A modified polyamide forward osmosis composite membrane resistant to biofouling, its preparation method and application

Abstract

This invention belongs to the field of membrane preparation technology, specifically relating to a modified polyamide forward osmosis composite membrane with anti-biofouling properties, its preparation method, and its application. This invention uses lignin-silver hybrid nanoparticles with an internal silver core and an external lignin shell to modify the polyamide membrane. The electronegative groups on the lignin endow the surface of the lignin-silver hybrid nanoparticles with abundant negatively charged groups, such as carboxyl and hydroxyl groups. After loading these nanoparticles onto the polyamide membrane, the nanoparticles are less prone to aggregation, and the membrane surface is negatively charged, repelling negatively charged bacteria and achieving an anti-adsorption effect. Silver decomposes in water to release silver ions, and the redox reaction of lignin on silver also releases electrons, generating hydroxyl radicals and other oxidizing groups, thereby achieving an antibacterial effect. The hydroxyl groups on the surface of the lignin-silver hybrid nanoparticles also improve the hydrophilicity of the polyamide membrane and increase water flux.

Description

Technical Field

[0001] This invention belongs to the field of membrane preparation technology, specifically relating to a modified polyamide forward osmosis composite membrane resistant to biofouling, its preparation method, and its application. Background Technology

[0002] Forward osmosis, as an emerging membrane process, is a desalination technology with lower energy consumption and lower cost. It uses the osmotic pressure difference across the membrane as the driving force to achieve the spontaneous diffusion of water from the feed liquid to the driving liquid. This spontaneous process, which does not require any external energy, has attracted the attention of many researchers and has broad application prospects in medical, food and agricultural irrigation fields.

[0003] Polyamide composite membranes are commonly used forward osmosis membranes. They are prepared by the interfacial polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC) to form a dense, heterogeneous active layer on a substrate. However, the rough surface and typical ridge-valley morphology of polyamide composite membranes, while imparting permeability and selectivity, also make them highly susceptible to fouling, especially biofouling, which severely affects membrane flux and lifespan. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a modified polyamide forward osmosis composite membrane with anti-biofouling properties, its preparation method and application. The modified polyamide forward osmosis composite membrane prepared by this method has excellent anti-fouling ability and good water flux.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a modified polyamide forward osmosis composite membrane resistant to biofouling, comprising the following steps:

[0007] A dispersion comprising lignin-silver hybrid nanoparticles and an aqueous solution of m-phenylenediamine is coated onto one side of a polysulfone-based membrane to modify it, thereby obtaining a lignin-silver hybrid nanoparticle-modified base membrane. The lignin-silver hybrid nanoparticle-modified base membrane includes a modified surface and an unmodified surface. The lignin-silver hybrid nanoparticles include a silver elemental core and a lignin shell chemically bonded to the silver elemental core.

[0008] A pyromellitic methyl chloride solution was coated onto the modified surface of the lignin-silver hybrid nanoparticle modified base membrane, and a polymerization reaction was carried out to obtain a modified polyamide forward osmosis composite membrane.

[0009] Preferably, the preparation method of the lignin-silver hybrid nanoparticles includes the following steps:

[0010] A silver salt aqueous solution and ammonia water were mixed to obtain a silver ammonia complex suspension;

[0011] The lignin alkaline solution and the silver ammonia complex suspension were mixed and subjected to a redox reaction to obtain lignin-silver hybrid nanoparticles.

[0012] Preferably, the redox reaction is carried out at room temperature for 1 to 5 hours.

[0013] Preferably, the mass ratio of lignin-silver hybrid nanoparticles to m-phenylenediamine in the dispersion is 2.25 to 18:1.

[0014] Preferably, the mass concentration of the intermediate-phenylenediamine in the aqueous solution of m-phenylenediamine is 2-3%.

[0015] Preferably, the modification time is 1 to 2 minutes.

