An oil stain self-cleaning composite filtration membrane and a preparation method and application thereof

Abstract

The application belongs to the technical field of membranes, and particularly relates to an oil stain self-cleaning composite filtration membrane and a preparation method and application thereof. The oil stain self-cleaning composite filtration membrane provided by the application comprises a polyvinylidene fluoride porous base membrane, one side of the polyvinylidene fluoride porous base membrane is enriched with CoFe2O4@PDA composite nanoparticles; the CoFe2O4@PDA composite nanoparticles have a core-shell structure, the inner core is CoFe2O4 nanoparticles, and the shell layer coated on the surface of the inner core is polydopamine; and the oil stain self-cleaning composite filtration membrane has a rough structure with unevenness on the surface of the side enriched with the CoFe2O4@PDA composite nanoparticles. The oil stain self-cleaning composite filtration membrane has high efficient oil-water separation capacity, stable anti-pollution performance and high efficient self-cleaning capacity.

Description

Technical Field

[0001] This invention belongs to the field of membrane technology, and specifically relates to an oil-stain self-cleaning composite filter membrane, its preparation method, and its application. Background Technology

[0002] Oily wastewater widely originates from oil extraction, chemical production, food processing, and residential discharge, typically containing large amounts of stable emulsified oil droplets, dissolved organic matter, and suspended solid particles. This type of wastewater is difficult to separate naturally, not only placing a severe burden on the ecological environment but also significantly increasing wastewater treatment costs. Currently used separation technologies include flotation, centrifugation, adsorption, and gravity sedimentation, but these generally suffer from high energy consumption, insufficient efficiency, and a tendency to cause secondary pollution. Membrane separation technology, due to its advantages of high efficiency, energy saving, and small footprint, has become an important means of treating emulsified oily wastewater. However, existing separation membranes exhibit low oil-water separation efficiency, and oil deposits on the membrane surface or in the membrane channels lead to decreased membrane flux and irreversible fouling, severely affecting membrane stability and lifespan.

[0003] Therefore, there is an urgent need to develop a composite membrane material that combines high-efficiency oil-water separation capability, stable anti-fouling performance, and high-efficiency self-cleaning capability. Summary of the Invention

[0004] The purpose of this invention is to provide an oil-stain self-cleaning composite filter membrane, its preparation method, and its application. This oil-stain self-cleaning composite filter membrane has the advantages of high-efficiency oil-water separation capability, stable anti-fouling performance, and high-efficiency self-cleaning capability.

[0005] The first aspect of the present invention provides an oil-stain self-cleaning composite filter membrane, the oil-stain self-cleaning composite filter membrane comprising a polyvinylidene fluoride (PVDF) porous substrate membrane, wherein one side of the polyvinylidene fluoride porous substrate membrane is enriched with CoFe2O4@PDA composite nanoparticles.

[0006] The CoFe2O4@PDA composite nanoparticles have a core-shell structure, with the core consisting of CoFe2O4 nanoparticles and the shell coating the surface of the core consisting of polydopamine.

[0007] The oil-stain self-cleaning composite filter membrane has an uneven, rough structure on one side of the surface where the CoFe2O4@PDA composite nanoparticles are enriched.

[0008] In some embodiments, the CoFe2O4 nanoparticles are spherical CoFe2O4 nanoparticles;

[0009] The CoFe2O4@PDA composite nanoparticles exhibit magnetic and visible light responsive properties.

[0010] In some embodiments, the water flux of the self-cleaning oil-stained composite filter membrane is 4000-4800 L·m at 25°C and 1 bar. -2 ·h -1 ·bar -1 .

[0011] A second aspect of the present invention provides a method for preparing the above-mentioned self-cleaning composite filter membrane for oil stains, comprising the following steps:

[0012] 1) CoFe2O4 nanoparticles were dispersed in Tris-HCl buffer (tris(hydroxymethyl)aminomethane) hydrochloride buffer, polydopamine monomers were added to carry out self-polymerization, and then magnetic solids were collected by magnetic separation to obtain CoFe2O4@PDA composite nanoparticles with polydopamine coating on the surface.

[0013] 2) Mix polyvinylidene fluoride, pore-forming agent, solvent and CoFe2O4@PDA composite nanoparticles obtained in step 1) to form a casting solution;

[0014] 3) The casting solution obtained in step 2) is coated on the workbench and then placed under an external magnetic field. Under the action of the external magnetic field, the CoFe2O4@PDA composite nanoparticles in the casting solution gather on the upper surface of the casting solution and are then immersed in a coagulation bath for phase transformation to obtain the oil-stain self-cleaning composite filter membrane.

[0015] PVDF membranes themselves have almost no pores, but by adding pore-forming agents, a porous structure can be formed, which helps with oil-water separation.

[0016] The casting solution is viscous, and the CoFe2O4@PDA composite nanoparticles are uniformly dispersed in the casting solution. Under the action of an external magnetic field, they only migrate to a certain extent and cannot be absorbed.

[0017] In some embodiments, the pH of the Tris-HCl buffer solution described in step 1) is 8.0-9.0;

[0018] In some embodiments, the mass ratio of the polydopamine monomer to the CoFe2O4 nanoparticles in step 1) is 1:(5-10).

[0019] In some embodiments, the CoFe2O4 nanoparticles described in step 1) are dispersed in Tris-HCl buffer to form a dispersion, wherein the mass concentration of the CoFe2O4 nanoparticles in the dispersion is 0.005-0.2 g / mL;

[0020] In some embodiments, the monomer of the polydopamine in step 1) includes at least one of dopamine and dopamine hydrochloride;

[0021] In some embodiments, the magnetic separation and collection of magnetic solids step is followed by a washing and drying step.

[0022] In some embodiments, the casting solution described in step 2) comprises, by mass percentage, 12.0wt%-13.0wt% polyvinylidene fluoride, 0.8wt%-1.5wt% pore-forming agent, 0.1wt%-0.5wt% CoFe2O4@PDA composite nanoparticles, and 85wt%-86.8wt% solvent.

