A high-flux photocatalytic membrane and a preparation method thereof

Abstract

The application constructs a new type of high-flux photocatalytic membrane which is stable in structure, high in permeation flux and has comprehensive performance such as photocatalytic performance. The two-dimensional MXene material with a sheet structure is obtained by peeling MAX with a mixed solution of LiF and HCl; NM88B@MXene powder is prepared by a solvothermal chemical method. The NM88B@MXene powder is added into deionized water and ultrasonically dispersed, and a NM88B@MXene composite membrane is constructed on a CA membrane substrate by a vacuum filtration method, which is used for treating dyes in industrial wastewater. The dye removal performance of the composite material in the NM88B@MXene composite membrane is explored. From the perspective of improving the structure of the membrane material itself, the treatment efficiency and the recycling property of the membrane are improved, so as to achieve the practical purpose of reducing the cost of industrial wastewater treatment. The application creatively prepares a new type of high-flux and anti-pollution photocatalytic membrane, greatly improves the water treatment efficiency, solves the membrane pollution problem from the source, and further widens the use range of MXene and Fe-MOFs.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, and specifically discloses a method for preparing a high-throughput photocatalytic membrane and the high-throughput photocatalytic membrane obtained by the method. Background Technology

[0002] Dyes are currently widely used in industries such as textiles, papermaking, printing, food, and cosmetics. The development of the dye industry has led to a continuous increase in dye wastewater production, which, if directly discharged, poses a significant threat to the surrounding ecological environment and human health. Membrane separation technology, with its advantages of simple operation, high efficiency, and environmental friendliness, is now widely used in industrial wastewater treatment. The development and preparation of membrane materials has always been one of the key and challenging aspects of membrane separation research. Traditional membrane materials have poor antifouling properties; during separation, pollutants are easily adsorbed and deposited on the membrane surface and between layers, leading to blockage of mass transfer channels, reduced service life, and limiting their practical application. Therefore, developing novel membrane materials with high flux and high antifouling performance is of great practical significance.

[0003] Due to the unique physicochemical properties of two-dimensional materials, high-performance separation membranes developed using them as substrates can often simultaneously achieve both permeability and selectivity. MXene is a novel two-dimensional transition metal carbide or carbonitride, whose general chemical formula can be represented as M... n+1 X n T x (Where M represents an early transition metal element, X represents carbon or nitrogen, and T represents the active group attached to the surface). Compared with graphene-based materials, MXene not only possesses the same characteristics of high specific surface area and high conductivity, but also has adjustable and controllable interlayer spacing and composition. The abundant -OH and -O functional groups on the surface endow MXene with superior reactivity and hydrophilicity. Nanocomposite membranes constructed using MXene as a substrate exhibit strong plasticity and flexibility, and have become a novel approach for developing new membrane materials. For example, Professor Wang Haihui's research group at South China University of Technology constructed a two-dimensional MXene membrane on anodized aluminum oxide (AAO) substrate using vacuum filtration and then used ferric hydroxide nanoparticles to create pores. The results showed that the permeation flux of this two-dimensional membrane reached as high as 1000 L / (m²). 2 With a flux density of ·h·bar, it achieves a rejection rate of over 90% for pollutants with a particle size greater than 2.5nm in water. Therefore, the two-dimensional material MXene has broad prospects in constructing high-flux membranes and breaking the trade-off effect between separation and permeability in the membrane field.

[0004] Kadja's group reported a novel method for preparing chloride-modified MXene membranes. MXene nanosheets were prepared by etching the MAX phase with a LiF-HCl mixed solution. 0.2 mg·mL⁻¹ of the nanosheets were then filtered using vacuum-assisted filtration. -1MXene suspension (2.0 mg·cm⁻¹) -2 MXene was deposited on a mixed cellulose ester (MCE) substrate membrane with an average pore size of 0.22 μm. Then, the MXene deposited on the MCE was modified by vacuum filtration using 10 mL of a 1M chloride solution (NaCl, KCl, and MgCl2) to prepare a modified MXene membrane. However, the flux improvement of this separation membrane was not significant (70–100 L·m⁻¹). -2 ·h -1 This limitation restricts its application in practical water treatment. Furthermore, while salt-modified MXene membranes possess some antifouling properties, they cannot remove pollutants in situ, have low reusability, and thus struggle to achieve ideal pollutant removal results in practical applications.

