Ionic liquid assisted MOF-808 / PVDF (Polyvinylidene Fluoride) mixed matrix membrane and preparation method thereof

Abstract

The invention provides a preparation method of an ionic liquid assisted MOF-808 / PVDF (Polyvinylidene Fluoride) mixed matrix membrane, which comprises the following steps: blending MOF-808 particles and PVDF powder by using an organic solvent to prepare a primary blended solution; adding an ionic liquid as an auxiliary solvent into the primary blended solution, continuously stirring for 12-48 hours until a uniformly mixed membrane casting solution is formed, and standing to remove bubbles; pouring the membrane casting solution on a glass plate, and immersing the glass plate in a deionized water bath to form a mixed matrix membrane; taking out the mixed matrix membrane, immersing the mixed matrix membrane in deionized water, changing water, taking out the mixed matrix membrane, and naturally airing at room temperature to prepare the ionic liquid assisted MOF-808 / PVDF mixed matrix membrane. The invention provides an ionic liquid assisted MOF-808 / PVDF (Polyvinylidene Fluoride) mixed matrix membrane. The mixed matrix membrane has the advantages of high flux, high interception effect, photocatalytic self-cleaning capability and high reusability.

Description

Technical Field

[0001] The present invention belongs to the field of separation membranes, and particularly relates to a preparation method of an ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane. Background Art

[0002] Metal-organic framework (MOF) is a novel porous material formed by the self-assembly of metal ions or metal clusters and organic ligands through coordination bonds. MOF has the advantages of high specific surface area, adjustable pore size, high crystallinity, etc., and shows great application potential in the fields of gas storage, separation, catalysis, sensing, etc. In addition, it is reported that some MOFs exhibit good photocatalytic performance under light irradiation conditions. Utilizing these characteristics, researchers usually use surface modification methods to use MOF as a membrane modifier to improve the performance of the membrane, such as:

[0003] Chinese Patent CN 202411239033.1 invented a preparation method of a zirconium-based amorphous MOF membrane. Metal ions Zr⁴⁺ are pre-assembled into metal clusters, and then an aqueous solution of the ligand and an oil-phase solution of the metal clusters are prepared. Using a hydrophilic polymer porous bottom membrane as a carrier, the carrier is alternately immersed in the aqueous solution or deprotonated aqueous solution and the oil-phase solution, thereby obtaining a series of stable MOF membranes; the experimental results show that the prepared modified membrane has good application prospects for the retention and removal of dyes in ethanol, but there is still great room for improvement in maintaining good retention performance and having a high flux for the modified membrane.

[0004] Chinese Patent CN 202410751053.0 invented an ultrathin MOF separation layer composite membrane and its preparation method. Copper hydroxide nanowires are attached to the substrate to prepare an intermediate layer; MOF nanosheets are horizontally deposited on the intermediate layer to form an ultrathin MOF separation layer, obtaining an ultrathin MOF separation layer composite membrane; the experimental results show that the prepared modified membrane can effectively improve solvent permeation while maintaining high dye retention and excellent mechanical stability, but the modified membrane still needs in-depth research in terms of anti-pollution performance and self-cleaning recyclability.

[0005] In summary, there is an urgent need to develop an MOF modified membrane that can have high flux, high retention effect, photocatalytic self-cleaning ability and high reusability. Summary of the Invention

[0006] In view of the above-mentioned disadvantages of the prior art, to solve the technical problems of low flux, poor retention effect and low reusability in the prior art;

[0007] The object of the present invention is also to provide a preparation method of an ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane, comprising the following steps:

[0008] a. Blend MOF-808 particles with PVDF powder using an organic solvent to obtain a preliminary blend solution.

[0009] b. Add an ionic liquid as an auxiliary solvent to the preliminary blend solution, continuously stir for 12 - 48 hours until a uniformly mixed casting solution is formed, and then let it stand for 3 - 24 hours to remove air bubbles.

[0010] c. Pour the casting solution onto a glass plate, spread it into a film with a uniform thickness using a coater, and then immerse the glass plate with the casting solution in a deionized water bath for phase inversion to form a mixed matrix membrane.

[0011] d. Take out the mixed matrix membrane, immerse it in deionized water for 6 - 24 h, change the water every 3 - 6 h, take it out and air-dry it naturally at room temperature to obtain the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane; wherein,

[0012] The organic solvent is one or more of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP);

[0013] The ionic liquid is one or more of 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-propyl-3-methylimidazolium chloride, and 1-propyl-3-methylimidazolium bromide.