[0023] In some embodiments, the pore-forming agent in step 2) includes polyvinylpyrrolidone (PVP).

[0024] And / or, the solvent includes N-methylpyrrolidone (NMP).

[0025] In some embodiments, the magnetic field strength in step 3) is 0.05-0.10 T, and the magnetic field application time is 0.5-2.0 min; for example, optionally, the magnetic field strength is 0.05T, 0.06T, 0.07T, 0.08T, 0.09T, or 0.10 T, and the magnetic field application time is 0.5 min, 0.7 min, 1 min, 1.3 min, 1.5 min, 1.8 min, or 2.0 min.

[0026] In some embodiments, the coagulation bath in step 3) comprises water; preferably, the coagulation bath in step 3) is deionized water.

[0027] In some embodiments, after applying the casting solution obtained in step 2) to the workbench surface in step 3), the process further includes a settling treatment before placing the workbench under an external magnetic field.

[0028] In some implementations, the settling time is 20s-60s.

[0029] After settling, air bubbles generated in the casting solution can be eliminated, preventing the film from having large pores.

[0030] A third aspect of the present invention provides the application of the above-described self-cleaning composite filter membrane for oil stains or the self-cleaning composite filter membrane for oil stains prepared by the above-described preparation method in the fields of mixture separation and / or photocatalysis.

[0031] In some embodiments, the above-described self-cleaning composite filter membrane or the self-cleaning composite filter membrane prepared by the above-described preparation method is used for the separation of oil and water mixtures.

[0032] The technical solution of the present invention has the following advantages:

[0033] This invention provides a new solution for the efficient and sustainable treatment of oily wastewater by directionally enriching CoFe2O4@PDA composite nanoparticles on the membrane surface to form a self-cleaning composite filter membrane. This membrane combines high water throughput, high oil rejection rate, high oil-water separation capability, stable antifouling performance, and high self-cleaning capability.

[0034] The self-cleaning composite filter membrane for oil stains has the following advantages:

[0035] (1) Significantly improves the hydrophilicity of the membrane surface and the superoleophobicity underwater.

[0036] The polydopamine (PDA) layer provides abundant polar groups, and the magnetic field-driven directional migration causes the particles to be uniformly concentrated on the surface, forming an uneven, rough hierarchical structure. This makes the membrane almost non-adherent to oil droplets underwater, and can stably resist fouling.

[0037] (2) Improve membrane flux and separation stability

[0038] Magnetic field modulation promotes the increase of surface pore size and the formation of synergistic water channels, which increases the pure water flux compared to the original PVDF porous membrane, and the oil-water separation performance is stable.

[0039] (3) Achieve efficient self-cleaning driven by visible light

[0040] The narrow bandgap of CoFe2O4 (≈1.4 eV) combined with the light absorption of PDA creates a synergistic effect, which can generate a large number of reactive oxygen free radicals under visible light, rapidly degrade oil stains, achieve efficient self-cleaning, and restore more than 99% flux over multiple cycles.

[0041] (4) The contamination-cleaning coupling mechanism is clear and reliable.

[0042] Combining experiments and molecular dynamics simulations, this invention reveals the mechanism of hydrogen bond network reconstruction and interfacial tension reduction of CoFe2O4@PDA at the oil-water interface, providing a theoretical basis for membrane fouling control. Attached Figure Description

[0043] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of the preparation process of the CoFe2O4@PDA / PVDF photocatalytic self-cleaning composite membrane in Example 1 of the present invention.

[0045] Figure 2The image shows the morphology of the CoFe2O4 and CoFe2O4@PDA composite nanoparticles in Example 1 of this invention.

[0046] in: Figure 2 Figure a shows the SEM image of CoFe2O4; Figure 2 Figure b in the middle is a SEM image of CoFe2O4@PDA; Figure 2 Image c is a TEM image of CoFe2O4@PDA; Figure 2 The d-plot in the figure is the EDX elemental distribution map of CoFe2O4@PDA (including the distribution of elements Co, Fe, N, C, and O).

[0047] Figure 3 The diagram shows the structural characterization of CoFe2O4 (marked as cobalt ferrite in the figure), PDA (marked as polydopamine in the figure), and CoFe2O4@PDA composite nanoparticles (marked as polydopamine-encapsulated cobalt ferrite in the figure) in Example 1 of the present invention.

[0048] in: Figure 3 Figure a shows the XRD patterns of CoFe2O4, PDA, and CoFe2O4@PDA composite nanoparticles; Figure 3 Figure b shows the FTIR spectra of CoFe2O4, PDA, and CoFe2O4@PDA composite nanoparticles; Figure 3 Figure c shows the XPS full spectrum of CoFe2O4, PDA, and CoFe2O4@PDA composite nanoparticles; Figure 3 Chinese d-graph Figure 3 China e-Map Figure 3 Figures f in the middle are high-resolution XPS images of Co 2p, Fe 2p, and N 1s of the CoFe2O4@PDA composite nanoparticles.

[0049] Figure 4 These are SEM comparison images and pore size measurement comparison images of different filter membranes in Examples 1-2 and Comparative Examples 1-2 of the present invention;

[0050] in, Figure 4 Comparative Example 1 is denoted as M0, Comparative Example 2 as M1, Example 1 as M2, and Example 2 as M3. Figure 4 Figure a is a SEM image of the filter membrane surface of Comparative Example 1, Figure b is a SEM image of the filter membrane surface of Comparative Example 2, Figure c is a SEM image of the filter membrane surface of Example 1 enriched with CoFe2O4@PDA composite nanoparticles on one side, and Figure d is a SEM image of the filter membrane surface of Example 2 enriched with CoFe2O4@PDA composite nanoparticles on one side. Figure 4Figure e shows the surface pore size measurement of the filter membrane in Comparative Example 1, Figure f shows the surface pore size measurement of the filter membrane in Comparative Example 2, Figure g shows the surface pore size measurement of the filter membrane in Example 1, and Figure h shows the surface pore size measurement of the filter membrane in Example 2.

