Method for preparing ZIF-8 / MXene photocatalytic nanofiltration membrane under assistance of electric field and application of ZIF-8 / MXene photocatalytic nanofiltration membrane

Abstract

The invention relates to the technical field of nanofiltration membranes, discloses a method for preparing a ZIF-8 / MXene photocatalytic nanofiltration membrane under the assistance of an electric field and application, and aims to overcome the defects of random co-deposition interface and disordered structure caused by property difference of a multi-element heterogeneous composite material under the driving of the electric field in the prior art. The method comprises the following steps: performing in-situ growth on ZIF-8 on the surface of MXene to form a composite dispersion liquid, and preparing an electrophoresis liquid with dopamine; and then, by taking the conductive substrate coated with the base film as an anode, firstly applying 3-8V forward voltage for 2-10 minutes, driving MXene to preferentially deposit to form a compact bottom layer, then switching polarity, applying 3-8V reverse voltage for 2-20 minutes, driving ZIF-8 / MXene compound to deposit and synchronously initiating dopamine polymerization crosslinking, thereby constructing the composite film with an ordered structure. According to the preparation method, controllable preparation of a membrane structure and interlayer spacing is realized, the obtained membrane has nano-screening and photocatalytic characteristics, the rejection rate of tetracycline and other antibiotics is greater than 95%, the degradation rate under ultraviolet light exceeds 90%, and the membrane is suitable for synchronous separation and deep degradation of antibiotic polluted water.

Description

Technical Field

[0001] This invention relates to the field of nanofiltration membrane technology, and in particular to a method for preparing ZIF-8 / MXene photocatalytic nanofiltration membranes with electric field assistance and its application. Background Technology

[0002] Nanofiltration membrane technology has become one of the key technologies in the field of water treatment due to its high efficiency in retaining polyvalent salt ions and small organic molecules under low pressure. Among them, two-dimensional transition metal carbides / nitrides (MXenes) are considered ideal materials for constructing high-performance nanofiltration membranes due to their unique two-dimensional layered structure and hydrophilicity. However, MXene nanosheets are prone to disordered stacking during the film formation process, resulting in uneven interlayer channels or even blockage. It is difficult to reconcile the permeate flux and rejection rate of the membrane. Increasing the membrane thickness or reducing the interlayer spacing in order to obtain a high rejection rate will sacrifice water flux. Secondly, the interlayers are only bound by weak van der Waals forces, which are prone to structural damage under long-term hydraulic shock or pressure fluctuations. Furthermore, traditional MXene membranes only have physical sieving functions and cannot further degrade the retained and enriched antibiotics, which poses a risk of aggravated membrane fouling and secondary pollution.

[0003] To regulate the stacked structure of MXene sheets, Li Jian and his team first published "Membranes with ZIF-8 regulated MXene nanosheet stacks for efficient molecular sieving". By growing zeolite imidazolium ester framework material (ZIF-8) in situ on the surface of MXene, the interlayer spacing is widened and a sieving channel of size is constructed, thereby improving the sieving performance of the membrane for specific molecules. However, the passive film formation methods such as vacuum filtration that this scheme relies on have limited control over the orientation, distribution and final thickness of the composite nanosheets in the membrane.

[0004] To address the challenge of precisely controlling the film formation process, Zainab Alansari et al.'s team, in their paper "MXene-Enhanced Electromembrane Systems for Advanced Water Applications: A Review," pointed out that by utilizing MXene's excellent conductivity and electronegativity, its directional migration and assembly can be driven through techniques such as electrophoretic deposition. Zezhen Zhang et al.'s team, in their paper "Preparation and performance of MXene-based electricfield-responsive separation membranes," further confirmed that applying an external electric field can effectively influence the deposition kinetics of MXene nanosheets, achieving preliminary control over film thickness and density.

