Preparation method of PVDF (Polyvinylidene Fluoride) super-hydrophilic composite membrane

Abstract

The invention provides a preparation method of a PVDF (Polyvinylidene Fluoride) super-hydrophilic composite membrane. Comprising the following steps: step 1, preparing chitosan pregel; step 2, preparing polyvinyl alcohol pregel; step 3, preparing CA pre-gel; step 4, preparing a PVDF-TC membrane; and step 5, preparing the PVDF-TCA super-hydrophilic composite membrane. The PVDF super-hydrophilic composite membrane is prepared by utilizing coordination and a chemical grafting method, TA-Cu is coordinated to form a metal-polyphenol network, and the metal-polyphenol network is connected with a CA hydrogel layer; the CA hydrogel has the characteristics of low probability of collapse, high mechanical property, good compatibility and the like, so that a complete hydrogel structure can be kept under continuous water flow impact; finally, the PVDF-TCA super-hydrophilic composite membrane with excellent anti-pollution performance, excellent oil-water separation efficiency and relatively high permeation flux is prepared.

Description

Technical Field

[0001] This invention relates to the fields of membrane distillation and PVDF membrane composite technology; and more particularly to a method for preparing a PVDF superhydrophilic composite membrane. Background Technology

[0002] With the rapid development of the food and catering industries, the large-scale discharge of oily wastewater from food processing has caused serious environmental hazards. Membrane separation technology has attracted widespread attention due to its advantages such as low energy consumption, high efficiency, and no phase change. Polyvinylidene fluoride (PVDF) membranes have been widely used in water treatment due to their high mechanical strength, chemical corrosion resistance, and chemical stability. However, hydrophilic PVDF membranes are easily fouled during oil-water separation, leading to pore blockage and decreased flux. By designing the wettability of the membrane surface, a superhydrophilic membrane surface with a stable hydration layer can be obtained, achieving underwater superoleophobicity. This can effectively alleviate membrane fouling during the separation of oily food wastewater. Hydrogel materials with strong hydration capabilities have also become ideal materials for the modification process. Using a PVDF membrane as the base membrane, a superhydrophilic PVDF composite membrane was prepared by modifying it with a metal-polyphenol network (MPN) and a hybrid hydrogel. When applied to the treatment of oily wastewater from the food industry, this composite membrane exhibits high permeation flux and excellent separation efficiency, while also demonstrating superior antifouling properties.

[0003] Therefore, a superhydrophilic gel modified layer was successfully constructed on the surface of PVDF membrane using coordination and chemical grafting methods to achieve the purpose of superhydrophilic / underwater superoleophobicity. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a PVDF superhydrophilic composite membrane.

[0005] This invention is achieved through the following technical solution:

[0006] This invention relates to a method for preparing a PVDF superhydrophilic composite membrane, comprising the following steps:

[0007] Step 1: Prepare chitosan (CS) pregel;

[0008] Step 2: Prepare polyvinyl alcohol (PVA) pregel;

[0009] Step 3: Mix the obtained chitosan (CS) pregel and polyvinyl alcohol (PVA) pregel with tetraethyl orthosilicate alcohol (TEOS) solution until homogeneous, and then add PVP aqueous solution to obtain CA superhydrophilic pregel. This CA superhydrophilic pregel is a pregel formed by four mixed substances.

[0010] Step 4: Immerse the PVDF membrane sequentially in tannic acid solution and CuCl2·2H2O solution to obtain the PVDF-TC membrane;

[0011] Step 5: Immerse the obtained PVDF-TC membrane in CA pregel, react for 30 min, and then dry at 55℃ to obtain the PVDF-TCA superhydrophilic composite membrane.

[0012] Preferably, in step 1, the method for preparing the chitosan (CS) pregel is as follows:

[0013] Chitosan (CS) powder was added to a 1% (v / v) acetic acid solution to obtain a mixed solution. The solution was then heated and stirred in a water bath until the powder was completely dissolved, thus obtaining a chitosan (CS) pregel.

