Water purification membrane and method for producing the same

Abstract

This invention discloses a water purification membrane and its preparation method, relating to the field of membrane material technology. In preparing the water purification membrane, medical absorbent cotton is used as the cellulose raw material. The cotton undergoes pretreatment and allylation. Pretreated medical absorbent cotton and allyl cellulose are mixed in a suitable ratio and dissolved in lithium chloride solution to form a spinning solution. Ferric chloride is then added for electrospinning. A 0.1 mol / L sodium hydroxide solution is used as the coagulation bath, allowing ferric chloride to diffuse to the outer surface of the fiber during spinning, generating ferric hydroxide while simultaneously forming a rich porous structure within the fiber, resulting in a fiber membrane. The fiber membrane is then crosslinked with polyethylene glycol diacrylate and a photoinitiator, and finally treated with pyrrole hydrochloride solution to obtain the water purification membrane. The water purification membrane prepared by this invention exhibits excellent mechanical properties, water flux, and filtration effect.

Description

Technical Field

[0001] This invention relates to the field of membrane materials technology, specifically to a water purification membrane and its preparation method. Background Technology

[0002] Water resources are a core foundation for human survival and social development. Currently, the global water supply and demand imbalance is becoming increasingly prominent. Population growth, urbanization, and various production activities have significantly increased water demand, compounded by water pollution, leading to a continuous reduction in available clean water resources. Water pollution is now exhibiting complex and diversified characteristics. While conventional pollutants continue to be discharged, various new trace pollutants are accumulating. The lack of a comprehensive control and treatment system for these pollutants creates highly concealed potential water environment risks, seriously affecting the safety of residential water use and the sustainable development of industry and agriculture. Therefore, developing efficient and stable water purification technologies has become a key research focus in the field of water treatment.

[0003] Filtration technology, with its advantages of simple operation, low energy consumption, wide applicability, and excellent separation effect, has become the mainstream water purification technology. Among them, filter membranes are the most widely used core filtration media. At present, most commercially available filter membranes are stretched porous membranes or phase separation membranes, which generally suffer from structural defects such as low porosity, poor pore connectivity, and large membrane thickness, thus limiting the overall purification performance of the filter membranes. Traditional filter membranes rely on the principle of pore size sieving to retain pollutants. There has long been a core contradiction between permeate flux and separation efficiency. The smaller the pore size, the higher the pollutant separation accuracy, but the mass transfer resistance of water molecules increases accordingly, and the permeate flux decreases significantly. Even under high-pressure operating conditions, it is difficult to achieve both high separation efficiency and high-flux water purification effect at the same time, which cannot meet the actual needs of current high-efficiency water treatment.

[0004] Compared to traditional membrane fabrication processes, electrospinning technology can produce nanofiber membranes with high specific surface area, high porosity, and excellent pore connectivity, effectively improving the water permeability of filter membranes. Cellulose, as a natural polymer material, is widely available, has excellent hydrophilicity, is biodegradable, and possesses abundant surface-active groups and great modification potential, making it an ideal substrate for preparing green, high-performance filter membranes. It can effectively address the performance shortcomings and secondary pollution problems of traditional filter membranes, possessing excellent application and research value. Summary of the Invention

[0005] The purpose of this invention is to provide a water purification membrane and its preparation method to solve the problems existing in the prior art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A water purification membrane, characterized in that the water purification membrane is prepared by electrospinning cellulose and allyl cellulose to obtain a fiber membrane, then crosslinking the fiber membrane with polyethylene glycol diacrylate and a photoinitiator, and finally treating it with pyrrole hydrochloride solution.

[0008] As an optimization, the allyl cellulose is prepared by reacting a compound containing a double bond that can react with cellulose.

[0009] As an optimization, the compounds containing double bonds include: acryloyl chloride, acrylic anhydride, acrylic acid, methyl acrylate, and glycidyl acrylate; the compounds containing double bonds include: acryloyl chloride, acrylic anhydride, acrylic acid, methyl acrylate, and glycidyl acrylate.

[0010] As an optimization, the photoinitiator is one or a mixture of photoinitiator 1173, photoinitiator 184, photoinitiator BP, and photoinitiator TPO.