[0005] Tang's research group prepared MIL-101(Fe) photocatalyst material using a solvothermal method. The morphology of the material was characterized by scanning electron microscopy. The material particles exhibited near-spherical, irregular polyhedral shapes, good dispersibility, and uniform particle size ranging from 0.5 to 1 μm. The results showed that MIL-101(Fe) possessed good photocatalytic performance (a degradation rate of 51.37% for methylene blue solution), demonstrating potential applications in environmental protection, such as the degradation of organic pollutants. However, this technology only possesses photocatalytic ability and is not based on the coupling of photocatalysis and membrane separation technologies. Photocatalytic separation and membrane separation are two completely different techniques and concepts. The MIL-101(Fe) photocatalyst material is prone to agglomeration in the degraded dyes, and long-term use may lead to a reduction in specific surface area during photodegradation, weakening the photocatalytic effect. Furthermore, the prepared photocatalyst material itself is difficult to separate and recover, easily causing secondary pollution to the degraded substances. In practical applications, it is difficult to achieve the desired effect of recycling the photocatalyst. Furthermore, powdered photocatalysts are mainly used to treat single pollutants, and their comprehensive treatment effect on multiple pollutants in complex aquatic environments still needs further research.

[0006] Based on the above analysis, a novel high-flux photocatalytic membrane with stable structure, high permeation flux, and comprehensive photocatalytic performance is urgently needed in this field. Summary of the Invention

[0007] In view of the above shortcomings, this invention creatively prepares a novel high-flux, anti-fouling photocatalytic membrane, which greatly improves water treatment efficiency and solves the membrane fouling problem at its source. It further broadens the application scope of MXene and Fe-MOFs, providing some reference for the development and construction of more novel high-performance membrane materials. This invention is achieved through the following technical means:

[0008] A method for preparing a high-throughput photocatalytic membrane, comprising:

[0009] (1) Preparation of MXene two-dimensional materials:

[0010] Two-dimensional MXene materials were prepared by etching the MAX phase with a LiF+HCl mixed reagent followed by ultrasonic-assisted exfoliation. Specifically:

[0011] At room temperature and pressure, 0.5 g of LiF was dissolved in 15 mL of HCl solution, and 0.5 g of Ti3C2T was added... X The powder was added to the solution and magnetically stirred at 30°C for 20 hours. It was then washed multiple times with deionized water (DI) at room temperature and pressure until the pH of the supernatant reached 6. After centrifugation several times at 3500 rpm, the supernatant was collected to obtain a multilayer Ti3C2T solution. X Nanosheets. The supernatant was sonicated in 200 mL of deionized water at 30 °C for 6 h, the dispersion was centrifuged for 30 min, and the MXene two-dimensional material was collected and freeze-dried for storage.

[0012] (2) Preparation of NM88B@MXene:

[0013] NM88B@MXene powder was prepared using a solvothermal chemical method, specifically:

[0014] 30 mg of MXene was mixed with 270 mg of FeCl3·6H2O and 181 mg of NH2-BDC, and then added to 15 mL of DMF in a beaker. The mixture was sonicated for 30 min to obtain a homogeneous solution. The homogeneous solution was transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene and allowed to react solvothermically at 110 °C for 12 h. After natural cooling to room temperature, the mixture was washed repeatedly by centrifugation at 8000 rpm with DMF and EtOH, and the brownish-black precipitate was collected. The collected precipitate was vacuum dried at 80 °C for 8 h to obtain NM88B@MXene powder for later use.

[0015] (3) Construction of high-throughput photocatalytic membranes

[0016] ① At room temperature and pressure, 15 mg of NM88B@MXene powder was added to 100 mL of deionized water and then sonicated for 20 min to obtain a precursor solution with a concentration of 0.15 g / L.