[0014] Preferably, the mass-to-volume ratio of the chitosan (CS) powder to the 1% (v / v) acetic acid solution is 0.1:90 to 0.1:110, where the unit of mass-to-volume ratio is g / mL. -1 The water bath temperature is 45℃.

[0015] Preferably, in step 2, the method for preparing the polyvinyl alcohol (PVA) pregel is as follows:

[0016] Weigh out polyvinyl alcohol (PVA) powder and add it to deionized water. Place the mixture in a water bath and heat it while stirring continuously for 8 hours until the polyvinyl alcohol (PVA) powder is completely dissolved to obtain polyvinyl alcohol (PVA) pregel.

[0017] Preferably, the mass-to-volume ratio of the polyvinyl alcohol (PVA) powder to deionized water is 1:90 to 1:110, and the unit of mass-to-volume ratio is g∙mL. -1 The water bath temperature was 85℃, and the stirring time was 8 hours.

[0018] Preferably, in step 3, the concentration of tetraethyl orthosilicate alcohol solution (TEOS) is 0.2% (v / v) and the concentration of PVP aqueous solution is 1% (v / v).

[0019] Preferably, in step 3, the volume ratio of chitosan (CS) pregel, polyvinyl alcohol (PVA) pregel, tetraethyl orthosilicate alcohol (TEOS) solution to PVP aqueous solution is 4:1:1:1.

[0020] Preferably, in step 4, the method for preparing the PVDF-TC membrane specifically includes:

[0021] S1, a TA mixture was prepared by dissolving tannic acid (TA) in Tris-HCl buffer solution (pH 8.5);

[0022] S2, the PVDF membrane is thoroughly immersed in tannic acid (TA) solution and CuCl2·2H2O solution in sequence to obtain PVDF-TC membrane.

[0023] Preferably, the mass-to-volume ratio of tannic acid (TA) to Tris-HCl buffer solution is 35:100 to 45:100;

[0024] Preferably, the soaking time is 15 min and the concentration of the CuCl2·2H2O solution is 0.5 mol / L.

[0025] The present invention has the following advantages:

[0026] (1) The method involved in this invention is to prepare a PVDF superhydrophilic composite membrane by coordination and chemical grafting, wherein TA-Cu coordinates to form a metal-polyphenol network (MPN), which is further connected to a CA hydrogel layer. The CA hydrogel has the characteristics of not collapsing, high mechanical properties and good compatibility, and can maintain an intact hydrogel structure under continuous water flow impact.

[0027] (2) The present invention successfully constructed a hydrogel layer with superhydrophilic / underwater superoleophobic properties on the surface of PVDF membrane. The resulting PVDF-TCA superhydrophilic composite membrane has excellent antifouling performance and excellent oil-water separation efficiency, while also having high permeation flux. Attached Figure Description

[0028] Figure 1 SEM images of PVDF membrane and PVDF-TCA superhydrophilic composite membrane;

[0029] Figure 2 FTIR spectra of PVDF membrane and PVDF-TCA superhydrophilic composite membrane;

[0030] Figure 3 AFM images of PVDF membrane and PVDF-TCA superhydrophilic composite membrane;

[0031] Figure 4 Comparison of water contact angle and underwater oil contact angle results for PVDF membrane and PVDF-TCA superhydrophilic composite membrane;

[0032] Figure 5 A comparison of the dynamic anti-organic fouling performance results of PVDF membrane and PVDF-TCA superhydrophilic composite membrane;

[0033] Figure 6 A comparison of the dynamic anti-biofouling performance results of PVDF membrane and PVDF-TCA superhydrophilic composite membrane;

[0034] Figure 7 A comparison of the oil-water separation performance of PVDF membrane and PVDF-TCA superhydrophilic composite membrane;

[0035] Figure 8 A comparison chart showing the performance of PVDF membranes and PVDF-TCA superhydrophilic composite membranes in filtering real catering wastewater. Detailed Implementation

[0036] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are merely further illustrations of the present invention, but the scope of protection of the present invention is not limited to the following embodiments.

