Mxene / bi2o3 heterojunction microspheres, film material comprising same, and application of film material to oily wastewater

Abstract

The application relates to the technical field of film materials, and discloses MXene / Bi2O3 heterojunction microspheres, a film material containing the same, application of the film material to oily wastewater, a preparation method of the MXene / Bi2O3 heterojunction microspheres, and a preparation method of the film material. After Ti3AlC2 is subjected to etching treatment, a suspension is obtained through dispersion. PMMA is added into the suspension, and MXene microspheres are obtained through reaction. The MXene microspheres and bismuth salt are dispersed in a solvent system, and the MXene / Bi2O3 heterojunction microspheres are obtained through hydrothermal reaction. The preparation method of the film material comprises the following steps: the MXene / Bi2O3 heterojunction microspheres and tannic acid are dispersed in a solvent to obtain a mixture; and the mixture is sprayed onto the surface of a film to obtain the film material. The crosslinking and hydrogen bond interaction between the tannic acid and the MXene ensure the physical stability and super-wetting characteristics of the functional layer, and the arrangement of the 3D MXene heterojunction effectively breaks through the limitation of the separation flux compared with the traditional physical stacking of the 2D MXene dense film.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of membrane materials, in particular to a MXene / Bi2O3 heterojunction microsphere, a membrane material comprising the same, and an application of the membrane material in oily wastewater. BACKGROUND

[0002] Nowadays, a large amount of complex oily wastewater is generated in oil exploitation, chemical industry and offshore oil spill accidents, which poses a great threat to the ecological environment and human health. For example, oilfield produced water contains various organic and inorganic substances such as alkanes, aromatic hydrocarbons, phenols, sulfur-containing compounds, and surfactants. In addition, there are also various microorganisms such as sulfate-reducing bacteria (SRB), saprophytic bacteria, and iron bacteria in complex oily wastewater. Therefore, it is urgent to develop efficient complex oily wastewater treatment technology and materials. Compared with traditional treatment methods, membrane separation technology has great application prospects in the field of oily wastewater treatment, and its advantages such as simple operation, low energy consumption, high separation efficiency and no secondary pollution cannot be ignored.

[0003] However, the separation membrane material prepared by the phase separation method has defects such as low porosity and poor oil adhesion resistance, which leads to very limited separation flux (less than 1000 L·m -2 ·h -1 ·bar -1 ). In addition, when the oil concentration in the wastewater reaches a certain level, the membrane material is easily contaminated by oil, which leads to a sharp decrease in separation efficiency and flux, which makes the polymer membrane material face severe challenges in the field of oil-water separation. Under this background, electrospun polymer fiber membranes have unique advantages in the field of oil-water separation due to their high specific surface area, surface adsorption energy and porosity. Currently, researchers use blending, surface grafting and interfacial polymerization to optimize the pore structure (such as pore size distribution, porosity and pore connectivity) of electrospun fiber membranes and change their surface properties to improve their filtration efficiency, water flux and mechanical properties, etc. For example:

[0004] Lin reported a high-efficiency two-dimensional photocatalytic composite membrane doped with Bi2O2CO3@MXene for water treatment, which has a pure water permeability of 815.3 L·m -2 ·h -1 ·bar -1 , a retention rate of emulsified oil of more than 99%, and a removal rate of dye of more than 98%. However, the stacking of two-dimensional MXene layers is not conducive to efficient treatment of oily wastewater.

[0005] Yang used a one-pot hydrothermal method to construct a BiOBr / Bi2MoO6@MXene ternary heterojunction for self-cleaning separation membranes. The membrane has a high permeability (1296.91 L·m -2 ·h -1 ·bar -1), the removal rates of antibiotics and dyes are as high as 90%. The results show that the synergistic properties of photocatalytic self-cleaning and super-hydrophobicity can effectively solve the pollution problems of oil and soluble organic matter. However, in the actual treatment of complex oily wastewater, microorganisms are also easy to adsorb and aggregate on the membrane surface, leading to complex pollution phenomena. SUMMARY

[0006] The technical problems solved by the present application are:

[0007] To solve the problem of poor effect of Bi2O2CO3@MXene in treating oily wastewater.

