VMT-LDH two-dimensional nano bipolar membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of wastewater treatment, and discloses a VMT-LDH two-dimensional nano bipolar membrane as well as a preparation method and application thereof. According to the method, a two-dimensional nano bipolar membrane structure is formed through layered suction filtration and electrostatic and bonding synergistic fixation, a positive-charge CoMgAl-LDH and a negative-charge VMT nanosheet form a zwitterion synergistic adsorption system, cationic dye is intercepted by VMT, and anionic dye is adsorbed by CoMgAl-LDH, so that the problem that a traditional material can only treat single-charge dye is solved, and the method has the advantages of simple operation, high efficiency, low cost and the like. The printing and dyeing wastewater with complex components can be treated. Meanwhile, dye molecule penetration is blocked through the steric hindrance effect, and the rejection rate and the water flux are both considered.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and specifically relates to a VMT-LDH two-dimensional nanobipolar membrane, its preparation method, and its application. Background Technology

[0002] Water pollution is becoming increasingly severe. As the world's largest producer and consumer of dyes, my country discharges massive amounts of dyeing and printing wastewater. This wastewater is complex in composition, high in organic toxins, deep in color, difficult to biodegrade, and exhibits carcinogenic, teratogenic, and mutagenic toxicity. Cationic dyes (such as methylene blue MB) and anionic dyes (such as methyl orange MO) are typical pollutants. Existing materials for treating dye wastewater mainly include activated carbon and graphene, but these materials have limitations in application, and there is an urgent need to develop inexpensive, efficient, and environmentally friendly alternatives. Specifically, activated carbon is significantly affected by environmental factors such as temperature, humidity, and air pressure, resulting in poor application stability and limiting its large-scale application in dye wastewater treatment. Graphene is expensive to prepare, and the heating process leaves behind toxic chemicals and impurities, posing environmental risks. Traditional adsorption materials are mostly based on porous structures, which do not fully utilize the active sites on the material surface, leading to low dye adsorption efficiency. They also struggle to simultaneously and efficiently treat both cationic and anionic dye wastewater, exhibiting limited selectivity and treatment efficiency.

[0003] Therefore, how to provide a VMT-LDH two-dimensional nanobipolar membrane, its preparation method and application, to meet the needs of complex dye wastewater treatment is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] In view of this, the present invention proposes a low-cost, environmentally friendly, scalable, and efficient two-dimensional nanobipolar membrane that can simultaneously and efficiently treat wastewater from cationic dyes (such as methylene blue MB) and anionic dyes (such as methyl orange MO), achieving a synergistic effect of high rejection rate, high water throughput and good renewability.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A VMT-LDH two-dimensional nanobipolar membrane is disclosed. The two-dimensional nanobipolar membrane has a three-layer composite structure, which includes a support layer, an intermediate functional layer, and an upper functional layer from bottom to top. The support layer is a CA membrane, the intermediate functional layer is an LDH material, and the upper functional layer is a VMT material.

[0007] The beneficial effects of the above technical solution are: selecting natural vermiculite and non-toxic LDH as core components reduces costs from the source, and the preparation process leaves no toxic chemical residues, solving the problems of high cost and toxic residues of existing materials.

[0008] Preferably, the pore size of the CA membrane is 0.22~0.8μm.

[0009] More preferably, the pore size of the CA membrane is 0.45 μm.

