A three-layer structure PVDF nano fenton composite membrane, a preparation method and application thereof

Abstract

This invention discloses a multilayer PVDF nano-Fenton composite membrane and its preparation method, comprising the following steps: Step 1: Adding PVDF powder, polyethylene glycol, and lithium chloride to dimethylacetamide, stirring until dissolved to obtain a casting solution; Step 2: Using an adjustable coating device, uniformly coating the casting solution onto a glass plate at a set thickness, then immersing it in water to obtain a porous PVDF membrane; Step 3: Preparing a mixed solution of MXene solution and flower-shaped TiO2@PDA@Fe3O4 nanorod Fenton catalyst according to a set ratio, and preparing a bilayer PVDF nanocomposite membrane using vacuum filtration; Step 4: Preparing a silicon-titanium precursor solution and coating it onto the surface of the bilayer PVDF nanocomposite membrane to form a trilayer PVDF nano-Fenton composite membrane. This invention also discloses the application of this trilayer PVDF nano-Fenton composite membrane in the treatment of methylene blue wastewater. Due to its unique structural design, it maintains excellent performance after recycling while ensuring the effectiveness of the Fenton catalytic reaction.

Description

Technical Field

[0001] This invention belongs to the field of new materials and environmental wastewater treatment, and relates to a three-layer PVDF nano-Fenton composite membrane, its preparation method and application. Background Technology

[0002] Industrial production processes generate large amounts of wastewater containing dyes, primarily originating from industries such as textile printing and dyeing, leather manufacturing, papermaking, and pigment production. Dye wastewater is characterized by its vibrant color, high organic pollutant content, and difficulty in biodegradation. Therefore, given the serious harm dye wastewater poses to the environment and human health, effective treatment is crucial. The Fenton reaction, as an advanced oxidation technology, can effectively degrade organic pollutants and has wide applicability in environmental remediation, thus attracting widespread attention. Polyvinylidene fluoride (PVDF), as an excellent polymer membrane material, has been widely used in membrane separation. Compared to other commercial membrane materials, PVDF membranes exhibit strong hydrophobicity, excellent chemical stability, selective permeability, and superior mechanical properties.

[0003] In recent years, combining advanced oxidation technology with membrane separation technology has become one of the cutting-edge technologies in wastewater treatment. Studies have shown that various nanomaterials can be combined with PVDF membranes to prepare PVDF nanocomposite membranes. For example, Zhu et al. used salt as a sacrificial "hard template" and filled Fe2O3 using a solution casting method to successfully prepare a porous PVDF / Fe2O3 membrane. This membrane exhibited excellent decomposition efficiency of organic pollutants under ultrasonic treatment. Li et al. first prepared a PVDF / PEMA composite membrane using a phase inversion method, and then filled it with Fe2O3... 3+ The minerals are converted into β-FeOOH particles and deposited on the composite membrane. β-FeOOH exhibits strong photo-Fenton catalytic activity, which can remove oil adsorbed on the membrane surface through catalytic degradation, thereby giving the nanocomposite membrane better self-cleaning performance and flux recovery rate.

[0004] In summary, how to combine porous PVDF membranes with heterogeneous nano-Fenton catalysts and how to solve problems such as easy catalyst detachment are important research topics for future functional PVDF nanocomposite membranes. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, this invention provides a three-layer PVDF nano-Fenton composite membrane, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a three-layer PVDF nano-Fenton composite film, characterized by comprising the following steps: Step 1: Add PVDF powder, polyethylene glycol and lithium chloride to dimethylacetamide, stir until dissolved to obtain casting solution, let stand overnight to remove bubbles, seal and store for later use; Step 2: Use an adjustable coating applicator to apply the casting solution onto a glass plate at a uniform speed to a set thickness, and then immerse it in water to produce a porous PVDF membrane. Step 3: Prepare a mixed solution by mixing MXene solution and flower-shaped TiO2@PDA@Fe3O4 nanorod Fenton catalyst in a set ratio, and form a catalyst layer on the porous PVDF membrane by vacuum filtration to prepare a bilayer PVDF nanocomposite membrane; Step 4: Prepare a silicon-titanium precursor solution of a set concentration, and uniformly coat it on the surface of the catalyst layer of the bilayer PVDF nanocomposite membrane. After reacting at room temperature, a protective layer is formed to obtain a three-layer PVDF nano-Fenton composite membrane.