[0008] The technical solutions adopted by the present application are:

[0009] In view of the above technical problems, the present application aims to provide a MXene / Bi2O3 heterojunction microsphere, a membrane material containing the same, and an application of the membrane material in oily wastewater.

[0010] The specific content is as follows:

[0011] Firstly, the present application provides a preparation method of a MXene / Bi2O3 heterojunction microsphere for a membrane material,

[0012] (1) Ti3AlC2 is dispersed to obtain a suspension after etching treatment; PMMA is added to the suspension, and MXene microspheres are obtained through reaction;

[0013] (2) The MXene microspheres and bismuth salt are dispersed in a solvent system, and the MXene / Bi2O3 heterojunction microspheres are obtained through hydrothermal reaction.

[0014] Secondly, the present application provides a MXene / Bi2O3 heterojunction microsphere obtained by the aforementioned preparation method.

[0015] Thirdly, the present application provides a preparation method of a heterojunction assembled membrane material, comprising the following steps:

[0016] (a) The MXene / Bi2O3 heterojunction microspheres and tannic acid are dispersed in a solvent to obtain a mixture;

[0017] (b) The mixture is sprayed onto the surface of the membrane to obtain the membrane material.

[0018] Fourthly, the present application provides a heterojunction assembled membrane material obtained by the aforementioned preparation method.

[0019] Fifthly, the present application provides an application of the aforementioned heterojunction assembled membrane material in oily wastewater.

[0020] The technical mechanism and beneficial effects of the present application are as follows:

[0021] (1) The ultra-thin layer structure of MXene monolayer nanosheets has more active sites and larger specific areas of heterojunction formation. These monolayer nanosheets are further processed into MXene microspheres with PMMA microspheres as a hard template. After mixing PMMA and MXene, the respective surface-rich functional groups allow spontaneous formation of van der Waals forces and hydrogen bonds, thereby obtaining MXene / PMMA composite microspheres. Due to electrostatic interaction, the negative charge on the surface of MXene adsorbs metal positive ions. Therefore, MXene containing oxygen functional groups is very easy to attract Bi 3+ , providing a carrier for in-situ growth of Bi2O3 nanoparticles.

[0022] (2) Based on the rich end groups (such as -OH and -O, etc.) on the surface of MXene, three-dimensional MXene microspheres are prepared by hydrogen bond wrapping using a template-assisted method. This microsphere has wide application prospects in the fields of catalysis and energy. Compared with two-dimensional sheet structure, the unique advantages of three-dimensional MXene microspheres mainly lie in the following two aspects: first, the specific surface area is larger, which can expand its application range through functional modification; second, it can effectively avoid the stacking of MXene sheets.

[0023] The versatility of the fiber composite membrane (photocatalytic self-cleaning, ultra-low sticky oil, antibacterial) enables it to have multiple anti-pollution capabilities, providing a unique advantage for the treatment of complex oily wastewater.

[0024] (3) The cross-linking and hydrogen bond interaction between tannic acid and MXene ensures the physical stability and super-wetting properties of the functional layer, and the arrangement of 3D MXene heterojunctions effectively breaks through the limitation of separation flux compared with the traditional physical stacking of 2D MXene dense membranes. The permeation flux of the composite membrane to various emulsions reaches 2717-3328 L·m -2 ·h -1 , and the retention rate is as high as 99.59%. After 150 minutes of visible light irradiation, the photocatalytic degradation efficiency of methylene blue reaches 96.1%. At the same time, the membrane has obvious inhibitory effect on the proliferation of Escherichia coli. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Fig. 1 is a microstructure diagram of each intermediate in Example 1; (a) monolayer MXene nanosheet, (b) 3D MXene microsphere, (d) Bi2O3@MXene microsphere, (e) Ag-modified Bi2O3@MXene heterojunction composite microsphere; (c) elemental mapping analysis of three-dimensional MXene microspheres.

