Deposition of nh2-mil-88b(fe) grafted pfxs hydrophilic and oleophobic modified pvdf membranes and methods of making the same

Abstract

The application provides a preparation method of a modified PVDF membrane with NH2-MIL-88B(Fe) deposition PFHxS hydrophilic and oleophobic modification, NH2-MIL-88B(Fe) is deposited on the surface of a PVDF membrane to form a deposition membrane, and then potassium tridecafluorohexane-1-sulfonate (PFHxS) is grafted on the surface of the deposition membrane to complete the modification of the hydrophilic and oleophobic modification of the PVDF membrane, so that the modified PVDF membrane is prepared. The application also provides a modified PVDF membrane with NH2-MIL-88B(Fe) deposition PFHxS hydrophilic and oleophobic modification. The modified membrane provided by the application has the advantages of simple preparation process, good hydrophilic and oleophobic performance and high reusability.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of polymer membrane separation materials, and particularly relates to a NH2-MIL-88B(Fe) grafted PFHxS hydrophilic and oleophobic modified PVDF membrane and a preparation method thereof. BACKGROUND

[0002] Polyvinylidene fluoride (PVDF) membrane is favored by researchers due to its high chemical stability and mechanical properties. However, the strong adhesion and low surface energy of the PVDF membrane itself make it easy for oil droplets to deposit in the pores or on the surface, causing rapid pollution of the membrane. Therefore, researchers have carried out physical and chemical modification of the PVDF membrane through various methods to enhance its anti-pollution performance, improve its separation efficiency, and prolong the service life of the membrane.

[0003] MOF (Metal-organic framework, MOF) is a new type of metal-organic hybrid material with a three-dimensional porous structure, which is composed of metal ions as central nodes and organic ligands coordinated to form a cage-like crystal structure. MOF has adjustable pore channels, ultra-high specific surface area, diverse framework composition, excellent post-modification properties, and other structural characteristics, and has a wide range of applications in gas separation, electricity, photocatalysts, medicine, water treatment, and other fields. Therefore, many researchers have applied MOF as a membrane modifier in the field of separation modification and membrane preparation, such as:

[0004] Chinese patent CN 202210715190.X discloses a preparation method of titanium dioxide / MOF(Fe) / polyacrylonitrile (PAN) nanofiber membrane. Titanium dioxide, NH2-MIL-88B(Fe) and PAN are dissolved in N,N-dimethylformamide solution to obtain a spinning solution, and the modified membrane is prepared by electrospinning technology. The experimental results show that the prepared modified membrane has good application prospects in the degradation of tetracycline hydrochloride and oil-water separation, but the interception performance of the modified membrane for different oil-water emulsions still has a lot of room for improvement, and there is a lack of in-depth research on the cyclic use performance and permeability of the modified membrane.

[0005] Chinese patent CN 202111440522.X discloses a preparation method of MIL-100(Fe) / polydimethylsiloxane (PDMS) membrane. The experimental results show that the prepared modified membrane has good application prospects in the capture of organic gases such as propane, and can be used for recovering low molecular weight hydrocarbons and other organic gases from mixed gases, but the preparation method of the modified membrane is complicated and has high operation cost.

[0006] In summary, a new type of MOF modified membrane with simple preparation process, good hydrophilic and oleophobic performance, and high reusability needs to be developed. SUMMARY

[0007] In view of the above-mentioned disadvantages of the prior art, the purpose of the present application is to provide a modified PVDF membrane with enhanced hydrophilicity and improved oleophobicity in the separation process, which is prepared by a simple method;

[0008] To achieve the above-mentioned purpose and other related purposes, the present application provides a preparation method of a NH2-MIL-88B(Fe) grafted PFHxS hydrophilic and oleophobic modified PVDF membrane,

[0009] depositing NH2-MIL-88B(Fe) on the surface of the PVDF membrane to form a deposition film, grafting potassium tridecafluorohexane-1-sulfonate (PFHxS) on the surface of the deposition film to complete the hydrophilic and oleophobic modification of the PVDF membrane, and preparing the modified PVDF membrane; wherein,

[0010] The reaction formula of PFHxS and NH2-MIL-88B(Fe) is:

[0011]

[0012] Preferably, the preparation process of the modified PVDF membrane is as follows:

[0013] a. dispersing NH2-MIL-88B(Fe) powder in ultrapure water to form a uniform NH2-MIL-88B(Fe) aqueous solution by ultrasonic;

[0014] b. dispersing PFHxS powder in ultrapure water, and then placing it on a magnetic stirrer to form a uniform PFHxS aqueous solution;