[0051] Figure 5 These are comparative AFM images of different filter membrane surfaces in Examples 1-2 and Comparative Examples 1-2 of the present invention;

[0052] in: Figure 5 Figure i in the diagram is the AFM image of the filter membrane surface in Comparative Example 1. Figure 5 Figure j in the diagram is the AFM image of the filter membrane surface in Comparative Example 2. Figure 5 The k-image in the image is the AFM image of the filter membrane surface in Example 1. Figure 5 The q-plot in the image is the AFM plot of the filter membrane surface in Example 2;

[0053] Figure 6 Comparison diagrams of surface roughness, XRD patterns, and XPS spectra of different filter membranes in Examples 1-2 and Comparative Examples 1-2 of the present invention;

[0054] in, Figure 6 Figure m in the figure is a comparison of the surface roughness of different filter membranes in Examples 1-2 and Comparative Examples 1-2; Figure 6 Figure n in the figure is a comparison of XRD patterns of different filter membranes in Examples 1-2 and Comparative Examples 1-2. Figure 6 The figure in the figure is a comparison of the XPS spectra of different filter membrane surfaces in Examples 1-2 and Comparative Examples 1-2;

[0055] Figure 7 These are test diagrams showing the wetting performance of the filter membranes in Examples 1-2 and Comparative Examples 1-2 of the present invention;

[0056] in, Figure 7 Figure a in the figure is a comparison diagram of the water contact angles of the filter membranes in Examples 1-2 and Comparative Examples 1-2; Figure 7 Figure b in the figure is a comparison of the water contact angle changes of the filter membrane surface from 0 s to 10 s in Examples 1-2 and Comparative Examples 1-2. Figure 7 Figure c in the figure is a comparison of the underwater oil contact angles of the filter membranes in Examples 1-2 and Comparative Examples 1-2;

[0057] Figure 8 The graphs show a comparison of the pure water flux and the oil-water emulsion separation performance of the filter membranes in Examples 1-2 and Comparative Examples 1-2 of the present invention.

[0058] in Figure 8 Figure a in the figure shows the pure water flux of the filter membranes in Examples 1-2 and Comparative Examples 1-2. Figure 8Figure b in the figure shows the water flux and rejection rate of the filter membranes in Examples 1-2 and Comparative Examples 1-2 during oil-water emulsion separation. Figure 8 Figure c in the figure shows the flux and rejection rate of the filter membrane prepared in Example 1 for different types of oil;

[0059] Figure 9 This is a test diagram of the photocatalytic self-cleaning performance of the composite membrane in an embodiment of the present invention;

[0060] in, Figure 9 Figure a shows the change in filter membrane flux in Example 2 and Comparative Example 1 after light exposure or water washing. Figure 9 Figure b in the figure shows a comparison of the flux recovery rates of the filter membranes in Example 2 and Comparative Example 1 under different cleaning methods. Figure 9 Figure c in Example 2 is a comparison of the flux recovery rate after each cleaning cycle in the 5 filtration cleaning cycles of the filter membrane.

[0061] Figure 10 This is a graph showing the flux change over time during five filtration and cleaning cycles of the filter membrane in Embodiment 2 of the present invention.

[0062] Figure 11 This is an EPR test image of the photocatalytic generation of reactive oxygen free radicals by the composite filter membrane in Example 1 of the present invention;

[0063] in, Figure 11 Figure a in the diagram is a comparison of the formation of •OH. Figure 11 The b-th graph in the image represents •O2. - Generate a comparison chart. Detailed Implementation

[0064] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0065] It should be understood that the terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” as used herein may also include the plural forms. The terms “comprising,” “including,” “containing,” and “having” are inclusive and therefore indicate the presence of the stated features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein are not construed as requiring them to be performed in a particular order described or illustrated unless the order of performance is explicitly indicated. It should also be understood that additional or alternative steps may be used.

[0066] In the description of the embodiments of this invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this invention, "multiple" means two or more, unless otherwise explicitly defined.

[0067] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0068] In the description of the embodiments of this invention, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0069] In the description of the embodiments of the present invention, the term "multiple" refers to two or more (including two), similarly, "multiple groups" refers to two or more (including two groups), and "multiple pieces" refers to two or more (including two pieces).

[0070] In the description of the embodiments of the present invention, unless otherwise explicitly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention according to the specific circumstances.

[0071] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or through existing methods; unless otherwise specified, the amounts of experimental reagents used are the amounts used in conventional experimental operations; unless otherwise specified, the experimental methods are conventional methods. It should be further noted that the following descriptions are merely exemplary and not intended to limit the specific scope of the invention. Moreover, the comparative examples below are selected to compare with the technical solutions of the present invention to demonstrate the advancement of the present invention, and do not necessarily represent prior art in this technical field.

[0072] A schematic diagram of the overall preparation process of the CoFe2O4@PDA / PVDF photocatalytic self-cleaning composite membrane of this invention can be found here. Figure 1 As shown, the process mainly includes three key steps: the formation of magnetic CoFe2O4@PDA nanoparticles, the preparation of the polymer casting solution, and magnetic field-assisted solvent-induced phase inversion (MNIPS) film formation. As illustrated, the magnetic CoFe2O4 particles first undergo surface functionalization through dopamine self-polymerization, resulting in enhanced hydrophilicity and interfacial bonding. Subsequently, these functionalized magnetic CoFe2O4@PDA nanoparticles are dispersed into a casting solution composed of PVDF, PVP, and NMP, and migrate to the film surface under the influence of an external magnetic field (e.g., a flat magnet), thus forming a continuous and uniform layer of magnetic CoFe2O4@PDA nanoparticles on the film surface. Finally, phase inversion is completed through water bath solidification, resulting in a composite film with significant hydrophilicity, enhanced roughness, and surface photocatalytic activity. Figure 1 The invention clearly demonstrates the unique membrane-forming strategy of magnetic field-controlled directional enrichment of nanoparticles on the membrane surface, which is also an important foundation for realizing the photocatalytic self-cleaning ability and efficient oil-water separation performance of the composite membrane.