[0026] Figure 2Microstructure images of the composite membranes prepared in Examples 1-6; (a-f) SEM images and digital photos of the M-0, M-2, M-4, M-6, M-8 and M-10 fiber membrane surfaces; (g) Element distribution maps of C, O, Ti, Bi, Ag elements on the surface of the M-6 membrane.

[0027] Figure 3 Wetting performance results of the composite membrane prepared in Example 16; (a) water contact angles of different fiber composite membranes, (b) oil contact angles under water, (c) oil contact angles of different oils under water in M-6, (d) dynamic adhesion of M-6 and isooctane under water.

[0028] Figure 4 Oil-water separation efficiency results of the composite membrane prepared in Example 16; (a) emulsion separation flux and retention rate of different membranes, (b) emulsion separation flux and retention rate of different oils; (c) emulsion separation flux and retention rate of M-6 in the cycle experiment.

[0029] Figure 5 Photocatalytic degradation of dyes performance results of the composite membrane prepared in Example 4.

[0030] Figure 6 Antibacterial performance results of the composite membranes prepared in Example 1 and Example 5; (a1-a3) are the growth photos of E. coli cells exposed to M-0 membrane, Bi2O3@MXene / PAN and M-6 membrane, respectively; (b) M-6 inhibition curve of E. coli cell density; (c1-c4) photos of E. coli colonies killed by M-6 under light exposure for different times (3 hours, 6 hours, 12 hours, 24 hours); (d1-d4) photos of E. coli colonies killed by M-6 in the dark for different times (3 hours, 6 hours, 12 hours, 24 hours). DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0032] <TECHNICAL SOLUTION>

[0033] Specifically,

[0034] The present application provides a kind of MXene / Bi2O3 heterojunction microspheres for membrane material, preparation method, comprising the following steps:

[0035] (1) First, a single-layer suspension of MXene nanosheets is prepared. 0.2-1 g of lithium fluoride is added to a 9 M hydrochloric acid solution (20 mL) and stirred vigorously at room temperature for 30 min, then 0.2-1.5 g of Ti3AlC2(MAX) is slowly added to the above solution and stirred at 30-60℃ for 18-40 h. After the reaction is completed, the suspension is centrifuged at 3000 rpm and washed with pure water until the pH value reaches 6-7. The MXene suspension is placed in a three-necked flask under nitrogen protection and subjected to ultrasonic centrifugation (4 h, 35℃). After the MXene suspension is centrifuged at 8000 rpm for 30 min, the supernatant is taken to obtain MXene nanosheets.

[0036] PMMA (1-3 g) is dispersed in deionized water and then mixed with the above MXene suspension. After stirring for 2 h, a gray-black precipitate is obtained, which is washed and collected by centrifugation with deionized water. Finally, drying at 60℃ for 6 h, MXene microspheres are obtained.

[0037] (2) Bi(NO3)3·5H2O (0.1-0.4 g) and MXene microspheres (1.0 g) are added to 80 mL of ethylene glycol and stirred magnetically at room temperature for 1 h. The resulting solution is transferred to a 100 mL hydrothermal reactor, which is then placed in a vacuum oven for 4 h (160℃). After cooling and centrifugation for 10 min (4200 rpm), the precipitate is washed several times with deionized water and ethanol. Then, vacuum drying for 12 h (60℃) gives Bi2O3@3D MXene microspheres.

[0038] Based on the MXene / Bi2O3 heterojunction microspheres prepared as described above, Ag-modified Bi2O3@3D MXene Schottky heterojunction microspheres are synthesized by loading Ag nanoparticles onto the above microspheres. MXene has a certain reducing property, which can reduce Ag + nanoparticles to Ag 0 nanoparticles and deposit them on the surface of semiconductor nanomaterials to form Ag-decorated materials with greater application potential.

