A method for preparing an antibacterial composite PVDF ultrafiltration membrane

Abstract

This invention relates to the field of membrane separation technology and provides a method for preparing an antibacterial composite PVDF ultrafiltration membrane. The preparation method includes: adding a stabilizer to water and stirring to dissolve it; adding silver nanoparticles and stirring to disperse them; then adding Ag-MOF and ultrasonically vibrating to allow the Ag-MOF to fully adsorb the silver nanoparticles, obtaining an antibacterial dispersion containing an Ag-MOF / silver nanoparticle composite; impregnating a PVDF-g-PAA ultrafiltration membrane in the above antibacterial dispersion and drying it to obtain the antibacterial composite PVDF ultrafiltration membrane; wherein the stabilizer is at least one of gelatin, guar gum, gum arabic, and pectin. The antibacterial composite PVDF ultrafiltration membrane prepared by this invention has good hydrophilicity, high mechanical strength, and excellent antibacterial function, and can be used in the field of water treatment.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and specifically to a method for preparing an antibacterial composite PVDF ultrafiltration membrane. Background Technology

[0002] Polymer separation membranes are materials used in modern high-efficiency separation, concentration, purification, and treatment equipment, and are widely applied in chemical, environmental protection, food, biological, pharmaceutical, electronics, power, metallurgy, textile, and seawater desalination fields, playing a vital role in modern energy, resource management, and environmental pollution control. Commonly used materials include polyvinylidene fluoride (PVDF), polysulfone, and polyvinyl chloride membranes.

[0003] Metal-organic frameworks (MOFs) are materials with supramolecular microporous network structures formed by the metal-ligand complexation between organic ligands and metal ions. Due to their special topology, regular internal arrangement, and channels of specific size and shape, they have advantages such as high porosity, large specific surface area, convenient synthesis, and variable framework size. Therefore, they have wide applications in adsorption, catalysis, membrane separation and other fields.

[0004] For example, CN111135733A discloses a MOFs polymer hollow fiber composite ultrafiltration membrane and its preparation method. First, a high-strength polyvinylidene fluoride / polyacrylic acid ultrafiltration membrane (PVDF / PAA ultrafiltration membrane) is prepared using a thermally induced phase separation method. Then, an ultrathin MOFs separation layer is grown in situ on the outer surface of the separation membrane using a chelation-assisted interfacial reaction method, which can be applied in the field of water treatment. However, this composite ultrafiltration membrane does not possess antibacterial properties.

[0005] Currently, ultrafiltration membranes are used as a pretreatment method in the process of producing purified water through reverse osmosis. However, on the one hand, ultrafiltration membranes can only adsorb proteins and small microorganisms in drinking water onto the surface of the membrane, preventing them from passing through, but they cannot kill them. As a result, the drinking water contains a large number of bacteria and microorganisms, and these diverse bacteria and microorganisms pose a serious threat to people's drinking water health. Therefore, it is necessary to develop a method for preparing ultrafiltration membranes with antibacterial functions. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing an antibacterial composite PVDF ultrafiltration membrane. The resulting composite ultrafiltration membrane contains both Ag-MOF and nano-silver, exhibiting advantages such as excellent antibacterial properties and stable and long-lasting antibacterial effects.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] On one hand, the present invention provides a method for preparing an antibacterial composite PVDF ultrafiltration membrane, comprising:

[0009] (1) Preparation of antibacterial dispersion

[0010] Add a stabilizer to water and stir to dissolve; add silver nanoparticles and stir to disperse; then add Ag-MOF and sonicate to allow Ag-MOF to fully adsorb the silver nanoparticles, thus obtaining an antibacterial dispersion containing Ag-MOF / silver nanoparticle complex;

[0011] (2) Preparation of antibacterial composite PVDF ultrafiltration membrane

[0012] The PVDF-g-PAA ultrafiltration membrane was impregnated in the above antibacterial dispersion and dried to obtain an antibacterial composite PVDF ultrafiltration membrane.

[0013] The stabilizer is at least one of gelatin, guar gum, gum arabic, and pectin.