[0010] This invention also provides a method for preparing the above-mentioned VMT-LDH two-dimensional nanobipolar film, comprising the following steps: (1) Take expanded VMT and deionized water, mix and float, select the VMT floating on the water surface, remove sand and mica impurities, and pulverize at high speed to obtain vermiculite powder; (2) Weigh vermiculite powder, add H2O2 solution, reflux in oil bath for preliminary stripping; (3) Wash the product obtained in step (2) with deionized water until neutral, add deionized water, put it into a high shear dispersion emulsifier for shearing, then centrifuge with a benchtop centrifuge, take the supernatant, and obtain VMT nanosheets; (4) Dissolve Co(NO3)2·6H2O, Mg(NO3)2·6H2O, Al(NO3)3·9H2O and urea in deionized water, disperse by ultrasonication, then reflux and transfer to a reaction vessel for thermal aging. (5) The product obtained in step (4) was washed three times by centrifugation with deionized water, then washed with ethanol and dried to obtain rose-shaped LDH. (6) Add rose-shaped LDH to deionized water, sonicate for 10 min, and then perform alternating shearing and sonication treatments multiple times. Then centrifuge to obtain regular polygonal sheet-like CoMgAl-LDH. (7) Place VMT nanosheets and CoMgAl-LDH into two containers respectively, add deionized water and PVA to each container, stir in an oil bath at 95°C for 1 h until PVA is completely dissolved, cool to room temperature, and obtain LDH dispersion and VMT dispersion respectively. (8) Lay the CA membrane flat on the vacuum filtration device, add deionized water to wet the membrane surface to ensure no air bubbles, and under a vacuum of 0.1 MPa, slowly pour the LDH dispersion into the vacuum filtration device to form the lower membrane; then pour the VMT dispersion in and continue to filter to make the two membranes tightly bonded. Dry naturally at room temperature to obtain the VMT-LDH two-dimensional nanobipolar membrane.

[0011] Preferably, in step (2), the mass-to-volume ratio of vermiculite powder to H2O2 solution is 1g:10mL, and the mass fraction of H2O2 solution is 30%; the solution is refluxed in an oil bath at 120℃ for 12h.

[0012] The beneficial effects of the above technical solution are: using the O2 generated by the decomposition of H2O2 to open up the weak interlayer forces (van der Waals forces + hydrogen bonds), and initially peeling off the layers.

[0013] Preferably, in step (3), the shearing time is 4 hours and the rotation speed is 10,000 r / min; The centrifugation time was 15 minutes, and the rotation speed was 5000 rad / min; The thickness of the VMT nanosheets is 180~320 nm.

[0014] The beneficial effects of the above technical solution are as follows: Through a two-step process of H2O2 chemical exfoliation and physical shearing, traditional bulk VMT is exfoliated into nanosheets, increasing the number of surface active sites by more than three times. The exfoliated nanosheets are stacked in situ, forming abundant micropores and mesopore channels, reducing water flow resistance. Furthermore, VMT exhibits excellent hydrophilicity, balancing adsorption sites and water permeability. This solves the problem of traditional vermiculite relying solely on its porous structure and insufficient utilization of active sites.

[0015] Preferably, in step (4), the molar ratio of Co(NO3)2·6H2O, Mg(NO3)2·6H2O, Al(NO3)3·9H2O, and urea is 1:1:1:25; The ultrasonic dispersion time is 30 min, the condensation reflux time is 2 h, and the thermal aging temperature is 120℃ for 12 h.

[0016] The beneficial effects of the above technical solution are as follows: According to Co 2+ Mg 2+ Al 3+ The LDH was prepared with a molar ratio of 1:1:1 to ensure that the LDH layer was positively charged; urea was used as a precipitant to ensure complete precipitation without any toxic byproducts.

[0017] Preferably, in step (5), the centrifugal washing speed is 12000 rad / min; Wash with ethanol until the pH of the filtrate is 6.5-7.0; The drying temperature is 80℃ and the time is 12 hours.

[0018] Preferably, in step (6), the shearing and ultrasonic treatment are performed three times, each time for 2 hours; The centrifugation speed was 5000 rad / min, and the time was 15 min.

[0019] The general formula for LDH is [M II 1-x MI Ⅲ x (OH)2] x+ [(A n ) x / n ·yH2O] x- Divalent metal ions (M) are required. II) and trivalent metal ions (M III ) Collaboratively form stable layers. Co 2+ Mg 2+ Al is a divalent ion. 3+ As trivalent ions, the combination of these three components satisfies charge balance requirements, forming a regular layered structure. CoMgAl-LDH is chemically stable, with high hydroxide bond energies between Co, Mg, and Al, making it less prone to dissolution or structural collapse during dye wastewater treatment and regeneration, suitable for long-term applications. The CoMgAl-LDH layers are positively charged, allowing for the specific adsorption of anionic dyes (such as MO) through electrostatic interactions, and Co... 2+ The presence of Mg can enhance the interaction with dye molecules and increase the adsorption capacity; 2+ This reduces the cost of material preparation, Al 3+ To ensure the regularity and specific surface area of ​​the layered structure.

