A gradient filtration multi-level functionalized separation membrane and a preparation method thereof

Abstract

The application discloses a preparation method of a gradient filtration multilevel functional separation membrane, and comprises the following steps: S1, a support layer is prepared by a film casting method, and a porous separation membrane is obtained as the support layer; and S2, a nanofiber layer is prepared by electrostatic spinning, and the nanofiber layer-porous separation membrane is obtained. The preparation method is simple and is beneficial to large-scale production.

Description

Technical Field

[0001] This invention relates to the field of separation membranes, specifically to a gradient filtration multi-stage functionalized separation membrane and its preparation method. Background Technology

[0002] With my country's economic development, accelerated urbanization, and continuous expansion of industrial scale, water pollution has become increasingly prominent. Existing wastewater treatment technologies all have some shortcomings. Physical methods such as flocculation and adsorption, after enriching pollutants, are difficult to separate from water bodies, and the recovery of flocculants and adsorbents is challenging. Chemical treatment methods require the application of additional chemical reagents, and may still generate toxic substances during the process, harming aquatic plants and animals. Biological methods utilize the metabolism of microorganisms to treat pollutants, but the treatment time is long, and microorganisms need to be cultivated in a specific environment.

[0003] Compared to the aforementioned wastewater treatment methods, membrane separation technology offers advantages such as ease of operation, environmental friendliness, short treatment time, and the ability to separate concentrated pollutants from water. However, existing membrane separation technologies have relatively limited functionality. Nanofiltration and reverse osmosis membranes are effective at treating heavy metal ions and small molecule compounds, but their small pore size makes them susceptible to fouling, reducing treatment efficiency, and they also have high requirements for influent water quality. Microfiltration and ultrafiltration membranes have larger pore sizes and better anti-fouling properties, but they cannot retain heavy metal ions and small molecule compounds. Therefore, the treatment capacity of a single type of membrane is limited and cannot meet the needs of complex wastewater treatment. Summary of the Invention

[0004] To address the aforementioned problems, this invention aims to provide a gradient filtration multi-layer functionalized separation membrane and its preparation method. The method involves constructing a nanofiber layer with supramolecular recognition function on the surface of an ultrafiltration membrane using electrospinning technology, thereby obtaining a multi-layer functionalized separation membrane with gradient filtration performance. The supramolecular compound nanofiber layer endows the membrane with the ability to remove heavy metal ions and small molecule compounds, thus enabling the functional separation membrane to remove pollutants at multiple scales. Simultaneously, the separation membrane acts as a support, enhancing the pressure resistance of the nanofiber layer. Furthermore, the nanofiber layer and the separation membrane provide a fixed substrate for the supramolecular compounds, facilitating the recycling and regeneration of the compounds after they have accumulated pollutants.

[0005] This invention is achieved through the following technical solution:

[0006] A method for preparing a gradient filtration multi-stage functionalized separation membrane includes the following steps:

[0007] S1. Preparation of support layer by casting method: The first polymer compound is dissolved in a solvent to prepare a casting solution, and then the casting solution is made into a gel layer and immersed in a coagulation bath prepared by the second polymer compound to obtain a porous separation membrane as the support layer.

[0008] S2. Electrospinning preparation of nanofiber layer: A mixed spinning solution prepared from a second polymer compound and a supramolecular compound is electrospinned onto a support layer to obtain a nanofiber layer-porous separation membrane; wherein...

[0009] The first polymeric compound is one or more of polyvinylidene fluoride (PVDF), polysulfone (PSF), polyethersulfone (PES), carboxymethyl cellulose (CA), polyacrylonitrile (PAN), polyvinyl chloride (PVC), and ethylene-vinyl alcohol copolymer (EVOH), with a molecular weight of 20,000-1,000,000; the second polymeric compound is one or more of polyvinyl alcohol (PVA), chitosan, polyacrylamide, polyacrylic acid, polyvinylpyrrolidone, and polymaleic anhydride, with a molecular weight of 5,000-500,000; and the supramolecular compound is one or more of calixarene, columnar aromatics, cucurbituril, α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, hydroxypropyl-β-cyclodextrin, sulfonic acid-β-cyclodextrin, and carboxymethyl-β-cyclodextrin.