[0039] That is,

[0040] The present application provides a preparation method of Ag-modified Bi2O3@3D MXene Schottky heterojunction microspheres, comprising the following steps:

[0041] Bi2O3@3D MXene (0.2-1 g) is dissolved in deionized water. 0.1 M AgNO3 solution (3 mL) is added and stirred for 30 min to reduce Ag ions to Ag 0 nanoparticles. After repeated centrifugation, washing and drying, Ag-modified Bi2O3@3D MXene Schottky heterojunction microspheres are prepared.

[0042] The application provides a fiber composite film constructed from the Ag-modified Bi2O3@3D MXene Schottky heterojunction microspheres and a PAN fiber film prepared in the foregoing manner.

[0043] Specifically,

[0044] (1) 0.5-5 g of polyacrylonitrile (PAN) was dissolved in 13.4 mL of an organic solvent (N,N dimethylformamide, DMF) and stirred at 70°C for 4 h to obtain a uniform solution. Then the solution was transferred to a 10 mL syringe, and PAN fibers were electrospun onto a tin paper template (voltage: 18.8 kV; distance: 12 cm; injection speed: 1.5 mL·h -1 ; humidity: 20%). Finally, the PAN fiber mat was peeled off from the tin paper template and hot-pressed between two smooth glass plates under a certain load at 130°C for 2 h.

[0045] (2) The Ag-modified Bi2O3@3D MXene Schottky heterojunction microspheres (0.2-0.5 g) and tannic acid (TA, 1.0 g) were ultrasonically dispersed in 95% ethanol (48.7 g) and stirred at 60°C for 1 h. Then the mixture was transferred to a spray gun (R2-F-08) and sprayed onto the surface of the PAN fiber mat as a support layer by an air compressor (HBF-10A) at a pressure of 0.2 MPa.

[0046] <EMBODIMENT>

[0047] Example 1

[0048] The preparation method of the Ag-modified Bi2O3@MXene / PAN fiber composite film comprises the following steps:

[0049] (1) Electrospinning

[0050] 2.0 g of polyacrylonitrile (PAN) was dissolved in 13.4 mL of an organic solvent (N,N dimethylformamide, DMF) and stirred at 70°C for 4 h to obtain a uniform solution. Then the solution was transferred to a 10 mL syringe, and PAN fibers were electrospun onto a tin paper template (voltage: 18.8 kV; distance: 12 cm; injection speed: 1.5 mL·h -1 ; humidity: 20%). Finally, the PAN fiber mat was peeled off from the tin paper template and hot-pressed between two smooth glass plates under a certain load at 130°C for 2 hours.

[0051] (2) Preparation of three-dimensional MXene microspheres

[0052] The 0.5 g of lithium fluoride was added to 9 M hydrochloric acid solution (20 mL) and stirred vigorously at room temperature for 30 min, then 0.5 g of Ti3AlC2(MAX) was slowly added to the above solution and stirred at 40℃ for 24 h. After the reaction was completed, the suspension was centrifuged at 3000 rpm and washed with pure water until the pH value reached 6-7. The MXene suspension was placed in a three-necked flask under nitrogen protection and subjected to ultrasonic centrifugation (4 h, 35℃). After the MXene suspension was centrifuged at 8000 rpm for 30 min, the supernatant was collected to obtain few-layer or single-layer MXene nanosheets. PMMA (1.5 g) was dispersed in deionized water and then mixed with the above MXene suspension. After stirring for 2 h, a gray-black precipitate was obtained, which was washed and collected by centrifugation with deionized water. Finally, it was dried at 60℃ for 6 h to obtain MXene microspheres.