[0017] ② A precursor solution with a concentration of 0.15 g / L was slowly filtered onto a CA membrane at a pressure of 0.1 MPa and a normal temperature using a vacuum filtration method to construct an NM88B@MXene composite membrane, i.e., a high-flux catalytic membrane.

[0018] The beneficial effects of this invention are as follows:

[0019] 1. The high-throughput photocatalytic membrane prepared in this invention achieves high throughput, high rejection rate, and strong photocatalytic ability of the composite membrane. The material is synthesized in situ using a solvothermal method, where metal cations are immobilized on the surface of MXene to form seed crystals, which are then coordinated with ligands to grow NM88B crystals on MXene nanosheets. SEM characterization of the powder is as follows: Figure 2 (a) Figure 2 As shown in (b), this alters the ordered stacked structure of the MXene sheets, increasing the interlayer spacing of the MXene membrane and creating more mass transfer channels. This significantly improves the flux of the composite membrane. SEM characterization of the membrane's surface and cross-section is shown below. Figure 2 (c) Figure 2 As shown in (d), the introduction of NM88B endows the composite membrane with visible light responsiveness, thereby improving the overall dye removal capability of the composite membrane.

[0020] 2. The high-flux photocatalytic membrane prepared by this invention endows the composite membrane with antifouling and self-cleaning capabilities. One of the most challenging problems in membrane separation is the easy accumulation and adhesion of contaminants on the membrane surface or into the membrane pores, leading to a shortened membrane lifespan and the subsequent need for large amounts of chemical cleaning agents to remove the contaminants. This invention combines the self-cleaning properties of the photocatalyst with the membrane process. After each cycle under illumination, the flux of the dye solution remains relatively stable, and the flux cutoff of NM88B@MXene composite membranes of different thicknesses ranges from 1847.99 to 1759.48 L / (m²). 2 (·h·bar). Meanwhile, the composite membrane maintains good dye removal efficiency, NM88B@MXene The composite membrane achieved a Congo red removal rate ranging from 98.86% to 95.20%. These experimental results demonstrate the high efficiency of this invention. High-flux photocatalytic membranes possess excellent self-cleaning capabilities, effectively addressing the industry pain point of membrane fouling at its source. This is beneficial for practical applications. To mitigate membrane fouling and reduce water treatment costs in international water treatment processes. Attached Figure Description

[0021] Figure 1 This is a process diagram for the fabrication of the NM88B@MXene composite membrane.

[0022] Figure 2 (a) is a SEM image of NM88B powder; Figure 2 (b) is a SEM image of NM88B@MXene-3 powder; Figure 2 (c) is a SEM image of the surface of the M3 membrane; Figure 2 (d) is a SEM image of the cross-section of the M3 membrane;

[0023] Figure 3 (a) represents the pure water flux of membranes M0 to M4; (b) represents the rejection rates of dyes CR, Rh B, and TB by membranes M0 to M4. Figure 3 (c) represents the removal rate of Rh B(c) by M1 to M4 within 120 min; Figure 3 (d) represents the removal rate of TB by M1 to M4 within 120 min. Detailed Implementation

[0024] The following are definitions of abbreviations and key terms in this invention:

[0025] MAX phase (Ti3AlC2), MXene (Ti3C2T x LiF (lithium fluoride), HCl (hydrochloric acid), DMF (N,N-dimethylformamide), NaCl (sodium chloride), KCl (potassium chloride), MgCl2 (magnesium chloride), EtOH (anhydrous ethanol), FeCl3·6H2O (ferric chloride hexahydrate), CA (cellulose acetate), NH2-BDC (2-aminoterephthalic acid), H2O2 (hydrogen peroxide), NH2-MIL-88B(Fe) (metal-organic framework material, NM88B)

[0026] The specific embodiments of the present invention will be further described in detail below with reference to the examples and accompanying drawings, but the embodiments of the present invention are not limited thereto. For process parameters not specifically specified, conventional techniques can be referred to.