[0011] A method for preparing a water purification membrane includes the following preparation steps:

[0012] (1) Mix cellulose and allyl cellulose to obtain mixed cellulose, wherein the allyl cellulose content is 20%~40%; mix lithium chloride and N,N-dimethylacetamide at a ratio of 1:15~20, stir at 80~90℃ for 20~30min to obtain lithium chloride solution, then add mixed cellulose, stir at 80~90℃ until completely dissolved to obtain a spinning solution with a mass fraction of 1% mixed cellulose;

[0013] (2) Add 1% of ferric chloride by weight of the spinning solution to the spinning solution and stir until completely dissolved. Spin the solution using an electrospinning machine. After spinning, wash the solution with deionized water until neutral and freeze dry to obtain a fiber membrane.

[0014] (3) Place the fiber membrane flat in the impregnation container, pour in the crosslinking treatment solution until the membrane is completely submerged, place it in a vacuum drying oven at 0.1 atmospheres, degas at room temperature, take it out, gently absorb the excess impregnation solution on the surface with filter paper, treat it with ultraviolet light at room temperature and pressure, and then let it stand at room temperature for more than 6 hours to obtain the crosslinked fiber membrane.

[0015] (4) Using pyrrole as a solute, the fiber membrane is placed flat in the impregnation container, and pyrrole hydrochloride solution is poured in until the membrane is completely submerged. The membrane is placed in a vacuum drying oven with a vacuum degree of 0.1 atmospheres, degassed at room temperature, removed, and then placed at room temperature and pressure for more than 6 hours. The membrane is washed with deionized water until neutral, and then freeze-dried to obtain a water purification membrane.

[0016] As an optimization, the cellulose in step (1) can be obtained by extraction and separation from any plant tissue containing fiber.

[0017] As an optimization, the cellulose in step (1) is pretreated medical absorbent cotton, which is obtained by tearing the medical absorbent cotton into pieces and soaking it in pure water, methanol and N,N-dimethylacetamide for 2 hours each, and then filtering and drying it; the manufacturer of the medical absorbent cotton is Guilin Tianhe Pharmaceutical Yiwei Co., Ltd.

[0018] As an optimization, the preparation method of the allyl fiber in step (1) is as follows: pretreated long-staple degreased cotton, hydrochloric acid with a mass fraction of 37.5% and acrylic acid are mixed evenly at a mass ratio of 1:15~20:30~40, reacted at 100℃ for 5~6h, and then placed in ice water for ultrasonic treatment for 20~30min. The turbid supernatant is separated by centrifugation at 8000rpm and dialyzed in pure water for more than 4 days with the pure water changed twice a day. The allyl cellulose is then dried to obtain the allyl cellulose.

[0019] As an optimization, the electrospinning machine in step (2) is a TL-ProBM electrospinning machine.

[0020] As an optimization, the electrospinning process parameters in step (2) are as follows: using a 22G spinning needle, a spinning voltage of 22kV, a flow rate of 5mL / h, a distance of 15cm between the needle and the collecting roller, and using a 0.1mol / L sodium hydroxide solution as the coagulation bath.

[0021] As an optimization, the preparation method of the crosslinking treatment solution in step (3) is as follows: weigh 16-20 parts of polyethylene glycol diacrylate, 3-4 parts of photoinitiator and 80-85 parts of anhydrous ethanol by mass, mix them evenly and prepare the solution; the polyethylene glycol diacrylate is of model PEG400DA and the manufacturer is Shanghai Baoyang Baoxin Biotechnology Co., Ltd.

[0022] As an optimization, the method of ultraviolet irradiation treatment in step (3) is as follows: 365nm ultraviolet mercury lamp, 50W / cm² light intensity, irradiation on both sides for 100s.

[0023] As an optimization, the method for preparing the pyrrole hydrochloride solution in step (4) is as follows: using 0.1 mol / L hydrochloric acid solution as solvent, prepare a 3 g / L pyrrole hydrochloride solution.

[0024] As an optimization, the pH value of the water purification membrane can be adjusted according to the properties of the wastewater during use to achieve a better filtration effect.

[0025] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0026] In preparing the water purification membrane, this invention uses medical degreased cotton as the cellulose raw material, pre-treats and allylates it, and prepares a spinning solution. Then, ferric chloride is added to perform electrospinning to obtain a fiber membrane. The fiber membrane is cross-linked with polyethylene glycol diacrylate and a photoinitiator, and finally treated with pyrrole hydrochloride solution to obtain the water purification membrane.