[0007] Furthermore, in step 1, the mass ratio of PVDF powder, polyethylene glycol, lithium chloride and dimethylacetamide is 1.5:0.1~0.3:1.0~2.0:12.5.

[0008] Furthermore, in step 2, the coating thickness is 200-500 μm, and the thickness of the resulting porous PVDF membrane is 100-200 μm.

[0009] Furthermore, in step 3, the mass ratio of MXene to flower-shaped TiO2@PDA@Fe3O4 nanorod Fenton catalyst is 50:5~20, and the thickness of the catalyst layer is 5~20 μm.

[0010] Furthermore, in step 4, the silicon-titanium precursor solution includes tetraethyl orthosilicate, ammonium fluorotitanate, boric acid, concentrated hydrochloric acid, water, and ethanol.

[0011] Furthermore, the mass ratio of tetraethyl orthosilicate, ammonium fluorotitanate, boric acid, concentrated hydrochloric acid, water, and ethanol is 85~95:5~15:0.9:12:70:50, and the thickness of the protective layer is 1~5μm.

[0012] A three-layer PVDF nano-Fenton composite membrane obtained by a method for preparing a three-layer PVDF nano-Fenton composite membrane.

[0013] Application of a product obtained by a method for preparing a three-layer PVDF nano-Fenton composite membrane in the treatment of methylene blue wastewater.

[0014] In summary, the advantages of this invention are: This invention combines a porous PVDF membrane with a heterogeneous nano-Fenton catalyst, providing excellent adsorption and catalytic performance. Furthermore, a nano-coating method addresses the issue of catalyst layer detachment during the reaction, effectively improving the product's recyclability. Using model pollutant molecules, the catalytic separation performance of this three-layer PVDF nano-Fenton composite membrane is investigated, elucidating the influence of various factors on its overall performance and revealing the reaction mechanism of this nanocomposite membrane system. This research not only provides a theoretical foundation and application value for the development of novel PVDF nanocomposite membranes but also offers new ideas and methods for the research and development of other functional nanomembranes. Attached Figure Description

[0015] Figure 1 This is a SEM image of the surface of the porous PVDF membrane prepared in Example 1 of the present invention; Figure 2 This is a SEM image of the cross-section of the porous PVDF membrane prepared in Example 1 of the present invention; Figure 3 This is a SEM image of the surface of the bilayer PVDF nanocomposite film prepared in Example 2 of the present invention; Figure 4 This is a SEM image of the cross-section of the bilayer PVDF nanocomposite membrane prepared in Example 2 of the present invention; Figure 5 This is a SEM image of the surface of the three-layer PVDF nano-Fenton composite film prepared in Example 3 of the present invention; Figure 6 This is a SEM image of the cross-section of the three-layer PVDF nano-Fenton composite film prepared in Example 3 of the present invention; Figure 7 The UV-Vis absorption curve of methylene blue catalyzed by the three-layer PVDF nano-Fenton composite film prepared in Example 3 of this invention.

[0016] Figure 8 This is a diagram showing the effect of cyclic Fenton catalytic reaction on the three-layer PVDF nano-Fenton composite membrane prepared in Example 3 of the present invention.

[0017] Figure 9 The image shows the effect of cyclic Fenton catalytic reaction on the bilayer PVDF nanocomposite membrane prepared in Comparative Example 1 of this invention. Detailed Implementation