[0010] Furthermore, the method includes step S3, where the nanofiber layer-porous separation membrane undergoes a first steam treatment with solvent vapor for 5 min-6 h, followed by a second steam treatment with crosslinking agent vapor for 5 min-6 h. During the experiment, the inventors discovered that after spinning the nanofiber layer onto the porous separation membrane, which serves as the support layer, the functional membrane still exhibited instability and lack of durability. To address this issue, the inventors selected a coagulation liquid component—a second polymer compound—as one of the spinning solutions when preparing the electrospinning solution. Then, the nanofiber layer-porous separation membrane underwent a first steam treatment with solvent vapor from the casting solution, followed by a second steam treatment with crosslinking agent vapor. This synergistically enhanced the interfacial bonding performance between the nanofiber layer and the support layer, significantly improving the overall stability and durability of the membrane during use, and facilitating recycling.

[0011] The crosslinking agent is one or more of epichlorohydrin, glutaraldehyde, adipic acid, glyoxal, and butyraldehyde.

[0012] The solvent is one or more of N,N-dimethylformamide, dimethyl sulfoxide, N,N-dimethylacetamide, methanol, ethanol, and acetic acid.

[0013] The ambient temperature for the first steam treatment is 20℃-80℃, and the ambient temperature for the second steam treatment is 20℃-80℃.

[0014] The concentration of the casting solution is 5wt%-50wt%, the concentration of the coagulation bath is 1wt%-20wt%, and the concentration of the mixed spinning solution is 1wt%-25wt%.

[0015] The mass ratio of the second polymer compound to the supramolecular compound in S2 is 1:10-10:1.

[0016] The gradient filtration multi-stage functionalized separation membrane prepared by the preparation method described above.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0018] 1. Unlike existing single-function or dual-function separation membranes, the multi-level functionalized separation membrane for gradient filtration prepared in this invention can filter various water pollutants of different scales, such as heavy metal ions, small molecule organic compounds, and large molecule organic compounds.

[0019] 2. The electrospun nanofiber layer improves the antifouling performance of the separation membrane, reduces the degree of fouling, and facilitates membrane cleaning. After prolonged operation, membrane fouling is inevitable, and the accumulation of contaminants within the membrane pores makes cleaning difficult. Adding a nanofiber layer reduces direct contact between contaminants and the membrane. Simultaneously, the nanofiber layer can retain some contaminants, further minimizing direct fouling. Furthermore, the relatively porous nature of the nanofiber layer facilitates easier cleaning and removal of contaminants.

[0020] 3. The porous separation membrane serves as a support layer for the electrospun nanofiber layer, enabling the nanofiber layer to withstand greater filtration pressure. Simultaneously, the nanofiber layer and the porous separation membrane provide a fixation matrix for supramolecular compounds, facilitating their adsorption and regeneration.

[0021] Electrospun nanofiber layers are relatively thin and have poor mechanical properties, making them unable to withstand high influent pressure. Spinning nanofiber layers onto the surface of porous separation membranes provides a rigid support layer, improving the nanofiber layer's ability to withstand influent pressure. Supramolecular compounds are very fine (powder-like), and when used alone, they are difficult to separate from the treated water after adsorbing pollutants, hindering true pollutant removal. Furthermore, they are difficult to recycle. By spinning nanofibers containing supramolecular compounds and fixing them to the separation membrane surface, a fixed matrix is ​​provided for the supramolecular compounds, effectively solving both of these problems.

[0022] 4. The preparation method of this invention is simple and conducive to large-scale production. The regeneration steps of the gradient filtration multi-layer functionalized separation membrane prepared by this invention are simple. Cleaning of the porous separation membrane and nanofiber layer, as well as desorption of the adsorbent, are achieved through a one-step backwashing. Typically, adsorbent regeneration requires the use of desorbents such as acids, chelating agents, or alcohols. Separation membrane regeneration requires backwashing with appropriate cleaning agents. Existing technologies for developing separation membranes with adsorption functions require step-by-step regeneration of adsorption performance and cleaning of the separation membrane. This invention prepares a functional separation membrane without step-by-step cleaning and regeneration; a one-step regeneration of the separation membrane, nanofiber layer, and supramolecular compound is achieved through a backwashing process using a mixture of desorbent and cleaning agent. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions of this invention are only used to explain this invention and are not intended to limit this invention.