[0015] c. fixing the PVDF membrane on a suction filtration device equipped with a sand core filter, filtering anhydrous ethanol, and then taking out the PVDF membrane and washing the membrane surface with deionized water; adding the NH2-MIL-88B(Fe) aqueous solution into the suction filtration device to deposit on the surface of the PVDF membrane, and then transferring the membrane prepared by the above steps to an oven for drying to obtain a NH2-MIL-88B(Fe) / PVDF membrane with a stable surface;

[0016] d. immersing the NH2-MIL-88B(Fe) / PVDF membrane in the PFHxS aqueous solution, placing the whole reaction system in a water bath shaker, and oscillating at room temperature for 24 h; after the reaction is completed, taking out the membrane prepared by the above steps and immersing it in deionized water for 12 h, changing the water every 6 h, and finally air-drying the membrane at room temperature to obtain the NH2-MIL-88B(Fe)

[0017] grafted PFHxS hydrophilic and oleophobic modified PVDF membrane.

[0018] Preferably, the concentration of the NH2-MIL-88B(Fe) aqueous solution in step a ranges from 0.1 to 10 mg / L.

[0019] Preferably, the mass of the NH2-MIL-88B(Fe) powder in step a is 1 mg, and the mass of the ultrapure water is 500 mL.

[0020] Preferably, the concentration of the PFHxS aqueous solution in step b ranges from 0.1 to 10 mg / L.

[0021] Preferably, the mass of the PFHxS in step b is 1 mg, and the mass of the ultrapure water is 500 mL.

[0022] Preferably, the suction filtration pressure of the suction filtration device is 0.05 to 0.2 MPa.

[0023] Preferably, the temperature of the oven in step c is 40 to 80℃, and the heating time is 10 to 60 min.

[0024] Preferably, the rotation speed of the magnetic stirrer is 400 to 600 r / min, and the shaking speed of the water bath shaker is 60 to 120 r / min.

[0025] A NH2-MIL-88B(Fe) grafted PFHxS hydrophilic and oleophobic modified PVDF membrane prepared according to the above preparation method.

[0026] The NH2-MIL-88B(Fe) grafted PFHxS hydrophilic and oleophobic modified PVDF membrane and the preparation method thereof have the following beneficial effects:

[0027] 1) The deposition of the NH2-MIL-88B(Fe) with high porosity in the present application increases the porosity of the PVDF membrane, providing more paths for water molecules to pass through the membrane, thereby increasing the pure water flux of the membrane;

[0028] 2) In the present application, the NH2-MIL-88B(Fe) powder is deposited on the surface of the PVDF membrane by vacuum suction filtration, which can be uniformly distributed and does not appear obvious agglomeration;

[0029] 3) The MOF-based membrane is prepared by vacuum filtration in the present application, which has the advantages of simple preparation process, low reaction condition requirement and easy control, low cost, and easy control and uniformity of membrane structure;

[0030] 4) In the present application, the PVDF membrane is modified by surface grafting PFHxS, and the hydrophilic sulfonic acid group and the oleophobic perfluoroalkyl group in PFHxS improve the hydrophilic and oleophobic properties of the PVDF membrane, and the hydrophilic sulfonic acid ammonium salt synthesized by the reaction of the amino group on NH2-MIL-88B(Fe) and the sulfonate in PFHxS further improves the hydrophilicity of the PVDF membrane;

[0031] 5) The amino group on the NH2-MIL-88B(Fe) of the present application reacts with the sulfonate in PFHxS in weakly acidic water (pH 6-7) to form an ammonium sulfonate salt, the reaction steps are simple, the operation process is simple, the reaction occurs in an aqueous solution, and only room temperature is required, without the use of catalysts or other solvents, green and environmentally friendly;

[0032] 6) The hydrophilic and oleophobic modified MOF / PVDF membrane prepared in the present application has good retention capacity for different types of oil-water emulsions, while still maintaining high permeation flux, and the flux recovery rate can still be maintained at a high level after multiple cycles of filtering oil-water emulsions, with good oil pollution resistance and multiple cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Figure for the cyclic separation effect of M2 membrane in Example 1 on n-hexadecane emulsion;

[0034] Figure 2 X-ray photoelectron spectroscopy (XPS) diagram of membranes M0, M1 and M2 in the examples of the present application. DETAILED DESCRIPTION

[0035] The following describes the embodiments of the present application by specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the specification.

