A g-c3n4 modified polyether sulfone filter membrane and a preparation method thereof

Abstract

The application provides a preparation method of g-C3N4 modified polyether sulfone filter membrane, comprising the following steps: S1, preparing g-C3N4 material: taking urea as a precursor, adopting a thermal condensation method to heat, and keeping warm for a period of time, and after cooling, pre-grinding and screening are carried out to obtain g-C3N4 powder; S2, modifying g-C3N4: the g-C3N4 powder prepared in S1 is configured into g-C3N4 water dispersion liquid, then ultrasonic treatment is carried out for a period of time, natural sedimentation is carried out, and the supernatant is taken; polyphenol small molecules and alkali liquor are added into the supernatant to react, then tobramycin is added to react, and after centrifugation, dispersion and freeze-drying, the modified g-C3N4 is obtained; S3, modifying polyether sulfone filter membrane: polyether sulfone, the modified g-C3N4 and an organic solvent are uniformly mixed, heated and stirred for a period of time until completely dissolved, then stirring, degassing are continued until no bubbles are observed, and the casting solution is obtained; the casting solution is formed into a film under certain conditions, and the modified polyether sulfone filter membrane is obtained; the preparation method can improve the hydrophilic property and the anti-pollution property of the filter membrane, and more importantly, the antibacterial property of the film is strengthened.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and more specifically, to a g-C3N4 modified polyethersulfone film and its preparation method. Background Technology

[0002] Membrane technology has been widely used in wastewater treatment due to its environmental friendliness, low cost, and economic advantages. However, biofouling remains a significant challenge in membrane applications. Irreversible fouling caused by bacterial adhesion and biofilm formation is a major limitation to the long-term use of membranes. Bacteria and released extracellular polymeric substances can clog membrane pores and form a concentrated layer of contaminants, leading to a significant reduction in membrane permeability. Polyethersulfone (PES), as a high-performance polymer material, possesses good chemical stability, thermal stability, acid and alkali resistance, and oxidation resistance. It has been widely used in ultrafiltration membrane applications. However, some shortcomings still exist: its surface is highly hydrophobic, making it prone to forming a membrane fouling layer, which reduces membrane performance and shortens its service life. Therefore, developing a highly hydrophilic and fouling-resistant polyethersulfone filter membrane has become an important research direction recently.

[0003] For example, Chinese patent CN109499393A discloses a method for preparing a superhydrophilic PVDF oil-water separation membrane. This method involves grafting aminated nanoparticles onto the surface of a plasma-treated hydrophobic PVDF membrane, followed by further grafting of polyamine polymers onto the PVDF membrane surface. However, surface chemical treatment can easily damage the membrane surface structure, leading to a decrease in membrane performance. Furthermore, it fails to improve the hydrophilicity of the membrane's interior and requires sophisticated equipment and is cumbersome to operate.

[0004] Furthermore, because the polyethersulfone molecule contains polar functional groups (such as -SO2), - -CO - (etc.). Therefore, in terms of molecular structure, polyethersulfone (PES) membranes possess a certain degree of hydrophilicity. However, due to their long molecular chains and strong intermolecular interactions, PES membranes exhibit hydrophobic properties under conditions of high surface tension. Furthermore, irreversible membrane fouling caused by bacterial adhesion and biofouling during application is the main limitation preventing the long-term use of PES membranes. Membrane fouling occurs when bacteria and microbial communities can grow on the surface of the PES membrane, forming a biofilm, which can lead to membrane fouling. Membrane clogging occurs when biocolloids and extracellular polymers produced by microorganisms adhere to the membrane pores, causing blockage. Membrane clogging restricts water permeability, increases operating pressure, and reduces membrane lifespan.

[0005] In summary, the interaction between polyethersulfone (PES) membranes and bacteria in wastewater treatment can lead to a series of technical problems such as membrane fouling and clogging, which in turn affect the use of PES membranes. Therefore, it is necessary to improve them. Summary of the Invention

[0006] The purpose of this invention is to provide a g-C3N4 modified polyethersulfone filter membrane and its preparation method, which can improve the hydrophilicity and antifouling properties of the filter membrane, and more importantly, enhance the antibacterial properties of the membrane.

[0007] The embodiments of the present invention are achieved through the following technical solutions:

[0008] A method for preparing a g-C3N4 modified polyethersulfone filter membrane includes the following steps:

[0009] S1. Preparation of g-C3N4 material: Using urea as a precursor, the material is heated by thermal shrinkage and kept at that temperature for a period of time. After cooling, it is pre-ground and sieved to obtain g-C3N4 powder.