[0016] Preferably, the solvent of the trimesoyl chloride solution is n-hexane; the mass concentration of trimesoyl chloride in the trimesoyl chloride solution is 0.15-0.2%; and the mass ratio of trimesoyl chloride to m-phenylenediamine in the trimesoyl chloride solution is 0.067-0.075:1.

[0017] Preferably, the polymerization reaction is carried out at room temperature for 60–90 seconds.

[0018] The present invention also provides a modified polyamide forward osmosis composite membrane for resisting biofouling prepared by the preparation method described above, comprising a polysulfone-based membrane and a modified polyamide membrane loaded on one side of the polysulfone-based membrane, wherein the modified polyamide membrane comprises a polyamide-based membrane and lignin-silver hybrid nanoparticles dispersed and fixed in the polyamide-based membrane.

[0019] The present invention also provides the application of the modified polyamide forward osmosis composite membrane with anti-biofouling properties described above in desalination.

[0020] This invention provides a method for preparing a modified polyamide forward osmosis composite membrane resistant to biofouling, comprising the following steps: coating a dispersion comprising lignin-silver hybrid nanoparticles and an aqueous solution of m-phenylenediamine onto one side of a polysulfone-based membrane for modification, thereby obtaining a lignin-silver hybrid nanoparticle modified base membrane, wherein the lignin-silver hybrid nanoparticle modified base membrane comprises a modified surface and an unmodified surface; the lignin-silver hybrid nanoparticles comprise a silver elemental core and a lignin shell chemically bonded to the silver elemental core; coating the modified surface of the lignin-silver hybrid nanoparticle modified base membrane with a trimesoyl chloride solution for polymerization reaction, thereby obtaining the modified polyamide forward osmosis composite membrane. This invention utilizes lignin-silver hybrid nanoparticles, with an internal silver core and an external lignin shell, to modify polyamide membranes. The electronegative groups on the lignin endow the surface of the lignin-silver hybrid nanoparticles with abundant negatively charged groups, such as carboxyl and hydroxyl groups, making them negatively charged and exhibiting good dispersibility. Therefore, after loading the lignin-silver hybrid nanoparticles onto the polyamide membrane, the nanoparticles are not prone to aggregation, and the negatively charged membrane surface can repel negatively charged bacterial surfaces, achieving an anti-adsorption effect. Silver can decompose into trace amounts of silver ions in water. These silver ions can adsorb microorganisms in the water, rendering the enzymes on which microorganisms depend for respiration inactive. The redox reaction of lignin on silver also releases electrons, generating hydroxyl radicals and other oxidizing groups, thereby achieving an antibacterial effect. In addition, the hydroxyl groups on the surface of the lignin-silver hybrid nanoparticles can undergo esterification with the acyl chloride groups of trimesoyl chloride to generate ester groups, thus fixing them in the polyamide membrane. Furthermore, the hydroxyl groups on the surface of the lignin-silver hybrid nanoparticles can also improve the hydrophilicity of the polyamide membrane and increase water flux. Attached Figure Description

[0021] Figure 1 SEM images of the polysulfone-based membrane, the modified polyamide forward osmosis composite membrane prepared in Examples 1 and 4 of this invention;

[0022] Figure 2 AFM characterization diagrams of the modified polyamide forward osmosis composite membranes prepared in Examples 1-4 of this invention and the polyamide membrane prepared in Comparative Example 1;

[0023] Figure 3 The water contact angle diagrams are shown for the modified polyamide forward osmosis composite membranes prepared in Examples 1-4 of this invention and the polyamide membrane prepared in Comparative Example 1.

[0024] Figure 4 The Zeta potential diagrams are of the modified polyamide forward osmosis composite membranes prepared in Examples 1-4 of this invention and the polyamide membrane prepared in Comparative Example 1.

[0025] Figure 5 The images show the antibacterial test results of the modified polyamide forward osmosis composite membranes prepared in Examples 1-4 of this invention and the polyamide membrane prepared in Comparative Example 1.

