A MIL-68(In) / POTS@PTFE hydrophobic membrane and its preparation method

Abstract

This invention discloses a MIL-68(In) / POTS@PTFE hydrophobic membrane and its preparation method, belonging to the field of polytetrafluoroethylene membrane processing and manufacturing technology. The invention first prepares a metal-organic framework material MIL-68(In), then modifies MIL-68(In) using 1H, 1H, 2H, 2H perfluorooctyltriethoxysilane (POTS), and finally deposits the modified MIL-68(In) solution onto the surface of a polytetrafluoroethylene (PTFE) membrane using a spray coating method to obtain the MIL-68(In) / POTS@PTFE hydrophobic membrane. Membrane; This invention utilizes MIL-68(In) to enhance compatibility with PTFE membranes. Simultaneously, after hydrolysis of one end of POTS, the siloxane group Si-O-CH2CH3, which is completely replaced by silanol group Si-OH, is chemically bonded to the surface of MIL-68(In). The Si-OH between the hydrophobic long chains undergoes a dehydration reaction to form a polysiloxane network structure. The fluorine atom groups contained in POTS effectively reduce the free energy of the MIL-68(In) surface, thus realizing the preparation of MIL-68(In) / POTS@PTFE membrane with further improved hydrophobicity.

Description

Technical Field

[0001] This invention belongs to the field of polytetrafluoroethylene membrane processing and manufacturing technology, specifically relating to a method for preparing a MIL-68(In) / POTS@PTFE hydrophobic membrane. Background Technology

[0002] In recent years, metal-organic frameworks (MOFs) have shown great potential in membrane applications due to their advantages such as large specific surface area, ease of synthesis, structural diversity, and modifiability. MOFs are crystalline porous materials with regular channels or cavities, constructed by interconnecting inorganic metal centers (metal ions or metal clusters) and organic functional groups through covalent or ion-covalent bonds. The size and properties of these channels can be controlled by modulating the organic ligands, overcoming the limitations of molecular sieve pores. MOFs possess unique properties such as porosity and large specific surface area, making them widely applicable in catalysis, energy storage, and gas adsorption and separation. Currently, MOFs are mainly classified into ZIF, UIO, and MIL series, and have been widely used in separation, catalysis, storage, and sensing.

[0003] Generally, methods for synthesizing metal-organic framework (MOF) films on substrates include: (1) in-situ synthesis, which involves direct synthesis on the substrate. However, most substrates do not have enough nucleation sites, making it impossible to directly synthesize continuous and dense MOF films. (2) chemical modification, which involves modifying the substrate through chemical reactions to increase heterogeneous nucleation sites and prepare MOF films. However, the interaction between the substrate and the MOF is weak in this method, and the MOF film is prone to detachment. (3) seed crystal method, which involves pre-coating a layer of nanoscale MOF seed crystals on the substrate and using the seed crystals as nucleation sites to synthesize MOF films. This method requires complex seed crystal preparation and coating steps, and the seed crystals on the substrate are prone to detachment during the synthesis process, making it difficult to prepare continuous and dense MOF films.

[0004] Polytetrafluoroethylene (PTFE) microporous membranes are produced by mixing PTFE resin particles with additives and other materials, followed by expansion, stretching, and heat setting at temperatures below their melting point to form a microporous membrane with excellent filtration performance. PTFE microporous membranes possess a fiber-interlaced microporous structure, exhibiting advantages such as high porosity, low resistance, high particle rejection rate, good temperature resistance, resistance to strong acids and alkalis, resistance to organic solvents, antioxidants, and aging. They also demonstrate outstanding chemical stability, excellent high and low temperature resistance, and good corrosion resistance, and are virtually insoluble in all known organic solvents. Therefore, exploring and developing a novel synthetic method for metal-organic framework membranes using PTFE membranes as MOFs carriers is of great significance for the industrial preparation of metal-organic framework membranes and the practical application of PTFE membrane surface modification.