[0005] However, existing electric field-assisted research mainly focuses on the co-deposition of single MXene or simple mixed suspensions. When dealing with complex multi-component systems where ZIF-8 / MXene composite nanosheets coexist with dopamine crosslinking agents, since MXene is a highly conductive sheet, ZIF-8 is a semiconductor crystal, and dopamine monomers can undergo oxidative polymerization under an electric field, the three components have significant differences in size, charge properties, and electrochemical behavior. Simple co-deposition under a constant electric field will lead to different migration rates of each component, making it difficult to form tightly bonded, structurally ordered heterojunctions and crosslinking networks inside the membrane. This results in limited photogenerated carrier transport efficiency, uneven mechanical enhancement effect, and poor batch-to-batch reproducibility of membrane performance, thus limiting the controllable preparation and performance upper limit of high-performance composite membranes. Summary of the Invention

[0006] The technical problem to be solved by this invention is that existing technologies have the disadvantage that multi-component heterogeneous composite materials are prone to random co-deposition interfaces and disordered structures due to differences in properties under electric field driving. To address this, we propose a method and application for electric field-assisted preparation of ZIF-8 / MXene photocatalytic nanofiltration membranes.

[0007] To achieve the above objectives, this application adopts the following technical solution: a method for electric field-assisted preparation of ZIF-8 / MXene photocatalytic nanofiltration membrane, comprising the following sequential steps: S1: Dispersing MXene powder in deionized water, adding zinc source and 2-methylimidazole, reacting at pH 6-8 to allow ZIF-8 to grow in situ on the MXene surface, centrifuging, washing, and redispersing to obtain a ZIF-8 / MXene composite dispersion; S2: Mixing dopamine solution with the composite dispersion to obtain an electrophoresis working solution, using a conductive substrate coated with a base film as the anode, immersing it together with the cathode in the working solution, first applying a forward DC voltage of 3-8V for 2-10 minutes, then switching the power supply polarity and applying a reverse DC voltage of 3-8V for 2-20 minutes to form a composite film layer on the anode surface; S3: Rinsing and drying the deposited composite film to obtain the ZIF-8 / MXene photocatalytic nanofiltration membrane.

[0008] Preferably, the MXene powder is a few-layer Ti3C2T. x Material.

[0009] Preferably, the concentration of the dispersion formed after the MXene powder is dispersed is 0.5-2.0 mg / mL.

[0010] Preferably, the zinc source is selected from zinc nitrate, zinc chloride, or a combination thereof.

[0011] Preferably, the molar ratio of the zinc source to 2-methylimidazole is 1:2 to 1:4.

[0012] Preferably, the concentration of the ZIF-8 / MXene composite dispersion in S1 is 0.5-2.0 mg / mL.

[0013] Preferably, the concentration of dopamine in the electrophoresis working solution in S2 is 0.1-0.5 mg / mL.

[0014] Preferably, the base membrane is an ultrafiltration membrane or microfiltration membrane made of polyethersulfone, polyvinylidene fluoride, nylon, or polyimide.

[0015] Preferably, the cathode is a platinum sheet or a graphite plate, and the distance between the cathode and the anode is 2-5 cm.

[0016] Application of an electric field-assisted preparation of ZIF-8 / MXene photocatalytic nanofiltration membrane in the purification of antibiotic-contaminated water.

[0017] The technical effects and advantages of this invention are as follows:

[0018] In this invention, by applying electric fields in different directions in stages, the deposition sequence and spatial structure of each functional component on the base film are precisely controlled. First, a positive voltage is applied to preferentially deposit negatively charged MXene nanosheets, forming a dense and highly conductive bottom layer. Then, the voltage is switched to reverse to drive the deposition of ZIF-8 / MXene composite sheets on the bottom layer, and simultaneously induces the oxidative polymerization of dopamine at the interface, forming a cross-linked network in situ. This solves the problems of easy stacking and disordered structure of traditional MXene membrane sheets. The prepared photocatalytic nanofiltration membrane has a rejection rate of more than 95% for various antibiotics such as tetracycline, can achieve a synchronous degradation rate of more than 90% under ultraviolet light, and exhibits good flux retention and structural stability during long-term operation. Attached Figure Description

[0019] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0020] Figure 1 This is a SEM image of a dried sample of the ZIF-8 / MXene composite dispersion of the present invention.