[0026] Figure 6 The diagram shows the basic permeation performance of the modified polyamide forward osmosis composite membranes prepared in Examples 1-4 of this invention and the polyamide membrane prepared in Comparative Example 1. Detailed Implementation

[0027] This invention provides a method for preparing a modified polyamide forward osmosis composite membrane resistant to biofouling, comprising the following steps:

[0028] A dispersion comprising lignin-silver hybrid nanoparticles and an aqueous solution of m-phenylenediamine is coated onto one side of a polysulfone-based membrane to modify it, thereby obtaining a lignin-silver hybrid nanoparticle-modified base membrane. The lignin-silver hybrid nanoparticle-modified base membrane includes a modified surface and an unmodified surface. The lignin-silver hybrid nanoparticles include a silver elemental core and a lignin shell chemically bonded to the silver elemental core.

[0029] A pyromellitic methyl chloride solution was coated onto the modified surface of the lignin-silver hybrid nanoparticle modified base membrane, and a polymerization reaction was carried out to obtain a modified polyamide forward osmosis composite membrane.

[0030] Unless otherwise specified, the present invention does not have special requirements on the source of the raw materials used in the preparation, and commercially available products well known to those skilled in the art can be used.

[0031] The present invention modifies a polysulfone-based membrane by coating a dispersion comprising lignin-silver hybrid nanoparticles and an aqueous solution of m-phenylenediamine onto one side of the membrane to obtain a lignin-silver hybrid nanoparticle modified base membrane.

[0032] In this invention, the lignin-silver hybrid nanoparticles have a particle size distribution of 50-60 nm and include a silver elemental core and a lignin shell chemically bonded to the silver elemental core.

[0033] In this invention, the preparation method of the lignin-silver hybrid nanoparticles includes the following steps:

[0034] A silver salt aqueous solution and ammonia water were mixed to obtain a silver ammonia complex suspension;

[0035] The lignin alkaline solution and the silver ammonia complex suspension were mixed and subjected to a redox reaction to obtain lignin-silver hybrid nanoparticles.

[0036] This invention involves mixing an aqueous solution of silver salts with ammonia water to obtain a silver ammonia complex suspension.

[0037] In this invention, the silver salt in the silver salt aqueous solution preferably includes silver nitrate; the mass concentration of the silver salt aqueous solution is preferably 0.0157-0.02 g / mL, more preferably 0.0157 g / mL; and the mass concentration of the ammonia water is preferably 5-7%, more preferably 5%.

[0038] In this invention, the mixing process of the silver salt aqueous solution and ammonia water is preferably to add the silver salt aqueous solution to the ammonia water.

[0039] After obtaining the silver ammonia complex suspension, the present invention mixes the lignin alkaline solution and the silver ammonia complex suspension to carry out a redox reaction to obtain lignin-silver hybrid nanoparticles.

[0040] In this invention, the mass concentration of lignin in the alkaline lignin solution is preferably 0.05–0.06 g / mL, more preferably 0.05 g / mL; the preparation process of the alkaline lignin solution is preferably to mix lignin and the alkaline solution and then perform ultrasonic dissolution; the lignin is preferably sulfate lignin; the ultrasonic dissolution power is preferably 40–60 W, more preferably 40–50 W; the ultrasonic dissolution time is preferably 2–3 min, more preferably 3 min; the alkaline solution is preferably a sodium hydroxide solution; the mass concentration of the sodium hydroxide solution is preferably 7.6–8%, more preferably 7.6%; the mass ratio of lignin to silver salt in the silver salt aqueous solution in the alkaline lignin solution is preferably 6–25:1, more preferably 10–25:1.

[0041] In this invention, the mixing process of the lignin alkaline solution and the silver ammonia complex suspension is preferably carried out under stirring conditions, by adding the lignin alkaline solution dropwise to the silver ammonia complex suspension; the stirring is preferably magnetic stirring; the stirring rate is preferably 500-800 r / min, more preferably 500-700 r / min.