[0053] (3) Preparation of Ag-modified Bi2O3@3D MXene Schottky heterojunction microspheres

[0054] Bi(NO3)3·5H2O (0.2 g) and MXene microspheres (1.0 g) were added to 80 mL of ethylene glycol and magnetically stirred at room temperature for 1 h. The resulting solution was transferred to a 100 mL hydrothermal reactor and then placed in a vacuum oven for 4 hours (160℃). After cooling and centrifugation for 10 minutes (4200 rpm), the precipitate was washed several times with deionized water and ethanol. Then, vacuum drying was performed for 12 h (60℃) to obtain Bi2O3@3D MXene microspheres. Bi2O3@3D MXene (0.5 g) was dissolved in deionized water. 0.1 M AgNO3 solution (3 mL) was added and stirred for 30 min to reduce Ag ions to Ag 0 After repeated centrifugation, washing and drying, Ag-modified Bi2O3@3D MXene Schottky heterojunction microspheres were prepared.

[0055] (4) Construction of Ag-modified Bi2O3@MXene / PAN fiber composite membrane

[0056] Ag-modified Bi2O3@3D MXene microspheres (0.3 g) and TA (1.0 g) were ultrasonically dispersed in 95% ethanol (48.7 g), and stirred at 60℃ for 1 h. Then 0 mL of the mixture was transferred to a spray gun (R2-F-08) and sprayed onto the surface of the PAN fiber mat as a support layer by an air compressor (HBF-10A) at a pressure of 0.2 MPa, named M-0.

[0057] Examples 2-6

[0058] This example 2-6 provides a method for preparing Ag-decorated Bi2O3@MXene / PAN multifunctional fiber composite membrane, which is as follows:

[0059] The specific operation method is the same as that in Example 1, and the only change is the volume of the spraying solution:

[0060] Example 2 is 2 mL; named M-2;

[0061] Example 3 is 4 mL; named M-4;

[0062] Example 4 is 6 mL; named M-6;

[0063] Example 5 is 8 mL; named M-8;

[0064] Example 6 is 10 mL; named M-10;

[0065] Thus, the Ag-decorated Bi2O3@MXene / PAN multifunctional fiber composite film with different heterojunction microsphere loading amounts is obtained.

[0066] <TEST EXAMPLE>

[0067] Test Example 1

[0068] In this test example, the single-layer MXene 3D nanosheet, MXene microsphere, Bi2O3@3D MXene microsphere, and Ag-modified Bi2O3@3D MXene composite microsphere in Example 1 are characterized for their microstructure, and the results are shown in FIGS. 1-4. Figure 1

[0069] The ultrathin layer structure of the MXene single-layer nanosheet has more active sites and larger specific regions formed by heterojunctions. These single-layer nanosheets are further processed into MXene microspheres using PMMA microspheres as a template. After mixing PMMA and MXene, the respective surface-rich functional groups allow the spontaneous formation of van der Waals forces and hydrogen bonds, thereby obtaining MXene / PMMA composite microspheres (~2 μm). The uniform distribution of C, O, and Ti elements further confirms the preparation of 3D MXene microspheres. Due to electrostatic interaction, the negative charge on the surface of MXene adsorbs Bi 3+ metal ions, providing a carrier for the in-situ growth of Bi2O3 nanoparticles. The successful loading of Bi2O3 nanoparticles on MXene microspheres with a size of about 30-40 nm indicates the successful assembly of Schottky heterojunctions. In addition, MXene has a certain reduction performance, which can reduce Ag + to Ag 0 nanoparticles and deposit them on the surface of semiconductor nanomaterials.

[0070] Test Example 2

[0071] ​The Ag-modified Bi2O3@3D MXene / PAN fiber composite membrane prepared in Example 1-6 was characterized for its microstructure, and elemental analysis was performed, and the resulting structure is shown in Figure 2 .