[0036] Example 1:

[0037] 1) Disperse 1 mg of NH2-MIL-88B(Fe) powder in 500 m of ultrapure water, and ultrasonicate for 30 min to form a uniform NH2-MIL-88B(Fe) aqueous solution;

[0038] 2) Fix the hydrophobic PVDF membrane in a suction filtration device equipped with a sand core filter, first filter a small amount of anhydrous ethanol, remove and wash the membrane surface with deionized water; pour the NH2-MIL-88B(Fe) aqueous solution into the ultrafiltration cup of the suction filtration device, and make the NH2-MIL-88B(Fe) deposit on the surface of the PVDF membrane under a pressure of 0.085 MPa, and finally transfer the prepared membrane to an oven for drying to obtain a surface-stable NH2-MIL-88B(Fe) / PVDF membrane, denoted as M1;

[0039] Example 2:

[0040] PFHxS powder 1 mg was dissolved in 500 mL ultrapure water, placed on a magnetic stirrer for stirring for 30 min, so that PFHxS was completely dissolved in ultrapure water to prepare a PFHxS aqueous solution; the NH2-MIL-88B(Fe) / PVDF membrane prepared in Example 1 was immersed in the PFHxS aqueous solution, and the whole reaction system was placed in a water bath shaker and oscillated at room temperature for 24 h; after the reaction was completed, the membrane prepared by the above steps was taken out and immersed in deionized water for 12 h, and the water was changed every 6 h, and finally the membrane was naturally dried at room temperature to prepare the MOF modified PVDF membrane, which was recorded as M2.

[0041] 1. In order to illustrate the hydrophilic and oleophobic modification effect of the modified membrane in the present application, the surface static contact angle of the modified membrane was tested by using a membrane surface contact angle / surface tension tester (Rame-Hart 500), and the results are shown in Table 1 (the original PVDF membrane (M0), NH2-MIL-88B(Fe) and the surface grafted modified membrane M1 (Example 1) and M2 (Example 2) prepared under different mass ratios are listed):

[0042] Table 1: Composition and basic properties of the membrane

[0043]

[0044] From the contact angle test of the membrane, it can be seen that the hydrophilicity of the original PVDF membrane (M0) is weak, and the water contact angle is only 111.0°; the hydrophilic and oleophobic performance of the membrane (M1) after depositing NH2-MIL-88B(Fe) is slightly improved, which is mainly due to the rich amino groups in the structure of NH2-MIL-88B(Fe). After grafting PFHxS onto the deposited membrane (NH2-MIL-88B(Fe) / PVDF membrane), the water contact angle of the modified membrane (M2) rapidly decreases to 55.4°, which is due to the reaction of NH2-MIL-88B(Fe) and PFHxS to generate hydrophilic ammonium sulfonate.

[0045] The underwater oil contact angle of the original PVDF membrane (M0) is 145.1°, and the underwater oil contact angle of M2 is increased to 180°, i.e. the modified membrane shows superoleophobicity, which is due to the introduction of a large amount of fluorine elements in PFHxS, which can greatly reduce the surface energy of the PVDF membrane.

[0046] 2. In the present application, a suction filtration device with a sand core filter is used, and under an operating pressure of 0.09 MPa, the oil-water emulsion separation performance of the prepared membrane M2 is tested by separating different types of oil-water emulsions (n-hexadecane, petroleum ether, dichloromethane and soybean oil), and the separation performance is mainly tested by permeation flux (J wThe performance of the membrane M2 is characterized by two indicators: the retention rate (R) of the contaminants and the rejection rate (R), as shown in Table 2. The membrane M2 exhibits excellent retention performance when filtering different types of oil-water emulsions.

[0047] Table 2: Membrane M2 filtration of different types of oil-water emulsions containing surfactants

[0048] Oil-water emulsion Permeate flux (J w ) / (L-m -2 ·h -1 )]]> R / ％ n-hexadecane 8593 99.35 petroleum ether 7132 98.93 methylene chloride 8526 98.78 soybean oil 5468 99.30

[0049] 3. In this invention, an ultrafiltration cup (MSC50, 300 mL) was used. An operating pressure of 0.09 MPa was applied to the oil-water emulsion (hexadecane and water volume ratio of 1:99) through a circulating filtration experiment. The oil-water emulsion separation performance and reusability of the modified membrane M2 were tested. Figure 1 As shown, after ten cycles of oil-water emulsion filtration, the permeate flux of membrane M2 only decreased slightly with increasing time, while the rejection rate for n-hexadecane-water emulsion remained above 99%, with no significant change in value. These results indicate that membrane M2 maintains excellent anti-fouling performance and reusability during long-term oil-water emulsion filtration.