[0042] In this invention, the temperature of the redox reaction is preferably room temperature, and the time is preferably 1 to 5 hours, more preferably 1 to 3 hours; the redox reaction is preferably carried out under stirring conditions; the stirring is preferably magnetic stirring; the stirring rate is preferably 500 to 800 r / min, more preferably 500 to 700 r / min.

[0043] This invention utilizes lignin to reduce silver ions in an aqueous solution of silver salts, generating lignin-silver hybrid nanoparticles with a core-shell structure of elemental silver and an outer layer of lignin. The silver core can continuously release silver ions and penetrate the lignin shell to affect bacterial cells. Conversely, the oxidatively active groups (quinone and semiquinone free radicals) dispersed on the outer shell surface may induce oxidative stress, a significant pathway accelerating bacterial death. The electronegative groups on lignin endow the surface of the lignin-silver hybrid nanoparticles with abundant negatively charged groups, such as carboxyl and hydroxyl groups, making them negatively charged and possessing good dispersibility. Therefore, when lignin-silver hybrid nanoparticles are loaded onto a polyamide membrane, the nanoparticles are less prone to aggregation, and the membrane surface becomes negatively charged, repelling the negatively charged bacterial surface and achieving an anti-adsorption effect. Furthermore, silver decomposes in water to release trace amounts of silver ions, which can adsorb microorganisms in the water, rendering their respiration enzymes inactive. The redox reaction of lignin on silver also releases electrons, generating oxidizing groups such as hydroxyl free radicals, thereby achieving an antibacterial effect. In addition, the hydroxyl groups on the surface of lignin-silver hybrid nanoparticles can improve the hydrophilicity of polyamide membranes and increase water flux.

[0044] After the redox reaction, the present invention preferably further includes: dialysis of the redox reaction product in water, wherein the molecular weight cutoff of the dialysis bag is 1000; the dialysis time is preferably 3-5 days, more preferably 3-4 days.

[0045] The present invention removes the solvent used in the redox reaction process by dialysis of the redox reaction product in water.

[0046] In this invention, the lignin-silver hybrid nanoparticles comprise a silver elemental core and a lignin shell chemically bonded to the silver elemental core.

[0047] After obtaining the lignin-silver hybrid nanoparticles, the present invention preferably mixes the lignin-silver hybrid nanoparticles with an aqueous solution of m-phenylenediamine to obtain a dispersion comprising the lignin-silver hybrid nanoparticles and the aqueous solution of m-phenylenediamine.

[0048] In this invention, the diamine in the aqueous diamine solution preferably includes m-phenylenediamine; the mass concentration of m-phenylenediamine in the aqueous diamine solution is preferably 2-3%, more preferably 2%; the mass concentration of lignin-silver hybrid nanoparticles in the dispersion is preferably 4.5-400 mg / L, more preferably 50-400 mg / L; the mass ratio of lignin-silver hybrid nanoparticles to m-phenylenediamine in the dispersion is preferably 2.25-18:1, more preferably 10-18:1.

[0049] The present invention does not have any particular limitation on the mixing process of the lignin-silver hybrid nanoparticles and the diamine aqueous solution; a mixing process well known in the art can be used to ensure that the materials are mixed evenly.

[0050] After obtaining the dispersion, the present invention coats the dispersion onto one side of a polysulfone-based membrane for modification, thereby obtaining a lignin-silver hybrid nanoparticle modified base membrane.

[0051] In this invention, the polysulfone-based membrane is preferably modified by immersing one side of it in the dispersion; the volume of dispersion adsorbed by the polysulfone-based membrane per square centimeter is preferably 40-50 mL, more preferably 45-50 mL; and the modification time is preferably 1-2 min, more preferably 2 min.

[0052] In this invention, the lignin-silver hybrid nanoparticle modified base film includes a modified surface and an unmodified surface.