[0021] Figure 2 This is another SEM image of the dried ZIF-8 / MXene composite dispersion sample of the present invention;

[0022] Figure 3 This is a cross-sectional SEM image of the ZIF-8 / MXene photocatalytic nanofiltration membrane of the present invention;

[0023] Figure 4 This is an EDS surface distribution diagram of C, N, and O elements in the ZIF-8 / MXene photocatalytic nanofiltration membrane of the present invention;

[0024] Figure 5 This is an EDS surface distribution diagram of F, Al, and Ti elements in the ZIF-8 / MXene photocatalytic nanofiltration membrane of the present invention;

[0025] Figure 6 This is an EDS surface distribution diagram of Zn element in the ZIF-8 / MXene photocatalytic nanofiltration membrane of the present invention;

[0026] Figure 7 This is an elemental layer diagram of the ZIF-8 / MXene photocatalytic nanofiltration membrane of the present invention;

[0027] Figure 8 This is the total EDS spectrum of the ZIF-8 / MXene photocatalytic nanofiltration membrane of the present invention;

[0028] Figure 9The continuous operation performance curve of the ZIF-8 / MXene photocatalytic nanofiltration membrane of the present invention is shown. Detailed Implementation

[0029] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0030] This invention provides a method for electric field-assisted preparation of ZIF-8 / MXene photocatalytic nanofiltration membranes, comprising the following steps performed sequentially:

[0031] S1: Add MXene powder to deionized water, sonicate at 200W for 30-45 minutes to disperse it, then centrifuge at 4000r / min for 10-15 minutes to remove unpeeled thick flakes and large particle impurities to obtain a stable and uniform MXene dispersion.

[0032] S2: Add zinc source and 2-methylimidazole to MXene dispersion, adjust the pH of the reaction system to between 6 and 8 using hydrochloric acid or sodium hydroxide solution, and stir the reaction at 25-35℃ for 6-12 hours to allow ZIF-8 to grow in situ on the MXene surface. After the reaction, centrifuge and wash the solid obtained, and redisperse it in deionized water to obtain ZIF-8 / MXene composite dispersion.

[0033] S3: Add dopamine solution to ZIF-8 / MXene composite dispersion and stir until homogeneous to obtain working solution for electrophoretic deposition;

[0034] S4: Using a conductive substrate covered with a base film as the anode and an inert electrode as the cathode, both are immersed in the electrophoresis working solution and connected to a DC power supply. First, a forward voltage of 3-8V is applied for deposition for 2-10 minutes. Then, the polarity is switched and a reverse voltage of 3-8V is applied to continue deposition for 2-20 minutes, so that the material is deposited on the surface of the anode substrate to form a composite film layer.

[0035] S5: Take out the deposited composite membrane, rinse the membrane surface with deionized water, and then place it in a vacuum drying oven and dry it at 45-55℃ for 6-12 hours to obtain the ZIF-8 / MXene photocatalytic nanofiltration membrane.

[0036] It should be noted that the MXene is a few-layer Ti3C2T obtained by etching titanium aluminum carbide (Ti3AlC2) in a lithium fluoride-containing hydrochloric acid solution for 48 hours, followed by intercalation and ultrasonic lift-off. xThe material has a sheet surface rich in hydrophilic functional groups such as -OH and -O, which are stably dispersed in water and exhibit negative charge.

[0037] To form a dispersion system suitable for electrophoresis, the obtained MXene powder needs to be mixed with deionized water to prepare a dispersion, and the concentration of the MXene dispersion is preferably 0.5-2.0 mg / mL.

[0038] In this invention, the zinc source is selected from one or a combination of zinc nitrate and zinc chloride;

[0039] Furthermore, to ensure the effective in-situ growth of ZIF-8 crystals on the surface of MXene nanosheets and to suppress their spontaneous homogeneous nucleation in solution, the molar ratio of zinc source to 2-methylimidazole needs to be controlled at 1:2-1:4.

[0040] After the reaction is complete, the ZIF-8 / MXene complex, after centrifugation and washing, needs to be redispersed in deionized water. The concentration of the ZIF-8 / MXene complex dispersion is preferably 0.5-2.0 mg / mL to ensure sufficient loading and stable dispersion of functional units in the electrophoresis solution.

[0041] The dopamine solution is prepared by dissolving dopamine hydrochloride in deionized water;

[0042] Furthermore, in order to achieve effective interfacial cross-linking and structural regulation during the deposition process, the concentration of dopamine in the final electrophoresis working solution needs to be controlled at 0.1-0.5 mg / mL.

[0043] The base membrane is a porous support for the composite functional layer, and can be an ultrafiltration membrane or microfiltration membrane made of polyethersulfone, polyvinylidene fluoride, nylon or polyimide. The inert electrode is preferably one of platinum sheet or graphite plate.