[0014] Preferably, the mass percentage range of MOF-808 added to the preliminary blend solution in step a is 0.1 - 2%.

[0015] Preferably, the mass percentage range of PVDF added to the preliminary blend solution in step a is 14 - 22%.

[0016] Preferably, the mass percentage of the organic solvent N,N-dimethylacetamide added to the preliminary blend solution in step a is 65 - 84%.

[0017] Preferably, the mass percentage range of 1-butyl-3-methylimidazolium chloride ionic liquid in the casting solution in step b is 8 - 25%.

[0018] Preferably, the temperature of the deionized water bath in step c is 40 - 80°C, and the phase inversion time is 30 - 120 s.

[0019] Preferably, the preparation steps of the preparation method are as follows:

[0020] a. Blend 1.5 wt.% of MOF-808 with PVDF using 65.6 wt.% of the organic solvent N,N-dimethylacetamide;

[0021] b. Add 16.4 wt.% of 1-butyl-3-methylimidazolium chloride ionic liquid as an auxiliary solvent, and continuously stir for 24 hours until a uniformly mixed casting solution is formed. Then, let it stand for 12 hours to remove bubbles.

[0022] c. Pour the casting solution onto a glass plate, and use a coater to evenly spread a film with a thickness of 300 μm. Then, immerse the glass plate with the casting solution in a deionized water bath for phase inversion to form a mixed matrix membrane.

[0023] d. Take out the membrane prepared by the above steps and immerse it in deionized water for 12 h, changing the water every 6 h. Finally, let the membrane air-dry naturally at room temperature to obtain the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane.

[0024] Preferably, the preparation steps of the preparation method are as follows:

[0025] a. Use 70 wt.% of the organic solvent N,N-dimethylformamide to blend 1.0 wt.% of MOF-808 with PVDF to obtain a preliminary blend solution.

[0026] b. Add 12.8 wt.% of the ionic liquid 1-butyl-3-methylimidazolium chloride as an auxiliary solvent to the preliminary blend solution, and continuously stir for 48 hours until a uniformly mixed casting solution is formed. Then, let it stand for 12 hours to remove bubbles.

[0027] c. Pour the casting solution onto a glass plate, and use a coater to evenly spread a film with a thickness of 300 μm. Then, immerse the glass plate with the casting solution in a deionized water bath for phase inversion to form a mixed matrix membrane.

[0028] d. Take out the mixed matrix membrane and immerse it in deionized water for 6 h, changing the water every 6 h. Take it out and air-dry naturally at room temperature to obtain the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane.

[0029] d. Take out the mixed matrix membrane and immerse it in deionized water for 6 h, changing the water every 6 h. Take it out and air-dry naturally at room temperature to obtain the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane.

[0030] Preferably, the preparation steps of the preparation method are as follows:

[0031] a. Use 74.5 wt.% of the organic solvent N-methylpyrrolidone to blend 1.5 wt.% of MOF-808 with PVDF to obtain a preliminary blend solution.

[0032] b. Add 8 wt.% of the ionic liquid 1-propyl-3-methylimidazolium chloride as an auxiliary solvent to the preliminary blend solution, and continuously stir for 48 hours until a uniformly mixed casting solution is formed. Then, let it stand for 12 hours to remove bubbles.

[0033] c. Pour the casting solution onto a glass plate, and use a coater to evenly spread a film with a thickness of 300 μm. Then, immerse the glass plate with the casting solution in a deionized water bath for phase inversion to form a mixed matrix membrane;

[0034] d. Take out the mixed matrix membrane and immerse it in deionized water for 6 h, change the water every 6 h, take it out and let it dry naturally at room temperature to obtain the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane.

[0035] An ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane is obtained by the above-mentioned method.