[0024] Example 1

[0025] PVDF with a molecular weight of 180,000 was dissolved in DMF and heated and stirred at 90°C for 2 hours to form a homogeneous casting solution. The casting solution was then immersed in a coagulation bath consisting of a 6 wt% aqueous solution of PVA with a molecular weight of 75,000 for 30 minutes. The formed separation membrane was then removed from the coagulation bath and immersed in deionized water for 12 hours to remove surface-adhered PVA.

[0026] 10g of carboxymethyl-β-cyclodextrin was dissolved in 90g of DMF to form a homogeneous solution. Then, 10g of PVA was added and stirred until completely dissolved. Electrospinning was then performed. The spinning voltage was 15kV, the humidity was 50%, the receiving device was the PVDF separation membrane prepared above, and the spinning time was 60min, resulting in a functional separation membrane with gradient filtration performance.

[0027] The prepared functional separation membrane was treated with DMF vapor and glutaraldehyde vapor for 10 min and 30 min, respectively, at ambient temperatures of 25℃ and 25℃.

[0028] The separation performance of the functional separation membrane was tested using a simulated wastewater mixture composed of copper ions, phenolphthalein, and bovine serum albumin (BSA). After one simulated wastewater filtration, the membrane removed 92% of copper ions, 98% of phenolphthalein, and 95% of BSA. After backwashing with a cleaning solution composed of hydrochloric acid and ethanol, the membrane flux recovery rate was 99%. After 10 simulated wastewater filtrations, the membrane removed 90% of copper ions, 95% of phenolphthalein, and 97% of BSA, with the flux recovery rate remaining at 90%.

[0029] Example 2

[0030] EVOH with a molecular weight of 200,000 was dissolved in DMSO and heated and stirred at 60°C for 2 hours to form a homogeneous casting solution. The casting solution was then immersed in a coagulation bath consisting of a 6 wt% aqueous solution of PVA with a molecular weight of 75,000 for 30 minutes. The formed separation membrane was then removed from the coagulation bath and immersed in deionized water for 12 hours to remove surface-adhered PVA.

[0031] 10g of carboxymethyl-β-cyclodextrin was dissolved in 90g of DMSO to form a homogeneous solution. Then, 10g of PVA was added and stirred until completely dissolved. Electrospinning was then performed. The spinning voltage was 15kV, the humidity was 50%, the receiving device was the PVDF separation membrane prepared above, and the spinning time was 60min, resulting in a functional separation membrane with gradient filtration performance.

[0032] The prepared functional separation membrane was treated with DMSO vapor and glutaraldehyde vapor for 10 min and 30 min, respectively, at ambient temperatures of 25℃ and 25℃.

[0033] The separation performance of the functional separation membrane was tested using a simulated wastewater mixture composed of copper ions, phenolphthalein, and bovine serum albumin (BSA). After one simulated wastewater filtration, the membrane removed 93% of copper ions, 97% of phenolphthalein, and 93% of BSA. After backwashing with a cleaning solution composed of hydrochloric acid and ethanol, the membrane flux recovery rate was 97%. After 10 simulated wastewater filtrations, the membrane removed 90% of copper ions, 94% of phenolphthalein, and 95% of BSA, with the flux recovery rate remaining at 91%.

[0034] Example 3

[0035] PES with a molecular weight of 150,000 was dissolved in DMAc and heated and stirred at 70°C for 3 hours to form a homogeneous casting solution. The casting solution was then immersed in a coagulation bath consisting of a 6 wt% aqueous solution of PVA with a molecular weight of 75,000 for 30 minutes. The formed separation membrane was then removed from the coagulation bath and immersed in deionized water for 12 hours to remove the PVA adhering to the surface.

[0036] 10g of carboxymethyl-β-cyclodextrin was dissolved in 90g of DMAc to form a homogeneous solution. Then, 10g of PVA was added and stirred until completely dissolved. Electrospinning was then performed. The spinning voltage was 15kV, the humidity was 50%, the receiving device was the PVDF separation membrane prepared above, and the spinning time was 60min, resulting in a functional separation membrane with gradient filtration performance.