[0037] Example 1

[0038] This embodiment relates to a method for preparing a PVDF superhydrophilic composite membrane, including the following steps:

[0039] Step 1: Add 0.1 g of CS powder to 100 mL of 1% (v / v) acetic acid solution to obtain a mixed solution. Place the solution in a 45°C water bath and heat and stir until the powder is completely dissolved to obtain CS pregel.

[0040] Step 2: Weigh 1 g of PVA powder and add it to 100 mL of deionized water. Then place the mixture in a water bath at 85°C and heat it while stirring continuously for 8 h until the PVA powder is completely dissolved, thereby obtaining PVA pregel.

[0041] Step 3: Mix the CS pregel and PVA pregel obtained in Steps 1 and 2 with 0.2% (v / v) TEOS alcohol solution at a volume ratio of 4:1:1 until homogeneous, and then add an equal volume of 1% (w / v) PVP aqueous solution to obtain CA pregel.

[0042] Step 4: Immerse the PVDF membrane sequentially in TA solution and CuCl2·2H2O solution for 15 min to obtain the PVDF-TC membrane, including the following steps:

[0043] S1. Dissolve 40 mg TA in 100 mL Tris-HCl buffer solution (pH 8.5) to prepare a TA mixture;

[0044] S2. Immerse the PVDF membrane sequentially in TA solution and 0.5 mol / L CuCl2·2H2O solution for 15 min to obtain the PVDF-TC membrane.

[0045] 5) Immerse the PVDF-TC membrane obtained in step 4 in CA pregel for 30 min, remove it and rinse it repeatedly with deionized water to remove surface impurities, thus obtaining a PVDF-TCA superhydrophilic composite membrane.

[0046] The PVDF-TCA superhydrophilic composite membrane prepared in Example 1 was characterized and analyzed for its properties.

[0047] See Figure 1 As shown, Figure 1 (a) shows that, compared to the rough macropores observed on the PVDF membrane surface, the PVDF-TCA superhydrophilic composite membrane exhibits a smooth and dense hydrogel structure, resulting in a significant reduction in membrane pore size. Figure 1 (b) shows that the original PVDF membrane has a rough surface, while the modified membrane cross-section shows a gradually thickening hydrogel structure. Due to the increased cross-linking degree of CS and PVA under the action of TEOS, the hydrogel layer becomes thick and dense. It can be observed that the hydrogel layer in the PVDF-TCA membrane completely covers the PVDF membrane.

[0048] See Figure 2 As shown, obvious CH4 (1400 cm⁻¹) is present in the PVDF membrane. -1 ) and CF (1179 cm) -1 Strong absorption peak. For PVDF-TCA membranes, this is typically observed in the 3000–3600 cm⁻¹ range. −1 The strong vibrational broadband is attributed to the overlapping stretching vibrations of the -OH group and the -NH bond of the primary amine group in CS, and is observed at 1627 and 1580 cm⁻¹. -1 At 1653 cm, distinct amide I and amide II bands are observed respectively; -1 1276 cm -1 The tensile vibrations of C=O and CN groups were observed at 1020 cm⁻¹, respectively, proving the successful introduction of PVP; -1 The vibration at the point confirmed that TEOS hydrolyzes in alcohol solution to form Si-O-Si bonds.

[0049] See Figure 3 As shown, the Ra and Rq values ​​of PVDF are 415.00 ± 7.64 nm and 540.00 ± 9.79 nm, respectively. The Ra and Rq values ​​of the PVDF-TCA superhydrophilic composite membrane are 299.67 ± 9.77 nm and 385.00 ± 8.96 nm, respectively. Compared to the PVDF membrane, the PVDF-TCA superhydrophilic composite membrane exhibits a smoother surface morphology.