[0072] Based on the abundant phenolic hydroxyl functional groups, tannic acid acts as an adhesive to establish intermolecular hydrogen bonds with MXene and Bi2O3, achieving chemical crosslinking. In addition, tannic acid also plays an anchoring role, which can fix the composite microspheres with Schottky heterojunction on the porous PAN fiber pad, thereby constructing a multifunctional composite membrane. Figure 2 The SEM images in FIG. 1 show the surface of the fiber membrane treated with Ag-modified Bi2O3@3D MXene microspheres of different contents. The PAN fiber pad can form a defect-free nanofiber membrane after hot pressing, with an average fiber diameter of about 0.58 μm. As the spraying amount increases, the density of Ag-modified Bi2O3@3D MXene microspheres on the fiber surface becomes denser, and the color of the membrane surface also gradually deepens. On the surface of M-8, the microspheres almost completely cover the PAN fiber pad, but as the thickness of the functional layer increases, small cracks appear between the microspheres. In general, the cracks on the surface of M-10 are more prominent and intense. In addition, elemental analysis of M-6 shows that the C, O, Ti, Bi, and Ag elements are uniformly distributed in the entire composite membrane material.

[0073] Test Example 3

[0074] In this test example, the Ag-modified Bi2O3@3D MXene / PAN fiber composite membrane prepared in Example 16 from microspheres of different loadings was tested for contact angle to characterize the wetting performance of the fiber composite membrane, as shown in Figure 3 .

[0075] The hydrophilicity of MXene and TA combined with the 3D rough array structure makes the water diffusion speed on the surface of the Ag-modified Bi2O3@MXene / PAN composite membrane faster than that of the original PAN fiber membrane. After increasing the functional layer, the time for the water contact angle of the composite membrane to decrease to 0° is shortened from 14 s to 2 s, indicating that the composite membrane has hydrophilicity. On the one hand, the rough surface composed of three-dimensional microspheres increases the specific surface area of the fiber membrane. On the other hand, the hydrophilic functional groups enriched by MXene and tannic acid and the hydrogen bond network constructed therebetween enhance the overall hydrophilicity of the composite membrane. In addition, the hydrophilic components of the functional layer can capture water and form a stable connected water pad on the surface of the fiber membrane to inhibit oil pollution. Therefore, effective and persistent oil-water separation performance can be ensured. The superhydrophilicity of the Ag-modified Bi2O3@MXene / PAN fiber composite membrane enables it to strongly interact with water molecules to form a hydration layer, thereby increasing the underwater oil contact angle (UWOCA) from 137.5° to 159.3°. In addition, the underwater oil contact angles of n-hexane, n-heptane, petroleum ether, 1,3,5-trimethylbenzene and isooctane are 151.4°, 152.9°, 154.6°, 164.4° and 158.6°, respectively. These angles greater than 150° indicate that the composite membrane has underwater superoleophobicity. On this basis, underwater dynamic oil adhesion experiments were carried out. Under the action of external force, the oil droplets were pressed on the surface of the membrane and then removed. The oil droplets can be completely separated from the surface of the membrane and remain the original complete spherical shape. In summary, these results indicate that the fiber composite membrane has excellent oil-repellent ability when facing the challenge of underwater oil.

[0076] Test Example 4

[0077] In this test example, the Ag-modified Bi2O3@3D MXene / PAN fiber composite membrane prepared in Example 16 was characterized for emulsion flux. The oil-water separation efficiency was characterized by total organic carbon (TOC) testing to demonstrate its oil-water separation effect, as shown in Figure 4 .

[0078] In this test example, the Ag-modified Bi2O3@3D MXene / PAN fiber composite membrane prepared in Example 16 was characterized for emulsion flux. The oil-water separation efficiency was characterized by total organic carbon (TOC) testing to demonstrate its oil-water separation effect, as shown in