[0037] The prepared functional separation membrane was treated with DMAc vapor and glutaraldehyde vapor for 10 min and 30 min, respectively, at ambient temperatures of 25℃ and 25℃.

[0038] The separation performance of the functional separation membrane was tested using a simulated wastewater mixture composed of copper ions, phenolphthalein, and bovine serum albumin (BSA). After one simulated wastewater filtration, the membrane removed 95% of copper ions, 99% of phenolphthalein, and 95% of BSA. After backwashing with a cleaning solution composed of hydrochloric acid and ethanol, the membrane flux recovery rate was 98%. After 10 simulated wastewater filtrations, the membrane maintained removal rates of 95% of copper ions, 99% of phenolphthalein, and 95% of BSA, with the flux recovery rate remaining at 93%.

[0039] Example 4

[0040] PVDF with a molecular weight of 180,000 was dissolved in DMF and heated and stirred at 90°C for 2 hours to form a homogeneous casting solution. The casting solution was then immersed in a coagulation bath consisting of a 6 wt% aqueous solution of PVA with a molecular weight of 75,000 for 30 minutes. The formed separation membrane was then removed from the coagulation bath and immersed in deionized water for 12 hours to remove surface-adhered PVA.

[0041] 10g of carboxymethyl-β-cyclodextrin was dissolved in 90g of DMF to form a homogeneous solution. Then, 10g of PVA was added and stirred until completely dissolved. Electrospinning was then performed. The spinning voltage was 15kV, the humidity was 50%, the receiving device was the PVDF separation membrane prepared above, and the spinning time was 60min, resulting in a functional separation membrane with gradient filtration performance.

[0042] The separation performance of the functional separation membrane was tested using a mixed simulated wastewater containing copper ions, phenolphthalein, and bovine serum albumin (BSA). After one simulated wastewater treatment, the membrane removed 90%, 94%, and 94% of copper ions, phenolphthalein, and BSA, respectively. After backwashing with a cleaning solution composed of hydrochloric acid and ethanol, the membrane flux recovery rate was 88%. After 10 simulated wastewater filtrations, the membrane removed 42%, 57%, and 98% of copper ions, phenolphthalein, and BSA, respectively, with the flux recovery rate remaining at 71%.

[0043] Transverse tensile strength (MPa) Example 1 0.42 Example 4 0.28

[0044] Compared to Example 1, Example 4 did not undergo secondary steam treatment, affecting the stability and durability of the membrane during use. Because glutaraldehyde (a crosslinking agent) was not used for steam treatment, the nanofiber layer was prone to dissolution, and the lack of solvent steam treatment caused the nanofiber layer to detach during filtration. Therefore, in one simulated filtration, compared to Example 1, the removal rates of copper ions and phenolphthalein, as well as the flux recovery rate, decreased. As filtration progressed, the drawbacks of not using secondary steam treatment became apparent. Due to the dissolution and detachment of the nanofiber layer, the removal rates of copper ions and phenolphthalein significantly decreased, and the membrane's antifouling performance was also weakened. After 10 simulated filtrations, the flux recovery rate significantly decreased.

[0045] Comparative Example 1

[0046] PVDF with a molecular weight of 180,000 was dissolved in DMF and heated and stirred at 90°C for 2 hours to form a homogeneous casting solution. The casting solution was then immersed in a coagulation bath consisting of a 6 wt% aqueous solution of PVA with a molecular weight of 75,000 for 30 minutes. The formed separation membrane was then removed from the coagulation bath and immersed in deionized water for 12 hours to remove surface-adhered PVA.

[0047] The prepared functional separation membrane was treated with DMF vapor and glutaraldehyde vapor for 10 min and 30 min, respectively, at ambient temperatures of 25℃ and 25℃.

[0048] The separation performance of the functional separation membrane was tested using a simulated wastewater mixture composed of copper ions, phenolphthalein, and bovine serum albumin (BSA). After one simulated wastewater filtration, the membrane removal rates for copper ions, phenolphthalein, and BSA were 0%, 0%, and 87%, respectively. After backwashing with a cleaning solution composed of hydrochloric acid and ethanol, the membrane flux recovery rate was 97%. After 10 simulated wastewater filtrations, the membrane removal rates for copper ions, phenolphthalein, and BSA were 0%, 0%, and 79%, respectively, with the flux recovery rate remaining at 76%.