[0036] The preparation method of the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane provided in this case has the following beneficial effects:

[0037] 1. The addition of MOF-808 with high porosity and high specific surface area in the present invention increases the porosity of the PVDF membrane, provides more paths for water molecules to pass through the membrane, and thus increases the pure water flux of the membrane;

[0038] 2. The addition of MOF-808 with high hydrophilicity and photocatalytic performance in the present invention makes the modified membrane have good anti-fouling ability and photocatalytic self-cleaning ability, and enhances the reusability of the modified membrane;

[0039] 3. The present invention adds 1-butyl-3-methylimidazole ionic liquid as an auxiliary solvent, which enhances the miscibility between MOF-808 and PVDF, makes MOF-808 evenly distributed in the modified membrane without obvious agglomeration;

[0040] 4. The present invention prepares the MOF-808 / PVDF mixed matrix membrane by a physical blending phase inversion method. The preparation process is simple, the reaction conditions are low and easy to control, the cost is low, and the membrane structure is easy to control and uniform;

[0041] 5. The MOF-808 / PVDF modified membrane prepared in the present invention has good rejection ability for different types of organic dyes, can maintain a high permeation flux at the same time, and has good photocatalytic self-cleaning cyclic use performance. Description of the Drawings

[0042] Figure 1 It is the infrared spectrogram of PVDF and MOF-808 / PVDF mixed matrix membrane of the present invention;

[0043] Figure 2 It is the photocatalytic self-cleaning cyclic separation effect diagram of the MOF-808 / PVDF mixed matrix membrane for Congo red dye solution. Detailed Embodiments

[0044] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0045] Example 1:

[0046] A preparation method of an ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane, comprising the following steps:

[0047] a. Using an organic solvent to blend MOF-808 particles and PVDF powder to obtain a preliminary blend;

[0048] b. Adding an ionic liquid as an auxiliary solvent to the preliminary blend, continuously stirring for 12 to 48 hours until a uniformly mixed casting solution is formed, and then standing for 3 to 24 hours to remove bubbles;

[0049] c. Pouring the casting solution onto a glass plate, spreading it into a film with a uniform thickness using a coater, and then immersing the glass plate with the casting solution in a deionized water bath for phase inversion to form a mixed matrix membrane;

[0050] d. Taking out the mixed matrix membrane and immersing it in deionized water for 6 to 24 hours, changing the water every 3 to 6 hours, taking it out and naturally drying it at room temperature to obtain the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane; wherein,

[0051] The organic solvent is one or more of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP); the ionic liquid is one or more of 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-propyl-3-methylimidazolium chloride, and 1-propyl-3-methylimidazolium bromide.

[0052] In the preliminary blend in step a, the mass percentage range of MOF-808 added is 0.1 to 2%. In the preliminary blend in step a, the mass percentage range of PVDF added is 14 to 22%. In the preliminary blend in step a, the mass percentage of the organic solvent N,N-dimethylacetamide added is 65 to 84%. In the casting solution in step b, the mass percentage range of 1-butyl-3-methylimidazolium chloride ionic liquid is 8 to 25%. In step c, the temperature of the deionized water bath is 40 to 80 °C, and the phase inversion time is 30 to 120 s.

[0053] Example 2:

[0054] a. Blending 1.5 wt.% of MOF-808 with PVDF using 65.6 wt.% of an organic solvent (N,N-dimethylacetamide);

[0055] b. Add 16.4 wt.% of ionic liquid (1-butyl-3-methylimidazolium chloride) as an auxiliary solvent, continuously stir for 24 hours until a uniformly mixed casting solution is formed, and then let it stand for 12 hours to remove bubbles;

[0056] c. Pour the casting solution onto a glass plate, use a coater to evenly spread a film with a thickness of 300 μm, and then immerse the glass plate with the coating solution in a deionized water bath for phase inversion to form a mixed matrix membrane;

[0057] d. Take out the membrane prepared by the above steps and immerse it in deionized water for 12 h, change the water every 6 h, and finally let the membrane dry naturally at room temperature to obtain the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane.

[0058] The following comparative experiments were conducted using a PVDF membrane and the MOF-808 / PVDF modified membrane prepared in Example 2:

[0059] 1. To illustrate the good water flux effect of the modified membrane in the present invention, a cross-flow filtration device was used to measure the pure water flux (Jw) of the PVDF membrane and the MOF-808 / PVDF modified membrane under an operating pressure of 0.2 MPa, as shown in Table 1. The MOF-808 / PVDF modified membrane showed extremely high water flux performance compared to the PVDF membrane.