[0010] S2. Modified g-C3N4: The g-C3N4 powder prepared in S1 was prepared into an aqueous dispersion of g-C3N4. After continuous sonication for a period of time, it was allowed to settle naturally and the supernatant was collected. Polyphenolic small molecules and alkaline solution were added to the supernatant for reaction, and then tobramycin was added for reaction. After centrifugation, dispersion and freeze-drying, modified g-C3N4 was obtained.

[0011] S3. Modified polyethersulfone filter membrane: After mixing polyethersulfone, modified g-C3N4 and organic solvent, heat and stir for a period of time until completely dissolved, continue stirring and degassing until no bubbles are visible, and the casting solution is obtained; the casting solution is then used to form a membrane under certain conditions to obtain the modified polyethersulfone filter membrane.

[0012] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects:

[0013] This invention introduces tobramycin onto the surface of g-C3N4, causing g-C3N4 to generate oxidizing active substances for sterilization under light irradiation. Simultaneously, the introduced tobramycin is released from the modified g-C3N4 under weakly acidic conditions, improving the material's biocompatibility and antibacterial properties. Furthermore, by blending modified g-C3N4 with polyethersulfone, this invention not only improves the hydrophilicity and antifouling properties of the filter membrane but also enhances its antibacterial properties. This gives the filter membrane of this invention significant technical advantages in wastewater treatment and separation, and is expected to bring higher efficiency, lower costs, and more sustainable operation to wastewater treatment systems. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 The images are SEM images of the filter membranes of Examples 1-6 of the present invention, magnified 5000x by scanning electron microscopy. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0017] The following is a detailed description of a g-C3N4 modified polyethersulfone filter membrane and its preparation method provided by an embodiment of the present invention.

[0018] A method for preparing a g-C3N4 modified polyethersulfone filter membrane includes the following steps:

[0019] S1. Preparation of g-C3N4 material: Using urea as a precursor, the temperature is raised by thermal shrinkage at a rate of 5-15℃ / min, held at 500-600℃ for 1-3 hours, and then pre-ground and sieved with an 80-120 mesh sieve to obtain g-C3N4 powder.

[0020] S2. Modified g-C3N4: The g-C3N4 powder prepared in S1 is subjected to ultrasonic exfoliation treatment, and a 0.1-2 mg / ml g-C3N4 aqueous dispersion is prepared. Then, it is continuously sonicated at a frequency of 30-60 kHz for 1-1.5 hours, and allowed to settle naturally. The supernatant is collected. Polyphenolic small molecules and alkaline solution are added to the supernatant for reaction, and then tobramycin is added for reaction. After centrifugation, dispersion, and freeze-drying, modified g-C3N4 is obtained.

[0021] By utilizing an alkaline solution to provide a weakly alkaline environment, the phenolic hydroxyl groups of polyphenols are oxidized to quinone structures, preparing for Schiff base reactions, Michael addition reactions, and hydrogen bonding among the three components. Tobramycin is then introduced onto the g-C3N4 surface to improve the antibacterial properties of the material.

[0022] S3. Modified polyethersulfone filter membrane: After mixing polyethersulfone, modified g-C3N4 and organic solvent, heat and stir for a period of time until the polymer is completely dissolved, continue stirring and degassing until no bubbles are visible, and the casting solution is obtained; the casting solution is then used to form a membrane under certain conditions to obtain the modified polyethersulfone filter membrane.

[0023] g-C3N4 possesses antibacterial properties, reducing the risk of biofouling on the membrane surface by inhibiting the growth of microorganisms and bacteria, thus enhancing the antibacterial performance of polyethersulfone membranes. This is crucial for controlling microorganisms, algae, and bacteria in wastewater treatment, helping to maintain membrane permeability and performance. To further enhance the performance of g-C3N4 and improve its biocompatibility, this invention involves nanoscale treatment and modification. Specifically, tobramycin is introduced onto the g-C3N4 surface through the physicochemical interactions (Michael addition, Schiff base reaction, and hydrogen bonding) of catechin, epigallocatechin gallate, and gallic acid. Under light irradiation, g-C3N4 generates oxidative active substances that kill bacteria, while the introduced tobramycin is released from the modified g-C3N4 under weakly acidic conditions, further enhancing the material's antibacterial properties. This invention, by blending modified g-C3N4 with polyethersulfone, not only improves the hydrophilicity and antifouling properties of the filter membrane but also strengthens its antibacterial performance. This gives the filter membrane of the present invention a significant technical advantage in the field of wastewater treatment and separation, and is expected to bring higher efficiency, lower cost and more sustainable operation to wastewater treatment systems.

[0024] Example 1

[0025] A g-C3N4 modified polyethersulfone membrane comprises the following components: 20g polyethersulfone, 100ml N,N-dimethylacetamide, 5ml catechin, 3.6g g-C3N4, and 70g urea.