[0044] During electrophoretic deposition, the distance between the cathode and anode should be maintained at 2-5 cm to ensure the uniformity of the electric field distribution and the stability of the deposition process.

[0045] It should be noted that in S4, a positive voltage of 3-8V is first applied for deposition for 2-10 minutes. During this stage, the negatively charged MXene nanosheets migrate towards the anode under the drive of the electric field and are preferentially deposited to form a dense conductive substrate.

[0046] Then, the polarity is switched, and a reverse voltage of 3-8V is applied to continue deposition for 2-20 minutes. At this time, the ZIF-8 / MXene composite sheets migrate towards the anode and are deposited on the bottom layer, while dopamine undergoes oxidative polymerization at the anode interface.

[0047] The ZIF-8 / MXene photocatalytic nanofiltration membrane prepared by the above method has both precise nano-sieving channels and highly efficient photocatalytic active sites.

[0048] The present invention also provides an application of the ZIF-8 / MXene photocatalytic nanofiltration membrane in purifying water bodies contaminated with antibiotics.

[0049] Specifically, the ZIF-8 / MXene photocatalytic nanofiltration membrane is assembled in a nanofiltration-photocatalysis integrated device. Under operating conditions of 0.1-0.5 MPa and 25-35℃, the water containing antibiotics is separated by nanofiltration. At the same time, ultraviolet light is applied to achieve simultaneous efficient retention and deep degradation of antibiotics.

[0050] Furthermore, the antibiotics include one or more of tetracycline antibiotics, sulfonamide antibiotics, and quinolone antibiotics.

[0051] The ZIF-8 / MXene photocatalytic nanofiltration membrane has a retention rate of more than 95% for the aforementioned antibiotics; under ultraviolet light irradiation, the degradation rate of retained and permeated antibiotics can reach more than 90%, thus achieving the purification of antibiotic-contaminated water bodies.

[0052] To specifically verify the comprehensive performance of the membrane prepared by this invention and the beneficial effects of the aforementioned parameter selection, a series of experimental examples are provided below for detailed explanation. Unless otherwise specified, all chemical reagents used in the experiments are of analytical grade, and the water is deionized water.

[0053] Experimental Example 1

[0054] This experimental example aims to characterize the microstructure of the ZIF-8 / MXene photocatalytic nanofiltration membrane prepared by the method of the present invention.

[0055] Following the above preparation method, ZIF-8 / MXene photocatalytic nanofiltration membrane samples were prepared, specifically including the following steps:

[0056] S1: Weigh 100mg of MXene powder and add it to 100mL of deionized water. Sonicate the mixture at 200W for 45min. Then, centrifuge the resulting dispersion at 4000r / min for 15min and take the supernatant to obtain the MXene dispersion.

[0057] S2: Measure 50 mL of the above MXene dispersion and add 0.37 g of zinc nitrate hexahydrate and 0.41 g of 2-methylimidazole sequentially. Stir magnetically to dissolve them. Adjust the pH of the mixture to 7.1 using 0.1 mol / L sodium hydroxide solution. Place the mixture at 30°C and stir continuously for 8 h. After the reaction is complete, centrifuge the reaction solution at 8000 r / min for 10 min, discard the supernatant, wash the precipitate three times with deionized water, and finally redisperse it in 50 mL of deionized water to obtain ZIF-8 / MXene composite dispersion.

[0058] S3: Mix 5 mL of 2.0 mg / mL dopamine hydrochloride solution with 45 mL of ZIF-8 / MXene composite dispersion and stir magnetically for 30 min to obtain the working solution;

[0059] S4: Fix a polyethersulfone ultrafiltration membrane onto a conductive carbon plate, use a platinum electrode as the cathode, and place it parallel to the anode in the electrophoresis tank. Adjust the distance between the two electrodes to 3 cm, inject the above electrophoresis working solution into the tank to ensure that the two electrodes are completely immersed, connect the DC power supply, first apply a positive voltage of 5V for 2 minutes, then switch the polarity and apply a reverse voltage of 5V for 15 minutes.

[0060] S5: After deposition, the substrate covered with the composite membrane was removed, the membrane surface was rinsed with deionized water, and then placed in a vacuum drying oven and dried at 50°C for 8 hours to obtain the ZIF-8 / MXene photocatalytic nanofiltration membrane.