[0020] Preferably, in step (7), the mass ratio of the CoMgAl-LDH and VMT nanosheets is 1~3:1~4.

[0021] More preferably, in step (7), the mass ratio of the CoMgAl-LDH and VMT nanosheets is 1:3.

[0022] The beneficial effects of the above technical solution are as follows: when the mass ratio of CoMgAl-LDH to VMT nanosheets is 1:3, the synergistic optimization of the number of active sites and channel structure is achieved. This balances a dye rejection rate of over 99% and a flow rate of 500 L·m⁻¹. -2 ·h -1 ·Mpa -1 above water flux.

[0023] In step (8), polyvinyl alcohol is used as a binder and is uniformly dispersed in the LDH and VMT dispersion to enhance the bonding force between the two functional layers. The CA membrane serves as a support membrane to ensure the stability of the membrane structure. The vacuum filtration pressure is fixed at 0.1 MPa to avoid membrane pore blockage due to excessive pressure and poor membrane bonding due to insufficient pressure.

[0024] This invention also provides the application of the above-mentioned VMT-LDH two-dimensional nanobipolar membrane in the treatment of cationic dye wastewater and anionic dye wastewater.

[0025] The present invention also provides a method for regenerating the above-mentioned VMT-LDH two-dimensional nanobipolar membrane, specifically: when the membrane rejection rate drops to 70% of the initial value, the two-dimensional nanobipolar membrane is placed in an ethanol solution, stirred at room temperature for 2 hours at a speed of 200 r / min to desorb the dye molecules adsorbed on the membrane surface, then taken out, rinsed with deionized water 3 times, and dried at room temperature for 6 hours to complete the regeneration.

[0026] The beneficial effects of the above technical solution are as follows: It utilizes the principle of "like dissolves like" in ethanol to desorb dye molecules adsorbed on the membrane surface, and ethanol does not damage the structure and charge characteristics of VMT-LDH. After membrane regeneration, it can be reused for dye wastewater treatment, maintaining stable performance even after five cycles.

[0027] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention utilizes layered filtration and electrostatic and adhesive synergistic fixation to form a two-dimensional nanobipolar membrane structure. Positively charged CoMgAl-LDH and negatively charged VMT nanosheets form a synergistic adsorption system for cationic and anionic dyes. VMT retains cationic dyes while CoMgAl-LDH adsorbs anionic dyes, overcoming the limitation of traditional materials that can only handle dyes with single charges. This allows for the treatment of complex dyeing and printing wastewater. Simultaneously, steric hindrance prevents dye molecules from penetrating, balancing retention rate and water flux.

[0028] 2. VMT nanosheets exhibit stable chemical properties, and their layered structure is minimally affected by environmental factors such as temperature, humidity, and air pressure. CoMgAl-LDH possesses excellent anti-aging properties and chemical stability. It forms a tightly packed composite membrane structure with PVA through electrostatic attraction, eliminating loose components and preventing detachment or performance degradation during use. Under various environmental conditions, the retention rates of MB and MO remain above 99% for extended periods without significant degradation, greatly improving application stability and meeting the complex requirements of industrial dye wastewater treatment.

[0029] 3. The membrane has good renewability and can be recycled 5 times. Even after the 5th cycle, the retention rate for MB is still approximately 60%, and the retention rate for MO reaches over 70%, while the water flux remains at 500 L·m⁻¹. -2 ·h -1 ·Mpa -1 The above describes the simple regeneration process, which requires no complex equipment, significantly reduces long-term usage costs, and solves the waste problem of traditional single-use adsorption materials.