[0073] Example 1

[0074] This embodiment provides a method for preparing a self-cleaning composite filter membrane for oil stains. A schematic diagram of the preparation process is shown below. Figure 1 As shown, it includes the following steps:

[0075] 1) Weigh 1.0 g of spherical CoFe2O4 nanoparticles and add them to 100 mL of Tris-HCl buffer solution with pH 8.5. Stir mechanically to form a uniform dispersion. Then add 200 mg of dopamine hydrochloride to the dispersion and continue stirring for 3 h to allow dopamine to self-polymerize under alkaline conditions and coat the surface of CoFe2O4, forming core-shell structured CoFe2O4@PDA composite nanoparticles (the core is CoFe2O4 nanoparticles, and the shell coating the surface of the core is polydopamine). Then collect the product by magnetic separation and wash it three times with deionized water. Dry it under vacuum at 60 °C to obtain CoFe2O4@PDA composite nanoparticles.

[0076] 2) Add 4.5 g PVDF and 0.5 g PVP to 32.1 g NMP solvent and stir until completely dissolved to form a transparent and homogeneous polymer solution. Then add the CoFe2O4@PDA composite nanoparticles obtained in step 1) and stir continuously at 300 r / min until a stable, non-agglomerated casting solution is obtained. The mass content of CoFe2O4@PDA composite nanoparticles in the casting solution is 0.5 wt%. The resulting casting solution has good rheological stability, which can provide the preconditions for particle migration in the subsequent phase transformation process.

[0077] 3) The casting solution obtained in step 2) is uniformly coated on the surface of a glass plate and left to stand in the air for 30 seconds. Then, a flat magnet with a size of 10 cm × 15 cm is placed 1 cm above the casting solution with a magnetic field strength of 0.10 T and a magnetic field duration of 0.5 min. This causes the CoFe2O4@PDA composite nanoparticles in the casting solution to migrate directionally to one side of the membrane surface under the action of the magnetic field and form an enrichment layer. The glass plate and the casting solution are then slowly immersed in deionized water (coagulation bath) to complete the solvent-inducible phase inversion (MNIPS) process. The glass plate is then immersed in deionized water to remove residual solvent, resulting in an oil-resistant self-cleaning composite filter membrane (denoted as M2).

[0078] Figure 2 shows the SEM image of CoFe2O4, and the SEM, TEM, and EDX elemental distribution maps of the CoFe2O4@PDA composite nanoparticles in this embodiment. Figure 2 Figure a shows the SEM image of CoFe2O4; Figure 2 Figure b in the middle is a SEM image of CoFe2O4@PDA; Figure 2 Image c is a TEM image of CoFe2O4@PDA; Figure 2 The d-plot in the image is the EDX elemental distribution map of CoFe2O4@PDA (including the distribution of elements Co, Fe, N, C, and O); from Figure 2 It can be seen that the CoFe2O4@PDA composite nanoparticles have good dispersion and complete morphology, and PDA forms a uniform coating layer on the surface;

[0079] Depend on Figure 2 It is evident that the CoFe2O4@PDA composite nanoparticles prepared in this invention exhibit typical characteristics in both morphology and structure. Figure 2 Figure a shows a SEM image of CoFe2O4, which reveals that the particles are approximately spherical with uniform size and an average size of about 82 nm. Figure 2 Figure b in the middle and Figure 2 Compared to Figure a, the surface of the particle is significantly smoother, indicating that after being coated with dopamine, a continuous PDA thin layer structure is formed on the particle surface, making the particle surface more uniform and the interface more stable. Figure 2 Figure c shows that the lattice fringe spacing is 0.256 nm, corresponding to the (311) crystal plane of CoFe2O4, indicating that the PDA coating did not destroy the crystal structure of CoFe2O4. Figure 2 The d-plot further confirms the uniform distribution of C, N, O, Fe, and Co through EDX elemental mapping, with the presence of N element in particular demonstrating that PDA has been successfully coated on the CoFe2O4 surface. Overall, Figure 2 This indicates that the CoFe2O4@PDA composite particles have good dispersibility, stability, and abundant nitrogen-containing functional groups on the surface, which provide key active sites for subsequent photocatalytic reactions and hydrophilic enhancement on the membrane surface.

[0080] The structural characterization diagrams of CoFe2O4 (labeled as cobalt ferrite in the figure), PDA (labeled as polydopamine in the figure), and CoFe2O4@PDA composite nanoparticles (labeled as polydopamine-encapsulated cobalt ferrite in the figure) in this embodiment are shown below. Figure 3 As shown, where: Figure 3 Figure a shows the XRD patterns of CoFe2O4, PDA, and CoFe2O4@PDA composite nanoparticles; Figure 3 Figure b shows the FTIR spectra of CoFe2O4, PDA, and CoFe2O4@PDA composite nanoparticles; Figure 3 Figure c shows the XPS full spectrum of CoFe2O4, PDA, and CoFe2O4@PDA composite nanoparticles; Figure 3 Chinese d-graph Figure 3 China e-Map Figure 3 The middle f figure shows the high-resolution XPS images of Co 2p, Fe 2p, and N 1s of the CoFe2O4@PDA composite nanoparticles.