[0027] Example 1

[0028] A method for preparing a high-throughput photocatalytic membrane, comprising:

[0029] (1) Preparation of MXene two-dimensional materials:

[0030] Two-dimensional MXene materials were prepared by etching the MAX phase with a LiF+HCl mixed reagent followed by ultrasonic-assisted exfoliation. Specifically:

[0031] At room temperature and pressure, 0.5 g of LiF was dissolved in 15 mL of HCl solution, and 0.5 g of Ti3C2T was added... X The powder was added to the solution and magnetically stirred at 30°C for 20 hours. It was then washed multiple times with deionized water (DI) at room temperature and pressure until the pH of the supernatant reached 6. After centrifugation several times at 3500 rpm, the supernatant was collected to obtain a multilayer Ti3C2T solution. X Nanosheets. The supernatant was sonicated in 200 mL of deionized water at 30 °C for 6 h, the dispersion was centrifuged for 30 min, and the MXene two-dimensional material was collected and freeze-dried for storage.

[0032] (2) Preparation of NM88B@MXene:

[0033] NM88B@MXene powder was prepared using a solvothermal chemical method, specifically:

[0034] 10 mg, 20 mg, 30 mg, and 40 mg of MXene were mixed with 270 mg of FeCl3·6H2O and 181 mg of NH2-BDC, respectively, and added to 15 mL of DMF in a beaker. The mixture was sonicated for 30 min to obtain four homogeneous solutions with different proportions. These homogeneous solutions were then transferred to 100 mL high-pressure reactors lined with polytetrafluoroethylene (PTFE) and subjected to a solvothermal reaction at 110 °C for 12 h. After natural cooling to room temperature, the solutions were washed repeatedly by centrifugation at 8000 rpm with DMF and EtOH, collecting the brownish-black precipitate. The collected precipitate was vacuum dried at 80 °C for 8 h to obtain four powders with different proportions (material addition amounts are shown in Table 1). The photocatalytic degradation performance of 10 mg of each of the different proportions of powder with 50 μL of H2O2 (30%) on the dye molecule Congo red (CR) in water was tested at room temperature and pressure to determine the optimal proportion.

[0035] Table 1. Preparation material addition amount for different proportions of NM88B@MXene

[0036]

[0037] (3) Construction of high-throughput photocatalytic membranes

[0038] ① Under normal temperature and pressure, a certain amount of NM88B@MXene powder in the optimal ratio was added to 100mL of deionized water, and then ultrasonically treated for 20min to obtain precursor solutions of different concentrations (the proportions are shown in Table 2).

[0039] ② Using vacuum filtration at 0.1 MPa pressure and room temperature, 100 mL of precursor solutions of different concentrations (0.05 g / L, 0.1 g / L, 0.15 g / L, and 0.2 g / L, respectively) were slowly filtered onto a CA membrane to construct four NM88B@MXene composite membranes of different thicknesses (corresponding to M1, M2, M3, and M4). A schematic diagram of the construction process is shown below. Figure 1 As shown.

[0040] ③ The permeation flux, rejection rate and degradation effect of Congo red (CR), Rhodamine B (Rh B), and Tribenzene blue (TB) dye molecules in water were tested at room temperature and pressure to serve as performance evaluation indicators and selection indicators for optimal thickness of the membrane.

[0041] Table 2. Preparation of precursor solutions of different concentrations

[0042]

[0043] according to Figure 3Experimental results show that the optimal ratio of NM88B@MXene composite membrane is NM88B@MXene-3 powder, and the optimal concentration (0.15 g / L) of the composite membrane (M3) results in a pure water flux of 2090.9 L / (m³). 2 ·h·bar), such as Figure 3 As shown in (a), the retention rates for the dyes Congo Red, Tribenzene Blue, and Rhodamine B were 98.6%, 64.6%, and 89.6%, respectively. Figure 3 As shown in (b), the photodegradation rates of the dyes Rhodamine B and Tribenzyl Blue after retention were 99.29% and 99.11%, respectively, as shown in Figure 1. Figure 3 As shown in (c) and (d), the pure water flux of the MXene membrane (M0) is only 278 L / (m²). 2 The membrane flux is 1000 μg / m³ (·h·Bar), while the rejection rates for dyes Congo Red, Rhodamine B, and Tribenzyl Blue are only 62.6%, 55.7%, and 31.5%, respectively, indicating almost no photodegradation ability for these three dyes. Therefore, this invention increases the membrane flux and significantly improves the efficiency of membrane-based water treatment.