[0079] The superhydrophilic / underwater superhydrophobic properties of the Ag-modified Bi2O3@MXene / PAN fiber composite membrane make it have great potential in effectively separating oil-water emulsions. For M-0, the flux reaches 6899 L·m -2 ·h -1, the retention rate was 78.68%. The hydrophilic functional group of the polyacrylonitrile fiber membrane with a microporous structure can ideally intercept macromolecular oil droplets. The higher the hydrophilic functional group of M-10, the lower the porosity, and the oil-water emulsion separation flux is 2038L·m -2 ·h -1 . However, the retention rate of the membrane is as high as 99.61%. Considering various factors affecting the morphology, structure and performance of the composite membrane, M-6 with excellent comprehensive performance is selected to evaluate the separation ability of different oils and fats. Obviously, M-6 has better separation effect on different oil emulsions (n-hexane: 2911L·m -2 ·h -1 , 99.41%; n-heptane: 2717L·m -2 ·h -1 , 99.32%; petroleum ether: 3328L·m -2 ·h -1 , 99.08%; 1,3,5-trimethylbenzene: 3267L·m -2 ·h -1 , 99.59%; isooctane: 2880L·m -2 ·h -1 , 99.51%). After 10 cycles of experiments, the flux of M-6 decreased to 2352L·m -2 ·h -1 , and the retention rate remained at 98.86%. It can be inferred that the Ag modified Bi2O3@MXene / PAN fiber composite membrane has excellent recycling ability and anti-pollution performance.

[0080] Test Example 5

[0081] Introducing photocatalytic performance into the composite membrane is an effective way to improve the anti-pollution performance of the membrane and synergistically treat organic pollutants. In this test example, the photocatalytic degradation of dyes by the Ag modified Bi2O3@MXene / PAN fiber composite membrane prepared in Example 4 was characterized, as shown in Figure 5 .

[0082] In order to explore the degradation efficiency of Ag-Bi2O3@MXene / PAN fiber composite membrane on different types of dyes, anionic (congo red, CR) and cationic (methylene blue, MeB) dyes were selected. It can be found that after 150 minutes of light irradiation, the degradation rate of MeB can reach 96.1%, while that of CR is only 68.2%. After 30 minutes of dark reaction, the degradation rate of methylene blue is about 42.7%, which is due to the negative charge of the functional layer on the surface of the composite membrane, which is more easily adsorbed by cationic dyes.

[0083] Test Example 6

[0084] In the actual complex oily wastewater, biofouling is another serious problem for membrane separation, which can reduce the efficiency of oil-water emulsion separation. In this test example, the antibacterial performance of the Ag modified Bi2O3@MXene / PAN fiber composite membrane prepared in Examples 1, 5 was characterized, as shown in Figure 6 .

[0085] Due to the release of Ag + and Bi 3+ antibacterial ions by Bi2O3 and Ag nanoparticles, the presence of Ag-Bi2O3@MXene three-dimensional heterojunction is expected to improve the antibacterial activity of the fiber composite membrane. In this paper, the antibacterial ability of the fiber composite membrane was evaluated by measuring the antibacterial zone diameter and calculating the number of bacteria. Figure 6 The antibacterial effect of pure PAN fiber pad (M-0), Bi2O3@MXene / PAN and M-6 under light conditions is shown. Obviously, there is no antibacterial circle in the pure polyacrylonitrile fiber, indicating that polyacrylonitrile has no antibacterial effect. On the contrary, there are obvious antibacterial zones on the edges of Bi2O3@MXene / PAN and M-6 membranes, and the sizes of the antibacterial zones are 5.5 and 6.3 mm, respectively. Therefore, M-6 was selected for further study of the bactericidal performance of E. coli NDM-1. After 12 h of culture, E. coli (10 7 CFU·mL -1 ) was suspended on the surface of M-6 and placed in light and dark conditions for 3, 6, 12 and 24 h, respectively. Obviously, the results show that the number of viable bacteria decreases significantly under light conditions. After 12 h of exposure, only a small amount of bacteria remained on the plate, and the logarithmic inactivation rate was about 3.87±0.23 log. After 24 h, the logarithmic inactivation rate reached 7.5±0.12 log. Even under dark conditions, M-6 showed a certain degree of bacterial growth inhibition, which was attributed to the rich active surface sites of Bi2O3 and Ag nanoparticles. These active sites can prevent the growth and reproduction of bacteria by interacting with their surfaces, ultimately producing antibacterial effects. The results show that the Ag modified Bi2O3@MXene / PAN fiber composite membrane can achieve a very good inhibitory effect (>99.99%) on E. coli.