[0081] Depend on Figure 3 visible, Figure 3 The XRD results in Figure a show that CoFe2O4 exhibits spinel-type characteristic diffraction peaks at positions such as 30.08°, 35.44°, and 62.58°, with sharp peak shapes, indicating that it possesses a good crystal structure. After PDA coating, the diffraction peak positions of CoFe2O4@PDA did not change significantly, indicating that the composite material still maintains its original crystal structure. Figure 3 In Figure b, the PDA is 1497 cm. -1 and 1606 cm -1 The characteristic peaks correspond to N–H and C–O functional groups, respectively, while CoFe2O4 has a peak at 415 cm⁻¹. -1 With 606 cm -1 The characteristic peaks correspond to Fe–O and Co–O bonds, respectively. CoFe2O4@PDA has absorption bands of both, proving that PDA has been successfully coated with CoFe2O4. Figure 3 The XPS full spectrum of the c-plot further confirmed the presence of five elements: C, N, O, Co, and Fe. The presence of N 1s provides strong evidence for the core-shell structure of the PDA. Figure 3 d-graph and Figure 3 The peak positions of Co 2p and Fe 2p in the e-graph clearly reveal the Co content in the CoFe2O4@PDA composite nanoparticles. 2+ / Co 3+ with Fe 2+ / Fe 3+ The synergistic presence of these elements indicates that the surface of this composite material can provide abundant electron transfer sites. Figure 3 In the f-figure, the pyridine nitrogen and amino group peaks of N 1s indicate that PDA in the CoFe2O4@PDA composite nanoparticles provides good hydrophilicity and complexation ability. Overall, Figure 3 The successful composite of CoFe2O4 and PDA was fully demonstrated, while maintaining the structural integrity required for photocatalysis and magnetism.

[0082] Example 2

[0083] This embodiment provides a method for preparing a self-cleaning composite filter membrane for oil stains. The only difference between this method and that of Embodiment 1 is that the magnetic field action time in step 3) is 2 minutes. The remaining steps are the same as those of Embodiment 1. (The resulting self-cleaning composite filter membrane for oil stains is denoted as M3).

[0084] Comparative Example 1

[0085] This comparative example provides a method for preparing a filter membrane, comprising the following steps:

[0086] 1) Add 4.5 g PVDF and 0.5 g PVP to 32.1 g NMP solvent, and stir until completely dissolved to form a transparent and homogeneous polymer solution. Continue stirring at 300 r / min until a stable, non-agglomerated casting solution is obtained.

[0087] 2) The casting solution obtained in step 1) is uniformly coated on the surface of the glass plate and left to stand in the air for 30 seconds. Then, the glass plate and the casting solution are slowly immersed in deionized water (coagulation bath) to complete the solvent-inducible phase inversion (MNIPS) process. The glass plate is then immersed in deionized water to remove residual solvent and obtain a filter membrane (denoted as M0).

[0088] The filter membrane used in this comparative example is a pure PVDF membrane with a smooth surface, strong hydrophobicity, and low surface roughness.

[0089] Comparative Example 2

[0090] This comparative example provides a composite filter membrane, which is the same as steps 1) and 2 of Example 1. The only difference from Example 1 is that in step 3), the casting solution obtained in step 2) is uniformly coated on the surface of a glass plate and left to stand in the air for 30 seconds. Then, the glass plate and the casting solution are slowly immersed in a coagulation bath (water) to complete the solvent-inducible phase inversion (MNIPS) process. The glass plate is then immersed in deionized water to remove residual solvent, and the composite filter membrane (denoted as M1) is obtained.

[0091] In this comparative example, the CoFe2O4@PDA composite nanoparticles in the composite filter membrane are randomly distributed inside the membrane, and no enrichment layer is formed on the surface.

[0092] Test Example 1

[0093] The oil-stain self-cleaning composite filter membranes of Examples 1-2 and the filter membranes of Comparative Examples 1-2 were subjected to microscopic morphology and structural characterization analysis, including SEM characterization analysis, pore size measurement, atomic force microscopy (AFM) testing, XRD characterization analysis and XPS characterization analysis.

[0094] The test results of SEM characterization analysis and pore size measurement are as follows: Figure 4 As shown, where: Figure 4 In this diagram, Comparative Example 1 is denoted as M0, Comparative Example 2 as M1, Example 1 as M2, and Example 2 as M3 (the same notation is used for other figures). Figure 4 Figure a is a SEM image of the filter membrane surface of Comparative Example 1, Figure b is a SEM image of the filter membrane surface of Comparative Example 2, Figure c is a SEM image of the filter membrane surface of Example 1 enriched with CoFe2O4@PDA composite nanoparticles on one side, and Figure d is a SEM image of the filter membrane surface of Example 2 enriched with CoFe2O4@PDA composite nanoparticles on one side. Figure 4Figure e is a measurement diagram of the surface pore size of the filter membrane in Comparative Example 1, Figure f is a measurement diagram of the surface pore size of the filter membrane in Comparative Example 2, Figure g is a measurement diagram of the surface pore size of the filter membrane in Example 1, and Figure h is a SEM image of the surface of the filter membrane in Example 2.

[0095] The surface of the oil-stain self-cleaning composite filter membranes (one side of the membrane surface enriched with CoFe2O4@PDA composite nanoparticles) of Examples 1-2 and the filter membranes of Comparative Examples 1-2 were tested using atomic force microscopy (AFM). The AFM characterization analysis results are as follows: Figure 5 As shown, where Figure 5 Figure i in the diagram is the AFM image of the filter membrane surface in Comparative Example 1. Figure 5 Figure j in the diagram is the AFM image of the filter membrane surface in Comparative Example 2. Figure 5 The k-image in the image is the AFM image of the filter membrane surface in Example 1. Figure 5 The q-plot in the figure is the AFM image of the filter membrane surface in Example 2. Surface roughness was measured using atomic force microscopy (AFM), and the results are shown in Table 1. Figure 6 As shown in the m-graph.

[0096] The oil-stain self-cleaning composite filter membranes of Examples 1-2 and the filter membranes of Comparative Examples 1-2 were characterized by XRD and XPS. The XPS characterization results are as follows: Figure 6 The n-plot and o-plot are shown in the diagram. Figure 6 The n-figure in the figure is the XRD pattern of different filter membranes in Examples 1-2 and Comparative Examples 1-2; Figure 6 The figure in the figure is a comparison of the XPS spectra of different filter membrane surfaces in Examples 1-2 and Comparative Examples 1-2.