[0061] To observe the intrinsic morphology of the composite material, the ZIF-8 / MXene composite dispersion was dropped onto a silicon wafer and dried to prepare a sample. The sample was then observed using a field emission scanning electron microscope (FET). Figure 1 and Figure 2 As shown.

[0062] according to Figure 1-2 The results showed that MXene nanosheets exhibited a typical wrinkled sheet structure, with a large number of uniformly sized spherical nanoparticles uniformly loaded on their surface. These particles were ZIF-8 grown in situ and showed no obvious aggregation.

[0063] Furthermore, the cross-section of the obtained ZIF-8 / MXene photocatalytic nanofiltration membrane was observed, referring to... Figure 3 As shown in the cross-sectional SEM image, the composite functional layer is tightly bonded to the base film and has a uniform thickness. Inside the functional layer, the MXene sheets and the ZIF-8 particles they support exhibit an ordered layered stacking structure along the direction parallel to the base film, and clear nanochannels are formed between the sheets.

[0064] Experimental Example 2

[0065] This experiment aims to analyze the elemental composition and spatial distribution of the same ZIF-8 / MXene photocatalytic nanofiltration membrane sample prepared in Experiment 1, in order to verify the composite state and uniformity of the functional components.

[0066] The surface of the membrane sample was characterized using a field emission scanning electron microscope equipped with an X-ray energy dispersive spectrometer. Before testing, the sample was directly fixed on conductive adhesive without gold spraying to ensure the accuracy of elemental analysis. Under the conditions of 10kV accelerating voltage, 10mm working distance and high vacuum, a representative flat area on the membrane surface was selected for testing.

[0067] Reference Figure 4-6 As shown, a surface scan is performed in the selected area, and X-ray signals of characteristic elements C, N, O, F, Al, Ti, and Zn are acquired simultaneously to generate a two-dimensional distribution map of each element.

[0068] Among them, the Ti element spots are uniformly dispersed overall, without large-area agglomeration regions, proving that the MXene nanosheets are well dispersed in the film and do not undergo disordered stacking; the Zn element spots uniformly cover the entire field of view, without local dense agglomeration, which corresponds to the morphology of uniformly loaded ZIF-8 particles in the SEM image, proving that ZIF-8 grows uniformly in situ on the MXene surface without particle agglomeration; the N element spots are uniformly dispersed and highly overlap with the distribution area of ​​Zn. N comes from both the imidazole ligand of ZIF-8 and the amino group of dopamine, proving that neither ZIF-8 nor dopamine is locally enriched.

[0069] F and Al elements are enriched in a small area. F is the surface terminal group of MXene, and Al is the residue after the MXene precursor is etched. The small amount of local enrichment is a normal residue of the synthesis process and does not form large-area agglomeration, so it has no negative impact on the overall structure and performance of the film.

[0070] Reference Figure 7 As shown, the distribution signals of the above elements are superimposed and pseudo-color rendered to generate a layered image of the elements, so as to intuitively show the distribution and correlation of different elements in spatial location.

[0071] Reference Figure 8 As shown, X-ray energy spectra are collected for selected areas, and the types of elements present on the sample surface are determined based on the energy positions of characteristic peaks.

[0072] Each characteristic peak in the spectrum corresponds to the target element. Among them, the C peak has the highest intensity and corresponds to the carbon layer of MXene, the imidazole ligand of ZIF-8, and the carbon chain of dopamine. It is the core identifier of the carbon-based component of the system. The N / O / F peaks show that N corresponds to the ligand of ZIF-8 and the amino group of dopamine, O corresponds to the oxygen-containing functional group on the surface of MXene, and F corresponds to the terminal group of MXene.

[0073] The Zn / Ti peaks are clearly visible, with the Lα / Kα characteristic peaks of Zn appearing, corresponding to the Zn element in ZIF-8, and the Kα / Kβ characteristic peaks of Ti appearing, corresponding to the Ti element in MXene.

[0074] Based on the above qualitative analysis, the energy spectrum was processed using the software provided with the instrument, and a standard-free quantitative analysis method was adopted. The results are shown in Table 1 below.