[0086] In summary, to efficiently treat complex oily wastewater, a novel Ag-modified Bi2O3@3D MXene Schottky heterojunction structure was designed based on 3D MXene microspheres. By combining the excellent hydrophilicity and strong adhesion of TA with MXene heterojunction microspheres, a multifunctional fiber composite membrane with adjustable porosity, ultra-low oil adhesion, and excellent physical screening effect was obtained by spraying method on PAN fiber pad. The results show that the cross-linking and hydrogen bonding interaction between tannic acid and MXene ensures the physical stability and super-wetting properties of the functional layer, while the arrangement of 3D MXene heterojunction effectively breaks through the limitation of separation flux compared with the traditional physical stacking of two-dimensional sheet MXene dense membrane. The permeation flux of M-6 composite membrane to various emulsions reaches 2717-3328 L·m -2 ·h -1 -1h-1, and the rejection rate is as high as 99.59%. In addition, the Ag-modified Bi2O3@3D MXene heterojunction structure endows the fiber composite membrane with photocatalytic and antibacterial activity. After 150 minutes of visible light irradiation, the removal rate of methylene blue reaches 96.1%. At the same time, the M-6 membrane has obvious inhibitory effect on the proliferation of Escherichia coli. Therefore, this study provides a new strategy for the synergistic development of composite antifouling membranes using super-wetting and multifunctional (photocatalytic and antibacterial activity), which shows potential application prospects in the purification of complex oily wastewater.

[0087] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a membrane material assembled from MXene / Bi2O3 heterojunctions, characterized in that, (1) Ti3AlC2 was etched and then dispersed to obtain a suspension; PMMA was added to the suspension, and MXene microspheres were obtained through the reaction. (2) MXene microspheres and bismuth salt were dispersed in a solvent system and subjected to hydrothermal reaction to obtain MXene / Bi2O3 heterojunction microspheres; The MXene / Bi2O3 heterojunction microspheres or Ag-modified MXene / Bi2O3 heterojunction microspheres and tannic acid are dispersed in a solvent to obtain a mixture; the mixture is sprayed onto the membrane surface to obtain a heterojunction assembled membrane material. The preparation method of Ag-modified MXene / Bi2O3 heterojunction microspheres is as follows: the MXene / Bi2O3 heterojunction microspheres are dispersed in a solvent, soluble silver salt is added, and Ag-modified MXene / Bi2O3 heterojunction microspheres are obtained by reaction.

2. The method for preparing the MXene / Bi2O3 heterojunction assembled membrane material according to claim 1, characterized in that, In (1), the etching process involves placing Ti3AlC2 in an etching solution and reacting it at 30~60℃ for 18~40h; and / or, In (1), the etching solution for etching is a treatment solution formed by dissolving lithium fluoride in hydrochloric acid solution.

3. The method for preparing the MXene / Bi2O3 heterojunction assembled membrane material according to claim 1, characterized in that, In (1), the mass ratio of Ti3AlC2 to PMMA is 0.2~1.5:1~3.

4. The method for preparing the MXene / Bi2O3 heterojunction assembled membrane material according to claim 1, characterized in that, (2) The hydrothermal reaction is performed by transferring the dispersion formed by dispersion to a hydrothermal reactor and then treating it at 130~180℃ for 2~6h.

5. The method for preparing the MXene / Bi2O3 heterojunction assembled membrane material according to claim 1, characterized in that, In (2), the mass ratio of MXene microspheres to bismuth salt is 1:0.1~0.

4.

6. A heterojunction assembled membrane material obtained by the preparation method as described in claim 1.

7. The application of a heterojunction-assembled membrane material as described in claim 6 in the treatment of oily wastewater.

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