[0027] First, by controlling the proportion of allyl cellulose, this invention obtains a membrane with excellent comprehensive performance in terms of mechanical properties and water flux, maintaining a high water flux while also exhibiting good filtration effect. Ferric chloride is added to the spinning solution, and sodium hydroxide solution is used as the coagulation bath. Ferric chloride diffuses into the sodium hydroxide solution and forms ferric hydroxide particles embedded in the fiber membrane, facilitating the formation of a hollow porous structure. Furthermore, in the subsequent polypyrrole reaction, under acidic conditions, ferric ions are dissolved and released, forming new pore structures that facilitate the in-situ generation of polypyrrole within the pores, thus improving the filtration effect.

[0028] Secondly, the use of polyethylene glycol diacrylate in crosslinking can compensate for hydrophilicity; vacuum defoaming is performed during both crosslinking and pyrrole hydrochloride solution treatment, allowing both to better enter the pores and exert their effects, thus improving the corresponding results.

[0029] Finally, during use, the degree of ionization of organic pollutants can be adjusted by pH to achieve a better filtration effect. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] To more clearly illustrate the method provided by the present invention, the following embodiments will be described in detail.

[0032] Example 1:

[0033] A method for preparing a water purification membrane mainly includes the following preparation steps:

[0034] (1) Tear the medical degreased cotton into pieces and soak it in pure water, methanol and N,N-dimethylacetamide for 2 hours each, filter and dry to obtain pretreated medical degreased cotton; mix the pretreated medical degreased cotton, hydrochloric acid with a mass fraction of 37.5% and acrylic acid in a mass ratio of 1:15:30, react at 100℃ for 5 hours, then place it in ice water for ultrasonic treatment for 30 minutes, centrifuge at 8000 rpm to separate the turbid supernatant, use a dialysis bag to dialyze in pure water for more than 4 days, change the pure water twice a day, and dry to obtain allyl cellulose; mix the pretreated medical degreased cotton and allyl cellulose to obtain mixed cellulose, in which the allyl cellulose content is 30%; mix lithium chloride and N,N-dimethylacetamide in a ratio of 1:15, stir at 80℃ for 20 minutes to obtain lithium chloride solution, then add mixed cellulose, stir at 80℃ until completely dissolved to obtain a spinning solution with a mass fraction of 1% mixed cellulose;

[0035] (2) Add 1% of ferric chloride by weight of the spinning solution to the spinning solution and stir until completely dissolved. Spin the solution using a TL-ProBM electrospinning machine with a 22G spinning needle, a spinning voltage of 22kV, a flow rate of 5mL / h, and a distance of 15cm between the needle and the collecting roller. Part of the collecting roller is immersed in a 0.1mol / L sodium hydroxide solution for collection. After spinning, wash the solution with deionized water until neutral and freeze dry to obtain a fiber membrane.

[0036] (3) Weigh 16 parts of polyethylene glycol diacrylate, 4 parts of 1173 photoinitiator and 80 parts of anhydrous ethanol by mass, mix them evenly and prepare a crosslinking treatment solution; place the fiber membrane flat in the impregnation container, pour in the crosslinking treatment solution until the membrane is completely submerged, place it in a vacuum drying oven at 0.1 atmospheres, degas at room temperature for 20 minutes, take it out, gently absorb the excess impregnation solution on the surface with filter paper, irradiate both sides for 100 seconds with a 365nm ultraviolet mercury lamp at 50W / cm² light intensity at room temperature and pressure, and let it stand at room temperature for 6 hours to obtain a crosslinked fiber membrane;

[0037] (4) Using pyrrole as solute and 0.1 mol / L hydrochloric acid solution as solvent, prepare a 3 g / L pyrrole hydrochloride solution. Place the fiber membrane flat in the impregnation container, pour in the pyrrole hydrochloride solution until the membrane is completely submerged, place it in a vacuum drying oven with a vacuum degree of 0.1 atmosphere, degas at room temperature for 30 min, take it out, place it at room temperature and pressure for another 6 h, wash with deionized water until neutral, freeze dry, and obtain a water purification membrane.