[0018] This invention provides a method for preparing a three-layer PVDF nano-Fenton composite film, comprising the following steps: Step 1.1: Add PVDF powder, polyethylene glycol and lithium chloride to dimethylacetamide, stir until dissolved to obtain casting solution, let stand overnight to remove bubbles, seal and store for later use. The mass ratio of PVDF powder, polyethylene glycol, lithium chloride and dimethylacetamide is 1.5:0.1~0.3:1.0~2.0:12.5. Step 1.2: Use an adjustable coating applicator to uniformly coat the casting solution onto a glass plate at a set thickness, and then immerse it in water to prepare a porous PVDF membrane. The coating thickness is 200-500 μm, and the thickness of the prepared porous PVDF membrane is 100-200 μm. Step 1.3: Prepare a mixed solution by mixing MXene solution and flower-shaped TiO2@PDA@Fe3O4 nanorod Fenton catalyst in a set ratio. Form a catalyst layer on a porous PVDF membrane by vacuum filtration to obtain a bilayer PVDF nanocomposite membrane. The mass ratio of MXene to flower-shaped TiO2@PDA@Fe3O4 nanorod Fenton catalyst is 50:5~20, and the thickness of the catalyst layer is 5~20 μm. Step 1.4: Prepare a silicon-titanium precursor solution of a set concentration, and uniformly coat it on the surface of the catalyst layer of the double-layer PVDF nanocomposite membrane. After reacting at room temperature, a protective layer is formed, thereby obtaining a three-layer PVDF nano-Fenton composite membrane. The silicon-titanium precursor solution includes tetraethyl orthosilicate, ammonium fluorotitanate, boric acid, concentrated hydrochloric acid, water, and ethanol in a mass ratio of 85~95:5~15:0.9:12:70:50. The thickness of the protective layer is 1~5μm.

[0019] The preparation method of the flower-shaped TiO2@PDA@Fe3O4 nanorod Fenton catalyst includes the following steps: Step 2.1: Take 1g of titanium dioxide P25, 4g of sodium chloride, 1g of disodium hydrogen phosphate and 0.01~0.04g of iron salt and grind and mix them in a mortar. Transfer the mixture to a quartz crucible and place it in a heating furnace for high-temperature melting growth reaction at 700℃~900℃ for 6~12h. After cooling to room temperature, boil the sintered product with deionized water to remove impurities. Then centrifuge, wash and collect the precipitate. Vacuum dry the precipitate to obtain iron-doped TiO2 nanorods. Iron salts are one or more of ferric nitrate, ferric chloride, and ferrous chloride.

[0020] Step 2.2: Take 1g of iron-doped TiO2 nanorods and add them to 100mL of Tris-HCl buffer solution with a pH of 7-9. Disperse the solution by sonication for 30min, then add 0.01-0.05g of dopamine and stir the mixture at room temperature for 12-24h. After the reaction is complete, filter the product and dry it under vacuum at 80℃ to obtain polydopamine-modified iron-doped TiO2 nanorods. Step 2.3: Take 0.1g of iron-doped TiO2@PDA nanorods, 0.05~0.15g of ferric chloride, 0.15g of sodium acetate and 0.04g of polyethylene glycol and add them to 20mL of ethylene glycol. Disperse and mix evenly by ultrasonication, pour into a reaction vessel, and solvothermal react at 160℃~180℃ for 12~24h. After cooling to room temperature, wash several times with ethanol and water, separate by magnet, and vacuum dry to obtain flower-like Fe3O4-coated polydopamine-modified iron-doped TiO2 nanorods (flower-like TiO2@PDA@Fe3O4 nanorod Fenton catalyst).

[0021] The present invention will be further described in detail below with reference to the embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way. Example

[0022] In the preparation method of the three-layer PVDF nano-Fenton composite film in this embodiment: In step 1.1, the masses of PVDF powder, polyethylene glycol, and lithium chloride added to dimethylacetamide are 3g, 0.3g, 2g, and 25g, respectively.

[0023] In step 1.2, the adjustable coating applicator is set to 300 μm, and the casting solution is uniformly coated onto the glass plate and then allowed to stand in the air for 30 s.

[0024] Reference Figure 1 The SEM image of the prepared porous PVDF membrane shows that small pores are observed on the surface.

[0025] Reference Figure 2 The SEM image of the prepared porous PVDF membrane cross section shows that the thickness of the porous PVDF membrane is 180 μm, and it contains finger-shaped pores, sponge pores and dense surface areas, which are relatively uniformly distributed.