[0097] Table 1

[0098]

[0099] Depend on Figure 4 It can be seen that the four filter membrane samples of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 show significant differences in surface morphology, roughness, and surface chemical structure. Figure 4 Figures a–d in the table show that the surface of the filter membrane M0 (without loaded particles) in Comparative Example 1 is extremely smooth. However, with the addition of CoFe2O4@PDA composite nanoparticles and a magnetic field, the surfaces of the filter membranes in Examples 1 and 2 become rough. In particular, Example 2 was subjected to the magnetic field for the longest time, and its membrane surface structure is the most obvious, exhibiting typical particle accumulation and rough protrusion structure. This indicates that the magnetic field-driven process achieved a large-scale directional enrichment of CoFe2O4@PDA composite nanoparticles. In Examples 1 and 2, the CoFe2O4@PDA composite nanoparticles are continuously distributed on the membrane surface, and the roughness is significantly improved. Figure 4The e-h diagram shows that the pore size on the membrane surface increases sequentially with particle enrichment, giving the membrane a more favorable water channel structure. Figure 5 AFM results for the i, j, k, and q plots and Figure 6 The results in Figure 1 and Table 1 further reveal that the roughness of the four filter membranes in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 are significantly different. Among them, the filter membrane in Example 2 is the roughest, and the arithmetic mean deviation Ra and root mean square deviation Rq values ​​are significantly higher than those of the other samples. This rough surface can significantly enhance the hydrophilicity and underwater superoleophobicity of the membrane. Figure 6 In the XRD results of the n-plot, the (311) and (440) diffraction peaks of CoFe2O4 appear in M1–M3, proving that the particles successfully entered the film and were enriched on the surface. Figure 6 XPS analysis of the o-plot showed that the N signal was strongest in Example 2 (M3), further verifying the co-enrichment of PDA and CoFe2O4. Figure 4 , Figure 5 , Figure 6 Overall, the results show that the magnetic field drive and functionalized nanoparticles together determine the surface properties of the composite film, which is the core mechanism for the high performance of the film.

[0100] Test Example 2

[0101] Wetting performance test of composite membrane

[0102] The water contact angle (WCA) and oil contact angle (UOCA) of the oil-stain self-cleaning composite filter membranes (one side of the membrane surface enriched with CoFe2O4@PDA composite nanoparticles) of Examples 1-2 and the membrane surfaces of Comparative Examples 1-2 were tested using 3 μL water droplets as test samples.

[0103] Water contact angle test method: Before testing, the membrane sample was thoroughly dried at room temperature and fixed on a clean glass slide to ensure a smooth surface. A drop of deionized water (approximately 2-5 μL) was slowly added to the membrane surface using a micro-syringe. The contact angle measurement instrument was used to characterize the wettability of the membrane surface in air. Three to five different areas were selected for testing each sample, and the average value was taken as the final data. The results are shown in Table 2. Figure 7 As shown in Figure a, the change in water contact angle during the test process is as follows: Figure 7 As shown in Figure b.

[0104] Oil contact angle test method (underwater oil drop): The test was conducted in an aqueous environment using a contact angle meter. First, the membrane sample was completely immersed in deionized water for at least 30 minutes to ensure thorough wetting and remove air from the pores. Then, the sample was horizontally fixed in a water tank, and a single drop of oil-phase diiodomethane was slowly added to the membrane surface using a micro-injection needle. The side-view profile image of the oil droplet on the membrane surface was captured in real time in an aqueous environment. For each sample, 3-5 different areas were selected to test the underwater oil contact angle of the filter membrane, and the average value was taken as the final data. The results are shown in Table 2 and... Figure 7 As shown in Figure c.

[0105] Table 2

[0106]

[0107] According to Table 2 and Figure 7 The results showed that in Comparative Example 1 (M0), the absence of CoFe2O4@PDA composite nanoparticles resulted in a larger WCA and a more hydrophobic surface. The WCA of Comparative Example 1 (M1), Example 1 (M2), and Example 3 (M3) gradually decreased with the enrichment of CoFe2O4@PDA composite nanoparticles; Example 3 (M3) exhibited the lowest WCA (most hydrophilic surface). Underwater oil contact angle (UOCA) testing showed that all composite films exhibited significant underwater superoleophobicity, with Example 3 (M3) showing the highest UOCA and the best performance. The significantly enhanced surface wettability of the film was attributed to the combined effect of the polar groups and rough structure of the CoFe2O4@PDA enriched layer.

[0108] Depend on Figure 7 It can be seen that, Figure 7 Figure a shows that as the content and enrichment of CoFe2O4@PDA nanoparticles increase, the water contact angle (WCA) of the membrane gradually decreases, indicating that the hydrophilicity of the membrane surface is enhanced accordingly; the lowest water contact angle of M3 indicates that magnetic field driving has a significant effect on improving the hydrophilicity of the membrane. Figure 7 The dynamic image shown in Figure b further demonstrates that the composite membrane can be completely wetted by water in a very short time. Figure 7 Figure c shows that in the underwater oil contact angle (UOCA) test, all composite films of the present invention exhibit underwater superoleophobicity of more than 150°, making it difficult for oil droplets to adhere to the film surface. Figure 7 In summary: Increased roughness, increased polar groups, and enriched particles together construct a stable hydrophilic-oleophobic interface, giving the membrane excellent antifouling ability during oil-water separation.

[0109] Test Example 3

[0110] The pure water flux of the filtration membranes from Examples 1-2 and Comparative Examples 1-2 was tested at 0.1 bar. The test results are as follows: Figure 8As shown in Figure a.

[0111] The oil-water emulsion separation performance of the filtration membranes from Examples 1-2 and Comparative Examples 1-2 was tested. The emulsion used was a hexane emulsion, composed of hexane / water / lipid-soluble diazo dye (Oil Red O) / sodium dodecyl sulfate (SDS), with a water to hexane volume ratio of 99:1, an SDS concentration of 0.2 g / L, and an Oil Red O concentration of 0.01 g / L. A stable emulsion was formed by stirring at 1000 rpm. The separation performance of the filtration membranes from Examples 1-2 and Comparative Examples 1-2 was tested at 0.1 bar, including emulsion permeate flux and oil phase (hexane) rejection rate. The test results are shown in Table 3. Figure 8 As shown in Figure b.