[0038] Example 2:

[0039] The allyl cellulose content in Example 2 was 20%, and the rest was the same as in Example 1.

[0040] Example 3:

[0041] The allyl cellulose content of Example 2 is 40%, and the rest is the same as in Example 1.

[0042] Comparative Example 1:

[0043] The allyl cellulose content of Comparative Example 1 was 0%, and the rest was the same as in Example 1.

[0044] Comparative Example 2:

[0045] The allyl cellulose content of Comparative Example 2 was 10%, and the rest was the same as in Example 1.

[0046] Comparative Example 3:

[0047] The allyl cellulose content of Comparative Example 3 was 50%, and the rest was the same as in Example 1.

[0048] Comparative Example 4:

[0049] The allyl cellulose content of Comparative Example 4 was 70%, and the rest was the same as in Example 1.

[0050] Comparative Example 5:

[0051] The allyl cellulose content of Comparative Example 5 was 90%, and the rest was the same as in Example 1.

[0052] Comparative Example 6:

[0053] The allyl cellulose content of Comparative Example 6 was 100%, and the rest was the same as in Example 1.

[0054] Comparative Example 7:

[0055] The steps (1) of Comparative Example 7 are as follows: microcrystalline cellulose, hydrochloric acid with a mass fraction of 37.5% and acrylic acid are mixed evenly in a mass ratio of 1:15:30, reacted at 100℃ for 5 hours, and then ultrasonically treated in ice water for 30 minutes. The turbid supernatant is separated by centrifugation at 8000 rpm and dialyzed in pure water for more than 4 days with the pure water changed twice a day. The supernatant is dried to obtain allyl cellulose. The microcrystalline cellulose and allyl cellulose are mixed evenly to obtain mixed cellulose, in which the allyl cellulose content is 30%. Lithium chloride and N,N-dimethylacetamide are mixed in a mass ratio of 1:15 and stirred at 80℃ for 20 minutes to obtain lithium chloride solution. The mixed cellulose is then added and stirred at 80℃ until completely dissolved to obtain a spinning solution with a mass fraction of 1% mixed cellulose.

[0056] The microcrystalline cellulose is industrial grade and manufactured by Wuhan Jiyesheng Chemical Co., Ltd.; the rest is the same as in Example 1.

[0057] Comparative Example 8:

[0058] Step (3) of Comparative Example 8 is as follows: 4 parts of 1173 photoinitiator and 80 parts of anhydrous ethanol are mixed evenly to prepare a crosslinking treatment solution; the fiber membrane is placed flat in the impregnation container, the crosslinking treatment solution is poured in until the membrane is completely submerged, and it is placed in a vacuum drying oven at 0.1 atmospheres. The membrane is degassed at room temperature for 20 minutes, then removed and the excess impregnation solution on the surface is gently absorbed with filter paper. At room temperature and pressure, the membrane is irradiated with a 365nm ultraviolet mercury lamp at a light intensity of 50W / cm² for 100s on both sides, and then left to stand at room temperature for 6 hours to obtain a crosslinked fiber membrane; the rest is the same as in Example 1.

[0059] Comparative Example 9:

[0060] Step (3) of Comparative Example 9 is as follows: Weigh 16 parts of polyethylene glycol diacrylate, 4 parts of 1173 photoinitiator and 80 parts of anhydrous ethanol by mass, mix them evenly, and prepare a crosslinking treatment solution; Place the fiber membrane flat in the impregnation container, pour in the crosslinking treatment solution until the membrane is completely submerged, let it stand for 20 minutes, take it out, gently absorb the excess impregnation solution on the surface with filter paper, and irradiate both sides for 100 seconds with a 365nm ultraviolet mercury lamp at a light intensity of 50W / cm² at room temperature and pressure, and let it stand at room temperature for 6 hours to obtain a crosslinked fiber membrane; the rest is the same as in Example 1.