[0014] In the preparation method of the antibacterial composite PVDF ultrafiltration membrane provided by the present invention, on the one hand, the stabilizer can prevent the aggregation of silver nanoparticles and play a role in stabilizing the silver nanoparticles. At the same time, the hydroxyl groups in the stabilizer can interact with Ag-MOF and play a role in stabilizing Ag-MOF. On the other hand, Ag-MOF (containing a silver metal-organic framework) serves as a carrier for silver nanoparticles, which can improve the dispersibility and stability of silver nanoparticles. Furthermore, the Ag+ in Ag-MOF and silver nanoparticles have a synergistic antibacterial effect, making the antibacterial agent more durable and efficient. On the other hand, the PVDF-g-PAA ultrafiltration membrane contains hydroxyl groups, which can increase the binding force between the Ag-MOF / silver nanoparticle composite and the ultrafiltration membrane. The carbonyl groups in the PVDF-g-PAA ultrafiltration membrane can bond with the hydroxyl groups in the stabilizer, making the binding between the Ag-MOF / silver nanoparticle composite and the ultrafiltration membrane more robust.

[0015] In a preferred embodiment of the present invention, the mass ratio of the stabilizer to water is 1-5:100. The content of the stabilizer should not be too high to prevent the viscosity from being too high after dissolution, which would be detrimental to the subsequent dispersion of nano-silver ions and mixing of Ag-MOF.

[0016] In a preferred embodiment of the present invention, the mass ratio of Ag-MOF to water is 10 to 30:100.

[0017] In a preferred embodiment of the present invention, the mass ratio of the nano-silver to water is 5-10:100.

[0018] Preferably, the average particle size of the silver nanoparticles is 1-20 nm. Silver nanoparticles with smaller average particle size can more easily enter the bacterial cell membrane, resulting in better antibacterial effects. Furthermore, silver nanoparticles with smaller average particle size are more easily adsorbed into the interior of Ag-MOF, leading to a longer-lasting antibacterial effect.

[0019] In a preferred embodiment of the present invention, the stabilizer is dissolved in water under the following conditions: at 40-60°C, stirred for 10-40 minutes.

[0020] In a preferred embodiment of the present invention, the conditions for dispersing the nano-silver in water are: stirring and dispersing at 40-60℃ for 4-12 hours, with a stirring rate of 1000-10000 rpm.

[0021] As a preferred embodiment of the present invention, the Ag-MOF adsorption conditions for silver nanoparticles are: ultrasonic dispersion at 40-60℃ for 3-6 hours.

[0022] This invention uses the hydrophilic monomer acrylic acid (AA) to graft and modify PVDF. The modification method can refer to CN105311970A, in which PVDF is treated with alkali and then polymerized with acrylic acid under the action of an initiator to obtain acrylic acid-grafted modified PVDF-g-PAA, and then PVDF-g-PAA ultrafiltration membrane is prepared by phase separation method; or refer to CN110975650A, PVDF-g-PAA ultrafiltration membrane is prepared by one-pot method; or refer to CN110975649A, PVDF is irradiated and grafted with acrylic acid, and then PVDF-g-PAA ultrafiltration membrane is prepared by phase separation method.

[0023] Preferably, the PVDF-g-PAA ultrafiltration membrane has a porosity of 50-80% and a thickness of 100-300 μm.

[0024] In a preferred embodiment of the present invention, the mass ratio of PVDF to PAA in the PVDF-g-PAA ultrafiltration membrane is 100:5-20, more preferably 100:10-20, such as 100:10, 100:11, 100:12, 100:13, 100:14, 100:15, 100:16, 100:17, 100:18, 100:19, 100:20, etc.

[0025] As a preferred embodiment of the present invention, the conditions for impregnating the PVDF-g-PAA ultrafiltration membrane with the antibacterial dispersion are: impregnation at room temperature for 0.5-1 h, and the impregnation can be assisted by vacuuming.

[0026] In a preferred embodiment of the present invention, the drying is performed by vacuum drying at 60-100°C for 4-12 hours.

[0027] On the other hand, the present invention provides an antibacterial composite PVDF ultrafiltration membrane obtained by the above preparation method.

[0028] On the other hand, the present invention provides the application of antibacterial composite PVDF ultrafiltration membrane in water treatment.