[0030] 4. The membrane structure of this invention is simple and easy to prepare, requiring only conventional equipment and no stringent reaction conditions. It is easy to operate and has a three-layer composite structure with no complex parts or assembly requirements, making it suitable for large-scale production and practical application. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings in this description are merely embodiments of the present invention.

[0032] Figure 1 This is a schematic diagram of dye filtration using the VMT-LDH two-dimensional nanobipolar membrane of the present invention.

[0033] Figure 2 The X-ray diffraction patterns are of the VMT nanosheets and rose-shaped LDH in Example 1.

[0034] Figure 3 In Example 1, a and b represent the hydrophilic test structures of VMT nanosheets and rose-shaped LDH, respectively.

[0035] Figure 4 In Example 1, f are SEM images of different materials; where a: rose-shaped LDH; b: CoMgAl-LDH; c: expanded VMT; d: VMT nanosheets; e: surface of VMT-LDH two-dimensional nanobipolar film; f: magnified surface of VMT-LDH two-dimensional nanobipolar film.

[0036] Figure 4 g represents the EDS analysis of CoMgAl-LDH in Example 1.

[0037] Figure 5 In the figures, a and b represent the dye rejection rates of the examples and comparative examples for MB and MO, respectively.

[0038] Figure 5 c and d are water flux diagrams for MB and MO in the examples and comparative examples, respectively. Detailed Implementation

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] This invention provides a VMT-LDH two-dimensional nanobipolar membrane, which is a three-layer composite structure comprising, from bottom to top, a support layer, an intermediate functional layer, and an upper functional layer; the support layer is a CA membrane, the intermediate functional layer is an LDH material, and the upper functional layer is a VMT material.

[0041] Example 1 A method for preparing a VMT-LDH two-dimensional nanobipolar film includes the following steps: (1) Take expanded VMT and deionized water and mix them at a liquid-solid ratio of 1:5 (mass-volume ratio) for flotation. Select the VMT floating on the water surface, remove sand and mica impurities, and pulverize at high speed to obtain vermiculite powder. (2) First stripping: Take 10g of vermiculite powder and place it in a round-bottom flask. Add 100mL of 30% H2O2 solution and reflux in an oil bath at 120℃ for 12h. Use the O2 generated by the decomposition of H2O2 to open up the weak interlayer forces (van der Waals forces + hydrogen bonds) for preliminary stripping. (3) Second stripping: The product obtained in step (2) was washed with deionized water until neutral, 500 mL of deionized water was added, and the product was placed in a high shear dispersion emulsifier (EM20D type) for shearing for 4 h at a speed of 10000 r / min. Then, it was centrifuged in a benchtop centrifuge (TDL80-2B type) at 5000 rad / min for 15 min. The supernatant was taken to obtain VMT nanosheets with a thickness of 228 nm, exposing the surface active sites. (4) Coprecipitation preparation: Co(NO3)2·6H2O, Mg(NO3)2·6H2O, Al(NO3)3·9H2O and urea were dissolved in 100mL of deionized water at a molar ratio of 1:1:1:25. The mixture was ultrasonically dispersed (KQ3200DV type, power 300W) for 30min, transferred to a 200mL three-necked flask and refluxed for 2h. Then it was transferred to a reaction vessel and heat-aged at 120℃ for 12h. (5) Washing and drying: Wash three times with deionized water at 12000 rad / min, then wash with ethanol until the pH of the filtrate is 7.0, and place it in a forced-air drying oven (DHG-9030A type) and dry at 80℃ for 12h to obtain rose-shaped LDH; (6) Peeling treatment: 5g of rose-shaped LDH was added to 300mL of deionized water and sonicated for 10min. Then, alternating shearing and sonication were performed (3 times each, 2h each time). Then, the mixture was centrifuged at 5000rad / min for 15min to obtain regular polygonal sheet-like CoMgAl-LDH, which is positively charged and adsorbs anionic dyes. (7) Control the total mass of VMT nanosheets and CoMgAl-LDH to 1.0g (the mass ratio of CoMgAl-LDH and VMT nanosheets is 1:3), add them to two beakers respectively, add 150mL of deionized water and 1.5g of PVA to each beaker, stir in an oil bath at 95℃ for 1h (using a heat-collecting constant temperature magnetic stirrer DF-101S) until PVA is completely dissolved, cool to room temperature, and obtain LDH dispersion and VMT dispersion respectively; (8) A CA membrane with a pore size of 0.45 μm was laid flat on a vacuum filtration device (SHB-III type circulating water multi-purpose vacuum pump), and 10 mL of deionized water was added to wet the membrane surface to ensure that there were no air bubbles. Under a vacuum of 0.1 MPa, the LDH dispersion was slowly poured into the vacuum filtration device and filtered for 30 min to form the lower membrane. Then the VMT dispersion was poured in and the filtration was continued for 30 min. Through the bonding effect of PVA and the electrostatic attraction between VMT (negatively charged) and LDH (positively charged), the two membranes were tightly bonded. The membrane was then naturally dried at room temperature for 12 h to obtain a VMT-LDH two-dimensional nanobipolar membrane with an effective filtration area of ​​0.001256 m². 2 .