[0053] After obtaining the lignin-silver hybrid nanoparticle modified base membrane, the present invention coats the surface of the lignin-silver hybrid nanoparticle modified base membrane with a trimesoyl chloride solution and carries out a polymerization reaction to obtain a modified polyamide forward osmosis composite membrane resistant to biofouling.

[0054] In this invention, the solvent of the trimesoyl chloride solution is preferably n-hexane; the mass concentration of trimesoyl chloride in the trimesoyl chloride solution is preferably 0.15-0.2%, more preferably 0.15%; the mass ratio of trimesoyl chloride to m-phenylenediamine in the trimesoyl chloride solution is preferably 0.067-0.075:1, more preferably 0.07-0.075:1; the polymerization reaction temperature is preferably room temperature, and the time is preferably 60-90 s, more preferably 60-80 s.

[0055] In this invention, the pyromellitic methyl chloride solution is preferably poured onto the surface of the lignin-silver hybrid nanoparticle modified base film; the volume of pyromellitic methyl chloride solution adsorbed on the surface of the lignin-silver hybrid nanoparticle modified base film per square centimeter is preferably 20-30 mL, more preferably 20-25 mL.

[0056] After the polymerization reaction is completed, the present invention preferably removes excess trimesoyl chloride solution from the surface of the lignin-silver hybrid nanoparticle modified base membrane, and then heat-treats the lignin-silver hybrid nanoparticle modified base membrane (to enhance the interaction between the base membrane and the polyamide active layer and to volatilize excess n-hexane solution from the membrane surface) to obtain a modified polyamide forward osmosis composite membrane resistant to biofouling.

[0057] In this invention, the heat treatment temperature is preferably 60-80°C, more preferably 60-70°C; the heat treatment time is preferably 10-15 min, more preferably 10-12 min; and the heat treatment equipment is preferably an oven.

[0058] The present invention preferably involves immersing the biofouling-resistant modified polyamide forward osmosis composite membrane in deionized water to remove residual solvent from its surface.

[0059] This invention generates a polyamide active layer on the surface of a polysulfone-based membrane through an interfacial polymerization reaction between diamine and trimesoyl chloride. The hydroxyl groups on the surface of the lignin-silver hybrid nanoparticles can undergo esterification with the acyl chloride groups of trimesoyl chloride to form ester groups, thereby immobilizing them within the polyamide membrane.

[0060] The present invention also provides a modified polyamide forward osmosis composite membrane for resisting biofouling prepared by the preparation method described above, comprising a polysulfone-based membrane and a modified polyamide membrane loaded on one side of the polysulfone-based membrane, wherein the modified polyamide membrane comprises a polyamide-based membrane and lignin-silver hybrid nanoparticles dispersed and fixed in the polyamide-based membrane.

[0061] In this invention, the preferred loading amount of lignin-silver hybrid nanoparticles on the surface of the modified polyamide forward osmosis composite membrane is 0.01–0.08 mg / cm³. 2 More preferably, it is 0.05–0.08 mg / cm³. 2 .

[0062] The present invention also provides the application of the modified polyamide forward osmosis composite membrane with anti-biofouling properties described above in desalination.

[0063] The present invention does not impose any particular limitation on the application of the modified polyamide forward osmosis composite membrane with anti-biofouling properties in desalination; any application method known in the art may be used.

[0064] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments thereof, but they should not be construed as limiting the scope of protection of the present invention.