[0026] The preparation method is as follows:

[0027] (1) Modification of nanoscale g-C3N4

[0028] The first step uses the heat shrinking method, a tubular furnace, urea as the precursor, a heating rate of 10℃ / min, holding at 550℃ for 2 hours, and cooling with the furnace at a cooling rate of 5℃ / min.

[0029]

[0030] The second step is pre-grinding. After preparation, carefully scrape the material with a spatula and pre-grind it in a mortar and pestle, collecting the ground product. Then, ball mill it together with 3mm zirconium ball milling beads at a speed of 300 rpm for 10 hours.

[0031] The third step is to sieve the powder using a 100-mesh sieve, set the pulse to F280, sieve for 3 minutes, and collect the powder for later use.

[0032] The fourth step involves ultrasonically exfoliating the prepared g-C3N4, preparing an aqueous dispersion of 1 mg / ml g-C3N4, continuously sonicating at 40 kHz for 1 hour, transferring it to a container for natural sedimentation for 24 hours, and then collecting the supernatant.

[0033] The fifth step involves modifying the prepared g-C3N4 by introducing tobramycin onto the g-C3N4 surface through the physicochemical interactions of catechins (Michael addition, Schiff base reaction, and hydrogen bonding).

[0034] Preparation of polyphenol / g-C3N4: Polyphenols and g-C3N4 were added to a round-bottom flask at a mass ratio of 1:1. 500 ml of g-C3N4 nano-dispersion (containing 150 mg g-C3N4) and 150 mg of catechin were added, and the mixture was stirred until homogeneous. The reaction conditions were 60℃, 600 rpm, and 24 hours. After the temperature reached 60℃, ammonia was added at 4 μL / mg of catechin and the reaction continued for 24 hours. Tobramycin was then added.

[0035] Preparation of polyphenol / g-C3N4@tobramycin: Add the three components in a round-bottom flask at a mass ratio of 1:1:1, add 150 mg of tobramycin, stir well, and react under the following conditions: 60℃, 600 rpm, 24 hours. Terminate the reaction after 24 hours.

[0036] Step 6: Transfer the reaction product to a 50ml centrifuge tube and centrifuge at 15000rpm for 5 minutes. Discard the supernatant and add water to balance the liquid. Repeat the above steps several times until a relatively clear supernatant is observed. Discard the supernatant and add an appropriate amount of deionized water to disperse it. Transfer the reaction product to a 10ml centrifuge tube and rapidly freeze it in liquid nitrogen. After freezing, open the cap, seal it with lint-free paper and secure it with rubber. Transfer it to a freeze dryer for freeze drying. After complete freeze drying, remove the centrifuge tube, remove the lint-free paper seal, and vortex to disperse the product for later use.

[0037] (2) Solution spinning

[0038] Polyethersulfone, modified nano-sized g-C3N4, and N,N-dimethylacetamide were added sequentially to a three-necked flask and heated to 70°C while stirring at 500 rpm using a digital hot plate. After the polymer was completely dissolved and stirred for at least 24 hours, the resulting solution was degassed without mixing for at least 2 hours until no bubbles were visible. The solution was cast onto a primary surface optical mirror using an 8-inch wide general-purpose doctor blade with a gate height of approximately 200 µm to prepare a 200 µm thick flat sheet membrane. The optical mirror was placed in air to allow the solvent to evaporate for 72 s, and then immersed in deionized water at room temperature (25 ± 1°C). The cast membrane was placed in a coagulation bath for 24 hours and then dried for 12 hours to obtain the filter membrane.

[0039] Example 2

[0040] The difference between this embodiment and Example 1 is that the concentration of the g-C3N4 aqueous dispersion is 0.5 mg / mL.

[0041] Example 3

[0042] The difference between this embodiment and Example 1 is that the concentration of the g-C3N4 aqueous dispersion is 0.75 mg / mL.

[0043] Example 4

[0044] The difference between this embodiment and Example 1 is that the concentration of the g-C3N4 aqueous dispersion is 1.25 mg / mL.

[0045] Example 5

[0046] The difference between this embodiment and Example 1 is that the concentration of the g-C3N4 aqueous dispersion is 1.5 mg / mL.

[0047] Example 6

[0048] The difference between this embodiment and Example 1 is that the polyphenol small molecule used is epigallocatechin gallate.

[0049] Example 7

[0050] The difference between this embodiment and Embodiment 1 is that gallic acid is used as the small molecule polyphenol.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 1 is that the concentration of the g-C3N4 aqueous dispersion is 0.25 mg / mL.