[0112] The following method was used to test the separation performance of the filter membrane prepared in Example 1 for different oils: A dead-end filtration device was used. Under a constant pressure of 1 bar, emulsions were prepared using n-heptane, isooctane, petroleum ether, and cyclohexane as test oils. The emulsion composition included test oil / water / lipid-soluble diazo dye (Oil Red O) / sodium dodecyl sulfate (SDS), with a water-to-test oil volume ratio of 99:1, an SDS concentration of 0.2 g / L, and an Oil Red O concentration of 0.01 g / L. The mixture was stirred at 1000 rpm to form a stable emulsion. Testing procedure: After pretreating the membrane samples to a stable state, the filter membrane prepared in Example 1 was used sequentially to perform permeation tests on the emulsions corresponding to each oil. The mass of oil permeating the membrane per unit time was recorded to calculate the flux. Simultaneously, the rejection rate was calculated by measuring the concentration of the target component in the feed liquid and permeate. During the test, good sealing and stable pressure were ensured, and the test was performed in triplicate to ensure data reliability. The flux test results are as follows: Figure 8 As shown in Figure c.

[0113] Table 3

[0114]

[0115] Depend on Figure 8 As shown in Table 3, in the hexane / water emulsion separation test, the permeate flux and rejection rates of different membrane samples in the examples and comparative examples showed significant differences. With the addition of nanoparticles and the enhancement of the magnetic field, the emulsion flux of the M1-M3 composite membrane gradually increased, while M3 (Example 2) showed the highest emulsion permeate flux, reaching 3000–3800 L·m. -2 ·h -1 ·bar -1Meanwhile, all composite membranes in the examples exhibited oil rejection rates greater than 99%. This performance improvement stems primarily from two factors: first, particle enrichment enhances the hydrophilicity of the membrane surface, making it easier for water to penetrate the membrane interior; second, increased surface roughness forms a stable oil repellency layer, significantly reducing oil droplet adhesion. In Example 2, M3 showed a slightly lower oil phase (n-hexane) rejection rate due to its excessively high CoFe2O4@PDA composite nanoparticle content, but it still maintained a relative oil phase (n-hexane) rejection rate of over 99%, and exhibited the highest water permeation flux. Figure 8 Overall, this invention demonstrates the advantages of the composite filtration membrane in oil-water emulsion treatment, namely high throughput and high retention.

[0116] Test Example 4

[0117] Photocatalytic self-cleaning performance test

[0118] Water was filtered through the membranes of Examples 1-2 and Comparative Examples 1-2, respectively. The initial water flux was tested. After filtering water for 30 minutes, the membranes were then filtered through the n-hexane emulsion in Example 2 for another 30 minutes to obtain fouled membranes. The fouled membranes were then soaked and washed with deionized water for 10 minutes or irradiated with a 300 W xenon lamp for 10 minutes. After cleaning, water was filtered through the membranes again, and the water flux of the cleaned membranes was tested. The flux change comparison graph between Example 2 and Comparative Example 1 is shown below. Figure 9 As shown in Figure a. The flux recovery rate was calculated, and the flux recovery rates of Example 2 and Comparative Example 1 under different cleaning methods were compared. Figure 9 As shown in Figure b. The flux recovery results of the filter membranes of Examples 1-2 and Comparative Examples 1-2 are shown in Table 4.

[0119] The filter membranes from Examples 1-2 and Comparative Examples 1-2 were used to filter water. The initial water flux was tested, and after filtration of water for 30 minutes, the n-hexane emulsion from Test Example 2 was filtered for another 30 minutes to obtain a uniformly fouled filter membrane. This uniformly fouled filter membrane was then immersed in deionized water and subjected to 300 W xenon lamp irradiation for 10 minutes for self-cleaning. This process of filtering water, filtering the emulsion from Test Example 2, and self-cleaning was repeated five times. The flux recovery rate for each cycle in Example 2 is shown in the bar chart below. Figure 9 As shown in Figure c, the flux of the filter membrane in Example 2 during the circulation process varies. Figure 10 As shown in Table 4, the flux recovery rate results of the filter membranes of Examples 1-2 and Comparative Examples 1-2 after 5 cycles of filtration of water, filtration of emulsion in Test Example 2, and self-cleaning cycle are shown in Table 4.

[0120] The CoFe2O4 and CoFe2O4@PDA composite nanoparticles from Example 1 were subjected to electron paramagnetic resonance (EPR) tests to characterize •OH and •O.2- The generation status of the electron paramagnetic resonance (EPR) test was determined. Two sets of control conditions were set up for the EPR test: In the dark state, the CoFe2O4@PDA composite nanoparticle dispersion containing a spin trapping agent was placed in a dark, sealed environment, and the baseline signal was directly obtained to eliminate interference from spontaneously generated active species or inherent spin signals in the absence of light; In the light-5-min state, a specific light source (xenon lamp) was used to continuously irradiate the CoFe2O4@PDA composite nanoparticle dispersion and the CoFe2O4 dispersion with the same concentration of spin trapping agent for 5 min. Immediately after irradiation, the electron paramagnetic resonance (EPR) test was performed to characterize the spin signals of active species such as hydroxyl radicals and superoxide radicals generated under photoexcitation, in order to evaluate the photoresponse performance of the material. The test results are as follows: Figure 11 As shown.

[0121] Table 4

[0122]

[0123] The results in Table 4 show that the flux recovery rate (FRR) of the filter membranes in Examples 1-2 of the present invention exceeds 99%, indicating that: (1) CoFe2O4@PDA composite nanoparticles can generate •OH and •O2. - (1) Active oxygen; (2) Polluted oil is degraded in situ; (3) The surface hydrophilic layer is restored.