[0044] Overall, the combination of NM88B and MXene not only enhances the permeability and flux of the composite membrane but also endows it with photocatalytic self-cleaning capabilities. This enables the membrane to efficiently remove various dyes, demonstrating promising prospects for practical applications and providing guidance for the development of novel membrane materials that combine retention and permeability.

[0045] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention. In the complete technical solution of the present invention, the self-cleaning photocatalytic MXene composite film can still be prepared through the following methods to achieve the purpose of the present invention:

[0046] 1. In addition to using a LiF+HCl mixed reagent to etch the MAX phase, if others use HF, NH4HF2, molten fluoride salts, NaOH and H2SO4 to etch and prepare MXene, the other steps are consistent with the technical solution of this invention, and a self-cleaning photocatalytic MXene composite film can also be prepared to achieve the purpose of this invention.

[0047] 2. The CA membrane used in this invention is used as the support layer of the composite membrane. If other people use organic polymer membrane materials such as polyethersulfone (PES), polyvinylidene fluoride (PVDF), or polysulfone (PSF) as the support layer, and other steps such as the preparation of NM88B@MXene, the preparation of MXene and the filtration and stacking method are consistent with the technical solution of this invention, a self-cleaning photocatalytic MXene composite membrane can also be prepared to achieve the purpose of this invention.

Claims

1. A method for preparing a high-throughput photocatalytic membrane, comprising: (1) Preparation of MXene two-dimensional materials: Dissolve 0.5 g LiF in 15 mL of HCl solution, then add 0.5 g Ti3C2T χ The powder was magnetically stirred to obtain a first solution; the first solution was washed with deionized water, followed by centrifugation, and the second supernatant was collected to obtain a multilayer Ti3C2T. χ Nanosheets; the second supernatant was ultrasonically treated in 200 mL of deionized water at 30 °C for 6 h to obtain a dispersion; After centrifuging the dispersion for 30 min, the MXene two-dimensional material was collected and freeze-dried for storage. (2) Preparation of NM88B@MXene powder: 30 mg MXene, 270 mg FeCl3·6H2O, and 181 mg NH2-BDC were mixed and added to 15 mL of N,N-dimethylformamide in a beaker. The mixture was sonicated for 30 min to obtain a homogeneous solution. The homogeneous solution was then transferred to a high-pressure reactor lined with polytetrafluoroethylene to complete the solvothermal reaction. After the reaction solution was allowed to cool naturally to room temperature, it was washed repeatedly by centrifugation at 8000 rpm using DMF and EtOH, and the precipitate was collected. The precipitate was then vacuum dried to obtain NM88B@MXene powder for later use. (3) Construction of high-throughput photocatalytic membranes: NM88B@MXene powder was added to deionized water and sonicated for 20 min to prepare a precursor solution; then 100 mL of the precursor solution was filtered onto a CA membrane to construct a high-flux catalytic membrane.

2. The preparation method according to claim 1, wherein: The precursor solution in step (3) is prepared at room temperature and pressure, and the concentration of the precursor solution is 0.15 g / L.

3. The preparation method according to claim 1, wherein: The high-throughput catalytic membrane described in step (3) was constructed at 0.1 MPa and room temperature.

4. The preparation method according to claim 1, wherein: The magnetic stirring temperature in step (1) is 30℃, and the stirring time is 20h.

5. The preparation method according to claim 1, wherein: Step (1) The first solution is washed with deionized water until the pH value is 6; the centrifugation speed is 3500 rpm.

6. The preparation method according to claim 1, wherein: The temperature of the solvothermal reaction in step (2) is 110°C and the reaction time is 12h.

7. The preparation method according to claim 1, wherein: The drying process in step (2) is carried out at a temperature of 80°C for 8 hours.

8. A high-throughput catalytic membrane prepared by the preparation method according to any one of claims 1 to 7.

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