[0050] See Figure 4 As shown, Figure 4 As shown in (a), the PVDF membrane has a WCA of 135.02 ± 0.01°, exhibiting a hydrophilic state. The PVDF-TCA composite membrane has a WCA of 10.07 ± 8.06°. Figure 4In (b), the UOCA values ​​of the PVDF membrane and the PVDF-TCA composite membrane are 50.82 ± 4.89° and 160.37 ± 2.49°, respectively. This indicates that the PVDF-TCA composite membrane has excellent underwater superoleophobic properties.

[0051] See Figure 5 As shown, the FRR (Fouling Retention Rate) of the PVDF membrane after filtration of BSA solution and subsequent cleaning was only 10.23%, while the FRR of the PVDF-TCA composite membrane remained at 88.40% after three fouling-cleaning cycles. This indicates that BSA only caused slight fouling to the membrane surface and did not form irreversible fouling. This is because the highly cross-linked hybrid hydrogel three-dimensional network structure can absorb more water, forming a more stable hydration layer, weakening the hydrophilic interaction between pollutants and the membrane surface, thereby effectively inhibiting protein adhesion to the membrane surface. Simultaneously, the PVA coating-modified filter membrane can maintain high flux and exhibit high protein rejection in oil-water emulsions. Therefore, the uniform modification of the CA hydrogel structure on the PVDF membrane surface gives the PVDF-TCA composite membrane excellent anti-protein fouling performance.

[0052] See Figure 6 As shown, the FRR of E. coli and S. aureus bacterial cultures are respectively... Figure 6 (a) and Figure 6 (b) During the bacterial filtration process, bacteria rapidly deposit and form a biofilm, causing a sharp decline in the flux of all membranes. After E. coli bacterial filtration, the FRR value of the PVDF membrane was only 17.12%. After simple cleaning, the FRR value of the PVDF-TCA composite membrane recovered to 89.95%. Figure 6 (a) of. Figure 6 As shown in (b), the overall trend of S. aureus filtration is basically the same as that of E. coli filtration, but S. aureus bacteria are prone to aggregation, forming larger bacterial groups that far exceed the membrane pore size range, resulting in more severe pore blockage. After three cycles, the FRR value of the PVDF membrane was 12.17%, while the recovery rate of the PVDF-TCA membrane was 84.77%, proving that the CA hybrid hydrogel provides the PVDF-TCA membrane with high cross-linking degree and high anti-biofouling performance. Furthermore, the superhydrophilic properties obtained through surface modification effectively inhibit the adhesion of microorganisms and organic matter, thereby enhancing the anti-biofouling performance.

[0053] See Figure 7 As shown, by Figure 7 As shown in (a), there are significant differences in TOC value and oil-water separation efficiency between the original membrane and the modified membrane. The PVDF membrane flux increased from 700 L / m³ within 30 min. -2 h -1 Rapidly reduced to 50 L m -2 h-1 The flux of the PVDF-TCA composite membrane decreased to 315.05 L / m² after 1 hour of filtration. -2 h -1 This indicates that the PVDF-TCA composite membrane has a lower water flux decay rate and exhibits higher antifouling and stability in the oil-water separation process. This can be attributed to the hybrid hydrogel of the PVDF-TCA composite membrane, which possesses a stable hydration layer and demonstrates stronger underwater anti-oil fouling performance. Figure 7 As shown in (b), the TOC value of the filtrate filtered through the PVDF membrane was 192.53 ± 12.04 mg / L, with a separation efficiency of only 87.60%. In contrast, the TOC value of the PVDF-TCA composite membrane was below 20 mg / L, and the separation efficiency reached 99.80%. Therefore, the PVDF-TCA composite membrane exhibits excellent stability and separation efficiency in oil-water separation, demonstrating great application potential.