[0049] Compared to Example 1, Comparative Example 1 lacked the removal capacity for copper ions and phenolphthalein due to the absence of carboxymethyl-β-cyclodextrin and the nanofiber layer. Furthermore, the absence of a nanofiber layer on the membrane surface reduced the membrane's removal capacity for bovine serum albumin (BSA) and decreased its resistance to BSA fouling. After 10 simulated wastewater filtration cycles, the flux decreased sharply, impacting the membrane's permeation separation performance.

[0050] Comparative Example 2

[0051] PVDF with a molecular weight of 180,000 was dissolved in DMF and heated and stirred at 90°C for 2 hours to form a homogeneous casting solution. The casting solution was then immersed in a coagulation bath consisting of a 6 wt% aqueous solution of PVA with a molecular weight of 75,000 for 30 minutes. The formed separation membrane was then removed from the coagulation bath and immersed in deionized water for 12 hours to remove surface-adhered PVA.

[0052] 10g of PVA was dissolved in 90g of DMF to form a homogeneous solution, and then electrospinned. The spinning voltage was 15kV, the humidity was 50%, the receiving device was the PVDF separation membrane prepared above, and the spinning time was 60min to obtain a functional separation membrane.

[0053] The prepared functional separation membrane was treated with DMF vapor and glutaraldehyde vapor for 10 min and 30 min, respectively, at ambient temperatures of 25℃ and 25℃.

[0054] The separation performance of the functional separation membrane was tested using a mixed simulated wastewater containing copper ions, phenolphthalein, and bovine serum albumin (BSA). After one simulated wastewater filtration, the membrane removal rates for copper ions, phenolphthalein, and BSA were 0%, 8%, and 92%, respectively. After backwashing with a cleaning solution composed of hydrochloric acid and ethanol, the membrane flux recovery rate was 97%. After 10 simulated wastewater filtrations, the membrane removal rates for copper ions, phenolphthalein, and BSA were 0%, 7%, and 89%, respectively, with the flux recovery rate remaining at 88%.

[0055] Compared to Example 1, this comparative example lacked carboxymethyl-β-cyclodextrin, resulting in the functional separation membrane having no ability to remove copper ions. However, the addition of a nanofiber layer on the membrane surface enhanced the membrane's ability to remove phenolphthalein, and the nanofiber layer further improved its resistance to bovine serum albumin fouling. After 10 simulated wastewater filtration cycles, the flux decreased only slightly, demonstrating a significant effect on maintaining the permeation separation performance of the functional separation membrane.

[0056] Comparative Example 3

[0057] PVDF with a molecular weight of 180,000 was dissolved in DMF and heated and stirred at 90°C for 2 hours to form a homogeneous casting solution. The casting solution was then immersed in a coagulation bath consisting of a 6 wt% aqueous solution of PVA with a molecular weight of 75,000 for 30 minutes. The formed separation membrane was then removed from the coagulation bath and immersed in deionized water for 12 hours to remove surface-adhered PVA.

[0058] 10g of carboxymethyl-β-cyclodextrin was dissolved in 90g of DMF to form a homogeneous solution. Then, 10g of PVA was added and stirred until completely dissolved. Electrospinning was then performed. The spinning voltage was 15kV, the humidity was 50%, the receiving device was the PVDF separation membrane prepared above, and the spinning time was 60min, resulting in a functional separation membrane with gradient filtration performance.

[0059] The prepared functional separation membrane was treated with DMF vapor and glutaraldehyde vapor for 7 h and 30 min, respectively, at ambient temperatures of 25 °C and 25 °C.

[0060] The separation performance of the functional separation membrane was tested using a simulated wastewater mixture containing copper ions, phenolphthalein, and bovine serum albumin (BSA). After one simulated wastewater filtration, the membrane removed 82% of copper ions, 78% of phenolphthalein, and 100% of BSA. After backwashing with a cleaning solution composed of hydrochloric acid and ethanol, the membrane flux recovery rate was 86%. After 10 simulated wastewater filtrations, the membrane removed 78% of copper ions, 74% of phenolphthalein, and 100% of BSA. The flux recovery rate remained at 57%.