[0053] Experimental Example 1 - Antibacterial Test

[0054] The filter membranes prepared in Examples 1-5 and Comparative Example 1 were subjected to antibacterial tests. *Escherichia coli*, a representative Gram-negative bacterium, and *Staphylococcus aureus*, a representative Gram-positive bacterium, were selected as test bacteria for the antibacterial tests. The results are shown in Table 1.

[0055] Table 1 - Antibacterial Test Results

[0056]

[0057] As shown in Table 1, the g-C3N4 modified polyethersulfone filter membrane prepared by the method of the present invention has excellent antibacterial properties, and exhibits better antibacterial properties with the increase of g-C3N4 aqueous dispersion concentration. This is mainly due to the introduction of modified g-C3N4, which endows the membrane with multiple properties such as antibacterial, antifouling and anticorrosion, bringing significant technical advantages to wastewater treatment and separation applications, and reducing the risk of biological pollution and bacterial adhesion.

[0058] Experiment Example 2 - SEM Test

[0059] The filter membranes prepared in Examples 1-6 were subjected to scanning electron microscopy at 5000x magnification. The results are shown in the figure. Figure 1 ,Depend on Figure 1 As can be seen, the SEM micrographs show a typical asymmetric structure. When g-C3N4 is used as an additive, the internal polyethersulfone microfiltration membranes all exhibit a loose and porous uniform structure, which can improve the hydrophilicity and antifouling properties of the membrane, and also enhance the antibacterial properties of the membrane.

[0060] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a g-C3N4 modified polyethersulfone filter membrane, characterized in that, Includes the following steps: S1. Preparation of g-C3N4 material: Using urea as a precursor, the material is heated by thermal shrinkage and kept at that temperature for a period of time. After cooling, it is pre-ground and sieved to obtain g-C3N4 powder. S2. Modified g-C3N4: The g-C3N4 powder prepared in S1 was prepared into an aqueous dispersion of g-C3N4. After continuous sonication for a period of time, it was allowed to settle naturally and the supernatant was collected. Polyphenolic small molecules and alkaline solution were added to the supernatant for reaction, and then tobramycin was added for reaction. After centrifugation, dispersion and freeze-drying, modified g-C3N4 was obtained. S3. Modified polyethersulfone filter membrane: After mixing polyethersulfone, modified g-C3N4 and organic solvent, heat and stir for a period of time until completely dissolved, continue stirring and degassing until no bubbles are visible, and the casting solution is obtained; the casting solution is then used to form a membrane under certain conditions to obtain the modified polyethersulfone filter membrane.

2. The method for preparing the g-C3N4 modified polyethersulfone filter membrane according to claim 1, characterized in that, In S1, the heating rate is 5-15℃ / min, the temperature is raised to 500-600℃, and the temperature is held for 1-3 hours.

3. The method for preparing the g-C3N4 modified polyethersulfone filter membrane according to claim 1, characterized in that, In S2, the concentration of g-C3N4 aqueous dispersion is 0.3-2 mg / mL.

4. The method for preparing the g-C3N4 modified polyethersulfone filter membrane according to claim 3, characterized in that, In S2, g-C3N4 aqueous dispersion was added at a mass ratio of g-C3N4 to polyphenol small molecules of 1:1, and the reaction was carried out at 50-70℃ and 500-700rpm for 20-30 hours.

5. The method for preparing the g-C3N4 modified polyethersulfone filter membrane according to claim 4, characterized in that, In S2, before adding the alkali solution, the temperature is raised to 50-70℃, and then the alkali solution is added at 3-5ul / mg of polyphenols.

6. The method for preparing the g-C3N4 modified polyethersulfone filter membrane according to claim 4, characterized in that, In S2, the mass ratio of tobramycin to polyphenol is 1-2:1; and the reaction is carried out at 50-70℃ and 500-700rpm for 20-30 hours.

7. The method for preparing the g-C3N4 modified polyethersulfone filter membrane according to any one of claims 1-6, characterized in that, In S2, the polyphenolic small molecules are one or more of catechin, epigallocatechin gallate, or gallic acid.

8. The method for preparing the g-C3N4 modified polyethersulfone filter membrane according to claim 1, characterized in that, In S3, the organic solvent is N,N-dimethylacetamide.

9. The method for preparing the g-C3N4 modified polyethersulfone filter membrane according to claim 1, characterized in that, In step S3, the casting solution is cast onto an optical mirror, and a flat sheet membrane is prepared using a doctor blade. Then, the solvent of the flat sheet membrane is evaporated, it is soaked in water, and dried to obtain the modified polyethersulfone filter membrane.

10. A g-C3N4 modified polyethersulfone filter membrane, characterized in that, It is prepared by any one of the preparation methods of claims 1-9.

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