[0005] The invention patent with publication number CN104959044A discloses a method for synthesizing metal-organic framework membranes. First, a multifunctional metal gel is fixed on a substrate. The gel enters the pores of the substrate, which can not only enhance the interaction between the substrate and the metal-organic framework material, but also provide more heterogeneous nucleation sites for the synthesis of metal-organic framework materials. Then, using the substrate containing the metal gel as the nucleation site, a continuous and rigid metal-organic framework membrane is synthesized under certain conditions. However, the main technical problem addressed by this invention is how to prepare a continuous and dense metal-organic framework membrane, enabling the metal-organic framework material to be synthesized inside the pores to enhance the membrane's hardness and compressive strength. It does not mention the impact on hydrophobic properties. Patent CN112808312A provides a method for preparing nano-metal-organic framework (MOF) catalytic membranes. It utilizes the microporous structure of a base membrane to synthesize nano-MOFs and directly assembles the nano-MOF catalytic membrane inside the base membrane via percolation. However, the assembly process of this nano-metal-organic framework (MOF) catalytic membrane requires controlling the number of solution percolations to regulate the catalyst loading in the membrane. Simultaneously, it requires controlling the magnitude of the driving force on both sides of the base membrane to control the fluid percolation rate, preventing the fluid residence time from being too short, which could lead to the lack of introduction of precursor ions or organic ligands into the membrane, or excessive base membrane resistance that prevents fluid percolation. The preparation process is cumbersome and has a long preparation cycle. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention uses 1H, 1H, 2H, 2H perfluorooctyltriethoxysilane (POTS) as a hydrophobic agent to modify MIL-68(In) hydrophobically, thereby reducing the free energy of the MIL-68(In) surface and preparing a MIL-68(In) / POTS@PTFE membrane with improved hydrophobicity.

[0007] The technical solution of the present invention is as follows:

[0008] One objective of this invention is to provide a method for preparing a MIL-68(In) / POTS@PTFE hydrophobic membrane, comprising the following steps:

[0009] S1. Pretreatment of polytetrafluoroethylene (PTFE) membrane: Cut the PTFE membrane into uniform squares, immerse them in an ethanol solution to remove organic solvents from the membrane surface and pores, and finally dry them.

[0010] S2. Preparation of metal-organic framework material MIL-68(In);

[0011] S3. Using 1H, 1H, 2H, 2H perfluorooctyltriethoxysilane POTS for MIL-68(In)

[0012] Hydrophobic modification was performed to prepare a modified MIL-68(In) / POTS solution;

[0013] S4. Modified MIL-68(In) is deposited on the surface of a PTFE membrane by spraying to obtain MIL-68.

[0014] (In) / POTS@PTFE hydrophobic membrane.

[0015] Furthermore, in S1, the cutting size is 2*2cm, and the soaking time is 2-3h.

[0016] Furthermore, in step S2, terephthalic acid is first uniformly dispersed in N,N-dimethylformamide, then In(NO3)3 is added, and after ultrasonic dispersion, the resulting mixed solution is transferred to an autoclave for reaction. After the reaction is completed and cooled to room temperature, the product is centrifuged and washed multiple times, and then dried to obtain MIL-68(In).

[0017] Furthermore, the N,N-dimethylformamide is 60 mL, and the molar ratio of terephthalic acid to In(NO3)3 is 6:7.

[0018] Furthermore, in step S3, POTS is first added to ethanol and stirred to disperse evenly. Then, the prepared MIL-68(In) is added to the POTS mixed solution and ultrasonicated until evenly dispersed to obtain a modified MIL-68(In) / POTS solution.

[0019] Furthermore, the reaction conditions in the autoclave are 100°C for 24 hours.

[0020] Furthermore, in step S3, POTS is first added to ethanol and stirred to disperse evenly. Then, the prepared MIL-68(In) is added to the POTS mixed solution and ultrasonicated until evenly dispersed to obtain a modified MIL-68(In) / POTS solution.