[0061] Compared with Example 1, Comparative Example 3 used DMF vapor treatment for too long, which caused the nanofiber layer to dissolve under prolonged solvent vapor treatment. Carboxymethyl-β-cyclodextrin was coated by the dissolved PVA, resulting in a decrease in the removal rate of copper ions and phenolphthalein. At the same time, the excessively long solvent vapor treatment made the membrane denser, reduced the flux, decreased the antifouling performance, and reduced the flux recovery.

[0062] Comparative Example 4

[0063] PVDF with a molecular weight of 180,000 was dissolved in DMF and heated and stirred at 90°C for 2 hours to form a homogeneous casting solution. The casting solution was then immersed in a coagulation bath consisting of a 6 wt% aqueous solution of PVA with a molecular weight of 75,000 for 30 minutes. The formed separation membrane was then removed from the coagulation bath and immersed in deionized water for 12 hours to remove surface-adhered PVA.

[0064] 10g of carboxymethyl-β-cyclodextrin was dissolved in 90g of DMF to form a homogeneous solution. Then, 10g of PVA was added and stirred until completely dissolved. Electrospinning was then performed. The spinning voltage was 15kV, the humidity was 50%, the receiving device was the PVDF separation membrane prepared above, and the spinning time was 60min, resulting in a functional separation membrane with gradient filtration performance.

[0065] The prepared functional separation membrane was treated with DMF vapor and glutaraldehyde vapor for 10 min and 7 h, respectively, at ambient temperatures of 25℃ and 25℃.

[0066] The separation performance of the functional separation membrane was tested using a mixed simulated wastewater containing copper ions, phenolphthalein, and bovine serum albumin (BSA). After one simulated wastewater filtration, the membrane removed 90%, 99%, and 96% of copper ions, phenolphthalein, and BSA, respectively. After backwashing with a cleaning solution composed of hydrochloric acid and ethanol, the membrane flux recovery rate was 97%. After 10 simulated wastewater filtrations, the membrane removed 88%, 97%, and 99% of copper ions, phenolphthalein, and BSA, respectively, with the flux recovery rate remaining at 73%.

[0067] Compared to Example 1, Comparative Example 4 used glutaraldehyde as a crosslinking agent for an excessively long treatment time. Excessive crosslinking leads to a denser membrane surface and smaller pores, weakening the membrane's antifouling performance. Therefore, after 10 simulated wastewater filtrations, the membrane flux recovery rate significantly decreased.

[0068] Comparative Example 5

[0069] PVDF with a molecular weight of 180,000 was dissolved in DMF and heated and stirred at 90°C for 2 hours to form a homogeneous casting solution. The casting solution was then immersed in a coagulation bath consisting of a 6 wt% aqueous solution of PVA with a molecular weight of 75,000 for 30 minutes. The formed separation membrane was then removed from the coagulation bath and immersed in deionized water for 12 hours to remove surface-adhered PVA.

[0070] 10g of carboxymethyl-β-cyclodextrin was dissolved in 90g of DMF to form a homogeneous solution. Then, 10g of PVA was added and stirred until completely dissolved. Electrospinning was then performed. The spinning voltage was 15kV, the humidity was 50%, the receiving device was the PVDF separation membrane prepared above, and the spinning time was 60min, resulting in a functional separation membrane with gradient filtration performance.

[0071] The functional separation membrane was prepared by DMF vapor treatment for 10 min at an ambient temperature of 25°C.

[0072] The separation performance of the functional separation membrane was tested using a simulated wastewater mixture composed of copper ions, phenolphthalein, and bovine serum albumin (BSA). After one treatment with the simulated wastewater, the membrane removed 91% of copper ions, 94% of phenolphthalein, and 95% of BSA. After backwashing with a cleaning solution composed of hydrochloric acid and ethanol, the membrane flux recovery rate was 87%. After 10 simulated wastewater filtrations, the membrane removed 58% of copper ions, 61% of phenolphthalein, and 96% of BSA, with the flux recovery rate remaining at 79%.