[0061] Comparative Example 10:

[0062] Step (3) of Comparative Example 10 is as follows: Weigh 16 parts of 1,4-butanediol diacrylate, 4 parts of 1173 photoinitiator and 80 parts of anhydrous ethanol by mass, mix them evenly, and prepare a crosslinking treatment solution; place the fiber membrane flat in the impregnation container, pour in the crosslinking treatment solution until the membrane is completely submerged, let it stand for 20 minutes, take it out, gently absorb the excess impregnation solution on the surface with filter paper, and irradiate both sides for 100 seconds with a 365nm ultraviolet mercury lamp at a light intensity of 50W / cm² at room temperature and pressure, and let it stand at room temperature for 6 hours to obtain a crosslinked fiber membrane; the rest is the same as in Example 1.

[0063] Comparative Example 11:

[0064] A method for preparing a water purification membrane mainly includes the following preparation steps:

[0065] (1) Tear the medical degreased cotton into pieces and soak it in pure water, methanol and N,N-dimethylacetamide for 2 hours each, filter and dry to obtain pretreated medical degreased cotton; mix the pretreated medical degreased cotton, hydrochloric acid with a mass fraction of 37.5% and acrylic acid in a mass ratio of 1:15:30, react at 100℃ for 5 hours, then place it in ice water for ultrasonic treatment for 30 minutes, centrifuge at 8000 rpm to separate the turbid supernatant, use a dialysis bag to dialyze in pure water for more than 4 days, change the pure water twice a day, and dry to obtain allyl cellulose; mix the pretreated medical degreased cotton and allyl cellulose to obtain mixed cellulose, in which the allyl cellulose content is 30%; mix lithium chloride and N,N-dimethylacetamide in a ratio of 1:15, stir at 80℃ for 20 minutes to obtain lithium chloride solution, then add mixed cellulose, stir at 80℃ until completely dissolved to obtain a spinning solution with a mass fraction of 1% mixed cellulose;

[0066] (2) The spinning solution was spun using a TL-ProBM electrospinning machine. A 22G spinning needle was used, the spinning voltage was 22kV, the flow rate was 5mL / h, the distance between the needle and the collecting drum was 15cm, and part of the collecting drum was immersed in a 0.1mol / L sodium hydroxide solution for collection. After spinning, the solution was washed with deionized water until neutral, and then freeze-dried to obtain a fiber membrane.

[0067] (3) Weigh 16 parts of polyethylene glycol diacrylate, 4 parts of 1173 photoinitiator and 80 parts of anhydrous ethanol by mass, mix them evenly and prepare a crosslinking treatment solution; place the fiber membrane flat in the impregnation container, pour in the crosslinking treatment solution until the membrane is completely submerged, place it in a vacuum drying oven at 0.1 atmospheres, degas at room temperature for 20 minutes, take it out, gently absorb the excess impregnation solution on the surface with filter paper, irradiate both sides for 100 seconds with a 365nm ultraviolet mercury lamp at 50W / cm² light intensity at room temperature and pressure, and let it stand at room temperature for 6 hours to obtain a crosslinked fiber membrane;

[0068] (4) Using pyrrole as solute and 0.1 mol / L hydrochloric acid solution as solvent, prepare a 3 g / L pyrrole hydrochloride solution, and then add 1% ferric chloride by mass of the pyrrole hydrochloride solution and mix evenly; place the fiber membrane flat in the impregnation container, pour in the pyrrole hydrochloride solution containing ferric chloride until the membrane is completely submerged, place it in a vacuum drying oven with a vacuum degree of 0.1 atmosphere, degas at room temperature for 30 min, and then place it under normal temperature and pressure for another 6 h to continue soaking, wash with deionized water until neutral, freeze dry, and obtain a water purification membrane.

[0069] Comparative Example 12:

[0070] Step (4) of Comparative Example 12 is as follows: using pyrrole as the solute and 0.1 mol / L hydrochloric acid solution as the solvent, a 3 g / L pyrrole hydrochloride solution is prepared. The fiber membrane is placed flat in the impregnation container, and the pyrrole hydrochloride solution is poured in until the membrane is completely submerged. The membrane is soaked at room temperature and pressure for 6.5 h, washed with deionized water until neutral, and freeze-dried to obtain the water purification membrane. The rest is the same as in Example 1.

[0071] Comparative Example 13:

[0072] The only difference between Comparative Example 13 and Example 1 is that step (4) is omitted, and the water purification membrane is obtained directly through step (3).