[0042] The regeneration method of VMT-LDH two-dimensional nanobipolar membrane is as follows: when the membrane rejection rate drops to 70% of the initial value, the two-dimensional nanobipolar membrane is placed in 50 mL of ethanol solution and stirred at room temperature for 2 h at a speed of 200 r / min to desorb the dye molecules adsorbed on the membrane surface. Then, it is taken out, rinsed with deionized water 3 times, and dried at room temperature for 6 h to complete the regeneration.

[0043] Examples 2 to 4 Based on Example 1, the mass ratio of CoMgAl-LDH and VMT nanosheets was changed to 1:1, 3:1, and 1:4, respectively, to obtain multiple VMT-LDH two-dimensional nanobipolar films as Examples 2 to 4.

[0044] Comparative Example 1 Expanded VMT was floated in a beaker with deionized water. The VMT floating on the surface was selected to remove impurities such as small sand grains and mica. The floated VMT was then added to a fine pulverizer and pulverized at high speed to obtain vermiculite powder. This powder was placed in a round-bottom flask with 100 mL of 30% H2O2 solution and refluxed in an oil bath at 120°C for 12 h. The H2O2 decomposition generated a large amount of O2, which opened up the vermiculite layers, resulting in the first peeling. After cleaning the VMT from the oil bath, it was placed in a beaker with 500 mL of deionized water and sheared in a shear press for 4 h to further peel off the vermiculite layers. The resulting shearing liquid was centrifuged at 5000 rad / min, and the supernatant was collected to obtain the fully peeled VMT. Figure 5 VMT in the middle.

[0045] Figure 1This is a schematic diagram of dye filtration using the VMT-LDH two-dimensional nanobipolar membrane of the present invention. The core working principle of the bipolar membrane is the synergistic effect of electrostatic specific adsorption and steric hindrance physical interception. Through the charge complementary characteristics of VMT and LDH, anionic and cationic dyes are targeted and captured respectively. Then, the porous structure formed by the stacking of nanosheets blocks the dye penetration, ultimately achieving the separation goal of highly efficient dye retention and high-flux pure water permeation, which is suitable for the treatment needs of dye wastewater with coexisting anions and cations.

[0046] Figure 2 The X-ray diffraction (XRD) patterns of VMT nanosheets and rose-shaped LDH from Example 1 are shown. Observation of the XRD peak shapes revealed that the characteristic reflection peaks of LDH at 2θ = 19.45°, 34.19°, 36.58°, and 60.24° exhibit good crystallinity. Furthermore, the reflection at 2θ = 19.45° is characterized by a high-intensity, broad line shape, indicating that hydrotalcite has relatively high crystallinity. No other crystalline phases were detected in the XRD pattern, indicating successful synthesis of the LDH material. In the XRD pattern of the VMT nanosheets, the peaks at 2θ = 8.90°, 18.60°, and 26.3° are characteristic peaks of vermiculite. Some weaker characteristic peaks were observed near 35°, which is because vermiculite originates from minerals, namely mica and biotite, and is subsequently formed through weathering or hydrothermal liquefaction. Furthermore, no other crystalline phases were detected in the spectrum, indicating successful preparation of the VMT nanosheets and the absence of other impurities in the material.