[0065] Example 1

[0066] 0.2 g of sulfate lignin was dissolved in 4 mL of 5 wt.% sodium hydroxide solution and sonicated at 40 W for 1 min to obtain an alkaline lignin solution. 0.314 g of silver nitrate was dissolved in 20 mL of pure water to obtain a silver nitrate solution. 5 mL of the silver nitrate solution was slowly added to 2.5 mL of 7.6 wt.% ammonia water to obtain a silver ammonia complex suspension. Under magnetic stirring at 500 r / min, the alkaline lignin solution was added dropwise to the silver ammonia complex suspension, and after stirring for 1 h, the mixture was dialyzed in deionized water for 3 days to obtain lignin-silver hybrid nanoparticles (Lig-AgNPs). 4.5 mL of the Lig-AgNPs was added to a 2 wt.% m-phenylenediamine aqueous solution to obtain a dispersion (where the mass concentration of Lig-AgNPs was 45 mg / mL). After immersing the polysulfone-based membrane in the dispersion for 2 minutes on one side, 20 mL of a 0.15 wt.% hexane solution containing trimesoyl chloride was uniformly poured onto the membrane surface. The polymerization reaction was carried out for 60 seconds, after which the excess solution was discarded. Finally, the membrane was transferred to a 60°C oven for heat treatment for 10 minutes. The membrane was then removed to obtain a modified polyamide forward osmosis composite membrane with anti-biofouling properties (calculated as TFC-0.01, wherein the loading of lignin-silver hybrid nanoparticles was 0.01 mg / cm³). 2 Soak it in deionized water for later use.

[0067] Example 2

[0068] The difference from Example 1 is that the mass concentration of Lig-AgNPs in the dispersion in Example 1 was replaced from 4.5 mg / L to 100 mg / L, and the loading of lignin-silver hybrid nanoparticles on the modified polyamide forward osmosis composite membrane (TFC-0.02) prepared in Example 1 was 0.02 mg / cm³. 2 The rest of the content is the same as in Example 1.

[0069] Example 3

[0070] The difference from Example 1 is that the mass concentration of Lig-AgNPs in the dispersion in Example 1 was replaced from 100 mg / L to 200 mg / L. The resulting modified polyamide forward osmosis composite membrane (TFC-0.04) had a lignin-silver hybrid nanoparticle loading of 0.04 mg / cm³. 2 The rest of the content is the same as in Example 1.

[0071] Example 4

[0072] The difference from Example 1 is that the mass concentration of Lig-AgNPs in the dispersion in Example 1 was replaced from 200 mg / L to 400 mg / L. The resulting modified polyamide forward osmosis composite membrane (TFC-0.08) had a lignin-silver hybrid nanoparticle loading of 0.08 mg / cm³. 2 The rest of the content is the same as in Example 1.

[0073] Comparative Example 1

[0074] The difference from Example 1 is that the mass concentration of Lig-AgNPs in the dispersion in Example 1 was replaced with 0 instead of 4.5 mg / L, resulting in a lignin-silver hybrid nanoparticle loading of 0 mg / cm³ on the prepared polyamide film (TFC). 2 The rest of the content is the same as in Example 1.

[0075] Performance testing

[0076] (1) The polysulfone-based membrane, the modified polyamide forward osmosis composite membranes prepared in Examples 1 and 4 were tested using scanning electron microscopy, and the results are as follows: Figure 1 As shown, a is a polysulfone-based membrane, b is the modified polyamide forward osmosis composite membrane prepared in Example 1, and c is the modified polyamide forward osmosis composite membrane prepared in Example 4.

[0077] Depend on Figure 1 As can be seen from image a, the surface of the polysulfone-based film is relatively smooth, but after the polyamide active layer is formed through interfacial polymerization, the film surface begins to become very rough, such as... Figure 1 As shown in Figure b, the membrane surface has a very typical ridge-valley shape, which is consistent with the morphology of polyamide layers described in existing literature. However, by introducing Lig-AgNPs into the aqueous phase MPD, the surface of the polyamide composite membrane prepared by interfacial polymerization is different from that of the membrane without Lig-AgNPs. This difference in morphology is caused by the addition of a higher concentration of Lig-AgNPs.