[0026] In step 1.3, take 2 mL of MXene solution with a concentration of 5 mg / mL, take 1 mg of flower-shaped TiO2@PDA@Fe3O4 nanorod Fenton catalyst, and add 18 mL of deionized water to prepare a mixed solution.

[0027] In step 1.4, the silicon-titanium precursor solution comprises tetraethyl orthosilicate, ammonium fluorotitanate, boric acid, concentrated hydrochloric acid, water, and ethanol in a mass ratio of 95:5:0.9:12:70:50, which are mixed by ultrasonication. Example

[0028] In the preparation method of the three-layer PVDF nano-Fenton composite film in this embodiment: In step 1.1, the masses of PVDF powder, polyethylene glycol, and lithium chloride added to dimethylacetamide are 3g, 0.3g, 2g, and 25g, respectively.

[0029] In step 1.2, the adjustable coating applicator is set to 300 μm, and the casting solution is uniformly coated onto the glass plate and then allowed to stand in the air for 30 s.

[0030] In step 1.3, take 2 mL of MXene solution with a concentration of 5 mg / mL, take 2 mg of flower-shaped TiO2@PDA@Fe3O4 nanorod Fenton catalyst, and add 18 mL of deionized water to prepare a mixed solution.

[0031] Reference Figure 3 The SEM image of the prepared bilayer PVDF nanocomposite membrane shows that a rough nanocomposite Fenton catalyst layer is formed on the surface of the porous PVDF membrane.

[0032] Reference Figure 4 The SEM image of the cross-section of the prepared bilayer PVDF nanocomposite membrane shows that a nanocomposite Fenton catalyst layer of about 10 μm is formed on the surface of the porous PVDF membrane.

[0033] In step 1.4, the silicon-titanium precursor solution comprises tetraethyl orthosilicate, ammonium fluorotitanate, boric acid, concentrated hydrochloric acid, water, and ethanol in a mass ratio of 90:10:0.9:12:70:50, which are mixed by ultrasonication. Example

[0034] In the preparation method of the three-layer PVDF nano-Fenton composite film in this embodiment: In step 1.1, the masses of PVDF powder, polyethylene glycol, and lithium chloride added to dimethylacetamide are 3g, 0.3g, 2g, and 25g, respectively.

[0035] In step 1.2, the adjustable coating applicator is set to 300 μm, and the casting solution is uniformly coated onto the glass plate and then allowed to stand in the air for 30 s.

[0036] In step 1.3, take 2 mL of MXene solution with a concentration of 5 mg / mL, take 3 mg of flower-shaped TiO2@PDA@Fe3O4 nanorod Fenton catalyst, and add 18 mL of deionized water to prepare a mixed solution.

[0037] In step 1.4, the silicon-titanium precursor solution comprises tetraethyl orthosilicate, ammonium fluorotitanate, boric acid, concentrated hydrochloric acid, water, and ethanol in a mass ratio of 85:15:0.9:12:70:50, which are mixed by ultrasonication.

[0038] Reference Figure 5 The SEM image of the prepared three-layer PVDF nano-Fenton composite film shows that a smooth SiO2 / TiO2 nano-protective layer is formed on the surface of the catalyst layer.

[0039] Reference Figure 6 The SEM image of the cross-section of the three-layer PVDF nano-Fenton composite film prepared by the method is shown, and it can be observed that the thickness of the SiO2 / TiO2 nano-protective layer is about 3 μm.

[0040] The catalytic application of the three-layer PVDF nano-Fenton composite membrane prepared in this embodiment in methylene blue solution includes: A 2cm diameter circular three-layer PVDF nano-Fenton composite membrane was added to 30 mL of a 20 mg / L methylene blue solution. After adsorption for 30 min, 0.5 mL of hydrogen peroxide was added for reaction. UV-Vis spectroscopy was used to sample and analyze the changes in MB concentration in the solution at regular intervals. To verify the recyclability of the nano-Fenton composite membrane, the membrane was repeatedly washed and used at least 5 times for Fenton catalytic reactions.