[0050] 4. X-ray photoelectron spectroscopy was used to analyze the surface elemental composition of different films. Figure 2 Oil-water emulsion n-hexadecane petroleum ether methylene chloride soybean oil Figure 1 Figure 2 Oil-water emulsion The XPS spectrum of the original PVDF membrane (M0) mainly shows C and F elements. The M1 membrane exhibits signals from three new elements, attributed to O, N, and Fe, confirming the successful loading of NH2-MIL-88B(Fe) onto the membrane surface. The XPS spectrum of the M2 membrane shows a weak S signal at 153 eV, which can be attributed to sulfonate in PFHxS. The C (285 eV) and O (530 eV) content in the M2 membrane is significantly higher than that in M0 and M1, mainly due to the large amounts of C and O in the grafted PFHxS. The enhancement of these characteristic peaks indicates the successful surface modification of the PVDF membrane.

[0051] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a hydrophilic and oleophobic modified PVDF membrane by depositing NH2-MIL-88B(Fe) grafted PFHxS, characterized in that, NH2-MIL-88B(Fe) is deposited onto the surface of a PVDF membrane to form a deposited film. Potassium tridecafluorohexane-1-sulfonate (PFHxS) is then grafted onto the surface of the deposited film to complete the hydrophilic and oleophobic modification of the PVDF membrane, thus obtaining the modified PVDF membrane. The reaction formula between PFHxS and NH2-MIL-88B(Fe) is as follows:

2. The method for preparing the NH2-MIL-88B(Fe)-grafted PFHxS hydrophilic and oleophobic modified PVDF membrane according to claim 1, characterized in that, The preparation process of the modified PVDF membrane is as follows: a. Disperse NH2-MIL-88B(Fe) powder in ultrapure water and sonicate to form a uniform NH2-MIL-88B(Fe) aqueous solution; b. Disperse PFHxS powder in ultrapure water, and then place it on a magnetic stirrer to stir and form a uniform PFHxS aqueous solution; c. Fix the PVDF membrane onto a filtration device equipped with a sand core filter, filter anhydrous ethanol, then remove the PVDF membrane and wash the membrane surface with deionized water; add the NH2-MIL-88B(Fe) aqueous solution into the filtration device to deposit it on the surface of the PVDF membrane, and then transfer the membrane obtained by the above steps to an oven to dry, to obtain a surface-stable NH2-MIL-88B(Fe) / PVDF membrane; d. Immerse the NH2-MIL-88B(Fe) / PVDF membrane in the PFHxS aqueous solution, place the entire reaction system in a water bath shaker, and shake at room temperature for 24 hours. After the reaction is completed, take out the membrane obtained by the above steps and immerse it in deionized water for 12 hours, changing the water every 6 hours. Finally, let the membrane air dry naturally at room temperature to obtain the NH2-MIL-88B(Fe) grafted PFHxS hydrophilic and oleophobic modified PVDF membrane.

3. The method for preparing the NH2-MIL-88B(Fe)-grafted PFHxS hydrophilic and oleophobic modified PVDF membrane according to claim 2, characterized in that, The concentration range of the NH2-MIL-88B(Fe) aqueous solution in step a is 0.1–10 mg / L.

4. The method for preparing the NH2-MIL-88B(Fe)-grafted PFHxS hydrophilic and oleophobic modified PVDF membrane according to claim 3, characterized in that, In step a, the mass of NH2-MIL-88B(Fe) powder is 1 mg, and the volume of ultrapure water is 500 mL.

5. The method for preparing the NH2-MIL-88B(Fe)-grafted PFHxS hydrophilic and oleophobic modified PVDF membrane according to claim 4, characterized in that, The concentration range of the PFHxS aqueous solution in step b is 0.1–10 mg / L.

6. The method for preparing the NH2-MIL-88B(Fe)-grafted PFHxS hydrophilic and oleophobic modified PVDF membrane according to claim 5, characterized in that, In step b, the mass of PFHxS is 1 mg and the volume of ultrapure water is 500 mL.

7. The method for preparing the NH2-MIL-88B(Fe)-grafted PFHxS hydrophilic and oleophobic modified PVDF membrane according to claim 6, characterized in that, The filtration pressure of the filtration device is 0.05 to 0.2 MPa.

8. The method for preparing the NH2-MIL-88B(Fe)-grafted PFHxS hydrophilic and oleophobic modified PVDF membrane according to claim 7, characterized in that, In step c, the oven temperature is 40–80°C and the heating time is 10–60 min.

9. The method for preparing the NH2-MIL-88B(Fe)-grafted PFHxS hydrophilic and oleophobic modified PVDF membrane according to claim 8, characterized in that, The magnetic stirrer has a rotation speed of 400–600 r / min, and the water bath shaker has a shaking speed of 60–120 r / min.

10. A PVDF membrane modified with NH2-MIL-88B(Fe) grafted PFHxS hydrophilic and oleophobic properties, characterized in that... The modified PVDF membrane prepared by the preparation method according to any one of claims 1 to 9.

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