[0029] Compared with the prior art, the present invention has the following technical effects:

[0030] (1) In the preparation method of the antibacterial composite PVDF ultrafiltration membrane provided by the present invention, on the one hand, the stabilizer can prevent the aggregation of silver nanoparticles and play a role in stabilizing silver nanoparticles. At the same time, the stabilizer contains hydroxyl groups that can interact with Ag-MOF and play a role in stabilizing Ag-MOF. On the other hand, Ag-MOF (containing silver metal-organic framework) serves as a carrier for silver nanoparticles, which can improve the dispersibility and stability of silver nanoparticles. Furthermore, Ag+ in Ag-MOF and silver nanoparticles have a synergistic antibacterial effect, making the antibacterial agent more durable and efficient. On the other hand, the PVDF-g-PAA ultrafiltration membrane contains hydroxyl groups, which can increase the binding force between the Ag-MOF / silver nanoparticle composite and the ultrafiltration membrane. The carbonyl groups in the PVDF-g-PAA ultrafiltration membrane can bond with the hydroxyl groups in the stabilizer, making the binding of the Ag-MOF / silver nanoparticle composite and the ultrafiltration membrane more robust.

[0031] (2) The antibacterial composite PVDF ultrafiltration membrane prepared by the present invention has good hydrophilicity, high mechanical strength and excellent antibacterial properties, and can kill bacteria and microorganisms in drinking water, making it suitable for use in the field of water treatment. Detailed Implementation

[0032] Unless otherwise stated, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. All patents and publications related to this invention are incorporated herein by reference in their entirety. The terms "comprising" or "including" are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

[0033] The preparation method of the antibacterial composite PVDF ultrafiltration membrane is described in detail below according to the embodiments provided by the present invention.

[0034] (1) Preparation of antibacterial dispersion

[0035] Add a stabilizer to water and stir to dissolve; add nano-silver and stir to disperse; then add Ag-MOF and sonicate to allow Ag-MOF to fully adsorb nano-silver, thus obtaining an antibacterial dispersion containing Ag-MOF / nano-silver complex.

[0036] According to an embodiment of the present invention, the stabilizer is at least one of gelatin, guar gum, gum arabic, and pectin, preferably gelatin.

[0037] According to the embodiments provided by the present invention, the mass ratio of the stabilizer to water is 1-5:100, for example: 1:100, 2:100, 3:100, 4:100, 5:100, etc.

[0038] According to the embodiments provided by the present invention, the conditions for dissolving the stabilizer in water by stirring are: stirring at 40-60°C for 10-40 minutes.

[0039] According to the embodiments provided by the present invention, the mass ratio of the nano-silver to water is 5-10:100, for example: 5:100, 6:100, 7:100, 8:100, 9:100, 10:100, etc.

[0040] According to the embodiments provided by the present invention, the average particle size of the nano-silver is 1-20nm, for example: 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, etc.

[0041] In some embodiments, the average particle size of the silver nanoparticles is 5-20 nm.

[0042] According to the embodiments provided by the present invention, the conditions for dispersing the nano-silver in water are: stirring and dispersing at 40-60℃ for 4-12 hours, with a stirring rate of 1000-10000 rpm.

[0043] In some embodiments, the nano-silver is dispersed in water under the following conditions: at 40-60°C for 4-8 hours, and at a stirring rate of 5000-10000 rpm.

[0044] There are no particular limitations on the preparation method of the Ag-MOF, and it can be prepared according to methods known in the art, such as the hydrothermal method.

[0045] According to the embodiments provided by the present invention, the mass ratio of Ag-MOF to water is 10 to 30:100, for example: 10:100, 15:100, 20:100, 25:100, 30:100, etc.

[0046] According to the embodiments provided by the present invention, the Ag-MOF adsorption conditions for silver nanoparticles are: ultrasonic dispersion at 40-60℃ for 3-6 hours.

[0047] 2. Preparation of antibacterial composite PVDF ultrafiltration membrane

[0048] The PVDF-g-PAA ultrafiltration membrane was impregnated in an antibacterial dispersion and dried to obtain an antibacterial composite PVDF ultrafiltration membrane.

[0049] According to the embodiments provided by the present invention, the porosity of the PVDF-g-PAA ultrafiltration membrane is 50-80%, and the thickness is 100-300 μm.

[0050] According to the embodiments provided by the present invention, the impregnation is performed at room temperature for 0.5-1 hour, and the impregnation can be assisted by vacuuming.