[0078] (2) The modified polyamide forward osmosis composite membranes prepared in Examples 1-4 were tested using atomic force microscopy, and the results are as follows: Figure 2 As shown, d is the modified polyamide forward osmosis composite membrane prepared in Comparative Example 1, e is the modified polyamide forward osmosis composite membrane prepared in Example 1, f is the modified polyamide forward osmosis composite membrane prepared in Example 2, g is the modified polyamide forward osmosis composite membrane prepared in Example 3, and h is the modified polyamide forward osmosis composite membrane prepared in Example 4.

[0079] Depend on Figure 2It can be seen that as the amount of Lig-AgNPs added increases, the surface roughness of the membrane gradually increases, and at the highest concentration, the surface roughness of the membrane is almost twice that of the original membrane. The possible reasons for this difference are: (1) At higher concentrations, lignin-silver hybrid nanoparticles will inhibit the interfacial polymerization reaction and change the surface morphology and roughness of the membrane; (2) The prepared membrane samples are not uniform, resulting in different roughnesses with large differences.

[0080] (3) The water contact angles of the modified polyamide forward osmosis composite membranes prepared in Examples 1-4 and the polyamide membrane prepared in Comparative Example 1 were measured. The specific testing method involved cutting a 1×2cm membrane sample, placing it flat, and then using an automatic dropper to measure the contact angle. The drop volume was 2-3 μL. The test results are as follows: Figure 3 As shown.

[0081] Depend on Figure 3 It can be seen that adding Lig-AgNPs can reduce the water contact angle of the membrane, and as the amount of Lig-AgNPs added increases, the water contact angle of the composite membrane gradually decreases, which is related to the fact that the introduced Lig-AgNPs are rich in hydrophilic groups.

[0082] (4) The Zeta potentials of the modified polyamide forward osmosis composite membranes prepared in Examples 1-4 and the polyamide membrane prepared in Comparative Example 1 were measured. Specifically, the Zeta potentials were measured using a solid surface Zeta potential meter within different pH ranges. The test results are as follows: Figure 4 As shown.

[0083] Depend on Figure 4 It can be seen that with the increase of Lig-AgNPs addition, the surface electronegativity of the modified polyamide positive osmosis composite membrane is enhanced, which is related to the increase of hydroxyl and other groups in Lig-AgNPs. The addition of Lig-AgNPs can enhance the anti-adsorption performance of the modified polyamide positive osmosis composite membrane by changing the hydrophilicity and zeta potential of the composite membrane.

[0084] (5) Antibacterial tests were conducted on the modified polyamide forward osmosis composite membranes prepared in Examples 1-4 and the polyamide membrane prepared in Comparative Example 1. The specific test method was as follows: *Pseudomonas aeruginosa* was initially cultured in LB medium for 16 hours until it reached the exponential growth stage. After washing away the culture medium, the membrane was resuspended in synthetic wastewater to 10 mL. A 1.5 cm × 1.5 cm membrane was placed in 10 mL of *Pseudomonas aeruginosa* suspension at 37°C. The membrane was removed at different times (0, 3, 6, 12, 24 hours) and gently rinsed three times. Unattached cells were removed using sterile synthetic wastewater. Bacteria attached to the membrane were removed by sonication and vortexing in 10 mL of synthetic wastewater. After appropriate dilution, the membrane was plated and incubated at 37°C for 24 hours before colony counting. The test results are as follows: Figure 5As shown.

[0085] Depend on Figure 5 It can be seen that as the amount of Lig-AgNPs added increases, the number of bacteria adhering to the modified polyamide forward osmosis composite membrane gradually decreases. The number of bacteria on the surface of the polyamide membrane without Lig-AgNPs is always higher than that of the modified polyamide forward osmosis composite membrane with Lig-AgNPs added. This indicates that the modified polyamide forward osmosis composite membrane with Lig-AgNPs added has a better antibacterial effect.