[0041] Figure 7 The UV-Vis absorption curves of methylene blue catalyzed by the prepared three-layer PVDF nano-Fenton composite membrane are shown. As can be seen from the figure, the concentration of methylene blue gradually decreases with the increase of reaction time, and the reaction is basically complete at about 12 hours.

[0042] also, Figure 8 The image shows the cyclic Fenton catalytic reaction effect of the prepared three-layer PVDF nano-Fenton composite membrane. After 5 uses, the catalytic reaction rate still reaches more than 90%.

[0043] Comparative Example 1 The difference between Comparative Example 1 and Example 3 is that Comparative Example 1 prepared a bilayer PVDF nanocomposite membrane using steps 1.1 to 1.3 of Example 3. A 2cm diameter circular block of the prepared bilayer PVDF nanocomposite membrane was added to 30 mL of a 20 mg / L methylene blue solution. After adsorption for 30 min, 0.5 mL of hydrogen peroxide was added for reaction. UV-Vis spectroscopy was used to sample and analyze the changes in MB concentration in the solution at regular intervals.

[0044] Reference Figure 9 The cyclic Fenton catalytic reaction effect of the double-layer PVDF nanocomposite membrane is shown in the figure. In the absence of SiO2 / TiO2 nanoprotective layer, the catalyst layer will fall off during the catalytic reaction, which will cause the catalytic reaction rate to gradually decrease with the increase of the number of reactions.

[0045] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing a three-layer structure PVDF nano-Fenton composite membrane, characterized in that, Includes the following steps: Step 1: Add PVDF powder, polyethylene glycol and lithium chloride to dimethylacetamide, stir until dissolved to obtain casting solution, let stand overnight to remove bubbles, seal and store for later use; Step 2: Use an adjustable coating applicator to apply the casting solution onto a glass plate at a uniform speed and to a set thickness, then immerse it in water to produce a porous PVDF membrane. Step 3: Prepare a mixed solution by mixing MXene solution and flower-shaped TiO2@PDA@Fe3O4 nanorod Fenton catalyst in a set ratio, and form a catalyst layer on the porous PVDF membrane by vacuum filtration to prepare a bilayer PVDF nanocomposite membrane; Step 4: Prepare a silicon-titanium precursor solution of a set concentration, and uniformly coat it on the surface of the catalyst layer of the bilayer PVDF nanocomposite membrane. After reacting at room temperature, a protective layer is formed to obtain a three-layer PVDF nano-Fenton composite membrane.

2. The method for preparing a three-layer PVDF nano-Fenton composite film according to claim 1, characterized in that, In step 1, the mass ratio of PVDF powder, polyethylene glycol, lithium chloride and dimethylacetamide is 1.5:0.1~0.3:1.0~2.0:12.

5.

3. The method for preparing a three-layer PVDF nano-Fenton composite film according to claim 1, characterized in that, In step 2, the coating thickness is 200-500 μm, and the thickness of the resulting porous PVDF membrane is 100-200 μm.

4. The method for preparing a three-layer PVDF nano-Fenton composite film according to claim 1, characterized in that, In step 3, the mass ratio of MXene to flower-shaped TiO2@PDA@Fe3O4 nanorod Fenton catalyst is 50:5~20, and the thickness of the catalyst layer is 5~20μm.

5. The method for preparing a three-layer PVDF nano-Fenton composite film according to claim 1, characterized in that, In step 4, the silicon-titanium precursor solution includes tetraethyl orthosilicate, ammonium fluorotitanate, boric acid, concentrated hydrochloric acid, water, and ethanol.

6. The method for preparing a three-layer PVDF nano-Fenton composite film according to claim 1, characterized in that, The mass ratio of tetraethyl orthosilicate, ammonium fluorotitanate, boric acid, concentrated hydrochloric acid, water, and ethanol is 85~95:5~15:0.9:12:70:50, and the thickness of the protective layer is 1~5μm.

7. A three-layer PVDF nano-Fenton composite membrane obtained by the preparation method according to any one of claims 1-6.

8. The application of a product obtained by the preparation method according to any one of claims 1-6 in the treatment of methylene blue wastewater.

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