[0021] Furthermore, in step S4, the modified MIL-68(In) / POTS solution is poured into a spray gun and uniformly sprayed onto the surface of the PTFE membrane prepared in step S1, and then dried and cured to obtain a MIL-68(In) / POTS@PTFE hydrophobic membrane.

[0022] Furthermore, the drying and curing conditions are 50-70℃ for 10-14 hours.

[0023] Furthermore, the number of spraying passes is 3-5.

[0024] The second objective of this invention is to provide a MIL-68(In) / POTS@PTFE hydrophobic membrane.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. This invention innovatively prepares a MIL-68(In) / POTS@PTFE hydrophobic membrane. It utilizes the metal-organic framework material MIL-68(In) to enhance the compatibility between the membrane and the PTFE membrane. Through the chemical bonding of the siloxane group Si-O-CH2CH3, which is completely replaced by silanol group Si-OH after the hydrolysis of one end of the bifunctional compound POTS, with the surface of MIL-68(In), the Si-OH between the hydrophobic long chains undergoes a dehydration reaction to form a polysiloxane network structure, thereby improving the hydrophobicity of the metal-organic framework-modified polytetrafluoroethylene membrane.

[0027] 2. In addition to carbon, the POTS used in this invention contains a large number of silicon and fluorine atomic groups with low surface energy in its internal hydrophobic molecules. This effectively reduces the free energy of the MIL-68(In) surface and increases its surface contact angle. After POTS hydrophobic treatment, the contact angle of POTS@PTFE is 103°. However, when modified MIL-68(In) is loaded, the contact angle of MIL-68(In) / POTS@PTFE can reach 128°, indicating that the MIL-68(In) / POTS@PTFE composite membrane preparation method provided by this invention can further improve the hydrophobic performance.

[0028] 3. This invention discloses a method for preparing a MIL-68(In) / POTS@PTFE hydrophobic membrane. MIL-68(In) is modified hydrophobically using 1H, 1H, 2H, 2H perfluorooctyltriethoxysilane (POTS) as a hydrophobic agent to reduce the surface free energy of MIL-68(In). The modified MIL-68(In) is then deposited onto the PTFE membrane surface using a multi-coating curing method. Compared to conventional hydrophobic membrane modification methods, this preparation method not only solves the technical challenge of weak adhesion between metal-organic frameworks and metal carriers such as PTFE membranes, making film formation difficult, but also offers simplicity, ease of operation, and easy structural control, thus possessing broad application prospects.

[0029] Figure Labels

[0030] Figure 1 The image shows the XRD pattern of MIL-68(In) prepared in Example 1 of this invention.

[0031] Figure 2 This is a SEM image of MIL-68(In) prepared in Example 1 of the present invention. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0033] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0034] In the quantitative experiments in the following examples, three replicate experiments were set up, and the average value of the results was taken.

[0035] Unless otherwise specified, the experimental methods in the following examples are conventional methods;

[0036] Example 1

[0037] This embodiment provides a MIL-68(In) / POTS@PTFE hydrophobic membrane, the preparation method of which includes the following steps:

[0038] S1. Cut the PTFE membrane into 2*2cm sizes, soak it in ethanol solution for 2 hours, then remove the organic solvent from the membrane surface and membrane pores and dry it.

[0039] S2. 1.08 mmol of terephthalic acid was uniformly dispersed in 60 mL of N,N-dimethylformamide, followed by the addition of 1.26 mmol of In(NO3)3. After ultrasonic dispersion for 1 h, the resulting mixed solution was transferred to an autoclave and reacted at 100 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed three times, and dried to obtain MIL-68(In). The structure and microstructure are shown below. Figure 1 and Figure 2 As shown.

[0040] S3. Add 1H, 1H, 2H, 2H perfluorooctyltriethoxysilane (POTS) to ethanol and stir to disperse evenly. Then weigh MIL-68(In) and add it to the above POTS mixed solution. Sonicate until evenly dispersed to obtain the modified MIL-68(In) / POTS solution.