[0086] (6) The modified polyamide forward osmosis composite membranes prepared in Examples 1-4 and the polyamide membrane prepared in Comparative Example 1 were tested using a forward osmosis testing device to assess their basic permeation performance (water flux and salt rejection rate). The specific testing method was as follows: deionized water was used as the raw material, and a 1 mol / L sodium chloride aqueous solution was used as the driving fluid. The feed and driving fluid were convected, and the flow rates of the feed liquid on both sides of the membrane were 350 ml / min. The operation was performed in AL-DS mode. Under the influence of the osmotic pressure difference, pure water in the feed solution continuously diffused into the driving fluid. An electronic balance was used to monitor the mass change of the feed solution, thereby obtaining the water flux of the FO membrane. The test results are as follows: Figure 6 As shown.

[0087] Depend on Figure 6 It can be seen that with the increase of Lig-AgNPs addition, the water flux of the modified polyamide forward osmosis composite membrane shows a trend of first increasing and then decreasing, with the addition amount being 0.02 mg / cm³. 2 The water flux reached its maximum at that time and then began to decline. This was mainly because excessive addition would cause Lig-AgNPs to accumulate on the membrane surface, increasing the resistance to water molecule permeation and ultimately leading to a decrease in water flux.

[0088] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a modified polyamide forward osmosis composite membrane resistant to biofouling, characterized in that, Includes the following steps: A dispersion comprising lignin-silver hybrid nanoparticles and an aqueous solution of m-phenylenediamine is coated onto one side of a polysulfone-based membrane to modify it, thereby obtaining a lignin-silver hybrid nanoparticle-modified base membrane, wherein the lignin-silver hybrid nanoparticle-modified base membrane comprises a modified surface and an unmodified surface. The lignin-silver hybrid nanoparticles comprise a silver elemental core and a lignin shell chemically bonded to the silver elemental core. A pyromellitic methyl chloride solution was coated onto the modified surface of the lignin-silver hybrid nanoparticle modified base membrane, and a polymerization reaction was carried out to obtain a modified polyamide forward osmosis composite membrane. The mass ratio of lignin-silver hybrid nanoparticles to m-phenylenediamine in the dispersion is 2.25–18:1; The mass ratio of pyromellitic methyl methacrylate (PMMC) in the PMMC solution to that in the m-phenylenediamine solution is 0.067–0.075:

1. The preparation method of the lignin-silver hybrid nanoparticles includes the following steps: A silver salt aqueous solution and ammonia water were mixed to obtain a silver ammonia complex suspension; A lignin alkaline solution and the silver ammonia complex suspension were mixed and subjected to a redox reaction to obtain lignin-silver hybrid nanoparticles. The lignin is sulfate lignin; The mass ratio of lignin to silver salt in the alkaline lignin solution is 6–25:

1.

2. The preparation method according to claim 1, characterized in that, The redox reaction was carried out at room temperature for 1–5 hours.

3. The preparation method according to claim 1, characterized in that, The mass concentration of the intermediate-phenylenediamine in the aqueous solution of m-phenylenediamine is 2-3%.

4. The preparation method according to claim 1, characterized in that, The modification time is 1 to 2 minutes.

5. The preparation method according to claim 1, characterized in that, The solvent of the trimesoyl chloride solution is n-hexane; the mass concentration of trimesoyl chloride in the trimesoyl chloride solution is 0.15-0.2%.

6. The preparation method according to claim 1 or 5, characterized in that, The polymerization reaction was carried out at room temperature for 60–90 seconds.

7. The modified polyamide forward osmosis composite membrane with anti-biofouling properties prepared by the preparation method according to any one of claims 1 to 6, characterized in that, It includes a polysulfone-based membrane and a modified polyamide membrane loaded on one side of the polysulfone-based membrane, wherein the modified polyamide membrane includes the polyamide-based membrane and lignin-silver hybrid nanoparticles dispersed and fixed in the polyamide-based membrane.

8. The application of the biofouling-resistant modified polyamide forward osmosis composite membrane as described in claim 7 in desalination.

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