[0047] Figure 3 In Figures a and b, the hydrophilicity test structures of VMT nanosheets and rose-shaped LDH in Example 1 are shown, respectively. The comparison revealed that VMT exhibits better hydrophilicity than LDH, almost completely penetrating the surface at 0.8 s. This is because the surface of expanded VMT displays more hydroxyl, carboxyl, and phenolic functional groups than LDH. These functional groups can form hydrogen bonds with water molecules, thus allowing for better binding. Furthermore, VMT has a larger pore size, contributing to its superior hydrophilicity compared to LDH.

[0048] Figure 4 In Example 1, f are SEM images of different materials; where a: rose-shaped LDH; b: CoMgAl-LDH; c: expanded VMT; d: VMT nanosheets; e: surface of VMT-LDH two-dimensional nanobipolar film; f: magnified surface of VMT-LDH two-dimensional nanobipolar film. Figure 4In Figure g, EDS analysis of CoMgAl-LDH from Example 1 is shown. The microstructure of the prepared material was observed and analyzed using scanning electron microscopy (SEM). The SEM image of LDH shows a rose shape composed of stacked hexagonal monolayers (a), which is consistent with the morphological characteristics of hydrotalcite-like materials. (b) shows the exfoliated hydrotalcite sheets; it can be seen that the LDH monolayers are regular polygons, indicating that the rose-shaped intermediate-entropy hydrotalcite was successfully exfoliated into hydrotalcite monolayers. (c) shows the SEM image of untreated expanded vermiculite; it can be seen that the untreated vermiculite is a layered structure, while the treated vermiculite has been exfoliated into vermiculite nanosheets with a thickness of 228 nm (d). (e) and (f) are surface electron microscopy images of the bipolar film; the roughness of the film surface is due to the irregular stacking of vermiculite monolayers. (g) shows the EDS analysis of LDH. The analysis shows that the main elements such as Co, Mg, and Al are uniformly distributed in the cross section, and each element conforms to the morphology shown in the scanning pattern.

[0049] Dye wastewater treatment experiment Prepare 25mg L -1 MB / MO dye wastewater; install the membranes obtained in each example and comparative example in a vacuum filtration device, control the vacuum degree to 0.1 MPa and room temperature; continuously filter for 14~18h, and periodically sample and test the absorbance of the filtrate; after the membrane performance degrades, treat it according to the regeneration method and reuse it.

[0050] The mass ratio of CoMgAl-LDH to VMT nanosheets ranged from 1:4 to 3:1, including the extreme values ​​(1:4, 3:1) and the intermediate values ​​(1:3, 1:1). All examples achieved a retention rate of over 98% and a concentration of 480 L·m⁻¹. -2 ·h -1 ·Mpa -1 The above water flux demonstrates that this invention can be implemented within this ratio range and solves the problems of limited selectivity and low efficiency of traditional materials. Furthermore, a 1:3 ratio was determined to be the optimal ratio, balancing a retention rate of over 99% and 500 L·m³. -2 ·h -1 ·Mpa -1 For the above water flux ratios, a ratio of 1:4 results in high water flux but a decreased interception rate, while a ratio of 3:1 meets the interception rate but results in insufficient water flux.

[0051] Figure 5 In the figures, a and b represent the dye rejection rates of the examples and comparative examples for MB and MO, respectively. Figure 5Figures c and d show the water flux diagrams for MB and MO in the examples and comparative examples, respectively. It can be seen that under a vacuum of 0.1 MPa and a CoMgAl-LDH to VMT nanosheet ratio of 1:3, the two-dimensional layered bipolar membrane maintained an excellent 99% retention rate for MB after 18 h. After 14 h, the retention rate for MO remained above 99%. VMT constitutes a larger proportion of the membrane material, thus resulting in a longer efficient retention time for MB compared to MO. This is because VMT is an anionic clay with negatively charged layers, effectively removing cationic pollutants such as ammonia nitrogen, heavy metals, phosphates, fluoride ions, rare earth ions, and organic matter from water. Hydrotalcite, on the other hand, is a cationic clay that can adsorb anions and possesses an extremely high specific surface area and a unique pore structure, thus exhibiting special adsorption capacity. It can achieve both adsorption of anionic dye pollutants and blocking of cationic dye pollutants in dyeing and printing wastewater. By stacking the two materials in situ to form a two-dimensional nanobipolar film, the combined effect of steric hindrance and charge interaction can achieve efficient removal of anionic and cationic pollutants from dye wastewater.