[0075]

[0076] Table 1

[0077] According to the data in Table 1, the weight percentage of Zn is 14.05% and the atomic percentage is 3.15%, while the weight percentage of N is 15.68% and the atomic percentage is 16.38%, which quantitatively confirms the successful loading and presence of the ZIF-8 component in the membrane.

[0078] Experimental Example 3

[0079] The aim is to evaluate the structural stability and performance retention of the ZIF-8 / MXene photocatalytic nanofiltration membrane prepared by the method of the present invention under continuous operation conditions.

[0080] ZIF-8 / MXene photocatalytic nanofiltration membrane samples were prepared using the same materials and processes as in Experimental Example 1.

[0081] After cutting the ZIF-8 / MXene photocatalytic nanofiltration membrane, it was assembled onto a membrane with an effective membrane area of ​​4.2 cm². 2 In the flat-plate cross-flow filter tank, an ultraviolet LED surface light source is integrated above the filter tank, with a main wavelength of 365nm and an output light intensity of 30mW / cm². 2 ;

[0082] A tetracycline aqueous solution with a concentration of 20 mg / L was used as the simulated pollutant feed liquid. Under constant temperature and pressure of 0.3 MPa and 25 °C, the circulation pump was turned on to make the feed liquid flow cross-flow onto the surface of the filter membrane at a flow rate of 10 cm / s. At the same time, the ultraviolet light source was turned on for continuous irradiation to simulate the nanofiltration-photocatalysis coupled operation process.

[0083] From the start of operation, samples were taken from the permeate side every 2 hours until a cumulative total of 48 hours. During each sampling, the permeate flow rate was recorded simultaneously to calculate the instantaneous permeate flux. The concentration of tetracycline in the permeate was measured at 357 nm using a UV-Vis spectrophotometer, and the membrane rejection rate at that time point was calculated. Another sample was taken from the feed side, and under the same UV irradiation conditions, the total organic carbon (TOC) content of the solution before and after the reaction was measured to calculate the membrane photocatalytic degradation rate corresponding to that operating time point. The results are shown in […]. Figure 9 As shown.

[0084] according to Figure 9 The results showed that the tetracycline rejection rate remained above 98.0% throughout the process with minimal fluctuations, proving that the nano-sieve structure of the membrane remained intact under long-term pressure and water flow shear. The photocatalytic degradation rate was consistently above 96.5%, indicating that the catalytic active sites of the ZIF-8 / MXene heterojunction did not undergo significant deactivation or loss. The permeate flux decreased by about 8% in the first 6 hours due to the initial compaction of the membrane structure, and then the downward trend was extremely gradual, with the flux retention rate reaching approximately 90.1% of the initial value by 48 hours.

[0085] Experiment Example 4

[0086] This experimental example aims to study the effect of the voltage application procedure during the electrophoretic deposition stage on the final membrane structure and its separation-catalytic performance.

[0087] This series of experiments is based on the preparation method described in Experiment 1. All materials, formulas and conditions are kept unchanged, and the only variable is the voltage application program in S4.

[0088] To investigate the effects of different voltage programs, a total of 9 experimental groups were set up. The total deposition time for all groups was controlled at 17 minutes. The only difference between each group and the standard method described in Experiment 1 was the voltage and time parameters used during electrophoretic deposition. The specific settings are as follows:

[0089] Group E1: First, apply a +5V DC voltage to the anode for 2 minutes; then, switch the power supply polarity and apply a -5V DC voltage to the anode for 15 minutes of deposition.

[0090] Group E2: First, apply a DC voltage of +3V to the anode for 2 minutes; then switch to a DC voltage of -5V and deposit for 15 minutes.

[0091] Group E3: First, apply a DC voltage of +8V to the anode for 2 minutes; then switch to a DC voltage of -5V and deposit for 15 minutes.

[0092] Group E4: First, apply a +5V DC voltage to the anode for 1 minute; then switch to a -5V DC voltage and deposit for 16 minutes.

[0093] Group E5: First, apply a +5V DC voltage to the anode for 5 minutes; then switch to a -5V DC voltage and deposit for 12 minutes.

[0094] Group E6: First, apply a +5V DC voltage to the anode for 2 minutes; then switch to a -3V DC voltage and deposit for 15 minutes.

[0095] Group E7: First, apply a +5V DC voltage to the anode for 2 minutes; then switch to a -8V DC voltage and deposit for 15 minutes.