[0051] According to the embodiments provided by the present invention, the drying is vacuum drying at 60-100℃ for 4-12 hours.

[0052] In some embodiments, the drying is performed by vacuum drying at 60-80°C for 4-8 hours.

[0053] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific conditions are not specified in the examples, they are performed according to the conditions described in the instruction manual, conventional conditions, or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0054] Example 1

[0055] The method for preparing the antibacterial composite PVDF ultrafiltration membrane provided in this embodiment includes the following steps:

[0056] (1) Preparation of antibacterial dispersion

[0057] Gelatin and deionized water were added to deionized water at a mass ratio of 1:100, and stirred at 50°C for 30 min to dissolve the gelatin. Nano-silver with an average particle size of 10 nm was added at a mass ratio of nano-silver to water of 5:100, and stirred at 5000 rpm at 50°C for 4 h to disperse the nano-silver. Then, Ag-MOF was added at a mass ratio of Ag-MOF to water of 20:100, and ultrasonically vibrated at 45°C for 5 h to allow Ag-MOF to fully adsorb the nano-silver, thus obtaining an antibacterial dispersion containing the Ag-MOF / nano-silver complex.

[0058] (2) Preparation of antibacterial composite PVDF ultrafiltration membrane

[0059] The PVDF-g-PAA ultrafiltration membrane (PVDF to PAA mass ratio of 100:10) was immersed in the above antibacterial dispersion at room temperature for 40 min, and then vacuum dried at 85℃ for 6 h to obtain the antibacterial composite PVDF ultrafiltration membrane.

[0060] Example 2

[0061] The method for preparing the antibacterial composite PVDF ultrafiltration membrane provided in this embodiment differs from that in Example 1 in that the mass ratio of gelatin to deionized water is 3:100.

[0062] Example 3

[0063] The method for preparing the antibacterial composite PVDF ultrafiltration membrane provided in this embodiment differs from that in Example 1 in that the mass ratio of gelatin to deionized water is 5:100.

[0064] Example 4

[0065] The preparation method of the antibacterial composite PVDF ultrafiltration membrane provided in this embodiment differs from that in Example 2 in that the mass ratio of nano-silver to water is 10:100.

[0066] Comparative Example 1

[0067] The preparation method of the antibacterial composite PVDF ultrafiltration membrane provided in this comparative example differs from that in Example 2 in that the stabilizer gelatin is not added.

[0068] Comparative Example 2

[0069] The preparation method of the antibacterial composite PVDF ultrafiltration membrane provided in this comparative example differs from that in Example 2 in that: in step (2), a PVDF ultrafiltration membrane is used instead of a PVDF-g-PAA ultrafiltration membrane.

[0070] Performance testing

[0071] 1. Water flux test

[0072] After the prepared composite ultrafiltration membrane was placed in deionized water for a period of time, a circular membrane piece with a diameter of 7.5 cm was cut and placed in a YL-300 ultrafiltration cup. It was pre-pressurized at 0.1 MPa for 40 min until the water flux was basically stable. Then, the test was measured at 0.1 MPa. The test results are shown in Table 1.

[0073] 2. Anti-pollution performance test

[0074] The ultrafiltration membrane was tested using a UV-Vis-IR spectrophotometer at 0.1 MPa using an external pressure method. Bovine serum albumin (BSA) with a molecular weight of 80,000 and a concentration of 1 g / L was used as the test sample. The retention rate of the ultrafiltration membrane was determined by measuring the residual amount of BSA on the membrane. Retention rate Where C p C represents the concentration of bovine serum albumin in the influent. f The concentration of bovine serum albumin in the purified water is shown in Table 1.

[0075] 3. Hydrophilicity test

[0076] The contact angle between the prepared ultrafiltration membrane and water was measured using a contact angle tester. The test results are shown in Table 1.

[0077] 4. Tensile strength

[0078] The tensile strength of the prepared ultrafiltration membrane was tested using a universal tensile testing machine. The test results are shown in Table 1.

[0079] 5. Antibacterial performance test

[0080] Escherichia coli was used as an indicator bacterium to culture the filtrate of the prepared membrane. The number of Escherichia coli in the filtrate was calculated by plate counting method, and the antibacterial rate was calculated. The test results are shown in Table 1.