[0052] from Figure 5 As can be seen from Figures c and d, the filtration rate for anionic and cationic polar dyes is fastest when the ratio of CoMgAl-LDH to VMT nanosheets is 1:4. The water flux of MB remains at 550 L·m⁻² after the third 4-hour period. -2 ·h -1 ·Mpa -1 For MO filtration, also at an LDH:VMT ratio of 1:4, the third 4-hour time yielded approximately 600 L·m³. -2 ·h -1 ·Mpa -1 High water flow rate.

[0053] The performance data of Example 1 of the present invention and existing membrane materials are shown in Table 1. It can be seen that the present invention simultaneously achieves high retention rate and high water flux, with efficient retention times of 18 h (MB) and 14 h (MO), respectively, and its stability is significantly better than that of existing membrane materials.

[0054] Table 1

[0055] Among them, UH-004 is sourced from: Lin, J. Ye, W. Baltaru, M.C. Tang, Y.P. Bernstein, N.J. Gao, P. Balta, S. Vald, M.; Volodin, A. Sotto, A. et al. Tight ultrafiltration membranes for enhanced separation of dyes and Na2SO4, during textile wastewater treatment..[J]. Membr. Sci. 2016, 514, 217-228. SPES is sourced from: Yin X, Zhang Z, Ma H, et al. Ultra-fine electrospun nanofibrous membranes for multicomponent wastewater treatment: Filtration and adsorption.[J]. Separation and Purification Technology, 2020, 242(prepublish): 116794-116794. UiO-66-NH2 is sourced from: Li J, Gong J, Zeng G, et al. The performance of UiO-66-NH2 / graphene oxide (GO) composite membrane for removal of differently charged mixed dyes.[J]. Chemosphere, 2019, 237, 124-517. Zr-MOFs-PUF is sourced from: Li J, Gong J, Zeng G, et al. Zirconium-based metal organic frameworks loaded on polyurethane foam membrane for simultaneous removal of dyes with different charges.[J]. Journal of Colloid And Interface Science, 2018, 527 267-279. SR-AOPS comes from: Yang H, Gong J, Zeng G, et al. Polyurethane foam membranesfilled with humic acid-chitosan crosslinked gels for selective andsimultaneous removal of dyes. [J]. Journal of ColloidAnd Interface Science, 2017, 50567-78. After five cycles of membrane regeneration, the rejection rate for the cationic dye MB2 was approximately 60%, and the water flux was maintained at 400 L·m2. -2 ·h -1 ·Mpa -1 The above applies; for anionic dyes MO: rejection rate ≥70%, water flux ≥500 L·m -2 ·h -1 ·Mpa -1 .

[0056] Conventional MOF-based membranes (such as UiO-66-NH2): After 3 cycles, the rejection rate drops to below 70%, and after 5 cycles, it drops to below 50%, with a significant decrease in water flux.

[0057] Polymer ultrafiltration membranes (such as SPES): have poor regeneration performance, with a rejection rate of less than 40% after 5 cycles and a water flux decline of more than 50%.

[0058] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. 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 of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A VMT-LDH two-dimensional nanobipolar film, characterized in that, The two-dimensional nanobipolar film has a three-layer composite structure, which includes a support layer, an intermediate functional layer and an upper functional layer from bottom to top; the support layer is a CA film, the intermediate functional layer is an LDH material and the upper functional layer is a VMT material.