[0054] See Figure 8 As shown, the treatment efficiency of PVDF membrane and PVDF-TCA composite membrane was measured using real catering wastewater. Significant differences were found in the indicators and color of the raw solution, PVDF membrane, and PVDF-TCA composite membrane filtrate. Figure 8 As shown in (a), the actual oily wastewater from catering contains a large amount of complex components such as organic matter, suspended solids and pigments, which leads to a rapid decrease in water flux during the oil-water separation process. Compared with PVDF membrane, the flux of PVDF-TCA composite membrane gradually stabilizes after a period of filtration. After cleaning the membrane with deionized water, the FRR value reaches 57.91%, while that of PVDF membrane is only 2.62%. This indicates that the complex components in the wastewater cause more serious clogging to PVDF membrane, while the modified membrane has stronger antifouling performance. Figure 8 In (b), compared to the PVDF membrane's separation efficiency of only 72.15%, the modified membrane's separation efficiency reached 97.74%, proving that although the FRR value of the PVDF-TCA membrane is slightly reduced, it still has good separation performance for actual catering wastewater.

[0055] As can be seen from the above data, the method of the present invention can improve the superhydrophilicity of the composite membrane by grafting CPTA hydrogel onto the surface of the PVDF membrane through a TA-Cu connecting layer, exhibiting excellent antifouling performance and oil-water separation performance, and having a high permeation flux.

[0056] Example 2

[0057] This embodiment relates to a method for preparing a PVDF superhydrophilic composite membrane, including the following steps:

[0058] Step 1: Add 0.1 g of CS powder to 110 mL of 1% (v / v) acetic acid solution to obtain a mixed solution. Place the solution in a 45°C water bath and heat and stir until the powder is completely dissolved to obtain CS pregel.

[0059] Step 2: Weigh 1 g of PVA powder and add it to 110 mL of deionized water. Then place the mixture in a water bath at 85°C and heat it while stirring continuously for 8 h until the PVA powder is completely dissolved, thereby obtaining PVA pregel.

[0060] Step 3: Mix the CS and PVA pregels obtained in Steps 1 and 2 with 0.2% (v / v) TEOS alcohol solution at a volume ratio of 4:1:1 until homogeneous, and then add an equal volume of 1% (w / v) PVP aqueous solution to obtain CA pregel.

[0061] Step 4: Immerse the PVDF membrane sequentially in TA solution and CuCl2·2H2O solution for 15 min to obtain the PVDF-TC membrane, including the following steps:

[0062] S1. Dissolve 35 mg TA in 100 mL Tris-HCl buffer solution (pH 8.5) to prepare a TA mixture;

[0063] S2. The PVDF membrane was successively immersed in TA solution and 0.5 mol / L CuCl2·2H2O solution for 15 min to obtain PVDF-TC membrane;

[0064] Step 5: Immerse the PVDF-TC membrane obtained in Step 4 in CA pregel and react for 30 min. After the reaction is complete, rinse the surface impurities repeatedly with deionized water to obtain the PVDF-TCA superhydrophilic composite membrane.

[0065] Example 3

[0066] This embodiment relates to a method for preparing a PVDF superhydrophilic composite membrane, including the following steps:

[0067] Step 1: Add 0.1 g of CS powder to 90 mL of 1% (v / v) acetic acid solution to obtain a mixed solution. Place the solution in a 45°C water bath and heat and stir until the powder is completely dissolved to obtain CS pregel.

[0068] Step 2: Weigh 1 g of PVA powder and add it to 90 mL of deionized water. Then place the mixture in a water bath at 85°C and heat it while stirring continuously for 8 h until the PVA powder is completely dissolved, thereby obtaining PVA pregel.

[0069] Step 3: Mix the CS and PVA pregels obtained in Steps 1 and 2 with 0.2% (v / v) TEOS alcohol solution at a volume ratio of 4:1:1 until homogeneous, and then add an equal volume of 1% (w / v) PVP aqueous solution to obtain CA pregel.

[0070] Step 4: Immerse the PVDF membrane sequentially in TA solution and CuCl2·2H2O solution for 15 min to obtain the PVDF-TC membrane, including the following steps:

[0071] S1. Dissolve 45 mg TA in 100 mL Tris-HCl buffer solution (pH 8.5) to prepare a TA mixture;

[0072] S2. Immerse the PVDF membrane sequentially in TA solution and 0.5 mol / L CuCl2·2H2O solution for 15 min to obtain the PVDF-TC membrane.