[0124] Depend on Figure 9 This demonstrates that the photocatalytic self-cleaning capability of the composite membrane is verified through three stages: fouling, photo-regeneration, and recovery. After fouling, the membrane's water flux significantly decreased, but after 30 minutes of visible light irradiation, the flux recovery rate (FRR) reached over 99%, indicating that contaminants on the membrane surface were almost completely removed. Combined with the EPR results, it can be seen that CoFe2O4@PDA can generate reactive oxygen species under light irradiation. These free radicals can achieve in-situ degradation of oil contaminants, restoring the membrane surface to its initial state. This figure fully demonstrates the composite membrane's significant photocatalytic regeneration capability, providing crucial evidence for its "self-cleaning" performance.

[0125] Depend on Figure 10 As can be seen, in multiple cyclic filtration experiments, the permeate flux and rejection rate of the composite filter membrane in Example 2 remained stable with almost no significant decrease. Even after 5 cycles, it maintained a high level of separation performance. This indicates that the CoFe2O4@PDA composite nanoparticles are firmly bonded to the membrane surface, resulting in a stable membrane structure that is not easily detached, and possesses excellent durability and long-term operational capability. This demonstrates that the composite membrane prepared by this invention possesses excellent structural stability and long-term antifouling ability.

[0126] This invention utilizes EPR testing to capture key reactive oxygen species generated during photocatalysis. Figure 11 It can be seen that, Figure 11 Figure a shows that the four-line peak of DMPO–·OH indicates the generation of hydroxyl radicals in the system. Figure 11 Figure b shows: DMPO–·O 2- The characteristic six-line peak confirms the presence of superoxide radicals. The co-existence of these radicals demonstrates that the CoFe2O4@PDA / PVDF composite membrane possesses multi-pathway photocatalytic oxidation capabilities, enabling rapid and efficient degradation of oil contaminants, thereby ensuring the membrane's long-lasting cleanliness during oil-water separation.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a self-cleaning composite filter membrane for oil stains, characterized in that, Includes the following steps: 1) CoFe2O4 nanoparticles were dispersed in Tris-HCl buffer, polydopamine monomers were added to carry out self-polymerization, and then magnetic solids were collected by magnetic separation to obtain CoFe2O4@PDA composite nanoparticles with polydopamine coating on the surface. 2) Mix polyvinylidene fluoride, pore-forming agent, solvent and CoFe2O4@PDA composite nanoparticles obtained in step 1) to form a casting solution; 3) The casting solution obtained in step 2) is coated on the workbench and then placed under an external magnetic field. Under the action of the external magnetic field, the CoFe2O4@PDA composite nanoparticles in the casting solution gather to the upper surface of the casting solution and are then immersed in a coagulation bath for phase transformation to obtain the oil-stain self-cleaning composite filter membrane. The oil-stain self-cleaning composite filter membrane has an uneven, rough structure on one side of the surface of the CoFe2O4@PDA composite nanoparticles enriched in it.

2. The method for preparing the self-cleaning composite filter membrane for oil stains according to claim 1, characterized in that, The pH of the Tris-HCl buffer solution mentioned in step 1) is 8.0-9.0; And / or, the mass ratio of the polydopamine monomer to the CoFe2O4 nanoparticles in step 1) is 1:(5-10).

3. The method for preparing the self-cleaning composite filter membrane for oil stains according to claim 1 or 2, characterized in that, The CoFe2O4 nanoparticles described in step 1) are dispersed in Tris-HCl buffer to form a dispersion, and the mass concentration of CoFe2O4 nanoparticles in the dispersion is 0.005-0.2 g / mL; And / or, the monomer of the polydopamine described in step 1) includes at least one of dopamine and dopamine hydrochloride; And / or, after the magnetic separation and collection of magnetic solids described in step 1) is completed, the steps of washing and drying are also included.

4. The method for preparing the self-cleaning composite filter membrane for oil stains according to claim 1 or 2, characterized in that, The casting solution described in step 2) comprises, by mass percentage, 12.0wt%-13.0wt% polyvinylidene fluoride, 0.8wt%-1.5wt% pore-forming agent, 0.1wt%-0.5wt% CoFe2O4@PDA composite nanoparticles, and 85wt%-86.8wt% solvent.

5. The method for preparing the self-cleaning composite filter membrane for oil stains according to claim 1 or 2, characterized in that, The pore-forming agent mentioned in step 2) includes polyvinylpyrrolidone; And / or, the solvent includes N-methylpyrrolidone.

6. The method for preparing the self-cleaning composite filter membrane for oil stains according to claim 1 or 2, characterized in that, The magnetic field strength mentioned in step 3) is 0.05-0.10 T, and the magnetic field application time is 0.5-2.0 min; The coagulation bath mentioned in step 3) includes water; And / or, after applying the casting solution obtained in step 2) to the workbench as described in step 3), the process also includes a settling treatment before placing it under an external magnetic field.

7. An oil-stain self-cleaning composite filter membrane prepared by the preparation method according to any one of claims 1-6, characterized in that, The oil-stain self-cleaning composite filter membrane includes a polyvinylidene fluoride porous substrate membrane, and one side of the polyvinylidene fluoride porous substrate membrane is enriched with CoFe2O4@PDA composite nanoparticles. The CoFe2O4@PDA composite nanoparticles have a core-shell structure, with the core consisting of CoFe2O4 nanoparticles and the shell coating the surface of the core consisting of polydopamine.

8. The self-cleaning composite filter membrane for oil stains according to claim 7, characterized in that, The CoFe2O4 nanoparticles are spherical CoFe2O4 nanoparticles; And / or, the water flux of the self-cleaning oil-stained composite filter membrane at 25°C and 1 bar is 4000-4800 L·m. -2 ·h -1 ·bar -1 .

9. The application of the self-cleaning composite filter membrane for oil stains as described in claim 7 or 8 in the fields of mixture separation and / or photocatalysis.

10. The application according to claim 9, characterized in that, The self-cleaning composite filter membrane according to claim 7 or 8 is used for the separation of oil and water mixtures.

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