[0073] Transverse tensile strength (MPa) Example 1 0.42 Comparative Example 5 0.40

[0074] Compared to Example 1, Comparative Example 5 used solvent vapor treatment, therefore the transverse tensile strength did not change significantly, indicating good interfacial bonding between the nanofiber layer and the separation membrane. Since no crosslinking agent glutaraldehyde vapor treatment was used, the nanofiber layer became unstable during use, weakening the separation membrane's removal capacity for copper ions and phenolphthalein. However, due to the good interfacial bonding, the difference from Example 1 was not significant after the first filtration. However, after 10 filtrations, the shortcomings of not using crosslinking agent glutaraldehyde treatment became apparent, significantly reducing the separation membrane's removal capacity for copper ions and phenolphthalein. Furthermore, the dissolved nanofiber layer entered the membrane with the filtrate, clogging the membrane pores and causing a significant decrease in the membrane flux recovery rate.

[0075] Comparative Example 6

[0076] PVDF with a molecular weight of 180,000 was dissolved in DMF and heated and stirred at 90°C for 2 hours to form a homogeneous casting solution. The casting solution was then immersed in a coagulation bath consisting of a 6 wt% aqueous solution of PVA with a molecular weight of 75,000 for 30 minutes. The formed separation membrane was then removed from the coagulation bath and immersed in deionized water for 12 hours to remove surface-adhered PVA.

[0077] 10g of carboxymethyl-β-cyclodextrin was dissolved in 90g of DMF to form a homogeneous solution. Then, 10g of PVA was added and stirred until completely dissolved. Electrospinning was then performed. The spinning voltage was 15kV, the humidity was 50%, the receiving device was the PVDF separation membrane prepared above, and the spinning time was 60min, resulting in a functional separation membrane with gradient filtration performance.

[0078] The prepared functional separation membranes were treated with glutaraldehyde vapor for 30 min at an ambient temperature of 25℃.

[0079] The separation performance of the functional separation membrane was tested using a simulated wastewater mixture composed of copper ions, phenolphthalein, and bovine serum albumin (BSA). After one treatment with the simulated wastewater, the membrane removed 92% of copper ions, 96% of phenolphthalein, and 94% of BSA. After backwashing with a cleaning solution composed of hydrochloric acid and ethanol, the membrane flux recovery rate was 91%. After 10 simulated wastewater filtrations, the membrane removed 57% of copper ions, 61% of phenolphthalein, and 97% of BSA, with the flux recovery rate remaining at 78%.

[0080]

[0081]

[0082] Compared to Example 1, Comparative Example 6 used glutaraldehyde vapor treatment as a crosslinking agent instead of solvent vapor treatment, resulting in poor interfacial bonding and a 26% decrease in transverse tensile strength. In the first simulated filtration, the poor interfacial bonding had no significant impact, and the removal rates of copper ions and phenolphthalein by the separation membrane were not significantly different compared to Example 1. However, as filtration progressed, due to the poor interfacial bonding, the nanofiber layer detached under the impact of the filtrate. After 10 simulated filtrations, the removal efficiency of the separation membrane for copper ions and phenolphthalein significantly decreased. Simultaneously, the detachment of the nanofiber layer reduced the membrane's antifouling performance and significantly decreased the flux recovery rate.

[0083] Comparative Example 7

[0084] PVDF with a molecular weight of 180,000 was dissolved in DMF and heated and stirred at 90°C for 2 hours to form a homogeneous casting solution. The casting solution was then immersed in a coagulation bath consisting of a 6 wt% aqueous solution of PVA with a molecular weight of 75,000 for 30 minutes. The formed separation membrane was then removed from the coagulation bath and immersed in deionized water for 12 hours to remove surface-adhered PVA.

[0085] 10g of carboxymethyl-β-cyclodextrin was dissolved in 90g of DMF to form a homogeneous solution. Then, 10g of PVA was added and stirred until completely dissolved. Electrospinning was then performed. The spinning voltage was 15kV, the humidity was 50%, the receiving device was the PVDF separation membrane prepared above, and the spinning time was 60min, resulting in a functional separation membrane with gradient filtration performance.