[0060] Table 1: Pure water flux of PVDF membrane and MOF-808 / PVDF modified membrane

[0061] membrane <![CDATA[Pure water flux (J w ) / L·m -2 ·h -1 > PVDF 3.88 MOF-808 / PVDF 116.16

[0062] 2. In addition, in the present invention, a cross-flow filtration device was used to conduct filtration experiments on dye solutions (Congo red, Acid red, Methyl blue) under an operating pressure of 0.2 MPa, and the rejection performance of the MOF-808 / PVDF mixed matrix membrane for dye molecules was measured. Its separation performance was mainly characterized by two indicators: permeation flux (J0) and rejection rate of dye (R_dye), as shown in Table 2:

[0063] dye <![CDATA[Permeation flux (J0) / L·m -2 ·h -1 > <![CDATA[R 染料 / %]]> Congo red 91.04 97.6 Acid red 84.04 90.2 Methyl blue 77.04 91.4

[0064] As can be seen from Table 2, the MOF-808 / PVDF modified membrane showed excellent rejection effects for different dyes while maintaining a high permeation flux.

[0065] 3. In the present invention, cross-flow filtration was used to conduct a photocatalytic self-cleaning cycle filtration experiment on Congo red dye solution to measure the dye rejection performance and reusability of the MOF-808 / PVDF modified membrane, as Figure 1As shown; after undergoing five photocatalytic self-cleaning cycle filtrations of Congo red dye solution, the permeation flux of the modified membrane only showed a slight decrease as the number of cycles increased, while the rejection rate of Congo red always remained above 95%, with no significant change in numerical value. These results indicate that the MOF-808 / PVDF modified membrane can still maintain excellent anti-fouling performance and reusability during long-term photocatalytic self-cleaning cycle filtrations of dye solutions.

[0066] 4. Figure 2 FT-IR infrared spectra of the MOF-808 / PVDF modified membrane and the PVDF membrane. The peaks at 1400 cm -1 and 1180 cm -1 originate from the stretching vibration of C-F in PVDF. After adding MOF-808, a new peak at 654 cm -1 from Zr-O in MOF-808 appears in the MOF-808 / PVDF modified membrane.

[0067] Example 3 (wt.% is mass percentage in the following content):

[0068] A preparation method of an ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane, comprising the following steps:

[0069] a. Using 70 wt.% of an organic solvent (N,N-dimethylformamide) to blend 1.0 wt.% of MOF-808 with PVDF to obtain a preliminary blend solution;

[0070] b. Adding 12.8 wt.% of an ionic liquid (1-butyl-3-methylimidazolium chloride) as an auxiliary solvent to the preliminary blend solution, continuously stirring for 48 hours until a uniformly mixed casting solution is formed, and then standing for 12 hours to remove bubbles;

[0071] c. Pouring the casting solution onto a glass plate, using a coater to uniformly spread a membrane with a thickness of 300 μm, and then immersing the glass plate with the casting solution in a deionized water bath for phase inversion to form a mixed matrix membrane;

[0072] d. Taking out the mixed matrix membrane, immersing it in deionized water for 6 h, changing the water every 6 h, taking it out and naturally drying it at room temperature to obtain the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane.

[0073] To illustrate the good water flux effect of the modified membrane in the present invention, a cross-flow filtration device was used to measure the pure water flux (Jw) of the PVDF membrane and the MOF-808 / PVDF modified membrane under an operating pressure of 0.2 MPa, as shown in Table 1. The MOF-808 / PVDF modified membrane exhibited extremely high water flux performance compared to the PVDF membrane.

[0074] Example 4 (wt.% is mass percentage in the following content):

[0075] A preparation method of an ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane, comprising the following steps:

[0076] a. Blending 1.5 wt.% of MOF-808 with PVDF using 74.5 wt.% of an organic solvent (N-methylpyrrolidone) to obtain a preliminary blend;

[0077] b. Adding 8 wt.% of an ionic liquid (1-propyl-3-methylimidazolium chloride) as an auxiliary solvent to the preliminary blend, continuously stirring for 48 hours until a uniformly mixed casting solution is formed, and then standing for 12 hours to remove bubbles;

[0078] c. Pouring the casting solution onto a glass plate, uniformly spreading a membrane with a thickness of 300 μm using a coater, and then immersing the glass plate with the casting solution in a deionized water bath for phase inversion to form a mixed matrix membrane;

[0079] d. Taking out the mixed matrix membrane, immersing it in deionized water for 6 h, changing the water every 6 h, taking it out and naturally drying it at room temperature to obtain the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane.