[0073] Comparative Example 14

[0074] Step (4) of Comparative Example 14 is as follows: the fiber membrane is placed flat in the impregnation container, 0.1 mol / L hydrochloric acid solution is poured in until the membrane is completely submerged, and it is placed in a vacuum drying oven with a vacuum degree of 0.1 atmospheres. The membrane is degassed at room temperature for 30 minutes, taken out, and then placed at room temperature and pressure for another 6 hours of soaking. It is then washed with deionized water until neutral, and freeze-dried to obtain a water purification membrane.

[0075] Experimental Example 1

[0076] Testing of mechanical properties and water flux

[0077] Tests were conducted using a water purification membrane with a thickness of 40±5μm.

[0078] Test method: The water purification membranes obtained in each embodiment and comparative example were tested for tensile strength and elongation at break using a tensile testing machine. The specimen shape was dumbbell-shaped, with a total specimen length of 120 mm, a distance between clamps of 86 ± 5 mm, a distance between marks of 40 ± 0.5 mm, a large shoulder radius of 25 ± 2 mm, a small shoulder radius of 14 ± 1 mm, an effective test width of 10 ± 0.5 mm, an end width of 25 ± 0.5 mm, and a tensile speed of 2 ± 0.5 mm / min.

[0079] Water flux test: Pure gravity filtration was used with a filter cup inner diameter of 1.5cm. Pure water was continuously added during the test to keep the liquid level 10cm above the water purification membrane surface. The test time was 1 minute. Water flux = volume of water permeated divided by the product of filtration time and effective membrane area.

[0080] Table 1

[0081]

[0082] A comparison of the experimental data in Table 1 reveals that the water purification membrane prepared by this invention has good mechanical properties and water flux.

[0083] Experimental comparisons of different allyl cellulose contents reveal the following:

[0084] The higher the allyl cellulose content, the higher the tensile strength. The strength increases almost linearly from 0 to 50%, but the increase slows down when it exceeds 50%. This is because the higher the allyl cellulose content, the denser the cross-linking and the higher the strength.

[0085] The elongation at break increases rapidly between 0% and 30%, increases slowly between 30% and 50%, and decreases after exceeding 50%. This is because as the proportion of allyl cellulose increases from 0% to 50%, the number of carbon-carbon double bonds that can participate in crosslinking increases. At the same time, the flexible crosslinking chain of polyethylene glycol diacrylate constructs a moderate covalent network, and the allyl groups weaken the dense hydrogen bonds of cellulose molecules, improving the molecular chain mobility, thus gradually increasing the elongation at break. When the modification ratio exceeds 50%, the crosslinking density is too high, limiting chain segment slippage. The high content of allyl hydrophobic agglomeration introduces microscopic defects, making the membrane structure denser, reducing the deformation space, and causing the elongation at break to continue to decrease.

[0086] Water flux decreased with increasing allyl cellulose content, and the decrease was even faster at 50%. This indicates that as the modification ratio increased, the crosslinking density increased, the fiber gaps were filled and compressed, and the effective water passage pore size decreased. At the same time, the modified allyl group is more hydrophobic than the hydroxyl group. When the content exceeds 50%, the hydrophobic effect and pore shrinkage have a dual effect, resulting in a rapid and precipitous decrease in flux.

[0087] Therefore, choosing an allyl cellulose content of 20% to 40% results in better overall performance.

[0088] Comparative Example 7 used microcrystalline cellulose. Through data comparison, it can be found that the overall performance is better when medical absorbent cotton is used as raw material. This may be because the cellulose molecular chain of medical cotton is long, the fiber is stretched and entangled, which improves the mechanical properties. At the same time, the pores are well permeable after molding. Microcrystalline cellulose is acid-hydrolyzed short rod-shaped microcrystals with a small aspect ratio, which makes it easy to stack tightly. It has many tortuous pores inside, which greatly reduces the resistance to water flow.

[0089] In Comparative Example 8, when polyethylene glycol diacrylate was not used, the mechanical properties decreased significantly, while the water flux increased slightly.

[0090] In Comparative Example 9, the mechanical properties decreased and the water flux increased during crosslinking without vacuum treatment. This is because vacuum treatment can eliminate air bubbles, making it easier for the crosslinking solution to penetrate the pores, resulting in a denser overall fiber stack and more uniform crosslinking.