[0041] S4. Pour the modified MIL-68(In) / POTS solution into the spray gun and spray it evenly 4 times onto the surface of the PTFE membrane prepared in S1. Then dry and cure at 60℃ for 14h to obtain the MIL-68(In) / POTS@PTFE hydrophobic membrane.

[0042] like Figure 1 and Figure 2 As shown, this embodiment not only achieved the preparation of MIL-68(In), but also MIL-68(In) has a large specific surface area.

[0043] Example 2

[0044] This embodiment provides a method for preparing a MIL-68(In) / POTS@PTFE hydrophobic membrane, comprising the following steps:

[0045] S1. Cut the PTFE membrane into 2*2cm sizes, soak it in ethanol solution for 2.5h, then remove the organic solvent from the membrane surface and membrane pores and dry it.

[0046] S2. 1.08 mmol of terephthalic acid was uniformly dispersed in 60 mL of N,N-dimethylformamide, followed by the addition of 1.26 mmol of In(NO3)3. After ultrasonic dispersion for 1 h, the resulting mixed solution was transferred to an autoclave and reacted at 100 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed three times, and dried to obtain MIL-68(In). The structure and microstructure are shown below. Figure 1 and Figure 2 As shown.

[0047] S3. Add 1H, 1H, 2H, 2H perfluorooctyltriethoxysilane POTS to ethanol and stir to disperse evenly. Then weigh MIL-68(In) and add it to the above POTS mixed solution. Sonicate until evenly dispersed to obtain a modified MIL-68(In) / POTS solution.

[0048] S4. Pour the modified MIL-68(In) / POTS solution into a spray gun and spray it evenly three times onto the surface of the PTFE membrane prepared in S1. Then, dry and cure it at 60°C for 12 hours to obtain the MIL-68(In) / POTS@PTFE hydrophobic membrane.

[0049] Example 3

[0050] This embodiment provides a method for preparing a MIL-68(In) / POTS@PTFE hydrophobic membrane, comprising the following steps:

[0051] S1. Cut the PTFE membrane into 2*2cm sizes, soak it in ethanol solution for 3 hours, then remove the organic solvent from the membrane surface and membrane pores and dry it.

[0052] S2. 1.08 mmol of terephthalic acid was uniformly dispersed in 60 mL of N,N-dimethylformamide, followed by the addition of 1.26 mmol of In(NO3)3. After ultrasonic dispersion for 1 h, the resulting mixed solution was transferred to an autoclave and reacted at 100 °C for 24 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed three times, and dried to obtain MIL-68(In). The structure and microstructure are shown below. Figure 1 and Figure 2 As shown.

[0053] S3. Add 1H, 1H, 2H, 2H perfluorooctyltriethoxysilane POTS to ethanol and stir to disperse evenly. Then weigh MIL-68(In) and add it to the above POTS mixed solution. Sonicate until evenly dispersed to obtain a modified MIL-68(In) / POTS solution.

[0054] S4. Pour the modified MIL-68(In) / POTS solution into the spray gun and spray it evenly 5 times onto the surface of the PTFE membrane prepared in S1. Then dry and cure at 70℃ for 10h to obtain the MIL-68(In) / POTS@PTFE hydrophobic membrane.

[0055] Comparative Example 1

[0056] This comparative embodiment provides a method for preparing a POTS@PTFE membrane, comprising the following steps:

[0057] S1. Cut the PTFE membrane into uniform squares (approximately 2*2cm), immerse them in an ethanol solution, then remove the organic solvent from the membrane surface and pores and dry them.

[0058] S2. After cleaning the spray gun, pour the POTS solution into the spray gun. Spray it evenly onto the surface of the PTFE membrane treated in S1.

[0059] S3. Place in an oven to dry, and obtain POTS@PTFE membrane.