[0073] Step 5: Immerse the PVDF-TC membrane obtained in Step 4 in CA pregel and react for 30 min. After the reaction is complete, rinse the surface impurities repeatedly with deionized water to obtain the PVDF-TCA superhydrophilic composite membrane.

[0074] This invention utilizes coordination and chemical grafting to successfully construct a CA superhydrophilic gel layer on the surface of a PVDF membrane. The prepared superhydrophilic composite membrane exhibits high permeation flux, as well as good oil-water separation performance and excellent antifouling properties.

[0075] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a PVDF superhydrophilic composite membrane, characterized in that, Includes the following steps: Step 1: Prepare chitosan pregel; Step 2: Prepare polyvinyl alcohol pregel; Step 3: Mix the obtained chitosan pregel and polyvinyl alcohol pregel with tetraethyl orthosilicate alcohol solution until homogeneous, and then add PVP aqueous solution to obtain CA pregel. Step 4: Immerse the PVDF membrane sequentially in tannic acid solution and CuCl2·2H2O solution to obtain the PVDF-TC membrane; Step 5: Immerse the PVDF-TC membrane in CA pregel, react for 30 min, and then dry at 55℃ to obtain the PVDF-TCA superhydrophilic composite membrane.

2. The method for preparing the PVDF superhydrophilic composite membrane as described in claim 1, characterized in that, In step 1, the preparation method of the chitosan pregel is specifically as follows: Chitosan powder was added to a 1% acetic acid solution to obtain a mixed solution. The solution was then heated and stirred in a water bath until the powder was completely dissolved, thus obtaining a chitosan pregel.

3. The method for preparing the PVDF superhydrophilic composite membrane as described in claim 2, characterized in that, The mass-to-volume ratio of the chitosan powder to the 1% acetic acid solution is 0.1:90 to 0.1:110, and the unit of mass-to-volume ratio is g / mL. -1 The water bath temperature is 45℃.

4. The method for preparing the PVDF superhydrophilic composite membrane as described in claim 1, characterized in that, In step 2, the specific method for preparing the polyvinyl alcohol pregel is as follows: Weigh polyvinyl alcohol powder and add it to deionized water. Place the mixture in a water bath and heat it while stirring continuously for 8 hours until the polyvinyl alcohol powder is completely dissolved to obtain polyvinyl alcohol pregel.

5. The method for preparing the PVDF superhydrophilic composite membrane as described in claim 4, characterized in that, The mass-to-volume ratio of the polyvinyl alcohol powder to deionized water is 1:90 to 1:110, and the unit of mass-to-volume ratio is g∙mL. -1 The water bath temperature was 85℃, and the stirring time was 8 hours.

6. The method for preparing the PVDF superhydrophilic composite membrane as described in claim 1, characterized in that, In step 3, the concentration of the tetraethyl orthosilicate alcohol solution is 0.2%, and the concentration of the PVP aqueous solution is 1%.

7. The method for preparing the PVDF superhydrophilic composite membrane as described in claim 1, characterized in that, In step 3, the volume ratio of chitosan pregel, polyvinyl alcohol pregel, tetraethyl orthosilicate alcohol solution and PVP aqueous solution is 4:1:1:

1.

8. The method for preparing the PVDF superhydrophilic composite membrane as described in claim 1, characterized in that, In step 4, the specific method for preparing the PVDF-TC membrane is as follows: S1, a TA mixture was prepared by dissolving tannic acid in Tris-HCl buffer solution; S2, the PVDF membrane is thoroughly immersed in tannic acid solution and CuCl2·2H2O solution in sequence to obtain PVDF-TC membrane.

9. The method for preparing the PVDF superhydrophilic composite membrane as described in claim 8, characterized in that, The mass-to-volume ratio of tannic acid to Tris-HCl buffer solution is 35:100 to 45:

100.

10. The method for preparing the PVDF superhydrophilic composite membrane as described in claim 8, characterized in that, The soaking time was 15 min, and the concentration of the CuCl2·2H2O solution was 0.5 mol / L.

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