[0091] Comparative Example 10 showed that replacing polyethylene glycol diacrylate with 1,4-butanediol diacrylate resulted in a slight decrease in elongation at break and water flux, indicating that the use of polyethylene glycol diacrylate can improve flexibility to a certain extent and compensate for some of the hydrophilicity.

[0092] Experimental Example 2

[0093] Filtration effect test:

[0094] Plotting the standard curve: Prepare Congo red aqueous solutions of different standard concentrations, and measure the absorbance at a wavelength of 497 nm using a UV-Vis spectrophotometer to plot the standard curve of Congo red aqueous solution concentration and absorbance.

[0095] Test method: Pure gravity filtration was used. The filter cup had an inner diameter of 1.5 cm. 200 mL of a 10 mg / L Congo red aqueous solution was filtered. During filtration, the liquid level was maintained at a height of 10 cm above the surface of the water purification membrane until all 200 mL of Congo red aqueous solution was added. The concentration of the Congo red aqueous solution after filtration was obtained according to the standard curve. The filtration efficiency was calculated as: 100% - (Concentration of Congo red aqueous solution after filtration / Congo red concentration before filtration) * 100%.

[0096] The water purification membrane was placed in pure water, ultrasonicated at room temperature for 24 hours, and then freeze-dried under vacuum. The filtration efficiency was then tested and calculated again after 24 hours of water washing. The results are shown in Table 2.

[0097] Table 2

[0098] Example 1 91.3% 82.1% Comparative Example 11 82.7% 56.5% Comparative Example 12 87.1% 73.8% There is iron 75.6% 69.0% pure 8.4% 9.2%

[0099] A comparison of the experimental data in Table 2 shows that the water purification membrane prepared by this invention has a good filtration effect.

[0100] Comparative Example 11 did not add ferric chloride during spinning, but added it in the final step. This indicates that when ferric chloride is added to the spinning solution, under the conditions of a sodium hydroxide coagulation bath during spinning, it diffuses and generates strong iron oxide, causing the fiber to form a centrally controlled porous structure. In the subsequent polypyrrole reaction, under acidic conditions, ferric ions are released and dissolved, forming new pore structures. This is beneficial for the in-situ generation of polypyrrole within the pores. Compared to mixing ferric chloride with pyrrole at the end, this method results in a richer pore structure, and the in-situ generation of polypyrrole within the pores is more stable, thus leading to better initial and long-term filtration effects.

[0101] In Comparative Example 12, the pyrrole hydrochloride solution was not treated under vacuum, resulting in a decrease in both initial and long-term filtration efficiency. This indicates that vacuum treatment can eliminate air bubbles, making it easier for the pyrrole hydrochloride solution to penetrate the pores and for ferric chloride to dissolve, thus improving both initial and long-term filtration efficiency.

[0102] Comparative Example 13 was not treated with pyrrole hydrochloride solution and was a cellulose membrane containing ferric hydroxide. Comparative Example 14 was treated with hydrochloric acid solution to remove the ferric hydroxide and was a pure cellulose membrane. According to the data analysis, the cellulose membrane containing ferric hydroxide has a certain filtration effect, which may be due to metal complexation or the oxidation of iron ions. The filtration effect of the pure cellulose membrane is very poor and can be ignored. The filtration effect is slightly improved after washing with water for 24 hours, which may be due to the water washing making the pores more open or the fluctuation of experimental error.

[0103] Experimental Example 3

[0104] Testing of the filtration environment for different types of organic pollutants:

[0105] The pH was adjusted using sodium hydroxide and hydrochloric acid. Methylene blue was used as a cationic contaminant, and aqueous solutions at different pH values ​​and concentrations of 10 mg / L were prepared. Congo red was used as an anionic contaminant, and aqueous solutions at different pH values ​​and concentrations of 10 mg / L were also prepared. The filtration effect of Example 1 was tested according to the method in Experimental Example 2. The absorbance of methylene blue was measured at 665 nm using a UV-Vis spectrophotometer. The results are shown in Table 3.

[0106] Table 3

[0107] pH=1 92.3% 3.1% pH=3 92.1% 5.0% pH=5 91.5% 8.4% pH=7 91.3% 21.2% pH=9 90.8% 43.6% pH=11 91.6% 59.3% pH=13 91.1% 91.8%

[0108] A comparison of the experimental data in Table 3 shows that the water purification membrane prepared by this invention has a good filtration effect.