[0096] Group E8: First, apply a +5V DC voltage to the anode for 2 minutes; then switch to a -5V DC voltage and deposit for 8 minutes.

[0097] Group E9: No voltage switching is performed, and a constant DC voltage of -5V is applied to the anode throughout the process. The total deposition time is 17 minutes.

[0098] The membrane samples prepared in each group were subjected to performance tests. The operating conditions and testing methods were the same as those in Experiment 3. Each group was tested in parallel 5 times. The results are shown in Table 2 below.

[0099]

[0100] Table 2

[0101] According to the data in Table 2, the photocatalytic degradation rate of group E9 ​​was lower than that of all groups using E1-E8, indicating that the timing-based voltage switching has a significant effect on constructing a highly efficient photocatalytic interface. When the forward voltage or time is insufficient, the incomplete initial MXene layer may lead to uneven loading of subsequent functional layers, resulting in decreased retention and catalytic performance. When the forward voltage or time is too high, it may lead to an excessively thick and dense bottom layer, sacrificing permeation flux. When the reverse voltage is too low or the time is too short, it may lead to insufficient development of functional layers. When the reverse voltage is too high, it may cause excessively rapid deposition and structural disorder.

[0102] Experimental Example 5

[0103] This experimental example aims to study the effect of dopamine concentration in the electrophoresis working solution on the final membrane structure and its separation-catalytic performance.

[0104] This series of experiments is based on the preparation method described in Experiment 1. All materials, formulas and conditions are kept constant. The only variable is the final concentration of dopamine in the electrophoresis working solution prepared in S3. The concentration is controlled by changing the volume of the added dopamine hydrochloride stock solution of known concentration.

[0105] A total of 8 experimental groups were set up, as follows:

[0106] Group D1: No dopamine hydrochloride added;

[0107] Group D2: The final concentration of dopamine was 0.05 mg / mL;

[0108] Group D3: The final concentration of dopamine was 0.10 mg / mL;

[0109] Group D4: The final concentration of dopamine was 0.20 mg / mL;

[0110] Group D5: The final concentration of dopamine was 0.30 mg / mL;

[0111] Group D6: The final concentration of dopamine was 0.50 mg / mL;

[0112] Group D7: The final concentration of dopamine was 0.80 mg / mL;

[0113] Group D8: The final concentration of dopamine was 1.00 mg / mL.

[0114] The membrane samples prepared in each group were subjected to performance tests. The operating conditions and testing methods were the same as those in Experiment 3. Each group was tested in parallel 5 times. The results are shown in Table 3 below.

[0115]

[0116] Table 3

[0117] According to the data in Table 3, although group D1 had the highest permeation flux, its rejection rate was lower than that of D2-D9, and the membrane layer was severely damaged after ultrasonication. When the dopamine concentration was in the range of 0.10-0.50 mg / mL, the prepared membrane had better performance, with the rejection rate steadily increasing to over 99%, while the photocatalytic degradation rate remained above 96%. When the concentration exceeded 0.50 mg / mL, the permeation flux dropped sharply, which is speculated to be due to the bulk polymerization or excessive deposition of excessive polydopamine, which severely blocked the mass transfer channels in the membrane, resulting in a significant reduction in the membrane's practicality.

[0118] Experimental Example 6

[0119] This experimental example aims to study the effect of the concentration of ZIF-8 / MXene composite dispersion on the final membrane structure and its separation-catalytic performance.

[0120] This series of experiments is based on the preparation method described in Experiment 1. All materials, formulations and conditions are kept constant. The only variable is the concentration of the ZIF-8 / MXene composite dispersion prepared in S2. The concentration is controlled by changing the volume of deionized water added during redispersion.

[0121] A total of 8 experimental groups were set up, as follows:

[0122] Group C1: The concentration of the composite dispersion was 0.2 mg / mL;

[0123] Group C2: The concentration of the composite dispersion was 0.5 mg / mL;

[0124] Group C3: The concentration of the composite dispersion was 1.0 mg / mL;

[0125] Group C4: The concentration of the composite dispersion was 1.5 mg / mL;

[0126] Group C5: The concentration of the composite dispersion was 2.0 mg / mL;

[0127] Group C6: The concentration of the composite dispersion was 2.5 mg / mL;

[0128] Group C7: The concentration of the composite dispersion was 3.0 mg / mL;

[0129] Group C8: The concentration of the composite dispersion was 4.0 mg / mL.