[0080] The above embodiments merely illustrate the principles and effects of the present invention, rather than limiting the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A preparation method of an ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane, characterized in that, It includes the following steps: a. Using an organic solvent to blend MOF-808 particles with PVDF powder to obtain a preliminary blend solution; b. Adding an ionic liquid as an auxiliary solvent to the preliminary blend solution, continuously stirring for 12 to 48 hours until a uniformly mixed casting solution is formed, and then standing for 3 to 24 hours to remove bubbles; c. Pouring the casting solution onto a glass plate, spreading it into a film with a uniform thickness using a coater, and then immersing the glass plate with the casting solution in a deionized water bath for phase inversion to form a mixed matrix membrane; d. Taking out the mixed matrix membrane and immersing it in deionized water for 6 to 24 hours, changing the water every 3 to 6 hours, taking it out and naturally drying it at room temperature to obtain the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane; wherein, The organic solvent is one or more of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP); The ionic liquid is one or more of 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-propyl-3-methylimidazolium chloride, and 1-propyl-3-methylimidazolium bromide.

2. The preparation method of the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane according to claim 2, wherein, The mass percentage range of MOF-808 added to the preliminary blend solution in step a is 0.1 to 2%.

3. The preparation method of the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane according to claim 2, characterized in that, The mass percentage range of PVDF added in step a is 14 to 22%.

4. The preparation method of the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane according to claim 3, wherein The mass percentage of the organic solvent N,N-dimethylacetamide added to the preliminary blend solution in step a is 65 to 84%.

5. The preparation method of the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane according to claim 4, wherein, The mass percentage range of 1-butyl-3-methylimidazolium chloride ionic liquid in the casting solution in step b is 8 to 25%.

6. The preparation method of the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane according to claim 5, characterized in that, In step c, the temperature of the deionized water bath is 40 to 80 °C, and the phase inversion time is 30 to 120 s.

7. The preparation method of the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane according to claim 6, characterized in that, The preparation steps of the preparation method are as follows: a. Using 65.6 wt.% of the organic solvent N,N-dimethylacetamide to blend 1.5 wt.% of MOF-808 with PVDF; b. Adding 16.4 wt.% of 1-butyl-3-methylimidazolium chloride ionic liquid as an auxiliary solvent, continuously stirring for 24 hours until a uniformly mixed casting solution is formed, and then standing for 12 hours to remove bubbles; c. Pouring the casting solution onto a glass plate, uniformly spreading a film with a thickness of 300 μm using a coater, and then immersing the glass plate with the casting solution in a deionized water bath for phase inversion to form a mixed matrix membrane; d. Taking out the membrane obtained through the above steps and immersing it in deionized water for 12 hours, changing the water every 6 hours, and finally naturally drying the membrane at room temperature to obtain the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane.

8. The preparation method of the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane according to claim 7, characterized in that, The preparation steps of the preparation method are as follows: a. Using 70 wt.% of the organic solvent N,N-dimethylformamide to blend 1.0 wt.% of MOF-808 with PVDF to obtain a preliminary blend solution; b. Adding 12.8 wt.% of the ionic liquid 1-butyl-3-methylimidazolium chloride as an auxiliary solvent to the preliminary blend solution, continuously stirring for 48 hours until a uniformly mixed casting solution is formed, and then standing for 12 hours to remove bubbles; c. Pour the casting solution onto a glass plate, and use a coater to evenly spread a film with a thickness of 300 μm. Then, immerse the glass plate with the casting solution in a deionized water bath for phase inversion to form a mixed matrix membrane; d. Take out the mixed matrix membrane and immerse it in deionized water for 6 h, change the water every 6 h, take it out and air-dry it naturally at room temperature to obtain the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane.

9. The preparation method of the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane according to claim 8, wherein, The preparation steps of the preparation method are as follows: a. Use 74.5 wt.% of the organic solvent N-methylpyrrolidone to blend 1.5 wt.% of MOF-808 with PVDF to obtain a preliminary blend solution; b. Add 8 wt.% of the ionic liquid 1-propyl-3-methylimidazolium chloride as an auxiliary solvent to the preliminary blend solution, continuously stir for 48 hours until a uniformly mixed casting solution is formed, and then let it stand for 12 hours to remove air bubbles; c. Pour the casting solution onto a glass plate, and use a coater to evenly spread a film with a thickness of 300 μm. Then, immerse the glass plate with the casting solution in a deionized water bath for phase inversion to form a mixed matrix membrane; d. Take out the mixed matrix membrane and immerse it in deionized water for 6 h, change the water every 6 h, take it out and air-dry it naturally at room temperature to obtain the ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane.

10. An ionic liquid-assisted MOF-808 / PVDF mixed matrix membrane, characterized in that, The mixed matrix membrane is obtained by the method according to any one of claims 1 to 9.

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