[0081] Table 1

[0082] Example Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 <![CDATA[Pure water flux (L / m 2 ·h)]]> 277 273 271 275 274 213 Retention rate (%) 95.7 94.6 93.7 94.3 96.1 86.7 Contact angle (°) 43.8 43.2 42.7 43.6 53.8 60.3 Tensile strength (MPa) 5.02 5.19 5.37 5.13 3.19 3.27 Antibacterial rate (E. coli %) 99.97 99.98 99.98 99.99 80.13 85.87

[0083] As can be seen from the data in Table 1, the antibacterial composite PVDF ultrafiltration membrane obtained in the embodiments of the present invention has good hydrophilicity, large water flux, high retention rate, good antifouling performance, and excellent antibacterial and mechanical properties.

[0084] In Comparative Example 1, no stabilizer was added to the uniformly dispersed solution, which caused the silver nanoparticles to easily aggregate and the stability of Ag-MOF to deteriorate, resulting in insufficient adsorption of silver nanoparticles and a significant decrease in the antibacterial, hydrophilic, and mechanical properties of the ultrafiltration membrane.

[0085] In Comparative Example 2, since the PVDF ultrafiltration membrane was not modified and did not contain hydroxyl and carboxyl groups, its binding force with the Ag-MOF / nano silver complex was poor, resulting in deterioration of both the hydrophilicity and mechanical properties of the obtained ultrafiltration membrane.

[0086] In the description of this specification, the references to terms such as "some embodiments," "other embodiments," "examples," and "examples" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0087] Although embodiments and examples of the present invention have been shown and described above, it is understood that the above embodiments and examples are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments and examples within the scope of the present invention.

Claims

1. A method for preparing an antibacterial composite PVDF ultrafiltration membrane, characterized in that, The preparation method comprises the following steps: (1) preparing an antibacterial dispersion liquid adding a stabilizer into water and stirring to dissolve; adding nano-silver and stirring to disperse; then adding Ag-MOF and ultrasonic oscillation to make the Ag-MOF fully adsorb the nano-silver, so as to obtain an antibacterial dispersion liquid containing Ag-MOF / nano-silver composite; (2) preparing an antibacterial composite PVDF ultrafiltration membrane immersing the PVDF-g-PAA ultrafiltration membrane in the antibacterial dispersion liquid and drying to obtain an antibacterial composite PVDF ultrafiltration membrane. The stabilizer is at least one of gelatin, guar gum, gum arabic and pectin.

2. The method for preparing the antibacterial composite PVDF ultrafiltration membrane according to claim 1, characterized in that, The mass ratio of PVDF to PAA in the PVDF-g-PAA ultrafiltration membrane is 100:5-20.

3. The method for preparing the antibacterial composite PVDF ultrafiltration membrane according to claim 1, characterized in that, The mass ratio of the stabilizer to water is 1-5:100; the mass ratio of Ag-MOF to water is 10-30:

100.

4. The method for preparing the antibacterial composite PVDF ultrafiltration membrane according to claim 1, characterized in that, The mass ratio of nano-silver to water is 5-10:100; the average particle size of the nano-silver is 1-20 nm.

5. The method for preparing the antibacterial composite PVDF ultrafiltration membrane according to claim 1, characterized in that, The stirring dissolving is performed at 40-60°C for 10-40 min.

6. The method of claim 1, wherein the antibacterial composite PVDF ultrafiltration membrane is prepared by the steps of: The stirring dispersion is performed at 40-60°C for 4-12 h at a stirring speed of 1000-10000 rpm.

7. The method for preparing the antibacterial composite PVDF ultrafiltration membrane according to claim 1, characterized in that, The ultrasonic oscillation is performed at 40-60°C for 3-6 h.

8. The method for preparing the antibacterial composite PVDF ultrafiltration membrane according to claim 1, characterized in that, The immersion is performed at room temperature for 0.5-1 h; and the drying is performed at 60-100°C for 4-12 h under vacuum.

9. The antibacterial composite PVDF ultrafiltration membrane prepared by the preparation method according to any one of claims 1-8.

10. The antibacterial composite PVDF ultrafiltration membrane according to claim 9 is applied in water treatment.