[0130] The membrane samples prepared in each group were subjected to performance tests. The operating conditions and testing methods were the same as those in Experiment 3. Each group was tested in parallel 5 times. The results are shown in Table 4 below.

[0131]

[0132] Table 4

[0133] According to the data in Table 4, the thickness of the membrane functional layer is positively correlated with the concentration of the composite dispersion. When the concentration of the composite dispersion is in the range of 0.5-2.0 mg / mL, the membrane thickness is moderate, which can form a complete and defect-free functional layer, thereby achieving high rejection rate, high photocatalytic degradation rate and high water permeation flux. When the concentration is too low, the membrane is too thin, and the functional layer may be discontinuous or incomplete, resulting in insufficient sieving capacity and catalytic activity. When the concentration is too high, the membrane is too thick. An excessively thick membrane not only increases the mass transfer resistance of water sharply, but also reduces the utilization rate of internal photocatalytic active sites and decreases the degradation efficiency due to the attenuation of light in the membrane layer and the excessively long mass transfer path of reactants.

[0134] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A method for electric field-assisted preparation of ZIF-8 / MXene photocatalytic nanofiltration membranes, characterized in that, The following steps are performed sequentially: S1: Disperse MXene powder in deionized water, add zinc source and 2-methylimidazole, react at pH 6-8 to allow ZIF-8 to grow in situ on the MXene surface, and redisperse after centrifugation and washing to obtain ZIF-8 / MXene composite dispersion. S2: Mix the dopamine solution with the composite dispersion to obtain the electrophoresis working solution. Use the conductive substrate coated with the base film as the anode and immerse it together with the cathode in the working solution. First, apply a forward DC voltage of 3-8V to deposit for 2-10 minutes. Then, switch the power supply polarity and apply a reverse DC voltage of 3-8V to deposit for 2-20 minutes to form a composite film layer on the anode surface. S3: Rinse and dry the deposited composite membrane to obtain the ZIF-8 / MXene photocatalytic nanofiltration membrane.

2. The method for preparing ZIF-8 / MXene photocatalytic nanofiltration membranes with electric field assistance according to claim 1 is characterized in that: The MXene powder is a few-layer Ti3C2T. x Material.

3. The method for preparing ZIF-8 / MXene photocatalytic nanofiltration membranes with electric field assistance according to claim 2, characterized in that: The concentration of the dispersion formed after the MXene powder is dispersed is 0.5-2.0 mg / mL.

4. The method for preparing ZIF-8 / MXene photocatalytic nanofiltration membranes with electric field assistance according to claim 1, characterized in that: The zinc source is selected from zinc nitrate, zinc chloride, or a combination thereof.

5. A method for preparing ZIF-8 / MXene photocatalytic nanofiltration membranes with electric field assistance according to claim 1 or 4, characterized in that: The molar ratio of the zinc source to 2-methylimidazole is 1:2 to 1:

4.

6. The method for preparing ZIF-8 / MXene photocatalytic nanofiltration membranes with electric field assistance according to claim 1, characterized in that: The concentration of the ZIF-8 / MXene composite dispersion in S1 is 0.5-2.0 mg / mL.

7. The method for preparing ZIF-8 / MXene photocatalytic nanofiltration membranes with electric field assistance according to claim 1, characterized in that: The concentration of dopamine in S2 in the electrophoresis working solution is 0.1-0.5 mg / mL.

8. The method for preparing ZIF-8 / MXene photocatalytic nanofiltration membrane with electric field assistance according to claim 1, characterized in that: The base membrane is an ultrafiltration or microfiltration membrane made of polyethersulfone, polyvinylidene fluoride, nylon, or polyimide.

9. The method for preparing ZIF-8 / MXene photocatalytic nanofiltration membranes with electric field assistance according to claim 1, characterized in that: The cathode is a platinum sheet or a graphite plate, and the distance between the cathode and the anode is 2-5 cm.

10. The application of an electric field-assisted preparation of ZIF-8 / MXene photocatalytic nanofiltration membrane as described in any one of claims 1-9 in the purification of antibiotic-contaminated water.

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