[0060] Performance testing

[0061] 1. Membrane contact angle test

[0062] Contact angle tests were performed on the PTFE membrane, the POTS@PTFE membrane prepared in Comparative Example 1 of the present invention, and the MIL-68(In) / POTS@PTFE membrane prepared in Example 1.

[0063] The test results are shown in Table 1.

[0064] As shown in Table 1, the contact angle of the MIL-68(In) / POTS@PTFE hydrophobic membrane prepared in Example 1 of the present invention is significantly larger than that of the PTFE membrane and the POTS@PTFE membrane prepared in Comparative Example 1, exhibiting stronger hydrophobic properties.

[0065] Table 1. Membrane contact angle test results

[0066] sample contact angle PTFE 113° POTS@PTFE 103° MIL-68(In) / POTS@PTFE 128°

[0067] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a MIL-68(In) / POTS@PTFE hydrophobic membrane, characterized in that, Includes the following steps: S1. Pretreatment of polytetrafluoroethylene (PTFE) membrane: Cut the PTFE membrane into uniform squares, immerse them in an ethanol solution to remove organic solvents from the membrane surface and pores, and finally dry them. S2. Preparation of metal-organic framework material MIL-68(In); S3. MIL-68(In) was hydrophobically modified using 1H,1H,2H,2H-perfluorooctyltriethoxysilane POTS to prepare a modified MIL-68(In) / POTS solution. S4. Modified MIL-68(In) is deposited on the surface of a PTFE membrane by spraying to obtain a MIL-68(In) / POTS@PTFE hydrophobic membrane.

2. The method for preparing a MIL-68(In) / POTS@PTFE hydrophobic membrane as described in claim 1, characterized in that, The cutting size in S1 is 2*2cm, and the soaking time is 2-3h.

3. The method for preparing a MIL-68(In) / POTS@PTFE hydrophobic membrane as described in claim 1, characterized in that, In step S2, terephthalic acid is first uniformly dispersed in N,N-dimethylformamide, then In(NO3)3 is added, and after ultrasonic dispersion, the resulting mixed solution is transferred to an autoclave for reaction. After the reaction is completed and cooled to room temperature, the product is centrifuged and washed multiple times, and then dried to obtain MIL-68(In).

4. The method for preparing a MIL-68(In) / POTS@PTFE hydrophobic membrane as described in claim 3, characterized in that, The N,N-dimethylformamide is 60 mL, and the molar ratio of terephthalic acid to In(NO3)3 is 6:

7.

5. The method for preparing a MIL-68(In) / POTS@PTFE hydrophobic membrane as described in claim 3, characterized in that, The reaction conditions in the autoclave were 100℃ for 24 hours.

6. The method for preparing a MIL-68(In) / POTS@PTFE hydrophobic membrane as described in claim 1, characterized in that, In step S3, POTS is first added to ethanol and stirred to disperse evenly. Then, the prepared MIL-68(In) is added to the POTS mixed solution and ultrasonicated until evenly dispersed to obtain a modified MIL-68(In) / POTS solution.

7. The method for preparing a MIL-68(In) / POTS@PTFE hydrophobic membrane as described in claim 1, characterized in that, In step S4, the modified MIL-68(In) / POTS solution is poured into a spray gun and uniformly sprayed onto the surface of the PTFE membrane prepared in step S1, and then dried and cured to obtain a MIL-68(In) / POTS@PTFE hydrophobic membrane.

8. The method for preparing a MIL-68(In) / POTS@PTFE hydrophobic membrane as described in claim 7, characterized in that, The drying and curing conditions are 50-70℃ for 10-14 hours.

9. The method for preparing a MIL-68(In) / POTS@PTFE hydrophobic membrane as described in claim 1, characterized in that, The number of spraying passes is 3-5.

10. A MIL-68(In) / POTS@PTFE hydrophobic membrane prepared by the method according to any one of claims 1-9.

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