[0086] The prepared functional separation membrane was treated with acetic acid vapor and glutaraldehyde vapor for 10 min and 30 min, respectively, at ambient temperatures of 25℃ and 25℃.

[0087] The separation performance of the functional separation membrane was tested using a mixed simulated wastewater containing copper ions, phenolphthalein, and bovine serum albumin (BSA). After one simulated wastewater filtration, the membrane removed 95% of copper ions, 97% of phenolphthalein, and 95% of BSA. After backwashing with a cleaning solution composed of hydrochloric acid and ethanol, the membrane flux recovery rate was 92%. After 10 simulated wastewater filtrations, the membrane removed 55% of copper ions, 57% of phenolphthalein, and 96% of BSA, with the flux recovery rate remaining at 72%.

[0088] Transverse tensile strength (MPa) Example 1 0.42 Comparative Example 7 0.25

[0089] Compared to Example 1, Comparative Example 7 used non-solvent acetic acid vapor and the crosslinking agent glutaraldehyde for steam treatment. Since acetic acid is a non-solvent, it could not improve the interfacial bonding between the nanofiber layer and the separation membrane, resulting in a 40% decrease in transverse tensile strength. In the first simulated filtration, poor interfacial bonding had no significant impact on the stability of the separation membrane, and the filtration performance was not significantly different from Example 1. However, as filtration continued, poor interfacial bonding made the nanofiber layer prone to detachment, reducing the stability of the separation membrane. After 10 simulated filtrations, the removal rates of copper ions and phenolphthalein by the separation membrane decreased. Simultaneously, due to the detachment of the nanofiber layer, the antifouling performance of the separation membrane was reduced, leading to a significant decrease in the membrane flux recovery rate.

[0090] 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 method for preparing a gradient filtration multi-stage functionalized separation membrane, characterized in that, Includes the following steps: S1. Preparation of support layer by casting method: The first polymer compound is dissolved in a solvent to prepare a casting solution, and then the casting solution is made into a gel layer and immersed in a coagulation bath prepared by the second polymer compound to obtain a porous separation membrane as the support layer. S2. Electrospinning preparation of nanofiber layer: The mixed spinning solution prepared by the second polymer compound and supramolecular compound is electrospinned on the support layer to obtain nanofiber layer, thus obtaining nanofiber layer-porous separation membrane. in The first polymeric compound is one or more of polyvinylidene fluoride, polysulfone, polyethersulfone, carboxymethyl cellulose, polyacrylonitrile, polyvinyl chloride, and ethylene-vinyl alcohol copolymer, with a molecular weight of 20,000-1,000,000; the second polymeric compound is one or more of polyvinyl alcohol, chitosan, polyacrylamide, polyacrylic acid, polyvinylpyrrolidone, and polymaleic anhydride, with a molecular weight of 5,000-500,000; the supramolecular compound is one or more of calixarene, columnar aromatics, cucurbita, α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, hydroxypropyl-β-cyclodextrin, sulfonic acid-β-cyclodextrin, and carboxymethyl-β-cyclodextrin.

2. The preparation method according to claim 1, characterized in that, It also includes S3, which involves first steam treating the nanofiber layer-porous separation membrane with solvent vapor for 5 min-6 h, and then steam treating it with crosslinking agent vapor for 5 min-6 h.

3. The preparation method according to claim 2, characterized in that, The crosslinking agent is one or more of epichlorohydrin, glutaraldehyde, adipic acid, glyoxal, and butyraldehyde; the solvent is one or more of N,N-dimethylformamide, dimethyl sulfoxide, N,N-dimethylacetamide, methanol, ethanol, and acetic acid.

4. The preparation method according to claim 1, characterized in that, The ambient temperature for the first steam treatment is 20℃-80℃, and the ambient temperature for the second steam treatment is 20℃-80℃.

5. The preparation method according to claim 1, characterized in that, The concentration of the casting solution is 5wt%-50wt%, the concentration of the coagulation bath is 1wt%-20wt%, and the concentration of the mixed spinning solution is 1wt%-25wt%.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the second high molecular weight compound and the ultrahigh molecular weight compound in S2 is 1:10-10:

1.

7. A gradient filtration multi-stage functionalized separation membrane prepared by the preparation method according to any one of claims 1-6.

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