag in a mass percentage of 0.1-0.5 wt. %, nano TiO ２ The nano Ag particles were added to a polyvinyl alcohol aqueous solution having a mass percentage of 0.2-1 wt. % and a mass percentage of 2-8 wt. %, and ultrasonically dispersed to obtain a suspension. A support grid was immersed in the suspension and then dried. The average particle size of the nano Ag particles was 20 nm, and the nano TiO particles were ２ The average particle size of the forward osmosis membrane is 5-10 nm, and the draw and feed liquids are 0.5 mol / L sodium chloride and 0.01 mol / L magnesium sulfate, respectively. The permeation flux of the membrane is 8-13 L / (m ２ *h) A forward osmosis membrane characterized in that the rejection of magnesium sulfate is greater than 97%.

2. The nano Ag and nano TiO ２ The forward osmosis membrane according to claim 1, wherein the mass ratio of the first to the second hydroxyl groups is 1:

2.

3. 3. The forward osmosis membrane of claim 2, wherein the thickness of the support grid is 30 μm-80 μm and the pore size is 100-200 mesh, and the thickness of the forward osmosis membrane is 50 μm-100 μm.

4. 4. The forward osmosis membrane of claim 3, wherein the support grid has a thickness of 30 μm, 50 μm, or 70 μm, a pore size of 100 mesh, 120 mesh, or 150 mesh, and the forward osmosis membrane has a thickness of 50 μm, 70 μm, or 100 μm.

5. 5. The forward osmosis membrane according to claim 1, wherein the hydrophilic polymer material is at least one of polyacrylonitrile, polyacrylate, polymethyl methacrylate, cellulose acetate, cellulose triacetate, polyvinyl alcohol, polyethylene oxide, and polyvinyl acetate.

6. 1. A method for manufacturing a forward osmosis membrane, the method comprising: (a) Preparation of antibacterial modified support grid: The support grid is a hydrophilic nonwoven fabric or polyester screen, and the antibacterial modified support grid is made of nano Ag, nano TiO ２ A modified support grid was prepared by the following method: nano Ag in a mass percentage of 0.1-0.5 wt. %, nano TiO ２ a mass percentage of 0.2-1 wt. % of the polyvinyl alcohol in an aqueous solution of 2-8 wt. %, and ultrasonically dispersing the mixture to prepare a suspension, and then immersing a support grid in the suspension and drying it; (b) preparing a casting solution: mixing a hydrophilic polymer in an aqueous solvent system to prepare a casting solution; (c) pouring the casting solution prepared in step (b) onto a glass plate covered with the antibacterial modified support grid prepared in step (a) to obtain an initial forward osmosis membrane having a specific thickness; (d) treating the outer layer of the initial forward osmosis membrane to remove the solvent and form a dense skin layer on the outer layer of the initial forward osmosis membrane to obtain a second initial forward osmosis membrane; (e) forming a phase separation membrane or an interface membrane on the second initial forward osmosis membrane to obtain the forward osmosis membrane; Including, The average particle size of the nano Ag is 20 nm, and the nano TiO ２ The average particle size of the forward osmosis membrane is 5-10 nm, and when 0.5 mol / L sodium chloride and 0.01 mol / L magnesium sulfate are used as the draw and feed liquids, respectively, the membrane permeation flux is 8-13 L / (m ２ *h), wherein the rejection rate of magnesium sulfate is greater than 97%.

7. 7. The method of claim 6, wherein the thickness of the support grid is 30 μm-80 μm, the pore size is 100-200 mesh, and the thickness of the forward osmosis membrane is 50 μm-100 μm.

8. 8. The method of claim 7, wherein the support grid has a thickness of 30 μm, 50 μm, or 70 μm, a pore size of 100 mesh, 120 mesh, or 150 mesh, and the forward osmosis membrane has a thickness of 50 μm, 70 μm, or 100 μm.

9. 9. The method according to claim 6, wherein the hydrophilic polymer material is at least one of polyacrylonitrile, polyacrylate, polymethyl methacrylate, cellulose acetate, cellulose triacetate, polyvinyl alcohol, polyethylene oxide, and polyvinyl acetate.

10. The method further includes the following steps: (b-1) degassing the cast liquid obtained in step (b); The step (c) further comprises pouring the casting liquid degassed in the step (b-1) onto a glass plate on which a hydrophilic support grid is placed, and using a film applicator to produce an initial forward osmosis membrane having a specific thickness; In the outer layer treatment and solvent removal step (d), the obtained initial forward osmosis membrane is left standing in air to volatilize the solvent and form a dense skin layer on the outer layer; In the step (e), the second initial forward osmosis membrane is immersed in deionized water to gel and undergo phase separation to form a membrane; (f) immersing the forward osmosis membrane obtained in step (e) in deionized water to remove residual organic solvent; (g) removing the forward osmosis membrane, rinsing it with deionized water, and storing it in a solution of sodium metabisulfite until use;

11. 11. The method of claim 10, wherein the hydrophilic support grid is a polyester screen having a thickness of 30 μm, 50 μm, or 70 μm and a pore size of 100 mesh, 120 mesh, or 150 mesh, and is used after being pre-cleaned. In the pre-cleaning step, the polyester screen is immersed in 10% sodium hydroxide or 2% hydrochloric acid for 1 hour to remove impurities adsorbed on the surface, and then rinsed with deionized water, dried, and stored. The initial forward osmosis membrane produced by the film applicator has a thickness of 30 μm to 100 μm.

12. 12. The method of claim 11, wherein in step (b) of the method, the mixing conditions are to mix uniformly by stirring at a temperature of 30-50°C for 12-48 hours, the degassing method is to leave the mixture to stand for 12-36 hours to fully degas, or to use ultrasonic waves to assist the degassing, and the standing in air conditions are to leave the mixture to stand in an environment with a temperature of 25°C or less and a humidity of 90% or more for 30-90 seconds to form a dense skin layer; in step (f) of the method, before immersing the membrane in deionized water, the membrane is placed in a water bath at 40-50°C for 5-20 minutes for heat treatment, and then immersed in deionized water for 12-36 hours to remove residual organic solvents; and in step (g) of the method, the concentration of sodium metabisulfite is 0.5-2%.

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