2. The VMT-LDH two-dimensional nanobipolar film according to claim 1, characterized in that, The pore size of the CA membrane is 0.22~0.8μm.

3. The method for preparing a VMT-LDH two-dimensional nanobipolar film according to any one of claims 1-2, characterized in that, Includes the following steps: (1) Take expanded VMT and deionized water, mix and float, select the VMT floating on the water surface, remove sand and mica impurities, and pulverize at high speed to obtain vermiculite powder; (2) Weigh vermiculite powder, add H2O2 solution, reflux in oil bath for preliminary stripping; (3) Wash the product obtained in step (2) with deionized water until neutral, add deionized water, put it into a high shear dispersion emulsifier for shearing, then centrifuge with a benchtop centrifuge, take the supernatant, and obtain VMT nanosheets; (4) Dissolve Co(NO3)2·6H2O, Mg(NO3)2·6H2O, Al(NO3)3·9H2O and urea in deionized water, disperse by ultrasonication, then reflux and transfer to a reaction vessel for thermal aging. (5) The product obtained in step (4) was washed three times by centrifugation with deionized water, then washed with ethanol and dried to obtain rose-shaped LDH. (6) Add rose-shaped LDH to deionized water, sonicate for 10 min, and then perform alternating shearing and sonication treatments multiple times. Then centrifuge to obtain regular polygonal sheet-like CoMgAl-LDH. (7) Place VMT nanosheets and CoMgAl-LDH into two containers respectively, add deionized water and PVA to each container, stir in an oil bath at 95°C for 1 h until PVA is completely dissolved, cool to room temperature, and obtain LDH dispersion and VMT dispersion respectively. (8) Lay the CA membrane flat on the vacuum filtration device, add deionized water to wet the membrane surface to ensure no air bubbles, and under a vacuum of 0.1 MPa, slowly pour the LDH dispersion into the vacuum filtration device to form the lower membrane; then pour the VMT dispersion in and continue to filter to make the two membranes tightly bonded. Dry naturally at room temperature to obtain the VMT-LDH two-dimensional nanobipolar membrane.

4. The method for preparing a VMT-LDH two-dimensional nanobipolar film according to claim 3, characterized in that, In step (2), the mass-to-volume ratio of vermiculite powder to H2O2 solution is 1g:10mL, and the mass fraction of H2O2 solution is 30%; the solution is refluxed in an oil bath at 120℃ for 12h.

5. The method for preparing a VMT-LDH two-dimensional nanobipolar film according to claim 3, characterized in that, In step (3), the shearing time is 4 hours and the rotation speed is 10,000 r / min; The centrifugation time was 15 minutes, and the rotation speed was 5000 rad / min; The thickness of the VMT nanosheets is 180~320 nm.

6. The method for preparing a VMT-LDH two-dimensional nanobipolar film according to claim 3, characterized in that, In step (4), the molar ratio of Co(NO3)2·6H2O, Mg(NO3)2·6H2O, Al(NO3)3·9H2O and urea is 1:1:1:25; The ultrasonic dispersion time is 30 min, the condensation reflux time is 2 h, and the thermal aging temperature is 120℃ for 12 h.

7. The method for preparing a VMT-LDH two-dimensional nanobipolar film according to claim 3, characterized in that, In step (5), the centrifugal washing speed is 12000 rad / min; Wash with ethanol until the pH of the filtrate is 6.5-7.0; The drying temperature is 80℃ and the time is 12 hours.

8. The method for preparing a VMT-LDH two-dimensional nanobipolar film according to claim 3, characterized in that, In step (6), the shearing and ultrasonic treatment are performed three times, each time for 2 hours; The centrifugation speed was 5000 rad / min, and the time was 15 min.

9. The method for preparing a VMT-LDH two-dimensional nanobipolar film according to claim 3, characterized in that, In step (7), the mass ratio of CoMgAl-LDH and VMT nanosheets is 1~3:1~4.

10. The application of the VMT-LDH two-dimensional nanobipolar membrane according to any one of claims 1-2 in the treatment of cationic dye wastewater and anionic dye wastewater.

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