[0109] This invention provides good filtration for anionic pollutants in any pH environment. However, for cationic pollutants, the higher the pH, the better the filtration effect. Therefore, during use, the degree of ionization of organic pollutants can be adjusted by pH to achieve better filtration results.

[0110] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. 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 water purification membrane, characterized in that, The water purification membrane is prepared by electrospinning cellulose, allyl cellulose and ferric chloride to obtain a fiber membrane, then crosslinking the fiber membrane with polyethylene glycol diacrylate and a photoinitiator, and finally treating it with pyrrole hydrochloride solution.

2. The water purification membrane according to claim 1, characterized in that, The allyl cellulose is prepared by reacting cellulose with a compound containing a double bond that can react with cellulose; the compound containing a double bond includes: acryloyl chloride, acrylic anhydride, acrylic acid, methyl acrylate and glycidyl acrylate.

3. The water purification membrane according to claim 1, characterized in that, The photoinitiator is one or a mixture of photoinitiator 1173, photoinitiator 184, photoinitiator BP, and photoinitiator TPO.

4. A method for preparing a water purification membrane, characterized in that, The preparation steps include the following: (1) Mix cellulose and allyl cellulose to obtain mixed cellulose, wherein the allyl cellulose content is 20%~40%; mix lithium chloride and N,N-dimethylacetamide, stir evenly at 80~90℃ to obtain lithium chloride solution, then add mixed cellulose, stir at 80~90℃ until completely dissolved to obtain a spinning solution with a mass fraction of 1% mixed cellulose. (2) Add 1% of ferric chloride by weight of the spinning solution to the spinning solution and stir until completely dissolved. Spin the solution using an electrospinning machine. After spinning, wash the solution with deionized water until neutral and freeze dry to obtain a fiber membrane. (3) Place the fiber membrane flat in the impregnation container, pour in the cross-linking treatment solution until the membrane is completely submerged, degas at room temperature under vacuum, take it out, gently absorb the excess impregnation solution on the surface with filter paper, treat with ultraviolet light at room temperature and pressure, and then let it stand at room temperature for more than 6 hours to obtain the cross-linked fiber membrane. (4) Using pyrrole as a solute, the fiber membrane is placed flat in the impregnation container, and pyrrole hydrochloride solution is poured in until the membrane is completely submerged. The membrane is degassed under vacuum at room temperature, removed, and then placed under normal temperature and pressure for more than 6 hours. It is then washed with deionized water until neutral, and freeze-dried to obtain a water purification membrane.

5. The method for preparing a water purification membrane according to claim 4, characterized in that, The cellulose described in step (1) can be obtained by extraction and separation from any plant tissue containing fiber.

6. The method for preparing a water purification membrane according to claim 5, characterized in that, The electrospinning process parameters in step (2) are as follows: a 22G spinning needle is used, the spinning voltage is 22kV, the flow rate is 5mL / h, the distance between the needle and the collecting roller is 15cm, and a 0.1mol / L sodium hydroxide solution is used as the coagulation bath.

7. The method for preparing a water purification membrane according to claim 4, characterized in that, The preparation method of the crosslinking treatment liquid in step (3) is as follows: weigh 16-20 parts of polyethylene glycol diacrylate, 3-4 parts of photoinitiator and 80-85 parts of anhydrous ethanol by mass, mix them evenly and prepare the solution.

8. The method for preparing a water purification membrane according to claim 4, characterized in that, The method of ultraviolet irradiation treatment in step (3) is as follows: 365nm ultraviolet mercury lamp, 50W / cm² light intensity, irradiation on both sides for 100s.

9. The method for preparing a water purification membrane according to claim 4, characterized in that, The method for preparing the pyrrole hydrochloride solution in step (4) is as follows: use 0.1 mol / L hydrochloric acid solution as solvent to prepare a 3 g / L pyrrole hydrochloride solution.

10. The method for preparing a water purification membrane according to claim 4, characterized in that, When in use, the pH value of the water purification membrane can be adjusted according to the properties of the wastewater to achieve a better filtration effect.

Images